The role of the basolateral nucleus of the amygdala in the pathway between the amygdala and the midbrain periaqueductal gray in the rat.

We electrophysiologically examined the connection between the basolateral nucleus of the amygdala (BLA) and the periaqueductal gray (PAG) and examined the role of the central nucleus of the amygdala (CNA) in this pathway. Train electrical stimulation of the BLA excited 21% (7/33) and inhibited 27% (9/33) of the cells recorded in the PAG. Chemical stimulation of the BLA excited 23% (13/56) and inhibited 16% (9/56) of the cells recorded in the PAG. Injection of lidocaine into the CNA by itself had no effect on PAG cells (n = 9) or on blood pressure but blocked the effect of BLA stimulation on PAG neurons in 78% of the cells recorded. It was concluded that: (1) PAG cells respond to BLA stimulation; (2) the majority of these cells are located in the dorsolateral and lateral columns of the PAG; and (3) the CNA modulates a majority of the activities of the BLA in the PAG.