Numerous studies suggest an essential role for the intermediate (IRt) and parvocellular (PCRt) reticular formation (RF) in consummatory ingestive responses. Although the IRt and PCRt contain a large proportion of neurons with projections to the oromotor nuclei, these areas of the RF are heterogeneous with respect to neurotransmitter phenotypes. Glutamatergic, GABAergic, cholinergic, and nitrergic neurons are all found in the PCRt and IRt, but the projections of neurons with these phenotypes to the motor trigeminal (mV) and hypoglossal nucleus (mXII) has not been fully evaluated. In the present study, after small injections of Fluorogold (FG) into mV and mXII, sections were processed immunohistochemically to detect retrogradely labeled FG neurons in combination with the synthetic enzymes for nitric oxide (nitric oxide synthase) or acetylcholine (choline acetyltransferase) or in situ hybridization for the synthetic enzyme for GABA (GAD65/67) or the brainstem vesicular transporter for glutamate (VGLUT2). In three additional cases, FG injections were made into one motor nucleus and cholera toxin (subunit b) injected in the other to determine the presence of dual projection neurons. Premotor neurons to mXII (pre-mXII) were highly concentrated in the IRt. In contrast, there were nearly equal proportions of premotor-trigeminal neurons (pre-mV) in the IRt and PCRt. A high proportion of pre-oromotor neurons were positive for VGLUT2 (pre-mXII: 68%; pre-mV: 53%) but GABAergic projections were differentially distributed with a greater projection to mV (25%) compared to mXII (8%). Significant populations of cholinergic and nitrergic neurons overlapped pre-oromotor neurons, but there was sparse double-labeling (<10%). The IRt also contained a high proportion of neurons that projected to both mV and MXII. These different classes of premotor neurons in the IRt and PCRt provide a substrate for the rhythmic activation of lingual and masticatory muscles.

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). The present 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, freelymoving rats and determined whether focal RF infusions of the GABA A agonist muscimol suppressed eating. Reticular formation infusions were centered in either the lateral tegmental field, comprised of the intermediate (IRt) and parvocellular (PCRt) RF, or in the nucleus gigantocellularis (Gi). Infusions of NPY 3-36 (5 ug/5ul) into 3V significantly increased feeding of solid food over a 90 minute period compared to the non-infused condition (4.3 ± 0.56 versus 0.57 ± 0.57g, p < .001). NPY 3-36 induced food intake was suppressed (1.7g ± 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 intra-oral 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. Keywords mastication; central pattern generatorFeeding is controlled by structures located in widespread regions of the brain (Broberger, 2005) (Berthoud, 2002;Morton, Cummings, Baskin, Barsh, & Schwartz, 2006) (Saper, Chou, & Elmquist, 2002). Within this distributed system are certain critical nodes that subserve specific functions. One node, the hypothalamus, is sensitive to humoral and neural signals reflecting homeostatic state and receives numerous other inputs; e.g., from the nucleus accumbens, a forebrain structure implicated in reward (Kelley, Baldo, & Pratt, 2005). Many of the integrative capacities of the hypothalamus are shared by the caudal nucleus of the solitary tract in the medulla (Grill, 2006), but an animal reliant solely on the brainstem does not feed (Grill & Norgren, 1978a). For this reason, the appetitive component of feeding is thought to be organized in the forebrain. Critically, however, the forebrain structures that monitor energy balance, generate craving, and sense the rewarding properties of food must at some point interface with substrates that actually produce the behavior of eating. Compared to the remarkable progress in unraveling the intricate circuitry of the hypothalamus, relatively little is known of these pathways. It is generally accepted that the lower brainstem contains the neural circuitry responsible for the generation of consummatory behavior but the precise locations of the...

The central distribution of QHCl-elicited Fos-like immunoreactivity (FLI) suggests the location of a brain stem circuit that controls the oral rejection response. Although many species display an oral rejection response to bitter stimuli, the distribution of FLI associated with this response has been investigated only in rats. Fos data are minimal for the mouse, a species of increasing importance, due to its use in molecular and transgenic studies and taste-evoked oromotor responses are also only incompletely described in these rodents. We investigated these questions in FVB/NJ mice and a related transgenic strain (FVB-Tg(GadGFP)4507) that expresses green fluorescent protein in a subset of GAD1-containing neurons. QHCl, sucrose, or water delivered through intraoral cannulae yielded behavioral profiles that clearly differentiated QHCl from sucrose. Similar to rat, the number of neurons expressing FLI in the medial third of the solitary nucleus was elevated following QHCl compared with the other stimuli. In mice expressing green fluorescent protein, there was a pronounced distribution of GABAergic neurons in the ventral half of the solitary nucleus. Approximately 15% of solitary neurons expressing Fos were GABAergic, but this proportion did not differ according to stimulus.

SUMMARY Fourteen apparently healthy patients with ileostomies were found to be depleted of total exchangeable sodium and potassium, but had normal serum electrolyte concentrations and normal extracellular fluid and total body water volumes. The low exchangeable sodium and potassiums were thus primarily due to depletion of the intracellular compartment. There was no evidence of renal or intestinal conservation of these ions and plasma aldosterone, renin activity, and prolactin concentrations were normal in most and only moderately raised in a few. This apparent lack of any hormonal compensatory change to the electrolyte depletion may be due to the normality of the extracellular fluid volume and electrolyte concentrations. These patients seem to have adapted to a stable but depleted intracellular sodium and potassium state.

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