Vagus Nerve Stimulation and Brainstem Cholinergic Neurons Modulate Experimental Pancreatitis Severity

Abstract

The nervous system maintains physiological homeostasis through neural reflex circuits that regulate organ function. A prototypical neural pathway is the inflammatory reflex, where action potentials originating in the cholinergic neurons residing in the brainstem dorsal motor nucleus (DMN) and transmitted in the vagus nerve inhibit production of inflammatory cytokines. Pancreatitis is an inflammatory condition leading to a significant risk of morbidity and mortality. Vagotomy or inhibition of vagus nerve mediated signaling result in an enhanced severity of experimental pancreatitis, although the function of vagus nerve signaling and DMN neurons in regulating inflammatory response and severity of pancreatitis is not known. Here, we show that vagus nerve stimulation (VNS) and optogenetic stimulation of DMN cholinergic neurons improve disease severity in acute pancreatitis assessed by serum amylase. Vagus nerve stimulation using a bipolar nerve cuff electrode (2 minutes, 300 mA, square, biphasic pulse, 250 uS phases, 50 uS interphase, 10 Hz) decreases circulating amylase levels as compared to sham stimulated controls (VNS vs sham: 3270 mU/mL ± 192.5 vs 4138 mU/mL ± 307.6, p = 0.0219; n = 10; mean ± S.E.M.). To selectively activate the cholinergic neurons in the DMN, we utilized ChAT-ChR2 transgenic mice that express the photoreactive ion channel, channel rhodopsin (ChR2), on cholinergic neurons, rendering them sensitive to 473 nm light. Selective optogenetic activation of DMN cholinergic neurons (5 minutes, 20 Hz, 25% duty cycle, 8-12 mW total power) significantly decreases circulating levels of amylase as compared to sham-stimulated controls (DMN vs sham stimulation: 2940 mU/mL ± 170.9 vs. 4043 mU/mL ± 264.4, p = 0.0074; n = 10 mice/group). Together, these results indicate activation of the inflammatory reflex, by stimulation of the cervical vagus nerve or DMN cholinergic neurons, is sufficient to attenuate the severity of caerulein-induced pancreatitis.