Two peptide transmitters co-packaged in a single neurosecretory vesicle

Numerous neurosecretory cells are known to secrete more than one peptide, in both vertebrates and invertebrates. These co-expressed neuropeptides often originate from differential cleavage of a single large precursor, and are then usually sorted in the regulated pathway into different secretory vesicle classes to allow separable release dynamics. Here, we use immuno-gold electron microscopy to show that two very different neuropeptides (the nonapeptide crustacean cardioactive peptide (CCAP) and the 30 kDa heterodimeric bursicon) are co-packaged within the same dense core vesicles in neurosecretory neurons in the abdominal ganglia of Periplaneta americana. We suggest that this co-packaging serves a physiological function in which CCAP accelerates the distribution of bursicon to the epidermis after ecdysis to regulate sclerotization of the newly formed cuticle.