Effects of iprindole on responses of single cortical and caudate neurones to monoamines and acetylcholine

Évolution des idées sur le mécanisme d'action des antidépresseurs : le concept d'hétéro-régulation des récepteurs

Des lès premières années d'utilisation clinique des antidépresseurs, les neurones à sérotonine (5-HT) et à noradrénaline (NA) ont été considérés comme les sites d'action privilégiés de ces médicaments.

En vingt ans, les idées sur leurs mécanismes d'action ont évolué parallèlement à la progression des connaissances et à l'obtention de nouvelles molécules actives :

C'est la stimulation - directe ou indirecte - des récepteurs sérotoninergiques (5-HT2) qui serait nécessaire à l'obtention d'un découplage β lors d'une stimulation des récepteurs β-adrénergiques.

Les molécules antidepressives n'auraient d'action thérapeutique qu'à condition d'agir de façon synergique sur les transmissions sérotoninergique et noradrénergique.

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Rolipram, a stereospecific inhibitor of calmodulin-independent phosphodiesterase, causes beta-adrenoceptor subsensitivity in rat cerebral cortex

Prolonged pretreatment of rats with the atypical antidepressant rolipram attenuates noradrenaline (NA) sensitivity of the cerebral cortical cAMP generating system. The development of this down-regulation is time (7 d treatment required) and dose dependent (EC50 = 0.35 mg/kg). Density of beta-adrenoceptor as measured by (-)-3H-dihydroalprenolol [(-)-3H-DHA] binding is also reduced by rolipram pretreatment. The effect of rolipram is absolutely stereospecific for the (-)-enantiomer (ED50 = 0.18 mg/kg). In addition, only with this isomer, a reduction in daily weight gain was found compared to sham treated controls. Presynaptic denervation using intracerebroventricular (i.c.v.) injections of 6-hydroxydopamine (6-OHDA) prior to or during rolipram treatment did not completely block the effect of a rolipram treatment on down-regulation of cerebral cortical beta-adrenoceptors. The data favor a pre- and postsynaptic action of rolipram different from all other antidepressants studied so far in this experimental setting. Rolipram is known as inhibitor of brain phosphodiesterase. Using partially purified calmodulin-independent phosphodiesterase from brain it is shown that exclusively the (-)-enantiomer of rolipram inhibits phosphodiesterase with an IC50 of 1.25 mumol/l whereas the (+)-isomer possesses little potency. Since a marked stereospecificity for the (-)-isomer of rolipram was displayed in all pharmacological parameters tested so far with (+)- and (-)-rolipram, it is suggested that stereospecific and isozyme specific inhibition of cAMP-phosphodiesterase is, at least in part, related to the mechanism of action of the potential antidepressant drug rolipram and possibly of other antidepressants as well.

The effects of iprindole on noradrenergic transmission in the rat anococcygeus muscle

The effects of iprindole on the contractile responses to field stimulation and to exogenously applied agents have been studied in the rat anococcygeus muscle. In addition the effects on the spontaneous overflow of 3H and that induced by field stimulation (following preloading of the tissue with [3H]-noradrenaline) are reported. Iprindole (10(-7)-5 X 10(-6) M) had no effect on the contractile responses to acetylcholine. Iprindole at 10(-7) or 10(-6) M was equieffective in potentiating the contractile responses to either field stimulation or to noradrenaline. With a higher concentration of iprindole (5 X 10(-6) M) the potentiation was greater. The responses to oxymetazoline were potentiated and inhibited by iprindole at 10(-8) and 10(-7) M, respectively. Iprindole at 10(-6) M potentiated the responses to tyramine. The effects of iprindole at 10(-7) and 5 X 10(-6) M on the responses to field stimulation and to noradrenaline were not altered by the presence of ouabain (5 X 10(-5) M), neostigmine (10(-6) M) or yohimbine (10(-7) M). In the presence of desipramine (10(-6) M), iprindole at 10(-7) M potentiated the contractile responses to field stimulation and to noradrenaline. The higher concentrations of iprindole (10(-6) and 5 X 10(-6) M) inhibited the contractile responses to field stimulation and to noradrenaline in the presence of desipramine. Iprindole (10(-7) M) had no effect on the relaxant responses to field stimulation. Iprindole at 10(-7) or 10(-6) M had no effect on the spontaneous overflow of 3H or that induced by field stimulation at 2 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Antidepressant drugs and ethanol: behavioral and pharmacokinetic interactions in mice

The interactions between ethanol and antidepressant drugs (both tricyclics and newer non-tricyclics) were studied in mice. The ability of these drugs to enhance the sedative effects of ethanol at two different doses (3.2 and 4.0 g/kg) was measured. The percentage of mice losing the righting-reflex was used for the lower dose, and the duration of ethanol-induced sleep was used at the higher dose. The relative order of potency was amitriptyline greater than or equal to imipramine > maprotiline = mianserin > desipramine greater than or equal to chlorimipramine > iprindole greater than or equal to alaproclate > norzimelidine greater than or equal to zimelidine. Amitriptyline (60 mg/kg) caused death in all mice when combined with 4.0 g/kg ethanol. Clinically established antidepressants which enhanced ethanol sedation only at doses considerably above therapeutic levels were zimelidine and iprindole. The relative potency of the antidepressants to enhance ethanol sedation is correlated with their inherent sedative properties which are in turn related to their ability to block central 5-HT, alpha-NA, muscarinic and H1-receptors. Amitriptyline (20 mg/kg) was found to increase ethanol plasma levels to 202, 167 and 132% of control values at 30, 60 and 90 min after ethanol administration, respectively. Desipramine, mianserin and alaproclate also increased ethanol plasma levels initially, but to a lesser extent. These findings suggest that in addition to their sedative effect, several antidepressants, particularly amitriptyline, are likely to interact with ethanol by increasing its concentration in plasma.

The action of microelectrophoretically applied (3,4-dihydroxy-phenylamino)-2-imidazoline (DPI) on single cortical neurones

1. The technique of microelectrophoresis was used in order to compare the actions of the imidazoline derivative, (3,4-dihydroxy-phenylamino)-2-imidazoline (DPI), with those of dopamine and phenylephrine on single neurones in the cerebral cortex of the rat anaesthetized with halothane. 2. DPI and phenylephrine were almost exclusively excitatory, whereas dopamine could evoke both excitatory and depressant responses. 3. In the case of excitatory responses, DPI appeared to be more potent than dopamine, and was approximately equipotent with phenylephrine. 4. The dopamine antagonist, haloperidol, could discriminate between excitatory responses to DPI and dopamine: responses to dopamine were abolished, whereas responses to DPI, and to a control agonist, acetylcholine, were unaffected. 5. The alpha-adrenoceptor antagonist, phenoxybenzamine, antagonized equally excitatory responses to DPI and phenylephrine. Responses to acetylcholine were not affected. 6. It is concluded that DPI does not stimulate dopamine receptors on cortical neurones; the excitatory responses of these cells to DPI may be mediated by alpha-adrenoceptors.

Potentiation of responses to monoamines by antidepressants after destruction of monoamine afferents

1 Stereotaxic lesioning and microiontophoretic techniques were used to study the effects of lesions of the medial forebrain bundle (MFB) on the potentiation by antidepressant drugs of responses to monoamines of cortical neurones.2 Active uptake of noradrenaline (NA) and 5 hydroxytryptamine (5-HT) by synaptosomes from the motor and somatosensory cortex was reduced to approximately 20%, 10 to 14 days following lesion of the MFB in rats.3 Unilateral lesions of the MFB caused changes in responsiveness of neurones to NA and 5-HT, applied by iontophoresis, in the cortex ipsilateral to the lesion. Excitatory responses to both amines were observed less frequently and depression was the predominant response. Excitatory responses on the lesioned side were significantly smaller than on the unlesioned side, but the size of depressant responses was unaltered.4 Viloxazine strongly potentiated responses of cortical neurones to NA and 5-HT on both sides of the brain of MFB-lesioned rats. There were no significant differences in the potentiation of responses to monoamines on the lesioned or unlesioned sides of the brain.5 Desipramine potentiated responses to NA of neurones in the cortex ipsilateral to MFB lesions.6 Chlorimipramine potentiated responses to 5-HT of neurones in the cortex ipsilateral to MFB lesions.7 It is concluded that antidepressants can potentiate responses to monoamines despite a profound reduction in presynaptic terminals. The potentiation is unlikely to be the result of blockade of monoamine uptake into presynaptic terminals, and is probably a postsynaptic effect of the antidepressant drugs.

Modification of cortical neuron responses to acetylcholine by viloxazine

Viloxazine, an antidepressant with no peripheral antiacetylcholine activity, was capable of reducing responses of single cortical neurons to acetylcholine. Acetylcholine responses could also be potentiated by viloxazine. Both potentiation and reduction by viloxazine were often seen in the same study, reduction of responses invariably preceding potentiation. These results suggest that viloxazine may have selective effects on central cholinergic receptors. Responses of cortical neurons to monoamines could also be potentiated by viloxazine although it has little effect on monoamine uptake. These results are compatible with the idea that potentiation of monoamine responses may occur by a postsynaptic mechanism.

Effects of viloxazine, its optical isomers and its major metabolites on biogenic amine uptake mechanisms in vitro and in vivo

Viloxazine hydrochloride (ICI 58,834, VIVALAN) a chemically novel antidepressant, shows selective inhibition of noradrenaline uptake into mouse heart in vivo and into rat brain in vitro. The noradrenaline uptake inhibitory activity resides primarily in one of the two optically active isomers, and it is suggested that in the conformation adopted for uptake by noradrenaline, the aryl and the amino groups are trans. In a comparison of in vivo and in vitro potency, tri- and tetracyclic antidepressants exhibit a good correlation. However, viloxazine possesses higher in vivo activity than would be expected from in vitro studies. The latter finding cannot be readily explained on the basis of known pharmacokinetic or metabolic factors.

Uptake inhibition of biogenic amines by newer antidepressant drugs: relevance to the dopamine hypothesis of depression

The dopamine theory of depression was studied by assessing the effect of antidepressant drugs on uptake of dopamine, noradrenaline, and serotonin in synaptosomes from rat brain. Five newer drugs--butriptyline, maprotiline, trimipramine, iprindole, and mianserine--exhibited rather potent inhibition of 3H-dopamine uptake in corpus striatum, as their IC50 values, which were in the order of 10(-6)-10(-5) M, were only about 50 times higher than for nomifensine (IC50 = 10(-7) M). The five drugs were weak, compared to chlorimipramine, on 14C-serotonin uptake in the whole forebrain, as their IC50 were about 10(-5) M. Butriptyline, trimipramine, and iprindole were very weak uptake inhibitors of 3H-noradrenaline in the occipital cortex. Their IC50 values were about 10(-6) M, which is almost 1000 times higher than for desmethylimipramine. These results are discussed in relation to comprehensive recent literature as further indicating a link between dopamine and depression.

Tricyclic antidepressant drugs as antagonists of muscarinic receptors in sympathetic ganglia

Close arterial injection of McN-A-343 into the superior cervical ganglion of the cat resulted in contractions of the nictitating membrane. The ganglionic effects of McN-A-343 but not those of DMPP were antagonized in a dose-related manner by 2-10 mug of desipramine, imipramine, chlorimpramine, iprindole and viloxazine. No correlation was found between the dose of each drug which blocked the effects of McN-A-343 and that required to potentiate the responses of the nictitating membrane to intra-arterial administration of noradrenaline. It is concluded that clinically effective antidepressant agents can block muscarinic receptors in neural tissue, even if they do not do so in smooth muscle and gland cells.

The action of microelectrophoretically applied L-3,4-dihydroxyphenylalanine (DOPA) on single cortical neurones

The technique of microelectrophoresis was used in order to compare the actions of L-3,4-dihydroxyphenylalanine (DOPA) and noradrenaline on single neurones in the cerebral cortices of cats and rats. DOPA could both excite and depress cortical neurones. Cells excited by DOPA were also excited by noradrenaline and cells depressed by DOPA were also depressed by noradrenaline. In the case of both excitatory and depressant responses, DOPA appeared to be less potent than noradrenaline. Responses to DOPA and noradrenaline could be antagonized by phentolamine and propranolol. Responses to acetylcholine were not affected. Responses to acetylcholine, but not responses to DOPA, were antagonized by atropine. The results indicate that locally applied DOPA may mimic the actions of noradrenaline on cortical neurones. Possible mechanisms for these effects of DOPA are discussed.

Potentiation by desipramine of neuronal responses to mescaline

The effect of desipramine on responses of single cortical neurones to mescaline was studied by the microelectrophoretic technique. Both potentiation and antagonism of responses to mescaline by desipramine were observed. The antagonism may be related to the alpha-adrenolytic action of desipramine. The potentiation is unlikely to reflect the uptake blocking action of desipramine, since desipramine does not block the uptake of mescaline in the cerebral cortex. It is suggested that the potentiation may be due to a post-synaptic action of desipramine.