[Possible role of positive reinforcement zones in the mechanisms of pain regulation and their relation to the endogenous opiate system].

The consequences of self-stimulation reaction (RSS) to pain threshold in tail withdrawal test (55 degrees C) and naloxone effect have been investigated in tests, using male rats with chronically implanted electrodes into the hypothalamus (AP = 1.5, L = 1.5, H = 8.5) and suture dorsal nucleus (AP = 7.0, L = 0, H = 7.0) (coordinates according to Fifková atlas). It was established that right after RSS, pain threshold in both zones increased 2-2.5-fold and 30 min later reached the initial level. Naloxone injected before RSS increased pain thresholds and decreased RSS frequency from hypothalamus but failed to change these RSS parameters from suture dorsal nucleus. However, naloxone did not affect the increase in pain thresholds caused by RSS from both zones. Taking into account the fact that analgesia appearing after RSS from the anterior hypothalamus as well as from suture dorsal nucleus is not reversed by naloxone, it is suggested that positive reward zones activation partially realized by opioidergic mechanisms or having no connection with them may lead to the development of non-opiate type analgesia.