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Biomedical subjects

D J Nutt

Publications and source records attributed to D J Nutt.

At least 163 records · Page 9Linked to original sources
PubMed1992

The effects of idazoxan and other alpha 2-adrenoceptor antagonists on urine output in the rat.

1. In normally-hydrated Wistar rats the alpha 2-adrenoceptor antagonist, idazoxan (1, 3, 10 mg kg-1 i.p.), increased urine output during the 6 h following injection. 2. The more selective and specific alpha 2-adrenoceptor antagonist, RX811059 (0.3, 1, 3 mg kg-1 i.p.), and the peripherally-acting alpha 2-adrenoceptor antagonist, L-659,066 (1, 3, 10 mg kg-1 i.p.), had no effect on urine output in normally-hydrated animals. 3. In rats given a 25 ml kg-1 water-load orally, idazoxan (10 mg kg-1, i.p.) produced an initial antidiuretic response which was followed by an increase in urine output which was apparent 4 and 6 h after drug administration. 4. RX811059 (1, 3 mg kg-1 i.p.) and L-659,066 (3, 10 mg kg-1 i.p.) significantly decreased urine output in water-loaded rats in the 2 h after injection. 5. The antidiuretic effects of L-659,066 were attenuated in Brattleboro rats which are deficient in vasopressin; only the highest dose (10 mg kg-1 i.p.) decreased urine output, and this was only a small response in comparison with its virtual abolition of urine output in water-loaded Wistar rats. 6. The results with the selective alpha 2-adrenoceptor antagonists in Wistar and Brattleboro rats suggest that alpha 2-adrenoceptors in the periphery may play a physiological role in the control of water balance through a mechanism which involves vasopressin. 7. The paradoxical diuretic effects of idazoxan contrast with the effects of the other alpha 2-adrenoceptor antagonists and therefore may be attributed to a property of this compound unrelated to alpha 2-adrenoceptor blockade.

Adrenergic alpha-Antagonists↗
PubMed1992

Characterization and autoradiographical localization of non-adrenoceptor idazoxan binding sites in the rat brain.

1. In rat whole brain homogenates, saturation analysis revealed that both [3H]-idazoxan and [3H]-RX821002, a selective alpha 2-adrenoceptor ligand, bound with high affinity to an apparent single population of sites. However, the Bmax for [3H]-idazoxan was significantly (P less than 0.01) greater than that for [3H]-RX821002. 2. In competition studies, (-)-adrenaline displaced 3 nM [3H]-idazoxan binding with an affinity consistent with [3H]-idazoxan labelling alpha 2-adrenoceptors. However, this displacement was incomplete since 23.68 +/- 1.11% of specific [3H]-idazoxan binding remained in the presence of an excess concentration (100 microM) of (-)-adrenaline. In contrast, unlabelled idazoxan promoted a complete displacement of [3H]-idazoxan binding with a Hill slope close to unity and an affinity comparable with its KD determined in saturation studies. 3. Displacement of [3H]-idazoxan binding by the alpha 2-adrenoceptor antagonists yohimbine, RX821002 (2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline) and RX811059 (2-(2-ethoxy-1,4-benzodioxan-2-yl)-2-imidazoline) was more complex, with Hill slopes considerably less than unity, and best described by a two-site model of interaction comprising a high and low affinity component. The proportion of sites with high affinity for each antagonist was similar (60-80%). 4. The rank order of antagonist potency for the high affinity component in each displacement curve (RX821002 greater than RX811059 greater than yohimbine) is similar to that determined against the binding of [3H]-RX821002 to rat brain, suggesting that these components reflect the inhibition of [3H]-idazoxan binding to alpha 2-adrenoceptors.The remaining component in each displacement curve exhibiting low affinity towards these antagonists is attributable to the displacement of [3H]-idazoxin from a non-adrenoceptor idazoxan binding site (NAIBS) since a comparable amount of [3H]-idazoxan binding was not displaced by an excess concentration of (-)-adrenaline.5. The displacement of [3H]-idazoxan binding by RX801023 (6-fluoro-(2-(1,4-benzodioxan-2-yl)-2-imidazoline) was also best described by a model assuming a two site interaction with 20.07 +/- 3.11% of the sites labelled displaying high affinity for RX801023. The Ki of RX801023 for the remainder of the sites labelled was similar to its Ki versus [3H]-RX821002, indicating that this drug displays improved affinity and NAIBS/z2-adrenoceptor selectivity compared with idazoxan.6. In autoradiographical studies, the distribution of 5 nM [3H]-idazoxan binding to sections of rat whole brain was consistent with that reported from previous studies and resembled the distribution ofM2-adrenoceptors. However, when sections of brain were coincubated with concentrations of alpha2-adrenoceptor agonists or antagonists predicted to saturate alpha2-adrenoceptors, there remained distinct areas of binding corresponding to discrete brain nuclei. This remaining binding was however displaced by unlabelled idazoxan (3 microM) or RX801023 (3 microM) indicative of the labelling of NAIBS.7. Quantitative autoradiography of NAIBS revealed several brain nuclei which contained higher densities of these sites than alpha2-adrenoceptors, notably the area postrema, interpeduncular nucleus,arcuate nucleus, ependyma and pineal gland.

Adrenergic alpha-Antagonists↗
PubMed1992

Attenuation of the behavioural effects of ethanol in mice by des-enkephalin-gamma-endorphin (ORG 5878).

This study shows inhibition of the increase in locomotor activity induced by ethanol (2 g/kg i.p.) in mice by a low dose (0.1 mg/kg i.p.) of the non-opioid beta-endorphin fragment ORG 5878 (des-enkephalin-gamma-endorphin). ORG 5878 (0.1 mg/kg i.p.) also significantly antagonised the large increase in electroshock seizure threshold produced by ethanol (1.5 g/kg i.p.). In contrast, the hypothermia induced by ethanol (2 g/kg i.p.) was not altered by ORG 5878 (0.1 mg/kg i.p.). The effects of ORG 5878 showed an abnormal dose-response relationship, in that a high dose (1 mg/kg i.p.) did not significantly suppress any of the behavioural effects of ethanol examined although there was some indication that it attenuated the stimulant action of ethanol. ORG 5878 (0.1, 1 mg/kg i.p.) did not have any intrinsic effects on locomotion, seizure threshold or body temperature in mice. These results are the first demonstration that ORG 5878 may act as an ethanol antagonist in some paradigms.

Animals↗
PubMed1991

Comparison of the effects of benzodiazepine and beta-carboline inverse agonists on body temperature in mice.

The effect of benzodiazepine and beta-carboline inverse agonists on body temperature in mice was investigated using doses shown to be pro-convulsant in other studies. The benzodiazepine partial inverse agonists Ro 15-3505 (0.1-30 mg/kg i.p.), Ro 15-4513 (0.1-10 mg/kg i.p.) and the fuller benzodiazepine inverse agonist Ro 19-4603 (0.03-0.3 mg/kg i.p.) had no effect on rectal temperature. Ro 19-4603 (1 mg/kg i.p.) produced a small hypothermic response. In contrast, the beta-carboline partial and full inverse agonists, FG 7142 (30, 60 mg/kg i.p.) and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (3, 10 mg/kg i.p.), produced large decreases in body temperature. These differential effects of benzodiazepine and beta-carboline inverse agonists on body temperature may provide further evidence for the existence of benzodiazepine receptor subtypes.

Animals↗
PubMed1991

Effect of benzodiazepine and beta-carboline antagonists and partial agonists on loprazolam- and ZK 93423-induced hypothermia.

The pharmacology of the hypothermia induced by benzodiazepine and beta-carboline full agonists in mice has been investigated using partial agonists and antagonists from both chemical series. The benzodiazepine antagonist flumazenil (10 mg/kg i.p.) blocked the hypothermia induced by loprazolam (3 mg/kg i.p.) but not that induced by the beta-carboline ZK 93423 (3 mg/kg i.p.). Both hypothermic responses were reduced by the beta-carboline antagonist ZK 93426 (3 mg/kg i.p.) and the benzodiazepine partial agonist Ro 17-1812 (10 mg/kg i.p.). On the other hand, the beta-carboline partial agonist ZK 91296 (30 mg/kg i.p.) blocked ZK 93423-hypothermia but not that induced by loprazolam. Thus, the hypothermic actions of benzodiazepine and beta-carboline agonists appear to be differentially antagonised by antagonists and partial agonists of the two chemical classes suggesting receptor subtype interactions which are non-uniformly related to the chemical class. These results cannot be explained simply in terms of pharmacokinetics or thermoregulatory effects of the compounds themselves. They suggest that, at least in the hypothalamus, different subtypes of benzodiazepine receptor may exist.

Animals↗
PubMed1991

Differential effects of selective mu-, kappa- and delta-opioid antagonists on electroshock seizure threshold in mice.

The effects of the selective opioid antagonists cyprodime (mu; 1, 3, 10, 30 mg/kg IP), norbinaltorphimine (kappa; 3, 10, 30 mg/kg IP) and naltrindole (delta; 0.3, 1, 3, 10 mg/kg IP) on electroshock seizure threshold in mice were compared with those of the universal opioid antagonist naloxone (0.3, 1, 10 mg/kg IP). Seizure threshold was increased by mu-receptor blocking doses of both cyprodime and naloxone, unaltered by norbinaltorphimine and decreased (in a dose-related manner) by all doses of naltrindole. The effects of naltrindole were similar to those of the established pro-convulsant agent bicuculline (1 mg/kg IP); however, naloxone and cyprodime produced relatively small increases in seizure threshold when compared with phenytoin (doses up to 30 mg/kg IP). The differential effects of mu-, kappa- and delta-receptor antagonists obtained in this study suggest that electroshock seizure threshold in mice may be controlled, at least in part, by a balance between endogenous opioids acting either pro-convulsantly through mu-receptors or anti-convulsantly via delta-receptors.

Animals↗
PubMed1991

Exploring the pharmacology of the pro-convulsant effects of alpha 2-adrenoceptor antagonists in mice.

The effects of selective and specific alpha 2-adrenoceptor antagonists on electroshock seizure threshold in mice were investigated. Idazoxan, at low doses, efaroxan, RX811059 and RX821002 significantly lowered seizure threshold. The alpha 1-agonist St 587 and the beta-agonist isoprenaline were also pro-convulsant. On the other hand the alpha 2-agonists clonidine and UK 14,304 produced small increases in seizure threshold. Anticonvulsant effects were also produced by low doses of the noradrenaline uptake inhibitor desipramine. This compound increases levels of noradrenaline in the synaptic cleft which could subsequently act at post-synaptic alpha 2-adrenoceptors. The pro-convulsant action of alpha 2-adrenoceptor antagonists could be explained in terms of two mechanisms: a) blockade of endogenous noradrenaline which may normally exert a tonic anti-convulsant influence on seizure threshold, through post-synaptic alpha 2-receptors and/or b) increased activation of alpha 1- and beta-adrenoceptors by elevated synaptic noradrenaline levels following blockade of pre-synaptic alpha 2-adrenoceptors. Of the alpha 2-antagonists tested, idazoxan was unusual in that high doses were not pro-convulsant; this difference may be explained by alpha 1-adrenoceptor mediated actions or be related to its recently described affinity at a non-adrenoceptor site--a function for which is currently unknown.

Adrenergic alpha-Agonists↗
PubMed1991

Pharmacology of saccadic eye movements in man. 1. Effects of the benzodiazepine receptor ligands midazolam and flumazenil.

A paradigm for assessing benzodiazepine receptor sensitivity was developed using intravenous midazolam in normal volunteers. After administration of incremental doses of midazolam, alterations in saccadic eye movement parameters and psychological self ratings were assessed. Significant changes included dose-dependent slowing of peak velocity, peak acceleration, peak deceleration, reduced saccade acceleration/deceleration ratio and saccade accuracy, and increased sedation self-ratings. Changes in saccade variables and sedation ratings were significantly correlated, and also correlated with plasma midazolam concentrations. No significant changes were seen in saccade latency or anxiety self-ratings. Pharmacological specificity of these changes was demonstrated by their reversal with the benzodiazepine antagonist flumazenil. This challenge paradigm appears to be a sensitive means of assessing benzodiazepine receptor function in man.

Adult↗
PubMed1991

Pharmacology of saccadic eye movements in man. 2. Effects of the alpha 2-adrenoceptor ligands idazoxan and clonidine.

The effects of alpha 2-adrenoceptor agonists and antagonists on saccadic eye movements were studied in normal volunteers using the agonist clonidine and the antagonist idazoxan. Changes in blood pressure, heart rate, and several psychological self-ratings were also recorded. Clonidine produced marked slowing of peak saccade velocity, acceleration and deceleration, with deceleration affected more than acceleration, but had no effect on saccade error or latency measurements. In contrast, most saccade parameters were not altered by idazoxan, although fatigue effects were eliminated. Blood pressure, heart rate, and self ratings of alertness were increased by idazoxan and reduced by clonidine, with opposite effects noted on sedation self-ratings. There were no correlations between the clonidine-induced changes in saccade parameters and changes in self-ratings. Although the slowing of some saccade parameters by clonidine may imply that alpha 2-adrenoceptors are involved in control of saccades, it may also be due to sedation. Although alpha 2-adrenoceptor antagonists may abolish fatigue effects, they cannot increase them over baseline values.

Adrenergic alpha-Antagonists↗
PubMed1991

Effects of chronic alpha 2-adrenoceptor blockade on platelet and lymphocyte adrenoceptor binding in normal volunteers.

Platelet and lymphocyte adrenoceptor binding was measured in 12 healthy male volunteers before and after 22 days treatment with the alpha 2-adrenoceptor antagonist idazoxan 40 mg tds. Platelet alpha 2-adrenoceptor number assessed by the agonist 3H-UK 14304 [correction of UK 14303] was significantly increased following idazoxan, with a smaller increase in antagonist binding (3H-rauwolscine). Lymphocyte beta-adrenoceptor number was unaltered by idazoxan, although the variance within the sample was significantly increased. Plasma MHPG levels were significantly reduced by chronic idazoxan. These data indicate upregulation of the platelet alpha 2-adrenoceptor in response to chronic blockade and suggest that this may reflect a similar change in presynaptic alpha 2-adrenoceptors which regulate norepinephrine release.

Adrenergic alpha-Antagonists↗
PubMed1991

Inhibition of baclofen-induced hypothermia in mice by the novel GABAB antagonist CGP 35348.

This study shows that the selective GABAB antagonist CGP 35348 had no effect on body temperature in mice in doses up to 300 mg/kg i.p. However, the highest dose abolished the hypothermia induced by the GABAB agonist baclofen (10 mg/kg i.p.) but not that produced by the GABA-mimetic progabide (200 mg/kg i.p.); the benzodiazepine agonist loprazolam (3 mg/kg i.p.); the alpha 2-agonist UK 14,304 (1 mg/kg i.p.) nor the mu-opioid agonist morphine (30 mg/kg i.p.). These findings, showing selective antagonism of GABAB receptors by CGP 35348, confirm that this compound may be a valuable tool for exploration of GABAB receptor function in vivo.

Animals↗
PubMed1991

Anticonvulsant activity of the imidazoline 6,7-benzoidazoxan.

The effects of the imidazoline 6,7-benzoidazoxan on seizure threshold were assessed using standard tests of anticonvulsant activity. Benzoidazoxan (10-30 mg/kg i.p.; 100 mg/kg p.o.) prevented tonic, but not clonic, convulsions induced by electroshock in mice. The increase in seizure threshold was of rapid onset, and, although of short duration, was comparable with that obtained using phenytoin and sodium valproate. Moreover, unlike sodium valproate, benzoidazoxan was an efficacious anticonvulsant at doses (20, 30 mg/kg i.p.) which did not impair rotarod performance. The anticonvulsant effects of benzoidazoxan were confirmed using the maximal electroshock test in mice (median effective dose, 13.2 mg/kg i.p.) and rats (anticonvulsant at 30 mg/kg i.p.). In addition, benzoidazoxan (10, 30 mg/kg i.p.) prevented tonic, but not clonic, seizures induced by bicuculline in mice. Thus, the imidazoline benzoidazoxan was found to be a novel anticonvulsant agent against electrically and chemically induced seizures in mice and rats with a profile of action similar to that of phenytoin.

Animals↗
PubMed1991

The effects of idazoxan and other alpha 2-adrenoceptor antagonists on food and water intake in the rat.

1. Idazoxan (1, 3, 10 mg kg-1, i.p.) produced a significant increase in food and water intake in freely feeding rats during the daylight phase. 2. The more selective and specific alpha 2-adrenoceptor antagonists, RX811059 (0.3, 1, 3 mg kg-1, i.p.) and RX821002 (0.3, 1, 3 mg kg-1, i.p.), did not produce hyperphagia in rats, however, the highest dose produced a significant increase in water intake. 3. The peripherally acting alpha 2-adrenoceptor antagonist, L-659,066 (1, 3, 10 mg kg-1, i.p.), did not affect food intake in the 4 h following injection, but the highest dose (10 mg kg-1), produced a large increase in water intake. 4. These results indicate that alpha 2-adrenoceptor antagonists may increase water intake by a peripherally mediated mechanism. 5. The lack of effect RX811059 and RX821002 on food intake contrasts with the large dose-related increases induced by idazoxan and suggests that the hyperphagic effects of idazoxan are not due to alpha 2-adrenoceptor blockade but may instead reflect its affinity for a non-adrenoceptor site, a property not shared by the other alpha 2-antagonists.

Adrenergic alpha-Antagonists↗
PubMed1991

The criteria of Cloninger et al. and von Knorring et al. for subgrouping alcoholics: a comparison in a clinical population.

There is increasing evidence that meaningful subgroups of alcoholics may exist. Cloninger et al. and von Knorring et al. have developed criteria to delineate what both call type 1 and type 2 alcoholism. However, when we compared their criteria in a predominantly inpatient sample of male alcoholics, we found large differences between the approaches in identifying type 1 and type 2 alcoholism. Concordance was equally low in a subsample of 34 alcoholics exhibiting antisocial behavior and when subjects were divided by whether the first alcohol-related problem began before or after 20 years of age. Similar findings emerged when we limited our analyses to primary alcoholics and alcoholics with no other mental disorders.

Adult↗
PubMed1991

Investigation of the different types of opioid receptor involved in electroconvulsive shock-induced antinociception and catalepsy in the rat.

The effects of novel opioid antagonists on the behavioural syndrome induced by electroconvulsive shock (ECS) in rats have been examined and compared with those of the established agent naloxone. A single ECS produced catalepsy and significantly increased tail immersion response times during the 15 min following the seizure. These responses were inhibited by a low dose of naloxone (1 mg kg-1, i.p.) and also by RX8008M (16-methylcyprenorphine; 1 mg kg-1, i.p.) which blocks mu- and delta- but not kappa-opioid receptor function. In comparison, the antinociception and catalepsy induced by ECS was not attenuated by the selective delta-receptor antagonist naltrindole (1 mg kg-1, i.p.). These results suggest that ECS-induced antinociception and catalepsy may be mediated by endogenous opioids acting at mu-opioid receptors and are consistent with biochemical studies showing the release of beta-endorphin in both animals and man following this procedure.

Analgesia↗