Anatomical and molecular properties of long descending propriospinal neurons in mice

Long descending propriospinal neurons (LDPNs) are interneurons that form direct connections between cervical and lumbar spinal circuits. LDPNs are involved in interlimb coordination and are important mediators of functional recovery after spinal cord injury (SCI). Much of what we know about LDPNs comes from a range of species, however, the increased use of transgenic mouse lines to better define neuronal populations calls for a more complete characterisation of LDPNs in mice. In this study, we examined the cell body location, inhibitory neurotransmitter phenotype, developmental provenance, morphology and synaptic inputs of mouse LDPNs throughout the cervical and upper thoracic spinal cord. LDPNs were retrogradely labelled from the lumbar spinal cord to map cell body locations throughout the cervical and upper thoracic segments. Ipsilateral LDPNs were distributed throughout the dorsal, intermediate and ventral grey matter as well as the lateral spinal nucleus and lateral cervical nucleus. In contrast, contralateral LDPNs were more densely concentrated in the ventromedial grey matter. Retrograde labelling in GlyT2GFP and GAD67GFP mice showed the majority of inhibitory LDPNs project either ipsilaterally or adjacent to the midline. Additionally, we used several transgenic mouse lines to define the developmental provenance of LDPNs and found that V2b positive neurons form a subset of ipsilaterally projecting LDPNs. Finally, a population of Neurobiotin (NB) labelled LDPNs were assessed in detail to examine morphology and plot the spatial distribution of contacts from a variety of neurochemically distinct axon terminals. These results provide important baseline data in mice for future work on their role in locomotion and recovery from SCI

Parallel ascending spinal pathways for affective touch and pain

The anterolateral pathway consists of ascending spinal tracts that convey pain, temperature and touch information from the spinal cord to the brain1,2,3,4. Projection neurons of the anterolateral pathway are attractive therapeutic targets for pain treatment because nociceptive signals emanating from the periphery are channelled through these spinal projection neurons en route to the brain. However, the organizational logic of the anterolateral pathway remains poorly understood. Here we show that two populations of projection neurons that express the structurally related G-protein-coupled receptors (GPCRs) TACR1 and GPR83 form parallel ascending circuit modules that cooperate to convey thermal, tactile and noxious cutaneous signals from the spinal cord to the lateral parabrachial nucleus of the pons. Within this nucleus, axons of spinoparabrachial (SPB) neurons that express Tacr1 or Gpr83 innervate distinct sets of subnuclei, and strong optogenetic stimulation of the axon terminals induces distinct escape behaviours and autonomic responses. Moreover, SPB neurons that express Gpr83 are highly sensitive to cutaneous mechanical stimuli and receive strong synaptic inputs from both high- and low-threshold primary mechanosensory neurons. Notably, the valence associated with activation of SPB neurons that express Gpr83 can be either positive or negative, depending on stimulus intensity. These findings reveal anatomically, physiologically and functionally distinct subdivisions of the SPB tract that underlie affective aspects of touch and pain

Expression of Pax-3 in the lateral neural plate is dependent on a Wnt- mediated signal from posterior nonaxial mesoderm

AbstractDuring early patterning of the vertebrate neuraxis, the expression of the paired-domain transcription factor Pax-3 is induced in the lateral portions of the posterior neural plate via posteriorizing signals emanating from the late organizer and posterior nonaxial mesoderm. Using a dominant-negative approach, we show in explant assays that Pax-3 inductive activities from the organizer do not depend on FGF, retinoic acid, or XWnt-8, either alone or in combination, suggesting that the organizer may produce an unknown posteriorizing factor. However, Pax-3 inductive signals from posterior nonaxial mesoderm are Wnt-dependent. We show that Pax-3 expression in the lateral neural plate expands in XWnt-8-injected embryos and is blocked by dominant-negative XWnt-8. Similarly, we show that the homeodomain transcription factor Msx-1, which like Pax-3 is an early marker of the lateral neural plate, is induced by posterior nonaxial mesoderm and blocked by dominant-negative XWnt-8. Finally, we show that Rohon–Beard primary neurons, a cell type that develops within the lateral neural plate, are also blocked in vivo by dominant-negative Xwnt-8. Together these data support a model in which patterning of the lateral neural plate by Wnt-mediated signals is an early event that establishes a posteriolateral domain, marked by Pax-3 and Msx-1 expression, from which Rohon–Beard cells and neural crest will subsequently arise

Direct evidence that ventral forebrain cells migrate to the cortex and contribute to the generation of cortical myelinating oligodendrocytes

AbstractCortical neuroepithelial cells generate neurons, astrocytes, and oligodendrocytes (OLs) in vitro. However, whether cortical OLs are derived from the cortical neuroepithelium or migrate from the ventral forebrain is under severe debate yet. This is due to the fact that OL progenitor cells (OPCs), as marked by the expression of PDGFRα or NG2, are generated at around embryonic day (E) 11 or 12 in the mouse ganglionic eminences, but the myelinating OLs appear during the second week postnatally in the cortex. There has been no labeling method for long-term glial cell-lineage tracing. Thus, we developed a new strategy: plasmid DNA encoding Cre recombinase was introduced into the Cre/loxP reporter forebrain in ventral- or dorsal-specific manner by in utero DNA electroporation. The reporter gfp gene is expressed permanently owing to the chromosomal DNA recombination. The GFP-labeled myelinating OLs were detected in the adult cortex when electroporation was targeted to the ventral neuroepithelium, demonstrating at least some of the myelinating OLs are derived from the ventral forebrain. However, when electroporation was targeted to the dorsal, we could not find GFP-labeled myelinating OLs. This suggests that the progenitors of cortical OPCs are absent or located at restricted regions in the dorsal forebrain (cortex) at E12

Genetic dissection of the common epilepsies

Purpose of reviewOnly two functionally validated susceptibility genes, CACNA1H and GABRD, have so far been identified in the common epilepsies using a candidate gene approach. The difficulty with the alternative statistical approach, where none of the suggested candidates has been functionally validated, may partly be due to the posited genetic architecture of the common epilepsies, such as the idiopathic generalized epilepsies. A subset of both rare and common variants from a much larger pool of susceptibility genes may contribute to disease risk. We review methods and designs for the genetic dissection of common epilepsies.Recent findingsGenetic association studies, though theoretically more powerful than linkage analysis, have not yet delivered validated susceptibility genes. Methodological flaws can undermine such studies but are correctable. Concerns remain, however, about the extent of underlying genetic heterogeneity in common epilepsies. Genome-wide association studies are increasingly feasible, but issues remain about their conduct and analysis. Meta-analysis may resolve conflicting association studies, facilitated by the establishment of databases of genetic association studies. Newer multi-locus and admixture mapping approaches are attractive alternatives to traditional association studies and may offer new insights into identifying epilepsy genes.SummaryWe conclude by emphasizing the importance of deeper endophenotyping using electroclinical, imaging, and molecular approaches to dissect the common epilepsies