Fastigial nucleus stimulation and excitatory spinal sympathetic activity in dog.

To locate the cerebellar-activated descending sympathetic pathways in the dog the fastigial nucleus (FN) was electrically stimulated in chloralose-anesthetized dogs while recording from sympathetic preganglionic neurons. Physiological interventions included lesions in the dorsolateral funiculus (DLF) of the spinal cord, myelotomy, arterial pressure changes, bilateral occlusion of the carotid arteries, and administration of clonidine. Multiunit activity at the T2 on T3 white ramus communicans was recorded on-line during rest and FN stimulation. Descending sympathetic activity (averaging 3.5 m/s) in the DLF was increased in response to FN stimulation but was significantly reduced by ipsilateral and eliminated by bilateral FN lesions. When testing for the effects of baroreceptor reflexes on the sympathetic pathway phenylephrine-induced hypertension decreased, but moderate hemorrhage increased the amount of preganglionic activity at rest and during FN stimulation. During hypertension and simultaneous carotid artery occlusion the amount of sympathetic activity that could be evoked was comparable to that evoked during normotensive states. Clonidine (IV) reduced the FN sympathoexcitation, but direct stimulation of the DLF indicated that clonidine had sympathoinhibitory activity at both medullary and spinal sites. In summary, rostral FN primarily excited ipsilateral descending sympathetic pathways in DLF, and this sympathoexcitation was partially inhibited by baroreceptor intervention.

Neural control of the heart during arrhythmias and exercise.

Involvement of neural activity during cardiovascular adjustments and during arrhythmias can be determined by comparing the results of cardiovascular changes after lesions are made in nuclei or pathways of the central nervous system or ablations of ganglia or nerves are made in the peripheral nervous system. The neural effects can be exaggerated if these systems are forced to perform at higher levels during a stressful situation. The purpose of this presentation is to discuss the responsiveness of the cardiovascular system after left or right stellate ganglionectomy and after lesions are made in the fastigial nucleus of the cerebellum in dogs stressed with submaximal exercise. These dogs are implanted with instruments that are designed to measure cardiovascular responses. Hypotheses for potential neural mechanisms are generated from the results of chronic animal studies, and these mechanisms are tested in anesthetized dogs and cats. Electrical stimulation of ascending and descending pathways in the central nervous system and stimulations such as coronary occlusion and mechanical probing are used to activate neural mechanisms in the anesthetized state. A general schema concerning the results of our studies provides further information about our approach to understanding the physiological role that the central nervous system may exert on the cardiovascular system during stress.

Effects of coronary artery occlusion on thoracic spinal neurons receiving viscerosomatic inputs.

Action potentials of single cells in the gray matter of the T2 to T4 spinal segments of chloralose-anesthetized cats were recorded during occlusion of the anterior descending branch of the left coronary artery. Only cells responding both to visceral and somatic afferent inputs were examined. In 53% of the cells the discharge frequency was unaffected by coronary artery occlusion (CAO). The remaining 47% could be classified by four response patterns: 1) in 18% frequency increased immediately following the onset of CAO; 2) in 22%, frequency increased 13.6 +/- 3.3 (SE) s after CAO and the increased frequency usually was associated with changes in the configuration of the electrocardiogram; 3) in 3%, frequency increased at the onset of CAO and then increased more approximately 11 s later; 4) in 4%, inhibition of spontaneous activity occurred during CAO. A noxious pinch applied to the somatic receptive field maximally excited 94% and inhibited 6% of the cells. Since viscerosomatic convergence provides a basis for referred pain, these cells could potentially be involved with transmission of nociceptive information to regions of the brain that integrate pain sensations.