Neuronal plasticity in the cingulate cortex of rats following esophageal acid exposure in early life.

Abstract

The cingulate cortex has been reported to be involved in processing pain of esophageal origin. However, little is known about molecular changes and cortical activation that arise from early-life esophageal acid reflux. Excitatory neurotransmission via activation of the N-methyl-d-aspartate (NMDA) receptor and its interaction with postsynaptic density protein 95 (PSD-95) at the synapse appear to mediate neuronal development and plasticity. We investigated the effect of early-life esophageal acid exposure on NMDA receptor subunits and PSD-95 expression in the developing cingulate cortex. We assessed NMDA receptor subunits and PSD-95 protein expression in rostral cingulate cortex (rCC) tissues of rats exposed to esophageal acid or saline (control), either during postnatal day (P) 7 to 14 and/or acutely at adult stage (P60) using immunoblot and immunoprecipitation analyses. Compared with controls, acid exposure from P7 to P14 significantly increased expression of NR1, NR2A, and PSD-95, measured 6 weeks after exposure. However, acute exposure at P60 caused a transient increase in expression of NMDA receptor subunits. These molecular changes were more robust in animals exposed to acid neonatally and rechallenged, acutely, at P60. Esophageal acid exposure induced calcium calmodulin kinase II-mediated phosphorylation of the subunit NR2B at Ser1303. Esophageal acid exposure during early stages of life has long-term effects as a result of phosphorylation of the NMDA receptor and overexpression in the rCC. This molecular alteration in the rCC might mediate sensitization of patients with acid-induced esophageal disorders.