Marco Virgili

Partial neuroprotection of in vivo excitotoxic brain damage by chronic administration of the red wine antioxidant agent, trans-resveratrol in rats

The antioxidant compound trans-resveratrol, is found in substantial amount in several types of red wine and is considered one of the substances responsible for the lower incidence of coronary heart diseases among regular consumers of such wines, an effect also known as the French paradox. It has also been proposed that resveratrol may have beneficial effects against neurodegenerative diseases. We report here that chronic administration of resveratrol to young-adult rats, significantly protects from the damage caused by systemic injection of the excitotoxin kainic acid, in the olfactory cortex and the hippocampus. The same treatment, however, is not able to give any significant protection in an ex vivo model of simulated ischemia on hippocampal slices in vitro. This first evidence of a partial neuroprotective action of chronic administration of resveratrol in vivo, suggests that other models of neurodegenerative injury, and in particular of excitotoxic brain damage, should be investigated in order to assess the potentiality for resveratrol to be used as a pharmacological tool for neuroprotection.

Akt pathway mediates a cGMP-dependent survival role of nitric oxide in cerebellar granule neurones

Apoptotic death results from disrupting the balance between anti‐apoptotic and pro‐apoptotic cellular signals. The inter‐ and intracellular messenger nitric oxide is known to mediate either death or survival of neurones. In the present work, cerebellar granule cells were used as a model to assess the survival role of nitric oxide and to find novel signal transduction pathways related to this role. It is reported that sustained inhibition of nitric oxide production induces apoptosis in differentiated cerebellar granule neurones and that compounds that slowly release nitric oxide significantly revert this effect. Neuronal death was also reverted by a caspase‐3‐like inhibitor and by a cyclic GMP analogue, thus suggesting that nitric oxide‐induced activation of guanylate cyclase is essential for the survival of these neurones. We also report that the Akt/GSK‐3 kinase system is a transduction pathway related to the survival action of nitric oxide, as apoptosis caused by nitric oxide deprivation is accompanied by down‐regulation of this, but not of other, kinase systems. Conversely, treatments able to rescue neurones from apoptosis also counteracted this down‐regulation. Furthermore, in transfection experiments, overexpression of the Akt gene significantly decreased nitric oxide deprivation‐related apoptosis. These results are the first evidence for a mechanism where endogenous nitric oxide promotes neuronal survival via Akt/GSK‐3 pathway.

Structural, neurochemical and behavioural consequences of neonatal blockade of NMDA receptor through chronic treatment with CGP 39551 or MK-801

Recent evidence suggests that NMDA receptors may be involved in survival of neurons and establishment of correct connectivity during development. We have treated rat pups from postnatal day 1 to 22 with daily s.c. injections of a competitive (CGP 39551) and a non-competitive (MK-801) antagonist of the NMDA receptor. Body weight of treated rats was decreased by 50-65% at postnatal day 24 and by 25-32% at 70 days of age. Brain weight was decreased by 16-24% at both ages. Among the different brain regions, the cerebellum and striatum appeared more decreased in size than the cortex and hippocampus. Only few minor, and in some cases transient, differences were measured in the cerebellum, the hippocampus and the cortex for a battery of neurochemical markers related to cholinergic, GABAergic and glutamatergic transmission as well as to astrocyte and oligodendrocyte activity. When tested in actometric cages from postnatal days 28 to 60, treated rats exhibited a dramatic increase of spontaneous locomotor activity which was maximal in 28-day-old animals (380% and 250% of control values in CGP 39551 and MK-801 groups, respectively) and was still significant at 60 days of age. Therefore, long-lasting alteration of motor behaviour is obtained by the schedule of chronic treatment adopted for the present experiments. Our results suggest that blockade of NMDA receptors during the critical period of brain maturation may result in permanent alteration of neural circuits.

Kainic Acid Differentially Affects the Synaptosomal Release of Endogenous and Exogenous Amino Acidic Neurotransmitters

Abstract: Presynaptic actions of kainic acid have been tested on uptake and release mechanisms in synaptosome‐enriched preparations from rat hippocampus and goldfish brain. Kainic acid increased in a Ca2+‐dependent way the basal release of endogenous glutamate and aspartate from both synaptosomal preparations, with the maximum effect (40–80%) being reached at the highest concentration tested (1 mM). In addition, kainic acid potentiated, in an additive or synergic way, the release excitatory amino acids stimulated by high K+ concentrations. Kainic acid at 1 mM showed a completely opposite effect on the release of exogenously accumulated D‐[3H]aspartate. The drug, in fact, caused a marked inhibition of both the basal and the high K+‐stimulated release. Kainic acid at 0.1 mM had no clear‐cut effect, whereas at 0.01 mM it caused a small stimulation of the basal release. The present results suggest that kainic acid differentially affects two neurotransmitter pools that are not readily miscible in the synaptic terminals. The release from an endogenous, possibly vesiculate, pool of excitatory amino acids is stimulated, whereas the release from an exogenously accumulated, possibly cytoplasmic and carrier‐mediated, pool is inhibited or slightly stimulated, depending on the external concentration of kainic acid. Kainic acid, in addition, strongly inhibits the high‐affinity uptake of L‐glutamate and D‐aspartate in synaptic terminals. All these effects appear specific for excitatory amino acids, making it likely that they are mediated through specific recognition sites present on the membranes of glutamatergic and aspartatergic terminals. The relevance of the present findings to the mechanism of excitotoxicity of kainic acid is discussed.

Alpha-synuclein protects cerebellar granule neurons against 6-hydroxydopamine-induced death.

The physiological role of alpha‐synuclein, a protein found enriched in intraneuronal deposits characterizing Parkinson’s disease, is debated. While its aggregation is usually considered linked to neuropathology, its normal function may be related to fundamental processes of synaptic transmission and plasticity. By using antisense oligonucleotide strategy, we report in this study that alpha‐synuclein silencing in cultured cerebellar granule cells results in widespread death of these neurons, thus demonstrating an essential pro‐survival role of the protein towards primary neurons. To study alpha‐synuclein expression and processing in a Parkinson’s disease model of neurotoxicity, we exposed differentiated cultures of cerebellar granule neurons to toxic concentrations of 6‐hydroxydopamine (6‐OHDA). This resulted in neuronal death accompanied by a decrease of the monomeric form of alpha‐synuclein, which was due to both decreased synthesis of the protein and its increased mono‐ubiquitination accompanied by nuclear translocation. The essential neuroprotective role of alpha‐synuclein was confirmed by the fact that subchronic valproate treatment, which increases alpha‐synuclein expression and prevents its nuclear translocation in cerebellar granule cells exposed to 6‐OHDA, significantly protected these neurons from 6‐OHDA insult. In agreement with the pro‐survival role of alpha‐synuclein in this model, subtoxic concentrations of alpha‐synuclein antisense oligonucleotides, aggravated 6‐OHDA toxicity towards granule neurons. Our results demonstrate that normal alpha‐synuclein expression is essential for the viability of primary neurons and that its pro‐survival role is abolished in 6‐OHDA neurotoxic challenge. These results are relevant to more precisely define the role of alpha‐synuclein in neuronal cells and to better understand its putative involvement in neurodegeneration.

Regional alterations of the NO/NOS system in the aging brain: a biochemical, histochemical and immunochemical study in the rat

We have used several approaches (immunohistochemistry and enzyme histochemistry, Western blotting, biochemical assay of Ca(2+)-dependent catalytic activity) in order to detect differences in neuronal nitric oxide synthase (nNOS) expression and activity in various brain regions of young-adult (4-month-old) and aged (28-month-old) rats. In most of the brain regions examined (striatum, neocortex, olfactory cortex and hippocampus) some significant decrease in the density per unit area of nNOS neurons, detected either through immunohistochemistry or enzyme histochemistry, was observed in aged rats. However, only in the striatum and olfactory cortex this was accompanied by a significant decrease of the catalytic activity of the constitutive, Ca(2+)-dependent NOS form. In these two regions, the relative level of expression of nNOS protein was also significantly decreased, as assessed by Western blotting of proteic extracts from young-adult and aged rats. Other observed differences were a paler stain of neurons in some brain areas of the aged rats and differences of cellular compartmentalization of the protein in the same rats, as assessed through confocal microscopy. The present observations demonstrate that the expression and activity of nNOS show regionally-specific alterations in the brain of aged healthy rats, with a trend towards decrease, rather than toward increase as suggested by some previous reports. Therefore, hypotheses implicating nitric oxide increase in brain aging should be reconsidered on the basis of a clear-cut distinction between the physiological and the pathological aspects of the aging process.

Protection from kainic acid neuropathological syndrome by NMDA receptor antagonists: Effect of MK-801 and CGP 39551 on neurotransmitter and glial markers

Systemic administration of kainic acid results in the development of a characteristic convulsive syndrome, accompanied by neuropathological alterations and loss of transmitter markers in some forebrain regions. Since some of these effects appear to involve the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors, the protection given by a non-competitive (MK-801) and a competitive (CGP 39551) NMDA receptor antagonist against the loss of glutamatergic and gamma-amino butyric acid (GABAergic) neurochemical markers was compared. Appropriate doses of both compounds (1 mg/kg MK-801 and 25 mg/kg CGP 39551) completely reversed the decrease of high affinity uptake of glutamate and activity of glutamate decarboxylase in the olfactory cortex, amygdala, hippocampus and lateral septum. In addition, they also essentially counteracted the increase of a glial marker, the enzyme glutamine synthetase, consequent to neuronal degeneration. The results confirmed that involvement of NMDA receptors is essential for the full expression of neuropathological effects of kainic acid. They also support the use of a competitive antagonist of the NMDA receptor, such as CGP 39551, to afford substantial protection against the excitotoxic damage, whilst giving fewer side effects and motor disturbances than MK-801.

Temporal, regional and cellular selectivity of neonatal alteration of the thyroid state on neurochemical maturation in the rat

SummaryThe effects of alteration of thyroid state on neurochemical maturation have been studied in rats made hypothyroid by daily injections of methimazole or hyperthyroid by daily supplementation with thyroid hormone (T3) from postnatal days 1 to 27. Biochemical assays on seven brain regions plus the spinal cord were carried out on 14 and 28 day-old rats as well as in adult rats after at least 40 days of recovery. 2′,3′cyclic nucleotide phosphohydrolase (CNPase), a specific marker for oligodendrocytes and myelination was significantly decreased in all regions except the spinal cord of hypothyroid rats. The astrocytic marker glutamine synthetase (GS) was slightly increased in the hippocampus of hypothyroid rats. Choline acetyltransferase (ChAT), a specific marker for cholinergic neurons, was decreased in the prefrontal and visual cortices, the striatum and the superior colliculus and increased in the cerebellum of hypothyroid rats; in addition, the enzyme activity was increased in the prefrontal cortex and striatum and decreased in the cerebellum of hyperthyroid rats. Acetyl-cholinesterase (AChE) activity was decreased in the prefrontal cortex and in the striatum of hypothyroid rats while 3H-quinuclidynil benzilate (QNB) muscarinic binding was decreased in all cortical areas and in the hippocampus of hypothyroid rats. Glutamate decarboxylase (GAD), a specific marker for GABAergic neurons, was decreased in the cortical areas of hypothyroid rats. Aromatic amino acid decarboxylase (AAD), a general marker for monoaminergic neurons, was unaffected. Alteration of neurochemical parameters was never observed in the spinal cord. Under our experimental conditions, the effects of alteration of thyroid state appeared graded and selective with respect to temporal, regional and cellular parameters.

Developmental effects of in vivo and in vitro inhibition of nitric oxide synthase in neurons

The diffusible chemical messenger nitric oxide (NO) is involved in neuronal plasticity and it is, therefore, supposed to play a role in brain development. A shortage of NO during the critical period of brain maturation may theoretically have long-lasting consequences on the organization of the adult brain. We have performed in neonatal rats a chronic inhibition of the enzyme responsible for NO production, nitric oxide synthase (NOS), from postnatal day 3 to postnatal day 23, through administration of the competitive antagonist N-nitro-L-arginine methylester (L-NAME). The calcium-dependent catalytic activity resulted almost completely inhibited throughout the period of treatment and it took more than 4 days after its suspension to get a full recovery. The expression of the neuronal isoform of the enzyme (nNOS), revealed by immunoblotting, was unchanged during the treatment and after it. The histochemical reaction for NADPH diaphorase was reduced at the end of the treatment and recovered in concomitance with the recovery of the catalytic NOS activity. No gross structural alterations were detected in brain morphology. The levels of three neurotransmitter-related and one astrocytic marker were unchanged in the cerebellum, hippocampus and cortex of 60-day-old rats which had been neonatally treated. A similar lack of significant effects on neurochemical brain maturation was also noticed in a parallel series of experiments, in which a short pulse of NOS inhibition was performed at a critical prenatal time of brain development, from gestational day 14 to gestational day 19. In vitro, chronic exposure of cerebellar granule cells to L-NAME (500 microM) resulted in slight decrease of surviving neurons after 8 days in culture and in better resistance to the challenge of stressful culture conditions. The present results suggest that the basic plan of brain organization can be achieved despite an almost complete NOS inhibition during the maturation period. In vitro, NOS inhibition may bring to more pronounced consequences on neuronal viability and function.

Regional maturation of neurotransmitter-related and glial markers during postnatal development in the rat

Neurotransmitter‐related (choline acetyltransferase, acetylcholinesterase, glutamate decarboxylase, l‐glutamate and GABA high affinity uptake) and glial neurochemical markers (glutamine synthetase, β‐alanine uptake and 2′,3′ cyclic nucleotide phosphohydrolase) have been quantitatively assayed in various regions of the rat CNS during normal postnatal development: spinal cord, cerebellum, superior colliculus, hippocampus, striatum, visual cortex, frontal sensory‐motor cortex and prefrontal cortex. In general, neurochemical markers show an obvious trend toward increasing levels in parallel with brain maturation. However, some relevant exceptions have been observed and discussed. Detailed knowledge of regional neurochemical brain maturation is important since it gives us information concerning some key events of brain development. In addition, this knowledge is the essential pre‐requisite for studies aimed at the alteration of specific regional and temporal parameters through experimental manipulation.