Baroreceptor influence on the relationships between discharges of different sympathetic nerves of the cat

1. The sympathetic nerve discharge (SND) of three different nerves and the arterial blood pressure (BP) were recorded simultaneously in baroreceptor-intact cats. The linear correlation between different nerve pairs was characterized by the coherence spectrum and its baroreceptor-related component was estimated by partialization of the coherence on the basis of the blood pressure signal. 2. The SND-SND coherence values were higher than those found earlier in baroreceptor-denervated cats. As shown by partial coherence analysis, in about 50% of the experiments with high SND-BP coherence (25 nerve pair recordings), this could be explained by superposition of the effects of common central sources of activity and of the additional common rhythmic input from the baroreceptors. Partialization was ineffective in 50% of the experiments with high SND-BP coherence (22 nerve pairs) and also when the SND-BP coherence was relatively low (17 nerve pairs). On the group average, after elimination of the components explained by baroreceptor influence, the peak SND-SND coherence no longer correlated with the SND-BP coherence and both the numerical values and the relative pattern of coherences between different nerves became similar to those characteristic for baroreceptor-denervated cats. 3. It is suggested that the method used in this study represents a 'theoretical barodenervation' and may be of great value in experiments, when surgical or chemical denervation of the baroreceptors does not represent a real option, e.g. in human subjects.