Motor neuron disease research breakthrough

Researchers have found that the insulin-like growth factor 1 (IGF-1) dramatically increases the in vitro growth of corticospinal motor neuron (CSMN) axons – projections that carry nerve impulses to the spinal motor neurons that connect to muscles. Additionally, blocking IGF-1 activity reduces that growth in both cultured cells and in living mice.

Jeffrey Macklis, director of the MGH-Harvard Medical School Center for Nervous System Repair, said: “Our findings that IGF-1 specifically enhances both the speed and extent of axon outgrowth of corticospinal motor neurons are the first direct evidence of growth factor control over the differentiation of these neurons.

“In addition to providing insight into the development and circuit formation of this critical population of neurons, these results might lead to the future ability to treat motor neuron disorders and spinal cord injuries.”

Although their cell bodies are located in the brain, CSMN axons extend down to the neurons they control in the spinal cord – extending as far as three feet in adult humans. These neurons degenerate in motor neuron diseases, and their damage contributes to loss of motor function in spinal cord injuries.

Since they are embedded among hundreds of other types of neurons in the cerebral cortex, it has been difficult to study CSMN, and little has been known about cellular and molecular factors that control their growth and development. In order to study growth factor controls over these cells, the researchers developed a new way of isolating pure populations of CSMN in culture and found that IGF-1 was a prime candidate for control over CSMN development.