Area postrema lesions produce feeding deficits in the rat: effects of preoperative dieting and 2-deoxy-D-glucose

Intraventricular alloxan impairs feeding to both central and systemic glucoprivation

Fourth ventricular alloxan injections impair the feeding response to systemically induced glucoprivation. However, the effect of alloxan on responses to centrally administered glucoprivic agents has not been assessed. Therefore, rats implanted with fourth ventricular cannulas were tested for feeding and glycemic responses to centrally administered 5-thioglucose (5TG, 120 micrograms/5 microliter) and subcutaneously administered 2-deoxy-D-glucose (2DG, 250 mg/kg, IP). Subsequently, alloxan (200 micrograms in 5 microliter), alloxan plus 3 M D-glucose, or the saline vehicle solution was injected into the fourth ventricle and the animals were then retested with systemic 2DG and intraventricular 5TG. Feeding responses to both centrally and systemically induced glucoprivic challenge were greatly impaired by alloxan treatment. Thus, feeding elicited by both centrally and systemically induced glucoprivation appears to be mediated by the same central neural substrate. The possibility that the alloxan-damaged cells are glucoreceptors is discussed. In contrast to glucoprivic feeding, the hyperglycemic response to glucoprivation was not impaired by alloxan. Therefore, the neural elements controlling this response may differ biochemically from those controlling feeding.

Alloxan-induced glucoprivic feeding deficits are blocked by D-glucose and amygdalin

Intracerebroventricular injection of alloxan, a pancreatic beta (B) cell cytotoxin, impairs glucoprivic feeding in rats. The goal of this experiment was to determine whether alloxan-induced impairment of glucoprivic feeding can be attenuated by agents which antagonize alloxan's toxicity in the B cell. Therefore, alloxan was co-administered into the fourth ventricle alone or in combination with D-glucose, L-glutamine, or amygdalin, all known antagonists of alloxan's B cell toxicity, or with L-glucose, which does not antagonize B cell toxicity. We found that alloxan produced deficits in glucoprivic feeding which were not attenuated by co-administration with L-glucose or L-glutamine. Alloxan/L-glucose treated rats ate 11% and 14% of control intake, respectively, after systemic administration of 2-deoxy-D-glucose (2DG, 250 mg/kg) and fourth ventricular 5-thioglucose (5TG, 120 micrograms/5 microliter). Alloxan/L-glutamine rats ate 20% and 22% of control intake after 2DG and 5TG, respectively. In contrast, D-glucose and amygdalin (15 mM) completely blocked alloxan-induced impairment of glucoprivic feeding and amygdalin (10 mM) exerted a partial protective effect. These behavioral results may indicate that in the brain, susceptibility to alloxan toxicity depends upon cellular characteristics shared with the B cell.

Area postrema/nucleus of the solitary tract ablations: analysis of the effects of hypophagia

The effect of hypophagia following lesions of the area postrema and caudal-medial aspect of the nucleus of the solitary tract AP/cmNTS) on body-weight, water intake and preference for palatable diets was examined. Following AP/cmNTS ablation, rats reduced pelleted-food intake to a degree which was sufficient to account for the weight loss and increased water:food ratios observed. Restricting food intakes of intact rats to levels taken by lesioned animals resulted in similar weight losses and increased water:food ratios. When offered both pelleted food and milk, lesioned rats took more calories as milk than did previously food-restricted intact rats. Thus, the hypophagia of AP/cmNTS lesioned rats does not account for their increased preference for milk diets. Lesioned rats ate less high-fat diet than did intact or sham-lesioned controls and did not increase their intakes when this diet was sweetened. At autopsy, retroperitoneal and epididymal fat-pad weights accounted for less of the total body weight of lesioned animals than controls suggesting that body-fat levels are reduced following AP/cmNTS ablation.

Glucoprivic responsivity after insulin in hypodipsic and in water deficit rats

Long Evans rats were made acutely hypodipsic through quinine adulteration of their water supply, and they ate normally in response to 2, 4, and 6 unit insulin injections. Other subjects were made chronically hypodipsic through adulteration; and while their glucoprivic feeding was lowered absolutely, it remained relatively elevated over their control session intake. These data indicate that subjects with reduced drinking abilities can respond to the insulin-induced glucoprivic challenge and that hydrational factors apparently do not serve as critical confounds in brain lesion investigations into the glucoprivic feeding response.

Overconsumption of preferred foods following capsaicin pretreatment of the area postrema and adjacent nucleus of the solitary tract

Lesions which destroy the area postrema (AP) and damage the adjacent nucleus of the solitary tract (NST) produce a constellation of behavioral signs which include overingestion of highly palatable food, exaggerated drinking in response to angiotensin II, diminished feeding in response to glucoprivation and chronically reduced body weight. The diversity of these signs, as well as the anatomical complexities of the AP and adjacent NST, suggest that more than one behaviorally relevant neural population may be damaged by lesions of these areas. Injections of the neurotoxin, capsaicin, made directly into the region of the AP and adjacent NST, cause rats to overconsume highly palatable foods when these foods are available during short (30 min) presentations or when they are available continuously. The capsaicin-treated animals, unlike rats with thermal lesions of the AP and adjacent NST, do not exhibit chronically reduced body weight or overdrink in response to angiotensin II. In addition, feeding in response to glucoprivation is undiminished in capsaicin-injected rats. These results suggest that thermal damage of the AP and adjacent NST causes overingestion of preferred foods by damaging a population of capsaicin-sensitive neurons. The other manifestations of thermal lesions of the AP and adjacent NST are probably mediated by neurons which are not susceptible to capsaicin-induced damage. Since small unmyelinated sensory neurons are most sensitive to damage by capsaicin, it may be that damage to small sensory neuron projections in the AP and/or adjacent NST produces the overconsumption of palatable foods.

Area postrema lesions disrupt food intake induced by cerebroventricular infusions of 5-thioglucose in the rat

The present experiment assesses the contribution of the area postrema (AP) to glucoprivic feeding in the rat. Lateral ventricular infusions of 5-thioglucose increased pelleted food intake in sham animals but not in animals with AP lesions. Drinking in response to infusion of angiotensin II into the lateral ventricle was not reduced by AP lesions. The data suggest that the AP is part of the brainstem circuitry underlying glucoprivic feeding.

Hypothalamic pathways involved in metabolic regulatory functions, as identified by track-tracing methods

The present review of the fiber connections of the hypothalamus has been concerned basically with recent data obtained by the aid of the autoradiographic and HRP tracer techniques. Evidence presented has shown that, besides confirming many of the older data, recent studies have resulted in the introduction of several conceptual modifications into the classic picture of hypothalamic hodological relationships. Among these conceptual modifications, the following can be mentioned: (1) the medially placed nuclei of the hypothalamus have a great number of long efferent and afferent connections with many extrahypothalamic structures; (2) many hypothalamic nuclei send direct projections to cell territories in the brainstem and spinal cord that contain preganglionic autonomic motor neurons; (3) several neural districts that lie caudal to the mesencephalon send direct projections to the hypothalamus; (4) in addition to the olfactory channel, other sensory pathways (including interoceptive and gustatory conduction lines) have a relatively direct access to hypothalamic mechanisms; (5) the hypothalamus sends fibers to several brainstem territories that give rise to widespread monoaminergic projections; and (6) there are anatomical pathways that establish reciprocal connections between the hypothalamus and the basal ganglia. Some of the possible physiological correlates of these anatomical findings in the context of metabolic regulatory functions have been briefly indicated.