Viscerofugal neurons recorded from guinea-pig colonic nerves after organ culture
Article first published online: 19 JUL 2012
© 2012 Blackwell Publishing Ltd
Neurogastroenterology & Motility
Volume 24, Issue 11, pages 1041–e548, November 2012
How to Cite
Hibberd, T. J., Zagorodnyuk, V. P., Spencer, N. J. and Brookes, S. J. H. (2012), Viscerofugal neurons recorded from guinea-pig colonic nerves after organ culture. Neurogastroenterology & Motility, 24: 1041–e548. doi: 10.1111/j.1365-2982.2012.01979.x
- Issue published online: 11 OCT 2012
- Article first published online: 19 JUL 2012
- Received: 3 May 2012 Accepted for publication: 6 June 2012
- enteric nervous system;
- organotypic culture;
Background Enteric viscerofugal neurons provide cholinergic synaptic inputs to prevertebral sympathetic neurons, forming reflex circuits that control motility and secretion. Extracellular recordings of identified viscerofugal neurons have not been reported.
Methods Preparations of guinea pig distal colon were maintained in organotypic culture for 4–6 days (n = 12), before biotinamide tracing, immunohistochemistry, or extracellular electrophysiological recordings from colonic nerves.
Key Results After 4–6 days in organ culture, calcitonin gene-related peptide and tyrosine hydroxylase immunoreactivity in enteric ganglia was depleted, and capsaicin-induced firing (0.4 μmol L−1) was not detected, indicating that extrinsic sympathetic and sensory axons degenerate in organ culture. Neuroanatomical tracing of colonic nerves revealed that viscerofugal neurons persist and increase as a proportion of surviving axons. Extracellular recordings of colonic nerves revealed ongoing action potentials. Interestingly, synchronous bursts of action potentials were seen in 10 of 12 preparations; bursts were abolished by hexamethonium, which also reduced firing rate (400 μmol L−1, P < 0.01, n = 7). DMPP (1,1-dimethyl-4-phenylpiperazinium; 10−4 mol L−1) evoked prolonged action potential discharge. Increased firing preceded both spontaneous and stretch-evoked contractions (χ2 = 11.8, df = 1, P < 0.001). Firing was also modestly increased during distensions that did not evoke reflex contractions. All single units (11/11) responded to von Frey hairs (100–300 mg) in hexamethonium or Ca2+-free solution.
Conclusions & Inferences Action potentials recorded from colonic nerves in organ cultured preparations originated from viscerofugal neurons. They receive nicotinic input, which coordinates ongoing burst firing. Large bursts preceded spontaneous and reflex-evoked contractions, suggesting their synaptic inputs may arise from enteric circuitry that also drives motility. Viscerofugal neurons were directly mechanosensitive to focal compression by von Frey hairs.