Ontogeny of catecholaminergic and cholinergic cell distributions in the cat's retina

Development of starburst cholinergic amacrine cells in the retina of Tupaia belangeri

"Starburst" cholinergic amacrines specify the response of direction-selective ganglion cells to image motion. Here, development of cholinergic amacrines was studied in the tree shrew Tupaia belangeri (Scandentia) by immunohistochemistry with antibodies against choline acetyltransferase (ChAT) and neurofilament proteins. Starburst amacrines expressed ChAT much earlier than previously thought. From embryonic day 34 (E34) onward, orthotopic and displaced subpopulations segregated from a single cluster of immunoreactive precursor cells. Orthotopic starburst amacrines rapidly took up positions in the inner nuclear layer. Displaced starburst amacrines were first arranged in a monocellular row in the inner plexiform layer, and, with a delay of 1 week, they descended to the ganglion cell layer. Conversely, dendritic stratification of displaced amacrines slightly preceded that of orthotopic ones. Starburst amacrines expressed the medium-molecular-weight neurofilament protein (NF-M) from E34 to postnatal day 11 (P11) and coexpressed alpha-internexin from E36.5 to P11. Consequently, neurofilaments composed of alpha-internexin and NF-M may stabilize developing dendrites of starburst amacrines. During the first 2 postnatal weeks, subpopulations of anti-NF-M-labeled ganglion cells costratified with the preexisting dendritic strata of starburst amacrines in the ON sublamina, OFF sublamina, or both. Hence, anti-NF-M-labeled ganglion cells may include direction-selective ones. Thereafter, NF-M and alpha-internexin proteins disappeared from starburst amacrines, and NF-M immunoreactivity was lost in the dendrites of ganglion cells. Our findings suggest that NF-M and alpha-internexin are important for starburst amacrines and ganglion cells to recognize each other and, thus, contribute to the formation of early developing retinal circuits in the inner plexiform layer.

Development of cholinergic amacrine cells is visual activity-dependent in the postnatal mouse retina

In the present study, we used immunocytochemistry to study the temporal and spatial arrangement of mouse cholinergic amacrine cells during postnatal retinal development under normal light/dark cycles and during visual deprivation. Choline acetyltransferase (ChAT)-immunolabeled cells were detected in the neuroblastic layer (NBL) and in the ganglion cell layer (GCL) at postnatal day 0 (P0). Between P3-5, two characteristic cholinergic bands were clearly identified in the inner plexiform layer (IPL). The signal intensity of somas and processes progressively increased over the first 2 postnatal weeks. Around eye opening at P12, cholinergic neurons were mature-like. This early developmental process was not altered by visual deprivation. After eye opening, the space between the two cholinergic bands increased continuously and the spatial regularity index changed constantly, indicating that the cholinergic neurons possibly underwent refinement during later postnatal development. The changes occurring following eye opening were retarded by visual deprivation. The morphologies of photoreceptors, horizontal cells, recoverin-positive OFF-cone bipolar cells, rod bipolar cells, dopaminergic amacrine cells, and Müller cells appeared normal. Their stratification in the outer plexiform layer (OPL) and the IPL was not affected by visual deprivation. However, glial cells grew vertically across the entire thickness of dark-reared retinas. Our results suggest that the development of cholinergic neurons before eye opening is independent of the lighting conditions. Their development after eye opening is greatly impeded by visual deprivation. This visual activity-dependent phase of development may be a critical period for the maturation and synaptic wiring of cholinergic amacrine cells in the mammalian retina.

Immunocytochemical development of the guinea pig retina

The aim of the present study was to establish the neurochemical profile of amacrine and horizontal cells during ontogeny in the guinea pig, a precocial species where significant retinal development occurs prenatally as opposed to altricial species where development largely occurs postnatally. The expression of neurochemical markers of horizontal cells and specific amacrine cell populations was investigated from 20 days of gestation (dg, term approximately 67 dg) to adulthood. Amacrine cell populations were identified immunohistochemically using antibodies to gamma-amino-butyric acid, cholineacetyltransferase, calbindin, calretinin, neuronal nitric oxide synthetase and tyrosine hydroxylase; horizontal cells were labelled with calbindin. All markers were present at 30 dg and had attained their mature (adult) laminar distribution and expression by 60 dg. Horizontal cells appeared in their final location at 30 dg with amacrine cell populations appearing in their final locations by 45 dg. Thus, in the guinea pig retina, the amacrine and horizontal cell populations investigated in this study are fully mature prior to birth.

Mice lacking specific nicotinic acetylcholine receptor subunits exhibit dramatically altered spontaneous activity patterns and reveal a limited role for retinal waves in forming ON and OFF circuits in the inner retina

Before phototransduction, spontaneous activity in the developing mammalian retina is required for the appropriate patterning of retinothalamic connections, and there is growing evidence that this activity influences the development of circuits within the retina itself. We demonstrate here that the neural substrate that generates waves in the mouse retina develops through three distinct stages. First, between embryonic day 16 and birth [postnatal day 0 (P0)], we observed both large, propagating waves inhibited by nicotinic acetylcholine receptor (nAChR) antagonists and small clusters of cells displaying nonpropagating, correlated calcium increases that were independent of nAChR activation. Second, between P0 and P11, we observed only larger propagating waves that were abolished by toxins specific to alpha3 and beta2 subunit-containing nAChRs. Third, between P11 and P14 (eye opening) we observed propagating activity that was abolished by ionotropic glutamate receptor antagonists. The time course of this developmental shift was dramatically altered in retinas from mice lacking the beta2 nAChR subunit or the beta2 and beta4 subunits. These retinas exhibited a novel circuit at P0, no spontaneous correlated activity between P1 and P8, and the premature induction at P8 of an ionotropic glutamate receptor-based circuit. Retinas from postnatal mice lacking the alpha3 nAChR subunit exhibited spontaneous, correlated activity patterns that were similar to those observed in embryonic wild-type mice. In alpha3-/- and beta2-/- mice, the development and distribution of cholinergic neurons and processes and the density of retinal ganglion cells (RGCs) and the gross segregation of their dendrites into ON and OFF sublaminae were normal. However, the refinement of individual RGC dendrites is delayed. These results indicate that retinal waves mediated by nAChRs are involved in, but not required for, the development of neural circuits that define the ON and OFF sublamina of the inner plexiform layer.

Choline acetyltransferase-immunoreactive neurons in the developing rat retina

The development of cholinergic cells in the rat retina has been examined with immunocytochemistry by using antisera against choline acetyltransferase (ChAT). ChAT-immunoreactive (IR) cells were first detected at embryonic day 17 (E17) in the transitional zone between the neuroblastic layer (NBL) and ganglion cell layer (GCL). At E20, ChAT-IR cells are located exclusively in the GCL. At postnatal day 0 (P0), ChAT immunoreactivity appeared for the first time in cells at the distal margin of the NBL. Two prominent bands of labeled processes were first visible at P3, and by P15, these two bands resembled those of the adult retina. In addition, ChAT immunoreactivity appeared transiently in horizontal cells from P5 to P10. The number of ChAT-IR cells increased steadily up to P15. This resulted in a 93.8-fold increase between E17 and P15 (680-63,800 cells). However, after P15, the number declined by 19% from 63,800 cells at P15 to 51,800 in the adult. At all ages, the spatial density of each ChAT-IR cell population in the central retina was higher than in the periphery. In both central and peripheral regions, the peak density of ChAT-IR cells in the GCL was attained at E20. However, in the INL, the peak densities occurred at P3 in the central region and at P5 in the peripheral region. Up to P15, the soma diameter of ChAT-IR cells in the INL and GCL in each region increased continuously, reaching peak values at P15. Our results demonstrate that ChAT immunoreactivity is expressed in early developmental stages in the rat retina, as in other mammals, and that acetylcholine released from ChAT-IR cells may have neurotrophic functions in retinal maturation.

Ontogeny of cholinergic amacrine cells in the oppossum (Didelphis aurita) retina

Immunocytochemistry for choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine, was used to determine the onset and to follow the maturation of the cholinergic cells in the retina of a marsupial, the South American opossum (Didelphis aurita). ChAT-immunoreactivity was first detected in amacrine cells in the ganglion cell layer by postnatal day 15 (P15) and in the inner nuclear layer by P35. Much later, at P50 a second sub-population of ChAT-immunoreactive cell bodies was evident in the inner nuclear layer. Processes from ChAT-immunoreactive amacrine cells were detected in the two bands of the inner plexiform layer before synaptogenesis. In the adult retina, these two bands correspond to sublamina 2 and 4 of the inner plexiform layer. In flat whole-mounted preparations, cholinergic cell density was 263 +/- 13 cells/mm2 in the ganglion cell layer and it was estimated a total of 24,000 cholinergic neurons. ChAT-immunoreactive somata showed a random pattern of distribution.

Dynamics of retinal waves are controlled by cyclic AMP

Waves of spontaneous activity sweep across the developing mammalian retina and influence the pattern of central connections made by ganglion cell axons. These waves are driven by synaptic input from amacrine cells. We show that cholinergic synaptic transmission during waves is not blocked by TTX, indicating that release from starburst amacrine cells is independent of sodium action potentials. The spatiotemporal properties of the waves are regulated by endogenous release of adenosine, which sets intracellular cAMP levels through activation of A2 receptors present on developing amacrine and ganglion cells. Increasing cAMP levels increase the size, speed, and frequency of the waves. Conversely, inhibiting adenylate cyclase or PKA prevents wave activity. Together, these results imply a novel mechanism in which levels of cAMP within an immature retinal circuit regulate the precise spatial and temporal patterns of spontaneous neural activity.

Dynamic processes shape spatiotemporal properties of retinal waves

In the developing mammalian retina, spontaneous waves of action potentials are present in the ganglion cell layer weeks before vision. These waves are known to be generated by a synaptically connected network of amacrine cells and retinal ganglion cells, and exhibit complex spatiotemporal patterns, characterized by shifting domains of coactivation. Here, we present a novel dynamical model consisting of two coupled populations of cells that quantitatively reproduces the experimentally observed domain sizes, interwave intervals, and wavefront velocity profiles. Model and experiment together show that the highly correlated activity generated by retinal waves can be explained by a combination of random spontaneous activation of cells and the past history of local retinal activity.

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.

Histogenesis and topographical distribution of tyrosine hydroxylase immunoreactive amacrine cells in the developing chick retina

There is a delay from the time when amacrine cells are generated to the time when the dopaminergic phenotype is first expressed, in the chick retina. In order to determine the birthdate of amacrine cells expressing the tyrosine hydroxylase (TH) phenotype, we combined autoradiography of [3H]thymidine incorporated into dividing cells with the immunocytochemical method for TH in mature retinas. We also investigated the morphogenesis and the topographical distribution of dopaminergic amacrine cells using radial and horizontal sections of the chick retina. Although TH immunoreactivity was first detected at E12, the morphological pattern of TH-immunoreactive (TH-IR) amacrine cells started to be defined at E16, with an increasing arborization complexity until hatching. The topographical distribution of dopaminergic cells revealed that TH-IR neurons were predominantly concentrated in the dorsal retina of E13 and E14 embryos. At E18 and PH2 the distribution of dopaminergic cells was uniform throughout the retina. Autoradiography of [3H]thymidine incorporated association with TH immunocytochemistry showed that dopaminergic amacrine cells are generated during a discrete period (E3 through E7) of amacrinogenesis that occurs from E3 to E9. Therefore, a delay of days between histogenesis of dopaminergic amacrine cells and their differentiation is observed.

Postnatal development of tyrosine hydroxylase immunoreactive amacrine cells in the rabbit retina: II. Quantiative analysis

Tyrosine hydroxylase (TH)-immunoreactive (IR) amacrine cells of the rabbit retina mature during the first four postnatal weeks, and their cellular development is described in the preceding paper (Casini, G., and N.C. Brecha, J. Comp. Neurol. 326:283-301, 1992). The present investigation is a quantitative analysis of the postnatal development of the TH-IR amacrine cell population. TH-IR amacrine cells gradually increase in size from birth (soma area of 44.7 +/- 12.4 microns2, mean +/- standard deviation) to adulthood (144.2 +/- 28.0 microns2). Cell density slightly increases from postnatal day (PND) 0 (41.9 +/- 9.5 cells/mm2) to PND 6 (47.2 +/- 7.2 cells/mm2), then markedly decreases from PND 6 to adulthood (17.8 +/- 5.3 cells/mm2) as a consequence of retinal growth. TH-IR cell number almost doubles from PND 0 (about 4,100 cells/retina) to adulthood (about 7,850 cells/retina). The increase in the total number of TH-IR amacrine cells can be explained by the generation of new TH-IR cells in the inner nuclear layer, a delay in the expression of the TH phenotype after neurogenesis by cells committed to be dopaminergic, or the acquisition of this dopaminergic phenotype by uncommitted cells. The development of the TH-IR amacrine cell mosaic was assessed by an evaluation of the distribution of nearest neighbor distances of TH-IR cells. There is a poor correlation between this distribution and a theoretical nonrandom distribution before PND 12. After this age, the nearest neighbor distance distribution shifts towards a nonrandom distribution, and is similar to that of the TH-IR amacrine cell population in the adult retina. The establishment of the TH-IR amacrine cell population mosaic is likely to be achieved through different interacting events, including intrinsic (e.g., genetic) factors, environmental influences, and nonuniform retinal growth. Overall, the population parameters analyzed in the present study approach adult values about the time of eye opening (PND 12) and they reach adult values by PND 26.

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.

Neurogenesis in the retinal ganglion cell layer of the rat

The present study has examined the birthdates of neurons in the retinal ganglion cell layer of the adult rat. Rat fetuses were exposed to tritiated thymidine in utero to label neurons departing the mitotic cycle at different gestational stages from embryonic days 12 through to 22. Upon reaching adulthood, rats were either given unilateral injections of horseradish peroxidase into target visual nuclei in order to discriminate (1) ganglion cells from displaced amacrine cells, (2) decussating from non-decussating ganglion cells, and (3) alpha cells from other ganglion cell types; or, their retinae were immunohistochemically processed to reveal the choline acetyltransferase-immunoreactive amacrine cells in the ganglion cell layer. Retinae were embedded flat in resin and cut en face to enable reconstruction of the distribution of labelled cells. Retinal sections were autoradiographically processed and then examined for neurons that were both tritium-positive and either horseradish peroxidase-positive or choline acetyltransferase-positive. Tritium-positive neurons in the ganglion cell layer were present in rats that had been exposed to tritiated thymidine on embryonic days E14-E22. Retinal ganglion cells were generated between E14 and E20, the ipsilaterally projecting ganglion cells ceasing their neurogenesis a full day before the contralaterally projecting ganglion cells. Alpha cells were generated from the very outset of retinal ganglion cell genesis, at E14, but completed their neurogenesis before the other cell types, by E17. Tritium-positive, horseradish peroxidase-negative neurons in the ganglion cell layer were present from E14 through to E22, and are interpreted as displaced amacrine cells. Choline acetyltransferase-positive displaced amacrine cells were generated between E16 and E20. Individual cell types showed a rough centroperipheral neurogenetic gradient, with the dorsal half of the retina slightly preceding the ventral half. These results demonstrate, first, that retinal ganglion cell genesis and displaced amacrine cell genesis overlap substantially in time. They do not occur sequentially, as has been commonly assumed. Second, they demonstrate that the alpha cell population of retinal ganglion cells and the choline acetyltransferase-immunoreactive population of displaced amacrine cells are each generated over a limited time during the periods of overall ganglion cell and displaced amacrine cell genesis, respectively. Third, they show that the very earliest ganglion cells to be generated in the temporal retina have exclusively uncrossed optic axons, while the later cells to be generated therein have an increasing propensity to navigate a crossed chiasmatic course.

Development of choline acetyltransferase-immunoreactive neurons in normal and intracranially transplanted retinas in rats

Retinas from embryonic day 14 (E14) Sprague-Dawley rats were transplanted to the tectum of newborn (P0) recipient rats, and the distribution pattern of choline acetyltransferase immunoreactivity (ChAT-I) in developing transplants was studied and compared with those observed in the retinas of normal developing rats. In normal retinas, ChAT-I cells were first identified in restricted regions in the ganglion cell layer (GCL) at P4, but were found to cover the entire GCL by P6. A second population of ChAT-I cells was detected in the inner nuclear layer (INL) at P8, and they were observed in most parts of the INL on P10 when two immunoreactive sublaminae began to appear in the inner plexiform layer (IPL). The adult pattern of having two distinct populations of ChAT-I cells, organized in mirror symmetrical fashion in the inner retinal layers was basically established by P12. The time course of development and overall distribution pattern of ChAT-I cells in developing retinal transplants on the whole were very similar to those observed in normal retinas. The first identification of these cells and the establishment of their final distribution pattern were made at stages corresponding to P4 and P12 of normal developing retinas respectively. However, ChAT-I somata were located in the INL at a much earlier stage compared with their counterparts in the normal retina, and a transient population of immunoreactive cells with their processes extending to retinal layers other than the IPL was observed in some transplants from P6 to P10. These features were not observed in normal developing retinas. These results suggest that the development of cholinergic neurons, especially the expression of their characteristic antigen and their final distribution pattern is largely determined by programmes which are intrinsic to the original retinal tissue, despite some minor deviation or variation in the developmental process which may occur under certain abnormal conditions.

Postembedding immunocytochemistry for GABA and glycine reveals the synaptic relationships of the dopaminergic amacrine cell of the cat retina

Postembedding electron microscope immunocytochemistry of glycine and GABA conjugated to colloidal gold has been applied to pre-embedded cat retina stained with the antibody against tyrosine hydroxylase (Toh+). Toh+ stained cells are the equivalent of A18 amacrine cells of Golgi descriptions (Kolb et al., '81). The dendrites of Toh+ cells synapse upon several different types of glycine-positive amacrine cell bodies. We suggest that these are the A8, A3/A4, and AII amacrine cell varieties by analogous immunocytochemical staining intensity, to glycine autoradiographic labeling intensity (Pourcho and Goebel, '85). The greatest number of synapses from Toh+ dendrites are directed at the least glycine-positive amacrine, which is the AII cell by all morphological criteria. A few glycine-positive profiles are also presynapatic to the Toh+ stained cell body itself. Toh+ profiles are also presynaptic to GABA-positive amacrine cell bodies. The commonest amacrine synapsed upon is very heavily labeled with GABA immunocytochemistry. We consider it to be the A17 amacrine cell, which is known to label strongly by [3H] muscimol autoradiography (Pourcho and Goebel, '83). The cell body of the Toh+ amacrine cell also receives many synapses, which appear to be GABA-positive, and Toh+ profiles running in stratum 1 of the inner plexiform layer (IPL) are both pre- and postsynaptic to GABA-positive amacrine cell profiles. In addition, the cell body and primary dendrites of the Toh+ cell receive input from a bipolar type and GABA- or glycine-negative profiles. GABA-positive profiles, belonging to the interplexiform cell (IPC), are synapsed upon by Toh+ profiles that run in the outer plexiform layer (OPL).(ABSTRACT TRUNCATED AT 250 WORDS)

NADPH-diaphorase reactivity in adult and developing cat retinae

We have examined the distribution and size of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase reactivity in adult and developing cat retinae. From late gestation E (embryonic day) 58 to adulthood, NADPH-diaphorase reactivity was detected in amacrine cells with somata located in the inner nuclear layer (INL) and ganglion cell layer (GCL) and in processes spreading in the middle strata of the inner plexiform layer (IPL). Reactivity was also present in small rounded profiles located in the outer plexiform layer (OPL) and thought to be cone pedicles. The number of NADPH-diaphorase reactive cells present in adult retinae was about 40,000, 75% of these somata were located in the GCL, the remainder in the INL. At birth, however, there was more than double this number of labelled somata (85,000), the total gradually declining to reach adult values by P (postnatal day) 25. This loss of NADPH-diaphorase reactive somata may be partly explained by natural cell death (apoptosis) or by loss of the active diaphorase from the cells. The density distributions of NADPH-diaphorase reactive cells in the INL and GCL of retinal wholemounts reached maxima in regions slightly inferior to the area centralis at all ages studied. The principal topographical difference between adult and developing retinae was that the density gradient of NADPH-diaphorase reactive cells was steeper in adults than at younger ages. During early development, the somal and dendritic field diameters of NADPH-diaphorase reactive cells at the area centralis were about the same size as those in the periphery; by adulthood, cells in the periphery were larger. The change in the somal diameter gradient apparently emerged because of a reduction in somal size of the centrally located cells. The change in the dendritic diameter gradient emerged because of a greater growth of peripheral cells as compared to central cells. We suggest that NADPH-diaphorase may have a role in the formation of synapses in the developing IPL.

Development of tyrosine hydroxylase-like immunoreactive structures in the chick retina: three-dimensional analysis

This study was designed to investigate the developmental profile of tyrosine hydroxylase-like immunoreactive structures in the chick retina in both frozen sections and wholemount preparations. In frozen sections, cells with tyrosine hydroxylase-like immunoreactivity were first detected in 10 to 15 cell rows from the innermost part of the inner nuclear layer on embryonic or incubation day 11. They were seen in the inner cell rows of the inner nuclear layer during later periods; by embryonic day 18, the immunoreactive cells were located 1 to 3 cell rows outward from the innermost part of the inner nuclear layer where mature immunoreactive cells mainly exist. The immunoreactive cells began to give rise to processes on embryonic day 13. The processes (possibly dendrites) gradually increased in number and intensity in sublayers 1 and 4 of the inner plexiform layer during prenatal life. Several days after hatching, an abrupt increase in immunoreactive processes was noted in sublayer 1 but not in sublayer 4. On the sixth postnatal day, retinal neural elements immunoreactive for tyrosine hydroxylase seemed to exhibit a distribution pattern similar to that of the adult chick. In wholemount retinas, immunoreactive cells were initially detected at the earliest stage of embryonic day 12 in a small circle termed "starting area" occupying the ventral part of the temporal retinal field. The closer to the "starting area," the earlier the retinal area began to express many immunoreactive cells. Thus tyrosine hydroxylase cell density in individual retinal areas, as represented by cell number per square millimeter, peaked in different developmental periods varying from embryonic day 12 to day 14. At this stage, immunoreactive cells were arranged irregularly in the retina. Thereafter, the cell density as well as total cell number gradually declined and reached a plateau around embryonic day 20 when tyrosine hydroxylase-like immunoreactive cells, like those in the mature retina, showed an even distribution throughout the retina.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphology and retinal distribution of tyrosine hydroxylase-like immunoreactive amacrine cells in the retina of developing Xenopus laevis

The development of neurons immunoreactive to tyrosine hydroxylase (TH-IR) in the retina of Xenopus laevis was investigated from stage 53 tadpoles to adult, by using an antibody against tyrosine hydroxylase. At all developmental stages, most of the immunoreactive somata were located in the inner nuclear layer, and a few in the ganglion cell layer. Immunoreactive processes arborized in the scleral and vitreal sublaminae of the inner plexiform layer, indicating that these cells were bistratified amacrine cells. However, occasionally a few immunoreactive processes were observed projecting to the outer plexiform layer, suggesting the presence of TH-IR interplexiform cells. The number of immunoreactive amacrine cells in the inner nuclear layer per retina increased from 204 at stage 53 tadpole to 735 in adult, while the number of immunoreactive amacrine cells in the ganglion cell layer did not change significantly over the same period. Retinal area increased from 1.95 mm2 at stage 53 to 23.40 mm2 in the adult, and correspondingly cell density in the inner nuclear layer decreased from 104/mm2 to 31/mm2. At all stages there was an increasing density towards the ciliary margin, but this gradient decreased with age. The soma size of immunoreactive amacrine cells increased with age, and was consistently larger in the central than in the peripheral retina. Dendritic field size was estimated to increase 13-fold, from stage 53 to adult. This study shows that tyrosine hydroxylase-like immunoreactive amacrine cells are generated continuously throughout life, that after metamorphosis the retina grows more by stretching than by cell generation at the ciliary margin, and that the increase of dendritic field size is proportional to the increase in retinal surface area.