The dorsal motor nucleus of the vagus (DMV) provides the parasympathetic motor output to the gastrointestinal (GI) tract and plays an integral role, along with the nucleus of the tractus solitarius (NTS), in the reflex control of gastric motility and compliance. In addition, each of these nuclei receive descending projections from hypocretin (HCRT)- containing neurons in lateral hypothalamus and oxytocin (OT)-containing neurons of the paraventricular nucleus (PVN) that together provide both the means for central control of GI activity and an important route for coordinating digestive processes with feeding behavior. A major objective of the proposed research is to define the cellular and synaptic actions of HCRT peptides and OT in the DMV and ascertain how they relate to the more global influence that these peptidergic inputs have on gastric-related functions. To accomplish this, we will conduct in vivo experiments and obtain patch clamp recordings in brain slices and cell culture from retrogradely labeled DMV neurons with defined GI projections.
In Aim 1, we will conduct microinjection experiments in anesthethized rats together with immunohistochemical studies to determine the sites and cellular substrates where HCRTs act in the DMV to stimulate gastric motor function. The pharmacological sensitivity of gastric responses to HCRT will also be examined to determine the nature of the vagal efferent pathways involved.
In Aim 2, patch recordings in slices will be used in conjunction with electrical stimulation in NTS to determine the effects of bath application of HCRTs or OT on the membrane properties and synaptic responses of identified GI-projecting DMV neurons. The neurochemistry of each sampled neuron will then be defined using single cell reverse transcription -polymerase chain reaction. Responses of individual cells to HCRT or OT application will be correlated with their specific GI target and chemical phenotype to test the hypothesis that these peptidergic signals exert opposing effects on gastric motility and tone by modulating the excitability of functionally distinct subpopulations of preganglionic vagal motor neurons.
In Aim 3, we will obtain whole-cell recordings from identified GI-projecting DMV neurons in culture to characterize the voltage dependent calcium (Ca 2+) conductances in these cells and determine whether HCRTs regulate excitability of neurochemically distinct groups of preganglionic neurons by modulating Ca 2+ influx through specific channels types. The proposed research will increase our understanding of hypothalamic mechanisms that control gastric-related functions, and in so doing may lead to the design of new interventions for effective weight management and treatment of digestive disorders such as gastric stasis or non-ulcer dyspepsia associated with alterations in gastric motility and stomach emptying.
