Phthalic acid amygdalopetal lesion of the nucleus basalis magnocellularis induces reversible memory deficits in rats

The basolateral amygdala (BLA) is extensively implicated in emotional learning and memory. The current study investigated the contribution of cholinergic afferents to the BLA from the nucleus basalis magnocellularis in influencing aversive learning and memory. Sprague-Dawley rats were given permanent unilateral phthalic acid (300 ng) lesions of the nucleus basalis magnocellularis and were chronically implanted with cannulas aimed at the ipsilateral BLA. Lesioned rats showed a pronounced inhibitory avoidance task retention deficit that was attenuated by acute posttraining infusions of the muscarinic cholinergic agonist oxotremorine (4 ng) or the indirect agonist physostigmine (1 microg) into the BLA. Continuous multiple-trial inhibitory avoidance training and testing revealed that lesioned rats have a mild acquisition deficit, requiring approximately 1 additional shock to reach the criterion, and a pronounced consolidation deficit as indicated by a shorter latency to enter the shock compartment on the retention test. Because lesioned rats did not differ from sham-operated controls in performance on a spatial water maze task or in shock sensitivity, it is not likely that the memory impairments produced by the phthalic acid lesions are due to any general sensory or motor deficits. These findings suggest that the dense cholinergic projection from the nucleus basalis magnocellularis to the BLA is involved in both the acquisition and the consolidation of the aversive inhibitory avoidance task.