PROTHORACICOTROPIC ACTIVITY IN THE BRAIN OF THE COCKROACH PERIPLANETA-AMERICANA

Co-incubation experiments of moulting glands with whole brains and crude brain extracts, respectively, were performed and analysed by ecdysone RIA to determine the prothoracicotropic activity in the brain of the cockroach Periplaneta americana. Two periods of prothoracicotropic activity in the brain of last-instar larvae were demonstrated. Both periods were related to a characteristic transient increase of ecdysone production by prothoracic glands in vitro. Prior to the first ecdysone peak from the moulting gland on the 23rd day, the first major peak of prothoracicotropic activity in the brain occurred on the 21st day in co-incubations with whole brains. A second peak was present at the end of the larval instar on about the 30th day, parallel to the main ecdysone peak. The increase in ecdysone production was about 40% in both periods- in co-incubations with crude brain extracts it was between 60 and 100%. In experiments with whole brains the prothoracicotropic activity appears about 5 days later than with brain extracts. Even the brain of imagines, at least up to the 10th day after the imaginal moult, had prothoracicotropic activity to a certain degree, i.e. 2/3 of the brain activity during the major peaks of the larval instar.