GM1 ganglioside attenuates convulsions and thiobarbituric acid reactive substances production induced by the intrastriatal injection of methylmalonic acid

The effects of the administration of monosialoganglioside (GM1) on methylmalonic acid (MMA)-induced convulsions, production of thiobarbituric acid reactive substances (TBARS) and on the striatal content of ascorbic acid and total non-protein thiol (SH) groups were evaluated in adult male rats. Animals received two intraperitoneal injections of GM1 (50 mg/kg) or saline (0.85% NaCl) spaced 24h apart. Thirty minutes after the second GM1 or saline injection, L-MMA (6 micromol) or NaCl (9 micromol) was injected into the right striatum and the animals were observed for the appearance of convulsions for 15 min. The animals were sacrificed and their striatal content of ascorbic acid, SH groups and TBARS was measured. The effect of GM1 on MMA-induced TBARS production in striatal homogenates was also evaluated in vitro.MMA injection caused convulsions (Sal-MMA: 9.8+/-1.4 episodes, which lasted 271+/-48 s) and increased the striatal content of TBARS (Sal-MMA: 149.0+/-11.5 nmol MDA/g tissue), but did not alter total striatal SH or ascorbic acid contents. GM1 pretreatment decreased MMA-induced convulsions (GM1-MMA: 6.3+/-2.0 episodes, which lasted 115.1+/-42.2s) and TBARS increase (GM1-MMA: 102.4+/-19.5 nmol MDA/g tissue). GM1 pretreatment increased ascorbic acid content of the striata (saline-pretreated: 1514+/-75.9; GM1-pretreated: 1878.6+/-102.8 microg ascorbic acid/mg tissue). MMA increased TBARS production in vitro, and GM1 had no effect on such MMA-induced effect.This study provides evidence that GM1 increases striatal ascorbic acid content and decreases MMA-induced neurotoxicity assessed by behavioral and neurochemical parameters.     

Alpha-lipoic acid increases insulin sensitivity by activating AMPK in skeletal muscle

Triglyceride accumulation in skeletal muscle contributes to insulin resistance in obesity. We recently showed that alpha-lipoic acid (ALA) reduces body weight and prevents the development of diabetes in diabetes-prone obese rats by reducing triglyceride accumulation in non-adipose tissues. AMP-activated protein kinase (AMPK) is a major regulator of cellular energy metabolism. We examined whether ALA lowers triglyceride accumulation in skeletal muscle by activating AMPK. Alpha2-AMPK activity was decreased in obese rats compared to control rats. Administration of ALA to obese rats increased insulin-stimulated glucose disposal in whole body and in skeletal muscle. ALA also increased fatty acid oxidation and activated AMPK in skeletal muscle. Adenovirus-mediated administration of dominant negative AMPK into skeletal muscle prevented the ALA-induced increases in fatty acid oxidation and insulin-stimulated glucose uptake. These results suggest that ALA-induced improvement of insulin sensitivity is mediated by activation of AMPK and reduced triglyceride accumulation in skeletal muscle.     

Inhibitory effect of ebselen on the oxidation of low density lipoprotein

The inhibitory effect of a synthesized glutathione peroxidase (GSHPX) mimic- ebselen, and its cofactor glutathione (GSH), on the oxidation of low density lipoprotein (LDL) induced by Cu²⁺ was studied by determination of hydroperoxides and thiobarbituric acid reactive substances (TBARS). Ebselen alone had a strong inhibitory effect on the oxidation of LDL. The lag time of LDL oxidation was prolonged with an increase in the concentration of ebselen. The inhibitory effect of 5 μM ebselen was equivalent to that of 50 μM α-tocopherol. When GSH was present, ebselen exhibited stronger inhibitory effect than when present alone. With 50 μM GSH, ebselen at a concentration as low as 5 μM could inhibit oxidation of LDL induced by 5 μM Cu²⁺ completely for at least 24 h. Ebselen at high concentrations (100 μM) decomposed hydroperoxides in pre-oxidized LDL and effectively prevented its further oxidation, but not in the present of EDTA. Low concentration of ebselen (5 μM) plus GSH (50 μM) decomposed hydroperoxides in pre-oxidized LDL whether EDTA was added or not.     

Selective stimulation of serotonin2c receptors blocks the enhancement of striatal and accumbal dopamine release induced by nicotine administration

The effects of acute and repeated nicotine administration on the extracellular levels of dopamine (DA) in the corpus striatum and the nucleus accumbens were studied in conscious, freely moving rats by in vivo microdialysis. Acute intraperitoneal (i.p.) injection of nicotine (1 mg/kg) increased DA outflow both in the corpus striatum and the nucleus accumbens. Repeated daily injection of nicotine (1 mg/kg, i.p.) for 10 consecutive days caused a significant increase in basal DA outflow both in the corpus striatum and the nucleus accumbens. Acute challenge with nicotine (1 mg/kg, i.p.) in animals treated repeatedly with this drug enhanced DA extracellular levels in both brain areas. However, the effect of nicotine was potentiated in the nucleus accumbens, but not in the corpus striatum. To test the hypothesis that stimulation of 5-HT (5-hydroxytryptamine, serotonin)(2C) receptors could affect nicotine-induced DA release, the selective 5-HT(2C) receptor agonist RO 60-0175 was used. Pretreatment with RO 60-0175 (1 and 3 mg/kg, i.p.) dose-dependently prevented the enhancement in DA release elicited by acute nicotine in the corpus striatum, but was devoid of any significant effect in the nucleus accumbens. RO 60-0175 (1 and 3 mg/kg, i.p.) dose-dependently reduced the stimulatory effect on striatal and accumbal DA release induced by an acute challenge with nicotine (1 mg/kg, i.p.) in rats treated repeatedly with this alkaloid. However, only the effect of 3 mg/kg RO 60-0175 reached statistical significance. The inhibitory effect of RO 60-0175 on DA release induced by nicotine in the corpus striatum and the nucleus accumbens was completely prevented by SB 242084 (0.5 mg/kg, i.p.) and SB 243213 (0.5 mg/kg, i.p.), two selective antagonists of 5-HT(2C) receptors. It is concluded that selective activation of 5-HT(2C) receptors can block the stimulatory action of nicotine on central DA function, an effect that might be relevant for the reported antiaddictive properties of RO 60-0175.     

Kaempferol protects against rat striatal degeneration induced by 3-nitropropionic acid

3-Nitropropionic acid (NPA) produces degeneration of striatum and some neurological disturbances characteristic of Huntington's disease in rodents and primates. We have shown that the flavonoid kaempferol largely reduced striatal damage induced by cerebral ischaemia-reperfusion in rats ( Lopez-Sanchez et al. 2007 ). In this work, we report that intraperitoneal (i.p.) administration of kaempferol affords an efficient protection against NPA-induced neurodegeneration in Wistar rats. We studied the effects of daily i.p. injections of 7, 14 and 21 mg of kaempferol/kg body weight during the NPA-treatment (25 mg/kg body weight/12 h i.p., for 5 days) on the neurological deficits, degeneration of rat striatum and oxidative stress markers. Intraperitoneal injections of 14–21 mg of kaempferol/kg body weight largely attenuated motor deficit and delayed mortality. The higher dose of kaempferol prevented the appearance of NPA-induced striatal lesions up to the end of treatment, as revealed by haematoxylin-eosin and TUNEL staining, and also NPA-induced oxidative stress, because it blocked the fall of reduced glutathione and the increase of protein nitrotyrosines in NPA-treated rats. It was found that striatal degeneration was associated with calpains activation and a large inactivation of creatine kinase, which were also prevented when the higher doses of kaempferol were administered.     

L-DOPA does not enhance hydroxyl radical formation in the nigrostriatal dopamine system of rats with a unilateral 6-hydroxydopamine lesion

The debate about the toxicity of L-DOPA to dopaminergic neurons has not been resolved. Even though enzymatic and nonenzymatic metabolism of L-DOPA can produce hydrogen peroxide and oxygen free radicals, there has been controversy as to whether L-DOPA generates an oxidant stress in vivo. This study determined whether acute or repeated administration of L-DOPA caused in vivo production of hydroxyl radicals in striatum and other brain regions in rats with a unilateral 6-hydroxydopamine lesion of the dopaminergic nigrostriatal projections. Salicylate trapping combined with in vivo microdialysis provided measurements of extracellular 2,3-dihydroxybenzoic acid (2,3-DHBA) in striatum following L-DOPA administration systemically (100 mg/kg, i.p.) or by intrastriatal perfusion (1 mM, via the microdialysis probe). Tissue concentrations of 2,3-DHBA and salicylate were also measured in striatum, ventral midbrain, and cerebellum following repeated administration of L-DOPA (50 mg/kg, i.p., once daily for 16 days). In each instance, treatment with L-DOPA did not increase 2,3-DHBA concentrations, regardless of the nigrostriatal dopamine system's integrity. When added to the microdialysis perfusion medium, L-DOPA resulted in a significant decrease in the striatal extracellular concentration of 2,3-DHBA. These results suggest that administration of L-DOPA, even at high doses, does not induce hydroxyl radical formation in vivo and under some conditions may actually diminish hydroxyl radical activity. Furthermore, prior damage to the nigrostriatal dopamine system does not appear to predispose surviving dopaminergic neurons to increased hydroxyl radical formation following L-DOPA administration. Unlike L-DOPA, systemic administration of methamphetamine (10 mg/kg, s.c.) produced a significant increase in the concentration of 2,3-DHBA in striatal dialysate, suggesting that increased formation of hydroxyl radicals may contribute to methamphetamine neurotoxicity.     

Exogenous Choline Enhances the Synthesis of Acetylcholine Only Under Conditions of Increased Cholinergic Neuronal Activity

Abstract: The effect of choline (60 mg/kg, i.p.) on fluphenazine- and pentylenetetrazol-induced alterations in the concentration of acetylcholine (ACh) and/or the rate of sodium-dependent high-affinity choline uptake (HACU) in rat striatum and hippocampus was studied. Systemic administration of the dopamine receptor blocking agent fluphenazine hydrochloride (0.5 mg/kg, i.p.) decreased the concentration of ACh in the striatum; this effect was prevented by the prior administration of choline. The central nervous system stimulant pentylenetetrazol (30 mg/kg, i.p.) reduced the concentration of ACh in both striatum and hippocampus and increased the velocity of HACU in the hippocampus. Pretreatment with choline totally prevented the depletion of ACh induced by pentylenetetrazol in the striatum. In the hippocampus, prior administration of choline prevented the pentylenetetrazol-induced increase in the rate of HACU and attenuated the effect of pentylenetetrazol on the levels of ACh. Results indicate that the acute administration of choline antagonizes pharmacologically induced alterations in cholinergic activity as assessed by the rate of HACU and the steady-state concentration of ACh. Furthermore, data support the hypothesis that the administration of choline increases the ability of central cholinergic neurons to synthesize ACh under conditions of increased neuronal activity.     

Specific oxidative stress profile associated with partial striatal dopaminergic depletion by 6-hydroxydopamine as assessed by a novel multifunctional marker molecule

Abstract

Real time oxidative stress in the extracellular compartment of rat striatum was characterized by microdialysis with synthetic non-dialyzable marker molecules composed of linoleic acid, tyrosine and guanosine (N-linoleoyl tyrosine (LT) and N-linoleoyl tyrosine 2′-deoxyguanosyl ester (LTG)). Partial dopaminergic deafferentation was induced by injection of 6-hydroxydopamine (250 μg) to the left lateral ventricle, which depleted ipsilateral striatal dopamine by 46% and dopaminergic cells in left substantia nigra by 44%, 5 weeks after administration. Resting microdialysate dopamine levels in dopamine-depleted striatum were not different from sham-operated rats, although the ratio of oxidized metabolites of dopamine to free dopamine was significantly increased. Hydroperoxide and epoxy products of the linoleoyl portion of LT and LTG were detected in the striatal microdialysate by LC/MS/MS following initial separation by HPLC and were significantly increased in dopamine-depleted compared with control striatum without an increase in guanosine or tyrosine oxidation or nitration. Systemic administration of N-acetyl cysteine (350 mg/kg i.p.) decreased the increment in hydroperoxide and epoxy metabolites to levels not significantly different from control. Oxidation activity towards polyunsaturated fatty acids is present in the extracellular space of partially dopamine-denervated striatum, whereas oxidized glutathione and oxysterol levels in striatal tissue are decreased, possibly indicative of a compensatory response.     

Endogenous Dopamine Facilitates Striatalln Vivo Acetylcholine Release by Acting on D1 Receptors Localized in the Striatum

Intrastriatal application of the D1 antagonist SCH 23390 by two procedures, reverse dialysis (20 microM) and local injection (0.45 nmol per striatum), elicited a reduction in acetylcholine (ACh) release superimposable on that induced by systemic administration. The novel selective D1 antagonist SCH 39166 produced a similar decreasing effect on striatal ACh release on local injection (0.45 nmol per striatum). On the other hand, local application of SCH 23390 into the frontal cortices (0.45 nmol per side) failed to alter striatal ACh overflow, indicating that the drug does not diffuse out of its injection site to any significant extent. The dopamine release inducer d-amphetamine (2 mg/kg s.c.) and the dopamine uptake inhibitor cocaine raised ACh release like the D1 agonists. These effects were completely blocked by 10 microM SCH 23390 applied by reverse dialysis. The results suggest that D1 receptors regulating ACh release are located in the striatum.     

The nNOS inhibitor,AR-R17477AR,prevents the loss of NF68 immunoreactivity induced by methamphetamine in the mouse striatum

The present study examined the time-course and regionally-selective changes in the levels of the neurofilament protein NF68 in the mouse brain induced by methamphetamine (METH). The ability of low ambient temperature, or of the specific neuronal nitric oxide synthase (nNOS) inhibitor AR-R17477AR, to protect against both long-term striatal NF68 and dopamine loss induced by METH (3 mg/kg, i.p.) was also studied. Seven days after METH administration (3, 6 and 9 mg/kg, i.p., three times at 3 h intervals), mice showed a reduction of about 40% in immunoreactivity for NF68 in the striatum. This effect was not produced in cortex after METH administration at the dose of 3 mg/kg. No difference from controls was observed when measurements were carried out 1 h and 24 h after the last METH injection at the dose of 3 mg/kg. The loss of NF68 immunoreactivity seems to be associated with the long-term dopamine depletion induced by METH, since no change in serotonin concentration is observed in either the striatum or cortex 7 days after dosing. Animals kept at a room temperature of 4 degrees C showed a loss of NF68 similar to those treated at 22 degrees C but an attenuation of dopamine depletion in the striatum. Pre-treatment with AR-R17477AR (5 mg/kg, s.c.) 30 min before each of the three METH (3 mg/kg, i.p.) injections provided complete protection against METH-induced loss of NF68 immunoreactivity and attenuated the decrease in striatal dopamine and HVA concentrations by about 50%. These data indicate that both the reduction of NF68 immunoreactivity and the loss of dopamine concentration are due to an oxidative stress process mediated by reactive nitrogen species, and are not due to changes in body temperature.     

Inhibition of adenylate cyclase activity by 5-aminolevulinic acid in rat and human brain

The effect of the haem precursor 5-aminolevulinic acid (ALA) on the production of cyclic adenosine-monophosphate (cAMP) by rat cerebellar membranes was investigated. It was found that ALA dose-dependently decreased cAMP levels (maximal inhibition of 38%, at 1 mM), due to an inhibition of basal adenylate cyclase activity. ALA also inhibited fluoride- and Gpp(NH)p-stimulated, but not the forskolin-stimulated adenylate cyclase activity. 5-Aminovaleric acid (an inhibitor of GABA(B) receptors) did not prevent the inhibition, indicating that it was not mediated by the activation of the G(i)-protein coupled GABA(B) receptor. In addition, the nucleotide binding site of G-protein appeared not to be affected by ALA since it did not inhibit [3H]Gpp(NH)p binding to our membrane preparation. Antioxidants (glutathione, ascorbate and trolox) completely prevented the inhibition indicating that ALA effect was mediated by an oxidative damage of adenylate cyclase. ALA also inhibited the activity of adenylate cyclase in membranes isolated from rat cortex and striatum and from human cortex. These results may be of value in understanding the neurochemical mechanisms underlying the neurotoxic effects of ALA.     

Characterization and Pharmacological Responsiveness of Dopamine Release Recorded by Microdialysis in the Substantia Nigra of Conscious Rats

The extracellular concentration of dopamine (DA) and 3,4-dihydroxyphenylacetic acid in the substantia nigra (SN) and striatum was estimated by microdialysis. The dialysate content of DA from the SN was recorded during infusion of a DA uptake blocker (nomifensine; 5 mumol/L) dissolved in the perfusion fluid. Perfusion of tetrodotoxin (1 mumol/L) produced a virtually complete disappearance of nigral and striatal DA release. Dendritic as well as terminal release of DA was inhibited for several hours when the nerve impulse flow in dopaminergic neurons was blocked by systemic administration of gamma-butyrolactone (750 mg/kg, i.p.). The systemic administration (0.3 mg/kg, i.p.) as well as infusion (1 mumol/L) of the D2 agonist (-)-N-0437 [2-(n-propyl-N-2-thienylethylamino)-5-hydroxytetralin] produced a significant decrease in the release of DA in both the striatum and the SN. DA levels were recorded in the striatum both with and without addition of nomifensine to the perfusion fluid. The decrease in the striatum after (-)-N-0437 was suppressed in the presence of nomifensine. Infusion (1 mumol/L) as well as systemic administration (40 mg/kg) of sulpiride caused a similar increase in the release of striatal DA; this increase was, in both experiments, potentiated by nomifensine coinfusion. Sulpiride administration induced a small increase in the release of nigral DA. Infusion of (-)-N-0437 or (-)-sulpiride into the nigra caused a moderate decrease and increase, respectively, of striatal DA level.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of δ-aminolevulinic acid synthetase and δ-aminolevulinic acid dehydrase by L-2-amino-4-methoxy-trans-3-butenoic acid in the rat

The rate limiting enzyme of heme biosynthesis, δ-aminolevulinic acid synthetase (ALA synthetase), and the second enzyme in the heme biosynthetic pathway, δ-aminolevulinic acid dehydrase (ALA dehydrase), were inhibited by the olefinic amino acid L-2-amino-4-methoxy - $\text{trans}$-3-butenoic acid (AMTB). Administration of AMTB (20 mg/kg; i.p.) to rats inhibited ALA synthetase and ALA dehydrase in control animals and in animals with markedly elevated activity of ALA synthetase which resulted from the administration of 3,5-dicarbethoxy-1,4-dimethyl-collidine (DDC, 200 mg/kg, i.p.) or allylisopropylacetamide (200 mg/kg, s.c.). AMTB also blocked the synthesis of rat hepatic porphyrins and inhibited the increase in the urinary excretion of δ-aminolevulinic acid and porphobilinogen following DDC (150 mg/kg, p.o.) administration. Preincubation of AMTB with liver mitochondria or a soluble fraction of liver decreased the activity of mitochondrial ALA synthetase and soluble ALA dehydrase, respectively.     

Biochemical effects of pretreatment with vitamins E and C in rats submitted to intrastriatal hypoxanthine administration

We previously demonstrated that intrastriatal injection of hypoxanthine, the major metabolite accumulating in Lesch-Nyhan disease, inhibited Na+,K+-ATPase activity and induced oxidative stress in rat striatum. In the present study, we evaluated the action of vitamins E and C on the biochemical alteration induced by hypoxanthine administration on Na+,K+-ATPase, TBARS, TRAP, as well as on superoxide dismutase (SOD), catalase (CAT) and glutathione-peroxidase (GPx) activities in striatum of adult rats. Animals received pretreatment with vitamins E and C or saline during 7 days. Twelve hours after the last injection of vitamins or saline, animals were divided into two groups: (1) vehicle-injected group and (2) hypoxanthine-injected group. For all parameters investigated in this research, animals were sacrificed 30 min after drug infusion. Results showed that pretreatment with vitamins E and C prevented hypoxanthine-mediated effects on Na+,K+-ATPase, TBARS and antioxidant enzymes (SOD, CAT and GPx) activities; however the reduction on TRAP was not prevented by these vitamins. Although extrapolation of findings from animal experiments to humans is difficult, it is conceivable that these vitamins might serve as an adjuvant therapy in order to avoid progression of striatal damage in patients affected by Lesch-Nyhan disease.     

Rat-1 Fibroblasts Engineered with GAD65 and GAD67 cDNAs in Retroviral Vectors Produce and Release GABA

Abstract: The effects of the adenosine A₁ agonist N ₆-cyclohexyladenosine (CHA) on MPTP-induced dopamine (DA) depletion in the striatum of C57BL/6 mice were studied. Twenty hours after a single injection of MPTP (30 mg/kg, s.c.), the toxin caused 62% depletion of striatal DA. CHA (0.2–3 mg/kg, s.c.), when given together with MPTP, prevented the toxin-induced DA depletion in a dose-dependent manner. This protective action was apparently mediated by the A¹ receptors, because this effect was selectively antagonized by pretreating the animals with the A₁ antagonist 8-cyclopentyl-1,3-dipropylxanthine (25 mg/kg, i.p.) but not with the A₂ antagonist 1,3-dipropyl-7-methylxanthine (25 mg/kg, i.p.). When CHA (3 mg/kg) was injected 5 h after MPTP administration, at which point striatal DA levels were already reduced significantly, a rapid and complete recovery of the striatal DA levels occurred. These neurochemical data suggest that the A₁ agonist CHA is potentially useful as a neuroprotective agent against MPTP-induced toxicity.     

Bilirubin is highly effective in preventing in vivo delta-aminolevulinic acid-induced oxidative cell damage

Delta-aminolevulinic acid (ALA), precursor of heme, accumulates in a number of organs, particularly in liver of patients with acute porphyrias or lead intoxication. This study characterizes the involvement of bilirubin as an antioxidant in a chronic intoxication with ALA. Female Wistar rats were injected intraperitoneally a daily dose of 40 mg ALA/body wt., during 10 days. A marked increase in lipid peroxidation and a decrease in GSH content were observed 24 h after the last injection of ALA. The activities of liver antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase were also diminished. ALA synthase (ALA-S) and heme oxygenase-1 were induced. Both ALA dehydratase (ALA-D) and porphobilinogenase (PBG-ase) activities were inhibited. Administration of bilirubin (5 mmol/kg body wt.) 2 h before ALA treatment entirely prevented the effects of ALA. Co-administration of ALA and Sn-protoporphyrin IX (Sn-PPIX; 100 microg/body wt., i.p.), a potent inhibitor of heme oxygenase, completely abolished its induction and provoked a marked decrease in liver GSH levels as well as an increase in lipid peroxidation. These results add further support to the proposal assigning bilirubin a key protective role against oxidative damage here induced by ALA.     

Cross-tolerance of dopamine metabolism to baclofen, γ-butyrolactone and HA-966 in the striatum and olfactory tubercle of the rat

Rats received 7 daily injections with baclofen (40 mg/kg), GBL (750 mg/kg) or HA-966 (100 mg/kg). Dopamine (DA) was measured in the striatum and olfactory tubercle (OT) of rats, sacrificed 0.5 h or 1 h after the last injection. Marked tolerance and cross-tolerance for the DA-elevating effect of these drugs was seen in the striatum, but not in OT. When on day 7 a unilateral lesion of the nigrostriatal pathway was made, also some tolerance to the DA increase in the striatum on the lesioned side was seen in HA-966-pretreated rats, but it was small compared to the tolerance after an additional drug administration in non-lesioned animals. A low dose of apomorphine (0.25 mg/kg, i.p.) had no effect on DA, dihydroxyphenylacetic acid DOPAC) or homovanillic acid (HVA) levels in the lesioned striata, whether the rats had been pretreated for 6 days with HA-966 or not. However, this dose of apomorphine had a significantly more lowering effect on striatal DOPAC and HVA levels on the unlesioned side of HA-966 pretreated rats. The results show that tolerance develops to the increase of DA synthesis, which is possibly receptor-mediated. This tolerance develops more readily in the striatum than in the olfactory tubercle.     

Treatment with Oxiracetam or Choline Restores Cholinergic Biochemical and Pharmacological Activities in Striata of Decorticated Rats

Interruption of the corticostriatal pathway by undercutting the frontal cortex resulted after 2 weeks in a 40% reduction of basal acetylcholine (ACh) release in vivo, and in inhibition of the striatal sodium-dependent high-affinity uptake of choline (SDHACU) to the same extent. The lesion, too, completely prevented the rise (about 35%) in striatal ACh content induced by oxotremorine and apomorphine acting at muscarine and dopamine receptors, respectively. Acute intraperitoneal injections of 100 mg/kg of either oxiracetam or choline chloride resulted in time-dependent recovery of ACh output from the striata of decorticated rats to control levels. Oxiracetam also normalized the ex vivo striatal SDHACU activity of decorticated rats 2 h after administration without any effect in sham-operated rats. Oxiracetam or choline chloride administered before oxotremorine (0.8 mg/kg, i.p.) or apomorphine (1 mg/kg, i.p.) reinstated the ACh-increasing effect of these agonists. It is suggested that choline chloride acts directly simply by being the precursor for ACh, whereas oxiracetam may act indirectly, possibly by increasing the availability of choline chloride for ACh synthesis. Furthermore, the frontally decorticated rat could constitute a useful model for studying means to restore the deficit in striatal cholinergic neurotransmission.     

Accumulation of protoporphyrin-IX (PpIX) in leukemic cell lines following induction by 5-aminolevulinic acid (ALA)

We investigated the amounts of protoporphyrin IX (PpIX) accumulated in noninduced cells and following 5-aminolevulinic acid (ALA)-induction. Following ALA administration PpIX increased in all leukemic cell lines under investigation (HEL 26-fold, HL60 6-fold, Jurkat 3-fold, ML2 2-fold) but not in lymphocytes. Compared to other cell lines studied, HEL cells showed the lowest basal level of PpIX and the largest relative increase in PpIX. Despite a high increase following ALA treatment, the PpIX level in HEL cells is almost as low as in lymphocytes. It is in agreement with their relatively low sensitivities of ALA-induced photodynamic therapy (ALA-PDT) shown previously [(Grebenová, D., Cajthamlová, H., Bartosová, J., Marinov, J., Klamová, H., Fuchs, O., Hrkal, Z., 1998. Selective destruction of leukemic cells by photo-activation of 5-aminolevulinic acid induced protoporphyrin IX. J. Photochem. Photobiol. B: Biol. 47, 74-81)]. The ferrochelatase activities in the individual cell lines are in good inverse correlation with PpIX amounts accumulated in the ALA-induced cells, but not with the relative increase (ratio) of PpIX levels from basal to ALA-induced ones. This is most apparent in HEL cells and lymphocytes. There is probably different regulation of heme biosynthesis in erythroid cells, which are therefore not suitable for the studies of ALA-PDT mechanism. PpIX was accumulated more extensively in absence of fetal calf serum than in its presence. The amounts of PpIX accumulated in cells decreased exponentially with increasing fetal calf serum concentration.     

Prolonged Alterations in Canine Striatal Dopamine Metabolism Following Subtoxic Doses of l-Methyl-4-Phenyl- 1,2,3,6-Tetrahydropyridine (MPTP) and 4''-Amino-MPTP Are Linked to the Persistence of Pyridinium Metabolites

Single toxic doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).HCl (2.5 mg/kg i.v.) and 4'-amino-MPTP.2HCl (22.5 mg/kg) induce loss of striatal dopamine (DA) and tyrosine hydroxylase (TH) activity and of nigral DA neurons in the dog. To examine the subacute neurochemical changes induced by low doses of MPTP and 4'-amino-MPTP, dose-response studies of these compounds were carried out in the dog, using 6- and 3-week survival times for these two compounds, respectively. Low single doses of MPTP (1.0, 0.5, and 0.1 mg/kg i.v.) and 4'-amino-MPTP (15, 7.5, and 3.75 mg/kg i.v.) did not cause depletion of canine striatal DA or TH or a loss of nigral neurons. However, levels of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were decreased in a dose-related fashion, with significant loss of DOPAC being evident 6 weeks after the lowest administered dose of MPTP and 3 weeks after 4'-amino-MPTP. This selective loss of DA metabolites following nontoxic doses of MPTP and 4'-amino-MPTP led to a shift in the ratio of DA to DOPAC or HVA, which was characteristic for each compound. The measurement of striatal 1-methyl-4-phenylpyridinium (MPP+) and 4'-amino-MPP+ levels revealed that high concentrations (up to 150 microM) persist in the striatum for weeks following administration of a single nontoxic dose of MPTP or 4'-amino-MPTP. A causal relationship between the striatal concentration of MPP+ or 4'-amino-MPP+ and the change in DA metabolism as reflected in the DA/DOPAC ratio is suggested by a significant correlation between these measures. It is suggested that presynaptic sequestration and retention of MPP+ and 4'-amino-MPP+ by striatal DA terminals result in the inhibition of the monoamine oxidase contained within these terminals.