Regulation of gastrointestinal function by the brain is an important but inadequately understood component of energy homeostasis in humans. The long-term objective of this project is to understand the local neuronal connectivity in the brainstem solitary complex. As the site of first central synaptic contact for sensory afferent fibers of the vagus nerve from the digestive tract, neurons in the nucleus tractus solitarius (NTS) process digestive system information prior to further integration via higher brain areas and eventual activation of motor output to the stomach. Included in the neuronal circuits controlling autonomic function are local synaptic circuits in the NTS, inputs from CNS regions outside the solitary complex, and reflex-circuit interactions with vagal motor neurons in the dorsal motor nucleus of the vagus nerve (DMV). Although the neuronal circuitry of the caudal solitary complex is the functional substrate for visceral sensory-motor integration relating to feeding behavior, local synaptic connectivity in the area has not been adequately described. We will use whole-cell patch-clamp recordings in brain slices to investigate the functional organization of the caudal solitary complex. We will identify neurons on the basis of their functional connections with the proximal stomach using in vivo labeling methods. We will also correlate synaptic responses with quantitative morphological features using biocytin labeling techniques. Both electrical stimulation of primary viscerosensory input and photoactivation of caged glutamate to stimulate discrete sites within the slice will be used to investigate the local amino acid-mediated synaptic circuitry of the region.
The specific aims of the proposal are designed to test hypotheses regarding the synaptic circuitry of the solitary complex. The specific hypotheses for the proposed research are: 1) Gastric-related principal neurons in the NTS are inhibited by a convergent system of local GABAergic neurons (i.e., lateral inhibition); 2) small, putative inhibitory NTS neurons are activated by local excitatory NTS neurons; and 3) stomach-projecting neurons in the DMV are directly inhibited by NTS input. These experiments will result in an understanding of neuronal connectivity within the NTS and between regions of the solitary complex. This information is highly relevant to the mechanistic understanding of feeding behaviors such as receptive relaxation and accommodation in the stomach. It will also enhance understanding of the mechanisms of action for treatments of digestive system-related disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK056132-05
Application #
6875032
Study Section
Integrative, Functional and Cognitive Neuroscience 8 (IFCN)
Program Officer
Sato, Sheryl M
Project Start
2001-06-01
Project End
2006-07-15
Budget Start
2005-05-01
Budget End
2006-07-15
Support Year
5
Fiscal Year
2005
Total Cost
$205,702
Indirect Cost
Name
Tulane University
Department
Anatomy/Cell Biology
Type
Schools of Arts and Sciences
DUNS #
053785812
City
New Orleans
State
LA
Country
United States
Zip Code
70118
Derera, Isabel D; Delisle, Brian P; Smith, Bret N (2017) Functional Neuroplasticity in the Nucleus Tractus Solitarius and Increased Risk of Sudden Death in Mice with Acquired Temporal Lobe Epilepsy. eNeuro 4:
Boychuk, Carie R; Smith, Bret N (2016) Glutamatergic drive facilitates synaptic inhibition of dorsal vagal motor neurons after experimentally induced diabetes in mice. J Neurophysiol 116:1498-506
Bach, Eva C; Halmos, Katalin Cs; Smith, Bret N (2015) Enhanced NMDA receptor-mediated modulation of excitatory neurotransmission in the dorsal vagal complex of streptozotocin-treated, chronically hyperglycemic mice. PLoS One 10:e0121022
Xu, Hong; Boychuk, Jeffery A; Boychuk, Carie R et al. (2015) Nicotine enhances inhibition of mouse vagal motor neurons by modulating excitability of premotor GABAergic neurons in the nucleus tractus solitarii. J Neurophysiol 113:1165-74
Boychuk, Carie R; Gyarmati, Peter; Xu, Hong et al. (2015) Glucose sensing by GABAergic neurons in the mouse nucleus tractus solitarii. J Neurophysiol 114:999-1007
Boychuk, C R; Halmos, K Cs; Smith, B N (2015) Diabetes induces GABA receptor plasticity in murine vagal motor neurons. J Neurophysiol 114:698-706
Smith, Bret N (2015) The Wanderer Falters: Central Vagal Dysregulation Triggers SUDEP. Epilepsy Curr 15:269-70
Halmos, K C; Gyarmati, P; Xu, H et al. (2015) Molecular and functional changes in glucokinase expression in the brainstem dorsal vagal complex in a murine model of type 1 diabetes. Neuroscience 306:115-22
Xu, H; Smith, B N (2015) Presynaptic ionotropic glutamate receptors modulate GABA release in the mouse dorsal motor nucleus of the vagus. Neuroscience 308:95-105
Blake, Camille B; Smith, Bret N (2014) cAMP-dependent insulin modulation of synaptic inhibition in neurons of the dorsal motor nucleus of the vagus is altered in diabetic mice. Am J Physiol Regul Integr Comp Physiol 307:R711-20

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