The α isoform of cGMP‐dependent protein kinase 1 (PKG1α) is expressed and functionally important in intrinsic primary afferent neurons of the guinea pig enteric nervous system

Background Intrinsic primary afferent neurons (IPANs) enable the gut to manifest reflexes in the absence of CNS input. PKG1α is selectively expressed in a subset of neurons in dorsal root ganglia (DRG) and has been linked to nociception and long‐term hyperexcitability. Methods We used immunoblotting, immunocytochemistry, and in vitro assays of IPAN‐dependent enteric functions to test hypotheses that subsets of primary neurons of the ENS and DRG share a reliance on PKG1α expression. Key Results PKG1α immunoreactivity was demonstrated in immunoblots from isolated myenteric ganglia. PKG1α, but not PKG1β, immunoreactivity, was coincident with that of neuronal markers (HuC/D; β3‐tubulin) in both enteric plexuses. PKG1α immunoreactivity also co‐localized with the immunoreactivities of the IPAN markers, calbindin (100%; myenteric plexus) and cytoplasmic NeuN (98 ± 1% submucosal plexus). CGRP‐immunoreactive DRG neurons, identified as visceral afferents by retrograde transport, were PKG1α–immunoreactive. We used intraluminal cholera toxin to determine whether PKG1α was necessary to enable stimulation of the mucosa to activate Fos in enteric neurons. Tetrodotoxin (1.0 µM), low Ca2+/high Mg2+ media, and the PKG inhibitor, N46 (100 µM), all inhibited Fos activation in myenteric neurons. N46 also concentration dependently inhibited peristaltic reflexes in isolated preparations of distal colon (IC50 = 83.3 ± 1.3 µM). Conclusions & Inferences These data suggest that PKG1α is present and functionally important in IPANs and visceral afferent nociceptive neurons. Intrinsic primary afferent neurons (IPANS) in each plexus of the enteric nervous system (ENS) express protein kinase G1a (PKG1a). These cells are important in the transduction of mucosal stimuli into activation of the ENS and thus initiation of peristaltic reflexes. Addition of cholera toxin (CTX) to the GI lumen stimulates the mucosa to release paracrine mediators such as 5‐HT to activate IPANs. The PKG1a‐selective antagonist, N46, inhibits the output of IPANs and thus the activation of the ENS and initiation of peristaltic reflexes.