Strain specific cholinergic changes in response to stress: analysis of a time-dependent avoidance variation

Investigators have established that the performance of an incompletely learned avoidance task is a U shaped function of the time since the original partial acquisition. Thus rats perform more poorly when retested at intermediate time intervals (1-8 hr) after training than they do when tested at longer post-acquisition intervals (24-48 hr). Studies have suggested that such time-dependent deficits are not related to changes in learning ability, but rather result from shock-induced motor suppression which interferes with active avoidance responding. Pharmacological studies utilizing drugs which effect cholinergic function have indicated that an inhibitory cholinergic system may be involved in mediating post-shock motor suppression. To obtain direct biochemical evidence for possible cholinergic mediation of post-shock motor suppression, measurements of high affinity choline uptake and acetylcholine turnover were made at varying time intervals following partial active avoidance training in F-344 rats. An increase in cholinergic function was found in the dorsal, but not the ventral hippocampus 30 min, 1 hr and 4 hr following acquisition training. These biochemical alterations were temporally correlated with deficits in active avoidance responding. We have reported that the immediate behavioral suppression observed in another rat strain (Sprague-Dawley, Zivic Miller Laboratories), which exhibits inferior active avoidance performance, is similarly correlated with cholinergic activation in the dorsal hippocampus [17]. These data support the hypothesis that the dorsal-hippocampal cholinergic system is involved in the mediation of stress-induced behavioral suppression.(ABSTRACT TRUNCATED AT 250 WORDS)