Sleeping. Eating. Reproduction. Memory. Name virtually any physiological process and the chances are good that neuropeptides will regulate it. By understanding how the secretion of neuropeptides is controlled at a cellular and molecular level we hope to shed some light on how this class of transmitter molecules are able to regulate higher-order behaviors.

Neuropeptides are widespread. The majority of neurons and many neuroendocrine cells synthesize 2 types of transmitters - classical neurotransmitters such as glutamate and neuropeptides. The former mediates the fast component of synaptic transmission, while neuropeptides are slower acting. It is now well established that neurons regulate these two classes of transmitters very differently. There are clear distinctions in the synthesis, sub-cellular localization, secretion, and post-synaptic actions of neuropeptides and classical transmitters. For example the two types of transmitters are even packaged into different cellular organelles: classical transmitters are found in small recycling vesicles, while neuropeptides are contained within large dense core granules that are filled via the trans Golgi network.

We are particularly interested in the observation that neurons can independently control the release of neuropeptides and classical transmitters. We would like to know how this is accomplished. Such differential control could be exerted at a variety of levels. We are studying three possibilities:

(1) The molecules that control the fusion of neuropeptide-containing dense core granules with the presynaptic membrane could be different from those that control the fusion of vesicles that contain classical transmitters. Do candidate proteins (such as the synaptotagmins) differentially control the secretion of neuropeptides and classical transmitters?

(2) The subcellular sites of neuropeptide and classical transmitter secretion could be different. For example, neuropeptide granules are not clustered together with synaptic vesicles at the active zone. How does this distribution arise and where on the presynaptic membrane does the fusion of dense core granules occur?

(3) The trafficking of dense core granules and clear vesicles might be different. For example, is there a readily releasable pool of peptidergic dense core granules?

To address these questions we are using a technique that we have recently developed called "FMRFamide-tagging." This technique is used to measure the secretion of neuropeptide Y, the most common vertebrate neuropeptide. The technique uses a combined molecular/electrophysiological approach that bypasses the slow, second messenger-mediated effect of neuropeptide Y and converts it into a fast synaptic membrane current.