MODULATION OF GANGLION-CELL ACTIVITY IN THE PINEAL-GLAND OF THE RAINBOW-TROUT - EFFECTS OF CHOLINERGIC, CATECHOLAMINERGIC, AND GABAERGIC RECEPTOR AGONISTS
R. Brandstatter et A. Hermann, MODULATION OF GANGLION-CELL ACTIVITY IN THE PINEAL-GLAND OF THE RAINBOW-TROUT - EFFECTS OF CHOLINERGIC, CATECHOLAMINERGIC, AND GABAERGIC RECEPTOR AGONISTS, Journal of pineal research, 21(2), 1996, pp. 59-72
Second order neurons within intact isolated pineal glands of the rainb
ow trout were explored by extracellular recordings to investigate modu
latory effects of putative intrapineal neurotransmitters. Acetylcholin
e, dopamine, and norepinephrine were found to increase ganglion cell a
ctivity in a majority of cells tested. The excitatory effects of acety
lcholine, dopamine, and norepinephrine were mimicked by muscarinic, do
pamine D2, and beta-adrenergic receptor agonists and significantly inc
reased with the applied light intensity, resulting in an attenuation o
f the ganglion cell response to light. GABA decreased discharge activi
ty 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 syn
aptic blockade with low Ca high Mg++-perfusion medium, whereas dopamin
e and norepinephrine exhibited no effects if applied during synaptic b
lockade, suggesting a differential cellular distribution of neurotrans
mitter receptors in the trout pineal gland. These data demonstrate tha
t ganglion cell activity in the trout pineal gland is under the influe
nce of several neurotransmitters, including acetylcholine, dopamine, n
orepinephrine, and GABA, which is in contrast to the originally propos
ed simple bineuronal transduction pathway from photoreceptors onto gan
glion 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 interne
uronal system.