GABA A receptors are involved in the analgesic effects of morphine microinjected into the central nucleus of the amygdala

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