Proprioceptive neurons (PNs) are essential for the proper execution of all our movements by providing muscle sensory feedback to the central motor network. Here, using deep single cell RNAseq of ...adult PNs coupled with virus and genetic tracings, we molecularly identify three main types of PNs (Ia, Ib and II) and find that they segregate into eight distinct subgroups. Our data unveil a highly sophisticated organization of PNs into discrete sensory input channels with distinct spatial distribution, innervation patterns and molecular profiles. Altogether, these features contribute to finely regulate proprioception during complex motor behavior. Moreover, while Ib- and II-PN subtypes are specified around birth, Ia-PN subtypes diversify later in life along with increased motor activity. We also show Ia-PNs plasticity following exercise training, suggesting Ia-PNs are important players in adaptive proprioceptive function in adult mice.
Spasms after spinal cord injury (SCI) are debilitating involuntary muscle contractions that have been associated with increased motor neuron excitability and decreased inhibition. However, whether ...spasms involve activation of premotor spinal excitatory neuronal circuits is unknown. Here we use mouse genetics, electrophysiology, imaging and optogenetics to directly target major classes of spinal interneurons as well as motor neurons during spasms in a mouse model of chronic SCI. We find that assemblies of excitatory spinal interneurons are recruited by sensory input into functional circuits to generate persistent neural activity, which interacts with both the graded expression of plateau potentials in motor neurons to generate spasms, and inhibitory interneurons to curtail them. Our study reveals hitherto unrecognized neuronal mechanisms for the generation of persistent neural activity under pathophysiological conditions, opening up new targets for treatment of muscle spasms after SCI.
Abstract This study was aimed at the isolation of neural precursor cells (NPCs) capable of resisting to a prolonged ischemic insult as this may occur at the site of traumatic and ischemic CNS ...injuries. Adult mice were anesthetized and then killed by cervical dislocation. The cadavers were maintained at room temperature or at 4 °C for different time periods. Post mortem neural precursors (PM-NPCs) were isolated, grown in vitro and their differentiation capability was investigated by evaluating the expression of different neuronal markers. PM-NPCs differentiate mostly in neurons, show activation of hypoxia-inducible factor-1 and MAPK, and express both erythropoietin (EPO) and its receptor (EPO-R). The exposure of PM-NPCs to neutralizing antibodies to EPO or EPO-R dramatically reduced the extent of neuronal differentiation to about 11% of total PM-NPCs. The functionality of mTOR and MAPK is also required for the expression of the neuronal phenotype by PM-NPCs. These results suggest that PM-NPCs can be isolated from animal cadaver even several hours after death and their self-renewable capability is comparable to normal neural precursors. Differently, their ability to achieve a neural phenotype is superior to that of NPCs, and this is mediated by the activation of hypoxia-induced factor 1 and EPO signaling. PM-NPCs may represent good candidates for transplantation studies in animal models of neurodegenerative diseases.
Spinal cord injury (SCI) is characterized by multiple sensory/motor impairments that arise from different underlying neural mechanisms. Linking specific sensory/motor impairments to neural mechanism ...is limited by a lack of direct experimental access to these neural circuits. Here, we describe an experimental model which addresses this shortcoming. We generated a mouse model of chronic spinal cord injury that reliably reproduces spasticity observed after SCI, while at the same time allows study of motor impairments
and in an
preparation of the spinal cord. The model allows for the combination of mouse genetics in
and
conditions with advanced imaging, behavioral analysis, and detailed electrophysiology, techniques which are not easily applied in conventional SCI models.
Locomotion is a fundamental motor function common to the animal kingdom. It is implemented episodically and adapted to behavioural needs, including exploration, which requires slow locomotion, and ...escape behaviour, which necessitates faster speeds. The control of these functions originates in brainstem structures, although the neuronal substrate(s) that support them have not yet been elucidated. Here we show in mice that speed and gait selection are controlled by glutamatergic excitatory neurons (GlutNs) segregated in two distinct midbrain nuclei: the cuneiform nucleus (CnF) and the pedunculopontine nucleus (PPN). GlutNs in both of these regions contribute to the control of slower, alternating-gait locomotion, whereas only GlutNs in the CnF are able to elicit high-speed, synchronous-gait locomotion. Additionally, both the activation dynamics and the input and output connectivity matrices of GlutNs in the PPN and the CnF support explorative and escape locomotion, respectively. Our results identify two regions in the midbrain that act in conjunction to select context-dependent locomotor behaviours.
The episodic nature of locomotion is thought to be controlled by descending inputs from the brainstem. Most studies have largely attributed this control to initiating excitatory signals, but little ...is known about putative commands that may specifically determine locomotor offset. To link identifiable brainstem populations to a potential locomotor stop signal, we used developmental genetics and considered a discrete neuronal population in the reticular formation: the V2a neurons. We find that those neurons constitute a major excitatory pathway to locomotor areas of the ventral spinal cord. Selective activation of V2a neurons of the rostral medulla stops ongoing locomotor activity, owing to an inhibition of premotor locomotor networks in the spinal cord. Moreover, inactivation of such neurons decreases spontaneous stopping in vivo. Therefore, the V2a “stop neurons” represent a glutamatergic descending pathway that favors immobility and may thus help control the episodic nature of locomotion.
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•Mouse V2a brainstem neurons are excitatory and project to the ventral spinal cord•Optogenetic activation of V2a neurons of the rostral medulla halts locomotion•These “V2a stop neurons” act by depressing locomotor rhythm generation•V2a stop neurons are needed for episodic locomotion
The ability to stop locomotion is regulated by genetically- and spatially-confined excitatory neurons in the brainstem that project to the spinal cord where they depress locomotor rhythm generation.
A number of rare copy number variants (CNVs) have been linked to neurodevelopmental disorders. However, because CNVs encompass many genes, it is often difficult to identify the mechanisms that lead ...to developmental perturbations.
We used 15q13.3 microdeletion to propose and validate a novel strategy to predict the impact of CNV genes on brain development that could further guide functional studies. We analyzed single-cell transcriptomics datasets containing cortical interneurons to identify their developmental vulnerability to 15q13.3 microdeletion, which was validated in mouse models.
We found that Klf13—but not other 15q13.3 genes—is expressed by precursors and neuroblasts in the medial and caudal ganglionic eminences during development, with a peak of expression at embryonic day (E)13.5 and E18.5, respectively. In contrast, in the adult mouse brain, Klf13 expression is negligible. Using Df(h15q13.3)/+ and Klf13+/− embryos, we observed a precursor subtype-specific impairment in proliferation in the medial ganglionic eminence and caudal ganglionic eminence at E13.5 and E17.5, respectively, corresponding to vulnerability predicted by Klf13 expression patterns. Finally, Klf13+/− mice showed a layer-specific decrease in parvalbumin and somatostatin cortical interneurons accompanied by changes in locomotor and anxiety-related behavior.
We show that the impact of 15q13.3 microdeletion on precursor proliferation is grounded in a reduction in Klf13 expression. The lack of Klf13 in Df(h15q13.3)/+ cortex might be the major reason for perturbed density of cortical interneurons. Thus, the behavioral defects seen in 15q13.3 microdeletion could stem from a developmental perturbation owing to selective vulnerability of cortical interneurons during sensitive stages of their development.
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