Session 28 : Neuro-pharmacologie

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Session 28 : Neuro-pharmacologie

276

EFFECTS OF SEROTONINERGIC ANTIDEPRESSANTS IN THE FORCED SWIMMING TEST IN WILD TYPE AND
5-HT1B KNOCKOUT MICE

A.C. Trillat1, I. Malagié1, M.C. Colombel, C. Jacquot1, M. Bourin2, R. Hen4 and A.M. Gardier3

1-Lab. Neuropharmacologie, Tour D 1, 2ème étage, Faculté de Pharmacie, 92296 Châtenay-Malabry, 2-Département de Pharmacologie, Faculté de Médecine, 44035 Nantes, 3-Faculté de Picardie Jules Verne, 80030 Amiens, France. 4-Center for Neurobiology and Behavior, Columbia University, New York, USA.

The forced swimming test is a behavioural model developed to predict the efficacy of antidepressant drugs. However, the mechanism of action of antidepressants in this test is still unclear. To evaluate the possible involvement of 5-HT1B receptors, we studied the anti-immobility effect of selective serotonin reuptake inhibitor (SSRI), paroxetine and that of the mixed serotonin/norepinephrine reuptake inhibitor, imipramine in wild type (129/Sv +/+) and 5-HT1B knockout mice (129/Sv -/-). Basal activity of 129/Sv +/+ mice (233

2 sec.). Furthermore, the administration of imipramine (32 mg/kg i.p.) 30 min before the test induced a significant decrease in the immobility time in 129/Sv +/+ (-15 %, P < 0.01) and in 129/Sv -/- mice (- 10%, P < 0.01) when compared to their respective saline group. By contrast, paroxetine (8 mg/kg, i.p) reduced significantly the immobility time (P < 0.001) in wild type mice, but not in knockout mice. This absence of sensitivity of 129/Sv -/- to paroxetine suggests that 5-HT1B receptors may be involved in the mechanism of action of SSRIs but not in that of imipramine-like drugs.

277

MALONATE-INDUCED OXIDATIVE STRESS TRIGGERS A DELETERIOUS INDUCIBLE NO-SYNTHASE (NOS 2) ACTIVITY IN THE RAT STRIATUM

L. Lecanu, I. Margaill, H. Boughali, B. Cohen-Tenoudji, R.G. Boulu and M. Plotkine

Laboratoire de Pharmacologie, Université René Descartes, 4 avenue de l’Observatoire, 75270 Paris cedex 06, France

Introduction

: Nitric oxide (NO) overproduction has been described to exert deleterious effects within the CNS. In particular, NO produced by NOS 2 may contribute to the neuronal death following ischaemia, excitotoxic insult and traumatic brain injury. Since an oxidative stress occurs during these situations, the aim of this study was to assess whether in the central nervous system (CNS), oxidative stress induces a deleterious NOS 2 activity.

Materials and methods

: For this purpose, the mitochondrial toxin malonate, described to promote free radicals production, was, infused into the left striatum of Sprague-Dawley male rats (3 µmoles in 1 µl). NOS activity and lesion volume were measured 48 hours after malonate infusion. To determine the role of free radicals in NOS 2 induction and the contribution of this isoform to the lesion, 5.11 mm3 (n=6) and was reduced by 70.5% by PBN and by 71.5% by AG.

Comments

: These results suggest that an oxidative stress in the CNS leads to NOS 2 expression. This may be one of the mechanisms by which oxidative stress exerts its deleterious effect. This raises the question of the existence of such a deleterious phenomenom in all neuropathologies where an oxidative stress occurs.

278

IMIDAZOLINE SPECIFIC BINDING SITES IN SYNAPTOSOMAL PLASMA MEMBRANES OF THE BOVINE BRAINSTEM

FMJ Heemskerk, M. Dontenwill, H. Greney, C. Vonthron and P. Bousquet

Laboratoire de Neurobiologie et de Pharmacologie Cardiovasculaire, Faculté de Médecine, Université L. Pasteur, 67000 Strasbourg, France

Non-adrenergic Imidazoline specific binding sites were characterized pharmacologically in crude cerebral membrane preparations but little is known about their subcellular localization in neurons. Since in the brainstem these sites are involved in cardiovascular regulation and peripherally imidazolines modulate neurotransmitter release, we tried to determine a possible (pre)synaptic localization in brainstem. We found a specific enrichment in synaptosome, purified synaptosomal plasma membrane (30 fmol/mg) and mitochondrial (83 fmol/mg) fractions as compared to other membrane fractions (3-8 fmol/mg). Synaptosomes appeared to be free of postsynaptic structures and purified synaptosomal plasma membranes were devoid of mitochondrial material, as determined by electron microscopy and by comparison with the distribution of marker enzymes such as monoamine oxydase. Our results show for the first time that these extramitochondrial Imidazoline specific bindins sites are neuronal and are located on presynaptic terminals. Unlabeled para-iodoclonidine and clonidine competed for [125I]-para-iodoclonidine binding with high affinities (IC50 = 46 nM and 1 nM) while surprisingly idazoxan did not compete. These extramitochodrial Imidazoline specific binding sites with a previously unknown pharmacology may therefore be a particular subtype of the I1 class of imidazoline receptors.

279

ISOFORM-SPECIFIC ALTERATIONS OF HUMAN APOLIPOPROTEIN E PROPERTIES BY OXIDATION

C. Jolivalt, B. Leininger-Muller, P. Bertrand, R. Herber, Y. Christen§, G. Siest

Centre du Médicament, UPRES, Faculté de Pharmacie, Université H. Poincaré Nancy 1, 30 rue Lionnois, 54000, Nancy, et § Institut IPSEN, 24 rue Erlanger, 75781 Paris cedex 16, France

Human apolipoprotein E (apo E) exists as three major isoforms E2, E3 and E4, and has been classically involved in cardiovascular disorders. With the recent demonstration of the linkage between apo E

would depend on oxidation. As the relationship betwen AD and apo E is isoform-specific and alterations in oxidative metabolism have been widely implicated in the development of AD, we investigated the alterations in apo E properties after oxidation and their isoform dependency.

Using a myeloperoxidase enzymatic system, we estimated the oxidation of human recombinant apo E by immunological detection of carbonyl groups. Apo E4 was more susceptible to oxidation than apo E3, itself more than apo E2. Oxidation of apo E lead to a decrease in the protein retention time on a RP-HPLC column, indicating conformation and/or hydrophobicity modifications. About 65% apo E isoforms incorporated in phospholipid discs. After oxidation, the yield of protein incorporated in such discs decreased to reach 33, 17, and 0.2% for apo E2, E3, and E4 respectively. In addition, only oxidation of apo E4 significantly enhanced A