NICOTINIC ACETYLCHOLINE-RECEPTORS ON HIPPOCAMPAL-NEURONS - DISTRIBUTION ON THE NEURONAL SURFACE AND MODULATION OF RECEPTOR ACTIVITY

The recent development of a technique that uses infrared microscopy fo r the visualization of well-defined areas on the surface of neurons, a nd a computerized system of micromanipulators led to the discovery tha t functional nicotinic acetylcholine receptors (nAChRs) are expressed at higher density on the dendrites than on the soma of rat hippocampal neurons. The finding that the expression of alpha-bungarotoxin-sensit ive, alpha 7-bearing, nAChRs and dihydro-beta-erythroidine-sensitive,a lpha 4 beta 2 nAChRs tends to increase along the dendritic length sugg ests that these receptors may be highly involved in the integration of synaptic functions in hippocampal neurons. The present report also di scusses the finding that ligands such as the anticholinesterase galant hamine can modulate the nAChR activity by binding to a novel receptor site, and that 5-hydroxytryptamine (5-HT) may serve as an endogenous l igand for this site. The ability of 5-HT to modulate the nAChR functio n in vivo supports the concept that the overall CNS function is determ ined not only by the neuronal network established by the neuronal wiri ng, but also by a chemical network established by the ability of a sin gle substance to act as the primary neurotransmitter in one system and as a co-transmitter in another system.