The Role of Parabrachial GABAA Receptors in Pain Modulation in Rats

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. 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. 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). 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.