UDC 615.844.4.015.4:612.822].076.9 Interest in the oral trigeminal nucleus (OTN) in connection with the study of pain has increased considerably after the discovery of a well-marked focus of evoked activity in it during nociceptive stimulation of the orofacial receptive fields. The so-called dual representation of pain in the trigeminal complex [2] called for a close study of all features of the organization of the various nuclei of this concept (the oral, in particular), which could be responsible for their specific role in the conduction of nociceptive and non-nociceptive signals in the CNS. Despite several investigations of the organization of the afferent input and neuronal responses of OTN, only a few investigators [4] have attempted to study this problem from the standpoint of discovery of different functional types of neurons, involved in the conduction of nociceptive and non-nociceptive signals, as has been done in relation to the caudal trigeminal nucleus [8]. From this point of view it is interesting to study the character of the effect of electroacupuncture (EAP), an effective modulator of nociceptive signals. The aim of this investigation was to study the effect of EAP on responses of neurons of different functional types in OTN to noceptive and non-nociceptive stimulation. EXPERIMENTAL METHOD Acute experiments were carried out on eight adult cats weighing 2.5-4 kg. The dissection was carried out under hexobarbital anesthesia (15 mg/kg, intraperitoneall y), and the animals were subsequently immobilized with suxamethonium and artificially ventilated. Unit activity was recorded extracellularly by glass microelecrodes with a tip 1-3 ~ in diameter, filled with 2 M KCI solution, and with a resistance of 4-10 M~, with the aid of a YC-10 electrophysiological complex ("Nihon Kohden," Japan). Pulsation of the brain was prevented by flooding its surface with agar-agar. Stimulation of the dental pulp and of the lip with square pulses, i and 0.i msec respectively in duration and with a strength of 0-50 mA, by means of an ESU-2 stimulator was used as testing stimulation. The nociceptive character of afferent stimulation of a particular intensity was determined by preliminary study of the thresholds of onset of non-nociceptive and nociceptive behavioral responses of the animals to both types of stimulation. Depending on the character of their response to electrical stimulation of the dental pulp and lip, the neurons were divided into three groups. Neurons of group i responded to weak stimulation and their response was unchanged when the strength of stimulation was increased. They were regarded as non-nociceptive low-threshold neurons (LT neurons). Neurons of the second group also began to respond to weak stimulation of lip or dental pulp, but the neuron discharged more strongly when its intensity was increased. Such neurons were classed as neurons with wide dynamic range (WDR neurons). Finally, neurons of the third group responded only to intensive stimulation of the dental pulp and lip, and they were accordingly characterized as specific nociceptors (SN neurons). EAP was applied through steel needles, inserted into the lower part of the base of the concha auriculae. The duration of the pulses was 1.2 msec, their frequency i Hz, their intensity about I0 mA, and stimulation lasted for 5-i0 rain. Research Institute of Reflex Therapy, Moscow. (Presented by Academician of the Academy