Jolanta Zagrodzka

Emotional changes related to age in rats--a behavioral analysis.

The present study investigated age-related differences in the emotional behavior of rats using factor analysis to identify motivational factors influencing spontaneous behavior in open field with illuminated center (OF), plus maze (EPM) and social interactions test. Animals of the same strain, bred under the same conditions, formed two experimental groups: young adults (YA, N=20) tested at the age of 4 months and old rats (OA, N=16) tested at the age of 24 months. The computer video based tracking system EthoVision was used for automated acquisition and analysis of data. The results of each test were analyzed separately for YA and OA by factor analysis. Two main independent factors emerged from the analysis of OF measures-factor 1, which appeared to reflect motor activity, and factor 2, reflecting anxiety. The measures best reflecting motor activity (distance moved in the peripheral zone) and anxiety (time spent in central zone) decreased significantly with age. Factor analysis for EPM measures revealed, in both groups, three independent factors. In YA, factor 1 reflected motor activity, factor 2-anxiety, in OA measures of anxiety loaded on factor 1, measures of activity on factor 2. Factor 3 in both groups appeared to represent a decision making process. The number of entries to the closed arms declined significantly in OA, showing an age related decrease of motor activity. Also, the ratio of open arms entries in relation to the total number of entries decreased in OA, indicating a higher anxiety level. Three independent factors emerged from the analysis of social interaction measures. The pattern of factor loading was different in young and old animals, although the number and time of social interactions did not show age-related differences. In addition to a decrease of motor activity we conclude that old rats also differ from young animals in emotional and social behavior.

22-kHz Ultrasonic vocalization in rats as an index of anxiety but not fear: behavioral and pharmacological modulation of affective state

Ultrasonic vocalization (USV) was found useful for differentiating fear and anxiety in rats. These affective states were established through a Pavlovian conditioning procedure. Danger stimulus, preceding unavoidable tail shock, elicited acute fear. Intertrial situational cues evoked anxiety. A safety signal (SS) indicating the omission of shock inhibited fear. Sustained 22-kHz USV characterized anxiety and was present between trials. A signal of danger resulted in immediate inhibition of vocalization, while a SS reversed this effect. These results are discussed in the context of three theories: Pavlovian, Bollesian and Konorskian. The anxiolytic drugs diazepam and buspirone (1 and 5 mg/kg) suppressed vocalization in the intertrial and SS periods. The reaction to the signal of danger remained complete inhibition of USV. Anxiogenic pentyletetrazole (1 and 5 mg/kg) enhanced intertrial vocalization, but did not affect its reoccurrence during the SS. Anxiogenic FG7142 (5 mg/kg) did not affect intertrial vocalization, but blocked its reappearance on the SS. It is suggested that the behavioral target of both anxiogenic drugs is different-pentyletetrazole supposedly exerts its anxiogenic effect by increasing situational anxiety, whereas FG7142 suppresses inhibition of fear.

Predatory versus alimentary behavior after amygdala lesions in cats

Abstract In cats the effort of small amygdala lesions on mouse-killing behavior and food intake was studied. After ventromedial amygdala lesions predatory behavior was abolished for several weeks whereas food intake was only slightly diminished. Lesions of dorsolateral amygdala did not impair the effective predatory behavior, but produced a decrease of food intake. It is supposed that within the amygdala in cats there exist separate regions connected with food getting, i.e., predatory behavior (ventromedial part of amygdala) and food intake from the bowl (dorsolateral part of amydala). Motivational basis of the predatory behavior and its relations with aggressive and alimentary mechanisms are discussed.

The effect of age on the dynamics and the level of c-Fos activation in response to acute restraint in Lewis rats

Recent studies have reported an age-related increase of anxiety in rodents with a concomitant decrease in neuronal activity in some of the key structures of the fear/anxiety circuit. In the present study we present evidence that distinct parts of this circuit are differentially affected by age in Lewis rats. The effect of ageing is observed both at the actual level of neuronal activation and its time-course. While the structures belonging to the HPA axis react with a bigger neuronal activation and almost no change in the shape of dynamics curve in response to restraint, the structures involved in higher processing of emotional cues (amygdala and hippocampus) become deficiently activated with age despite their generally higher basal level of activation.

Age increases anxiety and reactivity of the fear/anxiety circuit in Lewis rats.

A growing body of data indicates that changes in emotional behavior occur with age. Young Lewis rats are known to display hypofunction of the HPA axis. With age the reactivity of this axis is thought to increase with a concomitant rise in anxiety. In the current study, we investigate how and if the pattern of neuronal activation (measured as c-Fos protein expression) in Lewis rat brains changes with age and in response to novel environments differing in aversiveness. We found that distinct parts of the fear/anxiety circuit (i.e., the amygdalar complex, hippocampus and hypothalamus) undergo diverse age-related changes in response to behavioral challenges. While in the hypothalamus an increase in responsivity to mild stressors was observed with age, no such effect was present in the hippocampus. The amygdalar complex (especially the medial and cortical nuclei) on the other hand exhibited an age-dependent decrease in neuronal activation to mild stressors. This was accompanied by a marked increase in anxiety not correlated with a decline in locomotor activity.

Electrophysiological correlates of the limbic-motor interactions in various behavioral states in rats.

Depth electroencephalographic (EEG) activity was recorded from basolateral amygdala (BLA), ventral subiculum (VSB), n. accumbens (ACC) and subpallidal area (SPL) in freely moving rats, during locomotor tasks with various types of reinforcement in order to compare the strength of limbic-motor interactions in selected behavioral situations. For all EEG signals multichannel coherences (ordinary, multiple and partial) were calculated using autoregression model. Partial coherences indicate the level of synchronization between two signals, thus they were assumed to indicate the strength of direct connection between the structures from which these signals have been recorded. The partial coherences were calculated for six selected frequency bands and the strength of connections within the BLA-VSB-ACC-SPL circuit was estimated for two different behavioral situations and compared. It was found that the strength of connections is sensitive to changes in both motor and emotional aspects of behavioral situation: the strength of BLA-VSB, VSB-ACC, and ACC-SPL depended on motor demands of behavioral task; these of BLA-VSB increased in the highest frequency bands in all emotionally engaging situations when compared with well trained locomotive; the strength of ACC-SPL increased in situations when automatic stereotyped motor behavior was induced by biologically important stimuli, while it decreased or did not change in the motor tasks demanding more precise and quickly adjustable movements. The results are discussed according to the motor-limbic integration model of proposed by Mogenson and show the dynamics of its connections in relation to the motivational-emotional context of the task.

Changes in the Aggressive Behavior of Cats Treated with Amphetamine

Male, adult cats were tested in three different experimental conditions which might lead to aggressive display: (1) Cat-mouse interaction, (2) Predatory competition between two mice killers, (3) Conspecific interactions. DL-amphetamine in a dose of 1.5 mg/kg was administered every day for three weeks to one group of cats, whereas the other group was treated with saline. The following results were observed in amphetamine treated cats: (1) Inhibition or at least a prolonged latency of predatory attack, (2) loss of the dominant status, (3) total lack of offensive behavior and decrease of defensive postures. The results indicate that amphetamine in moderate doses acts to inhibit predatory attack and aggressive behavior in social situations.

Is Predatory Behavior a Model of Complex Forms of Human Aggression

The explosion of violence and crime in the contemporary world stimulates scientists to investigate intensively social, psychological, as well as biological aspects of multiple forms of human aggressive behavior and their complex mechanisms.