Effects of electrocoagulation of cerebral neurosecretory cells and implantation of corpora allata on oöcyte development in Locusta migratoria

The implantation of active corpora allata into intact Locusta females during growth accelerates pre-vitellogenic oöcyte growth and vitellogenesis. Localised stimulation of yolk deposition follows the implantation of active corpora allata between the ovarioles demonstrating a gonadotrophic rôle for the corpus allatum hormone. Electrocoagulation of the median neurosecretory cells of the brain prevents vitellogenesis whilst pre-vitellogenic oöcyte growth occurs normally. Implantation of active corpora allata into females with ablated cerebral neurosecretory cells promotes vitellogenesis in a proportion of test animals although mature oöcytes are never produced.It is suggested that the rôle of the median neurosecretory cells during egg development in Locusta is primarily concerned with the activation and maintenance of activity of the corpora allata. The corpus allatum hormone acts both metabolically and gonadotrophically.     

Immunocytochemical mapping of neuronal pathways from brain to corpora cardiaca/corpora allata in the cockroach Diploptera punctata with antisera against Met-enkephalin-Arg6-Gly7-Leu8

Summary Neuronal circuits in the brain and retrocerebral complex of the cockroach Diploptera punctata have been mapped immunocytochemically with antisera directed against the extended enkephalin, Met-enkephalin-Arg⁶-Gly⁷-Leu⁸ (Met-8). The pathways link median and lateral neurosecretory cells with the corpus cardiacum/corpus allatum complex. In females, nerve fibres penetrate the corpora allata and varicosities or terminals, immunoreactive to Met-8, surround the glandular cells. Males differ in having almost no Met-8 immunoreactivity in the corpora allata. The corpora cardiaca of both males and females are richly supplied with Met-8 immunoreactive material, in particular in the cap regions immediately adjacent to the corpora allata. A similarity in the amino-acid sequences of Met-8 and the C-terminus of the recently characterised allatostatins of D. punctata suggests that the pathways identified with the Met-8 antisera may be the same as those by which the allatostatins are transported from the brain to the corpus allatum. In comparative studies on the blowfly Calliphora vomitoria, similar neuronal pathways have been identified except that no sexual dimophism with respect to amounts of immunoreactive material within the corpus allatum has been observed. These results suggest a possible homology in the neuropeptide regulation of the gland.     

Localization and physiological effects of RFamides in the corpora allata of the cockroach Diploptera punctata in relation to allatostatins

The distribution of FMRFamide immunoreactivity in the brain-retrocerebral complex of adult female Diploptera punctata was examined. Immunoreactivity was observed in the brain and corpus allatum as well as in the corpus cardiacum. Immunoreactivity co-localized with allatostatin immunoreactivity within several lateral neurosecretory cells of the brain and in their endings within the corpus allatum. By in vitro radiochemical assay of juvenile hormone release, the effect of two native D. punctata RFamides, an FLRFamide (Leucomyosuppressin) and an FIRFamide were examined. The latter, for which the sequence (SKPANFIRFamide) is reported here, stimulated juvenile hormone release but acted only on corpora allata from females at the end of vitellogenesis (day 6). The interaction of these two RFamides and three D. punctata allatostatins, Dippu-AST 2, 5, and 7 were similarly examined. Only Dippu-AST 2 stimulated release of RFamides from the corpora allata and only on day 6 whereas both RFamides were able to attenuate the inhibitory activity of Dippu-AST 2.     

Neural control of the corpus allatum in the Colorado potato beetle, Leptinotarsa decemlineata: An electron microscope study utilizing the in vitro tannic acid Ringer incubation method

The release of material from neurosecretory synapses in the corpora allata of the Colorado potato beetle, Leptinotarsa decemlineata was visualised by an electron microscope procedure which involved tissue incubation in tannic acid. Using morphometry, the frequency of exocytosis phenomena was quantified in beetles kept under two different photoregimes. The number of exocytosis phenomena in the neurosecretory synapses in the corpora allata of beetles kept under short days was significantly higher than that of beetles reared under long-day conditions. In addition, the corpus allatum gland cells appeared to be more richly innervated by neurosecretory synapses under short-day than under long-day conditions. Previous studies using the in vitro radiochemical assay showed that the corpus allatum activity of short-day beetles is at least partly restrained by neurally mediated factors. The present morphological data strongly imply that this corpus allatum inhibitory substance is released from the neurosecretory synapses.     

Phe-Gly-Leu-amide allatostatin in the termite Reticulitermes flavipes: content in brain and corpus allatum and effect on juvenile hormone synthesis

In the subterranean termite Reticulitermes flavipes, allatostatins (ASTs) with the C-terminus Phe-Gly Leu-amide were localized by immunocytochemistry with antibody against a cockroach AST, Dippu AST-7. AST-immunoreactivity occurred in the corpus cardiacum and corpus allatum and in the lateral and medial neurosecretory cells of the brain that innervate these organs as well as in many other nerve cells of the brain. This was observed in workers, nymphs, soldiers and secondary reproductives. A radioimmunoassay, using anti-Dippu AST-11, demonstrated about 40 fmole equivalents of AST in brains of soldiers and secondary reproductives. The product of the corpora allata in this species was determined to be juvenile hormone III. Its synthesis by corpora allata of secondary reproductives, determined by in vitro radiochemical assay, was inhibited in a dose-dependent fashion by two cockroach allatostatins, Dippu AST-7 and Dippu AST-11. Thus, as in cockroaches and crickets, allatostatin-containing nerves innervate the corpora allata of this termite species and their production of juvenile hormone is inhibited by these neuropeptides.     

Regulation of the corpora allata in the black mutant of Manduca sexta

Regulation of corpus allatum activity in the black mutant strain of Manduca sexta was studied in vivo and in vitro. Allatectomy, denervation, and implantation studies demonstrated that black mutant corpus allatum activity remains low in both wild-type and black mutant host larvae. Attempts to distinguish humoral control mechanisms versus mechanisms dependent on intact allatal nerves indicated that intact allatal nerves were not required for the reduced black mutant corpus allatum activity in vivo. Incubation of corpora allata, using [1-¹⁴C]propionate as a juvenile hormone biosynthetic precursor and haemolymph as culture medium, confirmed that black mutant corpora allata are suppressed by a factor(s) in the haemolymph. Under identical conditions wild-type corpora allata were unaffected. Finally, the lowered black mutant corpus allatum activity in haemolymph in vitro correlates with the lowered juvenile hormone titre in black mutant larvae.     

Studies on the neurosecretory system and retrocerebral endocrine glands of Nezara viridula Linn. (Heteroptera: Pentatomidae)

The neurosecretory system and retrocerebral endocrine glands of Nezara viridula Linn. have been described on the basis of in situ preparations and histological sections employing the paraldehyde fuchsin (PF) and performic acid-victoria blue (PAVB) techniques. In the brain of N. viridula, there are two medial groups–each consisting of five neurosecretory cells which belong to A-type. The lateral neurosecretory cells are absent. The axons of the two groups of medial neurosecretory cells (MNC) compose the two bundles of neurosecretory pathways (NSP) that decussate in the anterodorsal part of the protocerebrum. The two pathways, after the cross-over, run deep into the protocerebrum and deutocerebrum and emerge as NCC-I from the tritocerebrum. The nervi corporis cardiaci-I (NCC-I) of each side which are heavily loaded with NSM terminate in the aorta wall. Thus, the neurosecretory material (NSM), elaborated in the medial neurosecretory cells of the brain, is stored in the aortic wall and nervi corporis cardiaci-I (NCC-I). The NCC-II are very short nerves that originate from the tritocerebrum and terminate in the corpora cardiaca (CC) of their side. Below the aorta, but dorsal to the oesophagus, lie two oval or spherical corpora cardiaca. A corpus allatum (CA) lies posterior to the corpora cardiaca (CC). The corpora cardiaca do not contain NSM; only the intrinsic secretion of their cells has been occasionally observed which stains orange or green with PF staining method. The corpus allatum sometimes exhibits PF positive granules of cerebral origin. A new connection between the corpus allatum and aorta has been recorded. The suboesophageal ganglion contains two neurosecretory cells of A-type which, in structure and staining behaviour, are similar to the medial neurosecretory cells of the brain. The course and termination of axons of suboesophageal ganglion neurosecretory cells, and the storage organ for the secretion of these cells have been reported. It is suggested that the aortic wall and NCC-I axons function as neurohaemal organ for cerebral and suboesophageal secretions.     

Morphology and ultrastructure of an isolated cell type corpora allata in adults of the bertha armyworm,Mamestra configurata Wlk. (Lepidoptera : Noctuidae)

There are 2 broad morphological types of corpora allata in adult Lepidoptera, a capsular type gland and an isolated cell type gland. Compared with the ubiquitous capsular corpus allatum, the isolated cell type has a narrow distribution in Lepidoptera and appears to be restricted to adult noctuids of the sub-family Hadeninae. The isolated cell corpora allata of adults of Mamestra configurata (Lepidoptera : Noctuidae) are composed of 30 – 40 large (ca 0.1 mm), semi-transparent, spherical, isolated cells held in 2 clusters by fine trachae and nerve fibers. These clusters lie directly beneath and in close proximity to the brain. Many similarities exist between the ultrastructure of the isolated cell corpora allata of M. configurata and the more common capsular gland. A high density of mitochondria, the arrangement of smooth endoplasmic reticulum in concentric “finger print” whorls, an interconnecting lacunae system of lipid vacuoles, and the presence of neurosecretory nerve endings are features commonly seen in active corpora allata of both types. The corpora allata of M. configurata are larger in the male, the calculated gland volume of males being more than 4 times that of females. Gland activity may change in senescent males as judged by the degeneration of the mitochondria, the reduction of the lacunae system and the dissolution of the smooth endoplasmic reticulum.     

Neuropepride Regulators of Insect Corpora Allata

SYNOPSIS. Neuropeptides of the insect brain that regulate juvenilehormone synthesis by the corpora allata include allatotropins,stimulatory modulators, and allatostatins, inhibitory modulators.A radiochemical assay for juvenile hormone synthesis by corporaallata in vitro was utilized in the high pressure liquid chromatographicisolation of brain neuropeptides leading to the determinationof their primary structure. Identified are an allatotropin andan allatostatin from a Lepidopteran, Manduca sexta, and a familyof five allatostatins from a Dictyopteran, Diploptera punctata.These neuropeptides are all unique, effective at low concentration(10^–10 to 10^–8 M), act quickly (within hrs) andappear to be effective only within the same order of insectsas that from which the peptides were isolated. The physiologicalstate of the corpora allata conditions the effectiveness ofthe allatostatins of D. punctata. These neuropeptide regulatorsof corpora allatal function may have multiple regulatory roles.This is indicated for D. punctata allatostatin I by specificreceptors in brain and fat body as well as in corpora allatalmembrane preparations, and also by immunocytochemical localizationof allatostatin I in medial nerve cells that terminate withinthe brain as well as in the lateral neurosecretory cells thatterminate on corpus allatum cells.     

Allatostatin-immunoreactive neurons projecting to the corpora allata of adult Diploptera punctata

Summary A monoclonal antibody against allatostatin I was used to demonstrate the allatostatin-immunoreactive pathways between the brain and the corpus cardiacum-corpus allatum complex in the adult cockroach Diploptera punctata. The antibody was two to three orders of magnitude more sensitive to allatostatin I than to the other four known members of the allatostatin family. Whole and sectioned brains in which immunoreactivity was localized with horseradish peroxidase-H₂O₂-diaminobenzidine reaction showed strongly immunoreactive cells in the pars lateralis of the brain with axons leading to and arborizing in the corpus cardiacum and the corpus allatum. Although many neurosecretory cells of the pars intercerebralis project to the corpora allata only, four strongly immunoreactive cells were evident here (two pairs on either side), and these did not project to the corpus cardiacum and corpus allatum but rather terminated within the protocerebrum in areas in which lateral cells also formed arborizations. Immunoreactivity was found in many other cells in the brain, especially in the tritocerebrum.     

The cardiacal neurosecretory system and associated organs of an adult mosquito, Aedes aegypti

Unlike most other insects, mosquitoes do not possess discrete corpora cardiaca composed of neuropile, intrinsic neurosecretory cells and glial cells. Cells homologous with the intrinsic neurosecretory cells of other insects are located at the junction of the neck and thorax of mosquitoes, close to the corpora allata. These cells are named cardiacal neurosecretory cells. Axons run forwards from the cardiacal neurosecretory cells into the allatal nerves. Neurosecretory release sites occur over almost the whole of the nervi corporum cardiacorum, allatal nerves and oesophageal nerves, and these nerves constitute a very extensive neurohaemal organ for many of the cerebral neurosecretory cells. The neurosecretory release sites of the cardiacal neurosecretory cells appear to be in the allatal nerves and possibly also on the perikarya of these cells.     

Cockroach allatostatin-immunoreactive neurons and effects of cockroach allatostatin in earwigs

A monoclonal antibody to allatostatin I of the cockroach Diploptera punctata was used to demonstrate the presence of allatostatin-immunoreactive cells and fiber tracts in the neuroendocrine system of the earwig Euborellia annulipes. The corpora cardiaca cells were not immunoreactive, nor were the neurosecretory endings of fiber tracts from the brain to the corpora cardiaca. No immunoreactive material was detected in the corpus allatum, although the corpus allatum contained neurosecretory endings, and some cells of the brain, including medial and lateral protocerebral cells, showed immunoreactivity. In addition, the recurrent and esophageal nerves were allatostatin-positive. The last abdominal ganglion contained immunoreactive somata, and immunoreactive axons of the proctodeal nerve innervated the rectum, anterior intestine, and posterior midgut. We did not detect reactive endocrine cells in the midgut. Allatostatin I at concentrations of 10^–5 and 10^–7 M did not inhibit juvenile hormone biosynthesis by E. annulipes corpora allata in vitro. This was true for glands of low activity from 2-day females and brooding females, as well as for relatively high activity glands from 10-day females. In contrast, 10^–7 M allatostatin I significantly and reversibly decreased hindgut motility. Motility was decreased in hindguts of high endogenous motility from 2-day females and in those of relatively low activity from brooding females. These results support the notion that a primary function of allatostatin might be to reduce gut motility. Arch. Insect Biochem. Physiol. 38:155–165, 1998. © 1998 Wiley-Liss, Inc.     

Neurons projecting from the brain to the corpora allata in orthopteroid insects: anatomy and physiology

Retrograde and orthograde labeling of neurons projecting to the corpus allatum was performed in locust, grasshopper, cricket, and cockroach species in order to identify brain neurons that may be involved in the regulation of juvenile hormone production. In the acridid grasshopper Gomphocerus rufus L., and the locusts Locusta migratoria (R.&F.) and Schistocerca gregaria Forskal, the corpora allata are innervated by two morphologically distinguishable types of brain neurons. One group of 9–13 neurons (depending on species) with somata in the pars lateralis extend axons via the nervus corporis cardiaci 2 and nervus corporis allati 1 to the ipsilateral corpus allatum, whereas two cells in each pars lateralis have bilateral projections and innervate both glands. No direct connection between the pars intercerebralis and corpus allatum has been found. In contrast, neurons with paired axons innervating both glands are not present in Periplaneta americana (L.) and Gryllus bimaculatus de Geer. Instead, two cells in each pars lateralis project only to the gland contralateral to their somata. Electrophysiological experiments on acridid grasshoppers have confirmed the existence of a direct conduction pathway between the two glands via the paired axons of four cells that have been identified by neuroanatomy. These cells are not spontaneously active under experimental conditions. Ongoing discharges in the left and right nerves are unrelated, suggesting that the corpora allata receive independent neuronal inputs from the brain.     

The activity of the corpora allata in the fourth and fifth larval instars of the migratory locust

The presence of juvenile hormone in the haemolymph of larvae of Locusta has been detected by a modified Galleria bioassay and these results are compared with indirect methods of estimating corpus allatum activity. Juvenile hormone is present in the haemolymph during the fourth larval instar except on the last day of the instar, and is absent from the haemolymph of the fifth and final larval instar except on the last day of the instar. Changes in the volumes of the corpora allata simply reflect changes in the growth of the whole insect and are of no value in predicting endocrine activity. Changes in the size of the cells of the corpora allata can be correlated with the presence of juvenile hormone in the haemolymph in the fourth larval instar, but similar changes in cell size occur in the fifth larval instar when no juvenile hormone is present in the haemolymph. The effects of the implantation of corpora allata are unreliable as estimates of corpus allatum activity as isolated corpora allata from fifth instar larvae release juvenile hormone. Indirect methods of measuring corpus allatum activity are thus shown to be unreliable. The R_f value of Locusta juvenile hormone as determined by thin-layer chromatography differs from that of Roeller's juvenile hormone, suggesting that the two hormones might be chemically distinct.     

Histological studies of the neurosecretory and retrocerebral complex of the water beetle,Hydrophilus olivaceus Fabr. (Insecta,Coleoptera)

The neurosecretory cells (NSC) in the breeding phases show gigantic sized droplets. NSC show two peaks of activity in females at midnight and at 9 A.M., while a single peak occurs in males between midnight and 3 A.M. Light has a triggering effect on the neurosecretory release. The corpus cardiacum is the main neurohaemal organ. It has a nerve core formed by the nervi corpus cardiacum I and II, which is surrounded by the glandular region. Intrinsic secretory chromophilic cells and chromophobic cells occur randomly. Aorta is probably not a storage-release centre. The corpora allata are lobulated structures, showing cyclical activity which is correlated with egg-maturation. No neurosecretory material occurs in allatum.     

Nadph-diaphorase activity in corpus allatum cells of the cockroach, Diploptera punctata

Using the fixation insensitive NADPH-diaphorase reaction as a histochemical marker for the enzyme nitric oxide synthase (NOS), we investigated the possible sites of putatively NOS-related NADPH-diaphorase in the brain and retrocerebral complex of the cockroach, Diploptera punctata. In the cerebral ganglion, NADPH-diaphorase expression was localized in antennal lobes, optic lobes, mushroom bodies and neurosecretory cells. The highest NADPH activity was detected in the corpora allata (CA). Spectrophotometric quantitation indicated that NADPH-diaphorase activity first increased and then decreased (cycled) in the CA of mated females. In addition, during the first ovarian cycle, NADPH-diaphorase activity fluctuated concurrently with cyclic changes in the size of corpus allatum cells. In virgin females, NADPH-diaphorase activity remained at a low level, but it increased if the neural connectives between CA and brain were severed, indicating that the brain inhibited NADPH-diaphorase expression in the CA. Although nerve terminals were abundant in the CA, NADPH-diaphorase was clearly endogenous and synthesized by glandular cells, as was shown by histochemical staining of the cytosol in all dissociated cells of the CA. We have also demonstrated NADPH-diaphorase activity in the CA of the American cockroach Periplaneta americana, the house cricket Acheta domesticus, the lepidopteran Leucania loreyi, and the fruit fly Drosophila melanogaster, suggesting that NOS occurs in the CA of most, if not all insects. It is therefore possible that corpus allatum cells release NO, along with juvenile hormone, which presumably can function as a messenger molecule.     

Precocene sensitivity of corpora allata in adult female Locusta migratoria after electrocoagulation of the pars intercerebralis neurosecretory cells

Destruction, by electrocoagulation, of the median neurosecretory cells of the pars intercerebralis of 2-day old adult female Locusta migratoria completely suppressed normal juvenile hormone-biosynthetic activity of the corpora allata in most animals. For example, 6 days after electrocoagulation the rates of spontaneous juvenile hormone biosynthesis, measured by radiochemical assay of freshly isolated glands, showed a median value of less than $\text{1}\text{100}$ that of the corresponding sham operated controls, which were then in mid-vitellogenesis. Injection of graded doses (200–1600 μg) of precocene I at this time, followed by assays five days later, resulted in a similar decline of both corpus allatum volume and precocene epoxidase activity (measured by radiochemical assays of precocene I dihydrodiol formation in vitro) in pars intercerebralis-coagulated and sham-operated animals, when expressed as a percentage of their own zero precocene controls. Electrocoagulation of the pars intercerebralis largely prevented the normal increase in both corpus allatum volume and its epoxidase activity, so that by age 13 days these parameters were about 2.5-fold lower in coagulated vs control (sham operated) animals. In fact, electrocoagulation had no marked effect on the value of epoxidase activity per unit corpus allatum volume. It is concluded that the corpora allata from this species and stage are sensitive to precocene irrespective of whether they are active in biosynthesis of juvenile hormone.     

THE NEUROENDOCRINE SYSTEM AND STOMATOGASTRIC NERVOUS SYSTEM OF THE ADULT TSETSE FLY GLOSSINA MORSITANS

The brain of Glossina morsitans Westwood contains four groups of neurosecretory cells which are stainable with chrome haematozylin and phloxin. The axons of these cells form a pair of nervi corporis cardiaci which pass posteriorly from the brain and innervate the corpora cardiaca and corpus allatum before uniting with a small ganglion posterior to the corpora cardiaca. This ganglion is considered to represent the fusion of the fusion of the hypocerebral and ventricular ganglia which remain separate in other insects.
There is no frontal ganglion in the adult Glossina and the recurrent nerve fuses with one of the nervi corporis cardiaci immediately behind the brain. The oesophageal nerves arising from the fused hypocerebral and ventricular ganglia innervate the oesophagus in the anterior part of the thorax, the proventriculus and the posterior extension of the oesophagus close to the crop. These nerves possess both sensory and motor nerve endings. The differences which exist between Glossina and other cyclorrhaphous Diptera with respect to their neuroendocrine/stomatogastric system are noted and considered in terms of the control of neuroendocrine function.     

Function of the neuroendocrine complex in diapausing Pyrrhocoris apterus females

The role of the brain in inhibiting the action of corpora allata in diapausing short-day females was investigated by transplantation experiments. The function of the transplanted glands was evaluated by oviposition. Active glands from long-day females remained active for a long period of time after transplantation into short-day females, although in situ corpora allata were inhibited shortly after the transfer of females from long to short day. Moreover, inactive glands from short-day females became active after transplantation into other short-day females. In contrast, corpora allata remained inhibited when transplanted together with the brain in the neuroendocrine complex (brain-corpora cardiaca-corpus allatum) where the nervous connections between the brain and corpus allatum remained intact. It is therefore suggested that short-day conditions inhibit corpora allata via nervous connections with the brain.     

Evidence for brain-derived neurotrophic factor-like neuropeptide in brain of the silk moth Bombyx mori during postembryonic periods

Brain-derived neurotrophic factor-like neuropeptide is produced in the brain of the silk moth, Bombyx mori. Immunocytochemical studies of brain and retrocerebral complex of larvae, prepupae, pupae and adults showed that four pairs of median neurosecretory cells and six pairs of lateral neurosecretory cells which had different immunoreactivities to BDNF peptide. Day-1 adult brains showed no evidence of neurons stained by anti-BDNF antibodies. Those reactivities, which were much stronger in median cells than in lateral cells, were the weakest in an earliest larval stage and a latest pupal stage but the strongest in late larval stage. Median neurosecretory cells projected their axons into the contralateral corpora allata by decussation in the median region, nerve corpora cardiaca (NCC) I, and nerve corpora allata (NCA) I, whereas lateral neurosecretory cells extended their axons to the ipsilateral corpora allata via NCC II and NCA I.