Differential increase in taurine levels by low-dose ethanol in the dorsal and ventral striatum revealed by microdialysis with on-line capillary electrophoresis.

Ethanol increases taurine efflux in the nucleus accumbens or ventral striatum (VS), a dopaminergic terminal region involved in positive reinforcement. However, this has been found only at ethanol doses above 1 g/kg intraperitoneally, which is higher than what most rats will self-administer. We used a sensitive on-line assay of microdialysate content to test whether lower doses of ethanol selectively increase taurine efflux in VS as opposed to other dopaminergic regions not involved in reinforcement (e.g., dorsal striatum; DS). Adult male rats with microdialysis probes in VS or DS were injected with ethanol (0, 0.5, 1, and 2 g/kg intraperitoneally), and the amino acid content of the dialysate was measured every 11 sec using capillary electrophoresis and laser-induced fluorescence detection. In VS, 0.5 g/kg ethanol significantly increased taurine levels by 20% for 10 min. A similar increase was seen after 1 g/kg ethanol, which lasted for about 20 min after injection. A two-phased taurine efflux was observed with the 2.0 g/kg dose, where taurine was increased by 2-fold after 5 min but it remained elevated by 30% for at least 60 min. In contrast, DS exhibited much smaller dose-related increases in taurine. Glycine, glutamate, serine, and gamma-aminobutyric acid were not systematically affected by lower doses of ethanol; however, 2 g/kg slowly decreased these amino acids in both brain regions during the hour after injection. These data implicate a possible role of taurine in the mechanism of action of ethanol in the VS. The high sensitivity and time resolution afforded by capillary electrophoresis and laser-induced fluorescence detection will be useful for detecting subtle changes of neuronally active amino acids levels due to low doses of ethanol.

Dietary taurine manipulations in aged male Fischer 344 rat tissue: taurine concentration, taurine biosynthesis, and oxidative markers.

Taurine (TAU) is a ubiquitous sulfur-containing amino acid that has been proposed to be an antioxidant. The concentration of TAU decreases during aging, which may increase susceptibility to oxidative stress. Our study attempted to elucidate the mechanism for the age-dependent decrease in TAU content by examining TAU biosynthesis in aged rats. We also examined the effects of dietary TAU manipulations on TAU content and oxidative markers in aged male Fischer 344 (F344) rats. Adult (9 months) and aged (26 months) rats fed control diets, aged rats fed control diet and TAU-supplemented (1.5%) water, and aged rats fed a TAU-deficient diet were used. We observed a significant age-related decrease in TAU content in liver, kidney, and cerebellum. Dietary TAU supplementation increased tissue TAU content, whereas dietary TAU restriction had no effect. Enzyme-dependent TAU synthesis showed an age-dependent reduction in liver that was decreased further by TAU supplementation. Protein carbonyl content was elevated in the cerebral cortex and kidney of aged rats and was attenuated by TAU supplementation. A trend for a decrease in protein and acid-soluble thiol contents in hepatic tissue of aged rats was observed, and this was attenuated with dietary TAU supplementation. Our data show that a decrease in hepatic TAU biosynthesis may cause, in part, the observed decline in tissue TAU content in aged F344 rats, and TAU supplementation can restore TAU levels. Our study indicates that a decline in TAU content may exacerbate oxidative stress in aged rats, which can be reversed by dietary TAU supplementation.

Effects of high salt diets and taurine on the development of hypertension in the stroke-prone spontaneously hypertensive rat.

Taurine is present in high concentrations in mammalian tissues and has been implicated in cardiovascular control mechanisms. The aim of the present study was to evaluate the ability of taurine to attenuate salt-induced elevations in blood pressure and markers of damage to the kidney and cardiovascular system in stroke prone spontaneously hypertensive rats (SPSHR). Male SPSHR (6 weeks old) were placed on high salt diets that contained 1% (w/w) NaCl added to their normal chow for 84 days and then were switched to 3% added NaCl for the remaining 63 days of the study. SPSHR was given 1.5% taurine in the drinking water (n = 8), a taurine free diet (n = 8) or normal chow (n = 8). A final control group (n = 6) was not given high salt diets. High salt diets caused an acceleration in the development of hypertension in all groups. Taurine supplementation reduced ventricular hypertrophy and decreased urinary excretion of protein and creatinine. The taurine free diet did not alter serum or urinary excretion of taurine, but did result in elevated urinary nitrogen excretion, increased serum cholesterol levels, and impaired performance in a spatial learning task. Alterations in dietary taurine intake did not alter urinary or serum electrolytes (Na+, K+), but taurine supplementation did attenuate a rise in serum calcium seen with the high salt diets. Urinary excretion (microg/24h) of epinephrine and dopamine was significantly reduced in SPSHR given 1% NaCl in the diet, but this effect was not seen in SPSHR on taurine free or supplemented diets. Taurine supplementation showed cardioprotective and renoprotective effects in SPSHR given high salt diets.

Taurine inhibition of metal-stimulated catecholamine oxidation.

Taurine is an abundant amino acid found in mammalian tissues and it has been suggested to have cytoprotective functions. The aim of the present study was to determine if taurine had the potential to reduce oxidative stress associated with metal-stimulated catecholamine oxidation. Taurine and structural analogs of taurine were tested for their ability to inhibit metal-stimulated quinone formation from dopamine or L-dopa. Oxidative damage to proteins and lipids were also assessed in vitro and the effects of taurine were determined. Taurine (20 mM) was found to decrease significantly ferric iron (50-500 microM)- and manganese (10 microM)-stimulated L-dopa or dopamine oxidation. Taurine had no effect on zinc-induced dopamine oxidation and slightly potentiated copper- and NaIO(4)-stimulated quinone formation. Ferric iron-stimulated lipid peroxidation was not affected by taurine (1-20 mM). Protein carbonyl formation induced by ferric iron (500 microM) and L-dopa (500 microM) was significantly reduced by 10 mM taurine. The cytotoxicity of L-dopa (250 microM) and ferric chloride (75 microM) to LLC-PK(1) cells was attenuated by 10 mM taurine or hypotaurine. Homotaurine alone stimulated L-dopa oxidation and potentiated the cytotoxic effects of ferric iron. Homotaurine was found to be cytotoxic when combined with L-dopa or L-dopa/iron. In contrast, hypotaurine inhibited quinone formation and protected LLC-PK(1) cells. These studies suggest that taurine may exhibit cytoprotective effects against the oxidation products of catecholamines by acting as a scavenger for free radicals and cytotoxic quinones.

Cysteine sulfinate decarboxylase and cysteine dioxygenase activities do not correlate with strain-specific changes in hepatic and cerebellar taurine content in aged rats.

Taurine is a free sulfur-containing amino acid that is found in abundance in mammalian tissues and fluids. Many biological roles have been proposed for this amino acid, including reducing oxidative stress and cytotoxicity. Taurine has previously been reported to decline in tissues during aging which could exacerbate an age-related increase in oxidative stress. The aim of the present study was to elucidate the mechanism responsible for the observed decline in tissue taurine content. We measured the activity of the major taurine biosynthetic enzymes, cysteine sulfinate decarboxylase and cysteine dioxygenase, in liver and cerebellar tissues of rats. Tissues from male adult and aged Fischer 344 (F344; 10 and 28 months), Sprague-Dawley (SD; 5, 20 and 25 months), and F344/Brown-Norway hybrid (FBNF1; 14 and 33.5 months) rats were used. We observed a significant decline in hepatic taurine content of the F344 animals but the decline in the liver of SD and FBNF1 animals was non-significant. Hepatic cysteine sulfinate decarboxylase and cysteine dioxygenase activities were significantly lower in aged F344 rats but not in the other strains. Cerebellar taurine content was significantly lower in aged F344 and SD rats without a concomitant decline in cysteine sulfinate decarboxylase activity. These results suggest that a decline in hepatic de novo taurine biosynthesis might be partially responsible for a reduction in tissue taurine content in F344 rats.

Kainic acid (KA)-induced seizures in Sprague-Dawley rats and the effect of dietary taurine (TAU) supplementation or deficiency.

Male Sprague-Dawley rats received TAU supplementation (1.5% in drinking water) or TAU deficient diets for 4 weeks to test for a possible neuroprotective role of TAU in KA-induced (10 mg/kg s.c.) seizures. TAU supplementation significantly increased serum and hippocampal TAU levels, but not TAU content in temporal cortex or striatum. TAU deficient diets did not attenuate serum or tissue TAU levels. Dietary TAU supplementation failed to decrease the number or latency of partial or clonic-tonic seizures or wet dog shakes, whereas a TAU deficient diet decreased the number of clonictonic and partial seizures. This study does not support previous observations of an anticonvulsant effect of TAU against KA-induced seizures. KA-treatment decreased alpha 2-adrenergic receptor binding sites and TAU content in the temporal cortex across all dietary treatment groups, supporting previous evidence of severe KA-induced damage and neuronal loss in this brain region.

Effects of dietary taurine supplementation or deprivation in aged male Fischer 344 rats.

Taurine is a sulfur amino acid that is present in high concentration in mammalian tissues and previously has been reported to decline in a number of tissues with advancing age. The aims of the present study were to examine: (1) the effects of dietary taurine supplementation; (2) the effects of taurine-free diets; (3) the ability of aged rats to conserve urinary taurine; and (4) the consequences of these dietary manipulations on some biochemical parameters. Male F344 rats (n = 30/group) 18 months of age were placed on control diets, diets supplemented with 1.5% taurine in the drinking water, or a taurine-free diet for 10 months. An adult control group (12 months old at the end of the study) on normal diets was included for comparison purposes. Significant (P < 0.05) age-related declines in taurine content were observed in the spleen, kidney, eye, cerebellum and serum. Taurine supplementation corrected these deficits in tissue content in aged rats and in many cases increased taurine content above that of adult controls. Urinary excretion of taurine was significantly (P < 0.05) reduced in aged rats indicating an increased need to conserve taurine. Taurine-deficient diets did not further exacerbate the age-related decline in tissue taurine content, suggesting biosynthetic adaptations to the lack of dietary taurine. Dietary taurine supplementation blunted age-related declines in serum IGF-1 and increases in serum creatinine and blood urinary nitrogen (BUN). These studies suggest that advanced aging results in a taurine-deficient state that can be corrected by dietary supplementation.

Neurochemical and neurobehavioral effects of neonatal administration of beta-N-methylamino-L-alanine and 3,3'-iminodipropionitrile.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that is characterized by a loss of motor neurons in the spinal cord, brain stem, and cortex. The present study examined the neurochemical and neurobehavioral consequences of the neonatal administration of IDPN and BMAA, two neurotoxins previously considered as experimental models of ALS. Sprague-Dawley rat pups (male and female) were injected SC with IDPN or BMAA. The following treatment groups (n = 5-14 per group) were studied; IDPN [100 mg/kg on postnatal days (PNDs) 2, 4, and 6], BMAA-A (500 mg/kg PND 5 only), BMAA-B (500 mg/kg PND 2 and 5), and BMAA-C (100 mg/kg PND 2 and 5). Neurobehavioral testing was performed and the rats were sacrificed at 101 days of age. Monoamine and amino acid content was measured by HPLC in brain regions and the spinal cord. IDPN treatment impaired the righting reflex and decreased forepaw suspension times. BMAA-A and BMAA-B males exhibited an increase in open field behavior. The hindlimb splay of BMAA-A females was increased. Other significant behavioral and endocrine effects were also seen with neonatal IDPN or BMAA treatment. IDPN females had increased spinal cord content of norepinephrine (NE), serotonin, and 5-hydroxyindoleacetic acid (5-HIAA). IDPN males had no alterations in spinal cord content of NE or Glu, but serotonin and 5-HIAA content were increased. BMAA-A and BMAA-B males also had elevated spinal cord 5-HIAA content whereas females were unaffected. Glu and Asp content in the spinal cord was elevated in the female BMAA-C group. Monoamines were also altered in the cerebellum, mediobasal hypothalamus, and hippocampus by IDPN and BMAA treatment. alpha 2-Adrenergic binding sites were increased in the spinal cord by IDPN and in the cerebellum by BMAA treatment. The results of this study clearly demonstrated that both IDPN and BMAA given neonatally can produce changes in motor function and spinal cord neurochemistry, although the pattern of the effects is both treatment and sex dependent. Neonatal exposure to either IDPN or BMAA resulted in permanent changes in adult neurochemistry that may be related to reorganizational effects induced by toxin-mediated neuroplasticity in developing neurons.

Effects of chronic ethanol exposure on GABA receptors and GABAB receptor modulation of 3H-GABA release in the hippocampus.

Chronic ethanol treatment (CET), sufficient for decreasing long-term potentiation (LTP) in rats, also enhances 3H-GABA release from hippocampal slices in these same animals. The mechanism for an increase in GABA release may involve changes in presynaptic receptors. Therefore, we characterized presynaptic autoreceptor modulation of 3H-GABA release in hippocampal slices from control and CET rats. The effects of a GABAB receptor agonist (baclofen) and antagonist [2-hydroxy (OH)-saclofen] were tested for their ability to modulate electrically stimulated 3H-GABA release from superfused hippocampal slices. Baclofen decreased stimulated release in a dose-dependent manner and 2-OH-saclofen increased release consistent with the existence of presynaptic GABAB autoreceptors in hippocampus. The GABAA antagonist bicuculline did not significantly modulate basal or stimulated release. When the effects of baclofen and 2-OH-saclofen were measured in animals 48 hr after withdrawal from CET, presynaptic modulation of release by baclofen and 2-OH-saclofen was decreased. In addition, we examined the density of 3H-baclofen and 3H-bicuculline binding in the hippocampal formation using quantitative autoradiographic techniques. We found that the density of 3H-baclofen binding sites was not affected by CET, whereas the density of 3H-bicuculline binding sites was increased by 28% in ethanol-treated rats. These data may explain how CET increases presynaptic regulation of GABA release from hippocampus that may contribute to the decrease in LTP seen in rats after CET.

Attenuation of leptin-mediated effects by monosodium glutamate-induced arcuate nucleus damage.

Leptin is a protein secreted by adipocytes that is important in regulating appetite and adiposity. Recent studies have suggested the presence of leptin receptors in the arcuate nucleus of the hypothalamus (ANH). Neonatal administration of monosodium glutamate (MSG) damages the ANH, resulting in obesity and neuroendocrine dysfunction. Neonatal administration of MSG was utilized to test the hypothesis that the anatomic site for many of leptin's actions is the ANH. Female control (n = 6) and MSG-treated rats (n = 7) were implanted for 14 days with osmotic minipumps containing phosphate-buffered saline or leptin (1 mg.kg-1.day-1). Leptin suppressed (P < 0.05) body weight gain in controls but did not suppress weight gain in MSG-treated rats. Leptin decreased (P < 0.05) fat depots in controls but had no effect in MSG-treated rats. Night feeding was suppressed (P < 0.05) in leptin-treated control rats. MSG-treated rats showed a suppression in food intake that was of a smaller magnitude and appeared later in the course of leptin treatment. These findings suggest that leptin mediates some physiological actions related to fat mobilization via receptors located in the ANH.

Attenuation of trimethyltin-evoked glutamate (GLU) efflux from rat cortical and hippocampal slices.

Trimethyltin (TMT) is a toxic alkyltin that produces neuronal necrosis in the CNS. TMT stimulates the efflux of the excitatory amino acid glutamate (GLU) from rat cortical slices. This release is concentration dependent, partially calcium dependent, but not inhibited by calcium channel blockers or a NMDA antagonist. In the present study the compounds furosemide, bumetanide, 4,4'-diisothiocy-anatostilbene-2,2'-disulfonic acid (DIDS), and DL-threo-beta-hydroxyaspartic acid (HAA) were tested for their ability to attenuate TMT-stimulated GLU efflux from rat cortical and hippocampal slices. Furosemide (1 mM) reduced the TMT-induced GLU efflux in cortical slices and hippocampal slices, but bumetanide (0.1 mM) had no effect on TMT-induced GLU efflux. DIDS (1 mM) demonstrated a trend toward decreasing GLU efflux from TMT stimulation in both the cortex and hippocampus, but this reduction was not significant. However, DIDS was able to prevent the decrease in intracellular GLU content produced by TMT in both the cortical and hippocampal slices. HAA (1 mM) increased the net GLU efflux in both cortical slices and hippocampal slices, and produced a significant depletion of the glutamate content of the slices. Taurine efflux was stimulated by TMT treatment but was not blocked by the chloride transport inhibitors. These data suggest that cell swelling-induced release of GLU may not be directly involved in TMT-induced GLU efflux, and that TMT does not appear to elicit GLU efflux by a mechanism involving reversal of the GLU transporter.

Endogenous excitatory amino acid release from brain slices and astrocyte cultures evoked by trimethyltin and other neurotoxic agents.

Trimethyltin (TMT) is a toxic alkyltin compound that is known to produce neuronal necrosis in the CNS. The present study examined the effects of TMT on the release of excitatory amino acids (EAA) from cortical slices prepared from adult and aged (24 months old) rats. The calcium dependence of TMT-induced EAA efflux was evaluated and compared to other neurotoxic agents. The actions of TMT were also evaluated in an astrocyte culture model to assess glial contributions to TMT-induced EAA efflux. TMT (10-1000 microM) evoked a dose-related increase in GLU and ASP efflux during a 30 min incubation period and this efflux was sustained or slightly higher during a 15 min recovery period. TMT-stimulated GLU efflux was not altered in aged rats. TMT-induced GLU efflux was significantly reduced by removing extracellular calcium and including 10 microM EGTA in the incubation media. Calcium channel blockers (nifedipine, verapamil, flunarizine, amiloride, neomycin) and MK-801 did not significantly attenuate TMT-induced GLU efflux. Diltiazem (25 microM) produced modest but inconsistent reductions in TMT-induced GLU efflux from brain slices, and significantly inhibited the leakage of lactate dehydrogenase (LDH) from TMT-treated astrocyte cultures. TMT did not increase GLU efflux from glial cultures during a 30 min incubation period, but did significantly elevate GLU efflux during the 15 min recovery period. TMT evoked the release of EAA by both calcium dependent and independent mechanisms in brain slices. TMT at high concentrations also produced a delayed increase in glial GLU efflux. These studies suggest that excitotoxic mechanisms may contribute to TMT-induced neurotoxicity.