Patterns of expression of brain-derived neurotrophic factor and tyrosine kinase B mRNAs and distribution and ultrastructural localization of their proteins in the visual pathway of the adult rat

We have examined the cellular and subcellular distribution and the patterns of expression of brain-derived neurotrophic factor (BDNF), and of its high affinity receptor, tyrosine kinase B (TrkB), in retinorecipient regions of the brain, including the superior colliculus, the lateral geniculate nucleus and the olivary pretectal nucleus. In the retinorecipient layers of the superior colliculus, BDNF protein and mRNA were present in the cell bodies of a subpopulation of neurons, and BDNF protein was present in the neuropil as punctate or fiber-like structures. In the lateral geniculate nucleus, however, BDNF mRNA was not detected, and BDNF protein was restricted to punctate and fiber-like structures in the neuropil, especially in the most superficial part of the dorsal lateral geniculate nucleus, just below the optic tract. At the ultrastructural level, BDNF protein was localized predominantly to axon terminals containing round synaptic vesicles and pale mitochondria with irregular cristae, which made asymmetric (Gray type I) synaptic specializations (R-boutons). Enucleation of one eye was followed by loss of BDNF immunoreactivity and disappearance of BDNF-positive R-boutons in the contralateral visual centers, confirming the retinal origin of at least most of these terminals. TrkB was present in postsynaptic densities apposed to immunoreactive R-boutons in the superior colliculus and lateral geniculate nucleus, and was also associated with axonal and dendritic microtubules. These findings suggest that BDNF is synthesized by a subpopulation of retinal ganglion cells and axonally transported to visual centers where this neurotrophin is assumed to play important roles in visual system maintenance and/or in modulating the excitatory retinal input to neurons in these centers.     

Retinofugal projections of an echolocating megachiropteran

The projection leading from the eye and the nuclear targets of the projection to the brainstem were identified in an echolocating megachiropteran (Rousettus aegyptiacus) following unilateral intraocular injections of radioactive amino acids. In the hypothalamus, the projection ended bilaterally in suprachiasmatic nuclei. In the ventral thalamus, it ended bilaterally in external and internal divisions of the ventral lateral geniculate nuclei. In the dorsal thalamus, the projection terminated bilaterally in the dorsal lateral geniculate nuclei and contralaterally in the lateral posterior nucleus. Input from the two eyes was segregated to laminae in the lateral division of the dorsal lateral geniculate nucleus. The contralateral projection ended in the dorsolateral and ventral portions of lamina 1, in lamina 2, the ventral portions of lamina 3, and an interlaminar fiber plexus. The ipsilateral projection ended in the dorsomedial portion of lamina 1, the dorsal portion of lamina 3, and the most superficial portion of lamina 1. Contralateral and ipsilateral input to the medial division of the dorsal lateral geniculate nucleus was for the most part segregated. The projection to the pretectum terminated in nuclei of the optic tract, pretectal olivary nuclei, and posterior pretectal nuclei. Although the input to the pretectal nuclei was bilateral, the contralateral projection was greater. The contralateral projection to the superior colliculus terminated throughout the rostral-caudal extent of the superficial gray layer. The ipsilateral projection to the superior colliculus ended in the superficial gray layer in the middle one-third of the superior colliculus only. On the contralateral side the projection to the outer portion of the superficial gray layer was especially heavy. The superior fascicle of the accessory optic tract was identified. It was traced to dorsal, lateral, and medial accessory optic nuclei. These results indicate that the visual system of Rousettus is more extensive than that of the echolocating microchiroptera and that it is similar to that described for nonecholocating Pteropus.     

Retinofugal projections in the rufous horseshoe bat, Rhinolophus rouxi

Summary The retinal projections in the horseshoe bat were studied with anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. Retinal fibers clearly terminate bilaterally in the lateral geniculate nuclei, superior colliculus, pretectal area, and nucleus of the optic tract. The suprachiasmatic nucleus and the lateral terminal nucleus of the accessory optic tract receive extremely weak, though bilateral retinal input. No projections to medial and dorsal accessory optic nuclei were found. There was a limited retinal projection to the ipsilateral dorsal geniculate nucleus. The focus of the ipsilateral projection corresponded to a less densely labeled region on the contralateral side. In this study an ipsilateral retinal projection to the anterior superior colliculus is documented for the first time in a Microchiropteran bat. In the contralateral superior colliculus retinal fibers terminate in a patch-like pattern at caudal levels.Abbreviations BSC brachium of the SC - CH optic chiasm - CP cerebral peduncle - IGL intergeniculate leaflet - dLGN dorsal lateral geniculate nucleus - vLGN ventral lateral geniculate nucleus: d dorsal, i intermediate, v ventral subdivision - LTN lateral terminal nucleus of accessory optic system - MGN medial geniculate nucleus - NOT nucleus of the optic tract - NSCH suprachiasmatic nucleus - ON optic nerve - OT optic tract - PA pretectal area - PON pretectal olivary nucleus - Rh.r. Rhinolophus rouxi - SC superior colliculus     

Retinofugal projections of the big brown bat,Eptesicus fuscus and the neotropical fruit bat,Artibeus jamaicensis

Retinal connections were studied in Eptesicus fuscus and Artibeus jamaicensis using anterograde axonal degeneration and autoradiographic techniques following unilateral enucleations and uniocular injections of radioactive amino acids. Although each retina projected bilaterally to the brainstem, the number of silver grains in the emulsion of autoradiographs indicated that nearly all fibers in the optic nerve entered the contralateral optic tract. Ipsilaterally, a major portin of the projection ended in the suprachiasmatic nucleus; caudal to the suprachiasmatic nucleus, the amount of label was so small that individual silver grains were counted to determine the location and quantity of lebel in other ipsilateral nuclei. In both species the retinal projection terminated bilaterally in the suprachiasmatic, dorsal lateral geniculate, ventral lateral geniculate, and pretectal olivary nuclei and contralaterally in the posterior pretectal nucleus, superficial gray layers of the superior colliculus, and nuclei of the accessory optic system. In Eptesicus the projection to the nucleus of the optic tract ended contralaterally, and in Artibeus it ended in this nucleus bilaterally. The results of this study revealed a basic theme in the optic projection of the two ecologically different microchirop. terans. The results differed, however, in that the projection was larger and visually related nuclei were better developed in Artibeus. Such variations are presumed to relate to eye size and the relative use of vision by the two chiropterans.     

大鼠上丘的传出投射——ARG法和WGA-HRP法研究

本实验将~3H-Leucine 或 WGA-HRP 定位注(导)入大鼠一侧上丘内,观察了上丘传出纤维的终止部位。上丘浅层的传出纤维下行终止于二叠体旁核(以同侧核的背、腹群为主)、同侧桥核的背外侧部;其上行投射终止于内侧膝状体、膝上核、顶盖前区后核、丘脑外侧后核(以上均为两侧性,以同侧为主)、同侧的内及外侧视束核和外侧膝状体的背侧及腹侧核。另外,在两侧视束和视束交叉处均有标记颗粒。上丘中、深层的传出纤维终止于同侧中央灰质、Darkschewitsch 核、Cajal 中介核、楔形核以及对侧上丘;上行终止于内测膝状体,膝上核、顶盖前区前核、丘脑外侧后核(以上均为两侧性,以同侧为主)、束旁核、未定带、丘脑腹侧核(以上均为同侧);下行终止于同侧的有二叠体旁区和二叠体旁核,桥核的背外侧部、下丘外侧部、桥脑和延髓网状结构、下橄榄核的外侧部;终止于对侧的有二叠体旁核、桥脑和延髓网状结构内侧部、下橄榄核的内侧副核、脊髓颈段前角。     

Rearrangements in the retino-geniculate projections of rats following ablation of the superior colliculus in infancy

Summary The superior colliculus was bilaterally or unilaterally ablated at different early postnatal ages in rats. When adult, each rat received a unilateral eye injection of Horesradish peroxidase to reveal the crossed and uncrossed retinal terminal fields within the dorsal lateral geniculate nucleus. Collicular ablation in the first seven days after birth, but not thereafter, produced a small hole or vacancy within the contralateral retinal terminal field which was occupied by an aberrant ipsilateral retinal terminal field. These rearrangements in the retino-geniculate projections occurred in the caudal quarter of the nucleus dorso-laterally just beneath the optic tract, solely ipsilateral to the ablated colliculus. Possible causes of the formation of these rearrangements are discussed, and similarities with other aberrant retinal projections following early damage to the visual system are considered.Abbreviations dLGN Dorsal geniculate nucleus - DTN Dorsal terminal nucleus of the accessory optic tract - HRP Horseradish peroxidase - LP Latero-posterior nucleus - NOT Nucleus of the optic tract - OT Optic tract - PO Olivary pretectal nucleus - PP Posterior pretectal nucleus - SC Superior colliculus - TMB Tetramethyl benzidine     

Subcortical afferent and efferent connections of the superior colliculus in the rat and comparisons between albino and pigmented strains

Summary Subcortical connections of the superior colliculus were investigated in albino and pigmented rats using retrograde and anterograde tracing with horseradish peroxidase (HRP), following unilateral injection of HRP into the superior colliculus. Afferents project bilaterally from the parabigeminal nuclei, the nucleus of the optic tract, the posterior pretectal region, the dorsal part of the lateral posterior-pulvinar complex and the ventral nucleus of the lateral lemniscus; and ipsilaterally from the substantia nigra pars reticulata, the pars lateralis of the ventral lateral geniculate nucleus, the intergeniculate leaflet, the zona incerta, the olivary pretectal nucleus, the nucleus of the posterior commissure, the lateral thalamus, Forel's field H₂, and the ventromedial hypothalamus. Collicular efferents terminate ipsilaterally in the anterior, posterior and olivary pretectal nuclei, the nuclei of the optic tract and posterior commissure, the ventrolateral part of the dorsal lateral geniculate nucleus, the pars lateralis of the ventral lateral geniculate nucleus, the intergeniculate leaflet, and the zona incerta; and bilaterally in the parabigeminal nuclei and lateral posterior-pulvinar complex (chiefly its dorsal part). The general topographical patterns of some of the afferent and efferent projections were also determined: the caudal and rostral parts of the parabigeminal nucleus project to the caudal and rostral regions, respectively, of the superior colliculus; caudal superior colliculus projects to the most lateral, and lateral superior colliculus to the most caudal part of the terminal field in the dorsal lateral geniculate nucleus; caudolateral superior colliculus projects to the caudal ventrolateral part of the ventral lateral geniculate nucleus, while rostromedial parts of the colliculus project more rostrally and dorsomedially. Following comparable injections in pigmented and albino animals, fewer retrogradely labelled cells were found in subcortical structures in the albino than in the pigmented rats. The difference was most marked in nuclei contralateral to the injected colliculus. Thus, the effects of albinism on the nervous system may be more widespread than previously thought.M. R. C. Scholar     

Uncrossed retino-geniculate and retino-tectal projections in the hereditary unilaterally microphthalmic rats

The dorsal lateral geniculate nucleus (CGLd) of the hereditary unilaterally microphthalmic rats showed a diminution of volume and an increase of neuronal density on the contralateral side of the vestigial eye without the optic nerve (about 60 and 160% of the normal, respectively; P less than 0.001). No significant changes were observed in the ipsilateral CGLd. Uncrossed retino-CGLd and -tectal projections were studied using the anterograde axonal transport of HRP in adult rats with the congenital unilateral microphthalmia. Aberrant expansions of the uncrossed retinal projection widely covered CGLd and the superficial layers of the superior colliculus (SCS). The distribution pattern of expanded uncrossed retinal pathway in the mutant was essentially similar to that of neonatally one-eyed rats.     

The accessory optic fiber system of the golden hamster with special reference to retinohypothalamic projection

The hamster accessory optic fiber system has been investigated with the use of de Olmos-Ingram and Fink-Heimer silver methods following the production of unilateral ocular enucleation. It was found that this fiber system consists of both crossed and uncrossed inferior and superior fasciculi. The fibers of the inferior fasciculus (anterior accessory optic tract) run along the medial edge of the cerebral peduncle and terminate within the medial terminal nucleus of the accessory optic system. The fibers of the superior fasciculus (posterior accessory optic tract) leave the main optic tract, pass superficially over the medial geniculate nucleus and the cerebral peduncle; they synapse within the dorsal, the lateral and the medial terminal accessory optic nuclei. The presence of a retinohypothalamic tract could not be confirmed.     

Ascending projections from the nucleus of the brachium of the inferior colliculus in the cat

Summary Ascending projections from the nucleus of the brachium of the inferior colliculus (NBIC) in the cat were studied by the autoradiographic tracing method. Many fibers from the NBIC ascend ipsilaterally in the lateral tegmentum along the medial border of the brachium of the inferior colliculus. At midbrain levels, fibers from the NBIC end in the superior colliculus, the pretectum, the central gray and the peripeduncular tegmental region bilaterally with ipsilateral predominance. NBIC fibers to the superior colliculus are distributed densely to laminae VI an III throughout the whole rostrocaudal extent of the colliculus. In the pretectum, NBIC fibers terminate in the anterior and medial nuclei and the nucleus of the posterior commissure. NBIC fibers to the dorsal thalamus are distributed largely ipsilaterally. Many NBIC fibers end in the dorsal and medial divisions of the medial geniculate body, but few in the ventral division. The NBIC also sends fibers to the suprageniculate, limitans and lateralis posterior nuclei and the lateral portion of the posterior nuclear complex; these regions of termination of NBIC fibers constitute, as a whole, a single NBIC recipient sector. Additionally, the NBIC sends fibers to the centralis lateralis, medialis dorsalis, paraventricular and subparafascicular nuclei of the thalamus.Abbreviations APtC Pars compacta of anterior pretectal nucleus - APtR Pars reticulata of anterior pretectal nucleus - BIC Brachium of infertior colliculus - CG Central gray - CL Nucleus centralis lateralis - CP Cerebral peduncle - D Dorsal division of medial geniculate body - IC Inferior colliculus - LG Lateral geniculate body - LP Nucleus lateralis posterior - Lim Nucleus limitans - M Medial division of medial geniculate body - MD Nucleus medialis dorsalis - ML Medial lemniscus - NBIC Nucleus of brachium of inferior colliculus - NPC Nucleus of posterior commissure - PN Pontine nuclei - Ppr Peripeduncular region - Pt Pretectum - Pbg Parabigeminal nucleus - Pol Lateral portion of posterior nuclear complex - Pom Medial portion of posterior nuclear complex - Pul Pulvinar - Pv Nucleus paraventricularis - R Red nucleus - SC Superior colliculus - Sg Nucleus suprageniculatus - Spf Nucleus subparafascicularis - V Ventral division of medial geniculate body - VPL Nucleus ventralis posterolateralis - VPM Nucleus ventralis posteromedialis - II,III,IV,VI Tectal laminae     

Cortical and subcortical connections of the pars compacta of the anterior pretectal nucleus in the rat.

The efferent and afferent connections of the dorsal part of the anterior pretectal nucleus, pars compacta (APc), were studied experimentally in the rat by using neurotracers. A restricted number of structures supply afferents to the anterior pretectal nucleus: the visual cortex (areas 17, 18 and 18a), ventral lateral geniculate nucleus and superficial layers of the superior colliculus. Additional afferents have been demonstrated originating from the Darkschewitsch nucleus, periaqueductal gray, zona incerta and anterior cingulate cortex. Efferent fibers are distributed to a sector of the deep mesencephalic nucleus just dorsolateral to the red nucleus, the basilar pontine gray, posterior and olivary pretectal nuclei, superficial layers of the superior colliculus, lateral posterior thalamic nucleus, ventral lateral geniculate nucleus and zona incerta. These anatomical observations indicate that the pars compacta of the anterior pretectal nucleus is closely related to visual centers, suggesting an involvement of this nucleus in visually mediated behavior.     

The primary optical projection in albino and pigmented rats]

1. We have studied by silver degeneration methods in transversal and horizontal brain series the pathways and the terminal nuclei of the primary optic system in albino and pigmented rats. 2. About 90% of the retinal axons are crossing in the Chiasma opticum. Differences between albino and pigmented rats are small. At the level of the lateral geniculate body (l.g.b.) the axons ramify. One branch is going in the optic tract or in the transversalsystem to the pretectum and tectum. The other branch goes as a collateral in the longitudinal system of the dorsal l.g.b. and ends here. 3. The optic fibers project--especially contralateral--to the following nuclei: veutral l.g.b. (lateral half), dorsal l.g.b., nucleus of the optic tract, Nc. olivaris praetectalis, Ncc. praetectales anterior et posterior and superior colliculus (laminae I-III). In the nuclei of the pretectal region are ipsilateral only a few degenerating fibers. 4. Especially in the dorsal l.g.b. but also in the superior colliculus the pigmented rats show ipsilateral an larger retinal input. 5. The ipsilateral fibers project to a special region in the dorsal l.g.b. This region is also innervated by contralateral axons. 6. In both the albino and pigmented rats the dorsal l.g.b. shows no lamination in the cytoarchitectonical picture and the ipsi- and contralateral input regions overlap. Therefore in the rat we can not speak from a laminated dorsal l.g.b. We have here--prepoperantly functional caused--a simple form of l.g.b. 7. The accessory optic system is only decussated. It includes the Fasciculus inferior tr. opt. accessorius, who projects only and direct to the median terminal nucleus and the Fasciculus superior tr. opticus accessorius. The last goes off from the optic tract at the level of the pretectal region and innervates all the 3 accessory optic nuclei. 8. In a few preparates we found references for a direct retino-hypothalamic connection (Nc. suprachiasmaticus and Nc. arcuatus hypothalami).     

Retinal projections to the subcortical visual system in congenic albino and pigmented rats

The primary visual pathway in albino mammals is characterized by an increased decussation of retinal ganglion cell axons at the optic chiasm and an enhanced contralateral projection to the dorsal lateral geniculate nucleus. In contrast to the primary visual pathway, little is known about the organization of retinal input to most nuclei of the subcortical visual system in albino mammals. The subcortical visual system is a large group of retinorecipient nuclei in the diencephalon and mesencephalon. These areas mediate a range of behaviors that include both circadian and acute responses to light. We used a congenic strain of albino and pigmented rats with a mutation at the c locus for albinism (Fischer 344-c/+; LaVail MM, Lawson NR (1986) Development of a congenic strain of pigmented and albino rats for light damage studies. Exp Eye Res 43:867-869) to quantitatively assess the effects of albinism on retinal projections to a number of subcortical visual nuclei including the ventral lateral hypothalamus (VLH), ventral lateral preoptic area (VLPO), olivary pretectal nucleus (OPN), posterior limitans (PLi), commissural pretectal area (CPA), intergeniculate leaflet (IGL), ventral lateral geniculate nucleus (vLGN) and superior colliculus (SC). Following eye injections of the neuroanatomical tracer cholera toxin-beta, the distribution of anterogradely transported label was measured. The retinal projection to the contralateral VLH, PLi, CPA and IGL was enhanced in albino rats. No significant differences were found between albino and pigmented rats in retinal input to the VLPO, OPN and vLGN. These findings raise the possibility that enhanced retinofugal projections to subcortical visual nuclei in albinos may underlie some light-mediated behaviors that differ between albino and pigmented mammals.     

Electromyographic studies of neck muscles in the intact cat

Summary Substance P (SP)-, vasoactive intestinal polypeptide (VIP)-, and cholecystokinin (CCK)-like immunoreactive (LI) neurons were found in the superior colliculus (SC) of the rat, and examined to ascertain whether they sent projection fibers to the dorsal lateral geniculate nucleus (LGNd). Immunocytochemical staining with antisera against SP, VIP, and CCK showed that many immunoreactive neuronal cell bodies were located in the superficial layers of the SC, especially in the stratum griseum superficiale. The pattern of distribution of these immunoreactive neuronal cell bodies in the SC was similar to that of neuronal cell bodies which were retrogradely labeled with WGA-HRP (wheat germ agglutinin-horseradish peroxidase conjugate) injected ipsilaterally into the LGNd. On the other hand, SP-, VIP- and CCK-LI axons were seen most densely in the lateral part of the LGNd, especially in the small-celled LGNd zone adjacent to the optic tract, where anterograde labeling was also observed after injection of WGA-HRP ipsilaterally into the superficial layers of the SC. When a lesion was produced by kainic acid injection into the superficial layers of the SC, axons showing SP-, VIP-, or CCK-LI in the LGNd ipsilateral to the lesion were markedly depleted. The results indicate that SC-LGNd projection neurons contain SP, VIP, and/or CCK in the rat.     

Lack of 5-HT(1B) receptor and of serotonin transporter have different effects on the segregation of retinal axons in the lateral geniculate nucleus compared to the superior colliculus

We have shown previously that raised levels of serotonin (5-hydroxytryptamine or 5-HT) during development prevent retinal ganglion cell axons from segregating into eye-specific regions in their principal targets: the superior colliculus and the dorsal lateral geniculate nucleus. Possible mediators of 5-HT in this system include its plasma membrane transporter, which is transiently expressed by a sub-population of retinal ganglion cells, and the presynaptic 5-HT(1B) receptor carried on retinal ganglion cell axons. We analysed the retinal projections of 5-HT(1B) knockout (n=15), serotonin transporter knockout (n=14), serotonin transporter/5-HT(1B) double knockout (n=4) and monoamine oxidase A/5-HT(1B) double knockout (n=3) mice.In all four different knockout mice, the ipsilateral retinal projection to the superior colliculus was more diffuse and lost its characteristic patchy distribution. The alterations were most severe in the serotonin transporter knockout mice, where the ipsilateral retinal fibres covered the entire rostrocaudal and mediolateral extent of the superior colliculus, whereas in the 5-HT(1B) and double knockout mice, fibres retracted from the caudal and lateral superior colliculus. Abnormalities in the 5-HT(1B) knockout mice appeared only after postnatal day (P) 4. Treatment with parachlorophenylalanine (at P1-P12) to decrease serotonin levels caused an exuberance of the ipsilateral retinal fibres throughout the superior colliculus (n=9). In the dorsal lateral geniculate nucleus in contrast, the distribution and size of the ipsilateral retinal projection was normal in all four knockout mice. In the serotonin transporter knockout mice however, the contralateral retinal fibres failed to retract from the mediodorsal dorsal lateral geniculate nucleus, an abnormality that was reversed by early treatment with parachlorophenylalanine and in the serotonin transporter/5-HT(1B) double knockout.OUR OBSERVATIONS INDICATE: (1) that the lack of 5-HT transporter and the associated changes in 5-HT levels impair the segregation of retinal axons in both the superior colliculus and the dorsal lateral geniculate nucleus; (2) that 5-HT and 5-HT(1B) receptors are necessary for the normal refinement of the ipsilateral retinal fibres in the superior colliculus, but are not essential for the establishment of eye-specific segregation in the thalamus. Thus, both an excess and a lack of 5-HT affect the refinement of the superior colliculus retinal projection, while the establishment of eye-specific patterns in the dorsal lateral geniculate nucleus appears not to be sensitive to the lack of 5-HT or 5-HT(1B) receptors.     

The differential distribution of the growth-associated protein-43 in first and higher order thalamic nuclei of the adult rat

Corticothalamic axons from layer 5 of primary and secondary auditory and visual areas have large terminals that make multiple synaptic contacts on proximal dendrites of relay cells in higher order thalamic nuclei and have been termed "driver" inputs. The corticothalamic cells express mRNA for the presynaptic growth-associated protein-43, in the adult rat [Feig SL (2004) Corticothalamic cells in layers 5 and 6 of primary and secondary sensory cortex express GAP-43 mRNA in the adult rat. J Comp Neurol 468:96-111]. In contrast, ascending driver afferents to first order nuclei (e.g. retinal, inferior collicular, and lemniscal) lose growth-associated protein-43 as mature synaptic terminals are established. Levels of immunoreactivity for growth-associated protein-43 are compared for first and higher order visual (lateral geniculate and lateral posterior), auditory (ventral and dorsal divisions of the medial geniculate), and somatosensory (ventral posterior and posterior) thalamic nuclei. At one week postnatal, staining for growth-associated protein-43 is uniform throughout first and higher order thalamic nuclei. By three weeks and thereafter, staining is denser in the higher order than first order thalamic nuclei. Electron microscopy shows growth-associated protein-43 in profiles with characteristics of afferents from layer 5 in LP and medial geniculate nucleus and no such label in retinal afferents in lateral geniculate nucleus. In these nuclei, approximately 25% of the profiles with characteristics of cortical afferents from layer 6 have label for growth-associated protein-43. The superficial layers of the superior colliculus also show growth-associated protein-43 positive profiles with characteristics of terminals from cortical layer 5. Some growth-associated protein-43 positive terminals were also positive for GABA in the thalamic nuclei studied and in the superior colliculus. The data suggest that sensory afferents to first order thalamocortical relays become stabilized once mature synaptic patterns are established, but the higher stages of information processing involving higher order thalamic relays, via cells in cortical layer 5, retain plasticity related to growth-associated protein-43 in the adult.     

A tectocortical visual pathway in the rat

Injections of tritiated leucine into the superior colliculus of the rat were used to study the efferents of the colliculus. The superficial layers of the colliculus project to the lateral posterior nucleus, the lateral geniculate nucleus and the pretectum. Two distinct subdivisions of the lateral posterior nucleus were found, a caudomedial region which receives a bilateral projection from the superior colliculus and an anterolateral region which receives a unilateral projection from the superior colliculus. Injections of horseradish peroxidase into the lateral prestriate visual cortex showed that the lateral posterior nucleus sends a dense projection to this area. There was no evidence that the caudomedial and anterolateral parts of the lateral posterior nucleus project to different regions of the lateral prestriate cortex.The tectothalamocortical pathway in the rat provides a major route outside the geniculostriate projection by which visual information from the retina can reach the cortex.     

Immunocytochemical mapping of NPY and VIP neuronal elements in the cat subcortical visual nuclei, with special reference to the pretectum and accessory optic system

The aim of this study was to describe the distribution patterns of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP)-immunoreactive (ir) neuronal elements in subcortical visual centers of the cat. Numerous NPY-ir neurons were present in the feline nucleus of the optic tract and in the anterior pretectal nucleus. Only a few NPY-ir neurons were found in the posterior, medial and olivary pretectal nuclei and in the accessory optic nuclei. Diffuse and heavily beaded NPY-ir fiber plexuses were observed throughout the superior colliculus, pretectum, and accessory optic system. Extensively arborising NPY-ir fibers were present in the mesencephalon and ventral lateral geniculate nucleus, while the dorsal visual thalamic nuclei contained only a few NPY-ir fibers. VIP-ir cells were present mainly in the accessory optic nuclei, and they were absent in the dorsal visual thalamus. Both NPY- and VIP-ir neurons were multipolar and fusiform in shape in the regions studied. Enucleation did not alter the appearance of NPY- and VIP-containing neuronal elements in the superior colliculus and pretectum while in the thalamus a subset of NPY-ir fiber population disappeared, indicating their retinal origin. Although there is a partial overlap in the topographical localization of the NPY- and VIP-ergic neurons in the pretectum, the colocalization of the two peptides could not be demonstrated. The present observations demonstrate the existence of two different and separate peptidergic (NPY and VIP) neuronal populations in the pretectum. Accepted: 18 May 1999     

Effects of neonatal and late unilateral enucleation on optokinetic responses and optic nerve projections in the rabbit

Summary Rabbits were unilaterally enucleated at the age of 0 or 21 days or at adult age. After survival times of 6–21 months optokinetic nystagmus (OKN) was measured and retinofugal connections were traced with anterograde transport of horseradish peroxidase or ³H leucine, injected into the eye. Non-enucleated animals served as controls. The asymmetry of monocular OKN in normal rabbits, characterized by a strong preference for pursuit of motion in the nasal (anterior) direction, was only slightly alleviated after enucleation. Responses to stimulation in the nasal direction were unchanged; responses to stimulation in the temporal direction showed modest improvements especially after enucleation at adult age and to a smaller degree after enucleation at 0 or 21 days. Redistribution of retinofugal fibers from the eye remaining after enucleation was very limited. Contralateral connections, including those to the lateral geniculate nucleus, showed a normal distribution. Of the ipsilateral connections, those to the lateral geniculate nucleus were normal in extent and density, while those to the superior colliculus were enhanced, in agreement with previous workers (Chow et al. 1973, 1981). Changes in ipsilateral pretectal projections were extremely small; particularly no connections to the nucleus of the optic tract were developed in any of the normal or enucleated animals. Of the accessory optic nuclei, the medial terminal nucleus received a very small ipsilateral projection in normal rabbits, which was markedly enhanced after enucleation especially at 0 and 21 days, but even at adult age. It is concluded that functional and anatomical plasticity of OKN circuits in the rabbit is very limited from the time of birth.     

Evidence for intrinsic expression of enkephalin-like immunoreactivity and opioid binding sites in cat superior colliculus

We have investigated the cellular localization of opioid peptides and binding sites in the cat's superior colliculus by testing the effects of retinal deafferentation and intracollicular excitotoxin lesions on patterns of enkephalin-like immunostaining and opiate receptor ligand binding. In normal cats, enkephalin-like immunoreactivity marks a thin tier in the most dorsal stratum griseum superficiale, small neurons of the stratum griseum superficiale, and patches of fibers in the intermediate and deeper gray layers. Eliminating crossed retinotectal afferents by contralateral eye enucleation had little immediate effect on this pattern, although chronic eye enucleation from birth did reduce immunoreactivity in the superficial layers. By contrast, fiber-sparing destruction of collicular neurons by the excitotoxins N-methyl-D-aspartate and ibotenic acid virtually eliminated enkephalin-like immunoreactivity in the neuropil of the upper stratum griseum superficiale, presumably by killing enkephalinergic cells of the superficial layers. Such lesions did not eliminate the patches of enkephalin-like immunoreactivity in the deeper layers. In normal cats, opiate receptor ligand binding is dense in the stratum griseum superficiale, particularly in its upper tier, and moderately dense in the intermediate gray layer. Contralateral eye removal had no detectable effect on the binding pattern, but excitotoxin lesions of the colliculus dramatically reduced binding in both superficial and deep layers. Some ligand binding, including part of that in the upper stratum griseum superficiale, apparently survived such lesions. Similar effects were observed in the lateral geniculate nucleus: enucleation produced no change in binding, whereas excitotoxin lesions greatly reduced specific opiate binding. We conclude that in the superficial collicular layers, both enkephalin-like opioid peptides and their membrane receptors are largely expressed by neurons of intrinsic collicular origin. The close correspondence between the location of these intrinsic opioid elements and the tier of retinal afferents terminating in the upper stratum griseum superficiale further suggests that opiatergic interneurons may modulate retinotectal transmission postsynaptically.