Deprenyl's effect at slowing progression of parkinsonian disability: the DATATOP study. The Parkinson Study Group

9-Methyl-β-carboline inhibits monoamine oxidase activity and stimulates the expression of neurotrophic factors by astrocytes

β-Carbolines (BC) are pyridoindoles, which can be found in various exogenous and endogenous sources. Recent studies revealed neurostimulative, neuroprotective, neuroregenerative and anti-inflammatory effects of 9-methyl-BC (9-Me-BC). Additionally, 9-me-BC increased neurite outgrowth of dopaminergic neurons independent of dopamine uptake into these neurons. In this study, the role of astrocytes in neurostimulative, neuroregenerative and neuroprotective properties of 9-me-BC was further explored.

9-Me-BC exerted anti-proliferative effects without toxic properties in dopaminergic midbrain and cortical astrocyte cultures. The organic cation transporter (OCT) but not the dopamine transporter seem to mediate at least part the effect of 9-me-BC on astrocytes. Remarkably, 9-me-BC stimulated the gene expression of several important neurotrophic factors for dopaminergic neurons like Artn, Bdnf, Egln1, Tgfb2 and Ncam1. These factors are well known to stimulate neurite outgrowth and to show neuroprotective and neuroregenerative properties to dopaminergic neurons against various toxins. Further, we show that effect of 9-me-BC is mediated through phosphatidylinositol 3-kinase (PI3K) pathway. Additionally, 9-me-BC showed inhibitory properties to monoamine oxidase (MAO) activity with an IC50 value of 1 µM for MAO-A and of 15.5 µM for MAO-B. The inhibition of MAO by 9-me-BC might contribute to the observed increased dopamine content and anti-apoptotic properties in cell culture after 9-me-BC treatment in recent studies. Thus, 9-me-BC have a plethora of beneficial effects on dopaminergic neurons warranting its exploration as a new multimodal anti-parkinsonian medication.

Phase IIb Study of Intranasal Glutathione in Parkinson's Disease

BACKGROUND

Reduced glutathione (GSH) is an endogenously synthesized tripeptide depleted early in the course of Parkinson's disease (PD) and GSH augmentation has been proposed as a therapeutic strategy in PD.

OBJECTIVE

This Phase IIb study was designed to evaluate whether a Phase III study of intranasal GSH, (in)GSH, for symptomatic relief is warranted and to determine the most appropriate trial design for a disease-modification study.

METHODS

This was a double-blind, placebo-controlled trial of 45 individuals with Hoehn & Yahr Stage 1-3 PD. Participants were randomized to receive intranasal placebo (saline), 100 mg GSH, or 200 mg GSH thrice daily for three months, and were observed over a one-month washout period.

RESULTS

All cohorts improved over the intervention period, including placebo. The high-dose group demonstrated improvement in total Unified PD Rating Scale (UPDRS) (-4.6 (4.7), P = 0.0025) and UPDRS motor subscore (-2.2 (3.8), P = 0.0485) over baseline, although neither treatment group was superior to placebo. One participant in the high-dose GSH cohort developed cardiomyopathy.

CONCLUSIONS

Although predicted improvements in PD total and motor scores were observed, these data do not suggest (in)GSH is superior to placebo after a three month intervention. The symptomatic effects are sufficient to warrant a delayed-start or wash-out design study for disease-modification trials. Whether long-term use of (in)GSH leads to clinical improvements that are sustained and significantly different than placebo will require appropriately-powered longer-duration studies in larger cohorts. The improvement in the placebo arm was more robust than has been observed in previous PD studies and warrants further investigation.

Assessment of disease progression and functional benefit in neurodegenerative disease: can we tell the difference?

Therapeutic strategies for neurodegenerative diseases include modalities intended to modulate disease progression as well as those whose intent is to improve or maintain functional capacity. As the search for pharmacodynamic markers has proved elusive, treatment outcomes most commonly reflect patient function. As a result, even when clinical trials show a beneficial effect, the underlying etiology of that benefit can be difficult to determine. This review summarizes recent trials in ALS and Parkinson's disease, with the goal of increasing understanding of how the choice of outcome measures influences what can be concluded from the results. Although most ALS trials have been negative in recent years, outcomes are reviewed in terms of potential conclusions that could have been drawn. Functional benefit has been established in a number of recent trials; however, the outcomes used have lead to uncertainty as to whether specific agents modify disease or alter function. In the absence of specific markers sensitive to alteration of disease specific pathways, the distinction between agents that alter underlying disease versus those that affect function may depend on underlying hypotheses rather than clinical trial results.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Our systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updated this review.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science to February 2011. We scanned bibliographies of relevant publications and asked pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimise the risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors. Random-effects model meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Seventy-eight randomised trials with 296,707 participants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the parallel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combination with vitamins, minerals, or other interventions. The duration of supplementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I(2)- of 12%. In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. Meta-regression analysis did not find a significant difference in the estimated intervention effect in the primary prevention and the secondary prevention trials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias demonstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Animal and physiological research as well as observational studies suggest that antioxidant supplements may improve survival.

OBJECTIVES

To assess the effect of antioxidant supplements on mortality in primary or secondary prevention randomised clinical trials.

SEARCH STRATEGY

We searched The Cochrane Library (Issue 3, 2005), MEDLINE (1966 to October 2005), EMBASE (1985 to October 2005), and the Science Citation Index Expanded (1945 to October 2005). We scanned bibliographies of relevant publications and wrote to pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention. Included participants were either healthy (primary prevention trials) or had any disease (secondary prevention trials).

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Trials with adequate randomisation, blinding, and follow-up were classified as having a low risk of bias. Random-effects and fixed-effect meta-analyses were performed. Random-effects meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Sixty-seven randomised trials with 232,550 participants were included. Forty-seven trials including 180,938 participants had low risk of bias. Twenty-one trials included 164,439 healthy participants. Forty-six trials included 68111 participants with various diseases (gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, endocrinological, or unspecified). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects meta-analysis (relative risk [RR] 1.02, 95% confidence interval [CI] 0.99 to 1.06), but significantly increased mortality in a fixed-effect model (RR 1.04, 95% CI 1.02 to 1.06). In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. In the trials with a low risk of bias, the antioxidant supplements significantly increased mortality (RR 1.05, 95% CI 1.02 to 1.08). When the different antioxidants were assessed separately, analyses including trials with a low risk of bias and excluding selenium trials found significantly increased mortality by vitamin A (RR 1.16, 95% CI 1.10 to 1.24), beta-carotene (RR 1.07, 95% CI 1.02 to 1.11), and vitamin E (RR 1.04, 95% CI 1.01 to 1.07), but no significant detrimental effect of vitamin C (RR 1.06, 95% CI 0.94 to 1.20). Low-bias risk trials on selenium found no significant effect on mortality (RR 0.91, 95% CI 0.76 to 1.09).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomised trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention. Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.

Autosomal dominant Parkinson’s disease and the route to new therapies

The pathogenesis of Parkinson's disease (PD) is not understood and there are currently no accepted disease modifying, neuroprotective treatments. There are two autosomal dominant PD genes, leucine-rich repeat kinase (LRRK)2 and alpha-synuclein. LRRK2 mutations are very common in patients with PD, accounting for 40% of patients with sporadic, nonfamilial disease in some ethnic groups. Alpha-synuclein mutations are much less frequent, but the importance of alpha-synuclein has been confirmed by the demonstration of alpha-synuclein deposition as Lewy bodies in patients with PD and Lewy body dementia. Pathogenic mutations in alpha-synuclein accelerate the formation of oligomers and fibrils. Mutations in LRRK2 lead to an enhancement in LRRK2 kinase activity. The further study and understanding of the route by which alpha-synuclein and LRRK2 lead to PD, and how these processes can be therapeutically manipulated, is likely to lead to new disease-modifying treatments.

The use of cannabinoids in multiple sclerosis

Naturally occurring cannabinoids including Delta9-tetrahydrocannabinol and cannabidiol as well as endocannabinoids and synthetic cannabinoids may have a role in modulating experimental models of multiple sclerosis. Recent clinical studies to treat symptoms of multiple sclerosis have shown varying results, which may reflect issues relating to the way in which such studies were conducted. There is now increasing interest in the potential role of cannabinoids not only in symptom relief, but also for their possible neuroprotective actions.

Parkinson's disease and anaesthesia

Parkinson's disease is an increasingly common disease of elderly patients who present a particular anaesthetic challenge. This review explores the epidemiology, aetiology, pathogenesis, and pathophysiology of the condition, particularly the possible role of genetic factors. The clinical features are described in detail and recent advances in medical management are highlighted. Controversies surrounding the use of the newer drugs and possible advances in neurosurgical interventions are discussed. Particular anaesthetic problems in patients with Parkinson's disease are respiratory, cardiovascular, and neurological. Potential drug interactions are described and recommendations are made about suitable anaesthetic techniques.

Molecular characterization of monoamine oxidases A and B

Monoamine oxidase A and B (MAO A and B) are the major neurotransmitter-degrading enzymes in the central nervous system and in peripheral tissues. MAO A and B cDNAs from human, rat, and bovine species have been cloned and their deduced amino acid sequences compared. Comparison of A and B forms of the enzyme shows approximately 70% sequence identity, whereas comparison of the A or B forms across species reveals a higher sequence identity of 87%. Within these sequences, several functional regions have been identified that contain crucial amino acid residues participating in flavin adenine dinucleotide (FAD) or substrate binding. These include a dinucleotide-binding site, a second FAD-binding site, a fingerprint site, the FAD covalent-binding site, an active site, and the membrane-anchoring site. The specific residues that play a role in FAD or substrate binding were identified by comparing sequences in wild-type and variants of MAO with those in soluble flavoproteins of known structures. The genes that encode MAO A and B are closely aligned on the X chromosome (Xp11.23), and have identical exon-intron organization. Immunocytochemical localization studies of MAO A and B in primate brain showed distribution in distinct neurons with diverse physiological functions. A defective MAO A gene has been reported to associate with abnormal aggressive behavior. A deleterious role played by MAO B is the activation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a proneurotoxin that can cause a parkinsonian syndrome in mammals. Deprenyl, an inhibitor of MAO B, has been used for the treatment of early-stage Parkinson's disease and provides protection of neurons from age-related decay.

Systemic administration of the propargylamine CGP 3466B prevents behavioural and morphological deficits in rats with 6-hydroxydopamine-induced lesions in the substantia nigra

The ability of CGP 3466B to attenuate the behavioural and morphological consequences of experimentally induced cell death was investigated in a recently updated animal model of Parkinson's disease. 6-Hydroxydopamine was infused bilaterally into the substantia nigra pars compacta of rats that were pretreated with desimipramine. Treatment with CGP 3466B (0.0014-1.4 mg/kg, injected subcutaneously) or its solvent was begun 2 h after the 6-OHDA injection, and maintained twice daily for 14 days. After a washout period of 14 days, changes in motor behaviour were evaluated, using the open field test (analysis of normal and abnormal stepping, e.g.) and the paw test (analysis of retraction time of limbs). Changes in learning and memory were evaluated with the help of the Morris water maze task. Following immunocytochemical staining of tyrosine hydroxylase, the extent of the lesion was quantified using a computerized system. CGP 3466B prevented all deficits produced by 6-hydroxydopamine (6-OHDA), though at different doses. It prevented: abnormal stepping (0.0014-0.014 mg/kg); increased forelimb and hindlimb retraction time (0.014-0.14 mg/kg and 0.0014-0.14 mg/kg, respectively); delayed learning (1.4 mg/kg); and reduced tyrosine hydroxylase immunoreactivity in the substantia nigra (0.0014-0.014 mg/kg). CGP 3466B (0.0014-0.14 mg/kg) induced no deficits in sham-treated rats. CGP 3466B (1.4 mg/kg), however, did not show any benefit on motor deficits in 6-OHDA-lesioned rats, and induced abnormal movements and decreased the tyrosine hydroxylase immunoreactivity in the substantia nigra pars compacta and the ventral tegmental area of sham-lesioned animals. It is concluded that CGP 3466B prevents all 6-OHDA-induced behavioural and immunocytochemical deficits, though at different doses. CGP 3466B is suggested to be a valuable agent for inhibiting the dopaminergic degeneration in patients with Parkinson's disease.

Relative sparing of calretinin containing neurons in the substantia nigra of 6-OHDA treated rat parkinsonian model

A certain calcium binding protein (CaBP) has been known to exert a neuroprotective effect in various neurodegenerative diseases. Using the 6-OHDA induced rat Parkinsonian model, we examined if calretinin (CR), one of CaBP family, could play the similar role in the Parkinson's disease because CR is profusely localized in dopaminergic neurons of the substantia nigra pars compacta (SNPC) of the rat. Employing immunohistochemical analyses, we found that the survival rate of CR neurons was significantly higher than that of tyrosine hydroxylase (TH) neurons in the SNPC of the Parkinsonian rat. Furthermore double-labeled fluorescent microscopy revealed that almost all surviving TH neurons were also positive to CR. Our data suggest that CR-positive neurons are less vulnerable to 6-OHDA and CR in the dopaminergic neurons may have a protective function for survival of these neurons in the experimentally induced Parkinsonian rat.

SELEDO: a 5-year long-term trial on the effect of selegiline in early Parkinsonian patients treated with levodopa

The SELEDO (from selegiline plus levodopa) study was carried out as a randomized, prospective, placebo-controlled, double- blind, multicenter long-term, 5-year trial to evaluate the possible advantages of combining selegiline and levodopa in the early treatment of Parkinson's disease. One-hundred-and-sixteen patients were randomized either to selegiline or placebo. Before starting the study medication, the levodopa dose was titrated to the individual requirements of each patient. The primary study end point (time when levodopa had to be increased by >50% of the titrated dose) was reached in 23 of 59 patients in the selegiline group and 26 of 48 patients in the placebo group. At the end of the 5 years' treatment period the rates derived from a life-table analysis were 50.4% in the selegiline group and 74.1% in the placebo group (P = 0.027, log-rank test). The median time to reach the primary end point was 4.9 years in the selegiline group and 2.6 years in the placebo group. In patients treated with selegiline, the mean levodopa dose changed only slightly over the 5 years of treatment compared to the initially titrated dose, but rose markedly in the placebo group, where the dose of levodopa had to be adjusted earlier than in the selegiline group. At the same time, the lower levodopa dosage in the selegiline group was accompanied by at least equal therapeutic efficacy (which is necessary for an unambiguous interpretation). Subgroup analyses showed greater benefit for selegiline treated) patients in the earlier stages. Long-term side effects appeared later in the selegiline group, although the difference was not significant. The early combination of selegiline and levodopa proved to be clearly superior to levodopa monotherapy.

Synergistic interactions between COMT-/MAO-inhibitors and L-Dopa in MPTP-treated mice

Four experiments were performed to investigate the anti-akinesia effects of combining a sub-threshold dose (5 mg/kg, s.c.) of L-Dopa with different doses and combinations of COMT and MAO inhibitors upon the hypokinesia observed in MPTP-treated mice. Ro 40-7592 (1 and 3 mg/kg, s.c.), a novel COMT inhibitor, 60 min before L-Dopa reinstated both locomotion and rearing during a 2-hr interval after L-Dopa in MPTP mice; control mice were unaffected. The combination of Ro 40-7592 (3 mg/kg, s.c.) and pargyline (5 mg/kg, s.c.), a MAO inhibitor, with L-Dopa produced increases in both the peak effect and duration of action indicating a distinct potentiation of the effects of Ro 40-7592 by pargyline. L-Deprenyl, a MAOB inhibitor, together with L-Dopa, restored locomotion and rearing behaviour at all three doses applied (1, 3 and 10 mg/kg, s.c.); in control mice, motor activity was stimulated at the higher doses (3 and 10 mg/kg, s.c.), independent of L-Dopa administration. Combining L-Deprenyl (3 mg/kg, s.c.) with Ro 40-7592 (3 mg/kg, s.c.) one hr before L-Dopa to MPTP mice potentiated the restorative effects of each compound by itself, although no increase in peak effect was obtained. In the control mice, L-Deprenyl plus Ro 40-7592 or L-Deprenyl, by itself, stimulated motor activity following injection of L-Dopa. Marked dopamine (DA) depletions in the striatum of MPTP-treated mice were evident. The present results demonstrate that the effects of the COMT/MAO inhibitors in combination, and in conjunction with L-Dopa (at a dose that was without effect by itself), were well in excess of a summation of their individual effects. It was concluded therefore that a synergism of the restorative, anti-akinesic action of these compounds in MPTP-treated mice could offer a broader therapeutic spectrum in the treatment of Parkinson's disorder.

Markers of dopamine depletion and compensatory response in striatum and cerebrospinal fluid

Though depletion of CSF homovanillic acid (HVA) concentration has often been regarded as a direct indicator of dopamine (DA) deficiency in Parkinson's Disease (PD), CSF HVA is normal in mildly affected patients. To explore why, we measured DA and its metabolites in striatum and CSF in rabbits receiving reserpine for 5 days. Reserpine, which depletes striatal DA by disrupting vesicular storage of the neurotransmitter, results in a compensatory increase of DA turnover. In response to a 96% depletion of striatal DA, its catabolic intermediates 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3-MT) decreased 64% and 92% in striatum, although the endproduct, HVA, was unchanged. In contrast, CSF concentrations of HVA and DOPAC increased significantly, though 3-MT and levodopa (LD) were unaltered. A 5-fold rise in striatal LD concentration after reserpine-induced DA depletion provided evidence for enhanced DA synthesis. As in PD, the compensatory increase of DA synthesis after reserpine administration confounds the ability of CSF HVA to reflect DA depletion.

Responses of forebrain neurons to the MAO-B blocker L-deprenyl

Despite the large amount of neuropharmacological data concerning catecholamine (CA) mechanisms of the mammalian brain, little is known yet about the effects of MAO-inhibitors on single neurons. The present series of experiments aim to elucidate these specific neurochemical attributes of forebrain cells. Single neuron activity was recorded by means of multi-barreled microelectrodes in the caudate nucleus, globus pallidus, and amygdala of both anesthetized rats and anesthetized or alert monkeys during microelectrophoretic application of the MAO-B blocker L-deprenyl (DEPR). CAs (dopamine and noradrenaline), glutamate, GABA, and acetylcholine were also applied. Nearly the half (46%) of all forebrain neurons tested responded, exclusively with inhibition, to DEPR, and the CA-sensitive cells were especially responsive to the MAO-B inhibitor. The time course of DEPR-induced neuronal suppression was short. In some cases, amphetamine (AMPH) and clorgyline (CLOR) were also applied microelectrophoretically. AMPH elicited similar activity changes to those seen after DEPR administrations, whereas CLOR applications were less effective. Our results provide evidence that DEPR can effectively modulate the activity of CA-sensitive neurons in the three different forebrain regions of two different species. On the basis of this data, the possible neurochemical mechanisms of DEPR action are discussed.

Effects of monoamine oxidase inhibitors and dopamine agonists on the behavior of mammal- and frog-eating snakes

Skin mucus of the frog, Xenopus laevis, induces climbing and attenuates tongue flicking in Nerodia sipedon; these effects are induced alone and are potentiated by L-deprenyl, a monoamine oxidase type B inhibitor (MAO-Bi), but not by clorgyline, an MAO type A inhibitor (MAO-Ai). Both MAO-A and MAO-B metabolize dopamine, with MAO-B having the higher affinity; MAO-A selectively metabolizes serotonin and norepinephrine and MAO-B is selective for phenylethylamine. It was hypothesized that clorgyline and L-deprenyl would differentially modulate tongue flicking and climbing in frog-eating (Nerodia erythrogaster) and mammaphagous (Elaphe o. obsoleta) snakes, based on physiological differences between the species. L-Deprenyl caused a decrease in tongue flicking and climbing by Elaphe and an increase in climbing by Nerodia, whereas clorgyline did not alter tongue flicking, climbing, or locomotor activity in either species. To further assess the role of dopamine, hybrid black/gray rat snakes, E. o. spiloides, were administered the D1 and D2 dopamine receptor agonists SKF 77434 (SKF 38393, N-allyl) and quinpirole, respectively. SKF 77434 and quinpirole attenuated climbing, but only SKF 77434 attenuated tongue flicking in Experiment 3; neither drug affected locomotor activity. Results suggest that dopaminergic stimulation by MAO-Bi and dopamine agonists modulates tongue flicking and climbing behaviors in snakes, and that the contrasting climbing reactions induced by MAO-Bi between Elaphe and Nerodia may be linked to quantitative differences in endogenous catecholamine levels and/or to the numbers and sensitivity of receptors.

Can our knowledge of monoamine oxidase (MAO) help in the design of better MAO inhibitors?

This paper presents a rapid overview of the mechanism by which monoamine oxidase (MAO) catalyzes the deamination of its substrates, and highlights the stereoselective nature of the active site of the enzyme. With the help of a few selected examples it is also discussed which structural factors are thought to have a preponderant influence on the affinity and selectivity of molecules towards the active site of either form of MAO. From the currently available data on the enzyme and its inhibition, it clearly appears that new MAO inhibitors, of whatever type, could be easily designed by structural modulation of molecules already found to have MAO inhibitory properties. As to whether better MAO inhibitors could be envisaged, it is suggested that MAO inhibition might be advantageously combined with other pharmacological properties for the treatment of pathological conditions, such as stroke and epilepsy, to the occurrence of which MAO activity might contribute. The rationale of this approach is presented.