Cutaneous Field Stimulation with Moderate Intensity Current Induces Nerve Proliferation in Rat Skin But Has No Effect on Dorsal Root Ganglia
Joanna Wallengren, Kristian Moller, Frank Sundler
Cutaneous field stimulation is used to treat localized itch. The aim of the present study was to determine whether such treatment induces neurochemical changes in the dorsal root ganglia in 30 rats using a pan-neuronal marker protein gene-product 9.5 (PGP 9.5) and calcitonin gene-related peptide (CGRP). Electrical stimulation using the currents of either 0.13 mA or 0.53 mA was given under general anaesthesia for 30 min per day for 10 days. Punch biopsies from the thoracal skin and the corresponding dorsal root ganglia were collected upon sacrifice. Both stimulation regimens induced proliferation of epidermal and dermal nerve fibers in the skin. The mean number of all cutaneous PGP-immunoreactive (IR) nerve fibers after the electrical stimulation with 0.13 mA was increased by 49% (p<0.001), the mean number of epidermal PGP-IR nerve fibers was increased by 25% (p=0.001) and the mean number of all CGRP-IR nerve fibers was increased by 65% (p<0.001) compared with controls. The mean number of all PGP-IR nerve fibers after the electrical stimulation with 0.53 mA was increased by 39% (p<0.001), the mean number of PGP-IR epidermal nerve fibers was increased by 30% (p=0.001) and the mean number of CGRP-IR nerve fibers was increasd by 65% (p<0.001) compared with controls. Only stimulation with 0.53 mA induced an up-regulation of sensory neuron markers in the dorsal root ganglia. The ratio of positive/negative PGP-IR cells was increased by 17% (p=0.002), the ratio of positive/negative CGRP-IR cells was increased by 12% (p=0.003) and the ratio of positive/negative VR1-IR cells was likewise increased by 10% (p=0.008) as compared with the control ganglia. We conclude that serial cutaneous electrical stimulation by a moderate current in rat does not induce neurochemical changes in the dorsal root ganglia.