[Effect of stimulation of the central gray substance on the low- and high-threshold responses of the reticular neurons in the pons and medulla oblongata].

The modulation of somatosensory responses of bulbar (n. reticularis gigantocellularis) and pontine (n. reticularis pontis caudalis) reticular neurons by electrical stimulation of periaqueductal gray matter (PGM) was studied in cats under light chloralose anaesthesia. PGM points which evoked the inhibition of nociceptive jaw opening reflex were stimulated. It was found that in most cases (88%) the PGM stimulation had an inhibitory effect on both nociceptive and non-nociceptive responses of reticular neurons. For bulbar cells with predominant high-threshold inputs nociceptive responses were depressed much stronger than non-nociceptive ones and in pontine neurons for which low-threshold inputs were predominant non-nociceptive responses were inhibited mainly. The data suggest that the inhibitory action of PGM stimulation on somatosensory activity of reticular neurons are based on the principle of the "control of their main synaptic input".