Feeding behavior is controlled by brain structures distributed in the cerebral cortex, limbic system and brainstem. In the brainstem, a central pattern generator (CPG) for mastication has been localized to the midline medullary reticular formation based on cortically induced rhythmic jaw movements (fictive mastication), or to the reticular formation (RF) between the trigeminal and facial motor nuclei based on chemically elicited rhythmic trigeminal discharge in a tissue slice preparation. Other studies, however, suggest a role for the lateral medullary RF in orchestrating ingestive oromotor activity. Direct behavioral evidence supporting the location of these CPGs, however, is lacking. Thus, the first study tested the hypothesis that the lateral medullary RF is essential for organizing oromotor patterns of ingestion and rejection. In the behaving rat, licking was induced by either intra-oral (IO) infusions of sucrose or saline, or sucrose presented in a bottle. Gaping (rejection) responses were elicited by IO delivery of quinine hydrochloride. All responses were measured electromyographically from the anterior digastric (jaw-opener) and geniohyoid (tongue-protruder) muscles. Inactivation of the lateral medullary RF with the GABA A agonist muscimol suppressed both licking and gaping. Infusions into other RF regions were ineffective, indicating an essential role for the lateral medullary RF. Because both excitatory and inhibitory amino acids (EAA, IAA) are involved in fictive mastication, we further examined whether they are also important for ingestive responses elicited by natural stimuli. In a second series of experiments, EAA and IAA antagonists were infused into the lateral medullary RF. It was found that (1) the lateral medullary RF is driven by glutamatergic inputs, mediated by both non-NMDA and NMDA receptors, (2) it is under tonic inhibition from GABAergic and glycinergic inputs, (3) this substrate is also involved in the suppression of eupnea that is mediated by non-NMDA receptors. These findings provide behavioral evidence to support the hypothesis that the lateral medullary RF is a multifunctional substrate that controls the oromotor nuclei to generate licking and gaping, and the oromotor components of gasping.
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|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Central pattern generator, Gabaa receptor, Glycine receptor, Nmda receptor, Non-nmda receptor, Taste oromotor processing|
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