Nicotinic receptor activation excites distinct subtypes of interneurons inthe rat hippocampus

We examined the function of nicotinic acetylcholine receptors (nAChRs) in i nterneurons of area CA1 of the rat hippocampus. CA1 interneurons could be c lassified into three categories based on nicotinic responses. The first cla ss was depolarized by alpha 7 nAChRs, found in all layers of CA1 and as a g roup, had axonal projections to all neuropil layers of CA1. The second clas s had both fast alpha 7 and slow non-alpha 7 nAChR depolarizing responses, was localized primarily to the stratum oriens, and had axonal projections t o the stratum lacunosum-moleculare. The third group had no nicotinic respon se. This group was found in or near the stratum pyramidale and had axonal p rojections almost exclusively within and around this layer. Low concentrati ons (500 nM) of nicotine desensitized fast and slow nAChR responses. These findings demonstrate that there are distinct subsets of interneurons with r egard to nicotinic receptor expression and with predictable morphological p roperties that suggest potential cellular actions for nicotinic receptor ac tivation in normal CNS function and during nicotine abuse.