EFFECTS OF FORMALIN AS A PERIPHERAL NOXIOUS STIMULUS ON THE NUCLEUS RETICULARIS PARAGIGANTOCELLULARIS NEURONS OF ANESTHETIZED RATS

In the present study, the effects of formalin as a peripheral noxious stimulus on spontaneously active units of the nucleus reticularis paragigantocellularis (PGi), a narrow region of the ventral pontine reticular formation, was examined in urethane anesthetized rats. Spontaneous discharge of the PGi neurons was variable, ranging from I to 37 spikes per second. Formalin as a chemical irritant and prolonged noxious stimulus induced changes in the firing of spontaneously active PGi neurons. There were three neuronal subpopulations in the PGi that responded to formalin: excited (19.35 %), inhibited (45.16 %) and unchanged (35.48 %). Thus we suggest that PGi neurons may be involved in the processing of information related to formalin as a chemical irritant.