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Biomedical subjects

A L Hudson

Publications and source records attributed to A L Hudson.

At least 37 records · Page 2Linked to original sources
PubMed2000

Behavioural and physiological effects induced by an infusion of antisense to alpha(2D)-adrenoceptors in the rat.

1. The aim of this study was to investigate the behavioural and physiological effects of an i.c.v. infusion of antisense oligonucleotide to the alpha(2D)-adrenoceptor subtype. Behavioural and physiological parameters were monitored for 2 days before the infusion, throughout the 3-day infusion period and for 3 days following the end of the infusion. 2. The antisense infusion resulted in a significant increase in behavioural activity characterized by increased locomotion and grooming scores. Behavioural activity scores of rats treated with antisense to alpha(2D)-adrenoceptors were significantly higher than those of rats treated with vehicle (H(2)O) or the mismatch toxicity control on day 4 and day 5 and, significantly higher than vehicle controls on day 6. 3. Body weight gain was significantly reduced in the antisense-treated rats at the end of the study compared to the vehicle (34%) and mismatch groups (30%), although daily food and water intakes were not significantly different at any time point. 4. Pupil diameters of rats infused with antisense to alpha(2D)-adrenoceptors were significantly greater than those of animals treated either with vehicle or mismatch oligonucleotide on day 5 of the study. On day 6, the pupil diameters of these animals were still significantly greater than the mismatch group. 5. In conclusion, an i.c.v. infusion of antisense to the alpha(2D)-adrenoceptor induced behavioural activation in rats, increased pupil diameter and reduced total weight gain. These effects were specific to the antisense-treated group and were fully reversed post-infusion.

Animals↗
PubMed1999

Extraction of active clonidine-displacing substance from bovine lung and comparison with clonidine-displacing substance extracted from other tissues.

Crude methanolic clonidine-displacing substance (CDS) extracted from bovine lung competed for radioligand binding from alpha2-adrenoceptors and I2-sites present in rat brain membranes, and from I1-sites present in rat brain and kidney membranes. There was no difference in the competition of [3H]clonidine binding to alpha2-adrenoceptors present in either rat or rabbit brain membranes by the crude CDS extract and therefore either tissue could be used to estimate the number of units of CDS present in extracts. Further purification by reverse phase high performance liquid chromatography (RP-HPLC), with UV detection, of extracts obtained from bovine lung, brain and rat brain exhibited similar three-peak profiles, previously reported. Corresponding fractions competed for radioligand binding to alpha2-adrenoceptors present in rat brain membranes, eluting between 19 and 23 min, which corresponded with the middle peak of the three-peaks. Therefore, we propose the CDS-like material eluting from all these tissues to be similar. Interestingly, CDS extracted from bovine adrenal glands under the same conditions showed a similar three-peak profile, but did not repeat the displacement of binding just at 19-23 min, but at every time point after 4 min. This suggests this tissue could represent a source of CDS in this species.

Adrenal Glands↗
PubMed1999

Novel selective compounds for the investigation of imidazoline receptors.

Over several years our group has sought to synthesize and identify selective ligands for imidazoline (I) receptors, in particular the I2 binding site. As a consequence, [3H]2-(2-benzofuranyl)-2-imidazoline (2BFI) has proved extremely useful for binding and autoradiographic studies. More recently we have synthesized a BU series of compounds and examined these for their affinities for both I1 and I2 binding sites. BU224 (2-(4,5-dihydroimidaz-2-yl)-quinoline) shows high affinity for I2 receptors with a Ki of 2.1 nM. BU226 (2-(4,5-dihydroimidaz-2-yl)-isoquinoline) demonstrated slightly higher affinity (Ki 1.4 nM) for I2 receptors, but overall BU224 displayed greater selectivity for I2 over I1 receptors (832-fold) than BU226 (380-fold). Both compounds showed low (microM) affinity for alpha 2-adrenoceptors. Given BU224's ability to cross the blood brain barrier, we predict that its in vivo effects are likely to be mediated via I2 receptors. Brain dialysis revealed BU224 to dose dependently (0-20 mg/kg i.p.) elevate basal noradrenaline in rat frontal cortex and basal dopamine in striatum. In a rat model of opiate withdrawal, behavioral studies showed that BU224 (10 mg/kg, s.c.) was able to reduce acute weight loss and diarrhea, but not the number of wet dog shakes associated with the withdrawal syndrome.

Animals↗
PubMed1999

Autoradiographical and behavioural effects of a chronic infusion of antisense to the alpha2D-adrenoceptor in the rat.

1. The aims of this study were, firstly to use receptor autoradiography to investigate the effect of antisense oligonucleotides to the alpha2D-adrenoceptor on receptor binding and, secondly to measure behavioural and physiological parameters to determine whether the chronic antisense infusion had any effect on alpha2-adrenoceptor function in vivo. 2. A 3 day infusion of antisense to the alpha2D-adrenoceptor significantly reduced specific [3H]-RX821002 binding in the septum (20 - 30%) and anterior hypothalamic area (20 - 30%). beta-Adrenoceptor expression was unaffected in those brain areas examined, indicating the antisense knockdown was specific to the alpha2-adrenoceptors. 3. On the second day of the infusion, the hypothermic response to UK 14,304 was significantly attenuated in the antisense-treated group compared with both vehicle and mismatch controls. The effect was fully reversible and a similar decrease in body temperature was observed in all the treatment groups 4 days after the end of infusion. 4. During the second day of the infusion, the effects of UK 14,304 on behaviour were reduced in the antisense-treated rats, but were not significantly lower than those of the vehicle and mismatch, UK 14, 304 controls. These trends were not observed 4 days after the end of the infusion. 5. In conclusion, antisense has been shown to selectively knockdown alpha2-adrenoceptor expression in specific brain areas. The consequence of this knockdown is a significant attenuation of UK 14,304-induced hypothermia and a reduction in its sedative actions. These changes were fully reversed 4 days after the end of the infusion.

Animals↗
PubMed1999

In vitro and in vivo approaches to the characterization of the alpha2-adrenoceptor.

1. In order to more fully understand the role of the alpha2-adrenoceptor in brain function, a combination of in vitro and in vivo techniques were utilized including radioligand binding, autoradiography, brain microdialysis and antisense oligonucleotides. 2. Binding studies showed the tritiated form of the selective alpha2-adrenoceptor antagonist, RX821002 (methoxy-idazoxan) labelled an apparent single population of sites in rat brain membranes with high affinity (1 nM), for which prazosin had low affinity (1107 nM). Similar studies in rabbit brain membranes found that prazosin and oxymetazoline were able to displace [3H]-RX821002 in a biphasic manner indicating the presence of subtypes of alpha2-adrenoceptors. 3. Receptor autoradiography revealed a distribution of [3H]-RX821002 binding in rat brain consistent with the labelling of all alpha2-adrenoceptor subtypes, namely alpha(2A/D-), alpha2B and alpha2C. 4. In rat, in vivo brain dialysis experiments demonstrated peripherally administered RX821002 elevated basal noradrenaline in frontal cortex and also, although to a lesser extent, in ventral hippocampus. RX821002 was also able to elevate extracellular dopamine in the striatum. 5. A 7-day i.c.v. infusion of an antisense oligonucleotide targeting the alpha(2A/D)-adrenoceptor, resulted in a significant reduction in the autoradiographic density of [3H]-RX821002 binding in specific brain areas, notably the lateral septal nuclei and anterior hypothalamic area. 6. Several years of research by our group has extended our knowledge of the pharmacology and function of the alpha2-adrenoceptor and has provided evidence of the roles of this receptor in the control of monoamine turnover. The successful use of antisense technology to knockdown expression of the alpha(2A/D) subtype provides future opportunities to explore the physiology of this receptor subtype.

Adrenergic alpha-Antagonists↗
PubMed1998

Characterisation and localisation of [3H]2-(2-benzofuranyl)-2-imidazoline binding in rat brain: a selective ligand for imidazoline I2 receptors.

In rat whole brain homogenates, saturation binding analysis revealed that both [3H]2-BFI (2-(2-benzofuranyl)-2-imidazoline) and [3H]idazoxan (in the presence of 5 microM rauwolscine) bound with high affinity to an apparent single population of sites. However, the Kd for [3H]2-BFI (1.74+/-0.14 nM) was significantly (P < 0.01) less than that for [3H]idazoxan (10.4+/-2.68 nM). In competition studies idazoxan, 2-BFI, BU224 (2-(4,5-dihydroimidaz-2-yl)-quinoline), amiloride and guanabenz displayed high affinity (Ki values = 7.32, 1.71, 2.08, 21.80 and 14.90 nM, respectively) for 70-80% of sites, and low microM affinity for the remaining 20-30% of sites labelled by [3H]2-BFI. In contrast, several alpha2-adrenoceptor, imidazoline I1 receptor and histamine receptor ligands exhibited only micromolar affinity for the [3H]2-BFI labelled site. Quantitative receptor autoradiography revealed high binding by [3H]2-BFI to discrete brain nuclei, notably the area postrema, interpeduncular nucleus, arcuate nucleus, mammillary peduncle, ependyma and pineal gland. These data indicate that [3H]2-BFI recognises imidazoline I2 receptors in rat brain with higher affinity and selectivity than [3H]idazoxan and thus represents a superior radioligand to [3H]idazoxan for the study of imidazoline I2 receptors.

Animals↗
PubMed1998

'Seeing through a glass darkly': casting light on imidazoline 'I' sites.

Although imidazoline sites have been the subject of research for several years, there is still controversy about their structure, diversity and physiology. The I1 site is thought to exist principally as a binding site and is widely purported to play a role in controlling systemic blood pressure, although this is still unclear. The majority of I2 sites are widely accepted as being allosteric sites on monoamine oxidase; however, even with selective ligands, their exact function remains to be determined. A putative I3 site modulates insulin secretion and could represent the first functional site to be pharmacologically defined with selective agonists and antagonists. The structure and relevance of the proposed endogenous ligand 'clonidine-displacing substance' remains elusive. A potential candidate for this substance is agmatine; however, although it is capable of displacing bound clonidine from imidazoline sites, it lacks the functionality ascribed to the clonidine-displacing substance. In this review, Richard M. Eglen and colleagues assess our knowledge of imidazoline sites in the light of recent data.

Adrenergic alpha-Agonists↗
PubMed1998

Potentiation of barbiturate-induced alterations in presynaptic noradrenergic function in rat frontal cortex by imidazol(in)e alpha2-adrenoceptor agonists.

1. In order to resolve the extent to which presynaptic noradrenergic mechanisms contribute to the anaesthetic-sparing effects of alpha2-adrenoceptor agonists in vivo microdialysis was used to investigate the combined effects of sodium pentobarbitone and imidazol(in)e alpha2-adrenoceptor agonists on extracellular levels of noradrenaline (NA) in the rat frontal cortex. 2. Dialysate levels of NA were markedly reduced by the addition of TTX (2 microM) or by the removal of calcium in the perfusate. These data imply that dialysate NA levels are ultimately dependent on exocytotic release mechanisms from afferent coeruleo-cortical neurones. 3. Systemic administration of sodium pentobarbitone (85 mg kg(-1), i.p.) induced general anaesthesia and reduced NA levels by 92% after 30 min. The restoration of basal levels 90 min later was closely associated with a return of the corneal blink reflex. 4. Basal NA levels in conscious animals were not affected by an intravenous infusion of equally radioactive solutions of either imidazoline (clonidine) or imidazole (mivazerol) alpha2-adrenoceptor agonists. The dose rate employed for each compound was 2 microg kg(-1) h(-1) over 2 h. 5. The co-administration of intravenous clonidine or mivazerol, each at 2 microg kg(-1) h(-1) for 2 h, with sodium pentobarbitone (85 mg kg(-1), i.p.), produced a marked and prolonged reduction in NA efflux. After 2 h, NA levels remained suppressed by 95% (clonidine) and 80% (mivazerol) and animals remained deeply anaesthetized. 6. The accumulation of tritium in brain tissue was 42-73% lower across all brain regions examined after [3H]-mivazerol administration than after [3H]-clonidine administration. Sodium pentobarbitone did not alter the accumulation of tritium in brain tissue after the administration of either alpha2-adrenoceptor agonist. 7. These data demonstrate that alpha2-adrenoceptor agonists potentiate the inhibitory effects of sodium pentobarbitone on extracellular levels of NA in the frontal cortex. Further studies will be necessary to establish a causal role of noradrenergic mechanisms in the potentiation of anaesthesia by selective alpha2-adrenoceptor agonists.

Adrenergic alpha-Agonists↗
PubMed1997

Identification of ligands selective for central I2-imidazoline binding sites.

Using radioligand binding techniques, several compounds selective for mammalian brain imidazoline 2 receptors have been identified. In rabbit brain membranes, a series of 6 and/or 7 aromatic-substituted derivatives of the alpha 2-adrenoceptor antagonist idazoxan were found to show moderate affinity for I2 receptors over alpha 2-adrenoceptors, in particular 6,7-dichloroidazoxan, which was 41 fold selective in favour of I2 receptors. Modification of the benzodioxan ring of idazoxan could also result in affinity and selectivity, which was moderate (2.7 nM, 161 fold) in the case of the 1,3-benzodioxan isomer of idazoxan (2-(1,3-benzodioxanyl)-2-imidazoline), and high (1.3 nM, 2873 fold) in the case of 2-(2-benzofuranyl-2-imidazoline) (2-BFI). Analogues of 2-BFI with halogenic substitutions of the aromatic ring were also found to retain high affinity and moderate to high selectivity for I2-sites. In particular, the 7-chloro (Ki 2.8 nM, 2192 fold) and the 4,6-dibromo (Ki 6.1 nM, 361 fold) analogues of 2-BFI. These new ligands should prove invaluable for investigating the pharmacology and physiology of I2 receptors.

Adrenergic alpha-Antagonists↗
PubMed1997

A series of novel imidazoline I2-receptor selective Schiff bases of 1-(benzylidenamino)-3,3-dimethylguanidine.

A series of 12 Schiff bases of 1-(benyzylidenamino)-3,3-dimethylguanidine were evaluated for their affinities at imidazoline I2-receptors and alpha 2-adrenoceptors in the guinea pig cerebral cortex by using a 2-curve assay with [3H]idazoxan as ligand and the simultaneous computer analysis of (-)adrenaline masked and non-masked competition curves. All of the dimethylguanidines were selective for I2-receptors with the selectivity ranging 6-110-fold, and the most selective being WAP8 (2-bromobenzylidenamino-3,3-dimethylguanidine) closely followed by FLA151 (2-chlorobenzylidenamino-3, 3-dimethylguanidine). Some of the dimethylguanidines were also tested for affinity at bovine kidney cortex I2-receptors and guinea pig alpha 1-adrenoceptors. These substances were found to have similar affinities for bovine kidney I2-receptors as for guinea pig cerebral cortex I2-receptors, but their affinities for the alpha 1-adrenoceptors were considerably lower.

Animals↗