Identification of Aplysia neurons containing immunoreactive FMRFamide

Electrophysiological and immunocytochemical techniques were used in the abdominal ganglion of Aplysia to identify neurons containing immunoreactive FMRFamide. Large numbers of neurons were immunoreactive for FMRFamide, including R2, L2, L3, L4, L5, L6, 2 cells tentatively identified as L12 and L13, and a previously unidentified cluster on the ventral surface of the right lower quadrant. There was also heavy labelling of fibers, often with beaded varicosities, throughout the neuropil, the cell layers, and the sheath overlying the ganglion. This data provides further evidence that FMRFamide is an important neurotransmitter in Aplysia. The demonstration of immunoreactive FMRFamide in the giant cholinergic neurons R2 and LP1(1) suggests that these well-studied and experimentally convenient cells use acetylcholine and an FMRFamide-like peptide as cotransmitters.