title: cAMP-dependent insulin modulation of synaptic inhibition in neurons of the dorsal motor nucleus of the vagus is altered in diabetic mice.
abstract: Pathologies in which insulin is dysregulated, including diabetes, can disrupt central vagal circuitry, leading to gastrointestinal and other autonomic dysfunction. Insulin affects whole body metabolism through central mechanisms and is transported into the brain stem dorsal motor nucleus of the vagus (DMV) and nucleus tractus solitarius (NTS), which mediate parasympathetic visceral regulation. The NTS receives viscerosensory vagal input and projects heavily to the DMV, which supplies parasympathetic vagal motor output. Normally, insulin inhibits synaptic excitation of DMV neurons, with no effect on synaptic inhibition. Modulation of synaptic inhibition in DMV, however, is often sensitive to cAMP-dependent mechanisms. We hypothesized that an effect of insulin on GABAergic synaptic transmission may be uncovered by elevating resting cAMP levels in GABAergic terminals. We used whole cell patch-clamp recordings in brain stem slices from control and diabetic mice to identify insulin effects on inhibitory neurotransmission in the DMV in the presence of forskolin to elevate cAMP levels. In the presence of forskolin, insulin decreased the frequency of inhibitory postsynaptic currents (IPSCs) and the paired-pulse ratio of evoked IPSCs in DMV neurons from control mice. This effect was blocked by brefeldin-A, a Golgi-disrupting agent, or indinavir, a GLUT4 blocker, indicating that protein trafficking and glucose transport were involved. In streptozotocin-treated, diabetic mice, insulin did not affect IPSCs in DMV neurons in the presence of forskolin. Results suggest an impairment of cAMP-induced insulin effects on GABA release in the DMV, which likely involves disrupted protein trafficking in diabetic mice. These findings provide insight into mechanisms underlying vagal dysregulation associated with diabetes.
authors.affiliation: Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky.
authors.forename: Camille B
authors.initials: CB
authors.lastname: Blake
authors.affiliation: Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky bret.smith@uky.edu.
authors.forename: Bret N
authors.initials: BN
authors.lastname: Smith
mesh_terms: D000818:Animals; D001933:Brain Stem / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D020126:Brefeldin A / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D003922:Diabetes Mellitus, Type 1 / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D004558:Electric Stimulation; D005260:Female; D051275:Glucose Transporter Type 4 / Q000037:antagonists & inhibitors / Q000378:metabolism; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism; D019469:Indinavir / Q000494:pharmacology; D053444:Inhibitory Postsynaptic Potentials; D007328:Insulin / Q000378:metabolism*; D008297:Male; D051379:Mice; D009433:Neural Inhibition / Q000187:drug effects; D021381:Protein Transport; D009435:Synaptic Transmission / Q000187:drug effects; D014630:Vagus Nerve / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; C495694:Slc2a4 protein, rat; D005576:Colforsin; D020126:Brefeldin A; D005680:gamma-Aminobutyric Acid; D019469:Indinavir; D000242:Cyclic AMP
keywords: GABA; diabetes; nucleus tractus solitarius; patch-clamp; vagus