1
|
Zarrindast MR, Fazli-Tabaei S, Semnanian S, Fathollah Y, Yahyavi SH. Effects of adrenoceptor agents on apomorphine-induced licking behavior in rats. Pharmacol Biochem Behav 2000; 65:275-9. [PMID: 10672980 DOI: 10.1016/s0091-3057(99)00198-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
In the present study, intraperitoneal (IP) administration of the dopaminergic receptor agonist apomorphine (0.1, 0.25, and 0.5 mg/kg) induced a dose-dependent licking in rats. The intraperitoneal injection of the alpha1'''adrenoceptor agonist phenylephrine (1-8 mg/kg) but not the alpha2-adrenoceptor agonist clonidine (0.025-0.05 mg/kg) decreased licking induced by apomorphine. The alpha-adrenoceptor antagonists prazosin, phenoxybenzamine, and yohimbine also reduced the apomorphine response significantly. The response induced by phenylephrine was decreased by a dose of prazosin. The beta1-adrenenocepor agonist dobutamine and beta2-adrenenocepor agonist salbutamol did not alter the apomorphine response. However, beta2-adrenenocepor antagonists atenolol and propranolol reduced the apomorphine effect. It may be concluded that alpha1- and possibly beta1-adrenoceptor mechanisms may be involved in modulation of licking behavior.
Collapse
Affiliation(s)
- M R Zarrindast
- Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Iran
| | | | | | | | | |
Collapse
|
2
|
Airio J, Ahtee L. The involvement of noradrenergic transmission in the morphine-induced locomotor hyperactivity in mice withdrawn from repeated morphine treatment. Br J Pharmacol 1999; 126:1609-19. [PMID: 10323593 PMCID: PMC1565948 DOI: 10.1038/sj.bjp.0702485] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. Our previous studies suggest that in addition to the cerebral dopaminergic systems the noradrenergic ones have a crucial role in the morphine-induced behavioural sensitization in mice. Therefore the effects of alpha2-adrenoceptor antagonist, idazoxan (1 and 3 mg kg(-1), i.p.) on morphine-induced locomotor hyperactivity as well as on morphine-induced changes in cerebral noradrenaline (NA) and striatal dopamine (DA) metabolism were studied in mice withdrawn for 3 days from 5 day repeated morphine treatment. The concentrations of NA, free 3-methoxy-4-hydroxyphenylethylene glycol (MOPEG), DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxytyramine (3-MT) were determined. 2. Acute morphine (10 mg kg(-1), s.c.) increased locomotor activity in control and in morphine-withdrawn mice; idazoxan alone did not alter the activity. Idazoxan pretreatment did not alter the locomotor hyperactivity induced by acute morphine in control mice but potentiated it in morphine-withdrawn mice. 3. Acute morphine elevated MOPEG less but increased DOPAC and HVA more clearly in morphine-withdrawn mice than in controls, and decreased 3-MT only in controls. Idazoxan alone did not alter the NA or DA metabolite concentrations in control mice, but elevated MOPEG as well as DOPAC in morphine-withdrawn mice. 4. In control mice idazoxan enhanced acute morphine's elevating effect on MOPEG. In withdrawn mice idazoxan counteracted the tolerance so that acute morphine elevated MOPEG in these mice to about similar level as in controls. 5. Idazoxan pretreatment abolished the HVA increasing effect of acute morphine both in control and withdrawn mice. In control mice idazoxan enhanced morphine's elevating effect on DOPAC and abolished morphine's decreasing effect on 3-MT. Idazoxan did not alter morphine's effects on DOPAC or 3-MT concentrations in withdrawn mice. 6. Our results show that in morphine-withdrawn mice idazoxan pretreatment reveals the morphine-induced locomotor sensitization. This most probably occurs by overcoming the tolerance towards the acute morphine-induced increase of cerebral NA turnover and release. It is suggested that in mice the cerebral noradrenergic in addition to the dopaminergic systems are major determinants of the behavioural sensitization to morphine.
Collapse
Affiliation(s)
- Juha Airio
- Department of Pharmacy, Division of Pharmacology and Toxicology, P.O. Box 56, FIN-00014 University of Helsinki, Finland
| | - Liisa Ahtee
- Department of Pharmacy, Division of Pharmacology and Toxicology, P.O. Box 56, FIN-00014 University of Helsinki, Finland
- Author for correspondence:
| |
Collapse
|
3
|
Savory CJ, Kostal L. The role of adrenoreceptors in control of stereotyped oral behavior in restricted-fed fowls. Pharmacol Biochem Behav 1994; 49:295-302. [PMID: 7824541 DOI: 10.1016/0091-3057(94)90424-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Effects on environmentally induced oral stereotypies (object pecking and drinker-directed activity) of preferential antagonists and agonists of adrenoreceptor subtypes were examined in individually caged broiler breeder fowls subjected to chronic food restriction. Three drugs in each category were injected intravenously at three doses, and their effects compared with a saline control treatment. With the antagonists, object pecking was suppressed more by prazosin (alpha 1) and propranolol (beta) than by yohimbine (alpha 2), while drinker-directed activity showed delayed stimulation with yohimbine and propranolol. With the agonists, drinker-directed activity was suppressed more by clonidine (alpha 2) than by isoproterenol (beta) and phenylephrine (alpha 1), while object pecking was inhibited by the high doses of clonidine and isoproterenol but showed delayed stimulation with the low dose of clonidine and (nonsignificantly) the high dose of phenylephrine. Initial suppression of both oral stereotypies by the high doses of yohimbine and isoproterenol, and high and medium doses of clonidine, may have been due to sedation, because in those instances it coincided with increased sitting, an activity not normally seen. Increased standing with clonidine and the medium dose of yohimbine may also reflect sedation. When there were no significant increases in sitting or standing to indicate sedation, responses of both stereotypies were essentially the same with all three adrenoreceptor subtypes; i.e., object pecking was inhibited by the antagonist but not the agonist, while drinker-directed activity was inhibited by the agonist but not the antagonist. It is concluded that alpha 1, alpha 2, and beta adrenoreceptors are all implicated in expression of these stereotypes, and that the two activities may be differentially controlled.
Collapse
Affiliation(s)
- C J Savory
- Roslin Institute (Edinburgh), Midlothian, UK
| | | |
Collapse
|
4
|
Berridge TL, Doxey JC, Roach AG, Smith CF. Selectivity profile of the α2-adrenoceptor antagonist efaroxan in relation to plasma glucose and insulin levels in the rat. Eur J Pharmacol 1992; 213:205-12. [PMID: 1355733 DOI: 10.1016/0014-2999(92)90683-u] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The effects of efaroxan (RX 821037A; 2-[2-(2-ethyl-2,3-dihydrobenzofuranyl)]-2-imidazoline HCl) at alpha 1- and alpha 2-adrenoceptors were investigated in isolated tissues, pithed rats and conscious rats. In isolated tissues, efaroxan competitively antagonised the inhibitory effects of p-aminoclonidine in the electrically stimulated (0.1 Hz) rat vas deferens, (pA2 = 8.89) and the contractile effects of phenylephrine on the rat anococcygeus muscle (pA2 = 6.03). Efaroxan had a selectivity ratio (alpha 2/alpha 1) of 724 compared to a value of 182 for idazoxan. In pithed rats, the i.v. doses of efaroxan (mumol/kg) producing 2-fold shifts in dose-response curves for UK-14,304 at prejunctional cardiac alpha 2-adrenoceptors and postjunctional vascular alpha 2-adrenoceptors, and for cirazoline at postjunctional vascular alpha 1-adrenoceptors, were 0.05, 0.13 and 2.96, respectively. In conscious fasted rats, prazosin (5 mg/kg p.o.) increased resting glucose levels and exacerbated the hyperglycaemic effects of UK-14,304 and adrenaline. In contrast, efaroxan (1-5 mg/kg p.o.) had little effect on resting plasma glucose but markedly antagonised the hyperglycaemic actions of UK-14,304 and adrenaline. Efaroxan increased resting plasma insulin levels and markedly potentiated the rise in insulin levels produced by adrenaline; this latter effect was prevented by the co-administration of propranolol. These results demonstrate that efaroxan is a potent and selective alpha 2-adrenoceptor antagonist and provide further support for the involvement of alpha 2-adrenoceptors in glucose homeostasis.
Collapse
Affiliation(s)
- T L Berridge
- Research and Development Laboratories, Reckitt and Colman Pharmaceuticals, Kingston-upon-Hull, U.K
| | | | | | | |
Collapse
|
5
|
Krystal JH, McDougle CJ, Woods SW, Price LH, Heninger GR, Charney DS. Dose-response relationship for oral idazoxan effects in healthy human subjects: comparison with oral yohimbine. Psychopharmacology (Berl) 1992; 108:313-9. [PMID: 1355923 DOI: 10.1007/bf02245117] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The effects of oral administration of the alpha 2 adrenergic receptor antagonists idazoxan (20 mg, 40 mg, 80 mg) and yohimbine (20 mg) were compared using a placebo-controlled within-subjects design. Healthy subjects completed 5 test days during which medication effects on mood and anxiety states, physiologic indices, plasma cortisol levels, and plasma levels of the norepinephrine metabolite 3-methoxy-4-hydroxy-phenylethylene glycol (MHPG) were assessed. Idazoxan dose-dependently increased plasma MHPG, plasma cortisol, systolic and diastolic blood pressure, and Panic Attack Symptom Scale scores in healthy subjects. Overall, yohimbine and idazoxan produced a similar pattern of behavioral and neuroendocrine responses. Since idazoxan possesses relatively greater receptor specificity compared to yohimbine, it may be a more useful alpha 2 antagonist in humans.
Collapse
Affiliation(s)
- J H Krystal
- VA-Yale Alcoholism Research Center, West Haven, CT 06516
| | | | | | | | | | | |
Collapse
|
6
|
Mavridis M, Colpaert FC, Millan MJ. Differential modulation of (+)-amphetamine-induced rotation in unilateral substantia nigra-lesioned rats by alpha 1 as compared to alpha 2 agonists and antagonists. Brain Res 1991; 562:216-24. [PMID: 1685341 DOI: 10.1016/0006-8993(91)90624-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In rats sustaining unilateral 6-hydroxy-dopamine lesions of the substantia nigra (SN), the indirect dopaminergic agonist, (+)-amphetamine (AMPH), dose-dependently induced robust, ipsilateral rotation: this could be dose-dependently abolished by the dopamine (D2/D1) antagonist, haloperidol. The selective alpha 1 antagonist, prazosin, dose-dependently attenuated the action of AMPH though rotation was not completely abolished. In the presence of a constant dose of prazosin, the dose-response curve for induction of rotation by AMPH was shifted to the right. The action of prazosin was mimicked by a further alpha 1 antagonist, corynanthine. In contrast, the selective alpha 1 agonist, ST 587, potentiated the rotation evoked by AMPH. The selective alpha 2 antagonist, idazoxan, dose-dependently potentiated the action of AMPH and, in the presence of a constant dose of idazoxan, the dose-response curve for AMPH was shifted to the left. This effect of idazoxan was mimicked by a further alpha 2 antagonist, yohimbine. In distinction, the selective alpha 2 agonist, UK 14,304, dose-dependently attenuated the action of AMPH, an action mimicked by the alpha 2 partial agonist, clonidine. Upon administration alone, the above mentioned drugs did not induce rotation. The data indicate that activation and antagonism of alpha 1 receptors enhance and inhibit rotation, respectively, whereas activation and antagonism of alpha 2 receptors inhibit and enhance rotation, respectively. These findings demonstrate an opposite alpha 1 and alpha 2 receptor-mediated control of rotation in this model. They suggest that an increase and decrease in noradrenergic tone, respectively, facilitate and inhibit locomotor activity controlled via the nigro-striatal dopaminergic pathway. The possible relevance of these findings to Parkinson's disease is discussed.
Collapse
Affiliation(s)
- M Mavridis
- FONDAX, Groupe de Recherche Servier, Paris, France
| | | | | |
Collapse
|
7
|
Nicholson AN, Pascoe PA. Presynaptic alpha 2-adrenoceptor function and sleep in man: studies with clonidine and idazoxan. Neuropharmacology 1991; 30:367-72. [PMID: 1677168 DOI: 10.1016/0028-3908(91)90062-g] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The effects of an alpha 2-adrenoceptor agonist, clonidine and an antagonist, idazoxan, were studied on nocturnal sleep in man. Clonidine increased non-rapid eye movement sleep and idazoxan reduced slow wave sleep and increased awake activity. Changes in the continuity of sleep with clonidine were similar to, and those with idazoxan opposite to, the effects of maprotiline, an inhibitor of the uptake of noradrenaline, used as an active control. These findings support the previous conclusion that raised levels of noradrenaline in the synapse, after inhibition of uptake, lead to increased presynaptic inhibition of release of transmitter in man. However, all three drugs decreased rapid eye movement (REM) sleep and the ratio of REM to nonREM sleep and this is believed to be due to a non-specific upset of the balance of influences which control the appearance of REM sleep.
Collapse
Affiliation(s)
- A N Nicholson
- Royal Air Force Institute of Aviation Medicine, Farnborough, Hampshire, U.K
| | | |
Collapse
|
8
|
Abstract
Six unrestrained bonnet macaques were each observed after oral administration of four dosages of yohimbine hydrochloride (0.10, 0.25, 0.50, and 0.75 mg/kg) and a placebo. Yohimbine significantly increased episodes of motoric activation and affective response interspersed with intervals of behavioral enervation. Yohimbine scores correlated closely with baseline levels; there was no dose-response relationship. Response to oral yohimbine differed in several ways from subcutaneous and intravenous sodium lactate infusions, including prominent enervative symptoms and the appearance of sexual arousal. In light of the appearance of cyclic enervative episodes, this study suggests limitations to primate models of panic disorder utilizing oral yohimbine.
Collapse
Affiliation(s)
- L A Rosenblum
- Department of Psychiatry, SUNY/Health Science Center, Brooklyn, NY 11203
| | | | | | | |
Collapse
|
9
|
Affiliation(s)
- B Scatton
- Synthélabo Research (LERS), Biochemical Pharmacology Group, Bagneux, France
| |
Collapse
|
10
|
Dickinson SL, Gadie B, Tulloch IF. Specific α2-adrenoreceptor antagonists induce behavioural activation in the rat. J Psychopharmacol 1990; 4:90-9. [PMID: 22282933 DOI: 10.1177/026988119000400207] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The behavioural effects of the specific and selective α(2)-adrenoreceptor antagonists, idazoxan, efaroxan and RX811059, have been investigated in the rat. All three drugs induced periods of behavioural activation characterized by increased locomotion and exploration (rearing and hole dipping). However, these effects were only apparent in animals which were fully habituated to their environments and thus displayed low baseline activity. The behaviour observed lay within the normal range of activity and was not apparent under conditions when exploration was stimulated such as in a novel environment. α( 2)-Adrenoreceptor antagonist- induced activation was a weak response when compared with the intense and prolonged hyperactivity, in both novel and non-novel environments, induced by the amine releaser D- amphetamine. Possible mechanisms involving a direct action of noradrenaline at postsynaptic α( 1)-adrenoreceptors (subsequent to enhanced presynaptic α(2)-receptor feedback blockade) or an indirect action of α(2)-antagonists on dopamine function in mesolimbic pathways are discussed.
Collapse
Affiliation(s)
- S L Dickinson
- Reckitt and Colman Psychopharmacology Unit, The School of Medical Sciences, University Walk, Bristol, BS8 1TD
| | | | | |
Collapse
|
11
|
Menon MK, Lloyd RL, Fitten LJ. Antagonism of the hypothermic effect of clozapine in mice by centrally-active alpha 2-adrenergic antagonists and alpha 1-adrenergic agonists. Psychopharmacology (Berl) 1990; 101:67-72. [PMID: 1971449 DOI: 10.1007/bf02253720] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Hypothermia induced by either clozapine or clonidine in mice was blocked by the alpha 2-adrenergic antagonists yohimbine, idazoxan, CH-38083, SKF 86466, and L-657,743. These effects were dose related, and the ID50 values for inhibition of clozapine- or clonidine-induced hypothermia were fairly comparable. The order of potency for blocking clonidine-induced hypothermia was: L-657,743 greater than CH-38083 greater than yohimbine greater than idazoxan greater than SKF 86466. A very similar blockade hierarchy for clozapine-induced hypothermia was observed, with the order of the two most effective compounds being reversed. Hypothermia induced by either compound was not blocked by the peripherally-acting, selective alpha 2-adrenergic antagonist, L-659,066, indicating that blockade by the other compounds occurred centrally. The centrally-acting, alpha 1-adrenergic agonists St 587, cirazoline, and SKF 89748 were very effective in blocking the response to clozapine, but ineffective in antagonizing clonidine-induced hypothermia. The ED50 values for the blockade of this response to clozapine, however, did not correlate with their reported potencies in stimulating either peripheral or central alpha 1-adrenergic receptors. This indicates that clozapine-induced hypothermia in mice is not a suitable model for evaluating the properties of central alpha 1-adrenergic compounds. Moreover, since the clonidine-induced hypothermia is not influenced by alpha 1-adrenergic agonists, this paradigm is preferable to clozapine-induced hypothermia in the assessment of alpha 2-adrenergic antagonism The ability of alpha 2-adrenergic antagonists to block clozapine-induced hypothermia may result from the central overflow of norepinephrine, which is known to be brought about by this group of compounds.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- M K Menon
- Veterans Administration Medical Center, Sepulveda, CA 91343
| | | | | |
Collapse
|
12
|
Abstract
The effect of clonidine (5-20 micrograms/kg i.v.) on the activity of single, identified dopamine neurons in the ventral tegmental area of the mesencephalon was studied in chloral hydrate-anesthetized male rats. Clonidine regularized cell firing without affecting the firing rate of the neurons. This effect was blocked by idazoxan (0.5 mg/kg i.v.) or yohimbine (1.0 mg/kg i.v.), but not by phentolamine (1.0 mg/kg i.v.), indicating that clonidine acts at central alpha 2-adrenoceptors. Idazoxan or yohimbine alone produced deregularization and excitation of cell firing. Pretreatment with reserpine (5 mg/kg s.c.) 4 h before the experiment abolished the neuromodulatory effect of clonidine. Thus, the regularization of ventral tegmental area dopamine cell firing by clonidine is indirect and dependent on endogenous monoamines in brain, and, in principle, a tonic adrenergic control of DA cell firing pattern is indicated. The regularization of DA cell activity produced by clonidine may underlie certain therapeutic neuropsychiatric actions of the drug.
Collapse
Affiliation(s)
- J Grenhoff
- Department of Pharmacology, Karolinska Institute, Stockholm, Sweden
| | | |
Collapse
|
13
|
Affiliation(s)
- C Bell
- Department of Physiology, University of Melbourne Medical Centre, Parkville, Victoria, Australia
| |
Collapse
|
14
|
Lane RF, Blaha CD, Rivet JM. Selective inhibition of mesolimbic dopamine release following chronic administration of clozapine: involvement of alpha 1-noradrenergic receptors demonstrated by in vivo voltammetry. Brain Res 1988; 460:398-401. [PMID: 2852047 DOI: 10.1016/0006-8993(88)90390-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The release of dopamine (DA) in vivo was compared in the striatum and nucleus accumbens following chronic (21 day) administration of clozapine (CLOZ) and repeated coadministration of haloperidol (HAL) and the alpha 1-noradrenergic (NE) receptor antagonist prazosin. Treatment with HAL reduced basal DA release in both brain regions, whereas treatment with CLOZ decreased basal DA release only in the accumbens. Chronic coadministration of HAL and prazosin resulted in decreased DA release in accumbens but not striatum. These results suggest that the alpha 1-NE receptor blocking properties of CLOZ may, in part, mediate its differential actions on nigrostriatal and mesolimbic DA release, an effect which may in addition contribute to its paucity of extrapyramidal side effects.
Collapse
Affiliation(s)
- R F Lane
- Institute of Neuroscience, University of Oregon, Eugene 97403
| | | | | |
Collapse
|
15
|
Pifl C, Pichler L, Kobinger W, Hornykiewicz O. The dopamine autoreceptor agonist, B-HT 920, preferentially reduces brain dopamine release in vivo: biochemical indices of brain dopamine, noradrenaline and serotonin in ventriculocisternal perfusates in the cat. Eur J Pharmacol 1988; 153:33-44. [PMID: 2463928 DOI: 10.1016/0014-2999(88)90585-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
B-HT 920 (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepine), a candidate for selective dopamine (DA) autoreceptor agonist activity, was tested for its interactions with biochemical parameters of brain dopaminergic, noradrenergic and serotoninergic systems as measured in ventriculocisternal perfusates of chloralose-anaesthetized cats. DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), noradrenaline (NA) and 5-hydroxyindolic acid (5-HIAA) were measured in samples of 30 min collection periods by high-pressure liquid chromatography with electrochemical detection. B-HT 920, in the dose range of 0.03-1 mg/kg i.v., promptly inhibited the efflux of DA and DOPAC in a dose-dependent manner. The 1 mg/kg dose of B-HT 920 reduced the DA levels below 25% of control levels for the whole length of the experiments. The HVA levels were reduced less and in a protracted manner. Only the highest dose of B-HT 920 tested (1 mg/kg) had a significant effect on the level of NA (marked, prompt reduction) and 5-HIAA (delayed, moderate reduction), reflecting its well known alpha 2-adrenoceptor agonist property. The effects of B-HT 920 on the dopaminergic indices were DA receptor-mediated as they were reversed by a low dose (0.05 mg/kg i.v.) of haloperidol. In contrast, the alpha 2-adrenoceptor blocking drug, idazoxan, 4 mg/kg i.v., while it reversed the NA and 5-HIAA reductions did not modify the effect of B-HT 920 on DA, DOPAC and HVA. Thus B-HT 920, in the dose range between 0.03-0.1 mg/kg, selectively affected brain dopaminergic parameters. Our experiments demonstrated that B-HT 920 causes an effective, long lasting and selective suppression of extracellular brain DA levels in vivo. B-HT 920 represents a promising compound for clinical use in pathological conditions known to be ameliorated by a reduction of brain DA activity, such as Huntington's disease, mania and schizophrenia.
Collapse
Affiliation(s)
- C Pifl
- Institute of Biochemical Pharmacology, University of Vienna, Austria
| | | | | | | |
Collapse
|
16
|
Kennett GA, Curzon G. Evidence that mCPP may have behavioural effects mediated by central 5-HT1C receptors. Br J Pharmacol 1988; 94:137-47. [PMID: 3401632 PMCID: PMC1853919 DOI: 10.1111/j.1476-5381.1988.tb11508.x] [Citation(s) in RCA: 263] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
1. The effects of 1-(3-chlorophenyl)piperazine (mCPP) and 1-[3-(trifluoromethyl)phenyl] piperazine (TFMPP) on activity of rats in a novel cage, and on the rotorod and elevated bar co-ordination tests was examined. 2. Peripherally administered mCPP and TFMPP dose-dependently reduced locomotion, rearing, and feeding scores but not grooming of freely fed rats placed in a novel observation cage. Yawning behaviour was increased. Similar effects were also observed after injection of mCPP into the 3rd ventricle. 3. Co-ordination on a rotating drum of both untrained and trained rats was impaired following mCPP but co-ordination on an elevated bar was not. 4. The hypoactivity induced by mCPP was opposed by three antagonists with high affinity for the 5-hydroxytryptamine (5-HT1C) site; metergoline, mianserin, cyproheptadine and possibly also by a fourth antagonist mesulergine. Metergoline, mianserin and cyproheptadine also opposed the reduction in feeding scores. However, neither effect of mCPP was antagonized by the 5-HT2-receptor antagonists ketanserin or ritanserin, the 5-HT3-receptor antagonist ICS 205-930, the 5-HT1A and 5-HT1B-receptor antagonists (-)-pindolol, (-)-propranolol and (+/-)-cyanopindolol or the 5-HT1A-, 5-HT2- and dopamine receptor antagonist spiperone. The specific alpha 2-adrenoceptor antagonist idazoxan was also without effect. 5. Hypoactivity induced by TFMPP was similarly antagonized by mianserin but unaffected by (+/-)-cyanopindolol. 6. These results suggest that the hypoactivity is mediated by central 5-HT1C-receptors and that mCPP and possibly TFMPP may be 5-HT1C-receptor agonists. 7. As mianserin, cyproheptadine and mesulergine in the absence of mCPP did not increase locomotion but increased the number of feeding scores, the activation of 5-HT1C-receptors may be of physiological importance in the control of appetite. The possible relevance of these results to the therapeutic and side-effects of clinically used antidepressants (particularly trazodone and mianserin) and anorexigenic drugs is discussed.
Collapse
Affiliation(s)
- G A Kennett
- Department of Neurochemistry, Institute of Neurology, Queen Square, London
| | | |
Collapse
|
17
|
Dickinson SL, Gadie B, Tulloch IF. Alpha 1- and alpha 2-adrenoreceptor antagonists differentially influence locomotor and stereotyped behaviour induced by d-amphetamine and apomorphine in the rat. Psychopharmacology (Berl) 1988; 96:521-7. [PMID: 2907662 DOI: 10.1007/bf02180034] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The importance of dopamine (DA) in mediating locomotor, exploratory and stereotyped behaviour in rodents is well established. Evidence also indicates a modulatory role for noradrenaline (NA) although, due to nonspecificity. of previously available agents, a precise role remains undefined. The effects of the specific and selective alpha-adrenoreceptor antagonists idazoxan (alpha 2) and prazosin (alpha 1) on behaviour induced by amphetamine and apomorphine have been investigated in the rat. d-Amphetamine (2 mg/kg) induced hyperactive locomotion and exploration. Pretreatment with prazosin (1 mg/kg) markedly reduced these responses. In contrast, pretreatment with idazoxan (20 mg/kg) only marginally altered d-amphetamine hyperactivity. Apomorphine (0.5 mg/kg) induced biphasic locomotor and exploratory activity. Neither alpha-antagonist affected the initial burst of activity (60 min), although prazosin inhibited whereas idazoxan potentiated the secondary phase (90-180 min). At higher dosage, amphetamine (6 mg/kg) and apomorphine (2 mg/kg) induced stereotyped behaviours. Prazosin pretreatment enhanced stereotyped gnawing and decreased sniffing and locomotion, whereas idazoxan increased locomotion and decreased amphetamine-induced mouth movements. These data indicate that DA-induced locomotor and stereotyped behaviours are differentially influenced (in opposite directions) by both alpha1- and alpha 2-adrenoreceptor antagonists. NA may thus modulate the expression and character of behaviour by influencing DA function in certain brain areas.
Collapse
Affiliation(s)
- S L Dickinson
- Department of Pharmacology, Reckitt & Colman plc, Kingston-Upon-Hull, North Humberside, UK
| | | | | |
Collapse
|
18
|
Routledge C, Marsden CA. Comparison of the effects of selected drugs on the release of hypothalamic adrenaline and noradrenaline measured in vivo. Brain Res 1987; 426:103-11. [PMID: 2446707 DOI: 10.1016/0006-8993(87)90429-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Intracerebral dialysis combined with high-performance liquid chromatography and electrochemical detection was used to monitor changes in extracellular posterior hypothalamic, noradrenaline, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindole acetic acid (5-HIAA) following administration of an inhibitor of phenylethanolamine-N-methyltransferase (LY87130); the alpha 2-antagonist idazoxan; the monoamine oxidase (MAO) inhibitor tranylcypromine, and a selective noradrenergic neurotoxin (DSP4) to the anaesthetised rat. LY87130 (50 mg/kg i.p.) decreased basal hypothalamic perfusate and whole-tissue levels of adrenaline by 100% and 64%, respectively, but was without effect on basal extracellular hypothalamic levels and whole-tissue levels of noradrenaline, DOPAC and 5-HIAA. Administration of the alpha 2-adrenoceptor antagonist idazoxan and the MAO inhibitor tranylcypromine elicited increases in hypothalamic extracellular levels of both adrenaline and noradrenaline by 208% and 229%, respectively. Idazoxan also increased hypothalamic extracellular 5-HIAA by 97% but was without effect on extracellular DOPAC. In contrast, tranylcypromine decreased hypothalamic extracellular levels of DOPAC and 5-HIAA by 72% and 50%, respectively. DSP4 depleted extracellular hypothalamic adrenaline and noradrenaline 360 min and 390 min postdrug, respectively, after causing an initial 3-fold increase in both these amines 150 min after drug administration. DSP4 was without effect on posterior hypothalamic extracellular DOPAC and 5-HIAA. These results demonstrate that the pharmacology of central adrenaline and noradrenaline is very similar and, with the exception of phenylethanolamine-N-methyl transferase inhibitors, none of the drugs investigated are able to differentiate between adrenergic and noradrenergic neurones.
Collapse
Affiliation(s)
- C Routledge
- Department of Physiology and Pharmacology, Nottingham Medical School, Queens Medical Centre, U.K
| | | |
Collapse
|
19
|
Dawson R, Nagahama S, Oparil S. Yohimbine-induced alterations of monoamine metabolism in the spontaneously hypertensive rat of the Okamoto strain (SHR). II. The central nervous system (CNS). Brain Res Bull 1987; 19:525-34. [PMID: 3690364 DOI: 10.1016/0361-9230(87)90068-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Steady state levels of monoamine neurotransmitters were examined in SHR, a genetic model of hypertension and compared to its normotensive control (WKY). SHR and WKY were also challenged with alpha 2-adrenergic antagonists, (yohimbine, YOH, idazoxan) or an alpha 1-antagonist (prazosin) and alterations in CNS monoamine metabolism evaluated. SHR were found to have elevated levels of NE and 5-HT in a number of brain regions involved in cardiovascular control when compared to WKY. DA levels and metabolism were also altered in the SHR. Blockade of alpha 2-adrenoceptors and other direct and indirect actions of YOH exacerbated the abnormalities in central monoaminergic neurotransmission in SHR. Significant decreases in NE content were produced by YOH or idazoxan treatment in both SHR and WKY, presumably the result of the inhibition of alpha 2-adrenoceptor medicated presynaptic control of NE release. YOH treatment abolished the differences in steady state levels of NE between SHR and WKY, however, idazoxan did not. YOH administration resulted in significant increases in DA and 5-HT in a number of brain regions of both SHR and WKY. Idazoxan or prazosin produced few changes in DA and 5-HT metabolism except for increases in DA content in the spinal cord and brainstem of SHR given idazoxan. The YOH-induced increases in DA and 5-HT content of SHR were of a greater magnitude than the WKY in several brain regions. DOPAC levels were significantly elevated by YOH in both WKY and SHR, reflecting the antidopaminergic properties of YOH. 5-HIAA content was significantly reduced by YOH in a number of brain regions in both SHR and WKY, however, this effect was attenuated in several brain regions in SHR. The results of the present study demonstrate the multifarious nature of the alterations in CNS monoamine metabolism in SHR.
Collapse
Affiliation(s)
- R Dawson
- Cardiovascular Research and Training Center, University of Alabama, Birmingham 35294
| | | | | |
Collapse
|
20
|
|
21
|
Dillen L, Claeys M, De Potter WP. Effects of the alpha 2-antagonist idazoxan on monoaminergic parameters measured in the cerebrospinal fluid of rabbits. Eur J Pharmacol 1987; 137:33-40. [PMID: 2440704 DOI: 10.1016/0014-2999(87)90179-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The alpha 2-antagonist idazoxan was administered intravenously to rabbits. The increase in central noradrenergic, dopaminergic and serotonergic activity was followed as a function of time by determining neuronal parameters in the cerebrospinal fluid (CSF) and was compared with changes previously determined after yohimbine. These parameters include the enzyme dopamine-beta-hydroxylase (D beta H), the noradrenergic metabolites 3-methoxy-4-hydroxyphenylmandelic acid (VMA) and 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), the dopaminergic metabolite 3-methoxy-4-hydroxyphenylacetic acid (HVA) and the serotonergic metabolite 5-hydroxyindole acetic acid (5-HIAA). Control experiments with physiological saline were also performed. D beta H activity increased to 211% in control experiments, and to 570 and 530%, respectively after yohimbine and idazoxan. Compared to the control experiments yohimbine was able to elevate VMA, MHPG and HVA concentrations, but 5-HIAA levels were reduced. Idazoxan caused increased MHPG concentrations, slight increases in VMA, little effect on HVA and no effect on 5-HIAA levels. We conclude that idazoxan was as potent as yohimbine as an alpha 2-antagonist in our in vivo experiments and that idazoxan shows a much greater selectivity with regard to the noradrenergic system.
Collapse
|
22
|
Russell VA, Nurse B, Lamm MC, Taljaard JJ. Effect of chronic antidepressant treatment on noradrenergic modulation of [3H]dopamine release from rat nucleus accumbens and striatal slices. Brain Res 1987; 410:78-82. [PMID: 3472627 DOI: 10.1016/s0006-8993(87)80023-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Unlike desipramine, a potent blocker of noradrenaline uptake, the antidepressant drugs, mianserin and citalopram did not, after chronic administration (28 days), attenuate the clonidine-induced inhibition of [3H]dopamine (DA) release from rat nucleus accumbens slices. Mianserin, like desipramine, failed to alter the isoproterenol-induced enhancement of [3H]DA release from rat nucleus accumbens and striatal slices. These findings suggest that antidepressant action does not necessarily involve desensitization of central alpha 2- or beta-adrenoceptors which influence neuronal transmission.
Collapse
|
23
|
Moore KE. Drug-induced changes in the efflux of dopamine and serotonin metabolites from the brains of freely moving rats. Ann N Y Acad Sci 1986; 473:303-20. [PMID: 2432822 DOI: 10.1111/j.1749-6632.1986.tb23625.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
|
24
|
Scheinin H, Virtanen R. Effects of yohimbine and idazoxan on monoamine metabolites in rat cerebrospinal fluid. Life Sci 1986; 39:1439-46. [PMID: 2430157 DOI: 10.1016/0024-3205(86)90548-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Effects of two alpha 2-adrenoceptor antagonists, idazoxan and yohimbine, on the concentrations of monoamine metabolites in cisternal cerebrospinal fluid (CSF) of freely moving rats were investigated. Both drugs caused a dose-dependent, up to 250% increase in the concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG) in CSF indicating enhanced release, metabolism and turnover of noradrenaline in the central nervous system (CNS). In addition, a similar increase in homovanillic acid (HVA) in CSF was observed, while the level of 5-hydroxyindoleacetic acid was unchanged. The present results demonstrate the usefulness of monitoring drug-induced alterations in noradrenergic activity in the CNS by measurement of free MHPG in repeatedly collected cisternal CSF samples from awake rats. The possibility that the observed increase in the concentration of HVA after the highly specific alpha 2-antagonist idazoxan reflects increased noradrenergic rather than dopaminergic neuronal activity is discussed.
Collapse
|
25
|
Scheinin H, MacDonald E, Scheinin M. Comparison of free MHPG in rat cerebrospinal fluid with free and conjugated MHPG in brain tissue: effects of drugs modifying noradrenergic transmission. Eur J Pharmacol 1986; 129:113-21. [PMID: 2876902 DOI: 10.1016/0014-2999(86)90342-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The changes of free 3-methoxy-4-hydroxyphenylglycol (MHPG) in cerebrospinal fluid (CSF) were compared with the corresponding alterations of free and conjugated MHPG in rat brain tissue after various pharmacological treatments modifying noradrenergic neurotransmission. In addition, the effects of the drug treatments on the concentration of noradrenaline (NA) in brain were determined. alpha-Methyl-p-tyrosine (an inhibitor of tyrosine hydroxylase) induced decreases in free and conjugated MHPG in CSF and brain; the free species appeared to decline more rapidly. Reserpine caused similar biphasic changes in free MHPG in CSF and brain but the rapid and transient initial increase in MHPG-SO4 was very weak. Pargyline (monoamine oxidase inhibitor) induced a sharp decline in the concentration of free MHPG in brain and CSF while MHPG-SO4 in brain definitely decreased more slowly. Relatively similar time courses were seen for all three MHPG parameters after administration of MPV-1248 (alpha 2-antagonist) and clonidine (alpha 2-agonist) i.e., increases and decreases, respectively. The present results support the validity of monitoring drug-induced acute changes in central turnover of NA by repeated measurements of free MHPG levels in rat cisternal CSF.
Collapse
|
26
|
Scheinin H. Enhanced noradrenergic neuronal activity increases homovanillic acid levels in cerebrospinal fluid. J Neurochem 1986; 47:665-7. [PMID: 3016178 DOI: 10.1111/j.1471-4159.1986.tb00662.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Idazoxan, a highly specific and selective alpha 2-adrenoceptor antagonist, caused a dose-dependent increase in the concentration of homovanillic acid (HVA) a metabolite of 3,4-dihydroxyphenylethylamine, in cisternal CSF of freely moving rats. This increase in HVA level could be antagonized by the alpha 2-adrenoceptor agonist medetomidine. The increase was directly proportional to the concurrent elevation in level of 3-methoxy-4-hydroxyphenylglycol, a metabolite of noradrenaline, in the CSF of individual rats and followed a similar time course. It is suggested that the HVA level in CSF may be increased under conditions of enhanced noradrenergic activity and that, in such situations, it reflects noradrenergic rather than dopaminergic neuronal activity. Care should be taken, therefore, when changes in central dopaminergic activity are assessed by measurements of HVA level in CSF.
Collapse
|
27
|
Abstract
The effects of alpha 2-adrenergic antagonists on amphetamine-induced locomotion and stereotypy were studied in mice. Six alpha 2-antagonists (i.e., yohimbine, rauwolscine, piperoxan, tolazoline, RX781094, and RS21361) selectively attenuated amphetamine-induced increases in locomotion at doses which did not effect amphetamine-induced stereotypies. Higher doses of the antagonists which attenuated baseline stereotypies also attenuated amphetamine-induced increases in stereotypies. The effect of the alpha 2-antagonists was qualitatively similar to that observed with the atypical antipsychotic clozapine. Furthermore, the in vivo relative potency of the alpha 2-antagonists in the present study was comparable to that reported in other studies. These results suggest that alpha 2-adrenergic receptors may modulate the effects of amphetamine on locomotion in mice.
Collapse
|
28
|
Skarsfeldt T, Hyttel J. The St 587-induced flexor reflex in pithed rats: a model to evaluate central alpha 1-receptor blocking properties. Eur J Pharmacol 1986; 125:333-40. [PMID: 2874039 DOI: 10.1016/0014-2999(86)90789-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A combination of reserpine, nialamide and the specific alpha 1-adrenoceptor agonist St 587 [2-(2-chloro-5-trifluoromethylphenylimino)-imidazolidine] induced a marked increase of the electrically stimulated flexor reflex in pithed rats. This increased reflex - which lasted for more than 3 h - could be inhibited by the alpha 1-receptor antagonist prazosin but not by the alpha 2-adrenoceptor antagonist idazoxan (RX 781094). A range of different drugs was tested, including 17 neuroleptics. Most of the neuroleptics showed marked inhibition of the St 587-induced reflex. Bromperidol, butaclamol and fluperlapine were weak inhibitors while pimozide was without effect. The results showed close correlation to alpha 1-receptor affinities in vitro (r = 0.84, P less than 0.001) while no correlation was found to either D-2 receptor affinities or to 5-HT2 receptor affinities in vitro (r = 0.43, P less than 0.2 and r = 0.41, P less than 0.05, respectively). It is concluded that inhibition of the St 587-induced flexor reflex in pithed rats is an in vivo test model for central alpha 1-receptor blocking properties.
Collapse
|
29
|
COMMUNICATION. Br J Pharmacol 1986. [DOI: 10.1111/j.1476-5381.1986.tb16594.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
|
30
|
Dearry A, Burnside B. Dopaminergic regulation of cone retinomotor movement in isolated teleost retinas: I. Induction of cone contraction is mediated by D2 receptors. J Neurochem 1986; 46:1006-21. [PMID: 2869104 DOI: 10.1111/j.1471-4159.1986.tb00612.x] [Citation(s) in RCA: 175] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In the retinas of lower vertebrates, retinal photoreceptors and melanin pigment granules of the retinal pigment epithelium (RPE) undergo characteristic movements in response to changes in light intensity and to signals from an endogenous circadian clock. To identify agents responsible for mediating light and/or circadian regulation of these retinomotor movements, we investigated the effects of hormones and neurotransmitters on cone, rod, and RPE movements in the green sunfish, Lepomis cyanellus. We report here that 3,4-dihydroxyphenylethylamine (dopamine) mimics the effect of light by inducing light-adaptive retinomotor movements in all three cell types. In isolated dark-cultured retinas, dopamine induced light-adaptive cone contraction with a half-maximal effect at 10(-8) M. This effect of dopamine was inhibited by antagonists with a potency order characteristic of D2 receptor mediation. The dopamine uptake blocker benztropine also induced light-adaptive cone contraction in isolated dark-cultured retinas, suggesting that there is continuous dopamine release in the dark but that concomitant uptake normally prevents activation of cone contraction. That dopamine plays a role in light regulation of cone movement is further suggested by the observation that light-induced cone contraction was partially inhibited by sulpiride, a selective D2 dopamine antagonist, or by Co2+, a blocker of synaptic transmission. Sulpiride also promoted dark-adaptive cone elongation in isolated light-adapted retinas, suggesting that continuous dopamine action is required in the light to maintain the light-adapted cone position. Dopamine can act directly on D2 receptors located on rod and cone inner/outer segments: dopamine induced light-adaptive retinomotor movements in isolated distal fragments of dark-adapted photoreceptors cultured in the dark. Together our results indicate that dopamine induces light-adaptive retinomotor movements in cones, rods, and RPE cells by activating D2 receptors. We suggest that, in vivo, dopamine plays a role in both light and circadian regulation of retinomotor movements.
Collapse
|
31
|
Elghozi JL, Laude D, Chaouloff F. Fusaric acid-induced elevation of homovanillic acid in the CSF as an index of brain noradrenaline synthesis. Eur J Pharmacol 1985; 117:363-7. [PMID: 4076351 DOI: 10.1016/0014-2999(85)90010-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The effect of the dopamine-beta-hydroxylase inhibitor, fusaric acid (FA), on cerebrospinal fluid (CSF) homovanillic acid (HVA) was studied in pentobarbitone-anesthetized rats. Idazoxan, a selective alpha 2-antagonist, accentuated the FA-induced HVA elevation in CSF while alpha-methyldopa pretreatment prevented this effect of FA on the HVA level in CSF. These results could indicate that the rate of dopamine synthesis in noradrenaline neurons could be the main determinant of the FA-induced HVA elevation.
Collapse
|
32
|
Goldman CK, Marino L, Leibowitz SF. Postsynaptic alpha 2-noradrenergic receptors mediate feeding induced by paraventricular nucleus injection of norepinephrine and clonidine. Eur J Pharmacol 1985; 115:11-9. [PMID: 2995083 DOI: 10.1016/0014-2999(85)90578-3] [Citation(s) in RCA: 156] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
This study examines the feeding response induced by hypothalamic noradrenergic stimulation, in terms of the type and synaptic position of its mediating receptor. Tests with norepinephrine or the alpha 2 receptor agonist clonidine, injected into the area of the paraventricular nucleus (PVN), revealed a potent feeding response in satiated animals. This response by either agonist was blocked, in a dose-dependent fashion, by local injection of the alpha 2-noradrenergic antagonists, rauwolscine and yohimbine. It was also blocked by the general antagonist, phentolamine. In contrast, it was unaffected by hypothalamic injection of the alpha 1-noradrenergic antagonists, prazosin and corynanthine. These results indicate that feeding elicited by noradrenergic stimulation in the region of the PVN is mediated through alpha 2-type receptors. These alpha 2 receptors appear to be located postsynaptically, since the effectiveness of clonidine in eliciting eating was undisturbed by prior injection of the catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine.
Collapse
|
33
|
Zetler G. Clonidine sensitizes mice for apomorphine-induced stereotypic gnawing: antagonism by neuroleptics and cholecystokinin-like peptides. Eur J Pharmacol 1985; 111:309-18. [PMID: 2862047 DOI: 10.1016/0014-2999(85)90637-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In mice sensitized for apomorphine by either scopolamine or teflutixol, clonidine antagonized the antistereotypic effect of ceruletide and haloperidol. The same effect of clonidine occurred in normal mice with methylphenidate-induced gnawing. In naive mice, clonidine alone had a sensitizing effect for the action of apomorphine leading to wire-gnawing. Yohimbine and rauwolscine (but not corynanthine) antagonized this effect of clonidine. The gnawing-inducing effect of methylphenidate was also enhanced by clonidine but not to the same extent as that of apomorphine. The stereotypic effect of apomorphine (in mice sensitized by either scopolamine or clonidine) was antagonized by yohimbine and rauwolscine but not by corynanthine. Apomorphine-induced wire gnawing was used as test of the antistereotypic effect of haloperidol, trifluoperazine, teflutixol, CCK-8, ceruletide and 8 related peptides. Ceruletide and 2 of its analogues were more potent than the neuroleptics; CCK-8 was 7 times less active than ceruletide. In conclusion, clonidine sensitized mice for the stereotypic effect (wire-gnawing) of apomorphine and methylphenidate. The clonidine-apomorphine effect permits the estimation of antistereotypic effects.
Collapse
|
34
|
Pettibone DJ, Pfleuger AB, Totaro JA. Comparison of the effects of recently developed alpha 2-adrenergic antagonists with yohimbine and rauwolscine on monoamine synthesis in rat brain. Biochem Pharmacol 1985; 34:1093-7. [PMID: 2859020 DOI: 10.1016/0006-2952(85)90614-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The effects of two recently developed alpha 2-adrenergic antagonists, RX 781094 and WY 26703, on the synthesis of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in rat brain were compared to those of yohimbine, its diastereoisomer rauwolscine, and mianserin. Intraperitoneal administration of these compounds increased cortical NE synthesis with the potency order: yohimbine, RX 781094, WY 26703 greater than rauwolscine greater than mianserin. Within a similar dose range, yohimbine, rauwolscine and WY 26703 also stimulated striatal DA synthesis and decreased hypothalamic 5-HT synthesis, while RX 781094 and mianserin were very weak or inactive. Yohimbine and the structurally-related WY 26703 were also active as DA antagonists in the gamma-butyrolactone model for DA autoreceptor function. Based on the drug-induced changes in monoamine synthesis as indication of receptor-mediated events, RX 781094 has greater selectivity as an alpha 2-antagonist than compounds structurally related to yohimbine.
Collapse
|
35
|
Hörtnagl H, Pichler L, Holzer-Petsche U, Hornykiewicz O, Kobinger W. B-HT 958--an antagonist at alpha 2-adrenoceptors and an agonist at dopamine autoreceptors in the brain. Eur J Pharmacol 1984; 106:335-44. [PMID: 6152218 DOI: 10.1016/0014-2999(84)90721-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
B-HT 958 (2-amino-6-(p-chlorobenzyl)-4H-5,6,7,8-tetrahydrothiazolo[5,4-d]az epine), a compound chemically related to clonidine-like drugs of the azepine type, was described previously as a mixed agonist-antagonist at peripheral alpha 2-adrenoceptor sites. In the present experiments the actions of B-HT 958 on brain noradrenergic and dopaminergic mechanisms were examined using behavioural, pharmacological and biochemical methods. (i) In the dog, intracisternally injected B-HT 958 (300 micrograms/kg) abolished the reflex bradycardia facilitated by the alpha 2-agonist B-HT 920 (10 micrograms/kg i.ci.). (ii) In the whole mouse brain as well as in the rat hypothalamus and neocortex, but not in the hippocampus, amygdala and nucleus accumbens B-HT 958 (5-20 mg/kg s.c.) accelerated the alpha-methyltyrosine (alpha-MT)-induced disappearance of noradrenaline. (iii) B-HT 958 decreased in a dose-dependent manner the exploratory activity of mice (ED50: 6.3 mg/kg s.c.) and slightly enhanced the motor activity of reserpine-treated mice only in high doses. (iv) B-HT 958 (20 mg/kg s.c.) lowered the level of homovanillic acid in the striatum and nucleus accumbens and dose dependently (1-20 mg/kg) slowed the alpha-MT-induced disappearance of dopamine in these 2 brain regions of the rat as well as in the whole mouse brain. (v) The gamma-butyrolactone-induced increase in DOPA levels was effectively antagonized by B-HT 958 (1 and 5 mg/kg s.c.) in the rat striatum and nucleus accumbens. These behavioural, pharmacological and biochemical observations indicate that B-HT 958 possesses central alpha-adrenoceptor blocking activity and exerts a strong agonistic effect on brain dopamine autoreceptors.
Collapse
|
36
|
Quock RM, Bloom AS, Sadowski JA. Possible noradrenergic involvement in naloxone potentiation of apomorphine-induced stereotypic climbing in mice. Pharmacol Biochem Behav 1984; 21:733-6. [PMID: 6096896 DOI: 10.1016/s0091-3057(84)80011-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Apomorphine-induced stereotypic climbing behavior in mice was significantly potentiated by pretreatment with the opiate receptor blocker naloxone. In animals additionally pretreated with alpha-methyl-p-tyrosine, brain levels of norepinephrine (NE) and dopamine (DA) were markedly reduced and naloxone potentiation of apomorphine-induced stereotypic climbing was blocked. In mice pretreated with diethyldithiocarbamic acid, brain NE was slightly reduced, brain DA was slightly elevated but naloxone potentiation of apomorphine-induced stereotypic climbing was unaltered. In animals pretreated with reserpine, both brain NE and DA were significantly reduced by naloxone potentiation of apomorphine-induced stereotypic climbing was not affected. In other experiments, pretreatment with low doses of the alpha-adrenergic receptor blocker BE-2254 failed to suppress climbing activity induced by apomorphine alone but did successfully prevent naloxone potentiation of apomorphine-induced stereotypic climbing. These findings suggest the possibility that NE and alpha-adrenergic receptors might play a role in the potentiating influence of naloxone upon apomorphine-induced stereotypic climbing activity in mice.
Collapse
|
37
|
Diggory GL, Buckett WR. Chronic antidepressant administration fails to attenuate apomorphine-induced decreases in rat striatal dopamine metabolites. Eur J Pharmacol 1984; 105:257-63. [PMID: 6510470 DOI: 10.1016/0014-2999(84)90617-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The responsiveness of the rat striatal dopamine (DA) receptor system to apomorphine (APO) was assessed after 10 days of antidepressant administration. Desipramine (DMI), dothiepin (DOTH), iprindole (IPR) and nomifensine (NOM) were administered intra-peritoneally, twice daily, to rats for 10 days and 42 h after the last drug dose, animals were injected with APO (25 or 200 micrograms/kg s.c., 15 min) or vehicle. Striatal content of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), assayed using a recently developed high-performance liquid chromatography-electrochemical detection (HPLC-ECD) method, showed that prolonged administration of all four antidepressant drugs failed to modify the effect of APO on DA metabolism. The results of these experiments therefore do not provide evidence to support the suggestion that subsensitivity in presynaptic DA 'autoreceptors' is a significant biochemical correlate of chronic antidepressant drug administration.
Collapse
|
38
|
van Oene JC, de Vries JB, Horn AS. The effectiveness of yohimbine in blocking rat central dopamine autoreceptors in vivo. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1984; 327:304-11. [PMID: 6514014 DOI: 10.1007/bf00506241] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The influence of various alpha-adrenoceptor antagonists (10 mg/kg i.p.) upon the rate of turnover of dopamine (DA) in the rat brain was investigated. Taking the levels of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) as a measure of the rate of DA turnover, it was found that prazosin and phenoxybenzamine decreased, whereas piperoxane and yohimbine increased the turnover rate both in the corpus striatum and in the tuberculum olfactorium. Azapetine, phentolamine and tolazoline as well as the beta-adrenoceptor antagonist propranolol were without a significant effect, whereas the DA antagonist haloperidol increased DOPAC and HVA levels and decreased the levels of DA itself. The possibility that the yohimbine-induced increase in the DA turnover rate was produced by a direct blockade of DA autoreceptors, was investigated under conditions where influences other than those elicited via DA autoreceptors are thought to be eliminated, i.e. in rats treated with reserpine or gamma-butyrolactone (GBL). In rats that were pretreated with reserpine, yohimbine (10 mg/kg i.p.) was found to be ineffective in antagonizing the reduction of the accumulation of 3,4-dihydroxyphenylalanine (DOPA) following decarboxylase inhibition, that was produced by the DA agonist apomorphine (2.0 mg/kg i.p.). In rats pretreated with reserpine, yohimbine (10 mg/kg i.p.) was also ineffective in antagonizing the reduction of the DOPAC and HVA levels produced by apomorphine (2.0 mg/kg i.p.), but it was effective in antagonizing the reduction of the HVA level that was produced by the selective DA autoreceptor agonist N,N-di-n-propyl-7-hydroxy-2-aminotetralin (DP-7-AT, 1.0 mg/kg i.p.).(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
|
39
|
Hadjiconstantinou M, Neff NH. Catecholamine systems of retina: a model for studying synaptic mechanisms. Life Sci 1984; 35:1135-47. [PMID: 6147740 DOI: 10.1016/0024-3205(84)90184-x] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The retina contains three catecholamine neurotransmitters: dopamine (DA); norepinephrine (NE); and epinephrine (EPI). DA and EPI appear to be associated with separate amacrine neurons that directly participate in the visual process. NE, in contrast, appears to be associated primarily with the sympathetic nerves that innervate the blood vessels of the retina. We present a synopsis of the anatomy, physiology, biochemistry and pharmacology of these retinal neurons. We also suggest that some diseases usually associated with catecholamines of brain may have their counterpart in retina.
Collapse
|
40
|
Walter DS, Flockhart IR, Haynes MJ, Howlett DR, Lane AC, Burton R, Johnson J, Dettmar PW. Effects of idazoxan on catecholamine systems in rat brain. Biochem Pharmacol 1984; 33:2553-7. [PMID: 6147143 DOI: 10.1016/0006-2952(84)90623-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Experiments have been performed to assess the potency of idazoxan (RX 781094) at alpha and beta-adrenoceptors and dopamine receptors and on catecholamine uptake processes in rat brain. The effects of idazoxan on the turnover rates of noradrenaline and dopamine have been determined. Radioligand binding studies with cerebral cortex membranes have demonstrated that idazoxan exhibits 46-fold selectivity for alpha 2-adrenoceptors labelled by (3H)-idazoxan (Mean Ki +/- S.E.M. = 3.1 +/- 0.4 nM) compared with alpha 1-adrenoceptors labelled by (3H)-prazosin (Mean Ki +/- S.E.M. = 142 +/- 27 nM). Under the same conditions, yohimbine showed 6-fold selectivity for alpha 2-adrenoceptors. Idazoxan had low affinity for beta-adrenoceptors labelled by (3H)-dihydroalprenolol (IC50 value greater than 10 microM), for dopamine receptors labelled by (3H)-domperidone (IC50 value greater than 20 microM), for the (3H)-noradrenaline uptake site in rat hypothalamus (IC50 = 31 microM) and for the (3H)-dopamine uptake site in rat striatum (IC50 value approximately 800 microM). In rats treated with alpha-methyl-p-tyrosine, idazoxan (10-80 mg/kg, po) produced a marked increase (63% at 10, 217% at 20 mg/kg, po) in the apparent rate of turnover of noradrenaline in rat cortex/striatum, without affecting the rate of turnover of dopamine. This was in contrast to yohimbine (5-20 mg/kg, po) which increased the turnover rates of both catecholamines. In the absence of alpha-methyl-p-tyrosine, idazoxan (5-40 mg/kg, po) produced a dose related increase in the MHPG concentration and a small (20-30%) reduction in the steady state concentration of NA; the duration of the reduction was dose-related. DA steady state concentrations were unaffected. Idazoxan is a new selective alpha 2-adrenoceptor antagonist which should prove a valuable investigative tool in neurochemical studies and which may be a useful clinical agent in the management of the affective disorders.
Collapse
|
41
|
Zetler G. Clonidine and yohimbine separate the sedation and the ptosis caused by cholecystokinin octapeptide and ceruletide. Eur J Pharmacol 1984; 102:333-40. [PMID: 6090162 DOI: 10.1016/0014-2999(84)90265-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The central depressant effects of ceruletide (CER, 0.04 mg/kg s.c.) and cholecystokinin octapeptide (CCK-8, 0.25 mg/kg s.c.) were compared with those of clonidine (0.04 mg/kg s.c.). At doses that were nearly equipotent with respect to motor inhibition (catalepsy, reduction in ambulation and exploratory rearing), only the peptides produced ptosis. Yohimbine (1 mg/kg s.c., 30 min) antagonized the effect of clonidine but not of the peptides. Clonidine (0.07-0.2 mg/kg s.c., 30 min) antagonised the ptotic action of the peptides, and this effect was abolished by yohimbine (0.2-1 mg/kg i.p.) but resistant to haloperidol (0.05 and 0.15 mg/kg i.p.). These results separate the behavioural effects of the peptides from those of clonidine and also the ptotic effect of the peptides from their effect on motor activity. The antiptotic effect of clonidine may originate from activated adrenergic autoreceptors.
Collapse
|
42
|
Arnt J, Bøgesø KP, Hyttel J, Larsen JJ, Svendsen O. Effects of S (+)-3-phenethyl-PP, a putative dopamine autoreceptors agonist with greater autoreceptor selectivity than 3-PPP enantiomers. Eur J Pharmacol 1984; 102:91-9. [PMID: 6148247 DOI: 10.1016/0014-2999(84)90341-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The experiments concerned the pharmacology of the enantiomers of the phenethyl-analogue (3-phenethyl-PP) of the putative dopamine (DA) autoreceptor agonist 3-PPP. In contrast to the almost equipotency of 3-PPP enantiomers, the phenethyl enantiomers showed marked stereoselectivity. S(+)-3-Phenethyl-PP had 25 times higher affinity to D-2 DA receptors in vitro than the R(-)-enantiomer. In vivo a similar potency difference was seen for the inhibition of motility, induction of circling behaviour in 6-OHDA-lesioned rats and emetic effect in dogs. None of the enantiomers induced stereotypy and hypermotility in normal rats or in rats pretreated with reserpine and alpha-methyl-p-tyrosine. In test models for antidopaminergic activity only slight activity of either enantiomer was observed. The S(+)-enantiomer had no antagonistic effect against apomorphine- and amphetamine-induced stereotypies, no cataleptogenic activity and only partially antagonized amphetamine-induced hypermotility. Apomorphine-induced emesis was weakly antagonized. The results indicate a greater and higher selectivity of S(+)-3-phenethyl-PP for DA receptors mediating sedation compared with 3-PPP enantiomers which previously have been shown to exert significant effects on postsynaptic DA receptors. Thus S(+)-3-phenethyl-PP may be a more selective model compound for the differential study of effects elicited by stimulation of pre- and postsynaptic DA receptors.
Collapse
|
43
|
|
44
|
Doxey JC, Lane AC, Roach AG, Virdee NK. Comparison of the alpha-adrenoceptor antagonist profiles of idazoxan (RX 781094), yohimbine, rauwolscine and corynanthine. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1984; 325:136-44. [PMID: 6144048 DOI: 10.1007/bf00506193] [Citation(s) in RCA: 146] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
In the present studies the potency and selectivity of idazoxan (RX 781094) were compared with yohimbine and its diastereoisomers rauwolscine and corynanthine in both functional studies and radioligand binding experiments. Prejunctional alpha 2- and postjunctional alpha 1-adrenoceptor antagonist potencies were assessed by determining pA2 values against clonidine on the stimulated rat was deferens and noradrenaline on the anococcygeus muscle, respectively. The rank order of prejunctional alpha 2-adrenoceptor antagonist potency was idazoxan greater than yohimbine greater than rauwolscine much greater than corynanthine. At postjunctional alpha 1-adrenoceptors the rank order of antagonist potency was rauwolscine greater than corynanthine greater than yohimbine greater than idazoxan. The selectivity values (alpha 2/alpha 1) for idazoxan, yohimbine, rauwolscine and corynanthine were 245, 45, 3 and 0.03 respectively. The selectivity and potency profiles established for these antagonists in functional studies were confirmed in radioligand binding studies utilising 3H-idazoxan (alpha 2) and 3H-prazosin (alpha 1) in rat cerebral cortex. In pithed rats intravenously administered idazoxan, yohimbine and rauwolscine fully reversed the inhibitory effects of clonidine on electrically-induced contractions of the vas deferens; idazoxan was approximately ten times more potent than both yohimbine and rauwolscine. Corynanthine was inactive. Idazoxan and yohimbine also fully antagonised the inhibitory effects of guanabenz on electrically-induced contractions of the anococcygeus muscle; idazoxan again was more than ten times more potent than yohimbine in this model. The inhibitory effects of guanabenz were less readily antagonised by rauwolscine indicating that the selectivity of this compound is less than that of yohimbine in this tissue. Corynanthine was again inactive.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
|
45
|
Perry BD, Simon PR, U'Prichard DC. Interactions of neuroleptic compounds at alpha 2-adrenergic receptor affinity states in bovine caudate nucleus. Eur J Pharmacol 1983; 95:315-8. [PMID: 6140181 DOI: 10.1016/0014-2999(83)90654-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Several recent studies have suggested a connection between neuroleptics and/or dopamine systems, and alpha 2-adrenergic receptors. Competition of a variety of neuroleptics at specific alpha 2-adrenergic binding sites (labeled with [3H]rauwolscine or [3H]p-aminoclonidine) in bovine caudate and cortex was examined. Few of the compounds were potent competitors, with (+)-butaclamol, alpha-flupenthixol, clozapine and pimozide the most potent (IC50 range 100-600 nM), while triflupromazine, mesoridazine, and haloperidol were the least potent (IC50 range 5 000-10 000 nM). These findings indicate that few, if any, of the examined neuroleptics have specific, high-affinity interactions with the multiple affinity states of the alpha 2-adrenergic receptor.
Collapse
|
46
|
Lane AC, Howlett DR, Walter DS. The effects of metal ions on the binding of a new alpha 2-adrenoceptor antagonist radioligand (3H)-RX 781094 in rat cerebral cortex. Biochem Pharmacol 1983; 32:3122-5. [PMID: 6639682 DOI: 10.1016/0006-2952(83)90261-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
|
47
|
Doxey JC, Gadie B, Lane AC, Tulloch IF. Evidence for pharmacological similarity between alpha 2-adrenoceptors in the vas deferens and central nervous system of the rat. Br J Pharmacol 1983; 80:155-61. [PMID: 6140052 PMCID: PMC2044981 DOI: 10.1111/j.1476-5381.1983.tb11061.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Seven alpha 2-adrenoceptor antagonists with diverse chemical structures have been examined for their effects at alpha 2-adrenoceptors in the vas deferens and central nervous system of the rat. Antagonist potency assessed against the presynaptic alpha 2-adrenoceptor agonist action of clonidine in the isolated vas deferens (RX 781094 greater than Wy 26703 greater than yohimbine greater than rauwolscine greater than piperoxan greater than mianserin greater than RS 21361) was highly correlated with the ability of these drugs to displace saturable [3H]-RX 781094 binding from cerebral cortex membranes. Similarly, antagonist potency in the vas deferens was highly correlated with antagonist activity in reversing the centrally-mediated mydriasis induced by the selective alpha 2-adrenoceptor agonist, guanoxabenz, in pentobarbitone-anaesthetized rats. The results indicate that the presynaptic alpha 2-adrenoceptors in the vas deferens are pharmacologically similar to characterized these alpha 2-adrenoceptors in the central nervous system of the rat.
Collapse
|