The Female Encounter Test: A Novel Method for Evaluating Reward-Seeking Behavior or Motivation in Mice

BACKGROUND

Reduced motivation is an important marker of psychiatric disorders, including depression. We describe the female encounter test, a novel method of evaluating reward-seeking behavior in mice.

METHODS

The test apparatus consists of three open chambers, formed with partitions that allow the animal to move freely from one chamber to another. A test male mouse is habituated in the apparatus, and subsequently a female and male mouse are introduced into a wire-mesh box in the left and right chamber, respectively. The time the test male mouse spends in the female or male area is measured for 10 min.

RESULTS

All six strains of mice tested showed a significant preference for female encounters. The preference was observed in 7-30-week-old mice. The preference was blocked by castration of the resident male test mouse, and was not affected by the phase of the menstrual cycle of the female intruder. The preference was impaired in mouse models of depression, including social isolation-reared, corticosterone-treated, and lipopolysaccharide-treated mice. The impairment was alleviated by fluvoxamine in isolation-reared and lipopolysaccharide-treated mice, and it was improved by the metabotropic glutamate 2/3 receptor antagonist LY341495 in corticosterone-treated mice. Encounter with a female, but not male, mouse increased c-Fos expression in the nucleus accumbens shell of test male mice. Furthermore, both the preference and encounter-induced increases in c-Fos expression were blocked by dopamine D1 and D2 receptor antagonists.

CONCLUSIONS

These findings indicate that motivation in adult male mice can be easily evaluated by quantitating female encounters.

Identification of the role of bone morphogenetic protein (BMP) and transforming growth factor-β (TGF-β) signaling in the trajectory of serotonergic differentiation in a rapid assay in mouse embryonic stem cells in vitro

The mechanism by which extracellular molecules control serotonergic cell fate remains elusive. Recently, we showed that noggin, which inactivates bone morphogenetic proteins (BMPs), induces serotonergic differentiation of mouse embryonic (ES) and induced pluripotent stem cells with coordinated gene expression along the serotonergic lineage. Here, we created a rapid assay for serotonergic induction by generating knock-in ES cells expressing a naturally secreted Gaussia luciferase driven by the enhancer of Pet-1/Fev, a landmark of serotonergic differentiation. Using these cells, we performed candidate-based screening and identified BMP type I receptor kinase inhibitors LDN-193189 and DMH1 as activators of luciferase. LDN-193189 induced ES cells to express the genes encoding Pet-1, tryptophan hydroxylase 2, and the serotonin transporter, and increased serotonin release without altering dopamine release. In contrast, TGF-β receptor inhibitor SB-431542 selectively inhibited serotonergic differentiation, without changing overall neuronal differentiation. LDN-193189 inhibited expression of the BMP signaling target gene Id, and induced the TGF-β target gene Lefty, whereas the opposite effect was observed with SB-431542. This study thus provides a new tool to investigate serotonergic differentiation and suggests that inhibition of BMP type I receptors and concomitant activation of TGF-β receptor signaling are implicated in serotonergic differentiation. Candidate-based screening for serotonergic induction using a rapid assay in mouse embryonic stem cells revealed that the bone morphogenetic protein (BMP) type I receptor kinase inhibitors selectively induce serotonergic differentiation, whereas the TGF-β receptor inhibitor SB-431542 inhibits the differentiation. These results suggest that inhibition of BMP type I receptors and concomitant activation of transforming growth factor-β (TGF-β) receptor signaling are involved in the early trajectory of serotonergic differentiation.

Behavioral characterization of mice overexpressing human dysbindin-1

Background

The dysbindin-1 gene (DTNBP1: dystrobrevin binding protein 1) is a promising schizophrenia susceptibility gene, known to localize almost exclusively to neurons in the brain, and participates in the regulation of neurotransmitter release, membrane-surface receptor expression, and synaptic plasticity. Sandy mice, with spontaneous Dtnbp1 deletion, display behavioral abnormalities relevant to symptoms of schizophrenia. However, it remains unknown if dysbindin-1 gain-of-function is beneficial or detrimental.

Results

To answer this question and gain further insight into the pathophysiology and therapeutic potential of dysbindin-1, we developed transgenic mice expressing human DTNBP1 (Dys1A-Tg) and analyzed their behavioral phenotypes. Dys1A-Tg mice were born viable in the expected Mendelian ratios, apparently normal and fertile. Primary screening of behavior and function showed a marginal change in limb grasping in Dys1A-Tg mice. In addition, Dys1A-Tg mice exhibited increased hyperlocomotion after methamphetamine injection. Transcriptomic analysis identified several up- and down-regulated genes, including the immediate-early genes Arc and Egr2, in the prefrontal cortex of Dys1A-Tg mice.

Conclusions

The present findings in Dys1A-Tg mice support the role of dysbindin-1 in psychiatric disorders. The fact that either overexpression (Dys1A-Tg) or underexpression (Sandy) of dysbindin-1 leads to behavioral alterations in mice highlights the functional importance of dysbindin-1 in vivo.

[Neurochemical basis for social encounter-induced hyperactivity in post-weaning isolation-reared mice]

Rearing rodents in social isolation from post-weaning causes abnormal behaviors in adulthood, such as hyper-locomotion, aggression, cognitive impairments, and depression- and anxiety-like behaviors. This social isolation is widely used as a model to study the effects of adverse early-life experiences on behavior and the neural mechanisms associated with neuropsychological development. Previous studies have shown abnormalities of dendritic spine density, synaptic protein levels and amine metabolism in the prefrontal cortex and hippocampus of isolation-reared animals, but the neurochemical basis for induction of abnormal behaviors is not known. We have established a novel methodology for assessing social interaction, focusing on the psychological stressor responsible for induction of abnormal behaviors as a transient environmental factor. This review summarizes the effect of a social encounter with an unfamiliar conspecific on behavior and neurochemistry in isolation-reared mice. The current analysis using the encounter response will provide new strategies to clarify the pathophysiology of psychiatric disorders including schizophrenia, depression and drug dependence.

Synergistic effect of 5-HT1A and σ1 receptor activation on prefrontal dopaminergic transmission under circulating steroid deficiency

Serotonin (5-HT)1A and σ1 receptors have been implicated in psychiatric disorders. We previously found that combined 5-HT reuptake inhibition and σ1 receptor activation has a synergistic effect on prefrontal dopaminergic transmission in adrenalectomized/castrated mice lacking circulating steroid hormones. In the present study, we examined the mechanisms underlying this neurochemical synergism. Systemic administration of fluvoxamine, a selective 5-HT reuptake inhibitor with agonistic activity towards the σ1 receptor, increased prefrontal dopamine (DA) levels, and adrenalectomy/castration potentiated this fluvoxamine-induced increase in DA. This enhancement of DA release was blocked by WAY100635 (a 5-HT1A receptor antagonist), but not by ritanserin (a 5-HT2 receptor antagonist), azasetron (a 5-HT3 receptor antagonist) or SB269970 (a 5-HT7 receptor antagonist). Individually, osemozotan (a 5-HT1A receptor agonist) and (+)-SKF-10,047 (a σ1 receptor agonist) did not alter prefrontal monoamine levels in adrenalectomized/castrated and sham-operated mice differentially. In contrast, co-administration of these drugs increased prefrontal DA levels to a greater extent in adrenalectomized/castrated mice than in sham-operated animals. Furthermore, co-administration of osemozotan and (+)-SKF-10,047 increased expression of the neuronal activity marker c-Fos in the ventral tegmental area of adrenalectomized/castrated mice, but not in sham-operated animals. These findings suggest that combined activation of 5-HT1A and σ1 receptors has a synergistic effect on prefrontal dopaminergic transmission under circulating steroid deficiency, and that this interaction may play an important role in the regulation of the prefrontal DA system.

Isolation rearing reduces mechanical allodynia in a mouse model of chronic inflammatory pain

Social isolation rearing in mice after weaning reduces pain sensitivity to acute pain, and this hypoalgesia is mediated by the descending serotonergic pain inhibitory system in which the spinal serotonin (5-HT)1A receptor is involved. However, it is not known whether isolation rearing affects pain sensitivity to neuropathic or inflammatory chronic pain. In this study, we examined the effects of isolation rearing on chronic pain induced by Freund's complete adjuvant (FCA) and partial sciatic nerve ligation using the von Frey test (to assess mechanical allodynia) and the plantar test (to assess thermal hyperalgesia). In the FCA model, isolation rearing reduced mechanical allodynia, but not thermal hyperalgesia. In contrast, isolation rearing had no effect on allodynia or hyperalgesia in the sciatic nerve ligation model. The isolation rearing-induced inhibition of allodynia was alleviated by intrathecal injection of WAY100635, a selective 5-HT1A receptor antagonist. FCA increased 5-HT turnover and decreased 5-HT1A receptor expression in the spinal cord of group-reared mice, while it did not have these effects in isolation-reared mice. These results suggest that FCA suppresses the serotonergic pain inhibitory system selectively in group-reared mice. Moreover, systemic administration of osemozotan, a selective 5-HT1A receptor agonist, inhibited FCA-induced mechanical allodynia in group-reared mice, and this effect of the drug was suppressed by intrathecal injection of WAY100635. Collectively, these findings suggest that isolation rearing selectively reduces FCA-induced mechanical allodynia in mice and that this effect is mediated by the activation of spinal 5-HT1A receptors.

Role of social encounter-induced activation of prefrontal serotonergic systems in the abnormal behaviors of isolation-reared mice

Isolation-reared male rodents show abnormal behaviors such as hyperlocomotion, aggressive behaviors, deficits of prepulse inhibition, and depression- and anxiety-like behaviors, but the neurochemical mechanism for the effects of psychological stress in these animals is not fully understood. This study examined the effects of social interactions between isolation-reared mice and intruder mice on brain monoaminergic systems. A cage was divided into two compartments by a mesh partition to prevent direct physical interactions. The 20-min encounter with an intruder elicited a restless and hyperexcitable state (hyperactivity) in male, but not in female, isolation-reared mice, whereas encounters with a sleeping intruder or a novel object did not. Although the encounter did not affect prefrontal neuronal-activity-marker c-Fos expression, dopamine (DA) levels, or serotonin (5-HT) levels in male group-reared mice or female isolation-reared mice, it increased prefrontal c-Fos expression, DA levels, and 5-HT levels in male isolation-reared mice. Furthermore, encounter-induced increases in c-Fos expression in the dorsal raphe nucleus and ventral tegmental area, but not in the nucleus accumbens shell, were much greater in isolation-reared than group-reared male mice. A 5-HT1A receptor agonist, a metabotropic glutamate 2/3 receptor agonist, and a gamma-aminobutyric acid A receptor agonist attenuated isolation-induced aggressive behaviors and encounter-induced hyperactivity, c-Fos expression in the prefrontal cortex and dorsal raphe nucleus, and increases in prefrontal 5-HT levels. These findings suggest that the prefrontal DA and 5-HT systems are activated by encounter stimulation in male isolation-reared mice, and the encounter-induced activation of 5-HT system triggers the induction of some abnormal behaviors in male isolation-reared mice. Furthermore, this study implies that the encounter stimulation-induced signal has a pharmacological significance.

Involvement of spinal 5-HT1A receptors in isolation rearing-induced hypoalgesia in mice

RATIONALE

Isolation rearing in rodents causes not only abnormal behaviors which resemble the clinical symptoms of schizophrenia but also hypoalgesia in thermal nociception models. However, the mechanism of the hypoalgesia is not known.

OBJECTIVES

The present study investigated the effect of isolation rearing on acute pain and the descending pain inhibitory pathways in mice.

RESULTS

Rearing in isolation for 6 weeks from post-weaning reduced pain sensitivity in the hot plate test and acetic acid-induced writhing test. Isolation rearing also reduced the intraplantar capsaicin-induced licking behavior. Capsaicin increased c-Fos expression, a neuronal activity marker, in the spinal cord and primary somatosensory cortex both in group- and isolation-reared mice, but this effect did not differ between groups. On the other hand, c-Fos expression in the anterior cingulate cortex, periaqueductal gray matter, and rostral ventromedial medulla, but not in the spinal cord or somatosensory cortex, was enhanced by isolation rearing. Systemic administration of WAY100635 (serotonin (5-HT)1A receptor antagonist), but not of ketanserin (5-HT2 receptor antagonist), prazosin (α1-adrenoceptor antagonist), or yohimbine (α2-adrenoceptor antagonist), attenuated isolation rearing-induced hypoalgesia in capsaicin-induced licking behavior. Attenuation of isolation rearing-induced hypoalgesia was also observed following the intrathecal injection of WAY100635. Naloxone, an opioid receptor antagonist, did not affect the hypoalgesia in isolation-reared mice.

CONCLUSIONS

These findings suggest that isolation rearing causes hypoalgesia in mouse models of acute pain and imply that the spinal 5-HT1A receptor activation probably through descending serotonergic inhibitory pathway is involved in isolation rearing-induced hypoalgesia.

Effect of overexpression of the brain-specific Na(+)/Ca(2+) exchanger splice variant NCX1.5 on NO cytotoxicity in HEK293 cells

Nitric oxide (NO) induces cytotoxicity in neuronal and glial cells via activation of the Na(+)/Ca(2+) exchanger (NCX). This study examined the role of the predominant brain-specific NCX splice variant NCX1.5 in NO-induced cytotoxicity in the HEK293 cell expression system. Cells were transfected with the plasmid construct pcDNA3.1/V5-His containing full-length rat NCX1.5 cDNA. There was no difference in the cytotoxic effects of the NO donors sodium nitroprusside and S-nitroso-N-acetylpenicillamine between control and transfected cells. These results suggest that NO cytotoxicity is not dependent on NCX1.5.

Effects of serotonin-norepinephrine reuptake inhibitors on locomotion and prefrontal monoamine release in spontaneously hypertensive rats

Catecholamine neurotransmission in the prefrontal cortex plays a key role in the therapeutic actions of drugs for attention-deficit/hyperactivity disorder (ADHD). Recent clinical studies show that several serotonin-norepinephrine reuptake inhibitors have potential for treating ADHD. In this study, we examined the effects of acute treatment with serotonin-norepinephrine reuptake inhibitors on locomotion and the extracellular levels of monoamines in the prefrontal cortex in spontaneously hypertensive rats (SHR), an animal model of ADHD. Adolescent male SHR exhibited greater horizontal locomotion in an open-field test than male WKY control rats. Psychostimulant methylphenidate (0.3 and 1 mg/kg), the selective norepinephrine reuptake inhibitor atomoxetine (1 and 3 mg/kg), and serotonin-norepinephrine reuptake inhibitors duloxetine (10 mg/kg), venlafaxine (10 and 30 mg/kg) and milnacipran (30 mg/kg) reduced the horizontal activity in SHR, but did not affect in WKY rats. The selective norepinephrine reuptake inhibitor reboxetine (10 mg/kg) and the tricyclic antidepressant desipramine (10 and 30 mg/kg) also reduced the horizontal activity in SHR, whereas the selective serotonin reuptake inhibitor citalopram (30 mg/kg) did not. Microdialysis studies showed that atomoxetine, methylphenidate, duloxetine, venlafaxine, milnacipran, and reboxetine increased the extracellular levels of norepinephrine and dopamine in the prefrontal cortex in SHR. Citalopram did not affect norepinephrine and dopamine levels in the prefrontal cortex, although it increased the serotonin levels. Neither duloxetine nor venlafaxine increased the dopamine levels in the striatum. These findings suggest that serotonin-norepinephrine reuptake inhibitors, similar to methylphenidate and atomoxetine, have potential for ameliorating motor abnormality in the SHR model.

Metabotropic glutamate 2/3 receptor antagonists improve behavioral and prefrontal dopaminergic alterations in the chronic corticosterone-induced depression model in mice

Metabotropic glutamate 2/3 (mGlu2/3) receptor antagonists have an antidepressant-like effect, but the exact mechanism still remains unclear. This study examined the effects of mGlu2/3 receptor antagonists in chronic corticosterone-treated mice which could be used as an animal model of depression. In the forced swim test, the mGlu2/3 receptor antagonists MGS0039 (1.0 mg/kg, i.p.) and LY341495 (0.3 mg/kg, i.p) significantly reduced the increased immobility time of mice pretreated with corticosterone (20 mg/kg, s.c.) for 21 days, while desipramine (30 mg/kg, i.p.) and fluoxetine (30 mg/kg, i.p.) did not. The antidepressant-like effect of LY341495 was not blocked by the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor antagonist NBQX (10 mg/kg, i.p.). Systemic administration of LY341495 did not affect basal release of glutamate, dopamine or serotonin in the prefrontal cortex of the control or chronic corticosterone-treated mice. Chronic corticosterone markedly enhanced high K(+)-induced release of dopamine, but not serotonin or glutamate, in the prefrontal cortex. This neurochemical change was blocked by systemic administration of MGS0039 and LY341495, but not desipramine or fluoxetine. These results suggest that chronic corticosterone-treated mice could be used as an animal model of treatment-resistant depression. This study also suggests that the prefrontal dopaminergic system is involved in the antidepressant-like effect of mGlu2/3 receptor antagonists in the chronic corticosterone-induced depression model.

mGlu2/3 and mGlu5 receptors: potential targets for novel antidepressants

Major depressive disorder is among the most prevalent forms of mental illness. All currently available antidepressant medications have stemmed from study of the mechanisms of serendipitously discovered drugs, and only 30-50% of patients exhibit remission and frequently at least 3-4 weeks are required for manifestation of significant therapeutic effects. To overcome these drawbacks, discovering novel neuronal mechanisms of pathophysiology of depression as well as more effective treatments are necessary. This review focuses on the metabotropic glutamate (mGlu) receptors and their potential for drug targets for the treatment of depression. In particular, accumulating evidence has indicated the potential importance and usefulness of agents acting on mGlu2/3 and mGlu5 receptors. Preclinical and clinical evidence of mGlu2/3 receptor ligands and mGlu5 receptor antagonists are described. Moreover, their potential in clinic will be discussed in the context of neuronal mechanisms of ketamine, an agent recently demonstrated a robust effect for patients with treatment-resistant depression. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Neuronal nitric oxide synthase inhibition attenuates the development of L-DOPA-induced dyskinesia in hemi-Parkinsonian rats

Long-term treatment with the dopamine precursor levodopa (l-DOPA) frequently induces dyskinesia in Parkinson's disease patients, which is a major complication of this therapy. Previous studies using animal models show that repeated administration of l-DOPA results in alterations of some signaling molecules, including ΔFosB, phospho-DARPP32 and phosoho-GluA1 (also referred to as GluR1 or GluR-A) AMPA receptor subunits. Moreover, an in vivo microdialysis study showed that l-DOPA increases nitric oxide (NO) production in the striatum. However, it is not known whether NO is involved in the development of dyskinesia. The present study examined the effects of NOS inhibitors on the development of l-DOPA-induced dyskinesia in the rats. Dyskinesia symptoms were triggered by daily administration of l-DOPA for 3-4weeks in unilateral 6-hydroxydopamine lesioned rats. Repeated treatments, 30min prior l-DOPA administration, of the nonselective NOS inhibitor, N(G)-nitro-l-arginine methyl ester, and the nNOS inhibitor 7-nitroindazole, but not the inducible NOS inhibitor aminoguanidine, attenuated the development of l-DOPA-induced dyskinesia. In agreement with the behavioral analysis, 7-nitroindazole reduced the l-DOPA-induced increases in ΔFosB, phospho-DARPP32 and phospho-GluA1 AMPA receptor subunit levels in the striatum of 6-hydroxydopamine-lesioned rats. Furthermore, aminoguanidine did not affect ΔFosB or phospho-GluA1 AMPA receptor subunit levels. These findings suggest that nNOS-derived NO is involved in the development of l-DOPA-induced dyskinesia through a post-synaptic mechanism.

[Pharmacological profiles of galantamine: the involvement of muscarinic receptor]

Galantamine, currently used in Japan for the treatment of Alzheimer's disease, may improve cognitive dysfunction and psychiatric illness in schizophrenia, major depression, bipolar disorder and alcohol abuse. It is a rather weak acetylcholinesterase inhibitor in vitro, but has additional allosteric potentiating effects at nicotinic receptors. We have found that galantamine increased acetylcholine levels in the brain. This suggests that the pharmacological effects of galantamine are mediated by not only nicotinic receptors but also muscarinic receptors. We found that galantamine, but not donepezil, improved prepulse inhibition (PPI) deficits in isolation-reared mice, although both drugs improved PPI deficits in an apomorphine model. The difference in the effects on PPI deficits between galantamine and donepezil may be explained by the effects on muscarinic receptors. This review summarizes the pharmacological profiles of galantamine, focusing on the importance of muscarinic receptors.