Masami Nakai

Neural mechanisms underlying motor dysfunction as detected by the tail suspension test in MPTP-treated C57BL/6 mice.

Contradictory data on behavioral changes in MPTP-treated C57BL/6 mice have been reported, even though the toxin-treated mice have been widely used for non-clinical studies as an in vivo model of Parkinsons disease (PD). We found that the duration of immobility in the tail suspension test (TST) was significantly increased in MPTP-treated C57BL/6 mice as compared with control mice without a significant change in the locomotor activity (LA). Dopamine (DA) contents and protein levels of tyrosine hydroxylase and dopamine transporter in the striatum were profoundly decreased in the toxin-treated mice. These behavioral and neurobiochemical changes were almost completely inhibited by a pretreatment with deprenyl, a monoamine oxidase-B inhibitor. The stimulation of dopaminergic neurotransmission induced by L-dopa or a dopamine D2 receptor agonist ameliorated the increase in immobility time. Threshold level of striatal DA that produced the increase in immobility time in MPTP-treated mice was estimated to be between 11 and 27% of control level. We concluded that the increase in immobility time in the TST was induced by the nigrostriatal dopaminergic degeneration and was thought to be a consequence of motor dysfunction in this mouse model of PD.

1H MRS identifies lactate rise in the striatum of MPTP-treated C57BL/6 mice

Mitochondrial dysfunction has been implicated in the death of nigrostriatal dopaminergic neurons in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐treated experimental models of Parkinsons disease (PD). Here we utilized proton magnetic resonance spectroscopy (1H MRS) to identify changes in energy metabolism in the striatum of MPTP‐treated C57BL/6 mice. Remarkable increases in lactate/creatine (Lac/Cr) ratio were observed at 2 h and then quickly returned to about the basal level by 7 h after injection of MPTP. Neurochemical and Western blot analyses revealed that dopamine contents and protein levels of tyrosine hydroxylase and dopamine transporter in the striatum were profoundly decreased at 3 days after MPTP treatment. Pretreatment with deprenyl, a monoamine oxidase B inhibitor, or GBR‐12909, a dopamine uptake inhibitor, almost completely attenuated both the increases in striatal Lac/Cr ratio and the subsequent loss of dopaminergic nerve terminals in MPTP‐treated mice. The present study indicates that 1H MRS is a sensitive measure of biochemical alterations of the brain in a mouse model of PD, and further shows that the increases in striatal Lac/Cr ratio induced by MPTP may be associated with mitochondrial energy crisis, followed by dopaminergic neurotoxicity.

Antidepressant-like responses to the combined sigma and 5-HT1A receptor agonist OPC-14523

The antidepressant-like activity of a novel compound, OPC-14523, was investigated in comparison with the conventional antidepressants, fluoxetine and imipramine. OPC-14523 bound with nanomolar affinities to sigma receptors (IC(50)=47-56 nM), the 5-HT(1A) receptor (IC(50)=2.3 nM), and the 5-HT transporter (IC(50)=80 nM). OPC-14523 inhibited the in vitro reuptake of 3H-5-HT (IC(50)=27 nM), but it showed very weak inhibitory activity on 3H-NE and 3H-DA reuptake. OPC-14523 did not inhibit MAO A or B activities or muscarinic receptors. A single oral administration of OPC-14523 produced a marked antidepressant-like effect in the forced swimming test (FST) with rats (ED(50)=27 mg/kg) and mice (ED(50)=20mg/kg) without affecting the general locomotor activity. In contrast, fluoxetine and imipramine each required at least four days of repeated dosing to show this activity. The acute activity of OPC-14523 was blocked by pretreatment with the sigma receptor antagonist NE-100 or the selective 5-HT(1A) receptor antagonist WAY-100635. The induction of flat body posture by OPC-14523 was blocked by the selective 5-HT(1A) receptor antagonist NAN-190, and forebrain 5-HT biosynthesis was attenuated by OPC-14523 at behaviorally effective doses. In contrast, OPC-14523, unlike fluoxetine, failed to inhibit 5-HT reuptake at oral doses below 100mg/kg. Thus, the acute antidepressant-like action of OPC-14523 is achieved by the combined stimulation of sigma and 5-HT(1A) receptors without inhibition of 5-HT reuptake in vivo.

Diminished catalepsy and dopamine metabolism distinguish aripiprazole from haloperidol or risperidone.

Catalepsy and changes in striatal and limbic dopamine metabolism were investigated in mice after oral administration of aripiprazole, haloperidol, and risperidone. Catalepsy duration decreased with chronic (21 day) aripiprazole compared with acute (single dose) treatment across a wide dose range, whereas catalepsy duration persisted with chronic haloperidol treatment. At the time of maximal catalepsy, acute aripiprazole did not alter neostriatal dopamine metabolite/dopamine ratios or homovanillic acid (HVA) levels, and produced small increases in dihydroxyphenylacetic acid (DOPAC). Effects were similar in the olfactory tubercle. Dopamine metabolism was essentially unchanged in both regions after chronic aripiprazole. Acute treatments with haloperidol or risperidone elevated DOPAC, HVA, and metabolite/dopamine ratios in both brain areas and these remained elevated with chronic treatment. The subtle effects of aripiprazole on striatal and limbic dopamine metabolism, and the decrease in catalepsy with chronic administration, illustrate fundamental differences in dopamine neurochemical actions and behavioral sequelae of aripiprazole compared to haloperidol or risperidone.

Age-related severity of dopaminergic neurodegeneration to MPTP neurotoxicity causes motor dysfunction in C57BL/6 mice

This study investigated the influence of advancing age on dopaminergic neuronal degeneration induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication from the perspective concerning the relationship between dopaminergic function and behavioral features. Young (10 weeks) and older (14-15 months) C57BL/6 mice were treated with one to four injections of MPTP (20 mg/kg at 2h intervals). Although young mice showed no mortality in either MPTP treatment, older mice exhibited mortality from only two injections of MPTP during the experimental period. An extensive dopaminergic cell loss was found in both the striatum and substantia nigra of older mice given one and two injections of MPTP with marked decrease in striatal dopamine (DA) levels, but not young mice. We also found a behavioral change in the tail suspension test associated with the extent of decrease in striatal DA levels in MPTP-treated older mice, but not in young mice. These results clearly present age-related vulnerability to MPTP neurotoxicity in C57BL/6 mice and strongly support our previous report showing that there is a critical threshold level of the decrement in striatal DA contents causing motor dysfunction in this mouse model of Parkinsons disease.

1-Methyl-4-phenylpyridinium (MPP+) Decreases Mitochondrial Oxidation-Reduction (REDOX) Activity and Membrane Potential (Δψm) in Rat Striatum

Mitochondrial dysfunction has long been implicated in the death of nigrostriatal dopaminergic neurons in Parkinsons disease (PD) and its experimental models. Here we further analyzed changes in the mitochondrial oxidation-reduction (REDOX) activity and membrane potential (Δψm) of striatal synaptosomes after the infusion of 1-methyl-4-phenylpyridinium (MPP+) into rat striatum. MPP+ (40 nmol) treatment produced decreases in mitochondrial REDOX activity and Δψm at 18 h, as measured by fluorometric analysis with both Alamar blue and JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolyl-carbocyanine iodide) dyes. At this time point, tyrosine hydroxylase (TH) and dopamine transporter (DAT) protein levels were not altered, but both decreased at 7 days after MPP+ (40 nmol) infusion. Both measures of mitochondrial dysfunction induced by MPP+ (40 nmol) at 18 h were attenuated, at least in part, by pretreatment with a selective dopamine uptake inhibitor GBR-12909 (1-(2-(bis(4-fluorophenyl)methoxy)ethyl)-4-(3-phenylpropyl) piperazine). In addition, GBR-12909 partially attenuated MPP+ (40 nmol)-caused a loss of striatal nerve terminal as indicated by decreases in TH and DAT immunoreactivities as well as dopamine and its metabolites levels. The present study indicates that decreases in mitochondrial REDOX activity and Δψm may play a role in MPP+-induced dopaminergic neurotoxicity, and further provides that improvement of mitochondrial dysfunction may be a better way to slow progressive dopaminergic neurodegeneration commonly associated with PD.

Differential effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the olfactory bulb and the striatum in mice

The present study was undertaken to examine whether 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes damage of dopaminergic glomerular cells of the olfactory bulb (OB) in C57BL/6 mice. At 3 days after MPTP treatment, dopamine level in the striatum and the OB decreased to 13% and 84% of the control mice, respectively. While a small reduction of tyrosine hydroxylase protein level was observed in the OB of MPTP-treated mice, dopamine transporter (DAT) was undetectable at the protein level in this region. These results indicate that the DAT protein level could account for resistance of the OB to the Parkinsonism-inducing toxin.

Increased hippocampal quinone reductase 2 in Alzheimer's disease.

Quinone reductase 2 (QR2), a detoxifying cytosolic flavoenzyme, is thought to play an important role in the acquisition and loss of memory. We determined the amount of QR2 in the hippocampus, amygdala, and superior frontal gyrus of Alzheimers disease (AD) patients with dementia by using western blot analysis. The level of QR2 was significantly higher in the hippocampus of AD patients than in that of the control subjects. The relation between QR2 and AD has not yet been determined; however, our results suggest that the increase in hippocampal QR2 might be a cause of AD or might promote the progression of AD by causing an increase in the toxic quinone levels and consequent loss of cognitive function.

The attenuating effect of carteolol hydrochloride, a β-adrenoceptor antagonist, on neuroleptic-induced catalepsy in rats

Abstract It is known that β-adrenoceptor antagonists are effective in the treatment of akathisia, one of the extrapyramidal side effects that occur during neuroleptic treatment. Neuroleptic-induced catalepsy, a model of neuroleptic-induced extrapyramidal side effects, was considered suitable as a model for predicting neuroleptic-induced akathisia in humans, although neuroleptic-induced catalepsy was not considered a specific test for neuroleptic-induced akathisia. Therefore, the effects of carteolol, a β-adrenoceptor antagonist, on haloperidol-induced catalepsy in rats were behaviorally studied and compared with those of propranolol and biperiden, a muscarinic receptor antagonist. Carteolol, as well as propranolol and biperiden, inhibited the haloperidol-induced catalepsy. The inhibitory effect of carteolol was almost comparable to that of propranolol, but was weaker than that of biperiden. Carteolol did not evoke postsynaptic dopamine receptor-stimulating behavioral signs such as stereotypy and hyperlocomotion in rats. Carteolol did not antagonize the inhibitory effects of haloperidol on apomorphine-induced stereotypy and locomotor activity in rats. In addition, carteolol did not evoke 5-HT1A receptor-stimulating behavioral signs such as flat body posture and forepaw treading and did not inhibit 5-hydroxytryptophan-induced head twitch in rats. Finally, carteolol did not inhibit physostigmine-induced lethality in rats. These results strongly suggest that carteolol improves haloperidol-induced catalepsy via its β-adrenoceptor antagonistic activity and is expected to be effective in the treatment of akathisia without attenuating neuroleptic-induced antipsychotic effects due to its postsynaptic dopamine receptor antagonistic activity.

MPTP neurotoxicity is enhanced by a restraint stress in C57BL/6 mice

Epidemiological studies reported that paraquat, a hervicide, is one of the environmental risk factors of Parkinson disease. Paraquat induced apoptosis in PC12 cells. The endoplasmic reticulum (ER) stress was found to be involved in this paraquat -induced apoptosis because upregulation of CHOP and activation of Jun-N-terminal kinase (JNK), ER stress activated substrates, were observed. Upregulation of mRNA of BiP, an ER-specific chaperone, and splicing of the mRNA of the X box binding protein were observed, indicating the occurrence of the unfolded protein response (UPR). Prominent production of reactive oxygen species (ROS) was observed after paraquat exposure. Pre-incubation of phytoestrogens such as resveratrol prevalent in the red wine and genistein derived from soybean reduced the paraquat -induced ROS. Resvertrol reduced the UPR and increased the viability of PC12 cells was increased. In contrast, genistein was less effective to prevent the ER stress and the paraquat-induced cell death.