The role of electrical coupling of Hb9 interneurons in generating the rhythms of locomotion.

Whether taking a stroll in a park or sprinting at full speed on a field, there are nerve cells in the spinal cord that are responsible for setting the different paces at which we move. The cells that act as pacemakers for the spinal cord have not been identified yet. A class of cells named Hb9 interneurons have been identified as candidates to play this role. They exhibit several features that predispose them to behave as a biological metronome, continually setting a beat for the spinal cord to follow. One feature of Hb9 interneurons is that they not only communicate with other neurons using chemicals known as neurotransmitters, but also by sharing electrical connections with their neighbours. This form of communication is more rapid than using neurotransmitters. It is believed that electrical communication between neurons enable them to fire together at frequencies unattainable if these neurons communicated only by using neurotransmitters. We propose to study whether these electrical communications between Hb9 interneurons and their neighbouring neurons allow them to greatly expand their ability to set paces that vary between crawling and sprinting at full speed. We will use mathematical models of these cells to demonstrate the benefits of the electrical communications that Hb9 interneurons share with others. Then we will record the activity of these cells in a live mouse spinal cord and disrupt their electrical communication to see if this hampers their ability to set different paces. The challenges faced in alleviating the suffering from movement disorders are two-fold: First, the ability to move the necessary muscles must be restored. Second, the ability to move these muscles at an appropriate rhythm has to be developed. By understanding how the spinal cord sets the pace of our movements, we will be in a better position to identify strategies that will enable the restoration of a full range of movement speeds to those suffering from movement disorders.