PSYCHOLOGICAL STATE AND TYPOLOGICAL PERSONALITY FEATURES OF CHILDREN RESIDENTS OF RADIOACTIVELY CONTAMINATED TERRITORIES IN THE REMOTE PERIOD OF CHORNOBYL СATASTROPHE. / PSYKhOLOGIChNYI STAN TA TYPOLOGIChNI RYSY OSOBYSTOSTI DITEI ­ MEShKANTsIV RADIOAKTYVNO ZABRUDNENYKh TERYTORII U VIDDALENYI PERIOD ChORNOBYL'S'KOÏ KATASTROFY.

OBJECTIVE: To evaluate the psycho-emotional state of children-residents of radioactively contaminated territoriesand to characterize the typological features of their personality in the remote period of the Chornobyl catastrophe. MATERIALS AND METHODS: Psycho-emotional status and typological personality traits were determined in 96 childrenaged 12 to 17 years, who resided in radioactively contaminated territories with a soil contamination density of 137Csabove 185 kBq/m-2, and were admitted for examination and treatment in the pediatric departments of the NRCRMclinic. Psycho-emotional state of children was determined using the test «non-existent animal¼, which was assessedin points on symptom complexes: anxiety, aggression and neuro-mental exhaustion. The questionnaire of A. Bassand A. Darkey was used to discriminate various aspects of the aggression symptom complex. In all children, the content of incorporated 137Cs was determined using a whole body counter. RESULTS: The results of the evaluation of the psycho-emotional state of children - residents of radioactively contaminated territories in the remote period of the Chornobyl catastrophe according to the test «non-existent animal¼showed, that the state of anxiety was registered in all 96 children (100 %); state of aggression - in 60 children(62.5 %); exhaustion - in 57 children (59.37 %). Depending on the prevalence of the one or another symptom complexes, or their combination, 5 groups of observations were formed and the personality traits of children characteristic for each group were determined. In the largest group I with the predominance of anxiety symptom complex(45,83 % of the total sample) were noted: stable tendency to perceive many life-threatening situations and environment, pessimistic assessment of one's own life perspective, constant high level of anxiety. Girls were in majorityin this group. For group II, which showed a combination of high rates of two symptom complexes - anxiety andaggression (18.75 % of the total sample), the characteristic personality traits were a constant high level of emotional tension, a tendency to perceive the environment with distrust and a sense of guilt that arouses. In group IIIof children (14.58 % of the total sample), the symptom complex of aggression with feelings of alienation, isolationand hostile attitude towards the environment prevailed. Group IV of children (16.67 % of the total sample), with thecombination of signs of exhaustion and anxiety, had poor ability to concentrate, memory and attention deficit disorders, decreased learning ability, constant fatigue and irritability, apathy, inactivity, and inertia. Group V (only 4.17 %of the total sample) was characterized by low (less than 2 points) indices of all three symptom complexes. Girls weremuch more prone to anxiety, boys were more aggressive, sometimes accompanied by anxiety. Symptom complex ofexhaustion was determined with the same frequency in both boys and girls. CONCLUSION: Assessment of psycho-emotional sphere of children - residents of radioactively contaminated territories in the remote period of the Chornobyl catastrophe according to the «non-existent animal¼ test revealed in of100 % of children the presence of anxiety signs, in the vast majority - the state of aggression and exhaustion. Therewere no probable associations between the content of incorporated 137Cs (in the range from 111 to 7024 Bq) and thepeculiarities of the psycho-emotional state of children.

Chronic Exposure to Ultrasonic Frequencies Selectively Increases Aggression in Rats.

We studied aggression in male Sprague-Dawley rats in a model of a depressive-like state induced by unpredictable treatment with ultrasonic waves with the frequencies of 20-45 kHz for 1, 2 or 3 weeks. We did not find any increase in the number of animals exhibiting aggression in the "resident-intruder" test after the treatment of any selected duration. However, the aggressive animals exposed to ultrasound exhibited the substantially increased number of attacks and their total duration as well as decreased latency of the first attack compared to the respective indices in the animals of the control group. Taking this into account, it is possible to suggest that the initial level of aggression increases in a model of ultrasonic chronic stress.

Thiamine and benfotiamine counteract ultrasound-induced aggression, normalize AMPA receptor expression and plasticity markers, and reduce oxidative stress in mice.

The negative societal impacts associated with the increasing prevalence of violence and aggression is increasing, and, with this rise, is the need to understand the molecular and cellular changes that underpin ultrasound-induced aggressive behavior. In mice, stress-induced aggression is known to alter AMPA receptor subunit expression, plasticity markers, and oxidative stress within the brain. Here, we induced aggression in BALB/c mice using chronic ultrasound exposure and examined the impact of the psychoactive anti-oxidant compounds thiamine (vitamin B1), and its derivative benfotiamine, on AMPA receptor subunit expression, established plasticity markers, and oxidative stress. The administration of thiamine or benfotiamine (200 mg/kg/day) in drinking water decreased aggressive behavior following 3-weeks of ultrasound exposure and benfotiamine, reduced floating behavior in the swim test. The vehicle-treated ultrasound-exposed mice exhibited increases in protein carbonyl and total glutathione, altered AMPA receptor subunits expression, and decreased expression of plasticity markers. These ultrasound-induced effects were ameliorated by thiamine and benfotiamine treatment; in particular both antioxidants were able to reverse ultrasound-induced changes in GluA1 and GluA2 subunit expression, and, within the prefrontal cortex, significantly reversed the changes in protein carbonyl and polysialylated form of neural cell adhesion molecule (PSA-NCAM) expression levels. Benfotiamine was usually more efficacious than thiamine. Thus, the thiamine compounds were able to counteract ultrasound-induced aggression, which was accompanied by the normalization of markers that have been showed to be associated with ultrasound-induced aggression. These commonly used, orally-active compounds may have considerable potential for use in the control of aggression within the community. This article is part of the Special Issue entitled 'Current status of the neurobiology of aggression and impulsivity'.

Unexpected results when assessing underlying aggressiveness in Japanese quail using photocastrated stimulus birds.

Aggressive behaviors can affect both animal welfare and productivity. Because the expression of aggressive behaviors is dependent on the quality of the opponent, they reflect relative rather than absolute levels of underlying aggressiveness. This study was aimed to characterize the aggressive responsiveness of photostimulated (14:10 h light:dark photoperiod) adult Japanese quail when interacting with a photocastrated (6:18 h light:dark photoperiod) counterpart in a novel test environment and to assesses interindividual variations. This was based on the assumption that photocastrated birds will not actively provoke an aggressive confrontation. Birds were reared in male-female pairs. Frequencies of behaviors (i.e., pecks, threats, chases, grabs, mounts) were determined during 10 min social interactions in a novel environment. A first experiment evaluated 78 encounters between a photostimulated male or female with either a photocastrated male or female (photocastration of sexually mature birds started at 11 wk of age). High interindividual variability was observed and in general, highly aggressive birds (performing 20 or more aggressive interactions) received little or no aggression from their test counterpart. However, unexpectedly, we also found that 37% and 32% of photocastrated males and females, respectively, performed aggressions toward their photostimulated counterparts, and initiated the aggressive interactions in a similar proportion than photostimulated males. Aggressive photocastrated males did not perform reproductive-type behaviors (i.e., grabs, mounts). Aggressiveness in the photocastrated birds was attributed to their social experience prior to photocastration. Therefore, a second experiment evaluated 106 encounters between a photostimulated male or female and a naive photocastrated male (photocastration started at 4 wk of age, prior to sexual development). Photocastrated males performed no aggressions toward their photostimulated counterparts. Consistently with previous studies, our findings show that naive photocastrated males can be used as a non-aggressive stimulus during a social interaction aimed to assess expression of aggressiveness in photostimulated birds. However, caution should be taken when applying the photocastration protocol considering that prior fighting and sexual experience or other physiological changes related with maturation can interfere during subsequent aggressive testing.

Effects of Chronic Exposure to Ultrasound of Alternating Frequencies on the Levels of Aggression and Anxiety in CBA and BALB/c mice.

Stress-induced changes in the behavior of CBA and BALB/c mice were studied after 3-week ultrasound exposure (22-45 kHz). The mice of both lines demonstrated increased aggression in the resident-intruder and social interest paradigms and reduced number of social interactions in the social interest test. Elevated plus maze test showed a decrease in anxiety level in CBA mice and an increase in this parameter in BALB/c mice. Chronic exposure to ultrasound induced an increase in aggression level in mice of both lines that was not directly related to changes in anxiety level.

Neuroimagen funcional en el estudio de las conductas agresivas en pacientes con esquizofrenia / Functional neuroimaging in the study of aggressive behaviour in patients with schizophrenia

Introduction. Although aggressive behaviours are not always very highly prevalent in schizophrenia, their occurrence does represent a significant problem for patients and those around them. Although neuroimaging studies have made it possible to further our knowledge of the biology of these behaviours, there is still a notable degree of clinical heterogeneity in the study samples that makes it difficult to obtain conclusive results that can be compared with each other. Aim. To determine whether there are variations in the brain activity, as measured with functional magnetic resonance imaging, of a homogenous group of patients with schizophrenia and aggressive behaviour. Patients and methods. The sample consisted of 32 patients with refractory schizophrenia and auditory hallucinations selected for the study. The subjects were submitted to a functional magnetic resonance imaging examination using an auditory paradigm with emotional stimulation, while the degree of aggressiveness was measured by means of the Brief Psychiatric Rating Scale. Results. Significant correlations were found between functional activation and the degree of aggressiveness, which show focal hyperactivations in patients with a greater association to violent behaviours. The areas identified were located in the left hippocampus (p < 0.003, corrected) and in the right medial frontal gyrus (p < 0.004, corrected). Conclusions. This study determines the association between the degree of aggressiveness and certain regions in the brain that are responsible for cognitive and emotional processing in a phenotypically very homogenous group of patients with chronic auditory hallucinations and schizophrenia. This alteration of the neuronal circuits can favour loss in the processes involved in empathy and sensitivity, thus favouring the appearance of aggressive behaviours(AU)

Introducción. Aunque las conductas agresivas no tienen una prevalencia muy elevada en la esquizofrenia, su desarrollo supone un problema significativo para los pacientes y su entorno. Pese a que los estudios de neuroimagen han permitido profundizar en el conocimiento biológico de estas conductas, sigue existiendo una notable heterogeneidad clínica en las muestras de estudio que hace difícil la obtención de resultados concluyentes y comparables entre sí. Objetivo. Determinar si existen variaciones en la actividad cerebral medidas con resonancia magnética funcional en un grupo homogéneo de pacientes con esquizofrenia y conducta agresiva. Pacientes y métodos. Se seleccionaron 32 pacientes con esquizofrenia y alucinaciones auditivas resistentes al tratamiento. Los sujetos se sometieron a una exploración por resonancia magnética funcional utilizando un paradigma auditivo de estimulación emocional, al tiempo que se recogió el grado de agresividad a través de la Brief Psychiatric Rating Scale. Resultados. Se obtuvieron correlaciones significativas entre la activación funcional y el grado de agresividad, que muestran hiperactivaciones focales en aquellos pacientes con mayor asociación a conductas violentas. Las áreas identificadas se localizaron en el hipocampo izquierdo (p < 0,003, corregida) y en la circunvolución frontal media derecha (p < 0,004, corregida). Conclusiones. Este estudio determina la asociación entre el grado de agresividad y ciertas regiones cerebrales responsables del procesamiento cognitivo y emocional en un grupo fenotípicamente muy homogéneo de pacientes con esquizofrenia y alucinaciones auditivas crónicas. Esta alteración de los circuitos neuronales puede favorecer una pérdida en los procesos de empatía y sensibilidad, favoreciendo la aparición de conductas agresivas(AU)

Chronic non-thermal exposure of modulated 2450 MHz microwave radiation alters thyroid hormones and behavior of male rats.

PURPOSE: The purpose of this investigation was to analyze the effects of leakage microwave (2450 MHz) irradiation on thyroid hormones and behavior of male rats. MATERIALS AND METHODS: Experiments were carried out on two groups of male rats (exposure and control, respectively). Radio-immuno assay (RIA) methods were used for estimation of 3,5,3'-triiodothyronine (T3), thyroxine (T4) and thyrotrophin or thyroid stimulating hormone (TSH). The assessments of behavioral changes were performed in Open-Field (OF) and Elevated Plus-Maze (EPM) apparatuses. RESULTS: Following chronic microwave exposure, rats were found hyperactive and aggressive on the 16th and 21st days. Behavioral changes in OF were analyzed and found to be significantly changed from controls (p < 0.05) for immobilization, rearing and ambulation behavior. In EPM, rats showed increased activity with decreased time spent in the open arm and more time spent in the center on the 11th (p < 0.05), 16th (p < 0.05) and 21st day (p < 0.01) after irradiation. Changes in behavioral parameters are also correlated with the trend of changes, compared to control animals, in hormonal blood levels of T3 (decreased on the 16th day, p < 0.05 and 21st day, p < 0.01) and T4 (increased on the 21st day, p < 0.05). CONCLUSION: Low energy microwave irradiation may be harmful as it is sufficient to alter the levels of thyroid hormones as well as the emotional reactivity of the irradiated compared to control animals.

Photoperiod alters central distribution of estrogen receptor alpha in brain regions that regulate aggression.

Testosterone or its metabolite, estrogen, regulates aggression in males of many mammalian species. Because plasma testosterone levels are typically positively correlated with both aggression and reproduction, aggression is expected to be higher when males are in reproductive condition. However, in some photoperiodic species such as Siberian hamsters (Phodopus sungorus), males are significantly more aggressive in short day lengths when the testes are regressed and circulating testosterone concentrations are reduced. These results led to the formation of the hypothesis that aggression is modulated independently of circulating steroids in Siberian hamsters. Thus, recent studies have been designed to characterize the role of other neuroendocrine factors in modulating aggression. However, aggression may be mediated by testosterone or estrogen despite basal concentrations of these steroids by increasing sensitivity to steroids in specific brain regions. Consistent with this hypothesis, we found that males housed under short days have increased expression of estrogen receptor alpha in the bed nucleus of the stria terminalis, medial amygdala, and central amygdala. Neural activation in response to an aggressive encounter was also examined across photoperiod.

Rapid effects of estradiol on male aggression depend on photoperiod in reproductively non-responsive mice.

In three genuses and four species of rodents, housing in winter-like short days (8L:16D) increases male aggressive behavior. In all of these species, males undergo short-day induced regression of the reproductive system. Some studies, however, suggest that the effect of photoperiod on aggression may be independent of reproductive responses. We examined the effects of photoperiod on aggressive behavior in California mice (Peromyscus californicus), which do not display reproductive responsiveness to short days. As expected, short days had no effect on plasma testosterone. Estrogen receptor alpha and estrogen receptor beta immunostaining did not differ in the lateral septum, medial preoptic area, bed nucleus of the stria terminalis, or medial amygdala. However, males housed in short days were significantly more aggressive than males housed in long days. Similar to previous work in beach mice (Peromyscus polionotus), estradiol rapidly increased aggression when male California mice were housed in short days but not when housed in long days. These data suggest that the effects of photoperiod on aggression and estrogen signaling are independent of reproductive responses. The rapid action of estradiol on aggression in short-day mice also suggests that nongenomic mechanisms mediate the effects of estrogens in short days.

[Aggressive behavior and radiosensitivity in rats'].

This paper aims to present the study of rats' individual radiosensitivity dependence on their individual aggressiveness. On total irradiation in sublethal doses (1.0, 1.5 and 3.5 Gy) and in doses close to LD50/30 (6, 7 and 8 Gy) there was investigated comparative radiosensitivity of non-aggressive and aggressive rats of Wistar line, as well as that of non-aggressive individuals during provoked aggressiveness by means of blocking serotonin synthesis with intraperitoneal (i/p) injection of 400 mg/kg of parachlorphenylalanine (pCPA). Muricidity served as a criterion for aggressiveness and as a criterion of radiosensitivity--cumulative function of survival, the changes of behavior in "Open feald", serotonine and catecholamine content in various brain structures and the dose dependence on the radiation modification of muricidity. It has been found that after 1 Gy total X-irradiation the rats do not lose aggressiveness. Nevertheless the ethalogical parameters change in considerable degree. In the doses of 1.5 and 3.5 Gy muricidity is eluminated in 15-18 and 5-9 days, correspondingly. I/p injection of pCPA after the elimination of aggressiveness provokes transient muricidity in the same terms and duration as it is in case of non-aggressive rats. The elimination of muricidity is associated with changes in content and distribution of biogenic amines in various structures of brain, as well as with reduction of locomotor and reference-research activity, on the one hand and with an increase of emotionality and stereotype activity, on the other hand. After X-irradiation in 6, 7 and 8 Gy the regression coefficients of the dependence of functions type of survival on irradiation dose in aggressive rats is significantly reliable both in comparison with non-aggressive rats and animals with provoked aggressiveness. The change of mortality-rate per unit of changing irradiation dose not depend on blocking of serotonin synthesis, which deficit is one of the distinct determinant of aggressiveness, on the one hand, and higher radiosensitivity, on the other hand. The obtained data allow to suppose that elimination of muricidity after the irradiation of rats in the sublethal doses is conditioned not only by the consequenses of radiation damage of neurobiological structures responsible for the organization of aggressive behavior but the activation of serotonergic system in the process of restitution after radiation trauma. On the other hand, higher radiosensitivity of aggressive rats compared with non-aggressive ones is connected with low serotonin content, thiols and some other biologically active substances which are endogenous radioprotectors determining individual radioresistance.

Photoperiod reverses the effects of estrogens on male aggression via genomic and nongenomic pathways.

Despite recent discoveries of the specific contributions of genes to behavior, the molecular mechanisms mediating contributions of the environment are understudied. We demonstrate that the behavioral effects of estrogens on aggression are completely reversed by a discrete environmental signal, day length. Selective activation of either estrogen receptor alpha or beta decreases aggression in long days and increases aggression in short days. In the bed nucleus of the stria terminalis, one of several nuclei in a neural circuit that controls aggression, estrogen-dependent gene expression is increased in long days but not in short days, suggesting that estrogens decrease aggression by driving estrogen-dependent gene expression. Estradiol injections increased aggression within 15 min in short days but not in long days, suggesting that estrogens increase aggression in short days primarily via nongenomic pathways. These data demonstrate that the environment can dictate how hormones affect a complex behavior by altering the molecular pathways targeted by steroid receptors.

Potentiating role of interleukin-1beta (IL-1beta) and IL-1beta type 1 receptors in the medial hypothalamus in defensive rage behavior in the cat.

Recently, this laboratory provided evidence that interleukin-1beta (IL-1beta), an immune and brain-derived cytokine, microinjected into the medial hypothalamus, potentiates defensive rage behavior in the cat elicited from the midbrain periaqueductal gray (PAG), and that such effects are blocked by a 5-HT2 receptor antagonist. Since this finding represents the first time that a brain cytokine has been shown to affect defensive rage behavior, the present study replicated and extended these findings by documenting the specific potentiating role played by IL-1beta Type 1 receptor (IL-1RI), and the anatomical relationship between IL-1beta and 5-HT2 receptors in the medial hypothalamus. IL-1beta (10 ng) microinjected into the medial hypothalamus induced two separate phases of facilitation, one at 60 min and another at 180 min, post-injection. In turn, these effects were blocked with pretreatment of the selective IL-1 Type I receptor antagonist (IL-1ra) (10 ng), demonstrating the selectivity of the effects of IL-1beta on medial hypothalamic neurons upon PAG-elicited defensive rage behavior. The next stage of the study utilized immunohistochemical methods to demonstrate that IL-1beta and 5-HT2 receptors were present on the same neurons within regions of the medial hypothalamus where IL-1beta and the IL-1beta receptor antagonists were administered. This provided anatomical evidence suggesting a relationship between IL-1RI and 5-HT2 receptors in the medial hypothalamus that is consistent with the previous pharmacological observations in our laboratory. The overall findings show that activation of IL-1RI in the medial hypothalamus potentiates defensive rage behavior in the cat and that these effects may also be linked to the presence of 5-HT2 receptors on the same groups of neurons in this region of hypothalamus.

Cranial electrotherapy stimulation reduces aggression in a violent retarded population: a preliminary report.

Nine aggressive, retarded patients refractory to conventional care at a maximum security hospital were given a 3-month course of cranial electrotherapy stimulation. Aggressive episodes declined 59% from baseline; seclusions were down 72%; restraints were down 58%; and use of prescribed-as-needed sedative medications decreased 53%. The most dramatic change was that of a disorganized, schizophrenic patient whose aggressive episodes declined from 62 to 9, seclusions from 53 to 8, restraints from 9 to 1 and PRNs from 25 to 1. No patients discontinued cranial electrotherapy stimulation (CES) because of side effects. This preliminary report indicates that CES appears to be an efficacious, safe, and cost-effective addition to the treatment regimen in this patient population.

Photoperiod affects neuronal nitric oxide synthase and aggressive behaviour in male Siberian hamsters (Phodopus sungorus).

Many nontropical animals display physiological and behavioural changes in response to seasonal environmental cues including photoperiod (day length). Male Siberian hamsters (Phodopus sungorus) housed in short photoperiod undergo testicular regression accompanied by reduced circulating testosterone and decreased reproductive behaviour. By contrast to the majority of small mammals studied, aggressive behaviour is elevated in short-day Siberian hamsters when blood testosterone concentrations are not detectable. Because gonadal steroid hormones influence neuronal nitric oxide synthase (nNOS), and this enzyme has been implicated in aggressive behaviour, we hypothesized that nNOS expression would be decreased in short-day male Siberian hamsters and negatively correlated with the display of territorial aggression. Adult male Siberian hamsters were individually housed in either long (LD 16:8 h) or short (LD 8:16 h) photoperiods for 10 weeks. Hamsters were assigned to one of two categories by assessing testicular volume and plasma testosterone values: (i) photoperiodic responsive (i.e. regressed testes and low testosterone concentrations) or (ii) photoperiodic nonresponsive (i.e. testes size and circulating testosterone concentrations equivalent to hamsters maintained in long days). At week 10, aggression was assessed using a resident-intruder test. Latency to initial attack, frequency of attacks and duration of total attacks were recorded during a 10-min aggression trial. Brains were collected immediately after behavioural testing and stained for nNOS expression using immunohistochemistry. All short day-housed hamsters were significantly more aggressive than long-day animals, regardless of gonadal size or testosterone concentrations. Short-day animals, both reproductively responsive and nonresponsive morphs, also had significantly less nNOS-immunoreactive cells in the anterior and basolateral amygdaloid areas and paraventricular nuclei compared to long-day hamsters. Together, these results suggest that seasonal aggression in male Siberian hamsters is regulated by photoperiod, through mechanisms that are likely independent from gonadal steroid hormones.

Adrenal hormones mediate melatonin-induced increases in aggression in male Siberian hamsters (Phodopus sungorus).

Among the suite of seasonal adaptations displayed by nontropical rodents, some species demonstrate increased territorial aggression in short compared with long day lengths despite basal levels of testosterone. The precise physiological mechanisms mediating seasonal changes in aggression, however, remain largely unknown. The goal of the present study was to examine the role of melatonin, as well as adrenal hormones, in the regulation of seasonal aggression in male Siberian hamsters (Phodopus sungorus). In Experiment 1, male Siberian hamsters received either daily (s.c.) injections of melatonin (15 microg/day) or saline 2 h before lights out for 10 consecutive days. In Experiment 2, hamsters received adrenal demedullations (ADMEDx), whereas in Experiment 3 animals received adrenalectomies (ADx); control animals in both experiments received sham surgeries. Animals in both experiments subsequently received daily injections of melatonin or vehicle as in Experiment 1. Animals in all experiments were tested using a resident-intruder model of aggression. In Experiment 1, exogenous melatonin treatment increased aggression compared with control hamsters. In Experiment 2, ADMEDx had no effect on melatonin-induced aggression. In Experiment 3, the melatonin-induced increase in aggression was significantly attenuated by ADx. Collectively, the results of the present study demonstrate that short day-like patterns of melatonin increase aggression in male Siberian hamsters and suggest that increased aggression is due, in part, to changes in adrenocortical steroids.

Short days and exogenous melatonin increase aggression of male Syrian hamsters (Mesocricetus auratus).

Many nontropical rodent species rely on photoperiod as a primary cue to coordinate seasonally appropriate changes in physiology and behavior. Among these changes, some species of rodents demonstrate increased aggression in short, "winter-like" compared with long "summer-like" day lengths. The precise neuroendocrine mechanisms mediating changes in aggression, however, remain largely unknown. The goal of the present study was to examine the effects of photoperiod and exogenous melatonin on resident-intruder aggression in male Syrian hamsters (Mesocricetus auratus). In Experiment 1, male Syrian hamsters were housed in long (LD 14:10) or short (LD 10:14) days for 10 weeks. In Experiment 2, hamsters were housed in long days and half of the animals were given daily subcutaneous melatonin injections (15 microg/day in 0.1 ml saline) 2 h before lights out for 10 consecutive days to simulate a short-day pattern of melatonin secretion, while the remaining animals received injections of the vehicle alone. Animals in both experiments were then tested using a resident-intruder model of aggression and the number of attacks, duration of attacks, and latency to initial attack were recorded. In Experiment 1, short-day hamsters underwent gonadal regression and displayed increased aggression compared with long-day animals. In Experiment 2, melatonin treatment also increased aggression compared with control hamsters without affecting circulating testosterone. Collectively, the results of the present study demonstrate that exposure to short days or short day-like patterns of melatonin increase aggression in male Syrian hamsters. In addition, these results suggest that photoperiodic changes in aggression provide an important, ecologically relevant model with which to study the neuroendocrine mechanisms underlying aggression in rodents.

Head-portion exposure to low-level X-rays reduces isolation-induced aggression of mouse, and involvement of the olfactory carnosine in modulation of the radiation effects.

Social isolation has been widely described to induce a compulsive aggressive behavior. The aggressiveness due to isolation in mice has often been used as a means for the better understanding of disturbed behavior in human beings. In the course of a study of the behavioral effects, we have noticed that fighting injuries, usually observed among male ICR mice, tend to decrease in mice irradiated with low-dose X-rays. We, therefore, quantitatively examined the effects of low-dose X-irradiation on aggressive behavior using a resident-intruder paradigm in which a resident mouse attacks an intruder that entered its territory. Male ICR white Swiss mice became gradually calm, and showed remarkably quiet behavior 7-10 days after whole-head 5 or 15 cGy X-irradiation. Only exposure of the anterior part of the head (olfactory system including orbits) also induced the remarkable suppression of the aggressive behavior. The olfactory system has direct access to the limbic system, a central part of the brain concerned with emotion. The calm behavior induced by low-dose X-irradiation might be related to the changes in the olfactory function. We also obtained data on brain biochemistry giving further support for the above low-dose effects on mouse behavior. The carnosine content and its synthetase activity in the olfactory bulbs decreased significantly after only the anterior part of the head had been exposed. Higher doses (25-35 cGy), however, did not induce such effects. The results suggest that the depression of aggressive behavior is limited to animals irradiated with the smaller doses.

Changes of aggressive behavior and brain serotonin turnover after very low-dose X-irradiation of mice.

Social isolation has been widely described to induce compulsive aggressive behavior and produce a large decrease of brain serotonin turnover in male mice. The aggressiveness by isolation in mice has been often used as a means for a better understanding of disturbed behavior in human beings. We found that male ICR white Swiss mice exhibiting isolation-induced aggression became gradually calm and showed remarkably quiet behavior 7 to 10 days after whole body irradiation of very low-dose X-rays (5-15 cGy). Higher doses (25-35 cGy), however, could not induce such effects. We also obtained the data on brain biochemistry giving a further support for the above low-dose effects on the mouse behavior. Brain serotonin turnover which has been known to be related to aggressive behavior in 5 or 15 cGy irradiated mice was faster than in aggressive control animals.

Onset of behavioral effects in mice exposed to 10 Gy 60Co radiation.

The effects of 10 Gray (Gy) 60 Co radiation on social behavior, locomotor activity, and body weight were assessed in individually housed male Swiss-Webster mice. In Experiment 1, aggressive behavior was evaluated prior to irradiation and for 7 d postirradiation by placing an untreated intruder in the irradiated or sham-irradiated resident's home cage for 5 min. Offensive aggressive behavior was not affected significantly by radiation until day 7 postirradiation, when attack latency increased, the frequency and duration of fighting decreased, and the frequency of bites, lunges, and chases decreased. Untreated intruder mice paired with irradiated resident mice showed a decrease in the duration of defensive upright postures and a decrease in the frequency of defensive upright postures, squeaks, and escapes on day 7 postirradiation. In Experiment 2, locomotor activity and body weight were monitored for 7 d postirradiation. Body weight was decreased in irradiated mice beginning 4 d postirradiation. Locomotor activity was suppressed in irradiated animals 90 min after irradiation and remained depressed throughout the 7-d testing period.

Effect of electron radiation on aggressive behavior, activity, and hemopoiesis in mice.

The behavioral and physiological effects of 10 Gray (Gy) LINAC electrons in male Swiss-Webster mice were followed for 12 days postirradiation (PR). In Experiment 1, aggressive behavior was assessed in irradiated or sham-irradiated resident mice using a resident-intruder paradigm. Aggressive offensive behavior in the irradiated residents was significantly decreased beginning 2 to 5 days PR, and remained suppressed. Defensive behavior in the nonirradiated intruders was decreased significantly by day 5 PR. In Experiment 2, spontaneous locomotor activity was monitored. Ambulation of irradiated mice was significantly depressed from day 5 PR on, while rearing was affected as early as day 2 PR and remained suppressed. Body weights of irradiated animals were significantly decreased by 5 days PR. In Experiment 3, blood parameters were examined. Compared to sham-irradiated controls, leukocytes, erythrocytes, and hematocrit of irradiated mice were reduced significantly beginning on day 1 PR and remained suppressed, while platelets and hemoglobin were decreased beginning day 2 PR. These results demonstrate that 10 Gy of high-energy electrons results in earlier behavioral deficits than has been observed previously with the same dose of gamma photons.