Restoration of dopamine release deficits during object recognition memory acquisition attenuates cognitive impairment in a triple transgenic mice model of Alzheimer's disease.

Previous findings indicate that the acquisition and consolidation of recognition memory involves dopaminergic activity. Although dopamine deregulation has been observed in Alzheimer's disease (AD) patients, the dysfunction of this neurotransmitter has not been investigated in animal models of AD. The aim of this study was to assess, by in vivo microdialysis, cortical and hippocampal dopamine, norepinephrine, and glutamate release during the acquisition of object recognition memory (ORM) in 5- and 10-mo-old triple-transgenic Alzheimer's disease mice (3xTg-AD) and to relate the extracellular changes to 24-h memory performance. Five- and 10-mo-old wild-type mice and 5-mo-old 3xTg-AD showed significant cortical but not hippocampal dopamine increase during object exploration. On a 24-h ORM test, these three groups displayed significant ORM. In contrast, 10-mo-old 3xTg-AD mice showed impaired dopamine release in the insular cortex during ORM acquisition, as well as significant impairment in ORM. In addition, cortical administration of a dopamine reuptake blocker produced an increase of dopamine levels in the 10-mo-old 3xTg-AD mice and attenuated the memory impairment. These data suggest that activation of the dopaminergic system in the insular cortex is involved in object recognition memory, and that dysfunction of this system contributes to the age-related decline in cognitive functioning of the 3xTg-AD mice.

Evaluation of the effects and mechanisms of action of flutriafol, a triazole fungicide, on striatal dopamine release by using in vivo microdialysis in freely moving rats.

The purpose of the present work was to assess the effects of flutriafol, a triazole fungicide, on in vivo dopamine (DA) release from rat striatum, using brain microdialysis coupled to high-performance liquid chromatography with electrochemical detection (HPLC-EC). Intrastriatal administration of flutriafol (1, 6 and 12 mM) produced significant concentration-dependent increases in DA levels to 218.5+/-51%, 1376+/-245% and 3093+/-345% compared with basal values, respectively. Those increases in DA levels could be due to an increased DA exocytotic release and/or a change in the activity of DA transporter (DAT). Thus, we investigated the effects of flutriafol (6mM) under Ca(++)- or Na(+)-free conditions, and after pretreatment with reserpine and TTX. When flutriafol was perfused in either Ca(++)- or Na(+)-free Ringer, the DA levels reduced 92% and 70%, respectively; perfusion of flutriafol in TTX-treated (10 microM) or reserpine-pretreated animals (10mg/kg), reduced the levels of DA to 73% and 86%, respectively. Co-infusion of flutriafol and nomifensine (20 microM) shows that the flutriafol-induced DA release did not involve the DAT. Our results suggest that flutriafol induces DA release via vesicular-, Ca(++)-, Na(+)- and TTX-dependent mechanism, being independent of DAT.

Halothane increases non-vesicular [(3)H]dopamine release from brain cortical slices.

Experimental data suggest that halothane anesthesia is associated with significant changes in dopamine (DA) concentration in some brain regions but the mechanism of this effect is not well known. Rat brain cortical slices were labeled with [(3)H]DA to further characterize the effects of halothane on the release of this neurotransmitter from the central nervous system. Halothane induced an increase on the release of [(3)H]DA that was dependent on incubation time and anesthetic concentration (0.012, 0.024, 0.048, 0.072 and 0.096 mM). This effect was independent of extracellular or intracellular calcium. In addition, [(3)H]DA release evoked by halothane was not affected by TTX (blocker of voltage-dependent Na(+) channels) or reserpine (a blocker of vesicular monoamine transporter). These data suggest that [(3)H]DA release induced by halothane is non-vesicular and would be mediated by the dopamine transporter (DAT) and norepinephrine transporter (NET). GBR 12909 and nomifensine, inhibitors of DAT, decreased the release of [(3)H]DA evoked by halothane. Nisoxetine, a blocker of NET, reduced the release of [(3)H]DA induced by halothane. In addition, GBR 12909, nisoxetine and, halothane decrease the uptake of [(3)H]DA into rat brain cortical slices. A decrease on halothane-induced release of [(3)H]DA was also observed when the brain cortical slices were incubated at low temperature and low extracellular sodium, which are known to interfere with the carrier-mediated release of the neurotransmitter. Ouabain, a Na(+)/K(+) ATPase pump inhibitor, which induces DA release through reverse transport, decreased [(3)H]DA release induced by halothane. It is suggested that halothane increases [(3)H]DA release in brain cortical slices that is mediated by DAT and NET present in the plasma membrane.

Monoamine transporter inhibitors and norepinephrine reduce dopamine-dependent iron toxicity in cells derived from the substantia nigra.

The role of dopamine in iron uptake into catecholaminergic neurons, and dopamine oxidation to aminochrome and its one-electron reduction in iron-mediated neurotoxicity, was studied in RCSN-3 cells, which express both tyrosine hydroxylase and monoamine transporters. The mean +/- SD uptake of 100 microm 59FeCl3 in RCSN-3 cells was 25 +/- 4 pmol per min per mg, which increased to 28 +/- 8 pmol per min per mg when complexed with dopamine (Fe(III)-dopamine). This uptake was inhibited by 2 microm nomifensine (43%p < 0.05), 100 microm imipramine (62%p < 0.01), 30 microm reboxetine (71%p < 0.01) and 2 mm dopamine (84%p < 0.01). The uptake of 59Fe-dopamine complex was Na+, Cl- and temperature dependent. No toxic effects in RCSN-3 cells were observed when the cells were incubated with 100 microm FeCl3 alone or complexed with dopamine. However, 100 microm Fe(III)-dopamine in the presence of 100 microm dicoumarol, an inhibitor of DT-diaphorase, induced toxicity (44% cell death; p < 0.001), which was inhibited by 2 microm nomifensine, 30 microm reboxetine and 2 mm norepinephrine. The neuroprotective action of norepinephrine can be explained by (1) its ability to form complexes with Fe3+, (2) the uptake of Fe-norepinephrine complex via the norepinephrine transporter and (3) lack of toxicity of the Fe-norepinephrine complex even when DT-diaphorase is inhibited. These results support the proposed neuroprotective role of DT-diaphorase and norepinephrine.

The selective serotonin reuptake inhibitor citalopram induces the storage of serotonin in catecholaminergic terminals.

We investigated whether selective inhibition of serotonin (5-hydroxytryptamine; 5-HT) transporter with citalopram leads to accumulation of 5-HT in catecholaminergic neurons. In the rabbit olfactory tubercle, citalopram (1-10 microM) inhibited [(3)H]5-HT uptake; however, the maximal degree of inhibition achieved was 70%. Addition of nomifensine (1-10 microM) was required for complete inhibition of [(3)H]5-HT uptake. In slices labeled with 0.1 microM [(3)H]5-HT, cold 5-HT (0.03-1 microM) induced a large increase in the efflux (release) of stored [(3)H]5-HT, an effect blocked by coperfusion with 1 microM citalopram. Similar concentrations (0.03-1 microM) of norepinephrine (NE) or dopamine (DA) failed to release [(3)H]5-HT. When labeling with 0.1 microM [(3)H]5-HT was carried out in the presence of citalopram, 1) low concentrations of 5-HT failed to release [(3)H]5-HT; 2) DA and NE were more potent and effective in releasing [(3)H]5-HT than in control slices; 3) coperfusion of NE, DA, or 5-HT with citalopram enhanced the release of [(3)H]5-HT induced by the catecholamines but not by 5-HT; and 4) coperfusion of NE or DA with nomifensine antagonized NE- and DA-evoked [(3)H]5-HT release, with a greater effect on NE than on DA. These results suggest that in the rabbit olfactory tubercle, where there is coexistence of 5-HT, NE, and DA neurons, inhibition of the 5-HT transporter led to accumulation of 5-HT in catecholaminergic terminals. Thus, during treatment with selective serotonin uptake inhibitors (SSRIs), 5-HT may be stored in catecholaminergic neurons acting as a false neurotransmitter and/or affecting the disposition of DA and/or NE. Transmitter relocation may be involved in the antidepressant action of SSRIs.

Mechanism of action of methylmercury on in vivo striatal dopamine release. Possible involvement of dopamine transporter.

Methylmercury (MeHg) produces significant increases in the spontaneous output of dopamine (DA) from rat striatal tissue. The mechanism through MeHg produces such increase in the extracellular DA levels could be due to increased DA release or decreased DA uptake into DA terminals. One of the aims of this study was to investigate the role of DA transporter (DAT) in the MeHg-induced DA release. Coinfusion of 400 microM MeHg and nomifensine (50 microM) or amphetamine (50 microM) produced increases in the release of DA similar to those produced by nomifensine and amphetamine alone. In the same way, MeHg-induced DA release was not attenuated under Ca(2+)-free conditions or after pretreatment with reserpine (10 mg/kg i.p.) or tetrodotoxin (TTX), suggesting that the DA release was independent of calcium and vesicular stores, as well as it was not affected by the blockade of voltage sensitive sodium channels. Thus, to investigate whether depolarization of dopaminergic terminal was able to affect MeHg-induced DA release, we infused 75 mM KCl through the dialysis membrane. Our results clearly showed a decrease induced by MeHg in the KCl-evoked DA release. Taken together, these results suggest that MeHg induces release of DA via transporter-dependent, calcium- and vesicular-independent mechanism and it decreases the KCl-evoked DA release.

Copper neurotoxicity is dependent on dopamine-mediated copper uptake and one-electron reduction of aminochrome in a rat substantia nigra neuronal cell line.

The mechanism of copper (Cu) neurotoxicity was studied in the RCSN-3 neuronal dopaminergic cell line, derived from substantia nigra of an adult rat. The formation of a Cu-dopamine complex was accompanied by oxidation of dopamine to aminochrome. We found that the Cu-dopamine complex mediates the uptake of (64)CuSO(4) into the Raúl Caviedes substantia nigra-clone 3 (RCSN3) cells, and it is inhibited by the addition of excess dopamine (2 m M) (63%, p < 0.001) and nomifensine (2 microM) (77%, p < 0.001). Copper sulfate (1 m M) alone was not toxic to RCSN-3 cells, but was when combined with dopamine or with dicoumarol (95% toxicity; p < 0.001) which inhibits DPNH and TPNH (DT)-diaphorase. Electron spin resonance (ESR) spectrum of the 5,5-dimethylpyrroline-N-oxide (DMPO) spin trap adducts showed the presence of a C-centered radical when incubating cells with dopamine, CuSO(4) and dicoumarol. A decrease in the expression of CuZn-superoxide dismutase and glutathione peroxidase mRNA was observed when RCSN-3 cells were treated with CuSO(4), dopamine, or CuSO(4) and dopamine. However, the mRNA expression of glutathione peroxidase remained at control levels when the cells were treated with CuSO(4), dopamine and dicoumarol. The regulation of catalase was different since all the treatments with CuSO(4) increased the expression of catalase mRNA. Our results suggest that copper neurotoxicity is dependent on: (i) the formation of Cu-dopamine complexes with concomitant dopamine oxidation to aminochrome; (ii) dopamine-dependent Cu uptake; and (iii) one-electron reduction of aminochrome.

Dopamine transporter mediated release of dopamine: role of chloride.

Using a rapid (0.5 ml/min) flow rate superfusion system, the dopamine (DA) transporter mediated release of DA is further explored, and compared to the depolarization evoked release of DA in rat striatal synaptosomes preloaded with radioactive DA (3H-DA). In this system external DA in the low microM range efficaciously releases the preloaded transmitter, the maximal response being reached at 3 microM DA. The external DA stimulated release is Ca(2+)-independent, Cl(-)-dependent, and blocked by both bupropion and nomifensine. The atypical antidepressant bupropion inhibits 3H-DA accumulation to rat striatal synaptosomes with a calculated IC50 of 1.3 x 10(-6) M. Among DA uptake blockers some are known to act as DA releasing agents. Here we found that the DA uptake blocker nomifensine (30 microM) is unable to modify the baseline release of 3H-DA, whereas bupropion (10 microM) clearly elevates the baseline release of 3H-DA in a Ca(2+)-independent and Cl(-)-dependent manner. The non releasing agent nomifensine blocks the release of 3H-DA induced by bupropion. The Ca(2+)-dependent, high K+ depolarization evoked release of 3H-DA is not modified by nomifensine and does not depend on the external Cl- concentration. When the depolarizing medium contains DA the carrier mediated release of 3H-DA induced by the external DA is additive to the high K+ induced response. A drastic drop in the external Cl- concentration induces 3H-DA release. This release of 3H-DA induced by low external Cl- levels is completely blocked by nomifensine, which only slightly diminished the release of 3H-DA induced by the absence of external Na+. On the basis of these results, it is concluded that: 1) Rapid perfusion flow rates eliminate DA reuptake. 2) DA uptake inhibitors either with or without DA releasing capabilities block the release of DA induced by microM levels of external DA. 3) By preventing translocation of the DA transporter mobile moiety, nomifensine may inhibit the release of DA induced by external DA or bupropion and by drastic drops in the external Cl- concentration. 4) In the absence of nomifensine, the DA transporter works under both resting and depolarized conditions, but in contrast to the GABA transporter (Sitges et al.: Neurochem Res 18:1081-1087, 1993), the DA transporter does not contribute to the amount of the DA released by depolarization. 5) Reversal of the DA uptake carrier is favored by conditions increasing the internal DA levels. 6) Cl- rather than Na+ is a major determinant in 3H-DA movements through the DA transporter.

Pharmacological modulation of endogenous dopamine and DOPAC outflow from nucleus accumbens.

The release of endogenous DA and DOPAC from nucleus accumbens slices were studied measuring net outflow of DA and DOPAC in the superfusate of static chambers, to analyze the correlation between DA and DOPAC outflows and identify which DA stores may serve as possible sources for DOPAC formation. Under resting conditions, or following stimulation with low (< 15 mM) KCl concentration, DOPAC outflow was greater than DA. When DA release was stimulated by higher (> 25 mM) KCl concentrations, DA outflow increased, proportionally more than DOPAC. In the virtual absence of Ca2+ in the Krebs solution DA outflow, induced by 25 mM KCl, was reduced to about 10%, while DOPAC outflow was only reduced to 45%. When the synthesis of DA was inhibited with alpha-MPT, DA and DOPAC outflow were unchanged during the first stimulation period. During a second stimulation period, however, their outflow were significantly reduced. Nomifensine, a DA uptake inhibitor, increased the basal DA outflow by about 100%, but only blocked DOPAC basal outflow by about 25%. The 25 mM KCl stimulated DA outflow was not affected by Nomifensine, while the stimulated DOPAC outflow was reduced by about 50%. These results demonstrate that there is a weak correlation between the outflows of DA and DOPAC, suggesting a complex relationship between the mobilization of the different DA pools and DOPAC outflow. The formation of DOPAC from some of these pools, appear to be dependent on the stimulation levels and on the pharmacological manipulation of the tissue.

Effect of low alcohol dose on behavioral "despair" in rats neonatally treated with antidepressant drugs.

Rat pups were treated with monoamine uptake inhibiting antidepressant drugs, desipramine, imipramine or nomifensine (5 mg/kg) during the second and third postnatal weeks, and their later behavioral "despair," measured by Porsolt's swim test, was examined. At the age of two months, the desipramine-treated rats showed lengthened immobility in the swim test, and thus probably increased behavioral "despair." They also responded to 1 g/kg alcohol by shortening the immobility to the level of control rats. Neonatal treatment with either imipramine or nomifensine did not affect the swim test behavior. The results suggest that a low, stimulatory dose of alcohol was able to reverse the lengthened immobility in the swim test of rats treated with desipramine during the early postnatal period.

Effect of nomifensine on platelet monoamine oxidase activity in chronic schizophrenic patients.

1. The levels of platelet MAO activity increase and the frequency of affective symptoms diminish in the depressed chronic schizophrenics treated with nomifensine. 2. Nomifensine has no inhibitory effect in vitro on platelet MAO activity in depressed schizophrenic pellets.

Reversal of the increase in apomorphine-induced stereotypy and aggression in REM sleep deprived rats by dopamine agonist pretreatments.

REM sleep deprivation (REMSD) induces augmented responses to dopaminergic agonists. Prolonged administration of neuroleptics induces a similar state, probably by the production of supersensitivity of dopaminergic receptors. Such a supersensitive state could be induced by REMSD as a result of impairment of dopamine neurotransmission. In order to test this hypothesis, bromocriptine, nomifensine, amphetamine, L-dopa, imipramine and electroconvulsive shock (ECS) were administered to rats during REMSD, and aggressive and stereotyped behaviors were measured. Amphetamine and L-dopa pretreatment attenuated the increases in apomorphine-induced stereotypy and aggression in REMSD rats, but ECS selectively reduced apomorphine-induced aggression. The other drugs tested were ineffective on both behavioral tests. Such a selective action may reflect different effects of ECS on different dopaminergic systems such as those involved with stereotypy and aggression. The results suggest that REMSD induces an increase in dopaminergic sensitivity which may be reversed by pretreatment with some dopaminergic agonists.

Efecto de la nomigensina sobre la secreción de prolactina en el puerperio y su repercusión sobre la lactancia / Effect of nomigensine on prolactin secretion during puerperium and its effect on lactation

Se investigó el efecto de la nomifensina sobre la secreción de prolactina en el puerperio así como su posible utilidad terapéutica como inhibidor de la lactancia en el postparto. Con este propósito se seleccionaron 20 mujeres puerperas normales con indicación médica para suprimir la lactancia. En una primera etapa del estudio, 12 de las 20 mujeres ingirieron en ayuno 200 mg de nomifensisna dentro de las primeras 12 a 24 horas postparto y las ocho restantes tomaron palcebo y se consideraron como testigo. En ambos grupos se cuantificaron por radioanálisis los niveles circulantes de prolactina en muestras de sangre venosa tomada antes y a intervalos de 15 y 30 minutos después de la nomifensina y el placebo. En la segunda etapa los pacientes del primer grupo continuaron tomando la nomifensina a la dosis de 100 mg cada 12 horas durante cinco días y se les cuantificó diariamente los niveles de prolactina hasta el final del estudio; y a las pacientes del grupo testigo se les prescribió bromocriptina para suprimir la lactancia. La nomifensina en la fase aguda produjo una disminución de los siguientes 60 a 180 minutos de su administración; en tanto que en el grupo testigo los cambios en la prolactina no fueron significativos. El descenso progresivo de la prolactina en las pacientes tratadas crónicamente con nomifensina fueron similares a los observados normalmente en mujeres puéroeras que no amamantan. Se concluye que la nomifensina a dosis terapéuticas como antidepresivo y durante el tiempo utilizado en este estudio, no fue eficaz para suprimir la lactogénesis por su deficiencia efecto sobre la secreción de prolactina

Influence of naloxone on analgesic effects of antidepressants in mice.

The present study investigates the effects of a tricyclic (imipramine) and two atypical antidepressants (nomifensine and mianserin ) on nociception to chemical and thermal stimuli in mice. The reversibility of these effects by the opioid antagonist naloxone was also assessed. Imipramine, nomifensine and mianserin produced a significant analgesic effect in both the acetic acid-induced writhing and hot plate tests. The analgesic action of imipramine was influenced by pretreatment with naloxone. These results suggest that different antidepressant drugs are capable of inducing antinociceptive effects in mice, probably mediated by opioid and non-opioid systems.