Visual pretectal neurons projecting to the dorsal lateral geniculate nucleus and pulvinar nucleus in the cat

We observed morphological subtypes of visual pretectal neurons ascending to the dorsal thalamus, following injections of wheat germ agglutinin conjugated to horseradish peroxidase into the dorsal lateral geniculate nucleus (LGNd) or the pulvinar nucleus. These neurons are composed of fusiform cells and small-sized multipolar cells in the olivary pretectal nucleus, superficial horizontal cells, fusiform cells, small-, medium- and large-sized multipolar cells in the optic tract nucleus, and small- and medium-sized multipolar cells in the posterior pretectal nucleus. When somal size of the neurons projecting to the LGNd was compared to the size of neurons projecting to the pulvinar, the neuronal groups were not identical.     

Serotonergic inhibition of the dorsal lateral geniculate nucleus

Electrophysiological studies were conducted on chloral hydrate-anesthetized rats to determine if the dorsal raphe nucleus (DR) exerts an inhibitory influence upon the dorsal lateral geniculate nucleus (dLGN), and if this inhibition is mediated by the release of serotonin (5-HT). Conditioning stimuli presented to the DR 100-400 ms before an optic tract (OT) shock significantly lowered the amplitude of OT shock-elicited, postsynaptic, field potentials of less than 3 ms latency. Rare, long-latency, field potentials (greater than 5 ms) were diminished in amplitude when preconditioning intervals were less than 15 ms. Six days after intracerebral injection of the 5-HT neurotoxin, 5,7-dihydroxytryptamine (8 micrograms), into the dLGN, significant reductions were observed in 5-HT and 5-hydroxyindole acetic acid in the dLGN. Field potentials recorded on the sixth day in indoleamine-depleted dLGN were significantly less inhibited by DR preconditioning. Intracerebral injections of a control solution neither altered monoamine levels nor the degree of inhibition by DR preconditioning. These data provide further evidence that inhibition of dLGN by DR is mediated by release of 5-HT.     

Projection from the pretectal nuclei to the dorsal lateral geniculate nucleus in the cat: a wheat germ agglutinin-horseradish peroxidase study

To study the projection from the pretectum to the dorsal lateral geniculate nucleus (LGNd) in the cat, we used anterograde and retrograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). Special attention was directed to the retinotopic maps of the pretectum and LGNd. Multiple restricted injections were made into different parts of the pretectum or LGNd. The pretectogeniculate pathway terminates mostly in the medial interlaminar nucleus (MIN) and layers A and A1, and to some extent in the lamina C within the ipsilateral LGNd. The lateral part of the nucleus of the optic tract (NTO) receives afferents from the superior retina, and the medial part of NTO and posterior pretectal nucleus (NPP) receives afferents from the inferior retina. There is no topographic organization in the retinal projection to the olivary pretectal nucleus (NOL). The lateral part of NTO projects ipsilaterally to the rostral portion of LGNd, which receives afferents from the superior retina. The medial part of NTO projects ipsilaterally to the caudal portion of LGNd, which receives afferents from the inferior retina. The NOL projects to all laminar parts of LGNd, ipsilaterally. The NPP projects largely to the ipsilateral MIN, which receives afferents from the pericentral and peripheral retina. These results suggest that similar parts of the retinotopic maps present in the pretectum and LGNd are connected.     

Synaptic delay in the lateral geniculate nucleus of the cat

Unitary, presynaptic spike potentials were observed in single cell recordings from the dorsal lateral geniculate nucleus of the cat. In 11 cells, spontaneous S potentials (extracellularly recorded excitatory postsynaptic potentials) were preceded at a fixed interval by a small wave (the 'T' potential). In another 14 cells, a T potential, although not detected in single traces, was revealed by averaging 20-100 samples synchronized to the peak of the S potential. Provided the field response was not too large a T potential could also be detected in the response to a stimulus to the optic nerve. The T potential would appear to be the spike potential of the afferent optic axon which is excitatory to the geniculate cell because it precedes the S potential at a very exact interval and also follows the corresponding retinal ganglion cell spike at a very exact interval and because the interval between T potential and S potential is reversibly decreased by cooling with a temperature coefficient characteristic of synapses. T potentials ranged in amplitude from 8 to 134 microV and were all predominantly positive-going suggesting a failure of the nerve impulse to invade fully the terminals of the optic nerve. The time from the positive peak of the T potential to the start of the S potentials was taken as a good measure of the synaptic delay. The T-S interval averaged 0.29 ms (+/- 0.045 ms S.D.).     

Amino acids in the dorsal lateral geniculate nucleus of the cat—collection in vivo

A dialysis sampling probe was used to collect amino acids from the dorsal lateral geniculate nucleus (LGN) in vivo. The sampling probe was equipped with an electrode to allow local stimulation and recording of nerve activity. The amino acids in the dialysates were determined fluorimetrically by precolumn derivation and hple-separation. Local electrical stimulation of the LGN caused a multifold increase in glutamate, aspartate and GABA levels. Smaller changes were observed for taurine, alanine and glycine. The results indicate that the dialysis sampling probe is rather atraumatic and can be used to detect stimulation-induced changes in extracellular amino acid concentrations.     

The morphology of corticofugal axons to the dorsal lateral geniculate nucleus in the cat

The structural features of corticogeniculate axons were studied in adult cats after labeling them with horseradish peroxidase (HRP). Injections of HRP into the optic radiations near the dorsal lateral geniculate nucleus result in Golgi-like filling of both geniculate relay neurons and corticogeniculate axons. In the present material at least two main types of axons could be defined. The most common type is called the type I axon because it so closely resembles the type I axons described by Guillery ('66, '67) in Golgi preparations. These fine axons have smooth surfaces and consistent fiber diameter. Most terminal swellings are at the ends of short collateral branches and these swellings form asymmetric synaptic contacts onto small and medium-sized dendrites. Type I axons typically innervate more than one lamina as well as interlaminar zones and they clearly arise from the cerebral cortex. The second type of axon is called the beaded axon because of its numerous swellings, en passant. These swellings frequently are larger than those on type I axons and they differ from previously described corticogeniculate axon terminals in their ultrastructural features. That is, their synaptic contacts appear symmetrical and they form axosomatic contacts. Because of these differences, the possibility that beaded axons are of subcortical origin, particularly from the perigeniculate nucleus, is discussed. When type I axons and geniculate relay neurons are filled in the same region of the nucleus it is possible to identify probable sites of synaptic contact by using the light microscope. Such analyses indicate that corticogeniculate axons synapse directly onto relay cells, primarily on peripheral dendritic branches. Further, it appears that single axons contact many geniculate neurons and that single neurons are contacted by many axons.     

Development of the projections from the dorsal lateral geniculate nucleus to the lateral suprasylvian visual area of cortex in the cat.

In the study reported in the preceding paper, we used retrograde labeling methods to show that the enhanced projection from the thalamus to the posteromedial lateral suprasylvian (PMLS) visual area of cortex that is present in adult cats following neonatal visual cortex damage arises at least partly from surviving neurons in the dorsal lateral geniculate nucleus (LGN). In the C layers of the LGN, many more cells than normal are retrogradely labeled by horseradish peroxidase (HRP) injected into PMLS cortex ipsilateral to a visual cortex lesion. In addition, retrogradely labeled cells are found in the A layers, which normally have no projection to PMLS cortex in adult cats. The purpose of the present study was to investigate the mechanisms of this enhanced projection by examining the normal development of projections from the thalamus, especially the LGN, to PMLS cortex. Injections of HRP were made into PMLS cortex on the day of birth or at 1, 2, 4, or 8 weeks of age. Retrogradely labeled neurons were present in the lateral posterior nucleus, posterior nucleus of Rioch, pulvinar, and medial interlaminar nucleus, as well as in the LGN, at all ages studied. Within the LGN of the youngest kittens, a small number of retrogradely labeled cells was present in the interlaminar zones and among the cells in the A layers that border these zones. Such labeled cells were virtually absent by 8 weeks of age, and they are not found in normal adult cats. Sparse retrograde labeling of C-layer neurons also was present in newborn kittens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Visual function in the ventral lateral geniculate nucleus of the cat

The visual receptive fields of 293 single units in the ventral lateral geniculate nucleus of the cat were studied. In addition to the wide variety of types described by others, a group of units responding differentially to color was identified that included units responding particularly to blue and others with opponent color properties. Some units with spontaneous firing and without definite visual receptive fields were inhibited by stimulation of the optic chiasm (OX). A study of latency of firing to OX stimulation suggested that these cells were driven by retinal ganglion cells of the W type. One-third of all units studied were binocularly driven.     

A quantitative study of the complex laminated body in the lateral geniculate nucleus of the cat

A quantitative study has been made of the proportions and distribution of cells with complex laminated bodies (CLBs) in the lateral geniculate nucleus of the cat. They develop between 55 and about 70 days postnatal and are distributed irregularly across the medio-lateral extent of lamina A. There was no indication that the proportion of cells with CLBs is higher in the region of lamina A where the area centralis is represented, but the proportion in the binocular segment as a whole was higher than for the monocular segment. In kittens reared with unilateral or bilateral eyelid suture the proportions of cells with CLBs was above normal in the deprived laminae and below normal in the undeprived laminae.     

Projections from the parabigeminal nucleus to the dorsal lateral geniculate nucleus in the tree shrew Tupaia glis

The parabigeminal nucleus receives its major input from the superficial layers of the superior colliculus via the tectoparabigeminal projection. An extensive reciprocal parabigeminotectal pathway has also been observed. This close connectional association between the superficial gray and the parabigeminal nucleus is reflected in the collicularlike response characteristics of parabigeminal neurons (see Sherk: Brain Res. 145:375-379, '78, J. Neurophysiol. 42:1640-1655, 1656-1668, '79a,b, for review). Further documentation of the connectional relationship between the superior colliculus and the parabigeminal nucleus comes from the present data. Thus, our retrograde and anterograde transport findings reveal an extensive projection from the parabigeminal nucleus to layers 3 and 6 and several interlaminar zones of the contralateral dorsal lateral geniculate nucleus. These same layers and interlaminar zones receive tectogeniculate axons and have been shown to contain small cells that project to layers 1 and 3 of area 17. In addition to the distribution of parabigeminal axons to tectally innervated, small-celled zones, considerable parabigeminal input also reaches layers 1 and 5 of the tree shrew lateral geniculate nucleus. Each of these layers is the ipsilaterally (i.e., retinal) innervated component of a matched pair (layers 1 and 2 are considered magnocellular, while 4 and 5 are parvicellular), and it has been shown that layer 1 projects to lamina IVa of area 17, while layer 5 projects to lamina IVB. When the total distribution of parabigeminogeniculate axons is considered, it is apparent that the cells of origin of each of the major (small-celled, parvi- and magnocellular) geniculocortical channels receives parabigeminal input. Such an extensive distribution of parabigeminal axons within the lateral geniculate nucleus suggests that the information they convey might play an important role in geniculocortical function(s).     

Ventral lateral geniculate nucleus afferents to the suprachiasmatic nucleus in the cat

The lateral geniculate complex innervates the hypothalamic suprachiasmatic nucleus (SCN). The location of neurons in the cat ventral lateral geniculate nucleus (vLGN) that give rise to the geniculohypothalamic tract has not been described. In this study, retrogradely labeled neurons were noted throughout the rostrocaudal extent of the medial vLGN following tracer injection into the SCN region. In addition, neuropeptide Y immunoreactive processes were also observed in the vLGN in this same medial zone and in the SCN. The data suggest that the medial zone of the cat vLGN may be homologous to the rodent intergeniculate leaflet (IGL).     

Quantitative analysis of the lateral geniculate nucleus in the mutant microphthalmic rat

A quantitative analysis of the lateral geniculate nucleus was carried out in the mutant microphthalmic rat. In the dorsal lateral geniculate nucleus (LGNd) of the microphthalmic rat we found the total volume and neuronal population were reduced by 45 and 68% of normal values, respectively. The size of normal LGNd neurons was 8 to 20 μm and that of mutant LGNd cells from 6 to 16 μm. Neurons of the normal LGNd were medium-size and round or oval, and their cell bodies were filled with Nissl substance. Microphthalmic LGNd neurons, on the other hand, had narrow cytoplasmic spaces with few Nissl granules, and pale cell nuclei. In the microphthalmic rat, the lateral part of the ventral lateral geniculate nucleus (LGNvl) also showed a marked reduction in the total volume and neuronal population which were 42 and 76% of normal values, respectively. The size of normal LGNvl neurons was 8 to 20 μm and that of the microphthalmic neurons from 6 to 16 μm. These findings suggested that a marked reduction in the size of the LGNd and LGNvl in the mutant can be attributed to a decrease in neuronal population to a diminution of cell size.     

The cholinergic influence upon rat dorsal lateral geniculate nucleus is dependent on state of arousal

Several lines of evidence suggest a role for acetylcholine (ACh) in mediating the effects of state of arousal on transfer of visual information through the lateral geniculate nucleus (LGN). Local application of cholinergic agonists to geniculate relay cells in anesthetized cats and rats produces predominantly facilitatory effects. This indicates that presynaptic release of ACh may be responsible for the increased excitability of LGN relay cells that is observed during waking and REM sleep. In this study in rats we have examined the influence of cholinergic agonists applied during the 3 natural states of arousal: waking, slow-wave (SW) sleep and rapid eye movement (REM) sleep. Pharmacological agents were iontophoretically administered to identified, single cells in head-restrained, unanesthetized rats free to sleep and wake. Application of cholinergic agonist produced state-dependent differences in response in all geniculate relay-cells studied. During both waking and REM sleep, a facilitatory response was always observed, whereas in SW sleep responses were of three types: no effect (62%), inhibition (24%), and biphasic inhibition followed by facilitation (14%). All response types were antagonized by scopolamine. In contrast to the qualitatively different state-dependent effects of cholinergic agonists, response to application of glutamate, with quantitative variations, was uniformly facilitatory in all states, though responses in SW sleep tended to be lower in magnitude. The effects of gamma-aminobutyric acid (GABA), glycine, and serotonin were inhibitory in all states. These data are consistent with the suggested role of ACh in mediation of increased relay-cell excitability during REM sleep and waking. Our findings, however, also indicate that in the transition from SW sleep to REM or waking, local release of ACh is not solely responsible for alterations in cell excitability.     

GABA-immunoreactive neurons in the rat dorsal lateral geniculate nucleus: light microscopical observations

The dorsal lateral geniculate nucleus (dLGN) of the rat was investigated immunocytochemically using an antiserum against the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). The appearance of GABA-immunopositive dendrites, dendritic appendages, and the size and shape of neuronal somata closely resembled the putative intrinsic neurons described previously in Golgi-impregnation studies of the rat dLGN.     

Cytodifferentiation and developing neuronal circuitry in the human lateral geniculate nucleus

The developing neural substrate in dorsal lateral geniculate nucleus of human fetuses and premature, full-term and postnatal infants, has been analysed using rapid Golgi impregnation, computerized image analysis, electronmicroscopy, and immunocytochemical method for localization of gamma-aminobutyric acid. Nuclear and cytoplasmic neuronal maturation is observed to extend over the entire period studied. Axodendritic synapses, presumably of retinal origin, are occasionally seen at 13-14 fetal weeks. They become increasingly apparent at 18-19 weeks. Dendrodendritic contacts are visualized at 15 weeks. Cortical terminals and occasional triadic contacts are evident around 21 weeks. The inhibitory interneurons containing gamma-aminobutyric acid are present in small numbers at 15-16 weeks; their numerical density increases considerably at 17 weeks but decreases thereafter. The presence of gamma-aminobutyric acid containing nerve cells and synaptic triads is indicative of the formation of inhibitory circuitry. At 15-16 weeks neurons are mostly bipolar although different forms of multipolar cells may be seen. By 24 weeks the radiated and bitufted multipolar neurons, neurons with beaded dendrites and neurons with axon-like dendritic processes are identifiable. There are no apparent differences in differentiation of neurons between the cranial and caudal parts of dorsal lateral geniculate nucleus. At 15-16 weeks, however, the cells of prospective magnocellular zone appear to be more mature than do the cells in the parvocellular zone. The neuronal soma increases continuously in size. Dendrite development starts at 15-16 weeks of gestation, thereafter the increase in number of their branches and their length is observed. Between 15-16 and 24 weeks, spines and filiform processes appear first on the proximal shafts of the dendrites and subsequently on their distal portion. There is increase in the number of filiform processes and hair-like appendages on geniculate neurons of premature infants born at 32 and 37 weeks of gestation and of a 4-day postnatal infant. Computerized quantitative data substantiate the progressive increase in growth parameters. The significance of comparative and functional aspect of the data is discussed.     

Afferent projections to the ventral lateral geniculate nucleus in the cat

Horseradish peroxidase (HRP) injections were made into the dorsal lateral geniculate nucleus (LGN_d) and ventral lateral geniculate nucleus (LGN_v) of the cat in order to define afferent projections to LGN_v. These were found from the superior colliculus, contralateral LGN_v, dorsal median raphe nucleus, locus coeruleus, ipsilateral pretectum, and various portions of visual cortex. While many cortical areas project to LGN_v (17, 18, 19, 21 and lateral suprasylvian), the heaviest input arises from areas 17 and 20. The cell bodies of origin are in layer 5 in contrast to layer 6 which projects to LGN_d.