The Distribution in the Cat Brain Stem of Neurones Activated by Vagal Non‐myelinated Fibres From the Heart and Lungs

Abstract

SUMMARYIn anaesthetized cats, right cardiac vagal branches were electrically stimulated and recordings of evoked 'slow wave' and single neurone activity were made in the brain stem. Short-latency ' slow wave' and multi-neuronal activity evoked by excitation ofmyelinated vagal afferent fibres were recorded in the medial and lateral subnuclei of the nucleus tractus solitarius, the area postrema, the dorsal vagal motor nucleus, the lateral reticular formation and the nucleus ambiguus. Long-latency responses evoked by vagal non-myelinated fibres were recorded in the medial subnucleus of the nucleus tractus solitarius, the area postrema, dorsal vagal motor nucleus, the parahypoglossal area and the lateral reticular formation dorsal to the nucleus ambiguus. A specific study was made ofseventy-two single neurones activated by non-myelinated afferent fibres in the cardiac branch. Thirty-four were shown to be synaptically activated, twenty-one were activated nonsynaptically and seventeen could not be classified. One neurone was also activated by myelinated cardiac afferent fibres, and two by thoracic vagal (including pulmonary) afferent fibres. Neurones were not spontaneously active. Indirect evidence suggests that the majority of the recordings of nonsynaptically activated neurones were likely to be from cell bodies. Neurones were located from the level of the obex to 3*0 mm rostral to it in the medial subnucleus of the nucleus tractus solitarius (45), and in the lateral subnucleus (2), the area postrema and its border with the medial subnucleus of the nucleus tractus solitarius (13), the dorsal vagal motor nucleus (9), the parahypoglossal area (1) and the lateral reticular formation dorsal to nucleus ambiguus (2). Recordings were made from fifteen neurones activated by myelinated fibres in the cardiac vagal branches, and twelve were excited synaptically. The neurones were located in the medial (8) and lateral (3) subnuclei of the nucleus tractus solitarius, the dorsal vagal motor nucleus (1) and the lateral reticular formation (1). Four neurones were also excited by vagal afferent fibres in the thoracic vagal nerve immediately caudal to the caudal cardiac branch.

Cranial Visceral Afferent Pathways through the Nucleus of the Solitary Tract to Caudal Ventrolateral Medulla or Paraventricular Hypothalamus: Target-Specific Synaptic Reliability and Convergence Patterns

“…However, individual afferent axons can branch extensively within NTS (Donoghue et al, 1981;Davies and Kubin, 1986), and some individual afferents deliver multiple terminal contacts onto the soma and proximal dendrites of single second-order NTS neurons (Anders et al, 1993). Such proximal somatodendritic contacts are consistent with other observations (Miller et al, 1983;Kalia and Richter, 1985;Chan et al, 2000;Sekizawa et al, 2003;Doyle et al, 2004).…”

Convergence properties of solitary tract neurones driven synaptically by cardiac vagal afferents in the mouse

“…2) together with the latency difference between evoked synaptic potentials from the vagus nerve and left ventricle is indicative of unmyelinated or C fibre inputs with an estimated conduction velocity of around 0·6 m s¢ (see Results). Previous studies in the cat demonstrated that electrical stimulation of a cardiac branch of the vagus nerve evoked excitatory responses in NTS neurones which were mediated by either myelinated or unmyelinated vagal afferents (Donoghue et al 1981;Bennett et al 1985). The finding that the innervation of the left ventricle is predominantly by unmyelinated vagal fibres in the cat (see Hainsworth, 1991, for review) is consistent with the present observations in mice.…”

“…Intracardiac injections of horseradish peroxidase resulted in dense afferent labelling in the dorsolateral subnuclei around the level of the obex and within the commissural NTS in the cat (Kalia & Mesulam, 1980). In agreement with these observations were the recording sites of NTS neurones responding to electrical stimulation of the cardiac branch of the vagus nerve in the cat (Donoghue, Fox, Kidd & Koley, 1981;Bennett, Goodchild, Kidd & McWilliam, 1985. To date, no attempts have been made to stimulate cardiac receptors using stimuli to excite both chemically and mechanically sensitive cardiac receptors selectively while recording from NTS neurones.…”

“…In addition, the finding of both DIS and DS NTS neurones is consistent with the results of Hines, Toney & Mifflin (1994), who described two populations of NTS neurones responding to either chemical stimulation of cardiopulmonary afferents or mechanical distension of the right atrium. Previous NTS studies were unable to characterize DIS and DS NTS neurones as they only employed electrical stimulation of a cardiac branch of the vagus nerve (Donoghue et al 1981;Bennett et al 1985Bennett et al , 1988Jones et al 1995). Indeed, this study is one of the first (see Hines et al 1994) to selectively stimulate both chemically and mechanically sensitive cardiac receptors to characterize NTS neurones, and, in this regard, the WHBP appears to be a viable preparation for studying the central integration of cardiac vagal afferent inputs.…”

“…The finding that the innervation of the left ventricle is predominantly by unmyelinated vagal fibres in the cat (see Hainsworth, 1991, for review) is consistent with the present observations in mice. Since the cardiac vagal branches in the cat contain afferents from both the ventricles and atria as well as the oesophagus and lungs (Bennett et al 1985), the inputs to NTS described by Bennett et al (1985) and Donoghue et al (1981) might originate from receptors of non-cardiac origin. There are no previous reports describing the response characteristics of NTS neurones during chemical or mechanical stimulation of the left side of the heart.…”