Neuroscience
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Selective immunotoxic cholinergic lesions in the nucleus basalis magnocellularis (NBM) impair visuospatial attention performance in a 5-choice serial reaction time task (5-CSRT task). The features of the reported deficits, however, do not perfectly match among studies, in which some lesions may have been too weak while others largely encroached onto the septal region. Using the 5-CSRT task, we therefore re-assessed the effects of NBM lesions that produced minimal septal damage. ⋯ Furthermore, overall performance levels decreased when the stimulus duration was shortened (i.e. 0.5-0.2 s) or its intensity attenuated, and rats with cholinergic lesions remained consistently impaired vs. controls. These results show that disruption of sustained visual attention functions by damage to the NBM cholinergic neurons can be evidenced despite weak or no effects on variables accounting for motivational, locomotion- or impulsivity-related biases. Discrepancies with previously reported results are discussed in terms of differences in lesion extent/specificity and training levels.
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The neurosteroid allopregnanolone (3alpha,5alpha-THP) is well characterized as a potentially therapeutic molecule which exerts important neurobiological actions including neuroprotective, antidepressant, anxiolytic, anesthetic and analgesic effects. We have recently observed that neurons and glial cells of the rat spinal cord (SC) contain various key steroidogenic enzymes such as 5alpha-reductase and 3alpha-hydroxysteroid oxido-reductase which are crucial for 3alpha,5alpha-THP biosynthesis. Furthermore, we demonstrated that the rat SC actively produces 3alpha,5alpha-THP. ⋯ These results demonstrate that glycine and gelsemine, acting via Gly-R, upregulate 3alpha,5alpha-THP biosynthesis in the SC. The data also revealed a structure-activity relationship of the analogs strychnine and gelsemine on neurosteroidogenesis. Possibilities are opened for glycinergic agents and gelsemine utilization to stimulate selectively 3alpha,5alpha-THP biosynthetic pathways in diseases evoked by a decreased neurosteroidogenic activity of nerve cells.
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The dorsal striatum (DS) is involved in various forms of learning and memory such as procedural learning, habit learning, reward-association and emotional learning. We have previously reported that bilateral DS lesions disrupt tone fear conditioning (TFC), but not contextual fear conditioning (CFC) [Ferreira TL, Moreira KM, Ikeda DC, Bueno OFA, Oliveira MGM (2003) Effects of dorsal striatum lesions in tone fear conditioning and contextual fear conditioning. Brain Res 987:17-24]. ⋯ Overall, the present results underscore that other routes, aside from the well-established CeA projections to the periaqueductal gray, may contribute to the acquisition/consolidation of the freezing response associated to a TFC task. It is suggested that CeA may presumably influence DS processing via a synaptic relay on dopaminergic neurons of the substantia nigra compacta and retrorubral nucleus. The present observations are also in line with other studies showing that TFC and CFC responses are mediated by different anatomical networks.
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The ventral tegmental area (VTA) is a nodal link in reward circuitry. Based on its striatal output, it has been subdivided in a caudomedial part which targets the ventromedial striatum, and a lateral part which targets the ventrolateral striatum [Ikemoto S (2007) Dopamine reward circuitry: two projection systems from the ventral midbrain to the nucleus accumbens-olfactory tubercle complex. Brain Res Rev 56:27-78]. ⋯ In general, these projections, like the spiralated striato-nigro-striatal loops, display a medial-to-lateral organization. This anatomical arrangement conceivably permits the ventromedial striatum to influence the activity of the lateral striatum. The caudal pole of the VTA appears to be a critical site for a global recruitment of the mesotelencephalic system.
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It remains unclear what neuronal mechanisms in humans are reflected in the activation of the ipsilateral hemisphere during the performance of unilateral movements. To address this question we combined transcranial magnetic stimulation (TMS), electroencephalography (EEG), and electromyographic (EMG) recordings of motor evoked potentials (MEPs). Compared with previous TMS studies, where changes in excitability might be related to both cortical and spinal mechanisms, our setup allowed a more direct evaluation of the cortical processes related to the performance of unilateral movements. ⋯ These results suggest that the increased excitability in the ipsilateral hemisphere was uncoupled from the modulation of the cortico-spinal output. Moreover, we show that the background neuronal activity during unilateral movements was different in the ipsi- and contralateral hemisphere. This difference most likely reflects inter-hemispheric balance between the excitation and inhibition which is required for the optimal performance of the unilateral movement.