Dopaminergic cell differentiation in the developing chick retina

Chemical signaling in the developing avian retina: Focus on cyclic AMP and AKT-dependent pathways

Communication between developing progenitor cells as well as differentiated neurons and glial cells in the nervous system is made through direct cell contacts and chemical signaling mediated by different molecules. Several of these substances are synthesized and released by developing cells and play roles since early stages of Central Nervous System development. The chicken retina is a very suitable model for neurochemical studies, including the study of regulation of signaling pathways during development. Among advantages of the model are its very well-known histogenesis, the presence of most neurotransmitter systems found in the brain and the possibility to make cultures of neurons and/or glial cells where many neurochemical functions develop in a similar way than in the intact embryonic tissue. In the chicken retina, some neurotransmitters or neuromodulators as dopamine, adenosine, and others are coupled to cyclic AMP production or adenylyl cyclase inhibition since early stages of development. Other substances as vitamin C and nitric oxide are linked to the major neurotransmitter glutamate and AKT metabolism. All these different systems regulate signaling pathways, including PKA, PKG, SRC, AKT and ERK, and the activation of the transcription factor CREB. Dopamine and adenosine stimulate cAMP accumulation in the chick embryo retina through activation of D1 and A2a receptors, respectively, but the onset of dopamine stimulation is much earlier than that of adenosine. However, adenosine can inhibit adenylyl cyclase and modulate dopamine-dependent cAMP increase since early developmental stages through A1 receptors. Dopamine stimulates different PKA as well as EPAC downstream pathways both in intact tissue and in culture as the CSK-SRC pathway modulating glutamate NMDA receptors as well as vitamin C release and CREB phosphorylation. By the other hand, glutamate modulates nitric oxide production and AKT activation in cultured retinal cells and this pathway controls neuronal survival in retina. Glutamate and adenosine stimulate the release of vitamin C and this vitamin regulates the transport of glutamate, activation of NMDA receptors and AKT phosphorylation in cultured retinal cells. In the present review we will focus on these reciprocal interactions between neurotransmitters or neuromodulators and different signaling pathways during retinal development.

Transporter mediated GABA release in the retina: Role of excitatory amino acids and dopamine

In general, the release of neurotransmitters in the central nervous system is accomplished by a calcium-dependent process which constitutes a common feature of exocytosis, a conserved mechanism for transmitter release in all species. However, neurotransmitters can also be released by the reversal of their transporters. In the retina, a large portion of GABA is released by this mechanism, which is under the control of neuroactive agents, such as excitatory amino acids and dopamine. In this review, we will focus on the transporter mediated GABA release and the role played by excitatory amino acids and dopamine in this process. First, we will discuss the works that used radiolabeled GABA to study the outflow of the neurotransmitter and then the works that took into consideration the endogenous pool of GABA and the topography of GABAergic circuits influenced by excitatory amino acids and dopamine.

GABAergic circuitry in the opossum retina: a GABA release induced by L-aspartate

Glutamate and gamma-amino butyric acid (GABA) are the major excitatory and inhibitory neurotransmitters, respectively, in the central nervous system (CNS), including the retina. Although in a number of studies the retinal source of GABA was identified, in several species, as horizontal, amacrine cells and cells in the ganglion cell layer, nothing was described for the opossum retina. Thus, the first goal of this study was to determine the pattern of GABAergic cell expression in the South America opossum retina by using an immunohistochemical approach for GABA and for its synthetic enzyme, glutamic acid decarboxylase (GAD). GABA and GAD immunoreactivity showed a similar cellular pattern by appearing in a few faint horizontal cells, topic and displaced amacrine cells. In an effort to extend the knowledge of the opossum retinal circuitry, the possible influence of glutamatergic inputs in GABAergic cells was also studied. Retinas were stimulated with different glutamatergic agonists and aspartate (Asp), and the GABA remaining in the tissue was detected by immunohistochemical procedures. The exposure of retinas to NMDA and kainate resulted the reduction of the number of GABA immunoreactive topic and displaced amacrine cells. The Asp treatment also resulted in reduction of the number of GABA immunoreactive amacrine cells but, in contrast, the displaced amacrine cells were not affected. Finally, the Asp effect was totally blocked by MK-801. This result suggests that Asp could be indeed a putative neurotransmitter in this non-placental animal by acting on an amacrine cell sub-population of GABA-positive NMDA-sensitive cells.

Adenosine as a signaling molecule in the retina: biochemical and developmental aspects

The nucleoside adenosine plays an important role as a neurotransmitter or neuromodulator in the central nervous system, including the retina. In the present paper we review compelling evidence showing that adenosine is a signaling molecule in the developing retina. In the chick retina, adenosine transporters are present since early stages of development before the appearance of adenosine A1 receptors modulating dopamine-dependent adenylate cyclase activity or A2 receptors that directly activate the enzyme. Experiments using retinal cell cultures revealed that adenosine is taken up by specific cell populations that when stimulated by depolarization or neurotransmitters such as dopamine or glutamate, release the nucleoside through calcium-dependent transporter-mediated mechanisms. The presence of adenosine in the extracellular medium and the long-term activation of adenosine receptors is able to regulate the survival of retinal neurons and blocks glutamate excitoxicity. Thus, adenosine besides working as a neurotransmitter or neuromodulator in the mature retina, is considered as an important signaling molecule during retinal development having important functions such as regulation of neuronal survival and differentiation.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Atypical effect of dopamine in modulating the functional inhibition of NMDA receptors of cultured retina cells

Cultured retina cells released accumulated [3H]GABA (gamma-aminobutyric acid) when stimulated by L-glutamate, N-methyl-D-aspartate (NMDA) and kainate. In the absence of Mg2+, dopamine at 200 microM (IC50 60 microM), inhibited in more than 50% the release of [3H]GABA induced by L-glutamate and NMDA, but not by kainate. This effect was not blocked by the D1-like dopamine receptor antagonist, R-(+)-7-chloro-8-hydroxy-3-methyl- -phenyl-2,3,4,5-tetrahydro- H-3-benzazepine hydrochloride (SCH 23390), neither by haloperidol nor spiroperidol (dopamine D2-like receptor antagonists). The dopamine D1-like receptor agonist R(+)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,diol hydrochloride (SKF 38393) at 50 microM, but not its enantiomer, also inhibited the release of [3H]GABA induced by NMDA, but not by kainate; an effect that was not prevented by the antagonists mentioned above. (+/-)-6-Chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepin e hydrobromide (SKF 812497) had no effect. Neither 8BrcAMP (5 mM) nor forskolin (10 microM) inhibited the release of [3H]GABA. Our results suggest that dopamine and (+)-SKF 38393 inhibit the glutamate and NMDA-evoked [3H]GABA release through mechanisms that seem not to involve known dopaminergic receptor systems.

The spatial organization of tyrosine hydroxylase-immunoreactive amacrine cells in the chicken retina and the consequences of myopia

We examined the spatial organization of the putative dopaminergic amacrine cells in the chicken retina and how this organization was affected by myopic eye enlargement. Myopia was produced by monocular lid suture for 4-7 months from hatching. Dopaminergic amacrine cells (TH-IR) were labelled by tyrosine hydroxylase immunohistochemistry. The somata of the TH-IR cells were usually located at the inner border of the inner nuclear layer; they gave rise to a dense plexus in stratum 1 (S1) of the inner plexiform layer, to a sparse plexus in stratum 3 (S3), and to short spiny dendrites at the border of strata 4 and 5 (S4/S5). The long thin processes in S1 and S3 could seldom be traced to their cell of origin, whereas the S4/S5 dendrites formed discrete fields that tiled the retina with little overlap. Lid suture resulted in retinal expansion of between 25-70%, but the total number of TH-IR amacrine cells was unaltered. Per retina, there were about 4700 TH-IR amacrine cells which showed a 3:1 density gradient from central to peripheral retina. The size of the S4/S5 dendritic fields increased proportionately in the expanded retinae, thus maintaining their coverage across the retina. The increase was achieved through scaled growth of the S4/S5 dendrites, involving both terminal and non-terminal dendrites. These findings suggest that the expansion of retinal neurons during myopia occurred through normal, albeit excessive, growth mechanisms.

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: 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 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)

GABA-like immunoreactivity in the developing chick retina: differentiation of GABAergic horizontal cell and its possible contacts with photoreceptors

The morphology of gamma-aminobutyric acid (GABA)-containing horizontal cells was examined in mature and developing chick retinas by GABA immunocytochemistry. In the outer plexiform layer of the mature retina, GABA-immunoreactive components were located in three different sublayers. In the inner (vitreal) layer most positively-stained fibres were laterally oriented processes from horizontal cells. Thick processes were found in the middle layer, and the relatively thin fibres in the outer (scleral) layer showed a concave curvature, suggesting their termination on photoreceptor terminals. By electron microscopy it was found that the principal cone pedicles were usually indented by immunoreactive lateral neurites of horizontal cells but that rod spherules faced only occasionally immunoreactive fibres. Accessory cones and single cones were also not usually indented by immunoreactive fibres. These observations may indicate that horizontal cells regulate the excitation of cone photoreceptors by several different inhibitory mechanisms. During retinal development, horizontal cells begin to extend lateral fibres by the ninth embryonic day, and some GABAergic horizontal cells also possess inwardly extending fibres until embryonic day 11. Between embryonic days 13 and 15, some immunoreactive cells were found among the bipolar cells, suggesting that they were still migrating to their final position. On embryonic day 17, the staining pattern was very similar to that of the mature retina. These results suggest that GABA immunohistochemistry may be an excellent tool for studying horizontal cell differentiation.

Development of two morphological types of retinopetal fibers in chick embryos, as shown by the diffusion along axons of a carbocyanine dye in the fixed retina

Centrifugal fibers to the retinas of chick embryos and hatched chicks have been examined and traced following staining by diffusion along their axonal membranes of the carbocyanine dye DiI in fixed tissue. In the older embryos and hatched chicks, the report of Dogiel (Arch. Mikrosk. Anat. 44:622-648, 1895) has been confirmed that there are two very different morphological types of centrifugal fiber. The restricted type ends as a relatively thick fiber, lacking varicosities, that runs for a short distance in the most sclerad level of the inner plexiform layer before terminating in a pericellular nest overlying the flask-shaped body of a single amacrine cell. Thin filaments occasionally leave the pericellular net, apparently to terminate on adjacent cells. The widespread type also runs in the most sclerad level of the inner plexiform layer, but it is thin, varicose, and highly branched, and its terminal arbor may span more than 1 mm, remaining at the same level. Both types of terminal arbor issue from parent axons in the optic fiber layer of the retina. A single parent axon gives either a single terminal fiber of the restricted type or several terminals of the widespread type, but never a mixture of the two. It is argued that the restricted and widespread types originate respectively from the neurons of the contralateral isthmo-optic nucleus and from the "ectopic" neurons scattered outside the isthmo-optic nucleus. In development, the centrifugal fibers reach the retina between E9 and E10 and initially run radially in the optic fiber layer, parallel to the retinofugal fibers but avoiding the dorsal retina. They dive into the inner plexiform layer at about E12. By E13, the terminal arbors are forming, and the widespread and restricted types can already be distinguished. The widespread type continues to increase its territory until about E18, and then appears to remain stable, whereas the restricted type attains its maximum ramification between E13 and E15 and then contracts. Prior to the retraction, the terminal territories of the restricted type fibers overlap, which may provide the anatomical basis for the interaxonal competition that apparently contributes to neuronal death in the isthmo-optic nucleus between E13 and E16. Axons of ganglion cells exhibit transient side branches between E11 and E13; these never reach as deep as the level where the centrifugal fibers run.

The emergence of GABA-accumulating neurons during retinal histogenesis in the embryonic chick

The emergence of GABA-accumulating neurons was studied from stages 29 to 40 during retinal histogenesis in the chick, covering embryonic (E) days E6-E14, using autoradiographic analysis following incubation of isolated retinas with [3H]GABA (2 microM). Analysis was restricted to central retina which is more advanced in its differentiation than the periphery. On E6 numerous mitotic figures were present along the scleral border of the unstratified neuroepithelium. Specific localization of [3H]GABA was associated initially with somata situated in middle regions of the retinal expanse. Occasionally contiguous pairs of labeled cells were seen. The inner plexiform layer makes its appearance during E7; at that time silver grains were present over cell bodies located in the ganglion cell layer and the proximal portion of the inner nuclear layer, those of probable amacrine cells. As retinal stratification continued, more cells were observed to have elaborated membrane systems for GABA uptake with varying degrees of affinity. By E8, although dividing, non-labeled cells were in close proximity, GABA-labeled cells were observed in positions of horizontal cells. By E14, the pattern of label distribution appeared essentially similar to that reported for adult retina, i.e. [3H]GABA labeling was observed over horizontal cells and their processes, subpopulations of amacrine cells which appear to ramify extensively across the inner plexiform layer, selected perikarya of the ganglion cell layer, and the nerve fiber layer. In addition, a subpopulation of labeled photoreceptors, some identified as cones by virtue of oil droplets, was observed. Thus, preferential accumulation of GABA appears during E6, prior to formation of either inner or outer plexiform layers. The localization of [3H]GABA demonstrates that ganglion and amacrine cell bodies are labeled initially, followed by horizontal cells. Specific accumulation of [3H]muscimol, a potent agonist of GABA receptors, appears about E12 over cells located in proximal regions of the inner nuclear layer; these somata later ramify in sublaminae 2 and 4 of the inner plexiform layer.

Effect of dopamine and haloperidol on the c-wave and light peak of light-induced retinal responses in chick eye

The relation between dopaminergic cells (and centrifugal fibers), the electroretinogram (ERG) c-wave, and the light peak were electrophysiologically investigated by observing the effects of a retrobulbar conduction block and intravitreal injection of either dopamine or haloperidol on these retinal responses. The retrobulbar conduction block (1% lidocaine) caused a decrease in the amplitude of the c-wave and the light peak in newly hatched chicks. Injections (2-20 microliters) containing dopamine (0.1-10 mM) or haloperidol (1.3-13 mM) were given intravitreously while the responses were recorded. Although intravitreous injection of saline for control resulted in no observable change in the responses, dopamine selectively augmented the c-wave of ERGs and the light peak, but not the a-, b-, and d-waves. Haloperidol decreased first the light peak and later the c-wave. The augmentation of the retinal responses by dopamine and their reduction by haloperidol was statistically significant. The estimated threshold concentration of dopamine in the vitreous cavity was 1-3.5 microM. Since in many species the interplexiform cells have been found to contain dopamine, we hypothesize that the modulatory effects on the c-wave and the light peak in this preparation may be due to a centrifugal feed-back loop which includes the interplexiform cells to the horizontal and bipolar cells and the horizontal cells to the cones.

Tyrosine hydroxylase immunohistochemistry fails to demonstrate dopaminergic interplexiform cells in the turtle retina

A number of catecholaminergic, presumably dopaminergic, cells could be observed in the turtle retina, because of their tyrosine hydroxylase immunoreactivity. They were amacrine cells with a pear-shaped soma and dendrites distributed in 3 sublayers within the inner plexiform layer. Neither sclerally directed TH-positive processes nor terminals in the outer plexiform layer were observed, suggesting that dopaminergic interplexiform cells do not exist in the turtle retina.

Expression and assembly of the erythroid membrane-skeletal proteins ankyrin (goblin) and spectrin in the morphogenesis of chicken neurons

The membrane-skeleton of adult chicken neurons in the cerebellum and optic system is composed of polypeptides structurally and functionally related to the erythroid proteins spectrin and ankyrin, respectively. Neuronal spectrin comprises two distinct complexes that share a common alpha subunit (Mr 240,000) but which have structurally distinct polymorphic subunits (beta' beta spectrin; Mr 220/225,000; gamma spectrin, Mr 235,000); the brain-specific form (alpha gamma spectrin or fodrin) and an erythrocyte-specific form (alpha beta' beta spectrin). Two structurally related isoforms of ankyrin have also been identified and are termed alpha (Mr 260,000) and beta (Mr 237,000) ankyrin. Immunofluorescence demonstrates that the variants of spectrin and ankyrin, respectively, have different distributions within neurons. On the one hand, alpha gamma spectrin and beta ankyrin are present throughout the neuron, in the perikaryon, dendrites, and axon, whereas alpha beta' spectrin and alpha ankyrin are localized exclusively in the perikaryon and dendrites where they are actively segregated from alpha gamma spectrin and other components of axonal transport. This asymmetric distribution of spectrin and ankyrin isoforms is established in distinct stages during neuronal morphogenesis. Early in cerebellar and retinal development, alpha gamma spectrin is expressed in mitotic cells. Subsequently beta ankyrin and alpha gamma spectrin are coexpressed in postmitotic cells and gradually accumulate on the plasma membrane in a uniform pattern throughout the neuron during the phase of cell growth. At the onset of synaptogenesis and the cessation of cell growth, their levels of synthesis decline sharply while the assembled proteins remained as stable membrane components. Concomitantly, there is a dramatic induction in the accumulation of alpha ankyrin and alpha beta' spectrin, whose assembly is limited to the plasma membrane of the perikarya and dendrites. These results demonstrate that two successive, developmentally regulated programs of ankyrin and spectrin expression and patterning on the plasma membrane are involved in the assembly of the spectrin-based asymmetry in the neuronal membrane-skeleton, and that their asymmetric distribution is actively maintained throughout the life of the neuron.

The patterns of expression of two ankyrin isoforms demonstrate distinct steps in the assembly of the membrane skeleton in neuronal morphogenesis

We have identified in chicken neurons two membrane-bound isoforms of goblin (ankyrin), the specific membrane attachment protein for spectrin in avian erythrocytes, which exhibit distinct patterns of expression and assembly during neuronal morphogenesis. Early in cerebellar and retinal development, neither goblin isoform is detected in mitotic cells. Subsequently, beta-goblin (Mr 237,000) is expressed in postmitotic cells, and gradually accumulates with alpha gamma (brain) spectrin on the neuronal plasma membrane during the phase of cell growth. At the onset of synaptogenesis and the cessation of cell growth, their levels of synthesis decline sharply while the assembled proteins remain as stable membrane components. Concomitantly, there is a dramatic induction in the accumulation of alpha-goblin (erythroid goblin; Mr 260,000) and alpha beta (erythroid) spectrin, whose assembly is limited to the plasma membrane of perikarya and dendrites.

Differentiation of monoamine accumulating neuron systems in cultured chick retina: an immunohistochemical and fluorescence histochemical study

Monoamine-containing neurons (dopamine and serotonin) have been reported to be localized among the cells in the inner nuclear layer (INL) of the chick retina. To examine the development of these neurons and whether they have an ability to synthesize serotonin (5-HT) or dopamine from exogenous precursors, we administered monoamines and their precursors in vitro as well as in situ and examined monoamine neuronal differentiation histochemically. In the chick retina, serotonin-containing neurons were found among amacrine cells. Two other types of serotonin-accumulating neurons were observed in the INL. One also had the ability to take up tryptophan and 5-hydroxytryptophan (5-HTP) and convert them to serotonin. In the monolayer culture from 61/2-day-old chick embryonic retinas, serotonin-containing neurons were observed on the 4th day of culture, increased in number until the 8th day, but had almost disappeared by the 15th day. After incubation of 8 day-cultures with 5-hydroxytryptophan, the number of serotonin-immunoreactive cells was at least twice that seen in untreated cultures. On the 20th day of culture, the same percentage of cells had the capability to take up serotonin, but the number of those which took up 5-hydroxytryptophan and decarboxylated it to serotonin had decreased markedly. Dopaminergic amacrine cells have also been found in the INL and shown to take up exogenously administered L-DOPA. In cultures, no dopamine-containing cells were observed with the present fluorescence histochemistry without prior incubation with DOPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Putative dopamine-containing cells in the retina of seven species demonstrated by tyrosine hydroxylase immunocytochemistry

Immunocytochemistry with antibodies to catecholamine synthesizing enzymes has revealed cells in the retina of chick, mouse, hamster, rat, guinea-pig, piglet and marmoset which contain tyrosine hydroxylase but not dopamine beta-hydroxylase. These findings suggest that the cells in question produce dopamine but that catecholamine synthesis does not proceed further to noradrenaline. Tyrosine hydroxylase-containing amacrine cells, located in the innermost part of the inner nuclear layer, were present in all the species studied. Some species showed atypically located amacrine cells in the inner plexiform or ganglion cell layer. In the rodents, the existence of tyrosine hydroxylase-containing interplexiform cells was suggested by the presence of a few short immunoreactive ascending processes. Three different morphological types of putative dopamine-containing cells were classified according to the level of ramification.

Segregation of two spectrin forms in the chicken optic system: a mechanism for establishing restricted membrane-cytoskeletal domains in neurons

The chicken optic system contains a brain-specific form of spectrin (alpha gamma-spectrin or fodrin) as a major membrane-associated, axonally transported cytoskeletal protein. We show here that the chicken optic system also contains an erythrocyte-specific form of spectrin (alpha beta' beta-spectrin), which has a more restricted distribution; it is confined to the plasma membrane of dendrites and cell bodies of retinal ganglion cells, is absent from the optic nerve fibers, and is not axonally transported from the retina into the optic nerve. During development of the optic system, the expression of alpha gamma-spectrin is constitutive in all cell types. On the other hand, the accumulation of alpha beta' beta-spectrin is detected in only the ganglion cells, and at a time in development which coincides with the phase of synaptogenesis. These results indicate the existence of a developmentally regulated mechanism that topologically segregates the erythroid and brain forms of spectrin from each other, and the former from axonal transport, and suggest that erythroid spectrin may be involved in establishing restricted membrane-cytoskeletal domains in neurons during synaptogenesis, and maintaining them in the adult cell.