Elsevier

Brain Research

Volume 641, Issue 2, 4 April 1994, Pages 265-272
Brain Research

Effects of ageing on sensory nerve function in rat skin

https://doi.org/10.1016/0006-8993(94)90153-8Get rights and content

Abstract

Human studies have shown an age-related decrease in modulation of skin vascular reactivity by sensory nerves that correlates with a decline in wound repair efficacy. Using a vacuum-induced blister model in the rat hind footpad, we have investigated age-related changes in pre- and post-terminal activity of primary afferents involved in skin neurovascular function. Changes in local skin blood flow were monitored using a laser Doppler flowmeter. Pre-terminal stimulation was achieved by electrical stimulation of the distal end of the sciatic nerve (10 V, 15 Hz and 0.5 ms) in three groups of young, old and neonatally pretreated capsaicin rats (3, 24 and 3 months old, respectively). The effect of post-terminal stimulation, achieved using local perfusion of 1 μM substance P (SP) over the blister base, was examined in young (3 months old), mature (12 months old) and aged (24 months old) rats. In addition to changes in SP responsiveness, other post-terminal changes studied included changes in smooth muscle reactivity to sodium nitroprusside (SNP), which acts directly on smooth muscle and to endothelial cell function using 3ifN-nitro-l-arginine(l-NORAG), a selective inhibitor of nitric oxide synthesis and endothelium-dependent relaxation. Electrical stimulation of the sciatic nerve in young rats induced an increase in local blood flow (within 1 min) that was maintained during the stimulation period, while the capsaicin group and the old group showed a significantly increased latency and decreased amplitude of the response. Perfusion of SP resulted in an increase in skin blood flow that underwent tachphylaxis in young rats, but which was significantly enhanced and maintained in old rats. There was no difference in the vasodilator response to SNP with age. On the other hand, there was an age-dependent increase in the contribution of endothelial mechanisms involving NO. Our study suggest that both pre- and post-nerve terminal function changes with ageing of the peripheral neurovascular apparatus. The similarity of the responses to electrical stimulation in capsaicin pretreated and old rats suggests similar pre-terminal mechanisms operate in the two groups, namely a decrease in the number of sensory nerves present and/or a decrease in their peptide content. The altered profile of the response to SP with age is suggestive of changes in post-terminal mechanisms involved in tachyphylaxis to SP. It is suggested that tachykinin receptors in old rats are up-regulated as a consequence of a pre-terminal defect in peptide release mechanisms of sensory nerves.

References (38)

  • SalveminiD. et al.

    Synthesis of a nitric oxide-like factor froml-arginine by rat serosal mast cells: stimulation of guanylate cyclase and inhibition of platelet aggregation

    Biochem. Biophys. Res. Commun.

    (1990)
  • WhiteD.M. et al.

    Release of Substance P from peripheral nerve terminals following electrical stimulation of the sciatic nerve

    Brain Res.

    (1985)
  • ArdronM.A. et al.

    Microvascular skin responses in elderly people with varicose leg ulcers

    Age Ageing

    (1991)
  • BarnesP.J. et al.

    Histamine is released from skin by substance P but does not act as the final vasodilator in the axon reflex

    Br. J. Pharmacol.

    (1986)
  • BillA. et al.

    Substance P: release on trigeminal nerve stimulation, effects in the eye

    Acta Physiol. Scand.

    (1979)
  • CoutureR. et al.

    Studies on the trigeminal antidromic vasodilatation and plasma extravasation in the rat

    J. Physiol.

    (1984)
  • Delay-GoyetP. et al.

    Relative involvement of substance P and CGRP mechanisms in antidromic vasodilation in the rat skin

    Acta Physiol Scand.

    (1992)
  • DochertyJ.P.

    Cardiovascular responses in ageing: a review

    Pharmacol. Rev.

    (1990)
  • DubbinP.N. et al.

    Inhibition of endothelial nitric oxide biosynthesis by N-nitrop-l-arginine

    Clin. Exp. Pharmacol. Physiol.

    (1990)
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