IMmunostaining for peptides of the egg-laying hormone/bag cell peptide precursor protein in the head ganglia of Aplysia

Abstract

Egg-laying hormone and alpha-bag cell peptide are two neuropeptides derived from a common precursor protein in the marine mollusk Aplysia. Previous studies indicate that they are neurotransmitters that co-exist in individual bag cell neurons and most bag cell processes in the abdominal ganglion. In the present investigation we used double-label immunocytochemistry with highly specific antisera to describe their distribution elsewhere in the CNS. We found that a small cluster of cells and their fibers in the pleural ganglion that were previously described as being immunoreactive for egg-laying hormone were also immunoreactive for alpha-bag cell peptide(1–9). A previously described group of small cell bodies in the cerebral ganglion also stained for both peptides. However, the fiber arborizations located near them were immunoreactive for alpha-bag cell peptide(1–9). but not egg-laying hormone. This suggests that there is alternative processing of the precursor protein or differential transport of the peptides from the cell bodies. The specificities of the antibodies indicate that all of the neurons that stain for egg-laying hormone-like peptides in the CNS synthesize peptides derived from the egg-laying hormone bag cell peptide precursor, rather than peptides derived from other members of the egg-laying hormone gene family. They also suggest that peptides derived from the related A or B precursor proteins are not synthesized in the CNS. or at levels too low to detect. The results are consistent with the proposal that the behavior associated with egg-laying is initiated and controlled by peptide transmitters derived from a single gene and expressed in specific neurons of the CNS.