Food-procuring Reflex Research Articles

Effects of Early Proinflammatory Stress on Anxiety and Depression-Like Behavior in Rats of Different Ages

Early proinflammatory stress created by administration of lipopolysaccharide (LPS) (50 μg/kg s.c.) on days 3 and 5 of postnatal life led to decreases in movement activity, reductions in exploratory behavior, and increases in anxiety in rats at adolescent age (1–1.5 months) in the open field and elevated plus maze tests. Greater changes in anxiety behavior were seen in males than females. Administration of LPS in early ontogeny induced signs of depression-like behavior at adolescent age in both males and females, this being detected in the anhedonia test as a reduction in the preference for 1% sucrose solution, unlike the situation in the control groups. The forced swimming test showed signs of depression-like behavior in males but not in females, but only on first testing. In adult rats (3–3.5 months), after increased handling and acquisition of food-procuring reflexes, these changes in anxiety and depression-like behavior largely disappeared. Administration of LPS at early age led to increased serum IL-1β levels in adult males after repeated stress exposure, while females showed increased corticosterone levels as compared with control animals. These results provide evidence of increased signs of anxious-depressive behavior in rats after early exposure to proinflammatory stress, along with sex-related differences and the possibility of correcting the negative consequences of stress in later life.

Carnosine modulates oxidative homeostasis and levels of neurotransmitters in the brain in models of learning with positive and negative reinforcement

We compared the effects of the dipeptide carnosine on learning and the biochemical parameters in the brain of rats trained for defensive and food-procuring conditioned reflexes. In the first series, the animals were trained for active avoidance behavior; in the second series, the rats were trained for the food-procuring conditioned reflex in a modified shuttle box. After training, the hypothalamus and cortex were dissected and used for evaluation of lipid peroxidation processes and the levels of monoamine neurotransmitters. The activating effect of carnosine was observed during the entire training period of defensive training, whereas during training for the food-procuring reflex it was observed only in the first two sessions. In both training series, impairments of oxidative homeostasis were found in the brain; these were efficiently corrected with carnosine. This effect of carnosine may explain its positive influence on learning. Moreover, in both models, carnosine increased the contents of the main monoamine neurotransmitters in the hypothalamus. These data led us to the conclusion about high prospectivity of further studies of the carnosine modulatory effects in the nervous system.

Alterations in Conditioned Food-Procuring Activity Related to Long-Term Pentylenetetrazole Kindling in Rats

We studied the mechanisms underlying impairment of conditioned food-procuring activity of rats in the state of long-term kindling induced by 120 injections of pentylenetetrazole (PTZ). In four animal groups, positive and negative modulation of the activity of the adrenergic and serotonergic neuromediatory systems was provided using introductions of ludiomil, α-methyl-para-tyrosine, L-tryptophan, or parachlorophenylalanine. Realization of the conditioned food-procuring reflex was estimated in the test with a radial labyrinth on the 30th, 60th, and 90th days. In the dynamics of PTZ-induced kindling, we observed intensification of cognitive dysfunctions, which was manifested in worsening of the results of training for the conditioned reflex. Similar effects, but of a significantly lower intensity, were found in kindling rats with activation of the noradrenergic and serotonergic systems. Therefore, the state of the above-mentioned systems is important for the development of cognitive dysfunctions under conditions of long-term PTZ-induced kindling.

Effect of Injury of the Cortico- and Rubro-Spinal Pathways on Operant Food-Procuring Reflexes in Cats

In experiments on cats with injury of the cortico- and rubro-spinal pathways, we studied the dynamics of recovery of operant (instrumental) food-procuring reactions at different durations of presurgery learning of animals. Operant manipulatory food-procuring movements were realized under conditions of horizontal and vertical tests, which required training for and support of a strictly defined pose in the course of performance of such movements and determined a specific pattern and stability of the coordinated motor phenomenon. The severity of abnormalities of operant food-procuring activity after transection of the lateral funiculus of the spinal cord at the level of С5-С6 and the time interval necessary for compensation of disorders of the developed manipulatory reaction depended significantly on the duration of presurgery motor learning and decreased considerably with increase in this duration. Such increase determined transformation of the pattern of postural rearrangement, which demonstrated no dependence on the amplitude and trajectory of the forthcoming operant phasic movements and was observed under conditions of both horizontal and vertical motor tests. Our results indicate that the main factor providing successful compensation of disorders of the developed operant habit in cats after injury of the cortico- and rubro-spinal pathways is active involvement of the tecto-and reticulo-spinal systems in the process of formation of the reflex. This can be due to an increase in the duration and intensity of presurgery learning of animals.

Effects of Oxytocin on the Formation of a Food-Procuring Reflex in Rats

In experiments on albino rats, we studied the process of formation of a food-procuring conditioned reflex (receipt of the food reward from one of two feedboxes designated by the visual conditioning signal) and characteristics of behavior in the open field test. It was found that course injections of oxytocin (4 μg daily, 15 min prior to the test for 12 days) relatively slightly influenced the process of development of the food-procuring conditioned reaction (animals reached the 80% critical level of correct differentiations practically simultaneously), but rats injected with oxytocin demonstrated smaller manifestations of anxiety, more rapid food-procuring activity, and higher intensity of motor/research activities in the open field. In general, food-procuring behavior under the action of oxytocin develops more effectively at the expense of formation of a more favorable emotional/autonomic background.

Fos Immunoreactivity in the Motor Cortex of Rats Realizing Operant Movements: Changes after Systemic Introduction of a NOS Blocker

The immunoreactivity with respect to the c-Fos protein in the primary motor cortex (area M1) of rats was subjected to comparative examination. As was found, the respective immunoreactivity patterns in layers II–VI of this zone in intact animals and rats realizing operant food-procuring reflexes, when observed under control conditions and after systemic injections of a blocker of neuronal NO synthase, 7-nitroindazole (7-NI), demonstrated noticeable specificities. Mean values of the density of Fos-immunopositive (Fos-ip) neurons in layers II–III of the M1 area (at the levels +2.7 and +2.2 mm from the bregma) in both rats after preliminary 7-NI injections and in animals performing operant reflexes, but with no such injections, were significantly lower than in the control intact group. At the same time, significantly greater numbers of Fos-ip neurons were found after 7-NI injections in rats realizing operant food-procuring reflexes (at the contralateral, with respect to the working forelimb, side of the motor cortex). It is supposed that NO-generating NADPH-diaphorase-reactive neurons and afferent projections (ascending from the subcortical limbic centers), which are localized in the M1 area, are involved in the formation of specific patterns of neuronal activity in the examined cortical layers. Suppression of functioning of neuronal NOS after systemic introduction of 7-NI modulates neuronal activity in superficial and deep layers of the M1 in different directions, and this occurs in both control rats and animals realizing food-procuring reflexes.

Expression of c-Fos Protein and Activity of NO Synthase in the Mesolimbic Dopaminergic Structures and Dorsolateral Striatum of Rats Realizing Operant Food-Procuring Reflexes

We studied the quantitative distributions of c-Fos-immunopositive (Fos-ip) and NADPH-diaphorasereactive (NADPH-dr) neurons in the mesolimbic and nigrostriatal dopaminergic (DAE) midbrain structures (at levels −5.3 to −6.04 mm caudally from the bregma) and in the dorsolateral striatum (−1.4 to −2.56 mm from the bregma) of the rat brain. Measurements were performed on intact animals, those after 24 h-long food deprivation, and rats after repetitive realization of operant food-procuring reflexes (n = 4 in all the three groups). In rats realizing operant reflexes for 30–40 min each day during 12 days, the mean number of Fos-ip neurons within frontal sections of the lateral part of the substantia nigra (SNL) significantly (P < 0.05) exceeded that in control and starving animals at all the levels examined. Such exceedance was also observed within borders of the ventral tegmental area (VTA). In rats realizing operant reflexes, Fos-ip neurons were grouped bilaterally in the mediodorsal part of the dorsolateral striatum (CPu), while distribution of the labeled cells in control and starving animals was relatively even across the entire area of frontal sections of this structure. The intensity of c-Fos expression in the CPu after realization of operant reflexes observed at the levels from −1.4 to −2.56 caudally from the bregma was significantly (P < 0.05) smaller than that in control animals. Significant numbers of NADPH-dr neurons were found only in the SNL and CPu; the mean numbers of such neurons in the examined structures showed no considerable differences in animals of all experimental groups. Relatively specific patterns of c-Fos expression and NADPH-diaphorase activity in the SN, TA, CP, and also in the central amygdalar nuclei found after realizations of operant reflex movements by the animals confirm the existence of clear correlations between motor and motivational/affective phenomena in the subcortical structures involved in the performance of complex emotionally charged motor acts.

Fos Immunoreactivity and NADPH-d Reactivity in the Brain Cortex of Rats Realizing Motivated Stereotyped Movements by the Forelimb

A comparative study of mmunoreactivity with respect to c-Fos protein in the motor (zones М1 and М2), medial prefrontal (PrL and IL), and cingular (Cg1 and Cg2) cortices allowed us to find significant differences between the intensities of expression of gene c-fos in these cortical regions in control rats (group 1) and animals trained to perform catching of food globules by the forelimb (i.e., realizing an operant food-procuring reflex, group 2). The density of distribution of Fos-immunoreactive (Fos-ir) neurons in rats of group 2 in motor and limbic cortical zones at +2.2 to +0.2 levels rostrally from the bregma were significantly lower than in control rats (Р Cg2 > М1 > М2 > > PrL. As is supposed, NADPH-d-r neurons (i.e., cells generating NO) are involved in the control of regional blood flow in the studied cortical regions.

The number of active Purkinje cells in the microelectrod track as an indicator of maturity of the cerebellum motor function in mature- and immature-born animals

In experiments on 5 age groups of anesthetized guinea pigs (from newborns to 4 weeks of postnatal ontogenesis), activity of cerebellum Purkinje cells (PC) (IV–VII lobules of cerebellar vermis) was studied in the single track of microelectrode passing through cell layers. It has been shown that as early as several hours after birth, in the superficial layer of cerebellar cortex, there are recorded occasional background-active, but functionally mature PC in the form of simple and complex spikes and accordingly reflecting synaptic PC activation by afferent inputs of mossy and climbing fibers. The functional manifestation of the guinea pig motor behavior at this period of ontogenesis is act of their standing. At this period of ontogenesis, in the newborn and one-day old guinea pigs, on average, from 1 to rarely 11 active PC are recorded in the single microelectrode track. At the one-week age, the highest number of active PC in the track somewhat increases, predominantly at the expense of the mean from the total number of cells in the track. In the 2-week old guinea pigs the mean number of active PC in the track somewhat falls, while in the 4-week old and adult animals it again exceeds, although slightly, the maximal number of PC in the track of newborn animals. The relatively high number of active PC at the very initial period of postnatal ontogenesis can indicate importance of motor function in the congenital food-procuring reflex.

Mechanisms of adaptation to flow reactions in rats after systemic blood arrest.

The rats survived 10- or 15-min systemic blood flow arrest were exposed to various extreme factors within the following 2 months. It was found that the processes leading to functional isolation of CNS play a protective role: they moderate behavioral response to acute stress and alleviate the degree of neuron damage induced by long-term stress during acquisition of a complex food-procuring reflex.

Network activity in neurons of the motor and prefrontal areas of the cortex in trained cats in conditions of systemic administration of m-cholinoreceptor blockers.

Experiments on five cats already trained to an operant conditioned food-procuring reflex to light were used to study the network activity of cells in the frontal and motor areas of the cortex accompanying disruption of conditioned reflex behavior in conditions of systemic administration of m-cholinoreceptor blockers. The activity of cortical neurons and their network properties were assessed using auto- and cross-correlation histograms. Doses of central m-cholinoreceptor blockers (the non-selective blocker scopolamine and the relatively selective m1-cholinoreceptor blocker trihexyphenidyl) disrupted performance of the operant motor reflex but had no effect on the appearance of contextual behavior and responses to switching on of the conditioned signal (standing up, elevating the paw). This was accompanied by 1) changes in the patterns of neuron activity in the moor and frontal areas of the cortex, with increases in train, rhythmic, and rhythmic train activity in cortical cells; 2) appearance of synchronicity in the operation of cortical neurons; 3) decreases in the numbers of direct interneuronal connections in the motor and frontal areas of the cortex and in the numbers of connections between these structures.

The role of muscarinic cholinoceptors in the retrieval of an operant food-related conditioned reflex in cats.

Experiments on cats showed that lesions affecting retrieval of an operant food-procuring reflex. occurring on a background of systemic administration of the centrally-acting muscarinic cholinoceptor blocker scopolamine (a non-selective M-cholinoceptor blocker) and trihexyphenidyl (a relatively selective M1-cholinoceptor blocker), might be associated with the central and peripheral side effects of these blockers, preventing performance of the conditioned reflex. It was established that when no side effects were present (low doses of trihexyphenidyl, 1 mg/kg), blockade of M1-cholinoceptors led to selective loss of the motor operant reflex while contextual behavior and other conditioned responses were retained or led to errors in performance of the reflex: this appears to be evidence that derangement of launching and performing the motor program is the most important component of the conditioned reflex. Systemic administration of trihexyphenidyl at a dose of 10 mg/kg, scopolamine at doses of 0.03 and 0.06 mg/kg, and the peripherally-acting non-selective blocker methylscopolamine at a dose of 0.03 mg/kg led to changes in the general functional state (disturbances in the emotional-motivational sphere), the extent of which depended on the individual sensitivity of the animal to the anticholinergic agents. The presence of side effects led to complete cessation of conditioned reflex activity, though this appeared not to be associated with memory impairment.

Involvement of the parafascicular nucleus of the thalamus and the cholinoreactive system of the neostriatum in controlling a food-procuring reflex in rats at different stages of learning.

A model of a Skinner box food-procuring reflex in rats was used to study the relationship between the strength applied to a pedal and disruption of the parafascicular nucleus of the thalamus and microinjections of the cholinolytic scopolamine and the cholinomimetic carbachol into the neostriatum at different stages of learning. In untrained rats at the stage of learning to press strongly on the pedal without the conditioned signal being switched on (i.e., every strong press was rewarded) showed (a) a decrease in the rate of learning to press strongly and an increase in the number of weak pedal presses after bilateral lesioning of the parafascicular nucleus of the thalamus; (b) that rats with bilateral lesions of this nucleus responded to microinjections of scopolamine into the neostriatum with increases in the number of strong presses, with no change in the number of weak pedal presses, while microinjections of carbachol decreased the number of strong and increased the number of weak presses as compared with the pre-microinjection baseline. In trained rats at the stage of recovery the reflex (i.e., strong pedal presses were reinforced only during exposure to the conditioned signal), lesioning of the parafascicular nucleus of the thalamus had the effect that the time required for recovery of the reflex became dependent on the level of pre-operative training; scopolamine microinjections into the neostriatum of rats achieving high levels of correct performances of the reflex only after surgery led to sharp degradation in performance of the reflex on the day of microinjections; microinjection of carbachol into the neostriatum of rats with low post-operative levels of performance of the reflex had no effect on this measure.

The effects of vasopressin on memory processes in Java monkeys.

The roles of vasopressin (arginine-vasopressin) in controlling conditioned operant food-procuring reflexes and various types of memory were studied in monkeys. Types of memory were: conditioned reflex, image (Hunter-Kerr test), short-term, and long-term. The effects of vasopressin were assessed in terms of objective measures of higher nervous activity: movement and autonomous functions. These studies showed that administration of vasopressin to monkeys had different effects on simple operant food-procuring responses and memory processes. Vasopressin had greater effects on memory processes and the restoration of memory after functional derangements of higher nervous activity. The question of the formation of the two types of effect of vasopressin on higher nervous activity is discussed in relation to the evolution of mammals.

Effects of lesioning of the parafascicular nucleus of the thalamus on an operant food-procuring reflex in rats.

thalamus are involved in organizing and performing food behavior remains open. The aim of the present work was to study the effects of lesioning of the parafascicular nucleus of the thalamus on the formation and performance of an operant food-procuring reflex in untrained rats and in rats trained to conditioned reflex responses. Studies were carried out on 33 male Sprague-Dawley rats. Animals were trained in a Skinner box. The conditioned signal consisted of rhythmic flashes of a white lamp. Reinforcement consisted of pieces of cheese (25-30 rag). Animals were kept on a limited diet (8 g of dried concentrated food per day per rat) from training day 3. Training was performed in three stages. In the first stage, rats were trained to associate a click accompanied by delivery of food into the feeder with reinforcement, the aim being to correct the pedal-pressing force for subsequent experiments. Training was continued until rats received reinforcement 20 times during ten-minute periods in the chamber, during which time 20 clicks were presented. Clicks were presented every 30 see. At the second stage of training, rats were trained to press the pedal to obtain food. Weak actions were initially reinforced, after which only strong pedal presses, opening the feeder, were reinforced. The second stage of training was continued until rats pressed the pedal 20 times during 10-min periods in the chamber. The conditioned signal (10 sec with a 20-sec interval) was introduced at the third stage of training. Pedal presses without the conditioned signal were not reinforced and were regarded as interstimulus responses. Each experiment consisted of 10 presentations of the conditioned signal. Rats were considered trained when they produced correct responses to at least 70% of conditioned signal presentations. High levels (70-90%) of reflex performance were stabilized in intact animals by repeated testing for an average of 18 days, after which surgery was performed. The effects of lesions to the parafascicular nucleus on the initial stage of learning were studied by operating on a second group of rats before training to the food-procuring reflex. Surgical procedures were performed under ketamine anesthesia (250 mg/kg). A stereotaxic atlas [4] was used to determine the coordinates for electrolytic lesioning (5 /zA, 20 sec) of the parafascicular nucleus of the thalamus. Experiments were restarted 6 days after surgery. Animals were sacrificed by decapitation under ketamine anesthesia when experiments were finished. Histological sections were prepared on a cryomicrotome and were stained by the Nissl method. Data were analyzed statistically using Student's t test. Parafascicular Nucleus Lesions in Trained Rats. Before surgery, all rats of this group (n = 21) were trained to associate a click with feed for 6-7 days, and to apply strong pressure to the pedal for a further 1-2 days. Animals reached high levels of correct performances after 1-2 days of training after introduction of the conditioned signal. After bilateral lesioning of the parafascicular nucleus (destruction of more than 40% of the structure on both sides), animals (n = 6) showed significant reductions in the levels of intersignal pedal pressings in the first 1-6 days of testing, as compared with the pre-operative level (4.17 + 0.56). The number of correct performances was significantly reduced on post-operative days 1-3, 5, and 6. On other days, the level of performances was not significantly different from baseline (79.33 + 7.81) (Fig. 1A). After unilateral lesions of the parafascicular nucleus, rats (n = 8) showed a significant reduction in the level of intersignal pressings on post-operative

Real-time distribution of linked spike activity in cortical neurons during learning in the cat.

Analysis of the distribution of linked spike activity showed changes occurring within the structure of interneuron functional connections during learning. In an electric shock defensive reflex, concentration of linked spikes from cat motor cortex neurons was observed on signal presentation, while in a conditioned food-procuring reflex to time, this was confined to the moment at which reinforcement was provided. This can be regarded as the appearance of a reflex at the level of interneuron interactions. This conclusion is supported by the observation that in well-trained animals, concentrations of linked spikes could be seen at the place of the conditioned reflex response, even in the absence of defensive and food-procuring movements.

Appearance of functional connections between neurons resulting from changes in the frequency of their spike activity during the performance by animals of conditioned-reflex food-procuring responses.

Cats were conditioned to a food-procuring reflex to time. Correlation analysis was applied to multineuron activity in the motor cortex to study the functional connections between neurons with changing and constant instantaneous spike frequencies on performance by the animals of the passive waiting phase of the conditioned reflex, the number of functional connections between "areactive" neurons was smaller than that between "reactive" neurons; during the phase of active waiting, the numbers of functional connections become similar. The increase in the number of functional connections between "areactive" neurons during the active waiting phase appears to reflect an intensification of the analysis and processing of information, while changes in the functional connections between "reactive" neurons was regarded as allowing the possibility of correcting functional structures in the case of a rapid change in the situation or state of the animal.

Spatial-temporal organization of the functions of cortical neurons in a conditioned reflex to time.

The impulse activity of neurons in the motor cortex of cats during the development of a conditioned food-procuring reflex in relation to a time interval of 2 min (CRT) was analyzed. It was demonstrated, by comparing the behavioral and neurophysiological correlates of the formation of the conditioned food-procuring reaction, that its formation is accompanied by extremely complex systemic transformations which are different for neuronal micro- and macrostructures. The systemic processes in the micro- and macrostructures differed with respect to the specific characteristics of spatial distribution, and with respect to the number, strength, and stability of the manifestation of the functional connections. The capacity of the neurons for functional orientation even at the initial levels of the formation of the reaction, an increase in the per cent of incidence of functional connections in the second half of the conditioned reflex interval, and the substantial destabilization of all neuronal units at the last, highest level of formation of the conditioned reflex food-procuring reaction were common to the micro- and macrostructures in this form of learning.

The temporal organization of the correlational association of neurons of the cat motor cortex.

The multineuronal activity was recorded in cats with a developed conditioned food-procuring reflex to time. Cross-correlation histograms were plotted on the basis of the impulse activity of individual neurons isolated from the multineuronal activity, and an analysis was made of the distribution in real time of the impulses constituting the peaks on these histograms. The secondary analysis of the histograms made it possible to identify the dynamics of the changes in the functional connections between neurons over the course of the phase of active waiting on the basis of the distribution of coupled impulses. It was demonstrated in simultaneously recorded neuronal pairs that the concentration of coupled impulses was observed at various moments in time. Neuronal pairs, the concentration of whose coupled impulses is found towards the end of the conditioned reflex interval, were noted; this is regarded as the manifestation of a conditioned reflex reaction at the level of interneuronal interaction.

Correlation relationships of evoked activity of the auditory cortex and the amygdalae of cats during conditioned reflex activity.

The character of the interaction (Spearman's correlation coefficient) between the structures before, and during the development, extinction, and restoration of an instrumental food-procuring reflex, as well as during the automatization of the reflex was determined on the basis of the averaged sound-induced activity (AEP) of symmetrical points of the auditory cortex (AI) and the amygdalae (abl) of cats. The co-tuning of the cortex and the amygdalae during the adaptation of the animal was found to be individual in character; this was replaced by close interactions during the formation of the reflex and by the disruption of their correlatedness during its extinction. The consolidation of the reflex prior to the stage of automatization was accompanied by attenuation of the connections between the cortex and the amygdala. The results attest to the complex and dynamic character of the interdependence in the cortex-amygdala system during conditioned reflex activity.