Suppression of V1 Feedback Produces a Shift in the Topographic Representation of Receptive Fields of LGN Cells by Unmasking Latent Retinal Drives

Transcranial magnetic stimulation in non-human primates: A systematic review

Transcranial magnetic stimulation (TMS) is widely employed as a tool to investigate and treat brain diseases. However, little is known about the direct effects of TMS on the brain. Non-human primates (NHPs) are a valuable translational model to investigate how TMS affects brain circuits given their neurophysiological similarity with humans and their capacity to perform complex tasks that approach human behavior. This systematic review aimed to identify studies using TMS in NHPs as well as to assess their methodological quality through a modified reference checklist. The results show high heterogeneity and superficiality in the studies regarding the report of the TMS parameters, which have not improved over the years. This checklist can be used for future TMS studies with NHPs to ensure transparency and critical appraisal. The use of the checklist would improve methodological soundness and interpretation of the studies, facilitating the translation of the findings to humans. The review also discusses how advancements in the field can elucidate the effects of TMS in the brain.

Treatment with Ginkgo biloba supplement modulates oxidative disturbances, inflammation and vascular functions in oxygen deprived hypothyroid mice: Involvement of endothelin-1/NO signaling pathways

A double-hit biological alteration involving exposure to oxygen deprivation in hypothyroid condition may exacerbate cellular oxidative and inflammatory disturbances comparative to a one-hit biological exposure. This study investigated the therapeutic effect of Ginkgo biloba as cardioprotective against aortic oxido-inflammatory disturbances following oxygen deprivation in hypothyroid mice. Male Swiss mice were partitioned into 5 groups (n = 6) for hypothyroidism (Carbimazole 1.2 mg/kg) and hypoxia induction. Group 1 (normal control), group 2 (hypoxic stress control), group 3 (hypoxic and hypothyroid stress), group 4 (hypoxic and hypothyroid stress and Ginkgo biloba 20 mg/kg; p.o) and group 5 (hypoxic and hypothyroid stress and Levothyroxine 10 μg/kg; p.o) for 14 days. Thereafter, serum and aorta was collected for biochemical evaluation. GBS did not up-regulate the serum thyroid hormone imbalances (tri-iodothyronine (T3), thyroxin (T4)) but maintains the TSH levels. The blood glucose level was reduced with decrease oxidative stress and inflammatory mediators in the serum/aorta indicated by inhibited redox status following treatment with GBS. Moreover, endothelin-1/nitric oxide signaling pathways were markedly regulated in the aorta. Conclusively, GBS acts as a therapeutic agent and may be consider as a potential vasodilator candidate in the management and control of hypoxic stress in hypothyroid condition. PRACTICAL APPLICATIONS: Treatment with Gingko biloba supplement abated endothelial abnormalities via elevation of nitric oxide release and suppression of endothelin activity in hypothyroid mice exposed to hypoxic hypoxia. The activity of myeloperoxidase enzyme and redo-inflammatory status was downregulated following treatment with Gingko biloba supplement in hypothyroid mice exposed to hypoxic hypoxia. Treatment with Gingko biloba supplement modulates hypothalamic-pituitary-adrenal (HPA) axis by inhibiting corticosterone release in hypothyroid mice exposed to hypoxic hypoxia.

Functional Convergence at the Retinogeniculate Synapse

Precise connectivity between retinal ganglion cells (RGCs) and thalamocortical (TC) relay neurons is thought to be essential for the transmission of visual information. Consistent with this view, electrophysiological measurements have previously estimated that 1-3 RGCs converge onto a mouse geniculate TC neuron. Recent advances in connectomics and rabies tracing have yielded much higher estimates of retinogeniculate convergence, although not all identified contacts may be functional. Here we use optogenetics and a computational simulation to determine the number of functionally relevant retinogeniculate inputs onto TC neurons in mice. We find an average of ten RGCs converging onto a mature TC neuron, in contrast to >30 inputs before developmental refinement. However, only 30% of retinogeniculate inputs exceed the threshold for dominating postsynaptic activity. These results signify a greater role for the thalamus in visual processing and provide a functional perspective of anatomical connectivity data.

An evolving view of retinogeniculate transmission

The thalamocortical (TC) relay neuron of the dorsoLateral Geniculate Nucleus (dLGN) has borne its imprecise label for many decades in spite of strong evidence that its role in visual processing transcends the implied simplicity of the term "relay". The retinogeniculate synapse is the site of communication between a retinal ganglion cell and a TC neuron of the dLGN. Activation of retinal fibers in the optic tract causes reliable, rapid, and robust postsynaptic potentials that drive postsynaptics spikes in a TC neuron. Cortical and subcortical modulatory systems have been known for decades to regulate retinogeniculate transmission. The dynamic properties that the retinogeniculate synapse itself exhibits during and after developmental refinement further enrich the role of the dLGN in the transmission of the retinal signal. Here we consider the structural and functional substrates for retinogeniculate synaptic transmission and plasticity, and reflect on how the complexity of the retinogeniculate synapse imparts a novel dynamic and influential capacity to subcortical processing of visual information.