Does the amygdala modulate adaptation to repeated stress?

Area of Science:

• Neuroscience
• Stress Physiology
• Behavioral Endocrinology

Background:

• Restraint stress activates the hypothalamic-pituitary-adrenal (HPA) axis, alters brain gene expression (c-fos), and increases cardiovascular function in rats.
• Repeated stress exposure leads to adaptation, characterized by habituation of corticosterone secretion and changes in hypothalamic gene expression.
• The neural mechanisms underlying stress response adaptation are not fully understood, prompting investigation into the amygdala's potential role.

Purpose of the Study:

• To investigate the role of the amygdala in the acute and adaptive responses to restraint stress in male rats.
• To determine if amygdala lesions affect HPA axis activation, c-fos expression, and cardiovascular responses to acute and repeated restraint.

Main Methods:

• Male rats underwent either large neurotoxic lesions or discrete lesions of the central nucleus of the amygdala.
• Acute and repeated restraint stress paradigms were employed to assess HPA axis activation (corticosterone, c-fos mRNA), and cardiovascular function (telemetry).
• Changes in corticosterone levels, c-fos mRNA expression in the paraventricular nucleus of the hypothalamus (PVN), and heart rate were measured.

Main Results:

• Large amygdala lesions did not prevent acute HPA axis activation, while central nucleus lesions exacerbated it.
• Rats with large amygdala lesions showed delayed habituation of corticosterone and c-fos responses to repeated restraint.
• Neither lesion type significantly altered acute or repeated restraint-induced tachycardia.

Conclusions:

• The amygdala and its central nucleus are not essential for acute HPA axis and cardiovascular responses to restraint stress.
• The central nucleus may play a modulatory role in the acute stress response.
• Adaptation to repeated stress is only modestly dependent on the amygdala, suggesting other neural circuits mediate habituation.