Basis for differential coupling between rhythmic discharges of sympathetic efferent nerves

The relationships between activities of three sympathetic efferents [vertebral (VN); cardiac (CN); and renal nerves (RN)] of 45 chloralose-urethan anesthetized cats were investigated using multivariate spectral analysis. The multiple coherences measuring the extent to which one nerve signal may be predicted from the other two were very high (0.77-0.83) at the peak frequency of synchronized rhythmic activity, indicating that specific components comprised < 20% of the power in the nerve signals. The pattern of sympathetic activity was characterized by the partial coherences calculated for different nerve pairs after the components common for all three nerve signals were removed. In baroreceptor-intact cats, partialization on the CN signal drastically reduced the coherences between the VN and RN (0.25), whereas the coherences between the CN activity and either of the vasoconstrictors remained high after partialization on the other vasoconstrictor (0.52 and 0.43). In baroreceptor-denervated cats, partial coherence was high between vertebral and cardiac nerves (0.52) and low between renal and any other nerve discharge (0.19-0.20). In individual experiments, five different patterns of coupling were observed, and their separation was tested by cluster analysis.