Characterization of the Aplysia californica cerebral ganglion F cluster

The cerebral ganglia neurons of Aplysia californica are involved in the dev elopment and modulation of many behaviors. The medially located F cluster h as been characterized using morphological, electrophysiological and biochem ical techniques and contains at least three previously uncharacterized neur onal population. As the three subtypes are located in three distinct layers , they are designated as top, middle, and bottom layer F-cluster neurons (C FT, CFM, and CFB). The CFT cells are large (92 +/- 25 mu m), white, nonunif ormly shaped, and located partially in the sheath surrounding the ganglion. These neurons exhibit weak electrical coupling, the presence of synchroniz ed spontaneous changes in membrane potential, and a generalized inhibitory input upon electrical stimulation of the anterior tentacular (AT) nerve. Si milar to the CFT neurons, the CFM neurons (46 +/- 12 mu m) are mainly silen t but do not show electrical coupling or synchronized changes in membrane p otential. Unlike the CFT neurons, the CFM neurons exhibit weak action poten tial broadening during constant current injection. Comparison of the peptid e profiles of CFT, CFM, and CFB (10-30 mu m) neurons using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry demonstrates d istinct peptide molecular weights for each neuronal subtype with the masses of these peptides not matching any previously characterized peptides from A. californica. The mass spectra obtained from the AT nerve are similar to the CFT neuron mass spectra, while upper labial nerve contains many peptide s observed in the CFM neurons located in nongranular neuron region.