Treatment with the noradrenaline re-uptake inhibitor atomoxetine alone and in combination with the α2-adrenoceptor antagonist idazoxan attenuates loss of dopamine and associated motor deficits in the LPS inflammatory rat model of Parkinson's disease.

The impact of treatment with the noradrenaline (NA) re-uptake inhibitor atomoxetine and the α2-adrenoceptor (AR) antagonist idazoxan in an animal model of Parkinson's disease (PD) was assessed. Concurrent systemic treatment with atomoxetine and idazoxan, a combination which serves to enhance the extra-synaptic availability of NA, exerts anti-inflammatory and neuroprotective effects following delivery of an inflammatory stimulus, the bacterial endotoxin, lipopolysaccharide (LPS) into the substantia nigra. Lesion-induced deficits in motor function (akinesia, forelimb-use asymmetry) and striatal dopamine (DA) loss were rescued to varying degrees depending on the treatment. Treatment with atomoxetine following LPS-induced lesion to the substantia nigra, yielded a robust anti-inflammatory effect, suppressing microglial activation and expression of the pro-inflammatory cytokine TNF-α whilst increasing the expression of neurotrophic factors. Furthermore atomoxetine treatment prevented loss of tyrosine hydroxylase (TH) positive nigral dopaminergic neurons and resulted in functional improvements in motor behaviours. Atomoxetine alone was sufficient to achieve most of the observed effects. In combination with idazoxan, an additional improvement in the impairment of contralateral limb use 7 days post lesion and a reduction in amphetamine-mediated rotational asymmetry 14 days post-lesion was observed, compared to atomoxetine or idazoxan treatments alone. The results indicate that increases in central NA tone has the propensity to regulate the neuroinflammatory phenotype in vivo and may act as an endogenous neuroprotective mechanism where inflammation contributes to the progression of DA loss. In accordance with this, the clinical use of agents such as NA re-uptake inhibitors and α2-AR antagonists may prove useful in enhancing the endogenous neuroimmunomodulatory potential of NA in conditions associated with brain inflammation.

Assessment of the analgesic effect of centhaquin in mouse tail flick and hot-plate tests.

BACKGROUND: Centhaquin is a centrally acting hypotensive drug like clonidine. Clonidine also produces analgesia and hypothermia in mice and potentiates morphine analgesia. Clonidine analgesia is blocked by idazoxan and naloxone while it is potentiated by BQ123 and sulfisoxazole. This study was conducted to determine the analgesic and hypothermic properties of centhaquin, and to assess whether it potentiates morphine analgesia. Yohimbine (α(2)-adrenergic antagonist), idazoxan (imidazoline/α(2)-adrenergic antagonist), naloxone (opioid antagonist), and BQ123 and sulfisoxazole (endothelin ET(A) antagonists) were used to study the involvement of these receptors in centhaquin analgesia and hypothermia. METHODS: Analgesic (tail flick and hot-plate tests) latencies and body temperatures were measured in male Swiss Webster mice treated with vehicle plus centhaquin, antagonists plus centhaquin or centhaquin plus morphine. RESULTS: Centhaquin produced dose-dependent analgesia which was partially blocked by yohimbine, idazoxan and naloxone. BQ123 and sulfisoxazole did not affect centhaquin analgesia. Morphine analgesia was not potentiated by centhaquin. Centhaquin produced mild hypothermia which was not blocked by yohimbine, idazoxan, naloxone, BQ123 or sulfisoxazole. CONCLUSIONS: This is the first report demonstrating the analgesic activity of centhaquin. The α(2)-adrenergic, imidazoline and opioid receptors are involved in mediating centhaquin analgesia. Endothelin ET(A) receptors do not play a role in centhaquin analgesia; centhaquin does not augment morphine analgesia.

The alpha(2) adrenoceptor antagonist idazoxan alleviates L-DOPA-induced dyskinesia by reduction of striatal dopamine levels: an in vivo microdialysis study in 6-hydroxydopamine-lesioned rats.

L-DOPA-induced dyskinesia is characterised by debilitating involuntary movement, which limits quality of life in patients suffering from Parkinson's disease. Here, we investigate effects of the a2 adrenoceptor antagonist idazoxan on L-DOPA-induced dyskinesia as well as on alterations of extracellular L-DOPA and dopamine (DA) levels in the striatum in dyskinetic rats. Male Wistar rats were unilaterally lesioned with 6-hydroxydopamine and subsequently treated with L-DOPA/benserazide to induce stable dyskinetic movements.Administration of idazoxan [(9 mg/kg, intraperitoneal (i.p.)]significantly alleviated L-DOPA-induced dyskinesia, whereas idazoxan (3 mg/kg, i.p.) did not affect dyskinetic behaviour.Bilateral in vivo microdialysis revealed that idazoxan 9 mg/kg reduces extracellular peak L-DOPA levels in the lesioned and intact striatum as well as DA levels in the lesioned striatum. In parallel, the exposure to idazoxan in the striatum was monitored.Furthermore, no idazoxan and L-DOPA drug-drug interaction was found in plasma, brain tissue and CSF. In conclusion, the decrease of L-DOPA-derived extracellular DA levels in the lesioned striatum significantly contributes to the anti-dyskinetic effect of idazoxan.

Modulation of inflammatory response via alpha2-adrenoceptor blockade in acute murine colitis.

Inflammatory bowel disease (IBD) is characterized by heavy production of proinflammatory cytokines such as tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta. Interactions of the autonomic nervous system with local immune cells play an important role in the development of IBD, and the balance of autonomic nerve function is broken in IBD patients with sympathetic overactivity. However, the function of catecholamines in the progress of colitis is unclear. In this study, we examined the role of catecholamines via alpha2-adrenoreceptor in acute murine colitis. The expression of tyrosine hydroxylase (TH) and dopamine b-hydroxylase (DBH), two rate-limiting enzymes in catecholamine synthesis, was detected by immunohistochemistry in murine colitis. Murine colitis was induced by dextran sodium sulphate or trinitrobenzene sulphonic acid (TNBS), and the mice were administered RX821002 or UK14304, alpha2-adrenoceptor antagonists or agonists. Colitis was evaluated by clinical symptoms, myeloperoxidase assay, TNF-alpha and IL-1beta production and histology. Lamina propria mononuclear cells (LPMCs) from mice with TNBS colitis were cultured in the absence or presence of RX821002 or UK14304, and stimulated further by lipopolysaccharide. TH and DBH are induced in LPMCs of inflamed colon, the evidence of catecholamine synthesis during the process of colitis. RX821002 down-regulates the production of proinflammatory cytokines from LPMCs, while UK14304 leads to exacerbation of colitis. Together, our data show a critical role of catecholamines via alpha2-adrenoreceptors in the progress of acute colitis, and suggest that use of the alpha2-adrenoceptor antagonist represents a novel therapeutic approach for the management of colitis.

Attenuation of ischemia-induced rat brain injury by 2-(-2-benzofuranyl)-2-imidazoline, a high selectivity ligand for imidazoline I(2) receptors.

OBJECTIVE: The aim of this study was to determine whether 2-(2-benzofuranyl)-2-imidazoline, an imidazoline I(2) receptor ligand, could protect against cell death from brain injury and improve the functional outcome after focal cerebral ischemia in rats. METHODS: Transient focal ischemia was induced by suture occlusion of the middle cerebral artery. Rats were intraperitoneally treated with a vehicle, 2-(2-benzofuranyl)-2-imidazoline or idazoxan immediately after focal ischemia. Infarct volume was assessed by 2,3,5-triphenyltrazolium chloride staining and neurobehavioral deficits were monitored. The volume of cell death in the penumbra after ischemia was determined by immunostaining using anti-cleaved caspase-3 antibody and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL). RESULTS: Both 2-(2-benzofuranyl)-2-imidazoline and idazoxan significantly improved the neurological score compared with the vehicle at 24 hours after focal ischemia. Treatment with 2-(2-benzofuranyl)-2-imidazoline or idazoxan also significantly reduced infarct volume and the number of both caspase-3- and TUNEL-positive cells in the penumbra compared with vehicle-treated rats (p<0.01 and p<0.05, respectively). CONCLUSION: The results suggest the neuroprotective role of 2-(2-benzofuranyl)-2-imidazoline and idazoxan in focal cerebral ischemia, and may therefore represent useful targets for developing new treatments for stroke.

Agomelatine: a new opportunity to reduce neuropathic pain-preclinical evidence.

Antidepressants are first-line treatments of neuropathic pain but not all these drugs are really effective. Agomelatine is an antidepressant with a novel mode of action, acting as an MT1/MT2 melatonergic receptor agonist and a 5-HT2C receptor antagonist that involves indirect norepinephrine release. Melatonin, serotonin, and norepinephrine have been involved in the pathophysiology of neuropathic pain. Yet, no study has been conducted to determine agomelatine effects on neuropathic pain in animal models. Using 3 rat models of neuropathic pain of toxic (oxaliplatin/OXA), metabolic (streptozocin/STZ), and traumatic (sciatic nerve ligation/CCI [chronic constriction nerve injury]) etiologies, we investigated the antihypersensitivity effect of acute and repeated agomelatine administration. We then determined the influence of melatonergic, 5-HT2C, α-2 and ß-1/2 adrenergic receptor antagonists in the antihypersensitivity effect of agomelatine. The effect of the combination of agomelatine + gabapentin was evaluated using an isobolographic approach. In STZ and CCI models, single doses of agomelatine significantly and dose dependently reduced mechanical hypersensitivity. After daily administrations for 2 weeks, this effect was confirmed in the CCI model and agomelatine also displayed a marked antihypersensitivity effect in the OXA model. The antihypersensitivity effect of agomelatine involved melatonergic, 5-HT2C, and α-2 adrenergic receptors but not beta adrenoceptors. The isobolographic analysis demonstrated that the combination of agomelatine + gabapentin had additive effects. Agomelatine exerts a clear-cut antihypersensitivity effect in 3 different neuropathic pain models. Its effect is mediated by melatonergic and 5-HT2C receptors and, although agomelatine has no affinity, also by α-2 adrenergic receptors. Finally, agomelatine combined with gabapentin produces an additive antihypersensitivity effect.

Imidazoline drugs stabilize lysosomes and inhibit oxidative cytotoxicity in astrocytes.

Oxidative stress is a primary pathogenesis in the brain, which is particularly vulnerable to oxidative stress. Maintenance of astrocyte functions under oxidative stress is essential to prevent neuronal injuries and to recover neuronal functions in various pathologic conditions. Imidazoline drugs have affinities for imidazoline receptors, which are highly distributed in the brain, and have been shown to be neuroprotective. This study presented the protective effects of several imidazoline drugs against oxidative cytotoxicity, in primary cultures of astrocytes. Imidazoline drugs, such as idazoxan, guanabenz, guanfacine, BU224, and RS-45041-190, showed protective effects against naphthazarin-induced oxidative cytotoxicity, as evidenced by LDH release and Hoechst 33342/propidium iodide staining. The imidazoline drugs stabilized lysosomes and inhibited naphthazarin-induced lysosomal destabilization, as evidenced by acridine orange relocation. Guanabenz inhibited, the leakage of lysosomal cathepsin D to cytosol, the decreased mitochondrial potential, and the release of mitochondrial cytochrome c, which were induced by naphthazarin. The lysosomal destabilization by oxidative stress and other apoptotic signals and subsequent cathepsin D leakage to the cytosol can induce apoptotic changes of mitochondria and eventually cell death. Therefore, lysosomal stabilization by imidazoline drugs may be ascribed to their protective effects against oxidative cytotoxicity.

The alpha 2-adrenoceptor antagonist idazoxan reverses catalepsy induced by haloperidol in rats independent of striatal dopamine release: role of serotonergic mechanisms.

The alpha(2)-adrenoceptor antagonist idazoxan may improve motor symptoms in Parkinson's disease and experimental Parkinsonism. We studied the effect of idazoxan on haloperidol-induced catalepsy in rats, an animal model of the drug-induced extrapyramidal side effects in man. Catalepsy was induced by a subcutaneous (s.c.) injection of haloperidol (1 mg/kg) and measured by the bar test for a maximum of 5 min. At 3 h after haloperidol, rats were given 0.16-5.0 mg/kg s.c. idazoxan, and descent latency was measured 1 h later. Idazoxan potently reversed haloperidol-induced catalepsy with an ED(50) of 0.25 mg/kg. This effect was mimicked by the selective alpha(2)-adrenoceptor antagonist RS-15385-197 (0.3 and 1 mg/kg orally). We assessed how dopaminergic mechanisms were involved in the anticataleptic effect of idazoxan by studying its effect on dopamine (DA) release in the striatum, with the microdialysis technique in conscious rats. Idazoxan (0.3 and 2.5 mg/kg) had no effect on extracellular DA and did not modify the rise of extracellular DA induced by haloperidol, indicating that changes of striatal DA release were not involved in the reversal of catalepsy. The anticataleptic effect of 2.5 mg/kg idazoxan (haloperidol+vehicle 288+/-8 s, haloperidol+idazoxan 47+/-22 s) was attenuated in rats given an intraventricular injection of 150 microg of the serotonin (5-HT) neurotoxin 5,7-dihydroxytryptamine (haloperidol+vehicle 275+/-25 s, haloperidol+idazoxan 137+/-28 s). The 5-HT(1A) receptor antagonist WAY100 635 (0.1 mg/kg s.c.) did not affect the anticataleptic effect of idazoxan. The results suggest that idazoxan reversed haloperidol-induced catalepsy by a mechanism involving blockade of alpha(2)-adrenoceptors and, at least in part, 5-HT neurons.

The alpha(2) antagonist idazoxan remediates certain attentional and executive dysfunction in patients with dementia of frontal type.

Abstract The mixed alpha(1)/alpha(2) adrenoceptor agonist clonidine has been shown by us previously to impair certain attentional and executive functions in healthy volunteers. The present investigation examines the effects of the alpha(2) adrenoceptor antagonist idazoxan (IDZ) on cognitive function in patients with dementia of frontal type (DFT). Using a placebo-controlled ABBA design, three DFT patients were given two doses of IDZ and tested on a range of computerised tests of attention, memory and executive function. Idazoxan was found to produce dose-dependent improvements in performance, particularly on tests of planning, sustained attention, verbal fluency and episodic memory. In contrast, IDZ produced deficits in performance on a test of spatial working memory. These results suggest that IDZ may be useful as a putative cognitive enhancer, particularly in patients showing a specific pattern of frontal lobe dysfunction.

The influence of chronic treatment with clonidine, yohimbine and idazoxan on morphine withdrawal.

Numerous previous attempts have been made to study the involvement of alpha2-adrenoceptors in the expression of morphine withdrawal by studying the effects of selective alpha2-agonists and antagonists administered immediately before precipitation of withdrawal by an opioid antagonist such as naloxone. In the present investigation, we examined the effects of chronic treatment with clonidine (alpha2-agonist), idazoxan and yohimbine (alpha2-antagonists), concomitantly administered with morphine, on the expression of the withdrawal signs. In contrast to their acute effects, clonidine potentiated, while yohimbine and idazoxan attenuated the withdrawal signs precipitated by naloxone in morphine-dependent mice. In addition, mice chronically treated only with yohimbine displayed withdrawal signs similar to those reported with morphine withdrawal and these signs were not influenced by naloxone administration. Mice chronically treated with clonidine displayed withdrawal signs similar to those reported with morphine withdrawal and these signs were further potentiated by naloxone administration. The results suggest that down-regulation of alpha2-adrenoceptors by morphine is a major adaptation contributing to development of dependence on opioids and also point the way to more effective treatment of narcotic dependence. This suggestion was based on the hypothesis that the suppression of noradrenergic system during chronic morphine treatment by alpha2-antagonists might diminish noradrenergic hyperactivity and consequently the development of dependence and withdrawal signs.

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.

Post-hypoxic frequency decline does not depend on alpha2-adrenergic receptors in the adult rat.

The aim of this study was to determine whether post-hypoxic frequency decline (PHFD) requires central activation of alpha2-adrenergic receptors. PHFD is defined as the undershoot in respiratory frequency that occurs immediately following brief hypoxic periods. Adult anesthetized, vagotomized rats were exposed to hypoxia (8% O2, mean=45 s) before and after intracerebroventricular (i.c.v.) infusion of vehicle or alpha2-antagonist. The efficacy of the i.c.v. antagonist was assessed by recording the response to intravenous injection of alpha2-agonist before and after the infusion. We compared breathing frequencies before, during, and after hypoxia, both before and after treatments. The decline in breathing frequency after hypoxia was not prevented by the alpha2-antagonists, RX 821002 or SK&F-86466. Guanabenz, an alpha2-agonist, prolonged baseline expiration and potentiated PHFD. Prior treatment with SK&F-86466 blocked the agonist-evoked response which was also reversed by subsequent administration of SK&F-86466. We conclude that PHFD does not require the activation of alpha2-adrenergic receptors, but that alpha2-adrenergic receptors can modulate resting and post-hypoxic respiratory frequency.

Noradrenoceptor antagonism with idazoxan improves L-dopa-induced dyskinesias in MPTP monkeys.

Treatment of Parkinson's disease with L-dopa is plagued in a majority of patients by dyskinesias. Noradrenaline/dopamine interactions are proposed on behavioral, biochemical, physiological and anatomical grounds. The aim of the study was to test the potential antidyskinetic effect of the alpha2-adrenoceptor antagonist, idazoxan, in a primate model of Parkinson's disease. Six female cynomolgus monkeys previously rendered parkinsonian by the toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and presenting an unchanged syndrome for several months were used. All responded readily to L-dopa but had developed dyskinesias which were manifested with each dose. In the first part of the study, seven doses of idazoxan (ranging from 0.25 mg/kg to 10 mg/kg, p.o.) were administered together with the vehicle or in combination with a fixed dose of L-dopa/benserazide (100/25 mg, p.o.). In the second part of the study, a fixed dose of idazoxan (7.5 mg/kg) was administered daily for 10 days and L-dopa was added to idazoxan on days 1, 4, 7 and 10. Vehicle (empty capsule) was used as control. Idazoxan, by itself (ranging from 5 mg/kg to 10 mg/kg), increased locomotor activity and improved the disability score with virtually no dyskinesias in three animals. In combination with L-dopa, idazoxan did not impair the antiparkinsonian response but significantly reduced dyskinesias in all six animals up to 65% at doses of 7.5 mg/kg and 10 mg/kg and delayed their onset, so that the "ON" state without dyskinesias was prolonged. The antidyskinetic effect of idazoxan was maintained when repeatedly administered for 10 days. On day 10, the locomotor response to L-dopa was significantly potentiated by chronic administration of idazoxan. Our results indicate that idazoxan has some antiparkinsonian effect of its own and may constitute a useful adjunct to L-dopa as it can reduce dyskinesias without impairing the relief of symptoms, this effect being maintained over time in this model.

The effect of the alpha2-adrenoreceptor antagonist idazoxan against 6-hydroxydopamine-induced Parkinsonism in rats: multiple facets of action?

The alpha2-adrenoreceptor antagonist idazoxan counteracts catalepsy induced by neuroleptic agents and improves Parkinsonian signs in 1-methyl-4-phenyl 1,2,3,6,tetrahydropyridine-treated monkeys and in patients. The present study addressed the question of whether systemic administration of idazoxan (1.5 mg/kg i.p.) improves Parkinsonian symptoms in a rat model of permanent dopaminergic neurodegeneration. Dopaminergic degeneration was induced by injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB). Parkinsonian behaviour was assessed by catalepsy and open-field exploratory behaviour tests. Since dopaminergic and serotonergic mechanisms are thought to account for the anti-cataleptic/anti-Parkinsonian property of idazoxan, dopamine, 5-hydroxytryptamine (5-HT) and its metabolites in the regions of the basal ganglia and prefrontal cortex were analysed by HPLC. 6-OHDA lesions in the MFB produced catalepsy and hypoactivity in the open field and depleted dopamine and its metabolites in the basal ganglia and prefrontal cortex, but did not affect 5-HT. Treatment with idazoxan counteracted the observed Parkinsonian behaviour in 6-OHDA-lesioned rats and increased the spontaneous open-field activity in control rats. In both 6-OHDA and control animals, idazoxan increased DA level in the prefrontal cortex, but not in any other structures including the striatum. Idazoxan also increased the levels of 5-HT in the anterior striatum, prefrontal cortex and the ventral tegmental area of both 6-OHDA and control animals. These findings indicate that systemic administration of idazoxan counteracts 6-OHDA-induced Parkinsonian symptoms in rats and that both dopaminergic and serotonergic mechanisms could contribute to its anti-Parkinsonian effect.

A double-blind study comparing idazoxan and bupropion in bipolar depressed patients.

BACKGROUND: There is a small body of evidence indicating that idazoxan, a potent and selective alpha-2 antagonist, may be effective in treating bipolar depressive disorder. The purpose of this prospective controlled study is to compare idazoxan to bupropion, an antidepressant which has been suggested to have some advantages over other antidepressants in treating bipolar depressed patients. METHODS: Bipolar I depressed patients were randomly assigned in this 6-week double-blind out-patient study to receive either idazoxan, titrated to 240 mg/day and placebo bupropion, or bupropion, titrated to 450 mg/day and placebo idazoxan. These doses were achieved after 2 weeks. Depression severity was assessed with the Hamilton Depression Rating Scale and possible psychosis with the Brief Psychiatric Rating Scale. Side effects, heart rate, weight, and orthostatic blood pressure were also monitored. RESULTS: Fourteen patients completed this study (seven in each group). Both idazoxan and bupropion demonstrated significant improvement over time with reductions in Hamilton scores of 50%. LIMITATIONS: Limitations of this study include lack of a placebo group and small sample size. CONCLUSION: In light of our preliminary findings suggesting the usefulness of idazoxan in bipolar depression, larger more rigorous studies are indicated.

Idazoxan reduces blood-brain barrier damage during experimental autoimmune encephalomyelitis in mouse.

We have previously shown that Idazoxan (IDA), an imidazoline 2 receptor ligand, is neuroprotective against spinal cord injury caused by experimental autoimmune encephalomyelitis (EAE) in mouse, an animal modal of multiple sclerosis (MS). However, the protective mechanism remains unclear. Here, we provided evidence to show that IDA confers neuroprotection through reduction in blood-brain barrier (BBB) damage. EAE was induced by immunizing C57 BL/6 mice with myelin oligodendrocyte glycoprotein35-55 amino acid peptide (MOG35-55). IDA was administrated for 14 days after MOG immunization at 2 mg/kg (i.p., bid). Significant reduction in BBB damage occurred in the IDA-treated group of mice compared with the saline-treated group, as evidenced by the reduction in Evan׳s blue content in the brain tissue and the reduced BBB tight junction damage viewed under a transmission electron microscope. Moreover, EAE-induced reductions in tight junction proteins (JAM-1, Occludin, Claudin-5 and ZO-1) were also significantly ameliorated in IDA-treated mice, all of which supported the notion that IDA reduced BBB damage. Interestingly, the expression levels of extracellular matrix metalloproteinase-9 (MMP-9) and the ratio of MMP-9 against tissue inhibitor of metalloproteinase-1 (TIMP-1), which is known to be associated with MS-induced BBB damage, were significantly reduced in IDA-treated group, lending further support to the hypothesis that IDA confers brain protection through reducing BBB damage. This study raised a possibility that IDA is a promising pro-drug for development against MS.

Effects of noradrenergic denervation on L-DOPA-induced dyskinesia and its treatment by α- and ß-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 ß-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 ß-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.

Idazoxan attenuates spinal cord injury by enhanced astrocytic activation and reduced microglial activation in rat experimental autoimmune encephalomyelitis.

Idazoxan, an imidazoline 2 receptor (I(2)R) ligand, has been shown to protect against brain injury in several animal models of neurological disorders. In the present study we investigated the effect of idazoxan on experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. EAE was induced by immunizing Wistar rats with guinea pig spinal cord homogenates emulsified in CFA, followed by daily treatment of idazoxan (0, 0.5 mg/kg, 1.5 mg/kg, 4.5 mg/kg, i.p, bid) for 10 days. The results showed that the treatment of idazoxan (1.5 mg/kg and 4.5 mg/kg) significantly decreased the incidence and alleviated inflammatory cell infiltration and demyelination in spinal cords and cerebral cortex. Furthermore, the protective effect of idazoxan on EAE was associated with the enhanced astrocytic activation and attenuated microglial activation and with the subsequent down-regulated expression of proinflammatory cytokines IL-12p40 and IFN-gamma and up-regulated expression of anti-inflammatory cytokines IL-10 and TGF-beta(1). Thus, the daily treatment of the I(2)R ligand idazoxan for 10 days attenuates EAE pathology by differential modulation of astrocytic and microglial activations, raising a possibility that the I(2)R ligand may be a novel strategy for treating EAE.

A simple rodent assay for the in vivo identification of agents with potential to reduce levodopa-induced dyskinesia in Parkinson's disease.

l-DOPA-induced dyskinesia (LID) remains a major complication of the treatment of Parkinson's disease (PD). Whilst the MPTP-lesioned primate provides an excellent animal model in which to develop new therapies, however, it is logistically difficult to employ widely. Thus, a simple rodent assay to screen multiple compounds as candidates for further study of their potential in LID would be a valuable addition to the drug development process. Here, we investigate how agents with demonstrated ability to reduce LID in man and monkey can regulate l-DOPA-induced behaviours in the reserpine-treated rat. Administration of l-DOPA (125 mg/kg) to reserpine-treated rats elicited high levels of both horizontal and vertical movement. Drugs that have previously been found to reduce LID in parkinsonian primates and PD patients without compromising the anti-parkinsonian efficacy of l-DOPA selectively and dose-dependently reduce vertical components of activity when co-administered with l-DOPA in the reserpine-treated rat. For instance, amantadine (1 mg/kg) and idazoxan (3 mg/kg) reduced vertical activity by 59% and 83%, respectively, while neither drug had significant effects on horizontal activity. In contrast, haloperidol (1 mg/kg), an agent lacking the ability to selectively reduce LID without compromising the anti-parkinsonian actions of l-DOPA, reduced both horizontal and vertical activity, by 98% and 99%, respectively. We also assessed the actions of an NMDA antagonist, a class of compound proposed to have potential as anti-dyskinetic agents. The effects of MK-801 were dose-dependent (0.01-0.5 mg/kg), at some doses (e.g., 0.05 mg/kg), providing selective reduction of vertical activity (90%), at others (e.g., 0.5 mg/kg), non-selective reduction of vertical and horizontal (99% and 77%, respectively). These observations highlight the association between potential anti-dyskinetic action and a selective reduction in l-DOPA-induced vertical activity in the reserpine-treated rat.

Combined alpha2 and D2/3 receptor blockade enhances cortical glutamatergic transmission and reverses cognitive impairment in the rat.

The alpha(2) adrenoceptor antagonist idazoxan enhances antipsychotic efficacy of classical dopamine D(2) antagonists in treatment-resistant schizophrenia. The mechanisms are not fully understood, but we have previously shown that the combination of idazoxan with the D(2/3) receptor antagonist raclopride, similarly to clozapine but not classical antipsychotic drugs, augments dopamine efflux in the prefrontal cortex, and also generates an enhanced suppression of the conditioned avoidance response. We have now investigated the effects of clozapine, raclopride, idazoxan and the combination of raclopride and idazoxan on (i) electrically evoked excitatory post-synaptic potentials and currents in pyramidal cells of the rat medial prefrontal cortex, using intracellular electrophysiological recording in vitro, (ii) the impaired cognitive function induced by the selective N-methyl-D-aspartate (NMDA) receptor antagonist MK-801, using the 8-arm radial maze test, (iii) the in-vivo D2, alpha(2A) and alpha(2C) receptor occupancies of these pharmacological treatments, using ex-vivo autoradiography. Whereas neither idazoxan nor raclopride alone had any effect, the combination exerted the same facilitation of glutamatergic transmission in rat prefrontal pyramidal neurons as clozapine, and this effect was found to be mediated by dopamine acting at D(1) receptors. Similarly to clozapine, the combination of idazoxan and raclopride also completely reversed the working-memory impairment in rats induced by MK-801. Moreover, these effects of the two treatment regimes were obtained at similar occupancies at D(2), alpha(2A) and alpha(2C) receptors respectively. Our results provide novel neurobiological and behavioural support for a pro-cognitive effect of adjunctive use of idazoxan with antipsychotic drugs that lack appreciable alpha(2) adrenoceptor-blocking properties, and define presynaptic alpha(2) adrenoceptors as major targets in antipsychotic drug development.