Autoradiographic evidence that transport of newly synthesized neuropeptides is directed to release sites in the X-organ--sinus gland of Cardisoma carnifex.

Sections of isolated X-organ--sinus gland neurosecretory systems of the crab, Cardisoma carnifex, were studied by light- and electron microscopy with conventional and autoradiographic procedures. The somata only were exposed to a pulse of 3H-leucine (5 min-5 h) and the entire system perfused with chase medium for various times (1-72 h) before fixation. Within 1 h, radiolabel is concentrated in Golgi complexes and nascent granules of both large and small somata. Label is undetectable in the terminal region following a 10 h chase. It is found in the nerve tract near terminals at 14 h, while after a 19 h chase, label is concentrated in terminal profiles abutting blood sinuses of the neurohemal organ (sinus gland). Following a 72 h chase, label is distributed throughout the terminal region. Each of the six morphologically distinguishable terminal types shows labelling. These observations show that the vast majority of newly formed granules are initially transported to release sites of the perisinus terminals. They thus provide an explanation for previous analyses indicating that newly synthesized peptides are preferentially secreted.