A quantitative study of changes in old age of 5-hydroxytryptamine-like immunoreactivity in perivascular nerves of the rabbit.

Quantitative immunohistochemical techniques were applied to whole mount stretch preparations of the femoral, saphenous and cerebral blood vessels of rabbits from before birth to old age (greater than 3 years) in order to study the effects of ageing processes on 5-hydroxytryptamine(5-HT)-like immunoreactive perivascular nerve plexuses. Immunostained perivascular nerve fibres first appeared at 30 days in utero in all the vessels studied with the exception of the saphenous vein where nerves appeared at one day after birth. Perinatal and early postnatal development showed a general increase in nerve density in all the vessels, which continued up to adulthood (6 months) in all vessels except the femoral artery and then showed a general and often statistically significant decline in old age. Comparison of these results with those of noradrenergic perivascular innervation showed by 5-HT tended to appear later in perinatal development and was more widely reduced in old age than noradrenaline.