A physiological role for nitric oxide in the centrally mediated sympathetic and somatomotor ejaculatory response in anesthetized male Wistar rats.

Neurones in the lumbosacral spinal cord are known to play a significant role in ejaculation. In these same areas neurones containing nitric oxide synthase (NOS) have been described. This raised the question as to whether there is a physiological role for nitrous oxide (NO) in the spinal cord in sexual behavior. We first established immunohistochemical localization of NOS positive neurones in the lumbosacral spinal cord. NOS positive neurones were found in several areas of the lumbosacral cord. Namely the intermediolateral column (IML) at L(1)-L(4) and sacral cord; the dorsal gray commissure above the central canal at L(1)-L(2); the ventral gray area of lamina X below the central canal at L(3)-L(4); the superficial laminae of the dorsal horn at all levels. Secondly, we examined the role of NO in the generation of synchronized bursting activity within the vas deferens nerve and associated penile muscles, typical of sexual responses in the male anesthetized rat. NO modulators were applied directly to the spinal cord at T(13)-L(4) via a catheter placed subdurally (intrathecal) and their effect on the genital responses evoked by systemic administration of p-chloroamphetamine (PCA) or apomorphine (apo) (both 1 mg/kg) was observed. All responses evoked by PCA (n=4) or apo (n=3) were abolished or reduced (n=1) during intrathecal NOS inhibition using N((G)) nitro-L-Arginine methyl ester (l-NAME, 200 mM, 20-microl). NOS inhibition using l-NAME was reversed with simultaneous intrathecal application of the NO substrate l-arginine (100 mM, 20-microl, n=3). The selective neuronal NOS inhibitor 1-(2-trifluoro-methylphenyl) imidazole (100 mM, 20-microl, TRIM) also abolished all responses evoked by PCA (n=3). There was evidence that the responses within the vas deferens nerve (VDN) after PCA or apo were enhanced following NO donation using sodium nitroprusside (SNP, 1 mM, 20-microl). Furthermore, a PCA-like response within the VDN was evoked following intrathecally applied l-glutamic acid (200 mM, 20-microl) in six of 26 animals and also by intrathecal SNP in two of eight animals. In conclusion the results suggest a significant excitatory role for NO in the bursting pattern of synchronized discharge generated in autonomic and somatic outflows from the lumbosacral cord by neurones governing ejaculation.