Hypothermic effects of dopamine D3 receptor agonists in the island of Calleja Magna.: Potentiation by D1 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 receptors have also a high affinity for the D-2 receptors. However, it is possible to study selectively D-3 receptor function because some brain 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 brain makes it possible to inject dopamine D-3 ligands into the vicinity of these D-3 receptors, and to study their behavioral role, with no concomitant action on D-2 receptors. We studied the effects on body temperature and on locomotion of unilateral microinjections of D-2/D-3 receptors ligands into the island of Calleja Magna and into the adjacent nucleus accumbens. The results show that D-3 agonists injected into the island of Calleja Magna decrease body temperature and that this effect is potentiated by simultaneous injection of the D-1 agonist SKF 38393. 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 weak effects on body temperature, but, when associated with a D-1 agonist, strongly stimulate locomotor activity. The effects on body temperature of unilateral microinjections of dopamine agonists into unilaterally 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.