PRIMARY VAGALLY MEDIATED DECELERATIONS IN HEART-RATE DURING TONIC RAPID EYE-MOVEMENT SLEEP IN CATS

Rapid eye movement (REM) sleep results in profound state-dependent alt erations in heart rate. The present study describes a novel phenomenon of a primary deceleration in heart rate that is not preceded or follo wed by increases in heart rate or arterial blood pressure and occurs p rimarily during tonic REM sleep. The goals were to characterize the pr imary decelerations and to provide insights on the underlying central and peripheral autonomic mechanisms. Cats were chronically implanted w ith electrodes to record electroencephalogram, pontogeniculooccipital wave activity in lateral geniculate nucleus, hippocampal theta rhythm, electromyogram, electrooculogram, respiration (diaphragm), and electr ocardiogram. Arterial blood pressure was monitored from a carotid arte ry catheter. R-R interval fluctuations were continuously tracked using customized software. The muscarinic blocking agent glycopyrrolate (0. 1 mg/kg iv) and the beta-adrenergic blocking agent atenolol (0.3 mg/kg iv) were administered in alternating sequence with a 90- to 120-min i nterval. Glycopyrrolate immediately eliminated the decelerations durin g REM sleep. Atenolol alone had no effect on their frequency. These fi ndings suggest that a change in the centrally induced pattern of auton omic activity to the heart is responsible for the primary deceleration s, namely, a bursting of cardiac vagal efferent fiber activity.