Respiratory rhythmicity in the activity of postganglionic neurones supplying the rat tail during hyperthermia

It has been suggested that thermoregulatory stimulation changes respiration -related rhythmicity in the activity of postganglionic sympathetic neurones supplying the rat tail to a distinct modulation independent of respiration . To study this possibility, single and few fibre recordings were made from ten filaments split from the ventral collector nerves of the rat during wh ole body warming. Sympathetic activity was analysed by autocorrelation and phrenic-triggered summation. All neurones except one were gradually inhibit ed and lost their on-going activity above a core temperature of 39-39.5 deg rees C while the frequency of the phrenic bursts increased significantly. D uring hyperthermia, all neurones tested exhibited a prominent respiratory m odulation in their activity which, compared to normothermia, was significan tly increased in strength, or even newly acquired. No other rhythm emerged. These results speak against the hypothesis that in the rat sympathetic pat hways controlling the tail vasculature and thus involved in thermoregulatio n, during hyperthermia become: controlled by central oscillators distinct f rom the respiratory rhythm generator. Rather, respiratory modulation appear s to remain the dominant rhythm as is common for sympathetic neurones suppl ying other cardiovascular targets. (C) 2000 Elsevier Science B.V. All right s reserved.