The Role of Parabrachial GABAA Receptors in Pain Modulation in Rats

Background & Objective: The parabrachial nucleus is a critical link in the transmission of short latency nociceptive information to midbrain neurons. GABA(A) receptors have bidirectional roles in controlling nociception and are abundant in the parabrachial region . We examined the effects of bilateral intra parabrachial microinjection of different doses of the GABA(A) receptor agonist, muscimol, and the GABA(A) receptor antagonist, bicuculline, on pain modulation using a tail-flick test . Materials & Methods: Rats were anaesthetized with sodium pentobarbital (55 mg/kg) and then special cannulas were inserted stereotaxically into the parabrachial nucleus. After 1 week of recovery, the effects of microinjection of muscimol, (62.5, 125,250 ng/side) or bicuculline, (50,100,200 ng/side) into the parabrachial on tail flick latencies were assessed. Tail-flick latencies were measured for 60 minutes every 5 min after drug microinjection. Results: Microinjection of muscimol (62.5, 125 ng/side) and bicuculline (50,100,200 ng/side) into the parabrachial did not have any statistically significant effect on tail-flick latency. Administration of, muscimol, (250 ng/side) produced thermal hyperalgesia (P<0.05). Conclusion: The results of the present study showed that in this model of pain gaba a receptors in the paracrachial region are not Endogenously activated but these receptors in this region have a potential to affect pain modulation.