Lorenzo Pieri

Benzodiazepine antagonist Ro 15-1788: neurological and behavioral effects.

In neurological and behavioral studies in mice, rats, dogs and squirrel monkeys, the imidazobenzodiazepinone Ro 15-1788 acted as a potent benzodiazepine antagonist. The antagonistic activity was both preventive and curative and seen at doses at which no intrinsic effects were detected. It was highly selective in that it acted against CNS effects induced by benzodiazepines but not against those produced by other depressants, such as phenobarbitone, meprobamate, ethanol, and valproate. The onset of action was rapid even after oral administration. Depending on the animal species studied, the antagonistic effects lasted from a few hours to 1 day. The acute and subacute toxicity of Ro 15-1788 was found to be very low. Benzodiazepine-like effects were not seen.

Caffeine antagonizes several central effects of diazepam

Abstract In spinal cats, caffeine (3–30 mg·kg −1 i.v.) reduced the increase of dorsal root potentials (DRPs) caused by diazepam (0.1–1 mg·kg −1 i.v.) without affecting the prolongation of DRPs evoked by phenobarbitone (10–20 mg·kg −1 i.v.). Caffeine antagonized the depression by diazepam, but not that by phenobarbitone, of the ventral root-evoked Renshaw cell discharge. In unrestrained cats, 50 mg·kg −1 caffeine i.p. abolished the elevation induced by 1 mg·kg −1 diazepam i.p. of the threshold for eliciting a rage reaction by stimulation of the lateral hypothalamus, but was ineffective against the threshold increase caused by 20 mg·kg −1 phenobarbitine i.p. In the horizontal wire test in mice, caffeine was more potent in reversing the depression of performance induced by diazepam that that by phenobarbitone (ED50 1.8 mg·kg −1 and 139 mg·kg −1 p.o., respectively). The reduction of skeletal muscle tone in mice produced by diazepam was antagonized by low doses of caffeine (ED50 0.53 mg·kg −1 p.o.). While caffeine at low doses (0.3-3 mg·kg −1 p.o.) abolished the anticonflict effect of diazepam in rats, high doses (ED50 160 mg·kg −1 p.o.) were necessary to antagonize the anticonvulsant effect of diazepam on pentylene-tetrazole-induced seizures in mice. The interaction between caffeine and diazepam is not due to a competition at the benzodiazepine receptors but may involve purinergic mechanisms.

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.

The pharmacology of Parkinson's disease: Basic aspects and recent advances

Basic aspects and recent advances in the understanding of the pharmacological mechanism of action of the clinically most used antiparkinson drugs are reviewed. Recent human and animal biochemical investigations clearly confirm and extend previous findings indicating that benserazide is much more potent than carbidopa as peripheral decarboxylase inhibitor. L-DOPA in combination with benserazide or carbidopa constitutes the best available therapy for Parkinsons disease (PD). To reduce peaks and rapid fluctuations of L-DOPA plasma levels (possibly responsible for peak-dose dyskinesias and end-of-dose deterioration) a slow-release formulation of L-DOPA in combination with benserazide or with benserazide plus catechol-O-methyltransferase inhibitors should be developed. In parkinsonian patients under long-term L-DOPA therapy monoamine oxidase inhibitors type B (MAO-B) e.g. (−)-deprenyl and firect dopamine receptor agonists (bromocriptine, lisuride, pergolide etc.), due to their L-DOPA-sparing effects, alleviate in some cases L-DOPA-induced side-effects e.g. dyskinesias and on-off phenomena. However, since (−)-deprenylm, due to its metabolism to (−)methamphetamine and (−)amphetamine, seem to have indirect sympathomimetic activity, new selective MAO-B inhibitors devoid of indirect sympathomimetic effects should be tested clinically to assess the functional role of pure MAO-B inhibition in the therapy of PD. The auxiliary therapy with direct dopmaine receptor agonists of the D-2 subtype represents another valid approach which should be further investigated in order to find novel dopamine agonists, less expensive than bromocriptine and strictly selective for D-2 receptor sites.

Convulsions induced by centrally administered NMDA in mice: effects of NMDA antagonists, benzodiazepines, minor tranquilizers and anticonvulsants

1 Convulsions were induced reproducibly by intracerebroventricular injection of N‐methyl‐D‐aspartic acid (NMDA) to conscious mice. 2 Competitive (carboxypiperazine‐propylphosphonic acid, CPP; 2‐amino‐7‐phosphonoheptanoic acid, AP7) and non‐competitive (MK801; phencyclidine, PCP; thienylcyclohexylpiperidine, TCP; dextrorphan; dextromethorphan) NMDA antagonists prevented NMDA‐induced convulsions. 3 Benzodiazepine receptor agonists and partial agonists (triazolam, diazepam, clonazepam, Ro 16–6028), classical anticonvulsants (diphenylhydantoin, phenobarbitone, sodium valproate) and meprobamate were also found to prevent NMDA‐induced convulsions. 4 Flumazenil (a benzodiazepine receptor antagonist) and the GABA agonists THIP and muscimol (up to subtoxic doses) were without effect. 5 Flumazenil reversed the anticonvulsant action of diazepam, but not that of MK801. 6 Results obtained in this model differ somewhat from those described in a seizure model with systemic administration of NMDA. An explanation for this discrepancy is offered. 7 This model is a simple test for assessing the in vivo activity of NMDA antagonists and also expands the battery of chemically‐induced seizure models for characterizing anticonvulsants not acting at NMDA receptors.

Physical dependence Induced In DBA/2J mice by benzodiazeplne receptor full agonists, but not by the partial agonist Ro 16-6028

Continuous administration of triazolam, alprazolam or diazepam for a 7-day period by means of minipumps or chronic (17 days) p.o. treatment with alprazolam induced clear physical dependence in DBA/2J mice as assessed by precipitation of a withdrawal syndrome with an i.v. injection of the benzodiazepine receptor partial inverse agonist Ro 15-3505. In contrast, no precipitated withdrawal signs were observed following chronic exposure to high doses of the benzodiazepine receptor partial agonist Ro 16-6028. The use of minipumps and precipitation with a benzodiazepine receptor antagonist permits a simple and rapid evaluation of the physical dependence liability of potent compounds acting at the benzodiazepine receptor. Furthermore, these results support the hypothesis that benzodiazepine receptor partial agonists are less likely to induce physical dependence than full agonists.

Turning in MFB-lesioned rats and antagonism of neuroleptic-induced catalepsy after lisuride and LSD.

Abstract The effects of lisuride, d-lysergic acid diethyl amide (LSD) and apomorphine were studied in rats with unilateral destruction of nigro-striatal nerve terminals either with 6-hydroxydopamine (6-OHDA) or 5, 6-dihydroxytryptamine (5,6-DHT). Lisuride at the dose of 50 μg kg −1 i.p. induced contralateral turning for more than 4 hours while the circling induced by LSD (200 μg kg −1 ) and apomorphine (1 mg kg −1 ) persisted for only one hour. Lisuride, a compound stimulating both dopamine (DA) and 5-hydroxytryptamine (5-HT) receptors induced a more intense turning in 6-OHDA than in 5,6-DHT lesioned rats. This might indicate a modulation of 5-HT on rotational behavior. Haloperidol (1 mg kg −1 i.p.) antagonized both lisuride- and LSD-induced turning. LSD, and much more persistently lisuride, counteracted the prochlorperazine-induced catalepsy. These findings correlate with the biochemical data indicating that lisuride is a very potent agonist at central dopaminergic receptors.

Effects of an intrathecally administered benzodiazepine receptor agonist, antagonist and inverse agonist on morphine-induced inhibition of a spinal nociceptive reflex

1 The effects of an intrathecally administered benzodiazepine receptor (BZR) agonist (midazolam, up to 50 μg), antagonist (flumazenil, Ro 15–1788, 5 μg) and inverse agonist (Ro 19–4603, 15 μg) on nociception and on morphine‐induced antinociception were studied in rats. 2 By themselves, none of these compounds significantly altered pain threshold. 3 The BZR agonist midazolam enhanced the morphine‐induced antinociceptive effect whereas the antagonist flumazenil did not alter it. In contrast, the BZR inverse agonist Ro 19–4603 decreased the morphine‐induced antinociceptive effect. 4 Naloxone (1 mg kg−1 i.p.) completely reversed all these effects. 5 These results demonstrate that BZR agonists and inverse agonists are able to affect, by allosteric up‐ or down‐modulation of γ‐aminobutyric acidA (GABAA)‐receptors, the transmission of nociceptive information at the spinal cord level, when this transmission is depressed by μ‐opioid receptor activation.

Mapping monoaminergic neurons with [3H]reserpine by autoradiography

The synthesis of [3H]reserpine of high specific activity is described. The accumulation of radioactivity in peripheral sympathetically innervated organs and in the brain after intravenous injection of [3H]reserpine to rats was measured biochemically and its localization studied by light-microscopic autoradiography. In most of the organs and tissues investigated minute quantities of [3H]reserpine persisted up to 10 days after injection. By autoradiography, it was observed that silver grains were unevenly distributed in various brain regions and peripheral organs 18 h and up to 10 days after administration of [3H]reserpine. In the brain the radiolabel selectively accumulated in distinct areas known to have a high monoamine content including the substantia nigra, nucleus (n.) raphe, locus coeruleus, n. dorsomedialis hypothalami and the n. arcuatus, where cell bodies as well as the neuropil were labelled; whereas in the neostriatum, n. septi lateralis, n. accumbens, n. tractus solitarii, eminentia mediana, hippocampus and cortex the label was confined to the neuropil. Supra-ependymal 5-hydroxytryptamine-containing nerves in the cerebroventricular system and the interplexiform layer of the retina also selectively accumulated the label, as did a network of nerve fibres in the iris, cells and paracellular areas of the superior cervical ganglia and chromaffin cells of the adrenal medulla. Pretreating (but not post-treating) animals with non-radioactive reserpine prevents, by up to 80%, the accumulation of radiolabel and abolishes to a great extent the autoradiographic localization. The fact that the persistently bound radiolabel is confined to monoaminergic neurons suggests that it is irreversibly bound to its target site, the amine-storing vesicle. Support for this interpretation comes from studies demonstrating a fast anterograde axonal transport of [3H]reserpine in the nigrostriatal tract after intranigral injection of the radiolabel. Altogether, these findings are in line with a wealth of neuropharmacological, endocrinological and clinical observations relating the effects of reserpine to its interaction with dopaminergic, noradrenergic and serotonergic neuronal systems. They demonstrate that [3H]reserpine of high specific activity is a useful tool in studies designed to map monoaminergic pathways in the brain and to further characterize amine-storing mechanisms.

Effects of spreading depression on the turnover of cerebral dopamine

Abstract Unilateral spreading depression (SD), induced in the rat by KCl, causes an increase in the homovanillic acid content of the ipsilateral, but not of the contralateral, cerebral hemisphere without concomitant changes of the dopamine (DA) and 5-hydroxyindoleacetic acid levels. The α-methyl-p-tyrosine-induced disappearance of cerebral DA is accelerated on the side of SD. It is concluded that persistent depolarization of striatal and/or cortical neurones leads to an enhanced DA turnover which is possibly due to disinhibition of the nigro-striatal dopaminergic pathway.