Absence of 5-HT(1B) receptors is associated with impaired impulse control in male 5-HT(1B) knockout mice

Fluoxetine response in impulsive-aggressive behavior and serotonin transporter polymorphism in personality disorder

BACKGROUND

Disturbances in central serotonin function have been implicated in impulsive and aggressive behavior. A deletion/insertion polymorphism within the 5-HT transporter promoter gene (5-HTTLPR) is thought to be associated with disturbed impulse control, anxiety, and depression. The serotonin transporter (5-HTT) is the primary action site for selective serotonin reuptake inhibitors (SSRIs). Several studies of major depression have shown that the l allele of 5-HTTLPR is associated with better SSRI antidepressant effects than the s allele.

METHODS

This study investigates the association between response of impulsivity to treatment with fluoxetine and 5-HTTLPR polymorphism in 49 personality disordered patients. Additionally, we studied TPH1, 5HT1B and 5HT2C receptor polymorphisms as predictors of response in this population.

RESULTS

Results reveal that patients with the l/l genotype of 5-HTTLPR had a significantly better response to fluoxetine when compared to s allele carriers, as evaluated on the basis of total (P<0.05) and Aggression subscale (P<0.01) Overt Aggression Scale Modified-score percentage change. There were no significant associations between fluoxetine response and TPH1 (A218C) (-6525 A>G) (-5806 G>T), HTR1B (G861C) and HTR2C (G68C) genotype groups.

CONCLUSION

This is the first study assessing the association between these polymorphisms and anti-impulsive response to fluoxetine in personality disorder. As the s genotype is associated with a poorer selective serotonin reuptake inhibitors response in major depression, bulimia nervosa and borderline personality disorder, it could represent a common biological background for SSRI response.

[Effect of social interaction on skin temperature in mice]

We investigated physiological and behavioral characteristics of socially stressed animals in a resident-intruder paradigm. ICR male mice (resident, n = 14) were exposed individually to a novel male conspecific (intruder, n = 14) in their homecage for 30 min. Along with behavioral analyses, the skin temperatures of both the resident and the intruder were measured simultaneously using a multipoint radiation thermometer. There were no significant differences between the resident and intruder in the amount of locomotion, flight and aggressive behaviors. The mean skin temperature of the residents during the interaction was higher than before the interaction. In addition, the skin temperatures of the intruders were consistently higher than the residents. The results suggest that social stress causes elevation in skin temperature as well as stress-induced hyperthermia in core temperature. Moreover, infrared radiation thermometers may provide an alternative means of measuring physiological parameters of two (or more) subjects simultaneously in the study of animal social behavior.

Exploration of 19 serotoninergic candidate genes in adults and children with attention-deficit/hyperactivity disorder identifies association for 5HT2A, DDC and MAOB

Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric disorder in which different genetic and environmental susceptibility factors are involved. Several lines of evidence support the view that at least 30% of ADHD patients diagnosed in childhood continue to suffer the disorder during adulthood and that genetic risk factors may play an essential role in the persistence of the disorder throughout lifespan. Genetic, biochemical and pharmacological studies support the idea that the serotonin system participates in the etiology of ADHD. Based on these data, we aimed to analyze single nucleotide polymorphisms across 19 genes involved in the serotoninergic neurotransmission in a clinical sample of 451 ADHD patients (188 adults and 263 children) and 400 controls using a population-based association study. Several significant associations were found after correcting for multiple testing: (1) the DDC gene was strongly associated with both adulthood (P=0.00053; odds ratio (OR)=2.17) and childhood ADHD (P=0.0017; OR=1.90); (2) the MAOB gene was found specifically associated in the adult ADHD sample (P=0.0029; OR=1.90) and (3) the 5HT2A gene showed evidence of association only with the combined ADHD subtype both in adults (P=0.0036; OR=1.63) and children (P=0.0084; OR=1.49). Our data support the contribution of the serotoninergic system in the genetic predisposition to ADHD, identifying common childhood and adulthood ADHD susceptibility factors, associations that are specific to ADHD subtypes and one variant potentially involved in the continuity of the disorder throughout lifespan.

Olfactory bulbectomy induces rapid and stable changes in basal and stress-induced locomotor activity, heart rate and body temperature responses in the home cage

BACKGROUND

Olfactory bulbectomy (OBX) in rats causes several behavioral and neurochemical changes. However, the extent and onset of physiological and behavioral changes induced after bulbectomy have been little examined.

METHODS

Male Sprague-Dawley rats received telemetric implants. Before and immediately after OBX surgery, basal and stress-induced heart rate, body temperature, and locomotor activity were measured in the home cage in sham (n=9) and OBX animals (n=11). Stress was induced using novel cage stress or witness stress.

RESULTS

Bulbectomized animals differed physiologically and behaviorally from shams. Nocturnally, OBX animals were significantly more active compared with shams, had a higher core body temperature and displayed a decreased heart rate variability. During the light period, OBX animals had a significantly lower basal heart rate and a reduced heart rate variability. These effects became apparent 2-3 days after OBX surgery, and were stable over time. After witness stress, OBX animals showed smaller autonomic (body temperature and heart rate) responses compared with shams, but showed no difference in locomotor responses. In contrast, novel cage stress led to increased locomotor responses in OBX rats compared with sham rats, while no differences were found in autonomic responses.

CONCLUSION

Removal of the olfactory bulbs results in rapid, stable and persistent changes in basal locomotor activity, body temperature, heart rate and heart rate variability. Although the sleep-wake cycle of these parameters is not altered, increases in circadian amplitude are apparent within 3 days after surgery. This indicates that physiological changes in the OBX rat are the immediate result of olfactory bulb removal. Further, stress responsivity in OBX rats depends on stressor intensity. Bulbectomized rats display smaller temperature and heart rate responses to less intense witness stress compared with sham rats. Increased locomotor responses to more intense novel cage stress are present in the home cage as well as the open field. The present study shows that olfactory bulbectomy has rapid and persistent influence on basal and stress-induced physiological parameters.

Is hyper-aggressiveness associated with physiological hypoarousal? A comparative study on mouse lines selected for high and low aggressiveness

Aggressiveness is often considered a life-long, persistent personality trait and is therefore expected to have a consistent neurobiological basis. Recent meta-analyses on physiological correlates of aggression and violence suggest that certain aggression-related psychopathologies are associated with low functioning of the hypothalamo-pituitary-adrenal (HPA) axis and autonomic nervous system (ANS). We tested this hypothesis in mice selected for high and low aggressiveness by measuring baseline plasma corticosterone levels and, via radiotelemetry, heart rate and core body temperature. The radiotelemetric recordings were made for 48 h under baseline undisturbed conditions and for 90 min after a handling stressor. Consistent with the hypoarousal hypothesis of violence, we found lower resting heart rates in two out of the three highly aggressive selection lines. In contrast, body temperature during the active phase, as another ANS-regulated physiological parameter, was higher in two out of three highly aggressive lines. The handling-induced tachycardiac and hyperthermic responses were similar across the six mouse lines except for the most docile and obese line, which showed a blunted reactivity. Besides significant differences between strains, no differences in plasma corticosterone levels were found between the high- and low-aggressive phenotypes. These results are discussed in relation to the different types of aggression (normal versus pathological) exhibited by the three highly aggressive lines. We conclude that while high trait-like aggressiveness is generally associated with a higher active phase core body temperature, only animals that express pathological forms of aggression are characterized by a low resting heart rate.

Serotonin and aggression

The neurotransmitter serotonin (5-HT) has been implicated in the modulation of aggression in animals and humans. A longstanding dogma that aggression and serotonergic activity are inversely related has to be abandoned in light of many new findings. Trait and state aggression are differentially regulated by the 5-HT system and different 5-HT receptors seem to be involved. Of the 14 different 5-HT receptors, the 5-HT(1B) receptor, particularly the postsynaptically located 5-HT(1B) heteroreceptor, plays a highly selective role in the modulation of offensive aggression. We are still far from understanding the complex role played by the serotonergic system in the modulation of a complex set of behaviors like aggression.

Stress, genes and the biology of suicidal behavior

Suicidal behavior is partly heritable. Studies seeking the responsible candidate genes have examined genes involved in neurotransmitter systems shown to have altered function in suicide and attempted suicide. These neurotransmitter systems include the serotonergic, noradrenergic, and dopaminergic systems and the hypothalamic-pituitary-adrenal axis. With some exceptions, most notably the serotonin transporter gene promoter polymorphism (HTTLPR), replication of candidate gene association studies findings has been difficult. This article reviews current knowledge of specific gene effects and gene-environment interactions that influence risk for suicidal behavior. Effects of childhood stress on development and how it influences adult responses to current stress are shown to be relevant for mood disorders, aggressive/impulsive traits, and suicidal behavior.

Mice lacking the immediate early gene Egr3 respond to the anti-aggressive effects of clozapine yet are relatively resistant to its sedating effects

Immediate early genes (IEGs) of the early growth response gene (Egr) family are activated in the brain in response to stress, social stimuli, and administration of psycho-active medications. However, little is known about the role of these genes in the biological or behavioral response to these stimuli. Here we show that mice lacking the IEG transcription factor Egr3 (Egr3-/- mice) display increased aggression, and a decreased latency to attack, in response to the stressful social stimulus of a foreign intruder. Together with our findings of persistent and intrusive olfactory-mediated social investigation of conspecifics, these results suggest increased impulsivity in Egr3-/- mice. We also show that the aggression of Egr3-/- mice is significantly inhibited with chronic administration of the antipsychotic medication clozapine. Despite their sensitivity to this therapeutic effect of clozapine, Egr3-/- mice display a marked resistance to the sedating effects of acute clozapine compared with WT littermate controls. This indicates that the therapeutic, anti-aggressive action of clozapine is separable from its sedating activity, and that the biological abnormality resulting from loss of Egr3 distinguishes these different mechanisms. Thus Egr3-/- mice may provide an important tool for elucidating the mechanism of action of clozapine, as well as for understanding the biology underlying aggressive behavior. Notably, schizophrenia patients display a similar decreased susceptibility to the side effects of antipsychotic medications compared to non-psychiatric controls, despite the medications producing a therapeutic response. This suggests the possibility that Egr3-/- mice may provide insight into the neurobiological abnormalities underlying schizophrenia.

Genetic variation in cortico-amygdala serotonin function and risk for stress-related disease

The serotonin system is strongly implicated in the pathophysiology and therapeutic alleviation of stress-related disorders such as anxiety and depression. Serotonergic modulation of the acute response to stress and the adaptation to chronic stress is mediated by a myriad of molecules controlling serotonin neuron development (Pet-1), synthesis (tryptophan hydroxylase 1 and 2 isozymes), packaging (vesicular monoamine transporter 2), actions at presynaptic and postsynaptic receptors (5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C, 5-HT3A, 5-HT4, 5-HT5A, 5-HT6, 5-HT7), reuptake (serotonin transporter), and degradation (monoamine oxidase A). A growing body of evidence from preclinical rodents models, and especially genetically modified mice and inbred mouse strains, has provided significant insight into how genetic variation in these molecules can affect the development and function of a key neural circuit between the dorsal raphe nucleus, medial prefrontal cortex and amygdala. By extension, such variation is hypothesized to have a major influence on individual differences in the stress response and risk for stress-related disease in humans. The current article provides an update on this rapidly evolving field of research.

Molecular biology of 5-HT receptors

Serotonin (5-hydroxytryptamine; 5-HT) is a monoamine neurotransmitter whose effects are mediated by at least 13 distinct G protein-coupled receptors (GPCRs) of the type A family which includes the monoamine receptors and a combination of ligand-gated ion channels (5-HT3) of the Cys loop family which constitutes heteropentamers. 5-HT receptors are currently divided into seven classes (5-HT1 to 5-HT7), based on structural, transductional and operational features. While this degree of physical diversity clearly underscores the physiological importance of serotonin, evidence for an even greater degree of operational diversity is supported by the existence of a great number of splice and editing variants for several 5-HT receptors, their possible modulation by accessory proteins and chaperones, as well as their potential to form homo or heteromers both at the GPCR and at the ligand-gated channel level.

Anti-aggressive effects of agonists at 5-HT1B receptors in the dorsal raphe nucleus of mice

RATIONALE

In rodents, serotonin 1B (5-HT(1B)) agonists specifically reduce aggressive behaviors, including several forms of escalated aggression. One form of escalated aggression is seen in mice that seek the opportunity to attack another mouse by accelerating their responding during a fixed interval (FI) schedule. Responses preceding the opportunity to attack may reflect aggressive motivation.

OBJECTIVE

This study investigated the effects of two 5-HT(1B) receptor agonists on the motivation to fight and the performance of heightened aggression.

MATERIALS AND METHODS

Male mice were housed as "residents" and performed nose-poke responses on an FI 10-min schedule with the opportunity to briefly attack an "intruder" serving as the reinforcer. In the first experiment, the 5-HT(1B) receptor agonist, CP-94,253 (0-10 mg/kg, IP), was given 30 min before the FI 10 schedule. To confirm that CP-94,253 achieved its effects via 5-HT(1B) receptors, the 5HT(1B/1D) receptor antagonist, GR 127,935 (10 mg/kg, IP) was administrated before the agonist injection. In the second experiment, the 5-HT(1B) agonist CP-93,129 (0-1.0 microg) was microinjected into the dorsal raphe 10 min before the FI 10 schedule.

RESULTS

The agonists had similar effects on all behaviors. CP-94,253 and CP-93,129 significantly reduced the escalated aggression towards the intruder at doses lower than those required to affect operant responding. The highest doses of CP-94,253 (10 mg/kg) and CP-93,129 (1.0 microg) decreased the rate and accelerating pattern of responding during the FI 10 schedule; lower doses were less effective. GR 127,935 antagonized CP-94,253's effects on all other behaviors, except response rate.

CONCLUSIONS

These data extend the anti-aggressive effects of 5-HT(1B) agonists to a type of escalated aggression that is rewarding and further suggest that these effects are associated with actions at 5-HT(1B) receptors in the dorsal raphe.

Effect of 5-HT1B receptor agonists injected into the prefrontal cortex on maternal aggression in rats

Serotonin (5-HT1B) receptors play an essential role in the inhibition of aggressive behavior in rodents. CP-94,253, a 5-HT1B receptor agonist, can reduce aggression in male mice when administered directly into the ventro-orbitofrontal (VO) prefrontal cortex (PFC). The objective of the current study was to assess the effects of two selective 5-HT1B receptor agonists (CP-94,253 and CP-93,129), microinjected into the VO PFC, on maternal aggressive behavior after social instigation in rats. CP-94,253 (0.56 microg/0.2 microL, N = 8, and 1.0 microg/0.2 microL, N = 8) or CP-93,129 (1.0 microg/0.2 microL, N = 9) was microinjected into the VO PFC of Wistar rats on the 9th day postpartum and 15 min thereafter the aggressive behavior by the resident female against a male intruder was recorded for 10 min. The frequency and duration of aggressive and non-aggressive behaviors were analyzed using ANOVA and post hoc tests. CP-93,129 significantly decreased maternal aggression. The frequency of lateral attacks, bites and pinnings was reduced compared to control, while the non-aggressive behaviors and maternal care were largely unaffected by this treatment. CP-94,253 had no significant effects on aggressive or non-aggressive behaviors when microinjected into the same area of female rats. CP-93,129, a specific 5-HT1B receptor agonist, administered into the VO PFC reduced maternal aggressive behavior, while the CP-94,253 agonist did not significantly affect this behavior after social instigation in female rats. We conclude that only the 5-HT1B receptor agonist CP-93,129 administered into the VO PFC decreased aggression in female rats postpartum after social instigation.

Ethanol-related behaviors in serotonin transporter knockout mice

BACKGROUND

Increasing evidence supports a role for 5-hydroxytryptamine (5-HT) and the 5-HT transporter (5-HTT) in modulating the neural and behavioral actions of ethanol (EtOH) and other drugs of abuse.

METHODS

We used a 5-HTT knockout (KO) mouse model to further study this relationship. 5-Hydroxytryptamine transporter KO mice were tested for the sedative/hypnotic, hypothermia-inducing, motor-incoordinating (via accelerating rotarod), and depression-related (via tail suspension test) effects of acute EtOH administration. Reward-related effects of EtOH were assessed in 5-HTT KO mice using the conditioned place preference (CPP) paradigm. 5-Hydroxytryptamine transporter KO mice were tested for voluntary consumption of EtOH in a modified 2-bottle choice test that measured the temporal organization of drinking over the circadian cycle via "lickometers."

RESULTS

Replicating previous findings, 5-HTT KO mice exhibited significantly increased sensitivity to EtOH-induced sedation/hypnosis relative to wild-type controls. Additionally, 5-HTT KO mice showed motor-coordination deficits at baseline and in response to EtOH. Hypothermic, pro-depressive-like, and reward-related effects of EtOH were no different across genotypes. Gross EtOH consumption was modestly reduced in 5-HTT KO mice, due to significantly lesser consumption during the peak period of drinking in the early dark phase.

CONCLUSIONS

Data extend the finding that loss of 5-HTT gene function alters certain neural and behavioral effects of EtOH, with implications for better understanding the pathophysiology and treatment of alcoholism.

Neurons expressing serotonin-1B receptor in the basolateral nuclear group of the amygdala in normally behaving and aggressive dogs

The present study aimed to quantify neurons expressing the serotonin-1B receptor and evaluate numerical differences in normally behaving and pathologically aggressive dogs in order to assess whether the serotonin-1B receptor is involved in pathological canine aggression. Because previous studies have reported structural alterations in the basolateral nuclear group (BNG) of the amygdaloid body of aggressive dogs, this structure was selected as region of interest in the present study. Indirect immunohistochemistry was applied to visualise the serotonin-1B-receptor-positive neurons. Immunoreactivity was located predominantly within the neuronal cell bodies and adjacent neuronal processes. In the aggressive dogs the BNGs contained a significantly higher number of serotonin-1B-receptor-positive neurons compared to the normally behaving dogs. This number was strongly correlated with the total number of neurons per BNG, which was also significantly increased in aggressive dogs compared to normal dogs. The percentage of neurons expressing the serotonin-1B receptor did not differ significantly between both groups. No significant asymmetries were observed for the number and percentage of serotonin-1B-receptor-positive neurons. Potential relationships between the present findings and the etiology of aggressive behaviour, the neuroprotective role of the serotonin-1B receptor and receptor dysfunction are discussed.

The stress-induced hyperthermia paradigm as a physiological animal model for anxiety: A review of pharmacological and genetic studies in the mouse

This paper reviews the function, brain mechanisms and pharmacology of stress-induced hyperthermia (SIH) in a broad context. Hyperthermia itself is induced by all stressful stimuli and can be found across numerous species, including humans. As a model for anxiety, the process of insertion of a rectal probe increases temperature ranging from about 0.5-1.5 degrees C in 10-15min is called SIH. This temperature increase can be blocked by anxiolytic drugs. The methodological as well as pharmacological aspects of the group- (G-SIH) and singly housed (SIH) version of the paradigm are described in detail. Also, an overview is presented about studies using the SIH procedure in genetically modified mice together with the potential interference with immunological induction of a febrile response. The paper also presents data that highlight some of the limitations of the SIH procedure for use of drugs like nicotine, which contain particular characteristics such as short in vivo half-life, and/or disturbance of thermoregulation. The advantages and disadvantages of the SIH procedure as a physiological model of anxiety are discussed.

Phenytoin normalizes exaggerated fear behavior in p-chlorophenylalanine (PCPA)-treated rats

Temporal lobe epilepsy may be associated with emotional difficulties such as depression and anxiety. Because the amygdala is involved in both epilepsy and emotion, common neural mechanisms in this temporal lobe structure may underlie the emotional disturbances observed in people with epilepsy. The neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) is implicated in many psychopathologies, and 5-HT also modulates amygdala excitability. Therefore, the present study uses the fear-potentiated startle (FPS) paradigm to investigate the effect of neuronal excitability on fear behavior in rats treated with p-chlorophenylalanine (PCPA) to chronically inhibit 5-HT synthesis. PCPA treatment selectively enhanced FPS in individually housed rats. The exaggerated FPS response was reduced to control level by the anticonvulsant phenytoin at 10mg/kg, and phenytoin at 30mg/kg further decreased FPS behavior. These data suggest that a subseizure state of neuronal excitability mediated by low 5-HT in brain fear circuits may be associated with pathological fear behavior.

From genes to aggressive behavior: the role of serotonergic system

Recent investigations in neurogenomics have opened up new lines of research into a crucial genetic problem-the pathway from genes to behavior. This paper concentrates on the involvement of protein elements in the brain neurotransmitter serotonin (5-HT) system in the genetic control of aggressive behavior. Specifically, it describes: (1) the effect of the knockout of MAO A, the principal enzyme in 5-HT degradation, (2) the association of intermale aggression with the polymorphism in the Tph2 gene encoding the key enzyme in 5-HT synthesis in the brain, tryptophan hydroxylase (TPH), and (3) the effect of selective breeding for nonaggressive behavior on 5-HT metabolism, TPH activity and 5-HT(1A) receptors in the brain. The review provides converging lines of evidence that: (1) brain 5-HT contributes to a critical mechanism underlying genetically defined individual differences in aggressiveness, and (2) genes encoding pivotal enzymes in 5-HT metabolism (TPH and MAO A), 5-HT-transporter, 5-HT(1A) and 5-HT(1B) receptors belong to a group of genes that modulate aggressive behavior.

5-HT(1B) receptors, ventral orbitofrontal cortex, and aggressive behavior in mice

RATIONALE

Systemic injections of 5-HT(1B) receptor agonists have been shown to have specific anti-aggressive effects in aggressive individuals. One site of action for these drugs is the 5-HT(1B) receptors in the ventral orbitofrontal cortex (VO PFC), an area that has been implicated in the inhibitory control of behavior and is a terminal region for 5-HT projections.

OBJECTIVE

To assess the anti-aggressive effects of the 5-HT(1B) receptor agonist CP-94,253 when microinjected into the VO PFC (0.1, 0.56, and 1.0 microg/0.2 microl) or into the infralimbic prefrontal cortex (IL PFC; 1.0 microg/0.2 microl) in separate groups of aggressive resident male mice. To confirm the 5-HT(1B) receptor as the critical site of action for the anti-aggressive effects, the 5-HT(1B/D) antagonist GR-127,935 was microinjected at 10.0 microg/0.2 microl into the VO PFC. After recovery from surgery, the anti-aggressive effects of microinjected CP-94,253 were studied during 5-min resident-intruder confrontations that were recorded and analyzed.

RESULTS

Microinjections of CP-94,253 (0.56 and 1.0 microg/0.2 microl) dose-dependently reduced the frequency of attack bites and sideways threats. This effect was behaviorally specific because non-aggressive motor activities were not significantly altered by the drug. In the IL vmPFC or in an area lateral to the VO PFC, CP-94,253 (1.0 microg/0.2 microl) did not have significant behavioral effects.

CONCLUSIONS

The results highlight the 5-HT(1B) receptors in the VO PFC as a particularly important site for the inhibition of species-typical aggressive behavior in male mice.

Effects of anpirtoline on regional serotonin synthesis in the rat brain: an autoradiographic study

Anpirtoline has been described as an agonist at 5-HT1B receptors with a relatively high potency. It also acts as an agonist at 5-HT1A receptors, but has a lower potency than at the 5-HT1B sites. There is very little known about the mechanism by which anpirtoline influences regional 5-HT synthesis. The aim of the present study was to investigate the effects of acutely and chronically administered anpirtoline on 5-HT synthesis in the rat brain using the autoradiographic alpha-[14C]methyl-L-tryptophan method. In the acute study, anpirtoline (2.0 mg/kg) was administered intraperitoneally 30 min before the tracer injection. The control rats were injected with the same volume of saline. In the chronic study, anpirtoline (2 mg/kg per day) was injected subcutaneously in saline once a day for 10 days. There were no significant differences between the plasma-free and total tryptophan concentrations between the anpirtoline treatment and the respective control groups. In the acute experiment, 5-HT synthesis rates in all of the brain areas investigated were significantly decreased by anpirtoline when compared to the saline-treated group. In the chronic anpirtoline experiment, 5-HT synthesis rates of almost all of the projection areas, as well as the raphe nuclei, were normalized or had a tendency to be normalized. These results suggest that it is likely that the terminal 5-HT1B receptors are involved in the regulation of 5-HT synthesis in the projection areas and that 5-HT synthesis, in the raphe, is likely influenced by anpirtoline's 5-HT1A and/or 5-HT1B agonistic properties.

Association between the 5HT1B receptor gene (HTR1B) and the inattentive subtype of ADHD

BACKGROUND

Preclinical and genetic studies have implicated the 5HT1B receptor gene (HTR1B) in attention-deficit/hyperactivity disorder (ADHD). Association with a single nucleotide polymorphism (SNP; G861C) has been observed, but more extensive linkage disequilibrium analyses have not been reported.

METHODS

To examine haplotype structure, we genotyped 21 SNPs in and around the gene in 12 multigenerational CEPH pedigrees. We identified a haplotype block encompassing HTR1B and performed haplotype and single-marker association analyses for the eight SNPs within or flanking this block in 229 families of ADHD probands. In light of previous studies suggesting distinct genetic influences on ADHD subtypes, we also examined association with the inattentive and combined subtypes.

RESULTS

We observed nonsignificant overtransmission of the G861 allele to ADHD offspring (one-tailed p = .07). Single-marker and haplotype tests of a haplotype block encompassing HTR1B revealed no other associations with ADHD. However, this haplotype block was associated with the inattentive subtype (global p < .01). Additionally, three SNPs in this block were nominally (p < .05) associated with the inattentive subtype, although these did not remain significant after correction for multiple testing. As reported in previous studies, we found paternal overtransmission of the G861 allele to offspring with ADHD; this appeared to be largely attributable to inattentive cases.

CONCLUSIONS

These analyses suggest that variation in the HTR1B gene may primarily affect the inattentive subtype of ADHD.

Role of Alcohol Consumption in Escalation to Violence

No other drug has been associated with aggressive and violent behavior more than alcohol has. A major characteristic of the link between alcohol and social interactions is the very large variation in who becomes more aggressive while drinking and who does not. Tracing the origins of these individual differences has led to a focus on predispositions, such as the antisocial behavior of Type 2 alcoholics. Successful development of an experimental procedure to model heightened aggressive behavior after voluntary consumption of alcohol has facilitated the neurobiologic analysis of the link between alcohol and aggression. From a pharmacologic perspective, consumption of low to moderate doses of alcohol engenders heightened aggressive behavior in a significant minority of individuals before the circulation of appreciable amounts of the aldehyde metabolite. Ionophoric receptors such as NMDA, 5-HT(3) and GABA(A) have been identified in the brain as major sites of action for alcohol in the dose range that is relevant for engendering heightened aggression. Actions at the GABA(A) receptor complex that depend on particular GABA(A) subunits appear to be necessary for alcohol-heightened aggression. Genes that encode the synthesis of these alpha and gamma subunits are potentially significant markers for those individuals that are prone to engage in heightened aggressive behavior after the consumption of alcohol. Of particular importance are the reciprocal interactions between GABA and serotonin. Activating specific serotonin receptor subtypes such as 5-HT(1B) receptors reduces alcohol-heightened aggressive behavior. How these GABAergic and serotonergic corticolimbic mechanisms for alcohol-heightened aggression develop during the adolescent period remains an area of urgent study.

Severe deficits in 5-HT2A-mediated neurotransmission in BDNF conditional mutant mice

BDNF is thought to provide critical trophic support for serotonin neurons. In order to determine postnatal effects of BDNF on the serotonin system, we examined a line of conditional mutant mice that have normal brain content of BDNF during prenatal development but later depletion of this neurotrophin in the postnatal period. These mice show a behavioral phenotype that suggests serotonin dysregulation. However, as shown here, the presynaptic serotonin system in the adult conditional mutant mice appeared surprisingly normal from histological, biochemical, and electrophysiological perspectives. By contrast, a dramatic and unexpected postsynaptic 5-HT2A deficit in the mutant mice was found. Electrophysiologically, serotonin neurons appeared near normal except, most notably, for an almost complete absence of expected 5-HT2A -mediated glutamate and GABA postsynaptic potentials normally displayed by these neurons. Further analysis showed that BDNF mutants had much reduced 5-HT2A receptor protein in dorsal raphe nucleus and a similar deficit in prefrontal cortex, a region that normally shows a high level of 5-HT2A receptor expression. Recordings in prefrontal slice showed a marked deficit in 5-HT2A -mediated excitatory postsynaptic currents, similar to that seen in the dorsal raphe. These findings suggest that postnatal levels of BDNF play a relatively limited role in maintaining presynaptic aspects of the serotonin system and a much greater role in maintaining postsynaptic 5-HT2A and possibly other receptors than previously suspected.

Do similar neural systems subserve aggressive and sexual behaviour in male rats? Insights from c-Fos and pharmacological studies

It is a common belief that male aggressive and sexual behaviour share many of the underlying neurobiological, neurological, pharmacological and neuroendocrine mechanisms. Therefore, we studied brain activation patterns in male rat after performance of aggressive and sexual behaviour and compared serotonergic pharmacology in the same paradigms to delineate possible similarities and differences. Patterns of Fos-immunoreactivity induced by aggressive and sexual encounters of Wild-type male Brown Norway rats were studied to localise the commonly activated (functionally shared) parts of the circuitry, and the specific (functionally different) parts of the neuronal circuitry. Some brain areas (caudal medial preoptic area and medial amygdala) were commonly activated, but other areas (e.g. posterodorsal parts of the medial amygdala, rostral preoptic and premammillary hypothalamus) showed remarkably specific differences in neural activation. 5-HT(1A) receptor agonists inhibit aggressive, but stimulate male sexual behaviour, whereas 5-HT(1B) receptor agonists inhibit both types of behaviour. Selective serotonin reuptake inhibitors share comparable inhibitory effects in aggression and sexual behaviour, although only at relatively high doses. We propose that separate hard-wired neural systems exist in the brain for aggressive and sexual behaviours, modulated via hierarchically 'higher-level' brain areas that are involved in the integration (gating) of the behavioural outcome of an organism.

Escalated aggressive behavior: Dopamine, serotonin and GABA

The ethical dilemma in aggression research is how to reconcile two divergent objectives, namely to avoid harm and injury as much as possible and, at the same time, how to study behavioral phenomena that validly represent the essence of the neurobiology of aggression. Clinical and preclinical aggression research focuses on different types of aggression. Preclinical studies are usually stimulated by an ethological approach and focus on the phylogeny, ontogeny, survival value and neural mechanisms of ritualized displays and signals. On the other hand, clinical studies focus on violent individuals and pathologically excessive forms of aggressive behavior. This review emphasizes research on escalated forms of aggression in animals and humans and their pharmacotherapy. The current experimental models to generate escalated levels of aggressive behavior in laboratory rely on social instigation, frustrative non-reward and alcohol drinking. These types of aggression are modulated by canonical neurotransmitters like dopamine, serotonin (5-HT) and GABA. It continues to be a main goal of much neurobiological research to find potential targets of pharmacological agents that interact with dopaminergic, GABAergic and serotonergic systems and have high efficacy and selectivity to reduce excessive levels of aggressive and violent behaviors without side-effects. While the mesocorticolimbic dopamine system is implicated in the initiation, execution, termination and consequences of aggressive behavior, drugs with a high affinity for dopamine D2 receptors lack specificity for reducing aggressive behavior. Current investigations point to 5-HT(1B) receptor subtypes as particularly relevant. First, they are differentially expressed in aggression-prone individuals relative to those who are not excessively aggressive. Second, these and also other 5-HT receptor subtypes emerge to be significant targets for anti-aggressive interventions. Positive modulators of GABA(A) receptors with specific subunit configuration may be relevant for heightening aggression, and these sites may be targets for intervention. A prerequisite for rational pharmacotherapies will be adequate characterization of serotonergic and GABAergic receptor regulation in individuals exhibiting escalated aggression.

5-HT1B receptors and aggression: A review

The serotonergic (5-HT) system in the brain is involved in the modulation of offensive aggressive behavior. The dogma that activity of the 5-HT system is inversely related to aggression is obsolete now. Research on the status of the 5-HT system before, during and after the execution of aggression is ongoing but has not yet led to a clear picture about the actual functional role of the 5-HT system, the more because state versus trait aggression seems to play a pivotal role in the outcome. Pharmacological challenges pinpoint 5-HT(1A) and 5-HT(1B) receptors as key players in the modulation of offensive aggression. This review emphasizes in particular the role of postsynaptic 5-HT(1B) (hetero) receptors as a premier site to modulate offensive aggression. Modulation of the firing and 5-HT release of the serotonergic neuron, via presynaptic 5-HT(1A) (auto) receptors, presynaptic 5-HT(1B) (auto) receptors and serotonergic transporters, may also have striking influences on aggression under certain conditions. Therefore, it is hypothesized that postsynaptic 5-HT(1B) (hetero) receptors directly influence the executive, consummatory phases of agonistic behavior, whereas presynaptic serotonergic feedback systems are particularly useful in the introductory (appetitive) phases of the agonistic behavioral complex.

Agitation After Traumatic Brain Injury

Posttraumatic agitation is a challenging problem for acute and rehabilitation staff, persons with traumatic brain injury, and their families. Specific variables for evaluation and care remain elusive. Clinical trials have not yielded a strong foundation for evidence-based practice in this arena. This review seeks to evaluate the present literature (with a focus on the decade 1995-2005) and employ previous clinical experience to deliver a review of the topic. We will discuss definitions, pathophysiology, evaluation techniques, and treatment regimens. A recommended approach to the evaluation and treatment of the person with posttraumatic agitation will be presented. The authors hope that this review will spur discussion and assist in facilitating clinical care paradigms and research programs.

The effects of SB 224289 on anxiety and cocaine-related behaviors in a novel object task

Cocaine facilitates dopamine transmission from ventral tegmental area (VTA) neurons that project to nucleus accumbens (NAcc), and previous experiments suggest that serotonin-1B (5-HT1B) receptors are involved in this effect. Specifically, activation of 5-HT1B receptors in VTA during cocaine exposure increases dopamine release in NAcc and enhances cocaine-induced locomotor activity, reward, and reinforcement. Thus, it is reasonable to hypothesize that blocking 5-HT1B activity may have the opposite effect. To investigate this hypothesis, SB 224289, a highly selective 5-HT1B antagonist, was used to block this receptor. In an open field/novel object exploration test, SB 224289 reduced cocaine-induced locomotion. However, SB 224289 also increased anxiety-like behavior, both alone and in combination with cocaine. This experiment gives evidence that 5-HT1B antagonists may reduce some of the behavioral effects of cocaine, but may have negative effects on anxiety as well.

Common genetic effects on variation in impulsivity and activity in mice

Impulsivity is a complex psychological construct that impacts on behavioral predispositions in the normal range and has been shown to have a genetic element through the examination of hereditary patterns of abnormal conditions such as attention deficit/hyperactivity disorder and obsessive compulsive disorder. In this study, we took advantage of the isogenic nature of inbred strains of mice to determine the contribution of genes to impulsive behaviors by examining the performance of four separate mouse strains in a novel murine delayed-reinforcement paradigm, during which the animals had to choose between rewards that were relatively small but available immediately and larger but progressively delayed rewards. To control for maternal effects, all the mice were cross-fostered to a common strain immediately after birth. Under these conditions, we found significant differences between the strains on behaviors indexing impulsive choice and on independent measures of locomotor activity, which subsequent heritability analysis showed could be related, in part, to genetic effects. Moreover, the two aspects of behavior were found to co-vary, with the more active animals also displaying more impulsive behavior. This was not attributable to mundane confounds related to individual task requirements but instead indicated the existence of common genetic factors influencing variation in both impulsivity and locomotor activity. The data are discussed in terms of the coexistence of impulsivity and hyperactivity, interactions between environmental and genetic effects, and possible candidate genes.

Hippocampal gene expression profiles in passive avoidance conditioning

Many experiments in the past have demonstrated the requirement of de novo gene expression during the long-term retention of learning and memory. Although previous studies implicated individual genes or genetic pathways in learning and memory, the collective behaviours of the genes is mostly unknown. We have used genome-scale screening by microarray analysis to examine the hippocampal expression of more than 1200 genes relevant to neurobiology during instrumental conditioning. Training rats on a step-through passive avoidance task led to unique patterns of gene expression when compared to naïve animals or those exposed to the conditioned or the unconditioned stimulus alone. The newly identified genes afford a quantitative view of the changes which accompany conditioning at the genomic level and enable deeper insights into the molecular basis underlying learning and memory.

Measuring impulsivity in mice using a novel operant delayed reinforcement task: effects of behavioural manipulations and d-amphetamine

RATIONALE

The increasing use of genetically modified mice to probe genetic contributions to normal and abnormal behaviours requires the development of sensitive and selective behavioural tasks.

OBJECTIVES

To develop a discrete trial assay of impulsivity (delayed reinforcement) that is tractable in mice utilising a mouse operant nine-hole box apparatus and to specify the task with respect to behavioural and pharmacological manipulations.

METHODS

Mice were trained to respond with a nose-poke to one of two visual stimuli; one response resulted in a small quantity of reinforcer, the other in a larger quantity of reinforcer. As the session proceeded increasing delay was introduced onto the response leading to the large reward. Hence, the nature of the choice was a small quantity of reinforcer immediately versus a larger but progressively delayed amount of reinforcer. At stable baseline performance the mice were challenged with a variety of task manipulations and systemic d-amphetamine in order to discern aspects of the underlying psychological and neurochemical substrates of the choice behaviour.

RESULTS

The mice showed a systematic shift in responding away from the large reinforcer with increasing delay (0, 2, 4, 8, 12 s), such that at the longest delay >80% of nose-pokes were for the smaller, immediate reinforcer. Task manipulations indicated that behaviour was controlled in a trial discrete manner by the contingency between delay and reward and was not due to non-specific factors such as satiation. d-Amphetamine had complex, dose dependent effects on choice behaviour which revealed dissociations between impulsive choice and hyperactivity.

CONCLUSIONS

We have successfully developed an assay of impulsivity in mice that will be of utility to examine impulsive behaviours and their genetic substrates. In addition, our data provided evidence of distinct dopaminergic mechanisms mediating aspects of impulsivity and hyperactivity.

Interaction of nitric oxide and serotonin in aggressive behavior

Nitric oxide (NO) modulates many behavioral and neuroendocrine responses. Genetic or pharmacological inhibition of the synthetic enzyme that produces NO in neurons evokes elevated and sustained aggression in male mice. Recently, the excessive aggressive and impulsive traits of neuronal NO synthase knockout (nNOS-/-) mice were shown to be caused by reductions in serotonin (5-HT) turnover and deficient 5-HT1A and 5-HT1B receptor function in brain regions regulating emotion. The consistently high levels of aggression observed in nNOS-/- mice could be reversed by 5-HT precursors and by treatment with specific 5-HT1A and 5-HT1B receptor agonists. The expression of the aggressive phenotype of nNOS-/- knockout mice requires isolated housing prior to testing. The effects of social factors such as housing condition and maternal care can affect 5-HT and aggression, but the interaction among extrinsic factors, 5-HT, NO, and aggression remains unspecified. Taken together, NO appears to play an important role in normal brain 5-HT function and may have significant implications for the treatment of psychiatric disorders characterized by aggressive and impulsive behaviors.

Differential modulation of feline defensive rage behavior in the medial hypothalamus by 5-HT1A and 5-HT2 receptors

Previous studies have established that the expression of defensive rage behavior in the cat is mediated over reciprocal pathways that link the medial hypothalamus and the dorsolateral quadrant of the midbrain periaqueductal gray matter (PAG). The present study was designed to determine the roles played by 5-HT(1A) and 5-HT(2C) receptors in the medial hypothalamus on the expression of defensive rage behavior elicited from electrical stimulation of the PAG. Monopolar stimulating electrodes were placed in the midbrain PAG from which defensive rage behavior could be elicited by electrical stimulation. During the course of this study, defensive rage was determined by measuring the latency of the "hissing" component of this behavior. Cannula-electrodes were implanted into sites within the medial hypothalamus from which defensive rage behavior could also be elicited by electrical stimulation in order that serotonergic compounds could be microinjected into behaviorally identifiable regions of the hypothalamus at a later time. Microinjections of the 5-HT(1A) receptor agonist 8-OHDPAT (0.1, 1.0 and 3.0 nmol) into the medial hypothalamus suppressed PAG-elicited hissing in a dose-dependent manner. Administration of the 5-HT(1A) antagonist p-MPPI (3.0 nmol) blocked the suppressive effects of 8-OHDPAT upon hissing. The suppressive effects of 8-OHDPAT were specific to defensive rage behavior because this drug (3 nmol) facilitated quiet biting attack. Microinjections of the 5-HT(2C) receptor agonist (+/-)-DOI hydrochloride into the medial hypothalamus (0.5, 1.0, and 3.0 nmol) facilitated the occurrence of PAG-elicited hissing in a dose-dependent manner. In turn, these facilitating effects were blocked by pretreatment with the selective 5-HT(2) antagonist, LY-53,857, which was microinjected into the same medial hypothalamic site. The findings of this study provide evidence that activation of 5-HT(1A) and 5-HT(2) receptors within the medial hypothalamus exert differential modulatory effects upon defensive rage behavior elicited from the midbrain PAG of the cat.

Operant learning and differential-reinforcement-of-low-rate 36-s responding in 5-HT1A and 5-HT1B receptor knockout mice

Previous studies with mice lacking 5-HT(1A) (1AKO) and 5-HT(1B) (1BKO) receptors in hippocampus-dependent learning and memory paradigms, suggest that these receptors play an important role in learning and memory, although their precise role is unclear. In the present study, 1AKO and 1BKO mice were studied in operant behavioural paradigms of decision making and response inhibition, to further study the putative involvement of these receptors in prefrontal cortex-dependent learning and memory. Moreover, because 1AKO mice have been shown to exhibit an antidepressant-like phenotype and 1BKO mice to be more impulsive in ethological studies, mice were trained in a differential-reinforcement-of-low-rates (DRL) procedure. Overall, results indicate that 1AKO and 1BKO mice display subtle differences in operant paradigms of decision making and response inhibition compared to wild type (WT) mice. In addition, when responding under a DRL 36-s schedule had stabilised, 1BKO mice showed a phenotype indicative of increased impulsivity, whereas 1AKO mice did not differ from WT mice. In conclusion, 5-HT(1B) receptors appear to play an important role in impulsivity and a minor role in prefrontal cortex-dependent learning and memory as shown by the results obtained in serial reversal learning and extinction. In contrast, 5-HT(1A) receptors appear to be involved in facilitation of autoshaping, but their role in impulsivity and prefrontal cortex-dependent learning and memory appears to be limited.

Stress-induced hyperthermia and anxiety: pharmacological validation

When mammals, including man, are confronted with a stressful event, their core body temperature rises, stress-induced hyperthermia. In mice, the stress-induced hyperthermia procedure has been developed to measure antistress or anxiolytic-like effects of psychoactive drugs. Group-housed and singly housed versions of the stress-induced hyperthermia generate comparable results. Because the number of animals needed to perform an experiment is much lower in the singly housed versus the group-housed procedure, the former is the test of choice for pharmacological testing. A typical stress-induced hyperthermia test starts with an injection 60 min before the first rectal temperature measurement (T(1)), followed by a second temperature measurement (T(2)) 10-15 min later. The difference DeltaT (=T(2)-T(1)) is the stress-induced hyperthermia. The procedure also measures the intrinsic activity of drugs on the basal body temperature and DeltaT is relatively independent from the intrinsic temperature effects of drugs. Anxiolytic drugs (benzodiazepines, 5-HT(1A) receptor agonists, alcohol) reduce DeltaT suggestive of anxiolytic-like effects. Because the parameter measured for anxiety in the stress-induced hyperthermia procedure is not dependent on locomotor activity, like in almost all other anxiety tests, the stress-induced hyperthermia procedure is an attractive addition to tests in the anxiety field. Because the stress-induced hyperthermia is also present with a comparable pharmacological profile in females, this procedure has a wide species and gender validity. The procedure was applied in various genetically modified mice [5-HT(1A) and 5-HT(1B) receptor knockout (KO) mice and corticotropin-releasing hormone overexpressing (CRH-OE) mice] to study phenotypic influences of the various mutations on aspects of anxiety. The stress-induced hyperthermia test in singly housed male and female mice appears a useful and extremely simple test to measure effects of drugs on certain aspects of anxiety or to help to determine phenotypic differences in mutant mice.

Reduced stress-induced hyperthermia in mGluR5 knockout mice

It hs been suggested that metabotropic glutamate receptor subtype 5 (mGluR5) play a role in the expression of anxiety, based on anxiolytic-like effects of the selective mGluR5 antagonist MPEP (2-methyl-6-(phenylethynyl)pyridine) in rodent models of anxiety, including stress-induced hyperthermia (SIH). To examine the suggested role of mGlu5 receptors in the expression of anxiety, we examined the stress response in mice lacking mGluR5 in several variations of the SIH procedure. In this paradigm, stress causes a mild increase in body temperature that can be blocked by known anxiolytic agents. Three procedures were employed: classical SIH using rectal-probe measurement of body temperature, and radiotelemetric measurement of body temperature in response to either saline injection or to the introduction of an intruder into the home cage. In all three procedures the mGluR5-knockout mice displayed a significant attenuation of the hyperthermic response to stress compared to littermate wild-type control mice. To confirm that our observations were likely to be due to the absence of mGluR5 in the knockout mice we also tested the effect of the recently described selective mGluR5 antagonist MTEP (3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine) in both the wild-type and mGluR5 knockout mice. Administration of MTEP in the wild-type mice, but not the mGluR5 knockout mice, attenuated SIH. That the mGluR5 knockout mice displayed an anxiolytic-like phenotype and that the mGluR5 antagonist, MTEP, showed a anxiolytic-like effect only in mice possessing mGluR5 further supports the suggestion that mGluR5 antagonists may be useful in the treatment of anxiety.

Behavioral and physiological mouse assays for anxiety: a survey in nine mouse strains

In order to find better and new treatments for anxiety in humans, a variety of paradigms are used to study anxiety-related processes in rodents. We studied mice in two different anxiety-related assays: the physiological stress-induced hyperthermia (SIH) paradigm and the behavioral light-dark exploration (LD) test. Eight inbred strains (129S6/SvEvTac, 129S1/SvImJ, A/J, BALB/cByJ, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ) and one outbred strain (CD1-ICR) were tested in both assays repeatedly. This study describes the first strain survey for the SIH paradigm. All strains showed an SIH response, but the magnitude of the response varied between lines. The inbred strain distribution pattern for the behavioral responses in the LD assay was not correlated with the SIH response. The lack of a significant correlation suggests that there is no genetic relation between such responses. Mice could be tested repeatedly in both assays without affecting the results. A new paradigm, in which both assays were combined, elucidated that behavioral responses were not altered by segments of the SIH paradigm. In contrast, exposure to the light-dark box instead of the home-cage showed a strain-dependent effect on the physiological response. We conclude that a combination of behavioral and physiological responses might lead to a better understanding in anxiety-related processes.

DNA variation and psychopharmacology of the human serotonin receptor 1B (HTR1B) gene

One of the neurotransmitter serotonin's receptors, HTR1B, is of interest for many neuropsychiatric traits, illnesses and treatments for multiple reasons, especially its tissue distribution, pharmacological profile and findings from mice lacking the receptor, along with reasons generally implicating serotonin. Eight mutation scans have uncovered sixteen polymorphisms in the coding sequence and surrounding 5'- and 3'-untranslated regions and much is now known of the distribution of these polymorphisms in various ethnic groups and their linkage disequilibrium relationships. Thus far, evidence exists that the uncommon missense T371G (Phe124Cys) and the common promoter region A-161T polymorphisms may exhibit functional effects and possibly that the common synonymous G861C (or more likely a variant in linkage disequilibrium with G861C) does as well. From the eighteen reported population-based case control studies of HTR1B to multiple disorders, several facts stand out. There exists preliminary evidence for association of G861C with i) antisocial alcoholism in the Finnish; ii) alcoholism in the presence of inactive aldehyde dehydrogenase 2 in the Japanese; iii) a history of suicide attempts in European-American personality disorder patients; and iv) minimum lifetime body mass index in Canadian bulimia nervosa patients. From the three reported family-based case control studies of HTR1B to various disorders, one provides preliminary evidence for association of G861C with obsessive compulsive disorder. Although many association studies have been completed, positive results should still be considered preliminary. As these preliminary reports are tested for replication with larger, more powerful samples, there should be increased clarity as to which findings remain robust; in some cases this will require the application of meta-analytic techniques.

Autonomic control of blood pressure in mice: basic physiology and effects of genetic modification

Control of blood pressure and of blood flow is essential for maintenance of homeostasis. The hemodynamic state is adjusted by intrinsic, neural, and hormonal mechanisms to optimize adaptation to internal and environmental challenges. In the last decade, many studies showed that modification of the mouse genome may alter the capacity of cardiovascular control systems to respond to homeostatic challenges or even bring about a permanent pathophysiological state. This review discusses the progress that has been made in understanding of autonomic cardiovascular control mechanisms from studies in genetically modified mice. First, from a physiological perspective, we describe how basic hemodynamic function can be measured in conscious conditions in mice. Second, we focus on the integrative role of autonomic nerves in control of blood pressure in the mouse, and finally, we depict the opportunities and insights provided by genetic modification in this area.

5-HT(1B) receptor knockout mice show no adaptive changes in 5-HT(1A) receptor function as measured telemetrically on body temperature and heart rate responses

Two presynaptic receptors play an important role in the regulation of serotonergic neurotransmission, i.e., the 5-HT(1A) and 5-HT(1B) receptor. The present study focuses on putative adaptive changes in the 5-HT(1A) receptor system in mice that lack 5-HT(1B) receptors (5-HT(1B) KO). 5-HT(1A) receptor sensitivity was assessed in vivo in two models of presynaptic 5-HT(1A) receptor activity: agonist-induced hypothermia and prevention of stress-induced hyperthermia. The effects of 5-HT(1A) receptor activation by flesinoxan (0.1-3.0 mg/kg s.c.) were determined telemetrically on body temperature and heart rate in 5-HT(1B) KO and wild-type (WT) mice. Flesinoxan induced hypothermia dose-dependently without affecting heart rate and prevented stress-induced hyperthermia and tachycardia equipotently in both genotypes. Specificity of these responses was confirmed by blockade with the selective 5-HT(1A) receptor antagonist WAY100635 (1.0 mg/kg s.c.). The importance of continuous sampling in freely moving subjects to improve appropriate characterization of mutants is discussed. 5-HT(1B) KO mice showed no shift in 5-HT(1A) receptor sensitivity compared to WT mice. This study found no indications for adaptive changes in presynaptic 5-HT(1A) receptor function in 5-HT(1B) KO mice as measured telemetrically on body temperature and heart rate responses.

Diverse actions of ovarian steroids in the serotonin neural system

All of the serotonin-producing neurons of the mammalian brain are located in 10 nuclei in the mid- and hindbrain regions. The cells of the rostal nuclei project to almost every area of the forebrain and regulate diverse neural processes from higher order functions in the prefrontal cortex such as integrative cognition and memory, to limbic system control of arousal and mood, to diencephalic functions such as pituitary hormone secretion, satiety, and sexual behavior. The more caudal serotonin neurons project to the spinal cord and interact with numerous autonomic and sensory systems. All of these neural functions are sensitive to the presence or absence of the ovarian hormones, estrogen and progesterone. We have shown that serotonin neurons in nonhuman primates contain estrogen receptor beta and progestin receptors. Thus, they are targets for ovarian steroids which in turn modify gene expression. Any change in serotoninergic neural function could be manifested by a change in any of the projection target systems and in this manner, serotonin neurons integrate steroid hormone information and partially transduce their action in the CNS. This article reviews the work conducted in this laboratory on the actions of estrogens and progestins in the serotonin neural system of nonhuman primates. Comparisons to results obtained in other laboratory animal models are made when available and limited clinical data are referenced. The ability of estrogens and progestins to alter the function of the serotonin neural system at various levels provides a cellular mechanism whereby ovarian hormones can impact cognition, mood or arousal, hormone secretion, pain, and other neural circuits.

Contribution of the 5-HT(1B) receptor to hypoxia-induced pulmonary hypertension: converging evidence using 5-HT(1B)-receptor knockout mice and the 5-HT(1B/1D)-receptor antagonist GR127935

5-Hydroxytryptamine (5-HT)(1B) receptors mediate contraction in human pulmonary arteries, and 5-HT(1B) receptor-mediated contraction is enhanced in pulmonary arteries from hypoxic rats. Here we further examine the role of this receptor in the development of pulmonary hypertension (PHT) by examining (1) the effects of a 5-HT(1B/1D)-receptor antagonist (GR127935) on hypoxia-induced PHT (CHPHT) in rats and (2) CHPHT in 5-HT(1B)-receptor knockout mice. In rats, hypoxia increased right ventricular pressure and right ventricular hypertrophy and induced pulmonary vascular remodeling associated with an increase in pulmonary arterial wall thickness. GR127935 (3 mg. kg(-1). d(-1)) reduced all of these indices. 5-HT(1)-mediated contraction was enhanced in pulmonary arteries of the CHPHT rats. The effects of GR127935 on PHT indices were associated with an attenuation of the enhanced contractile responses to 5-HT and the 5-HT(1)-receptor agonist, 5-carboxamidotryptamine (5-CT), in isolated pulmonary arteries. In wild-type mice, hypoxia increased right ventricular hypertrophy, which was absent in 5-HT(1B)-receptor knockout mice. Hypoxia increased pulmonary vascular remodeling in wild-type mice, and this was reduced in the 5-HT(1B)-receptor knockout mice. Hypoxia increased 5-HT(1)-mediated contraction in pulmonary arteries from the wild-type mice and this was attenuated in the 5-HT(1B)-receptor knockout mice. In conclusion, the 5-HT(1B) receptor plays a role in the development of CHPHT. One possible mechanism may be via enhanced 5-HT(1) receptor-mediated contraction of the pulmonary arterial circulation.

Amphetamine-induced locomotor activation in 5-HT(1B) knockout mice: effects of injection route on acute and sensitized responses

Knockout mice lacking serotonin(1B) (5-hydroxytryptamine(1B); 5-HT(1B)) receptors (1BKO) exhibit increased sensitivity to the stimulant and reinforcing effects of indirect dopamine (DA) agonists and are more reactive to mild stressors such as handling and the injection procedures that commonly occur when using the intraperitoneal (i.p.) route of drug administration. Since the intravenous (i.v.) route of administration allows minimal handling and injection-induced stress, the present study was designed to evaluate the effect of the administration route on amphetamine-induced locomotor activation and behavioural sensitization in 1BKO mice. For this purpose, 1BKO and wild-type (WT) control mice were administered i.p. or i.v. amphetamine in a within-session design, which allows evaluation of a complete dose-response curve within a single session. The locomotor stimulant effects of i.p. (0.5-4.0 mg/kg) and i.v. (0.6-1.2 mg/kg) amphetamine were investigated both acutely and following repeated treatments (four treatments at 48 h intervals). The results showed that acute i.p. amphetamine injection induced a significant higher horizontal activity peak effect in 1BKO mice, while this difference was less profound after acute i.v. injection. However, repeated i.p. or i.v. administration of amphetamine induced significantly higher locomotion in 1BKO mice. We conclude that the stimulant effects of amphetamine can be influenced by the route of administration in a genotype-dependent manner, and that route of drug administration (and associated variables) should be considered an important factor in studies of psychostimulant action in knockout mice.

Male and female 5-HT(1B) receptor knockout mice have higher body weights than wildtypes

5-HT(1B) receptors have a regulatory role in serotonergic activity and influence feeding behavior and body weight. Because the absence of 5-HT(1B) receptors may cause changes in this regulation, body weight was measured in male and female 5-HT(1B) receptor knockout (5-HT(1B) KO) and wildtype (WT) mice from weaning until the age of 30 weeks. In both genders, 5-HT(1B) KO mice had a higher body weight than WT mice (17% and 9%, respectively). Body weight was significantly higher for males over the entire period and for females from Week 18 onwards. Absolute food and water consumption were related to body weight. However, relative to body weight, males consumed more than females. 5-HT(1B) KO males drank strikingly more water. Housing mice singly reduced food and water intake in males, but not in females. Plasma leptin levels and most organ weights did not differ between genotypes, indicating that higher body weight in 5-HT(1B) KO mice is not related to obesity. Relative to body weight, brains and adrenals were larger in females, while heart and liver were smaller. Kidneys were smaller in females, but larger in 5-HT(1B) KO mice, while lungs showed opposite effects. Spleen and testes were smaller in 5-HT(1B) KO mice. Although 5-HT(1B) KO males are more aggressive, testosterone levels were not different from WT mice. Basal corticosterone levels were similar in all groups and increased in response to mild stress, particularly in females. Lifelong absence of 5-HT(1B) receptors in mice resulted in clear phenotypic differences in body weights and food and water intake. Lacking this receptor increases body growth, without signs of obesity. A potential genetic background effect influencing this phenotype is discussed.

The molecular neurobiology of stress--evidence from genetic and epigenetic models

Knowledge of the genetic and molecular events underlying the neuroendocrine and behavioural sequelae of the response to stress has advanced rapidly over recent years. The response of an individual to a stressful experience is a polygenic trait, but also involves non-genetic sources of variance. Using a combination of top-down (quantitative trait locus [QTL] and microarray analysis) and bottom-up (gene targeting, transgenesis, antisense technology and random mutagenesis) strategies, we are beginning to dissect the molecular players in the mediation of the stress response. Given the wealth of the data obtained from mouse mutants, this review will primarily focus on the contributions made by transgenesis and knockout studies, but the relative contribution of QTL studies and microarray studies will also be briefly addressed. From these studies it is evident that several neuroendocrine and behavioural alterations induced by stress can be modelled in mouse mutants with alterations in hypothalamic-pituitary-adrenal axis activity or other, extrahypothalamic, neurotransmitter systems known to be involved in the stress response. The relative contribution of these models to understanding the stress response and their limitations will be discussed.