Trigeminal orosensation and ingestive behavior in the rat.

Used a deafferentation procedure with male Wistar rats to examine the contributions of trigeminal orosensation to control of ingestive behavior. The procedure removed somatosensory input from the mouth while sparing olfaction, lingual taste, vibrissae inputs, and proprioceptive afferents from and efferents to the jaw muscles. Ss with sections of tongue or jaw muscle efferents served as controls. Bilateral trigeminal orosensory deafferentation was followed by effects on ingestive behavior, the magnitudes of which were proportional to the extent of the deafferentation. The trigeminal syndrome includes aphagia and adipsia, impairments in the sensorimotor control of eating and drinking, decreased responsiveness to food and water, and a reduction in the level of body weight regulation. Trigeminal deafferentation spared elementary ingestive movement patterns (biting, licking, and chewing) but disrupted their control by the perioral stimuli. Deficits in food intake varied with the sensory properties of the diet. Recovery of intake took place along a palatability gradient, and recovery of water intake paralleled that of dry food. The chronically reduced body weight was caused by persistent hypophagia and reflected reduced responsiveness to food. Findings suggest a considerable degree of overlap in the neural mechanisms mediating the sensorimotor and motivational control of intake in the rat. (76 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustation and ingestive behavior in the rat.

Studied the contribution of taste to the quantitative control of intake and body weight in 15 male Wistar rats. Gustatory deafferentation was produced by combined bilateral section of the chorda tympani and glossopharyngeal nerves and the pharyngeal branch of the vagus nerve. The procedure did not affect the condition of the mouth, impair orientation to sensory stimuli, or severely disrupt the consummatory sequence. Nevertheless, deafferented Ss showed reduced responsiveness to food and water, elevated quinine HCl aversion thresholds, and impaired feeding efficiency. Food and water intake and body weight remained below control levels for at least 40–50 days postoperatively. Food intake deficits were not observed when Ss were offered ad lib pablum, a result suggesting that increased palatability could compensate for decreased gustatory input. The order of recovery of food intake through different diet types suggests a heightened responsiveness to taste stimuli. The effects of gustatory deafferentation are compared with those seen after section of trigeminal orosensory nerves, and the differential contributions of oral taste and oral touch are discussed. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oral somatosensory factors in dietary self-selection in rats.

To study the mechanisms of the control of protein intake, 38 male albino Sprague-Dawley rats were subjected to partial trigeminal deafferentation. Oral somatosensory afferents from the lower anterior portion of the oral cavity were selectively sectioned, but somatosensation of the other parts of the mouth as well as gustatory and olfactory afferents were left intact. Ss were allowed to choose from 3 diets, only one of which contained protein. Before deafferentation, Ss chose a constant portion of their daily intake in the form of protein. After deafferentation, protein intake was all but eliminated at first but was resumed later; carbohydrate intake was reduced. When total intake had recovered to nearly preoperative values, the protein/total-intake ratio remained impaired, with deficits that ranged from seemingly random selection to extreme preferences. The variability of dietary selection between days was considerably higher than before surgery. The involvement of learning processes in homeostasis is discussed. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of taste in dietary self-selection in rats.

Conducted 3 experiments with 78 male albino Harlan and Sprague-Dawley rats in which Ss were subjected to 2 degrees of gustatory deafferentation—either the chorda tympani was sectioned alone or in combination with the glossopharyngeal nerve and the pharyngeal branch of the vagus. Ss were then presented with 2 diets, only 1 of which contained protein. Findings reveal that, after surgery, deficits were observed in body weight, food and water intake, and diet selection that were proportional to the extent of deafferentation. Approximately 76% of the Ss increased protein and decreased carbohydrate intake, but all Ss continued to select a nutritionally balanced diet (Exp I). When subjected to a nutritional challenge of intragastric protein or carbohydrate supplementation, the Ss compensated for calories and nutrients by selectively adjusting oral intake (Exp II). In saccharin preference tests, the preference as well as the total consumption of the test solutions was reduced (Exp III). Results support the hypothesis that dietary selection pattern of an animal not only reflects intrinsic factors (metabolic/physiological state) but also extrinsic factors such as the pallatability and accessibility of the diet. Findings are contrasted to the effects of oral somatosensory deafferentation and are interpreted as a change in preference within the limits of metabolic requirements. The different roles/mechanisms of the 2 sensory systems in regard to dietary self-selection are discussed. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oral somatosensory factors in dietary self-selection after food deprivation and supplementation.

In 2 experiments with 72 male albino Sprague-Dawley rats, trigeminally deafferented Ss were subjected to nutritional stresses while being allowed to balance protein and carbohydrate intake from 3 separate dietary fractions. Partially trigeminally deafferented Ss that had recovered a normal protein ratio (protein/total intake) underwent total food deprivation (Exp I) or intragastric (IG) supplementation of protein or carbohydrate suspensions (Exp II). In response to deprivation, control Ss increased protein intake above ad-lib levels, but not carbohydrate intake. In response to IG supplementation, they decreased protein intake disproportionately more than carbohydrate intake when the fluid consisted of protein and vice versa when the fluid consisted of carbohydrate. The recovered deafferented Ss showed no selective increase in protein intake after deprivation and no differential compensation to nutrient supplementation. This suggested that recovery of the protein ratio after partial trigeminal deafferentation could not fully replace the function of trigeminal somatosensory input. The possible roles of other orosensory and of postingestional factors for recovery are discussed. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trigeminal deafferentation and hunger in the pigeon (Columba livia).

In 2 experiments with a total of 48 White Carneaux and Silver King pigeons, the location and distribution of the pigeon's trigeminal nerve permitted afferentation of the oral region without affecting motor functions. Although trigeminal deafferentation did not affect drinking, it reduced the efficiency of the consummatory response of eating and disrupted motivational processes underlying hunger and weight regulation. Although the 2 types of deficit may be experimentally dissociated, trigeminal deafferentation invariably affected both sensorimotor and motivational mechanisms. The deficits in food intake and weight regulation seen after trigeminal deafferentation in the pigeon resembled some components of the "lateral hypothalamic syndrome" in the rat. Results are related to recent studies of the contribution of peripheral and central oropharyngeal factors to the neural control of food intake in both rat and pigeon. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

CCK-8 inhibits ingestive behavior in rats with lateral hypothalamic 6-OHDA lesions

Male rats were injected with 6-hydroxydopamine in the lateral hypothalamus and tested for ingestive behavior starting on the day after the injection. The rats did not eat food pellets but readily ingested an intraorally infused nutritive solution. If given three daily intraoral infusions, 6-hydroxydopamine-treated rats defended their body weight and were as sensitive to the inhibitory effect of cholecystokinin octapeptide on intake as controls. Dopamine was reduced by 94% in the dorsal striatum five days after the 6-hydroxydopamine injection. Noradrenaline and serotonin were less markedly affected. Thus, while appetitive ingestive behavior is disrupted, consummatory ingestive behavior and body weight regulatory competence are only marginally affected by massive damage to forebrain dopamine neural networks.     

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)     

Relation of consummatory responses and preabsorptive insulin release to palatability and learned taste aversions.

In 6 experiments with 68 male Sprague-Dawley rats, the oral stimulation arising from food in the mouth produced a stereotyped sequence of ingestive consummatory responses and a rapid release of insulin prior to the absorption of nutrients into the blood. Conversely, when noxious taste stimuli were infused into the mouth, a different, aversive set of consummatory responses was evoked, and no insulin was released. These experiments demonstrate that pairing a sapid taste solution with LiCl reversed the consummatory response sequence to subsequent presentations of that taste from ingestion to aversion and abolished the preabsorptive release of insulin to that taste; this indicated an experience-produced shift in the palatability of the taste. It was further shown that a palatable but categorically noncaloric taste elicited behavioral ingestion but no insulin release. It is concluded that separate but related control systems operate to produce consummatory behavior and ingestive neuroendocrine responses. (64 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: II. Independent ingestive behavior.

In 4 experiments, Charles River rat pups 3 days of age and older consumed large quantities of milk, sucrose, and wet mash when the Ss were placed in warm containers in which one of these diets had been spread on the floor. The volume of Ss" intake was directly related to the severity of food deprivation. Ingestive behavior occurred in the early part of the 30-min test, but later in the test, Ss stopped feeding and became quiescent. Their ingestive behavior thus resembled that of adults in (a) the motor aspects of feeding responses (licking and lapping), (b) the dependency on deprivation for intake, and (c) the pattern of intake termination. However, in Exp IV, when diet was restricted to a small area of the test container, young Ss consumed little diet. They did not appear able to direct or focus their ingestive responding. It was not until 9–12 days of age that Ss successfully consumed milk from a localized source. (29 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)     

Variation in human masticatory behavior under temporal constraints.

Recorded the consummatory behavior of 20 18-20 yr. old students asked to eat peanuts or carrots (a) at their normal rate, and (b) under constraints to hurry. It was found that Ss decreased their meal time when under temporal constraints by reducing the number of masticatory strokes, chewing faster, and making fewer and shorter pauses between bursts of chewing. The average forcefulness of each chewing stroke was greater when Ss were under constraints to hurry. These data are contrasted with previous studies examining consummatory behavior of food-deprived humans. It is suggested that the manner in which humans alter their consummatory behavior may depend upon the motivation for doing so and the type of foodstuff consumed. (23 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)     

Role of glucocorticoids in an abnormal grooming behavior in cats with pontile or frontal neocortical lesions.

Cats with pontile or frontal neocortical lesions display a tactually elicited dissociation of appetitive and consummatory grooming behaviors. In the present study with 75 adult male cats, systemic administration of glucocorticoids abolished the abnormal grooming behavior in cats with lesions, even when the stimulatory effect of glucocorticoids on serotonin metabolism was blocked by administration of para-chlorophenylalanine (PCPA). Microinjections of glucocorticoids into the superior colliculi also significantly decreased the abnormal grooming behavior. Adrenalectomized Ss did not display the abnormal grooming behavior, but the abnormal behavior did occur in PCPA-treated adrenalectomized Ss. Administration of either glucocorticoids or 5-hydroxytryptophan abolished the abnormal behavior in PCPA-treated adrenalectomized Ss. Thus, it appears that the pontile and frontal neocortical lesions produce deficits in both glucocorticoids and serotonin, and these deficits are necessary and sufficient conditions for inducing the abnormal grooming behavior. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of intrahippocampal administration of colchicine on incentive contrast and on radial maze performance.

Examined the behavior of rats given intradentate injections of colchicine (COL). In Exp 1, COL-treated, artificial cerebrospinal fluid (CSF)-treated, and untreated Ss did not differ in the intake of 32% and 4% sucrose solutions, nor did they differ in degree of successive negative contrast when the 32% solution was changed to 4% sucrose. In Exp 2, the COL-treated and CSF-treated Ss did not differ in degree of suppression in the intake of a 0.15% saccharin solution when it preceded 32% sucrose in once-daily pairings (anticipatory contrast), nor did they differ in reversal performance when saccharin–sucrose and saccharin–saccharin pairings were reversed. In Exp 3, the COL-treated Ss were substantially impaired in radial-arm maze performance compared with CSF-treated controls. Results suggest that a completely functioning hippocampus is not necessary for the memory of reward quality, the comparison of rewards, the suppression of behavior when reward is decreased, the formation of associations between 2 levels of reward, and the reversal of this association, as long as these processes are reflected in consummatory behavior. Data are interpreted in terms of differences between instrumental behavior and sensory memory and/or consummatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acute homeostatic imbalances reinstate sensorimotor dysfunctions in rats with lateral hypothalamic lesions.

It has previously been demonstrated that rats recovered from aphagia and adipsia after large bilateral electrolytic lesions of the lateral hypothalamic (LH) area do not show the normal feeding response to 2-deoxyglucose or drinking response to polyethylene glycol. The present work found that such homeostatic imbalances reinstate the profound sensorimotor impairments that are seen in the immediate postoperative period but abate in parallel with the gradual recovery of ingestive behaviors. Administration of alpha methyltyrosine or spiroperidol produced sensory and motor dysfunctions in male albino Sprague-Dawley rats with LH lesions that were similar to those observed after 2-deoxyglucose. Results suggest that the residual feeding and drinking deficits of Ss with LH lesions after apparent recovery of function do not reflect specific loss of putative gluco- and volume-regulatory contributions to ingestive behavior. Instead, they indicate continued impairments in nonspecific activational components of motivation that normally are mediated, in part, by central dopaminergic neurons. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of sympathectomy on the lateral hypothalamic lesion syndrome.

Two experiments with male Long-Evans rats examined sympathetic involvement in the lateral hypothalamic (LH) lesion syndrome. Ss were surgically or chemically sympathectomized and then given LH lesions. At 24 hrs postlesion, lesion-induced hyperglycemia but not hyperthermia was attenuated by splanchnicectomy and celiac ganglionectomy. Hyperthermia but not hyperglycemia was attenuated by adrenal demedullation, adrenalectomy, and daily neonatal guanethidine (50 mg/kg) treatment. Guanethidine-sympathectomized Ss also displayed lower basal temperatures, more perilesion chromatolysis, and more severe external symptoms than controls. No form of sympathectomy affected lesion-induced gastric pathology, plasma gastrin concentrations, or body weight loss, nor did any sympathectomy influence the recovery of ingestive behavior, daily food intake, the feeding response to 2-deoxy-dextro-glucose, or body weight maintenance in recovered LH-lesioned Ss. Results suggest that sympathetic hyperactivity contributed to some aspects of the acute LH syndrome: Hyperglycemia resulted from sympathetic outflow to the abdomen, whereas hyperthermia was determined by circulating catecholamines and extra-abdominal sympathetic innervation. Findings fail to support the hypothesis that chronic increases in sympathetic tone are responsible for the reduced food intake and body weight of the LH-lesioned Ss. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The propensity for nonregulatory ingestive behavior is related to differences in dopamine systems: Behavioral and biochemical evidence.

Investigated the relation between properties of dopaminergic neural systems and the predisposition to exhibit nonregulatory ingestive behavior in 54 male Long-Evans rats. It was found that Ss that ate and drank during electrical stimulation of the lateral hypothalamus (ESLH) showed greater behavioral sensitization to a series of amphetamine injections (3 mg/kg) than those that did not exhibit ingestive behavior during ESLH. In addition, footshock stress produced a greater increase in forebrain dopamine utilization in Ss that engaged in nonregulatory ingestive behavior. This evidence is consistent with the hypothesis that there are individual differences in the responsiveness of forebrain dopamine systems that are related to the behavioral predisposition to exhibit nonregulatory ingestive behavior. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)