Role of the neurokinin-1 receptors in ejaculation in anesthetized rats.

Introduction: Several lines of evidence indicate a role for substance P in the control of ejaculation, although its mode of action needs to be clarified.

Aim: The effects and sites of action of a selective antagonist for the substance P-preferred receptor (neurokinin-1 receptor subtype; NK1) were investigated in a pharmacological model of ejaculation.

Methods: Ejaculation was induced in anesthetized rats by intracerebroventricular (i.c.v.) delivery of the dopamine D3 receptor preferring agonist 7-hydroxy-2-(di-N-propylamino)tetralin (7-OH-DPAT). The effects of the selective NK1 antagonist RP67580 on 7-OH-DPAT-induced ejaculation were measured following intraperitoneal (i.p.), i.c.v., or intrathecal (i.t.) (third lumbar spinal segment; L3) administration.

Main Outcome Measures: Intraseminal vesicle pressure (SVP) and electromyogram of the bulbospongiosus muscle (BS) were recorded as physiological markers of emission and expulsion phases of ejaculation, respectively.

Results: Upon i.p., i.c.v., or i.t. administration, RP67580 significantly reduced the occurrence of ejaculation elicited by 7-OH-DPAT. A mild decrease in the occurrence of SVP and BS responses was observed in rats treated ip with RP67580, whereas only SVP responses were moderately affected following i.c.v. or i.t. administration.

Conclusion: These results show the multilevel regulation of 7-OH-DPAT-induced ejaculation by NK1 receptors.