Core Concepts
Spinal V1 inhibitory interneurons exhibit diversity in their timing of neurogenesis, synaptic targeting of motoneurons, and internal heterogeneity, with implications for their roles in motor control.
Abstract
The content examines the diversity of spinal V1 inhibitory interneurons, a major group of ventral inhibitory interneurons that play crucial roles in shaping motor output. The key findings are:
Neurogenesis timing divides V1 interneurons into early-born (Renshaw cells, Pou6f2-V1s) and late-born (Foxp2-V1s, Sp8-V1s) clades. Early-born and late-born V1 clades settle in distinct positions in the ventral horn.
Foxp2-V1s, the largest V1 clade, contain over half of all V1 interneurons and provide the densest inhibitory input to motoneuron cell bodies, especially on limb-related lateral motor column (LMC) motoneurons.
Foxp2-V1s exhibit further heterogeneity, with subgroups differing in neurogenesis timing, proprioceptive input, and location relative to motor columns.
Renshaw cells and a subset of Foxp2-V1s form the majority of V1 synapses on motoneuron cell bodies and proximal dendrites, while other V1 clades (Pou6f2, Sp8) have minimal representation.
The diversity of V1 interneurons likely enables their distinct roles in motor control, with implications for understanding their ontogenetic and phylogenetic origins.
Stats
The number of Foxp2-V1s per 50 μm thick section (ventral horn) significantly increases in lower lumbar segments from L3 to L6 compared to S1.
The ratio of Foxp2-V1 neurons to motoneurons remains relatively constant at roughly 2.5:1 throughout the lumbar cord.
Quotes
"Foxp2-V1 interneurons comprise 55.7% ±4.7 (mean±SD) of all genetically labeled Foxp2 neurons in the spinal cord."
"The highest density of Foxp2-V1 neurons cluster close to LMC motoneurons from L2 to L5."