Electrophysiological properties of motor neurons in a mouse model of severe spinal muscular atrophy: in vitro versus in vivo development.

Hongmei Zhang,Chiayen Wu,Natallia Robinson,Melissa A Harrington,Wenlan Wang,Wen-Liang Zhou

doi:10.1371/journal.pone.0011696

Abstract

We examined the electrophysiological activity of motor neurons from the mouse model of severe spinal muscular atrophy (SMA) using two different methods: whole cell patch clamp of neurons cultured from day 13 embryos; and multi-electrode recording of ventral horns in spinal cord slices from pups on post-natal days 5 and 6. We used the MED64 multi-electrode array to record electrophysiological activity from motor neurons in slices from the lumbar spinal cord of SMA pups and their unaffected littermates. Recording simultaneously from up to 32 sites across the ventral horn, we observed a significant decrease in the number of active neurons in 5–6 day-old SMA pups compared to littermates. Ventral horn activity in control pups is significantly activated by serotonin and depressed by GABA, while these agents had much less effect on SMA slices. In contrast to the large differences observed in spinal cord, neurons cultured from SMA embryos for up to 21 days showed no significant differences in electrophysiological activity compared to littermates. No differences were observed in membrane potential, frequency of spiking and synaptic activity in cells from SMA embryos compared to controls. In addition, we observed no difference in cell survival between cells from SMA embryos and their unaffected littermates. Our results represent the first report on the electrophysiology of SMN-deficient motor neurons, and suggest that motor neuron development in vitro follows a different path than in vivo development, a path in which loss of SMN expression has little effect on motor neuron function and survival.

Highlights

spinal muscular atrophy (SMA) is characterized by motor neuron loss and muscle atrophy, [1,2,3,4] and is caused by homozygous loss or mutation of the survival motor neuron gene 1, SMN1 [5,6]
Affected pups appear normal at birth, but within 48 hours show decreased movement, reduced suckling, labored breathing, and small size compared to wild type littermates, and they die before post-natal day 7 (P7)
The recordings demonstrate that the number of spiking motor neurons in the lumbar spinal cord was much lower in SMA mice than control mice

Summary

Introduction

SMA is characterized by motor neuron loss and muscle atrophy, [1,2,3,4] and is caused by homozygous loss or mutation of the survival motor neuron gene 1, SMN1 [5,6]. Affected pups appear normal at birth, but within 48 hours show decreased movement, reduced suckling, labored breathing, and small size compared to wild type littermates, and they die before post-natal day 7 (P7). Histological analysis of mutants on post-natal day 1 (P1) shows the normal number of spinal and brainstem motor neurons, but by P3–P5, motor neuron cell bodies in the spinal cord are 20–30% lower in number in the mutants than in age-matched controls, and many of the remaining neurons appear apoptotic. The severity of the SMA phenotype seems outpace the loss of motor neuron cell bodies, as even the most severely affected pups retain 60% or more of spinal motor neurons [11]

Methods

Results

Conclusion