Nigral inhibitory termination on efferent neurons of the superior colliculus: an intracellular horseradish peroxidase study in the cat

Intracellularly recorded responses of deeper tectal neurons to stimulation of the substantia nigra and the cerebral peduncle were obtained to demonstrate the monosynaptic inhibitory nature of the nigrotectal pathway in the cat. We also employed antidromic stimulation (contralateral predorsal bundle and superior colliculus) and intracellular labeling with HRP to demonstrate which types of tectal efferent neurons are nigrorecipient. The response to nigral stimulation in 61% of the cells studied was a monosynaptic IPSP of short duration. Recovered HRP-labeled nigrorecipient neurons include X1 (large multipolar radiating), X2 (tufted), X4 (medium-size vertical), X5 (medium-size horizontal), T1 (medium-size trapezoid radiating), T2 (small ovoid vertical), I (small sparsely ramified), and A (small horizontal) neurons. Nigrorecipient cells participate in all four of the major efferent axonal systems of the deeper tectal layers: crossed descending (X and T neurons), ipsilateral descending (I and T neurons), ascending (A, X, and T neurons), and commissural (T neurons). EPSPs accompanied by long-lasting hyperpolarizing potentials were recorded from the remaining tectal neurons in response to stimulation of the substantia nigra, cerebral peduncle, and pericruciate cortex. Collision experiments indicate that at least part of the excitatory responses of tectal neurons to nigral and penduncular stimulation are mediated by corticotectal fibers traversing the cerebral peduncle and the substantia nigra. Excitatory effects of nigral, peduncular, and cortical stimulation were disclosed in X neurons including the non-nigrorecipient large vertical neurons of the X3 subgroup. Cortical excitatory and nigral inhibitory inputs converge only on X neurons (X1, X2, X4, X5). In this case, nigrally evoked IPSPs were preceded by a brief EPSP. Collectively, these results demonstrate the inhibitory termination of the nigrotectal pathway on a wide variety of deeper tectal efferent neurons. Such findings imply the versatility of the nigral involvement in tectal mechanisms of gaze control. We suggest that the substantia nigra pars reticulata contacts tectal neurons differing as to their response properties and shapes the signal carried by all the major tectofugal bundles.     

Bonyfish lateral line efferent neurons identified by retrograde axonal transport of horseradish peroxidase (HRP)

Post-mortem brain tissue from 7 patients who died with a diagnosis of senile dementia of Alzheimer type (SDAT) was compared with tissue obtained from 7 control patients at routine post mortem. A significant fall in choline acetyltransferase (ChAT) activity was apparent in the cerebral cortex of the SDAT cases which was maximal in the temporal lobe. The fall in ChAT activity was not accompanied by changes in cortical vasoactive intestinal polypeptide (VIP) measured by radioimmunoassay.     

Retinal ganglion cell terminals in the hamster superior colliculus: an ultrastructural study.

The distribution, cross-sectional area, and presynaptic and postsynaptic characteristics of retinal ganglion cell axon terminals in the superior colliculus of normal adult female Syrian hamsters were investigated by quantitative ultrastructural techniques. After an intravitreal injection of horseradish peroxidase, most labelled axon terminals were found in the stratum griseum superficiale and stratum opticum of the contralateral superior colliculus. However, a small proportion (approximately 2%) of retinal ganglion cell axon terminals were located in deeper layers of the superior colliculus between the stratum opticum and the periaqueductal grey matter. Terminals were smaller in the upper two-thirds of the stratum griseum superficiale than in the lower one-third of this layer, the stratum opticum, and the stratum griseum intermedium. Presynaptic characteristics such as the length and number of contacts and the postsynaptic neuronal domains (somata, dendritic spines, or shafts) contacted by retinal ganglion cell axons in the superior colliculus were similar in all layers.     

Choline acetyltransferase-immunoreactive patches overlap specific efferent cell groups in the cat superior colliculus

Fibers containing acetylcholine (ACh) form distinct patches in the dorsal intermediate gray layer (IGL) of the cat superior colliculus (SC). Although these patches are known to overlap several afferent projections to SC, it is not known whether they are associated with specific postsynaptic cell groups. We have examined the relationship of these ACh fiber patches to specific efferent cell groups by combining retrograde transport of horseradish peroxidase (HRP) with choline acetyltransferase (ChAT) immunocytochemistry. Successful HRP injections were made into the predorsal bundle (PB), the tecto-pontine-bulbar pathway (TPB) and the cuneiform region (CFR), the inferior olive (IO), the dorsolateral pontine gray nucleus (PGD), and the pedunculopontine tegmental nucleus (PPTN). The distribution of HRP-labeled neurons which project to these targets was mapped by a computer-based microscope plotter. Distinct clusters of HRP-labeled neurons in the IGL were seen after three injections into the mesencephalic reticular formation that involved the caudal TPB and cuneiform region (CFR), and after one injection into the medial accessory nucleus of IO. As many as seven clusters of labeled neurons were found in some sections through the caudal one-half of SC after the TPB/CFR injections. Each cluster consisted of 3-20 cells, all of which were small to medium in size. In sections also tested for ChAT, the cell clusters in the TPB/CFR cases were found to overlap precisely the ACh patches in the IGL. In addition, SC neurons projecting to the IO formed clusters above the ChAT patches and in the intermediate white layer (IWL) of SC. None of the other HRP injections produced any obvious cell clusters in the deep layers of SC. These results are the first to show that specific cell groups, distinguished by size and projection site, form clusters that match the patch-like innervation of cholinergic afferents to SC. This modular organization may correspond to saccade-related cells that have also been reported to be organized into clusters in the cat SC. © 1993 Wiley-Liss,Inc.     

Cortical projections to the superior colliculus in the macaque monkey: A retrograde study using horseradish peroxidase

The topical and laminar distribution of corticotectal cells, as well as their size and morphology, were studied in the macaque monkey with the horseradish peroxidase (HRP) technique. After HRP injections restricted primarily to the superficial layers of the colliculus, labelled cells were found in visual cortex (areas 17, 18, and 19) and both in the frontal eye field (area 8) and the adjacent part of premotor cortex (area 6). The clustering of labelled cells in visual cortex indicated that each of the anatomically and functionally distinct visual areas has its own set of collicular projections. When intermediate and deeper layers of the colliculus were injected, labelled cells were found also in posterior parietal cortex (area 7) where they were concentrated mainly on the posterior bank of the intraparietal fissure, in inferotemporal cortex (areas 20 and 21), in auditory cortex (area 22), in the somatosensory representation SII (anterior bank of sylvian fissure, area 2), in upper insular cortex (area 14), in motor cortex (area 4), in premotor cortex (area 6), and in prefrontal cortex (area 9). In the motor and premotor cortex, labelled cells formed a continuous band which appeared to stretch across finger-hand-arm-shoulder-neck representation. Similarly, the cluster of labelled cells in area 2 may correspond to the finger-hand representation of SII. The cortical regions not containing labelled cells were the somatosensory representation SI (areas 3, 1 and 2) and the infraorbital cortex. Labelled cells were restricted to layer V of all cortical areas except in the primary visual cortex, where labelled cells were found in both layer V and layer VI. The size spectrum of corticotectal cells ranged from 14.8 μm (average diameter) in area 17 to 27.8 μm in area 6, comprising cells as small as 8 μm and as large as 45 μm. Labelled cells in posterior parietal (area 7), in auditory (area 22), and in motor cortex (area 4) were small and distributed over only a narrow range of sizes. Those in premotor cortex (area 6) were often large and had a wide range in size distribution. The differences in size and morphology of corticotectal neurons suggest that they do not form a uniform class of neurons.     

An ultrastructural study of cat lumbosacral gamma-motoneurons after retrograde labelling with horseradish peroxidase

Twelve retrogradely horseradish peroxidase (HRP)-labelled triceps surae motoneurons of gamma size (mean cell body diameter less than 38 micron) were studied ultrastructurally. The contours of the cell bodies, as observed in the transverse midnucleolus plane, were elongated to rounded. The axons identified all originated from the cell body. The mean diameter of the stem dendrites was 4.5 micron. A substantial part of the cell membrane was covered by glial extensions. The boutons and synaptic contacts apposing the gamma-motoneurons could be classified into two categories on the basis of the type of synaptic vesicles: S-type boutons with spherical synaptic vesicles and F-type boutons with flattened vesicles. In each neuron, the values for mean length and mean area of apposition, percentage synaptic covering, and packing density of S-type, F-type, and S+F-type boutons were estimated on the cell body and in two dendritic compartments. In comparison with alpha-motoneurons and Renshaw cells, the cell bodies of the gamma-motoneurons were covered by smaller and strikingly fewer boutons of both the S- and F-types. The values for percentage synaptic covering and packing density of boutons on the proximal dendrites were also lower for gamma-motoneurons than for both alpha-motoneurons and Renshaw cells, although the differences were less pronounced than on the cell body. No boutons of the C-, M-, and T-types described for alpha-motoneurons were found on the gamma-motoneurons.     

Mesencephalic and diencephalic afferents to the superior colliculus and periaqueductal gray substance demonstrated by retrograde axonal transport of horseradish peroxidase in the cat

The mesencephalic and diencephalic afferent connections to the superior colliculus and the central gray substance in the cat were examined by means of the retrograde transport of horseradish peroxidase (HRP). After deep collicular injections numerous labeled cells were consistently found in the parabigeminal nucleus, the mesencephalic reticular formation, substantia nigra pars reticulata, the nucleus of posterior commissure, the pretectal area, zona incerta, and the ventral nucleus of the lateral geniculate body. A smaller number of cells was found in the inferior colluculus, the nucleus of the lateral lemniscus, the central gray substance, nucleus reticularis thalami, the anterior hypothalamic area, and, in some cases, in the contralateral superior colliculus, Forel's field, and the ventromedial hypothalamic nucleus. Only the parabigeminal nucleus and the pretectal area showed labeled cells following injections in the superficial layers of the superior colliculus. In the cats submitted to injections in the central gray substance, labeled cells were consistently found in the contralateral superior colliculus, the mesencephalic reticular formation, substantia nigra parts reticulata, zona incerta and various hypothalamic areas, especially the ventromedial nucleus. In some cases, HRP-positive cells were seen in the nucleus of posterior commissure, the pretectal area, Forel's field, and nucleus reticularis thalami. A large injection in the mediodorsal part of the caudal mesencephalic reticular formation, which included the superior colliculus and the central gray substance, resulted in numerous labeled cells in nucleus reticularis thalami. The findings are discussed with respect to the suggested functional division of the superior colliculus into deep and superficial layers. Furthermore, the possible implications of labeled cells in zona incerta and the reticular thalamic nucleus are briefly discussed.     

An autoradiographic study of the efferent connections of the superior colliculus in the cat

The differential projections of the three main cellular strata of the superior colliculus have been examined in the cat by the autoradiographic method. The stratum griseum superficiale projects caudally to the parabigeminal nucleus and rostrally to several known visual centers: the nucleus of the optic tract and the olivary pretectal nucleus in the pretectum; the deepest C laminae of the dorsal lateral geniculate nucleus; the large-celled part of the ventral lateral geniculate nucleus; the posteromedial, large-celled part of the lateral posterior nucleus of the thalamus. Several of these projections are topographically organized. The stratum griseum profundum gives rise to most of the descending projections of the superior colliculus. Ipsilateral projections pass to both the dorsolateral and lateral divisions of the pontine nuclei, the cuneiform nucleus, and the raphe nuclei, and to extensive parts of the brainstem reticular formation: the tegmental reticular nucleus, and the paralemniscal, lateral, magnocellular, and gigantocellular tegmental fields. Contralateral projections descending in the predorsal bundle pass to the medial parts of the tegmental reticular nucleus and of some of the tegmental fields, the dorsal part of the medial accessory nucleus of the inferior olivary complex, and to the ventral horn of the cervical spinal cord. Ascending projections of the stratum griseum profundum terminate in several nuclei of the pretectum, the magnocellular nucleus of the medial geniculate complex and several intralaminar nuclei of the thalamus, and in the fields of Forel and zona incerta in the subthalamus. The strata grisea profundum and intermediale each have projections to homotopic areas of the contralateral superior colliculus, to the pretectum, and to the central lateral and suprageniculate nuclei of the thalamus. However, the stratum griseum intermediale has few or no descending projections.     

Afferent and efferent connections of the parabigeminal nucleus in cat revealed by retrograde axonal transport of horseradish peroxidase

Afferent and efferent connections of the parabigeminal nucleus (PBG) of the cat have been demonstrated by means of horseradish peroxidase (HRP) tracing technique. Following HRP injection in the PBG, labelled cells were observed mainly in the deep layers of the ipsilateral superior colliculus (SC). The other labelled structures were the prepositus hypoglossi complex (PH), the ventral nucleus of the lateral geniculate body (LGV), the locus coeruleus, the cuneiform nucleus, the periaqueductal gray and the dorsomedial hypothalamic area. Efferent projections of the PBG were investigated by HRP injection in SC, LGV, PH, hypothalamus and in some acoustic relays, i.e. medial geniculate body and inferior colliculus. Only the PBG-SC projection appeared to be well systematized. The positive labelling of the PBG following injection of LGV and hypothalamus is discussed in terms of the specificity of the injection. The absence of afferent and efferent connections of the PGB with any acoustic relay tends to exclude this nucleus from the auditory system in contrast to previous suggestions. On the basis of the close reciprocal PBG-SC connections a possible role of the PBG within visuomotor tectal function is proposed.     

Intrinsic circuitry in the cat superior colliculus: projections from the superficial layers.

The neuroanatomical tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was used to label the local projections of neurons whose cell bodies are located in the superficial layers of the cat superior colliculus. Small, localized groups of neurons in the superficial layers project to all regions of the ipsilateral colliculus, including the deep layers. Comparable distributions of labeled terminals are seen throughout the colliculus when the PHA-L injection site is located in the rostral, middle, or caudal one-third of the colliculus. In addition, there is some evidence of a topographic projection from superficial to deep layers. These results suggest that a complex anatomical substrate exists for communication between the superficial and deep layers of the colliculus. Connections such as these may underlie the transfer of visual information from neurons in the superficial layers to populations of neurons in the deep layers that respond prior to saccadic eye movements.     

Possible determinants of the degree of retrograde neuronal labeling with horseradish peroxidase

The male progeny of mother rats which had been undernourished during most of gestation and all of lactation were divided into two groups when weaned at 25 days. One group was nutritionally rehabilitated (G^?L^?) while the other was underfed for a further 9 weeks (G^?L^?W^?) before nutritional rehabilitation. Despite this further undernutrition the G^?L^?W^? rats eventually caught up in both body and brain weight with the G^?L^? group. Compared with control rats of the same age that had been well fed throughout life, the G^?L^? and G^?L^?W^? animals had permanent deficits in body and regional brain weights.At 36 weeks rats were given two tests of motor co-ordination. They were required (a) to run backwards on a revolving drum and (b) to cross a chasm bridged by a ladder or parallel rods for a food reward. Both previously undernourished groups did consistently worse than controls of the same age or of similar body weight on two measures of co-ordination: falls from the revolving drum and stumbles on the bridge-crossing test. It is postulated that these differences indicate impaired cerebellar function in the previously undernourished rats.     

Identification of cells of origin of tectopontine fibers in the cat superior colliculus: an experimental study with the horseradish peroxidase method.

The pontine projections from the superior colliculus in the cat have been studied by means of retrograde axonal transport of horseradish peroxidase (HRP). Following injections of HRP in the dorsolateral pontine nucleus, where the tectopontine fibers terminate, a fair number of labeled cells are found throughout the rostrocaudal extent of the ipsilateral superior colliculus. Relatively few of the labeled cells are of medium size (25-40 micron in diameter), more than 80% are small (10-25 micron), but no large cells are labeled. The cell bodies giving rise to tectopontine fibers are distributed in tectal layers deeper than the optic stratum (including this), with only a few in the deeper portion of the superficial gray layer. There are only few labelled cells in the relatively large lateral portion of the intermediate and deep gray layers were the largest neurons (more than 40 micron) are located. Most of these presumably belong to the tectoreticular and the tectospinal projections. The tectal neurons, distributed in various collicular layers, are supposed to receive different kinds of information from other parts of the central nervous system, e.g. from the retina, the cerebral cortex, the brain stem reticular formation, the spinal cord etc. The dorsolateral pontine nucleus appears to have a particular function in the integration of the input from the superior colliculus with those from other sources, especially from the inferior colliculus and the auditory cerebral cortex.     

Spinocerebellar tract neurons with axons passing through the inferior or superior cerebellar peduncles. A retrograde horseradish peroxidase study in rats

Using the retrograde horseradish peroxidase (HRP) method, we determined whether axons of the spinocerebellar tract (SCT) neurons pass through the superior (SCP) or the inferior (ICP) cerebellar peduncle in rats. Following bilateral section of either the SCPs or the ICPs, HRP was injected into the cerebellar anterior lobe and lobule VI, and the resulting labeled neurons were quantitatively examined throughout the length of the spinal cord. Almost all SCT neurons in the central cervical nucleus, Clarke's column and lamina VII of the third cervical (C3) to third thoracic (T3) segments and the T11 to fifth lumbar (L5) segments, and the majority of SCT neurons in the ventrolateral part of the anterior horn of the L6 to caudal (Ca) segments and laminae V of the C8-L5 segments and VII of the L6-Ca segments project their axons through the ICPs. The majority of spinal border cells (T11-L5) and a large number of SCT neurons in lamina VII of the C3-T3, T11-L5 and L6-Ca segments project their axons through the SCPs. A nearly equal number of SCT neurons in lamina VIII (C1-L6) send axons through the SCPs or the ICPs. The proportion of SCT neurons projecting via the SCPs versus those projecting via the ICPs was approximately 1:5.     

The abducens motor and internuclear neurons in the rabbit: retrograde horseradish peroxidase and double fluorescent labeling

Horseradish peroxidase and the fluorochromes Fast blue and propidium iodide were injected into the lateral rectus and retractor bulbi muscles and/or the oculomotor nucleus of the rabbit to determine the locations and basic morphology of motoneurons and internuclear neurons in the abducens nucleus. The 1000–1100 motoneurons found were distributed throughout the nucleus except in the rostral and caudal tips, but were most densely clustered in the dorsomedial area, especially in the middle third of the nucleus, where 60% of these cells were found. The rostral and caudal tips were composed of internuclear neurons, 25% of which lay in the rostral third of the nucleus, 35% in the middle third and 40% in the caudal third. In the middle third, interneurons occupied the ventral and lateral areas of the nucleus (where they mingled with motoneurons); in the rostral and caudal thirds they were more widely distributed. At the level of the caudal half of the nucleus it was impossible to distinguish clearly between the most lateral abducens interneurons and the most rostromedial labeled vestibular neurons. The abducens interneurons of the rabbit (320–380) thus differ in interesting respects from those described previously in either lateral eyed or frontal eyed mammals.     

A cholinergic projection to the rat superior colliculus demonstrated by retrograde transport of horseradish peroxidase and choline acetyltransferase immunohistochemistry

Acetylcholinesterase (AChE) has been localized by histochemistry in the superior colliculus and in the tegmentum of the caudal midbrain and rostral pons of the rat. The pattern of AChE localization in the superior colliculus was characterized by homogeneous staining in the superficial layers and patchlike staining in the intermediate gray layer. In the tegmentum, AChE was localized in the pedunculopontine nucleus (PPN), beginning rostrally at the caudal pole of the substantia nigra and extending caudally to the level of the parabrachial nuclei, and in the lateral dorsal tegmental nucleus (LDTN) of the central gray. The localization of AChE in these nuclei overlapped the distribution of neurons stained by immunohistochemistry using an antibody to choline acetyltransferase (ChAT), the synthesizing enzyme of the neurotransmitter acetylcholine. Other neighboring areas that were stained with AChE, but that did not contain ChAT-immunoreactive neurons, included the microcellular tegmental nucleus and the ventral tegmental nucleus. Neurons in the PPN and LDTN were determined to be potential sources of the cholinergic projection to the intermediate gray layer of the rat superior colliculus by double labelling with retrograde transport of horseradish peroxidase (HRP) combined with the immunohistochemical localization of ChAT. Three populations of neurons were identified. A predominantly ipsilateral ChAT-immunoreactive population was located in the pars compacta subdivision of PPN (PPNpc). Retrograde HRP-labelled neurons in the pars dissipata subdivision of the PPN (PPNpd), located ventral to the superior cerebellar peduncle (SCP) at the level of the inferior colliculus, composed a second population that was predominantly contralateral but was not ChAT immunoreactive. A third population of retrogradely labelled neurons was predominantly ipsilateral and ChAT immunoreactive and was located in the LDTN. These findings compared favorably with the full extent of the projection from this tegmental region revealed by retrograde transport of HRP from the superior colliculus when more compatible fixation and chromogen procedures were used. The results suggest that the PPN and the LDTN are two sources of the cholinergic input to the superior colliculus. Since the PPN also has extensive efferent, and afferent, connections with basal-ganglia-related structures, this cholinergic excitatory input to the superior colliculus, like the GABA-ergic inhibitory input from the substantia nigra pars reticulata, may provide the basis for an additional influence of the basal ganglia on visuomotor behavior.     

Morphological characteristics and terminating patterns of masseteric neurons of the mesencephalic trigeminal nucleus in the rat: an intracellular horseradish peroxidase labeling study

In order to study the morphological characteristics and terminating patterns of the neurons of the trigeminal mesencephalic nucleus (Vme), 55 masseteric neurons in Vme in the rat were stained by intracellular injection of horseradish peroxidase (HRP). Labeled cells were distributed throughout the nucleus. These neurons were divided into three types: uni- or pseudounipolar (type A, n = 43), bipolar (type B, n = 5), and multipolar cells (type C, n = 7). Each type was further divided into two subtypes according to the largest diameter of the perikarya (type a greater than or equal to 30 microns, type b less than 30 microns). The central processes of type Aa neurons projected to the following three groups of target nuclei: 1) nuclei functioning as interneurons, including supratrigeminal nucleus (Vsup), intertrigeminal nucleus (Vint), juxta-trigeminal region (Vjux), and parvicellular nucleus of the pontomedullary reticular formation (PcRF); 2) motor nuclei, including the trigeminal motor nucleus (Vmo), accessory facial nucleus (NVIIacs), accessory abducens nucleus (NVIacs), and a small number of labeled axons in the oculomotor nucleus and trochlear nucleus; 3) sensory nuclei, including the dorsomedial part of the principal trigeminal sensory nucleus (Vpdm) and the dorsomedial part of subnucleus oralis of the trigeminal spinal nucleus (Vodm). Labeled processes were dense in the Vsup, Vmo, and Vpdm. The proprioceptive pathway of the fifth nerve is discussed. Direct projections from type Aa neurons of Vme to the Vpdm and dorsolateral part of the Vsup contribute to conduction of the proprioceptive information from spindles of masticatory muscle to the contralateral thalamus in the rat. Different axon morphology, distribution, terminal branch density, and terminating patterns of type Aa neurons were noted in different functional groups of the projecting nuclei, especially in the Vsup, Vmo, and Vpdm. The highest terminal branching density, the most extensive distribution, and two different types of branching patterns (claw-like and comb-like) were observed in Vsup. Selective distribution and single-beaded or "Y"-shaped terminal branches were observed in Vmo. In the Vppdm the axonal branches were sparser than in the Vsup or Vmo, and had an arrangement like the branches of a weeping willow tree. These characteristics of anatomical organization might be related to the function of each projecting nucleus.     

Selective retrograde labeling of neurons of the cat vestibular ganglion with [3H]D-aspartate

D-[2,3-3H]Aspartate [( 3H]D-Asp) was injected in the cat vestibular nuclei. Labeling patterns resulting from retrograde axonal transport by the vestibular nerve fibers were observed in the vestibular ganglion neurons and also in the nerve fibers. The selectivity of such labeling, related to the neurotransmitter's specificity, is strongly indicated.