Activation of D2-like receptors induces sympathetic climactic-like responses in male and female anaesthetised rats.

In anaesthetised male rats an intravenous (i.v.) injection of p-chloroamphetamine (PCA) produced a specific patterned bursting response in the sympathetic vas deferens nerve (VDN) that corresponds to ejaculation. In the present, study selective dopamine agonists and antagonists were used to investigate whether dopaminergic mechanisms influence the generation of this ejaculatory-related response. Administration of a mixed D(1/2) receptor agonist (0.1-1.0 mg kg(-1) apomorphine i.v.) also evoked the characteristic bursting pattern responses in the VDN. Similar, but fewer, burst pattern responses could also be evoked by a selective D(2/3) receptor agonist (0.1-2.0 mg kg(-1) piribedil). Responses to 1.0 mg kg(-1) apomorphine were blocked by pretreatments with either 0.5 mg kg(-1) remoxipride (D(2) receptor antagonist) or 0.5 mg kg(-1) nafadotride (D(3) receptor antagonist), suggesting that D(2)-like receptors were involved. Responses could not be evoked by i.v. injections of apomorphine (1.0 mg kg(-1)) in anaesthetised male rats with a midthoracic spinal section, indicating that activation of D(2)-like receptors at supraspinal sites leads to an increase in the excitability of the lumbosacral pattern generator for ejaculation. In anaesthetised female rats a similar patterned bursting response occurred in the uterine nerve (UN) in response to apomorphine (0.5-2.0 mg kg(-1) i.v.). Thus a common neural mechanism may regulate sexual climactic reflexes in both sexes.