The retinal projection to the cat pretectum

From Whole-Brain Data to Functional Circuit Models: The Zebrafish Optomotor Response

Detailed descriptions of brain-scale sensorimotor circuits underlying vertebrate behavior remain elusive. Recent advances in zebrafish neuroscience offer new opportunities to dissect such circuits via whole-brain imaging, behavioral analysis, functional perturbations, and network modeling. Here, we harness these tools to generate a brain-scale circuit model of the optomotor response, an orienting behavior evoked by visual motion. We show that such motion is processed by diverse neural response types distributed across multiple brain regions. To transform sensory input into action, these regions sequentially integrate eye- and direction-specific sensory streams, refine representations via interhemispheric inhibition, and demix locomotor instructions to independently drive turning and forward swimming. While experiments revealed many neural response types throughout the brain, modeling identified the dimensions of functional connectivity most critical for the behavior. We thus reveal how distributed neurons collaborate to generate behavior and illustrate a paradigm for distilling functional circuit models from whole-brain data.

Retinal projections in the short-tailed fruit bat, Carollia perspicillata, as studied using the axonal transport of cholera toxin B subunit: Comparison with mouse

To provide a modern description of the Chiropteran visual system, the subcortical retinal projections were studied in the short-tailed fruit bat, Carollia perspicillata, using the anterograde transport of eye-injected cholera toxin B subunit, supplemented by the silver-impregnation of anterograde degeneration following eye removal, and compared with the retinal projections of the mouse. The retinal projections were heavily labeled by the transported toxin in both species. Almost all components of the murine retinal projection are present in Carollia in varying degrees of prominence and laterality. The projections: to the superior colliculus, accessory optic nuclei, and nucleus of the optic tract are predominantly or exclusively contralateral; to the dorsal lateral geniculate nucleus and posterior pretectal nucleus are predominantly contralateral; to the ventral lateral geniculate nucleus, intergeniculate leaflet, and olivary pretectal nucleus have a substantial ipsilateral component; and to the suprachiasmatic nucleus are symmetrically bilateral. The retinal projection in Carollia is surprisingly reduced at the anterior end of the dorsal lateral geniculate and superior colliculus, suggestive of a paucity of the relevant ganglion cells in the ventrotemporal retina. In the superior colliculus, in which the superficial gray layer is very thin, the projection is patchy in places where the layer is locally absent. Except for a posteriorly located lateral terminal nucleus, the other accessory optic nuclei are diminutive in Carollia, as is the nucleus of the optic tract. In both species the cholera toxin labeled sparse groups of apparently terminating axons in numerous regions not listed above. A question of their significance is discussed.

Autonomic control of the eye

The autonomic nervous system influences numerous ocular functions. It does this by way of parasympathetic innervation from postganglionic fibers that originate from neurons in the ciliary and pterygopalatine ganglia, and by way of sympathetic innervation from postganglionic fibers that originate from neurons in the superior cervical ganglion. Ciliary ganglion neurons project to the ciliary body and the sphincter pupillae muscle of the iris to control ocular accommodation and pupil constriction, respectively. Superior cervical ganglion neurons project to the dilator pupillae muscle of the iris to control pupil dilation. Ocular blood flow is controlled both via direct autonomic influences on the vasculature of the optic nerve, choroid, ciliary body, and iris, as well as via indirect influences on retinal blood flow. In mammals, this vasculature is innervated by vasodilatory fibers from the pterygopalatine ganglion, and by vasoconstrictive fibers from the superior cervical ganglion. Intraocular pressure is regulated primarily through the balance of aqueous humor formation and outflow. Autonomic regulation of ciliary body blood vessels and the ciliary epithelium is an important determinant of aqueous humor formation; autonomic regulation of the trabecular meshwork and episcleral blood vessels is an important determinant of aqueous humor outflow. These tissues are all innervated by fibers from the pterygopalatine and superior cervical ganglia. In addition to these classical autonomic pathways, trigeminal sensory fibers exert local, intrinsic influences on many of these regions of the eye, as well as on some neurons within the ciliary and pterygopalatine ganglia.

Central pupillary light reflex circuits in the cat: I. The olivary pretectal nucleus

The central pathways subserving the feline pupillary light reflex were examined by defining retinal input to the olivary pretectal nucleus (OPt), the midbrain projections of this nucleus, and the premotor neurons within it. Unilateral intravitreal wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) injections revealed differences in the pattern of retinal OPt termination on the two sides. Injections of WGA-HRP into OPt labeled terminals bilaterally in the anteromedian nucleus, and to a lesser extent in the supraoculomotor area, centrally projecting Edinger-Westphal nucleus, and nucleus of the posterior commissure. Labeled terminals, as well as retrogradely labeled multipolar cells, were present in the contralateral OPt, indicating a commissural pathway. Injections of WGA-HRP into the anteromedian nucleus labeled fusiform premotor neurons within the OPt, as well as multipolar cells in the nucleus of the posterior commissure. Connections between retinal terminals and the pretectal premotor neurons were characterized by combining vitreous chamber and anteromedian nucleus injections of WGA-HRP in the same animal. Fusiform-shaped, retrogradely labeled cells fell within the anterogradely labeled retinal terminal field in the OPt. Ultrastructural analysis revealed labeled retinal terminals containing clear spherical vesicles. They contacted labeled pretectal premotor neurons via asymmetric synaptic densities. These results provide an anatomical substrate for the pupillary light reflex in the cat. Pretectal premotor neurons receive direct retinal input via synapses suggestive of an excitatory drive, and project directly to nuclei containing preganglionic motoneurons. These projections are concentrated in the anteromedian nucleus, indicating its involvement in the pupillary light reflex.

Y-like retinal ganglion cells innervate the dorsal raphe nucleus in the Mongolian gerbil (Meriones unguiculatus)

Background

The dorsal raphe nucleus (DRN) of the mesencephalon is a complex multi-functional and multi-transmitter nucleus involved in a wide range of behavioral and physiological processes. The DRN receives a direct input from the retina. However little is known regarding the type of retinal ganglion cell (RGC) that innervates the DRN. We examined morphological characteristics and physiological properties of these DRN projecting ganglion cells.

Methodology/Principal Findings

The Mongolian gerbils are highly visual rodents with a diurnal/crepuscular activity rhythm. It has been widely used as experimental animals of various studies including seasonal affective disorders and depression. Young adult gerbils were used in the present study. DRN-projecting RGCs were identified following retrograde tracer injection into the DRN, characterized physiologically by extracellular recording and morphologically after intracellular filling. The result shows that DRN-projecting RGCs exhibit morphological characteristics typical of alpha RGCs and physiological response properties of Y-cells. Melanopsin was not detected in these RGCs and they show no evidence of intrinsic photosensitivity.

Conclusions/Significance

These findings suggest that RGCs with alpha-like morphology and Y-like physiology appear to perform a non-imaging forming function and thus may participate in the modulation of DRN activity which includes regulation of sleep and mood.

In vitro properties of neurons in the rat pretectal nucleus of the optic tract

The nucleus of the optic tract (NOT) has been implicated in the initiation of the optokinetic reflex (OKR) and in the modulation of visual activity during saccades. The present experiments demonstrate that these two functions are served by separate cell populations that can be distinguished by differences in both their cellular physiology and their efferent projections. We compared the response properties of NOT cells in rats using target-directed whole cell patch-clamp recording in vitro. To identify the cells at the time of the recording experiments, they were prelabeled by retrograde axonal transport of WGA-apo-HRP-gold (15 nm), which was injected into their primary projection targets, either the ipsilateral superior colliculus (iSC), or the contralateral NOT (cNOT), or the ipsilateral inferior olive (iIO). Retrograde labeling after injections in single animals of either WGA-apo-HRP-gold with different particle sizes (10 and 20 nm) or two different fluorescent dyes distinguished two NOT cell populations. One projects to both the iSC and cNOT. These cells are spontaneously active in vitro and respond to intracellular depolarizations with temporally regular tonic firing. The other population projects to the iIO and consists of cells that show no spontaneous activity, respond phasically to intracellular depolarization, and show irregular firing patterns. We propose that the spontaneously active pathway to iSC and cNOT is involved in modulating the level of visual activity during saccades and that the phasically active pathway to iIO provides a short-latency relay from the retina to premotor mechanisms involved in reducing retinal slip.

Fiber connections of the periventricular pretectal nucleus in a teleost, tilapia (Oreochromis niloticus)

Fiber connections of the periventricular pretectal nucleus were studied by a tract-tracing method in a teleost, tilapia. After tracer injections into the periventricular pretectal nucleus, labeled neurons were observed ipsilaterally in the area pretectalis pars ventralis, area pretectalis pars dorsalis, optic tectum and ventrolateral nucleus of semicircular torus, bilaterally in the ventromedial thalamic nucleus, principal sensory trigeminal nucleus and descending trigeminal nucleus, and contralaterally in the periventricular pretectal nucleus and corpus cerebelli. Two types of tectal neurons were labeled in the stratum album centrale and the stratum periventriculare. The somata in the stratum album centrale were large and oval or multipolar. The somata in the stratum periventriculare were pyriform with an apical dendrite that ramified at the boundary zone between the stratum griseum centrale and stratum fibrosum et griseum superficiale. Anterogradely labeled terminals were present in the ipsilateral area pretectalis pars dorsalis, optic tectum and corpus cerebelli, the bilateral ventromedial thalamic nucleus, lateral valvular nucleus, oculomotor nucleus and inferior olive, and the contralateral periventricular pretectal nucleus. The present study suggests that the periventricular pretectal nucleus conveys somatosensory and mechanosensory lateral line inputs in addition to the visual information to the cerebellum.

The pretectum: connections and oculomotor-related roles

Research over the past two decades in mammals, especially primates, has greatly improved our understanding of the afferent and efferent connections of two retinorecipient pretectal nuclei, the nucleus of the optic tract (NOT) and the pretectal olivary nucleus (PON). Functional studies of these two nuclei have further elucidated some of the roles that they play both in oculomotor control and in relaying oculomotor-related signals to visual relay nuclei. Therefore, following a brief overview of the anatomy and retinal projections to the entire mammalian pretectum, the connections and potential roles of the NOT and the PON are considered in detail. Data on the specific connections of the NOT are combined with data from single-unit recording, microstimulation, and lesion studies to show that this nucleus plays critical roles in optokinetic nystagmus, short-latency ocular following, smooth pursuit eye movements, and adaptation of the gain of the horizontal vestibulo-ocular reflex. Comparable data for the PON show that this nucleus plays critical roles in the pupillary light reflex, light-evoked blinks, rapid eye movement sleep triggering, and modulating subcortical nuclei involved in circadian rhythms.

Morphological features of chick retinal ganglion cells

On average, in chicks, the total number of retinal ganglion cells is 4.9 x 10(6) and the cell density is 10400 cells/mm2. Two high-density areas, namely the central area (CA) and the dorsal area (DA), are located in the central and dorsal retinas, respectively, in post-hatching day 8 (P8) chicks (19000 cells/mm2 in the CA; 12800 cells/mm2 in the DA). Thirty percent of total cells in the ganglion cell layer are resistant to axotomy of the optic nerve. The distribution of the axotomy resistant cells shows two high-density areas in the central and dorsal retinas, corresponding to the CA (5800 cells/mm2) and DA (3200 cells/mm2). The number of presumptive ganglion cells in P8 chicks is estimated to be 4 x 10(6) (8600 cells/mm2 on average) and the density is 13500 and 10200 cells/mm2 in the CA and DA, respectively, and 4300 cell/mm2 in the temporal periphery (TP). The somal area of presumptive ganglion cells is small in the CA and DA (mean (+/- SD) 35.7 +/- 9.1 and 40.0 +/- 11.3 microm2, respectively) and their size increases towards the periphery (63.4 +/- 29.7 microm2 in the TP), accompanied by a decrease in cell density. Chick ganglion cells are classified according to dendritic field, somal size and branching density of the dendrites as follows: group Ic, Is, IIc, IIs, Ills, IVc. The density of branching points of dendrites is approximately 10-fold higher in the complex type (c) than in the simple type (s) in each group. The chick inner plexiform layer is divided into eight sublayers according to the dendritic strata of retinal ganglion cells and 26 stratification patterns are discriminated.

Retinal projections in the cat: A cholera toxin B subunit study

The B fragment of cholera toxin (CTb) is a highly sensitive anterograde tracer for the labelling of retinal axons. It can reveal dense retinofugal projections to well-known retinorecipient nuclei along with sparse but distinct input to target areas that are not commonly recognized. Following a unilateral injection of CTb into the vitreous chamber of seven adult cats, we localized the toxin immunohistochemically in order to identify direct retinal projections in these animals. Consistent with previous findings, the strongest projections were observed in the superficial layers of the superior colliculus, the dorsal and ventral lateral geniculate nuclei, the pretectal nuclei, the accessory optic nuclei, and the suprachiasmatic nucleus of the hypothalamus. However, we also found labelled terminals in several other brain areas, including the zona incerta, the medial geniculate nucleus, the lateral posterior-pulvinar complex, the lateral habenular nucleus, and the anterior and lateral hypothalamic regions. The morphological characteristics of the retinal axon terminals in most of the identified novel target sites are described.

Cytoarchitectonic and connectional organization of the ventral lateral geniculate nucleus in the cat

The ventral lateral geniculate nucleus is a small extrageniculate visual structure that has a complex cytoarchitecture and diverse connections. In addition to small-celled medial and lateral divisions, we cytoarchitectonically defined a small-celled dorsal division. A large-celled intermediate division intercalated between the three small-celled divisions, which we divided into medial and lateral intermediate subdivisions. In WGA-HRP injection experiments, the different cytoarchitectonic divisions were shown to have connections with different nuclei. The medial division was reciprocally connected to the pretectum and projected to the superficial layers of the superior colliculus and the intralaminar nuclei. The medial intermediate division received projections from the intermediate layer of the superior colliculus and the lateral and interpositus posterior cerebellar nuclei, and projected to the intermediate layer of the superior colliculus, the periaqueductal gray of midbrain, and the intralaminar nuclei. The lateral intermediate divisions received projections from the pretectum, the intermediate layer of the superior colliculus, and the lateral and interpositus posterior cerebellar nuclei, and projected to the pretectum, superficial layers of the superior colliculus, and the pulvinar. The lateral division received projections from superficial layers of the superior colliculus and had reciprocal connections with the pretectum. The dorsal division received projections from the pretectum and had reciprocal connections with the periaqueductal gray of midbrain. The different cytoarchitectonic divisions of the ventral lateral geniculate nucleus are thus suggested to play different functional roles related to vision, eye and head movements, attention, and defensive reactions.

Morphologic analysis and classification of ganglion cells of the chick retina by intracellular injection of lucifer yellow and retrograde labeling with DiI

Retinal ganglion cells (RGCs) of chicks were labeled by using the techniques of intracellular filling with Lucifer Yellow and retrograde axonal labeling with carbocyanine dye (DiI). Labeled RGCs were morphologically analyzed and classified into four major groups: Group I cells (57.1%) with a small somal area (77.5 microm(2) on average) and narrow dendritic field (17,160 microm(2) on average), Group II cells (28%) with a middle-sized somal area (186 microm(2)) and middle-sized dendritic field (48,800 microm(2)), Group III cells (9.9%) with a middle-sized somal area (203 microm(2)) and wide dendritic field (114,000 microm(2)), and Group IV cells (5%) with a large somal area (399 microm(2)) and wide dendritic field (117,000 microm(2)). Of the four groups, Groups I and II were further subdivided into two types, simple and complex, on the basis of dendritic arborization: Groups Is, Ic, and Groups IIs, IIc. However, Group III and IV showed either a simple or complex type, Group IIIs and Group IVc, respectively. The density of branching points of dendrites was approximately 10 times higher in the complex types (18,350, 6,190, and 3,520 points/mm(2) in Group Ic, IIc, and IVc, respectively) than in the simple types (1,890, 640, and 480 points/mm(2) in Group Is, IIs, and IIIs). The branching density of Group I cells was extremely high in the central zone. The chick inner plexiform layer was divided into eight sublayers by dendritic strata of RGCs and 26 stratification patterns were discriminated. The central and peripheral retinal zones were characterized by branching density of dendrites and composition of RGC groups, respectively.

Retinal ganglion cell projections to the hamster suprachiasmatic nucleus, intergeniculate leaflet, and visual midbrain: bifurcation and melanopsin immunoreactivity

The circadian clock in the suprachiasmatic nucleus (SCN) receives direct retinal input via the retinohypothalamic tract (RHT), and the retinal ganglion cells contributing to this projection may be specialized with respect to direct regulation of the circadian clock. However, some ganglion cells forming the RHT bifurcate, sending axon collaterals to the intergeniculate leaflet (IGL) through which light has secondary access to the circadian clock. The present studies provide a more extensive examination of ganglion cell bifurcation and evaluate whether ganglion cells projecting to several subcortical visual nuclei contain melanopsin, a putative ganglion cell photopigment. The results showed that retinal ganglion cells projecting to the SCN send collaterals to the IGL, olivary pretectal nucleus, and superior colliculus, among other places. Melanopsin-immunoreactive (IR) ganglion cells are present in the hamster retina, and some of these cells project to the SCN, IGL, olivary pretectal nucleus, or superior colliculus. Triple-label analysis showed that melanopsin-IR cells bifurcate and project bilaterally to each SCN, but not to the other visual nuclei evaluated. The melanopsin-IR cells have photoreceptive characteristics optimal for circadian rhythm regulation. However, the presence of moderately widespread bifurcation among ganglion cells projecting to the SCN, and projection by melanopsin-IR cells to locations distinct from the SCN and without known rhythm function, suggest that this ganglion cell type is generalized, rather than specialized, with respect to the conveyance of photic information to the brain.

Pretectotectal pathway: an ultrastructural quantitative analysis in cats

Both the pretectum (PT) and the superior colliculus (SC) play an important role in directing eye movements and in sensorimotor coupling. A reciprocal connection between the PT and the SC has been described, which suggests a strong interplay between these two structures. We injected the cat SC with retrograde tracers and examined the labeled pretectotectal (PTT) cells at the light and electron microscopic level. PTT cells were distributed mostly in the nucleus of the optic tract and 93.1% contained gamma amino butyric acid (GABA). We also observed that PTT cells are located outside of pretectal regions distinguished by dense retinal terminals and clusters of cells that contain calbindin. This suggests that the GABAergic PTT cells are distinct from the GABAergic pretectogeniculate cells that have been previously described as being distributed within these regions. Finally, to determine the synaptic targets of PTT terminals, we injected the PT with anterograde tracers and examined terminals labeled in the SC at the ultrastructural level. The labeled PTT terminals were beaded fibers that were distributed mainly within the stratum griseum superficiale (SGS) of the SC. Using postembedding immunocytochemistry, 94.5% were found to be GABAergic. The PTT terminals were mostly small in size and primarily contacted GABA-negative dendrites (88.1%) and in some cases somata (4.7%). The remainder terminated on GABAergic dendrites (7.2%). Our results suggest that the PTT cells constitute a separate population of GABAergic efferent cells in the PT, which may function to inhibit the activity of non-GABAergic SC efferent cells in the SGS.

The thalamus as a monitor of motor outputs

Many of the ascending pathways to the thalamus have branches involved in movement control. In addition, the recently defined, rich innervation of 'higher' thalamic nuclei (such as the pulvinar) from pyramidal cells in layer five of the neocortex also comes from branches of long descending axons that supply motor structures. For many higher thalamic nuclei the clue to understanding the messages that are relayed to the cortex will depend on knowing the nature of these layer five motor outputs and on defining how messages from groups of functionally distinct output types are combined as inputs to higher cortical areas. Current evidence indicates that many and possibly all thalamic relays to the neocortex are about instructions that cortical and subcortical neurons are contributing to movement control. The perceptual functions of the cortex can thus be seen to represent abstractions from ongoing motor instructions.

Parcellation of the human pretectal complex: a chemoarchitectonic reappraisal

The pretectum is composed of numerous small nuclei that control various oculomotor functions. In all the non-human mammals investigated, the different pretectal nuclei have been named uniformly according to their structural and functional homology. However, the human pretectal nuclei still bear their traditional, in most cases misleading, nomenclature.In order to reveal the presumed chemoarchitectonic similarities between human and non-human pretectal nuclei, neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-immunohistochemistry was performed in the human pretectum, after being utilised successfully for the identification of different pretectal nuclei in the cat. No VIP neurones were observed in the human pretectal area, but numerous NPY cells were found in the 'nucleus lentiformis', and in the anterior bulge of the pretectum, while the 'nucleus sublentiformis' contained an abundant NPY fibre network. Some NPY neurones were present in the 'principal pretectal nucleus' as well. The olivary pretectal nucleus possessed NPY fibres, too. In the accessory optic system, the lateral terminal nucleus contained both NPY and VIP neurones, while in the dorsal terminal nucleus only NPY neurones were found. Our chemoanatomical findings were compared to the standard cytoarchitecture as well. Based on the homotopies in the spatial distribution pattern of NPY neurones in the cat and human pretectum, the current, widely accepted non-human anatomical nomenclature was applied to the morphologically homologous nuclei of the human pretectum. Accordingly, the 'nucleus lentiformis' (which contains numerous NPY cells) corresponds to the nucleus of the optic tract, the 'nucleus sublentiformis' (containing a dense network of NPY fibres) to the posterior pretectal nucleus, and the 'nucleus of the pretectal area' corresponds to the medial pretectal nucleus. We identified the anterior part of the pretectum as the human equivalent of the anterior pretectal nucleus in non-humans, including its two compact and reticular subdivisions. In addition, two accessory optic nuclei were verified chemoarchitectonically in the human brain.

The receptive fields of cat retinal ganglion cells in physiological and pathological states: where we are after half a century of research

Studies on the receptive field properties of cat retinal ganglion cells over the past half-century are reviewed within the context of the role played by the receptive field in visual information processing. Emphasis is placed on the work conducted within the past 20 years, but a summary of key contributions from the 1950s to 1970s is provided. We have sought to review aspects of the ganglion cell receptive field that have not been featured prominently in previous review articles. Our review of the receptive field properties of X- and Y-cells focuses on quantitative studies and includes consideration of the function of the receptive field in visual signal processing. We discuss the non-classical as well as the classical receptive field. Attention is also given to the receptive field properties of the less well-studied cat ganglion cells-the W-cells-and the effect of pathology on cat ganglion cell properties. Although work from our laboratories is highlighted, we hope that we have given a reasonably balanced view of the current state of the field.

The retinal ganglion cells that drive the pupilloconstrictor response in rats

It is well established that the pupillary light reflex (PLR) in rats is mediated by a direct retinal projection to the olivary pretectal nucleus (OPN). Although several authors have commented on the specific subpopulation of retinal ganglion cells (RGC) that project to the rat pretectum, much of this evidence is circumstantial, and depends mostly upon electrophysiological data (e.g., conduction velocity). Here, we have used microinjections of Fluoro-Gold into the OPN (pretectum and superior colliculus as controls) to retrogradely label RGCs projecting to this region. The retinae were whole-mounted, viewed under fluorescence, and the regional distribution pattern, laterality of projection, and cell soma sizes determined. The results show OPN injections label a small subpopulation of RGCs. In the contralateral retinae, labeled RGCs were most numerous and widespread, with 97% projecting to the contralateral pretectum. The highest density of cells in the contralateral retinae was found in the inferior and nasal retinal quadrants. In the ipsilateral retinae, the small number of labeled cells were concentrated in the periphery of the inferior and nasal retinal quadrants. A striking feature of both ipsilateral and contralateral retinae was the paucity of labeled cells found in the dorsal hemiretina (lower visual field). Cell size measurements indicate 90-95% of labeled RGCs had diameters of 9-13 microm, while most of the remaining cells had diameters of 20-25 microm. This would suggest class III cells may be the predominant RGC type mediating pupilloconstriction, although a smaller population of larger cells (e.g., class I and/or II) may also contribute to this pathway. The recent reports utilizing the PLR as an assay for the efficacy of intraretinal grafts has highlighted the significance of the regional distribution results. The extremely low number of labeled cells in the dorsal hemiretina would argue for the placement of such grafts in the ventral hemiretina.

Retrograde double-labeling study of retinal ganglion cells from the ipsilateral vLGN and SC in the albino rat

Retinal ganglion cells with branches to the ipsilateral ventral lateral geniculate nucleus (vLGN) and superior colliculus (SC) were studied by retrograde fluorescent double-labeling. Double-labeled cells were found in the ventral temporal crescent of the retina, with a few ipsilaterally projecting single-labeled cells scattered in this area. Single-labeled vLGN-projecting cells were found predominantly in the ventral-temporal crescent and to a lesser extent in the temporal and dorsotemporal octant. SC-projecting cells were present predominantly in the ventral-temporal crescent and to a lesser extent in the ventral and ventronasal octant. Our best animal model had 2200 ipsilaterally labeled cells. There were 451 (20.5%) double-labeled vLGN and SC-projecting cells, 561 (25.5%) single-labeled vLGN-projecting cells, and 1186 (53.9%) single-labeled SC-projecting cells.

Transneuronal retinal input to the primate Edinger-Westphal nucleus

The Edinger-Westphal nucleus of the oculomotor nuclear complex provides preganglionic parasympathetic innervation to the pupil. We labelled its retinal input by transneuronal autoradiography after an eye injection of [3H]proline in the macaque monkey. The primary retinal projection to the pretectum terminated in the ipsilateral and contralateral olivary nuclei. These nuclei were intensely labelled and sharply delimited, with a mean diameter of 590 microm and a rostrocaudal length of 2.52 mm. The caudal half of the olivary nucleus on each side broke into multiple clumps of label. Fragments of label also surrounded each olivary nucleus. The exact pattern of pretectal labelling varied considerably among animals and even from side to side in the same animal. In 5 of 6 monkeys, label from the olivary nucleus reached the Edinger-Westphal nucleus transneuronally. In transverse sections, the Edinger-Westphal label appeared as a circular patch located on either side of the midbrain ventral to the cerebral aqueduct in the central gray matter. It averaged 230 microm in diameter and 610 microm in length. In Nissl-stained sections, the autoradiographic label corresponded to a distinct nucleus comprised of neurons that were smaller than neurons in nearby somatic subdivisions of the oculomotor complex. The mean area of Edinger-Westphal neurons was 295 microm2. Transneuronal retinal input to the Edinger-Westphal nucleus mediating pupillary constriction terminates in a single, well-defined cell group in the midbrain.

Postnatal developmental changes of neurons expressing calcium-binding proteins and GAD mRNA in the pretectal nuclear complex of the cat

The postnatal development of the cat pretectum has been analysed with in situ hybridization and immunohistochemistry with the aim to establish the time course of morphological and neurochemical maturation of parvalbumin (PARV), calbindin-D28k (CALB), and glutamic acid decarboxylase (GAD) expressing neuronal populations. At birth, PARV-ir retinal afferents to the pretectum have already formed distinct termination zones which appear as 3 clusters separated by intercluster regions in coronal sections. The clusters contain two sets of large neurons expressing either PARV or CALB. The two sets of neurons differ in the time at which they grow rapidly. Both sets reach the adult size at P38. PARV-ir retinal fibers contact dendrites of large PARV-negative, and thus presumably CALB-ir neurons. A population of smaller CALB-ir neurons appears within the clusters during the second postnatal week. In intercluster regions, small PARV-ir and CALB-ir neurons are present at birth, but increase in number during development. Only PARV-ir intercluster neurons increase in size between P4 and P38. GAD neurons are present dorsal to the clusters and in intercluster regions from P0 onwards. However, within the clusters GAD neurons do not appear until the second postnatal week. The different onset of marker expression and cellular growth patterns suggest the existence of several populations of CaBP-ir excitatory and inhibitory neurons in the pretectum. The final complement of inhibitory neurons is not present until the second postnatal week. These developmental processes may correlate with the slow maturation of the pretectal motion processing system and the cortico-pretectal projection.

Evidence for greater sight in blindsight following damage of primary visual cortex early in life

This review compares the behavioral, physiological and anatomical repercussions of lesions of primary visual cortex incurred by developing and mature humans, monkey and cats. Comparison of the data on the repercussions following lesions incurred earlier or later in life suggests that earlier, but not later, damage unmasks a latent flexibility of the brain to compensate partially for functions normally attributed to the damaged cortex. The compensations are best documented in the cat and they can be linked to system-wide repercussions that include selected pathway expansions and neuron degenerations, and functional adjustments in neuronal activity. Even though evidence from humans and monkeys is extremely limited, it is argued on the basis of known repercussions and similarity of visual system organization and developmental sequence, that broadly equivalent repercussions most likely occur in humans and monkeys following early lesions of primary visual cortex. The extant data suggest potentially useful directions for future investigations on functional anatomical aspects of visual capacities spared in human patients and monkeys following early damage of primary visual cortex. Such research is likely to have a substantial impact on increasing our understanding of the repercussions that result from damage elsewhere in the developing cerebral cortex and it is likely to contribute to our understanding of the remarkable ability of the human brain to adapt to insults.

Dendritic morphology of projection neurons in the cat pretectum

The distribution and dendritic morphology of neurons in the cat pretectal nuclear complex were analyzed with respect to their projection to the ipsilateral dorsal lateral geniculate nucleus (LGNd) and the ipsilateral inferior olive (IO). Single and double retrograde tracing techniques were combined with intracellular injections of either horseradish peroxidase into electrophysiologically identified pretectal neurons or Lucifer Yellow into retrogradely labeled somata. Pretectal cells afferent to the LGNd were located in the nucleus of the optic tract (NOT), adjacent dorsal terminal nucleus of the accessory optic system (DTN), and posterior pretectal nucleus (NPP). Cells projecting to the IO were also distributed throughout the NOT-DTN and dorsal part of the NPP. Separate tracer injections (fluorogold and horseradish peroxidase [HRP] or granular blue) into the LGNd and the IO showed considerable overlap of labeled neurons in the NOT and dorsal NPP. Double-labeled neurons, however, were not observed after double tracer injections into LGNd and IO. Partial topographical segregation of the two populations was observed along the dorsoventral axis because LGNd-projecting neurons exhibited maximum density ventral to that of IO neurons. Pretectal cells to the LGNd had cell body diameters between 16 and 48 microns. Somatic shapes varied between fusiform and multipolar with considerable overlap between these two morphological appearances. Neurons projecting to the IO exhibited similar cell body sizes and their morphology also varied from fusiform to multipolar. Quantitative analysis of dendritic field size and orientation, number and order of dendritic arborizations, and symmetry of the dendritic tree revealed no statistically significant difference between the two neuronal populations. Hence, neurons of the two populations cannot be unequivocally identified just from the dendritic morphology. By contrast, dendritic morphology was correlated with the topographical location of either cell type within the pretectal nuclei rather than projection. Thus, the morphological appearance of neurons located dorsally predominantly was fusiform while neurons located ventrally mostly were multipolar.

Histochemical characterisation of the pretecto-geniculate projection in kitten and adult cat

Neurons in the pretectal nuclear complex projecting to the dorsal lateral geniculate nucleus (LGNd) in cat were studied at different postnatal ages by using a combination of retrograde tracing techniques with glutamic acid decarboxylase (GAD) in situ hybridisation and calbindin-D28K (CALB) and parvalbumin (PARV) immunocytochemistry. About 50% of the neurons retrogradely labelled from the LGNd expressed GAD mRNA and this percentage did not change during postnatal development. LGNd-projecting neurons were never observed to be CALB- or PARV-immunoreactive.

Projection of individual axons from the pretectum to the dorsal lateral geniculate complex in the cat

The dorsal lateral geniculate nucleus of the thalamus transmits visual signals from the retina to the cortex. Within the lateral geniculate nucleus, the ascending visual signals are modified by the actions of a number of afferent pathways. One such projection originates in the pretectum and appears to be active in association with oculomotor activity. Much remains unknown about the pretectal-geniculate projection. Our purpose was to examine for the first time individual axon arbors from the pretectum that project to the lateral geniculate nucleus, describing their topography and nuclear and laminar targets. We made injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin into the cat pretectum, targeting the nucleus of the optic tract. Serial 40 microns coronal sections were processed by using immunohistochemistry to reveal labeled axons that were then serially reconstructed using light microscopy. Pretectal-geniculate axons appeared morphologically heterogeneous in terms of swelling size, branching patterns, and laminar target. Most axons innervated the geniculate A laminae. A separate, smaller population innervated the C laminae. All axons exhibited substantially greater spread medial-laterally than rostral-caudally in the lateral geniculate nucleus, displaying a topographical organization for visual field elevation, but not azimuth. Many pretectal axons that projected to the LGN also innervated adjacent structures, including the medial interlaminar nucleus, the perigeniculate nucleus, and/or the pulvinar. These results indicate that the projection from the pretectum to the dorsal lateral geniculate nucleus is heterogeneous, is semitopographical, and may coordinate neural activity in the lateral geniculate nucleus and in neighboring visual thalamic structures in association with oculomotor events.

On the distribution of gamma cells in the cat retina

Ganglion cells of the cat retina that are neither alpha nor beta cells are often lumped for convenience into a single anatomical group--the gamma cells (Boycott & Wässle, 1974; Stone, 1983; Wässle & Boycott, 1991). Defined in this way, gamma cells are the morphological counterpart to the physiological W-cell class, which includes all ganglion cells that are neither Y (alpha) nor X (beta) cells. We have estimated the retinal distribution of gamma cells by using retrograde transport to label ganglion cells innervating the superior colliculus and by assuming that these included virtually all gamma cells and no beta cells. We excluded labeled alpha cells on the basis of soma size. Our data suggest that gamma cells represent just under half of the ganglion cells in most of the nasal retina, but only about a third of those in the area centralis and temporal retina. Gamma cells do not appear to be more highly concentrated in the nasal visual streak than are other ganglion cells. In the temporal retina, gamma cells with crossed projections to the brain are apparently at least twice as common as those with uncrossed projections.

Physiological characterization of pretectal neurons projecting to the lateral posterior-pulvinar complex in the cat

Pretectal neurons projecting to the lateral posterior-pulvinar complex (LP-P) in cats were electrophysiologically identified by their antidromic activation from the LP-P. Their responses to various visual stimuli and to electrical stimulation of the optic chiasm and the lateral geniculate nucleus (LGN) were characterized. In retrograde double-labelling experiments, the pretectal projections to the LP-P and to the LGN were tested for possible overlap. Forty-five neurons were antidromically activated from the LP-P; 55% of them could also be activated orthodromically from the optic chiasm. Most antidromically activated neurons responded to rapid movements of large textured visual stimuli as well as to 'on' or 'off' visual stimulation with short bursts. When stimulated with a slowly moving, large, structured visual stimulus, most cells showed a slight but significant activity increase. None of the neurons projecting to the LP-P was also activated antidromically from the LGN. Thus, the two populations are separate. This is supported by the results from the retrograde double-labelling experiments. None of the LP-P projecting neurons showed any directional selectivity to slow movements of large visual stimuli, a property by which pretectal neurons projecting to the inferior olive are characterized. Thus, neurons projecting to the LP-P do not bifurcate to the inferior olive. Response properties of neurons projecting to the LP-P were very similar to those of the 'jerk' neurons described by Schweigart and Hoffmann (Exp. Brain Res., 91, 273-283, 1992); therefore we believe them to be identical.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology of physiologically identified retinal X and Y axons in the cat's thalamus and midbrain as revealed by intraaxonal injection of biocytin

Prior morphological studies of individual retinal X and Y axon arbors based on intraaxonal labeling with horseradish peroxidase have been limited by restricted diffusion or transport of the label. We used biocytin instead as the intraaxonal label, and this completely delineated each of our six X and 14 Y axons, including both thalamic and midbrain arbors. Arbors in the lateral geniculate nucleus appeared generally as has been well documented previously. Interestingly, all of the labeled axons projected a branch beyond thalamus to the midbrain. Each X axon formed a terminal arbor in the pretectum, but none continued to the superior colliculus. In contrast, 11 of 14 Y axons innervated both the pretectum and the superior colliculus, one innervated only the pretectum, and two innervated only the superior colliculus. Two of the Y axons were quite unusual in that their receptive fields were located well into the hemifield ipsilateral with respect to the hemisphere into which they were injected. These axons exhibited remarkable arbors in the lateral geniculate nucleus, diffusely innervating the C-laminae and medial interlaminar nucleus, but, unlike all other X and Y arbors, they did not innervate the A-laminae at all. In addition to these qualitative observations, we analyzed a number of quantitative features of these axons in terms of numbers and distributions of terminal boutons. We found that Y arbors contained more boutons than did X arbors in both thalamus and midbrain. Also, for axons with receptive fields in the contralateral hemifield (all X and all but two Y axons), 90-95% of their boutons terminated in the lateral geniculate nucleus; the other two Y axons had more of their arbors located in midbrain.

A retrograde double-labelling study of retinal ganglion cells that project ipsilaterally to vLGN and LPN rather than dLGN and SC, in albino rat

We studied ipsilaterally projecting, double-labeled retinal ganglion cells that have bifurcating axons by retrograde fluorescent double-labeling in albino rats. Ten albino (Wistar, Japan Ceca) rats of either sex, weighing 350-400 g were used. With the rats in a state of deep anesthesia, we pressure-injected 0.02 microliter of 15% Evans blue (EB) into the right ventral lateral geniculate nucleus (vLGN), and 4% Fluoro-gold (FG) iontophoretically into the right posterior lateral thalamic nucleus (LP). The animals were perfused with formol-saline 48-72 h later and both the brain and eyes were exercised. The brain was sectioned coronally, and each retina was removed and mounted flat on a glass slide. Double-labeled cells were found in the ventral temporal crescent of the retina. In one animal and total number of ipsilaterally labeled cells was 566, and the percentage of double-labeled vLGN and LP projecting cells, single-labeled vLGN projecting cells, and single-labeled LP projecting cells were 29.8, 58.8 and 11.3, respectively.

Capacity of the retinogeniculate pathway to reorganize following ablation of visual cortical areas in developing and mature cats

The purpose of the present study was to determine the pattern and density of retinal projections to the dorsal lateral geniculate nucleus (dLGN) following ablation of visual cortical areas in developing cats of different postnatal ages and in mature cats. The terminations of retinal projections to the dLGN were evaluated following the injection of tritiated amino acids into one eye. Regardless of age, a visual cortical ablation of areas 17 and 18 induces massive death of neurons within the regions of the dLGN that are linked topographically to the cortical areas removed. However, the pattern of retinal projections to these degenerated regions of the dLGN differs depending upon whether the cortical lesion is incurred early in postnatal life or in adulthood. Following ablation on the day of birth (P1), virtually all surviving cells were found in the C-complex of dLGN with only a token number in the A-laminae. Correspondingly, retinal projections were maintained to the C-complex of the nucleus and were barely detectable in the degenerated A-laminae. However, in cats in which areas 17 and 18 had been removed in adulthood (> or = 6 months of age) retinal projections were maintained to the A-laminae even though nearly all neurons in those laminae had degenerated. Moreover, a subgroup of animals that incurred area 17 and 18 ablations at P1 showed that the modification of retinal projections to the A-laminae occurs within the first postnatal month, and an additional subgroup showed that retinal projections become increasingly resistant to the degenerative events in the dLGN that follow ablation of areas 17 and 18 at progressively older ages during the first postnatal month. Furthermore, retinal inputs also respond, in an age-dependent way, to degeneration of neurons in the C-complex induced by extension of the cortical ablation to include extrastriate visual areas.

Survey of the morphology of macaque retinal ganglion cells that project to the pretectum, superior colliculus, and parvicellular laminae of the lateral geniculate nucleus

In common with other vertebrates, the primate retina contains a number of different ganglion cell types that project to different regions in the brain. We wanted to determine how the different ganglion cell types, distinguished morphologically, mapped to these regions of the brain. We injected a fluorescent dye into one of three regions of a macaque brain: the superior colliculus (SC), the pretectal region, and the parvicellular laminae of the lateral geniculate nucleus. By means of an in vitro preparation, the retrogradely labelled ganglion cells were intracellularly injected with horseradish peroxidase, so as to reveal their dendritic morphology. When the dendritic-field diameters of the injected cells were plotted against retinal eccentricity, each of the three regions was found to receive input from a distinctive population of cells. The pretectal projection was dominated by cells with large dendritic fields. The SC projection was composed of a number of distinct types, with smaller dendritic fields. Parasol cells project to SC but are extremely rare. In addition to midget ganglion cells, the parvicellular laminae receive inputs from at least two additional groups. Parvicellular bistratified (PB) cells have bistratified dendritic fields, slightly larger than those of parasol cells. Parvicellular giant (PG) cells have dendritic-field diameters larger than that of any parasol cell, ranging from 250 microns to greater than 850 microns--the largest of any primate ganglion cells. In contrast to the retinal projections of the cat, in which a specific ganglion cell type can project to different regions of the brain, each of the regions in this survey appears to receive inputs from its own distinct group of ganglion cells.

Neuropeptide Y immunoreactivity identifies a group of gamma-type retinal ganglion cells in the cat

Ganglion cells within the cat retina have been traditionally grouped by morphological criteria into three major classes: alpha, beta, and gamma. The gamma-type cells have been least well characterized, but the available evidence indicates that this class comprises a relatively heterogeneous population of neurons. In the present study we demonstrate that an antibody for neuropeptide Y (NPY) recognizes a subpopulation of about 2,000 gamma-type ganglion cells. The NPY-immunoreactive (IR) neurons project to the superior colliculus and to the C layers of the lateral geniculate nucleus as demonstrated by retrograde labeling with fluorescent tracers (fluorogold or rhodamine latex microspheres). Virtually all of these cells disappear following lesions of the optic nerve. The NPY-IR ganglion cells were identified as gamma cells on the basis of soma size and dendritic branching patterns. The somas of these neurons are small (8-22 microns in diameter), and each cell is characterized by sparsely branching dendritic processes, usually extending into the middle third of the inner plexiform layer, the physiologically defined ON sublamina. These neurons are distributed across the entire retina, with the highest density at the area centralis. Within local regions of the retina, however, there was no indication that the NPY-IR gamma cells are arrayed in a regular mosaic pattern. These results provide the first evidence that the gamma class of ganglion cells of the cat retina can be subdivided on the basis of immunocytochemical properties.

Retinal projections to the pretectum, accessory optic system and superior colliculus in pigmented and albino ferrets

Retinal projections to the pretectal nuclei, accessory optic system and superior colliculus in pigmented and albino ferrets were studied using anterograde tracing techniques. Both Nissl- and myelin-stained material was used to identify the pretectal nuclei, nuclei of the accessory optic system and the layers of the superior colliculus. Following monocular injection of either horseradish peroxidase or rhodamine-B-isothiocyanate, four pretectal nuclei, including the nucleus of the optic tract, posterior pretectal nucleus, anterior pretectal nucleus and the olivary pretectal nucleus, could be identified to receive direct retinal input in both pigmented and albino strains. In the accessory optic system, retinal terminals were observed in the dorsal, lateral and medial terminal nuclei as well as in the interstitial nucleus of the superior fasciculus, posterior fibres. The retinal projection to the superior colliculus was found to innervate the three superficial layers. The retinal projections to the pretectal nuclei and nuclei of the accessory optic system in the pigmented animals were bilateral, although the label was most dense contralateral to the injected eye. Ipsilateral retinal projections to the pretectal nuclei and nuclei of the accessory optic system appeared to be absent in albino ferrets, i.e. they were invisible with our methods. In both pigmented and albino ferrets retinal terminals in the contralateral superior colliculus densely innervated the three superficial layers. In both strains the ipsilateral projection appeared as clusters which were absent in rostral and caudal poles. In pigmented animals the ipsilateral projection was much denser and more extensive than in albinos. Following injection of retrograde tracers into the brainstem at the level of the dorsal cap of the inferior olive, retrogradely labelled neurons in the pretectum were found in the ipsilateral nucleus of the optic tract. Their somata overlapped mainly with scattered retinal terminals close to the pretectal surface and rarely or not all with the deeper prominent terminal clusters. In the accessory optic system, inferior olive projecting neurons were observed in all four ipsilateral nuclei and fully coincided with the retino-recipient zones. In the superior colliculus, retrogradely labelled neurons were found contralateral to the injection site in the deep layers.

Lucifer yellow, retrograde tracers, and fractal analysis characterise adult ferret retinal ganglion cells

The dendritic morphology of retinal ganglion cells in the ferret was studied by the intracellular injection of lucifer yellow in fixed tissue. Ganglion cells were identified by the retrograde transport of red or green fluorescent microspheres that had been injected into different target nuclei, usually the lateral geniculate nucleus or superior colliculus. This approach allows the comparison of dendritic morphologies of ganglion cells in the same retina with different central projections and also identifies cells with branching axons. The digitised images of dendritic arbors were analysed quantitatively by a variety of measures. Dendritic complexity was assessed by calculating the fractal dimension of each arbor. The ferret has distinct alpha, beta, and gamma morphological classes of cells similar to those found in the cat. The gamma cell class was morphologically diverse and could be subdivided into "sparse," "loose," and "tight" groups, reflecting increasing dendritic complexity. Whereas the beta cell projection was limited to the lateral geniculate nucleus alone, alpha and gamma cells could project to either or both nuclei. Retinal ganglion cells labelled from the pretectal nuclei formed a morphologically distinct class of retinal ganglion cells. The ipsilateral projection lacked alpha cells and the most complex, "tight" gamma cells. However, ipsilaterally projecting "loose" gamma cells overlapped alpha cells in both soma and dendritic dimensions. Different morphological classes of retinal ganglion cells hence show characteristic axon behaviour both in their decussation at the chiasm and in which targets they innervate. Fractal measures were used to contrast variation within and between these identified classes.

GABAergic neurons and circuits in the pretectal nuclei and the accessory optic system of mammals

Two classes of GABAergic cell bodies have been described. They probably can be divided into GABAergic local interneurons and GABAergic projection neurons. GABAergic cell bodies receive few terminals which is in contrast to non-GABAergic somata, which receive many synaptic contacts. GABAergic dendrites that originate from GABAergic cell bodies, however, receive numerous terminals, both GABAergic and nonGABAergic. It can therefore be concluded that somatic inhibition is not present on GABAergic neurons, but does occur on nonGABAergic neurons. Furthermore, dendrites traverse large parts of the NOT/DTN forming a complex network that enables sampling and integration from a wide area. The projection to the IO is not GABAergic itself, but cells projecting to the IO receive a substantial GABAergic input, that probably originates in part from the MTN. Further investigation on the distribution of this input over a completely identified neuron would provide the quantitative data that are required to verify the above mentioned hypothesis. A GABAergic projection that originates in the pretectal nuclei is directed towards the superficial layers of the SC in the cat (Appell and Behan, 1990) and rat (Van der Want et al., 1991). A second GABAergic projection derives from the pretectum and reaches the LGN (Cucchiaro et al., 1991). Whether this projection originates from the same GABAergic cell bodies that project to the SC and the LGN or is derived from different populations remains to be determined. The ultrastructural studies of the NOT/DTN complex have shown that GABAergic terminals with different morphological characteristics are present and that the GABA positive F and P terminals are widely distributed over somata and the adjacent neuropil. The P terminals probably originate from dendrites of GABAergic interneurons while the F types originate from GABAergic projection and interneurons (Van der Want and Nunes Cardozo, 1988). One of these sources is located in the MTN differ from the intrinsic GABAergic terminals with respect to their relation to R terminals. GABAergic MTN terminals were never observed to receive R terminal input. This is in contrast with other GABAergic terminals which frequently do receive direct contact from R terminals. Within glomeruli triadic arrangements, formed by a single retinal terminal, a dendritic profile and second axonal profile dendritic profile and second axonal profile synapsing with the dendrite, were frequently encountered in the OPN (Campbell and Lieberman, 1985), but only occasionally in the NOT/DTN (Nunes Cardozo and Van der Want, 1987).(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for a direct retinal projection to the anterior pretectal nucleus in the cat

The retinal projections to the anterior pretectal nucleus were investigated using the anterograde transport of tritiated amino acids or horseradish peroxidase. Both Nissl and myelin stained tissue were used to identify the anterior pretectal nucleus and tissue containing labelled terminals was analyzed in each of the 3 stereotaxic planes. A restricted strip of bilateral terminal labelling was identified along the rostral border of the anterior pretectal nuclear subdivision, the pars compacta. The labelling was more dense contralaterally and extended for approximately three-quarters of the distance along this subdivision.

Prior optic nerve transection reduces capsaicin-induced degeneration in rat subcortical visual structures

Capsaicin is a neurotoxin capable of causing degeneration in specific sites throughout the neuraxis, including the suprachiasmatic nucleus (SCh), the ventrolateral geniculate nucleus (VLG), the intergeniculate leaflet (IGL), and the olivary and medial pretectal nuclei (OPT and MPT). In this experiment, we tested the hypothesis that capsaicin-induced terminal degeneration in the SCh, VLG, IGL, OPT, and MPT results from destruction of retinal ganglion cells and their axonal projections to these sites. In the first experiment, silver stains were used to examine degeneration in the retina induced by systemic capsaicin treatment. Capsaicin caused degeneration of ganglion cells, bipolar cells, and nerve terminals in the retina, which could be observed between 2 and 24 hours after treatment. In the second experiment, 15-day-old rat pups were enucleated unilaterally. Five days or 2, 5, or 10 months later, they were injected systemically with capsaicin and killed 6 hours (pups) or 18 hours (adults) later for analysis with a cupric silver stain. In rats of all ages, prior monocular enucleation reduced or eliminated capsaicin-induced degeneration in the contralateral SCh, VLG, IGL, OPT, and MPT. In the third experiment, rat pups were treated systemically with capsaicin or vehicle solution at 12 days of age and given unilateral intravitreal injections of cholera toxin conjugated to horseradish peroxidase (CT-HRP) 3 days prior to sacrifice at 20 days of age. Transport of CT-HRP to the SCh, VLG, IGL, MPT, and OPT was attenuated but not abolished by capsaicin pretreatment. Results suggest that capsaicin causes degeneration in the SCh, VLG, IGL, MPT, and OPT by selective destruction of a subpopulation of retinal ganglion cells with axonal projections to these sites.

The calcium binding protein calbindin-D 28K reveals subpopulations of projection and interneurons in the cat superior colliculus

The calcium binding protein calbindin-D 28K (CaBP) has been localized in the cat superior colliculus (SC). Four important features of SC organization have been revealed by using CaBP immunocytochemistry. 1) CaBP neurons formed three laminar tiers in SC, one within the upper one half of the superficial gray layer (SGL), the second bridging the deep optic (OL) and intermediate gray layers (IGL), and the third within the deep gray layer (DGL). 2) CaBP labeled several classes of interneuron in SC. In the upper CaBP tier, the labeled neurons were all small, but they varied in morphology and included horizontal, pyriform, and stellate neurons. A unique class of interneuron was labeled by anti-CaBP in the OL-IGL tier. This cell was stellate-like with highly varicose dendrites and broad dendritic trees. Other labeled neurons in the intermediate and deep tiers included nonvaricose stellate neurons and rare large neurons in the DGL. 3) A few anti-CaBP neurons were projection neurons. Virtually no CaBP neurons were retrogradely labeled after injections of HRP into the predorsal bundle and dorsolateral midbrain tegmentum or into the lateral posterior nucleus. However, 2.4% of anti-CaBP neurons were retrogradely labeled after HRP injections into the dorsal and ventral lateral geniculate nuclei. These represented 14.7% of all neurons projecting to the LGN complex. 4) A small percentage of CaBP neurons co-localized GABA. A two-chromagen double-labeling technique showed that about 4.0% of labeled neurons were labeled by both antibodies. In summary, antibodies to CaBP densely labeled subpopulations of neurons in the cat SC, most of which were interneurons, some of which projected to the LGN, and a few of which co-localized GABA.

A GABAergic projection from the pretectum to the dorsal lateral geniculate nucleus in the cat

To study the projection from the pretectum to the lateral geniculate nucleus, we placed wheat-germ agglutinin conjugated to horseradish peroxidase into the lateral geniculate nuclei of six cats, allowed this marker to be retrogradely transported by afferent axons to their parent somata in the pretectum, and revealed the label in these cells with stabilized tetramethylbenzidine histochemistry. In three cases we made large pressure injections that completely infiltrated the lateral geniculate nucleus and extended into neighboring thalamic nuclei; in the other three we made smaller iontophoretic injections largely confined to the A- and C-laminae of the lateral geniculate nucleus. In both types of injection we found labeled pretectal cells mainly in the nucleus of the optic tract but also found some cells labeled in the olivary pretectal nucleus and the posterior pretectal nucleus. After one of the larger injections we analysed both sides of the pretectum and found that 11% of the labeled cells were located contralaterally and were distributed in the same three nuclei. We analysed only the ipsilateral side in the remaining five cats. In those five experiments we also immunohistochemically stained the pretectal sections with an antibody directed against the neurotransmitter, GABA. Of the retrogradely labeled pretectal cells, 40% were also labeled for GABA, and those were similar in soma size (350 microns 2 in cross-sectional area) to those labeled only with the retrograde marker (331 microns 2). GABA-positive cells not labeled by retrograde transport were smaller (246 microns 2) than either of these other cells populations. These results indicate that at least 40% of the cells involved in the projection from the pretectum to the lateral geniculate nucleus are GABAergic. We suggest that this extrathalamic projection may serve to inhibit thalamic GABAergic cells. This, in turn, would disinhibit geniculate relay cells, thereby facilitating the geniculate relay of retinal information to cortex.

Dendritic morphologies of retinal ganglion cells projecting to the nucleus of the optic tract in the rabbit

Focal injections of Rhodamine-latex microspheres or Fast Blue were made in the nucleus of the optic tract (NOT) of four rabbits. After survival times of 8-10 days, both dyes were retrogradely transported to medium to large sized ganglion cell somas in the retinas contralateral, but not ipsilateral, to the injected NOT. Most labelled cells were located in or near the visual streak, but a significant percentage were also found in the midperiphery of both the inferior and superior retina. One hundred fifteen labelled cells in four living superfused retinas were impaled under visual control and successfully injected with Lucifer Yellow. The dendritic arborizations of 60 of these were drawn from photographic montages for morphological identification and analysis. Nearly all the injected ganglion cells had large, relatively dense dendritic trees that stratified narrowly in the proximal inner plexiform layer. The dendritic field size and dendritic density of these cells varied with eccentricity, but at all eccentricities their anatomical characteristics closely resembled those of intracellularly stained On directionally selective ganglion cells. In three of the four experiments, a small percentage of ganglion cells were also labelled in the visual streak that had bistratified morphologies resembling those of On-Off directionally selective ganglion cells.

Parasol and midget ganglion cells of the primate retina

We have intracellularly filled the dendritic arbors of 996 midget and parasol ganglion cells with horseradish peroxidase (HRP) in macaque and baboon retinas. Only minor differences in the properties of these cell groups were found between species. Ninety of these cells were cut from their retinas, embedded in methacrylate, and transversely sectioned. According to their depth of stratification, there are two types of parasol cells (termed a-parasol and b-parasol), and two types of midget ganglion cells (a-midget and b-midget). Each of these four types stratifies at a different level within the IPL. The dendritic fields of midget ganglion cells lie either near the border of the ganglion cell layer (GCL) or near the border of the amacrine cell layer (ACL). The dendrites of the two types of parasol cells stratify closer to the center of the IPL, where they divide it into three approximately equal parts. There was no vertical overlap in the dendritic fields of a-parasols and b-parasols; they were always separated by at least 1 micron. The border between the a- and b-sublaminae of the IPL, defined in terms of this narrow gap between the stratification of the two parasol cell types, lies approximately at the center of the IPL. The dendritic-field thickness for each of these types, on average, is no greater than 30% of the IPL thickness. At a similar location, there is no significant difference between the dendritic-field diameters of the two parasol types or between those of the two midget types. As previously reported (Perry et al.: Neuroscience 12:1101-1123, '84) the dendritic fields of both parasol and midget ganglion cells are smaller in the nasal retina than at a position in the temporal retina equidistant from the fovea. Because dendritic-field diameters prove to depend upon local ganglion-cell density, the scatter in these diameters as a function of retinal eccentricity is due in part to the asymmetric distribution of ganglion cells. We have devised a measure, termed equivalent eccentricity, that allows data points of cells from regions having the same local ganglion-cell density to be plotted at the same position on this scale. The use of this measure, rather than eccentricity per se, significantly reduces the scatter of dendritic-field diameters. The dendritic-field diameters of parasol cells within the nasal quadrant of the retina are not fully brought into line with those of cells lying elsewhere in the retina.(ABSTRACT TRUNCATED AT 400 WORDS)

The pupillary light reflex in normal and innate microstrabismic cats, II: Retinal and cortical input to the nucleus praetectalis olivaris

The anatomical substrate of the pupillary light reflex was investigated in normal and innate microstrabismic cats using anatomical methods as well as electrical stimulation. The bilateral retinal input to the nucleus praetectalis olivaris (NPO), the pretectal relay station in the subcortical pupilloconstrictor pathway, was identified to come from the ventral retina were the upper visual field is represented. Orthodromic electrical stimulation revealed that retinal information is transmitted to on-tonic neurons in the NPO mainly via slowly conducting axons probably originating from W- and X-type retinal ganglion cells. For the first time, a direct cortical input to on-tonic neurons in the NPO could be demonstrated. This cortical input originates from caudolateral parts of the occipital cortex. Putative input structures are those subdivisions of areas 19 and 20a where the upper part of the visual field is represented. A direct, predominantly contralateral projection with a weak ipsilateral component from NPO to the nucleus of Edinger-Westphal, and an interhemispheric connection between the NPOs could be demonstrated. With respect to the anatomical connections as described in this study, no differences between normal and innate microstrabismic cats could be found. The results are discussed with respect to the binocular summation of the pupillary light reflex and its reduction in subjects with impaired binocular vision.

The pupillary light reflex in normal and innate microstrabismic cats, I: Behavior and receptive-field analysis in the nucleus praetectalis olivaris

Neurons in the nucleus praetectalis olivaris (NPO) were antidromically identified by electrical stimulation of the nucleus of Edinger-Westphal (EW), the location of preganglionic pupilloconstrictor motoneurons. Electrical stimulation within the NPO leads to bilateral pupil constriction. Single neurons recorded in the NPO respond tonically to light stimuli, and their discharge frequency increases linearly with logarithmic increase in light intensity. This characteristic identifies NPO neurons as luminance detectors. They have large receptive fields mostly lying in the upper and contralateral quadrant of the visual field. Cats with impaired binocular vision show a significantly reduced binocular summation of the pupillary light reflex (BSP), i.e. the increase of pupil constriction during binocular illumination when compared to monocular illumination is less than in normal animals. The investigation of ocular dominance and subthreshold binocular interactions in the NPO of normal and innate microstrabismic cats revealed two possible mechanisms for BSP and its reduction in strabismic subjects. First, the percentage of neurons increasing their discharge rate by illuminating either eye is significantly reduced in the NPO of innate microstrabismic cats (6.6%) when compared to normal cats (22% of all neurons tested). Second, in most NPO neurons of normal cats the subthreshold influence of the ipsilateral eye leads to an increase in neuronal activity during binocular stimulation when compared to monocular stimulation of the contralateral eye (binocular summation). The subthreshold influence of the ipsilateral eye in most NPO neurons of microstrabismic cats, however, is inhibitory, i.e. the neuronal discharge rate during binocular stimulation is decreased when compared to monocular stimulation of the contralateral eye (binocular inhibition). However, there is no significant correlation between BSP and binocularity in the NPO in individual animals. This suggests that BSP may be additionally influenced by visual structures other than NPO.

Retinal ganglion beta cells project transiently to the superior colliculus during development

In adult cats, retinal ganglion cells of the beta class project almost exclusively to the lateral geniculate nucleus rather than to the superior colliculus (SC). We have examined whether this target specificity is present during early development. To identify ganglion cells that send axons to the SC in development, rhodamine-labeled microspheres were deposited in the SC at embryonic day (E) 38, E43, or postnatal day (P) 4. Retinae were then removed between E56 and P32 and kept alive in a tissue-slice chamber so that ganglion cells that had been retrogradely labeled with microspheres could be injected intracellularly with Lucifer yellow to reveal their morphological class. Many beta cells could be retrogradely labeled by microspheres injected into the SC at E38 or E43. They were indistinguishable from beta cells projecting to the lateral geniculate nucleus and were found even when a single injection was restricted to the caudal portion of the SC. In contrast, beta cells could not be retrogradely labeled by microspheres injected into the SC at P4. The disappearance of a beta-cell projection to the SC cannot be explained entirely by cell death since as late as P32, well after the major period of ganglion cell death, many beta ganglion cells labeled with microspheres at E38 were still present. These observations suggest that many beta cells initially extend an axon collateral to the SC that is subsequently lost some time after E43. Thus, to achieve the remarkable specificity present in the adult visual system, beta cells must withdraw axon collaterals from an entire target nucleus. Similar collateral elimination may give rise to the specificity of afferent connections in other sensory systems.

Projection from the superficial layers of the tectum to the pretectal complex in the cat

The projection from the superficial layers of the tectum to the pretectal complex in the cat was examined using the retrograde transport of wheat germ agglutinin-horseradish peroxidase. Restricted injections were made into different parts of the pretectum. Neurons in the superior colliculus were found to be arranged in a mediolateral array that corresponds to the rostromedial to caudolateral array of their axon projections to the nucleus of the optic tract and posterior pretectal nucleus. These results suggest that similar parts of the retinotopic maps present in the pretectum and superior colliculus are connected. The labeled cells in the superior colliculus were located within the deep part of stratum griseum superficiale and the superficial part of stratum opticum, and were composed of multipolar cells, vertical fusiform cells and horizontal cells. We conclude from this study that the cells of origin in the superior colliculus originate in the same region to which the contralateral retinal Y-cells project and that have also the morphological diversity, as do other tecto-thalamic neurons.

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.

Spatial organization of the retinal projection to the avian lentiform nucleus of the mesencephalon

Utilizing the horseradish peroxidase retrograde tracing technique and the 2-deoxy-D-glucose metabolic mapping technique, we have demonstrated in chickens the distribution of retinal ganglion cells that project to the lentiform nucleus of the mesencephalon (LM) and the retinotopic organization of the projection in the LM. Retinal ganglion cells labeled after a nearly complete injection into the LM were found in the four quadrants, distributed in a wide horizontal belt lying along both sides of the retinal equator and stretching from the temporal to the nasal retina. The HRP-labeled cells, which appeared round or oval, ranged from 25 to 840 micron 2 in size with most in the smaller size range. Results of partial HRP injections into the LM and metabolic mapping patterns in the LM produced by stimulation of half the retina with horizontal visual motion suggest that there is an orderly mapping of the retina onto the LM. The inferior temporal quadrant projects to the rostrodorsal LM; the inferior nasal quadrant projects to the caudodorsal LM. The superior temporal quadrant projects to the middle and ventral LM, extending from the rostral to the caudal pole, whereas the superior nasal quadrant projects to a small zone in the caudal LM. The mapping of the retinal quadrants in the LM is remarkably similar to that reported in the optic tectum of birds. We suggest that a common embryological anlage with the optic tectum and the arrangement of retinal axons in the optic tract are important factors in establishing the retinotopic organization of the LM.