Effects of the tripeptides TRH, MIF and MAF on the cerebral dopaminergic system

Some central effects of the tripeptides TRH (thyroliberine), MIF (melanostatine or C-terminal fragment of oxytocine) and MAF (C-terminal fragment of gastrine) have been studied in experiments on mice and rats. Upon intraperitoneal administration in mice, TRH and MIF exercise central stimulating effects: they reverse the reserpine-induced decrease in the rectal temperature, ptosis of the eyelids, hypomotility, decreased content of the cerebral homovanillic acid (HVA); they antagonize haloperidol catalepsy and the increased HVA concentration). The tripeptides potentiate apomorphine stereotypy in rats, when injected in the striatum. The results obtained characterize TRH and MIF as drugs which are capable of activating the cerebral dopaminergic receptors by antagonizing the effects of reserpine and haloperidol, MAF--as a substance acting similar to the dopaminergic receptor blockers. Consequently, the cerebral dopaminergic system is an important unit for the realization of the central effects of these low-molecular peptides.