HYPOTHERMIC EFFECTS OF DOPAMINE D-3 RECEPTOR AGONISTS IN THE ISLAND OF CALLEJA MAGNA - POTENTIATION BY D-1 ACTIVATION

The selective functions of D-3 receptors in the brain are still poorly understood, mainly because all the ligands active at dopamine D-3 rec eptors have also a high affinity for the D-2 receptors. However, it is possible to study selectively D-3 receptor function because some brai n structures, such as the islands of Calleja, contain D-3 and not D-2 receptors. The position of the island of Calleja Magna in the rat brai n makes it possible to inject dopamine D-3 ligands into the vicinity o f these D-3 receptors, and to study their behavioral role, with no con comitant action on D-2 receptors. We studied the effects on body tempe rature and on locomotion of unilateral microinjections of D-2/D-3 rece ptors ligands into the island of Calleja Magna and into the adjacent n ucleus accumbens. The results show that D-3 agonists injected into the island of Calleja Magna decrease body temperature and that this effec t is potentiated by simultaneous injection of the D-1 agonist SKF 3839 3. D-3 agonists have no effect on locomotor activity in the island of Calleja Magna. In the nucleus accumbens, the D-3 agonists have only we ak effects on body temperature, but, when associated with a D-1 agonis t, strongly stimulate locomotor activity. The effects on body temperat ure of unilateral microinjections of dopamine agonists into unilateral ly dopamine-depleted animals are the same as those in nondepleted ones . This indicates that the D-3 receptors are localized postsynaptically in the island of Calleja Magna. (C) 1998 Elsevier Science Inc.