Jean-Charles Blanchard

Possible involvement of nitric oxide in long-term potentiation

Long-term potentiation (LTP) in the hippocampus is known to involve NMDA (N-methyl-D-aspartate) receptors. Since activation of NMDA receptors in the cerebellum results in the formation of nitric oxide (NO), we studied the possible involvement of this messenger in hippocampal synaptic plasticity. We report here that the NO-synthase inhibitor, L-N omega-nitro-arginine, blocks LTP and that sodium nitroprusside, which releases NO, produces a long-lasting enhancement in synaptic efficacy which is not additive with tetanus-induced LTP.

A Role for Nitric Oxide in Long‐term Potentiation

Nitric oxide production in the cerebellum and induction of long‐term potentiation (LTP) in the hippocampus have some characteristics in common: both phenomena are induced by activation of N‐methyl‐D‐aspartate receptors and both are highly dependent on calcium‐mediated processes. Here we provide evidence that endogenous nitric oxide production is necessary for synaptic plasticity in the CA1 hippocampus of the rat. LTP recorded in slices was blocked in a concentration‐dependent manner by the nitric oxide synthase inhibitors L‐NG‐nitroarginine and L‐NG‐nitroarginine methyl ester, but L‐NG‐monomethylarginine was only marginally active. Bathing the slices with haemoglobin, a protein that scavenges nitric oxide, also resulted in a concentration‐dependent blockade of LTP. Nitric oxide released locally from hydroxylamine produced a stable potentiation of synaptic transmission that was not additive with LTP induced by high‐frequency stimulation. These results are fully consistent with the presumed retrograde messenger role of nitric oxide in LTP.

Neuroprotective actions of riluzole in rodent models of global and focal cerebral ischaemia

Riluzole (2 amino 6-trifluoromethoxybenzothiazole), when administered at 4 and 8 mg/kg i.p., 0.5, 4.5, 24 and 28 h after the initiation of ischaemia, significantly reduced the prevalence of slow wave, and increased the proportion of higher frequency activity seen in the quantified electrocorticogram (ECoG), during the weeks that followed a 6 min bilateral occlusion of the common carotid arteries in the Mongolian gerbil. In focal ischaemia, provoked in Fischer rats following the occlusion of the middle cerebral artery, administration of riluzole (8 mg/kg) at 30 min and 24.5 h post occlusion significantly reduced the volume of infarcted cortex. These activities of riluzole could be related to its inhibition of sodium channel activity, which in turn inhibits glutamate release.

In vitro and in vivo inhibition by zopiclone of benzodiazepine binding to rodent brain receptors

Abstract Up to now the only drugs known to be able to inhibit the binding of benzodiazepines to rodent brain receptors are members of this chemical family. Zopiclone (RP 27 267), a new drug with a pharmacological profile similar to that of chlordiazepoxide and nitrazepam but entirely different chemically from benzodiazepines, has been tested for its ability to inhibit benzodiazepine binding. In vitro and in vivo studies have shown that zopiclone is able to inhibit the binding of [3H] diazepam and [3H] flunitrazepam to brain receptors. The potency of zopiclone is quite comparable to that of diazepam and nitrazepam in vitro and to that of chlordiazepoxide in vivo . These results confirm the pharmacological similarities existing between zopiclone and the benzodiazepines.

Enzyme-resistant CCK analogs with high affinities for central receptors

Based on the results of the in vitro metabolism of CCK8 by various peptidases, we have synthesized three CCK analogs: Boc-Tyr(SO3H)-Nle-Gly-Trp-(N- Me)Nle-Asp-Phe-NH2 (compound I), Boc-Tyr(SO3H)-gNle-mGly-Trp-Nle-Asp-Phe-Nh2 (compound II), Boc-Tyr(SO3H)-gNle-mGly-Trp-(N-Me)Nle-Asp-Phe-NH2 (compound III). In in vitro enzymatic degradation studies, these compounds showed a high stability toward either enkephalinase or the enzymes present in crude rat brain membranes preparations. Moreover, in binding studies on guinea pig tissues, these CCK-related peptides were characterized by high apparent affinities for brain CCK receptors and by a broader range of affinities for pancreatic CCK receptors. This broad range of affinities was reflected by their pharmacological potencies in the guinea pig pancreatic amylase release and ileum contraction assays. These enzyme-resistant CCK analogs provide therefore valuable tools to investigate the pharmacology of CCK.

A non-peptide NK1-receptor antagonist, RP 67580, inhibits neurogenic inflammation postsynaptically.

1 The non‐peptide neurokinin NK1‐receptor antagonist, RP 67580 (3aR, 7a), a perhydroisoindolone derivative, powerfully reduced plasma extravasation in rat hind paw skin induced by local application of xylene (ID50 = 0.03 mg kg−1, i.v.) or capsaicin (ID50 = 0.06 mg kg−1, i.v.), or by i.v. injection of exogenous substance P (SP) or septide ([pGlu6,Pro9]SP(6–11)) (ID50 = 0.04–0.05 mg kg−1, i.v.). RP 67580 (1 mg kg−1, i.v.) also abolished capsaicin‐induced nasal fluid hypersecretion (by 82 ± 5%). These effects were found to be stereospecific, the enantiomer, RP 68651 (3aS, 7aS), being inactive at 1 mg kg−1, i.v. 2 In rats neonatally treated with capsaicin (50 mg kg−1, s.c.), plasma extravasation induced by SP was significantly increased (by 43 ± 7%). RP 67580 (1 mg kg−1, i.v.) completely inhibited the SP‐induced plasma extravasation in capsaicin neonatally treated‐animals, as it did in control animals. This result suggests that RP 67580 acts at the postsynaptic level for the inhibition of plasma extravasation. 3 Opioid receptor agonists, μ‐(morphine) and κ‐(PD‐117302) at 10 mg kg−1, s.c., in contrast to NK1‐receptor antagonists, did not inhibit plasma extravasation induced by exogenous SP. They were, however, partially effective against plasma extravasation induced by electrical nerve stimulation (74 ± 4% and 48 ± 9% inhibition at 10 mg kg−1, s.c. of morphine and PD‐117302, respectively, compared to 90 ± 3% inhibition obtained with RP 67580, 3 mg kg−1, s.c.). These results indicate the presynaptic action of opioid receptor agonists, in contrast to the postsynaptic action of NK1‐preceptor antagonists for the inhibition of plasma extravasation. 4 Ligature of the saphenous nerve distal to the point of electrical stimulation, local application of lignocaine to the saphenous nerve, neonatal capsaicin pretreatment, and colchicine at very low doses (120 μg kg−1 day−1 given for 3 days) were found to prevent plasma extravasation elicited by electrical nerve stimulation. 5 The foregoing results demonstrate that the non‐peptide NK1‐receptor antagonist, RP67580, is a potent inhibitor of plasma extravasation induced in skin by NK1‐receptor agonists, by local application of chemical irritants (capsaicin or xylene) or by electrical nerve stimulation. Moreover, opioid receptor agonists and colchicine inhibit plasma extravasation induced by electrical nerve stimulation but not that elicited by exogenous SP. Therefore, it is possible to inhibit neurogenic inflammation either at the presynaptic level with opioid receptor agonists and colchicine, or at the postsynaptic level with NK1‐receptor antagonists, and that the new non‐peptide NK1‐receptor antagonists may have a great potential for alleviation of inflammation in various pathological syndromes in man.

Effects of complete and partial lesions of the dopaminergic mesotelencephalic system on skilled forelimb use in the rat

This study compares certain behavioural consequences of partial and complete unilateral lesions of the dopaminergic mesotelencephalic system. We investigated skilled forelimb use, rotations induced by apomorphine and amphetamine, and dopaminergic metabolism of the nigrostriatal system of rats that had received a unilateral injection of 6-hydroxydopamine into the medial forebrain bundle. The rats classified Apo(+), that rotated after the administration of apomorphine, had a complete lesion of the nigrostriatal system, whereas those classified Apo(-), that did not rotate after the administration of apomorphine, had a partial lesion of the nigrostriatal system. In the Apo(+) rats, 99.8% of the dopamine in the striatum was depleted, as was 85% of that in the substantia nigra. For the Apo(-) rats, 72% of the dopamine in the striatum was depleted as was 56% of that in the substantia nigra. When investigated with the staircase test, the animals with the most severe dopamine depletions were those most impaired in the paw reaching task. Complete and partial unilateral depletions of the dopaminergic mesotelencephalic system impaired the hierarchic phases of paw reaching differently. A complete dopamine depletion, but not a partial one, decreased the number of attempts made with the contralateral paw, and induced a bias towards the ipsilateral paw. A partial dopamine lesion impaired the sensorimotor co-ordination of both paws, whereas the complete dopamine lesion had a greater effect on the contralateral paw than on the ipsilateral paw. The mild paw reaching impairments observed in animals with moderate depletions of dopamine are proposed as a model of the early symptoms of Parkinsons disease that may be useful for the development of protective or restorative therapies.

Pertussis toxin pretreatment abolishes the inhibitory effect of riluzole and carbachol on d[3H]aspartate release from cultured cerebellar granule cells

The release of D-[3H]aspartate from cultured cerebellar granule cells evoked by glutamic acid can be inhibited by riluzole and the muscarinic agonist carbachol. The combined application of maximally efficacious concentrations of riluzole and carbachol produces no greater inhibition than that seen with either agent alone, indicating that a common mechanism is involved. The effects of both agents are abolished when the cells have been pretreated with pertussis toxin, which suggests that this mechanism may involve a GTP-binding protein. The effect of pertussis toxin pretreatment is not mimicked by cholera toxin, nor does pertussis toxin pretreatment interfere with the inhibitory effect of the competitive excitatory amino acid receptor antagonist D-alpha-aminoadipic acid.

Neurotensin effects on evoked release of dopamine in slices from striatum, nucleus accumbens and prefrontal cortex in rat

SummaryThe effects of neurotensin (NT) on the K+-evoked release of endogenous and tritiated dopamine in striatum and on 3H-dopamine in slices from nucleus accumbens and prefrontal cortex were investigated. In striatum, NT (1–1000 nM) elicited a dose-dependent increase in endogenous and 3H-dopamine release. The dose-response curves were comparable with the two methods. Concerning the comparison of NT modulation of 3H-dopamine release in the three cerebral structures, the peptide induced a more marked effect in striatum with a maximal effect of 150% increase. In accumbens, NT (1–1000 nM) potentiated the K+-evoked 3H-dopamine release, but in contrast with striatum, the plateau corresponded to a 50% increase. In prefrontal cortex, NT (1–1000 nM) induced small but significant effects, with a maximal increase of 50% at 100 nM. Acetyl-NT (8–13) displayed an action similar to the natural peptide while NT (1–8) did not exhibit any effect, suggesting that the action of NT involved a receptor. The presence of tetrodotoxin did not alter the facilitating effects of NT in the three structures, indicating that interneurons were not involved in the action of NT. The comparison of the effects of NT showed that in terms of efficacy, NT induced an increase in dopamine release more marked in striatum than in nucleus accumbens and prefrontal cortex. These results are consistent with differences in NT receptors localization in these three dopaminergic structures.

Retrograde axonal transport of neurotensin in the dopaminergic nigrostriatal pathway in the rat

Although the existence of receptor transport has been clearly demonstrated in peripheral nerves, there is no clear cut evidence in the brain of such a process for neuropeptide receptors. Because of the localization of neurotensin receptors on dopaminergic terminals, the dopaminergic nigrostriatal pathway appears to be the system of choice for studying the axonal transport of neuropeptide receptors in the brain. When labelled neurotensin was injected into the rat striatum, a delayed accumulation of radioactivity in the ipsilateral substantia nigra was observed about 2 h after injection. An essential requirement to clearly observe this phenomenon was the pretreatment of animals with kelatorphan in order to prevent the labelled neurotensin degradation. The appearance of this labelling was prevented by injection of an excess of unlabelled neurotensin or of neurotensin 8-13, an active neurotensin fragment, but not by neurotensin 1-8, which had no affinity for neurotensin receptors. This process was saturable, microtubule-dependent and occurred only in mesostriatal and nigrostriatal dopaminergic neurons as identified after 6-hydroxydopamine lesion and by autoradiography. These results demonstrate that neurotensin was retrogradely transported by a process involving neurotensin receptors. The retrograde transport of receptor-bound neuropeptide may represent an important dynamic process which conveys information molecules from the synapse towards the cell body.