The effect of exercise training in cold on shivering and nonshivering thermogenesis in adult and aged C57BL/6J mice.

To understand the mechanisms of improvement of cold-induced heat production in aged mice following exercise training, the relative contributions of shivering and nonshivering thermogenesis to cold-induced metabolic responses were assessed in adult and aged C57BL/6J male mice, which inhabited sedentarily at room temperature, or were subjected either to a regimen of moderate intensity exercise training at 6 degrees C, or to sedentary repeated exposures to the same temperature. The main findings were that (1) aged mice had greater cold-induced nonshivering thermogenesis, but lower shivering than adult mice; (2) exercise training in a cold environment enhanced cold-induced nonshivering thermogenesis in adult mice, but suppressed it in aged animals; (3) exercise training in a cold environment increased shivering thermogenesis in both age groups, but this increase was much greater in aged mice; (4) the increase of cold-induced shivering thermogenesis was mainly responsible for increased cold tolerance in aged mice after exercise training in a cold environment.

Corticostriatal mechanisms of behavior.

This article presents the results of three series of experiments on cats, dogs, and lower primates, performed to investigate the structural, neurophysiological, and mediator mechanisms of the corticostriatal systems involved in the organization of behavior. Morphological studies of corticostriatal connections showed that along with the diffuse distribution of afferent terminals within the striatum, there were also elements of topical organization defined by anteroposterior and mediolateral gradients. Neurophysiological experiments on dogs and lower primates were used to study the spike activity of the prefrontal region of the cortex and the head of the caudate nucleus during training to conditioned first- and second-order reflexes and during the solution of complex problems involving delayed spatial selection. Studies demonstrated that while in dogs, most of the neurons recorded showed a transition to responses to the conditioned signal at a particular stage of carrying out a conditioned response, in monkeys all cells recorded showed specific responses at different periods of solving the task at all stages of the study. Neuropharmacological experiments on dogs showed that agents blocking glutamine receptors in the caudate nucleus had more pronounced effects at the phase of developing conditioned movement reflexes. Administration of these agents during the reflex reinforcement phase affected only the differentiation of inhibition. These results lead to the conclusion that the prefrontal area of the cortex and, to some extent, the caudate nuclei, act on incoming information specifying the current dominant need and the states of the external and internal environments, to carry out programmed actions and assess the results of these actions.

Change in heat loss as a part of adaptation to repeated cold exposures in adult and aged male C57BL/6J mice.

Previous studies have shown that adult mice increase cold-induced heat production as a result of repeated exposures to cold, but that aged mice do not. The objective of the present study was to investigate changes in heat loss during repeated cold exposures in adult and aged C57BL/6J mice. Mice were partially restrained for three hours at 6 degrees C, three times at one-week intervals. Dry heat loss was inferred from measurements of differential temperature between the incoming and outgoing air in the experimental chamber. During the first cold exposure, aged mice showed less heat loss (both total and adjusted for body temperature) than adult animals, suggesting greater peripheral vasoconstriction in aged mice. With repeated cold exposures, both age groups showed increased heat loss, but the aged mice showed greater increase of heat loss, so that by the third cold stress test, no significant differences in heat loss between adult and aged mice were observed. The increase of heat loss after repeated cold exposures in aged mice might reflect a lesser peripheral vasoconstriction, serving to reduce the possibility of tissue necrosis in the cold.

Neurophysiological mechanisms of cortical-subcortical interactions in the organization of behavior.

Experimental data are discussed within the framework of the fundamental areas of studies of the neurophysiological mechanisms of behavior. The first of these is the study of the activity of individual neurons, which is characterized by plastic rearrangements based on synaptic, molecular (neurochemical), and submolecular (genetic) processes. The second area is the study of the activity of neuron systems, which unite the cells of different microgroups, and of systems including neural elements of different brain structures. Data on plastic rearrangements of neuronal activity in different structures during different types of behavior lead to the conclusion that the brain has special systems of relationships which characterize the interactions of blocks of neurons, in which the plasticity of a single neuron can maintain the integration processes of the whole system. Our own data, along with results of Russian and foreign physiological and clinical investigations, suggest that neurons unite into different functional blocks at different phases of conditioned reflex behavior, thus determining the dominance status of different centers and the vector of a purposive behavioral act in a given situation at a given time. Possible directions for further basic studies of the interactions between innate and phylogenetically acquired functionally specific neuron units are discussed on the basis of hypotheses which have been advanced to explain the neurophysiological organizational mechanisms of higher brain functions.

The effect of exercise training in a cold environment on thermoregulation in adult and aged C57BL/6J mice.

We studied the effect of exercise training in cold environment (six weeks of daily, one-hour runs on a treadmill at ambient temperature of 6 +/- 1 degrees C at 60-65% of VO2max) on cold-induced metabolic heat production, heat loss, and cold tolerance in adult and aged C57BL/6J male mice. In adult mice, exercise training in cold environment resulted in greater cold-induced heat production and cold tolerance without changes in heat loss, similar to the effects of daily cold exposure without exercise. In aged mice, daily cold exposures did not affect cold tolerance and cold-induced heat production, but exercise training in the cold resulted in greater cold-induced heat production and cold tolerance. Heat loss in aged mice increased similarly after both repeated cold exposures and exercise training in the cold. Therefore, mechanisms of effect of exercise training on cold tolerance are different in adult and aged animals. Exercise training in cold environment does not affect cold-induced heat production and cold tolerance in adult mice, but improves them in aged animals.

Heat loss during cold exposure in adult and aged C57BL/6J mice.

Metabolic heat production (MHP), colonic temperature (Tco), and nonevaporative (dry) heat loss were measured in ADULT and AGED C57BL/6J male mice during cold exposure. Dry heat loss was assessed as a differential temperature (Td) between incoming and outgoing air through the chamber for indirect calorimetry. The average Td during cold exposure normalized to surface area for ADULT mice was significantly higher than that for the AGED animals (0.0618 +/- 0.0003 degree C/cm2 and 0.0553 +/- 0.0005 degree C/cm2, respectively). Linear regression analysis showed that at the same Tco AGED mice showed lower values of Td normalized to surface area, indicating that at the same body temperature they were losing less heat than ADULT animals. It was concluded that age-related decline in cold tolerance in mice is not due to a lack of ability to reduce heat loss during cold exposure. On the contrary, AGED animals had lower heat loss in comparison with ADULT. We suggest that augmentation of heat conservation mechanisms is an adaptive response to diminishing cold-induced heat production.

[The corticostriatal mechanisms of behavior]. / Kortikostriatnye mekhanizmy povedeniia.

Experiments in dogs, cats and monkeys revealed that, along with the diffuse principle of afferent terminal arrangement within the striatum, there exist some features of terminal organisation by the anterior-posterior and medio-lateral gradients. The data obtained suggest that the prefrontal cortex and the caudate nucleus head maintain programming of intentions and the evaluation of performed actions.

[Neurophysiological mechanisms of the cortical-subcortical interrelationships in the organization of behavior]. / Neirofiziologicheskie mekhanizmy korkovo-podkorkovykh vzaimootnoshenii v organizatsii povedeniia.

Specific intersystem relationships seem to exist characterising interrelationships among neurons within pools of which plasticity of a single neuron is able to maintain integration processes of the whole system. The neurons under study seem to become united into various functional blocks during different phases of conditioned behaviour which determines a formation of a dominant condition of the centres and vectors of a specific behavioural action in a given situation and at a given time.

Structure of neuronal activity of the caudate nucleus of monkeys during decision-making and the realization of the motor program in different variants of a delayed spatial choice task.

In this paper the results of investigations of the participation of caudate nucleus neurons in the decision-making process and the process of organization of the program of a future motor response during the performance by Macaca mulatta monkeys of a delayed spatial choice tasks of varying degrees of complexity are presented. The presence in the caudate nucleus of spatially selective neurons, which are subdivided into two groups, was established: the position of conditional signals is reflected in the activity of one of the groups, and the direction of the future motor response is reflected in the activity of the other. The decision-making process is reflected in the impulse activity of neurons of the head of the caudate nucleus in two of its aspects: as the formation or choice of a specific motor program (spatially selective activity) and as a transitional factor from the instructive to the executive phase of the behavior.

[The structure of the neuronal activity of the caudate nucleus in monkeys making a decision and realizing the motor program in different variants of a task of delayed spatial choice]. / Struktura neironnoi aktivnosti khvostatogo iadra obez'ian pri priniatii resheniia i realizatsii motornoi programmy v razlichnykh variantakh zadaniia na otsrochennyi prostranstvennyi vybor.

Spatial-selective neurons were found in the monkey caudate nucleus, the neurons being divided into two groups: one of them reflects the location of conditioned signals, the other--the direction of future motor response. The decision-making process is reflected in the unit activity in two aspects: as formation or choice of a concrete motor program, and as a transitory moment from instructive to executive phase of the behaviour.

[The neuronal activity of the caudate nucleus in monkeys during the realization of delayed behavior]. / Neironnaia aktivnost' khvostatogo iadra obez'ian pri realizatsii otsrochennogo povedeniia.

A greater part (64%) of recorded neurones of the caudate nucleus head changed its activity at various stages of fulfillment by the monkey of the task of delayed spatial choice. Most of them (46.5% of all studied) reacted at key depressing and/or taking food from the feeder. During signal presentation and with delay the frequency of impulse activity changed respectively in 17% and 14% of the studied neurones. Besides, 2 neurones had spatially-selective activity in the instructive period of the program. It can be suggested that caudate neurones participate in realization of the delayed behaviour not only during motor response fulfillment but in the instructive period as well--at the stage of perception and processing of the visual information and its storing in short-term memory.

[Characteristics of the activity of neurons of the parietal cortex of alert monkeys in comparison to the frontal and motor areas]. / Kharakteristika aktivnosti neironov temennoi kory bodrstvuiushchikh obez'ian v sravnenii s lobnymi i motornymi oblastiami.

Analysis was made of spike activity of nerve cells in the parietal cortex of alert Macaca mulatta when the animal performed the task of delayed alternative choice. The parietal cortex neurones (at the boundary between fields 5 and 7) were divided into two groups by the mean background frequency of their spike activity and by their functional properties. Cells with relatively low frequency (up to 10 imp/s) resemble by their functional properties prefrontal cortex neurones, whereas neurones with a background frequency over 10 imp/s reveal a similarity with motor cortex cells.

[Responses of neurons of the motor and frontal cortex of monkeys during performance of purposeful activity]. / Reaktsii neironov motornoi lobnoi oblastei kory mozga obez'ian pri vypolnenii tselenapravlennogo dvizheniia.

Neurones of the frontal cortex in alert monkey reveal most diverse rearrangements of spike activity at the programming stage of a behavioural task. Their responses depend on 1) position of the conditioned signal, 2) direction of the forthcoming movement toward reinforcement (feeding trough), and 3) efficiency of performing the goal-directed movement, which, if correct, is reinforced with food. Units in the motor cortex have higher background activity, they are most active during triggering stage and their activity does not reflect signal position and estimation of success (by reinforcement). The suggestion is made on the role of the frontal cortex in programming of movements and estimation of their efficiency, as well as on the role of the motor cortex in their coordinated achievement involving somatic processing of the connection.