Modulation of ganglion cell activity in the pineal gland of the rainbow trout: Effects of cholinergic, catecholaminergic, and GAB Aergic receptor agonists

Abstract

Second order neurons within intact isolated pineal glands of the rainbow trout were explored by extracellular recordings to investigate modulatory effects of putative intrapineal neurotransmitters. Acetylcholine, dopamine, and norepinephrine were found to increase ganglion cell activity in a majority of cells tested. The excitatory effects of acetylcholine, dopamine, and norepinephrine were mimicked by muscarinic, dopamine D2, and beta-adrenergic receptor agonists and significantly increased with the applied light intensity, resulting in an attenuation of the ganglion cell response to light. GABA decreased discharge activity in most cells tested. This effect, which could be mimicked with the GABAA receptor agonist piperidine, was independent from the adaptive status. Acetylcholine and GABA were still active if applied during synaptic blockade with low Ca++ high Mg(++)-perfusion medium, whereas dopamine and norepinephrine exhibited no effects if applied during synaptic blockade, suggesting a differential cellular distribution of neurotransmitter receptors in the trout pineal gland. These data demonstrate that ganglion cell activity in the trout pineal gland is under the influence of several neurotransmitters, including acetylcholine, dopamine, norepinephrine, and GABA, which is in contrast to the originally proposed simple bineuronal transduction pathway from photoreceptors onto ganglion cells. Since the above-mentioned neurotransmitters are believed to be released from pineal interneurons, we may conclude that ganglion cell activity in the teleost pineal gland is, similarly to the retina, the product of photoreceptor signals and a modulatory active interneuronal system.

Distribution of choline acetyltransferase (ChAT) immunoreactivity in the brain of the adult trout and tract-tracing observations on the connections of the nuclei of the isthmus

“…However, ChAT-ir nonganglionic cells have been reported in the pineal organ of Phoxinus (Ekström and Korf, 1986) and ChAT-ir photoreceptors in the pineal organ of lampreys and elasmobranchs (Pombal et al, 1997(Pombal et al, , 1999bAnadón et al, 2000). Studies carried out in salmonids have revealed the presence of acetylcholine receptors in this organ (Samejima et al, 1994) and have demonstrated that ACh causes changes in the activity of ganglion cells (Brandstä tter et al, 1995;Brandstä tter and Hermann, 1996). If a cholinergic network is present in the pineal organ of trout, it was undetectable by present immunocytochemical techniques.…”

Neuronal regulation of photo‐induced pineal photoreceptor proteins in carp Catla catla

“…The cholinergic (both muscarinic and nicotinic), adrenergic as well as dopaminergic receptors were detected in the rainbow trout pineal , in which the density of muscarinic receptors was two‐fold higher than the nicotinic receptors (Samejima et al. 1994) and the catecholamine receptors were located pre‐synaptically to pineal ganglion cells (Brandstätter and Hermann 1996). However, the relative role of different neuronal signals in the regulation of photo‐induced expression of photoreceptor proteins in the pineal remained unknown for any fish species.…”

Adrenergic and Cholinergic Regulation of in vitro Melatonin Release during Ontogeny in the Pineal Gland of Long Evans Rats

“…Since acetylcholine is a potent modulator of pineal cell activity in lower vertebrates, particularly fishes [39, 40], the presence of a cholinergic system within the pineal gland could be a phylogenetically conservative feature of this neuroendocrine organ. Data obtained by different laboratories on the role of acetylcholine in modulating melatonin production are not consistent [22, 32, 41, 42]and whether muscarinic and/or nicotinic receptors participate in the various effects of acetylcholine is still contradictory [35, 36, 43, 44].…”