Bimodality of cardiac vagal afferent C-fibres in the rat

Abstract

Vagal afferent C-fibres from the heart constitute an important input to the neurogenic cardiovascular regulation. These fibres respond to altered cardiac filling pressures and to chemical stimuli. In rats, we tested whether cardiac vagal afferent C-fibres react exclusively to one stimulus (chemical or mechanical) or whether the fibres are bimodal, i.e. responsive to either kind of stimulus. As a mechanical stimulus, an indwelling balloon was inflated in the aorta to increase left ventricular end-diastolic pressure. The serotonin 5HT(3) receptor agonist phenylbiguanide was injected into the pericardial sac as a chemical stimulus. An increase of fibre activity by more than two standard deviations compared with control was considered a response to a stimulus. Most fibres (42 out of 57) responded to both stimuli and were categorized as bimodal, 9 fibres were solely mechanosensitive and 6 were solely chemosensitive. Hence, the majority of cardiac vagal C-fibres are likely to be bimodal, responding to both cardiac filling pressure and serotonin 5HT(3) receptor stimulation. Our results emphasize the potential role of endogenous mediators in the afferent limb of cardiac reflexes.

Do distinct populations of dorsal root ganglion neurons account for the sensory peptidergic innervation of the kidney?

“…In general, sensory neurons innervating inner organs are composed mainly of the peptidergic subpopulation of B-type primary afferent neurons (22,35). The group of neurons with medium size and capacity likely to be polymodal and hence responsible for mechano-and chemoception (15,34) is thus probably linked mainly to C fibers. In this group, renal neurons were not only more sensitive to acidic stimulation in terms of action potential generation than neurons with projections from other, nonrenal sites but showed also higher membrane currents after acidic receptor stimulations with protons, which was the case for TRPV1-as well as for ASIC-mediated currents, as shown by use of the respective channel blockers capsazepine and amiloride.…”

Mechanosensitive cardiac C-fiber response to changes in left ventricular filling, coronary perfusion pressure, hemorrhage, and volume expansion in rats

“…On the other hand, acute and graded aortic obstruction used to increase LVEDP by some investigators increased cardiac vagal afferent nerve activity in single-unit recording experiments (31,47). Thus volume expansion or alternative measures able to increase LVEDP, i.e., to simulate central volume loading, increase cardiac vagal mechanosensory activity.…”

“…Within the nodose ganglion-where the cell bodies of these first-order sensory axons reside-mechanosensory information is relayed to the second neuron, traveling to the brain stem to be integrated. As a consequence, sympathetic nervous output is decreased to restore the baseline volume state (44,47).…”

“…Within the nodose ganglion-where the cell bodies of these first-order sensory axons reside-mechanosensory information is relayed to the second neuron, traveling to the brain stem to be integrated. As a consequence, sympathetic nervous output is decreased to restore the baseline volume state (44,47).In rats, RSNA suppression due to volume load can be abolished by bilateral cervical vagotomy (Vx) (23, 44). In rabbits, it was shown that selective blockade of cardiac afferents by intrapericardially administered procaine abolished volume-induced renal sympathoinhibition as seen with Vx or when Vx was combined with sinoaortic denervation (3).…”

Effects of anoxia, aglycemia, and acidosis on cytosolic Mg2+, ATP, and pH in rat sensory neurons

“…SENSORY NEURONS from the cervico-thoracic dorsal root ganglia (DRG) and vagal afferent nerve fibers originating from the nodose ganglion (NG) play a major role in the transmission of ischemic pain from the heart and other organs (3,5,7,13,30,72,75). Sensory neurons can be excited by a variety of pathophysiological stimuli (3,4,17,30,34), but under ischemic conditions it is thought that the primary stimulus is the intense acidosis that results from anaerobic respiration (5,12,31,38,40,41,46,53).…”