A technique for estimating activity in whole nerve trunks applied to the cervical sympathetic trunk, in the rabbit

The changes in sympathetic outflow may be evaluated from the amplitude of t he antidromic compound action potential (ACAP) according to the collision t echnique described by Douglas and Ritchie (Douglas, W.W. and Ritchie J.M., A technique for recording functional activity in specific groups of medulla ted and non-medullated fibers in whole nerve trunks. J. Physiol., 138 (1957 ) 19-30). This technique was revised, taking into account the depressant ac tion exerted by antidromic stimulation on sympathetic preganglionic neurone s (SPNs). Cervical sympathetic nerve (CSN) of rabbits was used as experimen tal model. Stimulation frequencies of 0.2-0.5 Hz were found to be sufficien tly low to avoid depressant actions on CSN spontaneous activity; they were employed to test the sensitivity of the technique during different experime ntal manoeuvres, such as changes in pulmonary-ventilation, baroreceptor unl oading and arousal stimuli. In addition a procedure was devised to calibrat e the ACAP amplitude: high frequency antidromic stimulation was used to ind uce a complete and transient inhibition of SPNs which allows to record the ACAP maximum amplitude. ACAPs recorded in various experimental conditions c an then be expressed as percentage of this value. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.