Abstract
The effects of age on the physiological properties of cervical motor neurons were examined in slices made from an excised spinal cord graft of ICR mice from the second day after birth to age 350 days. The membrane potential of post-natal day 2 (PD2) to PD350 was about -65 mV and did not change greatly with age, although it was slightly higher at PD2. However, there were significant changes in membrane resistance, which increased with age from about 15 to 30 MΩ. The depolarization induced by the excitatory amino acid agonists, kainic acid, NMDA and AMPA, decreased with aging in spite of the increase in membrane resistance. The motor neurons of the aged mice showed delayed recovery from excitation caused by excitatory amino acid agonists. By injecting Lucifer yellow CH into motor neurons, it was observed that the dendrite trees become thin, and some of the dendrite branches were missing in older animals.
Highlights
Neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) are due to the death of neurons, in the case of ALS of motor neurons
A number of different mutant genes have been found to be associated with ALS, including several different genes of superoxide dismutase 1 (SOD1) [1]
We describe membrane properties of cervical motor neurons obtained from normal ICR mice of different ages, which will serve as controls for study of motor neurons from the SOD1 mutant mice
Summary
Neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) are due to the death of neurons, in the case of ALS of motor neurons. A number of different mutant genes have been found to be associated with ALS, including several different genes of superoxide dismutase 1 (SOD1) [1]. Some of these genes have been introduced into mice, and they have been used for ethology, histological and physiological study as a model of the ALS [2]. Essential background for the electrophysiologic study of these mutant mice requires that one understand how the electrical properties of mouse motor neurons change with age. The spinal cord slice is a convenient preparation for measurements of membrane potential, membrane resistance, and response to excitatory amino acid agonists. Neuronal responses to excitatory amino acid agonists, kainate (KA), N-methyl-D-aspartic acid (NMDA), and amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) were recorded
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