The ontogeny of feeding in rats: I. Ingestive and behavioral responses to oral infusions.

Reports on 3 experiments with Charles River rat pups. When milk infusions were made through oral cannulas in the front of their mouths, 1–20 day old Ss actively ingested the diet, and their intake was related to the length of deprivation. Ss decreased their ingestive responding after they had consumed large volumes of milk. In addition, 1-, 3-, and 6-day-old Ss, when 24-hr deprived, exhibited an intense behavioral activation in response to milk infusion. The behavioral activation appeared to be stimulated primarily by taste and the opportunity to swallow. Milk infusions did not produce activation in older Ss; their behavior was more exclusively ingestive and food directed. Results demonstrate that (a) from birth, rat pups are capable of an active form of ingestion, independent of normal suckling from the mother; (b) such ingestion is controlled by physiological factors; (c) food has arousing properties in young animals; and (d) as pups grow older, their ingestive responding is refined from a generalized and nondirected activation to specific and directed feeding responses. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suckling behavior and intake control in the developing rat pup.

Studied the behavioral development of suckling and intake control in 2 experiments with Charles River CD strain rat pups. Ss were observed at the initiation, during the course, and at the termination of suckling from their anesthetized mothers. Diet was delivered intraorally through a fine tongue cannula which enabled control of timing and volume. The control of diet intake and the behavior at termination of suckling showed correlated changes from 5 to 20 days of age. When deprived of suckling (and food and water) for 8 hr, 5- and 10-day-old Ss consumed large volumes of diet (10% of body weight or greater) and terminated suckling only in the presence of extreme gastrointestinal filling. These Ss were immediately lethargic and slept after intake termination. Five-day-old Ss persisted in reattaching to the nipple when manually stimulated; 10-day-old Ss eventually refused to reattach. In contrast, 20-day-old Ss consumed more moderate volumes of diet (5% of body weight). These Ss also remained awake for a period after feeding and engaged in the exploratory and grooming activities characteristic of adult rats at the termination of feeding. These observations demonstrate major changes in suckling behavior during development. They suggest that intake control processes shift from indirect to direct and become more effective and specifically food intake related in older pups. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ontogeny of feeding in rats: V. Influence of texture, home odor, and sibling presence on ingestive behavior.

Determined with Charles River rat pups in 3 experiments that terry-cloth texture, home odor, and the presence of siblings modulated Ss' ingestive behavior. Unlike warmth, which affected ingestion in pups until at least 15 days of age, the relative importance of other cues varied with age. At 3 days, ingestion was dependent on warmth but was not influenced by the other cues. At 6 days, texture and home odor enhanced ingestive behavior (intake, activity, mouthing, and probing), but the presence of siblings had no effect. Home odor or terry-cloth texture did not alter the ingestive behavior of 12-day-olds, but the presence of siblings enhanced milk intake. Thus, during development, the external sensory controls for ingestion became progressively more complex. Warmth served as a primary permissive cue for ingestion, but as Ss grew older, such other cues as odor, texture, or social stimuli also gained significance. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of suckling in rats: Transitions toward adult ingestion.

Studied the suckling behavior of neonatal Sprague-Dawley rats on their own anesthetized mother from the day of birth until after weaning (35 days). Even newborn Ss were capable of nipple attachment without maternal assistance. Before 11–23 days of age, pups deprived of suckling for 22 hrs and nondeprived pups quickly attached to their mother's nipples, sucked, and remained attached to the nipple though no milk delivery occurred. Then behavior underwent at least 3 changes: (a) After 11–23 days of age, latency to attach became considerably elevated in nondeprived pups; (b) a 2nd change in latency occurred at 23–25 days of age, when nondeprived pups no longer even attached to the nipples of anesthetized mothers; and (c) about 14 days of age, deprived pups began to shift from 1 nipple to the next after initial attachment. These developmental changes were seen in other test situations in which pups were placed directly on a nipple and not required to search and when various periods of deprivation were utilized. These transitions were not critically dependent on the onset of visual function or on the pup's experience with food other than mother's milk. Suckling, therefore, in not an unmodified reflex but is an appetitive behavior that undergoes a series of changes during development. These transitions constitute major developmental events in the ontogeny of rat ingestive behavior. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Persisting deficits in rats "recovered" from transections of fibers which enter or leave hypothalamus laterally.

In a study with 36 female albino Sprague-Dawley rats, parasagittal knife cuts along the lateral border of the hypothalamus which transected most of the fibers that enter or leave the hypothalamus laterally reproduced the full spectrum of effects on food intake seen after lateral hypothalamic lesions. Ss were aphagic and adipsic for weeks or months and remained unresponsive to physiological signals that normally regulate feeding and drinking, even after voluntary ingestive behavior returned. Ss did not respond to insulin or 2-deoxy-D-glucose treatments (which decrease blood sugar or glucose utilization) and showed only a small increase in intake when exposed to low environmental temperatures. Food consumption appeared to be governed primarily by the palatability of the diet. Ss also did not respond to NaCl or polyethylene glycol treatments (which result in cellular dehydration or extracellular hypovolemia) and returned to a state of adipsia when food was removed. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sodium homeostasis in chronic decerebrate rats.

Two experiments examined physiological and behavioral concomitants of sodium need in supracollicularly transected and pair-fed intact male Sprague-Dawley rats. Chronic decerebrate Ss, like intact Ss, reduced their urine sodium output when placed on a sodium-deficient diet. Similarly, 24 hrs after sodium loading, decerebrate and intact Ss excreted comparable levels of the excess sodium. In the 2 hrs immediately following loading, decerebrate Ss excreted less sodium. In contrast, behavioral aspects of sodium homeostasis were completely absent in chronic decerebrate Ss. In separate experiments, intraoral intake and taste-reactivity responses elicited by intraoral infusions of NaCl were measured during sodium-replete and sodium-deficient conditions. In response to oral infusions of NaCl, intact Ss consumed significantly more and produced greater numbers of ingestive taste-reactivity responses when they were sodium deficient than when they were sodium replete. The same sodium-depletion treatments in chronic decerebrate Ss, however, altered neither the intraoral intake of NaCl nor the frequency of NaCl-elicited ingestive taste-reactivity responses. Results suggest that the behavioral compensatory responses that follow changes in the internal sodium state depend on forebrain mechanisms. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ontogeny of feeding in rats: III. Thermal determinants of early ingestive responding.

High ambient temperatures (38°C) stimulated high spontaneous levels of activity and high frequencies of behaviors normally associated with ingestion (mouthing and probing), particularly in young, 3- and 6-day-old Charles River CD rat pups (Exp I). The level of spontaneous behavior was highly correlated with body temperature and also depended on deprivation condition. Temperature played an important role in determining responses to food stimuli as well. When Ss were fed by oral infusion (Exp II) or by placing milk on the floor beneath them (Exp III), warm ambient temperatures were required for active ingestion. In Exp IV, body temperature and ambient temperature were manipulated independently to assess their relative importance for Ss' feeding behavior. Ss with a low (29°C) or normal (34°C) core temperature at the start of testing were fed in either a 24°C or a 34°C ambience. Regardless of body temperature, Ss' levels of intake, activity, mouthing, and probing were higher in a warm than in a cool ambience. Therefore, the suppressed ingestive behavior of Ss fed at cool temperatures occurred not simply because Ss became hypothermic and inactive. Perceived warmth appears to be a significant contextual cue that regulates pups' responses to food stimuli. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nutritive and nonnutritive determinants of milk intake of suckling rats.

Determined the factors that enhanced milk intake during deprivation in albino rats 15, 20, and 25 days of age. Ss were subjected, for 8 hrs, to 1 of 6 regimens. Results show that intake at Day 15 was reduced by the opportunity to suckle, independent of receiving a milk load. This same trend was apparent, although not as strong, among Day 20 Ss. By Day 25, nonnutritive suckling during the privation period no longer attenuated milk intake, although preloads did, whether or not they were paired with nonnutritive suckling. Thus, suckling in Ss became increasingly freed from oral demands and more responsive to the nutritive consequences. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dehydration inhibits suckling behavior in weanling rats.

Determined the relation between dehydration and suckling behavior in 567 Sprague-Dawley weanling rats 15, 20, and 23 days of age. After 15 days of age, intra- and extracellular dehydration sharply reduced both the number of Ss that suckled and the amount of milk consumed. Rehydration returned both behaviors to control levels. Thus, during the weaning period, the internal determinants of suckling are not homologous with those of drinking, but are more homologous with those governing feeding. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms for enhanced feeding in the cold in rats.

The effect of environmental cold upon feeding, food-motivated behavior, and gastric clearance of food was studied in 36 female Sherman rats in 4 experiments. Ss ate liquid diet in either a 5 or 22Deg. C ambient temperature (T-sub(a)) following (a) 24-hr food deprivation at T)a) of either 5 or 22Deg. C or (b) 0- or 48-hr food deprivation at T-sub(a) 22Deg. C. Ss ate more at 5 than at 22Deg. C regardless of the ambient temperature during deprivation. Ss increased feeding in the cold by increasing meal frequency but not meal size. Cold (5Deg. C) also enhanced the urge to eat. Ss barpressed for food more often in the cold on a VI 30-sec schedule when gastric clearance of food was prevented by a pyloric noose and when food cleared from the stomach normally. Quinine adulteration of food suppressed food intake only in the 22Deg. C. Cold (5Deg. C) enhanced gastric clearance of liquid food within 20 min of ingestion. Results support the view that the peripheral sensation of cold is an adequate stimulus for feeding and that cold T-sub(a) can stimulate feeding directly by increasing the urge to eat and indirectly, secondary to increased gastric clearance. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cholecystokinin elicits the complete behavioral sequence of satiety in rats.

Observed and scored the behavior of intact rats and rats with chronic gastric fistulas during a 60-min test period when they were offered liquid diet after 17 hr of food deprivation. The same 5 adult male Sprague-Dawley rats were employed in 2 experiments. Intact Ss and Ss with closed fistulas displayed a specific behavioral sequence at the end of each meal: They stopped eating, engaged in grooming and exploration for a short time, and then rested or slept. Thus, a fixed behavioral sequence characterized satiety in Ss. Although the behavioral sequence of satiety was fixed, the cessation of feeding was not a sufficient condition for the appearance of the rest of the sequence: Quinine adulteration of the liquid diet stopped sham feeding but did not elicit the complete sequence. Intraperitoneal injection of the intestinal hormone cholecystokinin during sham feeding, however, elicited the complete sequence of satiety. The observation that cholecystokinin not only stopped feeding but elicited the complete sequence of satiety supports the hypothesis that endogenous cholecystokinin is a satiety signal for the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failure by deprived hamsters to increase food intake: Some behavioral and physiological determinants.

Investigated the behavioral and physiological determinants of postfast anorexia in 165 golden hamsters. Six experiments varied the postfast feeding in photoperiods, feeding in different hamster strains, the effects of a liquid diet, Ss' adaptation to a restricted water schedule, food intake as a function of housing, and physiological changes during food deprivation. Postfast anorexia and/or the failure to adapt to a feeding schedule were not restricted to a particular photoperiod condition or hamster strain. The anorexia was also observed with a liquid diet, but Ss showed large increases in water intake on a water deprivation schedule. When Ss were group-housed, they pouched food during scheduled feeds and ate it later: Meal size was not increased. Measures of gastric fill and plasma metabolites indicated that filling and emptying of the forestomach occurred with a periodicity similar to that of spontaneous meals; data are consistent with strong peripheral satiation/satiety mechanisms in this species. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thiamin deprivation in ventromedial hypothalamic hyperphagic rats: Anorexia, specificity of food aversion, and a dietary consideration.

In 3 studies, the anorexic consequence of thiamine deprivation was investigated in ventromedial hypothalamic (VMH) hyperphagic CD male rats under either high-fat or low-fat (HF and LF, respectively) thiamine-free diet conditions. The LF diet maintained feeding significantly longer in thiamine-deprived VMH Ss than in intact Ss, whereas the HF diet sustained feeding in thiamine-deficient intact Ss and accelerated anorexia onset in vitamin-B1-deprived VMH Ss. This effect was noted under both ad lib and pair-feeding conditions. Thiamine-deprived VMH Ss subjected to weight control developed anorexia sooner than intact Ss regardless of the diet employed. The VMH Ss fed an HF diet failed to resume feeding after thiamine readministration, which is interpreted as a permanent aversion to this diet. The relation between dietary intake and conditioned taste aversion is discussed with reference to the VMH and intact rats. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral and neurochemical effects of neonatal administration of monosodium {l}-glutamate in mice.

Studied the feeding behavior, activity level, and thermoregulatory ability of 117 CL-1 mice made obese by neonatal administration of monosodium {l}-glutamate (MSG). The degree of obesity and other characteristics of the syndrome depended on age, diet, and housing condition. Carcass fat determinations demonstrated the presence of obesity in all MSG Ss; however, body weight was elevated over control levels only in adult mice caged in groups. Group-housed MSG Ss also failed to increase food intake in response to food deprivation and were both hypoactive and hypothermic. Individually caged MSG Ss showed normal activity levels and body temperature, an attenuated response to food deprivation, and an enhanced response to a high-fat diet. Since MSG obesity may be the consequence of damage to the dopamine-rich arcuate nucleus of the hypothalamus, a 2nd goal was to measure central catecholamines and examine any changes in the MSG S's behavioral responses to catecholaminergic drugs. Ss treated with MSG sustained some loss of hypothalamic dopamine, but no systematic relation between central catecholamines and behavioral aspects of the syndrome could be discerned. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Plasticity of normal feeding: Situational and individual factors.

Male hooded rats (N = 20) given experience feeding in a distinctive situation while food-deprived showed facilitated intake when tested nondeprived in the same situation. This situational feeding was vigorous and reliable in low-emotional Ss but not in high-emotional ones. These findings could not be accounted for by group differences in baseline intake by nutritional deficits resulting from the previous food deprivation schedule, nor the nonspecific arousal of consummatory behavior. Results indicate that feeding can be reliably controlled by external events independent of hunger or palatability. (French summary) (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separation of opioid from nonopioid mediation of affect in neonatal rats: Nonopioid mechanisms mediate maternal contact influences.

Established a causal distinction in infant rats between opioid- (OP) and non-OP-mediated determinants of behavior. Contact influences were mediated by non-OP pathways, and gustatory influences were OP-mediated. Naltrexone (NTX) did not diminish quieting exerted by contact with an anesthetized dam but reversed the quieting effects of morphine in isolated Ss. Naloxone (NLX) did not affect the latencies with which nondeprived or 8-hr deprived Ss 9, 12, 15, and 18 days old attached to nipples (NPs) of anesthetized dams, nor did NLX cause systematic change in NP attachment in 10- and 18-day old Ss from the NP when milk letdown was induced by oxytocin. NLX did not reduce milk intake in Day-10 Ss that, while suckling, received milk via indwelling cannulae in the anterior portion of the lower jaw or in Ss that obtained milk directly from their awake mother. Milk intake was significantly reduced by NTX in Day-10 Ss that obtained milk by licking it off a saturated substrate. In Day-10 Ss, intake of milk delivered via cannulae was reduced by NLX in Ss that were either isolated, in contact with an anesthetized dam, or attached to her NPs. Behavioral influences of the tactile (and possibly olfactory) qualities of the dam were not mediated by OP systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trigeminal deafferentation and ingestive behavior in rats.

For studying the role of orosensory input in the control of ingestive behavior, 46 male albino Wistar rats were subjected to varying degrees of trigeminal deafferentation in 2 experiments. Somatosensory branches that convey touch, temperature, and pain from the oral cavity were sectioned selectively, and muscles of mastication and taste afferents were left intact. Severe intake deficits were produced, including aphagia, adipsia, and prolonged hypophagia, accompanied by a corresponding decrease in body weight. The deficits were proportional to the extent of deafferentation and were most severe when upper and lower portions of the mouth were affected. Although somatosensory impairment affected the organization of the consummatory response, all Ss could bite, chew, and lick. Analysis of feeding patterns showed that minimally (mandibular) deafferented Ss compensated for the consummatory inefficiency by increasing meal duration but failed to initiate meals at the normal rate, thus keeping food intake below normal levels. Results suggest that oral somatosensory input is critical for the mechanisms that regulate ingestive behavior. (45 ref)) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tolerance to amphetamine anorexia: Role of learning versus body weight settling point.

Conducted 3 experiments with male Sprague-Dawley rats to study the development of tolerance to amphetamine (AM) anorexia. In Exp I, 19 Ss that had become tolerant to the suppressant effect of AM on milk intake were anorexic when offered other foods or water. These results appear to support a conditioning interpretation. In Exps II (38 Ss) and III (24 Ss), Ss made tolerant with milk as the diet showed prolonged anorexia when switched to Purina pellets or slightly bitter milk; but when switched from pellets or adulterated milk to milk, tolerant Ss were anorexic only 1 day and then ingested significantly more of the new diet. Results are inconsistent with a conditioning interpretation. Tolerant Ss maintained their weight below the level of saline controls despite the recovery of food intake, and the level at which they maintained their weight varied with the palatability of the diet. These results suggest that AM lowers the settling point for body weight and that tolerance to this effect does not develop. Thus, the reinstatement of prolonged anorexia when apparently tolerant Ss were switched to a less palatable diet can be understood as an attempt to attain a lower weight level. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food motivation and body weight levels in hypothalamic hyperphagic rats: A dual lipostat model of hunger and appetite.

Compared the food and water motivations of 26 normal and 29 hyperphagic female Carworth CFE rats using barpressing performance on continuous reinforcement, VI, and fixed-ratio schedules. Under conditions of food or water deprivation, hyperphagic Ss displayed normal barpressing rates for food or water when their body weights were limited to preoperative or control levels but subnormal barpressing rates when they were tested at obese body-weight levels. Under nondeprived conditions, dynamic hyperphagic Ss barpressed more than controls for a palatable milk diet, while obese hyperphagic Ss worked at control levels for this diet. The findings suggest a dual lipostat model of hunger and appetite to explain feeding and body weight regulations in normal and hypothalamic hyperphagic animals. (62 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of gastric reduction surgery on consummatory behavior in the rat.

When the gastric capacity of 10 male Sprague-Dawley rats were reduced by partitioning a portion of the cardiac region of the stomach, they ate significantly less than did 10 sham-operated Ss during restricted (2-hr) access to either a liquid or a solid diet. Experimental Ss not only ate less during 2-hr food access, they appeared to satiate more quickly than sham-operated Ss. In contrast, when food was continuously available, the food intake of experimental Ss did not differ from that of controls. In addition, the water intake of experimental Ss was not significantly different from that of controls under either ad-lib or restricted access. Thus, reducing stomach capacity by partitioning a portion of the cardiac region appears to produce a relatively specific disruption of feeding behavior under conditions of restricted access. Implications for the study of gastric feeding mechanisms and for the surgical treatment of morbid obesity in humans are discussed. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)