Showing papers in "Neurotoxicity Research in 2004"

Calcium binding protein markers of GABA deficits in schizophrenia — post mortem studies and animal models

Abstract: As quantitative neuroimaging continues to elucidate the gross neuropathology of schizophrenia, neurochemical and histological studies have contributed to defining this pathology in terms of neurotransmitter dysfunction. Increasingly, there is evidence implicating neurons containing the major inhibitory neurotransmitter of the brain — gamma-aminobutyric acid (GABA).

Plasticity at hippocampal to prefrontal cortex synapses is impaired by loss of dopamine and stress: importance for psychiatric diseases.

Abstract: The direct hippocampal to prefrontal cortex pathway and its changes in synaptic plasticity is a useful framework for investigating the functional operations of hippocampal-prefrontal cortex communication in cognitive functions. Synapses on this pathway are modifiable and synaptic strength can be turned up or down depending on specific patterns of activity in the pathway. The objective of this review will be to summarize the different studies carried out on this topic including very recent data and to underline the importance of animal models for the development of new and effective medications in psychiatric diseases. We have shown that long-term potentiation (LTP) of hippocampal-pre-frontal synapses is driven by the level of mesocortical dopaminergic (DA) activity and more recently that stress is also an environmental determinant of LTP at these cortical synapses. Stimulation of the ventral tegmental area at a frequency known to evoke DA overflow in the prefrontal cortex produces a long-lasting enhancement of the magnitude of hippocampal-prefrontal cortex LTP whereas a depletion of cortical DA levels generates a dramatic decrease in this LTP. Moreover, hippocampal stimulation induces a transient but significant increase in DA release in the prefrontal cortex, and an optimal level of D1 receptor activation is essential for LTP expression. We recently investigated the impact of stress on hippocampal-prefrontal LTP and demonstrated that exposure to an acute stress causes a remarkable and long-lasting inhibition of LTP. Furthermore, we demonstrated that tianeptine, an antidepressant which has a unique mode of action, and clozapine, an atypical antipsychotic when administered at doses normally used in human testing, are able to reverse the impairment in LTP. Stressful life events have a substantial causal association with psychiatric disorders like schizophrenia and depression and recent imaging studies have shown an important role of the limbic-cortical circuit in the pathophysiology of these illnesses. Therefore, we proposed that agents capable of reversing the impairment of plasticity at hippocampal to prefrontal cortex synapses have the potential of becoming new therapeutic classes of antidepressant or antipsychotic drugs.

Role of GABA(B) receptor in alcohol dependence: reducing effect of baclofen on alcohol intake and alcohol motivational properties in rats and amelioration of alcohol withdrawal syndrome and alcohol craving in human alcoholics.

Abstract: The present paper describes the results of recent preclinical and clinical studies conducted in this laboratory in order to characterize the anti-alcohol properties of the GABA(B) receptor agonist, baclofen. At a preclinical level, the repeated administration of non-sedative doses of baclofen dose-dependently suppressed the acquisition and maintenance of alcohol drinking behavior in selectively bred Sardinian alcohol-preferring (sP) rats tested under the homecage, 2-bottle "alcohol vs water" choice regimen. Acute injection of baclofen completely blocked the temporary increase in voluntary alcohol intake occurring after a period of alcohol abstinence (the so-called alcohol deprivation effect, which models alcohol relapses in human alcoholics). Acute treatment with baclofen also dose-dependently suppressed extinction responding for alcohol (an index of motivation to consume alcohol) in sP rats trained to lever-press for oral alcohol self-administration. Taken together, these results suggest the involvement of the GABA(B) receptor in the neural substrate mediating alcohol intake and alcohol motivational properties in an animal model of excessive alcohol consumption. Further, acutely administered baclofen dose-dependently reduced the severity of alcohol withdrawal signs in Wistar rats made physically dependent upon alcohol. Preliminary clinical surveys suggest that the anti-alcohol properties of baclofen observed in rats may generalize to human alcoholics. Indeed, a double-blind survey demonstrated that repeated daily treatment with baclofen was associated, when compared to placebo, with a higher percentage of subjects totally abstinent from alcohol and a higher number of days of total abstinence. Treatment with baclofen also suppressed the number of daily drinks and decreased the obsessive and compulsive components of alcohol craving. Finally, a single non-sedative dose of baclofen resulted in the rapid disappearance of alcohol withdrawal symptomatology, including delirium tremens, in alcohol-dependent patients. In both clinical studies, baclofen was well tolerated with minimal side effects. These results suggest that baclofen may represent a potentially effective medication in the treatment of alcohol-dependent patients.

Cannabinoids and gene expression during brain development.

Abstract: Cannabis is the most commonly used illicit drug in western societies, in particular among young people. It is consumed even by women during pregnancy and lactation, which result in a variety of disturbances in the development of their offspring, because, like other habit-forming drugs, cannabinoids, the psychoactive ingredients of marijuana, can cross the placental barrier and be secreted in the maternal milk. Through this way, cannabinoids affect the ontogeny of various neurotransmitter systems leading to changes in different behavioral patterns. Dopamine and endogenous opioids are among the neurotransmitters that result more affected by perinatal cannabinoid exposure, which, when animals mature, produce changes in motor activity, drug-seeking behavior, nociception and other processes. These disturbances are likely originated by the capability of cannabinoids to influence the expression of key genes for both neurotransmitters, in particular, the enzyme tyrosine hydroxylase and the opioid precursor proenkephalin. In addition, cannabinoids seem to be also able to influence the expression of genes encoding for neuron-glia cell adhesion molecules, which supports a potential influence of cannabinoids on the processes of cell proliferation, neuronal migration or axonal elongation in which these proteins are involved. In support of this possibility, CB1 receptors, which represent the major targets for the action of cannabinoids, are abundantly expressed in certain brain regions, such as the subventricular areas, which have been involved in these processes during brain development. Finally, cannabinoids might also be involved in the apoptotic death that occurs during brain development, possibly by influencing the expression of Bcl-2/Bax system. Also in support of this option, CB1 receptors are transiently expressed during brain development in different group of neurons which do not contain these receptors in the adult brain. This paper will review all evidence relating cannabinoids to the expression of key genes for neural development, trying to establish the future research addressed to elucidate the mechanisms involved in the epigenetic action of cannabinoids during brain development.

Neurotoxins and neurotoxic species implicated in neurodegeneration.

Abstract: Neurotoxins, in the general sense, represent novel chemical structures which when administered in vivo orin vitro, are capable of producing neuronal damage or neurodegeneration—with some degree of specificity relating to neuronal phenotype or populations of neurons with specific characteristics (i.e., receptor type, ion channel type, astrocyte-dependence, etc.). The broader term ‘neurotoxin’ includes this categorization but extends the term to include intra- or extracellular mediators involved in the neurodegenerative event, including necrotic and apoptotic factors. Moreover, as it is recognized that astrocytes are essential supportive satellite cells for neurons, and because damage to these cells ultimately affects neuronal function, the term ‘neurotoxin’ might reasonably be extended to include those chemical species which also adversely affect astrocytes. This review is intended to highlight developments that have occurred in the field of ‘neurotoxins’ during the past 5 years, including MPTP/MPP+, 6-hydroxydopamine (6-OHDA), meth-amphetamine; salsolinol; leukoaminochrome-o-semi-quinone; rotenone; iron; paraquat; HPP+; veratridine; soman; glutamate; kainate; 3-nitropropionic acid; peroxynitrite anion; and metals (copper, manganese, lead, mercury). Neurotoxins represent tools to help elucidate intra- and extra-cellular processes involved in neuronal necrosis and apoptosis, so that drugs can be developed towards targets that interrupt the processes leading towards neuronal death.

The role of signaling molecules in reward-related incentive learning.

Abstract: Reward-related incentive learning involves the acquisition by neutral stimuli of an enhanced ability to elicit approach and other responses. Previous studies have shown that both dopamine (DA) and glutamate (Glu) play critical roles in this type of learning. Signaling molecules are intracellular messengers that participate in the influence of transmitter-receptor events on intracellular function including transcription in the nucleus. In recent years studies have begun to implicate signaling molecules in incentive learning. Thus, inhibition of cyclic adenosine monophosphate-dependent protein kinase (PKA) in the nucleus accumbens (NAc), that is activated by DA acting at D1-like receptors, blocks the acquisition of conditioned approach responses, lever pressing for food, conditioned place preference (CPP) based on NAc injections of amphetamine or cocaine, and conditioned activity based on NAc injections of amphetamine. Similar effects have been observed with PKA inhibition in the basolateral amygdala or medial prefrontal cortex. If animals were trained prior to testing with PKA inhibitors in NAc, no effect was seen suggesting that PKA is more important for acquisition than expression of incentive learning. Inhibition of calcium-dependent protein kinase or mitogen-activated protein kinases in NAc similarly has been shown to block the acquisition of incentive learning. Results support a model of DA-Glu synaptic interactions that form the basis of incentive learning.

Low doses of domoic acid during postnatal development produce permanent changes in rat behaviour and hippocampal morphology

Abstract: It is well established that the developing brain is a highly dynamic environment that is susceptible to toxicity produced by a number of pharmacological, chemical and environmental insults. We report herein on permanent behavioural and morphological changes produced by exposing newborn rats to very low (subconvulsive) doses of kainate receptor agonists during a critical window of brain development. Daily treatment of SD rat pups with either 5 or 20 µg/kg of domoic acid (DOM) from postnatal day 8-14 resulted in a permanent and reproducible seizure-like syndrome when animals were exposed to different tests of spatial cognition as adults. Similar results were obtained when animals were treated with equi-efficacious doses of kainic acid (KA; 25 or 100 µg/kg). Treated rats had significant increases in hippocampal mossy fiber staining and reductions in hippocampal cell counts consistent with effects seen in adult rats following acute injections of high doses of kainic acid.In situ hybridization also revealed an elevation in hippocampal brain derived neurotrophic factor (BDNF) mRNA in region CA1 without a corresponding increase in neuropeptide Y (NPY) mRNA. These results provide evidence of long-lasting behavioural and histochemical consequences arising from relatively subtle changes in glutamatergic activity during development, that may be relevant to understanding the aetiology of seizure disorders and other forms of neurological disease.

Neurobehavioural deficits associated with apoptotic neurodegeneration and vulnerability for ADHD

Abstract: Several studies involving postnatal administration of the N-methyl-D-aspartate (NMDA) antagonists, dizocilpine (MK-801; 3 x 05 mg/kg, at 0800, 1600 and 2400 h) on Postnatal day 11, or Ketamine (1 × 50 mg/kg) or Ethanol (1 × 25 g/kg, Ethanol-Low, or 2 × 25 g/kg, 2-h interval, Ethanol-High) on Postnatal day 10, are described Some mice from each treatment/vehicle group were sacrificed 24 h after NMDA antagonist treatment and brain regions were taken for fluoro-jade staining analysis Functional analysis was initiated at 60 days of age All three treatments inducing an antagonistic action at NMDA receptors, MK-801, Ketamine and Ethanol-High induced a similar pattern of initial hypoactivity followed by marked and lasting hyper-activity in the motor activity test chambers In each case, the basal hyperactivity level was abolished by acute treatment with a low dose of D-amphetamine (025 mg/kg) All three treatments, MK-801, Ketamine and Ethanol-High, induced a deficit in acquisitive performance in the radial arm maze test of instrumental learning The deficit induced by postnatal MK-801 was abolished by acute treatment with the low dose of D-amphetamine All three treatments, MK-801, Ketamine and Ethanol-High, resulted in normal acquisitive performance during the first three test days in the circular swim with the submerged platform maintained in a constant position, but on the fourth test day, with the platform position shifted to a different “quadrant”, induced marked deficits Fluoro-jade staining analyses indicated a devastating cell degeneration in several brain regions of mice administered NMDA antagonists postnatally, including the hippocampus, frontal cortex, parietal cortex, and cerebellum Severe cell degeneration in the laterodorsal thalamus due to Ethanol or diazepam (5 mg/kg) appeared not to affect the different aspects of function The pattern of dysfunctional outcome and apoptotic cell loss following postnatal NMDA antagonist treatment offers a plausible similarity to the major aspects of ‘syndromatic continuity’ in ADHD, hyperactivity, inattention and impulsivity, thereby providing an interesting animal model of the disorder

Effect of stress on prefrontal cortex function.

Abstract: Stress is the major epigenetic factor that contributes to the etiology, pathophysiology, and treatment out-come of most psychiatric disorders. Understanding the mechanisms by which stress contributes to these processes can have important implications for improving therapeutic outcome. Considering that a dysfunctional prefrontal cortex has been implicated in many psychiatric disorders, such as schizophrenia and mood disorders, delineating mechanisms by which stress affects prefrontal cortex (PFC) function is critical to our understanding of the role of stress in influencing the disease process. This paper will review recent mechanistic information about the effects of stress on dopamine and glutamate neurotransmission in the PFC.

Clinical phenotypes associated with DISC1, a candidate gene for schizophrenia

Abstract: Genetic factors play an important part in the development of schizophrenia and bipolar disorder, and linkage analyses in families have successfully identified several chromosomal regions containing candidate genes. A single large pedigree has been described in which schizophrenia and depression segregate with a balanced chromosomal translocation involving the long arm of chromosome 1 and the short arm of chromosome 11. The gene named DISC1, disrupted at the chromosome 1 breakpoint, is a novel candidate gene that may have a role in the pathogenesis of schizophrenia. The cellular location and function of the protein coded by DISC1 is currently being investigated. The phenotype associated with DISC1 in the t (1;11) translocation family includes schizophrenia, schizoaffective disorder, recurrent major depression and bipolar disorder. Hence this locus is one of several now reported apparently showing linkage to both schizophrenia and bipolar disorder. The study of intermediate phenotypes or “endophenotypes” may clarify the relations between phenotype and genotype. Auditory event related potentials are EEG based physiological measures widely studied in schizophrenia. In particular the cognitive evoked potential, the P300 response generated during an “oddball” two-tone discrimination task consistently shows reduced amplitude in schizophrenia compared to controls. In members of the family with the t (1;11) translocation, P300 amplitude was reduced in relatives who carried the translocation compared to relatives with a normal karyotype. Furthermore the amplitude reduction was independent of the presence or absence of symptoms because asymptomatic translocation carriers showed similar P300 amplitude reduction as was found in translocation carriers who were diagnosed with schizophrenia, bipolar disorder or unipolar depression. The results confirm that subjects with schizophrenia who carry the t (1;11) translocation have similar phenotype to unrelated subjects with schizophrenia and a normal karyotype. Furthermore P300 amplitude may be a useful intermediate phenotype detecting the neuropathology of schizophrenia in “at risk” individuals even in the absence of clinical symptoms.

Neuroprotective properties of Valeriana officinalis extracts

Abstract: Valeriana officinalis have been used in traditional medicine for its sedative, hypnotic, and anticonvulsant effects There are several reports in the literature supporting a GABAergic mechanism of action for valerian The rationale of the present work is based on the concept that by decreasing neuronal network excitability valerian consumption may contribute to neuroprotection The aim of our investigation was to evaluate the neuroprotective effects of V officinalis against the toxicity induced by amyloid beta peptide 25-35 Abeta(25-35) Cultured rat hippocampal neurons were exposed to Abeta(25-35) (25 microM) for 24-48 h, after which morphological and biochemical properties were evaluated The neuronal injury evoked by Abeta, which includes a decrease in cell reducing capacity and associated neuronal degeneration, was prevented by valerian extract Analysis of intracellular free calcium (Ca(2+)i) indicated that the neuroprotective mechanisms may involve the inhibition of excess influx of Ca2+ following neuronal injury Moreover, membrane peroxidation in rat hippocampal synaptosomes was evaluated, and our data indicate that valerian extract partially inhibited ascorbate/iron-induced peroxidation In conclusion we show evidence that the signalling pathways involving Ca(2+)i and the redox state of the cells may play a central role in the neuroprotective properties of V officinalis extract against Abeta toxicity The novelty of the findings of the present work, indicating neuroprotective properties of valerian against Abeta toxicity may, at the long-term, contribute to introduction of a new relevant use of valerian alcoholic extract to prevent neuronal degeneration in aging or neurodegenerative disorders

Some aspects of the in vivo neuroprotective capacity of flavonoids: bioavailability and structure-activity relationship.

Abstract: On the basis of previous work showing that flavonoids structurally related to quercetin are neuroprotective for cells in culture, this work was directed towards determining if several flavonoids (quercetin, fisetin and catechin) could acutely and by an intraperitoneal (IP) route reach significant cerebral concentrations and either prevent or facilitate recovery from a brain lesion induced by focal ischemia in rats. Aqueous and liposomal preparations of quercetin, fisetin and catechin were administered IP in a single dose and assessed in the brain by HPLC at 30 min, 1 h, 2 h and 4 h. Ischemic damage from focal middle cerebral artery occlusion was assessed spectrophotometrically with 2,3,5,-triphenylltetrazolium chloride (TTC). Infarct volume was assessed by an image analysis system following perfusion with TTC. The status of the cerebral tissue was evaluated by hematoxylin-eosin. Flavonoids administered in aqueous preparations were undetected in the brain. Cerebral concentrations of catechin (10.5 ng/g), fisetin (8.23 ng/g) and quercetin (509 ng/g) were detected in the brain only after IP injection of the liposomal preparations. Spectrophotometric analysis of brain tissue with the TTC-technique showed that liposomal quercetin reduced ischemic damage and infarct volume after permanent occlusion of the middle cerebral artery (ischemic: 41.3 mm3 vs liposomal quercetin: 17 mm3). In liposomal quercetin-treated animals there was also recovery of the cytoarchitecture in ischemic areas of striatum and cortex. Although a liposomal preparation of fisetin had similar effects, catechin failed to protect brain tissue. In conclusion, early administration of liposomal preparations of quercetin and structurally related flavonoids are beneficial and neuroprotective in experimental focal ischemia.

Neuroprotective effect ofH. perforatum extracts on β-amyloid-induced neurotoxicity

Abstract: In the present study we assessed the neuroprotective role of aHypericum perforatum ethanolic extract and obtained fractions in amyloid-β peptide (Aβ)(25–35)-induced cell death in rat cultured hippocampal neurons. Lipid peroxidation was used as a marker of oxidative stress by following the formation of TBARS in rat cortical synaptosomes, after incubation with ascorbate/Fe2+, alone or in the presence of EC97 effective concentrations ofH. perforatum fractions. Induced lipid peroxidation was significantly inhibited by fractions containing flavonol glycosides, flavonol and biflavone aglycones, and by a fraction containing several phenols, mainly chlorogenic acid-type phenolics (21%,77%and 98%, respectively). Lipid peroxidation evaluated after incubation with 25 μM Aβ(25–35), was significantly inhibited byH. perforatum extract.

Stress kinases involved in tau phosphorylation in Alzheimer's disease, tauopathies and APP transgenic mice.

Abstract: Hyperphosphorylation and accumulation oftau in neurons (and glial cells) is one the main pathologic hallmarks in Alzheimer’s disease (AD) and other tauopathies, including Pick’s disease (PiD), progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease and familial frontotemporal dementia and parkinsonism linked to chromosome 17 due to mutations in thetau gene (FTDP-17-tau). Recent studies have shown increased expression of select active kinases, including stress-activated kinase, c-JunN-terminal kinase (SAPK/JNK) and kinase p38 in brain homogenates in all thetau opathies. Strong active SAPK/JNK and p38 immunoreactivity has been observed restricted to neurons and glial cells containing hyperphosphorylatedtau, as well as in dystrophic neurites of senile plaques in AD. Moreover, SAPK/JNK- and p38-immunoprecipitated sub-cellular fractions enriched in abnormal hyperphosphorylatedtau have the capacity to phosphorylate recombinattau and c-Jun and ATF-2 which are specific substrates of SAPK/JNK and p38 in AD and PiD. Interestingly, increased expression of phosphorylated SAPK/JNK and p38 in association with hyperphosphorylated tau containing neurites have been observed around sA4 amyloid deposits in the brain of transgenic mice (Tg2576) carrying the double APP Swedish mutation. These findings suggest that sA4 amyloid has the capacity to trigger the activation of stress kinases which, in turn, phosphorylatetau in neurites surrounding amyloid deposits. Reduction in the amyloid burden and decreased numbers of amyloid plaques but not of neurofibrillary degeneration has been observed in the brain of two AD patients who participated in an amyloid-s immunization trial. Activation of stress kinases SAPK/JNK and p38 were reduced together with decreasedtau hyperphosphorylation of aberrant neurites in association with decreased amyloid plaques. These findings support the amyloid cascade hypothesis oftau phosphorylation mediated by stress kinases in dystrophic neurites of senile plaques but not that of neurofibrillary tangles and neuropil threads in AD.

Serotonin neurotoxins — past and present

Abstract: Autoxidation pathways and redox reactions of dihydroxytryptamines (5,6- and 5,7-DHT) and of 6-hydroxydopamine (6-OH-DA) are illustrated, and their potential role in aminergic neurotoxicity is discussed. It is proposed that certain aspects of the cytotoxicity of 6-OH-DA and of the DHTs, namely redox cycling of their quinone- and quinoneimine-intermediates as a source of free radicals, may also apply to quinoidal reactive intermediates and to glutathionyl- or cysteinyl conjugates ("thioether adducts") of o-dihydroxylated (catechol-like) metabolites of certain substituted amphetamines (of methylenedioxymethamphetamine (MDMA) and of methylenedioxyamphetamine (MDA)). Despite similarities in their primary interaction with the plasmalemmal (serotonergic transporter/dopamine transporter, SERT/DAT) and vesicular monoamine transporters (VMAT2), MDMA and fenfluramine (N-ethyl-meta-trifluoromethamphetamine, Fen) differ substantially in many aspects of their metabolism, pharmacokinetics, pharmacology, and neurotoxicology profile; the consequences of these differences for neuronal response patterns and long-term survival prospects are not yet fully understood. However, sustained hyperthermia appears to be a critical factor in these differences. Methodological requirements for adequate detection and description of pre- and postsynaptic forms of drug-induced neurotoxicity are exemplified using recently published accounts. The inclusion of microglial markers into research strategies has widened contemporary pathogenetic concepts on methamphetamine (MA)-induced neurotoxicity as an example of inflammatory neurodegeneration, thus complementing the traditional ROS and RNS-dependent stress models. Amphetamine-type neurotoxicity studies may assist in elaborating of preventive strategies for human neurodegenerative disorders.

Domoic acid-induced neurotoxicity in the hippocampus of adult rats

Abstract: Domoic acid (DA), an agonist of non-N-methyl-D-aspartate (non-NMDA) receptor subtype including kainate receptor, was identified as a potent neurotoxin showing involvement in neuropathological processes like neuronal degeneration and atrophy. In the past decade evidence indicating a role for excitatory amino acids in association with neurological disorders has been accumulating. Although the mechanisms underlying the neuronal damage induced by DA are not yet fully understood, many intracellular processes are thought to contribute towards DA-induced excitotoxic injury, acting in combination leading to cell death. In this review article, we report the leading hypotheses in the understanding of DA-induced neurotoxicity, which focus on the role of DA in neuropathological manifestations, the formation of the retrograde messenger molecule nitric oxide (NO) for the production of free radicals in the development of neuronal damage, the activation of glial cells (microglia and astrocytes) in response to DA-induced neuronal damage and the neuroprotective role of melatonin as a free radical scavenger or antioxidant in DA-induced neurotoxicity. The possible implications of molecular mechanism underlying the neurotoxicity in association with necrosis, apoptosis, nitric oxide synthases (nNOS and iNOS) and glutamate receptors (NMDAR1 and GluR2) related genes and their expression in DA-induced neuronal damage in the hippocampus have been discussed.

Role of endocannabinoid system in mental diseases

Abstract: In the last decade, a large number of studies using Δ9-tetrahydrocannabinol (THC), the main active principle derivative of the marijuana plant, or cannabinoid synthetic derivatives have substantially contributed to advance the understanding of the pharmacology and neurobiological mechanisms produced by cannabinoid receptor activation.

Genetic and environmental factors interact to influence anxiety

Abstract: Both genetic and environmental factors influence normal anxiety traits as well as anxiety disorders. In addition it is becoming increasingly clear that these factors interact to produce specific anxiety-related behaviors. For example, in humans and in monkeys mutations in the gene encoding for the serotonin transporter result in increased anxiety in adults life when combined with a stressful environment during development. Another recent example comes from twin studies suggesting that a small hippocampus can be a predisposing condition that renders individuals susceptible to post traumatic stress disorder. Such examples illustrate how specific mutations leading to abnormal brain development may increase vulnerability to environmental insults which may in turn lead to specific anxiety disorders.

Enhaced induction of the immunoproteasome by interferon gamma in neurons expressing mutant huntingtin

Abstract: Huntington disease (HD) inclusions are stained with anti-ubiquitin and anti-proteasome antibodies. This, together with proteasome activity studies on transfected cell, suggested that alterations in the ubiquitin-proteasome system (UPS) might contribute to HD pathogenesis. In a previous work we reported that in a conditional mouse model of Huntington’s disease (HD94 mice), the chymiotrypsin- and trypsin-“like” activities of the proteasome are increased selectively in the affected and aggregate-containing brain regions: striatum and cortex. Moreover, in these areas a neuronal increase in the interferon-inducible subunits of the immunoproteasome LMP2 and LPM7 was observed. In order to test if the expression ofN-terminal mutant huntingtin (htt) by itself is sufficient to induce the change in proteasome catalytic activities as well as in LMP2 subunit expression, we performed enzymatic assays for the three different peptidase activities of the proteasome and western blot experiments in striatal cultured neurons from HD94 mice free of glial contamination. We found no changes in any of the activities in these cells. Furthermore, western blot analysis performed with specific antibody against LMP2 subunits, revealed no difference in levels of this subunit in striatal neurons from HD94 compared to control cultures. On the other hand, when the striatal cultures were treated with interferon-γ (IFN-γ) during 72 hours, a clear increase in LMP2 levels was observed in control neuronal cultures. Interestingly, this increase was much more pronounced (95% higher) in HD94 striatal cultures. These results indicate that although expression of mutant htt is not sufficient to induce the changes in proteasome catalytic core observed in HD, it synergizes the changes induced by IFN-γ. Furthermore, immunocytochemical studies revealed that HD94 striatal neurons expressing high levels of LMP2 subunit showed a pre-apoptotic appearance. These results suggest that the correlation between neuronal induction of the inmuno-proteasome and neurodegeneration found in HD brains is secondary to inflammatory processes.

Tau in neurodegenerative diseases: tau phosphorylation and assembly.

Abstract: The possible link between tau phosphorylation and tau assembly in these neurodegenerative diseases known as tauopathies is described. Additionally, this link is supported by anin vitro experiment showing the higher capacity of phosphotau to assemble in some specific conditions; and, by a recently reported experiment using a tau transgenic mouse model.

Serotoninergics attenuate hyperlocomotor activity in rats. Potential new therapeutic strategy for hyperactivity.

Abstract: Hyperactivity is thought to be associated with an alteration of dopamine (DA) neurochemistry in brain. This conventional view became solidified on the basis of observed hyperactivity in DA-lesioned animals and effectiveness of the dopaminomimetics such amphetamine (AMP) in abating hyperactivity in humans and in animal models of hyperactivity. However, because AMP releases serotonin (5-HT) as well as DA, we investigated the potential role of 5-HT in an animal model of hyperactivity. We found that a greater intensity of hyperactivity was produced in rats when both DA and 5-HT neurons were damaged at appropriate times in ontogeny. Therefore, previously we proposed this as an animal model of attention deficit hyperactivity disorder (ADHD) - induced by destruction of dopaminergic neurons with 6-hydroxydopamine (6-OHDA) (neonatally) and serotoninergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) (in adulthood). In this model effects similar to that of AMP (attenuation of hyperlocomotion) were produced by m-chlorophenylpiperazine (m-CPP) but not by 1-phenylbiguanide (1-PG), respective 5-HT2 and 5-HT3 agonists. The effect of m-CPP was shown to be replicated by desipramine, and was largely attenuated by the 5-HT2 antagonist mianserin. These findings implicate 5-HT neurochemistry as potentially important therapeutic targets for treating human hyperactivity and possibly childhood ADHD.

Common patterns of bcl-2 family gene expression in two traumatic brain injury models.

Abstract: Cell death/survival following traumatic brain injury (TBI) may be a result of alterations in the intracellular ratio of death and survival factors. Bcl-2 family genes mediate both cell survival and the initiation of cell death. Using lysate RNase protection assays, mRNA expression of the anti-cell death genes Bcl-2 and Bcl-xL, and the pro-cell death gene Bax, was evaluated following experimental brain injuries in adult male Sprague-Dawley rats. Both the lateral fluid-percussion (LFP) and the lateral controlled cortical impact (LCI) models of TBI showed similar patterns of gene expression. Anticell death bcl-2 and bcl-xL mRNAs were attenuated early and tended to remain depressed for at least 3 days after injury in the cortex and hippocampus ipsilateral to injury. Pro-cell death bax mRNA was elevated in these areas, usually following the decrease in anti-cell death genes. These common patterns of gene expression suggest an important role for Bcl-2 genes in cell death and survival in the injured brain. Understanding the regulation of these genes may facilitate the development of new therapeutic strategies for a condition that currently has no proven pharmacologic treatments.

Glutamate receptors modulate oxidative stress in neuronal cells. A mini-review

Abstract: Multiple lines of evidence demonstrate that reactive oxygen species (ROS) are involved in regulation of normal cell metabolism as second messengers Under extreme conditions, these molecules induce oxidative stress, which may stimulate (or accompany) a number of neurodegenerative processes In the glutamatergic system, ROS levels are under control of ionotropic and metabotropic glutamate receptors, which modulate ion fluxes through the neuronal membrane The Na+/K+-pump is also one of the important participants affecting stationary ROS levels through several distinct mechanisms This review describes the involvement of the Na+/K+-pump in intracellular signaling mechanisms via cross-talk between the pump and glutamate receptors in cerebellum granule cells Selective dysfunction of mGlu II receptors may also lead to abnormal protein phosphorylation (ie, tau phosphorylation), culminating in neurodegenerative disorders (ie, Alzheimer disease) Also, unregulated production of intracellular ROS resulting from an imbalance of ionotropic and metabotropic receptors may activate one or more protein kinases In summary, Glu receptor dysfunction, leading to a deficit in glutamate-mediated signal transduction may represent one of the earliest stages of neurodegenerative disorders The Na+/K+-pump is able to prevent over-production of intracellular ROS, thus increasing oxidative stability of neuronal cells

Gene expression during memory formation.

Abstract: For several decades, neuroscientists have provided many clues that point out the involvement ofde novo gene expression during the formation of longlasting forms of memory. However, information regarding the transcriptional response networks involved in memory formation has been scarce and fragmented. With the advent of genome-based technologies, combined with more classical approaches (i.e., pharmacology and biochemistry), it is now feasible to address those relevant questions-which gene products are modulated, andwhen the processes are necessary for the proper storage of memories- with unprecedented resolution and scale. Using one-trial inhibitory (passive) avoidance training of rats, one of the most studied tasks so far, we found two time windows of sensitivity to transcrip-tional and translational inhibitors infused into the hippocampus: around the time of training and 3–6 h after training. Remarkably, these periods perfectly overlap with the involvement of hippocampal cAMP/PKA (protein kinase A) signaling pathways in memory consolidation. Given the complexity of transcriptional responses in the brain, particularly those related to processing of behavioral information, it was clearly necessary to address this issue with a multi-variable, parallel-oriented approach. We used cDNA arrays to screen for candidate inhibitory avoidance learning-related genes and analyze the dynamic pattern of gene expression that emerges during memory consolidation. These include genes involved in intracellular kinase networks, synaptic function, DNA-binding and chro-matin modification, transcriptional activation and repression, translation, membrane receptors, and oncogenes, among others. Our findings suggest that differential and orchestrated hippocampal gene expression is necessary in both early and late periods of long-term memory consolidation. Additionally, this kind of study may lead to the identification and characterization of genes that are relevant for the pathogenesis of complex psychiatric disorders involving learning and memory impairments, and may allow the development of new methods for the diagnosis and treatment of these diseases.

The genetic relationship of personality to major depression and schizophrenia.

Abstract: Since ancient times, dimensions of personality have been linked with the liability to psychiatric illness. In modern times, several research approaches suggest that personality and the liability to psychiatric illness such as schizophrenia and major depression (MD) are influenced by many of the same genes. If this is true, it could shed light on the genetic architecture of psychiatric illness. It could also validate the use of personality measures in unaffected relatives in linkage and association studies of psychiatric illness. This approach could potentially increase statistical power to detect genetic effects. The personality trait neuroticism (N) may be genetically related to MD, while schizotypal traits may be genetically related to schizophrenia. Twin studies have reported that most of the covariation between N and MD is due to shared additive genetic factors. Adoption studies have demonstrated that the biological offspring of schizophrenic mothers are more likely to have schizotypal personality disorder than are children of control mothers.At the current time, only one genome wide scan of N has been published, which does show some overlap in linkage results with genome scans of MD. However,this should be replicated and more rigorously studied. At the present time, there are no established susceptibility genes for MD. When these are established, it will be necessary to assess their relationship with N. Currently, no genome scans of schizotypy have been published. Furthermore, although several putative susceptibility genes for schizophrenia have been reported and replicated, only one — catechol-O-methyltransferase (COMT) — has been tested in schizotypy.

Interactions of the mGluR5 gene with breeding and maternal factors on startle and prepulse inhibition in mice.

Abstract: Sensorimotor gating, measured by prepulse inhibition (PPI), is a fundamental form of information processing that is deficient in schizophrenia patients and mice lacking the gene for metabotropic glutamate receptor 5 (mGluR5). Both breeding strategies and mothering behaviors are capable of influencing the behavioral phenotype of knockout (KO) mice. Previous studies found a PPI deficit and increased startle magnitudes in mGluR5 KO mice derived from homozygous matings. Here we compared the PPI of mGluR5 wildtype (WT) and KO mice derived from heterozygous matings to that seen in mice derived from homozygous matings. Possible influences of postnatal mothering behaviors were examined using two different methods of cross-fostering. The potential developmental nature of the PPI deficit of the mGluR5 KO mice was also addressed via acute administration of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP)to C57BL/6J mice. The mGluR5 KO mice exhibited reduced PPI independently of breeding strategy or postnatal mothering behavior. Startle magnitude, however, varied with breeding strategy. The PPI deficit seen in the mGluR5 KO mice is not mimicked by acute administration of an mGluR5 antagonist, and is therefore most likely due to compensatory alterations in neuronal circuitry occurring during development independent of maternal behaviors in the postnatal environment.

Studies on homocysteine and dehydroepiandrosterone sulphate plasma levels in Alzheimer's disease patients and in Parkinson's disease patients.

Abstract: Homocysteine (HC) and dehydroepiandrosterone sulphate (DHEAS) plasma levels have been evaluated in groups of male and female patients with Parkinson’s Disease (PD) and in a group of female patients with Alzheimer’s Disease (AD) and compared with the corresponding plasma levels observed in a group of age-matched subjects. It has been confirmed that HC plasma levels are enhanced in both PD and AD patients. As far as the DHEAS plasma levels are concerned no changes have been observed in PD patients while a marked decrease has been observed in AD patients. These results support the view that while the pro-oxidant effects of HC and its agonist action at NMDA receptors can play a role in both neu-rodegenerative diseases, the role of DHEAS is more complex and may be an important factor only in certain neurodegenerative diseases. Thus, according to the present study DHEAS is likely to be involved in AD but not in PD.

The inhibition of acquired fear

Abstract: A conditioned stimulus (CS) associated with a fearsome unconditioned stimulus (US) generates learned fear. Acquired fear is at the root of a variety of disorders, among which are phobias, generalized anxiety, and the posttraumatic stress disorder (PTSD). The simplest way to inhibit learned fear is to extinguish it, which is usually done by repeatedly presenting the CS alone, so that a new association, CS-“no US”, will eventually overcome the previously acquired CS-US association. Extinction was first described by Pavlov as a form of “internal inhibition” and was recommended by Freud and Ferenczi in the 1920s (who called it “habituation”) as the treatment of choice for phobic disorders. It is used with success till this day, often in association with anxiolytic drugs. Extinction has since then been applied, also successfully and also often in association with anxiolytics, to the treatment of panic, generalized anxiety disorders and, more recently, PTSD. Extinction of learned fear involves gene expression, protein synthesis,N-methyl-D-aspartate (NMDA) receptors and signaling pathways in the hippocampus and the amygdala at the time of the first CS-no US association. It can be enhanced by increasing the exposure to the “no US” component at the time of behavioral testing, to the point of causing the complete uninstallment of the original fear response. Some theorists have recently proposed that reiteration of the CS alone may induce a reconsolidation of the learned behavior instead of its extinction. Reconsolidation would preserve the original memory from the labilization induced by its retrieval. If true, this would of course be disastrous for the psychotherapy of fear-motivated disorders. Here we show that neither the CS nor retrieval cause anything remotely like reconsolida-tion, but just extinction. In fact, our findings indicate that the reconsolidation hypothesis is essentially incorrect, at least for the form of contextual fear most commonly studied in rodents. Therefore, it seems safe to continue using extinction-based forms of therapy for anxiety disorders secondary to acquired fear. Further, it is useful and desirable to devise procedures by which the “no US” component of the extinction is strengthened in order to alleviate the symptoms of victims of acquired fear.

Alpha and beta estradiol protect neuronal but not native PC12 cells from paraquat-induced oxidative stress.

Abstract: Oxidative stress is currently considered a mediator of cell death in several neurodegenerative diseases. Notably, it may play an important role in the degeneration of dopamine neurons of the substantia nigra in Parkinson’s disease. We examined the effect of a strong oxidant, the herbicide paraquat, on cell distress using native and neuronal pheochromocytoma PC12 cells. Paraquat administration for 8 hours induced a significant cellular death in both native and in neuronal PC12 cells. Since the anti-oxidant properties of estrogens may promote neuroprotectionin vitro andin vivo, we then investigated the ability of estradiol stereoisomers, 17α-estradiol and 17β-estradiol, to rescue PC12 cells submitted to paraquat-induced oxidative stress. Our results show a protective effect of both estradiol stereoisomers in neuronal PC12 cells treated with paraquat, whereas this effect could not be observed in native PC12 cells. We also demonstrate that estrogen receptor β protein expression is modulated by paraquat administration in native PC12 cells, while paraquat does not change estrogen receptor β expression in neuronal PC12 cells. Paraquat also decreases estrogen receptor α in neuronal PC12 cells, thus suggesting new routes for paraquat to collapse cellular metabolism. Besides, the oxidation of dihydrodhodamine-123 into fluorescent rhodamine in the presence of paraquat but not in presence of paraquat and 17α-estradiol or 17β-estradiol,sustain a possible direct scavenging role of both estradiol stereoisomers.

Dopamine D2 agonist priming in intact and dopamine-lesioned rats

Abstract: Receptor priming is a recently discovered phenomenon by which receptor agonists produce abrupt and long-lived supersensitization of receptors. Induction of dopamine (DA) D2 receptor supersensitivity by the agonist quinpirole was discovered approximately 15 years ago, and was found to occur consistently if rats were treated repeatedly at daily or weekly or monthly intervals with low or high doses of quinpirole. In this review we summarize and discuss some of the major studies that underlie DA D2 receptor supersen-sitivity, describe behavioral processes that are known to be altered by DA D2 receptor supersensitivity, and discuss the importance of DA innervation on expression of enhanced behaviors. DA D2 receptor supersen-sitivity represents one of the neural mechanisms implicated in psychiatric disorders. Also, DA D2 receptor supersensitivity and increased DA D3 receptor expression are associated with motor dyskinesias, as in L-DOPA-treated Parkinson’s disease patients. An understanding of receptor priming, a knowledge of the types of behavioral expression associated with DA D2 receptor supersensitivity, and an understanding of mechanisms associated with receptor supersen-sitization, can lead to improvements in the treatments of psychiatric and neurological disorders.