NADPH-diaphorase reactivity in adult and developing cat retinae

Inhibition of endocytosis suppresses the nitric oxide-dependent release of Cl- in retinal amacrine cells

Our lab has previously shown that nitric oxide (NO) can alter the synaptic response properties of amacrine cells by releasing Cl- from internal acidic compartments. This alteration in the Cl- gradient brings about a positive shift in the reversal potential of the GABA-gated current, which can convert inhibitory synapses into excitatory synapses. Recently, we have shown that the cystic fibrosis transmembrane regulator (CFTR) Cl- channel is involved in the Cl- release. Here, we test the hypothesis that (acidic) synaptic vesicles are a source of NO-releasable Cl- in chick retinal amacrine cells. If SVs are a source of Cl-, then depleting synaptic vesicles should decrease the nitric oxide-dependent shift in the reversal potential of the GABA-gated current. The efficacy of four inhibitors of dynamin (dynasore, Dyngo 4a, Dynole 34-2, and MiTMAB) were evaluated. In order to deplete synaptic vesicles, voltage-steps were used to activate V-gated Ca2+ channels and stimulate the synaptic vesicle cycle either under control conditions or after treatment with the dynamin inhibitors. Voltage-ramps were used to measure the NO-dependent shift in the reversal potential of the GABA-gated currents under both conditions. Our results reveal that activating the synaptic vesicle cycle in the presence of dynasore or Dyngo 4a blocked the NO-dependent shift in EGABA. However, we also discovered that some dynamin inhibitors reduced Ca2+ signaling and L-type Ca2+ currents. Conversely, dynasore also increased neurotransmitter release at autaptic sites. To further resolve the mechanism underlying the inhibition of the NO-dependent shift in the reversal potential for the GABA-gated currents, we also tested the effects of the clathrin assembly inhibitor Pitstop 2 and found that this compound also inhibited the shift. These data provide evidence that dynamin inhibitors have multiple effects on amacrine cell synaptic transmission. These data also suggest that inhibition of endocytosis disrupts the ability of NO to elicit Cl- release from internal stores which may in part be due to depletion of synaptic vesicles.

Nitric oxide production and the expression of two nitric oxide synthases in the avian retina

Nitric oxide (NO) is known to exert multiple effects on the function of many retinal neurons and their synapses. Therefore, it is equally important to understand the potential sources of NO within the retina. To explore this, we employ a combination of 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM) based NO detection and immunohistochemistry for the NO synthetic enzymes, neuronal and endothelial nitric oxide synthase (nNOS and eNOS). We find DAF signals in photoreceptors, horizontal cells, amacrine cells, efferent synapses, Müller cells, and cells in the ganglion cell layer (GCL). nNOS immunoreactivity was consistent with the DAF signal with the exception that horizontal cells and Müller cells were not clearly labeled. eNOS-like immunoreactivity (eNOS-LI) was more widespread with photoreceptors, horizontal cells, occasional bipolar cells, amacrine cells, Müller cells, and cells in the GCL all showing labeling. Double labeling with antibodies raised against calretinin, syntaxin, and glutamine synthetase confirmed that horizontal cells, amacrine cells, and Müller cells (respectively) were expressing eNOS-LI. Although little or no nNOS labeling is observed in horizontal cells or Müller cells, the expression of eNOS-LI is consistent with the ability of these cells to produce NO. Together these results suggest that the capability to produce NO is widespread in the chicken retina. We propose that multiple forms of regulation for nNOS and eNOS play a role in the patterning of NO production in the chicken retina.

Expression of nicotinamide adenine dinucleotide phosphate-diaphorase in the retina of postnatal golden hamsters deprived of light stimulation

Nicotinamide Adenine Dinucleotide Phosphate-Diaphorase (NADPH-d) expressing neurons in the retina of golden hamsters have been identified to be a subset of amacrine cells that provide a major source of Nitric Oxide (NO) in retina. This subset of amacrine cells in mouse retina was recently proved to contain the circadian clock gene Per1 (D.Q. Zhang, T. Zhou, G.X. Ruan, D.G. McMahon, Circadian rhythm of Period 1 clock gene expression in NOS amacrine cells of the mouse retina, Brain Res., 1050 (2005) 101-109). However, it remains unknown whether these clock-related NADPH-d amacrine cells can be regulated by light stimulation and thus synchronized to ambient day/night cycle. A previous study has reported that NADPH-d expressing amacrine cells in postnatal hamsters exhibited a surge after eye-opening (D. Tay, Y.C. Diao, Y.M. Xiao, K.F. So, Postnatal development of nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons in the retina of the golden hamster, J. Comp. Neurol., 446 (2002) 342-348) suggesting a possible effect of light on the NADPH-d amacrine cells. In order to further reveal the relationship between NADPH-d amacrine cells and light stimulation, the present study focuses on the changes of the expression of NADPH-d in the retina of postnatal hamsters reared in completely deprived light conditions. Prior to eye opening, P12 hamster pups were subjected to either bilateral eyelid suturing or dark rearing. On P28 a subgroup of light deprived hamsters was returned to lighting conditions and the expression of NADPH-d activities in the retina was assessed. In hamsters reared in the 12:12 light-dark cycle, the number of NADPH-d amacrine cells in the ganglion cell layer (GCL) increased right after eye-opening and reached the adult level gradually. However, hamsters subjected to both bilateral eyelid suturing and dark rearing, the number of NADPH-d amacrine cells in GCL was maintained at a low level but increased again upon returning to the 12:12 light-dark condition. In contrast, the number of NADPH-d expressing amacrine cells in the inner nuclear layer (INL) remained low and unaltered regardless of the lighting environment. This study demonstrates that there are two subpopulations of NADPH-d expressing amacrine cells with respect to different locations in the retina of hamsters. Different from those in INL, the NADPH-d amacrine cells in GCL of postnatal hamsters are dependent on the lighting environment implicating that these clock-related amacrine cells and the production of NO might be under a modulation of light stimulation.

Postnatal development of nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons in the retina of the golden hamster

The histochemical method was used to investigate the postnatal development of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) -positive neurons in retinas of the golden hamster. NADPH-d-positive neurons were discernible in the retina at postnatal day (P)1. From P4 onward to adulthood, when the retina acquired its laminated characteristics, NADPH-d- positive neurons were observed in the inner nuclear layer (INL) and the ganglion cell layer (GCL). Results showed that NADPH-d-positive neurons in INL and GCL followed different time courses and patterns in their development. NADPH-d-positive neurons in INL underwent a sharp increase from P4 to P8 (3.6-fold), followed by a decrease to 46% of the maximum at P12. This value was maintained relatively constant to the adult level. The mean diameters of NADPH-d-positive neurons in INL, which were smaller than those in the GCL for all ages, increased from P8 to P12 and from P20 to adulthood. As for neurons in the GCL, the increase in cell number was not so apparent for the earlier postnatal days until P20; thereafter, an obvious increase to the adult level was observed. The mean diameters of the NADPH-d-positive cell bodies in the GCL increased with age, except for P16-P20, during which time there was a slight and insignificant decrease. The tendency of changes in cell density was basically similar to that of the total number for both the INL and the GCL. Between P12 and P20, the density distribution map of the NADPH-d-positive neurons underwent dramatic changes: The highest density shifted from the upper central retina at the earlier postnatal days to the lower central retina in the adult. The two waves of increase in NADPH-d-positive neurons coincide with the process of axonal elongation and synaptogenesis and the acquisition of visual function and experience. It is suggested that these NADPH-d-positive neurons are related to these two developmental events.

Selective nicotinamide adenine dinucleotide phosphate-diaphorase histochemical labeling of Müller radial processes and photoreceptors in the earliest stages of retinal development in the tadpole

To investigate potential sources of nitric oxide production in the early stages of retinal development we used, in the tadpole, nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry that was reported to reveal nitric oxide synthase isoforms in the retina. In the first stages of optic vesicle differentiation, prior to optic cup invagination, histochemical positivity was detected in the radial processes of Müller cells, that provide a scaffold for migrating retinal neuroblasts, and was soon followed by intense staining of photoreceptors. These events preceded retinal laminar patterning and the appearance of histochemical positivity in other retinal cell populations. The findings indicate that nitric oxide synthase is expressed during early retinogenesis at selective sites, which are implicated in the guidance of migrating cells and in phototransduction.

Neuronal nitric oxide synthase immunoreactive neurons in the mammalian retina

The development of immunocytochemistry has led to a better understanding of synaptic transmission carried out by neuroactive substances in the mammalian brain, including the retina. In the mammalian retina, nitric oxide (NO) is widely accepted as a neuromodulator. Histochemistry based on NADPH-d and immunocytochemistry based on nitric oxide synthase (NOS) have been used to identify the presence of nitric oxide in the mammalian retina. Certain types of amacrine cells and a class of displaced amacrine cells have been labeled consistently in all mammalian retinae studied to date. Other cell types showing NADPH-d reactivity or NOS immunoreactivity varied between species. NADPH-d reactive or NOS immunoreactive amacrine cells may serve as a source of NO for amacrine, bipolar, and ganglion cells in the inner retina, whereas interplexiform cells, bipolar cells, and horizontal cells may serve as a source of NO for the outer retina of mammals.

Nitric oxide (NO.) stabilizes whereas nitrosonium (NO+) enhances filopodial outgrowth by rat retinal ganglion cells in vitro

Recent observations suggest that nitric oxide (NO(.)) can increase or decrease growth cone motility. Here, these apparently paradoxical results are explained by distinct actions of different NO-related species. Filopodial morphology of 223 rat retinal ganglion cells was monitored under computer-enhanced video microscopy in the presence of NO synthase (NOS) substrates or inhibitors, donors of specific NO-related species, and membrane-permeant cyclic nucleotide analogs. Physiological NOS activity induced filopodial outgrowth, whereas inhibition of NOS stabilized filopodia. Similar to NOS, nitrosonium (NO(+) transfer) and peroxynitrite (ONOO(-)), which can regulate the activity of growth-associated proteins by S-nitrosylation and oxidation, respectively, induced filopodial outgrowth. In contrast, NO(.), which stimulates guanylate cyclase to increase cGMP, stabilized filopodial activity. Thus disparate NO-related species may offer a dynamic process of filopodial growth regulation.

An experimental basis for implicating excitotoxicity in glaucomatous optic neuropathy

Most therapy for glaucoma is directed at the management of the intraocular pressure (IOP). Conventional wisdom holds that excessive pressure within the eye leads to the ganglion cell loss/optic nerve damage seen in this disease. Both glutamate and elevated IOP can selectively damage the retinal ganglion cells in the mammalian eye. We have identified an elevated level of glutamate in the vitreous humor of glaucoma patients (27 microM as compared to 11 microM in the control population). This concentration of glutamate suffices--on its own--to kill retinal ganglion cells. It is plausible that the IOP may represent an initial insult that precipitates the production of excessive glutamate. Therefore, even if glutamate elevation is an epiphenomenon associated with the course of the disease, it may contribute to ganglion cell loss in humans. Lowering the IOP may slow down glutamate production, but if nothing is done to block the toxic effects of glutamate as well, visual loss may result despite excellent IOP control. If interventions can be found to retard the production or toxic effects of glutamate, it may be possible to slow glaucomatous visual loss.

Nitric oxide synthase-containing cells in the retina, pigmented epithelium, choroid, and sclera of the chick eye

Nitric oxide is a nonconventional neurotransmitter that is produced as needed by the enzyme nitric oxide synthase (NOS). NOS has been detected in numerous neural structures, including distinct populations of retinal neurons in a variety of vertebrate species. The purpose of this study was to identify NOS-containing cells in the retina and extraretinal ocular tissues of hatched chicks. NOS was detected in frozen sections by using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry and antisera to neuronal NOS. In the retina, NADPH-diaphorase and NOS immunolabelling were present in four subtypes of amacrine cells, some ganglion cells, efferent fibers, efferent target cells, and neuronal processes in both plexiform layers, whereas diaphorase alone was detected in photoreceptor ellipsoids and Müller cells. In addition, NADPH-diaphorase and immunoreactive NOS were detected in axon bundles and innervation to vascular smooth muscle in the choroid, whereas stromal and endothelial cells in the choroid, scleral chondrocytes, and the retinal pigmented epithelium contained only NADPH-diaphorase. The excitotoxin quisqualate destroyed all but one subtype of NOS-immunoreactive amacrine cell and caused increased NADPH-diaphorase activity in Müller cells. We conclude that nitric oxide is produced by many different cells in the chick eye, including retinal amacrine and ganglion cells, Müller cells, retinal pigmented epithelium, and cells in the choroid, and likely has a broad range of visual and regulatory functions.

Role of nitric oxide in photoreceptor survival in embryonic chick retinal cell culture

The presence of nitric oxide synthase (NOS) in chick retina during development has allowed us to study the role of nitric oxide (NO) during retinal differentiation in dissociated chick retinal cell culture from embryonic day 6. We have demonstrated the presence of nicotinamide adenine dinucleotide phosphate diaphorase staining in these cultures after 3 days in vitro (Div), with a maximal intensity after 8 Div, corresponding to embryonic day 14. Immunohistochemistry studies confirmed the presence of the two isoforms of NOS, NOS-I and -III, in dissociated retinal cell cultures at 8 Div. Addition of NG-monomethyl-L-arginine, a NOS inhibitor, to retinal cell cultures prevented NO production but did not modify the appearance and the survival of ganglion and amacrine cells. However, immunohistochemical analysis with distinct markers for photoreceptor cells (rods and cones) showed that inhibition of endogenous NOS in retinal cell cultures prevented the developmental decrease of rod number between 5 and 8 Div, thus supporting the hypothesis that NO may be involved in the cell death of rods during the development of the retina.

Development of NADPH-diaphorase expression in chemosensory systems of the opossum, Monodelphis domestica

Using NADPH-diaphorase histochemistry, the present study describes development of olfactory and vomeronasal systems in postnatal opossums, Monodelphis domestica. NADPH-dependent staining is absent at and around the time of birth. By 2 weeks of age and through adulthood, intense staining is seen along the luminal surface of the olfactory epithelium (OE) and of the vomeronasal sensory epithelium (VNE), as well as in Bowman's glands of the OE. Staining of the adult VNE is not homogeneous; it is restricted to the superficial 2/3 of the epithelium. At 2 weeks of age, staining in the brain is seen only at the surface of the ventricles and in blood vessels. At 1 month of age and through adulthood, staining of varying intensity is seen in individual olfactory bulb glomeruli, although the incoming olfactory axons are relatively unstained. Interestingly, whereas at 30 days of age, staining of the accessory olfactory bulb (AOB) glomeruli is uniform, 2 weeks later and in the adult, NADPH staining is concentrated in the rostral half, with little or no staining observed in the posterior portion. Darkly stained periglomerular cells are seen throughout the extent of the differentially-stained glomerular layer. From 30 days of age and through adulthood, intense NADPH staining is also observed in the islands of Calleja, as well as in cells of the dorsal cortex, often associated with the path of the rostral migratory stream.

Developmental expression of nitric oxide synthase isoform I and III in chick retina

During our studies on the multiple possible functions of nitric oxide (NO) in chick retinal development and physiology, we have demonstrated the presence and the activity of NO synthase (NOS-I and III) in certain neuronal populations (photoreceptors, amacrine cells in the inner nuclear and ganglion cells) and also in synaptic-rich regions in the developing chick retina. Both enzymes, detected by nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase, immunohistochemistry and Western blotting, appeared between embryonic days 6 and 12, and followed a spatial and temporal pattern of expression which correlated with the differentiation of the neuronal layers. Evaluation of the conversion of [3H]-labeled arginine to [3H]-citrulline, confirmed the presence of a calcium-dependent NOS activity in the cytosolic and particulate retinal extracts during the development. This pattern of NOS expression suggests that the regulated release of NO during key phases of development might be one mechanism involved in the regulation of retinal differentiation.

Changes in NADPH diaphorase reactivity and neuronal nitric oxide synthase in the rat retina following constant illumination

The distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) reactivity and neuronal nitric oxide synthase immunoreactivity (nNOS-IR) was investigated in the rat retina during photoreceptor regeneration. Photoreceptor damage and the disappearance of a NADPHd reactive/nNOS-IR band corresponding to inner photoreceptor segments were observed after continuous exposure to light irradiation. Both events were reversible after 20 days of total darkness. Also a progressive decrease in the number and in the staining intensity of NADPHd reactivity in amacrine cells were found along the first 3-6 days of darkness stabilizing thereafter in both illuminated and control groups. However, staining intensity in the former group remained more elevated than in the latter one. NOS activity in the retina varies depending on functional and pathological states.

Morphologic maturation of tachykinin peptide-expressing cells in the postnatal rabbit retina

Tachykinin (TK) peptides, which include substance P, neurokinin A, two neurokinin A-related peptides and neurokinin B, are widely present in the nervous system, including the retina, where they act as neurotransmitters/modulators as well as growth factors. In the present study, we investigated the maturation of TK-immunoreactive (IR) cells in the rabbit retina with the aim of further contributing to the knowledge of the development of transmitter-identified retinal cell populations. In the adult retina, the pattern of TK immunostaining is consistent with the presence of TK peptides in amacrine, displaced amacrine, interplexiform and ganglion cells. In the newborn retina, intensely immunostained TK-IR somata are located in the ganglion cell layer (GCL) and in the inner nuclear layer (INL) adjacent to the inner plexiform layer (IPL). They are characterized by an oval-shaped cell body originating a single process without ramifications. TK-IR processes are occasionally observed in the IPL and in the outer plexiform layer (OPL). Long TK-IR fiber bundles are observed in the ganglion cell axon layer. TK-IR profiles resembling small somata are rarely observed in the INL adjacent to the OPL. At postnatal day (PND) 2, some TK-IR cells display more complex morphologic features, including processes with secondary ramifications. Long TK-IR processes in the IPL are often seen to terminate with growth cones. Between PND 6 and PND 11 (eye opening), there is a dramatic increase in the number of immunolabeled processes with growth cones both in the IPL and in the OPL and the mature lamination of TK-IR fibers in laminae 1, 3 and 5 of the IPL is established. TK-IR cells attain mature morphological characteristics and the rare, putative TK-IR somata in the distal INL are no longer observed. After eye opening, growth cones are not present and the pattern typical of the adult is reached. These observations indicate that the development of TK-IR cells can be divided into an early phase (from birth to PND 6) in which these cells establish their morphological characteristics, and a later phase (from PND 6 to eye opening) in which they are involved in active growth of their processes and likely in synapse formation. Since TK peptides are thought to play neurotrophic actions in the developing nervous system and they are consistently present in the retina throughout postnatal development, they may also act as growth factors during retinal maturation.

Nitric oxide synthase in tiger salamander retina

Previous studies have indicated that nitric oxide, a labile freely diffusible biological messenger synthesized by nitric oxide synthase, may modulate light transduction and signal transmission in the retina. In the present work, the large size of retinal cells in tiger salamander (Ambystoma tigrinum) allowed the utilization of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry and nitric oxide synthase immunocytochemistry to delineate the cell-specific intracellular localization of nitric oxide synthase. NADPH-diaphorase activity was highly concentrated in the outer retina, in rod and cone inner segment ellipsoids, and between and adjacent to the photoreceptor cell bodies in the outer nuclear layer. Examination of enzymatically isolated retinal cells indicated that outer nuclear layer NADPH-diaphorase activity was localized to the distal processes of the retinal glial (Müller) cells and to putative bipolar cell Landolt clubs. Less intense NADPH-diaphorase activity was seen in the photoreceptor inner segment myoid region, in a small number of inner nuclear layer cells, in cap-like configurations at the distal poles of cells in the ganglion cell layer and surrounding ganglion cell layer somata, and in punctate form within both plexiform layers, the pigment epithelium, and the optic nerve. Nitric oxide synthase-like immunoreactivity was similarly localized, but was also concentrated along a thin sublamina centered within the inner plexiform layer. The potential for nitric oxide generation at multiple retinal sites suggests that this molecule may play a number of roles in the processing of visual information in the retina.

NADPH-diaphorase expression in neurons and glia of the normal adult rat retina

In the rat retina, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) staining has been described previously in a population of amacrine cells, most of which were located in the inner nuclear layer. In the present study, a number of parameters such as the nature of the fixative, the time of fixation and photointensification were optimised to obtain the strongest possible reaction for this enzyme. As a result, a very different staining pattern emerged: with short paraformaldehyde fixation, numerous neurons (identified as a combination of ganglion cells and amacrines) were labelled in the ganglion cell layer, NADPH-d-positive amacrine cells (described previously) were seen in the inner nuclear layer and Müller cells were labelled strongly, particularly in the inner retina. Glutaraldehyde fixation of the same duration resulted in the preferential staining of Müller cells while neurons appeared less reactive. Therefore, fixation conditions are a determining factor in the cellular localisation of NADPH-d in the rat retina. By taking fixation into account, future studies should gain more rigorous insights into the possible functions of this enzyme in the vertebrate retina.

Differentiation of short-wavelength-sensitive cones by NADPH diaphorase histochemistry

NADPH diaphorase (NADPH dehydrogenase; EC 1.6.99.1) histochemistry labels neurons that synthesize the neurotransmitter nitric oxide (NO). In retina, it has been demonstrated that NO can affect the metabolism of cGMP in rod photoreceptors. To investigate potential involvement of NO in cone photoreceptor activity, we utilized NADPH diaphorase histochemistry to study the cone-dominated retina of the tree shrew (Tupaia belangeri). Unexpectedly, our results revealed different NADPH diaphorase activity in the cellular subcompartments of the spectral classes of cone photoreceptors. Although all cones showed intense labeling of inner segment ellipsoids, the short-wavelength-sensitive (SWS or "blue-sensitive") cones and the rods displayed intense staining of the myoid inner segment subcompartment as well. Furthermore, only SWS cones and rods displayed surface labeling of their nuclei. These findings indicate a manner in which SWS cones differ biochemically from other cone types and in which they are more similar to rods. Such differences may underlie some of the unusual functional properties of the SWS cone system, which have been attributed to postreceptoral processes.

Specific cell types in cat retina express different forms of glutamic acid decarboxylase

We studied the expression of glutamate decarboxylase (GAD), GAD65 and GAD67, in cat retina by immunocytochemistry. About 10% of GABAergic amacrine cells express only GAD65 and 30% express only GAD67. Roughly 60% contain both forms of the enzyme, but GAD67 is present only at low levels in the majority of these double-labeled amacrine cells. The staining pattern in the inner plexiform layer (IPL) for the two GAD forms was also different. GAD65 was restricted to strata 1-4, and GAD67 was apparent throughout the IPL but was strongest in strata 1 and 5. This indicates that somas, as well as their processes, are differentially stained for the two forms of GAD. Cell types expressing only GAD65 include interplexiform cells, one type of cone bipolar cell, and at least one type of serotonin-accumulating amacrine cell. Cell types expressing only GAD67 include amacrine cells synthesizing dopamine, amacrine cells synthesizing nitric oxide (NO), and amacrine cells accumulating serotonin. Cholinergic amacrine cells express a low level of both GAD forms. Our findings in the retina are consistent with previous observations in the brain that GAD65 expression is greater in terminals than in somas. In addition, in retina most neurons expressing GAD67 also contain a second neurotransmitter as well as GABA, and they tend to be larger than neurons expressing GAD65. We propose that large cells have a greater demand for GABA than small cells, and thus require the constant, relatively unmodulated level of GABA that is provided by GAD67.

Modulation of ion channels in rod photoreceptors by nitric oxide

Subcellular compartments in the outer retina of the larval tiger salamander were identified as likely sites of production of nitric oxide (NO), a recently recognized intercellular messenger. NADPH diaphorase histochemistry and NO synthase immunocytochemistry labeled photoreceptor ellipsoids and the distal regions of bipolar and glial cells apposing photoreceptor inner segments, suggesting a role for NO in visual processing in the outer retina. We investigated the actions of NO on several rod photoreceptor ion channels. Application of the NO-generating compound S-nitrosocysteine increased Ca2+ channel current and a voltage-independent conductance, but had no affect on voltage-gated K+ or nonspecific cation currents. Given the steep relation between voltage-dependent Ca2+ influx and photoreceptor synaptic output, these results indicate that NO could modulate transmission of the photoresponse to second order cells.

The localization of nitric oxide synthase in the rat eye and related cranial ganglia

Nitric oxide synthase is the biosynthetic enzyme for the free radical neurotransmitter nitric oxide. Using an affinity-purified antiserum, nitric oxide synthase was found to be localized to peripheral ocular nerve fibers, related cranial ganglia, and the retina of the rat. In the eye, nitric oxide synthase-like immunoreactive peripheral nerve fibers were visualized mainly in the choroid and about limbal blood vessels. The anterior uvea was quite sparsely innervated, and the cornea was negative. Many principal neurons in the pterygopalatine ganglion were immunoreactive for nitric oxide synthase while very few cells stained in the superior cervical and trigeminal ganglia. Virtually all nitric oxide synthase-like immunoreactive pterygopalatine cells were also immunostained for vasoactive intestinal polypeptide; nitric oxide synthase also partially co-localized with neuropeptide Y in some of the neurons of this ganglion. Pterygopalatine ganglionectomy significantly reduced the number of peripheral nitric oxide synthase-like immunoreactive nerve fibers in the eye. A variety of immunoreactive retinal cells were seen. Most cells in the inner nuclear layer or ganglion cell layer corresponded morphologically to amacrine cells and displaced amacrine cells. Interplexiform cells and occasional faintly stained cells in the outer portion of the inner nuclear layer also were visualized. Nicotinamide adenine dinucleotide phosphate diaphorase histochemistry generally stained cells of similar distribution but did reveal somewhat more extensive localizations in peripheral ocular tissues, the ciliary ganglion, and the retina, compared with nitric oxide synthase immunohistochemistry. Nitric oxide synthase thus localizes to peripheral ocular nerve fibers, chiefly parasympathetic in nature and derived from the pterygopalatine ganglion, and to several cell types in the retina. Nitric oxide probably acts as a choroidal vasodilator of parasympathetic origin in the eye; the neuropeptide co-localizations in the pterygopalatine ganglion suggest complex neuromodulatory interactions. The retinal localizations imply potential neurotransmitter functions for nitric oxide in this tissue.

Postnatal development of tyrosine hydroxylase immunoreactive amacrine cells in the rabbit retina: I. Morphological characterization

The present and accompanying (Casini, G., and N.C. Brecha, J. Comp. Neurol. 326:302-313, 1992) papers investigate the postnatal development of tyrosine hydroxylase (TH)-immunoreactive (IR) amacrine cells in the rabbit retina. This study is focused on a detailed analysis of the patterns of cellular growth and differentiation of TH-IR amacrine cells, which serve as a model to gain insights into the mechanisms underlying developmental changes associated with the maturation of amacrine cells. Faintly staining TH-IR neurons are present in the proximal inner nuclear layer of newborn retinas. They are characterized by a large nucleus and usually a single primary process lacking varicosities. At postnatal day (PND) 6, TH-IR processes display more complex morphological characteristics, including a few varicosities, and second- and third-order ramifications. Growth cones are often seen. At PNDs 10 and 12 (eye opening), TH-IR cells have general morphological characteristics similar to adult TH-IR amacrines. They display 2-5 primary processes, which start forming a complex network of fibers in lamina 1 of the inner plexiform layer (IPL). TH-IR processes are also present in lamina 3 and rarely in lamina 5 of the IPL. Many fibers ending in growth cones are observed. In addition, very rare, thin TH-IR fibers are present in the outer plexiform layer. At PND 19, TH-IR fibers form a complex, dense network in lamina 1 of the IPL, and loose networks in laminae 3 and 5. Growth cones are not observed at this age. At PND 26, a few "ring-like" structures formed by TH-IR fibers in lamina 1 of the IPL are observed for the first time. In adult retinas, the "ring-like" structures are more numerous than at PND 26. A second, rare type of TH-IR cell ("type B") is encountered in all retinal regions beginning at PND 10. These cells are characterized by weak immunostaining and a small soma size. The present findings show that a significant differentiation of TH-IR neurons occurs during the first 10-12 PNDs. Eye opening is an important period for the maturation of TH-IR amacrines and, more generally, for the maturation of the IPL.

Development of catecholaminergic, indoleamine-accumulating and NADPH-diaphorase amacrine cells in rabbit retinae

We have investigated the ontogeny of four classes of amacrine cells in the rabbit retina. In particular, the distribution, number, soma diameter, dendritic field diameter, and pattern of dendritic stratification were studied in catecholaminergic (CA) and indoleamine-accumulating (IA) amacrines and in two classes of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase amacrine cells. The first CA and IA cells are observed on the 27th postconceptional day (27PCD) and the first NADPH-diaphorase cells on 28PCD. These first cells are concentrated in the central part of the visual streak, and at subsequent ages, cells in this part of the streak have larger somata and more mature dendritic fields than those elsewhere, supporting the notion that the peak density region is a developmentally advanced part of the retina. Throughout development, amacrine cells of all classes are concentrated in the visual streak, with their density reaching minima at the superior and inferior retinal margins. As their total number increases, the difference in cell density between the streak and the periphery decreases, presumably because proportionately more cells are added at the periphery. Their total number peaks around 42PCD, followed by a decline of 12-31% to adult values. Once the peak number of cells has been reached, the difference in cell density between the streak and periphery begins to increase. The rate of this increase is closely correlated with the increase in retinal area. This redistribution of amacrine cells, as well as a greater expansion of their dendritic fields in peripheral retina, is almost certainly the product of nonuniform retinal expansion.