The cardiac-related rhythm in preganglionic sympathetic activities of developing piglets

This investigation was performed to determine whether partial spectral analysis of preganglionic sympathetic nerve discharges would reveal age-related differences in the distribution of baroreceptor afferent information to brainstem sympathetic-related neurons. Any influence of baroreceptor afferent activity on ordinary spectra of cervical sympathetic and splanchnic nerves was removed by partialization using the arterial blood pressure signal which represented baroreceptor activity. An absence of statistically significant coherence in partialized nerve spectra would indicate that sympathetic-related neurons receive peripheral baroreceptor afferent input, but are not interconnected, whereas the presence of significant coherence would mean that these neurons are interconnected. Ordinary spectral analysis did not demonstrate age-related differences in the relationship between nerve activity and baroreceptor afferent input. In many animals, large peaks, located at cardiac frequencies (range 2.75-5.6 Hz), were noted in ordinary nerve autopower spectra, and were significantly correlated in ordinary coherence spectra. Partialization of nerve spectra eliminated or reduced cardiac-related peaks in autopower spectra regardless of age, and, in 8 of 10 animals, reduced coherence estimates to non-significant values. In two animals, 19 and 36 days old, significant coherence values remained after partialization. These results demonstrated that cardiac-related peaks in coherence in spectra of preganglionic splanchnic and cervical sympathetic nerves were dependent upon peripheral afferent baroreceptor input in most animals. Further, the finding that significant residual coherence was absent in most cases suggested a paucity of intrabulbar pathways connecting brainstem sympathetic-related neurons.