Co-localization of GABA_B receptor and serotonin in neurons of central endogenous pain control system of rats

AIM To investigate the co localization of GABA B receptor (GABA BR) and serotonin (5 HT) in neurons of the midbrain periaqueductal gray (PAG), raphe nuclei and gigantocellular reticular nucleus pars α (GiA) of the rat. METHODS Immunofluorescence histochemical double or triple staining technique was used with specific antibodies against GABA BR and 5 HT or GABA BR, 5 HT and GABA. RESULTS Densely stained GABA BR and 5 HT like immunoreactive double labelled neuronal cell bodies were observed in the dorsal raphe nucleus (DR), median raphe nucleus (MnR), pontine raphe nucleus (PnR), nucleus raphe magnus (NRM), nucleus raphe obscurus (ROb) and nucleus raphe pallidus (RPa). Additionally, GABA BR/5 HT double labelled neuronal cell bodies were also found in the PAG and GiA. GABA like immunoreactive terminals were found to be in close appositions with GABA BR/5 HT double labelled neuronal cell bodies and proximal dendrites. CONCLUSION GABA BR and 5 HT co exist in majority of the serotonergic neurons in the PAG, raphe nuclei and GiA; GABA ergic terminals form close contacts with GABA BR/5 HT double labeled neurons; GABA might regulate the activities of serotonergic neurons through GABA BR by which to modulate the noxious information transmission.