Neurosecretory Axons Research Articles

Degeneration and Regeneration of Neurosecretory Systems

Publisher Summary Degenerative and regenerative phenomena have substantially contributed to the knowledge of neurosecretory systems. The general structural organization, the degeneration, and regeneration of neurosecretory neurons, and the process of neurosecretion are identical throughout the animal kingdom. In the first phase after interruption of a neurosecretory axon, the proximal and distal stumps react identically with the development of a dense system of tubular formations and with an increase in other axoplasmic organelles conveyed to the stumps from more proximal or more distal portions of the axon. During the second phase growth, cones containing numerous tubular formations and vesicles start to sprout from the axon in the proximal stump as an initiation of regeneration. The third phase in the proximal stump leads to the progressive establishment of new axon terminals in contact with a newly developed vascular plexus; these terminals are identical to those observed in the normal neural lobe.

Influence of 6-hydroxydopamine on hypothalamic control of prolactin and ACTH secretion in the teleost fish, Tilapia mossambica.

Electron microscope studies revealedthat 6-hydroxydopamine (6-HODA) destroyed the aminergic (type ‘B’) neurosecretory axons entering the rostral pars distalis of the teleost Tilapia mossambic

Heart activity and its control in the adult blowfly, Calliphora erythrocephala

Heart activity has been recorded from semi-isolated preparations, from intact flies, and from flies after nerve sections and other experimental treatment. The physiological behaviour of semi-isolated hearts differs so much from in vivo conditions that pharmacological experiments, including application of endocrine gland extracts, need particularly careful interpretation. The results of all the experimental and morphological evidence (including electron microscopy) of this study may be summarized as follows: The blowfly has an innervated myogenic heart. The basic myogenic rhythm (about 350 beats/min)—in this study termed ‘intact resting level’—may be altered by (1) inhibitory segmental nerves, inhibition coinciding with appendage movements, and (2) stimulatory neurosecretory axons, likewise originating in the thoracic ganglion mass and innervating the myocardium. Ether anaesthesia affects the nervous regulation, allowing myogenic activity to persist; CO 2 also abolishes cardiac pacemaker activity. The heart does not appear to be influenced by substances from the brain-retrocerebral endocrine complex, including the corpus cardiacum. The pericardial cells do not appear to produce heart accelerating factors.

Fine structure of a neurosecretory axon in a crustacean skeletal muscle

Un axone neuro-secreteur a extremites localisees dans le muscle squelettique du craneCarcinus est decrit. Ces extremites contiennent 6 sortes de vesicules ayant les diametres de 1300 a 3700 A. Il est suggere que es petites vesicules correspondent a la phase de retablisement de la membrane, pendant la decharge des granules euro-secreteurs. On suppose aussi que cet axone peutetre l'intermediaire d'une influence trophique du nerf sur le muscle.

Anin situStudy of the Hypothalamic Neurosecretory System of the Freshwater CatfishAilia coila(Ham.)

The hypothalamo-neurohypophysial complex of Ailia coila is well demonstrated with the help of in situ staining procedure. Both pars magnocellularis and pars parvocellularis components of the nucleus preopticus contribute to the formation of the right and the left main neurosecretory tracts. Anterior one third of these tracts are loosely set and posteriorly they became more compact. From the posterior two thirds of the main tracts several pairs of lateral tracts were given off which join at the midline to form the paired median tracts. The median and the main tracts jointly enter the pituitary as the common tract. The common tract on entering the pituitary often divides into two or more branches and enter the pars intermedia independently. The rostral pars distalis is least innervated by the neurosecretory axons. Since the proximal pars distalis has varying amount of AF-positive cells, and the pars intermedia has the bulk of the neurosecretory axons both these regions are stained dark in the in situ preparations. Bulk preparations provide a clear topographic picture of the entire neurosecretory system, which is very difficult to visualise in tissue sections and in their reconstructions.

The ultrastructure of the corpus cardiacum of Aedes sollicitans and the histology of the cerebral neurosecretory system of mosquitoes.

Abstract The anatomy of the cerebral neurosecretory system is essentially the same in adult Aedes sollicilans, A. aegypti. A. taeniorhynchus, A. triserialus , and Culex pipiens . Four paired groups of neurosecrotory cells, medial. lateral, anterior, and ventral, are located in the brain. The axons of the medial and lateral neurosecretory cells (nervi corporis cardiaci I and II) emerge from the ventral surface of the brain. enter the aortal wall, and form the corpus cardiacum. Electron micrographs of the corpus cardiacum of A. sollicilans reveal that the ganglion cells and neuropile are not concentrically arranged as in other insect ganglia. Instead, the corpus cardiacum is a linearly arranged ganglion in which the ganglion cells are centrally located between an anterior and posterior neuropile. Thus the corpus cardiacum consists of three regions: an anterior neuropile, a central region of ganglion cells, and a posterior region containing neuropile but mainly composed of neurosecretory terminals of the lacunar neurohemal site. The corpus cardiacum is a neurohemal organ located in the head of mosquitoes in contrast to other Diptera, in which it is found in the neek and thorax. Two neurohemal sites were found in this corpus eardiacum; an aortic neurohemal site in which neurosecretory axons extend between the muscle fibers of the aorta and terminate in the lunen, and a lacunar neurohemal site in the posterior region of the corpus cardiacum. In the lacunar site the neurosecretory axons terminate in extracellular channels which are confluent with the hemocoel. The axons of the lacunar site are associated with a type of glial cell restricted to this region. Five different types of neurosecretory axons were noted in the corpus cardiacum based upon relative size and density of the granules and density of the axoplasm. Two different types of axons were usually found paired in the lacunar release site, encapsulated by a glial cell process. The cephalic aorta associated with the corpus cardiacum is composed of two parallel layers of muscle, the internal and external aortal muscle. Although closely apposed, the corpus cardiacum and hypocerebral ganglion are two distinet ganglia, separated by muscle or glial sheaths. The hypocerebral ganglion terminates posteriorly in an interganglionic nerve which connects the two ganglia. A pair of neurosecretory nerves extend caudally from the corpus cardiacum. Each bifurcates; the dorsal branch becomes the nervus corporis allati, the ventral branch is the nervus ocsophagci. Each esophageal nerve is joined by a nonneurosecretory stomatogastric nerve, thereby forming the two ventricular nerves that continue to the ventricular ganglia in the thorax. Large secretory cells are located adjacent to the anterior and occasionally the posterior margins of the corpora allata. These cells contain numerous electron dense and lucent granules. Although an axonlike process appears to extend from these cells, they have no glial association and their soma are directly apposed; hence their identity as a neurosecretory cell or an endocrine cell requires further investigation, and the name X-cells has been retained until the function of these cells can be determined.

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Ultrastructural changes of the pars tuberalis and median eminence of rats following hypophysectomy.

The pars tuberalis of the hypophysis and the external layer of the median eminence were studied by electron microscopy using hypophysectomized rats. Twenty day-old and adult rats were hypophysectomized and examined at various intervals (from 10 to 150 days) afterwards. Several hypophysectomized adult rats were adrenalectomized and examined 3 days later.Ten days after hypophysectomy, the external layer of the median eminence indicated several neurosecretory axons containing large vesicles (1, 500-3, 000A) with osmiophilic interior and aminergic axons with small cored vesicles (800-1, 200A) and clear vesicles (300-500A). Thereafter these axons steadily increased in number, especially the neurosecretory axons, and extended deeply into the pars tuberalis making contact with the surface of the glandular cells.In spite of the alterations mentioned above, the fine structures of the tuberalis cells showed no remarkable changes, while the anterior hypophysial cells in the remnant of the sectioned stalk changed remarkably in their cytoplasmic appearance.In the adrenalectomized adult rats, whose hypophysis had been removed 30 days earlier, the anterior hypophysial tissue in the remnant of the stalk sectioned indicated many active ACTH cells (KUROSUMI and KOBAYASHI, 1966), while the tuberalis cells did not show any alteration in their cytoplasmic details.These observations may suggest that the tuberalis cells, unlike the anterior hypophysis, are not under the neurohumoral control of the hypothalamus in spite of their topographical and embryological association.

Histology and ultrastructure of the neurohypophysis of the South American lungfish, Lepidosiren paradoxa.

The neurohypophysis of the South American lungfish Lepidosiren paradoxa has been studied with light and electron microscopy, including the Falck-Hillarp technique for catecholamines. The pars nervosa hypophyseos is a well-marked, dorsally located subdivision of the pituitary gland composed of lobes or follicles, each one constituted of a central core of ependymal cells, a subependymal hilar region made up of nerve fibers and a peripheric palisade zone of nerve endings which contact capillary vessels. Four types of neurosecretory axons can be distinguished under the electron microscope. Type I, the most common, contains spherical elementary granules of high electron density, 1500–1800 A in diameter. The scarce type II axons contain irregularly-shaped elementary granules. Type III contains only small clear vesicles, 400–600 A in diameter. Type IV, mostly present in regions of the gland contacting the pars intermedia, contain large granulated vesicles, 900–1000 A in diameter. The Falck-Hillarp technique revealed axons with a positive reaction for catecholamines at sites corresponding approximately to the location of type IV of the electron microscope. Ependymal cells are of large size, linking the cerebrospinal fluid, the nerve endings and the blood vessels. A conspicuous membrane-bound, spherical dense material, 1400–2000 A in diameter, is observed in both the apical and vascular processes of these cells. The ependymal processes which traverse the hilar and palisade regions contain structures resembling degenerated neurosecretory axons. These results are discussed in relation with the currently available information on the comparative anatomy of the pars nervosa. The possible functional significance of ependymal cells and of each type of axon are also discussed. This study was aided by the following grants: NIH NS 06953 to Prof. De Robertis, Consejo Nacional de Investigaciones Cientificas y Tecnicas to Prof. Zambrano, Comision de Investigaciones Cientificas de la Provincia de Buenos Aires and Comision de Investigaciones Cientificas de la Universidad Nacional de la Plata: to Prof. Iturriza. The authors are indebted to Prof. De Robertis for his generosity in granting us his laboratory facilities, and to Dr. F. J. J. Risso and Mr. A. Fernandez (Resistencia, Chaco) who provided the specimens used in this study. The able microtechnical assistance of Miss L. Riboldazzi and Mrs. R. Rana and the photographic work of Mr. A. Saenz are much appreciated.

Studies in the comparatige neuroendocrinology of polychaete reproduction

The neuroendocrine systems of different polychaete groups exhibit a considerable diversity of structure and a remarkable diversity of function. In nereid polychaetes, a hormone originating from the prostomium exerts a dual influence, having both an inhibitory action, and a tropic action on maturation. The rate of secretion of the hormone declines during the life cycle and is subject to environmental and feedback influences. In syllid polychaetes, a comparable factor originates from the pharynx. In sone other polychaetes, inhibitory influences are apparently absent and cerebral secretions appear to promote gametogenesis, although different stages in this process are subject to their influence in different groups. Cerebral neuroendocrine systems exhibit a high degree of concentration, and their components include simple sensory receptors, neurosecretory cells, neurosecretory axon tracts, neurosecretory release structures (“neurosecretory neuropiles”) on the inside surface of the brain capsule, and epithelia of possible endocrine function (“infracerebral glands”) closely associated with the brain. Each system appears to be the source of a multiplicity of hormones, of unknown function in most cases.

Tetrapodlike features of the hypothalamohypophysial vascularization in the air-breathing teleost, Heteropneustes fossilis (Bl.)

In Heteropneustes fossilis the midventral floor of the hypothalamus is the site of the formation of median neurosecretory tracts and the uniting place of the median and the main tracts. Hence this area has a close network of neurosecretory axons, and at least some of them seem to terminate in this region. It is also the site of formation of the capillary plexus, which is in close contact with the neurosecretory axons. Thus, it is comparable to the median eminence of the tetrapods. Blood from the primary capillary plexus is conducted into the pituitary by portal vessels, which largely irrigate both pars distalis and pars intermedia. Some of them, along with the direct branches of the median hypophysial arteries, contribute to the formation of the interface vascular plexus lying in between the rostral neurohypophysis and pars distalis. From the interface vascular plexus also, blood vessels penetrate into the glandular pituitary. Thus the rostral neurohypophysis also functions as a median eminence.

Histology, histochemistry, and ultrastructure of neurosecretory cells in the optic lobe of the cockroach, Periplaneta americana

In the region of the distal optic chiasma of each optic lobe of Periplaneta americana, there is a group of about 120 monopolar neurosecretory cells. These cells do not stain with paraldehyde fuchsin but remain acidophilic after oxidation. They stain red or sometimes indigo with the azan technique. Histochemically, the neurosecretory material is positive for protein and the amino acids tryptophan and arginine but negative for 1, 2-glycols and strongly acidic groups. At the ultrastructural level, the cytoplasm of the cells contain many elementary neurosecretory granules 100 to 170 nm in dia. The cells also contain well-developed Golgi bodies and endoplasmic retieulum. The axons from these cells run toward the interior of the optic lobe. In this region, axons containing dense granules (mean diameter 70 nm) and synaptic vesicles synapse onto the axons from the neurosecretory cells. The neurosecretory axons then cross over to the anterior side of the optic lobe and run towards the brain. The function of these neurosecretory cells is unknown, but they may be involved with photoperiodically controlled activity rhythms.

Antidromic and orthodromic responses of paraventricular and supraoptic neurosecretory cells

Extracellular recordings were made from 132 paraventricular and 385 supraoptic neurons. One hundred and eighteen (90%) of the paraventricular and 323 (84%) of the supraoptic units were identified as neurosecretory neurons by virtue of an antidromic response to neurohypophysial stimulation. Neurosecretory cells manifested many properties characteristic of neurons with class C axons; 5.5% were silent under pentobarbital anesthesia. Approximately 10% of neurosecretory cells exhibited all-or-none jumps to shorter antidromic latencies as neurohypophysial stimulus strength was increased, suggesting branching of neurosecretory axons. Stimulation of the neurohypophysis inhibited the spontaneous activity of a majority of neurosecretory cells. Histograms of supraoptic neurosecretory cell activity after response to electrical stimulation of either vagus revealed long-latency (129 msec) excitatory responses, suggesting activation by polysynaptic pathways. Bilateral input from both vagi on individual cells was demonstrated. Histograms of supraoptic neurosecretory cell activity after electrical stimulation of the carotid sinus nerve also showed long-latency (83 msec) excitatory responses, suggesting activation by polysynaptic pathways. Convergence of carotid sinus and vagal activation was demonstrated on individual cells. These results provide evidence in support of the hypothesis that ADH release is related to an increase in the discharge rate of supraoptic neurosecretory cells.

Uptake of ferritin into neurosecretory terminals

The release of neurosecretory products from terminals in the corpus cardiacum has been described in a few insect species (Scharrer 1963, 1968; Johnson 1966; Bowers & Johnson 1966; Normann 1965; Smith & Smith 1966; Smith 1970). Exocytosis has been suggested as the mechanism of release in Calliphora erythrocephala (Normann 1965, 1969) and in Carausius morosus (Smith & Smith 1966; Smith 1970), whereas fragmentation into ‘synaptoid’ regions has been indicated in Periplaneta americana (Scharrer 1963, 1968) and in Myzus persicae (Johnson 1966; Bowers & Johnson 1966). It is clear that structures representing both these features exist and differences in interpretation may depend on the sequence of events contributing to release. Using an electron-dense marker, an attempt has been made to determine the origin of the small vesicles which occur in neurosecretory axons and to throw some light on the dynamics of the release process.

Neurosecretory cells and their axon pathways in Culiseta inornata (Williston) (Diptera: Culicidae).

Paired medial, intermediate, and anterior groups of neurosecretory cells are present in the protocerebrum of Culiseta inornata (Williston). The medial and intermediate cells seem to persist through larval, pupal, and adult stages; the anterior cells become inconspicuous about the time of adult emergence. Axons of the intermediate neurosecretory cells could not be traced for an appreciable distance, but axons of the medial cells could be traced to a neurohaemal organ on the aorta, and they appear to constitute the NCC I. Branches of the anterior-cell axons seem to constitute the NCC II, and other branches of these axons in fourth-instar larvae and young pupae can be traced into the ventral nerve chain. From the neurohaemal organ some neurosecretory axons pass into the oesophageal nerves, and the expanded posterior portion of each oesophageal nerve in adults may be a storage and release organ of neurosecretory material. A neurosecretory pathway can be traced from the neurohaemal organ to the corpora allata in adults; it is probably present also in larvae. Conspicuous neurosecretory axons of uncertain origin, which are distinct from the anterior-cell axons, can be traced from the protocerebrum through the circumoesophageal connectives and along the whole length of the ventral nerve chain in fourth-instar larvae; these axons are present, probably in a similar form, also in younger larvae, in pupae, and in newly emerged adults.

Ultrastructural Analysis of the Neuroendocrine Apparatus of Oncopeltus fasciatus (Heteroptera)

Abstract In Oncopeltus fasciatus, the A‐cells of the pars intercerebralis and their tracts are stainable in situ with the performic acid‐victoria blue (PAVB) method. The axons from these cells, after traversing the corpus cardiacum, terminate in the anterior part of the aorta which thus serves as the neurohemal organ. Ultrastructurally, four types of secretory neurons are distinguishable in the pars intercerebralis region: pic‐I with granules measuring 1000–3000 Å in diameter; pic‐II with granules of irregular size and shape, the elongate ones showing mean dimensions of 2400 × 1400 Å; pic‐III with less electron‐dense granules measuring 1000–2700 Å in diameter; pic‐IV, present not only in the pars intercerebralis but also in adjacent regions of the brain, with variable proportions of granules measuring 700–1800 A and dense‐cored vesicles measuring 1000–2400 Å. The nervi corporis cardiaci contain at least three types of neurosecretory axons, based on granule content, presumably representing pic‐I, pic‐II and pic‐III neurons. The wall of the aorta contains endings of at least three distinct types, again representing pic‐I, pic‐II and pic‐III neurons, and thus provides the neurohemal site for these three types of protocerebral neurosecretory cells. Axons of pic‐IV neurons appear to enter the cerebral neuropil. The corpus cardiacum is composed of two types of parenchymal secretory cells, with electron‐dense granules measuring 1300–3000 Å and 1000–2300 Å in diameter, respectively. The corpus cardiacum also contains interstitial cells and some axons of extrinsic origin, with and without granules. The corpus allatum may be paired or median, and receives a small number of at least two types of axons. The corpora allata of some reproducing females show a large number of PAVB‐stainable inclusions which appear to be modified cytoplasmic organelles, but are definitely not neurosecretory material. The hypocerebral ganglion is composed of two types of secretory‐appearing neurons and glial cells. The two neuronal types contain secretory granules, 1000–3000 Å and 900–2100 Å in diameter, respectively. Axons of the recurrent nerve also may contain occasional granules. In this heteropteran insect, the two principal functions of the corpus cardiacum appear to be spatially separated: the neurohemal function is subserved by the aortic wall, which permits release of material into both the aortic lumen and the hemocoel, and the intrinsic endocrine function is possessed by the parenchymal cells.

Hormonal content and ultrastructure of the disconnected neural lobe of the grass frog ( Rana pipiens)

Based on changes in ultrastructure and vasotocin content, two postoperative phases can be distinguished in the neural lobes disconnected from the hypothalamus. During the first phase (first 2 days after transection) only very few axons start to degenerate, and the vasotocin content does not differ from that of the control glands. Axons filled with tubular formations are more numerous than in the controls. The second phase (6th to 9th postoperative days) is characterized by the degeneration of most of the neurosecretory axons and by a dramatic fall in the vasotocin content of the glands. During this phase, the number of Golgi complexes in the pituicytes increases considerably. Simultaneously, the appearance of well organized canaliculi lined by pituicytes is observed. A second cell type, in addition to pituicytes, is observed in the second phase. These cells have a charteristic nucleus and a cytoplasm mainly occupied by rough endoplasmic reticulum and lipid droplets. The pituicytic reorganization and the appearance of a new type of cell indicate that the chronically disconnected neural lobe is not a dead formation but a structure that may play some unknown functional role. The capillaries of the disconnected neural lobe are characterized by the widening of the endothelial fenestrations and the disappearance of their membrane, which results in a direct communication between the capillary lumen and the perivascular space. White blood cells are densely packed against the capillary walls, and most of these cells have processes that penetrate the endothelial openings and contact the perivascular basement membrane.

Ultrastructural studies on the corpora cardiaca‐allata complex of the adult alfalfa weevil, Hypera postica

AbstractThe organization of the corpora cardiaca and corpora allata of the female alfalfa weevil, Hypera postica, generally parallels that reported for other insects with extrinsic neurosecretory axons, intrinsic neurosecretory cells, and interstitial or glial cells appearing in both glands.Connecting the brain with the cardiacum are the extrinsic neurosecretory axons containing granules between 600 and 2200 Å. Granules with a diameter of up to 4000 Å are found in the intrinsic secretory cells of the corpus cardiacum.From the lobed corpus cardiacum, axons extend along a short nerve trunk into the ovoid corpus allatum. A characteristic of this gland is the presence of a layer of axons, ensheathing most of the corpus allatum and situated beneath an external basement membrane. These axons are believed to have their origin in the protocerebral neurosecretory cells. Although the c. allatum is known to be engaged in the release of hormonally active material, the cytoplasmic organization does not strongly reflect such activity.The glands of the diapausing weevil appear similar to those of the active weevil with a reduction in cytoplasm and a consequent folding of the plasma membrane.

Neuronal transformation of ependymal cells in the median eminence of the grass frog (Rana pipiens) after transection of the proximal neurohypophysis.

Dramatic changes have been observed at the light microscopic and ultrastructural levels in the neurosecretory axons of the distal stump of the transected proximal neurohypophysis (Dellmann & Owsley, 1968, 1969; Sterba & Brückner, 1969; Dellmann & Rodriguez, 1970). Besides phagocytic pituicytes (Dellmann & Owsley, 1968, 1969; Sterba & Brückner, 1969), large cells have been reported to occur in the median eminence (Dellmann & Owsley, 1968), characterized by a very light-staining cytoplasm and granules stainable with paraldehyde fuchsin. This report deals with the ultrastructure of these cells and their possible significance. The investigations were carried out on grass frogs, Rana pipiens, killed 6 and 12 hr., 1, 1·5, 2, 6 and 9 days after transection of the proximal neurohypophysis. The areas adjacent to the lesion were fixed in situ with a threefold aldehyde mixture (Rodriguez, 1969), carefully dissected out and processed according to the procedure described elsewhere (Dellmann & Rodriguez, 1970)

The ultrastructural distribution of succinic dehydrogenase activity in the supraoptico-neurohypophyseal system of the rat.

The succinic dehydrogenase (SDH) activity in the supraoptico-neurohypophyseal system of the rat was studied by means of electron microscopic histochemistry aiming at the explanation of earlier findings pointing out the consistently negative reaction of this enzyme in the axon terminals. SDH activity was found to be localized in the mitochondria of neurosecretoy neurons and pituicytes. The hypothalamic as well as the neurohypophyseal portions of neurosecretory axons have markedly stained mitochondria. In contrast to this, axon terminals devoid of neurosecretory material contain non-reacting mitochondria similarly to the previously described distribution of SDH activity in other regions of the nervous system. Accordingly SDH activity could be revealed neither in the mitochondria of axon terminals synapsing on the neurosecretory perikarya nor in the mitochondria of those neurohypophyseal boutons lacking neurosecretory granules. The more uniform distribution of SDH-activity in neurosecretory than in non-neurosecretory neurons points to the possible role of axoplasmic flow in causing within the neurons the described proximodistal decrease of SDH-activity.