POTASSIUM, BUT NOT ATROPINE-STIMULATED CORTICAL ACETYLCHOLINE EFFLUX,IS REDUCED IN AGED RATS

Using in vivo microdialysis, cortical acetylcholine (ACh) efflux was m easured in freely moving Brown Norway/Fischer 344 Fl rats, aged 4 or 2 2 months. The effects of local, intracortical perfusion of atropine (1 .0 or 100.0 mu M) via the dialysis probe were compared to local K+ (10 0.0 mM) stimulation in the presence of elevated extracellular Ca2+ (2. 5 mM). Basal cortical ACh efflux in aged rats was similar to that of y oung animals. Administration of atropine (1.0 or 100.0 mu M) via the c ortical dialysis probe substantially increased cortical ACh efflux, bu t did not differentially stimulate ACh efflux in young and aged rats. In contrast, ACh efflux stimulated locally with K+ and Ca2+ was signif icantly reduced in aged rats relative to young adults. The implication s of the dissociable effects of K+-depolarization and muscarinic block ade for local regulation of cortical ACh efflux in aged animals are di scussed.