Mesencephalic influence on the intake of sodium chloride and water in the rat

FoxP2 brainstem neurons project to sodium appetite regulatory sites

The transcription factor Forkhead box protein 2 (FoxP2) is expressed in two cell groups of the brainstem that have been implicated in sodium appetite regulation: the pre-locus coeruleus (pre-LC) and parabrachial nucleus--external lateral-inner subdivision (PBel-inner). Because the connections of these two groups are unknown, neuroanatomical tracing methods were used to define their central projections. The pre-LC outputs were first analyzed using an anterograde axonal tracer--Phaseolus vulgaris leucoagglutinin (PHAL) to construct a brain map. Next, we examined whether the FoxP2 immunoreactive (FoxP2+) neurons of the pre-LC contribute to these projections using a retrograde neuronal tracer--cholera toxin β-subunit (CTb). CTb was injected into selected brain regions identified in the anterograde tracing study. One week later the rats were killed, and brainstem sections were processed by a double immunohistochemical procedure to determine whether the FoxP2+ neurons in the pre-LC and/or PBel-inner contained CTb. FoxP2+ pre-LC neurons project to: (1) ventral pallidum; (2) substantia innominata and bed nucleus of the stria terminalis; (3) paraventricular, central medial, parafascicular, and subparafascicular parvicellular thalamic nuclei; (4) paraventricular (PVH), lateral, perifornical, dorsomedial (DMH), and parasubthalamic hypothalamic nuclei; and (5) ventral tegmental area (VTA), periaqueductal gray matter (PAG), dorsal and central linear raphe nuclei. FoxP2+ PBel-inner neurons project to the PVH and DMH, with weaker connections to the LHA, VTA, and PAG. Both the pre-LC and PBel-inner project to central sites implicated in sodium appetite, and related issues, including foraging behavior, hedonic responses to salt intake, sodium balance, and cardiovascular regulation, are discussed.

The effects of sodium appetite on the responses of cells in the zona incerta to the sight or ingestion of food, salt and water in sheep

Single-unit recordings were made from neurones in the zona incerta (ZI) of conscious sheep in response to the sight/visual approach or ingestion of various foods, salts and water. Animals were given parotid fistulae so that effects of sodium appetite, induced by not replacing the sodium lost in the saliva, could be assessed. When sodium depletion was prevented by giving the animals 1% sodium bicarbonate in their drinking water, the majority of cells (45 out of 49) responded most strongly to the sight or visual approach of food compared to water or salt. Four cells responded best to the sight of water, but none to the sight of salt and salt solutions. When a sodium appetite was stimulated, by removing the 1% sodium bicarbonate replacement for 4-6 days, there was a significant change in response profiles of ZI cells. The majority of cells responded most strongly to the sight of salts or salt solutions (35 out of 49) and significantly fewer cells responded most strongly to food (8 out of 49). The number of cells responding primarily to water was not affected (6 out of 49). For 3 cells responding to salts it was shown that, after repeated ingestion of salt over several hours, food became a more potent stimulus. A similar decreased response to foods during sodium depletion, and an increased one to salts, was seen in ZI cells which responded to the ingestion of both solids and liquids. These results show that changing an animal's motivational state produces significant changes in the responses of cells in the ZI responding to the sight or visual approach of substances.(ABSTRACT TRUNCATED AT 250 WORDS)

Noradrenergic innervation of the paraventricular nucleus: specific role in control of carbohydrate ingestion

Acute injections of norepinephrine (NE) into the hypothalamic paraventricular nucleus (PVN) have been shown to elicit eating in satiated rats. The present report examines the effects of acute and chronic PVN infusion of NE on intake of various liquid and mixed solid diets and on selection of the pure macronutrients, carbohydrate, protein, and fat. The results demonstrate that noradrenergic stimulation of the PVN (40 nmoles of NE) reliably enhances ingestion of pure sucrose diets (liquid and solid) and also of sweet and non-sweet milk solutions. Saccharin intake, in contrast, is unaffected. In preference tests, rats injected with NE show a greater increase in consumption of sucrose cubes compared with lab chow pellets, but exhibit an equivalent preference for sweet and non-sweet carbohydrate-rich diets. Tests with the three pure macronutrients simultaneously available reveal, after NE injection, a strong and selective increase in consumption of carbohydrate, with little or no change in intake of fat and, in some cases, a suppression of protein intake. This clear preference for carbohydrate can be seen with chronic NE infusion (5 nmoles every 30 min over a 14-day period), as well as after acute NE injection (40 nmoles), and also with long-term (24-hr) as well as short-term (1-hr) food intake measurements. This and other evidence suggests that the PVN noradrenergic system may play a specific and unique role in the control of carbohydrate ingestion.

A reassessment of the brain mechanisms that control thirst

The classic " hypothalamocentric " theory of thirst has increasingly been challenged because the effects of hypothalamic lesions are not as behaviorally or anatomically specific as earlier research indicated. Instead, the attention of investigators in the field has increasingly been drawn to the lateral preoptic region and the tissues surrounding the anterior third ventricle. The present paper reviews these developments and proposes that still another diencephalic structure, the subthalamic region known as the zona incerta, may play a major role in the regulation of thirst and water intake.

Parabrachial nuclei damage in infant rats produces residual deficits in gustatory preferences/aversions and sodium appetite

Ten-day-old rats sustained bilateral electrolytic lesions of the parabrachial nuclei in the pons (PBN). Growth measures and tests of sensorimotor, feeding and drinking behaviors, sodium appetite, and gustatory capacities were made between ages 1 and 150 days. PBN rats displayed a transient period of attenuated suckling, as evidenced by body weight loss. When tested soon after weaning, PBN rats were hyperdipsic in response to cellular dehydration and during food deprivation. This effect, however, was temporary. When tested as adults, PBN rats were hypodipsic in response to extracellular fluid volume depletion, they displayed alterations in sodium appetite, showed "exaggerated" preferences and aversions to saccharin and NaCl solutions, and they displayed attenuated quinine aversions. These results are generally similar to the behaviors of rats sustaining more central gustatory pathway lesions as adults. The functional significance of the PBN in the developing rat for preference/aversion and sodium appetite behaviors are discussed.