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

Skin bloodflow on the rat's paws using laser Doppler flowmeter, electrical activity of the heart (ECG) and respiration were measured simultaneously. T he signals were recorded for 20 minutes, both before and after denervatiron , 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, we re transected. Experiments were performed on 15 adult Wistar rats under gen eral 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 blo od flow spectrum. They correspond to the main peaks in the spectra of the E CG (around 3.3 Hz) and respiration (around 1.3 Hz). Several additional peak s were observed in the low frequency region, from 0.01 to 0.7 Hz, in all me asured signals. In this frequency region the relative energy contribution o f the blood flow oscillations decreased after denervation only in the dener vated left hind paw. This difference was not statistically significant at 3 7 degrees C (p=0.098, Kruskal-Wallis test) but became statistically signifi cant 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 flo w of the denervated paw. Within this region the relative energy contributio n decreased significantly in two intervals, from 0.01 to 0.08 Hz and fi-om 0.08 to 0.2 Hz (p = 0.023). In the higher frequency region, from 0.7 to 5 H z, o statistically significant differences were obtained in any paws when c ompared before and after denervation at the same core temperature. We concl ude that the activity of lumbar sympathetic neurones contributes to low fre quency skin blood flow oscillations.