Expression of type 1 corticotropin-releasing factor receptor in the guinea pig enteric nervous system

Reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, electrophysiological recording, and intraneuronal injection of the neuronal tracer biocytin were integrated in a study of the functional expression of corticotropin-releasing factor (CRF) receptors in the guinea pig enteric nervous system. RT-PCR revealed expression of CRF₁ receptor mRNA, but not CRF₂, in both myenteric and submucosal plexuses. Immunoreactivity for the CRF₁ receptor was distributed widely in the myenteric plexus of the stomach and small and large intestine and in the submucosal plexus of the small and large intestine. CRF₁ receptor immunoreactivity was coexpressed with calbindin, choline acetyltransferase, and substance P in the myenteric plexus. In the submucosal plexus, CRF₁ receptor immunoreactivity was found in neurons that expressed calbindin, substance P, choline acetyltransferase, or neuropeptide Y. Application of CRF evoked slowly activating depolarizing responses associated with elevated excitability in both myenteric and submucosal neurons. Histological analysis of biocytin-filled neurons revealed that both uniaxonal neurons with S-type electrophysiological behavior and neurons with AH-type electrophysiological behavior and Dogiel II morphology responded to CRF. The CRF-evoked depolarizing responses were suppressed by the CRF₁/ CRF₂ receptor antagonist astressin and the selective CRF₁ receptor antagonist NBI27914 and were unaffected by the selective CRF ₂ receptor antagonist antisauvagine-30. The findings support the hypothesis that the CRF₁ receptor mediates the excitatory actions of CRF on neurons in the enteric nervous system. Actions on enteric neurons might underlie the neural mechanisms by which stress-related release of CRF in the periphery alters intestinal propulsive motor function, mucosal secretion, and barrier functions.