In situ hybridisation studies using a
digoxigenin-labelled
DNA probe encoding the
Leu-callatostatin prohormone of the blowflies Calliphora vomitoria and Lucilia cuprina have revealed a variety of neurones in the brain and thoracico-abdominal
ganglion, peripheral neurosecretory neurones, and endocrine cells of the midgut. With two exceptions, the hybridising cells are the same as those previously identified in immunocytochemical studies of sections and whole-mounts using
Leu-callatostatin COOH-terminal-specific
antisera. Within the brain and suboesophageal
ganglion, there is a variety of neurones ranging from a single pair of large cells situated in the dorsal protocerebrum, to the several pairs of neurones in the tritocerebrum, some of which, in immunocytochemical preparations, can be seen to project via axons in the cervical connective to the thoracico-abdominal
ganglion. In the medulla of the optic lobes, numerous small interneurones hybridise with the probe, as do clusters of similar-sized neurones close to the roots of the ocellar nerves. These results indicate that the
Leu-callatostatin neuropeptides of the brain play a variety of roles in neurotransmission and neuromodulation. There are only three pairs of
Leu-callatostatin-immunoreactive neurones in the thoracico-abdominal
ganglion, at least two pairs of which project axons along the median abdominal nerve to provide extensive innervation of the hindgut. The
Leu-callatostatin peripheral neurosecretory cells are located in close association with both nerve and muscle fibres in the thorax. In addition to neuronal
Leu-callatostatin, the presence of the
peptide and its
mRNA has been demonstrated in endocrine cells in the posterior part of the midgut. These observations provide an example of a named brain/gut
peptide in an insect.