Pii: S0306-4522(98)00515-6

In vivo microdialysis was used to measure the effects of partial deafferentation of cortical cholinergic inputs on acetylcholine efflux in young (four to seven months) and aged (24–28 months) male F344/BNNIA rats. Partial deafferentation was produced by bilateral infusions of the immunotoxin 192 immunoglobulin G-saporin (0.56 mg/1.0 ml) or its vehicle solution into the ventral pallidum/substantia innominata region of the basal forebrain. The lesion produced comparable (65%) decreases in basal cortical acetylcholine efflux in young and aged rats. Presentation of a complex environmental stimulus (exposure to darkness/palatable food), in conjunction with the systemic administration of the benzodiazepine receptor weak inverse agonist ZK 93 426, increased cortical acetylcholine efflux in young shams, aged shams and young lesioned rats, but not in aged lesioned rats. Administration of the benzodiazepine receptor partial inverse agonist FG 7142, in the absence of the environmental stimulus, comparably stimulated cortical acetylcholine efflux in young and aged sham rats. FG 7142-induced increases in acetylcholine efflux were attenuated by approximately 50% following partial deafferentation in both young and aged rats. These results suggests that, under certain conditions, ageing potently interacts with the integrity of the cortical cholinergic afferent system. The effects of ageing on cortical cholinergic function may be most potently revealed by experiments assessing age-related limitations in the responsiveness of a partially deafferented cholinergic system to certain behavioral and/or pharmacological stimuli. q 1999 IBRO. Published by Elsevier Science Ltd.