Comp. Bmchrm. Phwol. Vol. 68A. pp. 25 lo SO 0 Pergamon Press Ltd 1981. Printed in Great Britain 0300.Y629!8l/OIOl-0025602.00/0 zyxwvutsrq THE NEURAL CONTROL OF RELEA SE OF HYPERLIPAEMIC HORMONE FROM THE CORPUS CARDIACUM OF LOCUSTA MIGRATORIA I. ORCHARD and B. G. LOUGHTON Department of Biology, York University, Downsview, Ontario, Canada M3J IP3 (Received 24 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON April 1980) Abstract-l. The neural control of the release of hyperlipaemic hormone has been studied in isolated corpora cardiaca of Locusta migratoria using electrical stimulation of the nervi corporis cardiaci I and II, and assaying the bathing medium for hyperlipaemic activity. 2. Stimulation of nervus corpus cardiacum II (NCC II) results in the release of hormone which is dependent upon the arrival of compound action potentials within the glandular lobe of the corpus cardiacum. 3. Sodium deficient Ringer and Ringer containing 10m6M tetrodotoxin abolish the compound action potential and with it the release of hormone. 4. The mechanism of release is dependent upon the presence of extracellular calcium-ions. 5. Stimulation of nervus corpus cardiacum I (NCC I) alone does not result in the release of hyperlipae- mic hormone, but the presence of action potentials in NCC I potentiates the hyperlipaemic effect obtained by NCC II stimulation. INTRODUCTION The glandular lobe of the corpus cardiacum (CC) of locusts contains two hormones with hyperlipaemic activity. Adipokinetic hormone (AKH) has been puri- fied, characterized and synthesized (Stone et al., 1976; Broomfield & Hardy, 1977) and more recently, a second peptide with adipokinetic activity has been purified and characterized (Carlsen et al., 1979). This second peptide accounts for some 20% of the total hyperlipaemic activity of the locust CC (Carlsen et al., 1979) and may be the hyperglycaemic factor pre- viously reported to lie within the glandular lobe (Goldsworthy & Mordue, 1974). It is generally accepted that the hyperlipaemic hor- mone(s) is synthesized by the intrinsic glandular cells of the glandular lobe (Stone et al., 1976). One of its functions is to elevate the level of lipid in the haemo- lymph during flight (Stone et al., 1976; Carlise & Loughton, 1979). The secretory activity of the intrin- sic glandular cells appears to be under the control of axons containing electron dense granules of about 1OOnm diameter, which make typical synaptic junc- tions with the glandular cells (Rademakers, 1977a). Transplantation experiments suggest that these axons exert a secretomotor control over the glandular cells (Rademakers, 1977a) and that the cell bodies of the axons lie outside the CC. Cell bodies containing sec- retory granules of the same size as those found within the axon terminals are located in the lateral areas of the protocerebrum (Rademakers, 1977b). The axons of these cell bodies run via the nervus corpus cardia- cum II (NCC II) into the glandular lobe and so may be the cells responsible for synaptic activation of the glandular cells. Experiments which involve the sectioning of nerves have suggested that hyperlipaemia may be under the control of both NCC II and NCC I, since both nerves need to be severed to prevent the increase in haemo- lymph lipid during flight (Goldsworthy et nl., 1972). However, these studies did not examine if the increase in lipid was a result of hyperlipaemic hormone. Since haemolymph lipid can increase in the absence of cir- culating hormone (Goldsworthy & Cheeseman, 1978) such nerve sectioning experiments may be ambiguous. We have set out to examine the control of the release of hyperlipaemic hormone(s) directly by elec- trical stimulation of NCC I and NCC II of isolated CC followed by the assay of hyperlipaemic activity in the bathing medium. Since our estimation of hyperli- paemia did not differentiate between AKH (Stone et al., 1976) and the second peptide (Carlsen et al., 1979) we use the term hyperlipaemic hormone to include both peptides. Electrical stimulation has previously been used to examine the release of hormone from insect CC (Berlind, 1977), but all of these studies suffer from the inability to define the physiological basis of the stimulation. We have overcome this prob- lem by monitoring the compound action potential which results from electrical stimulation so that we can be sure that the current intensities used are physiological. Our studies show that release of hyperlipaemic hor- mone is under the direct control of NCC II. Stimu- lation of NCC I does not induce release, but does potentiate the response obtained by stimulation of NCC II. MATERIALS AND METHODS Locusta migratoria were reared under crowded con- ditions in the manner described by Tobe & Loughton (1969). The CC and accompanying nerves (see Fig. 1) were dissected from adult locusts, cleared of adhering fatbody and washed in physiological Ringer (Hoyle, 1955). 25