Low and high frequency non-linear interactions in the sympathetic discharge: contribution of spinal centers

When biological oscillators interact as a result of nonlinear mechanisms several phenomena such as period doubling, phase locking, complex and irregular behaviors may occur. These behaviors depend on the degree of the coupling among the rhythmic generators and on the amplitude and frequency of the relevant oscillations. In decerebrate artificially ventilated cats low (around 0.1 Hz) and high (around 0.3 Hz) frequency rhythms present in the preganglionic efferent sympathetic activity directed to the heart are affected by forced periodical ventilation. These interactions result in various ratios between sympathetic discharge and ventilatory cycles (1:1, 1:2, 1:3, 1:4 and lower). After spinal section, as a consequence of the reduction of the coupling between central oscillators, external ventilation and sympathetic activity, irregular behaviors including broad band patterns, weak low frequency rhythms and period-three periodicities are classified.