Viscerofugal neurons recorded from guinea-pig colonic nerves after organ culture.

Hibberd, T. J.; Zagorodnyuk, V. P.; Spencer, N. J.; Brookes, S. J. H.

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 −4 mol L−1) evoked prolonged action potential discharge. Increased firing preceded both spontaneous and stretch-evoked contractions (χ2 = 11.8, df = 1, P 2 -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.

NEURONS; GUINEA pigs as laboratory animals; COLON physiology; ORGAN culture; INTESTINAL infections

Neurogastroenterology & Motility, 2012, Vol 24, Issue 11, p1041

1350-1925

Academic Journal

10.1111/j.1365-2982.2012.01979.x