Angela B. Lange

Release of identified adipokinetic hormones during flight and following neural stimulation in Locusta migratoria

Fractionation of methanol extracts of perfusate and haemolymph on thin-layer chromatography was used to separate hormones associated with haemolymph lipid regulation in Locusta. Electrical stimulation of the nervi corporis cardiaci II (NCC II) of isolated corpora cardiaca resulted in the release of three hormones into the perfusate; hypolipaemic hormone and two adipokinetic hormones. The two adipokinetic hormones co-migrated with synthetic adipokinetic hormone (adipokinetic hormone I) and with the RF value similar to Carlsens peptide (adipokinetic hormone II). These two adipokinetic hormones were also present in small amounts in the haemolymph of unflown Locusta, and shown to be released during a 30-min flight. The adipokinetic hormone II fraction from the NCC II-stimulated perfusate and haemolymph also possessed hyperglycaemic activity when assayed in ligated locusts. It is concluded that NCC II controls the release of adipokinetic hormones during flight and that two adipokinetic hormones are released during flight. One of these hormones adipokinetic hormone II also acts as a hyperglycaemic hormone illustrating that a hyperglycaemic hormone is released, during flight.

The hormonal control of haemolymph lipid during flight in Locusta migratoria

Fractionation of methanolic extracts of haemolymph on thin layer chromatography, followed by bioassay, has been used to measure the titres of adipokinetic hormones I and II in the haemolymph of flown locusts. These titres have been correlated with the elevation in haemolymph lipid. Haemolymph lipid elevates in a biphasic manner during locust flight. A rise in lipid occurs during the first 10 min of flight. Lipid levels then plateau between 10 and 20 min. A second, more pronounced elevation begins at 20 min and continues for up to 60 min. The titre of adipokinetic hormone I elevates 10–15 min after flight commences while that of hormone II elevates between 15–30 min. Adipokinetic hormone I contributes 80% of the activity at 30 min but only 45% at 60 min. It is suggested that the elevation in haemolymph lipid during the first 10 min of flight may not be induced by adipokinetic hormone I or II. The role of octopamine in this initial elevation is proposed and discussed.

An oviposition-stimulating factor in the male accessory reproductive gland of the locust, Locusta migratoria

The data derived from mating experiments demonstrate that mating has an accelerating effect on oviposition in the female Locusta migratoria. The effect of mating could be mimicked by injection of extracts of the male accessory reproductive gland. The oviposition-stimulating factor was localized in the opalescent gland of the male accessory gland and was transferred to the female via the spermatophore during copulation. Gel filtration of an extract of the opalescent gland revealed a 13,000 Da protein, which, when injected into virgin female locusts, could stimulate the oviposition rate to that seen in mated females. Extracts of the corpus cardiacum also stimulated oviposition when injected into virgin female locusts. This increase was not observably different from that seen after mating. The relevance of these findings will be discussed.

The transfer of prostaglandin-synthesizing activity during mating in Locusta migratoria

The presence and distribution of a prostaglandin-synthesizing complex within the reproductive system of the orthopteran, Locusta migratoria has been examined. This complex, assayed by its ability to stimulate the synthesis of prostaglandins from precursor, was localized in the opalescent gland and seminal vesicle of the male accessory reproductive gland. No activity was found in any other part of the male accessory gland or in either the secretions or an homogenate of the testis. This differs from that previously described in Teleogryllus commodus where the prostaglandin synthetase was localized in the testis (Loher et al., 1981) and from Acheta domesticus where it was localized in the seminal vesicles of the accessory gland and in the testes (Destephano and Brady, 1977). Prostaglandin-biosynthetic activity was found in the contents of the spermatophore and this activity was transferred to the spermathecae of females during mating. The prostaglandin-biosynthetic activity from the opalescent gland was mostly associated with two high molecular weight fractions. Injection of 1 or 10 μg of prostaglandin E2 or F2α into the haemocoel of virgin females did not stimulate oviposition and neither did injections of 1 μg into the common oviducal region. The functional significance of this prostaglandin-synthesizing complex is discussed in relation to its role in mated female locusts.

Neural inhibition of egg-laying in the locust, Locusta migratoria

Abstract The role of the oviducal nerves during egg-laying in Locusta migratoria has been examined. Section of the oviducal nerves did not inhibit egg-laying in any observable way. Electrical stimulation of the oviducal nerves resulted in a contraction of the common and lower lateral oviducts which propelled ovulated eggs up towards the ovaries. Recordings from oviducal nerves using chronically implanted electrodes showed that electrical activity was low during actual egg-laying, but high at times when egg-laying was not occurring (i.e. during digging behaviour, or following interruption of egg-laying). During these periods of high activity recurrent bursts of action potentials occurred. Similar patterns of electrical activity were recorded in semi-intact preparations using suction electrodes applied to exposed oviducal nerves of locusts which had been interrupted during the process of egg-laying. High frequency bursts of activity were recorded simultaneously from both left and right oviducal nerves. It is concluded that one function of the oviducal nerves is to inhibit egg-laying at inappropriate times, by inducing contractions of the oviducts which propel eggs back towards the ovaries. These nerves therefore provide a physiological basis for part of the adaptive ovipositional activities of locusts.

The effects of precocene II on early adult development in male Locusta

Abstract Haemolymph protein synthesis and the accumulation of protein in haemolymph and accessory reproductive gland of normal adult male locusts were compared to that of males treated with precocene II. The precocene-treated insects showed a lower level of protein synthesis in both the fat body (source of haemolymph protein) and accessory reproductive gland. Topical application of juvenile hormone reversed the effects of precocene treatment. It would appear that the observed effects are the result of a reduction in juvenile hormone titre in the treated animals.

Insect Myosuppressins/FMRFamides and FL/IRFamides/NPFs

ABSTRACT Since the discovery of the molluscan cardioacceleratory peptide FMRFamide [ 8 ], a variety of neuropeptides that share the C-terminal RFamide have been characterized from both invertebrates and vertebrates. In insects these include the myosuppressins, the N-terminally extended FMRFamides (found only in dipterans) and FL/IRFamides, the neuropeptide Fs (NPFs), and the sulfakinins (discussed in Chapter 28 ). Although often referred to collectively as FMRFamide-related peptides (FaRPs), it is now clear that these peptide families are distinct and not related to one another. The extended RFamides are found throughout the central nervous system (CNS) in a variety of neuronal types, the stomatogastric nervous system, and within endocrine cells of the midgut. The genes for the peptides and their receptors have been cloned, and structure–activity relationships established in some cases. Many biological processes appear to be influenced by these peptides, including reproduction, circulation, ecdysis, and development. However, these peptides seem to be particularly involved in aspects of feeding, digestion, and/or food transport.

An analysis of the secretions of the male accessory reproductive gland of the African migratory locust

The male accessory reproductive gland of the mature adult Locusta has been examined during early adult development. The protein content of the accessory gland increased markedly over the first 15 d...

The selective accumulation of vitellogenin in the locust oocyte

The selectivity of vitellogenin absorption by the locust oocyte was examined by comparing the uptake of vitellogenin and a haemolymph protein of similar molecular weight (MHP). Though both proteins occurred in the haemolymph at approximately the same concentration there occurred a 500-fold difference in accumulation of vitellogenin over MHP during a 24-h period. Surprisingly MHP did not accumulate in the oocyte during vitellogenesis.

Proctolin in Insects

ABSTRACT The neuropeptide proctolin (RYLPT) was discovered in the cockroach Periplaneta americana, where it was considered a neurotransmitter associated with hindgut visceral muscle. Proctolin was the first insect neuropeptide to be sequenced and is now known to be widely distributed in insects and other arthropods and to be extremely active on a variety of arthropod visceral and skeletal muscle preparations. The gene for proctolin has been cloned in Drosophila, as too has the gene for its receptor. Structure–activity studies have identified the critical positions in the proctolin structure that enable binding to the receptor and biological activity, and agonists and antagonists have been designed. Many biological processes appear to be influenced by proctolin, which is involved in regulating muscles associated with posture, the digestive system, the reproductive system, and the circulatory system. Proctolin may also act as a releasing factor for hormones and/or act as a neurohormone.