Effects of lesions of the central nucleus of the amygdala on anxiety-like behaviors in the rat.

The effects of lesions of the central nucleus of the amygdala on anxiety-like behaviors in the rat were determined using two animal models, the conditioned suppression of drinking (CSD) and defensive burying paradigms. For CSD conflict testing, water-restricted rats were trained to drink water from a tube that was occasionally electrified (0.25 mA); electrification was signaled by a tone. CSD test sessions were 10 min in duration and were conducted 4 days per week. After at least 3 weeks of conflict testing, both punished (30-40 shocks per session) and unpunished (10-12 ml water per session) responding had stabilized. Subjects then received bilateral electrolytic lesions of the central nucleus of the amygdala or sham lesions. After a 1-week recovery period, CSD conflict testing was reinstated and continued for 20 weeks. Amygdaloid-lesioned subjects accepted significantly more shocks than did sham controls. In addition, acute challenges with the benzodiazepine chlordiazepoxide (2.5-10 mg/kg, IP, 30-min pretreatment), the barbiturate phenobarbital (20 mg/kg, IP, 10-min pretreatment), and carbamazepine (10 mg/kg, IP, 10-min pretreatment) produced an increase in punished responding in both amygdaloid-lesioned and sham-treated subjects. Analysis of covariance (ANCOVA)-based adjusted means for the change in shocks received were not significantly different between the two groups. Following completion of the CSD studies, subjects were tested in the defensive burying paradigm. Although there was no significant difference between lesioned and sham-treated subjects on the percent of animals that exhibited burying, subjects with lesions of the central nucleus of the amygdala exhibited a significantly greater latency to initiate defensive burying.(ABSTRACT TRUNCATED AT 250 WORDS)