[Effect of morphine on the change in the nociceptive and non-nociceptive evoked potentials in the orbitofrontal and secondary somatosensory areas of the cerebral cortex in different functional states].

The effect of morphine on alterations in nociceptive and non-nociceptive evoked potentials (EP) elicited in the second somatosensory (S2) and orbito-frontal cortex of the brain was studied in acute experiments on cats. Administration of morphine in a dose of 5 mg/kg to the above-mentioned structures caused an increase in the amplitude of EP to non-nociceptive stimulation and a decrease of EP to nociceptive stimulation. Under alternate functional inactivation of the orbito-frontal cortex and S2 a unidirectional effect of the projection cortex on the associative orbito-frontal cortex was observed, manifested by a decrease of EP in the orbito-frontal cortex. Administration of morphine with the S2 cooled led to further decrease of EP followed by their restoration in the orbito-frontal cortex, in response to both nociceptive and non-nociceptive stimulation. Meanwhile administration of morphine, with the orbito-frontal cortex cooled, elicited the response in the S2 analogous to that observed after administration of morphine with intact orbito-frontal cortex: a decrease of EP to nociceptive stimulation and an increase of EP to non-nociceptive stimulation. It is suggested that the S2 plays an important role in control of nociceptive and non-nociceptive input to the CNS.