The ergolene derivative MPME induces in the rat a behavioural syndrome associated with activation of dopamine D-1 receptors belonging to the dotted type of forebrain dopamine nerve terminals

Bromocriptine-induced rotation: characterization using a striatal efferent lesion in the mouse

Two lesion techniques were used to elucidate the mode of action of bromocriptine (BRC)-induced behavior in mice. With the first lesion, a unilateral 6-hydroxydopamine (6-OHDA) preparation, BRC administration resulted in contralateral rotation which was blocked by alpha-methyl-para-tyrosine (AMPT), comparable to previous reports using rats. After striatonigral/entopeduncular lesion, mice did not rotate in response to doses of BRC up to 30 mg/kg but did show general activation which was also inhibited by AMPT pretreatment. It is concluded that BRC does not elicit rotation when there is no dopaminergic asymmetry such as that caused by a unilateral 6-OHDA lesion or no asymmetry in the striatonigral or striatoentopeduncular efferents. Since BRC-induced behaviors are dependent on intact presynaptic dopamine and BRC is predominantly a D-2 agonist, behaviors elicited in response to BRC must be the result of coactivation of D-1 receptors by endogenous dopamine. Thus, the behavioral effects of BRC, and perhaps D-2 agonists in general, must be mediated by efferents other than the striatonigral and striatoentopeduncular pathways.

The effect of selective D1 and D2 dopaminergic agents on sexual receptivity in the female rat

A number of dopaminergic drugs was tested for their effect on female sexual receptivity in ovariectomised plus adrenalectomised rats primed with oestradiol benzoate. The selective D1 agonist (SKF 38393 5-40 mg/kg) and D1 antagonist (SCH 23390 0.1-10 mg/kg) had no significant effect on sexual behaviour. The results of administration of mixed dopaminergic agents (DOPA, 10-50 mg/kg with benserazide or 100-200 mg/kg alone and haloperidol 0.01-1.0 mg/kg) and selective D2 dopaminergic agents (LY 171555 2.5-800 micrograms/kg, BHT 920 0.01-1.0 mg/kg and sulpiride 5-80 mg/kg) indicate that a central dopaminergic system has an inhibitory control on female sexual activity exerted through D2 receptors. Any stimulatory effects of the exogenous agonists were probably due to an action on presynaptic D2 receptors. The predominance of the D2 pre- and post-synaptic receptor activity appears to be influenced by the sexual receptivity of the animal.