Median Neurosecretory Cells Research Articles

Neurosecretion and hydroelectrolytic regulation in Artemia salina (author's transl)

The activity of Artemia protocerebral median neurosecretory cells is stimulated when animals are grown in media whose tonicity is lower than that of sea weater. The substance liberated by these cells could regulate the tonicity of the internal medium.

Reproductive growth in normal, allatectomized, median-neurosecretory-cell-cauterized, and ovariectomized females of Melanoplus sanguinipes

Changes in the weight of the whole insect, fat body, and ovary during successive gonotrophic cycles have been measured. The effects of ovariectomy, cautery of the median neurosecretory cells (mNSC), or removal of the corpora allata (CA) on the development of the fat body and reproductive system have also been observed.After an initial period of somatic growth, changes in body weight are very largely due to growth of the proximal oocytes and to oviposition. Yolk deposition begins when the oocytes are1.0 mm long and occurs most rapidly during the final stages of their development. Vitellogenesis begins in the penultimate oocytes when the proximal oocytes are 3.0–3.5 mm long. Ovariectomy results in a significant increase in the weight of the fat body. Removal of the CA prevents oocyte development beyond the 1-mm stage and production of secretion in the lateral oviducts. Both effects can be reversed by treating operated insects with juvenile hormone. Cautery of the mNSC, provided it is carried out within 3 h of emergence, also inhibits oocyte growth and delays the appearance of secretion in the lateral oviducts.

Methylxanthine inhibition of neurosecretion in the brain and corpus cardiacum of Cecropia

The fine-structure of the median neurosecretory cells and corpora cardiaca of the Cecropia silkmoth during the first 7 days after transfer from cold conditions to room temperature was compared to that of similar animals whose development was arrested with aminophylline. The major difference observed was the failure of the intrinsic secretory cells of the corpus cardiacum to degenerate in the arrested animals. This failure to degenerate coincides with the expected period of brain hormone release. After long periods of arrest, the medial neurosecretory cells and their axons became distended with neurosecretory granules. The significance of these observations in the initiation of adult development is discussed.

Neurosecretory cells and aorta as neurohaemal organ in the earwig, Euborellia annulipes lucas (Dermaptera : Labiduridae)

The neurosecretory system and retrocerebral-endocrine-aortal-complex of Euborellia annulipes have been described using performic acid resorcin fuchsin (PARF) and performic acid victoria blue (PAVB) techniques. There are 2 medial groups of neurosecretory cells (MNC). Each of them consists of compactly arranged 10–14 A-cells and a small number of B-cells. The axons of MNC, on each side of the brain lobe, converge at a point, and form a medial neurosecretory pathway (NSP). The 2 pathways, formed in this manner, decussate posterior to the corpus centrale, and run separately behind the brain. From the latter, they emerge as nervi corporis cardiaci—I (NCC—I) that enter the cephalic aorta (AO). Thus, the neurosecretory material (NSM) of the medial neurosecretory cells (A and B) transported via NCC—I is stored in the cephalic aorta (AO). The latter is packed with abundant NSM in mature earwings. Lateral sides of the brain contain a few B-cells. The B-cell secretion is transported to the corpora cardiaca (CC) through nervi-corporis cardiaci—II (NCC—II). Thus, CC store secretions of lateral cells and the products of their own chromophil cells. Corpora cardiaca are 2 elongate bodies composed of 2 types of cells. Although, the aorta is associated with the CC, migration of A-cell NSM from AO to CC was not observed. The corpus allatum (CA) is a globular body whose anterior part is attached with the posterior parts of the CC, and the dorsal surface associated with the ventral wall of the aorta. The gland consists of only one type of parenchymal cells. Migration of A-cell NSM from AO to CA is not observable.

Ultrastructure of retrocerebral complex of the earwig, Euborellia annulipes, and rôle of aorta as a neurohaemal organ

The ultrastructure of the retrocerebral endocrine-aortal complex of the earwig, Euborellia annulipes has been studied. The space between the inner and outer stromal layers of the aorta is occupied by numerous axon terminals and pre-terminals containing large electron dense granules (NS-I) of approximately 100 to 220 nm and a few axon terminals having small granules (NS-II) of approximately 40 to 90 nm; the former appear to belong to medial neurosecretory A-cells, and the latter to the B-cells of the brain. The corpora cardiaca consist of intrinsic cells with mitochondria and multivesicular bodies. Granules of type NS-II and NS-III are observed in the axon terminals and pre-terminals in the corpora cardiaca. The NS-II are identical to those found in the aorta and are probably the secretions of the lateral B-cells. Granules of type NS-III are 40 to 120 nm and electron dense, and are intrinsic in origin. Similar granules occur in the intrinsic cells of the corpora cardiaca. E M studies have confirmed the rôle of the aorta as a neurohaemal organ for the medial neurosecretory cells, and the corpora cardiaca for the lateral neurosecretory cells of the brain. The corpora cardiaca also act as a reservoir for the intrinsic secretion. The corpus allatum is a solid body consisting of parenchymal cells with prominent nuclei, mitochondria, and endoplasmic reticulum. In between its cells are occasional glial cells and also neurosecretory as well as non-neurosecretory axons. The gland is devoid of A-cell NSM.

Neuroendocrine control of moulting cycle in mealworms: Histology and autoradiography of cephalic components

Fluctuations in the activities of the cephalic neuroendocrine system of larval mealworms ( Tenebrio molitor) have been investigated by autoradiographic and histological techniques. Shortly after ecdysis, the proteinaceous granules in the cytoplasm of the ‘A’ type medial neurosecretory cells of the brain undergo a marked increase in numbers per cell and in chromophilia; both numbers and stain density reach a maximum about two-thirds of the way through interval between ecdyses and then both decline precipitously. The cyclic histological changes are nicely correlated with overall patterns of protein synthesis, as demonstrated by incorporation of 3H-amino acids into the medial cells. Paradoxically no cyclicity was observed downstream: no fluctuations in numbers or chromophilia of stainable inclusions were detected in the axons of the medial neurosecretory cells, in the corresponding efferent nerves to the corpora cardiaca, or within the cardiaca themselves. Mechanisms are proposed to account for this apparent paradox, and the patterns of protein synthesis within the ‘A’ type medial neurosecretory cells are correlated with previously determined fluctuations in moulting hormone activity.

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.

Some problems of homeostasis of haemolymph metabolites in the locust

Sectioning of the afferent nerves (NCCI and II) to the locust corpora cardiaca, glandular lobe removal, cardiacectomy, or removal of the median neurosecretory cells of the brain, have no long-term effect on blood lipid concentration. After removal of the glandular lobe, haemolymph carbohydrate concentration is lowered and remains significantly so from the second to the sixth day after the operation but returns to normal within 10 to 15 days. Severance of the afferent nerves to the corpora cardiaca does not, however, affect blood carbohydrate concentration. The injection of a concentrated extract of glandular lobes into locusts deprived of their glandular lobes does not elicit a hyperglycaemic effect even when blood carbohydrate levels are low. Cauterization of the median neurosecretory cells of the brain, sectioning of the NCCI and II, or removal of the glandular lobes of the corpora cardiaca have no effect on haemolymph protein. After dilution of haemolymph constituents by the injection of water, carbohydrate and protein concentrations are not rapidly restored to their initial values. The lipid concentration, however, rapidly returns to its pre-injection level due to the mobilization of 16:16, 16:18, and 18:18 diglycerides. This occurs even in glandular lobe deprived, median neurosecretory cell cauterized, or headless locusts. These diglycerides are mobilized following the injection of solutions containing lipid, carbohydrate, and/or protein, and are the same diglycerides that are released from the fat body in response to adipokinetic hormone. It is concluded that the injection of large volumes of fluid causes lipid mobilization but adipokinetic hormone does not apear to be involved, and the mechanism of blood lipid homeostasis in the resting locust is not clear.

Axonal pathways in the brain-retrocerebral neuroendocrine complex of Manduca sexta (L.) (Lepidoptera: Sphingidae)

Axonal pathways of the various neurosecretory cell groups in the brain of larvae and pupae of Manduca sexta were studied, using a cobalt diffusion and precipitation technique. Five groups of cells were found to send axons to each retrocerebral complex. Axons from the fused nervi corporis cardiaci I and II arise from 2 ipsilateral dorsomedial groups, a controlateral anteromedial group, and a controlateral dorsolateral group. Axons from the NCC III arise from a group of ipsilateral tritocerebral neurosecretory cells. All of the cell groups sending axons through the NCC I+II innervate the corpus allatum. By contrast, only a few of the axons making up the NCC I+II appear to terminate in the corpora cardiaca (CC). The tritocerebral cells send axons to the CC only. Extensive migration of neurosecretory cells takes place during metamorphosis. The dorsomedial cells of the larva migrate laterad to become the lateral neurosecretory cells of the pupa and adult. The anteromedial cells of the larva migrate dorsad to become the medial neurosecretory cells of the pupa and adult.

Endocrine activity during caste differentiation in Zootermopsis angusticollis Hagen (Isoptera): a morphometric and autoradiographic study

The diameters of the median neurosecretory cells (MNC) and their nuclei, and the volumes of the corpora cardiaca (CC) and corpora allata (CA) were measured in termites (Zootermopsis angusticollis) of differing age, sex, and caste. The synthetic activities of the MNC and CA were estimated autoradiographically.No significant differences in the diameters of the MNC and their nuclei were observed between insects of differing age, sex, and caste, with the exception of primary reproductives whose MNC are significantly larger than those of larvae of the same instar. The six types of MNC distinguishable histologically differ in their nuclear diameter : cell diameter ratios and in their rates of [3H]uridine and [3H]cystine incorporation.The volumes and (or) synthetic activities of the CA change markedly during the differentiation of reproductives and soldiers. The CA of recently molted primary and supplementary reproductives are several times larger than those of larvae and nymphs of the previous instar, yet their synthetic activity remains low. In contrast, the CA of presoldiers and soldiers are only slightly larger than those of previous instar larvae, but show high synthetic activity. The data are discussed in terms of the endocrine control of caste differentiation.

Neurosecretory system of the earwig Labedura riparia, and the rôle of the aorta as a neurohaemal organ

The neurosecretory system of Labedura riparia has been described from sections and whole mounts using a variety of techniques. The pars intercerebralis contains two clusters of medial neurosecretory cells (MNC), each cluster consisting of 8 to 10 A-cells and occasional B-cells. The lateral sides of the brain have a few B-cells. The axons of the median neurosecretory cells terminate in the cephalic aorta (AO), whereas the axons of the lateral neurosecretory cells (LNC) terminate in the corpora cardiaca (CC). It appears that the neurosecretory material (NSM) elaborated in the MNC is stored in the cephalic aorta and that elaborated in the LNC is stored in the corpora cardiaca, which are two oval or elongate bodies composed of large chromophobe and small chromophil cells. Posteriorly there is the oval or elongate corpus allatum (CA) attached to the CC by thick nerves. The CA consists of one cell type only. Both CC and CA contain no A-cell neurosecretory material. It has been suggested that the neurosecretory system of L. riparia is composed of two complexes. One is formed by the medial neurosecretory cells for which the aorta functions as a neurohaemal organ, and the other is formed by lateral neurosecretory cells-lateral neurosecretory pathways-nervi corporis cardiaci-II in which the corpora cardiaca function as a neurohaemal organ.

Fonction chromatrope de la pars intercerebralis chez l'acridien Oedipoda coerulescens

The median neurosecretory cells of the protocerebrum of fifth instar larvae and 1- or 2-day-old adults of Oedipoda coerulescens produced more fuchsinophilic material when reared on dark backgrounds than on pale ones. In the latter case, the neurosecretory cell bodies were almost completely devoid of neurosecretion. The same differences were found in the anterior lobes of the corpora cardiaca. Individuals implanted with pars intercerebralis from donors reared on a dark background showed dark pigmentation no matter what their own background colour (and conversely). Black or red pigmentation appeared on absorbent grounds whereas a pale one was produced on reflecting grounds with high levels of incident light predominantly between 576 and 588 mμ. The significance of these results is discussed. A possible scheme for the interaction of environmental factors and pigmentation is suggested.

Fine structure of median neurosecretory cell in diapause and non-diapause brains of the silkworm, Bombyx mori

Electron micrographs of the larval brain of the silkworm, Bombyx mori, show that the largest median neurosecretory cell of the diapause egg producer may participate in the production of lipo-granules, and that of the non-diapause egg producer in the production of electron-lucent vesicles. It was found that there were ribosome-like particles in the diapause median neurosecretory cell, and they gradually developed into highly dense particles and lined up along the smooth-surfaced endoplasmic reticulum. They finally became lipo-granules.

Interactions of the ring gland, ovaries, and juvenile hormone with brain neurosecretory cells in Musca domestica

The staining intensity (median neurosecretory cell index) of the median neurosecretory cells (MNC) in Musca domestica increased as oögenesis progressed from stages 2 to 10. The amount of neurosecretory material within the MNC was dependent upon the presence of ovaries with developing or mature follicles. Ovariectomized flies had a median neurosecretory index that was 50 per cent less than that of control flies with mature eggs. In addition, we found that ring gland removal decreased the staining frequency of three different neurosecretory cell groups; increased staining frequency in another; increased the amount of neurosecretory material within the MNC fibre tract; increased the cytoplasmic area of types A and A′ MNC. Furthermore, neither the juvenile hormone analogue nor the ring gland had a direct effect on the median neurosecretory cell index but did influence neurosecretory activity indirectly by activating the ovaries. We hypothesize that an ovarian hormone—the oöstatic hormone—regulates either the release from or synthesis of neurosecretory material within the MNC.

Preuves radiochimiques et physiologiques d'une activation par électrostimulation des cellules neurosécrétrices de la pars intercerebralis chez Locusta migratoria (insecte orthoptère)

The pars intercerebralis (PI) of the African locust ( Locusta migratoria migratorioides) was stimulated electrically and the effects of this on (a) radioactivity of the PI (median) neurosecretory cell bodies) and corpora cardiaca (containing the axon terminals of these cells), and (b) sexual maturation were studied. Electrical stimulation of the PI induces: (1) A quantitative decrease in neurosecretory material in the median neurosecretory cells (axon terminals and cell bodies); (2) An increase in synthetic activity of the median neurosecretory cell bodies; (3) An increase in neurosecretory material transported to the corpora cardiaca. It seems that a quantitative decrease in neurosecretory material in the cell bodies is not directly associated with electrostimulation but with release at the axon terminals. Pars intercerebralis electrostimulation accelerates male and female maturation. These radiochemical and physiological results show that electrostimulation induces activation of the neurosecretory cells.

Effects of corpora allata on the activity of the cerebral neurosecretory system of Locusta migratoria migratorioides R. & F

Allatectomy reduces the synthetic activity of the cerebral neurosecretory system of Locusta migratoria migratorioides. Since the median neurosecretory cells are thought to produce an allatotrophic factor it is possible that a close interrelationship exists between the two endocrine centres. This possibility was investigated further by inactivating the cerebral neurosecretory system by allatectomy or starvation and subsequently implanting supernumerary active corpora allata. After corpus allatum implantation into allatectomized L. migratoria females a significant stimulation of neurosecretory synthesis, transport, and release occurs. Starved female locusts implanted with active corpora allata show elevated rates of synthesis and transport of neurosecretion. It is concluded that a positive feedback of corpus allatum hormone on the median neurosecretory A-cells occurs. It is suggested that such a feedback system facilitates the continuous production of batches of eggs under favorable conditions. Such a relationship may affect the interpretation of the results of endocrine surgery.

Rupture de la diapause ovarienne d'Anacridium aegyptium par stimulation électrique des cellules neurosécrétrices médianes de la pars intercerebralis

Oögenesis and the physiological activity of the corpora allata were studied in adult females of the Egyptian locust ( Anacridium aegyptium), in ovarian diapause, after electrical stimulation in vivo of the pars intercerebralis. This stimulation provokes (1) a decrease in the quantity of fuchsinophilic material present in the median neurosecretory cell bodies and in the internal cardiac tract, (2) an increase in the physiological activity of the corpora allata (measured by its chromatropic effect on larvae of Locusta), and (3) rupture of the ovarian diapause (advance of maturation of the oöcytes and oviposition by 5 months, and initiation of the ovarian cycle). In the control animals, the same electrical stimulations of various regions of the central nervous system (tritocerebrum, first ganglion of the abdominal cord) have no effect on these phenomena. In allatectomized females, electrical stimulations of the pars intercerebralis are followed by a slight growth of oöcytes, without a deposit of yellow vitellus. The diapause is not broken. Section of the allatocardiac nerves or rupture of the allatocardiac and allato-suboesophageal nervous connexions do not change the physiological state of the corpora allata. In the case of females in which the corpora allata have been disconnected, electrical stimulations of the pars intercerebralis succeed in activating the corpora allata and breaking the ovarian diapause. The aggregate of these results confirms that in locusts the control of the brain over the physiological activity of the corpora allata is above all neuroendocrine.

Structural and electrophysiological properties of nymphal and adult insect medial neurosecretory cells: An In vitro analysis

Medial neurosecretory cells (MNSC) from protocerebral nuclei of nymphal and adult cockroaches were cultured in a chemically defined medium in combination with embryonic organs or ovaries from the same species, for periods ranging between 2 and 12 weeks. Under these conditions, neurosecretory cells show vigorous outgrowth of large diameter axons, which differs in many respects from that previously observed from other neuronal embryonic, nymphal and adult explants cultured in the same medium. MNSC explants exhibit spontaneous unit electrical activity which is characterized by a low rate of discharge (1/sec) and regular interspike intervals. This activity contrasts with the spontaneous bursting discharges observed in long-term cultures of the neurosecretory cell population of the corpora cardiaca from nymphal and adult cockroaches.

Changes in the neurosecretory cells, corpus cardiacum and corpus allatum during pregnancy in Glossina austeni Newst. (Diptera, Glossinidae)

AbstractThe neurosecretory cells of the pars intercerebralis, the corpus cardiacum and the corpus allatum were examined in histological sections of Glossina austeni Newst. females fixed at daily intervals over the first two cycles of pregnancy. Two groups of neurosecretory cells corresponding to the lateral and median cells of other insects were recognised. The median neurosecretory cells were found to undergo cyclic changes of net synthesis and net release, which were correlated with ovulation and larviposition. The single ellipsoid corpus allatum undergoes cyclic changes in volume and histological appearance which are correlated with changes in the volume of the milk gland.

Ultrastructure of the neurosecretory system of the Colorado potato beetle, Leptinotarsa decemlineata (Say)

The pathways of axonal transport of secretions from neurosecretory cells (NSC) in the medial group (viz. A-, A1, B-, and C-type NSC) and the lateral group (L-type NSC) are described. Individual axons can be recognized in the electron microscope by the kind of neurosecretory particles they contain. In general, the secretions from the medial NSC are carried to the contralateral nervi corporis cardiaci (NCC), those from the lateral NSC to the ipsilateral NCC. Some axons from the A-type NSC, in addition, may run to ipsilateral NCC. All A-type axons have collaterals which run to the ipsilateral NCC. The medial and lateral bundles of “mixed” axons run through one paired NCC but remain separated spatially. Release of secretion from the C-type NSC can take place before the corpus cardiacum is reached.