[Influence of neurotransmitters on the antinociceptive effect of midbrain stimulation].

In experiments on rats with implanted electrode-cannules there were studied the effects of L-tryptophane (25 mg/kg intraperitoneally) and microinjections of serotonin (20 micrograms), dopamine (10 micrograms) and proserine (5 micrograms) into the area of periaqueductal central gray on the antinociceptive effect caused by stimulation of the same "points" of the midbrain. L-tryptophane, serotonine and proserine (in the presence of methylatropine) potentiated the effect of subthreshold antinociceptive stimulation which could be tested from the modifications of thresholds of the development of some complex pain reaction components under electrical stimulation of the rat tail. Dopamine did not have such an effect. The potentiating effect of serotonine is not eliminated by naloxone.