The contribution of lumbar sympathetic neurones activity to rat's skin blood flow oscillations.

Skin blood flow on the rat's paws using laser Doppler flowmeter, electrical activity of the heart (ECG) and respiration were measured simultaneously. The signals were recorded for 20 minutes, both before and after denervation, at core temperature 37 degrees C and 38.5 degrees C, that was maintained constant during the recordings. Spinal nerve fibres, at the level L3-L4, were transected. Experiments were performed on 15 adult Wistar rats under general anaesthesia. The oscillations in the measured signals were analysed in the time-frequency domain using wavelet transform. On the frequency region from 0.7 Hz to 5 Hz two characteristic peaks were observed in the skin blood flow spectrum. They correspond to the main peaks in the spectra of the ECG (around 3.3 Hz) and respiration (around 1.3 Hz). Several additional peaks were observed in the low frequency region, from 0.01 to 0.7 Hz, in all measured signals. In this frequency region the relative energy contribution of the blood flow oscillations decreased after denervation only in the denervated left hind paw. This difference was not statistically significant at 37 degrees C (p=0.098, Kruskal-Wallis test) but became statistically significant at 38.5 degrees C (p=0.017). Relative energy contribution of the low frequency region, from 0.01 to 0.7 Hz, decreased 2.5-fold in the blood flow of the denervated paw. Within this region the relative energy contribution decreased significantly in two intervals, from 0.01 to 0.08 Hz and from 0.08 to 0.2 Hz (p=0.023). In the higher frequency region, from 0.7 to 5 Hz, o statistically significant differences were obtained in any paws when compared before and after denervation at the same core temperature. We conclude that the activity of lumbar sympathetic neurones contributes to low frequency skin blood flow oscillations.