Development and ageing of perivascular adrenergic nerves in the rabbit. A quantitative fluorescence histochemical study using image analysis.

Age-related changes in vascular adrenergic nerves of 5 contrasting arteries in the rabbit were studied from before birth through to old age. Adrenergic nerves were demonstrated on stretch preparations using glyoxylic acid fluorescence histochemistry. Quantitative estimates of the densities of nerve fibres and varicosities were obtained by automated light microscopic image analysis. The early stages of development of vascular innervation were similar in all the vessels studied. They consisted of a period of outgrowth of axons; a period of rapid increase in density and formation of varicosities; and a later period of more gradual nerve growth. The timing of these stages varied greatly between the different vessels. The larger vessels, i.e. the carotid, renal and femoral arteries, had a well-developed innervation at birth, whilst the innervation of the smaller mesenteric and basilar arteries was sparse. Nerve loss occurred between 6 weeks and 6 months in the femoral artery and in old age (3 years or over) in the renal and carotid arteries. The large elastic arteries were, in general, more densely innervated than the smaller muscular arteries throughout life. The innervation of the different vessels became increasingly diverse between birth and adulthood, indicating a relationship between the pattern of vascular innervation and local physiological requirements. Factors which could influence age-related changes in nerve pattern and density are discussed.