SYMPATHETIC MODULATION OF SENSORY NERVE ACTIVITY WITH AGE - HUMAN ANDRODENT SKIN MODELS

1. Sensory nerves serve an afferent role and mediate neurogenic compon ents of inflammation and tissue repair via an axon reflex release of s ensory peptides at sites of injury, Dysfunction of these nerves with a ge could contribute to delayed tissue healing. 2. Complementary animal and human skin models were used in the present studies to investigate changes in the modulation of sensory nerve function by sympathetic ef ferents during ageing, Laser Doppler flowmetry was used to monitor neu rogenic skin vascular responses. 3. The animal model used skin of the hind footpad of anaesthetized rats combined with electrical stimulatio n of the sciatic nerve, while the human model comprised capsaicin elec trophoresis to the volar surface of the forearm, Sympathetic modulatio n was effected by systemic phentolamine pretreatment in animals and lo cal application in the human model. 4. The results obtained from the h uman model confirmed the reported decline in sensory nerve function an d showed no change in sympathetic modulation with age, The results fro m the animal model confirm and expand results obtained from the human model. 5. The use of low (5 Hz) and high (15 Hz) frequency electrical stimulation (20 V, 2 ms for 1 min) revealed a preferential response of aged sensory nerves to low-frequency electrical stimulation parameter s with differential sympathetic modulation that is dependent on the fr equency of stimulation.