Intracellular recording from cardiac ganglion neurons receiving functional vagal inputs

Abstract

Cardiac vagal tone is an important indicator of cardiovascular health, and its loss is an independent risk factor for arrhythmias and cardiac mortality. Thus, it is important to elucidate the factors that modulate cardiac vagal ganglionic transmission. Using the working heart‐ brainstem preparation (Paton 1996, J.Neurosci Meth. 65, 63‐), we report the first intracellular recordings from functionally connected cardiac vagal ganglion cells in situ. The atria were dissected from the ventricles, pinned out, stabilized with a nylon mesh foot, and ganglion cells (n=33) were impaled with sharp microelectrodes (0.5M KCl; 80‐120 MOhm). Spontaneous EPSPs and action potentials (AP) occurred most commonly in post‐inspiration. Activation of bradycardic reflexes (baro‐, chemo‐, nasotrigeminal) increased dramatically EPSP frequency producing AP and atrial rhythm slowing. Spontaneous and reflexly‐evoked AP were mostly triggered by suprathreshold unitary EPSPs rather than by summation of subthreshold EPSPs. Stimulation of the right cervical vagus evoked EPSPs with a latency of 30‐40 ms. Thus, it is possible to record intracellularly from functionally intact cardiac vagal ganglion cells, which exhibit appropriate patterns of ongoing and reflex excitatory synaptic drives. Future studies will elucidate how cardiac vagal transmission may be modified in health and disease.RMcA holds an NHMRC Principal Research Fellowship; JFRP holds a Royal Society Wolfson Research Merit Award; AEP is a Wellcome Trust Advanced Clinical Fellow