Proceedings of The Physiological Society

University of Leeds (2002) J Physiol 544P, S010


Cardiac vagal afferent fibres projecting to nucleus tractus solitarii and cervical spinal dorsal horn in the rat

Eric K.A. Corbett*, Jim Deuchars†, Peter N. McWilliam‡ and Trevor F.C. Batten*

Schools of *Medicine, †Biomedical Sciences and ‡Healthcare Studies, University of Leeds, Leeds LS2 9JT, UK

Vagal afferent fibres from the heart may play a role in reflex control of the circulation in hypertension and heart failure (Hainsworth, 1991) and in conveying nociceptive information associated with ischaemic heart disease (Foreman, 1999). In this study, the central distribution of afferent fibres from the heart was investigated by injecting cholera toxin B-subunit (CTb, 0.02 ml of 1 % aqueous solution) into the pericardium in halothane (95 % in O2) anaesthetised, artificially ventilated adult (250-300 g, n = 10) Wistar rats. After a 10-day recovery period, the rats were humanely killed by perfusion with aldehyde fixatives under halothane anaesthesia, and vibratome sections of the medulla and spinal cord were labelled with mouse, goat or rabbit antibodies to CTb for fluorescence immuno-histochemistry. CTb labelled axons formed en passant and terminal varicosities bilaterally in the nucleus tractus solitarii (NTS), and at caudal levels formed a band in the dorsal part of the commissural subnucleus, in the dorsomedial subnucleus and around the tractus solitarius. At area postrema level, they were prominent in the dorsomedial and interstitial NTS subnuclei, but were sparsely distributed in the medial subnucleus. More rostrally, they maintained the same position, but were markedly reduced in number. Examination in coronal, parasagittal and horizontal planes revealed labelled axons entering the commissural NTS bilaterally, and at progressively more caudal levels these could be followed in bundles laterally to the central canal, from where they radiated along the interface of the dorsal horn with the overlying white matter. Beaded fibres and varicosities were seen surrounding neuronal perikarya in the superficial cervical dorsal horn. The vagal origin of these fibres was confirmed by their elimination on the ipsilateral side in unilaterally vagotomised rats, and by no reduction in their numbers after removal of the sympathetic stellate ganglion. Both these procedures were performed under halothane anaesthesia immediately before injection of CTb. Dual labelling with specific antibodies to vesicular glutamate transporters VGLUT1 and VGLUT2 (Varoqui et al. 2002) suggested that subpopulations of the vagal fibres express VGLUT1 and are glutamatergic in nature.

Our observations are consistent with vagal afferent fibres from the heart having predominantly excitatory central projections terminating in areas of the medulla oblongata and cervical spinal cord that are concerned with both cardiovascular and nociceptive reflex control.

This work was supported by a British Heart Foundation Project Grant .

All procedures accord with current UK legislation.

Where applicable, experiments conform with Society ethical requirements