Sympathetic rhythms in spinal cats.

Simultaneous recordings from preganglionic sympathetic nerves at different spinal levels, cervical sympathetic and greater splanchnic, reveal the presence of common periodicities as shown by cross-correlation and power spectral analysis; the major types of periodicities are cardiac, respiratory and 10/sec rhythm. These common periodicities could be explained in two ways: (1) there are common periodic inputs to the two types of preganglionic neurons; and (2) there are feedback connections in the spinal cord between the two groups of neurons. To distinguish between these two possibilities, spinal cord transections at C2-C3 were performed on decerebrate unanesthetized cats; recordings were then taken at hourly intervals for more than 12 h, during which time activity gradually increased but still remained small compared to pre-section levels. This low level activity showed no sign of periodicity. Asphyxia of sufficient duration produced increased activity in sympathetic nerves. Splanchnic activity during asphyxia had 2-3/sec oscillations; but the cross-correlation histograms (CCHs) of cervical sympathetic and splanchnic activity were almost flat. Strychnine excited spinal cord neurons more effectively than asphyxia; the CCHs showed locking of activity in phrenic, cervical sympathetic and splanchnic nerves on a slow time-scale (1-5 sec), but no appreciable locking of cervical sympathetic and splanchnic activity on a faster time-scale (100-500 msec) such as occurs in the intact animal. Thus, while there can be oscillation of sympathetic activity at the spinal cord level, the normally occurring synchrony of oscillations between different segmental levels is dependent on inputs from the brain stem.