Abstract
Electrical activity of sympathetic preganglionic neurons in the upper thoracic cord of anesthetized cats was recorded with extracellular microelectrodes. The neurons were identified by their antidromic response to stimulation of the ipsilateral sympathetic cervical nerve. Of a total of 210 units observed, only 44 (21%) were spontaneously active. The discharge pattern was "regular" in 7%, "bursty" in 15%, and "irregular" in 78% of the units. The mean discharge rate was 1.4 spikes/s (range 0.1–5.6) and in any one cell changed little with time. Most spike trains showed a lack of short (i.e. less than 100 ms) interspike intervals. Interpolation of an antidromic impulse in the "regular" spike trains caused a resetting of the rhythm, thus suggesting that the rhythm is endogenous to the sympathetic preganglionic neuron itself. Spontaneous activity was observed in a decentralized, deafferented segment of spinal cord, thus suggesting that the activity can be autochthonous. Injection of a pressor drug resulted in a transient depression of the rate of spontaneous firing. Hemorrhage caused a transient increase of the rate of firing in some units, in others a transient decrease or complete arrest.
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