and can be located in cholinergic, peptidergic, and adrenergic neurons [58]. In AtT20 cells, a corticotroph-like cell line, NESP55 has been shown to be exported out into the medium, a process which can be blocked markedly by lowering the temperature and modestly by treatment with a cAMP analog (8-bromo-cAMP) [59]. In different tissues, differential post-translational processing of NESP55 leads to smaller peptides, which appear to accumulate during antegrade transport of this protein along the axon [58]. One of the putative peptide products, Leu-Ser-Ala-Leu (LSAL), which may be produced by prohormone convertase cleavage, has been identified as an endogenous antagonist of the serotonergic 5-HT1B receptor subtype [53], although this possibility and its potential biological significance have yet to be investigated.
