Baratin, a nonamidated neurostimulating neuropeptide, isolated from cockroach brain: Distribution and actions in the cockroach and locust nervous systems

During the purification of tachykinin-related peptides from the brain of th e cockroach Leucophaea maderae, a few other peptides were collected in adja cent high-performance liquid chromatography fractions. Edman degradation, m ass spectrometry, and chemical synthesis revealed that one of these peptide s had the sequence DNSQWGGFA. This nonamidated nonapeptide was designated b aratin and appears not to be related to any known insect peptide. Baratin w as not found to be bioactive in the L. maderae hindgut or oviduct muscle co ntraction assay. (Both synthetic nonamidated and amidated baratin were test ed.) To screen for possible sites of action, we raised a rabbit antiserum t o baratin. We found baratin-immunoreactive (BAR-IR) interneurons throughout the cockroach central nervous system. Some prominent brain neuropils were supplied by BAR-IR neuron processes: the central body, the calyx, and lobes of the mushroom bodies, parts of the optic lobe, and the tritocerebral neu ropil. Additionally we found BAR-IR neurosecretory cells in the median neur osecretory cell group with processes supplying the storage lobe of the corp ora cardiaca. In each of the thoracic and abdominal ganglia processes of BA R-IR projection neurons and local neurons were seen. The baratin antiserum also labeled neurons in the brain of the locust Locusta migratoria, some of which are similar to those of the cockroach. A prominent system of interga nglionic BAR-IR processes was found in the locust subesophageal, thoracic, and abdominal ganglia. This was formed by four large projection neurons wit h cell bodies in the abdominal ganglia A1-2. The processes of these BAR-LR neurons are distributed dorsally and laterally in each of the ventral nerve cord ganglia. When baratin (10(-6)-10(-4) M) was applied to desheathed abd ominal ganglia of locusts and cockroaches, we could monitor bursts of actio n potentials in neurons with axons in the anterior abdominal nerve (nerve 1 ), but not in the posterior nerve (nerve 2). In ganglia displaying spontane ous rhythmic firing in units of nerve 1, baratin strengthened the rhythmic pattern. Thus baratin appears to have a role in modulation of motor pattern s in abdominal ganglia. The immunocytochemical findings suggest further mod ulatory actions of baratin in different circuits of the brain and ventral n erve cord. (C) 2000 Wiley-Liss, Inc.