Figure 6. Kainic acid-induced lesion of the medial septal region blocked avoidance learning in formalin induced-conditioned place avoidance task.

Avoidance was measured by the CPA score, which is the difference in time spent in the preferred (pain-paired) compartment between test (day 4) and preconditioning (day 2) days of conditioned place avoidance (CPA) training. A negative score indicates avoidance behaviour. In the medial septum diagonal band (‘MSDB’) group (a), Sham animals (i.e. vehicle-treated animals) showed avoidance when conditioned with saline-formalin (‘F-CPA’) as compared to animals conditioned with hind paw injection of saline-saline (‘S-CPA’). Neuronal destruction with kainic acid (KA) pre-treatment (see Fig. 4) blocked the formalin-induced avoidance response. In the ‘Amygdala’ group (b), bilateral excitotoxic lesion of the amygdala with intra-amygdaloid microinjection of ibotenic acid (Ibo) also eliminated the formalin-induced avoidance response. The diagrammatic representations in (b) shows the extent of lesion induced across the anterior-posterior axis of amygdala by ibotenic acid. The shaded and hatched regions represent the largest and the smallest areas of lesion within the amygdala. The number on the right of each diagram represent the anterior-posterior coordinate corresponding to the diagram. In the ‘Morphine i.p’ (intraperitoneal) group (c), systemic administration of an anti-nociceptive dose of morphine (5 mg/kg, Mor) abolished the formalin-induced avoidance response compared to that seen in vehicle-treated (Veh) group. Morphine or vehicle were administered just before hind paw injection of formalin during conditioning in the F-CPA experiment. Data are mean ± SEM. Statistical significance: (a) ^#p < 0.05 vs. other groups; (b) *p < 0.05 vs. Sham; (c) *p < 0.05 vs. Veh. Statistical analyses were performed using one-way ANOVA (a) or unpaired t-test (b,c).