Morphometric classification of neurosecretory granules in the neurohypophysis of the hagfish,Eptatretus burgeri

Summary Neurosecretory axons in the neurohypophysis of the hagfish, Eptatretus burgeri, were statistically classified into six types according to the size of secretory granules. These types are comparable with those in higher vertebrates. The concentration of each axon type is different in three regions: anterior dorsal wall, posterior dorsal wall, and ventral wall. The regional differences of the hagfish neurohypophysis are discussed in relation to the regional differentiation of the tetrapod neurohypophysis into the median eminence and the pars nervosa.We wish to express our appreciation to Professor Hideshi Kobayashi for the guidance of this study. It was aided by grants from the Ford Foundation and the Ministry of Education to Professor H. Kobayashi, and also by grants from the Population Council, New York and the Ministry of Education to Professor S. Ishii.     

Nervous system of the snailHelix aspersa

Summary The fine structure of neurosecretory nerves and endings associated with the sheath of the infraesophageal ganglion ofHelix aspersa is described. The sheath is a neurohemal organ whose vascularized stroma receives both monoaminergic and peptidergic endings. The latter occur along the surface of the nerves or scattered within the stroma. They include a complex population of vesicular profiles. The granular vesicles (1300–3000 Å in diameter) exhibit structural modifications that may be related to the intra-axonal release of their neurohormones. The agranular vesicles (500–2000 Å in diameter) occur in large numbers and lie mostly adjacent to the axon surface. Synaptoid specializations seem to represent active sites for the extracellular discharge of neurosecretory material. The monoaminergic endings so far studied lack synaptoid specializations and contain small granular (800–1300 Å in diameter) and agranular (700 Å in diameter) vesicles. Two kinds of non-neural cells are associated with the nerves: glial cells and melanocytes.Partly supported by Conicyt (Grant 105) and Comisión de Investigación Científica Universidad de Chile (Grant 48). The technical assistance of Mr. Arnold van Dun is gratefully acknowledged. We also thank the Department of Physics, Faculty of Physical Sciences and Mathematics, University of Chile, for the use of a Philips EM-300 electron microscope.     

Release of neurosecretory material by protrusions of bounding membranes extending through the axolemma,in Diphyllobothrium dendriticum (Cestoda)

Summary The release of neurosecretory material was studied in the cestode tapeworm Diphyllobothrium dendriticum. In plerocercoid larvae cultivated in vitro the neurosecretory vesicles release their content by way of protrusions extending through the axolemma into the intercellular space. The released material is directed predominantly towards the muscles. No omega figures were detected. The significance of this new type of release is discussed.The authors are greatly indebted to Mrs. Annukka Kärkkäinen and Mr. Esa Nummelin for technical assistance     

A functional unit consisting of an eversible gland with neurosecretory innervation and a proprioreceptor derived from a complex sensillum in an insect

Summary The eversible sac of the antennal tip in Hypogastrura socialis (Collembola) has been reconstructed from serial ultrathin sections. The organ contains 3 specialized epidermal glandular cells and the dendrites of 2 sensory cells encapsulated by an enveloping cell. The following features of the system are particularly remarkable and have been analyzed in detail: (1) a neurosecretory innervation of the glandular cells, (2) the structure of the dendritic outer segments within the sac, and (3) the structure of the complex sensillum, from which these dendrites may be derived. The system may be thought of as providing an example of phylogenetic transformation of an exteroceptor into a mechanoreceptive proprioceptor. A functional model is proposed which involves control of the mechanism of evagination as well as of the secretory discharge.     

Immunocytochemical localization of Bombyx-PTTH-like molecules in neurosecretory cells of the brain of the migratory locust,Locusta migratoria

Summary Using a monoclonal antibody directed against a synthetic pentadecapeptide corresponding to the N-terminus of the prothoracicotropic hormone (PTTH) of Bombyx mori, we report the presence of immunoreactive molecules in a large number of median neurosecretory cells of the pars intercerebralis of the migratory locust, Locusta migratoria. These cells correspond to the A₁ cell type which we show to contain also neuroparsins, a family of predominant neurohormones of the migratory locust. In contrast, PTTH-like molecules are absent from A₂ cells of the pars intercerebralis which contain Locusta insulin-related peptide (LIRP). Developmental studies show the presence of PTTH-related substances in neurosecretory cells of Locusta migratoria from late embryogenesis to adult development, including ageing vitellogenic female adults.     

尼罗罗非鱼神经垂体的超微结构研究

尼罗罗非鱼神经垂体存在A_1、A_2和B型神经分泌纤维,其终端与腺细胞、毛细血管、组织间隔、基板或脑垂体细胞形成直接轴——腺突触联系、间接轴——腺联系和直接轴——脑垂体细胞突触联系,构成下丘脑对脑垂体腺细胞支配的三种联系形式。在神经垂体组织中还存在Ⅰ型和Ⅱ型两种结构和功能不同的脑垂体细胞。     

Electron microscopic study of the orthograde axonal transport of horseradish peroxidase in the supraoptico-neurohypophysial tract of the rat

Summary Horseradish peroxidase (HRP) has been used as a protein tracer in order to visualize the ultrastructural sites of the orthograde transport of protein macromolecules in the hypothalamo-neurohypophysial tract of the rat. After a local injection of HRP within the supraoptic nucleus, the reaction product was observed: (1) mainly in tubules of the smooth endoplasmic reticulum in the more proximal part of the axons, and (2) in granules and microvesicles of the axon terminals. Observations on thick sections clearly showed the existence of a relationship between the smooth endoplasmic reticulum containing HRP and the labeled granules or microvesicles. These data are in good agreement with previous findings showing the existence of direct continuity between tubules of the smooth endoplasmic reticulum and a fraction of the neurosecretory granules and microvesicles. This evidence further reinforces the hypothesis that the latter organelles may possibly originate locally in the axons from the tubules of the smooth endoplasmic reticulum which may therefore be proposed as a possible vehicle for a non-granular intra-axonal transport of neurosecretory material in neurosecretory neurons.     

The posterior pituitary of the garden dormouse (Eliomys quercinus L.)

Summary Ultrastructural examination of the posterior pituitary of the garden dormouse (Eliomys quercinus L.) was carried out at different times in the annual cycle of this hibernating rodent. Obvious differences between experimental groups have not been observed, and the results presented here must be considered as general features of the garden dormouse posterior pituitary. Neurosecretory axons and endings can be divided into two types, according to different aspects of neurosecretory granules (NSG) and microvesicles (MV). One type contains spherical NSG with homogeneous cores and round MV. In the other type, NSG have various, often elongated, shapes. Their content shows two types of crystalline structures and most of the MV have flattened aspects. As it is very unlikely that this duality in NSG is a result of an artefact of fixation, three hypotheses are presented as explanation. The duality of NSG might be related either to their hormonal content (oxytocin or vasopressin) or to their degree of maturation. Moreover, both explanations may be valid. In the species studied, pituicytes often contain concentric lamellar structures of the endoplasmic reticulum (whorls), the significance of which remains obscure.This work was supported in part by grants of INSERM (C.R.L. n 73.1091.7 and A.T.P. n 4.74.25)     

Immunocytochemical study of the hypothalamo-neurohypophysial system

Summary Antisera, with cross reactive antibodies removed by affinity chromatography, were used in the immunoperoxidase-bridge technique to study the distribution of oxytocin and vasopressin together with neurophysin in the hypothalamo-neurohypophysial system of the rat. The hormones were demonstrated in different areas of the supraoptic nucleus (SON) and paraventricular nucleus (PVN), in neurosecretory fibres of the hypothalamoneurohypophysial tract, median eminence, and in nerve terminals of the neurohypophysis. Intact normal and rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain), and rats dehydrated by the administration of oral hypertonic saline were studied. In dehydrated rats the hormone concentration in the neurons, and the number of neurons containing hormone varied according to the time of dehydration stress.The observations support the hypotheses that: 1) oxytocin and oxytocinneurophysin, and vasopressin and vasopressin-neurophysin are synthesised in different neurons and are transported along different axons; 2) the SON and PVN are functionally indistinguishable in that neurons containing oxytocin or vasopressin are present in both nuclei; and 3) the two types of neurons respond to osmotic stimulation in a way that is qualitatively the same but quantitatively different.This work was supported by a grant from the Medical Research Council of New Zealand