Destruction of norepinephrine terminals in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice reduces locomotor activity induced by L-dopa

Serotonin as a biomarker of toxin-induced Parkinsonism

BACKGROUND

Loss of dopaminergic neurons underlies the motor symptoms of Parkinson's disease (PD). However stereotypical PD symptoms only manifest after approximately 80% of dopamine neurons have died making dopamine-related motor phenotypes unreliable markers of the earlier stages of the disease. There are other non-motor symptoms, such as depression, that may present decades before motor symptoms.

METHODS

Because serotonin is implicated in depression, here we use niche, fast electrochemistry paired with mathematical modelling and machine learning to, for the first time, robustly evaluate serotonin neurochemistry in vivo in real time in a toxicological model of Parkinsonism, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

RESULTS

Mice treated with acute MPTP had lower concentrations of in vivo, evoked and ambient serotonin in the hippocampus, consistent with the clinical comorbidity of depression with PD. These mice did not chemically respond to SSRI, as strongly as control animals did, following the clinical literature showing that antidepressant success during PD is highly variable. Following L-DOPA administration, using a novel machine learning analysis tool, we observed a dynamic shift from evoked serotonin release in the hippocampus to dopamine release. We hypothesize that this finding shows, in real time, that serotonergic neurons uptake L-DOPA and produce dopamine at the expense of serotonin, supporting the significant clinical correlation between L-DOPA and depression. Finally, we found that this post L-DOPA dopamine release was less regulated, staying in the synapse for longer. This finding is perhaps due to lack of autoreceptor control and may provide a ground from which to study L-DOPA induced dyskinesia.

CONCLUSIONS

These results validate key prior hypotheses about the roles of serotonin during PD and open an avenue to study to potentially improve therapeutics for levodopa-induced dyskinesia and depression.

Whether the Subacute MPTP-Treated Mouse is as Suitable as a Classic Model of Parkinsonism

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice model is one of the most common animal models for Parkinson's disease (PD). It is classified into three types: acute, subacute, and chronic intoxication models. The subacute model has attracted much attention for its short period and similarity to PD. However, whether subacute MPTP intoxication in mouse mimics the movement and cognitive disorders of PD still remains highly controversial. Therefore, the present study reassessed the behavioral performances of subacute MPTP intoxication in mice using open field, rotarod, Y maze,  and gait analysis at different time points (1, 7, 14, and 21 days) after modeling. Results of the current study showed that although MPTP-treated mice using subacute regimen showed severe dopaminergic neuronal loss and evident astrogliosis, they failed to display significant motor and cognitive deficits. Besides, expression of mixed lineage kinase domain-like (MLKL), a marker of necroptosis, was also significantly increased in the ventral midbrain and striatum of MPTP-intoxicated mice. This evidently implies that necroptosis may play an important role in MPTP-induced neurodegeneration. In conclusion, the findings of the present study suggest that subacute MPTP-intoxicated mice may not be a suitable model for studying parkinsonism. However, it can help in revealing the early pathophysiology of PD and studying the compensatory mechanisms which occur in early PD that prevent the emergence of behavioral deficits.

Behavioral and neurochemical interactions of the tricyclic antidepressant drug desipramine with L-DOPA in 6-OHDA-lesioned rats. Implications for motor and psychiatric functions in Parkinson's disease

RATIONALE

The pharmacological effects of antidepressants in modulating noradrenergic transmission as compared to serotonergic transmission in a rat model of Parkinson's disease under chronic L-DOPA therapy are insufficiently explored.

OBJECTIVES

The aim of the present study was to investigate the effect of the tricyclic antidepressant desipramine administered chronically alone or jointly with L-DOPA, on motor behavior and monoamine metabolism in selected brain structures of rats with the unilateral 6-OHDA lesion.

METHODS

The antiparkinsonian activities of L-DOPA and desipramine were assessed behaviorally using a rotation test and biochemically based on changes in the tissue concentrations of noradrenaline, dopamine and serotonin and their metabolites, evaluated separately for the ipsi- and contralateral motor (striatum, substantia nigra) and limbic (prefrontal cortex, hippocampus) structures of rat brain by HPLC method.

RESULTS

Desipramine administered alone did not induce rotational behavior, but in combination with L-DOPA, it increased the number of contralateral rotations more strongly than L-DOPA alone. Both L-DOPA and desipramine + L-DOPA significantly increased DA levels in the ipsilateral striatum, substantia nigra, prefrontal cortex and the ipsi- and contralateral hippocampus. The combined treatment also significantly increased noradrenaline content in the ipsi- and contralateral striatum, while L-DOPA alone decreased serotonin level on both sides of the hippocampus.

CONCLUSIONS

The performed analysis of the level of monoamines and their metabolites in the selected brain structures suggests that co-modulation of noradrenergic and dopaminergic transmission in Parkinson's disease by the combined therapy with desipramine + L-DOPA may have some positive implications for motor and psychiatric functions but further research is needed to exclude potential negative effects.

Increase in telencephalic dopamine and cerebellar norepinephrine contents by hydrostatic pressure in goldfish: the possible involvement in hydrostatic pressure-related locomotion

Fish are faced with a wide range of hydrostatic pressure (HP) in their natural habitats. Additionally, freshwater fish are occasionally exposed to rapid changes in HP due to heavy rainfall, flood and/or dam release. Accordingly, variations in HP are one of the most important environmental cues for fish. However, little information is available on how HP information is perceived and transmitted in the central nervous system of fish. The present study examined the effect of HP (water depth of 1.3 m) on the quantities of monoamines and their metabolites in the telencephalon, optic tectum, diencephalon, cerebellum (including partial mesencephalon) and vagal lobe (including medulla oblongata) of the goldfish, Carassius auratus, using high-performance liquid chromatography. HP affected monoamine and metabolite contents in restricted brain regions, including the telencephalon, cerebellum and vagal lobe. In particular, HP significantly increased the levels of dopamine (DA) in the telencephalon at 15 min and that of norepinephrine (NE) in the cerebellum at 30 min. In addition, HP also significantly increased locomotor activity at 15 and 30 min after HP treatment. It is possible that HP indirectly induces locomotion in goldfish via telencephalic DA and cerebellar NE neuronal activity.

Noradrenergic-Dopaminergic Interactions Due to DSP-4-MPTP Neurotoxin Treatments: Iron Connection

The investigations of noradrenergic lesions and dopaminergic lesions have established particular profiles of functional deficits and accompanying alterations of biomarkers in brain regions and circuits. In the present account, the focus of these lesions is directed toward the effects upon dopaminergic neurotransmission and expression that are associated with the movement disorders and psychosis-like behavior. In this context, it was established that noradrenergic denervation, through administration of the selective noradrenaline (NA) neurotoxin, DSP-4, should be performed prior to the depletion of dopamine (DA) with the selective neurotoxin, MPTP. Employing this regime, it was shown that (i) following DSP-4 (50 mg/kg) pretreatment of C57/Bl6 mice, both the functional and neurochemical (DA loss) effects of MPTP (2 × 20 and 2 × 40 mg/kg) were markedly exacerbated, and (ii) following postnatal iron (Fe(2+), 7.5 mg/kg, on postnatal days 19-12), pretreatment with DSP-4 followed by the lower 2 × 20 mg/kg MPTP dose induced even greater losses of motor behavior and striatal DA. As yet, the combination of NA-DA depletions, and even more so Fe(2+)-NA-DA depletion, has been considered to present a movement disorder aspect although studies exploring cognitive domains are lacking. With intrusion of iron overload into this formula, the likelihood of neuropsychiatric disorder, as well, unfolds.

Effects of noradrenergic denervation by anti-DBH-saporin on behavioral responsivity to L-DOPA in the hemi-parkinsonian rat

Dopamine (DA) replacement with l-DOPA remains the most effective pharmacotherapy for motor symptoms of Parkinson's disease (PD) including tremor, postural instability, akinesia, and bradykinesia. Prolonged L-DOPA use frequently leads to deleterious side effects including involuntary choreic and dystonic movements known as L-DOPA induced dyskinesias (LID). DA loss in PD is frequently accompanied by concomitant noradrenergic (NE) denervation of the locus coeruleus (LC); however, the effects of NE loss on L-DOPA efficacy and LID remain controversial and are often overlooked in traditional animal models of PD. The current investigation examined the role of NE loss in L-DOPA therapy by employing the NE specific neurotoxin anti-DA-beta hydroxylase saporin (αDBH) in a rat model of PD. Rats received unilateral 6-hydroxydopamine lesions of the medial forebrain bundle to deplete nigral DA and intraventricular injection of vehicle (DA lesioned rats) or αDBH (DANE lesioned rats) to destroy NE neurons bilaterally. Results indicated that αDBH infusion drastically reduced NE neuron markers within the LC compared to rats that received vehicle treatment. Behaviorally, this loss did not alter the development or expression of L-DOPA- or DA agonist-induced dyskinesia. However, rats with additional NE lesions were less responsive to L-DOPA's pro-motor effects. Indeed, DANE lesioned animals rotated less and showed less attenuation of parkinsonian stepping deficits following high doses of L-DOPA than DA lesioned animals. These findings suggest that severe NE loss may reduce L-DOPA treatment efficacy and demonstrate that degradation of the NE system is an important consideration when evaluating L-DOPA effects in later stage PD.

Extended wakefulness: compromised metabolics in and degeneration of locus ceruleus neurons

Modern society enables a shortening of sleep times, yet long-term consequences of extended wakefulness on the brain are largely unknown. Essential for optimal alertness, locus ceruleus neurons (LCns) are metabolically active neurons that fire at increased rates across sustained wakefulness. We hypothesized that wakefulness is a metabolic stressor to LCns and that, with extended wakefulness, adaptive mitochondrial metabolic responses fail and injury ensues. The nicotinamide adenine dinucleotide-dependent deacetylase sirtuin type 3 (SirT3) coordinates mitochondrial energy production and redox homeostasis. We find that brief wakefulness upregulates SirT3 and antioxidants in LCns, protecting metabolic homeostasis. Strikingly, mice lacking SirT3 lose the adaptive antioxidant response and incur oxidative injury in LCns across brief wakefulness. When wakefulness is extended for longer durations in wild-type mice, SirT3 protein declines in LCns, while oxidative stress and acetylation of mitochondrial proteins, including electron transport chain complex I proteins, increase. In parallel with metabolic dyshomeostasis, apoptosis is activated and LCns are lost. This work identifies mitochondrial stress in LCns upon wakefulness, highlights an essential role for SirT3 activation in maintaining metabolic homeostasis in LCns across wakefulness, and demonstrates that extended wakefulness results in reduced SirT3 activity and, ultimately, degeneration of LCns.

Effects of noradrenergic denervation on L-DOPA-induced dyskinesia and its treatment by α- and β-adrenergic receptor antagonists in hemiparkinsonian rats

While L-3,4-dihydroxyphenylalanine (L-DOPA) remains the standard treatment for Parkinson's disease (PD), long-term efficacy is often compromised by L-DOPA-induced dyskinesia (LID). Recent research suggests that targeting the noradrenergic (NE) system may provide relief from both PD and LID, however, most PD patients exhibit NE loss which may modify response to such strategies. Therefore this investigation aimed to characterize the development and expression of LID and the anti-dyskinetic potential of the α2- and β-adrenergic receptor antagonists idazoxan and propranolol, respectively, in rats receiving 6-OHDA lesions with (DA lesion) or without desipramaine protection (DA+NE lesion). Male Sprague-Dawley rats (N=110) received unilateral 6-hydroxydopamine lesions. Fifty-three rats received desipramine to protect NE neurons (DA lesion) and 57 received no desipramine reducing striatal and hippocampal NE content 64% and 86% respectively. In experiment 1, the development and expression of L-DOPA-induced abnormal involuntary movements (AIMs) and rotations were examined. L-DOPA efficacy using the forepaw adjusting steps (FAS) test was also assessed in DA- and DA+NE-lesioned rats. In experiment 2, DA- and DA+NE-lesioned rats received pre-treatments of idazoxan or propranolol followed by L-DOPA after which the effects of these adrenergic compounds were observed. Results demonstrated that moderate NE loss reduced the development and expression of AIMs and rotations but not L-DOPA efficacy while anti-dyskinetic efficacy of α2- and β-adrenergic receptor blockade was maintained. These findings suggest that the NE system modulates LID and support the continued investigation of adrenergic compounds for the improved treatment of PD.

L-Dihydroxyphenylalanine modulates the steady-state expression of mouse striatal tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine and its metabolites in an MPTP mouse model of Parkinson's disease

AIMS

l-3,4-Dihydroxyphenylalanine (L-DOPA) is the most effective symptomatic treatment for Parkinson's disease (PD), but PD patients usually experience a successful response to L-DOPA therapy followed by a progressive loss of response. L-DOPA efficacy relies on its decarboxylation by aromatic l-amino acid decarboxylase (AAAD) to form dopamine (DA). So exogenous L-DOPA drives the reaction and AAAD becomes the rate limiting enzyme in the supply of DA. In turn, exogenous L-DOPA regulates the expression and activity of AAAD as well as the synthesis of DA and its metabolites, changes that may be linked to the efficacy and side-effects of L-DOPA.

MAIN METHODS

One-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse PD model was utilized to study the effects of L-DOPA on the steady-state level and activity of AAAD, tyrosine hydroxylase (TH), DA and the metabolites of DA. The MPTP and control mice were treated twice daily with PBS or with 100mg/kg of L-DOPA for 14days and the expression and activity of AAAD, the expression of TH and the levels of DA and its metabolites were determined 24h after L-DOPA or PBS treatment, when exogenous L-DOPA is eliminated.

KEY FINDINGS

In the MPTP model, L-DOPA reduced the steady-state expression and the activity of striatal AAAD by 52% and 50%, respectively, DA and metabolites were also significantly decreased.

SIGNIFICANCE

The outcome shows that while L-DOPA replenishes striatal DA it also down-regulates AAAD and the steady-state synthesis and metabolic capability of the dopaminergic system. These findings are important in the precipitation of L-DOPA induced side effects and the management of L-DOPA therapy.

Noradrenaline and Parkinson's disease

Parkinson's disease (PD) is characterized by the degeneration of dopamine (DA) neurons in the substantia nigra pars compacta, and motor symptoms including bradykinesia, rigidity, and tremor at rest. These symptoms are exhibited when striatal dopamine concentration has decreased by around 70%. In addition to motor deficits, PD is also characterized by the non-motor symptoms. However, depletion of DA alone in animal models has failed to simultaneously elicit both the motor and non-motor deficits of PD, possibly because the disease is a multi-system disorder that features a profound loss in other neurotransmitter systems. There is growing evidence that additional loss of noradrenaline (NA) neurons of the locus coeruleus, the principal source of NA in the brain, could be involved in the clinical expression of motor as well as in non-motor deficits. In the present review, we analyze the latest evidence for the implication of NA in the pathophysiology of PD obtained from animal models of parkinsonism and from parkinsonian patients. Recent studies have shown that NA depletion alone, or combined with DA depletion, results in motor as well as in non-motor dysfunctions. In addition, by using selective agonists and antagonists of noradrenaline alpha receptors we, and others, have shown that α2 receptors are implicated in the control of motor activity and that α2 receptor antagonists can improve PD motor symptoms as well as l-Dopa-induced dyskinesia. In this review we argue that the loss of NA neurons in PD has an impact on all PD symptoms and that the addition of NAergic agents to dopaminergic medication could be beneficial in the treatment of the disease.

Potential mechanisms underlying anxiety and depression in Parkinson's disease: consequences of l-DOPA treatment

Though the most recognizable symptoms of Parkinson's disease (PD) are motor-related, many patients also suffer from debilitating affective symptoms that deleteriously influence quality of life. Dopamine (DA) loss is likely involved in the onset of depression and anxiety in PD. However, these symptoms are not reliably improved by DA replacement therapy with l-3,4-dihydroxyphenylalanine (l-DOPA). In fact, preclinical and clinical evidence suggests that l-DOPA treatment may worsen affect. Though the neurobiological mechanisms remain unclear, recent research contends that l-DOPA further perturbs the function of the norepinephrine and serotonin systems, already affected by PD pathology, which have been intimately linked to the development and expression of anxiety and depression. As such, this review provides an overview of the clinical characteristics of affective disorders in PD, examines the utility of animal models for the study of anxiety and depression in PD, and finally, discusses potential mechanisms by which DA loss and subsequent l-DOPA therapy influence monoamine function and concomitant affective symptoms.

Dual motor response to l-dopa and nociceptin/orphanin FQ receptor antagonists in 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) treated mice: Paradoxical inhibition is relieved by D(2)/D(3) receptor blockade

Motor activity of mice acutely treated with the parkinsonian toxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) was monitored for 6 days using behavioral tests which provide complementary information on motor function: the bar, reaction time, drag, stair climbing, grip, rotarod and footprinting tests. These tests consistently disclosed a prolonged motor impairment characterized by akinesia, bradykinesia, speed reduction, loss of coordination and gait patterns. This impairment was associated with approximately 60% loss of striatal dopamine terminals, as revealed by tyrosine hydroxylase immunohistochemistry, and was attenuated by dopaminergic drugs. Indeed, the dopamine precursor, l-dopa (1-10 mg/kg), and the D(3)/D(2) receptor agonist pramipexole (0.0001-0.001 mg/kg) promoted stepping activity in the drag test (a test for akinesia/bradykinesia). The novel nociceptin/orphanin FQ receptor (NOP) antagonist 1-[1-(cyclooctylmethyl)-1,2,3,6-tetrahydro-5-(hydroxymethyl)-4-pyridinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (Trap-101, 0.001-0.1 mg/kg), an analogue of 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397), also promoted stepping and synergistically or additively (depending on test) attenuated parkinsonism when combined to dopamine agonists. High doses of l-dopa (100 mg/kg), pramipexole (0.1 mg/kg), Trap-101 and J-113397 (1 mg/kg), however, failed to modulate stepping, worsening immobility time and/or rotarod performance. Low doses of amisulpride (0.1 mg/kg) reversed motor inhibition induced by l-dopa and J-113397, suggesting involvement of D(2)/D(3) receptors. This study brings further evidence for a dopamine-dependent motor phenotype in MPTP-treated mice reinforcing the view that this model can be predictive of symptomatic antiparkinsonian activity provided the appropriate test is used. Moreover, it offers mechanistic interpretation to clinical reports of paradoxical worsening of parkinsonism following l-dopa. Finally, it confirms that NOP receptor antagonists may be proven effective in reversing parkinsonism when administered alone or in combination with dopamine agonists.

5-HT2A receptor antagonists improve motor impairments in the MPTP mouse model of Parkinson's disease

Clinical observations have suggested that ritanserin, a 5-HT(2A/C) receptor antagonist may reduce motor deficits in persons with Parkinson's Disease (PD). To better understand the potential antiparkinsonian actions of ritanserin, we compared the effects of ritanserin with the selective 5-HT(2A) receptor antagonist M100907 and the selective 5-HT(2C) receptor antagonist SB 206553 on motor impairments in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP-treated mice exhibited decreased performance on the beam-walking apparatus. These motor deficits were reversed by acute treatment with L-3,4-dihydroxyphenylalanine (levodopa). Both the mixed 5-HT(2A/C) antagonist ritanserin and the selective 5-HT(2A) antagonist M100907 improved motor performance on the beam-walking apparatus. In contrast, SB 206553 was ineffective in improving the motor deficits in MPTP-treated mice. These data suggest that 5-HT(2A) receptor antagonists may represent a novel approach to ameliorate motor symptoms of Parkinson's disease.

Effect of the additional noradrenergic neurodegeneration to 6-OHDA-lesioned rats in levodopa-induced dyskinesias and in cognitive disturbances

Parkinson's disease is a motor and cognitive disorder characterised by a progressive loss of the substantia nigra pars compacta (SNc) dopaminergic neurons as well as of the locus coeruleus (LC) noradrenergic neurons. It has been suggested that LC neurodegeneration might influence levodopa-induced motor disturbances and cognitive performance. We investigated the influence of dopaminergic and noradrenergic lesions on levodopa-induced dyskinesias and on working memory in rats. Two groups of animals were used: (1) rats with a dopaminergic lesion induced by a unilateral administration of the neurotoxin 6-hydroxydopamine (6-OHDA), and (2) rats with a combined lesion of the dopaminergic and noradrenergic systems induced by 6-OHDA and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), respectively. Dyskinesias were evaluated on days 1, 8, 15 and 22 of chronic levodopa treatment (6 mg/kg, twice at day, i.p.). Working memory was evaluated by a radial-arm maze (1) before lesions, (2) before levodopa administration and (3) after 22 days of levodopa treatment. Total, axial, limb and orofacial dyskinesias not differed significantly between both groups. Working memory tasks worsened in both lesioned groups reaching significance in terms of time of performance (P < 0.05). The number of repeated entries in the same arm (errors) was only significant in the double-lesioned group (P < 0.05). This behaviour was not different from the one observed after chronic levodopa treatment. These results suggest that levodopa-induced dyskinesias in the 6-OHDA-lesioned rats were not affected by the additional noradrenergic lesion, whereas this last condition was sufficient to worse the cognitive performance deficit produced by the dopaminergic lesion.

Inhibition of the outgrowth and elongation of neurites from pheochromocytoma cells by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and preventive effects of dimethylsulfoniopropionate in the presence of nerve growth factor

The combined effects of dimethylsulfoniopropionate (DMSP) (10(-3), 10(-4) and 10(-5) M) with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (5 ng/mL) and the nerve growth factor (NGF) (5 ng/mL) on the outgrowth and elongation of neurites from pheochromocytoma (PC12) cells were examined on RPMI medium containing fetal bovine serum and horse serum with penicillin and streptomycin in collagen-coated dishes for 5 d. The growth was higher in increasing order of the DMSP (10(-3) M), MPTP and NGF, the DMSP (10(-5) M), MPTP and NGF, the MPTP and NGF group and the control group up to 3 d, but not in the NGF and the DMSP (10(-4) M), MPTP and NGF groups. The growth in all the experimental groups showed plateaus from days 4 to 5. The appearance of neurites from the cells in all the groups showed maxima on the 3rd day. The administration of NGF significantly stimulated the outgrowth of neurites from the cells, while the supplementation of MPTP noticeably inhibited the appearance of neurites even in the presence of NGF up to 5 d. However, the addition of DMSP (10(-3 )and 10(-4) M) to the latter group completely prevented the inhibition of the MPTP. These facts were significantly supported by the photographs of neurite-bearing cells on the 3rd day and also by the photometric analyses examining the reaction of MPTP to DMSP, NGF or Collagen IV.

Modulation of the motor response to dopaminergic drugs in a parkinsonian model of combined dopaminergic and noradrenergic degeneration

Besides dopaminergic deficiency, other neurotransmitter systems such as noradrenergic nuclei are affected in Parkinson's disease. Locus coeruleus degeneration might influence the response to dopamine replacement and the presence of long-term complications such as dyskinesias. In this scenario of noradrenergic and dopaminergic neurodegeneration, behavioural effects induced by dopaminergic-interacting drugs are incompletely known. We investigated whether noradrenergic lesion modulates the levodopa (l-DOPA) response and modifies the response to adenosine antagonists and its interaction with l-DOPA. We examined the motor behaviour induced by: 1) subthreshold doses of l-DOPA (2mg/kg, i.p.), 2) the adenosine-receptor antagonist caffeine (10mg/kg), and 3) the combination of l-DOPA (2mg/kg) and caffeine (10mg/kg). Each study was done in two experimental conditions: a) rats with unilateral 6-OHDA lesion and b) rats with a lesion of the nigrostriatal pathway (6-OHDA) combined with selective denervation of locus coeruleus-noradrenergic terminal fields by N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4). While only 28% of the 6-OHDA-lesioned animals presented circling behaviour after l-DOPA challenge, all (100%) double-denervated animals rotated after the same l-DOPA dose (p<0.05). No statistical differences in the percentage of rotating animals were observed between single- and double-denervated rats after caffeine challenge. Combined l-DOPA-caffeine challenge produced rotational behaviour in all (100%) single- and double-denervated rats. No differences in total turns were observed between single- and double-denervated animals in each treatment condition. These findings suggest that additional noradrenergic denervation selectively decreases the motor threshold to l-DOPA treatment without modifying the magnitude or the pattern of the motor response to adenosinergic antagonism.

Functional consequences of iron overload in catecholaminergic interactions: the Youdim factor

The influence of postnatal iron overload upon implications of the functional and interactive role of dopaminergic and noradrenergic pathways that contribute to the expressions of movement disorder and psychotic behaviours in mice was studied in a series of experiments. (1) Postnatal iron overload at doses of 7.5 mg/kg (administered on Days 10-12 post partum) and above, invariably induced a behavioural syndrome consisting of an initial (1st 20-40 min of a 60-min test session) hypoactivity followed by a later (final 20 min of a 60-min test session) hyperactivity, when the mice were tested at adult ages (age 60 days or more). (2) Following postnatal iron overload, subchronic treatment with the neuroleptic compounds, clozapine and haloperidol, dose-dependently reversed the initial hypoactivity and later hyperactivity induced by the metal. Furthermore, DA D(2) receptor supersensitivity (as assessed using the apomorphine-induced behaviour test) was directly and positively correlated with iron concentrations in the basal ganglia. (3) Brain noradrenaline (NA) denervation, using the selective NA neurotoxin, DSP4, prior to administration of the selective DA neurotoxin, MPTP, exacerbated both the functional (hypokinesia) and neurochemical (DA depletion) effects of the latter neurotoxin. Treatment with L-Dopa restored motor activity only in the animals that had not undergone NA denervation. These findings suggest an essential neonatal iron overload, termed "the Youdim factor", directing a DA-NA interactive component in co-morbid disorders of nigrostriatal-limbic brain regions.

A beam-walking apparatus to assess behavioural impairments in MPTP-treated mice: pharmacological validation with R-(-)-deprenyl

A beam-walking apparatus has been evaluated for its ability to detect motor impairments in mice acutely treated with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg, s.c., single or double administration). Mice subjected to MPTP lesioning showed deficits in motor performance on the beam-walking task, for up to 6 days post-MPTP administration, as compared to saline-treated controls. In addition, MPTP-treated mice were detected to have a marked depletion in striatal dopamine levels and a concomitant reduction in substantia nigra (SN) tyrosine hydroxylase (TH) immunoreactivity, at 7 days post-MPTP administration, indicative of dopaminergic neuronal loss. Pre-administration of the potent MAO-B inhibitor R-(-)-deprenyl at 3 or 10 mg/kg, 30 min, s.c, significantly inhibited the MPTP-induced reduction in SN TH-immunoreactivity, striatal dopamine depletions and impairments in mouse motor function. The data described in the present study provides further evidence that functional deficits following an acute MPTP dosing schedule in mice can be quantified and are related to nigro-striatal dopamine function.

Levodopa-induced hyperactivity in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The present study examines the motor responses of 10- to 12-month-old, male C57 mice that were either given intraperitoneal (IP) injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 30 mg/kg per day) or vehicle for 10 consecutive days, followed by IP injections of levodopa (200 mg/kg) plus carbidopa (25 mg/kg). Five days of MPTP exposure resulted in the Straub tail phenomenon and pronounced hypokinesia. However, during the next 5 days, motor activity returned to baseline, even with continued MPTP treatment. After 10 to 14 days of rest, all mice were then treated with levodopa/carbidopa twice daily for multiple, consecutive days. However, only the previously MPTP-treated animals became hyperkinetic, as compared to levodopa-treated control animals that were not previously exposed to MPTP. Abnormal activity included scratching, running, gnawing, and jumping movements. Hyperactivity lasted for approximately 2 hours after each levodopa injection and then returned to baseline, but the amount of hyperkinesia increased with additional days of levodopa treatment, even though the daily levodopa dose was not changed. These results demonstrate that levodopa can cause reproducible hyperactivity in mice that were previously exposed to MPTP.

Comorbidity implications in brain disease: Neuronal substrates of symptom profiles

The neuronal substrates underlying aspects of comorbidity in brain disease states may be described over psychiatric and neurologic conditions that include affective disorders, cognitive disorders, schizophrenia, obsessive-compulsive disorder, substance abuse disorders as well as the neurodegenerative disorders. Regional and circuitry analyses of biogenic amine systems that are implicated in neural and behavioural pathologies are elucidated using neuroimaging, electrophysiological, neurochemical, neuropharmacological and neurobehavioural methods that present demonstrations of the neuropathological phenomena, such as behavioural sensitisation, cognitive impairments, maladaptive reactions to environmental stress and serious motor deficits. Considerations of neuronal alterations that may or may not be associated with behavioural abnormalities examine differentially the implications of discrete areas within brains that have been assigned functional significance; in the case of the frontal lobes, differential deficits of ventromedial and dorsolateral prefrontal cortex may be associated with different aspects of cognition, affect, remission or response to medication thereby imparting a varying aspect to any investigation of comorbidity.

Movement disorders: neurodevelopment and neurobehavioural expression

Braak and co-workers have recently shown that movement disorders such as Parkinson's disease develop progressively over years with early neuronal losses in brainstem regions caudal to the substantia nigra. The relevance of this finding to notions of comorbidity between movement disorders and psychiatric symptoms was recognised at the recent meeting concerning, "Implications of Comorbidity for the Etiology and Treatment of Neuropsychiatric Disorders" held in Oct. 2005 in Mazagon, Spain. The identification of stages in the early development of neurodegenerative disorders appeared to unify multiple, diverse findings. These included: novel therapeutic innovations for Parkinson's disease, Alzheimer's disease and depression in the aged; the neurochemical ontogeny of drug-induced oral dyskinesias; the types of chemical agents abused in neuropsychiatric states; postnatal iron overload effects upon the functional and interactive role of dopaminergic and noradrenergic pathways that contribute to the expression of movement disorders; and the spectrum of motor symptoms expressed in schizophrenia and attention deficit hyperactivity disorder and the eventual treatment of these disorders. A continued focus on a number of neuropsychiatric diseases as progressive disorders may lead to further advances in understanding their etiology and in developing better therapeutics.

Further validation of LABORAS™ using various dopaminergic manipulations in mice including MPTP-induced nigro-striatal degeneration

The automated behavioural apparatus, LABORAS (Laboratory Animal Behaviour Observation, Registration and Analysis System), has been further validated with respect to the ability of the system to detect behavioural impairments in mice, following various dopaminergic manipulations. Initially data were obtained from mice administered with amphetamine, haloperidol, SCH23390, apomorphine and L-DOPA, with the focus on locomotor and grooming activities. The data recorded by LABORAS on administration of these pharmacological tool compounds, is comparable with published findings using standard LMA systems and conventional observer methods. In addition the home cage behaviour of mice administered with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) using an acute dosing regimen was also investigated. In LABORAS, mice subjected to MPTP lesioning showed deficits in spontaneous motor activity at day 6-7 post-MPTP administration, over a 24 h test period, as compared to saline treated controls. The data captured and analysed using LABORAS, suggests that the automated system is able to detect both pharmacologically and lesion-induced changes in behaviour of mice, reliably and efficiently.

Postnatal iron overload destroys NA-DA functional interactions

C57/BL6 mice were administered either postnatal iron (Fe(2+) 7.5 mg/kg, on postnatal days 10-12) or vehicle, followed by administration of either DSP4 (50 mg/kg, s.c., 30 min after injection of zimeldine, 20 mg/kg, s.c.) or vehicle (saline) at 63 days of age. Three weeks later, iron/vehicle treated, DSP4/vehicle treated mice were injected with either a low dose of MPTP (2 x 20 mg/kg, with a 24-hr interval between injections) or vehicle. Behaviour testing took place a further three weeks (spontaneous behaviour and L-Dopa induced) and two weeks (clonidine-L-Dopa induced) later. Postnatal iron administration exacerbated the bradykinesia induced by MPTP and virtually abolished all spontaneous motor activity in NA-denervated mice that were MPTP-treated. Postnatal iron administration reduced markedly the restoration of motor activity by suprathreshold L-Dopa (20 mg/kg) following a 60-min habituation to the test chambers. Pretreatment with DSP4 effectively eliminated the restorative effect of L-Dopa in the MPTP mice. The synergistic effects of co-administration of clinidine (1 mg/kg) with a subthreshold dose of L-Dopa (5 mg/kg) in elevating the motor activity of MPTP mice were reduced markedly by postnatal iron administration, as well as by pretreatment with DSP4. NA-denervation by DSP4, after postnatal iron treatment, totally abolished the activity-elevating effects of the alpha-adrenoceptor agonist + DA-precursor combination in MPTP mice, and virtually eliminated these effects in saline (non-MPTP) mice. Postnatal iron administration caused enduring higher levels of total iron content in all the groups with an increased level in mice treated with DSP4 followed by MPTP. These divergent findings confirm the direct influence of NA innervation upon dopaminergic functional expression and indicate a permanent vulnerability both in the noradrenergic and dopaminergic pathways following the postnatal infliction of an iron overload.

Ameliorating effect of dimethylsulfoniopropionate on the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's disease of mice

The effect of dimethylsulfoniopropionate (DMSP) on the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's disease (PD) of mice was examined for 5 d. The distilled water (the control group) and the DMSP solution at 5 x 10(-4) M (the DMSP group) were supplemented ad libitum to six mice each in two groups for 2 wk. An appropriate amount of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) solution (20 mg/kg body wt) was then intraperitoneally injected into all the test mice once a day initially for 3 d, which definitely made the control mice similar to the PD-model mice. The moving ability (running power) of the mice in both groups was measured using an automatic Wheel Running Instrument. The immobility duration of the upside-down mice in both groups was estimated by a newly developed polygraph (RMP-6008M, Nihon Koden Co., Ltd., Japan). The results indicated that the mice in the DMSP group showed a stronger moving ability and a shorter immobility duration compared to the mice in the control group during the experimental period. Furthermore, the amounts of catecholamines (dopamine and norepinephrine) in the brains except for the cerebellums of all the test mice were estimated 2 d after the last MPTP injection, which demonstrated that the brains of the mice in the DMSP group accumulate larger amounts of catecholamines, especially dopamine, than them in the control group. Accordingly, the administration of low concentrations of DMSP proved to prevent and/or ameliorate the decreased mobility and the typical immobility (Akinesia) of the MPTP-induced PD-model mice probably due to increased amounts of dopamine in the brains of the DMSP group mice.

Influence of noradrenaline denervation on MPTP-induced deficits in mice

C57/BL6 mice were administered either DSP4 (50 mg/kg, s.c., 30 min after injection of zimeldine, 20 mg/kg, s.c.) or vehicle (saline) at 63 days of age. Three weeks later, one group (n = 10) of DSP4-treated and one group of vehicle-treated mice were administered MPTP (2 x 40 mg/kg, s.c., 24 hours between injections; the High dose groups), one group (n = 10) of DSP4-treated and one group of vehicle-treated mice were administered MPTP (2 x 20 mg/kg, s.c., 24 hours between injections; the Low dose groups), and one group (n = 10) of DSP4-treated and one group of vehicle-treated mice were administered vehicle. Three weeks later, all six groups were tested in motor activity test chambers, followed by injections of L-Dopa (20 mg/kg, s.c.), and then tested over a further 360 min in the activity test chambers. It was found that pretreatment with the selective NA neurotoxin, DSP4, deteriorated markedly the dose-dependent motor activity deficits observed in the vehicle pretreated MPTP treated mice. These 'ultra-deficits' in the spontaneous motor behaviour of MPTP-treated mice were observed over all three parameters: locomotion, rearing and total activity, and were restricted to the 1(st) and 2(nd) 20-min periods. Administration of L-Dopa (20 mg/kg) following the 60-min testing of spontaneous behaviour restored the motor activity of Vehicle + MPTP treated mice (neither the Vehicle + MPTP-Low nor the Vehicle + MPTP-High groups differed from the Vehicle-Vehicle group, here) but failed to do so in the DSP4 pretreated mice. Here, a dose-dependent deficit of L-Dopa-induced motor activity (over all three parameters) was obtained thereby offering further evidence of an 'ultra-deficit' of function due to previous denervation of the NA terminals. The present findings support the notion that severe damage to the locus coeruleus noradrenergic system, through systemic DSP4, disrupts the facilitatory influence on the nigrostriatal DA system, and interferes with the ability of the nigrostriatal pathway to compensate for or recover from marked injury, MPTP treatment.

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 Parkinson's 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.

Treatment with alpha2-adrenoceptor antagonist, 2-methoxy idazoxan, protects 6-hydroxydopamine-induced Parkinsonian symptoms in rats: neurochemical and behavioral evidence

Noradrenaline, not only functions as a synaptic transmitter, but also promotes neural differentiation and regenerative processes. In Parkinson's disease, besides the dopaminergic degeneration, noradrenergic neurons of locus coeruleus origin degenerate as well. Drugs enhancing noradrenergic transmission in the locus coeruleus (e.g. alpha2-adrenoceptor antagonists) have been shown to be neuroprotective against Huntington's and ischemic animal models. However, in Parkinsonian animal models, most of the studies evaluated the worsening of experimental nigral neurodegeneration after locus coeruleus lesions. Here, it has been tested, whether treatment with the selective alpha2-adrenoceptor antagonist, 2-methoxy idazoxan (2.5 mg/kg i.p., twice daily for 5 days), before an experimental lesion to nigra, protects dopaminergic neurodegeneration. Dopaminergic degeneration was produced by 6-hydroxydopamine lesion in the median forebrain bundle. The concentrations of dopamine, 5-hydroxytryptamine and its metabolites were analysed in the various regions of the basal ganglia. The concentrations of noradrenaline and dopamine were measured in the regions innervated by locus coeruleus neurons and in the basal ganglia respectively, after 2-methoxy idazoxan treatment. The Parkinsonian behavior was assessed by catalepsy and activity test. 2-Methoxy idazoxan specifically increased the concentration of noradrenaline in the brain regions, innervated by locus coeruleus neurons. 6-OHDA lesion strongly depleted the concentration of dopamine and its metabolites in the striatum and SN, producing catalepsy and hypoactivity. Multiple treatments with 2-methoxy idazoxan reduced some of the observed neurochemical and behavioral indices of 6-hydroxydopamine-induced Parkinsonism, indicating neuroprotection. Although the mechanism underlying the neuroprotective property remains elusive, the therapeutic usage of alpha2-antagonists might be helpful in slowing the neuronal death and progression of Parkinson's disease.

Noradrenergic mechanisms in neurodegenerative diseases: a theory

A deficiency in the noradrenergic system of the brain, originating largely from cells in the locus coeruleus (LC), is theorized to play a critical role in the progression of a family of neurodegenerative disorders that includes Parkinson's disease (PD) and Alzheimer's disease (AD). Consideration is given here to evidence that several neurodegenerative diseases and syndromes share common elements, including profound LC cell loss, and may in fact be different manifestations of a common pathophysiological process. Findings in animal models of PD indicate that the modification of LC-noradrenergic activity alters electrophysiological, neurochemical and behavioral indices of neurotransmission in the nigrostriatal dopaminergic system, and influences the response of this system to experimental lesions. In models related to AD, noradrenergic mechanisms appear to play important roles in modulating the activity of the basalocortical cholinergic system and its response to injury, and to modify cognitive functions including memory and attention. Mechanisms by which noradrenaline may protect or promote recovery from neural damage are reviewed, including effects on neuroplasticity, neurotrophic factors, neurogenesis, inflammation, cellular energy metabolism and excitotoxicity, and oxidative stress. Based on evidence for facilitatory effects on transmitter release, motor function, memory, neuroprotection and recovery of function after brain injury, a rationale for the potential of noradrenergic-based approaches, specifically alpha2-adrenoceptor antagonists, in the treatment of central neurodegenerative diseases is presented.

Behavioral changes are not directly related to striatal monoamine levels, number of nigral neurons, or dose of parkinsonian toxin MPTP in mice

Behavioral analyses of mice intoxicated by the parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) have generated conflicting results. We therefore analyzed the relationship between behavioral changes, loss of monoamine levels, and loss of dopaminergic cell bodies in groups of mice intoxicated with acute or subchronic MPTP protocols. Despite a higher degree of neuronal loss in the mice intoxicated using subchronic protocols, dopamine loss was severe and homogeneous in the striatum in all groups. Dopamine levels were less severely reduced in the frontal cortex in the three groups of MPTP-intoxicated mice. Norepinephrine and serotonin levels in the striatum were decreased only in the mice intoxicated with the acute protocol. The most surprising result was that the mice intoxicated with the subchronic protocols were more active than the saline-treated mice. As reported in rats with dopamine depletion in the prefrontal cortex, the hyperactivity observed in our mice could be due to the reduced dopamine levels detected in this structure.

Potentiation of parkinsonian symptoms by depletion of locus coeruleus noradrenaline in 6-hydroxydopamine-induced partial degeneration of substantia nigra in rats

Parkinson's disease is characterized not only by a progressive loss of dopaminergic neurons in the substantia nigra but also by a degeneration of locus coeruleus noradrenergic neurons. The present study addresses the question of whether a partial neurodegeneration of dopaminergic neurons using 6-hydroxydopamine in rat, not sufficient to produce motor disturbances, is potentiated by prior selective denervation of locus coeruleus noradrenergic terminal fields using N-ethyl-2-bromobenzylamine. Two types of denervations, one causing dopamine deficiency alone and the other causing noradrenaline and dopamine deficiency, were performed. Noradrenaline, 5-hydroxytryptamine, 5-hydroxyindole acetic acid, dopamine and its metabolites were analysed in various brain regions. Behaviour was evaluated by catalepsy tests and activity box. N-ethyl-2-bromobenzylamine selectively depleted noradrenaline from neurons of locus coeruleus origin. Decreased dopamine content in the striatum, substantia nigra and pre-frontal cortex was observed after dopaminergic lesion with 6-hydroxydopamine (42.9%). Additional locus coeruleus noradrenaline depletion with N-ethyl-2-bromobenzylamine aggravated the dopamine depletion (61.2%). The lesion in the noradrenergic and dopaminergic neurodegenerated group was not sufficient to induce consistent catalepsy and akinesia. However, after a subthreshold dose of haloperidol (0.1 mg/kg), the expression of catalepsy and akinesia was strong in the dual-lesioned group and less in the 6-hydroxydopamine-lesioned group. These results indicate that denervation of locus coeruleus noradrenergic terminals with N-ethyl-2-bromobenzylamine potentiates the 6-hydroxydopamine-induced partial dopaminergic neurodegeneration and parkinsonian symptoms. Based on the present findings and existing reports, it can be concluded that noradrenergic neurons of locus coeruleus have neuromodulatory and neuroprotective properties on the dopaminergic neurons of basal ganglia and that noradrenergic degeneration may contribute to the aetiology and pathophysiology of Parkinson's disease.

Both short- and long-acting D-1/D-2 dopamine agonists induce less dyskinesia than L-DOPA in the MPTP-lesioned common marmoset (Callithrix jacchus)

The current concept of dyskinesia is that pulsatile stimulation of D-1 or D-2 receptors by L-DOPA or short-acting dopamine agonists is more likely to induce dyskinesia compared to long-acting drugs producing more continuous receptor stimulation. We now investigate the ability of two mixed D-1/D-2 agonists, namely pergolide (long-acting) and apomorphine (short-acting), to induce dyskinesia in drug-nai;ve MPTP-lesioned primates, compared to L-DOPA. Adult common marmosets (Callithrix jacchus) were lesioned with MPTP (2 mg/kg/day sc for 5 days) and subsequently treated with equieffective antiparkinsonian doses of L-DOPA, apomorphine, or pergolide for 28 days. L-DOPA, apomorphine, and pergolide reversed the MPTP-induced motor deficits to the same degree with no difference in peak response. L-DOPA and apomorphine had a rapid onset of action and short duration of effect producing a pulsatile motor response, while pergolide had a slow onset and long-lasting activity producing a continuous profile of motor stimulation. L-DOPA rapidly induced dyskinesia that increased markedly in severity and frequency over the course of the study, impairing normal motor activity by day 20. Dyskinesia in animals treated with pergolide or apomorphine increased steadily, reaching mild to moderate severity but remaining significantly less marked than that produced by L-DOPA. There was no difference in the intensity of dyskinesia produced by apomorphine and pergolide. These data suggest that factors other than duration of drug action may be important in the induction of dyskinesia but support the use of dopamine agonists in early Parkinson's disease, as a means of delaying L-DOPA therapy and reducing the risk of developing dyskinesia.

Behavioral phenotyping of the MPTP mouse model of Parkinson's disease

In mice, the systemical or intracranial application of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can lead to severe damage to the nigrostriatal dopaminergic system. This can result in a variety of symptoms concerning motor control resembling those in human Parkinson's disease, such as akinesia, rigidity, tremor, gait and posture disturbances. The aim of this work is to review a variety of behavioral paradigms for these and other symptoms, which have been used to characterize behavioral changes in mice after MPTP treatment. Main results are summarized, and general influential factors as well as potential problems in the experimental procedures are discussed, which should be taken into account when conducting behavioral analyses in mice with parkinsonian symptoms. Since there is reliable evidence (e.g. from strain comparisons) that the susceptibility of the nigrostriatal pathway to neurodegeneration is probably genetically influenced, relevant genes can be expected to be identified in the future. Therefore, the points discussed here will be useful not only for further applications in the MPTP mouse model, but also more generally for the behavioral characterization of future mouse models of PD, e.g. mice with a manipulation of genes relevant to the function of the basal ganglia.

Strain-dependent recovery of open-field behavior and striatal dopamine deficiency in the mouse MPTP model of Parkinson's disease

The neurotoxin MPTP can damage dopamine systems in the brains of rodents, cats, or monkeys, and is therefore widely used to model degenerative processes that underlie human Parkinson's disease. Here, we investigated the relationships between behavioral and neurochemical effects of systemic MPTP treatment in C57Bl/6 and Balb/c mice. Initially, different doses of MPTP were used to determine which of them might be useful to establish severe striatal dopamine depletions. These data showed that four injections of 20mg/kg at two hour intervals, were more efficient than 10 or 15mg/kg per injection. However, this dose was not usable due to its severe lethality in females. In contrast, 4x 15mg/kg had a low risk of lethality and led to substantial dopamine depletions, which were more severe in the neostriatum than the ventral striatum, and more severe in C57 than in Balb mice. In the first open field test, which was performed two hours after the last injection, this treatment led to severe behavioral inactivation in all parameters taken (distance and speed of locomotion, peripheral activity, frequency and duration of rearing). This effect was seen in both strains and gender. Thereafter, recovery differed between strains, since Balb mice, which had sustained the smaller lesions, had completely recovered on the subsequent day, whereas similar recovery took longer in C57 mice. On the fourth day, all groups appeared largely normal; however, the measure of rearing behavior still showed a deficit in C57 mice. This deficit on day 4 was correlated with neostriatal dopamine depletion; that is, the larger the lesion, the less the number and duration of rearings. Interestingly, these relationships were also observed with respect to ventral striatal dopamine damage, which was correlated with the rearing deficit not only on day 4, but also on day 1. These data will be discussed with respect to mechanisms of toxicity, functional recovery, and the function of striatal dopamine systems.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) reduces norepinephrine concentrations in the olfactory bulbs of male mice

Male retired breeder C57/Bl and CD-1 mice were treated with either MPTP or its vehicle. At 7-10 days post-treatment, catecholamine concentrations within the olfactory bulbs (OB) and hypothalamus were determined. Norepinephrine concentrations within the OB were significantly decreased in MPTP-treated mice. These effects were more pronounced in the CD-1 (50% reduction) compared to the C57/Bl (20% reduction) strain. No effects of MPTP were observed on norepinephrine concentrations within the hypothalamus. Dopamine concentrations in the OB and hypothalamus did not differ between MPTP- and vehicle-treated mice in either strain. Overall, catecholamine concentrations within the OB, but not the hypothalamus, were significantly greater in C57/Bl compared to CD-1 mice. The reduction in OB norepinephrine concentration in the MPTP-treated animals may be related to the olfactory deficits which accompany Parkinson's disease.