Presence of an Inhibitory Glycinergic Current in Dorsal Motor Nucleus of the Vagus Neurons Regulating Gastric Functions in Offspring of Maternal High Fat Diet Rats
Authors: McMenamin Caitlin , Travagli R. Alberto , Browning Kirsteen 
Published: June 2021

The perinatal period is critically important in the development of autonomic neurocircuits innervating the gastrointestinal (GI) tract influencing gastric emptying and appetite regulation. Maternal overnutrition during this perinatal time period has been shown to predispose offspring to obesity, possibly due to developmental alterations in autonomic neurocircuits. Previous studies suggest there is an increased inhibitory tone of gastric projecting dorsal motor nucleus of the vagus nerve (DMV) neurons of rats fed a maternal high fat diet (HFD), but the underlying mechanisms have yet to be determined. The aims of this study were to assess the effects of a perinatal HFD on (i) inhibitory synaptic inputs to gastric‐projecting DMV neurons and (ii) gastric tone and motility.Whole cell patch clamp recordings (n=6–8 per group) were made from gastric projecting DMV neurons in brainstem slices from Sprague‐Dawley rats (4–6 weeks of age) fed either a control or HFD (14 or 60%kcal from fat, respectively) from embryonic day 13. Gastric motility and tone (n=4–6 rats per group) was measured via miniature strain gauges attached to the antrum and corpus of anesthetized rats.Superfusion of the non‐selective GABAA receptor antagonist, bicuculline (50μM), induced a larger inward current in DMV neurons from maternal HFD vs control animals (44.6±7.9pA vs 21.7±1.7pA; P<0.05). In contrast, inward currents of similar magnitude were evoked in maternal HFD vs control neurons in response to the phasic (synaptic) GABAA receptor antagonist, gabazine (25μM), (10.5±1.0pA vs 8.6±1.4pA); subsequent addition of bicuculline uncovered a larger tonic (extrasynaptic) GABAA current (26.2±2.0pA vs 15.3±1.2pA), suggesting a greater overall inhibition of maternal DMV neurons due to a larger tonic GABAA current. Since bicuculline may be non‐selective at higher concentrations, we investigated whether other inhibitory neurotransmitters were also playing a role. The glycine receptor antagonist, strychnine (1μM), induced an inward current in maternal HFD, but not control, DMV neurons (22.8±2.1pA vs 2.9±1.5pA). Strychnine also increased the rise time (3.8±0.3ms vs 2.8±0.2ms), decay time (6.3±0.8ms vs 4.1±0.5ms), and half width (5.9±0.7ms vs 3.9±0.4ms; P<0.05 for each) of miniature inhibitory postsynaptic currents (mIPSCs) in maternal HFD neurons, but had no effect in control neurons (mIPSC rise time, 3.0±0.2ms vs 3.1±0.2ms; decay time 3.6±0.2ms vs 3.7±0.4ms; half‐width 3.5±0.2ms vs 3.6±0.4ms; P>0.05 for each). Microinjection of strychnine (300pmoles/60nl) into the DMV increased gastric tone and motility in the antrum in maternal HFD rats (364±130mg increase in tone and 233±199% increase in motility) but not in control rats (29.5±29.5mg increase in tone and 13±26% increase in motility), suggesting that tonic glycinergic inputs onto DMV neurons decreases vagal efferent outflow and reduces basal gastric motility and tone in maternal HFD rats.The studies suggest that perinatal overnutrition results in the expression of a novel tonic glycinergic input onto gastric projecting DMV neurons, increasing the inhibitory drive to the stomach. Such alterations in brainstem neurocircuit development as a consequence of maternal over‐nutrition may induce gastric dysmotility and dysregulated gastointestinal reflexes, hence influencing offspring to develop obesity.Support or Funding InformationFunded by NIH 078364 and NSF IOS1148978