Primary afferent depolarization of tooth pulp afferents by stimulation in nucleus raphe magnus and the adjacent reticular formation in the cat: effects of bicuculline.

In decerebrate cats electrical stimulation in nucleus raphe magnus (NRM) and the adjacent region of the reticular formation (NRGC) produced a decrease in the threshold of antidromic responses evoked in the tooth pulp following stimulation in the trigeminal nucleus oralis. This primary afferent depolarization (PAD) of Adelta afferents was unaffected by naloxone given intravenously. Bicuculline, given intravenously or applied directly to the terminal region by iontophoresis, selectively antagonised the PAD evoked by stimulating in NRM. The results suggest that GABA is involved in mediating presynaptic inhibition of Adelta tooth pulp input following stimulation in NRM.