Victor J. Nickolson

Effect of the acquisition enhancing drug piracetam on rat cerebral energy metabolism. Comparison with naftidrofuryl and methamphetamine

The effects of Piracetam, Naftidrofuryl and methamphetamine on several parameters of cerebral energy metabolism have been studied. At variance with some reports in the literature neither Piracetam nor Naftidrofuryl affected the cerebral contents of adenine nucleotides and, accordingly, both substances were without effect on the adenylate energy charge. This disagreement is explained by methodological differences. Methamphetamine also had no effect on cerebral adenine nucleotides. Piracetam increased the activity of adenylate kinase (EC 2.7.4.3) in isotonically diluted rat brain homogenates without altering the K(M) of the enzyme for ADP as substrate. It is concluded that although Piracetam has no effect on the cerebral energy metabolism under normal conditions, it may have a beneficial effect under marginal conditions like those met during hypoxia, by virtue of its adenylate kinase stimulating action. It is suggested that this action is responsible for the protective effect of Piracetam against cerebral hypoxia. It may also be related to the enhancement of acquisition under training conditions where cerebral energy metabolism is disturbed. Chemicals/CAS: adenylate kinase, 9013-02-9; methamphetamine, 28297-73-6, 51-57-0, 537-46-2, 7632-10-2; naftidrofuryl, 31329-57-4; piracetam, 7491-74-9; Adenosine Diphosphate, 58-64-0; Adenosine Monophosphate, 61-19-8; Adenosine Triphosphate, 56-65-5; Adenylate Kinase, EC 2.7.4.3; Furans; Methamphetamine, 537-46-2; Nafronyl, 31329-57-4; Piracetam, 7491-74-9; Pyrrolidinones

Comparative pharmacology of mianserin, its main metabolites and 6-azamianserin

SummaryMianserin, its main metabolites (8-hydroxymianserin, desmethylmianserin and mianserin-N-oxide) and a mianserin analogue, 6-azamianserin (ORG 3770), were compared with regard to effects on monoamine uptake systems, α-adrenoceptors, rat exploratory activity and rat muricidal behaviour. Mianserin and desmethylmianserin inhibited noradrenaline uptake into synaptosomes (IC50s 30 and 60 nM, respectively) whereas the other compounds were much less active. Synaptosomal serotonin uptake was only inhibited to a small extent by desmethylmianserin (IC50 6 μM) and 8-hydroxymianserin (IC50 9 μM). Dopamine uptake was not affected by any of the compounds tested. All compounds except mianserin-N-oxide blocked presynaptic α-receptors as shown by the potentiation of high-K-induced release of noradrenaline from rat cerebral cortex slices. For mianserin and 6-azamianserin this blockade was shown to be stereoselective. Desmethylmianserin was less potent than mianserin. Binding of 3H-dihydroergocryptine to rat cerebral cortex membranes was inhibited by all compounds except mianserin-N-oxide. Again, desmethylmianserin was less active than mianserin. None of the compounds appeared to block presynaptic α-receptors in preference to postsynaptic α-adrenoceptors. This was confirmed by the fact that the compounds studied failed to antagonize clonidine-induced sedation in the open field. Clonidine-induced diuresis, however, was stereoselectively inhibited by 6-azamianserin, but the involvement of α2-receptors in this phenomenon is not firmly established.Antihistamine properties as determined by 3H-mepyramine binding to rat brain membranes were most pronounced for 6-azamianserin. Mianserin was slightly less potent and desmethylmianserin and 8-hydroxymianserin were 10 and 30 times less potent than mianserin, respectively.Muricidal behaviour was inhibited by all compounds except mianserin-N-oxide. The least active was 8-hydroxymianserin. In contrast to mianserin and desmethylmianserin, the blockade of muricidal behaviour by 6-azamianserin was non-specific since it occurred at doses which caused a strong depression of rat open field behaviour. Mianserin was less sedative than 6-azamianserin whereas the metabolites showed no sedative effects at doses up to 32 mg/kg in the open field.It is concluded that the main metabolites of mianserin possess pharmacological properties which may add to the therapeutic potential of mianserin. Clinical testing of 8-hydroxymianserin and 6-azamianserin may give an answer to the question whether the antidepressant effect of mianserin is solely based upon its interaction with presynaptic α-adrenoceptors or is due to a concomitant blockade of noradrenaline reuptake.

A comparison of the physicochemical and biological properties of mirtazapine and mianserin

Although the chemical structures of the antidepressants mirtazapine and mianserin are closely related there are considerable differences in their biological properties. To find an explanation of this, various physicochemical properties of mirtazapine and mianserin were measured or calculated.

Effects of the potential neuroleptic peptide des-tyrosine1-γ-endorphin and haloperidol on apomorphine-induced behavioural syndromes in rats and mice

Abstract The effects of haloperidol and Des-Tyr 1 -γ-endorphin (DTγE) were studied on climbing induced in mice by high doses of apomorphine and on the yawning syndrome induced in rats by low doses of apomorphine. Haloperidol in a dose of 0.0046 mg/kg s.c. potentiated climbing whereas at higher doses climbing was inhibited (ED 50 =0.03 mg/kg). DTγE had no effect on climbing under normal conditions in doses up to 2 mg/kg s.c.. After three days of handling and saline pre-injections DTγE potentiated climbing in doses from 0.1 to 1 mg/kg. Haloperidol inhibited yawning induced by low doses of apomorphine (ED 50 =0.01 mg/kg). DTγE, on the other hand, potentiated yawning induced by low apomorphine at doses of 0.02 and 0.04 mg/kg s.c.. From the point of view that low doses of apomorphine predominantly activate presynaptic dopamine autoreceptors while higher doses predominantly activate postsynaptic dopamine receptors the following tentative conclusions are drawn. 1) Haloperidol blocks presynaptic dopamine autoreceptors at low doses and postsynaptic dopamine receptors at higher doses. 2) DTγE sensitizes presynaptic dopamine autoreceptors at low doses, thereby strengthening the local feedback mechanism at the dopaminergic nerve ending, and sensitizes postsynaptic dopamine receptors at higher doses.

Detailed analysis of the effects of apomorphine and d-amphetamine on spontaneous locomotor behaviour of rats as measured in a TV-based, automated open-field system

Rat open field behaviour was measured in a TV-based, automated system. Habituation was evident in saline-treated rats. Most variables measured declined over a 10 min period. Apomorphine affected rat open-field behaviour bimodally, i.e. low doses of apomorphine (0.02-0.08 mg/kg, s.c.) decreased most aspects of rat open-field behaviour, whereas at higher doses (0.2 and 0.5 mg/kg, s.c.) various aspects of open-field behaviour were stimulated. Rearing and average speed, however, were monotonically depressed. Amphetamine (1 and 2 mg/kg) stimulated most aspects of rats open-field behaviour, including rearing. Speed was not affected by amphetamine. Habituation was more pronounced after low doses of apomorphine than after saline treatment and was absent after high doses of apomorphine and after amphetamine. The results represent a detailed analysis of apomorphine and amphetamine effects on rat open-field behaviour and show that the distinct components of this behaviour are affected differentially.

Differences in presynaptic α-blockade, noradrenaline uptake inhibition, and potential antidepressant activity between (+)- and (-)mianserin

The effect of racemic mianserin on K+-evoked tritium release from rat brain cortex slices previously incubated with 3H-l-noradrenaline was studied. Racemic mianserin (10-9-10-5M) increased stimulation-induced release dose-dependently. As methysergide, metiamide, and cyproheptadine failed to do so, it was concluded that this effect was probably not caused by the antihistamine or antiserotonin activity of racemic mianserin, but due to its α-adrenolytic effect. Evaluation of the effects of the enantiomers (+)(S)mianserin and (-)(R)mianserin showed that the α-adrenolytic effect resided in the (+)isomer, whereas the (-)isomer was inactive at a concentration of 10-6M. Inhibition of noradrenaline into rat hypothalamic synaptosomes also showed stereospecificity in that (+)mianserin was about 300-times more active than (-)mianserin. Inhibition of rat muricidal behavior, a test for potential antidepressant activity, showed a similar dissociation in the effects of the two enantiomers, in that (+)mianserin was active, whereas (-)mianserin was not.

Effects of des-tyr1 -γ-endorphin on dopamine release from various rat brain regions in vitro

Abstract In rat striatum, nucleus accumbens and frontal cortex slices 6×10 −8 M of the potential neuroleptic peptide des-Tyr-γ-endorphin (DTγE) did not affect basal dopamine release but depressed K + -evoked release. Haloperidol at 5×10 −6 M increased both basal and K + -induced release in striatal and nucleus accumbens slices whereas it increased only basal dopamine release in frontal cortex slices. At 5×10 −8 M haloperidol, however, had no effect. It is concluded that DTγE may decrease dopaminergic activity in the brain by depressing depolarization-induced dopamine release, possibly via a presynaptic mechanism.

Dopamine Uptake by Rat Striatal Synaptosomes: Time‐and Temperature‐Dependent Decay and Protection by Dithiothreitol and Dopamine

The uptake of [3H]dopamine (DA) into rat striatal synaptosomes in the presence of a monoamine oxidase inhibitor was studied using a filtration technique. After a 10‐min preincubation period, a fast initial uptake of [3H] DA was seen. Uptake reached a maximum after 4 min of incubation. If incubation was continued for more than 7 min, a gradual decrease in synaptosomal [3H]DA levels was found. Uptake was dependent on preincubation time; initial uptake velocity and maximal uptake decreased irreversibly with increasing preincubation periods. Moreover, the capacity of the synaptosomes to retain the [3H]DA during longer incubation times was progressively affected. The decrease in initial uptake activity was due to a decrease in the Vmax of the transport system. Dithiothreitol (2.8 mM) protected synaptosomal uptake activity against deterioration at 37°C. Also, DA itself (10‐7M) stabilized the uptake mechanism if added to the suspension before preincubation was started. Since [3H]DA uptake observed after loading the synaptosomes with labeled DA was similar to the uptake seen if the synaptosomes were not previously loaded with DA, it was concluded that under these conditions synaptosomal DA is completely exchangeable with exogenous substrate. Prolonged storage of the synaptosomes at 0°C also resulted in a time‐dependent decrease in uptake activity (t1/2= 116 min). The addition of unlabeled DA or dithiothreitol to the suspension did not affect instability at 0°C.

Presynaptic α-block and inhibition of noradrenaline and 5-hydroxytryptamine reuptake by a series of compounds related to mianserin

A structure‐activity relationship study was undertaken for a variety of structural analogues of the tetracyclic antidepressant mianserin. Presynaptic α‐blocking activity in vitro was evaluated measuring the potentiation of depolarization‐induced noradrenaline (NA) release from rat cerebral cortex slices. Inhibition of NA and 5‐hydroxytryptamine reuptake was measured in rat hypothalamic or striatal synaptosomes, respectively. Presynaptic α‐blockade was only found in molecules with an overall bent shape. Flat rigid molecules or flexible ones were not active. Six‐membered, chair‐formed D‐rings (containing the ‐NCH3 moiety) appeared better than 5‐ or 7‐membered ones. Heteroatom substitution, but not hydroxylation or methylation, of the bridge between the two aromatic rings left presynaptic α‐blockade unaffected. N‐Demethylation and aromatic methyl‐ or chlorine‐subsitution reduced presynaptic α‐blockade. In pyridine ring‐substituted analogues the localization of the heteroatom appeared to be crucial. 5‐Hydroxytryptamine reuptake inhibitory activity was only found in desmethylmianserin. NA reuptake inhibition was found in many mianserin analogues, especially those with an exocyclic ‐N(CH3)2 moiety. Structure activity relationships for NA reuptake inhibition differed from those for presynaptic α‐blockade and were generally less stringent. For both properties simple additivity relationships appeared to be absent.

Dopamine uptake by rat striatal synaptosomes: a compartmental analysis.

Abstract: Dopamine (DA) uptake into synaptosomes from rat corpus striatum was studied in the presence of a monoamine oxidase (MAO) inhibitor and dithiothreitol, by means of a filtration technique. Under these conditions a steady state develops rapidly in which the synaptosomal DA content remains constant while the continuing DA uptake is counterbalanced by DA efflux from the synaptosome. Exchange of synaptosomal [3H]DA and [14C]DA was measured under these conditions. In timecourse experiments it was found that exchange could be described significantly better by a three‐compartment model than by a two‐compartment model. However, if synaptosomes from reserpine‐pretreated animals were used, analysis according to a three‐compartment model did not result in a significantly better fit compared with a two‐compartment model. Subsequently, kinetic transfer parameters describing DA fluxes between compartments at different DA concentrations were calculated from the fitted exchange curves. A Michaelis‐Menten kinetic analysis indicated that only the in‐series three‐compartment configuration, in which DA is taken up from the medium into one synaptosomal compartment, from which it can subsequently be transferred to a second compartment without direct access to the medium, gave kinetically acceptable results. Transfer parameters in synaptosomes from reserpine‐treated rats were comparable to those parameters describing DA transport between the medium and the first intrasynaptosomal compartment as measured under control conditions. Morover, it was found that potassium depolarization of synaptosomes resulted in a release of DA in a quantity similar to that found in the second intrasynaptosomal compartment. It is suggested that the two intrasynaptosomal compartments found correspond to a cytoplasmatic and vesicular DA pool, respectively. The functional significance of these findings is discussed in terms of the regulation of DA levels within the nerve terminal.