HETEROGENEITY OF NEURONAL NICOTINIC ACETYLCHOLINE-RECEPTORS IN THIN SLICES OF RAT MEDIAL HABENULA

1. Neuronal nicotinic acetylcholine receptors in slices of rat medial habenula were studied using patch clamp recording techniques. 2. Whole cell current responses to cytisine could be blocked by hexamethonium, as expected for nicotinic receptors. The whole cell current-voltage r elations were linear at negative membrane potentials, but showed stron g inward rectification when chloride currents were minimized. 3. When 1 mM Ca2+ (0 mM Mg2+) was present in the external recording solution, the single channel conductances elicited by acetylcholine or nicotine in twenty patches were in the range 39-58 pS, with a mean of 47 pS. Th ere appeared to be at least two groups of conductances. 4. In the open point amplitude distributions of three patches, the most common ampli tude corresponded to 41 pS (81% of the area). In another four patches the most common amplitude corresponded to a mean conductance of 51 pS (83% of the area). Direct transitions between open levels were rare. 5 . Channel closed times were not significantly different for the two co nductance groups. However, for the four patches with predominantly 51 pS openings, the means of the distributions of open times longer than two filter rise times averaged 5.8 ms. Those patches with predominantl y 41 pS openings averaged 14 ms. Also, for patches with predominantly 51 pS openings the overall mean burst length was 5.8 ms, whereas for p atches with predominantly 41 pS openings it was 16.1 ms. 6. These obse rvations suggest that 51 and 41 pS openings result from the activity o f at least two, but possibly more, different receptor subtypes. We con clude that nicotinic receptors in the rat ventral medial habenula are heterogeneous.