Age-dependent modulation of neuropeptide Y on adrenergic transmission of guinea pig vas deferens

Maturational and maintenance effects of testosterone on terminal axon density and neuropeptide expression in the rat vas deferens

Testosterone causes growth of many pelvic ganglion cells at puberty and their maintenance during adulthood. Here we have focused on two populations of pelvic ganglion cells that project to the rat vas deferens: noradrenergic neurons that innervate the smooth muscle and synthesize neuropeptide Y, and cholinergic neurons that primarily innervate the mucosa and contain vasoactive intestinal peptide. We have assessed the muscle innervation after pre- or postpubertal castration, using immunohistochemistry to determine axon density and radioimmunoassay to quantify levels of neuropeptides in tissue extracts. Our results show that androgen deprivation in each period causes substantial effects. Noradrenergic axons in the muscle increase in density after castration, partly due to organ size being smaller than age-matched controls. However, when corrected for target size, there is an overall decrease in total number of axons. This implies that androgen exposure at puberty has a direct effect on neurons to ensure that the adult pattern of innervation is attained, and that this is not simply by matching terminal field to target size. Similar effects of pre- and postpubertal castration imply that continued exposure to testosterone is necessary to maintain normal target innervation. Castration in both time periods increased the density of axons containing vasoactive intestinal peptide, however the effects of castration on the total number of these axons in the muscle were more variable. The concentration of vasoactive intestinal peptide increased substantially following either pre- or postpubertal castration although absolute amounts per vas deferens were decreased. Effects on neuropeptide Y concentration were less pronounced but the total amount per vas deferens was decreased after pre- or postpubertal castration. Our study shows that the action of testosterone (or a metabolite) on a pelvic ganglion cell soma is likely to reflect a change in its terminal field, but that these effects are not mediated simply by testosterone influencing the size of its target organ.

Developmental changes in sympathetic contraction of the circular muscle layer in the guinea-pig vas deferens

Contractile responses of the circular muscle of the isolated vas deferens to electrical stimulation (10-80 Hz) and to noradrenaline significantly decreased with increasing age in 3-week-, 10-week- and 18-month-old guinea pigs, observed by the cannula insertion method. There were no significant differences in the contractile responses induced by alpha,beta-methylene ATP or BaCl2 between 3 and 10 weeks old, but the responses to alpha,beta-methylene ATP or BaCl2 decreased in 18-month-old guinea pigs. The contractile response to electrical stimulation was monophasic in 3-week-old guinea pigs, a small portion of which remained after the treatment with prazosin. Desensitisation of P2X-purinoceptors with alpha,beta-methylene ATP significantly inhibited the contractile responses to stimulation with relatively low frequencies, and the combination of both prazosin and alpha,beta-methylene ATP abolished the stimulation-induced contractions. In 10-week- and 18-month-old guinea pigs electrical stimulation evoked a transient contraction followed by a second contraction at the offset of the stimulation (the after-response). The after-responses were blocked by prazosin. These results show that the dominant component of sympathetic cotransmission is noradrenaline; a purinergic component also exists in the sympathetic contraction in the circular muscle of the vas deferens in young guinea pigs, but is virtually absent in the later stages of development. The sympathetic contractions of the circular muscles significantly decrease with increasing age and this appears to be due to changes in postjunctional, rather than prejunctional, mechanisms.