Level Of Food Motivation Research Articles

Involvement of Peripheral Opioid Receptors in the Realization of Food Motivation Into Eating Behavior.

The involvement of peripheral opioid receptors in the mechanisms of eating behavior is still unclear. The aim of this work was to study the role of peripheral, predominantly gastric mu and delta opioid receptors in the realization of food motivation in conditions of different energy costs for eating behavior. Experiments were performed under a between-sessions progressive ratio schedule of reinforcement in food-deprived rats. The level of food motivation was calculated using a self-developed method. Food intake, motor activity, and metabolic rate were recorded in fed and hungry animals. Results showed that intragastric administration of the mu opioid receptor agonist DAMGO led to an increase in the level of food motivation in the light variant of operant feeding behaviors. Food consumption did not change. At high costs for feeding behavior, the administration of DAMGO did not alter food motivation; however, food consumption and motor activity were reduced. Intragastric administration of the delta opioid receptor agonist DADLE did not lead to changes in the level of food motivation and physical activity, but inhibition of feeding behavior was observed in all reinforcement schedules. Three regulatory pathways of eating behavior in difficult food conditions by peripheral, predominantly gastric opioid receptors are hypothesized: environmental-inhibitory afferentations and suppression of the realization of food motivation into behavior; homeostatic-inhibitory action on food motivation; and rewarding-suppression of the anticipatory reinforcement.

Effect of peptide agonists of peripheral opioid receptors on operant feeding behavior and food motivation in rats.

We studied the effect of intragastric administration of peptide agonists of μ-opioid receptors (DAMGO) and δ-opioid receptors (DADLE) on food consumption and food motivation during operant feeding behavior of different intensity and effectiveness. To obtain one food granule, trained rats should press a lever 1 time (day 1), 2 times (day 2), 4 times (day 3), 8 times (day 4), 16 times (day 5), or 32 times (day 6). Activation of δ-opioid receptors in the stomach was followed by suppression of feeding behavior at low energy expenditure. The level of food motivation under these conditions practically did not differ from the control. Activation of μ-opioid receptors in the stomach suppressed energy-consuming feeding behavior, which was accompanied by an increase in the level of food motivation. It can be hypothesized that protein metabolites exhibiting μ-opioid activity probably provide afferent signals into CNS via the vagus nerve to terminate energy expenditure under adverse conditions (although food motivation is not satisfied). Food motivation under these conditions probably contributes to the behavior aimed towards the search for more available food.

Method for determining the level of food motivation in rats.

A new method for the quantitative evaluation of the level of food motivation was developed. This method takes into account not only the information, but also the energy component of operant feeding behavior of different intensity and effectiveness with a simultaneous study of metabolism by means of indirect calorimetry. Our experiments showed that an increase in the number of lever pressing episodes (from 1 to 8) to obtain one food granule during operant feeding behavior is accompanied by a progressive decrease in the level of food motivation. The level of food motivation remains practically unchanged with an increase in the ratio of pressing episodes to 16 and 32 (despite consumption of food).

Effects of Electrical Stimulation of the Hunger Center in the Lateral Hypothalamus and Food Reinforcement on Impulse Activity of the Stomach in Rabbits under Conditions of Hunger and Satiation

Stimulation of the lateral hypothalamus in preliminary fed animals in the presence of the food is associated with successful food-procuring behavior, accompanied by regular generation of high-amplitude slow electrical waves by muscles of the lesser curvature, body, and antrum of the stomach, which was reflected in the structure of temporal organization of slow electrical activity in the form of unimodal distribution of slow wave periods typical of satiation state. Despite increased level of food motivation caused by stimulation of the lateral hypothalamus, the additional food intake completely abolished the inhibitory effects of hunger motivation excitement on slow electrical muscle activity in the lesser curvature, body, and antrum of the stomach of satiated rabbits. Changes in slow electrical activity of the stomach muscles in rabbits deprived of food over 24 h and offered food and associated food-procuring behavior during electrical stimulation of the lateral hypothalamus have a two-phase pattern. Despite food intake during phase I of electrical stimulation, the downstream inhibitory effect of hunger motivation excitement on myogenic pacemaker of the lesser curvature of stomach abolishes the stimulating effect of food reinforcement on slow electrical muscle activity in the lesser curvature, body, and antrum of the stomach. During phase II of electrical stimulation, the food reinforcement decreases inhibitory effect of hunger motivation excitement on myogenic pacemaker of the lesser curvature that paces maximal rhythm of slow electrical waves for muscles activity in the lesser curvature, body, and antrum of the stomach, which is reflected by unimodal distribution of slow electrical wave periods. Our results indicated that the structure of temporal organization of slow electrical activity of the stomach muscles reflects convergent interactions of food motivation and reinforcement excitations on the dorsal vagal complex neurons in medulla oblongata.

Characteristics of Rabbit Food-Procuring Behavior as an Indicator of Changes in the Level of Hunger Motivation

We proposed new method for measuring dynamic changes in hunger motivation in rabbits in the course of satisfaction of nutritional need by weight, time, and rate parameters of effective food-procuring behavior. Transformation of the amount of food eaten into the electric signals was performed using electronic weighing machine incorporated into hardware and software system. The most conclusive characteristic for decrease in hunger motivation in the course of first effective food-procuring act was the period of food-procuring cycles, which values increase significantly as animal satisfies its nutritional need, whereas amount of the food consumed for each food-procuring cycle remains constant. Integral characteristics of food-procuring behavior reflect higher level of food motivation in the course of first effective food-procuring act in comparison to the subsequent ones.

Method of Evaluation of Dynamic Changes in Food Motivation in Rabbits during Successful Food-Procuring Behavior

We developed a method for evaluation of dynamic changes in the level of food motivation in rabbits during successful food-procuring behavior. Quantitative and temporal parameters of food consumption over each successive cycle of food-procuring behavior were used. The amount of consumed food was converted into electrical signal using an electronic balance incorporated into a hardware-software complex. Temporal parameters of food-procuring activity were determined by changes in electric signal in real-time mode. This method makes it possible to record simultaneously food-procuring activity and impulse activity of masticator muscles and esophageal muscles, which enables parallel analysis of rhythms of food consumption, mastication, and swallowing.

Effects of Electrical Stimulation of the Hunger Center in the Lateral Hypothalamus and Food Reinforcement on Impulse Activity of the Proper Masticatory Muscle in Rabbits under Conditions of Hunger and Satiation

Threshold stimulation of the lateral hypothalamus in starving and preliminary fed (satiated) rabbits in the absence of feed induces searching behavior associated with burst-like impulse activity of proper masticatory muscle with a bimodal distribution of interpulse intervals, what represents an anticipatory type of reaction. The increase in the level of food motivation during threshold stimulation of the lateral hypothalamus in starving and satiated rabbits with the food offered led to successful food-procuring behavior, during which the frequency and amplitude of spike bursts in the proper masticatory muscle become comparable with those under conditions of natural foraging behavior stimulated by the need in nutrients. Motivational excitation and backward afferentation from food reward are addressed to the same neurons of the masticatory center in the medulla oblongata.

Functional Asymmetry of the Frontal Cortex and Lateral Hypothalamus of Cats During an Operant Food-Related Conditioned Reflex

The extent of correlation and the latency of evoked potentials to sound, recorded bilaterally in the frontal cortex and lateral hypothalamus of cats, were studied at different stages of the acquisition of an operant food-related reflex and during sudden transfer to 30% food reinforcement. High correlation coefficients between the evoked responses of the cortex and hypothalamus with left-sided dominance were seen in conditions of high levels of food motivation at the beginning of each experiment and in conditions of the high-probability appearance of the acquired conditioned reflex throughout the rest of the experiment. Comparison of the peak latencies of the early positive (P55-80) components of evoked potentials on the right and left sides showed that shorter latent periods were seen in the cortex on the left side at all behavioral stages, while this occurred (on the left side) in the hypothalamus only when the conditioned reflex was unfixed, while after fixation of the reflex and provision of 30% reinforcement, shorter latent periods were seen on the right side. It is concluded that the high level of left-sided correlation of evoked potentials in the hypothalamus was associated with the motivational and motor components of purposive behavior and was not associated with the emotional tension of the animals provoked by the disruption of the food reinforcement stereotype.

Organization of neural networks in the neocortex.

Implanted semimicroelectrodes were used in conscious cats to record spike discharges from groups of close-lying neurons, i.e., multineuron activity, in the deep layers of the frontal and motor areas of the cortex at different levels of food motivation. Spike activity was extracted from 4-7 neurons and interneuronal interactions were studied by cross-correlation analysis between neighboring neurons in each zone (local networks) and between neurons in two zones (distributed networks) with analysis epochs of 0-100 msec. The results showed that neurons in local networks can be divided into two subgroups: neurons with high-amplitude spikes and a predominance of output (divergent) connections and neurons with low-amplitude spikes and a predominance of input (convergent) connections. Local networks are based on powerful monosynaptic connections (with delays of up to 2 msec) between large and small neurons. Most connections in distributed networks were between small neurons in local networks of the frontal cortex and large neurons in local networks in the motor cortex. Food deprivation for 24 h mainly affected late (with delays of 2-100 msec) cross-correlation interneuronal relationships in both local and distributed networks.

Functional organization of local neural networks in the cat neocortex. Relationship to the level of food motivation.

Implanted semimicroelectrodes were used to record multineuron activity--spike discharges from groups of close-lying neurons--in the deep layers of the frontal and motor cortex in conscious cats with different levels of food motivation. Spike activity from 4-7 neurons was extracted from multineuron activity, and interneuron interactions were studied by cross-correlation analysis. Neurons in local networks were divided into two subgroups: neurons with high-amplitude spikes with a predominance of output (divergent) connections, and neurons with low-amplitude spikes and a predominance of input (convergent) connections. Food deprivation lasting 24 h affected mainly the nature of interneuron interactions in the range of late cross-correlational connections (with delays of 2-100 msec).

The behavior of ants in a maze in response to a change from food motivation to protective motivation.

The ability of Myrmica rubra scout ants to modify the foraging habit, formed in a symmetrical multiple-choice maze, in the situation in which the reinforcement (syrup) was replaced with a brood of the same species was studied. When the "test" was performed at the same high level of food motivation of the family as applied during training, the ants were able successfully to transfer to another type of social behavior - transporting of the brood. When the high-level food motivation was replaced with a low-level motivation, some of the ants were unable to modify the habit. Preliminary utilization in these conditions of reinforcement as a switching factor addressing the motivational system for protective behavior promoted successful performance of the "test." Criteria allowing identification of different methods of modifying behavior during the switch from food motivation to protective motivation were developed. A total of 37.5% of the ants transferred the strategy formed during training: 40.6% showed gradual remodeling. while 21.9% of individuals immediately used the new strategy.

Integrative activity of cortical neurons in the systems organization of food behavior.

The spike activity of neurons in the visual and parietal areas of the cerebral cortex was studied in cats at sequential steps of operant food-procuring behavior. Cells had individual patterns of spike activity, and changes in different areas of the cortex were associated with the modality of the conditioned stimulus, the level of food motivation, and the effectiveness of achieving the step-by-step results of behavior. The distribution of spike activity on the axon of a neuron reflected the dynamics of its integrative activity and depended on the pre-existing functional state of the cell and the ongoing synaptic activation during the development of key mechanisms of the central architecture of the functional system for the behavioral act.

Time organization of frontal-motor cortex interneuron interactions in the cat neocortex in conditions of different levels of food motivation.

Studies were carried out in conscious cats with recording of multicellular activity in moderate hunger and after 24-h food deprivation. Cross-correlation analysis was used to assess statistical interneuron interactions between closely-located neurons in the frontal and sensorimotor regions of the neocortex (local networks), and between the cells of these regions (distributed networks). One-day food deprivation increased the number of interactions formed within both local and distributed neuron networks. Increases in intercortical connections between the frontal and motor regions was seen at all time intervals studied (0-100 msec), though the most significant changes occurred at time intervals of up to 30 msec.

Variety in the flavor of food enhances eating in the rat: A controlled demonstration

The effect of variety in the flavor of food on rats' consumption of a meal was examined in two experiments in which the confounding factors of diet composition and palatability could be ruled out. Experiment 1 showed that rats ate more of a four-course meal when each course was flavored differently than when each course was flavored the same; furthermore, this “variety effect” did not appear to depend upon the rats' prior experience with the flavors. Experiment 2 replicated and extended these findings by showing that the enhancement of eating by variety did not depend critically upon the rat's level of food motivation. The results were discussed in terms of their implications for the etiology and control of obesity, as well as for theories of satiety. It was suggested that the “variety effect” may represent an adaptive mechanism in the control of feeding.

Role of the frontal lobes in integrative activity of the brain in Macaca mulatta.

Unit activity in the frontal cortex (s. principalis) during the performance of a complex behavior program--nonspecific expectation after a warning stimulus, conditioned stimulus, and delay period, trigger signal, and alternative choice, followed by food award--was studied by the multineuronal recording method. Processes of combination of external stimuli into an integrated program, retention of stimulus traces in the memory, and correct and incorrect problem solving were reflected in the unit activity of s. principalis. The level of the correct responses of choice and the corresponding correlates in modifications of unit activity depended directly on the level of food motivation. The results are discussed from the standpoint of the evolutionary formation of the thalamo-frontal association system of the brain, connected with the formation of behavior programs in accordance with current biological motivation.