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Published on: November 25, 2014
Suppression of third ventricular NPY-elicited feeding following medullary reticular formation infusions of muscimol
Joseph B Travers1, Kenneth Herman, Susan P Travers
1Division of Oral Biology, College of Dentistry, The Ohio State University, Columbus, OH 43210, USA. Travers.1@osu.edu
Abstract:
The appetitive component of feeding is controlled by forebrain substrates, but the consummatory behaviors of licking, mastication, and swallowing are organized in the brainstem. The target of forebrain appetitive signals is unclear but likely includes regions of the medullary reticular formation (RF). This study was undertaken to determine the necessity of different RF regions for mastication induced by a descending appetitive signal. We measured solid food intake in response to third ventricular (3V) infusions of the orexigenic peptide neuropeptide Y 3-36 in awake, freely moving rats and determined whether focal RF infusions of the GABAA agonist muscimol suppressed eating. RF infusions were centered in either the lateral tegmental field, comprising the intermediate (IRt) and parvocellular (PCRt) RF, or in the nucleus gigantocellularis (Gi). Infusions of NPY 3-36 (5 microg/5 microl) into 3V significantly increased feeding of solid food over a 90-min period compared with the noninfused condition (4.3 g +/- 0.56 vs. 0.57 g +/- 0.57, p < .001). NPY 3-36-induced food intake was suppressed (1.7 g +/- 0.48) by simultaneous infusions of muscimol (0.6 mM/100 nl) into the IRt/PCRt (p < .01). Coincident with the decrease in feeding was a decrease in the amplitude of anterior digastric muscle contractions in response to intraoral sucrose infusions. In contrast, infusions of muscimol into Gi had no discernible effect on food intake or EMG amplitude. These data suggest that the IRt/PCRt is essential for forebrain-initiated mastication, but that the Gi is not a necessary link in this pathway.
Insights
Forebrain feeding signals require brainstem regions for mastication. The intermediate and parvocellular reticular formation (IRt/PCRt) are essential for neuropeptide Y-induced eating behaviors in rats.
Area of Science:
- Neuroscience
- Physiology
Background:
- Feeding behavior involves both appetitive (forebrain) and consummatory (brainstem) components.
- The specific brainstem targets of forebrain appetitive signals remain largely unknown.
- The medullary reticular formation (RF) is a potential candidate for integrating these signals.
Purpose of the Study:
- To investigate the necessity of specific medullary RF regions for mastication.
- To determine if the lateral tegmental field (IRt/PCRt) or nucleus gigantocellularis (Gi) are critical for forebrain-initiated feeding.
Main Methods:
- Rats received third ventricular infusions of neuropeptide Y 3-36 (NPY) to stimulate appetite.
- Focal infusions of muscimol (GABAA agonist) were delivered to the IRt/PCRt or Gi to inhibit neuronal activity.
- Solid food intake and digastric muscle activity (EMG) were measured.
Main Results:
- NPY infusion significantly increased solid food intake.
- Muscimol infusion into the IRt/PCRt suppressed NPY-induced feeding and reduced masticatory muscle activity.
- Muscimol infusion into the Gi did not affect feeding or muscle activity.
Conclusions:
- The intermediate and parvocellular reticular formation (IRt/PCRt) are essential for forebrain-controlled mastication.
- The nucleus gigantocellularis (Gi) is not a necessary component in this specific feeding pathway.
