Ying Zhang

V1 spinal neurons regulate the speed of vertebrate locomotor outputs

The neuronal networks that generate vertebrate movements such as walking and swimming are embedded in the spinal cord. These networks, which are referred to as central pattern generators (CPGs), are ideal systems for determining how ensembles of neurons generate simple behavioural outputs. In spite of efforts to address the organization of the locomotor CPG in walking animals, little is known about the identity and function of the spinal interneuron cell types that contribute to these locomotor networks. Here we use four complementary genetic approaches to directly address the function of mouse V1 neurons, a class of local circuit inhibitory interneurons that selectively express the transcription factor Engrailed1. Our results show that V1 neurons shape motor outputs during locomotion and are required for generating ‘fast’ motor bursting. These findings outline an important role for inhibition in regulating the frequency of the locomotor CPG rhythm, and also suggest that V1 neurons may have an evolutionarily conserved role in controlling the speed of vertebrate locomotor movements.

V3 Spinal Neurons Establish a Robust and Balanced Locomotor Rhythm during Walking

A robust and well-organized rhythm is a key feature of many neuronal networks, including those that regulate essential behaviors such as circadian rhythmogenesis, breathing, and locomotion. Here we show that excitatory V3-derived neurons are necessary for a robust and organized locomotor rhythm during walking. When V3-mediated neurotransmission is selectively blocked by the expression of the tetanus toxin light chain subunit (TeNT), the regularity and robustness of the locomotor rhythm is severely perturbed. A similar degeneration in the locomotor rhythm occurs when the excitability of V3-derived neurons is reduced acutely by ligand-induced activation of the allatostatin receptor. The V3-derived neurons additionally function to balance the locomotor output between both halves of the spinal cord, thereby ensuring a symmetrical pattern of locomotor activity during walking. We propose that the V3 neurons establish a regular and balanced motor rhythm by distributing excitatory drive between both halves of the spinal cord.

Functional Subpopulations of V3 Interneurons in the Mature Mouse Spinal Cord

V3 interneurons (INs) are a major group of excitatory commissural interneurons in the spinal cord, and they are essential for producing a stable and robust locomotor rhythm. V3 INs are generated from the ventral-most progenitor domain, p3, but migrate dorsally and laterally during postmitotic development. At birth, they are located in distinctive clusters in the ventral horn and deep dorsal horn. To assess the heterogeneity of this genetically identified group of spinal INs, we combined patch-clamp recording and anatomical tracing with cluster analysis. We examined electrophysiological and morphological properties of mature V3 INs identified by their expression of tdTomato fluorescent proteins in Sim1Cre/+; Rosafloxstop26TdTom mice. We identified two V3 subpopulations with distinct intrinsic properties and spatial distribution patterns. Ventral V3 INs, primarily located in lamina VIII, possess a few branching processes and were capable of generating rapid tonic firing spikes. By contrast, dorsal V3 INs exhibited a more complex morphology and relatively slow average spike frequency with strong adaptation, and they also displayed large sag voltages and post-inhibitory rebound potentials. Our data suggested that hyperpolarization-activated cation channel currents and T-type calcium channel currents may account for some of the membrane properties of V3 INs. Finally, we observed that ventral and dorsal V3 INs were active in different ways during running and swimming, indicating that ventral V3 INs may act as premotor neurons and dorsal V3 INs as relay neurons mediating sensory inputs. Together, we detected two physiologically and topographically distinct subgroups of V3 INs, each likely playing different roles in locomotor activities.

Doxorubicin-Loaded Dextran-Modified GoldMag Nanoparticles for Targeting Hepatocellular Carcinoma

Doxorubicin (Dox) is one of the most widely used chemotherapeutic agents for many types of cancer, including hepatocellular carcinoma. However, clinical applications of Dox are limited due to its non-selective cytotoxicity that results in severe adverse effects. To tackle this problem targeted delivery of Dox exclusively to tumour milieu has become clinically prioritised. In this study, we first synthesized and validated Dextran coated GoldMag Nanoparticles (DGMNs) as a potential delivery vehicle for Dox. We then evaluated the cytotoxicity of Dox-DGMNs, the drug and carrier composites, under guidance of external magnetic field (EMF) in hepatocellular carcinoma cell lines and in tumour grafts. Intriguingly, DGMNs exhibited the capacity to prolong Dox release in vitro; hence, Dox-DGMNs significantly enhanced the therapeutic efficiency of the drug in vitro and in vivo, especially under EMF. However, DGMNs were able to significantly decrease systemic adverse effects and inhibit tumour growth compared to the intravenous application of free Dox. Molecular analysis revealed that tumour cells were more affected by Dox-DGMNs with EMF than Dox-DGMNs or Dox alone in terms of apoptosis and DNA damage marker expression. Overall, DGMNs exhibited a substantial potential to serve as a promising drug delivery carrier for magnetically targeted cancer therapy.