In vitro methods for the analysis of motor function in the developing spinal cord of the chick embryo

The isolated spinal cord of the chick embryo spontaneously generates episodes of motor activity in vitro that can be recorded from muscle nerves and ventral roots. In vitro systems provide stable conditions for intra- and extra-cellular recordings and enable pharmacological and ionic manipulations of the neuronal environment. Studies of motor activity generated by isolated spinal cord have revealed the existence of co-ordinated motor output from early in development, in which antagonist motoneurons alternate in their activity and synergists are co-active. Intra-cellular recordings from single neurons and electronic recordings from muscle nerves have provided insight into the mechanism of flexor and extensor alternation. These studies have revealed that flexor and extensor motoneurons receive a similar de-polarization during each cycle of motor activity, but that the two classes of motoneuron process the de-polarization differently. Flexors fire late in each cycle whereas extensors fire early, which leads to a pattern of alternation. The cellular mechanisms responsible for the differences in the firing behavior of flexor and extensor motoneurons are currently being investigated using techniques that are only possible using the in vitro preparation.