The role of the paravertebral ganglia in human sympathetic neural discharge patterns

Do the ganglia contribute to the ordered behaviour of postganglionic neuronal discharge within the sympathetic nervous system? To further understand the functional organization of the sympathetic nervous system we employed the microneurographic approach to record muscle sympathetic nerve activity (MSNA) and a continuous wavelet transform to study postganglionic action potential (AP) behaviour during nicotinic blockade at the ganglia (trimethaphan camsylate, 1-7mg min(-1)) in seven females (37 +/- 5 years). Trimethaphan elicited a progressive reduction in sympathetic outflow characterized by fewer integrated bursts with decaying amplitude. Underlying trimethaphan-mediated attenuations in integrated MSNA were reductions in AP incidence (186 +/- 101 to 29 +/- 31 AP(100 beats)(-1)) and AP content per integrated burst (7 +/- 2 to 3 +/- 1 APs burst(-1)) (both P<0.01) in the final minute of detectable bursting activity in the trimethaphan condition, compared to baseline. We observed an ordered de-recruitment of larger to smaller AP clusters active at baseline (14 +/- 3 to 8 +/- 2 active AP clusters, P<0.01). Following cessation of integrated bursts in the trimethaphan condition, the smallest 6 +/- 2 sympathetic AP clusters persisted to fire in an asynchronous pattern (49 +/- 41AP (100 beats)(-1)) in all participants. Valsalva's manoeuvre did not increase the incidence of these persistent APs (60 +/- 42 AP(100 beats)(-1), P=0.52), or recruit any larger APs in six of seven participants (6 +/- 1 total AP clusters, P=0.30). These data suggest that the ganglia participate in the ordered recruitment of differently sized postganglionic sympathetic nerves.