Lateralized amygdala activation: importance in the regulation of anxiety and pain behavior

The amygdala is involved in the emotional responses to fear including anxiety and heightened pain reporting. In a rodent model, bilateral activation of the central amygdala (CeA) with corticosterone (CORT) produces anxiety-like behavior, somatic allodynia and visceral hypersensitivity. Although hemisphere-specific processing differences between the left and right amygdala have been reported, it remains unclear whether the right or left CeA is involved in the production of anxiety-like behavior, and abnormal somatic and visceral perception. The goal of the present study was to investigate the hypothesis that lateralized corticoid-mediated mechanisms in the CeA produce anxiety as well as abnormal pain perception.

Anesthetized rats received stereotaxic implants of cholesterol (Chol; 30 μg) or CORT (30 μg) micropellets onto the left, right or both dorsal margins of the CeA. Following implantation (5-7 days), anxiety-like behavior was assessed on the elevated plus-maze (EPM), somatic allodynia was measured using Von Frey filaments, and visceral sensitivity was quantified as a visceromotor response (VMR) to colorectal distention (CRD) at 0-60 mmHg.

Unilateral implants of CORT onto either the left or right CeA produced anxiety-like behavior and somatic allodynia. However, our data illustrated that the bilateral placement of CORT onto the CeA was required to increase visceral sensitivity.

These results provide evidence that there is no hemispheric lateralization of the CeA involved in corticoid-mediated anxiety-like behavior and heightened pain reporting.