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

Abstract

Although interleukin-1β (IL-1β) administration produces nonuniform changes in the level of sympathetic nerve discharge (SND), the effect of IL-1β 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-1β and mild hypothermia (60 min after IL-1β, 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-1β did not alter renal-IBAT coherence values in the 0- to 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-1β and during hypothermia. 3) Hypothermia after IL-1β significantly reduced the coupling (0–2 Hz and CF) between renal-IBAT but not splenic-lumbar SND bursts. 4) Combining IL-1β and mild hypothermia had a greater effect on renal-IBAT 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.