Histamine sensitive intrinsic cardiac and intrathoracic extracardiac neurons influence cardiodynamics. Armour, J. A. Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia
APStracts 2:0307R, 1995.
Studies were performed to determine whether: 1) histamine can modify the spontaneous activity of mammalian intrinsic cardiac neurons in situ, 2) histamine sensitive neurons exist in intrathoracic intrinsic cardiac and extracardiac ganglia which are involved in cardiac regulation, and 3) histamine sensitive intrathoracic cardiac neurons possess H1 or H2 receptors. Histamine (10 [mu]l; 100 [mu]M) when applied adjacent to spontaneously active canine right atrial neurons in situ increased ongoing activity of some of them. Histamine when administered into the local arterial blood supply of these neurons (0.1 ml; 100 [mu]M) not only increased their activity, but induced cardiac augmentation. Cardioaugmentor responses were also elicited when histamine (10 [mu]l or 0.1 ml; 100 [mu]M) was administered into limited loci within stellate and middle cervical ganglia which were connected to the heart, but not in ganglia surgically disconnected from the heart. Neuronal and cardiac responses no longer were elicited following local administration of the H1-selective receptor antagonist triprolidine. They were unaffected by local application of the H2-selective receptor antagonist cimetidine. No cardiac augmentation was elicited when histamine was applied to intrathoracic autonomic neurons following timolol (1 mg/kg iv) administration. These data indicate that: 1) histaminergic neurons exist in intrinsic cardiac and intrathoracic extracardiac ganglia which are involved in cardiac regulation, 2) these neurons possess H1 receptors and 3) histamine-sensitive intrathoracic neurons directly or indirectly activate cardiac adrenergic neurons thereby inducing cardiac augmentation. 

Received 10 May 1995; accepted in final form 1 November 1995.
APS Manuscript Number R280-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95