Characterisation of lamina I anterolateral system neurons that express Cre in a Phox2a-Cre mouse line

A recently developed Phox2a::Cre mouse line has been shown to capture anterolateral system (ALS) projection neurons. Here, we used this line to test whether Phox2a-positive cells represent a distinct subpopulation among lamina I ALS neurons. We show that virtually all lamina I Phox2a cells can be retrogradely labelled from injections targeted on the lateral parabrachial area (LPb), and that most of those in the cervical cord also belong to the spinothalamic tract. Phox2a cells accounted for ~ 50–60% of the lamina I cells retrogradely labelled from LPb or thalamus. Phox2a was preferentially associated with smaller ALS neurons, and with those showing relatively weak neurokinin 1 receptor expression. The Phox2a cells were also less likely to project to the ipsilateral LPb. Although most Phox2a cells phosphorylated extracellular signal-regulated kinases following noxious heat stimulation, ~ 20% did not, and these were significantly smaller than the activated cells. This suggests that those ALS neurons that respond selectively to skin cooling, which have small cell bodies, may be included among the Phox2a population. Previous studies have defined neurochemical populations among the ALS cells, based on expression of Tac1 or Gpr83. However, we found that the proportions of Phox2a cells that expressed these genes were similar to the proportions reported for all lamina I ALS neurons, suggesting that Phox2a is not differentially expressed among cells belonging to these populations. Finally, we used a mouse line that resulted in membrane labelling of the Phox2a cells and showed that they all possess dendritic spines, although at a relatively low density. However, the distribution of the postsynaptic protein Homer revealed that dendritic spines accounted for a minority of the excitatory synapses on these cells. Our results confirm that Phox2a-positive cells in lamina I are ALS neurons, but show that the Phox2a::Cre line preferentially captures specific types of ALS cells

A model of Endothelin-1-mediated focal ischemia in the mouse forelimb motor cortex

Ischemic stroke is a debilitating medical event with the majority of sufferers experiencing long-term disability and motor impairments. While front line treatment such as anti-embolic medication and rehabilitation can improve the condition, many individuals remain significantly disabled. Experimental therapies involving genetic interventions hold potential for treatment of ischemic stroke, but many therapies go untested due to a lack of small cortical ischemic injury mode ls in the mouse. Models of ischemic stroke should be small, reproducible and produce measurable behavioural deficits in order to see recovery after therapy. Additionally, the injury should avoid damage to neural precursor cells (NPCs) which are often targeted by genetic approaches to modify their survivability and plasticity post stroke. This highlights the demand for a small cortical ischemic injury model in the mouse, where transgenic technologies can be used to their full potential. Existing models of ischemic injury, such as middle cerebral artery occlusion (MCAO) produce large amounts of ischemic damage, but may prove more difficult to regenerate and/or eliminate behavioural deficits post-stroke. Endothelin-1 (ET-1), a potent vasoconstrictive peptide, was used to induce ischemia in the mouse cortex. ET- 1 injected into the mouse cortex produced a small but significant infarct. To determine whether ET-1-induced infarcts could produce behavioural deficits, injections were targeted to the mouse forelimb motor cortex (FMC) and the amount of infarct encompassing the FMC was correlated with behavioural deficits. To analyze this, two-dimensional topological maps of cortical infarct depth were created and the deeper parts o r injury correlated with behavioural deficits. Using standard behavioural tests adapted for use with mice, the mouse staircase test was shown to correlate with FMC infarct location and depth. The mouse cylinder test of fore limb asymmetry did not correlate with FMC infarct location and depth; despite this, a new analysis termed paw-dragging did correlate with FMC infarct location and depth. The results demonstrated that the FMC is functionally subdivided such that staircase deficits correlated with damage to the anterior FMC as opposed to the posterior FMC. As well, a small cortical infarct produced by ET- l induced PC prolife ration and migration. At 14 days post-injection, there were significantly more neuroblasts in the subventricular zone (SVZ) and the corpus callosum ipsilateral to injury. As NPCs proliferate and migrate toward ET-1-induced cortical infarcts, there is potential for therapeutic intervention to improve regeneration of lost tissue. This study provides a foundation for manipulating NPCs and analyzing their integration into the peri-infarct cortex

DCC is required for the development of nociceptive topognosis in mice and humans.

Avoidance of environmental dangers depends on nociceptive topognosis, or the ability to localize painful stimuli. This is proposed to rely on somatotopic maps arising from topographically organized point-to-point connections between the body surface and the CNS. To determine the role of topographic organization of spinal ascending projections in nociceptive topognosis, we generated a conditional knockout mouse lacking expression of the netrin1 receptor DCC in the spinal cord. These mice have an increased number of ipsilateral spinothalamic connections and exhibit aberrant activation of the somatosensory cortex in response to unilateral stimulation. Furthermore, spinal cord-specific Dcc knockout animals displayed mislocalized licking responses to formalin injection, indicating impaired topognosis. Similarly, humans with DCC mutations experience bilateral sensation evoked by unilateral somatosensory stimulation. Collectively, our results constitute functional evidence of the importance of topographic organization of spinofugal connections for nociceptive topognosis

Phox2a defines a developmental origin of the anterolateral system in mice and humans

Anterolateral system neurons relay pain, itch and temperature information from the spinal cord to pain-related brain regions, but the differentiation of these neurons and their specific contribution to pain perception remain poorly defined. Here, we show that virtually all mouse spinal neurons that embryonically express the autonomic system-associated Paired-like homeobox 2A (Phox2a) transcription factor innervate nociceptive brain targets, including the parabrachial nucleus and the thalamus. We define Phox2a anterolateral system neuron birth order, migration and differentiation, and uncover an essential role for Phox2a in the development of relay of nociceptive signals from the spinal cord to the brain. Finally, we also demonstrate that the molecular identity of Phox2a neurons is conserved in the human foetal spinal cord. The developmental expression of Phox2a as a uniting feature of anterolateral system neurons suggests a link between nociception and autonomic nervous system function

DCC Is Required for the Development of Nociceptive Topognosis in Mice and Humans

Summary: Avoidance of environmental dangers depends on nociceptive topognosis, or the ability to localize painful stimuli. This is proposed to rely on somatotopic maps arising from topographically organized point-to-point connections between the body surface and the CNS. To determine the role of topographic organization of spinal ascending projections in nociceptive topognosis, we generated a conditional knockout mouse lacking expression of the netrin1 receptor DCC in the spinal cord. These mice have an increased number of ipsilateral spinothalamic connections and exhibit aberrant activation of the somatosensory cortex in response to unilateral stimulation. Furthermore, spinal cord-specific Dcc knockout animals displayed mislocalized licking responses to formalin injection, indicating impaired topognosis. Similarly, humans with DCC mutations experience bilateral sensation evoked by unilateral somatosensory stimulation. Collectively, our results constitute functional evidence of the importance of topographic organization of spinofugal connections for nociceptive topognosis. : Da Silva et al. show that the axon guidance receptor DCC is necessary for the lateralization of spinothalamic projections. Mice lacking Dcc in the spinal cord have abnormal somatosensory cortex activation in response to noxious stimulation and fail to accurately localize noxious stimuli. DCC mutations in humans lead to mirroring of somatosensory stimuli. Keywords: topographic organization, nociception, spinothalamic, DCC, commissural, behavior, mutation, mirror movement disorder, pain, somatosensory system, human genetic

Outcomes in Newly Diagnosed Atrial Fibrillation and History of Acute Coronary Syndromes: Insights from GARFIELD-AF

BACKGROUND: Many patients with atrial fibrillation have concomitant coronary artery disease with or without acute coronary syndromes and are in need of additional antithrombotic therapy. There are few data on the long-term clinical outcome of atrial fibrillation patients with a history of acute coronary syndrome. This is a 2-year study of atrial fibrillation patients with or without a history of acute coronary syndromes