Lucyna Antkiewicz-Michaluk

Neurochemical changes induced by acute and chronic administration of 1,2,3,4-tetrahydroisoquinoline and salsolinol in dopaminergic structures of rat brain.

The finding that endogenous tetrahydroisoquinolines may be involved in the etiology of Parkinsons disease suggests that their administration may cause changes resembling those observed in parkinsonian brain. We tested, using a high-performance liquid chromatography method, how single and chronic administration of 1,2, 3,4-tetrahydroisoquinoline and salsolinol affects dopamine and serotonin metabolism in the neurons of extrapyramidal and mesolimbic dopaminergic systems. We report that chronic administration of tetrahydroisoquinoline and salsolinol causes a decrease in a dopamine metabolism: the effect of tetrahydroisoquinoline was limited to the striatum, while salsolinol caused also a dramatic decline of dopamine level in the substantia nigra. The effect of both compounds on serotonin metabolism was small or absent. The tetrahydroisoquinolines produced no changes in the nucleus accumbens. The results indicate that tetrahydroisoquinoline and salsolinol specifically affect the nigrostriatal dopamine system, but only when administered chronically, and thus are compatible with the view that endogenous tetrahydroisoquinolines may participate in pathogenesis of Parkinsons disease.

Different action on dopamine catabolic pathways of two endogenous 1,2,3,4-tetrahydroisoquinolines with similar antidopaminergic properties

The effect of single and multiple 1‐methyl‐1,2,3,4‐tetrahydroisoquinoline (1MeTIQ) and 1‐benzyl‐1,2,3,4‐tetrahydroisoquinoline (1BnTIQ) administration on concentrations of dopamine and its metabolites: homovanillic acid (HVA) and 3,4‐dihydroxyphenylacetic acid (DOPAC) and 3‐methoxytyramine (3MT) in three brain areas was studied HPLC with electrochemical detection in Wistar rats. The rate of dopamine catabolism in the striatum along the N‐oxidative and O‐methylation pathways was assessed by calculation of the ratio of appropriate metabolites to dopamine concentration. In addition, the spontaneous and apomorphine‐stimulated locomotor activity, and muscle rigidity was studied after acute administration of 1MeTIQ and 1BnTIQ. We have found that 1MeTIQ did not change the level of dopamine and HVA in all investigated structures both after a single and chronic administration. However, the levels of intermediary dopamine metabolites, DOPAC and 3MT, were distinctly affected. The level of DOPAC was strongly depressed (by 60–70%) while the level of extraneuronal matabolite 3MT was significantly elevated (by 170–200%). In contrast to 1MeTIQ, 1BnTIQ depressed the level of dopamine (by approximately 60%) and increased the level of total metabolite, HVA, (by 40%) especially in the striatum, but the levels of DOPAC and 3MT remained unchanged. The paper has shown that 1MeTIQ and 1BnTIQ produced different effects on dopamine catabolism. Potential neuroprotective compound 1MeTIQ did not change the rate of total dopamine catabolism, it strongly inhibited the monoamine oxidase (MAO)‐dependent catabolic pathway and significantly activated the catechol‐O‐methyltransferase (COMT)‐dependent O‐methylation. In contrast 1BnTIQ, a compound with potential neurotoxic activity, produced the significant increase of the rate of dopamine metabolism with strong activation of the oxidative MAO‐dependent catabolic pathway. Interestingly, both compounds produced similar antidopaminergic functional effects: antagonism of apomorphine hyperactivity and induction of muscle rigidity. The results may explain the biochemical basis of the neuroprotective and of the neurotoxic properties endogenous brain tetrahydroisoquinoline derivatives.

Effects of various Ca2+ channel antagonists on morphine analgesia, tolerance and dependence, and on blood pressure in the rat.

Following the finding that nifedipine enhances morphine analgesia and prevents the development of dependence, we have now compared the effect of nifedipine with these of other L-type Ca2+ channel antagonists, nimodipine (a dihydropyridine) and verapamil (a phenylethylalkylamine). Male Wistar rats received the antagonist 20 min before each injection of morphine. Analgesia was measured in a hot-plate test, and the development of dependence was assessed in the naloxone precipitation test after 13 days of morphine (20-30 mg/kg i.p.) administration. L-type Ca2+ channels were assayed in the cerebral cortex as [3H]nitrendipine binding sites. Blood pressure was monitored from the tail by a non-invasive method. We found that all three Ca2+ antagonists enhanced the analgesia, and prevented development of the naloxone-precipitated withdrawal syndrome, although they differed in their efficacy. Nifedipine and verapamil effectively blocked the development of tolerance. While chronic morphine up-regulated L-type Ca2+ channels, co-administration of the antagonists completely prevented this effect. The effects of Ca2+ channel antagonists cannot be ascribed to their potential circulatory effects as, at the dose used, none affected significantly the arterial blood pressure.

Chronic administration of antidepressant drugs increases the density of cortical [3H]prazosin binding sites in the rat

Administration of antidepressants (imipramine, citalopram) or antidepressant neuroleptics (levomepromazine, chlorprothixene) for 14-24 days enhanced by 20-30% the density of [3H]prazosin binding sites in the membranes from the cerebral cortex of the rat, without significant change in their affinity.

Chronic electroconvulsive treatment enhances the density of [3H]prazosin binding sites in the central nervous system of the rat

Chronic electroconvulsive treatment (ECT) given daily for 10 days enhanced the density of [3H]prazosin binding sites in the membranes from the spinal cord and cerebral cortex of the rat 24 h after the last shock. Similar effect (investigated only in cortical membranes) was produced by spaced ECT (5 shocks at 72 h intervals). The effect was preceded by a decrease in the density of [3H]prazosin binding sites, observed 2 h after the last shock and disappeared within 48 h.

Reduction of morphine dependence and potentiation of analgesia by chronic co-administration of nifedipine

Nifedipine, 5 mg/kg IP, potentiated the morphine-induced analgesia measured in the hot-plate, but not in the tail-flick test. Further experiments were carried out using the hot-plate test only. Pretreatment with nifedipine partially restores the analgesic action of morphine in morphine-tolerant rats. Co-administration of nifedipine with morphine in a chronic experiment did not prevent the loss of morphine efficiency (an increase in latency of 44% was not significant) and did not prevent the debilitating effect of chronic morphine administration reflected by an inhibition of the body weight gain, but prevented naloxone-induced withdrawal syndrome (quantified by counting head shakes) in the test carried out 24 h after the injection of nifedipine, when the drug did not affect morphine analgesia. Chronic treatment with either morphine or nifedipine did not produce a significant increase in the density of [3H] naloxone or [3H]prazosin binding sites in the cortex and in the rest of the brain (measured 24 h after the last dose), but the combined treatment resulted in a significant increase in the cortical [3H]prazosin binding site density. The present results suggest that opiate tolerance and physical dependence may be separated by coadministration of nifedipine and suggest that the combined chronic treatment with morphine and nifedipine may increase the efficacy of morphine during chronic treatment and prevent development of abstinence.

The attenuating effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in human neuroblastoma SH-SY5Y cells.

Memantine, a clinically used N-methyl-D-aspartate (NMDA)-receptor antagonist, has been shown to prevent apoptotic neuronal damage connected with the over-activity of NMDA receptors. In the present study, we examined the effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in the SH-SY5Y cell line which does not possess functional NMDA receptors. Electrophysiological recordings and toxicity studies showed no response to NMDA-evoked currents in this cell line, irrespective of the stage of its neuronal differentiation. Memantine (0.1-2 microM) attenuated staurosporine-induced apoptosis as evidenced by reversal of the changes in mitochondrial membrane potential (DeltaPsi(m)) and decreased caspase-3 activity, lactate dehydrogenase (LDH) release and DNA fragmentation. Wortmannin (10 nM) and LY 294002 (10 microM) (inhibitors of phosphatidylinositol-3-kinase, PI3-K) reversed the inhibitory effect of memantine on the staurosporine-induced LDH release, suggesting that the PI3-K/Akt prosurvival pathway is a possible target for antiapoptotic action of memantine. Memantine at low micromolar concentrations also attenuated salsolinol- and doxorubicin-induced LDH release and DNA fragmentation, but only in the case of salsolinol was this effect accompanied by a decrease in caspase-3 activity. The present data indicate that memantine attenuates the toxic effects of various proapoptotic agents and the cytoprotective effect of memantine does not seem to be connected with its action on NMDA receptor but rather with its influence on intracellular pathways engaged in cellular survival/apoptotic processes.

Protective effect of 1-methyl-1,2,3,4-tetrahydroisoquinoline against dopaminergic neurodegeneration in the extrapyramidal structures produced by intracerebral injection of rotenone

The aim of this paper was to investigate whether rotenone, a pesticide causing experimental parkinsonism, causes direct damage to dopaminergic structure when injected intracerebrally and whether this action may be prevented by peripheral administration of 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), an endogenous compound with anti-dopaminergic activity. Male Wistar rats were injected unilaterally into the median forebrain bundle with 2 microg rotenone, and received 1MeTIQ, 50 mg/kg i.p. 1 h before and then daily for 21 d. To compare the effect of intracerebral and peripheral treatment, rotenone was also given once or for 7 d in a dose of 10 mg/kg s.c. Dopamine, serotonin and their metabolites were assessed by HPLC in the substantia nigra and striatum. While a single subcutaneous rotenone dose did not produce any change in striatal dopamine metabolism, the multiple treatments resulted in changes suggesting a shift in the metabolism towards oxidative desamination and reduction of O-methylation. In contrast to systemic injections, intracerebral-administered rotenone produced a decrease in dopamine and its metabolites content in the striatum (dopamine decrease by 70%) and substantia nigra (dopamine decrease by 35%), without affecting the serotonin system. As those changes were observed 21 d after the injection of rotenone, they suggest a durable neurotoxic effect. The treatment with 1MeTIQ strongly reduced the fall of striatal dopamine concentration. The data suggest that rotenone given peripherally affects metabolic processes in dopaminergic neurons, and this seems to result from its neurotoxic action, which may be observed after an intracerebral injection. 1MeTIQ is able to counteract the damaging action of rotenone and seems to be a potential neuroprotective agent.

Role of calcium channels in effects of antidepressant drugs on responsiveness to pain

The effect of acute and chronic treatment with three antidepressant drugs on the cortical L-type calcium channel (measured as [3H]nitrendipine binding sites) and on the responsiveness to pain (assessed in the hot-plate test) was tested on the Wistar rat. Acute administration of antidepressants did not affect the characteristics of calcium channels and did not significantly prolong the hot-plate latency. However, a combination of antidepressants with nifedipine brought about analgesia. Chronic administration of imipramine did not significantly affect the characteristics of calcium channels but produced a moderate analgesic effect. In contrast, chronic administration of citalopram and chlorprothixene increased the density of [3H]nitrendipine binding sites and induced hyperalgesia, which was nullified by acute administration of nifedipine. The results confirm that calcium channels may be involved in analgesia and hyperalgesia and indicate that chronic treatment with some antidepressant may induce an increase in the density of cortical calcium channels.

Behavioural and biochemical studies of citalopram and WAY 100635 in rat chronic mild stress model

Reversal of chronic mild stress (CMS)-induced decrease of sucrose consumption has been studied in rats after 2, 7, 14, and 35 days treatment with imipramine, citalopram (both 10 mg/kg per day, i.p.), WAY 100635 (0.2 mg/kg sc, b.i.d.), and citalopram plus WAY 100635. Bmax, Kd, and functional status [cyclic AMP (cAMP) generation] of beta1-adrenoceptors were assessed in cortical tissue at the same time points. Citalopram reversed CMS-induced reduction of sucrose intake at an earlier time point than imipramine. WAY 100635 was not effective and did not potentiate the effect of citalopram. CMS produced increase of Bmax. Imipramine decreased Bmax in controls (Days 2, 7, 14, and 35) and normalised Bmax in stressed animals (Day 35). Citalopram, WAY 100635, and the combination increased Bmax in stressed animals and controls (Days 14 and 35). Inconsistent changes of Kd values and of cAMP responses to noradrenaline (NA) stimulation were observed. Thus stress- and drug-induced effects on beta1-adrenoceptors do not appear to be a common biochemical marker of antidepressant-like activity in the CMS model.