RESUMO

Cerebellar-thalamo-striatal synaptic communication has been implicated in a wide range of behaviors, including goal-directed actions, and is altered in cerebellar dystonia. However, its detailed connectivity through the thalamus and its contribution to the execution of forelimb movements is unclear. Here, we use trans-synaptic and retrograde tracing, ex vivo slice recordings, and optogenetic inhibitions during the execution of unidirectional or sequential joystick displacements to demonstrate that the deep cerebellar nuclei (DCN) influence the dorsal striatum with a very high probability. We show that this mainly occurs through the centrolateral (CL), parafascicular (PF), and ventrolateral (VL) nuclei of the thalamus, observing that the DCN→VL and DCN→CL pathways contribute to the execution of unidirectional forelimb displacements while the DCN→PF and DCN→thalamo→striatal pathways contribute to the appropriate execution of forelimb reaching and sequential displacements. These findings highlight specific contributions of the different cerebellar-thalamo-striatal paths to the control of skilled forelimb movement.

Assuntos

RESUMO

Differences in the intrinsic properties of intralaminar thalamo-striatal neurons such as expressing low-threshold-spikes (LTS) or after hyperpolarizing potentials (AHPs) of different duration have been attributed to different maturation stages. However, two morphological types: "diffuse" and "bushy" have been described. Therefore, we explored whether electrophysiological differences persist in adult mice using whole cell recordings. Some recorded neurons were identified by intracellular labeling with biocytin and double labeling with retrograde or anterograde tracings using Cre-mice. We classified these neurons by their AHPs during spontaneous firing. Neurons with long duration AHPs, with fast and slow components, were mostly found in the parafascicular (Pf) nucleus. Neurons with brief AHPs were mainly found in the central lateral (CL) nucleus. However, neurons with both AHPs were found in both nuclei in different proportions. Firing frequency adaptation differed between these neuron classes: those with prolonged AHPs exhibited firing frequency adaptation with fast and slow time constants whereas those with brief AHPs were slow adapters. Neurons with more prolonged AHPs had significant higher input resistances than neurons with brief AHPs. Both cell classes could fire in two modes: trains of single action potentials at depolarized potentials or high frequency bursts on top of LTS at more hyperpolarized potentials. LTS were probably generated by Cav3 calcium channels since they were blocked by the selective antagonist TTA-P2. About 11% of neurons with brief AHPs and 55% of neurons with prolonged AHPs do not show LTS and bursts, even when potassium currents are blocked.

Assuntos

RESUMO

The main objective of this work was to investigate the effect of hybridization on the mechanical and thermal properties of intralaminar natural fiber-reinforced hybrid composites based on sisal. Ramie, sisal and curauá fibers were selected as natural fiber reinforcements for the epoxy matrix based composites, which were produced by the hand lay-up technique. Tensile, flexural and impact tests were carried out according to American society for testing and materials (ASTM) standards to characterize the hybrid composites, while differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to evaluate the thermal properties. It was found that the mechanical properties are improved by hybridization of sisal based composites. The thermal analysis showed that the hybridization did not significantly affect the thermal stability of the composites. A scanning electron microscopy (SEM) was used to examine the fracture surface of the tested specimens. The SEM images showed a brittle fracture of the matrix and fiber breakage near the matrix.

RESUMO

Posterior cervical spine fixation is a key component in achieving spinal arthrodesis for treating various cervical spine pathologies including neoplastic, inflammatory, traumatic and degenerative diseases. Historically, various wiring techniques had played major roles in posterior cervical spine fixation. Today, posterior cervical screw fixation is utilized by most spine surgeons instead of wiring for its superior biomechanical strength. A review of lateral mass, pedicle, intralaminar and transfacet screw fixation techniques in the subaxial cervical spine is presented in a detailed fashion. A comparison among different posterior cervical subaxial fixation techniques is also included. Although the safety of freehand techniques was demonstrated in the majority of the existing studies, real-time navigation is becoming increasingly utilized for cervical screw insertion, especially for cervical pedicle screws, where the freehand technique is technically demanding and may carry a higher risk of neurovascular injury. Several different posterior screw fixation techniques exist for the subaxial cervical spine with generally low complication rate. Spine surgeons should be familiar with these techniques and choose the optimal technique based on each patient's individual anatomy and surgical needs.

RESUMO

STUDY DESIGN: A narrative literature review. OBJECTIVES: To review the surgical techniques of posterior screw fixation in the subaxial cervical spine. METHODS: A broad literature review on the most common screw fixation techniques including lateral mass, pedicle, intralaminar and transfacet screws was performed on PubMed. The techniques and surgical nuances are summarized. RESULTS: The following techniques were described in detail and presented with illustrative figures, including (1) lateral mass screw insertion: by Roy-Camille, Louis, Magerl, Anderson, An, Riew techniques and also a modified technique for C7 lateral mass fixation; (2) pedicle screw fixation technique as described by Abumi and also a freehand technique description; (3) intralaminar screw fixation; and finally, (4) transfacet screw fixation, as described by Takayasu, DalCanto, Klekamp, and Miyanji. CONCLUSIONS: Many different techniques of subaxial screw fixation were described and are available. To know the nuances of each one allows surgeons to choose the best option for each patient, improving the success of the fixation and decrease complications.

RESUMO

The thalamic midline/intralaminar complex is part of the higher-order thalamus, which receives little sensory input, and instead forms extensive cortico-thalamo-cortical pathways. The midline thalamic nuclei connect with the medial prefrontal cortex and the medial temporal lobe. On the other hand, the intralaminar nuclei connect with the fronto-parietal cortex. Taking into account this connectivity pattern, it is not surprising that the midline/intralaminar complex has been implicated in a broad variety of cognitive functions, including memory process, attention and orientation, and also reward-based behavior. Serotonin (5-HT) is a neurotransmitter that exerts different post-synaptic roles. Serotonergic neurons are almost entirely restricted to the raphe nuclei and the 5-HT fibers are distributed widely throughout the brain, including the midline/intralaminar complex. The present study comprises a detailed description of the morphologic features and semiquantitative analysis of 5-HT fibers distribution in the midline/intralaminar complex in the rock cavy, a typical rodent of the Northeast region of Brazil, which has been used by our group as an anatomical model to expand the comprehension about phylogeny on the nervous system. The 5-HT fibers in the midline/intralaminar nuclei of the rock cavy were classified into three distinct categories: (1) beaded fibers, which are relatively fine and endowed with large varicosities; (2) fine fibers, with thin axons and small varicosities uniformly distributed in whole axon; and (3) stem axons, showing thick non-varicose axons. Moreover, the density of 5-HT fibers is variable among the analyzed nuclei. On the basis of this diversity of the morphological fibers and the differential profile of optical density among the midline/intralaminar nuclei of the rock cavy, we conclude that the serotonergic system uses a diverse morphologic apparatus to exert a large functional repertory in the midline/intralaminar thalamic nuclei.

Assuntos