Differential effects of post-training muscimol and AP5 infusions into different regions of the cingulate cortex on retention for inhibitory avoidancein rats

Adult male Wistar rats were bilaterally implanted with indwelling cannulae in four different coordinates of the cingulate cortex: (1) the anterior cin gulate (AC), (2) the rostral region of the posterior cingulate (RC), (3) th e upper portion of the caudal region of the posterior cingulate (UC), and ( 4) the lower portion of the caudal region of the posterior cingulate (LC). After recovery, animals were trained in a step-down inhibitory avoidance ta sk (3.0-s, 0.4-mA foot shock). Either immediately, or 90 or 180 min after t raining, animals received a 0.5-mu I infusion of vehicle (phosphate buffer, pH 7.4), of muscimol (0.5 mu g), or of AP5 (5.0 mu g). Retention testing w as carried out 24 h after training. Muscimol was amnestic when given into a ny of the three coordinates of the posterior cingulate cortex 90 min after training, and when given into LC immediately post-training. In addition, AP 5 was amnestic when given into UC 90 min post-training, but not when given into any other region and/or at any other time. None of the treatments had any effect when given into AC. The results suggest that memory processing o f the inhibitory avoidance task is regulated by the posterior but not by th e anterior cingulate cortex, through muscimol-sensitive synapses, relativel y late after training. AP5-sensitive synapses appear to play a very limited role in these processes, restricted to UC. (C) 1999 Academic Press.