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A R Lieberman

Publications and source records attributed to A R Lieberman.

At least 55 records · Page 3Linked to original sources
PubMed1995

Organization of serotoninergic projections from the raphé nuclei to the anterior thalamic nuclei in the rat: a combined retrograde tracing and 5-HT immunohistochemical study.

We combined retrograde transport of horseradish peroxidase (HRP) with 5-hydroxytryptamine (5-HT) immunohistochemistry to study serotoninergic projections to the anterior thalamic nuclei (ATN) of the rat. Small iontophoretic injections of HRP into the anterodorsal thalamic nucleus resulted in double-labelled neurons predominantly in the ventromedial and also in the ventrolateral part of the ipsilateral dorsal raphé (DR). A smaller number of double-labelled neurons was also found in the dorsomedial part of the nucleus, predominantly ipsilaterally, and in the median raphé nucleus (MnR), close to the midline. After injection into the medial subdivision of the anteroventral thalamic nucleus, the pattern of labelling in DR and MnR was similar to that detected following injections into the anterodorsal thalamic nucleus. However, injection into the posterior subdivision of the anteroventral thalamic nucleus resulted in bilateral retrograde labelling of a few 5-HT-containing neurons in the dorsolateral part of the DR. Labelling in the ventromedial, ventrolateral and dorsomedial regions of DR and MnR was similar to that detected after injections into the medial subdivision of the anteroventral thalamic nucleus. After all injections into the ATN, double-labelled cells were found throughout the rostrocaudal extent of MnR and throughout the rostral two-thirds of DR. The caudal extension of DR was devoid of double-labelled cells. Although double-labelled cells were observed bilaterally in the dorsolateral part of the DR, the projection from DR to ATN was predominantly ipsilateral. These results show that there is an internal organization within DR such that subnuclei of the DR can be defined on the basis of their efferent projections to specific subdivisions of the ATN.

Afferent Pathways↗
PubMed1995

GABAergic projections from the thalamic reticular nucleus to the anteroventral and anterodorsal thalamic nuclei of the rat.

We have studied GABAergic projections from the thalamic reticular nucleus to the anterior thalamic nuclei of the rat by combining retrograde labelling with horseradish peroxidase and GABA-immunohistochemistry. Small iontophoretic injections of the tracer into subnuclei of the anterior thalamic nuclear complex resulted in retrograde labelling of cells in the rostrodorsal pole of the ipsilateral thalamic reticular nucleus. All of these cells were also GABA-positive. The projections were topographically organized. Neurons located in the most dorsal part of the rostral reticular nucleus projected to the dorsal half of both the posterior sub-division and the medial subdivision of the anteroventral thalamic nucleus, and to the rostral portion of the anterodorsal thalamic nucleus. Immediately ventral to this group of neurons, but still within the dorsal portion of the reticular nucleus, a second group of neurons, extending from the dorsolateral to the dorsomedial edge of the nucleus, projected to the ventral parts of the posterior and medial subdivisions of the anteroventral nucleus. Following injection of tracer into the dorsal part of the rostral anteroventral nucleus, retrograde labelled GABA-containing cell bodies were also found in the ipsilateral anterodorsal nucleus.

Animals↗
PubMed1995

Regenerative and other responses to injury in the retinal stump of the optic nerve in adult albino rats: transection of the intracranial optic nerve.

The response to injury of the proximal (retinal) stump of the intracranially transected optic nerve in adult rats has been studied by electron microscopy. The central part of the retinal stump of the optic nerve underwent severe ischaemic damage resulting in the formation by 3 days postoperation (dpo) of a cone-shaped region of necrotic tissue which extended from a base occupying most of the cross-sectional area of the nerve at the cut end to an apex within the intraorbital part of the nerve and only 2-3 mm from the eyeball. A mixture of apparently viable and dead or dying cells and axons was present in an intermediate zone surrounding the ischaemic core. Apparently intact nerve fibres occupied most of the periphery of the optic nerve. Small bundles of sprout-like axons were seen in the intermediate zone at 3 dpo, and by 5 dpo such sprouts were present at the periphery of the degenerative core. By 7 dpo, the sprouts were also found in the centre of the degenerative core, accompanied by astrocyte processes. The number of axonal sprouts present in the degenerative core and intermediate zone was much higher at 2 and 4 wk postoperation (wpo) than at 7 dpo, then declined gradually by 6 and 8 wpo. These results show that intracranial transection of the rat optic nerve produces extensive degeneration in the proximal stump and effectively produces an intraorbital axotomy of many retinal ganglion cells. Nevertheless, surviving axons display the ability to produce regenerative sprouts which persist for considerably longer than those produced after intraorbital injury.

Animals↗
PubMed1995

The effects of a lesion or a peripheral nerve graft on GAP-43 upregulation in the adult rat brain: an in situ hybridization and immunocytochemical study.

We have sought to determine (1) if thalamic neurons upregulate the growth associated protein GAP-43 as a response to injury, or if a peripheral nerve graft is required to induce, enhance or sustain such a response, and (2) if thalamic neurons with different regenerative potentials also display different GAP-43 responses. Levels of GAP-43 protein (detected by LM and EM immunohistochemistry) and of GAP-43 mRNA (detected by in situ hybridization) were compared in the thalamus of adult rats between 1 d and 180 d after making a stab lesion or after implanting a peripheral nerve autograft. Stab injury is a sufficient stimulus to cause a transient upregulation in GAP-43 expression by neurons in the thalamus (both around the graft tip and in particular in the thalamic reticular nucleus) in the first week after injury but this response is both prolonged, and enhanced in the presence of a peripheral nerve graft. In addition, we demonstrate directly, by double labelling, that neurons of the thalamic reticular nucleus displaying high levels of the mRNA for GAP-43, have axons regenerating in the distal portion of the graft. These findings lend direct support to the hypothesis that upregulation of the GAP-43 gene is essential for prolonged regenerative axonal growth. We also demonstrate GAP-43 protein in graft Schwann cells and in brain astrocytes close to the site of graft implantation.

Animals↗
PubMed1994

Reinnervation of Pacinian corpuscles by CNS axons after transplantation to the dorsal column: incidence and ultrastructure.

We have investigated the capacity of injured axons in the spinal dorsal columns of young adult rats to reinnervate grafted Pacinian corpuscles. A branch of the hindlimb interosseous nerve with a group of crural Pacinian corpuscles attached to it was autotransplanted to the surface of the spinal cord and the nerve stump was implanted into the dorsal column. Two to three months later 16 grafts were removed for examination by light and electron microscopy. By 3 months after transplantation almost all Schwann cell columns of the grafted nerve branch were occupied by regenerated myelinated and unmyelinated axons. Of 41 corpuscles examined by electron microscopy 24 were reinnervated by 1-3 myelinated fibres which gave rise to multiple terminals in the inner core. The remaining corpuscles appeared to be denervated. Only two of the reinnervated corpuscles contained regenerated endings which reiterated the distinct ultrastructure of normal presynaptic terminals of CNS axons, characterized by clusters of lucent vesicles and paramembranous densities. All other corpuscles were reinnervated by terminals which resembled peripheral mechanosensory endings as they contained mitochondria and very few vesicles. One such corpuscle was coinnervated by small terminals filled with large dense cored vesicles. We assume that the majority of grafted Pacinian corpuscles have been reinnervated by dorsal column axons and that the regenerated terminals with the ultrastructure of peripheral mechanosensory endings derive from central axons of primary sensory neurons, which are apparently capable of constructing mechanosensory-like terminals in response to signals from the Pacinian corpuscles. The vesicle-filled endings are probably formed by second order sensory neurons, corticospinal neurons and small peptidergic neurons unable to adjust their terminals to the new target.

Animals↗
PubMed1994

Regenerative and other responses to injury in the retinal stump of the optic nerve in adult albino rats: transection of the intraorbital optic nerve.

The proximal stump of the optic nerve was examined by electron microscopy from 1 d to 8 wk (dpo/wpo) after intraorbital transection. At 1 dpo a layer of axonal, cytoplasmic and myelin debris approximately 15 microns thick was present at the cut end. A zone approximately 25 microns thick of abnormal and partly degenerate tissue composed of many swollen axons filled with organelles of predominantly abnormal appearance lay between the zone of debris and more proximal levels of the optic nerve, which retained a normal appearance. The earliest putative axonal sprouts were seen at 1 dpo in this zone. By 2 dpo, bundles of small nonmyelinated axons containing microtubules, almost certainly axonal sprouts, had grown out from more proximal regions of the proximal stump and extended as far as its cut end. By 3 dpo, large numbers of axonal sprouts, as well as large numbers of macrophages and newly formed blood vessels, were seen close to the cut end of the proximal stump. Glial cells were not seen to accompany these early outgrowing bundles of axonal sprouts. By 5 dpo, the number of sprouts and macrophages had increased; many bundles of sprouts were now in contact with the surface of astrocytes, which were partly covered by basal lamina. At 7 dpo most of the macrophages had disappeared from the most distal part of proximal stump and bundles of axonal sprouts, associated with astrocytes, which in some cases had penetrated and were fasciculating such bundles, were present at the cut end. The regenerating axonal sprouts in the scar-like tissue at the distal end of the proximal stump of the optic nerve declined in numbers sharply at 2 wpo and only a few sprout-like axonal profiles were present by 8 wpo. Thus while ultimately abortive the early regenerative response is vigorous and involves the outgrowth of a large number of axonal sprouts in the first week after injury.

Animals↗
PubMed1993

Differential regenerative growth of CNS axons into tibial and peroneal nerve grafts in the thalamus of adult rats.

Segments of peripheral nerve were autografted into the thalamus of adult rats. The peroneal nerve was used in one group, the tibial nerve (which has approximately twice the cross-sectional area of the peroneal nerve) in a second group, and two lengths of peroneal nerve side by side in a third group. Between 1 and 4 months later HRP was applied to the distal end of each graft to label neurons which had regenerated their axons into the graft. Serial coronal sections of each brain were reacted to reveal retrogradely transported HRP, and the positions of all labeled neurons were recorded in camera lucida drawings. In all three groups a few labeled neurons resembling thalamocortical projection cells were found in the dorsal thalamus close to the graft tip (mean number, 29 in the single peroneal group; 22 in the tibial group; and 14 in the double-peroneal group). However, neurons in the thalamic reticular nucleus (TRN) regenerated much more successfully into the larger nerve grafts; many more retrogradely labeled cells were found in animals with tibial or double-peroneal nerve grafts (mean number, 1.1 in the single-peroneal group; 272 in the tibial group; and 163 in the double-peroneal group). These neurons were concentrated in the sector of TRN known to project to the part of the dorsal thalamus containing the graft tip. The largest numbers of labeled neurons were found when the graft tip encroached upon the TRN. These results suggest that both graft size and graft position are critical determinants of the extent of axonal regeneration from the TRN. Larger grafts may be more copiously invaded by regenerating axons because such grafts damage larger numbers of TRN axons when implanted and/or because they stimulate regeneration by releasing critical quantities of neurotrophic factors.

Animals↗
PubMed1993

Some aspects of the synaptic circuitry underlying inhibition in the ventrobasal thalamus.

We describe here, and review, the ultrastructural features and synaptic relationships of flat-vesicle containing, presumptively inhibitory presynaptic elements in the glomerular and extraglomerular neuropils of the thalamic ventrobasal (VB) nucleus in monkey, cat and rat. This account is based on EM study of normal material, LM and EM immunocytochemistry for GABA, anterograde tracing with HRP and EM of physiologically characterized interneurons intracellularly injected with HRP. It emerges clearly from this study that attempts to categorize flat-vesicle containing terminals in thalamic tissue as either F-boutons (axon terminals with flattened synaptic vesicles and Gray type II synaptic specializations) or P-boutons (dendritic appendages of interneurons with flattened vesicles) by examining only single sections are likely to produce unreliable results. In many cases it is only by studying serial sections that such profiles can be unambiguously identified. Within glomeruli the P-boutons participate in triplet (triadic) synapses which are thought to mediate rapid feed forward inhibition of projection cells, and serial synaptic arrays involving other P-boutons. Since P-boutons from more than one interneuron are present in individual VB glomeruli, P-bouton to P-bouton synapses may mediate disinhibition of interneurons. We show that dendritic shafts of interneurons make and receive synaptic contacts and that in the monkey, at least, reciprocal synaptic contacts between shafts or between a shaft and a P-bouton are not uncommon. Finally, we confirm that in the rat VB there are insignificant numbers of P-boutons or cells with the morphological and transmitter characteristics of interneurons and we suggest that comparative electrophysiological studies of inhibitory events in rat VB versus those in cat or monkey VB during transmission of somatosensory information might help to clarify the roles of thalamic intrinsic neurons.

Animals↗
PubMed1993

Effects of chronic alcohol consumption and of dehydration on the supraoptic nucleus of adult male and female rats.

Ethanol ingestion affects the hypothalamo-neurohypophysial system resulting in increased diuresis, dehydration and hyperosmolality. We studied the supraoptic nucleus, of the hypothalamus, in ethanol-treated rats, to determine if ethanol alone and/or the associated disturbances of water metabolism lead to structural alterations in a nucleus known to play a central role in fluid homeostasis. Groups of male and female rats were ethanol-treated until 12 and 18 months of age and compared with age-matched pair-fed controls. Twelve and 18-month-old control groups and 12-month-old water control groups (rats submitted to chronic dehydration) were also included in this study in an attempt to differentiate between the effects of undernutrition and dehydration/hyperosmolality, and the specific neurotoxic effects of ethanol. We estimated the volume of the supraoptic nucleus and the numerical density of its neurons and calculated the total number of supraoptic neurons. The volume of both supraoptic neurons and neuropil were also estimated. In immunostained material the ratio of vasopressin to oxytocin neurons and the cross-sectional areas of the two neuronal types were evaluated. There was marked neuronal loss in alcohol-treated rats, but the volume of the supraoptic nucleus was increased. The increase in the volume of the supraoptic nucleus correlated with and was due to increases in the volume was particularly marked for vasopressin neurons. No significant differences were found between controls and pair-fed controls in any of the parameters investigated. In water control rats, the volume of the supraoptic nucleus and of the supraoptic neurons and neuropil was also greater than in pair-fed controls. However, the variations found were not as marked as in ethanol-treated rats and there was no cell loss. These findings reveal, for the first time, that chronic ethanol consumption affects the morphology of supraoptic neurons and neuropil and, consequently, the structure of the entire supraoptic nucleus. Moreover, this study supports the view that ethanol has direct neurotoxic effects on supraoptic neurons because the alterations that occur are not mimicked in animals in which water metabolism alone is disturbed.

Animals↗
PubMed1993

The supraoptic nucleus of the adult rat hypothalamus displays marked sexual dimorphism which is dependent on body weight.

The neurons of the supraoptic nucleus in the rat hypothalamus are reported not to possess receptors for gonadal steroids and sexual dimorphism has not previously been described in this nucleus. We have analysed this nucleus in groups of Sprague-Dawley rats (six males or six females per group), one, two, six, 12 and 18 months after birth. Body and brain weights were recorded, the volume of the nucleus was determined from the right hemisphere and all other quantitative parameters were determined from the left nucleus. In addition, different groups of four male and four female rats aged two and 18 months were analysed after immunocytochemical staining to distinguish between vasopressin and oxytocin neurons. The total number of neurons was constant in all groups studied, despite which the volume of the supraoptic nucleus increased progressively with age in both males and females. The cross-sectional areas and volumes of supraoptic neurons also increased with age. The volume density of the neuropil remained constant in all groups and there was a progressive decrease with age in the numerical density of neurons. Immunocytochemistry revealed that the age-dependent increases in the size of the neurons involved primarily the vasopressin neurons. The age-related changes were much greater in males than in females, resulting in significant differences between the sexes at two, six, 12 and 18 months with respect to the volume of the supraoptic nucleus, the cross-sectional areas of neuronal somata and nuclei, and the volume of supraoptic neurons. Thus the supraoptic nucleus and its vasopressin neurons are larger in adult males than in age-matched females. Since we have also shown that body weight is very closely correlated with changes in the size of supraoptic neurons, and adult male rats are heavier than females of the same age, we suggest that these size changes reflect adaptation of the vasopressin neurons of the supraoptic nucleus to increasing functional demands associated with the regulation of water balance in bodies of increasing size.

Aging↗
PubMed1992

Regeneration of adult rat CNS axons into peripheral nerve autografts: ultrastructural studies of the early stages of axonal sprouting and regenerative axonal growth.

If one end of a segment of peripheral nerve is inserted into the brain or spinal cord, neuronal perikarya in the vicinity of the graft tip can be labelled with retrogradely transported tracers applied to the distal end of the graft several weeks later, showing that CNS axons can regenerate into and along such grafts. We have used transmission EM to examine some of the cellular responses that underlie this regenerative phenomenon, particularly its early stages. Segments of autologous peroneal or tibial nerve were inserted vertically into the thalamus of anaesthetized adult albino rats. The distal end of the graft was left beneath the scalp. Between five days and two months later the animals were killed and the brains prepared for ultrastructural study. Semi-thin and thin sections through the graft and surrounding brain were examined at two levels 6-7 mm apart in all animals: close to the tip of the graft in the thalamus (proximal graft) and at the top of the cerebral cortex (distal graft). In another series of animals with similar grafts, horseradish peroxidase was applied to the distal end of the graft 24-48 h before death. Examination by LM of appropriately processed serial coronal sections of the brains from these animals confirmed that up to several hundred neurons were retrogradely labelled in the thalamus, particularly in the thalamic reticular nucleus. Between five and 14 days after grafting, large numbers of tiny (0.05-0.20 microns diameter) nonmyelinated axonal profiles, considered to be axonal sprouts, were observed by EM within the narrow zone of abnormal thalamic parenchyma bordering the graft. The sprouts were much more numerous (commonly in large fascicles), smoother surfaced, and more rounded than nonmyelinated axons further from the graft or in corresponding areas on the contralateral side of animals with implants or in normal animals. At longer post-graft survival times, the number of such axons in the parenchyma around the graft declined. At five days, some axonal sprouts had entered the junctional zone between the brain and the graft. By eight days there were many sprouts in the junctional zone and some had penetrated the proximal graft to lie between its basal lamina-enclosed columns of Schwann cells, macrophages and myelin debris. Within the brain, sprouts were in contact predominantly with other sprouts but also with all types of glial cell.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Pupillary constriction in response to light in rodents, which does not depend on central neural pathways.

We show here that the widely held belief that reflex constriction of the mammalian pupil in response to light depends exclusively upon neural pathways between eye and brain is in need of revision. We investigated the response of the pupil to light in dark-adapted rodents (golden hamsters; hooded rats; albino rats) subjected to a variety of surgical and pharmacological interventions designed to destroy or block all of the neural pathways and structures through which the reflex could be mediated. The interventions included bilateral intraorbital optic nerve section, or unilateral intracranial optic nerve section with enucleation of the contralateral eye, combined in some cases with bilateral removal of the superior cervical ganglia and/or pinealectomy; topical application of atropine; intraocular injection of tetrodotoxin (TTX). Golden hamsters and hooded rats, but not albino rats, retained an effective constriction of the pupil in response to light after all of these interventions, although the constriction was less and slower than in normal animals. These findings show that hamsters and hooded rats have both a neurally mediated fast light reflex that can be eliminated by severing connections between eye and brain, by blockade of cholinergic transmission to iris smooth muscle, and by blockade of action potentials by TTX; and a local, slower constriction in response to light, which remains after all these procedures. We have also confirmed previous observations of Bito and Turansky (1975) that pupillary constriction in response to light occurs in isolated in vitro anterior chamber preparations of hamster and hooded rat eyes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

GAP-43 in the axons of mammalian CNS neurons regenerating into peripheral nerve grafts.

Although mature mammalian CNS neurons do not normally regenerate axons after injury, it is well established that they will regrow axons over long distances into peripheral nerve implants. We have autografted segments of sciatic nerve into the brains of adult albino rats and have used light and electron microscopic immunocytochemistry to examine the distribution of the growth associated protein GAP-43 in and around the graft in the first two weeks following implantation. GAP-43 was present, 3-14 days after grafting, in small non-myelinated axonal sprouts in the brain parenchyma around the proximal tip of the graft. At 11-14 days after implantation similar sprouts within the graft itself were GAP-43 immunoreactive. The sprouts were either naked or associated with other cell processes (chiefly of Schwann cells; to a lesser extent of astrocytes). We also show that small numbers of neuronal perikarya around the tip of the graft become GAP-43 immunoreactive 11-14 days after implantation. Thus mature mammalian CNS neurons regenerating axons into a PNS graft display a marked increase in their content of GAP-43. In addition, we report that small plaques of GAP-43 reaction product are sometimes present on the plasma membranes of Schwann cells or astrocytes adjacent to immunoreactive axons, and that narrow sheet-like or filopodial processes of astrocytes, Schwann cells and possibly other non-neuronal cell types, may contain small amounts of GAP-43.

Animals↗
PubMed1990

Reinnervation of transplanted pacinian corpuscles by ventral root axons: ultrastructure of the regenerated nerve terminals.

This study addresses two questions. Can mature, denervated and transplanted Pacinian corpuscles accept innervation from motor axons? If so, does the alien target influence the structural characteristics of the regenerated motor axon terminals? Pacinian corpuscles from the hind leg of young rats, together with a segment of the nerve branch through which they receive their sensory innervation, were autotransplanted to the surface of the spinal cord and the nerve stump anastomosed to the central stump of a transected lumbar ventral root. Between 4 and 5 months later the grafts were studied by electron microscopy. Ventral root axons regenerated through the endoneurial tubes of the grafted nerve to reach the corpuscles, most of which became reinnervated by one to three myelinated fibres. The fibres lost their myelin sheaths before entering the inner core, branched, and gave rise to multiple terminals in the inner core. The regenerated terminals were packed with spherical synaptic vesicles and closely resembled normal motor nerve terminals. Thus motor axons are able to reinnervate Pacinian corpuscles but the structural characteristics of the terminals are apparently not modified by the alien target tissue. This finding contrasts with previous studies, in which it was found that terminals of the central axons of large dorsal root ganglion cells, induced to reinnervate Pacinian corpuscles, displayed the structural characteristics of peripheral sensory endings rather than those of dorsal root terminals in the spinal cord.

Animals↗
PubMed1990

Development of the mammalian retinogeniculate pathway: target finding, transient synapses and binocular segregation.

This review is concerned with the development of the mammalian retinogeniculate projection from the perspective of our studies on the hamster and to a lesser extent on the cat. In these, and other mammalian species, axons from the two eyes initially spread throughout the dorsal lateral geniculate nucleus (dLGN) and thus completely overlap. Later they segregate, the axons from each eye coming to occupy discrete, non-overlapping territories within the dLGN. The process of segregation to establish the adult pattern coincides with the death of retinal ganglion cells projecting to inappropriate areas of the dLGN and with the loss, by degeneration or retraction, of the axons and/or axonal branches initially located within inappropriate territory of the dLGN. These events occur in the early postnatal period in hamsters, before the eyes have opened, and in cats and monkeys they occur entirely during embryonic life: thus, they do not depend on the onset of normal visual function. If one eye is removed before segregation has begun, the terminal fields of the crossed and uncrossed axons from the remaining eye do not segregate, suggesting that segregation in normal development may depend on some form of interaction between retinal ganglion cells from the two eyes. Attractive and/or repulsive influences exerted by the dLGN on retinogeniculate axons may also be involved in the formation of eye-specific territories. Experimental ultrastructural studies in hamster and cat show that the overlap phase is associated with the formation, by inappropriately located axons, of transient synapses similar to those made by retinogeniculate axons in appropriate parts of the dLGN. In the cat, the transient synapses are made by the axon trunk and by side branches of retinogeniculate axons with terminal arbors in appropriate parts of the nucleus; the transient synapses disappear as the side branches are shed or retracted during the segregation period. Because of good evidence that electrical activity of the retinogeniculate axons may be involved in binocular segregation of inputs, we suggest that the formation and elimination of transient synapses play a significant role in the development of the orderly retinogeniculate projections.

Aging↗
PubMed1988

Dendritic invagination of developing optic tract axons in the hamster.

Between E15 and P4 in the hamster, axons of retinal ganglion cells in the optic tract over the dorsal lateral geniculate nucleus, are invaginated by, and make synaptic contacts with, small processes interpreted as tips or appendages of geniculate dendrites. In some cases a branch-like protrusion emerges from the axon at or close to the invagination. We hypothesize that the invaginations may be part of the mechanism by which retinocollicular axons are induced to branch and establish the retinogeniculate pathway.

Animals↗
PubMed1987

Ultrastructural organisation of the projection from the superior colliculus to the ventral lateral geniculate nucleus of the rat.

Retinorecipient regions of the ventral lateral geniculate nucleus of the thalamus and the superior colliculus of the midbrain are linked by reciprocal axonal projections. In this study we have investigated the ultrastructural characteristics, the distribution, and the postsynaptic targets of the terminals of axons projecting to the ventral lateral geniculate nucleus from the superior colliculus. Horseradish peroxidase was injected into the superior colliculi of adult albino rats, and the Hanker-Yates method was used to visualize anterogradely and retrogradely transported peroxidase in the ventral lateral geniculate nuclei 24 hours following the injection. Labelled terminals were found in the lateral and ventrolateral parts of the external division of the ipsilateral ventral lateral geniculate nucleus. The labelled terminals were confined to areas of simple, nonglomerular neuropil. They were 0.45-1.5 micron in diameter; contained small, dark mitochondria and spherical synaptic vesicles; and established Gray type I (asymmetrical) synaptic contacts with the dendritic shafts, dendritic spines, and occasionally cell bodies of cells with the ultrastructural characteristics of projection cells. A few labelled terminals established synaptic contact with retrogradely labelled cells. Thus, in the rat, the projection from the superior colliculus gives rise to a uniform population of axon terminals in the nonglomerular neuropil of the lateral portion of the ventral lateral geniculate nucleus, which synapse with, and are probably excitatory to, geniculocollicular and other projection cells.

Animals↗