Retinal projections in sockeye salmon smolts (Oncorhynchus nerka)

Summary The retinal projections in 2-year-old salmon smolt (Oncorhynchus nerka) are significantly different from those observed in other teleosts examined to date in that the projections are more extensive. Very noticeable are extensive projections to most of the dorsal thalamus, to all layers of the optic tectum, and into the periaqueductal gray of the torus semicircularis. The salmon smolt has bilateral retinal projections to the diencephalon and pretectum. A small retinal projection to the lateral habenular nucleus has not been described previously. Although these findings suggest striking differences in retinal projections among teleosts, this variation may relate to age differences since the previously studied teleosts were adults.     

Central projections of the pineal complex in the silver lamprey Ichthyomyzon unicuspis

Summary The central projections of the pineal complex of the silver lamprey Ichthyomyzon unicuspis were studied by injection of horseradish peroxidase. The pineal tract courses caudally along the left side of the habenular commissure, and a few fibers penetrate the brain through the caudalmost portion of this commissure. Most of the fibers, however, continue caudally and enter the brain through the posterior commissure. The pineal tract projects bilaterally to the subcomissural organ, the superficial and periventricular pretectum, the posterior tubercular nucleus, the dorsal and ventral thalamus, the dorsal hypothalamus, the optic tectum, the torus semicircularis, the midbrain tegmentum, and the oculomotor nucleus. A few fibers decussate in the tubercular commissure, but the course of these decussate fibers could not be followed owing to the bilateral nature of the projections. No retrogradely labeled cells were found in the brain. With the exception of the projections to the optic tectum and torus semicircularis, the pineal projections in the silver lamprey are similar to those reported in other anamniote vertebrates.     

Retinofugal and retinopetal projections in the teleost Channa micropeltes (Channiformes)

Summary Retinofugal and retinopetal projections were investigated in the teleost fish Channa micropeltes (Channiformes) by means of the cobaltous lysine and horseradish peroxidase (HRP) tracing techniques. Retinofugal fibers cross completely in the optic chiasma. A conspicious lamination is present in those parts of the optic tract that give rise to the marginal branches of the optic tract. This layering of optic fibers continues in the marginal branches to mesencephalic levels. Retinal projections to the preoptic and hypothalamic regions are sparse; they are more pronounced in the area of pretectal nuclei. The medial pretectal complex and the cortical pretectal nucleus are more fully differentiated than in other teleostean species. Further targets include the thalamus and the optic tectum. The course of major optic sub-tracts and smaller fascicles is described. Retinopetal neurons are located contralaterally in a rostral and a caudal part of the nucleus olfactoretinalis, and in a circumscribed nucleus thalamoretinalis. The present findings are compared with reports on other teleost species.     

Retinal projections in the catfish,Mystus vittatus (Bloch) as revealed by tracer studies with horseradish peroxidase

Summary The retinal efferents of the catfish, Mystus vittatus, were investigated with the use of the horseradish peroxidase (HRP) technique. Most retinal fibres extended contralateral to the eye that had received HRP label, while a few fascicles projected to the ipsilateral side without decussation in the optic chiasma. The contralateral fibres projected to the suprachiasmatic nucleus, the nucleus opticus dorsolateralis, the nucleus of the posterior commissure, the nucleus geniculatus lateralis, pretectal nuclear complex, and to two layers of the optic tectum, i.e., stratum fibrosum et griseum superficiale and stratum griseum centrale. The accessory optic tract arose from the inner area of the optic tract and extended ventromedially to the accessory optic nucleus. The ipsilateral fascicles projected to almost all the above mentioned nuclei, but these projections were comparatively sparse. The ipsilateral retinal projection was restricted to the rostral tectum.     

Retinal projections in a snake, Thamnophis sirtalis

The retinofugal projections of the snake Thamnophis sirtalis were studied by the method of experimentally induced Wallerian degeneration stained by the Fink-Heimer method. The retinal ganglion cells project to all parts of the contralateral lateral geniculate complex, nucleus lentiformis mesencephali, nucleus geniculatus pretectalis, nucleus posterodorsalis, basal optic nucleus and superficial layers of the optic tectum. In addition, the retinofugal projections were observed terminating in portions of the ipsilateral lateral geniculate complex and nucleus posterodorsalis. Examination of the morphology of the retinal terminal areas stained for Nissl substance with cresyl violet led to the conclusion that these regions are well differentiated and should not be considered poorly developed when compared with other reptilian forms such as turtles.     

Retinofugal projections in the eel,Anguilla anguilla L. (Teleostei), visualized by the cobalt-filling technique

The retinofugal projections in the eel were studied by use of the cobalt-filling technique. The optic tract projects contralaterally to the hypothalamic optic nucleus, the anterior periventricular nucleus, the lateral geniculate nucleus, the dorsomedial optic nucleus, four pretectal recipient areas, the optic tectum, and the tegmentum. Small ipsilateral projections were demonstrated in the hypothalamic optic nucleus, the dorsomedial optic nucleus, and the optic tectum.     

Target areas innervated by PACAP-immunoreactive retinal ganglion cells

The retinohypothalamic tract (RHT) originates from a subset of retinal ganglion cells (RGCs). The cells of the RHT co-store the neurotransmitters PACAP and glutamate, which in a complex interplay mediate light information to the circadian clock located in the suprachiasmatic nuclei (SCN). These ganglion cells are intrinsically photosensitive probably due to expression of melanopsin, a putative photoreceptor involved in light entrainment. In the present study we examined PACAP-containing retinal projections to the brain using intravitreal injection of the anterograde tracer cholera toxin subunit B (ChB) and double immunostaining for PACAP and ChB. Our results show that the PACAP-containing nerve fibres not only constituted the major projections to the SCN and the intergeniculate leaflet of the thalamus but also had a large terminal field in the olivary pretectal nucleus. The contralateral projection dominated except for the SCN, which showed bilateral innervation. PACAP-containing retinal fibres were also found in the ventrolateral preoptic nucleus, the anterior and lateral hypothalamic area, the subparaventricular zone, the ventral part of the lateral geniculate nucleus and the nucleus of the optic tract. Retinal projections not previously described in the rat also contained PACAP. These new projections were found in the lateral posterior nucleus, the posterior limitans nucleus, the dorsal part of the anterior pretectal nucleus and the posterior and medial pretectal nuclei. Only a few PACAP-containing retinal fibres were found in the superior colliculus. Areas innervated by PACAP-immunoreactive fibres also expressed the PACAP-specific PAC1 receptor as shown by in situ hybridization histochemistry. The findings suggest that PACAP plays a role as neurotransmitter in non-imaging photoperception to target areas in the brain regulating circadian timing, masking, regulation of sleep-wake cycle and pupillary reflex.Abbreviations 3v Third ventricle - ac Anterior commissure - AD Anterodorsal thalamic nucleus - AH Anterior hypothalamic area - APTD Anterior pretectal nucleus, dorsal part - ChB Cholera toxin subunit B - CPu Caudate putamen - CPT Commissural pretectal nucleus - DGL Dorsal geniculate nucleus - IGL Intergeniculate leaflet - LH Lateral hypothalamic area - LP Lateral posterior thalamic nucleus - LS Lateral septum - MB Mammillary body - MPO Medial preoptic nucleus - MPT Medial pretectal nucleus - oc Optic chiasma - OPT Olivary pretectal nucleus - OT Nucleus of the optic tract - PACAP Pituitary adenylate cyclase-activating polypeptide - PAC1 PACAP receptor type 1 - PAG Periaqueductal gray - Pe Periventricular hypothalamic nucleus - PLi Posterior limitans thalamic nucleus - PPT Posterior pretectal nucleus - PVT Paraventricular thalamic nucleus - PVN Paraventricular hypothalamic nucleus - RGCs Retinal ganglion cells - RHT Retinohypothalamic tract - SCN Suprachiasmatic nucleus - SC Superior colliculus - SNR Substantia nigra, reticular part - SON Supraoptic nucleus - SPVZ Subparaventricular zone - VGL Ventral geniculate nucleus - VIP Vasoactive intestinal peptide - VPAC1 VIP/PACAP receptor type 1 - VPAC2 VIP/PACAP receptor type 2 - VLPO Ventrolateral preoptic nucleus - VTA Ventral tegmental areaThis study was supported by The Danish Biotechnology Center for Cellular Communication and The Danish Neuroscience Programme. J.H. is postdoc funded by the Danish Medical Research Council (Jr. No. 0001716)     

Retinal projections in the chain pickerel (Esox niger Lesueur)

Summary The retinal projections inEsox niger, as determined with the aid of a modified cobalt-lysine method, are considerably more extensive in the diencephalon and pretectum than in other teleost fishes so far examined. Although most retinal axons terminate contralaterally, rare fibers can be traced to the same aggregates ipsilaterally. The retinohypothalamic projection appears larger than hitherto reported in teleosts, and the dorsomedial optic tract issues fibers to a series of cell clusters extending from the rostral thalamus to mid-torus levels. A retinal projection to a presumed ventrolateral optic nucleus (VLO) is described for the first time in a teleost. Other targets of retinal fibers include the nucleus geniculatus lateralis ipse of Meader (GLI), the pretectal nucleus (P), the cortical nucleus and a well-developed ventromedial optic nucleus (VMO). The projection to the optic tectum is principally to the stratum fibrosum et griseum superficiale (SFGS) and stratum marginale (SM), but a considerable number of axons also course through the stratum album centrale (SAC) before terminating there or piercing the stratum griseum centrale (SGC) and terminating in SFGS. Rare terminal arborizations of retinal fibers were also observed in stratum griseum centrale (SGS) and in the stratum griseum periventriculare (SGC) in restricted portions of the tectum. Because of the relatively large size of the visual structures inE. niger it is a potentially useful model for future experimental studies on the visual system.     

Efferent projections from the lateral septal nucleus to the anterior hypothalamus in the rat: A study combining Phaseolus vulgaris-leucoagglutinin tracing with vasopressin immunocytochemistry

Summary The tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected into the lateral septum of the rat at different rostrocaudal locations to study the efferent septal projections to the anterior hypothalamus. For spatial correlation of these septofugal elements with the vasopressinergic system a dual immunocytochemical technique was used (i) to demonstrate nerve fibers and their corresponding bouton-like structures labeled with the tracer, and (ii) to identify vasopressin in the same section. The hypothalamic paraventricular and supraoptic nuclei, the accessory hypothalamic magnocellular system, and the suprachiasmatic nucleus are recipients of PHA-L-labeled fibers from all parts of the lateral septum. Close appositions between (i) these axons and their varicosities, and (ii) vasopressin-immunoreactive perikarya and their processes, putatively indicating functional interrelationships, were observed in all these nuclear areas, especially in their neuropil formations.Abbreviations F fornix - OC optic chiasm - OT optic tract - PVN paraventricular nucleus - SCN suprachiasmatic nucleus - SON supraoptic nucleus - III third ventricle     

Retinofugal and retinopetal connections in the upside-down catfish (Synodontis nigriventris)

Summary The retinofugal and retinopetal connections in the upside-down catfish Synodontis nigriventris were studied by use of the horseradish-peroxidase (HRP) techniques, autoradiography, and degeneration-silver methods. An unusual retinal projection to the torus semicircularis as well as projections to the retina from three different sources in the brain are described. After intra-ocular injections of HRP, labeled cells were found in the optic tectum, the dorsomedial optic nucleus and one of the pretectal nuclei. These new findings support the basic hypothesis (i) that neuronal connections are more extensive in primitive brains, and (ii) that the evolutionary development of more complex brains involves the loss of some selected connections.     

Demonstration of retinal afferents in the RCS rat,with reference to the retinohypothalamic projection and suprachiasmatic nucleus

In the Royal College of Surgeons (RCS) rat, characterized by inherited retinal dystrophy, retinal projections to the brain were studied using anterograde neuronal transport of cholera toxin B subunit upon injection into one eye. The respective immunoreactivity was found predominantly contralateral to the injection site in the lateral geniculate nucleus, superior colliculus, nucleus of the optic tract, medial terminal nucleus of the accessory optic tract, and bilateral hypothalamic suprachiasmatic nuclei. Although terminal density was somewhat reduced in dystrophic rats, the projection patterns in these animals appeared similar to those seen in their congenic controls and were comparable to the visual pathways described for the rat previously. In dystrophic rats, the number of cell bodies exhibiting immunoreactivity to vasoactive intestinal polypeptide, viz. a population of suprachiasmatic neurons receiving major retinohypothalamic input, was reduced by one-third, and some differences were observed in the termination pattern of the geniculohypothalamic tract, as revealed by immunoreactivity to neuropeptide Y in the suprachiasmatic nucleus.This study was supported by grants from the DFG (Re 644/2-1) and the NMFZ, Mainz (to S.R.).     

Retinal projections in the Northern Water snake Natrix sipedon sipedon (L.)

Retinal projections were studied experimentally in the Northern water snake using modifications of the Nauta silver impregnation technique. Contralaterally, the retina projects to nucleus geniculatus lateralis pars dorsalis and pars ventralis, nucleus lentiformis mesencephali and nucleus geniculatus pretectalis. A sparse projection was also observed to nucleus ovalis. An additional afferent thalamic projection to nucleus ventrolateralis was found in two cases. The retina projects ipsilaterally to the dorsolateral portion of nucleus geniculatus lateralis pars dorsalis, and sparsely to nucleus lentiformis mesencephali and nucleus geniculatus pretectalis. Nucleus posterodorsalis receives dense bilateral retinal projections. Contralaterally, the retina also projects to the superficial layers of the tectum (layers 8–13 of Ramón) and to nucleus opticus tegmenti. Armstrong's findings that the retinal projections in Natrix are qualittatively similar to those in lizards were confirmed. However there are marked quantitative differences among the various pathways and their corresponding nuclei. These differences are particularly striking in comparing the visual projections to the dorsal thalamus, the retino-tecto-rotundal and the retino-geniculate systems. The first is reduced in volume and the second is markedly increased in volume in comparison with lizards. These data lend support to the theories of Walls that snakes evolved from fossorial lizards and of Underwood that the eyes of these lizards underwent reduction but not complete degeneration. Qualitatively the retinal projections are conservative among lizards and snakes, but a history of reduction of these pathways in ancestral snakes with a selective increase in the retino-geniculate system as a surface niche was reattained is reflected in the anatomy of this ophidian visual system.     

Anterograde labelling from the optic nerve reveals multiple central targets in the teleost,Lethrinus chrysostomus (Perciformes)

Summary Cobaltous-lysine is transported anterogradely from the optic nerve of the teleost, Lethrinus chrysostomus (Lethrinidae, Perciformes). The marginal optic tract is labelled in longtitudinal bands of light and dark staining fibres which persists caudally within the ventral division but not in the dorsal division. This species possesses multiple central targets in the contralateral preoptic, diencephalic, pretectal, periventricular and tectal regions of the brain. In addition, a greater subdivision of the marginal optic tract is found to project to various nuclei. Ipsilateral projections are found in the suprachiasmatic nucleus and in the region of the horizontal commissure. Projections are also found in the telencephalic region of the nucleus olfactoretinalis and the thalamic region of the nucleus thalamoretinalis. The retinotopicity of some of these nuclei, found in previous studies, is discussed in relation to the possibility of specific sub-populations of retinal ganglion cells having different central targets.Abbreviations used in the Text and Figures A nucleus anteriorthalami - AO accessory optic nucleus - AOT accessory optic tract - AxOT axial optic tract - BO nucleus of the basal optic root - C cerebellum - HCv ventral division of horizontal commissure - I nucleus intermedius thalami - IL inferior lobe - MdOT medial optic tract - MO medulla oblongata - MOTd dorsal division of the marginal optic tract - MOTi intermediate division of the marginal optic tract - MOtv ventral division of the marginal optic tract - O olfactory bulb - OT optic tract - PC nucleus pretectalis centralis - PCo posterior commissure - Pd nucleus pretectalis dorsalis - PG preglomerular complex - PPd nucleus pretectalis periventricularis, pars dorsalis - PPv nucleus pretectalis periventricularis, pars ventralis - PSm nucleus pretectalis superficial pars magnocellularis - PSp nucleus pretectalis superficialis, pars parvocellularis - Sn suprachiasmatic nucleus - TEL telencephalon - TeO optic tectum - TL torus longtitudinalis - TrOlfR tractus olfactoretinalis - VCg granular layer of the valvula cerebelli - VCm molecular layer of the valvula cerebelli - VM nucleus medialis thalami - VL nucleus ventrolateralis thalami - VMdOT ventro-medial optic tract     

Terminal distribution of retinal fibers in the tegu lizard (Tupinambis nigropunctatus)

Summary The retinal projections in the tegu lizard were traced using degeneration-silver methods. Bilateral projections were found to the dorsolateral geniculate and the posterodorsal nuclei. Unilateral, crossed projections were traced to the suprachiasmatic nucleus, the ventrolateral geniculate nucleus, the mesencephalic lentiform nucleus, nucleus geniculatus praetectalis, the ectomammillary nucleus, and the optic tectum. Some of these connections are distinctly different from those reported in other reptiles and suggest that important interspecific variations occur among reptiles.     

Olivary projections from the pretectal region in the cat studied with horseradish peroxidase and tritiated amino acids axonal transport

The organization of the projection from the pretectal region to the inferior olive in the cat was studied with autoradiographic and horseradish peroxidase (HRP) methods. After injections of HRP into the olive in six cats, cells were labeled ipsilaterally in the anterior pretectal nucleus (NPA), the posterior pretectal nucleus (NPP), the nucleus of the optic tract (NOT), and the dorsal terminal nucleus of the accessory optic tract (DTN). In three experiments, tritiated amino acids were injected into those parts of the pretectal region which contained labeled cells in the HRP experiments, and the projections to the olive were plotted. Both NPA and NPP projected to the rostral half of the dorsal accessory olive, the rostromedial margin of the ventral lamella, and the lateral part of the ventrolateral outgrowth. NOT projected to the caudal half of the dorsal cap, while DTN projected to both the dorsal cap and nucleus beta. The projections are entirely ipsilateral.     

Retinal projections in the electric catfish (Malapterurus electricus)

Summary The poorly developed visual system of the electric catfish was studied with silver-degeneration methods. Retinal projections were entirely contralateral to the hypothalamic optic nucleus, the lateral geniculate nucleus, the dorsomedial optic nucleus, the pretectal nuclei including the cortical nucleus, and the optic tectum. The small size and lack of differentiation of the visual system in the electric catfish suggest a relatively small role for this sensory system in this species.     

Bilateral feedback projections to the forebrain in the premotor network for singing in zebra finches

A discrete neural circuit mediates the production of learned vocalizations in oscine songbirds. Although this circuit includes some bilateral pathways at midbrain and medullary levels, the forebrain components of the song control network are not directly connected across the midline. There have been no previous reports of bilateral projections from medullary and midbrain vocal control nuclei back to the forebrain song system, but the existence of such bilateral corollary discharge pathways was strongly suggested by the recent observation that unilateral stimulation of a forebrain song nucleus during singing leads to a rapid readjustment of premotor activity in the contralateral forebrain. In the present study, we used neuroanatomical tracers to demonstrate bilateral projections from (a) the rostral ventrolateral medulla (RVL), which may control respiratory aspects of vocalization, to nucleus uvaeformis (Uva), and (b) the dorsomedial intercollicular nucleus (DM), a midbrain vocal control region, to Uva. Both RVL and DM receive descending projections from the forebrain song nucleus robustus archistriatalis, and Uva projects directly to the forebrain song nuclei interfacialis and high vocal center. We suggest that the bilateral feedback projections from DM and RVL to Uva function to coordinate the two hemispheres during singing in adult songbirds and to convey internal feedback of premotor signals to the forebrain in young birds that are learning to sing. © 1998 John Wiley & Sons, Inc. J Neurobiol 34: 27–40, 1998     

Brain stem innervation of the caudal neurosecretory system

Summary The innervation of the caudal neurosecretory system of Poecilia sphenops (black molly) was studied by use of the retrograde horseradish peroxidase (HRP) method. The structure of the caudal neurosecretory system in this species was well suited for application of HRP procedures. Acrylamide/HRP gel implants were placed in the nucleus of the caudal neurosecretory system. Two neuronal groups which contained HRP filled cells were found in the brain stem. Bilateral projections originate from the dorsal tegmentum of the midbrain and the reticular nucleus of the medulla.Supported by PHS 5429-19-4 and BNS 8206452The authors wish to thank Drs. R. Parsons, S. Freedman and J. Wells for reading this report and A. Angel for photographic assistance     

Nervous connections of the parietal eye in adult Lacerta s. sicula Rafinesque as demonstrated by anterograde and retrograde transport of horseradish peroxidase

Summary Subsequent to the injection of horseradish peroxidase into the parietal eye of adult Lacerta sicula, the course of the parietal nerve and its projections were determined.The parietal nerve enters the left habenular ganglion where it branches into a medial and a lateral route. Some nerve fibers decussate within the habenular commissure. Whereas this pathway exhibits a striking asymmetry at the level of the habenular ganglia, its projections to the dorsolateral nucleus of the thalamus, the periventricular hypothalamic area, the preoptic hypothalamic and telencephalic regions, and the pretectal area are arranged in a strictly symmetric manner. A possible innervation of tegmental areas could not be proven due to the presence of endogenous peroxidase within these regions. No parietal nerve fibers were observed in the optic tectum.In a few animals investigated, scattered labeled perikarya were located in the periventricular hypothalamic gray indicating a parietopetal innervation in Lacerta sicula. The injection of horseradish peroxidase into one of the lateral eyes revealed terminal areas of the optic nerve within the preoptic region, and the thalamic and pretectal nuclei, displaying partial overlapping with the projections of the parietal nerve to these areas.From the present investigation further evidence is obtained that the pineal complex of lower vertebrates is a component of the photoneuroendocrine system. Particular emphasis is placed upon the nervous connections between the parietal eye and the hypothalamus, described for the first time in the present study.Supported by the Deutsche Forschungsgemeinschaft (Grant Ko 758/1)In partial fulfillment of the requirements of the degree of Dr. med., Faculty of Medicine, Justus Liebig University of Giessen     

Contralateral projections of the optic tectum in the zebra finch (Taenopygia guttata castanotis)

Summary Efferent projections of the optic tectum of zebra finches were investigated by injection of the radioactive anterograde tracer ³H-proline. In addition to a variety of ipsilateral projections, some contralateral connections were found. Quantitative evaluation of the recrossing tecto-rotundal and nucleus subpraetectalis/nucleus interstitio-praetecto-subpraetectalis projection revealed that these connections are much stronger than previously believed. In contrast, the tecto-tectal projection is very weak, as has been shown previously. Further support for this comes from results obtained using injections of retrograde tracers. The role of the different projections in conveying information from the ipsilateral eye to the ectostriatum, the telencephalic end-station of the tectofugal pathway, is discussed.