Evidence for a neurotransmitter role for 5-hydroxytryptamine in chick retina

Abstract

Retinal 5-hydroxytryptamine levels were reduced by local injection of a-fluoromethyldopa, an inhibitor of aromatic L-amino acid decarboxylase, or reserpine, indicating that this amine is both synthesized and stored in this tissue. The retinae of light-adapted chicks have higher levels of 5-hydroxytryptamine and its major metabolite, 5-hydroxyindoleacetic acid, than dark-adapted animals. The turnover of 5-hydroxytryptamine appears to be greater in the light after inhibition of synthesis. Conversely, the rate of synthesis of 5-hydroxytryptamine appears to be greater in the dark. The possible interaction of dopaminergic neurons and the 5-hydroxytryptamine-containing cells and the effect of a-fluoromethyldopa on this relationship are discussed. The data lend support to the notion that 5-hydroxytryptamine in chick retina may have a neurotransmitter function.Much evidence has been accumulated to indicate that the biogenic amines, norepinephrine, dopamine, and 5-hydroxytryptamine (5-HT),3 may be the neurotransmitters for some neurons in the central nervous system. In the vertebrate retina, dopamine has been identified as the possible transmitter for a class of amacrine cells with cell bodies in the inner nuclear layer (Ehinger, 1976). Sufficient 5-HT to justify a possible neuronal role for this amine has been measured only in chick (Suzuki et al., 1975) and bovine retina (Thomas and Redburn, 1979).

Neurotransmitter-related features of the retinal pigment epithelium

“…This idea was strengthened by analysis of monoamine content by HPLC (Table 3) which revealed serotonin to be a significant component and of both the pigment epithelium and the neural retina. The absolute values for serotonin and dopamine in the neural retina agreed well with those reported for chick retina (Parkinson and Rando, 1981) and were also similar to values reported by Ehinger et al ( 1981 ). The concentrations of monoamine metabolites such as 5-hydroxyindole acetic acid and dihydroxyphenyl acetic acid were too low to permit quantitation in these tissues.…”

“…This may reflect a relatively slow rate of turnover of retinal monoamines or a rapid efflux of metabolites by way of the vascular system. and is similar to the results obtained by Parkinson and Rando (1981 ). The content of several neuropeptides in the two tissues was compared (Table 4).…”

“…These include receptors for benzodiazepine (Altstein et al, 1981 ;Osborne, 1980;Paul et al, 1980), strychnine (Borbe, Muller and Wollert, 1981;Schaeffer and Anderson, 1981 ), muscarinic acetylcholine (Hruska et al, 1978;Vogel and Nirenberg, 1976), dopamine (Magistretti and Schordoret, 1979;Redburn and Kyles, 1980) and GABA (Osborne, 1981, 198la;Schaeffer, 1980;Yazulla and Brecha, 1981 ;Pourcho, 1981 ). These findings imply the presence of a variety of neurotransmitter species within the neural retina and several of these have been described including GABA, glycine, acetylcholine and dopamine (Watling, 1981 ;Yazulla and Schmidt, 1976), norepinephrine (Osborne, 1981 b), glutamate and aspartate (Berger et al, 1977;Altschuler et al, 1982), and serotonin (Suzuki et al, 1977;Osborne et al, 1981 ;Parkinson and Rando, 1981). However, no comparison with pigment epithelium has been attempted.…”

Indoleamine‐mediated reciprocal modulation of on‐centre and off‐centre ganglion cell activity in the retina of the cat.

“…Some non-mammalian species such as goldfish, frog, lizard or chick possess comparatively large concentrations of retinal serotonin (Parkinson & Rando, 1981;Osborne, Nesselhut, Nicholas, Patel & Cuello, 1982). Thus, it is not surprising that serotonin-containing neurones can be demonstrated in these species with antibodies raised against serotonin (Osborne, 1982;Osborne et al 1982).…”

Effect of Reserpine on the Differentiation of the External Granular Layer of the Cerebellum in the Chick Embryo

“…We used 162 cerebella of chick embryos of Ross-1 strain and divided them into two groups: control and experimental, which were treated either on the third or on the sixth day o f incubation; 30/d of a sterile saline solution was injected into the yolk sack of the control embryos and 30/xl of 1.15 M reserpine into the experimental embryos, according to tech nique described by Parkinson and Rando [1981]. Batches of embryos were sacrificed at 13, 15, 17 and 21 days of incubation.…”