Inhibition from nucleus raphe magnus of tooth pulp responses in medial reticular neurones of the cat can be antagonized by bicuculline.

In decerebrate cats stimulation in nucleus raphe magnus (NRM) inhibited the response of neurones in the medial brain stem reticular formation to electrical stimulation of the tooth pulp. These evoked responses were also reduced by iontophoretically applied GABA. The inhibition from NRM was blocked by bicuculline applied by iontophoresis in 10 out of 16 neurones and the actions of GABA were also antagonized. Inhibition following stimulation in the contralateral reticular formation was not blocked by bicuculline. The results suggest that GABA is involved as a neurotransmitter in mediating the effects of NRM stimulation on reticular neurones.