Effect of 5-[3-[((2S)-1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3-benzodioxole HCl (MKC-242), a novel 5-HT1A-receptor agonist, on aggressive behavior and marble burying behavior in mice

The effect of SSRIs on unconditioned anxiety: a systematic review and meta-analysis of animal studies

RATIONALE

Selective serotonin reuptake inhibitors (SSRIs) are the first choice of treatment for anxiety-like disorders. However, which aspects of anxiety are affected by SSRIs is not yet fully understood.

OBJECTIVE

We aimed to systematically review the effect of six clinically effective SSRIs on four aspects of unconditioned anxiety: approach-avoidance behaviour (elevated plus maze), repetitive behaviour (marble burying), distress behaviour (ultrasonic vocalization), and activation of the autonomous nervous system (stress-induced hyperthermia).

METHODS

We identified publications by searching Medline and Embase databases and assessed the risk of bias. A random effects meta-analysis was performed and moderator effects were analysed with Bayesian penalized meta-regression.

RESULTS

Our search yielded 105 elevated plus maze, 63 marble burying, 11 ultrasonic vocalization, and 7 stress-induced hyperthermia articles. Meta-analysis suggested that SSRIs reduce anxiety-like behaviour in the elevated plus maze, marble burying and ultrasonic vocalization test and that effects are moderated by pre-existing stress conditions (elevated plus maze) and dose dependency (marble burying) but not by duration of treatment or type of SSRI. The reporting quality was low, publication bias was likely, and heterogeneity was high.

CONCLUSION

SSRIs seem to reduce a broad range of unconditioned anxiety-associated behaviours. These results should be interpreted with caution due to a high risk of bias, likely occurrence of publication bias, substantial heterogeneity and limited moderator data availability. Our review demonstrates the importance of including bias assessments when interpreting meta-analysis results. We further recommend improving the reporting quality, the conduct of animal research, and the publication of all results regardless of significance.

Lopez S, Amodeo DA. Impact of specific serotonin receptor modulation on restricted repetitive behaviors

Restricted, repetitive behaviors (RRBs) are commonly divided into two behavioral categories, lower-order and higher-order RRBs. Individuals displaying lower-order motoric RRBs may express repetitive hand flapping behaviors, body rocking back and forth movements, and continuous body spinning. Higher-order RRBs most commonly cover the behavior inflexibility and cognitive rigidity commonly found in disorders such as autism spectrum disorder and obsessive-compulsive disorder. Various neuropsychiatric disorders are plagued by RRBs yet no FDA-approved treatments have been identified. In rodents, lower-order RRBs are commonly measured through various tasks, such as repetitive self-grooming, marble burying, and stereotypic motor behaviors. This review focuses on the effects that modulation of specific serotonin receptors have on lower-order RRBs. Although there is research examining how changes in 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2B, 5-HT2C, 5-HT3, 5-HT6, and 5-HT7 receptor modulation, more research has focused on the 5-HT1A, 5-HT2A, and 5-HT2C receptors. The accumulating data suggest that increasing 5-HT1A activation decreases RRBs while blocking 5-HT1A activation has no effect on RRBs. While there are mixed findings regarding the impact of 5-HT2A modulation on RRBs, the general trend shows mixed effects of 5-HT2A receptor activation RRB expression, whereas blockade generally decreases RRBs. 5-HT2C receptor activation can modulate RRBs in either direction depending on the 5-HT2C drug used, blocking 5-HT2C activation only seems to show therapeutic properties when 5-HT2C activation is already elevated. The other 5-HT receptors have been explored far less but show promise as potential targets for regulating RRBs. Although it is less clear due to the involvement of 5-HT1D, 5-HT1A activation increases RRBs, and blocking 5-HT1A tends to decrease RRBs. 5-HT2B activation could reduce RRBs, while inhibiting 5-HT2B does not impact RRBs. Increasing 5-HT3 has not been shown to affect RRBs. Yet, increases in RRBs have been observed in Htr3a KO mice. 5-HT6 receptor activation can increase RRBs, while blocking 5-HT6 activity tends to decrease RRBs. Lastly, neither increasing or blocking 5-HT7 activity can reduce RRBs. In sum, there is no uniform pattern in whether all specific 5-HT receptors affect RRBs in either direction, instead, there is evidence suggesting that different 5-HT receptors can modulate RRBs in different directions. Further researching the less explored receptors and aiming to understand why these receptors can differently modulate RRBs, may play a key role in developing therapeutics that treat RRBs.

Tandospirone, a Partial 5-HT1A Receptor Agonist, Administered Systemically or Into Anterior Cingulate Attenuates Repetitive Behaviors in Shank3B Mice

BACKGROUND

Several cases of autism spectrum disorder have been linked to mutations in the SHANK3 gene. Haploinsufficiency of the SHANK3 gene contributes to Phelan-McDermid syndrome, which often presents an autism spectrum disorder phenotype along with moderate to severe intellectual disability. A SHANK3 gene deletion in mice results in elevated excitation of cortical pyramidal neurons that alters signaling to other brain areas. Serotonin 1A receptors are highly expressed on layer 2 cortical neurons and are known to have inhibitory actions. Serotonin 1A receptor agonist treatment in autistic cases with SHANK3 mutations and possibly other cases may restore excitatory and inhibitory balance that attenuates core symptoms.

METHODS

A series of experiments investigated the effects of acute tandospirone treatment on spatial learning and self-grooming, subchronic treatment of tandospirone on self-grooming behavior, and the effect of tandospirone infusion into the anterior cingulate on self-grooming behavior.

RESULTS

Only male Shank3B+/- mice exhibited a spatial learning deficit and elevated self-grooming. Acute i.p. injection of tandospirone, 0.01 and 0.06 mg/kg in male Shank3B+/- mice, attenuated a spatial acquisition deficit by improving sensitivity to positive reinforcement and reduced elevated self-grooming behavior. Repeated tandospirone (0.06 mg/kg) treatment attenuated elevated self-grooming behavior in male Shank3B+/- mice. Tandospirone injected into the anterior cingulate/premotor area reduced self-grooming behavior in male Shank3B+/- mice.

CONCLUSIONS

These results suggest that stimulation of cortical serotonin 1A receptors may reduce repetitive behaviors and cognitive impairments as observed in autism spectrum disorder, possibly by attenuating an excitation/inhibition imbalance. Further, tandospirone may serve as a treatment in autism spectrum disorder and other disorders associated with SHANK3 mutations.

Similarities and dissimilarities in the effects of benzodiazepines and specific serotonin reuptake inhibitors (SSRIs) in the defensive marble burying test: A systematic review and meta-analysis

One problem areas of animal models and tests for neuropsychiatric disorders is unclear reproducibility, including both internal and external validity. One way to examine external validity is with systematic reviews and meta-analyses, a standard practice in clinical research that is relatively neglected in preclinical research. Considering the need to evaluate the validity and reproducibility of frequently used animal models, this study presents a meta-analysis of the effects of prototypic benzodiazepines and specific serotonin reuptake inhibitors (SSRIs) in the mouse defensive marble burying test (MBT). These drug groups were selected because although they differ in their biological targets as well as in their clinical use, they are both commonly used for the treatment of anxiety disorders. A PubMed literature search was performed to identify studies that examined the effects of benzodiazepines (diazepam, alprazolam, chlordiazepoxide, clonazepam) or SSRIs (fluoxetine, citalopram, escitalopram, fluvoxamine, paroxetine) in the MBT in mice. For benzodiazepines, 73 experiments were included. Benzodiazepines effect size was 2.04 and Q statistics was 1959 with a significant correlation between dose and effect size (r = 0.31, p = 0.007). For SSRIs we identified 47 experiments. Effect size of SSRIs was 2.24 and Q statistics was 493.38. No correlation was found between dose and effect size (r = 0.23, p = 0.12). The current results support the external validity of the defensive marble burying test as a screening test for anxiolytic effects. However, these results indicate that significant attention should be given to the administration schedules of benzodiazepines and SSRIs.

A critical inquiry into marble-burying as a preclinical screening paradigm of relevance for anxiety and obsessive-compulsive disorder: Mapping the way forward

Rodent marble-burying behavior in the marble-burying test (MBT) is employed as a model or measure to study anxiety- and compulsive-like behaviors or anxiolytic and anticompulsive drug action. However, the test responds variably to a range of pharmacological interventions, and little consensus exists regarding specific methodologies for its execution. Regardless, the test is widely applied to investigate the effects of pharmacological, genetic, and behavioral manipulations on purported behaviors related to the said neuropsychiatric constructs. Therefore, in the present review we attempt to expound the collective translational significance of the MBT. We do this by (1) reviewing burying behavior as a natural behavioral phenotype, (2) highlighting key aspects of anxiety and obsessive-compulsive disorder from a translational perspective, (3) reviewing the history and proof of concept of the MBT, (4) critically appraising potential methodological confounds in execution of the MBT, and (5) dissecting responses of the MBT to various pharmacological interventions. We conclude by underlining that the collective translational value of the MBT will be strengthened by contextually valid experimental designs and objective reporting of data.

Preclinical characterization of ACH-000029, a novel anxiolytic compound acting on serotonergic and alpha-adrenergic receptors

Anxiety disorders are serious and common mental diseases, yet there is still a need for the development of more effective anxiolytics with better safety profiles than benzodiazepines and serotonin reuptake inhibitors. The serotonergic and noradrenergic systems have reciprocal interactions and are intricately related to the pathogenesis of anxiety. In this study, the anxiolytic-like effect of the novel compound ACH-000029, 3-(2-(4-(2-methoxyphenyl) piperazine-1-yl) ethyl) quinazoline-4(3H)-one, is reported. This compound acts at selected serotonergic (5-HT1A and 5-HT1D partial agonism and 5-HT2A antagonism) and α-adrenergic (α-1A, 1B and 1D antagonism) receptors, with good selectivity over other G-protein-coupled receptors. ACH-000029 exhibited high blood-brain barrier permeation and acute anxiolytic effects in the marble burying (MB) and light-dark box (LDB) models of anxiety over the dose ranges of 8-32 mg/kg i.p. and 16-30 mg/kg p.o. The anxiolytic activity was comparable to that observed for serotonin reuptake inhibitors (paroxetine and fluoxetine) and benzodiazepines (alprazolam, diazepam and clobazam). The analysis of the whole-brain c-fos expression following oral dosing showed that ACH-000029 regulated regions highly associated with the processing of environmental stimuli and anxiety behavior, such as the amygdala, paraventricular nucleus of the thalamus, retrosplenial dorsal, pallidum, bed nuclei of the stria terminalis, and locus ceruleus. No safety concerns were identified for ACH-000029 in the functional observational battery up to 50 mg/kg i.p. and in the nonprecipitated withdrawal test up to 30 mg/kg p.o. twice daily for 20 days. This work supports the further development of ACH-000029 as a drug candidate for the treatment of anxiety disorders. The analysis of the in vitro pharmacology and brain regions regulated by this compound may also lead to the exploration of other indications within the psychiatry field.

Back to basics: A methodological perspective on marble-burying behavior as a screening test for psychiatric illness

Animal models of human psychiatric illness are valuable frameworks to investigate the etiology and neurobiology underlying the human conditions. Accurate behavioral measures that can be used to characterize animal behavior, thereby contributing to a model's validity, are crucial. One such measure, i.e. the rodent marble-burying test (MBT), is often applied as a measure of anxiety- and compulsive-like behaviors. However, the test is characterized by noteworthy between-laboratory methodological differences and demonstrates positive treatment responses to an array of pharmacotherapies that are often of little translational value. Therefore, using a naturalistic animal model of obsessive-compulsive disorder, i.e. the deer mouse (Peromyscus maniculatus bairdii), the current investigation attempted to illuminate the discrepancies reported in literature by means of a methodological approach to the MBT. Five key aspects of the test that vary between laboratories, viz. observer/scoring, burying substrate, optional avoidance, the use of repeated testing, and determinations of locomotor activity, have been investigated. Following repeated MB tests in four different burying substrates and in two zone configurations, we have demonstrated that 1) observer bias may contribute to the significant differences in findings reported, 2) MB seems to be a natural exploratory response to a novel environment, rather than being triggered by aberrant cognition, 3) burying substrates with a small particle size and higher density deliver the most accurate results with respect to the burying phenotype, and 4) to exclude the influence of normal exploratory behavior on the number of marbles being covered, assessments of marble-burying should be based on pre-occupation with the objects itself.

5-HT1A receptor-dependent modulation of emotional and neurogenic deficits elicited by prolonged consumption of alcohol

Repeated episodes of binge-like alcohol consumption produce anxiety, depression and various deleterious effects including alterations in neurogenesis. While the involvement of the serotonin receptor 1 A (5-HT1A) in the regulation of anxiety-like behavior and neurogenesis is well documented, its contribution to alcohol withdrawal-induced anxiety and alcohol-induced deficits in neurogenesis is less documented. Using the Drinking-In-the-Dark (DID) paradigm to model chronic long-term (12 weeks) binge-like voluntary alcohol consumption in mice, we show that the selective partial activation of 5-HT1A receptors by tandospirone (3 mg/kg) prevents alcohol withdrawal-induced anxiety in a battery of behavioral tests (marble burying, elevated-plus-maze, open-field), which is accompanied by a robust decrease in binge-like ethanol intake (1 and 3 mg/kg). Furthermore, using triple immunolabelling of proliferation and neuronal differentiation markers, we show that long-term DID elicits profound deficits in neurogenesis and neuronal fate specification in the dorsal hippocampus that are entirely reversed by a 2-week chronic treatment with the 5-HT1A partial agonist tandospirone (3 mg/kg/day). Together, our results confirm previous observations that 5-HT1A receptors play a pivotal role in alcohol drinking behavior and the associated emotional and neurogenic impairments, and suggest that 5-HT1A partial agonists represent a promising treatment strategy for alcohol abuse.

Anxiolytic effects of herbal ethanol extract from Gynostemma pentaphyllum in mice after exposure to chronic stress

In this study, the effects of herbal ethanol extracts of Gynostemma pentaphyllum (GP-EX), on chronic electric footshock (EF) stress-induced anxiety disorders were investigated in mice, which were orally treated with GP-EX (30 mg/kg and 50 mg/kg) once a day for 14 days, followed by exposure to EF stress (2 mA, with an interval and duration of 10 s for 3 min). After the final exposure to EF stress, the elevated plus-maze and marble burying tests were performed, and the levels of dopamine and serotonin in the brain, the serum levels of corticosterone, and the expression of c-Fos in the paraventricular nuclei (PVN) were determined. Treatment with GP-EX (30 mg/kg and 50 mg/kg) significantly recovered the number of entries into open arms and time spent on open arms, which was reduced by chronic EF stress. GP-EX (30 mg/kg and 50 mg/kg) also reduced the number of marbles buried, which was increased by chronic EF stress. In addition, electric EF stress significantly decreased the levels of dopamine and serotonin in the brain, which was recovered by treatment with GP-EX (30 mg/kg and 50 mg/kg). The serum levels of corticosterone, which were markedly increased by chronic EF stress, were reduced by treatment with GP-EX (30 mg/kg and 50 mg/kg). Chronic EF stress-induced increases in c-Fos expression were also markedly reduced by GP-EX (30 mg/kg and 50 mg/kg) in the PVN. These results suggest that GP-EX shows anxiolytic functions, determined by the elevated plus-maze and marble burying tests, which are mediated by modulating the activity of dopamine and serotonin neurons as well as the expression of c-Fos in the brain, and the serum levels of corticosterone. Clinical trials of herbal GP-EX and its bioactive components need further investigation.

Hippocampus-specific deletion of tissue plasminogen activator "tPA" in adult mice impairs depression- and anxiety-like behaviors

Anxiety and depression are multifactorial disorders that have become prominent health problems all over the world. Neurotrophic factors have emerged underlying pathogenesis of these diseases. Although a number of studies indicate that the hippocampus-brain-derived neurotrophic factor (BDNF) may be involved in these psychiatric illnesses, little is known about the molecular mediators of these disorders. In this study we further investigate the role of tissue plasminogen activator (tPA), a serine protease involved in pro-BDNF cleavage to BDNF, in depression and anxiety-like behaviors in adult mice. To address this issue, we investigated the effect of hippocampus tPA manipulation, using viral vectors, on anxiety- and depression-like behaviors, including the marble burying test (MBT), elevated plus maze (EPM), tail suspension test (TST), novelty suppressed feeding (NSF) and forced swim test (FST). Our results showed that tPA knock-down - using lentiviral vectors expressing specific short hairpin RNAs (LV-shRNA) - increased the number of buried marbles together with the digging time in the MBT and decreased the time spent in open the arms of an EPM. In addition, tPA-knock down in the hippocampus increased immobility in the FST and TST, and increased time to feed in the NSF test. These effects were reversed when tPA-over-expressing vectors (LV-tPA) were injected in the hippocampus. We also found that BDNF protein levels were elevated in the hippocampus of mice receiving tPA-expressing vectors. Together, our results imply that tPA manipulation may provide an effective therapeutic intervention for depression and anxiety disorders.

Pharmacokinetic interaction between tandospirone and fluvoxamine in the rat contextual conditioned fear stress model and its functional consequence: Involvement of cytochrome P450 3A4

AIMS

In a previous study it was demonstrated that the anxiolytic action of tandospirone, a 5-hydroxytryptamine (5-HT)(1A) receptor agonist, is facilitated by cytochrome P450 (CYP) 3A4 inhibitors, such as ketoconazole and cimetidine. It is also known that fluvoxamine, a selective serotonin re-uptake inhibitor (SSRI), inhibits CYP3A4. The purpose of the present study was to clarify the pharmacokinetic interaction between tandospirone and fluvoxamine and to evaluate their combined effect in the rat anxiety model.

METHODS

The anxiolytic action of co-administration of tandospirone and fluvoxamine was examined using the rat contextual conditioned fear stress model. After testing the conditioned fear, plasma concentrations of tandospirone and its major metabolite 1-(2-pyrimidyl) piperazine were determined.

RESULTS

One day after fear conditioning, both tandospirone (60 mg/kg, p.o.) and fluvoxamine (60 mg/kg, p.o.) significantly inhibited conditioned freezing and their combination effect was additive. In addition, plasma concentration of tandospirone was increased by fluvoxamine.

CONCLUSIONS

There is a CYP3A4-related drug-drug interaction between tandospirone and fluvoxamine. Therefore, fluvoxamine may facilitate the anxiolytic effect of tandospirone via CYP3A4 inhibition.

Role of serotonin in obsessive–compulsive disorder

Obsessive–compulsive disorder (OCD) is a psychiatric disorder consisting of obsessions and compulsions. Over the past two decades, it has been suggested that OCD might be related to the functioning of brain serotonin systems, mainly because of the antiobsessional efficacy of selective serotonin-reuptake inhibitors (SSRIs). Although the efficacy of SSRIs suggests a role of the serotonergic system in OCD, the exact function of serotonin is still unclear. Is the serotonergic system implicated in the pathophysiology of OCD, or is it implicated in the treatment effect in OCD? Do SSRIs compensate for a fundamental abnormality of the serotonergic system, or do SSRIs modulate an intact serotonergic system to compensate for another neurotransmitter mechanism? This review summarizes evidence supporting a role for the serotonin transporter and serotonin receptor subtypes in the pathophysiology and treatment of OCD.

Attenuation of estrous cycle-dependent marble burying in female rats by acute treatment with progesterone and antidepressants

Premenstrual dysphoric disorder (PMDD) is characterized by the recurrence of a cluster of physical and negative mood symptoms, especially irritability, appearing when estrogen and progesterone levels decrease during the late luteal phase of the menstrual cycle. The aim of the present study was to explore a new potential model of premenstrual irritability. It has been suggested that burying of harmless objects by rodents may reflect a form of impulsive or anxiety-like behavior. This study demonstrates changes in burying behavior during various phases of the estrous cycle in some but not all female rats. Burying behavior was found to be enhanced at metestrus and decreased at proestrus, characterized by low and high ovarian hormone levels, respectively. No habituation of the cycle-dependent burying was observed. Enhanced burying was not observed in reproductive senescent and ovariectomized females characterized by stable, low levels of ovarian hormones. Increased marble burying at metestrus was reversed by acute treatment with antidepressants fluoxetine, desipramine, nomifensine, the benzodiazepine agonist diazepam, and progesterone, while the neuroleptic chlorpromazine was without effect. Reversal of cycle-dependent burying was unrelated to the drugs' effects on locomotor activity. These results indicate that estrous cycle-dependent marble-burying behavior displayed by a subgroup of female rats might be a manifestation of ovarian hormone-dependent irritability. This manifestation may be used to elucidate the neuroendocrine mechanisms triggering premenstrual irritability, and the detailed mode of action of antidepressants when used for PMDD.

Effects of cytochrome P450 (CYP) 3A4 inhibitors on the anxiolytic action of tandospirone in rat contextual conditioned fear

The azapirone derivatives, including tandospirone and buspirone, are anxiolytics with 5-HT(1A) receptor agonistic action. Previous in vitro studies have suggested these azapirone derivatives are mainly metabolized by the cytochrome P450 (CYP) 3A4 isoform. The purpose of this study was to clarify the effects CYP3A4 inhibitors have on the anxiolytic action of tandospirone in a conditioned fear stress rat model. One day after fear conditioning, the orally administered tandospirone (30-100 mg/kg) significantly inhibited conditioned freezing in a dose-dependent manner. Co-administration of oral tandospirone and CYP3A4 inhibitors [ketoconazole (10 mg/kg, i.p.) and cimetidine (200 mg/kg, p.o.)] markedly inhibited conditioned freezing. Ketoconazole significantly increased the anxiolytic effect of buspirone similar to tandospirone. As with freezing behavior, the plasma concentrations of tandospirone and buspirone were increased by CYP3A4 inhibitors. This suggests the CYP3A4 isoform is involved in the metabolism of tandospirone, in vivo. Therefore, drugs with CYP3A4 inhibitory property may facilitate the anxiolytic effect of tandospirone when treating human anxiety disorders.

Gabrb3 gene deficient mice exhibit increased risk assessment behavior, hypotonia and expansion of the plexus of locus coeruleus dendrites

Gabrb3 gene deficient (gabrb3(-/-)) mice, control littermates (gabrb3(+/+)) and their progenitor strains C57Bl/6J and 129/SvJ were assessed for changes in the morphology of the main noradrenergic nuclei, the locus coeruleus (LC) and LC-associated behaviors including anxiety and muscle tone. While the area defined by the cell bodies of the LC was found not to differ between gabrb3(-/-) mice and controls, the pericoerulear dendritic zone of the LC was found to be significantly enlarged in gabrb3(-/-) mice. Relative to controls, gabrb3(-/-) mice were also found to be hypotonic, as was indicated by poor performance on the wire hanging task. Gabrb3(-/-) mice also exhibited a significant increase in stretch-attend posturing, a form of risk assessment behavior associated with anxiety. However, in the plus maze, a commonly used behavioral test for assessing anxiety, no significant difference was observed between gabrb3(-/-) and control mice. Lastly, relative to controls, gabrb3(-/-) mice exhibited significantly less marble burying behavior, a method commonly used to assess obsessive-compulsive behavior. However, the poor marble burying performance of the gabrb3(-/-) mice could be associated with the hypotonic condition exhibited by these mice. In conclusion, the results of this study indicate that the gabrb3 gene contributes to LC noradrenergic dendrite development with the disruption of this gene in mice resulting in an enlarged plexus of LC dendrites with a concurrent reduction in muscle tone and marble burying behavior, an increase in risk assessment behavior but no change in the plus maze parameters that are commonly used for assessing anxiety.

Role of serotonin type 1A receptors in fluvoxamine-induced inhibition of marble-burying behavior in mice

This study examined the roles of presynaptic and postsynaptic serotonin type 1A receptors in fluvoxamine-induced inhibition of marble-burying behavior in mice. The effect of fluvoxamine was attenuated by the serotonin type 1A receptor antagonist WAY100635 at 1 mg/kg, while it was enhanced by the antagonist at 0.1 mg/kg. Fluvoxamine (30 mg/kg) and WAY100635 (0.1 and 1 mg/kg) did not affect spontaneous locomotor activity. These results suggest that the effect of fluvoxamine is mediated by postsynaptic serotonin type 1A receptors and it is enhanced by an inhibition of presynaptic serotonin type 1A receptors.

Reduction in 5-HT1A receptor density, 5-HT1A mRNA expression, and functional correlates for 5-HT1A receptors in genetically defined aggressive rats

The present experiments tested the hypothesis that one of the critical mechanisms underlying genetically defined aggressiveness involves brain serotonin 5-HT1A receptors. 5-HT1A receptor density, the receptor mRNA expression in brain structures, and functional correlates for 5-HT1A receptors identified as 8-OH-DPAT-induced hypothermia and lower lip retraction (LLR) were studied in Norway rats bred for 59 generations for the lack of aggressiveness and for high affective aggressiveness with respect to man. Considerable differences between the highly aggressive and the nonaggressive rats were shown in all three traits. A significant decrease in B(max) of specific receptor binding of [3H]8-OH-DPAT in the frontal cortex, hypothalamus, and amygdala and a reduction in 5-HT1A receptor mRNA expression in the midbrain of aggressive rats were found. 5-HT1A receptor agonist 8-OH-DPAT (0.5 mg/kg, i.p.) produced a distinct hypothermic reaction in nonaggressive rats and did not affect significantly the body temperature in aggressive rats. Similar differences were revealed in 8-OH-DPAT-induced LLR: LLR was expressed much more in nonaggressive than in aggressive animals. Additionally, 8-OH-DPAT (0.5 mg/kg i.p.) treatment significantly attenuated the aggressive response to man. The results demonstrated an association of aggressiveness with reduced 5-HT1A receptor expression and function, thereby providing support for the view favoring the idea that brain HT1A receptor contributes to the genetically defined individual differences in aggressiveness.

Psychostimulant-induced behavior as an animal model of obsessive-compulsive disorder: an ethological approach to the form of compulsive rituals

Rats treated chronically with the D2/D3 dopamine receptor agonist quinpirole show a pattern of behavior that meets a set of ethologically derived criteria of compulsive behavior in obsessive-compulsive disorder (OCD). Moreover, in both quinpirole-treated rats and OCD patients, the structure of compulsive rituals appear similar in being composed of relatively few motor acts that are organized in a flexible yet recurrent manner. In addition, the development of compulsive behavior in quinpirole-treated rats is attenuated by the OCD pharmacotherapeutic drug clomipramine. These similarities support the validity of quinpirole-treated rats as a psychostimulant-induced animal model of OCD. Considering that the induction of compulsive behavior in the rat model involves chronic hyperstimulation of dopamine receptors, this raises the possibility that dopaminergic mechanisms may play a role in OCD, at least in some subtypes of this disorder.

2,3,4,5-tetrahydro- and 2,3,4,5,11,11a-hexahydro-1H-[1,4]diazepino[1,7-a]indoles: new templates for 5-HT(2C) agonists

The design and synthesis of the novel 2,3,4,5-tetrahydro-1H-[1,4]diazepino[1,7-a]indole 5 is described. This azepinoindole has excellent affinity for 5-HT(2C) (K(i) 4.8 nM) and modest selectivity over 5-HT(2A) ( approximately 4-fold). Several N- and C(11)-substituted analogues of 5 were prepared, as were a number of biaryl indoline derivatives. The anxiolytic potential for the azepinoindole template 5 is demonstrated by activity in a mouse shock-aggression assay.

Defensive burying in rodents: ethology, neurobiology and psychopharmacology

Defensive burying refers to the typical rodent behavior of displacing bedding material with vigorous treading-like movements of their forepaws and shoveling movements of their heads directed towards a variety of noxious stimuli that pose a near and immediate threat, such as a wall-mounted electrified shock-prod. Since its introduction 25 years ago by Pinel and Treit [J. Comp. Physiol. Psychol. 92 (1978) 708], defensive (shock-prod) burying has been the focus of a considerable amount of research effort delineating the methodology/ethology, psychopharmacology and neurobiology of this robust and species-specific active avoidance or coping response. The present review gives a summary of this research with special reference to the behavioral (face and construct) and pharmacological (predictive) validity of the shock-prod burying test as an animal model for human anxiety. Emphasis is also placed on some recent modifications of the paradigm that may increase its utility and reliability as to individual differences in expressed emotional coping responses and sensitivity to pharmacological treatments. Overall, the behavioral and physiological responses displayed in the shock-prod paradigm are expressions of normal and functionally adaptive coping patterns and the extremes of either active (i.e., burying) or passive (i.e., freezing) forms of responding in this test cannot simply be regarded as inappropriate, maladaptive or pathological. For this reason, the shock-prod paradigm is not an animal model for anxiety disorder or for any other psychiatric disease, but instead possesses a high degree of face and construct validity for normal and functionally adaptive human fear and anxious apprehension. However, the apparent good pharmacological validation (predictive validity) of this test reinforces the view that normal and pathological anxiety involves, at least partly, common neurobiological substrates. Therefore, this paradigm is not only suitable for screening potential anxiolytic properties of new drugs, but seems to be especially valuable for unraveling the neural circuitry and neurochemical mechanisms underlying the generation of active and passive coping responses as different expressions of anxiety.

Effects of diazepam and flumazenil on food competition behavior in high- and low-aggression pigeons

The food competition interaction test performed with food-restricted pigeons with previously consolidated dominance is a useful tool for the study of offensive and defensive social aggression. In the present study, we examined the effect of GABA-A-benzodiazepine (BZD) receptor manipulation on aggression, emotion, feeder control, and eating behavior in high- and low-aggression female pigeons maintained at 80% of their normal weight and exposed to food competition interactions. The pigeons were divided into pairs by previously ranked high-aggression females (total time spent in aggression over 60 s/5 min; n=6 pairs) and low-aggression females (time spent in aggression less than 10 s/5 min; n=6 pairs). In Experiment 1, a pigeon in each pair of high- and low-aggression subjects were treated daily with an oral dose of diazepam (DZP, 0.6 mg/kg/0.3 ml) for 8 days. The other animal received the vehicle. On Day 8, food competition trials (10 min) were performed 30 min after treatments. In Experiment 2, pigeons were injected subcutaneously with flumazenil (FZL, 0.1 mg/kg/1 ml) or saline and exposed to a food competition trial 30 min after injections. In Experiment 3, one animal in each pair received DZP for 8 days. The other animal received the vehicle. On Day 8, the DZP-treated subjects were injected subcutaneously with FZL (0.1 mg/ kg/1 ml) 30 min before the oral dose of DZP. Trials were performed 30 min after DZP or vehicle administration. In Experiment 1, it was found that the DZP group of high-aggression pigeons showed lower scores of aggression (P<.05) and emotional responses (P<.05) than controls. The other group-scored behaviors were not affected. The DZP low-aggressions, however, showed scores of aggression eightfold higher than their controls (P<.05) but the other scored behaviors were not changed. In Experiment 2, FZL injection did not induce intrinsic effects on aggression either in the high- or in the low-aggression group. Experiment 3 showed that the emotional and aggressive responses to DZP were neutralized by FZL. This shows that GABA-A-BZD receptor mechanisms are implicated in the DZP responses in high- and low-aggression pigeons.

Effect of YM992, a novel antidepressant with selective serotonin re-uptake inhibitory and 5-HT 2A receptor antagonistic activity, on a marble-burying behavior test as an obsessive-compulsive disorder model

YM992 ((S)-2-[[(7-fluoroindan-4-yl)oxy]methyl]morpholine) monohydrochloride is a novel antidepressant with selective serotonin (5-hydroxytryptamine, 5-HT) re-uptake inhibition and 5-HT(2A) receptor antagonistic activity. The effects of YM992 and two selective 5-HT re-uptake inhibitors (SSRIs) were studied in a marble-burying behavior test as a model of an obsessive-compulsive disorder (OCD) in mice at doses of 5, 10 and 15 mg/kg, i.p. YM992 and fluoxetine significantly inhibited marble-burying behavior at a dose of 15 mg/kg (i.p.) without affecting spontaneous locomotor activities. Citalopram also significantly inhibited the behavior at doses of 5, 10 and 15 mg/kg (i.p.) without affecting spontaneous locomotor activities. These results suggest that YM992, as well as SSRIs, may exhibit anti-OCD activity in addition to an antidepressive effect in clinical use.

Decreased marble burying behavior in female mice lacking neuromedin-B receptor (NMB-R) implies the involvement of NMB/NMB-R in 5-HT neuron function

Neuromedin B (NMB) is a mammalian bombesin-like peptide distributed widely in the central nervous system. This peptide exerts its function via the NMB receptor (NMB-R). Female NMB-R-deficient mice were used to study the role that NMB/NMB-R may play in 5-HT neuron function since this relationship was suggested in previous in vitro studies. As 5-HT neurons are thought to modulate marble burying behavior, a role for NMB-R in this behavior was assessed. Relative to wild-type mice, NMB-R-deficient mice showed decreased marble burying behavior. However, depletion of 5-HT by treatment with p-chlorophenylalanine (p-CPA) increased burying behavior in NMB-R-deficient mice suggesting that increased levels of 5-HT in the brain cause a decrease in burying behavior in NMB-R-deficient mice. While HPLC analysis showed that 5-HT content in the whole brain does not differ between NMB-R-deficient and wild-type mice, an immunohistochemical analysis of brain sections showed that 5-HT expression in the dorsal raphe (DR) nucleus is elevated in NMB-R-deficient mice. Furthermore, a quantitative RT-PCR analysis revealed that 5-HT(1A)-receptor gene expression is downregulated in NMB-R-deficient mice at the whole brain level. These behavioral and biological results suggest that NMB/NMB-R may modulate 5-HT neuronal activity by affecting DR function.

Stereospecific blockade of marble-burying behaviour in mice by selective, non-peptidergic neurokinin1 (NK1) receptor antagonists

By analogy with the selective serotonin reuptake inhibitor, fluvoxamine, and the tricyclic agent, clomipramine, the novel, selective, non-peptidergic NK(1) receptor antagonist, GR205,171, dose-dependently and completely blocked marble-burying behaviour in mice: Inhibitory Dose(50)s (ID(50)s), 4.5, 4.8 and 7.6 mg/kg, respectively. In contrast to GR205,171, its isomer, GR226,206, which displays substantially lower affinity for NK(1) receptors, was inactive (> 40.0 mg/kg). By analogy with GR205,171, a further, selective NK(1) antagonist, RP67,580, abolished marble-burying behaviour with an ID(50) of 11.9 mg/kg. At doses significantly reducing marble-burying behaviour, GR205,171 and RP67,580 little influenced motor behaviour. In conclusion, like fluvoxamine and clomipramine, selective, non-peptidergic NK(1) receptor antagonists block marble-burying in mice. Although the biological bases of this behaviour remain unclear, these observations underpin the contention that NK(1) receptors may be implicated in affective disorders.

Involvement of benzodiazepine binding sites in an antiaggressive effect by 5-HT(1A) receptor activation in isolated mice

The effect of the benzodiazepine receptor antagonist flumazenil was examined on an antiaggressive effect of (S)-5-[3-[(1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3- benzodioxole HCl (MKC-242), a 5-HT(1A) receptor agonist. MKC-242 (0.1-1.0 mg/kg, p.o.) selectively reduced isolation-induced aggressive behavior in a dose-dependent manner. Flumazenil (10 mg/kg, i.p.) antagonized the antiaggressive effects of MKC-242 and diazepam, although it alone did not affect the behaviors of isolated mice. These findings suggest that a gamma-aminobutyric acid(A) (GABA(A)) receptor system is involved in the antiaggressive effect by 5-HT(1A) receptor activation.

Female gastrin-releasing peptide receptor (GRP-R)-deficient mice exhibit altered social preference for male conspecifics: implications for GRP/GRP-R modulation of GABAergic function

We studied female GRP-R-deficient mice with respect to olfactory function and social behavior toward male conspecifics. Results of a food exploration test (hidden cookie method) revealed that the olfactory ability of these mutant mice is identical to that of wild-type mice. However, when preference toward either a socially dominant or subordinate male mouse was assessed in a social preference test, wild-type mice showed a greater preference for socially dominant males than did GRP-R-deficient mice. In contrast, in a social investigation test to an anesthetized male mouse, GRP-R-deficient mice exhibited greater investigatory behavior toward the target male than did wild-type mice. When female C57BL/6J mice were given diazepam (0, 1, 2 or 4 mg/kg, i.p.), their investigatory behavior to the anesthetized male target was increased in a dose-dependent manner. Conversely, i.p. administration of bicuculline (1 mg/kg) significantly decreased the social investigatory behavior of female GRP-R-deficient mice, but not of wild-type mice. These results indicate that female GRP-R-deficient mice exhibit altered responsiveness to male conspecifics relative to their wild-type counterparts, and suggest that this outcome may be attributable, at least in part, to altered GABAergic function in these mutant mice.

Low cholesterol and violent crime

BACKGROUND

Community cohort studies and meta-analyses of randomized trials have shown a relation between low or lowered cholesterol and death by violence (homicide, suicide, accident); in primates, cholesterol reduction has been linked to increased behavioral acts of aggression (Kaplan J, Manuck S. The effects of fat and cholesterol on aggressive behaviour in monkeys. Psychosom. Med 1990;52:226-7; Kaplan J, Shively C, Fontenot D, Morgan T, Howell S, Manuck S et al. Demonstration of an association among dietary cholesterol, central serotonergic activity, and social behaviour in monkeys. Psychosom. Med 1994;56:479-84.). In this study we test for the first time whether cholesterol level is related to commission of violent crimes against others in a large community cohort.

METHODS

We merged one-time cholesterol measurements on 79,777 subjects enrolled in a health screening project in Varmland, Sweden with subsequent police records for arrests for violent crimes in men and women aged 24-70 at enrollment; and with information on covariates. We performed a nested case control comparison of cholesterol in violent criminals - defined as those with two or more crimes of violence against others - to cholesterol in nonoffenders matched on age, enrollment year, sex, education and alcohol, using variable-ratio matching, with a nonparametric sign test.

RESULTS

One hundred individuals met criteria for criminal violence. Low cholesterol (below the median) was strongly associated with criminal violence in unadjusted analysis (Men: risk ratio 1.94, P=0.002; all subjects risk ratio 2.32, P<0.001). Age emerged as a strong confounder. Adjusting for covariates using a matching procedure, violent criminals had significantly lower cholesterol than others identical in age, sex, alcohol indices and education, using a nonparametric sign test (P=0.012 all subjects; P=0.035 men).

CONCLUSIONS

Adjusting for other factors, low cholesterol is associated with increased subsequent criminal violence.

Postsynaptic 5-hydroxytryptamine(1A) receptor activation increases in vivo dopamine release in rat prefrontal cortex

5-Hydroxytryptamine (5-HT) plays a role in the regulation of 3, 4-dihydroxyphenylethylamine (dopamine) neurons in the brain, but the precise mechanism of regulation by 5-HT(1A) receptors of dopamine release has not been defined. The present study describes the effect of 5-¿3-[[(2S)-1,4-benzodioxan-2ylmethyl]amino]propoxy¿-1, 3-benzodioxole HCl (MKC-242), a highly potent and selective 5-HT(1A) receptor agonist, on dopamine release in the prefrontal cortex using microdialysis in the freely moving rat. Subcutaneous injection of MKC-242 (0.3 - 1.0 mg kg(-1)) increased extracellular levels of dopamine in the prefrontal cortex. The effect of MKC-242 in the prefrontal cortex was antagonized by pretreatment with the selective 5-HT(1A) receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohe xanecarboxamide (WAY100635; 1 mg kg(-1), i.p.). Local application of WAY100635 (10 microM) via a microdialysis probe antagonized the effect of systemic MKC-242 in an increasing dopamine release, and locally infused 8-hydroxy-2-(di-n-propylamino)tetralin (10 microM) increased dopamine release in the prefrontal cortex. MKC-242 increased cortical dopamine release in the rats pretreated with 5, 7-dihydroxytryptamine (150 microgram, i.c.v.) that caused an almost complete reduction in cortical 5-HT content. The effect of MKC-242 to increase dopamine release was also observed in the hippocampus, but not in the striatum or nucleus accumbens. Fluoxetine, a selective serotonin reuptake inhibitor, increased dopamine release in the prefrontal cortex, but not in the nucleus accumbens, while buspirone, a 5-HT(1A) receptor agonist, increased dopamine release in both brain regions. The present results indicate that activation of postsynaptic 5-HT(1A) receptors increases dopamine release in a brain region-specific manner.