W. P. Burkard

Benzodiazepine antagonist Ro 15-1788: binding characteristics and interaction with drug-induced changes in dopamine turnover and cerebellar cGMP levels.

Abstract: The recently discovered benzodiazepine antagonist Ro 15‐1788 was characterized in binding studies, and its potency and selectivity were determined in vivo by interaction with drug‐induced changes in dopamine turnover and cerebellar cGMP level. Ro 15‐1788 reduced [3H]flunitrazepam binding in the brain in vivo with a potency similar to that of diazepam and effectively inhibited [3H]diazepam binding in vitro (IC50= 2.3 ± 0.6 nmol/liter). [3H]Ro 15‐1788 bound to tissue fractions of rat cerebral cortex with an apparent dissociation constant (KD) of 1.0 ± 0.1 nmol/liter. The in vitro potency of various benzodiazepines in displacing [3H]Ro 15‐1788 from its binding site was of the same rank order as found previously in [3H]diazepam binding. Autoradiograms of [3H]Ro 15‐1788 binding in sections of rat cerebellum showed the same distribution of radioactivity as with [3H]flunitrazepam. The attenuating effect of diazepam on the chlorpromazine‐ or stress‐induced elevation of homovanillic acid in rat brain was antagonized by Ro 15‐1788. Among a series of compounds which either decreased or increased the rat cerebellar cGMP level, only the effect of benzodiazepine receptor ligands (diazepam, zopiclone, CL 218 872) was antagonized by Ro 15‐1788. Thus, Ro 15‐1788 is a selective benzodiazepine antagonist acting at the level of the benzodiazepine receptor in the central nervous system. Peripheral benzodiazepine binding sites in kidney and schistosomes were not affected by Ro 15‐1788.

Blockade of central 5-hydroxytryptamine receptors by methiothepin

SummaryMethiothepin (1-[10,11-dihydro-8-(methylthio)dibenzo[b,f] thiepin-10-yl]-4-methylpiperazine maleate), a representative of a new class of neuroleptics, is shown to be an antagonist of 5-hydroxytryptamine (5-HT) at receptors in the CNS. The neuropharmacological evidence was obtained by observing its effects on ponto-geniculo-occipital (PGO) spikes induced in curarized cats by either the benzoquinolizine Ro 4-1284 or p-chlorophenylalanine. Methiothepin a) increased the number of drug-induced spikes, b) antagonized the inhibitory action of 5-HTP and LSD on the spikas, and c) induced PGO-spikes by itself in untreated animals. The turnover of 5-HT in the rat brain was accelerated by methiothepin as indicated by virtually unaltered 5-HT levels, an increase of 5-hydroxyindole acetic acid, an enhancement of the 5-HT increase induced by a MAO inhibitor and by an increase of tryptophan levels in the brain.

Biochemistry and pharmacology of moclobemide, a prototype RIMA

RIMA is a term for reversible inhibitors of monoamine oxidase (MAO) with preference for MAO-A; moclobemide is a prototype of this new class of antidepressants and is a highly selective inhibitor of MAO-A in vitro. This inhibition is reversible by dialysis in vitro, which accounts for the dose-dependent duration of in vivo enzyme inhibition of 12–24 h. Moclobemide increases the content of serotonin, noradrenaline and dopamine in the brain, and decreases that of their deaminated metabolites. Its biochemical, neurological and behavioural effects indicate that it increases the extracellular concentration of the classic monoamine neurotransmitters/neuromodulators — in particular 5-HT. Potentiation of the cardiovascular effects of tyramine is less pronounced after taking moclobemide than after irreversible MAO-A inhibitors. Understanding of the physiological role of MAO and of the events that link inhibition of the enzyme with modulation of neuronal activities in the CNS remains incomplete. A major physiological role of intraneuronal MAO is to keep cytosolic amine concentration very low, to enable the neuronal monoamine carriers to produce a net inward transport of monoamines, and thereby to act as the first step in the termination of action of extracellular monoamines. MAO is likely to have a similar function in non-monoaminergic cells with respect to the monoamine carriers they contain. In addition to the classic monoamines, “trace” amines may become functionally active after MAO inhibition. An alternative role for MAO is that of a scavenger, preventing natural substrates from accumulating in monoaminergic neurons and interacting with storage, release, uptake and receptor function of monoamines.

Ro 15-4513: Partial inverse agonism at the BZR and interaction with ethanol☆

The imidazobenzodiazepinone derivative Ro 15-4513 has the activity profile of a partial inverse (low efficacy) agonist at the benzodiazepine receptor (BZR). It reverses central nervous depressant effects of diazepam, and, in part, of phenobarbitone and ethanol in mice, rats and cats in behavioural, electrophysiological, and neurochemical paradigms. The interaction of Ro 15-4513 with barbiturates and ethanol is due to its inverse agonistic (negative allosteric modulatory) property at the BZR, as it was reversed by the selective BZR blocker flumazenil (Ro 15-1788). In the present experiment situations, other BZR partial inverse agonists in subconvulsant or overt convulsant doses were less effective against ethanol effects than Ro 15-4513. Possible mechanisms for this differential activity of BZR inverse agonists are discussed.

Inhibition of decarboxylase of aromatic amino acids by 2,3,4-trihydroxybenzylhydrazine and its seryl derivative

N-(2,3,4-Trihydroxybenzyl)hydrazine [Ro 4-5127] and N1-(dl-seryl)-N2-(2,3,4-trihydroxybenzyl)hydrazine [Ro 4-4602] are powerful inhibitors of the decarboxylase of aromatic amino acids in vitro. Their effect is not reversible by dialysis or addition of pyridoxal-5′-phosphate. The inhibition by trihydroxybenzylhydrazine seems to be pseudo-irreversible and competitive. In vivo, i.e. after a single intraperitoneal injection of the drugs into rats, the activity of the decarboxylase is markedly reduced in kidney and to a lesser degree in brain. The seryl compound, however, causes in vivo no or only weak inhibition of other enzymes, such as monoamine oxidase, diamine oxidase, catecholamine-O-methyl transferase, transaminase of aromatic amino acids, tryptophan hydroxylase; in vitro, the seryl derivative does not affect the histidine decarboxylase or dopamine-β-oxidase either, nor does it alter the spontaneous release of C14-catecholamines in the rat heart in vivo.

Lysergic acid diethylamide: evidence for stimulation of cerebral dopamine receptors.

In the rat, lysergic acid diethylamide (LSD) decreased the striatal and retinal content of homovanillic acid. LSD did not change the level of dopamine (DA), but delayed the a-methyl-p-tyrosine-induced disappearance of this amine in the teldiencephalon. In the cat, LSD diminished the DA output into the perfusate of the caudate nucleus. Furthermore, LSD increased the activity of adenylate cyclase in striatal homogenates of rat. These and other findings indicate that in the central nervous system LSD stimulates DA receptors which may be involved in LSD-induced phychosis.

Effect of 6-Hydroxydopamine on behaviour and cerebral amine content in rats

250γ 6-Hydroxydopamin intraventrikulär pro Ratte vermindern nach 10 Tagen den Gehalt von Noradrenalin und Dopamin etwa um 50%. Hingegen wird 5-Hydroxytryptamin nur geringfügig beeinflusst. Das gleichzeitig gemessene exploratorische Verhalten und die lokomotorische Aktivität sind praktisch unverändert.

A new inhibitor of decarboxylase of aromatic amino acids

N-(DL-Seryl)-N′-(2,3,4-trihydroxybenzyl)hydrazin (Ro 4-4602) bewriktin vitro starke Hemmung der Decarboxylase, die durch Pyridoxal-5′-phosphat nicht und durch Dialyse nur wenig vermindert werden kann. Nach i.p. Applikation der Substanz kommt es zu starker Verminderung der Decarboxylase-Aktivität und zu mässiger Herabsetzung von 5-Hydroxytryptamin und Noradrenalin in verschiedenen Organen. Monoaminoxydase des Gehirns wirdin vivo durch Ro 4-4602 nicht beeinflusst.

CATECHOLAMINE INDUCED INCREASE OF CYCLIC ADENOSINE 3′,5′‐MONOPHOSPHATE IN RAT BRAIN IN VIVO

Abstract— Four catecholamines injected into the cerebral ventricles increased the content of cyclic adenosine 3′,5′‐monophosphate (cAMP) in vivo in the whole brain of rats. The highest rise (2.6‐fold) was measured 2 min after an injection of 100 μg epinephrine. Isoproterenol and norepinephrine were less active and dopamine hardly increased the cAMP level. These results are compatible with the view that physiological actions of catecholamines in the nervous system may be mediated by an increase of CAMP.

Two sites of 5-hydroxytryptamine uptake in blood platelets

Abstract In isolated blood platelets of guinea pigs, reserpine and imipramine inhibit the uptake of small amounts of 14 C-5HT. Thereby, reserpine increases the formation of 5HT metabolites (mainly 5-hydroxyindoleacetic acid), whereas imipramine decreases the 5HT metabolism in normal as well as in reserpinized platelets. Ouabaine, KCN and NaF also inhibit the formation of metabolites from oxogenous 14 C-5HT by reserpinized platelets. It is concluded that in guinea pigs the 5HT accumulation in the platelets occurs by two separate mechanisms, probably operating at the intracellular storage organelles and the cell membrane respectively. The membrane transport seems to be linked to the energy metabolism of the platelets.