title: Cardiac receptors with non-medullated vagal afferents in the rat.
abstract: The characteristics of 22 atrial receptors in 15 normotensive adult male Wistar rats were investigated. All the receptor afferents were included in the C-fibre group with conduction velocities from 0.4 to 1.2 m/sec. No atrial medullated receptors or ventricular C-fibre endings were found. Two receptors were located in right atrium and 2 receptors throughout left atrium. Upon elevation of the left atrial pressure the receptor discharge was markedly elevated with thresholds from 2.5 to 9 mmHg in mean left atrial pressure. Ten of the atrial receptors displayed a clear cardiac rhythmicity upon activation and the discharge correlated with the v-wave, indicating distension as the cause of receptor activation. The maximal firing rate in most receptors was very high (up to 70 Hz), but 8 receptors had maximal firing rates below 25 Hz. These low frequency receptors had higher threshold and showed a more irregular firing. Thus, there is a substantial population of atrial receptors with vagal non-medullated afferents in the rat heart and the thresholds for many of these receptors are so low that they are likely to be active during normal conditions.
mesh_terms: D000818:Animals; D001794:Blood Pressure; D004558:Electric Stimulation; D006325:Heart Atria / Q000294:innervation*; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology*; D009200:Myocardial Contraction; D009412:Nerve Fibers / Q000502:physiology; D009431:Neural Conduction; D009475:Neurons, Afferent / Q000502:physiology*; D051381:Rats; D014630:Vagus Nerve / Q000502:physiology*