Action of dopamine receptor agonists in forebrain and hypothalamus: rotational behavior, ovulation, and dopamine turnover.

An ergolene derivative having a piperazine-phenyl side chain instead of a peptide side chain causes rotational behavior in experimental rats and appears to activate mainly limbic DA receptors when given in vivo, in contrast to amino acid ergot alkaloids, which appear to activate all DA receptors when given systemically. Theophyllamine and caffeine were found to cause considerable enhancement of the action of DA formed from DOPAP AND DA receptor agonists such as apomorphine, piribedil, and amino acid alkaloids on supersensitive DA receptors. Many DA receptor agonists such as apomorphine, piribedil, and CB 154 have in common the property to induce hypothermia in mice, an effect that may be related to actions on limbic DA receptors. Many DA receptors agonists such as apomorphine, piribedil, ergocornine, and CB 154 are able to block ovulation in immature rats treated with PMS. It is likely that this blockade is related to activation of a DA receptor in the median eminence controlling LRF secretion. DA receptor agonists antagonize sexual activity in the female rat, whereas DA receptor blocking agents enhance it. DA neurons may therefore subserve an inhibitory role in the control by hormones of sexual behavior. It is of considerable interest that there appear to exist inhibitory DA receptors with regard to both LRF secretion and sexual behavior.