Colocalization of muscarinic and nicotinic receptors in cholinoceptive neurons of the suprachiasmatic region in young and aged rats.

In the present study muscarinic and nicotinic cholinergic receptors in the SCN region were demonstrated and analyzed, employing monoclonal antibodies to purified muscarinic and nicotinic cholinergic receptor proteins. A near-total colocalization of the two acetylcholine receptor subclasses in cholinoceptive neurons of the SCN area was found. The antibodies applied to aging rat brain (at 30-34 months) revealed a clear decrease in immunoreactivity in senescence albeit with a high level of individual variability. Furthermore, in 8 out of 10 aged animals examined a considerable increase of astrocytes possessing muscarinic cholinergic receptors was observed.