State of Stress-Marker Organs in Rats with Various Behavioral Characteristics during Repeated Stress Exposures.

Changes in the relative weight of stress-marker organs in rats with various behavioral patterns in the open-field test were studied after repeated stress exposures on the model of daily 4-h immobilization over 8 days. Involution of the thymus and spleen in behaviorally passive specimens was found after single stress, as well as under conditions of 3- and 8-fold immobilizations. The weight of these organs in active animals remained practically unchanged after acute stress, but decreased on day 3 and particularly on day 8 of repeated stress exposures. As differentiated from passive rats (open-field test), behaviorally active specimens were characterized by hypertrophy of the adrenal glands after single and 3-fold stress procedures. Our results complement the data on individual features of the peripheral and central mechanisms for the stress response in mammals. These data illustrate the importance of individual approach to studying systemic organization of physiological functions under normal conditions and during negative emotiogenic exposures.

Nociceptive Reactions in Rats during Repeated Stress Exposure.

Changes in nociceptive sensitivity of rats with various behavioral patterns in the open-field test were studied after repeated stress exposure on the model of daily 4-h immobilization for 8 days. The tail-flick latency in response to light-heat stimulation in passive and active specimens decreased most significantly on days 2 and 7, respectively. However, this parameter did not differ from the baseline on day 8 of observations. Vocalization threshold during electrocutaneous stimulation in behaviorally active animals did not change over the first 7 days of repeated stress exposure, but increased significantly on day 8 of the study. The emotional component of nociception in passive animals increased on day 3, but decreased on days 4 and 6 of the experiment. Therefore, repeated stress exposure in rats is mainly accompanied by an increase in the perceptual component of nociception. Variations in the emotional component of nociceptive sensitivity after stress loads are manifested in the initial increase and subsequent decrease in this parameter. The observed changes are more pronounced in behaviorally passive rats than in active animals. These data illustrate the specifics of stress-induced changes in nociception of specimens with various individual and typological characteristics. Our results hold much promise for the development of new individual approaches to modulation of pain sensitivity in humans under conditions of negative emotiogenic exposures.

Frequency and Spatial and Temporal Characteristics of Neuronal Spike Activity in Dorsal Hippocampal Field CA1 in Behaviorally Active and Passive Rats after Stimulation of the Lateral and Ventromedial Hypothalamus.

We studied the neuronal mechanisms of the various emotional and motivational states in Wistar rats with different behavioral activities. Stimulation of the ventromedial hypothalamus had more pronounced effect on the frequency of action potentials in neurons of the dorsal hippocampus than stimulation of the lateral hypothalamus. However, stimulation of the lateral hypothalamus produced stronger effect on spatial and temporal characteristics of fi ring pattern than stimulation of the ventromedial hypothalamus. Neurons of the dorsal hippocampus in active rats were less sensitive to stimulation of the lateral and ventromedial hypothalamus than in passive animals.

[OPEN FIELD BEHAVIOR AS A PREDICTIVE CRITERIA REFLECTING RATS CORTICOSTERONELEVEL BEFORE AND AFTER STRESS].

In the presented study we investigated the possibility to use the open field behavior data for prediction of corticosterone level in rat blood plasma before and after stress. It is shown that the most reliable open field behavior parameters, reflecting high probability of significant upregulation of corticosterone after 3 hours of immobilization, are the short latency of first movement and low locomotor activity during the test. Rats with high corticosterone at normal non-stress conditions are characterized by low locomotor activity and on the contrary long latency period for the entrance of open field center.

[Effects of the δ-sleep inducing peptide on neuronal activity in the dorsal hippocampus of rats with different behavior in the open field after stimulation of the positive and negative emotionalistic structures of the brain].

We studied the cerebral mechanisms of positive and negative emotions in rats with different behavior in open field, reflecting stress resistance and neuronal effects of delta-sleep-inducing peptide (DSIP). In 20 male Wistar rats 107 neurons of dorsal hippocampus (57 neurons in active in open field--prognostically resistant to emotional stress and 50 inpassive--prognostically predisposed rats) were registered after positive (lateral hypothalamus--LH) and negative (ventromedial hypothalamus--VMH) emotional centers electric stimulation. Hippocampal neurons in active rats were less sensitive to stimulation of LH and VMH compared with passive ones. DSIP microiontophoretic application before LH stimulation decreases neuronal responses in both active and passive animals. DSIP increases dorsal hippocampus neurons sensitivity to VMH stimulation in active rats and decreases in passive ones.

Neuronal activity in the dorsal hippocampus after lateral hypothalamus stimulation: effects of delta-sleep-inducing peptide.

We studied central effects of delta-sleep-inducing peptide in the mechanisms of positive emotional state formation in rats. In Wistar rats preliminary tested in an open field, the reactions of 57 neurons of the dorsal hippocampus were analyzed during lateral hypothalamus stimulation and microionophoretic application of delta-sleep-inducing peptide. It was found that the number of neurons not responding to stimulation in the lateral hypothalamus surpassed the number of sensitive neurons (63 and 37%, respectively). Hippocampal neurons in active animals were less sensitive to stimulation of the lateral hypothalamus than in passive rats (33 vs. 42%) After application of delta-sleep-inducing peptide, only 28% neurons responded to stimulation. Thus, delta-sleep-inducing peptide reduced the sensitivity of hippocampal neurons to stimulation of the lateral hypothalamus.