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Circuits and Synapses

We are examining the self assembly of the heart circuitry. The bilateral heart tubes (HT) are innervated by a segmentally repeated motor neuron (HE) and a neuromodulator (HA, not shown). In turn the HE's are synaptically driven by CNS interneurons (HN). Our earlier work showed that the HE selects the HT as a target after projecting many other branches. Contact with the HT is required for the HE to remodel itself. Some of our current emphasis is on how the presynaptic terminals on the HT interact with the target and change from questing growth cone to specialized synapse (ie, FMRFamide expressing).

By challenging neurons to grow upon various targets we found that the young HT provided a very permissive substrate for outgrowth. Above left is a cultured nerve with many axons (red) grown upon the HT (blue). We then specifically labeled the HE with dye and found that while axons from other neurons (green) grew extensively over the HT, the HE selectively stopped. Some of our current work is aimed at examining HE synaptogenesis as a possible explanation for this.


Since we now know that signals derived from targets and pathways play key roles in development we are starting to focus more on the transition between growing tip and specialized synapse. Specifically, we have found some components of the vesicle release machinery (red) (ie SNAP-25) are present in developing neurons and growth cones (above left), well before the expression of neuropeptides and synapse formation. We later find the expected colocalization of SNARE components and neuropeptides, blue arrowheads (above, center) and are currently examining ideas about how molecules involved in synaptic signaling might also play a role in the process of synaptogenesis. These studies are being extended into the circuit one level by examining the highly selective CNS synapses between interneurons and the HE (above right).

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This page is maintained by John Jellies,
Department of Biological Sciences
Western Michigan University, Kalamazoo, MI 49008