Marika Eller

Chronic variable stress and partial 5-HT denervation by parachloroamphetamine treatment in the rat: effects on behavior and monoamine neurochemistry

Chronic variable stress (CVS) and manipulations of 5-HT-ergic neurotransmission are increasingly used as animal models of depression. In the present study, CVS for 2 weeks and a partial lesion of 5-HT projections by a small dose of parachloroamphetamine (PCA, 2 mg/kg) were applied independently or in combination. CVS reduced significantly the gain in body weight and increased the number of defecations in the open field test. PCA reduced body weight only within the first 24 h after its administration. Consumption of sucrose solution and its preference to water in non-deprived rats were significantly higher in PCA-pretreated rats 2 weeks after CVS compared to control animals. In the forced swimming test, both PCA and CVS treatments reduced immobility on the first but not the second session. Both treatments reduced significantly the time rats spent in social interaction. CVS also elicited an increase in the weight of the right adrenal, but this effect was not present in the PCA-pretreated group. PCA reduced 5-HT and 5-HIAA levels in the frontal cortex, hippocampus, and septum by approximately 20%. CVS increased HVA levels in the frontal cortex. Applied together, PCA pretreatment and CVS increased dopamine turnover in the frontal cortex. Conclusively, this study has provided evidence that chronic variable stress, which elicited expected physiological and neurochemical changes, does not reduce sucrose intake or preference in non-deprived animals, but, instead, may increase it after partial 5-HT-ergic denervation; and that partial 5-HT-ergic denervation by a low dose PCA treatment has a long-lasting effect on forced swimming and social behavior similar to chronic stress.

Tickling-induced 50-kHz ultrasonic vocalization is individually stable and predicts behaviour in tests of anxiety and depression in rats

Manipulation of juvenile rats in a way that mimics the rough-and-tumble play and resembles tickling elicits 50-kHz ultrasonic vocalizations (USVs) that have been proposed as a measure of positive affect. In the present experiments the stability of the 50-kHz USV response (chirping) over 1.5 months of daily manipulation and the effect of tickling was studied. By the second week of tickling rats of both sexes developed a level of 50-kHz USVs that remained individually characteristic. During tickling the rats also emitted low levels of 22-kHz USVs. No correlation was found between the two types of USVs. In tests used in anxiety and depression research, tickling on its own had an anxiolytic effect in many experimental settings. Significantly lower levels of [(35)S]GTPgammaS binding to the dopamine-activated receptor-G protein complex in striatum and serotonin transporter levels in the frontal cortex were found in female control rats as compared to males. These differences were eliminated by tickling. Rats which expressed high level of chirping (HC-rats) were similar to low-chirping (LC) rats in anxiety measures but had lower activity in an exploration test and lower sucrose preference. LC-rats adopted more active coping strategies in the forced swimming test. These findings suggest that there are individually characteristic 50-kHz USV response levels to tickling in rats, and that HC- and LC-rats are similar with regard to anxiety levels but have different coping strategies to novelty. The anxiolytic-like changes in behaviour that were brought about by tickling could be mediated by changes in dopamine- and serotonergic systems.

Rats with persistently low or high exploratory activity : Behaviour in tests of anxiety and depression, and extracellular levels of dopamine

Behaviour in novel environments is influenced by the conflicting motivators fear and curiosity. Because changes in both of these motivational processes are often simultaneously involved in human affective disorders, we have developed the exploration box test which allows separation of animals belonging to clusters with inherent high neophobia/low motivation to explore and low neophobia/high motivation to explore (LE and HE, respectively). In a novel home-cage, no behavioural differences were found between LE- and HE-rats, suggestive that it is not the general locomotor activity but specific features of the exploration box test that bring about the differences. In studies on both Wistar and Sprague-Dawley rats we found that the trait of exploratory activity remains stable over long periods of time and that LE and HE animals display differences in many other behavioural tests related to mood disorders. Namely, LE animals were found to display enhanced anxiety-like behaviour and to be generally less active in the elevated plus-maze, used more passive coping strategies in the forced swimming test, and acquired a more persistent association between neutral and stressful stimuli in fear conditioning test. LE animals consumed more sucrose solution in non-deprived conditions. We also found that both at baseline and in response to d-amphetamine (0.5mg/kg) administration, LE-rats had lower extracellular dopamine levels in striatum but not in nucleus accumbens. In conclusion, LE-rats appear more inhibited in their activity in typical animal tests of anxiety and are more susceptible to acute stressful stimuli.

Rat behavior after chronic variable stress and partial lesioning of 5-HT-ergic neurotransmission: effects of citalopram.

Deficits in serotonergic (5-HT-ergic) neurotransmission and stressful life events have been implicated in affective disorders, and chronic variable stress (CVS) can elicit behavioral changes reminiscent of increased emotionality, anxiety and atypical depression after partial 5-HT depletion. This study examined the effect of chronic citalopram treatment (10 mg/kg daily) on these changes. Parachloroamphetamine (PCA) (2 mg/kg) reduced the levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex, increased anxiety in the social interaction test, and increased activity in the open field. CVS reduced social activity in the social interaction test and immobility time in the forced swimming test. Reduction of excrements left during immobilization indicated partial adaptation with the CVS. Specific stressors had different effects on body weight gain, shorter lasting stressors having a smaller effect in general than those that lasted longer. Combination of CVS and PCA increased sucrose intake after two weeks of stress. In addition, combination of the two treatments reduced diving in the forced swimming test. Citalopram prevented the increase in sucrose consumption in the PCA+CVS rats, and in 5-HT-depleted animals blocked the increase in struggling and reduced the number of defecations in the forced swim test. In conclusion, citalopram treatment prevented several effects of either 5-HT depletion or combined PCA+CVS treatment, suggesting that these behavioral changes could be used in studies on the neural mechanisms underlying emotional behavior that may have relevance to the neurobiology of depression.

Effects of partial locus coeruleus denervation and chronic mild stress on behaviour and monoamine neurochemistry in the rat

It has been proposed that lesions of the ascending noradrenergic projections render animals more vulnerable to stress. In this study, the effects of partial denervation of the locus coeruleus (LC) by DSP-4 (10 mg/kg) treatment, chronic mild stress (CMS) and their combination were examined. DSP-4 was administered to rats 1 week before the onset of CMS, which was applied for 5 weeks. In the forced swimming test, the immobility time was decreased by both DSP-4 and CMS. In the open field test, the number of defecations was increased after DSP-4 treatment plus CMS. Partial LC denervation decreased the levels of noradrenaline (NA) by 34%, increased NA turnover, and decreased the density of beta-adrenoceptors in the cerebral cortex. CMS decreased the binding affinity of beta-adrenoceptors, an effect not observed in the DSP-4 treated animals. In conclusion, 6 weeks after partial LC denervation NA turnover is increased in the cortex, and the effect of CMS on emotionality is enhanced.

The effects of CRA 1000, a non-peptide antagonist of corticotropin-releasing factor receptor type 1, on adaptive behaviour in therat☆

Intracerebrally administered CRF has been demonstrated to elicit several behavioural deficits in novel and potentially stressful experimental paradigms, and to promote activity in familiar situations. This study examined the effect of CRA 1000, a novel non-peptide antagonist of CRF(1)receptors, on rat behaviour in tests of anxiolytic and antidepressant activity and novelty-oriented behaviour. CRA 1000 (1.25-10 mg/kg) had no major effect in elevated plus-maze and social interaction tests. However, CRA 1000 (5 mg/kg) significantly reduced immobility in the forced swimming test, suggesting an antidepressant-like effect. In the exploration box test, CRA 1000 (1.25 mg/kg) had an anxiolytic effect on rat exploratory behaviour both in intact rats and after lesioning of the projections of locus coeruleus by DSP-4 (50 mg/kg) treatment. A higher dose of CRA 1000 (5 mg/kg) tended to have anxiolytic-like effects in DSP-4 pretreated rats, but in intact animals this dose prevented the increase in exploration which develops with repeated exposure to initially anxiety-provoking situations. Taken together, these experiments demonstrate that CRF1 receptor blockade by CRA 1000 has antidepressant-like effects, does not have a robust anti-anxiety effect in non-stressed animals, but does have anxiolytic-like effects in more complex tasks, which can be observed also after denervation of the locus coeruleus projections. However, large doses of CRF1 receptor antagonists may reduce motivation of exploratory behaviour in familiar environments.

Levels of transcription factors AP-2α and AP-2β in the brainstem are correlated to monoamine turnover in the rat forebrain

Abstract The transcription factors AP-2α and AP-2β are implicated to play an important role during embryonic development of different parts of the brain, and in targeted regulation of gene expression in the adult brain. Several monoaminergic genes have binding sites for AP-2 in regulatory regions. We have in the present study, analysed the association between AP-2 levels in the brainstem of rats ( n =9) and monoamine levels in the frontal cortex, septum and hippocampus. Several regionally specific correlations were found between AP-2α and AP-2β and specific monoamines in the rat forebrain. The data support our notion that the transcription factor AP-2 family is involved in the regulation of the monoaminergic systems and, therefore, might be involved in the pathophysiology of neuropsychiatric disorders.

Amphetamine-induced locomotion, behavioral sensitization to amphetamine, and striatal D2 receptor function in rats with high or low spontaneous exploratory activity: differences in the role of locus coeruleus.

Individual differences in novelty-related behavior are associated with sensitivity to various neurochemical manipulations. In the present study the amphetamine-induced locomotor activity and behavioral sensitization to amphetamine (0.5 mg/kg) was investigated in rats with high or low spontaneous exploratory activity (HE- and LE-rats, respectively) after partial denervation of the locus coeruleus (LC) projections with a low dose of the selective neurotoxin DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine; 10 mg/kg). DSP-4 produced a partial depletion (about 30%) of noradrenaline in the frontal cortex of both HE- and LE-rats; additionally the levels of metabolites of dopamine and 5-HT were reduced in the frontal cortex and nucleus accumbens of the LE-rats. Amphetamine-stimulated locomotor activity was attenuated by the DSP-4 pretreatment only in the HE-rats and this effect persisted over repeated testing. Behavioral sensitization to repeated amphetamine was evident only in the LE-rats with intact LC projections. Repeated amphetamine treatment reduced D(2) receptor mediated stimulation of [(35)S]GTPgammaS-binding and dopamine-dependent change in GDP-binding affinity in the striatum, but only in HE-rats. The absence of amphetamine sensitization in HE-rats could thus be related to the downregulation by amphetamine of the G protein stimulation through D(2) receptors. Conclusively, acute and sensitized effects of amphetamine depend on the integrity of LC projections but are differently regulated in animals with high or low trait of exploratory activity. These findings have implications to the neurobiology of depression, drug addiction, and attention deficit hyperactivity disorder.

Effects of low dose N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine administration on exploratory and amphetamine-induced behavior and dopamine D2 receptor function in rats with high or low exploratory activity

Individual differences in behavioral traits are associated with sensitivity to various neurochemical and psychopharmacological manipulations. In this study exploratory and amphetamine-induced behavior in rats with persistently high or low exploratory activity (HE and LE, respectively) was examined before and after a partial denervation of the locus coeruleus (LC) projections with the selective neurotoxin DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine; 10 mg/kg). Partial LC denervation prevented the increase in exploratory activity over repeated test sessions in the LE animals, but had no effect in HE-rats. Amphetamine- (0.5 mg/kg) induced locomotor activity was attenuated by DSP-4 pretreatment only in HE-rats. These results suggest differential involvement of LC noradrenergic transmission in novelty- and amphetamine-induced behavior in animals with persistent differences in novelty-related behavior. In addition to partial noradrenaline depletion in the frontal cortex and hippocampus, which occurred in both HE- and LE-rats, DSP-4 treatment also decreased the content of dopamine and its metabolites in the nucleus accumbens, and the metabolite levels in striatum, but only in the LE-animals. 5-HIAA levels were also reduced in the nucleus accumbens and striatum in LE-rats by the neurotoxin. D(2) receptor function, as determined by dopamine-stimulated [(35)S]GTPgammaS binding, was increased by DSP-4 treatment in the striatum of LE-rats, but reduced in HE-rats. No effect of partial LC denervation was found on dopamine-stimulated [(35)S]GTPgammaS binding in the nucleus accumbens. Together these findings suggest that LC noradrenergic neurotransmission is differently involved in dopaminergic mechanisms which mediate novelty-related vs amphetamine-induced behavior.

Rats with high or low sociability are differently affected by chronic variable stress

Depression is strongly related to social behavior. We have previously shown that social behavior of rats is individually stable. The purpose of the present study was to compare the sensitivity of animals with different sociability to chronic variable stress (CVS). Four social interaction tests were performed with 60 single-housed male Sprague-Dawley rats. Twenty rats with the lowest and 20 with the highest average social activity time were selected as low sociability (LS) and high sociability (HS) rats, respectively. Both groups were further divided into control and stress groups with equal average body weight. The CVS procedure lasted for 3 weeks. The stressors applied were cold water and wet bedding, imitation of injection, stroboscopic light, movement restriction in a small cage, tail pinch with a clothespin, and strong illumination during the predicted dark phase. In HS-rats, but not in LS-rats, CVS reduced sucrose intake compared with baseline after 3 weeks, suggesting that HS-rats are more vulnerable to anhedonia elicited by CVS. LS-animals were more anxious in the social interaction and open field tests, but stress eliminated differences with HS-animals in the social interaction test and increased their activity in the forced swimming test. In LS-rats stress increased ex vivo dopamine levels and reduced 5-HT levels in the frontal cortex, suggesting that the increased behavioral activity after stress may be related to increased impulsivity. This study thus revealed that animals with high sociability trait are more vulnerable to anhedonia elicited by chronic stress in conditions of single housing.