Isolation and partial characterization of neuropeptides that mimic prolonged inhibition produced by bag cell neurons in Aplysia.

The bag cell neurons of the marine mollusk Aplysia are part of a neural system that utilizes four neuropeptides as neurotransmitters. The peptides, derived from the egg-laying hormone/bag cell peptide (ELH/BCP) precursor protein, are released during a 20-min burst discharge of the bag cells and produce several types of responses in various abdominal ganglion neurons. In the identified neurons L3 and L6, bag cell activity produces prolonged inhibition that lasts for more than 2 h. One of the bag cell peptides, alpha-BCP, mediates an early component of the inhibition in these neurons. To identify the co-transmitter mediating the prolonged component of inhibition, we purified material from an acid extract of abdominal ganglia using molecular sizing high-pressure liquid chromatography (HPLC) on TSK 250-125 followed by two steps of reverse-phase HPLC on C4 or C18. We isolated three inhibitory factors that mimic the prolonged component of inhibition. Mass spectroscopy and partial amino acid sequence analysis indicate one factor is ELH [2-36], that is, ELH that lacks the first, N-terminal amino acid. This inhibitory activity was similar in potency to that of ELH and is the first to be described for an ELH-related peptide. The two other factors were approximately 3,300 and 4,700 Da and were effective at 10- and 50-fold lower concentration, respectively, than ELH or its fragment. Amino acid composition analysis suggests that they are not derived from the ELH/BCP precursor protein. The 4,700 Da factor is effective at the lowest concentration and produces an effect that lasts as long as 100 min.(ABSTRACT TRUNCATED AT 250 WORDS)