The nigrotectal projection and tectospinal neurons in the rat. A light and electron microscopic study demonstrating a monosynaptic nigral input to identified tectospinal neurons

In order to investigate the nigro-tecto-spinal pathway in the rat, the pattern of termination of nigrotectal fibres and the distribution of tectospinal neurons have been investigated in a light and electron microscopic study of the superior colliculus. In addition, the pattern of termination of nigrotectal fibres was compared to the pattern of acetylcholinesterase staining. The light microscopic studies showed that the nigrotectal fibres, which had been identified by anterograde transport of horseradish peroxidase from the substantia nigra, terminated in a distinctive clustered pattern throughout the rostrocaudal extent of the stratum griseum intermedium, stratum album intermedium and adjacent dorsal portion of the stratum griseum profundum of the ipsilateral superior colliculus. The clusters of nigrotectal terminals formed a series of branching, interconnected longitudinal columns which largely corresponded with the pattern of acetylcholinesterase staining. The tectospinal neurons, which had been identified by retrograde transport of horseradish peroxidase from the spinal cord, had mainly large-sized somata, were stellate in shape with multiple long dendrites, and formed variable-sized clusters of 4-15 neurons within lateral regions of the ventral stratum album intermedium and dorsal stratum griseum profundum. In experiments where both the nigrotectal terminals and the tectospinal neurons were labelled by the transport of horseradish peroxidase, the clusters of tectospinal neurons largely corresponded with the regions of densest nigrotectal fibre termination in the lateral regions of the superior colliculus. In addition, a small contralateral nigrotectal projection was localized in the rostrolateral region of the superior colliculus where the crossed fibres terminated in a clustered pattern in alignment with clusters of tectospinal neurons in this region. Electron microscopic examination of the superior colliculus following ibotenic acid lesions in the substantia nigra and horseradish peroxidase injections in the spinal cord showed multiple degenerating nigrotectal boutons in synaptic contact with the soma and the mainstem and secondary dendrites of labelled tectospinal neurons in the lateral regions of the stratum album intermedium and stratum griseum profundum of the superior colliculus. The majority of the degenerating nigrotectal boutons showed electron-lucent degenerative changes and were in axodendritic contact. All of the identified nigrotectal synapses were of the symmetrical type.(ABSTRACT TRUNCATED AT 400 WORDS)     

The striatonigral projection and nigrotectal neurons in the rat. A correlated light and electron microscopic study demonstrating a monosynaptic striatal input to identified nigrotectal neurons using a combined degeneration and horseradish peroxidase procedure

In a light and electron microscopic study of the substantia nigra of the rat, the distribution and morphology of nigrotectal neurons and the pattern of termination of striatonigral fibres have been examined following the placement of horseradish peroxidase injections in the superior colliculus and kainic acid lesions in the dorsal striatum. In confirmation of previous findings, nigrotectal neurons which had been identified by the retrograde transport of horseradish peroxidase from the superior colliculus had mainly medium sized somata, varied from fusiform to stellate in shape and were found in mainly ventral regions of the rostral two-thirds of the substantia nigra pars reticulata. On electron microscopic examination, single and multiple (from two to six) degenerating striatonigral boutons were found in synaptic contact with the soma, proximal mainstem dendrites and small dendrites (but mainly on small dendrites) of labelled nigrotectal and unlabelled nigral neurons in the ventral region of the pars reticulata. In addition, a small number of degenerating striatonigral boutons formed axoaxonic synapses with degenerating or normal boutons which were presynaptic to nigral dendrites. Almost all of the identified striatonigral synapses were of the symmetrical type, although a few degenerating boutons established asymmetrical synaptic contacts on unlabelled dendrites. These findings provide evidence of a monosynaptic input from the dorsal striatum to nigrotectal projection neurons in the substantia nigra and thus demonstrate the existence of a bineuronal pathway from the striatum through the substantia nigra to the superior colliculus. The possible significance of the pattern of termination of striatonigral fibres in the substantia nigra is discussed with reference to the known dendritic arborization of nigral neurons.     

Ultrastructure of degenerating cerebellothalamic terminals in the ventral medial nucleus of the cat

Summary Terminal degeneration of cerebellar afferents in the ventral medial thalamic nucleus (VM) was studied in cats at the ultrastructural level after uni- or bilateral lesions in the brachium conjunctivum (BC). To achieve discrete lesions within the BC, a new very accurate stereotaxic technique was used. Numerous large terminals belonging to a population of so-called LR boutons were observed degenerating in the VM. The boutons displayed a wide variety of degenerative changes. Some revealed the features of the classical neurofilamentous type of degeneration. Others, although containing a slightly increased number of neurofilaments, featured much more prominently large numbers of coated vesicle shells and heavy accumulations of a flocculent electrondense material. Degeneration in a third group of boutons similar to some extent to the light type of degeneration was characterized by tight clumping of enormously swollen or distorted synaptic vesicles within a light matrix. At later stages, however, all these boutons were believed to become shrunken and electron-dense since intermediate stages between the light- and dark-appearing boutons were observed. The degenerating cerebellar boutons formed asymmetrical synaptic contacts. Groups of 3 or 4 boutons terminated upon dendrites of projection neurons synapsing more frequently on spines than on dendritic stems. The synaptic contacts between cerebellar boutons and the vesicle-containing dendrites of local circuit neurons were encountered as often if not more than the contacts on projection neuron dendrites. Triads consisting of cerebellar boutons and dendrites of both types of neurons were observed very regularly. This synaptic arrangement provides the anatomical basis for the modification of cerebellar input in the VM by interneurons.     

The cerebellotectal pathway in the grey squirrel

Summary In the well laminated superior colliculus of the grey squirrel the cells of origin of the crossed descending pathway to the brainstem gaze centers are contained within the inner sublamina of the intermediate grey layer. The technique of anterograde transport of horseradish peroxidase was used to determine whether the pathway from the cerebellum to the superior colliculus terminates in this region. The technique of retrograde transport of horseradish peroxidase was used to localize the source of this pathway within the cerebellum and to determine the morphology of the cerebellotectal neurons. The grey squirrel cerebellotectal pathway provides two terminal fields to the superior colliculus: a diffuse projection into the deep grey layer and a more concentrated, interrupted projection into the inner sublamina of the intermediate grey layer. The more concentrated projection overlies precisely the tectal sublamina that contains the cells of origin of the predorsal bundle. In contrast to animals with frontal eyes, the cerebellotectal pathway in the grey squirrel was found to project almost entirely contralaterally and the vast majority of the cells of origin for the pathway were distributed ventrally, in the caudal pole of the posterior interpositus nucleus and the adjacent region of the dentate. The labelled cells in both cerebellar nuclei were large and displayed similar morphologies.Abbreviations BC Brachium conjunctivum - BP Brachium pontis - CN Cochlear nuclei - D Dentate nucleus of the cerebellum - DLG Dorsal lateral geniculate nucleus - DLPG Dorsal lateral pontine grey - I Interpositus nucleus of the cerebellum - IC Inferior colliculus - III Oculomotor nucleus - IO Inferior olive - ITB Ipsilateral tectobulbar pathway - F Fastigial nucleus of the cerebellum - MG Medial geniculate nucleus - NRTP Nucleus reticularis tegmenti pontis - OPT Stratum opticum - PAG Periaqueductal grey - PDB Predorsal bundle - PB Parabigeminal nucleus - PH Prepositus hypoglossi - PUL Pulvinar nucleus - PT Pretectum - RN Red nucleus - SAI Stratum album intermediale (intermediate white layer) - SAP Stratum album profundum (deep white layer) - SGI Stratum griseum intermediale (intermediate grey layer) - SGP Stratum griseum profundum (deep grey layer) - SGS Stratum griseum superficiale (superficial grey layer) - SN Substantia nigra - sV Sensory division of the trigeminal complex - Ve Vestibular nuclei - VII Facial nucleus - VLG Ventral lateral geniculate nucleus     

Electron microscopic study of GABA-immunoreactive neuronal processes in the superficial gray layer of the rat superior colliculus: their relationships with degenerating retinal nerve endings

Summary GABA-immunoreactive neuronal elements were detected in the stratum griseum superficiale or superficial gray layer of the rat superior colliculus in an electron microscopic study, using postembedding immunocytochemistry with protein A-gold as a marker. In addition to neuronal somata, two types of GABA-immunoreactive neuronal processes were observed. Numerous profiles of axon terminals (1 m in diameter) with clear round or pleomorphic synaptic vesicles and mitochondria were found to establish mostly symmetrical synaptic contacts with GABA-immunonegative dendrites of various diameters. Some axosomatic synapses could also be observed. The gold particle density in this axon terminal compartment was between seven and 13 times the background level. The stratum griseum superficiale also included GABA-immunoreactive dendrites, some of which contained clear synaptic vesicles. These dendritic profiles always formed the presynaptic component of dendrodendritic synaptic contacts. The density of the gold particles in the dendritic compartment, taken as a whole, was between three and 13 times the background level. Furthermore, the relationship between the GABA-immunoreactive neuronal elements and degenerating retinal nerve endings identified in the left stratum griseum superficiale following enucleation of the right eye was investigated after a 7-day survival period. The profiles of degenerating retinal nerve endings (0.7 m in diameter) were found to be devoid of any specific labelling. Most of the retinal boutons established axodendritic synapses of the asymmetrical type with an immunonegative dendrite, which was also contacted in some cases by a GABA-immunopositive axon terminal. Other retinal endings were presynaptic to GABA-immunopositive dendritic profiles with synaptic vesicles, some of which were found to contact in turn an unlabelled dendrite, thereby completing serial synaptic relationships. More rarely, retinal endings formed the presynaptic component of possible axoaxonic synapses with GABA-positive terminals presumed to be axonic in nature. It can be concluded that the retinal input to the superficial gray layer often converges with a GABAergic axonal input on a dendritic target, the neurotransmitter specificity of which is unknown. In other cases, retinal terminals synaptically contact GABA-immunolabelled conventional and presynaptic dendrites and probably also some axon terminals; this might provide an anatomical substrate for the control of GABA release from these GABAergic processes. These results indicate that transmitter GABA plays an important role in retinocollicular transmission.     

Contralateral corticofugal projections to cat visual thalamus

Summary Contralateral corticofugal projections from visual cortical areas to thalamic nuclei were demonstrated in the cat using anterograde transport of tritiated proline. Thalamic nuclei receiving projections from contralateral visual cortex include both subdivisions of the lateral-posterior nucleus, the posterior nucleus of Rioch, and the posterior nuclear complex.Abbreviations BIC brachium of the inferior colliculus - BN nucleus of the brachium of the inferior colliculus - BSC brachium of the superior colliculus - C dorsal lateral geniculate nucleus, C laminae - CG central gray matter - D nucleus of Darkschewitz - FR fasciculus retroflexus - FTC central tegmental field - H habenula - IPN interpeduncular nucleus - LGNd dorsal lateral geniculate nucleus, A laminae - LGNv ventral lateral geniculate nucleus - LP lateral posterior complex - LPi interjacent division of lateral posterior complex - LPl lateral division of lateral posterior complex - LPm medial division of lateral posterior complex - M mammillary body - MGM magnocellular division of medial geniculate nucleus - MGN medial geniculate nucleus - MGP parvocellular division of medial geniculate nucleus - MIN medial interlaminar division of lateral geniculate nucleus - MML medial medullary lamina - NOT nucleus of the optic tract - OT optic tract - P cerebral peduncle - PA anterior pretectal nucleus - PC nucleus of the posterior commissure - PM medial pretectal nucleus - PO posterior nuclear group - PoC posterior commissure - POi intermediate division of posterior nuclear complex - POL pretectal olivary nucleus - POm medial division of posterior nuclear complex - PPT posterior pretectal nucleus - PUL pulvinar - RN red nucleus - RNR posterior nucleus of Rioch - SG suprageniculate nucleus - SGI stratum griseum intermedium of superior colliculus - SGP stratum griseum profundum of superior colliculus - SCSl lower division of stratum griseum superficiale of superior colliculus - SGSu upper division of stratum griseum superficiale of superior colliculus - SN substantia nigra - SO stratum opticum of superior colliculus - TC tectal commissure - III III nerve - IIIN nucleus of III nerve     

Laminar origin of ipsilateral tectopontine pathways

The purpose of these experiments was to identify the cells of origin of the ipsilateral tectopontine pathways in the grey squirrel (Sciurus carolinensis). Following injections of tritiated amino acids into individual collicular laminae, labelled fibers could be traced to the dorsolateral pontine nuclei and overlying lateral pontine tegmentum. Fibers originating in stratum griseum superficiale terminated most heavily within the pontine nuclei whereas those arising from stratum griseum profundum terminated most heavily within the tegmentum. After horseradish peroxidase was injected into the dorsolateral pontine nuclei, cells labelled with reaction product were found in all 3 grey laminae of the superior colliculus, but the majority were located in stratum griseum superficiale. In contrast, when horseradish peroxidase was injected into the tectorecipient pontine tegmentum, most of the labelled cells were located in stratum griseum profundum.These results indicate that each of the 3 grey laminae of the superior colliculus projects to both the dorsolateral pontine nuclei and the lateral pontine tegmentum. However, the pathway to the pontine nuclei arises chiefly in stratum griseum superficiale while the tectotegmental pathway arises chiefly in stratum griseum profundum.     

Synaptic organization of GABAergic inputs from the striatum and the globus pallidus onto neurons in the substantia nigra and retrorubral field which project to the medullary reticular formation.

Anatomical tract-tracing and immunohistochemical techniques involving correlated light and electron microscopy were used to determine whether the descending striatal and pallidal afferents to the substantia nigra pars reticulata converge onto individual neurons projecting to the pontomedullary and medullary reticular formation in the rat. Injections of biocytin into the ventrolateral region of the striatum and Phaseolus vulgaris-leucoagglutinin into the ventrolateral and caudal regions of the globus pallidus led to overlapping anterogradely labelled terminal fields within the dorsolateral substantia nigra pars reticulata. These terminal fields were punctuated by neurons which had been retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into the lateral pontomedullary reticular formation. The anterogradely labelled striatal and pallidal terminals displayed different morphological characteristics; the striatal terminals were small and diffusely distributed throughout the neuropil without any particular neuronal association whereas the pallidal terminals were large and formed pericellular baskets around the perikarya of retrogradely and non-retrogradely labelled nigral neurons. In areas of the substantia nigra where there was an overlap between the two terminal fields, individual retrogradely labelled nigroreticular neurons were found to be apposed by both sets of anterogradely labelled terminals. Electron microscopic analysis revealed that the striatonigral and pallidonigral terminals displayed different ultrastructural features, the striatal terminals were small, contained few mitochondria and formed symmetric synaptic contacts predominantly with the distal dendrites of nigroreticular neurons whereas the pallidal terminals were large, contained numerous mitochondria and formed symmetric synaptic contacts preferentially with perikarya and proximal dendrites of nigroreticular neurons. Post-embedding immunohistochemical staining revealed that both striatonigral and pallidonigral terminals, some which formed synaptic contact with nigroreticular neurons, displayed GABA immunoreactivity. Examination of twelve retrogradely labelled neurons in the electron microscope revealed that all received synaptic inputs from both sets of anterogradely labelled terminals. In addition to the substantia nigra pars reticulata, neurons of the retrorubral field were also retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into pontomedullary reticular formation. These retrorubroreticular neurons were part of a continuum of labelled cells which extended from the dorsolateral substantia nigra pars reticulata caudally into the retrorubral field. When combined with anterograde tracing methods it was found that the retrorubroreticular neurons received synaptic inputs from pallidal terminals which were morphologically similar to the pallidonigral terminals and formed symmetric synapses with the neuronal somata and proximal dendrites. In contrast to nigroreticular neurons, the stratonigral terminals were not seen in contact with retrorubroreticular cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Time of origin of neurons of the rat superior colliculus in relation to other components of the visual and visuomotor pathways

Summary Groups of pregnant rats were injected with two successive daily doses of ³H-thymidine from gestational day 12 and 13 (E12+E13) until the day before parturition (E21+22) in order to label all the multiplying precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labelled) on specific days was determined in the separate layers of the superior colliculus. Neurogenesis begins with the production of a few large multipolar neurons in layers V and IV on day E12; the bulk (87%) of these cells are generated on day E13. This early-produced band of large neurons, the intermediate magnocellular zone, divides the superior colliculus into two cytogenetically distinct regions. In both the deep and the superficial superior colliculus neuron production is relatively protracted. In the deep superior colliculus neuron production peaks on day E15 in layer VII, on day E15 and E16 in layer VI, and on day E16 (the large neurons excluded) in layer V, indicating an inside-out sequence. In the superficial superior colliculus peak production time of layer III cells is on day E15 and of layer IV cells on day E16; peak production time of both layer I and II is on day E16 but in the latter region neuron production is more prolonged and ends on day El8. One interpretation of these results is that the two pairs of superficial layers are produced in an outside-in sequence. These three cytogenetic subdivisions of the superior colliculus may be correlated with its structural-functional parcellation into an efferent spinotectal, a deep somatomotor and a superficial visual component.A comparison of neurogenesis in different components of the visuomotor and visual pathways of the rat indicates that the motor neurons of the extraocular muscles, the abducens, trochlear and oculomotor nuclei, and neurons of the nucleus of Darkschewitsch are produced first. Next in line are source neurons of efferents to the bulb and the spinal cord: those of the Edinger-Westphal nucleus and the intermediate magnocellular zone of the superior colliculus. These are followed by the relay neurons of the dorsal nucleus of the lateral geniculate body. The neurons of the superficial superior colliculus and of the visual cortex implicated in visual sensori-motor integrations are produced last.Abbreviations A aqueduct - ap stratum album profundum (layer VII) - bi brachium of the inferior colliculus - c caudal - CGd central gray, pars dorsalis - CGl central gray, pars lateralis - CGv central gray, pars ventralis - dm deep magnocellular zone - EW Edinger-Westphal nucleus - gi stratum griseum intermediale (layer IV) - gp stratum griseum profundum (layer VI) - gs stratum griseum superficiale (layer II) - IC inferior colliculus - im intermediate magnocellular zone - LGd lateral geniculate nucleus, pars dorsalis - ll lateral lemniscus - lm stratum lemnisci (layer V) - MG medial geniculate nucleus - ND nucleus of Darkschewitsch - NO nucleus of the optic tract - op stratum opticum (layer III) - ot optic tract - r rostral - SC superior colliculus - vIII third ventricle - ZO stratum zonale (layer I) - III oculomotor nucleus - IV trochlear nucleus - Vm mesencephalic nucleus of the trigeminal - VI abducens nucleus     

Effects of lesions of the nucleus of the optic tract on optokinetic nystagmus and after-nystagmus in the monkey

Summary 1. The nucleus of the optic tract (NOT) and the dorsal terminal nucleus (DTN) of the accessory optic system were lesioned electrolytically or with kainic acid in rhesus monkeys. When lesions involved NOT and DTN, peak velocities of optokinetic nystagmus (OKN) with slow phases toward the side of the lesion were reduced, and optokinetic after-nystagmus (OKAN) was reduced or abolished. The jump in slow phase eye velocity at the onset of OKN was smaller in most animals, but was not lost. Initially, there was spontaneous nystagmus with contralateral slow phases. OKN and OKAN with contralateral slow phases were unaffected. 2. Damage to adjacent regions had no effect on OKN or OKAN with two exceptions: 1. A vascular lesion in the MRF, medial to NOT and adjacent to the central gray matter, caused a transient loss of the initial jump in OKN. The slow rise in slow phase velocity was prolonged, but the gain of OKAN was unaffected. There was no effect after a kainic acid lesion in this region in another animal. 2. Lesions of the fiber tract in the pulvinar that inputs to the brachium of the superior colliculus caused a transient reduction in the buildup and peak velocity of OKN and OKAN. 3. In terms of a previous model (Cohen et al. 1977; Waespe et al. 1983), the findings suggest that the indirect pathway that activates the velocity storage integrator in the vestibular system to produce the slow rise in ipsilateral OKN and OKAN, lies in NOT and DTN. Activity for the rapid rise in OKN, carried in the direct pathway, is probably transmitted to the pontine nuclei and flocculus via an anatomically separate fiber path-way that lies in the MRF. A fiber tract in the pulvinar that inputs to the brachium of the superior colliculus appears to carry activity related to retinal slip from the visual cortex to NOT and DTN.Abbreviations used in Figures BIC brachium of the inferior colliculus - BSC brachium of the superior colliculus - C caudate nucleus - CG central gray - CL Centralis lateralis - dbc decussation of the brachium conjunctivum - DTN dorsal terminal nucleus of the accessory optic system - IC inferior colliculus - Hb habenular nucleus - hc habenular commissure - LD lateralis dorsalis - LGn lateral geniculate nucleus - MD medialis dorsalis - MGn medial geniculate nucleus - MLF median longitudinal fasciculus - MRF mesencephalic reticular formation - cMRF central mesencephalic reticular formation - NL nucleus limitans - NLL nucleus of the lateral lemniscus - NOT nucleus of the optic tract - PB parabigeminal nucleus - pc posterior commissure - Pi pineal gland - PON pretectal olivary nucleus - Pt pretectum - Pulv pulvinar - R nucleus reticularis - RN red nucleus - RpN raphe nucleus - RTP nucleus reticularis tegmenti pontis - SC superior colliculus - SCpit superior cerebellar peduncle - VPL ventralis postero-lateralis - VPM ventralis posteromedialis - III oculomotor nucleus - IV trochlear nucleus - IVn trochlear nerve - Vm mesencephalic trigeminal nucleus     

Comparison of the ultrastructure of cortical and retinal terminals in the rat superior colliculus

We compared the ultrastructure and synaptic targets of terminals of cortical or retinal origin in the stratum griseum superficiale and stratum opticum of the rat superior colliculus. Following injections of biotinylated dextran amine into cortical area 17, corticotectal axons were labeled by anterograde transport. Corticotectal axons were of relatively small caliber with infrequent small varicosities. At the ultrastructural level, corticotectal terminals were observed to be small profiles (0.44 +/- 0.27 microm(2)) that contained densely packed round vesicles. In tissue stained for gamma amino butyric acid (GABA) using postembedding immunocytochemical techniques, corticotectal terminals were found to contact small (0.51 +/- 0.69 microm(2)) non-GABAergic dendrites and spines (93%) and a few small GABAergic dendrites (7%). In the same tissue, retinotectal terminals, identified by their distinctive pale mitochondria, were observed to be larger than corticotectal terminals (3.34 +/- 1.79 microm(2)). In comparison to corticotectal terminals, retinotectal terminals contacted larger (1.59 +/- 1.70 microm(2)) non-GABAergic dendrites and spines (73%) and a larger proportion of GABAergic profiles (27%) of relatively large size (2.17 +/- 1.49 microm(2)), most of which were vesicle-filled (71%). Our results suggest that cortical and retinal terminals target different dendritic compartments within the neuropil of the superficial layers of the superior colliculus.     

Cellular and subcellular localization of 5-hydroxytryptamine1B receptors in the rat central nervous system: immunocytochemical, autoradiographic and lesion studies.

The localization of 5-hydroxytryptamine1B receptors in the rat central nervous system was investigated using anti-peptide antibodies that recognize a selective portion of the third intracytoplasmic loop of the receptor protein. At the light microscope level the densest 5-hydroxytryptamine1B receptor-like immunoreactivity was observed in ventral pallidum, globus pallidus, substantia nigra and dorsal subiculum. In addition, moderate immunoreactivity was found in the entopeduncular nucleus, the superficial gray layer of the superior colliculus, the caudate-putamen and the deep nuclei of the cerebellum. This distribution matched perfectly that previously described from radioligand binding studies. At the ultrastructural level, 5-hydroxytryptamine1B receptor-like immunoreactivity was associated with axons and axon terminals in the three areas examined: substantia nigra, globus pallidus and superficial gray layer of the superior colliculus. In all cases, immunostaining was located on the plasma membrane of unmyelinated axon terminals and in the cytoplasm close to the plasmalemma. Synaptic differentiations were never labelled but, in some cases, 5-hydroxytryptamine1B receptor-like immunoreactivity was found in their close vicinity. Injection of kainic acid into the neostriatum resulted in a marked decrease in receptor-like immunoreactivity in the globus pallidus and the substantia nigra, consistent with the location of 5-hydroxytryptamine1B receptors on terminals of striatopallidal and striatonigral fibres, respectively. A reduction in 5-hydroxytryptamine1B receptor-like immunoreactivity was also noted in the superficial gray layer of the superior colliculus after contralateral enucleation, as expected of the location of 5-hydroxytryptamine1B receptors on the terminals of retinocollicular fibres. In both lesion experiments, immunolabelled degenerating terminals were observed in the projection areas. Anterograde labelling experiments coupled with immunocytochemical detection further showed that 5-hydroxytryptamine1B receptors in the substantia nigra are located on axons of striatal neurons. These data provide anatomical support for the idea that 5-hydroxytryptamine1B receptors act as terminal receptors involved in presynaptic regulation of the release of various neurotransmitters, including 5-hydroxytryptamine itself.     

Distribution of the tecto-thalamic projection neurons in the hereditary microphthalmic rat

Summary Tecto-thalamic projections in the hereditary bilaterally microphthalmic rat were studied by means of WGA-HRP injection into the dorsal lateral geniculate nucleus (LGNd) and the lateroposterior thalamic nucleus (LP). Histological study in the mutant rats showed that whereas LGNd and superficial layers of the superior colliculus (SC) suffered from a remarkable reduction in size, LP had no histological changes as compared to the normal animals. Unilateral injection of the tracer into the microphthalmic LGNd showed that WGA-HRP positive neurons were present mostly in the ipsilateral str. griseum superficiale (SGS) of the SC. However, the number of labeled SGS neurons of the microphthalmic animals was about 3% of the normal. Although cell bodies of the normal tecto-LGNd neurons in the SGS were spindle-form in shape and issued one or two proximal dendrites from each pole, the microphthalmic tecto-LGNd neurons showed an irregular contour and their dendrites were not so intensively labeled. Unilateral injections of WGA-HRP into the LP revealed that the tecto-LP neurons were mainly distributed in the ipsilateral str. opticum of the colliculus. (SO) in both normal and microphthalmic animals. However, the number of labeled SO cells in the microphthalmic rat was about one-half of the normal. Furthermore, the size of labeled tecto-LP neurons was smaller than that of the normal ones, and they showed irregular round to oval cell bodies with equivocally labeled dendrites, in contrast to the normal tecto-LP neurons with polygonal cell bodies extending three or more dendrites in a radial fashion. These results indicate that there exist the tecto-LGNd and -LP projection neurons in the microphthalmic rat and that their laminally segregated projection is fundamentally preserved. However, the number of the tecto-thalamic projection neurons, especially of the tecto-LGNd cells, was markedly diminished in the mutant tectum compared to normals.Abbreviations CST cortico-spinal tract - DRN dorsal raphe nucleus - DTN dorsal tegmental nucleus - LGNd pars dorsalis of the lateral geniculate nucleus - LLN nucleus of the lateral lemniscus - LM medial lemniscus - LP lateroposterior thalamic nucleus - MGN medial geniculate nucleus - MRF midbrain reticular formation - OT optic tract - P pretectal area - PAG periaqueductal gray - PB parabigeminal nucleus - PN pontine nuclei - PCS superior cerebellar peduncle - SGS superficial gray layer of the superior colliculus - SO stratum opticum of the superior colliculus - SN substantia nigra - Vm motor nucleus of the trigeminar nerve - Vs sensory nucleus of the trigeminar nerve     

Laminar organization of the substantia nigra pars reticulata in the cat

Using a semihorizontal section plane tangential to the ventral surface of the cerebral peduncle, the authors re-examined cyto-, myelo- and dendroarchitecture, acetylcholinesterase activity, afferent fibers, and efferent projection neurons of the substantia nigra pars reticulata. In the semihorizontal section plane, the substantia nigra pars reticulata was a disc-shaped nucleus and contained two to three myelinated fiber bundles running from anteromedial to posterolateral. Bands of high acetylcholinesterase activity existed parallel to the anteromedial-posterolateral direction. The Golgi silver impregnation study revealed that many nigral neurons extended their varicose dendrites anteromedially and posterolaterally. In cases with injections of wheat germ agglutinated horseradish peroxidase into the neostriatum or injections of tritiated leucine into the subthalamic nucleus, anterogradely labeled afferent fibers and axon terminals in the substantia nigra pars reticulata were organized into bands in the same anteromedial-posterolateral direction. In cases with injections of wheat germ agglutinated horseradish peroxidase into either the superior colliculus, the pedunculopontine tegmental nucleus or the ventromedial nucleus of the thalamus, retrogradely labeled neurons were also clustered along the anteromedial-posterolateral direction with their dendrites extending anteromedially and posterolaterally. The present findings strongly suggest that the substantia nigra pars reticulata has a laminar organization.     

Topographic projections from the basal ganglia to the nucleus tegmenti pedunculopontinus pars compacta of the cat with special reference to pallidal projections

Summary Projections from the basal ganglia to the nucleus tegmenti pedunculopontinus pars compacta (TPC) were studied by using anterograde and retrograde tracing techniques with horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) in the cat. Following WGA-HRP injections into the medial TPC area, a substantial number of retrogradely labeled cells were seen in the entopeduncular nucleus (EP) and medial half of the substantia nigra pars reticulata (SNr), whereas following WGA-HRP injections into the lateral TPC area, labeled cells were marked in the caudal half of the globus pallidus (GP) and lateral half of the SNr. To confirm the retrograde tracing study, WGA-HRP was injected into the EP or the caudal GP, and anterograde labeling was observed in the TPC areas. Terminal labeling was located in the medail TPC area in the EP injection case, while terminal labeling was observed in the lateral TPC area in the caudal GP injection case. Projections from the striatum to the pallidal complex (the EP and the caudal GP) were also studied autoradiographically by injecting amino acids into various parts of the caudate nucleus and the putamen. Terminal labeling was distributed over the whole extent of the EP and the rostral GP following injections into the rostral striatum (the head of the caudate nucleus or the rostral part of the putamen), while terminal labeling was distributed over the caudal GP following injections into the caudal striatum (the body of the caudate nucleus or the caudal part of the putamen). From these findings, we conclude that there exists a medio-lateral topography in the projection from the basal ganglia to the TPC: The EP receives afferent projections from the rostral striatum and projects to the medial TPC area, whereas the caudal GP receives projections from the caudal striatum and sends fibers to the lateral TPC area.Abbreviations BC brachium conjunctivum - CD caudate nucleus - CP cerebral peduncle - DBC decussation of the brachium conjunctivum - EP entopeduncular nucleus - GP globus pallidus - IC internal capsule - ICo inferior colliculus - LH lateral habenular nucleus - ML medial lemniscus - PN pontine nuclei - PUT putamen - SCo superior colliculus - SI substantia innominata - SN substantia nigra - SNc substantia nigra pars compacta - SNr substantia nigra pars reticulata - STN subthalamic nucleus - TH thalamus - TPC nucleus tegmenti pedunculopontinus pars compacta     

Branched output neurons of the rat subthalamic nucleus: electrophysiological study of the synaptic effects on identified cells in the two main target nuclei, the entopeduncular nucleus and the substantia nigra

The synaptic responses of entopeduncular and nigral cells to subthalamic stimulation were studied with extracellular recording techniques in rats with and without chronic lesions. Entopeduncular output cells were identified by antidromic activation from the lateral habenula, ventral anterior thalamic nucleus and tegmenti pedunculopontine nucleus. Nigral cells projecting to superior colliculus were identified by antidromic discharge. Stimulation of the subthalamic nucleus produced a short latency suppression of spontaneous activity (10-60 ms duration) of 89% of the entopeduncular cells tested in chronically lesioned rats. Of these cells, 50% were identified as projecting to lateral habenula. On the other hand, subthalamic nucleus stimulation produced a short latency excitation of 73% of the nigral cells tested (4.16 +/- 0.07 ms). Forty-eight percent of these cells projected to superior colliculus. The subthalamic fibres which terminate in entopeduncular nucleus and substantia nigra, come from the same neuronal population since the majority, if not all, rat subthalamic neurones send branched projections to both these nuclei. Therefore, the two different types of responses recorded in these nuclei are elicited by the activation of a single neuronal population. This dual effect could be easily explained if one of the responses is mediated by local interneurones. If not, the same transmitter induces the two responses. The entopeduncular nucleus and substantia nigra which are the main target nuclei of the subthalamic nucleus, are also the only known outputs of the striatum. The subthalamic efferent cells could thus modulate the activity of the entire striatal descending output. It is noteworthy that this subthalamic control is different in entopeduncular nucleus than in substantia nigra.     

Convergence of synaptic inputs from the striatum and the globus pallidus onto identified nigrocollicular cells in the rat: a double anterograde labelling study.

Two major sources of afferent synaptic inputs to projection neurons in the rat substantia nigra reticulata are the striatum and the globus pallidus. In order to understand better the functional relationships between these two afferents in the control of the activity of nigrofugal neurons, experiments have been performed to test the possibility that single nigrofugal cells receive convergent synaptic inputs from the striatum and the globus pallidus. To address this question we have used two different approaches. First, we have developed a double anterograde labelling technique suitable for both light and electron microscopy and combined this procedure with the retrograde transport of lectin-conjugated horseradish peroxidase in order to retrogradely label the nigrocollicular cells. Second, we have combined the anterograde transport of Phaseolus vulgaris-leucoagglutinin from the globus pallidus and immunocytochemistry for DARPP-32 as a marker for the striatal terminals, with the retrograde transport of lectin-conjugated horseradish peroxidase from the superior colliculus. In the double anterograde labelling experiment, biocytin was injected in the striatum, Phaseolus vulgaris-leucoagglutinin in the globus pallidus and lectin-conjugated horseradish peroxidase in the superior colliculus. Following these injections, rich plexuses of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals were found in the ventral two-thirds of the substantia nigra. The biocytin-positive terminals (striatonigral) were generally small and formed rich plexuses without any apparent neuronal association whereas the Phaseolus vulgaris-leucoagglutinin-labelled terminals (pallidonigral) were much larger and formed baskets around the perikarya of retrogradely and non retrogradely labelled cells in the substantia nigra reticulata. In areas of the substantia nigra reticulata where the fields of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals overlapped, the perikarya and the proximal dendrites of retrogradely and non retrogradely labelled cells were found to be apposed by numerous Phaseolus vulgaris-leucoagglutinin-immunoreactive pallidonigral terminals and a few biocytin-labelled striatonigral terminals. In the sections prepared for electron microscopy, the biocytin was localized using 3,3'-diaminobenzidine tetrahydrochloride whereas Phaseolus vulgaris-leucoagglutinin was localized using benzidine dihydrochloride. It was thus possible to distinguish the biocytin- from the Phaseolus vulgaris-leucoagglutinin-labelled terminals in the electron microscope by the texture of the reaction product associated with them.4+ Examination of 231 biocytin-labelled (striatonigral) terminals and 105 Phaseolus vulgaris-leucoagglutinin-immunoreactive (pallidronigral) terminals revealed that the striatonigral terminals were generally small, contained few mitochondria and formed symmetric synapses predominantly with the distal dendrites (77%) and far less frequently with the perikarya (3%) of substantia nigra reticulata cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Early establishment of adult-like nigrotectal architecture in the neonatal cat: a double-labeling study using carbocyanine dyes

Virtually nothing is known about the ontogeny of substantia nigra, pars reticulata projections to the midbrain superior colliculus, even though this pathway is critical for the basal ganglia modulation of midbrain-mediated visuomotor behaviors. The present studies used the lipophilic carbocyanine dyes 1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate and 1,1'-dioctodecyl-3,3,3',3'-tetramethylindodi, 4-chlorobenzenesulfonate salt to examine the crossed and uncrossed nigrotectal projections in neonatal cats, from parturition to 14 days postnatal (the technical limits of the tracing technique). In retrograde experiments, paired placement of the dyes in each superior colliculus produced numerous retrogradely-labeled nigrotectal neurons, with the uncrossed neurons far out numbering their crossed counterparts. No double-labeled neurons were observed, indicating that crossed and uncrossed nigrotectal neurons are segregated at birth. In anterograde experiments, dye placements into each substantia nigra, pars reticulata resulted in an iterative series of labeled patches, aligned medial-to-lateral across the intermediate and deep superior colliculus, a pattern reminiscent of the adult. Uncrossed neonatal axons had simple linear morphologies with few branch points; by contrast, crossed axons displayed more extensive terminal arbors that were distributed diffusely throughout the rostrocaudal extent of the contralateral superior colliculus In the final series of experiments, one dye was placed unilaterally in the substantia nigra, pars reticulata, while the second dye was positioned in the predorsal bundle, in order to bilaterally label superior colliculus output neurons. Although both crossed and uncrossed axons appeared to have contacted superior colliculus output neurons, crossed axons preferentially targeted the soma and proximal dendrites, whereas uncrossed terminals were distributed more distally. Throughout this early postnatal period, no significant changes in cellular morphologies or gross modification of terminal projection patterns were observed; however, the presence of growth cones in even the oldest animals studied suggests that the refinement of the nigrotectal projections extends well into postnatal life. Nevertheless, the segregation of crossed and uncrossed nigrotectal neurons into a highly organized afferent mosaic that has established synaptic contacts with superior colliculus output neurons indicates that many of the salient features characterizing nigrotectal projections are established prior to the onset of visual experience.     

The lateral cervical nucleus in the cat III. An electron microscopical study after transection of spinal afferents

Summary The ultrastructure of terminal degeneration within the lateral cervical nucleus (LCN) after transection of its spinal afferent fibers 2 days–2 years earlier is described. The degeneration after 2 days was of both the neurofilamentous and dense type. The highest number of degenerating terminals, about 15%, was found after 4–5 days. Then most of the degenerating boutons were of the dense type. The degenerating terminals had synaptic contact with cell bodies and dendrites of LCN-neurons. Removal of the degenerating boutons seemed to be effected by a phagocytic cell present in increased number compared to the normal LCN. In cases with long survival times an increase in the number of astroglial filaments was observed. In an animal where the spinal afferents to the LCN had been cut 2 years earlier a decrease in medium size of the neurons was observed. The amount of dendritic spines was also considerably smaller than normally.     

Anticonvulsant role of nigrotectal projection in the maximal electroshock model of epilepsy--II. Pathways from substantia nigra pars lateralis and adjacent peripeduncular area to the dorsal midbrain.

Lesion evidence suggests that the superior colliculus is essential for mediating the anticonvulsant properties of nigral suppression in the electroshock model of epilepsy. However, our companion paper [Redgrave et al. (1991) Neuroscience 46, 379-390] established that the region of dorsal midbrain where bicuculline was most effective in suppressing tonic hindlimb extension did not correspond well with the known distribution of nigrotectal terminals. The purpose of the present anatomical study was, therefore, to investigate in more detail ventral midbrain connections to the dorsal midbrain anticonvulsant zone in rat. Small injections (10-20 nl) of a 1% solution of wheatgerm agglutinin conjugated with horseradish peroxidase were made specifically into the region of dorsal midbrain where bicuculline was maximally effective. Numerous retrogradely labelled cells were found in substantia nigra pars lateralis and adjacent peripeduncular area but not in substantia nigra pars reticulata. Retrogradely labelled cells were also located in ventral zona incerta. When wheatgerm agglutinin-horseradish peroxidase injections were made into lateral substantia nigra, a region of anterogradely transported reaction product characteristic of nerve terminals was observed in the caudolateral deep layers and underlying reticular tissue; this area corresponded well to the dorsal midbrain anticonvulsant zone. These data suggest that, in the electroshock model of epilepsy, direct connections between substantia nigra pars lateralis and adjacent peripeduncular area and the dorsal midbrain anticonvulsant zone could be critical for mediating the anticonvulsant properties previously attributed to substantia nigra pars reticulata. During the course of this study, anterograde projections from substantia nigra pars lateralis and adjacent peripeduncular area to both superficial and intermediate layers of the ipsilateral superior colliculus were noted. Additional experiments using retrograde transport of the fluorescent tracer Fast Blue confirmed these projections.