GABAAreceptors are involved in the analgesic effects of morphine microinjected into the central nucleus of the amygdala

Abstract

The central nucleus of the amygdala (CeA) has an important role in pain perception and analgesia. Opioid and GABAA receptors, which are both involved in pain modulation, are found in high concentration in the CeA. The present study was designed to examine the interaction of opioidergic and GABAergic systems in the CeA during modulation of acute thermal pain. In the present study, different doses of morphine (25, 50 and 100μg/rat), either alone or after 5min pretreatment with the selective GABAA receptor agonist muscimol (60ng/rat) or the selective GABAA receptor antagonist bicuculline (50ng/rat), were injected bilaterally into the CeA of each rat. Tail-flick latencies (TFL) were measured every 5min for 60min. The results revealed that microinjection of morphine into the CeA significantly increased TFL in a dose-dependent manner. Microinjection of bicuculline or muscimol in combination with morphine into the CeA increased and decreased TFL, respectively. It seems that morphine in the CeA facilitates the function of descending inhibitory systems by interacting with the activity of local GABAA receptors.