Developmental origin of long‐range neurons in the superficial dorsal spinal cord

Abstract

The dorsal spinal cord, which is essential for somatosensory transmission, comprises a heterogeneous population of neurons with distinct axonal lengths and projection patterns. Although the developmental origin of local-circuit interneurons in the dorsal spinal cord has been well characterized, that of long-range neurons extending axons over a long distance such as supraspinal projection neurons and propriospinal neurons is largely unknown. In this study, we performed birthdate and lineage analyses of these long-range neurons in the mouse dorsal spinal cord. Unilateral injection of a retrograde neuronal tracer, cholera toxin B, into the brain or spinal cord efficiently labeled supraspinal projection neurons localized in Rexed's lamina I and the dorsolateral funiculus (DLF) and long-range propriospinal neurons localized in the DLF, all of which had ipsi- and contralaterally projecting populations. Most of these neurons were born between E9.5 and E10.5, much earlier than in the case of the neurogenesis of local-circuit neurons. Lineage analysis using an Lbx1-Cre mouse line demonstrated that most long-range neurons were derived from Lbx1-positive neuronal progenitors, except in the case of the contralaterally projecting propriospinal neurons. Characterization of their neurotransmitter identity revealed that almost all of the supraspinal projection neurons were excitatory, whereas the long-range propriospinal neurons comprised both excitatory and inhibitory populations. These results suggest that the supraspinal projection neurons were derived from the early-born dI5 progenitor domain and that the long-range propriospinal ones arose from several early-born progenitor domains.

Phox2a Defines a Developmental Origin of the Anterolateral System in Mice and Humans

“…A recent study argues that some AS neurons express Tac1 (Huang et al, 2019); our molecular profiling suggests that the early population of dI5 Lmx1b+ Tac1+ neurons likely gives rise to Tac1+ AS neurons, that this population does not overlap with early-born Phox2a-expressing dI5 neurons, and that there at least two molecularly distinct Lamina I AS neuron subpopulations: Phox2a+ and Tac1+. Contrary to the notion that spinal neurons are born in a ventral-to-dorsal order (Nornes and Carry, 1978), superficial dorsal horn Phox2a neurons are born concurrently with motor neurons, as suggested recently for spinofugal neurons (Nishida and Ito, 2017). Ascl1 (expressed in dI5 progenitors) and Ptf1a (expressed in dI4 progenitors) were previously shown to promote and inhibit dI5 neuron fates, respectively (Glasgow et al, 2005;Helms et al, 2005).…”

Conserved genetic signatures parcellate cardinal spinal neuron classes into local and projection subsets

“…This matrix provides a simple labeling index to define neuronal subsets. The postsynaptic targets of group-Z neurons within each cardinal population are predicted from projection neuron-tracing studies (26,29,31,37,38). Local connections and collaterals are not shown (26,27).…”

“…3E and fig. S17) (5,31). Near the midline, the boundary between group-N and group-Z is not absolute, and there is sparse intermingling of NeuroD2 + and Zfhx3 + neurons.…”

Involvement of Brn3a-positive spinal dorsal horn neurons in the transmission of visceral pain in inflammatory bowel disease model mice

“…CTB injection into the lateral parabrachial nucleus was described previously [14]. For CTB injection into the nucleus of the solitary tract (NTS), a fine glass capillary (tip diameter: ∼50 μm) connected with Hamilton syringe was used.…”

“…Transverse sections of the lumbosacral spinal cord of the mice were prepared using a cryostat (20 µm sections). Immunohistochemistry of the spinal dorsal horn sections was performed as previously described (18). Antibodies used in the current study are goat anti-c-fos (1:200, Santa Cruz Biotechnology, Dallas, TX, USA, sc-52), rabbit anti-c-fos (1:500, Synaptic Systems, Goettingen, Germany, 226003), mouse anti-Brn3a (1:300, Sigma, St. Louis, MO, USA, MAB1585), rabbit anti-Pax2 (1:500, Thermo Fisher Scientific Inc., Waltham, MA, USA, 71-6000), goat anti-cholera toxin B (CTB, 1:5,000, List Biological Laboratories, Campbell, CA, USA, 703), rabbit anti-PKCγ (1:100, Santa Cruz Biotechnology, sc-211), Alexa 594-conjugated donkey anti-goat IgG (1:300, Invitrogen, Carlsbad, CA, USA, A11058), Alexa 594-conjugated goat anti-mouse IgG (1:300, Invitrogen, A11032), Alexa 488-conjugated donkey anti-mouse IgG (1:300, Invitrogen, A21202), Alexa 488-conjugated donkey anti-rabbit IgG (1:300, Invitrogen, A21206), and Cy5-conjugated donkey anti-mouse IgG antibodies (1:300, Jackson ImmunoResearch, West Grove, PA, USA, 715-175-150).…”