NEUROEFFECTOR TRANSMISSION IN A SIMPLE SALIVARY GLAND

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The long-term goal of this basic research program is a fundamental understanding of the biophysical and biochemical processes involved in the neuronal control of exocrine gland function. In this application, we propose to continue ongoing studies of a relatively simple salivary gland system from the aquatic snail Helisoma trivolvis which offers a number of important technical advantages as a model system. In the first series of experiments, we will use the technique of Multiple-Site Optical Recording of Transmembrane Voltage (MSORTV) to simultaneously record electrical activity in up to 124 separate gland regions in order to: 1) characterize and quantify the passive spread of current between acinar and ductal gland regions, 2) map the terminal fields of the two effector neurons to the gland (SEN's) and determine the extent of terminal field overlap, and 3) assess the effects of temporal dispersion of the SEN nerve terminal spikes on the evoked electrical response of acinar and ductal cells. In the second series of experiments, that have been added to this revised application, we propose to continue our investigations of a recently identified nanopeptide that is highly excitatory for the snail salivary gland and may serve as the transmitter substance released by the SEN's at the neuroglandular junction. Conventional immunohistochemical techniques will be used to determine the presence (or absence) of this peptide (SCPB) in the SEN's and in the salivary gland. We will also investigate the large after-hyperpolarization of the Type II gland response evoked by SCPB to determine whether it represents a Ca+2-mediated K+ conductance. In a related series of experiments, we wish to compare the effects of focal application of SCPB and acetylcholine to see if these excitatory gland substances, when presented simultaneously, facilitate the electrical and/or secretory response of acinar cells. In a third series of experiments, which have also been added in revision, we will use a new fluorescent indicator (QUIN 2/AM) to monitor the cytosolic concentration of ionized calcium following neuronal and pharmacological stimulation. Through the use of conventional ion-sensing electrodes, we will characterize the interrelationship between stimulation, electrical activity, intracellular calcium and electrolyte secretion.