Nucleus basalis lesions: implication of basoamygdaloid cholinergic pathways in memory

Previous studies have shown a lack of association between cortical choline acetyltransferase (ChAT) activity and severity of memory impairment following excitotoxic lesions of the nucleus basalis magnocellularis (NBM). It recently has been proposed that the differential effects of NBM injections of various excitotoxins on amygdaloid and cortical ChAT may explain this result. The present study evaluated the mnemonic effect of unilateral intra-NBM infusions of the excitotoxins phthalic acid and quisqualic acid, which decrease ChAT activity primarily in the amygdala and cortex, respectively. Rats were trained in a double Y-maze, lesioned, and allowed to recover for 1 week prior to memory assessment. Behavioral results showed impaired working but not reference memory following phthalic acid lesions, and no significant effect following quisqualic acid lesions. Biochemical analysis in a second group of subjects confirmed that phthalic acid lesions produced a large decrease in basolateral amygdaloid ChAT, but had little effect on cortical ChAT activity. Conversely, quisqualic acid lesions produced a large decrease in cortical, but not basolateral amygdaloid, ChAT activity. These results suggest that the NBM amygdalopetal cholinergic pathways play a role in mnemonic functioning.