Ventral Lateral Geniculate Nucleus Research Articles

The anatomical substrates subserving the pupillary light reflex in rats: Origin of the consensual pupillary response

While the olivary pretectal nucleus has been shown to be central to the pupillary constriction response in rats, it is not at all clear at which level the consensual response is generated. To examine this we have investigated the efferent projections of this nucleus, as well as the effect of unilateral lesions of the olivary pretectal nucleus, on the direct and consensual pupillary light reflexes. The results demonstrate that the olivary pretectal nucleus projects bilaterally to the Edinger-Westphal nucleus, as well as to the nucleus of the posterior commissure, which itself projects bilaterally to the Edinger-Westphal nucleus. The olivary pretectal nucleus also projects to the ipsilateral ventral lateral geniculate nucleus. Unilateral lesions of the olivary pretectal nucleus decrease, but do not abolish, the direct and consensual pupillary light reflexes by as much as 66%. Since some degree of consensual response remains, this is likely to be due to the bilateral projection from the olivary pretectal nucleus, either directly or indirectly through the nucleus of the posterior commissure, to the Edinger-Westphal nucleus. These results show that while the bilateral projection from the olivary pretectal nucleus to the Edinger-Westphal nucleus contributes to the consensual pupillary light reflex, the bilateral retinal projection to the olivary pretectal nucleus is the more determinant component of the pathway. In addition to providing insights into the anatomical substrates of the pupillary response, this work also provides a background to ongoing studies of the retinal graft-mediated pupillary light reflex, as well as serving as a model of a relatively simple reflex system.

Ascending projections of posterior canal-activated excitatory and inhibitory secondary vestibular neurons to the mesodiencephalon in cats.

The axonal projections of 62 posterior canal (PC)-activated excitatory and inhibitory secondary vestibular neurons were studied electrophysiologically in cats. PC-related neurons were identified by monosynaptic activation elicited by electrical stimulation of the vestibular nerve and activation following nose-up rotation of the animal's head. Single excitatory and inhibitory neurons were identified by antidromic activation following electrical stimulation of the contralateral and ipsilateral medial longitudinal fasciculus, respectively. The oculomotor projections of identified neurons were confirmed with a spike-triggered averaging technique. The axonal projections of the identified neurons were then studied by systematic, antidromic stimulation of the mesodiencephalon. Excitatory neurons showed two main types of axonal projections. In one type, axonal branches were issued to the interstitial nucleus of Cajal, central gray, and thalamus including the ventral posterolateral, ventral posteromedial, ventral lateral, ventral medial, centromedian, central lateral, lateral posterior, and ventral lateral geniculate nuclei. The other type was more frequently observed, giving off axon collaterals to the above-mentioned regions and to Forel's field H as well. Inhibitory neurons issued axonal branches to limited areas which included the central gray, interstitial nucleus of Cajal, its adjacent reticular formation and caudalmost part of Forel's field H, but not the rostral part of the Forel's field H and the thalamus. These results suggest that PC-related excitatory neurons participate in the genesis of vertical eye movements and in the perception of the vestibular sensation, and that PC-related inhibitory neurons seem to take part only in the genesis of vertical eye movements.

An oriented framework of neuronal processes in the ventral lateral geniculate nucleus of the rat demonstrated by NADPH diaphorase histochemistry and GABA immunocytochemistry

This study investigated the morphology and quantitative distribution of neurons containing NADPH diaphorase activity in the ventral lateral geniculate nucleus of the rat. The pattern of diaphorase staining revealed a strongly reactive lateral subdivision and a weakly staining medial subdivision. A characteristic feature of the diaphorase staining in the lateral part was its “stripe-like” appearance. These “diaphorase stripes” resulted from regions of strong somatic and neuropil diaphorase activity lying between unstained fibre bundles coursing dorsoventrally through the nucleus. Two distinct populations of diaphorase reactive cell types were present—class A and class B neurons. The ratio of class A to class B diaphorase neurons was approximately 14:1 (A:B). Diaphorase reactive neurons made up 73% of the total neuron population in the lateral subdivision, and 31% in the medial subdivision. A third population of cells was found exclusively in the optic tract—class C neurons. Quantitative analyses in the coronal and sagittal planes indicated that the principal processes of both class A and class B neurons were oriented preferentially—either parallel with, or perpendicular to the outlying optic tract. Diaphorase enzyme histochemistry in combination with GABA immunocytochemistry demonstrated the co-localization of GABA immunoreactivity in the majority of class B neurons, whereas class A and class C neurons were GABA immunonegative. Furthermore a large population of GABA-immunoreactive neurons was present that were not stained for diaphorase activity. From this and previous studies, it can be concluded that a high proportion of the diaphorase reaction class A neurons are geniculotectal projection cells, while diaphorase reaction class B neurons represent a numerically small subpopulation of “local-circuit” inhibitory neurons. Since diaphorase activity co-localizes with nitric oxide synthase, the results indicate the likely involvement of nitric oxide in the neuronal operations of both subpopulations of geniculotectal projection neurons and “local-circuit” GABAergic neurons in the rat's ventral lateral geniculate nucleus.

Cholera toxin mapping of retinal projections in pigeons (Columbia livia), with emphasis on retinohypothalamic connections.

Anterograde transport of cholera toxin subunit B (CTb) was used to study the retinal projections in birds, with an emphasis on retinohypothalamic connections. Pigeons (Columbia livia) were deeply anesthetized and received unilateral intraocular injections of CTb. In addition to known contralateral retinorecipient regions, CTb-immunoreactive fibers and presumptive terminals were found in several ipsilateral regions, such as the nucleus of the basal optic root, ventral lateral geniculate nucleus, intergeniculate leaflet, nucleus lateralis anterior, area pretectalis, and nucleus pretectalis diffusus. In the hypothalamus, CTb-immunoreactive fibers were observed in at least two contralateral cell groups, a medial hypothalamic retinorecipient nucleus, and a lateral hypothalamic retinorecipient nucleus. To compare retinorecipient hypothalamic nuclei in pigeons with the mammalian suprachiasmatic nucleus, double-label experiments were conducted to study the existence of neurophysin-like immunoreactivity in the retinorecipient avian hypothalamus. The results showed that only cell bodies in the medial hypothalamic nucleus contained neurophysin-like immunoreactivity. The results demonstrate CTb to be a sensitive anterograde tracer and provide further anatomical information on the avian equivalent of the mammalian suprachiasmatic nucleus.

Reciprocal connections of the motor neocortical area with the contralateral thalamus in the hedgehog (Erinaceus europaeus) brain.

Horseradish peroxidase unilateral injections in various neocortical areas (prefrontal, somatosensory, auditory, visual) of the hedgehog (Erinaceus europaeus) brain resulted in labelling of nuclei in the ipsilateral thalamus known from studies in other species and in the hedgehog to project to these areas. However, injections in the motor area resulted in retrograde and anterograde labelling of nuclei in both the ipsilateral and contralateral thalamus. These nuclei included the ventral lateral nucleus (VL), the intralaminar nuclei (ILN), the mediodorsal nucleus (MD) and midline nuclei. Large unilateral injections located mainly laterally in the thalamus labelled cells, contralaterally, in the ventral lateral geniculate nucleus, the intergeniculate leaflet and the reticular nucleus of the thalamus, but never in VL, ILN and MD. The present results confirm previously described bilateral thalamocortical projections from the VL to the somatosensorimotor area in this species (Regidor and Divac, Brain Behav. Evol., 39, 265-269, 1992) and in addition demonstrate that (i) bilateral thalamocortical projections are established preferentially with the motor area, (ii) several nuclei are involved in such connections, (iii) these connections are reciprocal and topographically organized, and (iv) labelling in the contralateral thalamus observed in the present study is not a result of transneuronal transport of the tracer through thalamothalamic connections. This organization is unique among mammals and supports previous anatomical and electrophysiological findings, on the basis of which it has been suggested that the hedgehog retains a primitive character in neocortical and thalamic evolution.

Topographic distribution of efferent fibers originating from homotopic or heterotopic transplants: heterotopically transplanted neurons retain some of the developmental characteristics corresponding to their site of origin

The present study was undertaken to determine whether the topographical distribution of cortical efferents is exclusively dependent on environmental cues or is also controlled by intrinsic factors. For that purpose, we used a sensitive tract tracing method ( Phaseolus vulgaris leucoagglutinin) to compare the pattern of efferent fibers of homotopic and heterotopic transplants of embryonic (E16) neocortex. Our findings indicate that transplants of embryonic sensorimotor cortex placed homotopically in the sensorimotor cortex of newborn rats distribute a set of efferent projections not fundamentally different from that of normal sensorimotor cortex. The pattern of efferents arising from transplants of embryonic occipital cortex heterotopically placed in the sensorimotor cortex of newborns is strikingly different. Heterotopically transplanted neurons: (i) only rarely contact normal targets of the motor cortex; (ii) systematically project towards normal targets of the visual cortex (primary and secondary visual cortical areas, dorsal and ventral lateral geniculate nuclei, lateral dorsal and lateral posterior thalamic nuclei, anterior pretectal nucleus and superficial and intermediate layers of the superior colliculus); (iii) distribute fibers to structures normally receiving fibers from both motor and visual cortices (caudate-putamen, pontine nuclei), either exclusively into the visual cortico-recipient zone of the structure or into both visual and motor cortico-recipient zones. Taken together, these results seem to indicate that the heterotopically transplanted cells have retained certain anatomical characteristics of their locus of origin.

Electrophysiological evidence for presynaptic nicotinic receptors in the avian ventral lateral geniculate nucleus.

1. Whole-cell patch-clamp recording in embryonic chick brain slices was used to examine the effect of nicotinic receptor activation on synaptic activity in neurons of the ventral lateral geniculate nucleus (LGNv). In LGNv neurons with input resistances < 250 M omega, bath perfusion of the nicotinic agonist, carbachol (10-30 microM), in the presence of 0.5-1.0 microM tetrodotoxin (TTX) and 1.0 microM atropine, produced a dramatic increase in the frequency of spontaneous postsynaptic currents (n = 8/8), while eliciting little or no direct postsynaptic response. The nicotinic antagonist, dihydro-beta-erythroidine (DH beta E; 30-100 microM) had no effect on basal synaptic currents, but blocked the carbachol-induced enhancement of spontaneous currents, demonstrating that activation of nicotinic receptors is responsible for this effect. 2. The gamma-aminobutyric acid A (GABAA) receptor antagonist, bicuculline (10-20 microM), blocked the basal spontaneous synaptic currents (n = 4) as well as the carbachol-induced enhancement of these events (n = 3), indicating that these currents are likely to be GABAergic inhibitory postsynaptic currents (IPSCs). 3. Because the nicotinic agonist-induced increase in IPSC frequency occurred during blockade of synaptic transmission with TTX, the enhancement of synaptic activity is not dependent upon action potential propagation. This is in marked contrast to our results in chick lateral spiriform neurons in which nicotinic agonist-induced increases in spontaneous GABAergic IPSCs were completely abolished in the presence of TTX. The data indicate that the nicotinic receptors mediating the increase in IPSC frequency in the LGNv are likely to be located directly on presynaptic nerve terminals.

NADPH-d (dihydronicotinamide adenine dinucleotide phosphate diaphorase) activity in geniculo-tectal neurons of the rat

Retrograde transport of horseradish peroxidase (HRP) and dihydronicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry were used in order to determine whether NADPH-d-positive neurons of the ventral lateral geniculate nucleus (LGv) project to the superior colliculus (SC). Our results show that intensely stained NADPH-d neurons are restricted to the lateral half of the magnocellular division of LGv (LGv-MC), where they represent 50% of the total number of retrogradely labeled neurons. These findings indicate: (1) that LGv provides an important NADPH-d input to SC, and (2) that within the population of geniculo-tectal neurons, which constitute a morphologically well defined neuronal type, there are two different subclasses, one being NADPH-d positive and the other NADPH-d negative.

Laminar Distribution of the Cells of Origin of Ascending and Descending Tectofugal Pathways in Turtles: Implications for the Evolution of Tectal Lamination; pp. 264–273

The major outputs of the tectum appear fundamentally similar in all vertebrate species, suggesting that the major types of tectal output neurons have been evolutionarily conserved across a wide variety of vertebrate species. Nonetheless, tectal lamination patterns vary dramatically among vertebrates. To explore the basis of this variation in lamination at a neuronal level, the laminar distribution of the cells of origin of the major ascending and descending tectofugal pathways was determined in turtles using retrograde HRP labeling and the results compared to those from similar studies in diverse other species. Four major tectal outputs were studied: 1) the ipsilateral ascending projection to nucleus rotundus of thalamus; 2) the ipsilateral ascending projection to the dorsal and ventral lateral geniculate nuclei of the thalamus; 3) the crossed descending projection to paramedian regions of the pons and medulla; and 4) the ipsilateral descending projection to cell groups of the ventrolateral pons and medulla. The projection to nucleus rotundus was found to arise exclusively from multipolar neurons of the stratum griseum centrale, while the projection to the geniculate nuclei was found to arise from radial cells with long ascending dendrites in the stratum griseum periventriculare. The crossed descending projection to the paramedian hindbrain was found to arise almost exclusively from large multipolar neurons, the majority of which were located in the stratum griseum centrale and some of which were located in the stratum griseum periventriculare. This pathway was also found to give rise to a collateral projection that ascends in the ipsilateral hypothalamus. The ipsilateral descending projection was found to arise from multipolar neurons in the stratum griseum centrale and stratum griseum periventriculare, from radial and pyramidal neurons in the stratum griseum periventriculare, and from radial neurons in stratum griseum et fibrosum superficiale. These results show that the laminar distribution of the cells of origin of tectofugal pathways in turtles does not fit the simple notion that the midbrain roof is organized into superficial layers containing neurons with ascending projections and deep layers containing neurons with descending projections. Rather, individual layers in turtles appear to give rise to both ascending and descending projections, with there being evidence that each projection arises largely from a separate set of neurons. The pattern of distribution of the cells of origin of these various pathways is different in turtles than in either birds, mammals, frogs, salamanders or teleosts. Such results suggest that considerable interspecific variation occurs in the extent to which individual homologous neuronal populations migrate superficially during tectal development.

Laminar Distribution of the Cells of Origin of Ascending and Descending Tectofugal Pathways in Turtles: Implications for the Evolution of Tectal Lamination; pp. 254–263

The major outputs of the tectum appear fundamentally similar in all vertebrate species, suggesting that the major types of tectal output neurons have been evolutionarily conserved across a wide variety of vertebrate species. Nonetheless, tectal lamination patterns vary dramatically among vertebrates. To explore the basis of this variation in lamination at a neuronal level, the laminar distribution of the cells of origin of the major ascending and descending tectofugal pathways was determined in turtles using retrograde HRP labeling and the results compared to those from similar studies in diverse other species. Four major tectal outputs were studied: 1) the ipsilateral ascending projection to nucleus rotundus of thalamus; 2) the ipsilateral ascending projection to the dorsal and ventral lateral geniculate nuclei of the thalamus; 3) the crossed descending projection to paramedian regions of the pons and medulla; and 4) the ipsilateral descending projection to cell groups of the ventrolateral pons and medulla. The projection to nucleus rotundus was found to arise exclusively from multipolar neurons of the stratum griseum centrale, while the projection to the geniculate nuclei was found to arise from radial cells with long ascending dendrites in the stratum griseum periventriculare. The crossed descending projection to the paramedian hindbrain was found to arise almost exclusively from large multipolar neurons, the majority of which were located in the stratum griseum centrale and some of which were located in the stratum griseum periventriculare. This pathway was also found to give rise to a collateral projection that ascends in the ipsilateral hypothalamus. The ipsilateral descending projection was found to arise from multipolar neurons in the stratum griseum centrale and stratum griseum periventriculare, from radial and pyramidal neurons in the stratum griseum periventriculare, and from radial neurons in stratum griseum et fibrosum superficiale. These results show that the laminar distribution of the cells of origin of tectofugal pathways in turtles does not fit the simple notion that the midbrain roof is organized into superficial layers containing neurons with ascending projections and deep layers containing neurons with descending projections. Rather, individual layers in turtles appear to give rise to both ascending and descending projections, with there being evidence that each projection arises largely from a separate set of neurons. The pattern of distribution of the cells of origin of these various pathways is different in turtles than in either birds, mammals, frogs, salamanders or teleosts. Such results suggest that considerable interspecific variation occurs in the extent to which individual homologous neuronal populations migrate superficially during tectal development.

Postnatal development of NADPH-diaphorase activity in the superior colliculus and the ventral lateral geniculate nucleus of the rat

We have studied the postnatal development of dihydronicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in the superior colliculus (SC) and the ventral lateral geniculate nucleus (LGv) of the rat. We describe two different developmental patterns of NADPH-diaphorase activity. The first pattern, observed in the deep layers of the SC, shows a transient activity during the first week which progressively decreases during the following two weeks. The second pattern is observed in the superficial layers of the SC and in the LGv. They become positive during the first week, their NADPH-d activity increases progressively during the second and third weeks, reaching the adult pattern at the fourth week. On the whole, the developmental chronology of the laminar distribution of NADPH-d in the SC displays an inside-out pattern. Our results suggest that NADPH-d activity may play different roles at different stages of the developing nervous system.

Processing of photic information within the intergeniculate leaflet of the lateral geniculate body: Assessed by neuropeptide Y immunoreactivity in the suprachiasmatic nucleus of rats

Entrainment of the arcadian pacemaker in the suprachiasmatic nucleus is accomplished by two neural pathways, the retinohypothalamic and geniculohypothalamic tracts. The geniculohypothalamic tract, which originates from the intergeniculate leaflet and a portion of the ventral lateral geniculate nucleus, is composed of fibers immunoreactive to neuropeptide Y. To assess the processing of photic information by the geniculohypothalamic tract, neuropeptide Y immunoreactivity in the suprachiasmatic nucleus of rats kept under various external lighting conditions was determined by enzyme immunoassay of micropunched tissues. Neuropeptide Y levels in the suprachiasmatic nucleus steadily increased when rats were exposed to continuous light and reached a peak in 2 h before returning to basal level. The amount of increase did not depend on intensity and duration of light exposure. A light pulse as short as 5 min elicited a similar rise in neuropeptide Y, indicating that the response is due to the sudden transition from dark to light. This response, however, was only observed when the dark to light transition occurred at circadian time 0 (subjective dawn) of the pacemaker. A light pulse at circadian time 0, which effectively induces the increase in neuropeptide Y level, does not significantly shift the phase of the circadian rhythm. This observation indicates that the photic pathway utilizing neuropeptide Y may be functional only when the endogenous circadian rhythm is synchronized to external light and dark cycles. Administration of an excitatory amino acid antagonist (MK-801) blocked the increase of neuropeptide Y by light, while an agonist ( N-methyl- d-aspartate) induced similar facilitatory effects to that of light on the neuropeptide Y level in the rat suprachiasmatic nucleus. These results suggest that the geniculohypothalamic tract processes photic information so as to facilitate distinction of the transition between light and darkness that occurs either at subjective dawn or dusk.

Immunohistochemical study of the pattern of rapid expression of c‐fos protein in the visual cortex of dark‐reared kittens following initial exposure to light

Brief alterations to the nature of the visual input during critical periods in the early life of cats and monkeys can result in rapid anatomical and physiological changes in the central visual pathways. The immediate early genes (IEGs) represent a possible way in which these changes could be mediated since the protein products of a number of these genes have been shown to be induced rapidly in neurons in response to a variety of transsynaptic stimuli. Immunohistochemical methods were employed to examine the tempo and pattern of expression of Fos, the protein product of the c-fos gene, induced in the visual cortex of kittens dark-reared from birth to 30 days of age by brief periods of binocular visual exposure. In visual cortical area 17, the number of Fos immunoreactive cells increased rapidly from virtually zero in control kittens that received no visual exposure, to reach high levels in animals that received between 1 and 2 hours of visual experience. Immunoreactive cells were absent in the dorsal lateral geniculate nucleus, but were numerous in the ventral lateral geniculate nucleus, and in area 17, were most numerous in the extragranular layers (2, 3 and 6) but sparse in lower layer 4 and layer 5, and virtually absent in layer 1. Substantial constitutive Fos immunoreactivity was observed in area 17 of normal 30-day-old kittens but very few immunopositive cells were evident in adult animals. However, Fos immunoreactivity was observed in the visual cortex of a dark-reared (for 30 days) adult animal following a brief period of visual exposure, a finding that suggests that Fos might serve other roles in the visual cortex in addition to those it might play uniquely during development. It is suggested that Fos, in combination with the protein products of a select number of other IEGs, may mediate a variety of rapid changes in the visual cortex including those that underlie visual system plasticity during early postnatal life.

Localization of somatostatin receptors in subcortical visual centres of the rat during development. Effect of neonatal enucleation on the expression of somatostatin receptors

Previous studies have shown that both somatostatin and somatostatin receptors are expressed in the visual system of the rat early during ontogenesis, suggesting that somatostatin plays a role in the development of visual functions. In the present study, we have examined the localization of somatostatin receptors in the lateral geniculate nucleus and the superior colliculus of the developing rat by autoradiography, and we have investigated the effect of neonatal enucleation on the density of receptors in young and adult animals. In the dorsal part of the lateral geniculate nucleus, somatostatin receptors were transiently expressed during the first two postnatal weeks, while in the ventral part, receptors were detected during the whole developmental period. In the superior colliculus, a high density of somatostatin receptors was measured before eye opening; thereafter the concentration of receptors decreased markedly in the whole structure to reach the adult level. Uni- or bilateral enucleation one day after birth only induced minor modifications of the expression of somatostatin receptors in the lateral geniculate nucleus and colliculus. Conversely, bilateral enucleation caused a significant reduction of the density of receptors in the inter-geniculate leaflet and the medial zone of the ventral lateral geniculate nucleus. Taken together, these results indicate that, in the relay nuclei, somatostatin receptors are not borne by retinal afférents. The presence of high densities of receptors in the lateral geniculate nucleus and superior colliculus during development suggests that somatostatin exerts trophic activities in these structures. In adult rat, somatostatin is probably involved in the modulation of visual information in the superior colliculus, but not in the dorsal lateral geniculate nucleus.

The histaminergic innervation of the lateral geniculate complex in the cat.

The histaminergic innervation of the thalamic dorsal and ventral lateral geniculate nuclei and the perigeniculate nucleus of the cat was examined immunohistochemically by means of an antibody to histamine. We find histamine-immunoreactive neurons in the cat brain are concentrated in the ventrolateral portion of the posterior hypothalamus, confirming a previous report. However, this cell group also spreads into medial, dorsal, and extreme lateral regions of the posterior hypothalamus and extends as far rostral as the optic chiasm. Histamine-labeled fibers cover all regions of the lateral geniculate complex, but the density of labeling varies. The ventral lateral geniculate nucleus (vLGN) is most densely labeled, the A laminae of the dorsal lateral geniculate are sparsely labeled, and the geniculate C laminae and the perigeniculate nucleus show intermediate amounts of label. Thus, histaminergic fibers demonstrate a predilection for zones innervated by the W-cell system. Labeled fibers exhibit few branchings and numerous en passant swellings, lending a beaded appearance. The vLGN showed more instances of fibers with larger-sized swellings (up to 2 microns). Following injections of biotinylated tracers into the hypothalamus, we find labeled fibers throughout the lateral geniculate complex. The anterogradely labeled fibers resemble the histaminergic fibers in morphology, distribution, and relative bouton size. Thus, the hypothalamus appears to be the source of the histaminergic fibers in the lateral geniculate complex. Histamine-labeled fibers in the dorsal lateral geniculate nucleus (dLGN) exhibit uncommon ultrastructural morphology. Many extremely large, round, or elliptical vesicles fill the fiber swellings. Swellings are directly apposed to a variety of other dendritic and axonal profiles, but thus far no convincing synaptic contacts have been seen. The distribution and appearance of these histaminergic fibers resembles those reported for serotonergic fibers. Our results support the idea that histamine works nonsynaptically as a neuromodulator in the lateral geniculate complex, affecting the level of visual arousal.

Identification of Rat Brainstem Sites with Neuronal Fos Protein Induced by Acoustic Stimulation with Pure Tones

Induction of Fos, a proto-oncogene c-fos protein product, was immunohistochemically examined in the rat brainstem by using pure tone stimuli (0.25 kHz, 4kHz and 8 kHz) at 60 and 80 dB sound pressure levels for 30 min. In comparison with non-stimulated control rats, the brainstem of sound-stimulated rats exhibited distinct Fos-labeled neuronal cell nuclei in i) the ascending auditory nuclei, ii) the brainstem sites which receive afferents from the auditory nuclei, i.e. the pretectum and rostroventrolateral reticular nucleus, iii) the parvocellular part of the ventral lateral geniculate nucleus, lateral reticular nucleus, ventral border region of the spinal trigeminal nucleus, and the medial vestibular and spinal vestibular nuclei, all of which lack established auditory projections, and iv) the brainstem sites where some Fos-labeled neurons were present in controls. Sound stimulation at 80 dB led to widespread Fos-labeling in all these sites. Sound stimulation at 60 dB caused a decrease in number of positive cells in the brainstem sites and yielded a tone-dependent subregional distribution pattern in the dorsal cochlear nucleus and central nucleus of the inferior colliculus.

Stimulation of the hamster ventral lateral geniculate nucleus induces Fos-like immunoreactivity in suprachiasmatic nucleus cells

The suprachiasmatic nucleus (SCN) functions as a pacemaker for circadian rhythms in rodents. Its activity and, therefore, circadian rhythms, are synchronized by light information from both a direct retinal projection and an indirect projection from the thalamic intergeniculate leaflet (IGL) and ventral lateral geniculate nucleus (vLGN) (geniculohypothalamic tract; GHT). The GHT also appears to be important for synchronizing circadian rhythms to non-photic cues. Light can activate expression of several immediate-early genes in the SCN, including c- fos. We examined whether electrical stimulation of the GL/vLGN region would induce Fos-like immunoreactivity (lir) in the hamster SCN. Electrical stimulation was given for one hour during the dark period of the lighting cycle. Stimulation at night of the IGL and adjacent LGN regions induced Fos-lir in cells in the SCN. Labeled cells were found in the dorsolateral part of the caudal SCN, and not in rostral or central regions of the SCN, nor in the ventral part of the caudal SCN. These results indicate that activation of cells contributing to the hamster GHT can induce Fos-lir in a restricted region of the caudal SCN.

Cerebellar connections of the ventral lateral geniculate nucleus in the rat.

The connections between the deep cerebellar nuclei and the ventral lateral geniculate nucleus (LGv) were investigated in rats using orthograde and retrograde transport of horseradish peroxidase. Following injections into the deep cerebellar nuclei there was orthograde transport to the contralateral medial LGv and adjacent zona incerta. Injections restricted to LGv consistently labelled a small cluster of cells in the contralateral posterior interposed nucleus. Injections into regions surrounding LGv produced distinctively different patterns of orthograde and retrograde labelling.

Visual discrimination performance after lesions of the ventral lateral geniculate nucleus in pigeons ( Columba livia)

Pigeons were trained to perform simultaneous pattern and color discrimination tasks. After their training was completed, bilateral electrolytic lesions were made in the ventral lateral geniculate nucleus (GLv). Following the surgery, they were retrained to their preoperative performance levels. Lesions of GLv caused no deficits in pattern discrimination performance. The birds which had been trained for discrimination of red vs. magenta showed a slight decline in their performance. This impaired performance on color discrimination was not, however, as severe as that of a bird with lesions in the nucleus rotundus. These results suggest that GLv plays some role in the detection of short wavelengths of light.

Immunohistochemical localization of calretinin in the rat lateral geniculate nucleus and its retino-geniculate projection

In the present study, we examined the distribution of calretinin-immunoreactive neuronal cell bodies and fibers in the lateral geniculate nucleus of the rat. In normal rats, clusters of immunoreactive cell bodies were found in: (i) the rostral portion of the ventral lateral geniculate nucleus pars medialis (VLGM), (ii) the intergeniculate leaflet (IGL), (iii) the intermediate region between the VLGM and the ventral lateral geniculate nucleus pars lateralis (VLGL), (iv) the caudomedial portion of the VLGM, and (v) the caudolateral portion of the VLGM. In the dorsal lateral geniculate nucleus (DLG), immunoreactive cell bodies were rarely observed. After uni- or bilateral eye enucleation, no significant alteration in the morphological features or distribution of immunoreactive cell bodies was detected in the lateral geniculate nucleus. In normal rats, immunoreactive fibers formed dense plexuses in: (i) the DLG, (ii) the external layer of the VLGL, (iii) the internal layer of the VLGL, (iv) the IGL, (v) the caudomedial portion of the VLGM, and (vi) the optic tract. After unilateral eye enucleation, immunoreactive fibers in the external layer of the VLGL and in the optic tract almost totally disappeared on the contralateral side to the lesion. Unilateral eye enucleation caused a significant decrease of immunoreactive fibers in the DLG and in the internal layer of the VLGL, but a substantial number of immunoreactive fibers still remained there. In the IGL and the caudomedial portion of the VLGM, no observable alteration in the distribution of immunoreactive fibers was detected after uni- or bilateral eye enucleation. In conclusion, (i) subpopulations of neurons of the lateral geniculate nucleus are distinguished by the presence of calretinin immunoreactivity, and (ii) calretinin is a chemical component of subpopulations of the contralateral retino-geniculate pathway, which terminate in the DLG and in the external and internal layers of the VLGL.