Effects of prolonged exposure to histamine on guinea pig intestinal neurons

Intracellular microelectrodes were used to study the effects of prolonged exposure to histamine on the electrophysiological behavior of AH/type-2 neurons in the myenteric plexus of the guinea pig small intestine. Application of histamine activated H2 receptors to convert the neurons to a heightened state of excitability. Heightened excitability was evident as repetitive spike discharge made possible, in part, by suppression of postspike after-hyperpolarization. The hyperexcitable state persisted unchanged for prolonged periods of 4.5 hr in the continued presence of histamine, suggesting that desensitization may never occur in vivo. The results are interpreted as a neural correlate for the pathophysiology associated with microscopic colitis and other inflammatory conditions involving mast cell hyperplasia.