Conclusion
Our results demonstrate that insulin inhibits parasympathetic neuronal circuitry in the brainstem, while not affecting sympathetic neuronal activity in the spinal cord.
Methods
In this study, we used several genetically engineered mouse models to label distinct populations of neurons within the brainstem and the spinal cord for whole-cell patch clamp recordings and to assess several in vivo metabolic functions.
Results
We first confirmed that insulin directly inhibited cholinergic (parasympathetic preganglionic) neurons in the DMV. We also found inhibitory effects of insulin on both the excitatory and inhibitory postsynaptic currents recorded in DMV cholinergic neurons. In addition, GABAergic neurons of the DMV and nucleus tractus solitarius were inhibited by insulin. However, insulin had no effects on the cholinergic sympathetic preganglionic neurons of the spinal cord. Finally, we obtained results suggesting that the insulininduced inhibition of parasympathetic preganglionic neurons may not play a critical role in the regulation of glucose homeostasis and gastrointestinal motility.