The effects of ageing on the sympathetic nerve supply of arterial vessels are unclear. For example, in the rabbit, a decrease in the density of the nerve supply of the carotid and femoral arteries occurred between 6 weeks and 6 months and between 6 months and 3 years, whereas that of the basilar artery was well maintained over this period (Cowan et al. 1982). By contrast, in Wistar rats, sympathetic nerve density of the basilar and internal carotid arteries reached a peak at 4 weeks and decreased from 8 weeks to 27 months of age (Mione et al. 1988). We have compared sympathetic nerve densities of the middle cerebral, basilar, femoral and caudal ventral arteries (MCA, BA, FA and CVA, respectively) in male Wistar rats of 4, 8 and 40 weeks (n = 8, 7 and 7, respectively).

Arteries were taken after the rats had been killed by cervical dislocation according to UK legislation. They were prepared as whole mount stretch preparations by using the glyoxylic acid method for demonstrating noradrenergic nerves (Cowan et al. 1982). Photomicrographs were taken with epi-illumination and standard filters for fluorescence and analysed quantitatively using image analysis. Nerve densities were assessed as fluorescent area, expressed as percentage surface area of vessel, and as surface density, expressed as number of nerve fire intercepts mm^-1 on a squared grid placed on the vessel image. The results obtained with the two methods were similar.

For MCA, nerve density increased from 0.274 ± 0.012 at 4 weeks to 0.355 ± 0.027 at 8 weeks and then fell to 0.272 ± 0.053 intercepts mm^-1 at 40 weeks (means ± S.E.M.; *, ***: P < 0.05, 0.0001, respectively, 4 or 40 weeks vs. 8 weeks, ANOVA with Fisher’s post-hoc test). A similar pattern was observed in BA. By contrast, in CVA, nerve density increased from 0.324 ± 0.021* at 4 weeks to 0.390 ± 0.023 at 8 weeks and increased further to 0.432 ± 0.051* intercepts mm^-1 at 40 weeks. Moreover, in FA, nerve density was unchanged between 4 and 8 weeks (0.192 ± 0.011 and 0.184 ± 0.016 intercepts mm^-1, respectively), but increased substantially between 8 and 40 weeks (to 0.372 ± 0.030***).

These results suggest that there are regional differences in the effects of ageing on the density of the sympathetic nerve supply to arterial vessels, with cerebral vessels showing a decrease in nerve density from adult to older age and peripheral arteries supplying muscle and cutaneous circulations showing an increase in nerve density with age.