Brain structure & function
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The present study investigated the short-term and long-term synaptic plasticity of excitatory synapses formed by the nucleus reuniens (RE) and entorhinal cortex (EC) on the distal apical dendrites of CA1 pyramidal cells. RE-CA1 synapses are implicated in memory involving the hippocampus and medial prefrontal cortex. Current source density (CSD) analysis was used to identify excitatory and inhibitory currents following stimulation of RE or medial perforant path (MPP) in urethane-anesthetized mice in vivo. ⋯ After TBS of the MPP, the MPP-CA1 distal dendritic synapse could manifest LTP or long-term depression, but the non-tetanized RE-CA1 synapse was typically potentiated. Heterosynaptic potentiation of the RE to CA1 distal synapses may occur after repeated activity of EC afferents, or spread of MPP stimulus currents to coursing RE afferents. The results indicate a propensity of RE-CA1 distal excitatory synapses to show PPF, LTP and gamma oscillations, all of which may participate in memory processing by RE and EC.
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Despite its prevalence and high disease burden, the pathophysiological mechanisms underlying chronic migraine (CM) are not well understood. As CM is a complex disorder associated with a range of sensory, cognitive, and affective comorbidities, examining structural network disruption may provide additional insights into CM symptomology beyond studies of focal brain regions. Here, we compared structural interconnections in patients with CM (n = 52) and healthy controls (HC) (n = 48) using MRI measures of cortical thickness and subcortical volume combined with graph theoretical network analyses. ⋯ Taken together, examining structural correlations between brain areas may be a more sensitive means to detect altered brain structure and understand CM symptomology at the network level. These findings contribute to an increased understanding of structural connectivity in CM and provide a novel approach to potentially track and predict the progression of migraine disorders. This study is registered on ClinicalTrials.gov (Identifier: NCT03304886).
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In humans, sensorimotor cortical areas receive relevant dopaminergic innervation-although an anatomic description of the underlying fiber projections is lacking so far. In general, dopaminergic projections towards the cortex originate within the ventral tegmental area (VTA) and are organized in a meso-cortico-limbic system. Using a DTI-based global tractography approach, we recently characterized the superolateral branch of the medial forebrain bundle (slMFB), a prominent pathway providing dopaminergic (and other transmitters) innervation for the pre-frontal cortex (Coenen et al., NeuroImage Clin 18:770-783, 2018). ⋯ As expected, the tract is characterized by a decussation at the ponto-mesencephal level and a projection covering the superior-frontal and precentral cortex. In addition to the physiological role of these particular bundles, the physiological and pathophysiological impact of dopaminergic signaling within sensorimotor cortical fields becomes discussed. However, some limitations have to be taken into account in consequence of the method: the transmitter content, the directionality, and the occurrence of interposed synaptic contacts cannot be specified.
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The cerebellar intrinsic connectivity is of remarkable regularity with a similar build repeated many times over. However, several modifications of this basic circuitry occur that can provide important clues to evolutionary adaptations. We have observed differences in the wiring of the cerebellar output structures (the deep cerebellar nuclei, DCN) with higher dendritic length density in the phylogenetically newer DCN. ⋯ We also detected a higher percentage of co-labelled vGluT1 and 2 boutons in the macaque than we found in the rat. In summary, these results confirm that the hyposcalled dendrites of the monkey LN/dentate also show a lower number of vGluT1+ boutons per neuron. These results provide further support of our model relating the dendritic morphology of the LN/dentate neurons to the morphology of the specially enlarged LN/dentate nucleus in primates.
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The sledge runner fasciculus (SRF) has been recently identified as a discrete fiber tract of the occipital lobe and has been allegedly implicated in the axonal connectivity of cortical areas conveying spatial navigation and visuospatial imagery. However, detailed knowledge regarding its anatomic and tractographic morphology is lacking. We thus opted to investigate the anatomy and connectivity of the SRF through cadaveric dissections and DTI studies. ⋯ Dissection and tractographic findings showed a good correspondence regarding SR topography, morphology and axonal connectivity. Our results support the hypothesis that the SRF is involved in the structural axonal connectivity of cerebral areas that strongly activate during spatial navigation and visuospatial imagery. Furthermore detailed anatomo-imaging evidence is provided on the microanatomic architecture of this newly discovered fiber tract.