RESUMO
Dopamine (DA) modulates basal ganglia (BG) activity for initiation and execution of goal-directed movements and habits. While most studies are aimed to striatal function, the cellular and molecular mechanisms underlying dopaminergic regulation in other nuclei of the BG are not well understood. Therefore, we set to analyze the dopaminergic modulation occurring in subthalamo-nigral synapse, in both pars compacta (SNc) and pars reticulata (SNr) neurons, because these synapses are important for the integration of information previously processed in striatum and globus pallidus. In this study, electrophysiological and pharmacological evidence of dopaminergic modulation on glutamate release through calcium channels is presented. Using paired pulse ratio (PPR) measurements and selective blockers of these ionic channels, together with agonists and antagonists of DA D2 -like receptors, we found that blockade of the CaV 3 family occludes the presynaptic inhibition produced by the activation of DA receptors pharmacologically profiled as D3 -type in the STh-SNc synapses. On the contrast, the blockade of CaV 2 channels, but not CaV 3, occlude with the effect of the D3 agonist, PD 128907, in the STh-SNr synapse. The functional role of this differential distribution of calcium channels that modulate the release of glutamate in the SN implies a fine adjustment of firing for both classes of neurons. Dopaminergic neurons of the SNc establish a DA tone within the SN based on the excitatory/inhibitory inputs; such tone may contribute to processing information from subthalamic nucleus and could also be involved in pathological DA depletion that drives hyperexcitation of SNr neurons.
Assuntos
Canais de Cálcio/metabolismo , Neurônios Dopaminérgicos/metabolismo , Substância Negra/metabolismo , Subtálamo/metabolismo , Potenciais Sinápticos , Animais , Bloqueadores dos Canais de Cálcio/farmacologia , Dopamina/metabolismo , Agonistas de Dopamina/farmacologia , Neurônios Dopaminérgicos/fisiologia , Ácido Glutâmico/metabolismo , Masculino , Ratos , Ratos Wistar , Substância Negra/citologia , Substância Negra/fisiologia , Subtálamo/citologia , Subtálamo/fisiologiaRESUMO
As the largest tarsal bone and the most inferior bone in the body, the calcaneus is responsible for supporting the axial load from the weight of the body. It is most commonly fractured after a fall from a height in which axial loads exceed its support capacity. Calcaneal fractures account for 60% of all tarsal fractures. Conventional radiography is commonly used for initial evaluation of calcaneal injury but has the typical disadvantages of two-dimensional imaging. Modern assessment of calcaneal fractures relies heavily on multidetector computed tomography (CT), which allows better visualization and characterization of fracture lines and fragment displacement. Calcaneal fractures observed at CT have been divided into intra- and extraarticular fractures on the basis of subtalar joint involvement. The Sanders classification system for intraarticular fractures is the most commonly used system because it correlates with clinical outcomes and involves less interobserver variability. The classification of extraarticular fractures has been less controversial and makes use of anatomic landmarks on the calcaneus to divide the bone into anterior, middle, and posterior areas. Soft-tissue involvement is an important aspect of calcaneal fracture assessment because it has been linked with poor functional outcomes. Familiarity with the normal anatomy of the calcaneus, the classification of calcaneal fractures, and the various complications of these fractures is essential for treatment assessment, especially if surgical intervention is required.