Effect of cortisol on a model of stereotyped behavior of rabbits in the form of thumping.

Experiments conducted on 10 adult male Chinchilla rabbits showed that single 5-sec electrostimulation of the region of the medial hypothalamus induces a series of stereotyped behavioral responses in the form of synergic thumping on the floor of the experimental chamber. When the stimuli are repeated every 1.5-2 min adaptation to stimulation is observed, which is expressed in a gradual decrease of the number of thumps. To study the pharmacological and hormonal effects on the described behavior, an experimental model is proposed which consists of two series of stimulation, each of which consists of 10 successive stimuli. The investigated pharmacological agent (cortisol [hydrocortisone] hemisuccinate) was injected into the animals in the interval between the two series of stimulation. A statistical analysis of the experimental results showed that intraperitoneal injection of cortisol in doses of 10 and 20 mg/kg enhances the simulation-induced behavioral response and shortens the latent period of its manifestation compared with the control. Key words: rabbit, electrostimulation, medial hypothalamus, stereotyped behavior, cortisol.

[Changes in the duration of pauses between self-stimulations in response to cortisol]. / Izmeneniia dlitel'nostei pauz mezhdu samostimuliatsiiami pod vliianiem kortizola.

Intraperitoneal administration of glucocorticoid hormone cortisol (10 mg/kg) decelerated the self-stimulation (SS) frequency within 5-7 min. The maximal effect occurred within 10 to 20 min. Histograms of pauses duration between SS revealed a shift of mean values from 2.0-2.5 to 4-6 sec. A sharp increase of long pauses transformed chiefly mono- modal forms of control histograms into bimodal those under the hormonal effect. Behaviourally this was manifested by occurrence of burst type of SS responses when series of uninterrupted instrumental responses alternated with prolonged pauses between them. The data obtained are considered from the stand-point of systemic approach to analysis of organization of willed behaviour and role of cortisol in central mechanisms of positive reinforcement.

[Effect of cortisol on a model of stereotypical behavior in the rabbit in the form of hindlimb thumping]. / Izuchenie vliianiia kortizola na modeli stereotipnogo povedeniia krolikov v forme udarov zadnimi lapami.

A 5-sec electrical shock applied to the rabbit medial hypothalamus induced series of stereotype behavioral responses in the form of synergic blows with hindlimbs. Adaptation to the stimulation occurred in repetition of the stimuli every 1.5-2.0 min. Pharmacological experiments revealed that intraperitoneal administration of cortisol (10 and 20 mg/kg) enhanced the stimulation-induced behavioral response and shortened its latency.

[Autonomic correlates of the formation of a functional self-stimulation system]. / Vegetativnye korreliaty formirovaniia funktsional'noi sistemy samorazhdrazheniia.

Capability of intracerebral electrostimulation to serve as an unconditioned reinforcing stimulus in classical conditioning was studied in rabbits. Changes of such vegetative characteristics as respiration frequency and ECG were taken as criterion of conditioned response (CR) elaboration. In preliminary experiments, optimal parameters of stimulation maintaining the highest level of instrumental self-stimulation behaviour were found for each of the animals. Isolated presentation of the unconditioned reinforcing stimulus led to the increase of respiratory rate. Such kind of stimulation induced tachicardia in 5 animals, bradicardia in 3 ones, and in the remaining 6 rabbits a biphasic reaction was observed with initial tachicardia changing for bradicardia. Reactions were taken as CRs if they were similar to those to the unconditioned stimulus and appeared at the moment of omitted reinforcement. After 10 pairings of conditioned sound stimulus with positive reinforcement, CR changes of the two vegetative parameters were observed in 21,4 per cent of cases. After 40 pairings CRs were observed in 87,5 per cent of trials for cardiac and in 78,5 per cent cases for respiratory components. The results obtained confirm the idea of validity and efficiency of intracerebral stimulation of self-stimulation zones as a factor of positive reinforcement.

[Relation between the dynamics of a species-specific motor reaction and the duration of diencephalic stimulation]. / Dinamika vidospetsificheskoi dvigatel'noi reaktsii u krolikov v zavisimosti ot dlitel'nosti stimuliatsii mezhutochnogo mozga.

Species-specific reaction of thumping behaviour with the hind limbs in response to electrical stimulation of the ventromedial, dorsomedial and caudal parts of the hypothalamus was studied in chronic experiments on rabbits. Reaction of avoidance dominated during current action of various durations (1-20 s). The specific reaction under study appeared after the termination of stimulation and lasted for 30-120 s. The number of kicks in response to single stimulation depended on its duration (T). With T rising from 1 to 10 s, the number of kicks increased; with T being equal to 20 s, it decreased. The latency of the first kick after the termination of stimulation regularily increased with increase of its duration, and reaction intensity maxima shifted to the right along the axis of time. Possible mechanisms of limb kicking behaviour are discussed based on a transition of avoidance reaction during stimulus action to emotional reaction in post-stimulus period.

[Changes in the level of cortisol in the blood of rabbits during self stimulation]. / Izmenenie urovnia kortizola v krovi krolikov vo vremia samostimuliatsii.

The time-course of changes in the blood plasma cortisol level during activation of the positive reinforcement system was studied in experiments on adult chinchilla male rabbits. The self-stimulation status of the brain lateral hypothalamus was utilized as a model for positive reinforcement. The basal cortisol level in intact rabbits, determined by means of radioimmunoassay, was equal to 5.31 +/- 0.87 micrograms% over a period of 10 to 2 hours p.m. The blood collection procedure, using the method of the ear marginal vein dissection, increases the cortisol concentration 30 minutes after blood collection by 19.4%, i.e. augments its level up to 6.37 +/- 0.90 micrograms%. A significant rise (P less than 0.01) of hormone release into the blood (two-fold) is seen 5 to 15 minutes following the self-stimulation test. Cortisol level remains heightened 1 hour after the self-stimulation experiment. The intensity of the corticotropic activity was not dependent on the hypothalamus, stimulated by force or by animals themselves. On the basis of the data obtained it is concluded that the hormonal response is directly dependent both on hypothalamic electric stimulation and on the motivative mechanism activation. The very positive reinforcement, timing to the post-stimulating period and being of full value only during the adaptive behavioral act, is not stress-inducing.

[Relation between the strength of stimulation of hypothalamic structures in the rabbit and behavior in the form of striking with the paws]. / Povedenie v forme udarov lapami u krolikov v zavisimosti ot sily élektricheskogo razdrazheniia gipotalamicheskikh struktur mozga.

The behaviour in the form of tappings with forepaws after electric stimulation of 5 s duration was studied in rabbits with electrodes chronically implanted in the diencephalon. This species-specific behaviour is described following stimulations of threshold strength and gradually increasing to three thresholds. It has been found out that frontal, medial and posterior nuclei of the hypothalamus possess the greatest ability for eliciting such behaviour. During stimulation motor signs of avoidance behaviour dominate. The tappings are observed only in the post-stimulation period. Stimulation with two thresholds strength elicits the greatest number of tappings. There is a reliable relation between the number of tappings and total duration of the reaction. The possibility of reinforcing properties of the tappings based on emotional fear reaction to stimulation is discussed.

[Spike activity of dorsal hippocampus neurons of rabbits during self stimulation]. / Issledovanie spaikovoi aktivnosti neironov dorzal'nogo gippokampa krolikov pri samostimuliatsii.

Responses of 47 neurones of the dorsal hippocampus were studied in a chronic experiment on free-behaving rabbits during self-stimulation behaviour. The achievement by the animals of the instrumental habit of pressing the lever produced stimulation of the lateral hippocampus. It was found that different hippocampal neurones change the frequency of their discharges at different stages of self-stimulation behaviour: some at the stage of the animal's approach to the lever, others during stimulation and still others in the poststimulation period. Inhibition and activation reactions in most of the neurones were of opposite direction at the moment of stimulation and in the poststimulation period. During the reinforcing stimulation the hippocampal theta-neurones were the most reactive.

[Qualitatively similar effects of microiontophoretic applications of corticotropin and hydrocortisone in the hippocampal and hypothalamic neurons of rabbits]. / Kachestvenno skhodnye éffekty mikroionoforeticheskikh applikatsii kortikotropina i gidrokortizona u neironov gippokampa i gipotalamusa krolikov.

A comparison was made of the responses of hypothalamic, septal and hippocampal neurons to microionotophoretic applications of corticotropin (ACTH) and hydrocortisone. A reliable positive correlation of medium significance was found in the hippocamp, less pronounced positive correlation in the hypothalamus and no correlation in the septum. The data obtained indicate that the hippocampal and hypothalamic brain structures are characterized by functional similarity of the mechanisms of neuronal sensitivity to each hormonal substance. It is unlikely that the neurophysiological processes participating in the response of nervous cells to ACTH and hydrocortisone applications are similar, this suggestion being supported by the presence of a number of exceptions and absence of the correlation in the septum.

[Inhibitory effect of hydrocortisone and corticotropin on the self stimulation reaction]. / Ugnetaiushchee vliianie gidrokortizona i kortikotropina na reaktsiiu samorazdrazheniia.

The effect of hydrocortisone and ACTG on the frequency of self-stimulation reaction (SS) was studied. It was shown that hydrocortisone markedly suppresses the central mechanism of the positive reinforcement. SS frequency is lowered 10-15 minutes after the drug administration and recovered in one hour. The changes in the frequency of SS in response to ACTG are simular to the hydrocortisone effect, but are less intensive and in some cases depend on the location of the stimulating electrodes.