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pubmed:abstractText |
The existence and subunit identification of the nicotinic cholinergic receptors in the rat pineal gland were examined by autoradiography, using [3H]cytisine and [125I]alpha-bungarotoxin as labelled ligands. The experiments performed with radioactive cytisine did not reveal specific binding, while iodinated alpha-bungarotoxin disclosed moderate specific binding density, suggesting that the nicotinic cholinergic receptor in the rat pineal is structurally organized with the alpha 7 or alpha 8 subunits present, the only ones that bind alpha-bungarotoxin with high affinity. In vitro functional experiments using pineal explants demonstrated that the binding site may represent a readily accessible nicotinic cholinergic receptor. Nicotine, though having no effect per se on the synthesis and release of melatonin, significantly diminished, in a dose-dependent manner, the norepinephrine-stimulated melatonin accumulation. This effect could be blocked by coincubation with the cholinergic antagonist d-tubocurarine, suggesting that the nicotinic cholinergic receptor in the rat pineal could be involved in the functional regulation of the gland.
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