Distribution of adrenergic nerves and changes in neuromuscular transmission in the mouse vas deferens during postnatal development

Abstract

Fluorescence due to catecholamines is first observed in longitudinally orientated nerve bundles during the first postnatal day. Fine fluorescent nerves are present within the circular muscle coat by the postnatal day 5 and in the longitudinal coat from about day 9. The density of this innervation increases rapidly with the development of the muscle coats. The resting membrane polarization of the smooth muscle cells increased with age, from 67 mV at 10 days to 74 mV at 6 months. Excitatory junction potentials (EJP's) in response to intrinsic nerve stimulation were not observed for mice of less than 18 days. The EJP's evoked in vasa from mice of from 18 days to 25–30 days decayed from peak amplitude in up to 160 msec, compared to about 60 msec in vasa from adult mice. In contrast, the rise time of the EJP and the synaptic delay for transmission were the same for EJP's in vasa from mice of all ages. It has been shown that the time of decay of the EJP is not determined by inactivation of transmitter by uptake into peripheral nerve fibers. The configuration of the EJP's was consistent from 30 days, which corresponds with the onset of puberty in mice. The presence of nerve fibers containing catecholamines, observed either by fluorescent histochemical methods or as small granular vesicles in electron microscopic studies, does not necessarily indicate the presence of a functional transmission process in developing tissue.