Distinguishing the primary from secondary effects and compensatory mechanisms is of crucial importance in understanding adult-onset neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). Transgenic mice that overexpress the G93A mutation of the human Cu-Zn superoxide dismutase 1 gene (hSOD1 G93A mice) are a commonly used animal model of ALS. Whole-cell patch-clamp recordings from neurons in acute slice preparations from neonatal wild-type and hSOD1 G93A mice were made to characterize functional changes in neuronal activity. Hypoglossal motoneurons (HMs) in postnatal day 4 (P4)-P10 hSOD1 G93A mice displayed hyperexcitability, increased persistent Na ϩ current (PC Na ), and enhanced frequency of spontaneous excitatory and inhibitory transmission, compared with wild-type mice. These functional changes in neuronal activity are the earliest yet reported for the hSOD1 G93A mouse, and are present 2-3 months before motoneuron degeneration and clinical symptoms appear in these mice. Changes in neuronal activity were not restricted to motoneurons: superior colliculus interneurons also displayed hyperexcitability and synaptic changes (P10 -P12). Furthermore, in vivo viral-mediated GFP (green fluorescent protein) overexpression in hSOD1 G93A HMs revealed precocious dendritic remodeling, and behavioral assays revealed transient neonatal neuromotor deficits compared with controls. These findings underscore the widespread and early onset of abnormal neural activity in this mouse model of the adult neurodegenerative disease ALS, and suggest that suppression of PC Na and hyperexcitability early in life might be one way to mitigate or prevent cell death in the adult CNS.

Significance This study reports on the beneficial effects of forcing high expression of the transcription factor activating transcription factor 3 (ATF3) in ALS. ALS is a noncurable adult-onset disease that attacks motor neurons, resulting in paralysis and death. ATF3 overexpression in motor neurons in an ALS mouse model modifies gene expression and drives the neurons into a prosurvival and proregenerative state, increasing motor neuron survival and maintaining axonal connection with muscle by promoting axonal sprouting. ATF3 overexpression results in markedly improved muscle strength and function and delayed disease onset but only slightly increased lifespan. Molecular mechanisms that promote axonal sprouting could substantially improve quality of life in ALS, although additional approaches will be required to overcome progressive motor neuron deterioration.

NR3B is a modulatory subunit of the NMDA receptor, abundantly expressed in both cranial and spinal somatic motoneurons and at lower levels in other regions of the brain as well. Recently, we found the human NR3B gene (GRIN3B) to be highly genetically heterogeneous, and that approximately 10% of the normal European-American population lacks NR3B due to homozygous occurrence of a null allele in the gene. Therefore, it is especially important to understand the phenotypic consequences of the genetic loss of NR3B in both humans and animal models. We here provide results of behavioral analysis of mice genetically lacking NR3B, which is an ideal animal model due to homogeneity in genetic and environmental background. The NR3B(-/-) mice are viable and fertile. Consistent with the expression of NR3B in somatic motoneurons, the NR3B(-/-) mice showed a moderate but significant impairment in motor learning or coordination, and decreased activity in their home cages. Remarkably, the NR3B(-/-) mice showed a highly increased social interaction with their familiar cage mates in their home cage but moderately increased anxiety-like behaviour and decreased social interaction in a novel environment, consistent with the inhibitory role of NR3B on the functions of NMDA receptors. This work is the first reporting of the functional significance of NR3B in vivo and may give insight into the contribution of genetic variability of NR3B in the phenotypic heterogeneity among human population.