Activation of CRF1 receptors expressed in brainstem autonomic nuclei stimulates colonic enteric neurons and secreto-motor function in male rats

Abstract

Background: Hypothalamic corticotropin-releasing factor (CRF) receptor 1 (CRF₁ ) plays a role in acute stress-related stimulation of colonic motor function. Less is known on CRF₁ signaling in the brainstem.

Methods: We investigate CRF₁ expression in the brainstem and the colonic response to 4^th ventricle (4V) injection of CRF and urocortin (Ucn) 2 (3 µg/rat) in chronically cannulated male rats.

Key results: Transcripts of CRF₁ wild-type 1a and splice variants 1c, 1e, 1f, 1o along with three novel variants 1a-2 (desK-110 in exon 5), 1p (-exon 7), and 1q (exon 5 extension) were identified in the pons and medulla. The area postrema, nucleus tractus solitarius, dorsal motor nucleus of the vagus, locus coeruleus, and Barrington's nucleus isolated by laser capture microdissection expressed 1a, 1a-2, and 1p but not 1q. Compared to 4V vehicle, 4V CRF induced fecal pellet output (FPO) and diarrhea that were blocked by the CRF antagonist, astressin-B. CRF₂ agonist, Ucn2 had no effect on basal or CRF-induced FPO. CRF actions were correlated with the induction of c-Fos immunoreactivity in myenteric neurons of the proximal and distal colon (pC, dC) and submucosal neurons of dC. c-Fos immunoreactivity occurred in 39% and 37% of myenteric cholinergic and 7% and 58% of nitrergic neurons in the pC and dC, respectively.

Conclusions & inferences: CRF_1a and its splice variants are expressed in brainstem nuclei, and activation of CRF₁ signaling at the level of the brainstem stimulates colonic secretory-motor function through activation of colonic enteric neurons.

Keywords: CRF1 receptor isoforms; brainstem; c-Fos; colon; pChAT; rat; urocortin 2.