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

Abstract

During the purification of tachykinin-related peptides from the brain of the cockroach Leucophaea maderae, a few other peptides were collected in adjacent high-performance liquid chromatography fractions. Edman degradation, mass spectrometry, and chemical synthesis revealed that one of these peptides had the sequence DNSQWGGFA. This nonamidated nonapeptide was designated baratin and appears not to be related to any known insect peptide. Baratin was not found to be bioactive in the L. maderae hindgut or oviduct muscle contraction assay. (Both synthetic nonamidated and amidated baratin were tested.) To screen for possible sites of action, we raised a rabbit antiserum to 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 neuropil. Additionally we found BAR-IR neurosecretory cells in the median neurosecretory cell group with processes supplying the storage lobe of the corpora cardiaca. In each of the thoracic and abdominal ganglia processes of BAR-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 interganglionic BAR-IR processes was found in the locust subesophageal, thoracic, and abdominal ganglia. This was formed by four large projection neurons with cell bodies in the abdominal ganglia A1-2. The processes of these BAR-IR 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 abdominal ganglia of locusts and cockroaches, we could monitor bursts of action potentials in neurons with axons in the anterior abdominal nerve (nerve 1), but not in the posterior nerve (nerve 2). In ganglia displaying spontaneous rhythmic firing in units of nerve 1, baratin strengthened the rhythmic pattern. Thus baratin appears to have a role in modulation of motor patterns in abdominal ganglia. The immunocytochemical findings suggest further modulatory actions of baratin in different circuits of the brain and ventral nerve cord.