Basolateral amygdala lesions do not prevent memory of context-footshock training

Abstract

The present studies examined the effects of basolateral amygdala (BLA) lesions induced prior to or after context-footshock training on 48-h memory, using several retention measures. In experiment 1, male Sprague-Dawley rats with bilateral BLA lesions (NMDA, 12.5 mg/mL, 0.2 microL) were given footshock training in one compartment of a two-compartment alley. Rats were habituated to the alley and 24 h later were given two footshocks in the shock compartment. Retention was tested 48 h later, using latency to enter the shock compartment and time spent freezing as measures of memory. Two days later, they were tested again and received a footshock on each re-entry of the shock compartment prior to remaining in the safe compartment for 200 consecutive seconds. The BLA lesions did not block retention as assessed by freezing or number of re-entries of the shock compartment. In experiment 2, no prior habituation was given, and only one footshock was used for the training. BLA lesions did not block retention, as indicated by latencies to enter the shock compartment on a 48-h test or by number of entries of the shock compartment. Experiment 3 examined the effects of the GABAA agonist muscimol infused into the BLA prior to the 48-h retention test. The muscimol infusions decreased retention test entrance latencies but did not block retention as assessed by the number of subsequent entries of the shock compartment. These findings provide additional evidence that an intact BLA is not required for the acquisition or retention of context-footshock training.

Figure 1

Photomicrographs of a sham lesion (A), the smallest included lesion (B), the largest included lesion (C), and a representative needle track from the drug infusion in the BLA (D). Arrows indicate the extent of the neurotoxic lesion.

Figure 2

The largest and smallest BLA lesions included for experiment 1 (A) and experiment 2 (B).

Figure 3

Latencies to enter the shock compartment during retention testing for sham and BLA-lesioned animals in experiment 1. ^*P < 0.001 compared with sham (no prior shock training group; N = 6 to 11 animals per group).

Figure 4

Freezing behavior during the 10-min retention testing. †P < 0.05 compared with lesion (no prior shock training group); ^*P < 0.05 compared with sham (no prior shock training group; N = 6 to 11 animals per group).

Figure 5

CMIA trials needed to reach the 200-sec criterion for sham- and BLA-lesioned rats. †P < 0.001 compared with lesion (no prior shock training group); ^*P < 0.0001 compared with the sham (no prior shock training group; N = 6 to 11 animals per group).

Figure 6

Latencies to enter the shock compartment during CMIA testing in experiment 2 for sham- and BLA-lesioned animals. †P < 0.005 compared with lesion (no prior shock training group); ^*P < 0.0001 compared with sham (no prior shock training group; N = 8 to 13 animals per group). The maximum latency was 200 sec.

Figure 7

CMIA trials needed to reach the 200-sec criterion for sham and BLA-lesioned rats in experiment 2. †P < 0.005 compared with lesion (no prior shock training group); ^*P < 0.0001 compared with sham (no prior shock training group; N = 8 to 13 animals per group).

Figure 8

Latencies to enter the shock compartment during CMIA testing in experiment 3 for muscimol- and saline-infused rats. ^*P < 0.001 compared with saline (no prior shock training group; N = six to nine animals per group). The maximum latency was 200 sec.

Figure 9

CMIA trials needed to reach the 200-sec criterion for muscimol- and saline-infused rats in experiment 3. †P < 0.05 compared with muscimol (no prior shock training group); ^*P < 0.05 compared with saline (no prior shock training group; N = six to nine animals per group).