Blockade of morphine analgesia by both pertussis and cholera toxins in the periaqueductal gray and locus coeruleus.

Overview

Rats demonstrating analgesia following microinjection of morphine into the periaqueductal gray (PAG) or locus coeruleus (LC) were injected with either pertussis toxin, cholera toxin or saline into the same brain region. Both pertussis and cholera toxin blocked the analgesic effect of morphine at both injection sites for up to 7 days after toxin treatment. These results indicate that morphine analgesia is a complex response involving systems dependent upon Gs as well as Gi or Go proteins.