Regional Differences in the Density of Perivascular Nerves and Varicosities, Noradrenaline Content and Responses to Nerve Stimulation in the Rabbit Ear Artery

Abstract

Quantitative image analysis of fluorescent nerves following histochemical localization of monoamines in stretch preparations of the rabbit ear artery (REA) reveals marked differences in the density of innervation between the proximal and distal regions. The innervation in the proximal region is about twice as dense as that in the distal region and there are approximately 10,500 and 6,500 varicosities per mm² vessel area in these two regions, respectively. These varicosities have approximately the same mean diameter throughout the length of the vessel. The noradrenaline contents per gram wet weight of tissue in the proximal and distal regions are 1.93 and 0.94 µg, respectively. It is estimated that noradrenaline contents per mm² nerve plexus area are 0.30 and 0.08 ng and that the nerve endings contain 2.8 × 10^–14 and 1.2 × 10^–14 g per varicosity in the proximal and distal REA, respectively. Sympathetic nerve stimulation in vitro with frequencies up to 8 Hz elicits larger and faster contractions in the proximal REA and the threshold frequency is less than in the distal region. This study also indicates that care should be taken to use the same region when using the REA for pharmacological and physiological studies.