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Affective disorders are often accompanied by changes in motivation and anxiety. We investigated the genome-wide gene expression patterns in an animal model of depression that separates Wistar rats belonging into clusters of persistently high anxiety/low motivation to explore and low anxiety/high motivation to explore (low explorers and high explorers, LE and HE, respectively), in three brain regions previously implicated in mood disorders (raphe, hippocampus and the frontal cortex). Several serotonin-, GABA-, and glutamatergic genes were differentially expressed in LE- and HE-rats. The analysis of Gene Ontology biological process terms associated with the differentially regulated genes identified a significant overrepresentation of genes involved in the neuron development, morphogenesis, and differentiation; the most enriched pathways from the Kyoto Encyclopedia of Genes and Genomes were the Wnt signalling, MAPK signalling, long-term potentiation, and long-term depression pathways. These findings corroborate some expression data from other models of depression, and suggest additional targets., (2009 Elsevier B.V. All rights reserved.)

An attempt was made to establish whether the anxiogenic effect of cat odour differs in female wild-type and CCK(2) receptor deficient mice, having different exploratory activity in the elevated plus-maze. The exposure of wild-type and homozygous CCK(2) receptor deficient mice to cat odour did not reveal substantial differences between the two genotypes. The number of contacts with the cat odour impregnated cloth was reduced and the frequency of stretch-attend postures was increased similarly in wild-type and homozygous mice. However, the following exposure of mice to the elevated plus-maze established differences as homozygous mice displayed increased exploratory activity in the plus-maze. The cat odour exposure significantly reduced exploratory activity only in homozygous mice. Together with the increased exploratory activity we established in homozygous mice significantly increased expression of the Oprm1 gene in the frontal cortex and mesencephalon. The exposure of mice to cat odour caused only minor changes in the gene expression of wild-type mice, whereas in homozygous animals a significantly increased expression of the Mc3r gene in the frontal cortex and temporal lobe, and the Pomc1 gene in the temporal lobe, mesencephalon and mesolimbic area was established. In conclusion, CCK(2) receptor deficient mice displayed reduced anxiety compared to their wild-type littermates in the plus-maze test. This behavioural effect seems to be related, at least partly, to an increased tone of opioid system in the brain. Moreover, homozygous mice respond to the exposure of cat odour with an increased anxiety. This effect seems to be related to the increased function of the melanocortin system in the brain structures of genetically modified mice.

Rationale: Evidence suggests that gamma-aminobutyric acid (GABA) and cholecystokinin (CCK) have opposite roles in the regulation of anxiety., Objectives: The aim of our work was to study the behaviour of CCK(2) receptor deficient mice in light-dark exploration and fear conditioning tests. Moreover, the action of diazepam and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), having the opposite effect on GABA(A) receptors, was evaluated on the exploratory behaviour in these mice. Expression levels of GABA(A) receptor subunit genes were also measured., Methods: Light-dark exploration and fear conditioning tests were used to determine changes in anxiety of mice. The action of diazepam (0.5-2 mg/kg i.p.) and DMCM (0.25-1 mg/kg i.p.) was studied in the light-dark box. The effect of DMCM was also evaluated in the motor activity test to demonstrate that its anti-exploratory action was not related to motor suppression. Expression levels of GABA(A) receptor subunit genes were determined by means of real-time polymerase chain reaction (qRT-PCR)., Results: Female mice lacking CCK(2) receptors displayed increased exploratory activity in the light-dark box compared to their wild-type (+/+) littermates. Locomotor activity in the motility boxes and the intensity of freezing did not differ in wild-type (+/+) and homozygous (-/-) mice. Treatment with diazepam (0.5 mg/kg) increased the number of transitions in wild-type (+/+) animals, whereas in homozygous (-/-) mice diazepam (0.5-2 mg/kg) reduced exploratory activity. Administration of DMCM (0.25-1 mg/kg) induced an anxiogenic-like effect in homozygous (-/-) mice, but did not change their locomotor activity. Gene expression analysis established a 1.6-fold increase in the expression of the alpha2 subunit of GABA(A) receptors in the frontal cortex of homozygous (-/-) mice., Conclusion: Genetic invalidation of CCK(2) receptors induced an anxiolytic-like action in exploratory, but not in conditioned models of anxiety. The observed reduction in anxiety in homozygous (-/-) mice is probably related to an increased function of GABAergic system in the brain.

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.

Background: The objective of the study was to investigate the effects of the nitric oxide synthase (NOS) inhibitors 7-nitroindazole (7-NI), N(G)-nitro-L-arginine (L-NOARG), and N(G)-nitro-L-arginine methyl ester (L-NAME) on the behavior of mice in the staircase test., Methods: NOS inhibitors 7-NI (20-120 mg/kg), L-NOARG (20 and 40 mg/kg), and L-NAME (20 and 40 mg/kg) were administered intraperitoneally (i.p.) 30 min prior to the staircase test. Staircase test consisted of placing a mouse in an enclosed staircase with five steps and recording the number of rearings made and the number of steps climbed during a 3-min period., Results: 7-NI and L-NOARG did not have a significant effect on the behavior of mice in the staircase test. L-NAME caused a decrease in the number of rearings without changes in the number of steps taken., Conclusions: NOS inhibitor L-NAME but not 7-NI or L-NAME induced an anxiolytic effect in the staircase test.

Effects of the nitric oxide synthase (NOS) inhibitors 7-nitroindazole (7-NI), N(G)-nitro-L-arginine (L-NOARG) and N(G)-nitro-L-arginine methyl ester (L-NAME) on the behaviour of control and small-platform (SP)-stressed mice in the plus-maze test were studied. SP stress was induced by placing mice on SPs (3.5 cm diameter) surrounded by water for 24 h. This model contains several factors of stress like rapid eye movement (REM) sleep deprivation, isolation, immobilization and falling into the water. The plus-maze test was carried out with control and SP-stressed mice. SP stress induced an anxiolytic-like effect that was evidenced by increased percentage of time spent on the open arms of the plus-maze. The administration of NOS inhibitors 7-NI (20.0-120.0 mg/kg) and L-NOARG (20.0 and 40.0 mg/kg) induced an anxiolytic effect and the administration of L-NAME (20.0 and 40.0 mg/kg)--an anxiogenic effect in control mice. In SP-stressed mice, the effects of NOS inhibitors were changed. Contrary to control mice, 7-NI at a dose of 20.0 mg/kg induced an anxiogenic effect in SP-stressed mice and other doses of 7-NI, with exception of 80.0 mg/kg, as well as L-NOARG and L-NAME were without any effect. On the basis of these data, we can propose that SP stress induced changes in the function of L-arginine-NOS-NO pathways. It is also proposed that the behavioural effects of NOS inhibitors can be changed in stressed animals.

Small platform (SP) stress was induced by placing mice on small platforms (3.5 cm diameter) surrounded by water for 24 h. This model contains several factors of stress like rapid eye movement (REM) sleep deprivation, isolation, immobilization and falling into the water. The staircase test consisted of placing a mouse in an enclosed staircase with 5 steps and recording (1) the number of steps and (2) rearings made during 3 min. SP stress increased the exploratory activity of mice in the staircase test as evidenced by an increase in the number of steps and rearings made In control mice diazepam (0.25 and 0.5 mg/kg) induced an anxiolytic effect in the staircase test as evidenced by a decrease in the number of rearings without changes in the number of steps. In SP stressed mice the anxiolytic effect of diazepam was not seen and the sedative effect as evidenced by a decrease in the number of steps was more pronounced. Buspirone at a dose of 1.0 mg/kg did not have effect on the behaviour of control or SP stressed mice in the staircase test. To study possible diurnal variations the staircase test was carried out at 3 different times of a day (08:00, 14:00, 20:00) with control and SP stressed mice. The exploratory activity of control mice in the staircase test gradually increased from 08:00 to 20:00 as evidenced by an increased number of steps and rearings made. SP stress increased the exploratory activity of mice irrespective of the time of testing. In conclusion, on the basis of these data the authors can propose that SP stress increases the exploratory activity of mice in the staircase test and induces a hyposensitivity of mice to the anxiolytic effect of diazepam. The effect of SP stress on the behaviour of mice in the staircase test is not caused by the disruptance of diurnal rhythms.

The effects of flumazenil, Ro 154513 and beta-CCM in the staircase test were studied in control and small platform (SP) stressed mice. SP stress was induced by placing mice on small platforms (3.5 cm in diameter) surrounded by water for 24 h. This model contains several factors of stress, such as rapid eye movement sleep deprivation, isolation, immobilization and falling into the water. The staircase test consisted of placing a mouse in an enclosed staircase with five steps and recording: (i) the number of rearings and (ii) steps made during 3 min. SP stress increased the exploratory activity of mice in the staircase test as demonstrated by an increase in the number of rearings and steps made. In control mice flumazenil (2.0 and 10.0 mg/kg), Ro 15-4513 (1.0 and 3.0 mg/kg) and beta-CCM (1.0 and 2.0 mg/kg) exerted an anxiogenic effect that was demonstrated by an increase in the number of rearings without significant changes in the number of steps. Similar to control mice, flumazenil induced an anxiogenic effect in SP stressed mice as demonstrated by an increase in the number of rearings. However, the sedative effect of flumazenil as demonstrated by a decrease in the number of steps made was more pronounced in SP stressed mice. In the SP stressed mice, the anxiogenic effect of Ro 15-4513 and beta-CCM was masked by their strong sedative effect and a decrease in both measures of exploratory activity (number of rearings and number of steps). These data suggest that SP stress induces hypersensitivity to the sedative effect of flumazenil, Ro 15-4513 and beta-CCM in the staircase test.

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., (Copyright 2001 Harcourt Publishers Ltd.)

Objective: To investigate whether a 5-hydroxytryptamine (5-HT) reuptake inhibitor (paroxetine) has an anxiogenic-like effect and what possible pharmacological mechanism underlies that action., Methods: We used the rat elevated plus-maze paradigm followed by measurement of locomotor activity. Some of the rats were subjected to handling and adaptation to the experimental situation, while the rest were naive to the test situation. Paroxetine was administered as a single treatment and in combination with the 5-HT1A receptor agonist (8-OH-DPAT) or 5-HT2A/2C receptor antagonist (deramciclane)., Results: The administration of paroxetine induced an anxiogenic-like action in rats adapted to handling, but not in handling naive animals. Treatment with paroxetine (0.1-2 mg/kg) reduced the number of open arm visits and time spent in open arms, and the ratio between open and total arm entries in the elevated plus-maze. Paroxetine also decreased the number of line crossings and head-dips. Paroxetine caused the strongest anti-exploratory action at a dose of 0.5 mg/kg. Paroxetine did not suppress the locomotor activity of rats, showing that the described anti-exploratory effect was behaviourally specific to the plus-maze. Pretreatment with 8-OH-DPAT (0.05 mg/kg) completely reversed the anxiogenic-like action of paroxetine, whereas treatment with deramciclane (2 mg/kg) affected only the number of closed arm visits. Deramciclane (0.5-2 mg/kg) and 8-OH-DPAT (0.01-0.1 mg/kg) changed neither exploratory behaviour nor locomotor activity if given as single treatments to the habituated rats., Conclusion: The 5-HT reuptake inhibitor, paroxetine, at a low dose (0.5 mg/kg) induces an anxiogenic-like action in handling adapted rats. The effectiveness of 8-OH-DPAT against paroxetine probably supports a role of both pre- and postsynaptic 5HT-ergic mechanisms in the anxiogenic-like action of paroxetine.

DSP-4 is a neurotoxin highly selective for the noradrenergic nerve terminals of the locus coeruleus projections. Data on the effect of DSP-4 treatment on amphetamine-induced hyperlocomotion are contradictory. In this study, DSP-4 (50 mg/kg) caused reduction of noradrenaline levels by 70% in the cerebral cortex and by 79% in the cerebellum. This treatment resulted in upregulation of dopamine D2 receptors in the striatum as evidenced by [3H]-raclopride binding. In an open field test, DSP-4 reduced locomotor activity. D-Amphetamine (1.5 mg/kg) caused a similar increase in locomotor activity in control and DSP-4-pretreated animals not familiar to the apparatus. However, when the rats were habituated to the test apparatus, the effect of amphetamine on horizontal activity was significantly larger in the DSP-4-pretreated animals. These data suggest that supersensitivity of D2 receptors develops after locus coeruleus denervation, but that the enhanced efficacy of amphetamine in DSP-4-treated rats is masked by neophobia.

The effect of acute and chronic desipramine (10 mg/kg) and citalopram (10 mg/kg) treatment on rat exploratory behavior in the recently developed exploration box test was studied on 5 consecutive days. Acute desipramine but not citalopram treatment decreased the time spent exploring, the number of line crossings, rears, investigative approaches, entries into the large arena, and sum of exploratory events. After 3 weeks of pretreatment, both desipramine and citalopram attenuated rat exploratory behavior, whereas the number of entries into the large arena was unchanged. In the open field test, acute desipramine or citalopram treatment (5, 10, 15 mg/kg) attenuated rat exploratory behavior in a dose-dependent manner. In the subsequent rota-rod test, neither desipramine nor citalopram treatment (0-20 mg/kg) impaired motor performance capacity. In an additional experiment, [3H]raclopride binding was unchanged after single as well as 3 weeks of desipramine or citalopram treatment in the rat brain neostriatum. Our experiments demonstrate that acute citalopram treatment in the open field test and chronic citalopram treatment in the exploration box test attenuate rat exploratory behavior, but these effects may not be implicated with enhanced anxiety or changed dopamine D2 receptor characteristics.

A method to measure various aspects of exploratory behavior was further characterized using standard pharmacological treatments known to induce anxiety, or anxiolysis, or locomotor activation. FG 7142, an anxiogenic beta-carboline, induced a dose-dependent reduction in the rat exploratory behavior. A single FG 7142 (20 mg/kg) treatment before behavioral testing had a carry-over effect on rats' behavioral performance on the two subsequent days. When FG 7142 (20 mg/kg) was administered during five consecutive days before behavioral testing, its anxiogenic-like effect first deepened, but waned off by the fifth session. Diazepam at the dose of 0.5 mg/kg had no effect of its own, but blocked the anxiogenic-like effect of FG 7142 (10 mg/kg) treatment. At a higher dose (1 mg/kg), diazepam treatment reduced exploratory behavior, but this effect was not carried over to the drug-free sessions on the subsequent day. Buspirone and gepirone (both 1 mg/kg), the 5-HT1A receptor agonists, had no effect. D-Amphetamine, a locomotion-enhancing drug which has anxiogenic-like properties in several tests of exploratory behavior, increased the activity of rats at the dose of 0.5 mg/kg, but at the dose of 1 mg/kg the only effect was a reduction in the number of rearings: this effect was not carried over to the subsequent retest. On the basis of the results described in this article and elsewhere, we suggest that this technique can be useful for separating a true anxiogenic drug from other compounds which influence exploratory activity.

Forty-five male Wistar rats were selected according to their behavior in the elevated plus-maze. They were separated as follows: animals with low exploratory activity ('anxious'), an 'intermediate' group and animals having high exploratory activity ('non-anxious'). Various receptor binding studies and hormonal assays were also performed in these selected rats. The affinity of 5-hydroxytryptamine 5-HT2A receptors in the frontal cortex was lower in the 'anxious' rats compared to home-cage controls and 'non-anxious' animals. Moreover, the number of cholecystokinin (CCK) receptors in the hippocampus was significantly elevated in the 'anxious' group compared to home-cage control animals. The blood levels of growth hormone (GH) were significantly lower in the 'non-anxious' rats compared to 'anxious' counterparts. In conclusion, it seems likely that the decreased exploratory activity of rats is related to the increased 5-hydroxytryptamine (5-HT) and CCK mediated neurotransmission in the brain. The different serum levels of GH in the selected rats probably reflect alterations in the activity of 5-HT and CCK.

The effects of cholecystokinin (CCK) CCKA receptor antagonist devazepide (10 micrograms/kg and 1.0 mg/kg), CCKB receptor antagonist L 365260 (1.0 mg/kg), and CCKB receptor agonist CCK tetrapeptide (CCK-4, 75 micrograms/kg), and their concomitant administration with antidepressants desipramine (10 mg/kg) and citalopram (10 mg/kg) on rat exploratory behaviour were studied in the recently developed exploration box test. In addition, the effects of repeated administration of despiramine (10 mg/kg) and citalopram (10 mg/kg) were studied. After acute administration, CCK-4 decreased significantly the number of line crossings, rears, investigative approaches, and the time spent exploring. The time of latency and the number of entries into large arena were unchanged. Desipramine reduced all observed criterions of rat behaviour, but citalopram was ineffective. Devazepide (1.0 mg/kg) and L 365260 (1.0 mg/kg) had no effect on rat behaviour after acute or repeated administration. L 365260 (1.0 mg/kg) blocked the antiexploratory effect of CCK-4, whereas devazepide (10 micrograms/kg) did not. No interaction of CCK-4, devazepide, or L 365260 treatment with antidepressant treatment was found. Our results suggest that the administration of a CCKB agonist diminishes rat exploratory behaviour, but neither CCKA nor CCKB receptor blockade induces changes on rat exploratory behaviour in the free exploration paradigm.

The aim of the present study was to investigate the effects of cholecystokinin (CCK) CCK(A) and CCKB receptor antagonists SR 27897 B, devazepide, L 365260 and PD 135158 (CAM 1028) on exploratory behaviour in the elevated zero-maze in the rat. For further validation of the elevated zero-maze, the effects of a reference anxiolytic diazepam (0.25, 0.5, 1.0, 2.0 mg/kg), a non-benzodiazepine (BDZ) anxiolytic buspirone (0.04, 0.2, 1.0, 5.0 mg/kg), BDZ receptor inverse agonists FG 7142 (5, 10, 15, 20 mg/kg) and DMCM (0.1, 0.5, 1.0, 1.5 mg/kg), and a BDZ receptor antagonist flumazenil (10 mg/kg) were studied. Diazepam decreased the number of stretched-attend postures in all doses used and increased the percentage of time spent exploring in open parts at doses of 0.5 and 1.0 mg/kg. The effects of diazepam were blocked by flumazenil. FG 7142 and DMCM had effects only in subconvulsive doses (20 mg/kg and 1.5 mg/kg). Flumazenil and buspirone failed to show any effect. The CCK(A) receptor antagonists were also without any effect. The CCK(B) receptor antagonists L 365260 (1.0 and 5.0 mg/kg) and PD 135158 (100 microg/kg) had a significant anxiolytic-like effect. The CCK(B) receptor antagonists increased the number of open part entries, the number of head dips, the percentage of time spent exploring in the open part and decreased the number of stretched-attend postures. These data support the hypothesis of the involvement of the CCK(B) receptor subtype in the neurobiological mechanisms of anxiety.

The present study has been divided into two sets. In the first set, the aim of the experiments was to investigate the dose-response effect of selective serotonin re-uptake inhibitor (SSRI) citalopram on rat exploratory behaviour in the elevated plus-maze. In the second set of experiments, the effect of cholecystokinin (CCK) CCKA and CCKB receptor antagonists, devazepide and L 365260, on citalopram-induced decrease of exploratory behaviour in the elevated plus-maze was studied. Citalopram (5 and 10 mg/kg) decreased the number of open and total arm entries, line crossings on open arms, and percentage of time spent exploring in open arm. Dose 15 mg/kg was without any effect on rat exploratory behaviour. Devazepide (0.01 and 1.0 mg/kg) failed to modify any of the citalopram-induced changes observed. L 365260 (1.0 mg/kg) reversed most of the effects of citalopram: the numbers of open and total arm entries, the number of line crossings, and the percentage of time spent exploring in open arms. L 365260 at dose level 0.01 mg/kg was ineffective. These results support the involvement of the CCKB receptor subtype in SSRI-induced anxiogenic-like effects in rodents.

The effect of DSP-4, a neurotoxin selectively affecting the projections of the locus coeruleus, upon exploratory behaviour of rats was studied in a complex exploration test, including a choice between open and enclosed areas and both inquisitive and inspective exploration elements. One week after DSP-4 (50 mg/kg i.p.) administration, the neurotoxin-treated rats did not explore a novel open area to any extent on the first exposure to the apparatus; however, on the third day of testing, these animals began to explore the area and the novel objects. Diazepam (0.5 mg/kg) treatment did not change the behaviour of control rats, but significantly increased the exploratory activity of the DSP-4-treated animals. LY 288513, a selective CCKB receptor antagonist (0.01 mg/kg), prevented the increase in exploratory activity in the DSP-4-treated rats, but increased the exploratory activity of controls on the third exposure to the test situation. The results of this investigation suggest that DSP-4 treatment reduces neotic behaviour by increasing neophobia rather than by decreasing exploratory drive. The divergence reported between the relative potencies of CCKB receptor antagonists in exploratory activity and other anxiety tests may in part be due to the effects of these drugs on exploratory drive.