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 μm 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. © 1993 Wiley-Liss, Inc.     

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.     

Different distributions of large and small retinal ganglion cells in the cat after HRP injections of single layers of the lateral geniculate body and the superior colliculus

Retinal ganglion cells were labeled with HRP after injecting layers of GL or single strata within the stratum griseum superficiale (SGS). Only small cells were labeled after injecting small cell C layers and upper SGS. Only large cells were labeled after injecting lower SGS. Small and large cells were labeled after injecting medial interlaminar nucleus (MIN) and layers A and A₁.     

Thalamic projections to the lateral suprasylvian visual area in cats with neonatal or adult visual cortex damage.

Previous transneuronal anterograde tracing studies have shown that the retino-thalamic pathway to the posteromedial lateral suprasylvian (PMLS) visual area of cortex is heavier than normal in adult cats that received neonatal damage to visual cortical areas 17, 18, and 19. In contrast, the strength of this projection does not appear to differ from that in normal animals in cats that experienced visual cortex damage as adults. In the present study, we used retrograde tracing methods to identify the thalamic cells that project to the PMLS cortex in adult cats that had received a lesion of visual cortex during infancy or adulthood. In five kittens, a unilateral visual cortex lesion was made on the day of birth, and horseradish peroxidase (HRP) was injected into the PMLS cortex of both hemispheres when the animals were 10.5 to 13 months old. For comparison, HRP was injected bilaterally into the PMLS cortex of three cats 6.5 to 13.5 months after they received a similar unilateral visual cortex lesion as adults. In cats with a neonatal lesion, retrograde labeling was found in the large neurons that survive in the otherwise degenerated layers A and A1 of the lateral geniculate nucleus (LGN) ipsilateral to the lesion. Retrograde labeling of A-layer neurons was not seen in the undamaged hemisphere of these animals or in either hemisphere of animals that had received a lesion as adults. As in normal adult cats, retrograde labeling also was present in the C layers of the LGN, the medial interlaminar nucleus, the posterior nucleus of Rioch, the lateral posterior nucleus, and the pulvinar nucleus ipsilateral to a neonatal or adult lesion. Quantitative estimates indicate that the number of labeled cells is much larger than normal in the C layers of the LGN ipsilateral to a neonatal visual cortex lesion. Thus the results indicate that the heavier than normal projection from the thalamus to PMLS cortex that exists in adult cats after neonatal visual cortex damage arises, at least in part, from surviving LGN neurons in the A and C layers of the LGN. Although several thalamic nuclei, as well as the C layers of the LGN, continue to project to PMLS cortex after an adult visual cortex lesion, these projections appear not to be affected significantly by the lesion.     

The postnatal development of retinal projections in strepsirrhine galagos (Otolemur garnettii)

Here, we describe the postnatal development of retinal projections in galagos. Galagos are of special interest as they represent the understudied strepsirrhine branch (galagos, pottos, lorises, and lemurs) of the primate radiations. The projections of both eyes were revealed in each galago by injecting red or green cholera toxin subunit B (CTB) tracers into different eyes of galagos ranging from postnatal day 5 to adult. In the dorsal lateral geniculate nucleus, the magnocellular, parvocellular, and koniocellular layers were clearly labeled and identified by having inputs from the ipsilateral or contralateral eye at all ages. In the superficial layers of the superior colliculus, the terminations from the ipsilateral eye were just ventral to those from the contralateral eye at all ages. Other terminations at postnatal day 5 and later were in the pregeniculate nucleus, the accessory optic system, and the pretectum. As in other primates, a small retinal projection terminated in the posterior part of the pulvinar, which is known to project to the temporal visual cortex. This small projection from both eyes was most apparent on day 5 and absent in mature galagos. A similar reduction over postnatal maturation has been reported in marmosets, leading to the speculation that early retinal inputs to the pulvinar are responsible for the activation and early maturation of the middle temporal visual area, MT.     

Visual projections to the pontine nuclei in the rabbit: orthograde and retrograde tracing studies with WGA-HRP

Visual projections to the pontine nuclei in the rabbit were examined by means of both orthograde and retrograde tracing of WGA-HRP. The tecto-pontine projection was examined following microinjections of WGA-HRP in the right superior colliculus. The projection to the pontine nuclei is strictly ipsilateral and terminates at middle and caudal levels of the pons. The projection is absent in rostral pontine nuclei. The strongest projection is to the dorsal border of the dorsolateral pontine nuclei and is the only projection seen when the primary injection site is confined to superficial laminae. When the primary injection site also includes intermediate and deep laminae, patches of labelled terminals are also seen within dorsolateral, lateral, peduncular, paramedian, and ventral pontine nuclei as well as in the contralateral nucleus reticularis tegmenti pontis. The striate corticopontine projection was also examined with orthograde tracing of WGA-HRP. The striate corticopontine projection is ipsilateral. Most labelled terminals were seen in dorsolateral and lateral pontine nuclei throughout the rostral half of pons with some additional terminal labelling in paramedian and peduncular nuclei. Labelled terminals were also seen in ventral pontine nuclei throughout the middle and caudal levels of the pons. In a retrograde tracing study, visual projections to the pontine nuclei were examined following microinjections of WGA-HRP into the pontine nuclei. Labelled cells were seen ipsilaterally in superficial and deep laminae of the superior colliculus and in layer V of striate and surrounding occipital cortex. The pontine nuclei also receive ipsilateral projections from the ventral lateral geniculate, the nucleus of the optic tract, anterior and posterior pretectal nuclei, and the dorsal and medial terminal nuclei of the accessory optic system. These pathways are potential sources of visual input to the cerebellum.     

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. © 1995 Wiley-Liss, Inc.     

Central projections of melanopsin-expressing retinal ganglion cells in the mouse

A rare type of ganglion cell in mammalian retina is directly photosensitive. These novel retinal photoreceptors express the photopigment melanopsin. They send axons directly to the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), and olivary pretectal nucleus (OPN), thereby contributing to photic synchronization of circadian rhythms and the pupillary light reflex. Here, we sought to characterize more fully the projections of these cells to the brain. By targeting tau-lacZ to the melanopsin gene locus in mice, ganglion cells that would normally express melanopsin were induced to express, instead, the marker enzyme beta-galactosidase. Their axons were visualized by X-gal histochemistry or anti-beta-galactosidase immunofluorescence. Established targets were confirmed, including the SCN, IGL, OPN, ventral division of the lateral geniculate nucleus (LGv), and preoptic area, but the overall projections were more widespread than previously recognized. Targets included the lateral nucleus, peri-supraoptic nucleus, and subparaventricular zone of the hypothalamus, medial amygdala, margin of the lateral habenula, posterior limitans nucleus, superior colliculus, and periaqueductal gray. There were also weak projections to the margins of the dorsal lateral geniculate nucleus. Co-staining with the cholera toxin B subunit to label all retinal afferents showed that melanopsin ganglion cells provide most of the retinal input to the SCN, IGL, and lateral habenula and much of that to the OPN, but that other ganglion cells do contribute at least some retinal input to these targets. Staining patterns after monocular enucleation revealed that the projections of these cells are overwhelmingly crossed except for the projection to the SCN, which is bilaterally symmetrical.     

Visual resolution of retinal ganglion cells in monocularly-deprived cats

The spatial resolution of 87 on-centre retinal ganglion cells was measured at different retinal eccentricities in the retina of the deprived eye of two monocularly-deprived cats. Intra-ocular recording techniques were employed in order that particular attention could be placed on ganglion cells in the region of the area centralis. The spatial cut-off frequencies of both major classes of on-centre ganglion cells were comparable to those observed in normal retinas at similar retinal eccentricities. In particular there was no evidence of any loss of spatial resolution of either class of cell in the vicinity of the area centralis as has been reported in the retina of the deviating eye of strabismic cats.     

Effects of beta-adrenergic blockers on glutamate-induced calcium signals in adult mouse retinal ganglion cells

Betaxolol, a selective beta(1)-adrenoceptor antagonist, is an antiglaucoma drug commonly used to lower the intraocular pressure (IOP) in treatment of glaucoma. Recent evidence has also shown that it attenuates ligand- and voltage-gated currents in retinal ganglion cells, which may lead to reduction of intracellular calcium and prevention of glutamate-induced ganglion cell damage in glaucoma. In the present study, we examined the effectiveness of betaxolol and other beta-adrenergic blockers on glutamate-induced calcium signals. Dissociated adult mouse retinal ganglion cells were immuno-labeled with antibody CD90.2 and loaded with Fura-2AM. Calcium signals were recorded with optical recording techniques. Low doses of glutamate cause an increase in intracellular calcium that may result in pathological changes in ganglion cells. The action of glutamate could be reversibly suppressed by beta-adrenergic blockers and the order of inhibitory potency is (s)(-)-propranolol>betaxolol>timolol, with average IC(50) of 78.05, 235.7 and 2167.05, microM, respectively. Betaxolol compressed the dose-response curve of glutamate. The EC(50) of glutamate was shifted from 6.19 to 23.53 microM, indicating that betaxolol acts as a non-competitive inhibitor of glutamate response in retinal ganglion cells. Our data are consistent with previous reports that betaxolol and other beta-adrenergic blockers may exert its neuroprotective action by suppression of glutamate-induced intracellular calcium increase in retinal ganglion cells.     

Visual response properties of ventral lateral geniculate nucleus cells projecting to the pretectum and superior colliculus in the cat

The visual properties of cells in the cat ventral lateral geniculate nucleus (LGV) identified antidromically from the pretectum and/or superior colliculus (projection cells) were studied in comparison with those of LGV neurons which could not be activated antidromically (non-projection cells). ON-phasic receptive fields (RFs) were relatively predominant in 27 projection cells, whereas ON-tonic RFs were found more commonly in the non-projection group. The distribution of the RF centers revealed a centroperipheral gradient of the visual field representation within the LGV that the central visual field was more densely organized.     

Identification of ventral lateral geniculate nucleus cells projecting to the pretectum and superior colliculus in the cat

Among 235 histologically identified cells of the ventral lateral geniculate nucleus (LGV) in the cat, 66 responded antidromically to electrical stimulation of the pretectum (PT) and/or superior colliculus (SC): 22 projected to PT, 22 to SC and 22 to both sites. The LGV cells were innervated by optic tract fibers corresponding to axons of X- as well as W-type retinal ganglion cells.     

Differential co-localization of nicotinic acetylcholine receptor subunits with calcium-binding proteins in retinal ganglion cells

Immunohistochemistry was used to examine the co-occurrence of nicotinic acetylcholine receptor subunits with calcium-binding proteins in ganglion cells of the chick retina. The α3 subunit was rarely observed in ganglion cells containing calbindin, calretinin, or parvalbumin. On the other hand, the α8 subunit was more often co-localized with all calcium-binding proteins studied. These results may be related to the high calcium permeability of nicotinic receptors that contain the α8 subunit.     

Distributions of vesicular glutamate transporters 1 and 2 in the visual system of tree shrews (Tupaia belangeri)

Vesicular glutamate transporter (VGLUT) proteins regulate the storage and release of glutamate from synapses of excitatory neurons. Two isoforms, VGLUT1 and VGLUT2, are found in most glutamatergic projections across the mammalian visual system, and appear to differentially identify subsets of excitatory projections between visual structures. To expand current knowledge on the distribution of VGLUT isoforms in highly visual mammals, we examined the mRNA and protein expression patterns of VGLUT1 and VGLUT2 in the lateral geniculate nucleus (LGN), superior colliculus, pulvinar complex, and primary visual cortex (V1) in tree shrews (Tupaia belangeri), which are closely related to primates but classified as a separate order (Scandentia). We found that VGLUT1 was distributed in intrinsic and corticothalamic connections, whereas VGLUT2 was predominantly distributed in subcortical and thalamocortical connections. VGLUT1 and VGLUT2 were coexpressed in the LGN and in the pulvinar complex, as well as in restricted layers of V1, suggesting a greater heterogeneity in the range of efferent glutamatergic projections from these structures. These findings provide further evidence that VGLUT1 and VGLUT2 identify distinct populations of excitatory neurons in visual brain structures across mammals. Observed variations in individual projections may highlight the evolution of these connections through the mammalian lineage. J. Comp. Neurol. 523:1792–1808, 2015. © 2015 Wiley Periodicals, Inc.     

Influence of the visual cortex upon receptive field organization of lateral geniculate cells in rabbits

In anesthetized rabbits, the receptive fields of lateral geniculate cells were mapped prior to and following the interruption of the corticogeniculate feed-back. Visual cortex (V.C.) was depressed by a focal application of 3 M KCl. The responsiveness of the V.C. was verified by monitoring the visually evoked potentials. In off- and on-center cells, the surround excitatory responses were remarkably reduced and even fully abolished in most units. In contrast, the center excitation remained unmodified. These effects were reversible. In some on-center units the center response had also decreased, and was replaced by an evoked inhibitory response. Relay cells and interneurons which yielded on and off responses over the entire area of the receptive field exhibited a loss of only one of the evoked discharges. It is concluded that the V.C. exerts mostly a specific desinhibitory action upon the geniculate network. This action affects either the center or the surround responses differentially. The results are compared with those obtained from cats.     

Correlation between different types of retinal ganglion cells and their projection pattern in the albino rat

Injecting Fluoro-Gold (FG) and Evans-Blue (EB) into the right dLGN and SC in the adult albino rat, ipsilaterally projecting double-labeled retinal ganglion cells were mainly seen in the ventrotemporal crescent. They were mainly large sized cells. The ipsilaterally projecting double-labeled cells tended to have larger somata than the single- and double-labeled cells projecting to the contralateral superior colliculus and/or dorsal nucleus of the lateral geniculate body.     

Increased expression of specific recognition molecules by retinal ganglion cells and by optic pathway glia accompanies the successful regeneration of retinal axons in adult zebrafish

Retinal ganglion cells (RGCs) in adult zebrafish can regenerate their axons. We show that successful axonal regeneration is accompanied by the re-expression by RGCs of mRNAs encoding specific recognition molecules that are expressed at high levels in the larval retina but are down-regulated in the adult. Message levels for l1.1 and l1.2 (two homologs of mammalian L1), n-cam (homologous to mammalian N-CAM), beta3 (related to the beta3 and beta2 subunits of mammalian Na, K-ATPase), and tn-c (homologous to mammalian tenascin-C) were high in larval RGCs undergoing axonogenesis and low in adult RGCs. After an optic nerve crush, axotomized adult RGCs showed increased levels of l1.1, l1.2, and n-cam mRNA expression, whereas the levels of beta3 and tn-cmRNA remained unchanged. The optic nerve crush also induced the expression of some of these mRNAs in the optic nerve and tract where they are not normally detectable. This lesion induced up-regulation by presumptive glia was observed for l1.1, l1.2, n-cam and beta3 but not for tn-c. The combination of a neuronal (intrinsic) response to axotomy with an environmental (extrinsic) response may be an important determinant allowing for the successful axonal regeneration. © 1996 Wiley-Liss, Inc.     

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 Clea) rats of either sex, weighing 350–400 g were used. With the rats in a state of deep anesthesia, we pressure-injected 0.02 μl 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 excised. 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 the total number of ipsilaterally labeled cells was 566, and the percentages 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.     

Activation of lateral geniculate neurons by norepinephrine: Mediation by an α-adrenergic receptor

Adrenergic receptors in the vicinity of neurons in the lateral geniculate nucleus (LGN) of the rat were pharmacologically characterized using extracellular single-cell recording and microiontophoretic techniques. Application of norepinephrine (NE) at low iontophoretic currents (1–15 nA) produced a delayed activation of most LGN neurons. This activation was mimicked by various sympathomimetic amines. The relative potency series of agonists was typical of postsynaptic α-adrenergic receptors:epinephrine>NE>phenylephrine α-methylnorepinephrine>dopamine>isoproterenol. The α-antagonists phentolamine, piperoxane and WB-4101, when applied at low iontophoretic currents (<10nA), produced a selective, dose-dependent and reversible blockade of the response to NE. The β-antagonist sotalol had weak and variable effects at these currents. At low currents, the presynaptic α-agonist clonidine was also able to block the response to NE but, at higher currents, produced a partial activation of some units, suggesting that it is a weak agonist. The ability of sympathomimetic amines to activate LGN neurons correlates well with their reported affinities for brainα₁-adrenoceptors labeled with [³H]WB-4101. It is concluded that NE activates neurons in the LGN via a postsynaptic orα₁-adrenergic receptor.