Kainic acid lesions of the cat's midbrain periaqueductal grey region and emotional-defensive response evoked by carbachol injection to the same loci.

Injections of carbachol (CCh) through a chronic cannula into the midbrain periaqueductal grey region (PAG) of the cat induced an emotional-defensive response (EDR) which was evaluated by duration and number of growls in a 30-min experimental session. That response was examined before and after injection of kainic acid (KA) to the same loci of midbrain. Injections of this excitotoxin into the PAG decreased EDR level. The degree of changes depended on the agent dose. A low KA dose (3 microgram/2 microliters) produced only prolongation of EDR latency, whereas a high dose of KA (6 micrograms/2 microliters) brought a statistically significant reduction of response level (reaching approximately 80%). The results have demonstrated the sensitivity of these cells of the PAG that are responsible for EDR.