Coexistence and cooperation between neuropeptide Y and norepinephrine in nerve fibers of guinea pig vas deferens and seminal vesicle.

Fluorescence immunocytochemistry of guinea pig vas deferens and seminal vesicle revealed dense networks of nerve fibers containing both neuropeptide Y (NPY) and dopamine-beta-hydroxylase (DBH), a marker for adrenergic neurons. The effects of norepinephrine (NE) and NPY on the smooth musculature of these organs were studied in vitro. NE inhibited the response to electrical nerve stimulation and increased the basic tension in the vas deferens and contracted the smooth muscle of the seminal vesicle, but had no effect on the contractile response to transmural stimulation in the latter organ. NPY had similar effects on the vas and vesicula, i.e. it inhibited the electrically induced contractions and had no effect on the basic tension. The results suggest a role for NPY as a transmitter that acts before the site of the neuromuscular junction to modulate the release of other transmitters from motor nerve fibers in the smooth musculature.