Effects of dopaminergic agonists and antagonists on the muscarinic and dopaminergic receptors from rat neostriatum

This work presents the effects of dopaminergic agonists (mazindol 10 mg/kg, p.o., MAZ, and apomorphine 1 mg/kg, i.p., APO) and antagonists (pimozide 20 mg/kg, p.o., PIM, and sulpiride 100 mg/kg, p.o., SUL) on muscarinic (MR) and dopaminergic receptors (DR) in the rat neostriatum from animals treated daily during I days. The results (fmol/mg protein) showed that MAZ caused a 37% increase in MR. No effect was observed with PIM but it blocked the effect of MAZ. A 20% increase was seen with SUL. Its association with APO did not alter MR, but blocked MAZ effect. It was also observed that MAZ and APO tended to increase Mi-like receptors (283.3 +/- 15.18 and 291.9 +/- 28.22, respectively), while a decrease was also seen with the association of SUL plus APO (206.2 +/- 13.85). On MZ-like receptors, an increase was observed with PIM plus MAZ (31.1 +/- 1.78) and with APO alone (38.1 +/- 1.44). The increase seen with APO was blocked by PIM and SUL (26.2 +/- 1.78 and 21.2 +/- 0.78, respectively). MAZ increased D2-like receptor (261.6 +/- 13.63), and this effect had a tendency to be blocked by PIM and SUL (224.1 +/- 18.02 and 226.6 +/- 10.88, respectively). Similarly, it increased D1-like receptors (261.0 +/- 16.89). A greater effect was seen with PIM plus MAZ (357.6 +/- 33.72) or plus APO (307.0 +/- 15.40), as related to either one alone (261.0 +/- 16.89 and 156.1 +/- 17.96, respectively). SUL (142.9 +/- 9.95) was devoid of effect, but blocked the effect of MAZ (184.1 +/- 6.96). The work showed that dopaminergic agonists and antagonists have the ability to interact with MR and to influence both systems. (C) 1997 Elsevier Science Inc.