[Combined lesions of ventro-medial hypothalamus and dorso-medial thalamus: effects on interspecific social behavior, emotional reactivity and feeding behavior in the rat].
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Feed intake was measured following injections of gamma-aminobutyric acid (GABA), muscimol (a GABA agonist), and picrotoxin (a GABA antagonist) into the lateral ventricles of satiated sheep. Doses ranging from 0.20 to 3200 nmol of GABA did not affect feeding behavior at 15, 30, 60, and 120 min postinjection. A dose of 160 nmol of muscimol induced a marked increase in feeding, comparable to that provoked by an injection of 78 mumol of pentobarbital. Muscimol-induced feeding was blocked effectively by a preinjection of picrotoxin. These observations implicate that neurons sensitive to gamma-aminobutyric acid may be involved in the control of feeding behavior in ruminants.
Feeding at the beginning of the night is probably dependent on the rat's immediate energy requirements while feeding at the end may have an anticipatory function. This latter feeding peak may be mainly controlled by a circadian pacemaker. The aim of this study was to investigate the relative contribution of satiety signals and circadian pacemakers in the control of feeding behavior. Food intake was monitored after infusion of liquid food into the stomach during several parts of the day-night cycle to prevent a possible influence of oral sensations. It is demonstrated that intragastric infusion is more effective in suppressing intake during daytime and the first half of the dark phase than during the second half of the dark phase. Suppressions of food intake are mainly due to delaying the first occurrence of food ingestion, whereas the size of that meal is less affected. During the last period of the night no significant delay could be brought about. These experiments suggest that in the rat a circadian pacemaker dominates feeding motivation during the end of the night thereby strongly interacting with caloric control of feeding behavior.
Evidence indicates that feeding behavior in rats is controlled by a mechanism that integrates information about different aspects of fuel metabolism. We investigated the neural substrate for this integrated control by measuring the effect of metabolic inhibitors given alone and in combination on food intake and neuronal activity as reflected by the expression of c-Fos protein. Combined administration of methyl palmoxirate (5 mg/kg po), an inhibitor of fatty acid oxidation, and 2,5-anhydro-D-mannitol (150 mg/kg ip), which decreases liver ATP content, increased feeding in rats more than expected on the basis of eating responses after treatment with either inhibitor given alone. Combined treatment also produced a synergistic increase in Fos-like immunoreactivity in several brain areas, including the nucleus of the solitary tract, area postrema, and parvocellular portion of the hypothalamic paraventricular nucleus. These findings provide strong evidence for the involvement of selected brain regions in the metabolic control of food intake and suggest that metabolic information used to control feeding behavior is integrated in the periphery or at the level of the brain stem.
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The feeding behavior of four Munich miniature pigs (29-43 kg) housed in pairs of two, was observed for two consecutive weeks. Pigs were conditioned to operate a computer-controlled recording system equipped with feeders delivering a precise food release per response and were then fed ad libitum. In addition to the descriptive analysis of feeding behavior, Walsh-Fourier Spectral Analysis was utilized to investigate the temporal patterns of food ingestion and the synchronisation of feeding patterns between the animals housed together. The pigs had up to 48% of their daily energy intake during the dark cycle and there was a substantial reduction of food intake from the first to the second week. Furthermore, pigs housed together synchronized feeding behavior from week 1 to week 2. The recording system has been shown to be highly reliable and valid and provides an excellent tool for the investigation of ingestive behaviors in miniature pigs.
Conceptually, the neural regulation of feeding behavior is proposed to be a function of the activities of a long-term (day to day) and a short-term (meal to meal) control system. Although these two control systems are presumably involved in a continuous and dynamic interaction, they can be behaviorally and anatomically separated by specific regulatory challenges and brain lesions. Utilizing this general regulatory model for the hypothalamic control of feeding behavior, the effects of estrogen on a variety of behavioral indices of energy regulation are reviewed and discussed. The effects of ovarian hormones on the feeding behavior of both prepubertal and adult female rats when faced with a series of regulatory tests shown to provide specific information about the long- and short-term control of feeding behavior leads to the following conclusions. Modulation of feeding behavior by ovarian hormones is detectable well before the time of puberty in the female rat and is expressed in terms of a 4-day periodicity that is very similar to adult animals. Estrogen appears to modulate feeding behavior primarily by modifying the long-term control of feeding behavior or else the manner in which nutrients are integrated into this long-term system. It is further proposed that estrogen acts upon metabolically specific and unique neural elements in the hypothalamus whose function is to translate error signals derived from the long-term integration of body nutrients into appropriate readjustments in feeding behavior. Although this dual-regulatory model for the hypothalamic control of feeding behavior can account for the majority of the effects of estrogen on feeding behavior, further studies suggest that an "extrahypothalamic" mechanism must mediate certain aspects of the neural control of feeding behavior as well as the behavioral effects of estrogen. Specifically, the present model system can account for the role of carbohydrates in the neural control of feeding behavior, but fats and possibly proteins can modify feeding behavior independent of the hypothalamus. Likewise, estrogen can influence the efficiency with which nutrient loads of fats and proteins can modify subsequent feeding behavior and therefore this proposed "extrahypothalamic" mechanism may mediate those effects of estrogen on feeding behavior that cannot be accounted for by the present dual-regulatory model.
Problems related to feeding behavior in horses fall into three main categories: underconsumption, overconsumption, and abnormal consumption. Anorexia may be caused by a variety of diseases and overcome by removing the underlying causes (pain, fever), and physical or chemical stimulation of appetite. "Hypophagia" may be caused by poor dentition, disease, or stress. Again, removal of the cause or stimulation by physical or chemical means may improve intakes. Acute and chronic overconsumption of feeds are reflections of the normal controls (or lack thereof) of feeding in the horse. The only reliable prevention is to limit access to feeds. Abnormal eating behaviors such as pica or coprophagy are usually caused by a dietary imbalance or boredom. Coprophagey, however, is a normal behavior in young foals. Drinking disorders are rare, the only common one being the avoidance of "strange" water. Masking water at home with specific flavors such as peppermint or vinegar may encourage the horse to drink water from other sources to which the "home" flavor has been added.
The striking similarity between aquatic feeding behaviors in fishes and tetrapods and terrestrial prey transports in tetrapods and their contrasts to terrestrial tongue projection kinematics have led to a general hypothesis that terrestrial prey capture evolved from terrestrial prey transport, which, in turn, evolved from aquatic feeding behavior. This hypothesis is examined in Salamandra salamandra by comparing the kinematics of prey capture and transport before and after metamorphosis in the same group of eight individuals. Kinematics of aquatic and terrestrial strikes and transports are used to describe the metamorphosis of feeding behavior in S. salamandra and provide the first kinematic description of both aquatic and terrestrial feeding behaviors in the family Salamandridae. On the basis of the shared characteristics among the four behaviors, the two aquatic behaviors are most similar, and these are more similar to terrestrial transports than to terrestrial strikes. Given the ontogenetic polarity of these behaviors in salamanders, I suggest, on the basis of the shared similarities and functional shifts, that terrestrial transport is an intermediate behavior between aquatic feeding and terrestrial tongue projection. These results support the hypothesis that a shift from aquatic feeding to terrestrial transport to terrestrial tongue projection represents an evolutionary transformation series in the evolution of terrestrial feeding in early tetrapods.
Feeding behavior mutants of the fruit fly Drosophila melanogaster having point-mutations were isolated. The defects were analyzed in order to study the mechanism of feeding behavior. Point-mutations named febB (three allele) and febA (three allele) were located between the X-chromosome markers cho and cv and between the markers cv and v, respectively. The febB mutants showed a higher acceptance threshold of the proboscis extension reflex than wild-type flies and showed a normal chemosensory response to the electrophysiological test. The mutant (febB2) showed a higher starvation tolerance than the wild-type fly, but this was not a cause of the high acceptance threshold. Mosaic analysis was applied to the mutant. Internal tissues were suspected to be the primary focus of the abnormal behavior.
Short-term feeding behavior of pigs has been analyzed using random process models and log-normal models. Both were successful despite very different underlying assumptions relating to the theory of control. Feeder visits of growing pigs, housed individually from 17 to 52 kg live weight, were recorded electronically over a continuous period of 35 days. For the combined data, intervals between visits to the feeder greater than 30 min could be described well by the negative exponential model. The starting probability of a visit was constant at around 0.3, suggesting randomness. Disaggregating the data for individual pigs or for individual weeks did not change this conclusion. Intervals in the day were of a different nature to those at night, and disaggregation of the data into these two periods revealed that the negative exponential model was not satisfactory for either period. The starting probability for both periods increased with time since the last visit. This is consistent with the idea of satiety. Therefore, the apparent randomness in the data pooled across the day and night is an artefact caused by pooling itself, and is not in conflict with the satiety concept. The implications of data handling are discussed with reference to studies of the physiological control of food intake.
Feeding behavior was compared between infected and uninfected field-collected groups of Anopheles gambiae sensu lato and An. funestus from western Kenya. A significantly greater percentage (81%) of Plasmodium falciparum-infected An. gambiae s.l. females probed on experimental hosts (hamsters) than did uninfected females (38%). Among those females that initiated probing, there was no effect of infection status on the ability to take a bloodmeal. Plasmodium falciparum-infected An. gambiae s.l. probed more often (mean = 4.0) and for a longer time (mean = 277 sec) than did their uninfected counterparts (mean = 2.4 probes and mean probing time = 214 sec). Results for the small number of An. funestus that fed followed the same trend. Among infected An. gambiae s.l. females, there was no effect of sporozoite density on either the number of probes made or the total probing time. Among uninfected females, there was no difference in feeding behavior between nulliparous and parous females. In laboratory experiments, female age had no effect on blood-feeding behavior. Our findings provide evidence that natural malaria infection modifies the feeding behavior of Anopheles females.
Feeding behavior in Aplysia fasciata and A. oculifera is modified by pairing the behavior with reinforcing consequences. Successful and unsuccessful attempts to transfer food from the buccal cavity to the crop act as positive and negative reinforcers, respectively. A number of changes in feeding behavior occur as a result of pairing of feeding with the negative reinforcer: feeding responses become less effective in leading to the entry of food into the buccal cavity; when food does enter the buccal cavity, it exits sooner; swallowing responses after food entry are less likely to occur; Aplysia eventually cease responding to food. Pairing successful transfer of food into the crop with feeding behavior produces opposite effects. Behavioral change is specific to pairing, as shown by lack of change when reinforcement is explicitly unpaired with feeding behavior. Behavioral change is specific to foods with a particular taste and texture; generalization to alternate foods was not observed. In spite of cessation of feeding, animals remain aroused, as shown by low response latency to alternate foods. Memory of response change persists for at least 48 hr.
The recovered feeding behavior and effects of electrical stimulation of the dorsal hippocampus (HIP) and frontal cortex (FC) on different stages of feeding behavior were studied in rabbits after bilateral lesions of the lateral hypothalamus (LH). Severe damages to food motivation were recorded, which were primarily manifested by the absence of active search for food by hungry animals. Electrical stimulation of HIP and FC inhibited feeding behavior. This was shown by the increased latent period of feeding behavior and by the arrest of the already developed food reaction. The preservation of fronto-hippocampal inhibition after intravenous injection of droperidol (0.3 mg/kg) and atropine (1 mg/kg) seen in experimental animals (comparatively to intact ones) indicates that in rabbits with bilateral LH lesions the feeding behavior is realized by the new integration of cholinergic and dopaminergic brain structures.
The feeding behavior of Aplysia californica can be classically conditioned using tactile stimulation of the lips as a conditioned stimulus (CS) and food as an unconditioned stimulus (US). Moreover, several neural correlates of classical conditioning have been identified. The present study extended previous work by developing an in vitro analog of classical conditioning and by investigating pairing-specific changes in neuronal and synaptic properties. The preparation consisted of the isolated cerebral and buccal ganglia. Electrical stimulation of a lip nerve (AT4) and a branch of the esophageal nerve (En2) served as the CS and US, respectively. Three protocols were used: paired, unpaired, and US alone. Only the paired protocol produced a significant increase in CS-evoked fictive feeding. At the cellular level, classical conditioning enhanced the magnitude of the CS-evoked synaptic input to pattern-initiating neuron B31/32. In addition, paired training enhanced both the magnitude of the CS-evoked synaptic input and the CS-evoked spike activity in command-like neuron CBI-2. The in vitro analog of classical conditioning reproduced all of the cellular changes that previously were identified following behavioral conditioning and has led to the identification of several new learning-related neural changes. In addition, the pairing-specific enhancement of the CS response in CBI-2 indicates that some aspects of associative plasticity may occur at the level of the cerebral sensory neurons.
We studied the feeding rhythms and feeding patterns of adult Long-Evans rats treated with monosodium glutamate (MSG) in their early post-natal period. This treatment is known to induce neuronal degeneration in the arcuate nucleus (ARC), a major hypothalamic site implicated in the regulation of feeding. Neonatal rats were treated intraperitoneally with MSG or saline (controls) alone on the first days of life. At age of 6 months, male control and male MSG rats were placed in our automatic feeding system, and the structure of feeding behavior and diurnal feeding rhythms were analysed. On a 24 hours basis, MSG rats ate less than control rats (-24%). This hypophagia resulted from a mild diurnal hyperphagia (+6%) and a pronounced nocturnal hypophagia (-34%). This hypophagia was the main consequence of a decrease of meal size in MSG rats (-37%) and was associated with an increase in meal duration (+52%). It was also associated with a total disappearance of the two feeding peaks that normally occur at light and dark onset in the rat (-90% 2 h after dark onset and -49% 2 h before light onset). These results indicate that neonatal treatment with MSG induces important changes in feeding patterns and feeding rhythms in the adulthood. These changes might be related to the disappearance of neurotransmitters located in the arcuate nucleus.
The pharmacology of adult Phormia regina (Meigen) feeding behavior was explored by injecting candidate drugs into starved blowflies and then determining their responsiveness to aqueous sucrose, via the proboscis extension reflex. d-Amphetamine caused responsiveness to fall dramatically, while related drugs and biogenic amines had varying effects. When d-amphetamine-treated flies were fed 1 M sucrose, they consumed significantly more than control flies. Electrophysiological studies demonstrated that the responses of tarsal sugar receptor neurons to aqueous sucrose were not significantly altered by d-amphetamine. These observations are compatible with our hypothesis that octopamine positively modulates blowfly feeding behavior and suggest that other aromatic biogenic amines affect feeding behavior in this insect.