AGE-RELATED-CHANGES IN SYMPATHETIC MODULATION OF SENSORY NERVE ACTIVITY IN RAT SKIN

Objectives: Sensory nerves play an important role in mediating neuroge nic inflammation and subsequent tissue healing. A decrease in sensory nerve function with increasing age has been reported to correlate with poor tissue healing. Sympathetic nerves are known to modulate sensory nerve function, and changes in this modulation could also have import ant implications with ageing. The aims of this study were to examine t he effect of different frequency electrical stimulation (ES) on the mi crovascular responses obtained to sensory nerve activation in young, a ged and capsaicin-pretreated rats and modulation of these responses by sympathetic efferents. Methods: Using laser Doppler flowmetry, vascul ar responses to antidromic ES of the sciatic nerve were monitored in t he base of vacuum-induced blisters in the hind footpad. The non-select ive alpha-adrenoceptor antagonist phentolamine (3 mg/kg, i.v.) was adm inistered 20 min prior to ES. Results: At high frequency ES (20V, 2ms, 15Hz for 1min), the vascular response in old rats was significantly r educed (46% decrease, p < 0.05) compared to young control. At low freq uency ES (20 V, 2ms, 5Hz for 1 min) however, older rats produced simil ar vascular responses to the young. Capsaicin-pretreated rats showed s ignificantly reduced vascular responses to both high and low frequency ES, regardless of age. Pretreatment with phentolamine significantly i ncreased the microvascular response in young rats at high (87%) and lo w (36%) frequency ES. In contrast, phentolamine significantly increase d the ES-induced response in old rats at high frequency only (147% inc rease). Conclusions: The results suggest that the aged sensory nerve r esponds preferentially to low frequency ES and that sympathetic effere nts exert an inhibitory modulatory effect on the vascular response evo ked by sensory nerve stimulation. There are age-related changes in sym pathetic modulation of sensory nerve-mediated responses which is depen dent on stimulation frequency.