1. The present paper deals with the central mechanisms responsible for the defence-like differential pattern of spinal sympathetic outflow elicited by electrical activation of the midbrain periaqueductal grey (PAG) in urethane-anaesthetized, baroreceptor-denervated cats. The pattern is characterized by increases in the 10 Hz discharges of the inferior cardiac (CN) and renal (RN) sympathetic nerves and a decrease in 10 Hz activity of the vertebral sympathetic nerve (VN) that supplies vasoconstrictor outflow to the forelimb. 2. The model used to explain this pattern is based on the self-organizing properties of a system of coupled brainstem oscillators rather than the activation of point-to-point hard-wired connections leading to increases in sympathetic outflow to some targets and decreases to others. 3. The fact that VN 10 Hz activity was inhibited by PAG stimulus frequencies equal to or just above, but not just below, that of the free-running (control) rhythm argues against a 'hard-wired' model. 4. The evidence supporting the hypothesis that the defence-like pattern is an emergent property of a system of coupled oscillators includes changes in the phase lag of VN 10 Hz activity relative to that in the CN, temporal correlation of the changes in phase angle and 10 Hz powers and the direct relationship between the magnitude of the change in phase angle and the degree to which PAG stimulation reciprocally affected the 10 Hz discharges of the CN and VN. 5. It is proposed that changes in phase angle reflect the reorganization of the coupling of 10 Hz oscillators and that such changes in state lead to differential patterns of spinal sympathetic outflow.

Adrenergic Fibers↗

PubMedDate not supplied

The functional significance of the 10-Hz sympathetic rhythm: a hypothesis.

This paper reviews work from our laboratory on the 10-Hz rhythm in sympathetic nerve discharge of the cat and offers a hypothesis on its functional significance. The rhythm is ubiquitous to the discharges of sympathetic nerves with different cardiovascular targets and arises from a system of coupled nonlinear brain stem oscillators, each of which has a selective relationship with a different portion of the spinal sympathetic outflow. The 10-Hz rhythmic discharges of sets of sympathetic nerves are differentially related and the pattern of relationships in one experiment can be the reverse of that in the next. We hypothesize that nonuniform and dynamic coupling of the central circuits controlling different sympathetic nerves is the basis for the formulation of complex cardiovascular response patterns that include differential changes in regional blood flows.

Animals↗