Neuroprotection and aging of the cholinergic system: a role for the ergoline derivative nicergoline (Sermion).

The aging brain is characterized by selective neurochemical changes involving several neural populations. A deficit in the cholinergic system of the basal forebrain is thought to contribute to the development of cognitive symptoms of dementia. Attempts to prevent age-associated cholinergic vulnerability and deterioration therefore represent a crucial point for pharmacotherapy in the elderly. In this paper we provide evidence for the protective effect of nicergoline (Sermion) on the degeneration of cholinergic neurons induced by nerve growth factor deprivation. Nerve growth factor deprivation was induced by colchicine administration in rats 13 and 18 months old. Colchicine induces a rapid and substantial down-regulation of choline acetyltransferase messenger RNA level in the basal forebrain in untreated adult, middle-aged and old rats. Colchicine failed to cause these effects in old rats treated for 120 days with nicergoline 10 mg/kg/day, orally. Moreover, a concomitant increase of both nerve growth factor and brain-derived neurotrophic factor content was measured in the basal forebrain of old, nicergoline-treated rats. Additionally, the level of messenger RNA for the brain isoform of nitric oxide synthase in neurons of the basal forebrain was also increased in these animals. Based on the present findings, nicergoline proved to be an effective drug for preventing neuronal vulnerability due to experimentally induced nerve growth factor deprivation.

Reboxetine: a pharmacologically potent, selective, and specific norepinephrine reuptake inhibitor.

BACKGROUND: Reboxetine is a potent antidepressant, with efficacy comparable to that of imipramine, desipramine, and fluoxetine, and has improved side-effect profile. The basis of its efficacy and improved tolerability is sought through studies of reboxetine in a number of pharmacological models of depression. METHODS: Pharmacological selectivity for uptake systems was defined by uptake and binding assays for the three monoamine uptake sites. Specificity was determined in 39 different receptor and 6 enzyme assays. In vivo selectivity was defined by measurement of neuronal firing rates in the locus coeruleus, dorsal raphe, and substantia nigra. Reserpine-induced blepharospasm and hypothermia, clonidine-induced hypothermia, defined reboxetine's in vivo pharmacology. Reboxetine's antidepressant potential was evaluated behaviorally by the tail-suspension test, forced swimming, and the DRL72 operant responding test. RESULTS: Reboxetine is a potent, selective, and specific norepinephrine reuptake inhibitor (selective NRI) as determined by both in vitro and in vivo measurements. Unlike desipramine or imipramine, reboxetine has weak affinity (Ki > 1,000 nmol/L)for muscarinic, histaminergic H1, adrenergic alpha1, and dopaminergic D2 receptors. In vivo action of reboxetine is entirely consistent with the pharmacological action of an antidepressant with preferential action at the norepinephrine reuptake site. Reboxetine showed an antidepressant profile in all tests of antidepressant activity used. Significant decreases in immobility were observed in the tail suspension test and behavioral despair test. Increased efficiency in responding was observed in the DRL72 test. CONCLUSIONS: Reboxetine is a potent, selective, and specific noradrenergic reuptake inhibitor. It has a superior pharmacological selectivity to existing tricyclic antidepressants and selective serotonin reuptake inhibitors when tested in a large number of in vitro and in vivo systems. Given the pharmacological profile, reboxetine is expected to be a selective and potent tool for psychopharmacological research. The use of reboxetine in the clinic will also help clarify the role norepinephrine plays in depression.

Neuroprotective effects of nicergoline in immortalized neurons.

We studied the potential neuroprotective action of nicergoline in immortalized hypothalamic GT1-7 cells exposed to agents which deplete levels of reduced glutathione, thus causing oxidative stress and cell death. Treatment with diethylmaleate (1 mM), buthionine sulfoximine (500 microM) or menadione (10-50 microM) caused diffuse GT1-7 cell degeneration, as assessed by using either the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay or the fluorescent dyes fluorescein diacetate and propidium iodide. Pre- and/or co-exposure of the cells to nicergoline significantly prevented diethylmaleate- or buthionine sulfoximine-induced neuronal death, whereas nicergoline was ineffective against menadione-induced toxicity. This effect was concentration-dependent and was mimicked by the classical antioxidants idebenone and vitamin E, and did not depend on interference with protein kinase C. Interestingly, the antineurodegenerative activity of nicergoline and vitamin E or idebenone was not additive, suggesting that these compounds share some intracellular mechanism(s) responsible for their protective effects. In conclusion, the present data indicate that nicergoline has neuroprotective activity, possibly mediated by the antioxidant activity of the molecule, and give support to the potential use of nicergoline in the prevention and therapy of neurodegenerative diseases.

Effects of nicergoline on age-related decrements in radial maze performance and acetylcholine levels.

The effects of chronic oral administration of nicergoline (5.0 mg/kg; bid) on locomotor activity, eight-arm radial maze performance plus striatal, cortical, and hippocampal acetylcholine (ACh) levels were examined in young and aged Wistar rats. Chronic nicergoline administration did not modify either the locomotor activity or radial maze learning in young rats. Young rats learned the radial maze procedure rapidly and improved their performance throughout the successive training sessions. Radial maze performance in young rats was characterised by very few arm reentries. Aged rats were hypoactive and did not explore or enter the radial maze arms, and consequently performed poorly in the radial maze throughout the training sessions. Nicergoline treatment did not significantly modify locomotor activity in aged rats. Aged rats treated with nicergoline also performed poorly initially but improved with repeated training in the radial maze. This improvement was associated with an increasing number of arms being entered and very few arm reentries. Reduced acetylcholine (ACh) levels were also associated with age. Aged rats had significantly reduced levels of ACh in the straitum and cortex, but not the hippocampus as compared to young rats. Nicergoline treatment did not change ACh levels in young rats, but substantially restored the reduced ACh levels in aged rats. These results indicate that nicergoline is an effective cognitive enhancer in a learning model of age-related deficits and that these results may be related to changes in the cholinergic system.

Modulation of phosphoinositide turnover by chronic nicergoline in rat brain.

Basal and agonist-stimulated phosphoinositide (PI) turnover and inositol 1,4,5 -trisphospate (InsP3) content in rat brain were investigated after chronic nicergoline (SERMION) treatment. Oral administration of nicergoline (5 mg/kg b.i.d. for 7 weeks) enhanced the basal turnover of PI in the cerebral cortex compared to controls. This effect was paralleled by a significant rise of cortical InsP3 levels. No significant changes of noradrenaline- or carbachol-induced accumulation of [3H]-inositol-I-phophate ([3H]-InsP1) were found in cortices from nicergoline-treated rats. On the contrary, in the striatum nicergoline significantly potentiated the responsiveness of noradrenaline- and carbachol-stimulated PI turnover, leaving unchanged the basal production of [3H]-InsP1 and InsP3 levels. The results suggest that the interaction of nicergoline with PI transducing pathway might have relevance to the mechanisms of action of nicergoline.

Modulation of hippocampal ACh release by chronic nicergoline treatment in freely moving young and aged rats.

The effects of nicergoline on basal and K(+)-stimulated release of ACh in the hippocampus of 3- and 19-month old rats has been studied by microdialysis. A significant decrease of basal ACh release (59%) was found in aged vehicle treated rats in comparison to young rats. High-K+ (100 mM) in the perfusate strongly increased the release of ACh by up to 6-fold over the baseline of both young and aged rats. Chronic oral administration of nicergoline to aged rats (5 mg/kg b.i.d. for 6 weeks) significantly reversed (93%) the age-related decrease of basal release of ACh, leaving the increase due to K+ depolarization unchanged. In young animals, nicergoline did not affect the basal output of ACh, but enhanced the K(+)-evoked release of ACh by 39%. Results from this study demonstrate that nicergoline treatment increases the ability of hippocampal cholinergic terminals to release ACh, and suggest that this drug can reset the cholinergic impairement associated with aging.

FCE 23884, substrate-dependent interaction with the dopaminergic system. I. Preclinical behavioral studies.

FCE 23884, a newly synthetized ergoline derivative, shows dopamine (DA) agonist or antagonist properties depending on the functional state of the biological substrate. The compound behaves as a full DA antagonist in normal animals, but shows full agonist properties in denervated models in the same dose range. In normal animals, FCE 23884 impairs Sidmans avoidance in rats, reduces spontaneous locomotion in mice and monkeys and antagonizes apomorphine-induced climbing behavior in mice, yawning in rats, emesis in dogs and amphetamine-induced toxicity in grouped mice. After experimental procedures resulting in severe DA depletion, FCE 23884 behaves as a powerful DA-agonist mainly at D-1 receptors. FCE 23884 induces contralateral turning behavior in 6-hydroxydopamine-lesioned rats and reverses 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced akinesia in monkeys and reserpine-induced hypokinesia in mice. These results indicate that the antagonist or agonist activity of FCE 23884 is substrate-dependent and mostly related to the presence or absence of DA. This leads to the apparently paradoxical suggestion that the compound could be useful both in psychotic states and extrapyramidal diseases, i.e., in clinical conditions characterized by either excessive or impaired DAergic neurotransmission.

FCE 23884, substrate-dependent interaction with the dopaminergic system. II. Preclinical biochemical studies.

The effects of FCE 23884 [4-(9,10-didehydro-6-methylergolin-8 beta-yl) methyl-piperazine-2,6-dione] were examined using a variety of biochemical methods. In vitro assays showed that FCE 23884 bound to D-2, alpha-2 and 5-hydroxytryptamine1A sites with Ki values of 6.5, 4.0 and 4.0 nM, respectively. The affinity for D-1 and S-2 receptors was moderate (submicromolar range) and slight or negligible for alpha-1, cholinergic and sigma receptors. In normal rats, FCE 23884 accelerated markedly dopamine (DA) turnover in the neostriatum and nucleus accumbens as indicated by the increased ratios of dihydroxphenyl acetic acid/DA and homovanillic acid/DA. The compound enhanced DA synthesis and utilization rate. After gamma-butyrolactone treatment, a model to study DA autoreceptors function, FCE 23884 almost antagonized completely the gamma-butyrolactone reversal induced by apomorphine on l-dihydroxyphenylalanine accumulation in the two brain areas. In addition, FCE 23884 induced a rapid 20-fold increase of serum prolactin confirming its DA antagonistic profile in normal rats. In contrast with these antidopaminergic properties, FCE 23884 consistently stimulated basal adenylate cyclase activity in vitro (ED50 = 0.6 microM) and elicited a rapid increase of cyclic AMP formation in the neostriatum of normal (35%) and reserpinized (82%) rats in vivo. Furthermore in this last condition both the DA turnover and synthesis rate in the neostriatum and nucleus accumbens decreased after treatment with FCE 23884. These neurochemical data support the behavioral studies indicating that FCE 23884 possesses mixed DA antagonist and agonist properties depending on the experimental conditions, the distinguishing factor being presence or absence of DA.(ABSTRACT TRUNCATED AT 250 WORDS)

GABA content and synthesis in the aging rat brain.

The content and synthesis of GABA were measured in the cortex and striatum of young adult (4 months), mature (14 months), and old (24 months) male Wistar rats. GABA synthesis was determined from the GABA accumulation induced by aminooxyacetic acid (AOAA). Aging did not affect GABA content in the cortex (1.03 +/- 0.04 mumoles/g in young and 1.06 +/- 0.04 mumoles/g in old rats), or in the striatum (1.63 +/- 0.04 mumoles/g in young and 1.56 +/- 0.05 mumoles/g in old rats). Aging did not significantly change the AOAA-induced GABA accumulation in the striatum (+34% in young, +16% in mature, and +28% in old rats), but significantly reduced it in the cortex where this process takes place to a greater extent than in the striatum: +164% in young, +116% in mature, and +120% in old animals. It can be concluded that while in the striatum aging did not affect AOAA-induced GABA accumulation, in the cortex this was less in mature than young rats, with no further change in the old ones. GABA content was not affected by aging in either region.

Preparation of 7-oxaaporphine derivatives and evaluation of their dopaminergic activity.

A series of 7-oxaaporphine derivatives was prepared. The compounds were evaluated as dopaminergic agents. None of them showed either affinity for dopamine receptors or activity in vivo in the climbing behavior (mice) and turning behavior (6-hydroxydopamine-lesioned rats) tests. The lack of activity is tentatively related to the effect of the oxygen atom on the pKa of these molecules.

Effect of ergolines on neurotransmitter systems in the rat brain.

The interaction of nicergoline with various monoaminergic receptors and its effects on monoamine turnover were studied in specific rat brain areas in comparison with those of its metabolites, 10-methoxy-1,6-dimethyl-ergoline-8 beta-methanol (MMDL) and 10-methoxy-6-methyl-ergoline-8 beta-methanol (MDL). Nicergoline showed marked in vitro affinity for alpha 1-noradrenergic receptors (IC50 = 0.2 nM), less for alpha 2, S1 and S2 (IC50 about 10(-7) M). Its strong interaction with alpha 1-receptors was confirmed in vivo. The affinity of the other ergolines for alpha 1-receptors was lower than that of nicergoline. The level of monoamine metabolites (HVA and DOPAC for dopamine, MOPEG-SO4 for noradrenaline and 5-HIAA for serotonin) was taken as a measure of their turnover in the rat brain. A single dose of nicergoline (20 mg/kg, s.c.) strongly enhanced noradrenaline turnover, less that of dopamine. These effects, probably due to the interaction with alpha-receptors, were more marked after parenteral than oral administration. MMDL shared nicergoline's effect on dopamine and MDL that on noradrenaline, but they were less active than the parent compound. The most interesting results were obtained after chronic treatment (6-7 weeks) with rather low doses: 5 mg/kg b.i.d. of nicergoline and equimolar doses of the metabolites. Nicergoline and MMDL both enhanced dopamine turnover, especially in mesolimbic areas. In conclusion, the present report confirms and extends previous results on nicergoline's effects on catecholamine turnover and shows that its metabolite MMDL shares its effects on dopamine. Finally, it is particularly interesting that both ergolines were more effective in old than in young rats.

Effect of aging on monoamines and their metabolites in the rat brain.

Concentrations of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their acid metabolites were assayed in specific brain areas of Wistar rats of various ages. DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were significantly lower in striatum and mesolimbic areas of old (24 mos) rats than young adult (3 mos), but not mature (12 mos) rats. The decrease of homovanillic acid (HVA) was significant in mesolimbic areas but not in striatum. Neither cortical NE nor its metabolite methoxyhydroxyphenylglycol sulphate (MHPG-SO4) were significantly changed by aging. 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the brainstem showed a tendency to a decrease and increase respectively in aged animals compared with young adults, but the differences were not statistically significant. However, the ratio of 5-HIAA to 5-HT concentrations was significantly higher in aged animals. The conclusion can be drawn that, in these brain areas, DA is more vulnerable to aging than NE and 5-HT, the metabolism of the latter being even enhanced.

Brain dopamine autoreceptors in aging rats.

The function of dopamine (DA) autoreceptors is evaluated in vivo in striatum and mesolimbic regions of young adult (4 months), mature (14 months) and old (26 months) male Wistar rats. gamma-Butyrolactone (GBL)-induced dihydroxyphenylalanine (DOPA) accumulation in rats also treated with an inhibitor of aromatic L-aminoacid decarboxylase was used to determine the presence of synthesis-modulating nerve terminal autoreceptors while its reversal with apomorphine served as an index of autoreceptor stimulation. GBL-induced DOPA accumulation in striatum is very high at all three ages (130-150% increase in comparison with controls) as is its reversal by apomorphine (65-80% decrease in comparison with GBL alone). In mesolimbic regions, GBL has much less effect than in striatum (31% rise at 4 and 26 months, 12% rise at 14 months), but apomorphine's effect is of the same order of magnitude (down 60-80%). The conclusion can be drawn that aging does not significantly affect DA autoreceptor function in striatum and mesolimbic areas.

Brain catecholamine content and turnover in aging rats.

The content and turnover of catecholamines were evaluated in various brain regions of young adult (4-months) and aged (24-months) male rats. Turnover was assessed from the concentrations of acid metabolites and the decline of catecholamine content after synthesis blockade with alpha-methyl-p-tyrosine. Dopamine was reduced by aging in striatum, mesolimbic areas, and hypothalamus. Dopamine metabolites and turnover rate were significantly lower in striatum and mesolimbic areas of aged than of young animals. Hypothalamic norepinephrine content and turnover rate were unchanged in aged compared to young rats but its metabolite (MHPG-SO4) was increased in the cortex. These findings point to an extensive impairment of brain dopamine metabolism in aging rats, whereas norepinephrine seems to be less impaired.