RESUMEN
Thiamethoxam is a neonicotinoid insecticide, a group of pesticides that acts selectively on insect nicotinic acetylcholine receptors (nAChRs), with only a little action on mammalian nAChRs. Nevertheless, the selectivity of neonicotinoids for the insect nAChRs may change when these substances are metabolized. Therefore, we aimed to determine the potential effects of thiamethoxam on mammalian brain, testing the performance in the open field and elevated plus-maze of rats exposed to this insecticide and, in order to establish the neurochemical endpoints, we measured the acetylcholinesterase activity in different brain regions (hippocampus, striatum and cortex) and the high-affinity choline uptake (HACU) in synaptosomes from rat hippocampus. Treated animals received thiamethoxam (25, 50 or 100mg/kg) for 7 consecutive days. The results showed that treatment with thiamethoxam induced an increase in the anxiety behavior at two doses (50 or 100mg/kg). Moreover, there was a significant decrease in both HACU and acetylcholinesterase activity. Our hypothesis is that thiamethoxam (or its metabolites) could be acting on the central rats nAChRs. This would produce an alteration on the cholinergic transmission, modulating the anxiety behavior, acetylcholinesterase levels and HACU.
Asunto(s)
Conducta Animal/efectos de los fármacos , Encéfalo/efectos de los fármacos , Insecticidas/toxicidad , Nitrocompuestos/toxicidad , Oxazinas/toxicidad , Sistema Nervioso Parasimpático/efectos de los fármacos , Tiazoles/toxicidad , Acetilcolinesterasa/metabolismo , Animales , Encéfalo/enzimología , Colina/metabolismo , Relación Dosis-Respuesta a Droga , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Actividad Motora/efectos de los fármacos , Neonicotinoides , Ratas , Ratas Wistar , TiametoxamRESUMEN
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.
Asunto(s)
Ganglios Basales/efectos de los fármacos , Dopamina/metabolismo , Fungicidas Industriales/toxicidad , Locomoción , Microdiálisis , Triazoles/toxicidad , Animales , Ganglios Basales/metabolismo , Calcio/metabolismo , Cromatografía Líquida de Alta Presión , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática/efectos de los fármacos , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática/metabolismo , Inhibidores de Captación de Dopamina , Técnicas Electroquímicas , Exocitosis/efectos de los fármacos , Femenino , Nomifensina/farmacología , Potasio/metabolismo , Ratas , Ratas Sprague-Dawley , Reserpina/farmacología , Sodio/metabolismo , Bloqueadores de los Canales de Sodio/farmacología , Tetrodotoxina/farmacología , Factores de TiempoRESUMEN
The present study was carried out in order to compare the effects of administration of organic (methylmercury, MeHg) and inorganic (mercury chloride, HgCl 2 ) forms of mercury on in vivo dopamine (DA) release from rat striatum. Experiments were performed in conscious and freely moving female adult Sprague-Dawley (230-280 g) rats using brain microdialysis coupled to HPLC with electrochemical detection. Perfusion of different concentrations of MeHg or HgCl 2 (2 muL/min for 1 h, N = 5-7/group) into the striatum produced significant increases in the levels of DA. Infusion of 40 muM, 400 muM, or 4 mM MeHg increased DA levels to 907 ± 31, 2324 ± 156, and 9032 ± 70 percent of basal levels, respectively. The same concentrations of HgCl 2 increased DA levels to 1240 ± 66, 2500 ± 424, and 2658 ± 337 percent of basal levels, respectively. These increases were associated with significant decreases in levels of dihydroxyphenylacetic acid and homovallinic acid. Intrastriatal administration of MeHg induced a sharp concentration-dependent increase in DA levels with a peak 30 min after injection, whereas HgCl 2 induced a gradual, lower (for 4 mM) and delayed increase in DA levels (75 min after the beginning of perfusion). Comparing the neurochemical profile of the two mercury derivatives to induce increases in DA levels, we observed that the time-course of these increases induced by both mercurials was different and the effect produced by HgCl 2 was not concentration-dependent (the effect was the same for the concentrations of 400 muM and 4 mM HgCl 2 ). These results indicate that HgCl 2 produces increases in extracellular DA levels by a mechanism differing from that of MeHg.
Asunto(s)
Animales , Femenino , Ratas , Cuerpo Estriado/efectos de los fármacos , Dopamina , Cloruro de Mercurio/farmacología , Compuestos de Metilmercurio/farmacología , Cromatografía Líquida de Alta Presión , Cuerpo Estriado , Relación Dosis-Respuesta a Droga , Electroquímica , Ácido Homovanílico/metabolismo , Microdiálisis , Oxidorreductasas/metabolismo , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
The present study was carried out in order to compare the effects of administration of organic (methylmercury, MeHg) and inorganic (mercury chloride, HgCl 2 ) forms of mercury on in vivo dopamine (DA) release from rat striatum. Experiments were performed in conscious and freely moving female adult Sprague-Dawley (230-280 g) rats using brain microdialysis coupled to HPLC with electrochemical detection. Perfusion of different concentrations of MeHg or HgCl 2 (2 microL/min for 1 h, N = 5-7/group) into the striatum produced significant increases in the levels of DA. Infusion of 40 microM, 400 microM, or 4 mM MeHg increased DA levels to 907 +/- 31, 2324 +/- 156, and 9032 +/- 70% of basal levels, respectively. The same concentrations of HgCl 2 increased DA levels to 1240 +/- 66, 2500 +/- 424, and 2658 +/- 337% of basal levels, respectively. These increases were associated with significant decreases in levels of dihydroxyphenylacetic acid and homovallinic acid. Intrastriatal administration of MeHg induced a sharp concentration-dependent increase in DA levels with a peak 30 min after injection, whereas HgCl 2 induced a gradual, lower (for 4 mM) and delayed increase in DA levels (75 min after the beginning of perfusion). Comparing the neurochemical profile of the two mercury derivatives to induce increases in DA levels, we observed that the time-course of these increases induced by both mercurials was different and the effect produced by HgCl 2 was not concentration-dependent (the effect was the same for the concentrations of 400 microM and 4 mM HgCl 2 ). These results indicate that HgCl 2 produces increases in extracellular DA levels by a mechanism differing from that of MeHg.
Asunto(s)
Cuerpo Estriado/efectos de los fármacos , Dopamina/metabolismo , Cloruro de Mercurio/farmacología , Compuestos de Metilmercurio/farmacología , Animales , Cromatografía Líquida de Alta Presión , Cuerpo Estriado/metabolismo , Relación Dosis-Respuesta a Droga , Electroquímica , Femenino , Ácido Homovanílico/metabolismo , Microdiálisis , Oxidorreductasas/metabolismo , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
The possible protective effects of glutathione (GSH), cysteine (CYS) and methionine (MET) on the Methylmercury (MeHg)-induced dopamine (DA) release from rat striatum were investigated using in vivo microdialysis coupled to HPLC with electrochemical detection. Intrastriatal infusion of MeHg 400 microM increased extracellular DA levels to 1941 +/- 199% in terms of basal levels. Infusion of MeHg 400 microM in GSH 400 microM pretreated animals, only increased striatal DA levels to 465 +/- 104%, in terms of basal levels, this increase being 76% lower than induced by MeHg alone. Conversely, the infusion of MeHg 400 microM after infusion of GSH 400 microM increased DA levels to 1019 +/- 96% in terms of basal levels, this increase being 47.5% lower than that observed in MeHg non-pretreated animals. The infusion of MeHg 400 microM in CYS 400 microM -pretreated animals, increased striatal DA levels to 740 +/- 149%, in terms of basal levels, this increase being 62% lower than that induced by MeHg in non-pretreated animals. The infusion of MeHg 400 microM in MET 400 microM pretreated animals increased striatal DA levels to 2011 +/- 230% in terms of basal, an increase that was not significantly different from that produced by MeHg 400 muM alone. In summary, the administration of compounds containing free -SH groups prevented the MeHg-induced DA release from rat striatum, probably due to the binding of MeHg to -SH groups. This would result in a lower metal availability to interact with -SH membrane proteins groups, which would decrease MeHg ability to interact with DA transporter.
Asunto(s)
Cuerpo Estriado/efectos de los fármacos , Cisteína/farmacología , Dopamina/metabolismo , Glutatión/farmacología , Compuestos de Metilmercurio/toxicidad , Fármacos Neuroprotectores/farmacología , Animales , Cromatografía Líquida de Alta Presión , Cuerpo Estriado/metabolismo , Femenino , Metionina/farmacología , Microdiálisis , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
The present study was carried out in order to determine the effects of intrastriatal administration of different doses (40 microM, 400 microM, and 4mM) of methylmercury (MeHg) on dopaminergic system of rat striatum. Experiments were performed in conscious and freely moving rats using brain microdialysis coupled with liquid chromatography. Intrastriatal administration of MeHg produced significant increases in dopamine (DA) striatal levels (907+/-7%, 1870+/-319%, and 7971+/-534% for the doses of 40, 400 microM, and 4mM, with respect to basal). The increase in DA levels was associated with significant decreases in extracellular levels of its main metabolites dihydroxyphenylacetic acid (DOPAC) and homovallinic acid (HVA) (65.0+/-3.0% and 52.2+/-1.3%, respectively) using the dose of 4mM MeHg, whereas nonsignificant changes in metabolite levels were observed with the doses of 40 and 400 microM MeHg. A second infusion of 4mM MeHg 24h after first infusion also produced a rise of DA levels, but this increase was very small as compared with that produced by first infusion (7971+/-534% versus 985+/-186%). This second infusion of 4mM MeHg also decreased DOPAC and HVA levels, but this decrease was not significant as compared with that observed after first infusion (65.0+/-3.0% and 52.2+/-1.3% versus 62.4+/-5.2% and 63.4+/-7.4%, respectively). We discuss these effects based on a stimulated DA release and/or a decreased DA intraneuronal degradation.
Asunto(s)
Dopamina/fisiología , Compuestos de Metilmercurio/toxicidad , Neostriado/fisiología , Ácido 3,4-Dihidroxifenilacético/metabolismo , Animales , Cromatografía Líquida de Alta Presión , Dopamina/metabolismo , Espacio Extracelular/efectos de los fármacos , Espacio Extracelular/metabolismo , Femenino , Ácido Homovanílico/metabolismo , Compuestos de Metilmercurio/administración & dosificación , Microdiálisis , Microinyecciones , Neostriado/efectos de los fármacos , Neostriado/metabolismo , Neurotransmisores/metabolismo , Ratas , Ratas Sprague-Dawley , Transmisión Sináptica/efectos de los fármacosRESUMEN
The possible protective effects of NMDA receptor antagonists dizocilpine (MK-801) and D(-)-2-amino-5-phosphonopentanoic acid (AP5), and nitric oxide synthase (NOS) inhibitors L-nitro-arginine methyl ester (L-NAME) and 7-nitro-indazol (7-NI) on the methylmercury (MeHg)-induced dopamine (DA) release from rat striatum were investigated using in vivo microdialysis. Intrastriatal infusion of 400 microM or 4 mM MeHg increased the extracellular DA levels to 1941+/-199 and 7971+/-534% with respect to basal levels. Infusion of 400 microM or 4 mM MeHg in 400 microM MK-801 pretreated animals, increased striatal DA levels to 677+/-126 and 2926+/-254%, with respect to basal levels, these increases being 65 and 63% smaller than those induced by MeHg in non-pretreated animals. Infusion of 400 microM or 4 mM MeHg in 400 microM AP5 pretreated animals, increased striatal DA levels to 950+/-234 and 2251+/-254% with respect to basal levels, these increases being 51 and 72% smaller than those induced by MeHg in non-pretreated animals. Infusion of 400 microM MeHg in 100 microM L-NAME or 7-NI pretreated animals, increased the extracellular DA levels to 1159+/-90 and 981+/-292%, with respect to basal levels, these increases being 40 and 50% smaller than those induced by MeHg in non-pretreated animals. In summary, MeHg acts, at last in part, through an overstimulation of NMDA receptors with possible NO production to induce DA release, and administration of NMDA receptor antagonists and NOS inhibitors protects against MeHg-induced DA release from rat striatum.
Asunto(s)
Dopamina/metabolismo , Inhibidores Enzimáticos/farmacología , Antagonistas de Aminoácidos Excitadores/farmacología , Compuestos de Metilmercurio/farmacología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , 2-Amino-5-fosfonovalerato/farmacología , Animales , Cuerpo Estriado/efectos de los fármacos , Cuerpo Estriado/metabolismo , Maleato de Dizocilpina/farmacología , Dopamina/biosíntesis , Femenino , Óxido Nítrico Sintasa/biosíntesis , Ratas , Ratas Sprague-Dawley , Receptores de N-Metil-D-Aspartato/metabolismoRESUMEN
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.
Asunto(s)
Cuerpo Estriado/metabolismo , Dopamina/metabolismo , Glicoproteínas de Membrana , Compuestos de Metilmercurio/farmacología , Proteínas del Tejido Nervioso , Anfetamina/farmacología , Animales , Calcio/análisis , Cuerpo Estriado/efectos de los fármacos , Medios de Cultivo/química , Medios de Cultivo/farmacología , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática , Inhibidores de Captación de Dopamina/farmacología , Femenino , Soluciones Isotónicas/química , Soluciones Isotónicas/farmacología , Proteínas de Transporte de Membrana/fisiología , Nomifensina/farmacología , Potasio/farmacología , Ratas , Ratas Sprague-Dawley , Reserpina/farmacología , Solución de Ringer , Tetrodotoxina/farmacologíaRESUMEN
The present report describes the activity of NADPH-diaphorase (NADPHd) in area 17 of autopsied normal human visual cortex. Four human brains from autopsy tissue (4-8 h postmortem) were fixed by immersion in 4 per cent paraformaldehyde in 0.1 M sodium phosphate buffer, pH 7.2-7.4, or in 10 per cent formalin for 24 h. NADPHd histochemistry was done using the malic enzyme indirect method. The neurpile pattern of enzyme activity presented a clear six layer appearance. Cell morphology and the laminar distribution of 73 NADPHd-positive neurons are descrived. All neurons found in area 17 of human cortex were sparsely spiny or smooth cells, located in all cortical layers exept layer 4c. Quantitative analysis of the branching pattern of the dendritic tree was carried out. A symmetrical pattern was observed with no particular dendritic bias except for a few white matter and layer 1 cells. Larger dendritic fields were found in white matter cells when compared to the other corical layers. Comparison of cell densities for gray and white matters showed that 85 per cent of the NADPHd-positive neurons were located in the white matter. NADPH was colocalized with nitric oxide synthase which produces nitric oxide, a short-life neuromediator implicated in synaptic plasticity, neuroprotection, and neurotoxicity. thus, the spatial distribution of the NADPHd cells is important for posterior functional studies of the neuromediators in the brain