Spatial discrimination learning and choline acetyltransferase activity in streptozotocin-treated rats: effects of chronic treatment with acetyl-l-carnitine

Treatment of rats with i.c.v. injected streptozotocin (STREP) may provide a relevant model of neurodegeneration that is induced by a decrease in the central metabolism of glucose. Acetyl-l-carnitine (ALCAR) enhances the utilization of alternative energy sources and by such a mechanism of action ALCAR could antagonize the effects of STREP treatment. In this study the effects of chronic treatment with ALCAR were evaluated on spatial discrimination learning in the Morris task and choline acetyltransferase (ChAT) activity of middle-aged STREP-treated rats. Chronic treatment with ALCAR attenuated both the STREP-induced impairment in spatial bias and the decrease in hippocampal ChAT activity. These findings indicate that ALCAR treatment has a neuroprotective effect, although further studies are needed to characterize the mechanism of action of ALCAR in this model.     

Effects of Central Injection of Kyotorphin and l-Arginine on Oxytocin and Vasopressin Release and Blood Pressure in Conscious Rats

Intracerebroventricular (ICV) administration of an inhibitor of nitric oxide synthase (NOS) increases oxytocin but not vasopressin secretion, in dehydrated rats [38]. Surprisingly, central injection of l-arginine, the substrate for NOS, caused a similar effect. Kyotorphin (l-tyrosyl-l-arginine), a dipeptide formed from l-arginine by kyotorphin synthetase in the brain may mediate this magnocellular response. Therefore, the dose and time responses of hormone release were compared following ICV injection of kyotorphin and l-arginine to conscious rats that were normally hydrated or deprived of water for 24 h. In water-sated rats, both l-arginine and kyotorphin increased blood pressure and plasma glucose levels coincident with elevating circulating levels of oxytocin, but not vasopressin. In dehydrated animals, both l-arginine and kyotorphin increased plasma oxytocin levels with a similar time course but only kyotorphin decreased vasopressin release. d-arginine, like l-arginine, stimulated secretion of oxytocin, indicating a nonstereospecific effect. A kyotorphin receptor antagonist (l-leucyl-l-arginine) given ICV to dehydrated animals elevated plasma oxytocin and prevented the decrease in vasopressin levels after kyotorphin. Thus, kyotorphin, but not l-arginine, appears to attenuate release of vasopressin either directly from magnocellular neurons or indirectly via modulating compensatory reflexes activated by the pressor response. On the other hand, an excess of l-arginine and kyotorphin within the CNS may mimic the stress response by augmenting release of oxytocin and activating the sympathetic nervous system to increase blood pressure and plasma glucose levels.     

Higher free D-aspartate and N-methyl-D-aspartate levels prevent striatal depotentiation and anticipate L-DOPA-induced dyskinesia

In Parkinson's disease (PD) progressive alteration of striatal N-methyl-d-aspartate receptors (NMDARs) signaling has emerged as a considerable factor for the onset of the adverse motor effects of long-term levodopa (l-DOPA) treatment. In this regard, the NMDAR channel blocker amantadine is so far the only drug available for clinical use that attenuates l-DOPA-induced dyskinesia (LID). In this study, we examined the influence of a basal corticostriatal hyper-glutamatergic transmission in the appearance of dyskinesia, using a genetic mouse model lacking d-Aspartate Oxidase (DDO) enzyme (Ddo^−/− mice). We found that, in Ddo^−/− mice, non-physiological, high levels of the endogenous free d-amino acids d-aspartate (d-Asp) and NMDA, known to stimulate NMDAR transmission, resulted in the loss of corticostriatal synaptic depotentiation and precocious expression of LID. Interestingly, the block of depotentiation precedes any change in dopaminergic transmission associated to 6-OHDA lesion and l-DOPA treatment. Indeed, lesioned mutant mice display physiological l-DOPA-dependent enhancement of striatal D1 receptor/PKA/protein phosphatase-1 and ERK signaling. Moreover, in line with synaptic rearrangements of NMDAR subunits occurring in dyskinetic animal models, a short l-DOPA treatment produces a dramatic and selective reduction of the NR2B subunit in the striatal post-synaptic fraction of Ddo^−/− lesioned mutants but not in controls. These data indicate that a preexisting hyper-glutamatergic tone at NMDARs in Ddo^−/− mice produce abnormal striatal synaptic changes that, in turn, facilitate the onset of LID.     

The effect of acetyl-L-carnitine administration on persons with Down syndrome

Since previous investigations reported improvements in cognition of patients with dementia after acetyl-L-carnitine therapy and since there is an increased risk for persons with Down syndrome to develop Alzheimer disease, this study was designed to investigate the effect of acetyl-L-carnitine administration on neurological, intellectual, and social functions in adults with Down syndrome. In this double-blind study we enrolled 40 individuals with Down syndrome and administered acetyl-L-carnitine to the study group during a six months period. Specified examinations and psychological tests were given to persons in both the study and control groups at the start of the investigation and at 3, 6, and 9 months. A detailed analysis of the data revealed that acetyl-L-carnitine administration did not enhance central nervous system functions and that it did not benefit persons with Down syndrome.     

Inhibition of nitric oxide synthase dramatically potentiates seizures induced by kainic acid and pilocarpine in rats

We investigated whether the severity of convulsions evoked by kainic acid and pilocarpine is modified in nitric oxide synthase inhibitor-treated rats. We found that chronic treatment (4 days) withN_w-nitro-l-arginine greatly potentiates seizures induced by both convulsants suggesting a potential role for nitric oxide in mechanisms regulating seizure induction and propagation.     

Increased neuronal nitric oxide synthase expression in brain following portacaval anastomosis

It has previously been suggested that increases of l-arginine uptake into brain following portacaval shunting may result in increased activities of constitutive neuronal nitric oxide synthase (nNOS). In order to further address this issue, nNOS protein and gene expression were studied by Western blot analysis using a monoclonal nNOS antibody and RT-PCR respectively in the brains of rats following portacaval shunting or sham operation. Portacaval shunting resulted in a 2-fold increase (P<0.01) in nNOS protein and a concomitant 2.4-fold increase (P<0.01) in nNOS mRNA. Increased nNOS activity in brain and the resulting increase in nitric oxide production could contribute to the increased cerebral blood flow and to the pathogenesis of hepatic encephalopathy in chronic liver disease.     

Chronic administration of l-NAME in drinking water alters working memory in rats

To examine the role of nitric oxide (NO) in the maintenance of working memory of rats, the effects of chronic administration (in drinking water) of the NO synthase inhibitor, N^w-nitro-l-arginine methyl ester (l-NAME), on this behavior was examined with a simple test of remembering recently explored objects. Unlike other working memory tasks that require a subject to perform for a reward such as food or water or to avoid shock, our task measured spontaneous exploration of novel and familiar objects and has been described as a “pure” working memory task [9]. Normal subjects spend significantly more time in contact with new environmental components and less time with familiar objects. A subject that extensively reexplores a stimulus with which it has previous experience is presumed to exhibit some memory loss associated with the object. Memory changes were evaluated by measuring the relative time subjects explored familiar versus new stimulus objects. Rats (n = 15) that chronically drank l-NAME (≈ 90 mg/kg/day) for 14 days spent significantly less time exploring a novel object than did rats (n = 13) that drank only tap water (p < .05). This effect of t.-NAME was abolished by concurrent administration of l-Arginine (≈ 4.5 g/kg/day). Total object exploration was not affected by our drug treatments, suggesting that our object discrimination task is not activity dependent. These data are consistent with the hypothesis that NO is required for some forms of working memory.     

Acute autonomic and sensory neuropathy: a case report

Summary A female patient with acute autonomic and sensory neuropathy is described. Urinary disturbance developed rapidly and was followed by orthostatic syncope, absence of lacrimation, salivation and sweating, and sensory impairment. Muscle strength had been consistently normal despite diffuse muscular atrophy. Marked decrease in the number of small myelinated and unmyelinated fibres was revealed in biopsied sural nerve. Eighteen months after the onset, her autonomic symptoms have partially improved.     

l-DOPA metabolism in cortical and striatal tissues in an animal model of Parkinsonism

Rats with unilateral 6-hydroxydopamine lesions of the midbrain tegmentum were treated with 25 mg/kg l-DOPA methyl ester/2 mg/kg carbidopa. The effects of the l-DOPA treatment upon serum, neocortical, and striatal l-DOPA and 3-O-methyl dopa (3-OMD) concentrations were measured. The highest l-DOPA and 3-OMD concentrations were obtained in the serum and in a ratio of approximately 2:1. In the brain, there was a uniform distribution of 3-OMD but l-DOPA concentrations were highly nonhomogeneous. Regression line equations for the statistically significant correlation coefficients between l-DOPA and tissue dopamine concentrations suggested that l-DOPA generated 50–60 times as much dopamine in the intact striatum as in cortex. The regional variation of l-DOPA concentration appears related to the capability of the brain tissue to generate and store dopamine from l-DOPA. In addition, the findings suggest that the behavioral ineffectiveness of l-DOPA in intact animals is related to its capacity to transform l-DOPA to tissue bound dopamine.     

l-Arginine ameliorates cerebral blood flow and metabolism and decreases infarct volume in rats with cerebral ischemia

Effects ofl-arginine, 300 mg/kg, i.p., on the regional cerebral blood flow (rCBF), brain metabolism, and infarct volume were examined in spontaneously hypertensive rats subjected to occlusion of both left middle cerebral artery and left common carotid artery. Rats treated withl-arginine had higher rCBF, determined by hydrogen clearance method, in the ischemic core (7 ± 1 ml/100 g/min, mean ± S.E.M.) and penumbral regions (16 ± 2) than did rats treated with saline (5 ± 0 and 7 ± 1, respectively). Simultaneously,l-arginine attenuated metabolic derangement in the ischemic tissue at 60 min, i.e. well maintained adenosine triphosphate (ATP) in ischemic region (1.29 ± 0.07 mmol/kg inl-arginine group vs. 1.05 ± 0.06 in saline group), and also close to normal levels in ATP (2.61 ± 0.02 mmol/kg vs. 2.45 ± 0.05), glucose (2.29 ± 0.12 mmol/kg vs. 1.80 ± 0.17) and lactate (1.63 ± 0.10 mmol/kg vs. 2.24 ± 0.21) in periischemic region. In another experiment, the effects ofl-arginine on rCBF in the subcortical regions and on infarct volume were evaluated.l-arginine, compared with saline, increased rCBF by 8 ml/100 g/min in the ischemic side and reduced infarct volume by 29% at 24 h of ischemia. These findings support thatl-arginine may be potentially useful for the treatment of acute cerebral ischemia.     

Aromatic L-amino acid decarboxylase is present in serotonergic fibers of the striatum of the rat. A double-labeling immunofluorescence study

The aim of the present study is to examine whether serotonergic fibers of the striatum of the rat contain aromaticl-amino acid decar?ylase (AADC). By use of a double-labeling immunofluorescence method, we showed that AADC was localized in serotonergic fibers of the striatum and cerebral cortex as well as in serotonergic cell bodies of the midbrain raphe nuclei. We previously demonstrated that serotonergic fibers of the rat striatum contained dopamine after intraperitoneal injection ofl-dopa. These findings suggest that dopamine is produced from the injectedl-dopa in serotonergic fibers of the rat striatum.     

Neurotoxicity, Blood-Brain Barrier Breakdown, Demyelination and Remyelination Associated With NMDA-Induced Lesions of the Rat Lateral Hypothalamus

Excitotoxins have been widely used to make lesions in the brains of experimental animals because they have the ability to destroy neurones while sparing fibres of passage. Because loss of fibres of passage can confound the interpretation of lesion effects, this property is of considerable value. Recently, however, there have been reports indicating that excitotoxins acting at different sites within the rat CNS not only destroy neurones but also strip myelin from fibres and compromise the integrity of the blood-brain barrier. However, some reports also indicate that the myelin content of the lesioned area recovers. Excitotoxic lesions of the lateral hypothalamus have been shown to produce local demyelination. The present studies sought to investigate this effect further by (1) defining the time course of demyelination and possible remyelination after excitotoxic lesions of the lateral hypothalamus made with n-methyl-d-aspartate (NMDA); (2) establishing the relationships between neuronal loss, de- and remyelination after various doses of NMDA; and (3) examining the integrity of the blood-brain barrier using an immunohistochemical probe. Our data show that after injection of NMDA into the lateral hypothalamus there was neuronal loss, blood-brain barrier disruption (followed by recovery over approximately 12 days), triggering of reactive gliosis, invasion of the lesioned area by cells from outwith the CNS, demyelination over an area coexistent with but not exceeding the area of neuronal loss, and remyelination. Remyelination occurred over a period of 3 months following the production of the lesion and was associated initially with blood vessels. It occurred across the whole of the lesioned area, not by encroachment from the borders. All doses of NMDA that produced neuronal death also produced demyelination. These data confirm that excitotoxic lesions of the lateral hypothalamus demyelinate fibres, but show for the first time that remyelination occurs here. They are consistent with reports concerning excitotoxin actions at other CNS sites and indicate that de- and remyelination after excitotoxic lesions is a ubiquitous process. Consideration should be given to this when using excitotoxins to make fibre-sparing lesions.     

Effects of Dietary Supplementation with N-Acetyl Cysteine, Acetyl-l-Carnitine and S-Adenosyl Methionine on Cognitive Performance and Aggression in Normal Mice and Mice Expressing Human ApoE4

In addition to cognitive impairment, behavioral changes such as aggressive behavior, depression, and psychosis accompany Alzheimer’s Disease. Such symptoms may arise due to imbalances in neurotransmitters rather than overt neurodegeneration. Herein, we demonstrate that combined administration of N-acetyl cysteine (an antioxidant and glutathione precursor that protects against Abeta neurotoxicity), acetyl-l-carnitine (which raises ATP levels, protects mitochondria, and buffers Abeta neurotoxicity), and S-adenosylmethionine (which facilitates glutathione usage and maintains acetylcholine levels) enhanced or maintain cognitive function, and attenuated or prevented aggression, in mouse models of aging and neurodegeneration. Enhancement of cognitive function was rapidly reversed upon withdrawal of the formulation and restored following additional rounds supplementation. Behavioral abnormalities correlated with a decline in acetylcholine, which was also prevented by this nutriceutical combination, suggesting that neurotransmitter imbalance may contribute to their manifestation. Treatment with this nutriceutical combination was able to compensate for lack of dietary folate and vitamin E, coupled with administration of dietary iron as a pro-oxidant (which collectively increase homocysteine and oxidative damage to brain tissue), indicating that it provided antioxidant neuroprotection. Maintenance of neurotransmitter levels and prevention of oxidative damage underscore the efficacy of a therapeutic approach that utilizes a combination of neuroprotective agents. An erratum to this article can be found at     

Correlation between the Movement Disorders Society Unified Parkinson's Disease rating scale (MDS-UPDRS) and the Unified Parkinson's Disease rating scale (UPDRS) during L-dopa acute challenge

While Movement Disorders Society Unified Parkinson’s Disease rating scale (MDS-UPDRS) validation has been exhaustive; performance evaluation to detect acute changes arising after administration of a single dose of l-dopa has yet to be explored. To determine the correlation between UPDRS and MDS-UPDRS during the acute challenge with ldopa and the MDS-UPDRS equivalent to 30% cutoff score of UPDRS for defining responsiveness, 64 patients were assessed. Consecutive assessments were performed immediately before and after administration of a single dose of l-dopa/carbidopa 250/25 mg using the motor section of the UPDRS and the MDS-UPDRS. Good diagnostic accuracy, consistent with published findings of high correlation between scales was observed. Area under the curve (AUC) was 0.99 (CI = 0.97–1.00, P < 0.001) and maximum Youden index (Y = 0.905) corresponded to a cutoff of 24.5%. In conclusion we have found an excellent correlation between UPDRS and MDS-UPDRS and that the 30% of variation in UPDRS score used for predicting sustained long term l-dopa response was equivalent to 24% in MDS-UPDRS.     

Differential effects of NMDA and non-NMDA antagonists on the activity of aromatic l-amino acid decarboxylase activity in the nigrostriatal dopamine pathway of the rat

This study examined the acute effects of a variety of NMDA and non-NMDA antagonists on the activity of aromatic l-amino acid decarboxylase (AADC) in the corpus striatum (CS) and substantia nigra (SN) of the rat. Sixty min pretreatment with the high affinity NMDA receptor-channel blockers MK 801 (0.01, 0.1 and 1 mg/kg) and phencyclidine (4 mg/kg) elevated AADC activity in both the CS and SN (2- to 3-fold). Even more striking increases in AADC were noted with 40 mg/kg amantadine (3.8-fold for CS, 9.0-fold for SN), 40 mg/kg memantine (3.4-fold for CS, 3.1-fold for SN; 20 mg/kg no effect) and 40 mg/kg dextromethorphan (3.4-fold for CS, 6.2-fold for SN, in 6/10 `responders'). Similarly pronounced increases in AADC activity in CS (1.9-fold) and SN (2.8-fold) were detected after administering clonidine (2 mg/kg). R-HA 966 (5 mg/kg, not 1 mg/kg) modestly raised AADC activity in CS (0.45-fold) and not SN. Other drugs had no effect on the activity of the decarboxylase enzyme, including CGP 40116 (1 and 5 mg/g), eliprodil (10 mg/kg), NBQX (10 mg/kg, 30 min pretreatment) and atropine (1 mg/kg). These experiments indicate that blocking the NMDA receptor-channel (and to a lesser extent the glycine site) or stimulating α₂-adrenoceptors, profoundly increases AADC activity, more especially in the SN than CS. By contrast, inhibiting the NMDA glutamate recognition or polyamine sites, AMPA or muscarinic receptors is without effect on AADC in either brain region. The ability of amantadine and memantine to potentiate the antiparkinsonian actions of l-DOPA in the clinic, may be due to facilitated decarboxylation of l-DOPA by the brain.     

Exogenousl-5-hydroxytryptophan is decarboxylated in neurons of the substantia nigra pars compacta and locus coeruleus of the rat

The aim of the present study is to examine by immunohistochemistry whether exogenousl-5-hydroxytryptophan (l-5HTP) is decarboxylated in neurons of the substantia nigra pars compacta (SNC) and locus coeruleus (LC) of the rat. In normal rats, neurons of the SNC and LC stained intensely for aromaticl-amino acid decarboxylase (AADC). No serotonin (5HT)-positive cells were found in the two regions of the normal rats. In rats that were intraperitoneally injected withl-5HTP alone, the SNC neurons stained deeply for 5HT, but the LC neurons showed only a faint staining for 5HT. In rats that intraperitoneally received both a monoamine oxidase (MAO) inhibitor andl-5HTP, when compared with thel-5HTP-injected rats, the LC neurons became much darker in 5HT staining, but the SNC neurons showed only a slight increase in 5HT staining. The present findings suggest that (i) AADC in dopaminergic neurons of the SNC and in noradrenergic neurons of the LC can catalyze the in vivo decarboxylation of exogenousl-5HTP to produce 5HT, and (ii) most of the newly produced 5HT in the LC neurons is rapidly degraded by endogenous MAO.     

Behavioral symptoms in adult rats after postnatal l-nitro-arginine

We addressed experimentally the suggestion by Gally et al. [Gaily J. A., Read Montague P., Reeke G. N. Jr and Edelman G. M. (1990) Proc. Natl Acad. Sci. U.S.A.87, 3547–3551] that nitric oxide may play a role in the use-dependent modification of synaptic efficacy in the developing nervous system. In a preliminary control experiment, we treated rat pups from postnatal day 8 to postnatal day 22 with a nitric oxide synthase blocker (l-nitro-arginine) and compared their growth curves and brain weights to those of saline injected control pubs. No significant differences were found after the 14 days of nitric oxide synthase inhibition. In the subsequent experiment, we inhibited nitric oxide synthesis in rat pups from postnatal day 8 to day 29 and assessed their place learning ability and open field behavior as adults. We found an increased speed of habituation of locomotion in an open field in 5-month-old rats that had been treated postnatally with a nitric oxide synthase blocker. There was no difference between treated and nontreated rats with respect to place learning in a water maze. We conclude that perturbation of nitric oxide production during early postnatal development does not preclude normal learning and memory function in the adult.     

Neurotoxicity of monosodium-l-glutamate in pregnant and fetal rats

Summary Monosodium-l-glutamate given subcutaneously to pregnant rats caused acute necrosis of the acetylcholinesterase-positive neurons in the area postrema. The same effect has been observed in the area postrema of fetal rats. The process of neuronal cell death and the elimination of debris by microglia cells proved to be similar in pregnant animals and in their fetuses. However, embryonal neurons were more sensitive to glutamate as judged by the rapidity of the process and the dose-response relationship. These observations raise the possibility of transplacental poisoning in human fetuses after the consumption of glutamate-rich food by the mother.Dedicated to Prof. T. H. Schiebler, Würzburg on the occasion of his 65th birthday     

Trihexyphenidyl Potentiation ofl-DOPA: Reduced Effectiveness Three Years Later in MPTP-Induced Chronic Hemiparkinsonian Monkeys

The effects of a combination of trihexyphenidyl andl-DOPA methyl ester given i.m. were studied 3–5 years after MPTP induced hemiparkinsonism in five female adultMacaca nemistrinamonkeys. Three years later, these studies were repeated to determine if the drug combination was equally effective. Although the combination of trihexyphenidyl andl-DOPA produced potentiation in both studies, 3 years later it was quantitatively less. This was due primarily to the reduced effectiveness ofl-DOPA methyl ester in a dose of 12.5 mg/kg i.m. Even though the combination was less effective in subsequent years, the animals continued to show the same clinical signs of hemiparkinsonism. Reduced effectiveness of the drug combination does not appear to be due to a lessening of MPTP-induced hemiparkinsonism, but rather to the reduced effectiveness ofl-DOPA.     

Modulation of extracellular glutamate concentration by nitric oxide synthase inhibitor in rat transient forebrain ischemia

The purpose of the present study was to clarify the effect of topical administration of a nitric oxide synthase inhibitor on extracellular glutamate concentration in transient forebrain ischemia. Two microdialysis probes were inserted into the bilateral striata of Wistar rats. N^G-Nitro-l-arginine (l-NNA) with or withoutl-arginine was topically administered into the unilateral striatum through one of the microdialysis probes, while Ringer's solution was perfused into the contralateral striatum as the control, and 14 minutes of forebrain ischemia was applied. The extracellular glutamate concentration during ischemia and subsequent reperfusion was statistically significantly higher on the 100 μMl-NNA-perfused side than on the control side, but 1 MMl-NNA was ineffective. When 100 μMl-NNA was perfused together with 500 μMl-arginine, the glutamate concentration did not differ from that on the control side. Moreover, administration of 500 μMl-arginine significantly suppressed the glutamate elevation after reperfusion. The fact that the lower dose ofl-NNA increased the accumulation of glutamate during ischemia and reperfusion without altering the blood flow may indicate that nitric oxide affords protection against ischemic neuronal damage. However, since the higher dose ofl-NNA did not affect the glutamate concentration, it appears that the effect of nitric oxide on extracellular glutamate concentration in forebrain ischemia differs, depending on the degree of the inhibition of NOS activity.