PHARMACOLOGICAL AND IMMUNOHISTOCHEMICAL EVIDENCE FOR SEROTONERGIC MODULATION OF CHOLINERGIC NUCLEUS BASALIS NEURONS

Identified electrophysiologically by low threshold bursts and transien t outward rectification, cholinergic nucleus basalis neurons were reco rded and labelled intracellularly in guinea-pig basal forebrain slices . By means of a triple labelling immunofluorescent technique, serotoni n-immunoreactive fibres were visualized in close proximity to the soma and dendrites of the biocytin-labelled, choline acetyl transferase (C hAT)-immunoreactive cells. By bath application, 5-hydroxytryptamine (5 -HT) produced a direct hyperpolarization of the identified cells which was mimicked by 5-HT1A receptor agonists, suggesting that it may inhi bit the tonic firing but also modulate the low threshold bursting of t he cholinergic nucleus basalis neurons.