Elsevier

Biological Psychiatry

Volume 67, Issue 12, 15 June 2010, Pages 1120-1127
Biological Psychiatry

Archival Report
Sidman Instrumental Avoidance Initially Depends on Lateral and Basal Amygdala and Is Constrained by Central Amygdala-Mediated Pavlovian Processes

https://doi.org/10.1016/j.biopsych.2009.12.002Get rights and content

Background

The lateral (LA) and central (CE), but not basal (B), amygdala nuclei are necessary for reactive Pavlovian fear responses such as freezing. The amygdala also plays a key role in the acquisition and expression of active instrumental defensive behaviors, but little is known about the specific roles of amygdala nuclei. Using a Sidman active avoidance (AA) task, we examined the necessity of LA, B, and CE for learning and performance. Pavlovian freezing was simultaneously assessed to examine the contributions of amygdala nuclei to the transition from reactive to active defensive responding.

Methods

Rats received electrolytic lesions of LA, CE, or B before AA training, or following overtraining. Rats that expressed low levels of AA performance during training received bilateral electrolytic lesions to CE to eliminate competing freezing reactions and rescue AA. AA performance and freezing were assessed.

Results

Damage to LA and B, but not CE, impaired the acquisition of AA. Performance of AA became amygdala-independent following overtraining. CE lesions abolished Pavlovian freezing and rescued instrumental AA performance in rats that expressed low levels of avoidance responses and high levels of freezing during training.

Conclusions

Although the acquisition of Pavlovian fear depends on LA and CE, but not B, acquisition of instrumental AA is dependent on LA and B, but not CE. CE-dependent Pavlovian processes that control freezing can constrain avoidance behavior. Performance of well-trained AA becomes independent of all three amygdala nuclei. Thus, it appears that different output pathways of LA mediate reactive and active conditioned defensive responding.

Section snippets

Subjects

Male Sprague–Dawley rats (Hilltop Labs, Scottdale, Pennsylvania) initially weighing 250–300 g were individually housed in plastic Nalgene cages on a 12-hour light–dark cycle in a temperature-controlled room (22°C). Ad libitum food and water were available throughout the experiment. All procedures were performed in accordance with National Institutes of Health's guidelines and were approved by the New York University Animal Care and Use Committee.

Surgery

Rats were anesthetized with ketamine and xylazine

Histology

The percentage of combined bilateral damage for each amygdala nuclei in the experiments are shown in Table 2. The study included 111 rats, 35 of which were part of the sham groups. The remaining 78 rats received bilateral electrolytic lesions aimed at the LA, B, or CE. Of these animals, 33 were excluded because of minimal damage to the target structure or excessive damage to adjacent amygdala nuclei. Animals were excluded from the study if they did not have at least 40% combined bilateral

Discussion

These experiments expand our understanding of amygdala function by identifying roles for specific amygdala nuclei in various aspects of instrumental AA. The main conclusions that we draw are 1) LA and B are critical for the acquisition of instrumental AA, but CE is not; 2) well-trained AA responses become LA- and B-independent and continue to be CE-independent; 3) the CE can constrain AA, possibly by inducing Pavlovian responses such as freezing that compete with AA performance. We now discuss

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