[Changes in pain reactions and 3H-naloxone binding to opiate receptors of the hypothalamus and midbrain in rats after repeated swimming in cold water]. / Izmenenie bolevykh reaktsii i sviazyvaniia 3H-naloksona s opiatnymi retseptorami gipotalamusa i srednego mozga krys posle mnogokratnogo plavaniia v kholodnoi vode.

The dynamics of nociceptive reactions and character of 3H-naloxone binding to hypothalamus and midbrain synaptic membranes were studied in rats subjected to repeated cold swim stress (3 min. daily during 3, 5 and 15 days). It was shown that an increase of latencies of background nociceptive reactions (hot-plate and tail-flick tests) was accompanied by an ambiguous changes of kinetic parameters of 3H-naloxone binding in the studied brain structures. The results suggest that an increase of antinociceptive systems tone under repeated cold swim stress may be caused by a dynamic transformation of opiate u-receptor apparatus in various brain structures.