Since the heart muscle seemed to attract the HE motor neuron, we wanted to know what signal(s) were being used. So, we placed embryonic heart muscle in a dish and found that axons from the CNS would explode upon its surface! Axons seemed to love to grow all over the young muscle.
But were these axons of the HE motor neuron?
No.
In another experiment we labeled the HE motor neuron red and all other neurons green. It turned out that the HE seemed to be the ONLY neuron that did not like to grow all over the heart muscle.
It appeared that while all neurons "like" to grow upon young muscle, the heart muscle specifically instructs the HE motor neuron to STOP. We suggest this stop signal is a requirement for the growth cone to initiate the process of remodelling into a stable synaptic connection.
But....in vivo we found that complete synapses do not appear for over another week. What are they waiting for?