BRAIN RESEARCH ELSEVIER Brain Research 661 (1994) 97-103 Research report Posttraining infusion of lidocaine into the amygdala basolateral complex impairs retention of inhibitory avoidance training Marise B. Parent *, James L. McGaugh Center,[or ttle Neurobiology of Learning and Memory, and Department of Pwchobiolo~,9', Uniz'ersity (~¢" CahJ'ornia. Ir~'im'. lrt'ine, CA 92717-3800. USA Accepted 19 July 1994 Abstract The present experiment examined the role of the central nucleus and basolateral complex in the retention of inhibitory avoidance training by reversibly inactivating these regions with lidocaine immediately following training. Male Sprague-Dawley rats were surgically implanted bilaterally with cannulae aimed at the central nucleus or the basolateral complex. One week later, they received one trial inhibitory avoidance training (0.45 mA; 1 s), followed immediately by infusions of lidocainc hydrochloride or buffer (10 p,g/0.25 /zl). Retention was tested 2 days after training. Immediate posttraining infusions of lidocaine into the central nucleus did not affect retention performance; in contrast, immediate posttraining infusions of lidocaine into the basolateral complex significantly impaired retention performance. In addition, the effect of posttraining infusions of lidocainc into the basolateral complex was time-dependent: infusions administered 6 h after training also impaired memory, but infusions administered 24 h after training had no effect. Immediate posttraining infusions of lidocaine also impaired the retention performance of rats trained with a more intense footshock (0.75 mA). However, at the higher footshock intensity, administration of lidocaine 6 h after training had no effect on retention performance. The time- and footshock-dcpendent retrograde impairment of memory produced by posttraining reversible inactivation of the basolateral complex suggests that this region of the amygdala is inw~lved in the consolidation of memory for inhibitory avoidance training. Keywords: Amygdala; Central nucleus; Basolateral complex; Lidocaine; Inhibitory avoidance; Learning: Memory; Retcntion 1. Introduction Extensive evidence indicates that retention of aver- sively motivated learning is influenced by manipula- tions of the amygdala performed after learning. Post- training electrical stimulation [16,32], lesions [28], and chemical stimulation [22,35] of the amygdala affect inhibitory avoidance retention performance. The ef- fects of posttraining amygdala manipulations on mem- ory are time-dependent: the treatments affect memory most effectively when administered immediately after learning and are less effective as the training-treat- ment interval is lengthened. Recently, it was reported that posttraining reversible inactivation of the amyg- dala with tetrodotoxin (TTX) produces a time-depend- * Corresponding author. Department of Psychology, Gilmer Hall, University of Virginia, Charlottesville, VA 22901, USA. Fax: (1) (804) 982-4785; e-mail: mbp4m~zvirginia.edu. 0006-8993/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0006-8993(94)00905-8 ent retrograde inhibitory avoidance retention impair- ment [5]. The use of posttraining reversible inactivation limits the disruption of neural activity to the period immediately following learning: neural activity is intact during learning and retrieval. As a result, these find- ings are consistent with extensive evidence indicating that the amygdala is involved in the consolidation of inhibitory avoidance learning [33-35]. The amygdala is composed of heterogeneous regions that can be subdivided on the basis of histochemistry, cytoarchitectonics, connectivity, physiology, and func- tion [11,42,50]. The central nucleus and the basolateral complex are two areas within the amygdala that have been extensively implicated in learning and memory [1,50]. The findings of lesion studies suggest that the involvement of the central nucleus and basolateral complex varies with different learning tasks. For exam- ple, lesions to areas within the basolateral complex, but not lesions of the central nucleus, impair retention of