Altered frequency responses of sympathetic nerve discharge bursts after IL-1 and mild hypothermia

Kenney, M. J., F. Blecha, R. J. Fels, and D. A. Morgan. Altered frequency responses of sympathetic nerve discharge bursts after interleukin-1 and mild hypothermia. J Appl Physiol 93: 280–288, 2002. First published April 5, 2002; 10.1152/japplphysiol.01250.2001.—Although interleukin-1 (IL-1 ) administration produces nonuniform changes in the level of sympathetic nerve discharge (SND), the effect of IL-1 on the frequency-domain relationships between discharges in different sympathetic nerves is not known. Autospectral and coherence analyses were used to determine the effect of IL-1 and mild hypothermia (60 min after IL-1 , colonic temperature from 38°C to 36°C) on the relationships between renal-interscapular brown adipose tissue (IBAT) and splenic-lumbar sympathetic nerve discharges in chloralose-anesthetized rats. The following observations were made. 1) IL-1 did not alter renal-IBAT coherence values in the 0to 2-Hz frequency band or at the cardiac frequency (CF). 2) Peak coherence values relating splenic-lumbar discharges at the CF were significantly increased after IL-1 and during hypothermia. 3) Hypothermia after IL-1 significantly reduced the coupling (0–2 Hz and CF) between renalIBAT but not splenic-lumbar SND bursts. 4) Combining IL-1 and mild hypothermia had a greater effect on renalIBAT SND coherence values than did mild hypothermia alone. These data demonstrate functional plasticity in sympathetic neural circuits and suggest complex relationships between immune products and SND regulation.