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Recent reports indicate that neurons are particularly sensitive to hydrogen peroxide (H2O2). The present study was undertaken to investigate the putative role of astrocytes in the modulation of the neurotoxic effect of H2O2. The exposure to H2O2 of cultured striatal neurons from mouse embryos induced a concentration-dependent (10–1000 microM) cell death as estimated 24 hr later. Two methods were used to estimate neuronal survival: the 3-[4,5-dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide assay or an enzyme-linked immunosorbent assay with antibodies directed against an antigen located in neurons (microtubule-associated protein-2). The neurotoxic effect of H2O2 on neurons cocultured with astrocytes was strongly attenuated compared with that observed on a pure population of neurons seeded at the same density. Moreover, the protective effect of astrocytes depended on the astrocytes/neurons ratio, a significant neuroprotection being detectable for 1 astrocyte to 20 neurons. Catalase seems to be the main hydrogen peroxidase activity involved in the neuroprotective effect of astrocytes. Indeed, in the culture conditions used, this enzymatic activity was enriched in this cell type compared with neurons; its inhibition, and not that of glutathione peroxidase, reduced the disappearance rate of the oxidant. On the contrary, glutathione peroxidase appeared to be the main enzymatic activity involved in the neuronal defense against H2O2 toxicity. Therefore, astrocytes could delay neuronal death in pathological situations in which H2O2 has been, at least partially, demonstrated to be involved.

Dopamine can be released in the substantia nigra for the dendrites of nigrostriatal dopaminergic neurones, to be involved there in the self-regulation of the dopaminergic cells, to control the release of neurotransmitters from nigral afferent fibres and to influence the activity of nigral non-dopaminergic cells.

Corticostriatal projections originate from the entire cerebral cortex and provide the major source of glutamatergic inputs to the basal ganglia. Despite the importance of corticostriatal connections in sensorimotor learning and cognitive functions, plasticity forms at these synapses remain strongly debated. Using a corticostriatal slice preserving the connections between the somatosensory cortex and the target striatal cells, we report the induction of both non-Hebbian and Hebbian forms of long-term potentiation (LTP) and long-term depression (LTD) on striatal output neurons (SONs). LTP and LTD can be induced selectively by different stimulation patterns (highfrequency trains vs low-frequency pulses) and were evoked with similar efficiency in non-Hebbian and Hebbian modes. Combination of LTP-LTD and LTD-LTP sequences revealed that bidirectional plasticity occurs at the same SONs and provides efficient homeostatic mechanisms leading to a resetting of corticostriatal synapses avoiding synaptic saturation. The effect of temporal relationship between cortical stimulation and SON activity was assessed using spike-timing-dependent plasticity (STDP) protocols. An LTP was observed when an action potential was triggered in the striatal neuron before the cortical stimulus, and, conversely, an LTD was induced when the striatal neuron discharge was triggered after the cortical stimulation. Such STDP was reversed when compared with those described so far in other mammalian brain structures. This mechanism may be essential for the role of the striatum in learning of motor sequences in which sensory and motor events are associated in a precise time sequence.

Spinal tuberculosis (TB) accounts for about 2% of all cases of TB. New methods of diagnosis such as magnetic resonance imaging (MRI) or percutaneous needle biopsy have emerged. Two distinct patterns of spinal TB can be identified, the classic form, called spondylodiscitis (SPD) in this article, and an increasingly common atypical form characterized by spondylitis without disk involvement (SPwD). We conducted a retrospective study of patients with spinal TB managed in the area of Paris, France, between 1980 and 1994 with the goal of defining the characteristics of spinal TB and comparing SPD to SPwD. The 103 consecutive patients included in our study had TB confirmed by bacteriologic and/or histologic studies of specimens from spinal or paraspinal lesions (93 patients) or from extraspinal skeletal lesions (10 patients). Sixty-eight percent of patients were foreign-born subjects from developing countries. None of our patients was HIV-positive. SPD accounted for 48% of cases and SPwD for 52%. Patients with SPwD were younger and more likely to be foreign-born and to have multiple skeletal TB lesions. Neurologic manifestations were observed in 50% of patients, with no differences between the SPD and SPwD groups. Of the 44 patients investigated by MRI, 6 had normal plain radiographs; MRI was consistently positive and demonstrated epidural involvement in 77% of cases. Bacteriologic and histologic yields were similar for surgical biopsy (n = 16) and for percutaneous needle aspiration and/or biopsy (n = 77). Cultures for Mycobacterium tuberculosis were positive in 83% of patients, and no strains were resistant to rifampin. Median duration of antituberculous chemotherapy was 14 months. Surgical treatment was performed in 24% of patients. There were 2 TB-related deaths. Our data suggest that SPwD may now be the most common pattern of spinal TB in foreign-born subjects in industrialized countries. The reasons for this remain to be elucidated.

Hydrogen peroxide (H2O2) is suspected to be involved in numerous brain pathologies such as neurodegenerative diseases or in acute injury such as ischemia or trauma. In this study, we examined the ability of pyruvate to improve the survival of cultured striatal neurons exposed for 30 min to H2O2, as estimated 24 hr later by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide assay. Pyruvate strongly protected neurons against both H2O2 added to the external medium and H2O2 endogenously produced through the redox cycling of the experimental quinone menadione. The neuroprotective effect of pyruvate appeared to result rather from the ability of alpha-ketoacids to undergo nonenzymatic decarboxylation in the presence of H2O2 than from an improvement of energy metabolism. Indeed, several other alpha-ketoacids, including alpha-ketobutyrate, which is not an energy substrate, reproduced the neuroprotective effect of pyruvate. In contrast, lactate, a neuronal energy substrate, did not protect neurons from H2O2. Optimal neuroprotection was achieved with relatively low concentrations of pyruvate (

The hippocampus, the prefrontal cortex, and interconnected neural circuits are implicated in several aspects of cognitive and memory processes. The present review is dedicated to the description of the anatomo‐functional characteristics of the hippocampo‐prefrontal pathway and related neuronal circuits in the rat. This pathway, which originates from the hippocampal CA1/subiculum fields, innervates the prelimbic/medial orbital areas of the prefrontal cortex (PL/MO). Its synaptic influence on cortical pyramidal neurons consists in an early monosynaptic excitation followed by an inhibition and, in some cases, a late excitation. These later effects are likely due to the subsequent activation of the local cortical network. PL/MO areas and the CA1/subiculum both send projections to the nucleus accumbens, a region of the ventral striatum which is particularly implicated in goal‐directed behavior. Therefore, emphasis is placed on respective projections from PL/MO areas and from the CA1/subiculum on the “core” and the “shell” regions of the nucleus accumbens, as well as on their interconnected circuits. Signals which are directed to the prefrontal cortex through these circuits might modulate hippocampo‐prefrontal inputs. Finally, the direct and/or indirect relationships of the hippocampus, prefrontal cortex, and nucleus accumbens with the ventral tegmental area/substantia nigra pars compacta complex (VTA/SNC) (where dopamine neurons are located) will also be described, because these neurons are known to modulate synaptic transmission and plasticity in their target structures and to play a fundamental role in motivational processes. Hippocampus 10:411–419, 2000 © 2000 Wiley‐Liss, Inc.