Neuritogenic steroid glycosides from crown-of-thorns starfish: Possible involvement of p38 mitogen-activated protein kinase and attenuation of cognitive impairment in senescence-accelerated mice (SAMP8) by peripheral administration.

Novel steroid glycosides, acanthasterosides A1, B1, and B3, have been isolated from the crown-of-thorns starfish Acanthaster planci. Acanthasterosides B1 and B3 having two separated xyloses induced neurite outgrowth as like as nerve growth factor (NGF) in the rat pheochromocytoma cell line PC12, whereas acanthasteroside A1, having one xylose, did not induce neurite outgrowth. The acanthasteroside B3 induced neuritogenesis via the significant activation of p38 mitogen-activated protein kinase after the activation of the small G-protein Cdc42 rather than via Ras-MEK-ERK pathway that is predominantly activated by NGF. Following subcutaneous administration, acanthasteroside B3 attenuated cognitive impairment of senescence-accelerated mice (SAMP8) in two different cognitive tests. Liquid chromatography-mass spectrometry-assisted quantitative analysis demonstrated that acanthasteroside B3 could be transported into the brain via the circulatory system in mice. Thus, acanthasteroside B3 (and possibly B1) are a novel class of potential drug candidates for neurodegenerative diseases.

Multiple nicotinic acetylcholine receptor subtypes regulate social or cognitive behaviors in mice repeatedly administered phencyclidine.

Habitual smoking in patients with schizophrenia (SCZ) is considered to improve their own psychoses or to develop a vulnerability to psychological dependence on (-)-nicotine ([-]-NIC) by stimulating nicotinic acetylcholine receptors (nAChRs) in the central nervous system. In the present study, we investigated whether habitual smoking is due to get therapeutic effect or to psychological dependence and which nAChR subunits are associated with them using mice that were repeatedly administered phencyclidine (PCP: 10 mg/kg/day, s.c. for 14 days) as SCZ-like model mice. Mice that were repeatedly administered PCP showed impairments in social or cognitive behaviors; decreased expression of α7 and/or α4 nAChR subunits in the prefrontal cortex (PFC); and increased expression of α7, α4, and ß2 nAChR subunits in the nucleus accumbens (NAc). These changes were attenuated by repeated administration of (-)-NIC. The attenuating effects on behavioral impairments were prevented by a selective α7 nAChR antagonist and a selective α4ß2 nAChR antagonist. At non- or weak effective dose by themselves, co-administration of (-)-NIC (0.03 mg/kg) and risperidone (0.03 mg/kg) showed synergistic effects on behavioral impairments in PCP-administered mice. Repeated (-)-NIC administration did not affect the performance of conditioned place preference, while it showed behavioral sensitization to (-)-NIC in the PCP-administered mice. Repeated (-)-NIC administration did not affect the performance of conditioned place preference, while it showed behavioral sensitization to (-)-NIC and attenuating effect on haloperidol-induced catalepsy in the PCP-administered mice. Our findings suggest that habitual smoking in SCZ might be attributed to get therapeutic and reduce side effects mediated by α7 and α4ß2 nAChR activation by (-)-NIC.

Involvement of nicotinic acetylcholine receptors in behavioral abnormalities and psychological dependence in schizophrenia-like model mice.

The smoking incentive in patients with schizophrenia (SCZ) depends on stimulation of nicotinic acetylcholine receptors (nAChRs) in the central nervous system. To detect potential predictor genes for nicotine responses in SCZ, we explored common factor using research data in human and animal samples. In lymphoblastoid cell lines from SCZ, the mRNA expression level of α7 nAChR subunit was decreased. In SCZ-like model mice of phencyclidine (PCP; 10 mg/kg/day, subcutaneously for 14 days)-administered mice, the mRNA expression level of α7 nAChR subunit and protein expression level of α7 or α4 nAChR subunit were significantly decreased in the prefrontal cortex during PCP withdrawal. Protein, but not mRNA, expression levels of α7, α4, and ß2 nAChR subunits were significantly increased in the nucleus accumbens. Acute (-)-nicotine [(-)-NIC: 0.3 mg/kg, s.c.] treatment attenuated impairments of social behaviors and visual recognition memory. These effects of (-)-NIC were completely blocked by both methyllycaconitine, a selective α7 nAChR antagonist, and dihydro-ß-erythroidine (DHßE), a selective α4ß2 nAChR antagonist. (-)-NIC did not induce conditioned place preference, but enhanced sensitivity to methamphetamine-induced hyperactivity. These findings suggest that α7 nAChR is associated with development of disease and is implicated in the therapeutic effect of nicotine in SCZ. The smoking incentive in SCZ might be attributed to treat their own symptoms, rather than a result of (-)-NIC dependence, by stimulating α7 and/or α4ß2 nAChRs.

Galantamine improves enhanced impulsivity, impairments of attention and long-term potentiation induced by prenatal nicotine exposure to mice.

Prenatal nicotine exposure (PNE) causes behavioral abnormalities in offspring, such as an enhancement of impulsivity and decrease in attention at adolescence. Here we examined the effects of galantamine (GAL) on the behavioral and electrophysiological changes induced by PNE in mice. Pregnant C57BL/6J mice were exposed to nicotine (0.2 mg/mL) dissolved in sweetened (2% saccharin) drinking water during gestational day 14 and perinatal day 0 (P0). At the ages of postnatal days 42-49 (P42-P49), female offspring displayed impulsivity in the cliff avoidance test and impairment of visual attention in the object-based attention test. Decrease of long-term potentiation (LTP) and extracellular glutamate levels were observed in the prefrontal cortex of PNE mice. Systemic treatment with GAL (1 mg/kg, s.c.), an allosteric potentiating ligand for the nicotinic acetylcholine receptor (nAChR) and a weak cholinesterase inhibitor, attenuated the enhancement of impulsivity and impairment of attention induced by PNE in mice. Further, GAL reversed the impairment of LTP induced by PNE in the prefrontal cortex of mice, although it failed to attenuate the decrease of extracellular glutamate levels. The effects of GAL were blocked by an α 7 nAChR antagonist, methyllycaconitine (1 mg/kg, i.p.). These results suggest that PNE during cortex development affects nicotinic cholinergic-dependent plasticity and formation of impulsivity and attention. Furthermore, GAL could be a useful drug for cognitive impairments-related to attention deficit hyperactivity disorder.

Prenatal nicotine exposure decreases the release of dopamine in the medial frontal cortex and induces atomoxetine-responsive neurobehavioral deficits in mice.

Increased risk of attention-deficit/hyperactivity disorder (AD/HD) is partly associated with the early developmental exposure to nicotine in tobacco smoke. Emerging reports link tobacco smoke exposure or prenatal nicotine exposure (PNE) with AD/HD-like behaviors in rodent models. We have previously reported that PNE induces cognitive behavioral deficits in offspring and decreases the contents of dopamine (DA) and its turnover in the prefrontal cortex (PFC) of offspring It is well known that the dysfunction of DAergic system in the brain is one of the core factors in the pathophysiology of AD/HD. Therefore, we examined whether the effects of PNE on the DAergic system underlie the AD/HD-related behavioral changes in mouse offspring. PNE reduced the release of DA in the medial PFC (mPFC) in mouse offspring. PNE reduced the number of tyrosine hydroxylase (TH)-positive varicosities in the mPFC and in the core as well as the shell of nucleus accumbens, but not in the striatum. PNE also induced behavioral deficits in cliff avoidance, object-based attention, and sensorimotor gating in offspring. These behavioral deficits were attenuated by acute treatment with atomoxetine (3 mg/kg, s.c.) or partially attenuated by acute treatment with MPH (1 mg/kg, s.c.). Taken together, our findings support the notion that PNE induces neurobehavioral abnormalities in mouse offspring by disrupting the DAergic system and improve our understanding about the incidence of AD/HD in children whose mothers were exposed to nicotine during their pregnancy.

Prenatal phencyclidine treatment induces behavioral deficits through impairment of GABAergic interneurons in the prefrontal cortex.

RATIONALE: We previously reported that prenatal treatment with phencyclidine (PCP) induces glutamatergic dysfunction in the prefrontal cortex (PFC), leading to schizophrenia-like behavioral deficits in adult mice. However, little is known about the prenatal effect of PCP treatment on other types of neurons. OBJECTIVES: We focused on γ-aminobutyric acid (GABA)-ergic interneurons and evaluated the effect of prenatal PCP exposure on the neurodevelopment of GABAergic interneurons in the PFC. METHODS: PCP was administered at the dose of 10 mg/kg/day to pregnant dams from embryonic day 6.5 to 18.5. After the pups were reared to adult, we analyzed their GABAergic system in the PFC using immunohistological, biochemical, and behavioral analyses in adulthood. RESULTS: The prenatal PCP treatment decreased the density of parvalbumin-positive cells and reduced the expression level of glutamic acid decarboxylase 67 (GAD67) and GABA content of the PFC in adults. Additionally, prenatal PCP treatment induced behavioral deficits in adult mice, such as hypersensitivity to PCP and prepulse inhibition (PPI) deficits. These behavioral deficits were ameliorated by pretreatment with the GABAB receptor agonist baclofen. Furthermore, the density of c-Fos-positive cells was decreased after the PPI test in the PFC of mice treated with PCP prenatally, and this effect was ameliorated by pretreatment with baclofen. CONCLUSIONS: These findings suggest that prenatal treatment with PCP induced GABAergic dysfunction in the PFC, which caused behavioral deficits.

Prenatal Nicotine Exposure Impairs the Proliferation of Neuronal Progenitors, Leading to Fewer Glutamatergic Neurons in the Medial Prefrontal Cortex.

Cigarette smoking during pregnancy is associated with various disabilities in the offspring such as attention deficit/hyperactivity disorder, learning disabilities, and persistent anxiety. We have reported that nicotine exposure in female mice during pregnancy, in particular from embryonic day 14 (E14) to postnatal day 0 (P0), induces long-lasting behavioral deficits in offspring. However, the mechanism by which prenatal nicotine exposure (PNE) affects neurodevelopment, resulting in behavioral deficits, has remained unclear. Here, we report that PNE disrupted the proliferation of neuronal progenitors, leading to a decrease in the progenitor pool in the ventricular and subventricular zones. In addition, using a cumulative 5-bromo-2'-deoxyuridine labeling assay, we evaluated the rate of cell cycle progression causing the impairment of neuronal progenitor proliferation, and uncovered anomalous cell cycle kinetics in mice with PNE. Accordingly, the density of glutamatergic neurons in the medial prefrontal cortex (medial PFC) was reduced, implying glutamatergic dysregulation. Mice with PNE exhibited behavioral impairments in attentional function and behavioral flexibility in adulthood, and the deficits were ameliorated by microinjection of D-cycloserine into the PFC. Collectively, our findings suggest that PNE affects the proliferation and maturation of progenitor cells to glutamatergic neuron during neurodevelopment in the medial PFC, which may be associated with cognitive deficits in the offspring.

Evaluation of cognitive behaviors in young offspring of C57BL/6J mice after gestational nicotine exposure during different time-windows.

Gestational nicotine exposure is associated with cognitive abnormalities in young offspring. However, practical strategies for prevention or treatment of impaired cognitive behaviors of offspring are not available due to the lack of systematic investigation of underlying mechanism. Therefore, this study aimed at examining the effects of gestational and/or perinatal nicotine exposure (GPNE) on cognitive behaviors in offspring of C57BL/6J mice to provide systematic behavioral data. Pregnant mice were exposed to nicotine via sweetened drinking water during six time-windows, including gestational day 0 to day 13 (G0-G13), G14-postnatal day 0 (P0), G0-P0, G14-P7, G0-P7, and P0-P7. During P42-P56 days, both male and female offspring were given a battery of behavioral tests. Depending on the time of exposure, GPNE impaired working memory, object-based attention, and prepulse inhibition in male and female offspring to different extents. Nicotine exposure during G14-P0 also decreased norepinephrine turnover in the prefrontal cortex on P28 and P56. Overall results indicate that nicotine exposure during any time-windows of development impairs cognitive behaviors in offspring, and suggest that certain time-windows, e.g., G14-P0, should be selected for further studies on the underlying neurochemical or molecular mechanisms.

Evaluation of emotional behaviors in young offspring of C57BL/6J mice after gestational and/or perinatal exposure to nicotine in six different time-windows.

Nicotine replacement treatments are being alternatively applied as an aid to smoking cessation during pregnancy. However, the effects of nicotine exposed at the prenatal stage on the emotional behaviors in offspring are not well understood due to the lack of systematic investigations. The current study has therefore initially aimed to evaluate emotional behaviors in young mouse offspring (postnatal day 28-36) which experienced gestational and/or perinatal nicotine exposure (GPNE) in six different time-windows. Pregnant C57BL/6J mice were exposed to nicotine via sweetened (2% sucrose) drinking water during 6 different time-windows including gestational day 0-day 13 (G0-G13), G14-perinatal day 0 (P0), G0-P0, G14-P7, G0-P7, and P0-P7. During P28-P36 days, both male and female offspring were given a battery of behavioral tests including light and dark box test, marble burying behavior test, novelty-suppressed feeding test, sociability and social novelty preference test, social avoidance tube test, and elevated plus maze test. GPNE during G0-P0, G14-P0, G14-P7, and G0-P7 induced abnormal behaviors in male and female offspring to different extent. Results indicated that nicotine at any time points of gestational and/or perinatal period impairs emotional behaviors in offspring, and suggested certain time-windows for further neurochemical or molecular studies in relation with GPNE-induced emotional abnormalities.

MAGE-D1 regulates expression of depression-like behavior through serotonin transporter ubiquitylation.

The ubiquitin-proteasome system (UPS) controls the stability of most cellular proteins. The polymorphism of UPS-related genes is associated with major depression disorder, but less is known about the molecule that plays a role in depression by modulating the UPS. Melanoma antigen gene-D1 (MAGE-D1) interacts with RING E3 ubiquitin ligase and is implicated in protein degradation. MAGE-D1 may thus play an important role in the CNS via ubiquitylation. Here, we clarified a novel role of MAGE-D1 in emotional functions, namely its modulation of ubiquitylation to the serotonin transporter (SERT). The MAGE-D1 knock-out and knockdown by small interfering RNA (siRNA) in the prefrontal cortex showed depression-like behavior, such as a decrease in exploratory behavior in both the home cage and novel apparatus, a decrease in social interaction, increased immobility time during forced swimming and tail suspension, and a decrease in sucrose preference without any anxiety, or cognitive or motor dysfunction. Acute and chronic (28 d) administration of sertraline (10 mg/kg) and imipramine (20 mg/kg) reversed all or part of depression-like behavior in knock-out mice. In these mice, the serotonergic function in the prefrontal cortex and hippocampus was hypoactive, accompanied by hyperexpression of SERT attributable to a decrease in ubiquitylation. Furthermore, MAGE-D1 binds to SERT via the necdin homology domain. MAGE-D1 overexpression in cells resulted in a decrease in serotonin uptake activity and the protein level of SERT but an increase in ubiquitylated SERT. Together, the present findings suggest a novel role for MAGE-D1 in depressive behaviors: modulating SERT ubiquitylation.

Intake of fermented soybean (natto) increased locomotor activity in mice.

We fed mice food granules containing fermented soybean (natto in Japanese) powder (hereafter "natto granules") for 14 d to investigate whether natto granules had any effects on mouse behavior. We noted an enhancement of locomotor activity in natto-granule-fed mice compared to control and soybean-pellet-fed mice. This enhanced locomotor activity was blocked by a low dose of haloperidol (1 microg/kg i.p.), a dopamine receptor antagonist, but not by methysergide, a serotonin 5-HT(1/2) receptor antagonist. The results suggest that the enhanced locomotor activity induced by continuous intake of natto granules in mice is sensitive to haloperidol.

A neuroactive steroid, dehydroepiandrosterone sulfate, prevents the development of morphine dependence and tolerance via c-fos expression linked to the extracellular signal-regulated protein kinase.

In the present study, we investigated how the neurosteroid, dehydroepiandrosterone sulfate (DHEAS) affects the development of morphine dependence and tolerance in mice. Mice administered morphine (10 mg/kg) twice a day for 5 days developed tolerance to the analgesic effect and dependence as shown by a severe withdrawal syndrome induced by naloxone. Co-administration of DHEAS (10 mg/kg) with morphine significantly inhibited the development, but not the expression, of tolerance to morphine-induced analgesia and the naloxone-precipitated withdrawal. The expression of c-fos mRNA was observed in the frontal cortex and thalamus of mice showing signs of naloxone-precipitated withdrawal, while the expression of c-fos mRNA was significantly diminished by co-administration of DHEAS with morphine. On the naloxone-precipitated withdrawal, mice showed a significant elevation of cyclic AMP (cAMP) levels in the thalamus, whereas chronic administration of DHEAS with morphine did not affect the increase in cAMP. Interestingly, repeated co-administration of DHEAS with morphine prevented the withdrawal-induced phosphorylation of extracellular signal-regulated protein kinase (ERK) 2 in the frontal cortex. These results showed that DHEAS prevented the development of morphine tolerance and dependence and suggested that the attenuating effects of DHEAS might result from the regulation of c-fos mRNA expression, which is possibly involved the signaling activation of ERK, but not of cAMP pathway.

Molecular mechanisms in dizocilpine-induced attenuation of development of morphine dependence: an association with cortical Ca2+/calmodulin-dependent signal cascade.

We investigated how dizocilpine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, affects the development of morphine dependence in mice. Co-administration of dizocilpine (0.25 mg/kg) and morphine (10 mg/kg) for 5 days attenuated the development of tolerance to the antinociceptive effects of morphine. The withdrawal manifestation induced by the naloxone-challenge (5 mg/kg) was significantly reduced in mice that were treated with a combination of dizocilpine and morphine, compared to the mice treated with morphine and saline. The present study revealed a significant increase in c-Fos protein expression in the cortex and thalamus of mice showing naloxone-precipitated withdrawal syndrome. The combination of dizocilpine and morphine prevented the increase of c-Fos protein expression in the cortex and thalamus. Interestingly, repeated co-administration of dizocilpine and morphine prevented the withdrawal-induced phosphorylation of Ca2+/calmodulin kinase II (p-CaMK II) in the cortex, but not in the thalamus. Acute dizocilpine treatment prior to the naloxone-challenge and repeated treatment with dizocilpine alone had no effect on analgesia, withdrawal manifestations, p-CaMK II levels or c-Fos protein levels. These results showed that co-administration of dizocilpine and morphine prevented the development of morphine tolerance and dependence and suggested that the preventive effect of dizocilpine results from the regulation of c-Fos protein expression, which is possibly involved in the activation of the Ca2+/calmodulin-dependent signal cascade in the cortex.

Role of tumor necrosis factor-alpha in methamphetamine-induced drug dependence and neurotoxicity.

Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is now emerging as an important modulator of the function of the CNS. Methamphetamine (METH) is a widely abused psychostimulant that causes euphoria, hyperactivity, and drug dependence. High doses of METH cause long-term neurotoxicity in dopaminergic neurons. In this study, we investigated a role of TNF-alpha in METH-induced dependence and neurotoxicity. Repeated treatment with METH (2 mg/kg for 5 d) in rats induced a significant increase in TNF-alpha mRNA and protein expression in the brain. Exogenous TNF-alpha (1-4 microg) blocked locomotor-stimulating and rewarding effects of METH, as well as METH (4 mg/kg; four times at 2 hr intervals)-induced dopaminergic neurotoxicity in mice. To examine a role of endogenous TNF-alpha in behavioral and neurochemical effects of METH, we used mice with targeted deletions of the TNF-alpha gene. TNF-alpha-(-/-) mice showed enhanced responses to the locomotor-sensitizing, rewarding, and neurotoxic effects of METH compared with wild-type mice. We also examined the role of TNF-alpha in METH-induced dopamine (DA) release and uptake in vitro and in vivo in C57BL/6 mice. Exogenous TNF-alpha (4 microg) attenuated the METH-induced increase in extracellular striatal DA in vivo and potentiated striatal DA uptake into synaptosomes in vitro and in vivo. Furthermore, TNF-alpha activated vesicular DA uptake by itself and diminished the METH-induced decrease in vesicular DA uptake. Our findings suggest that TNF-alpha plays a neuroprotective role in METH-induced drug dependence and neurotoxicity by activating plasmalemmal and vesicular DA transporter as well as inhibiting METH-induced increase in extracellular DA levels.