Strain specific alterations in hippocampal cholinergic function following acute footshock

Abstract

Previous studies have shown that differences between Z-M and F-344 rats in active avoidance acquisition are due to variation in stress-induced motor response, rather than to differences in general learning ability. Thus F-344 rats, which become active when exposed to shock, are more likely to make avoidance responses and learn to associate an active response with ommision of shock than are Z-M rats, which reduce their activity in response to shock. The hypothesis that cholinergic neurons in the hippocampus contribute to the stress-induced motor suppression seen in Z-M rats derives from pharmacologic studies employing micro-injection of cholinergic antagonists. The present studies further investigate this hypothesis through assessment of acetylcholine turnover and high affinity choline uptake in discrete brain regions of Z-M and F-344 rats. Increases in cholinergic function in the dorsal hippocampus were observed in Z-M, but not F-344 rats following acute footshock. Cholinergic alterations were not seen in the ventral hippocampus or striatum of Z-M rats. The strain specific alterations in dorsal hippocampal cholinergic function correlate with documented motor suppression in Z-M rats and motor activation in F-344 rats during acute shock, and suggest that this cholinergic system mediates a suppressive behavioral response to environmental stress.