Neurosecretory Cell Bodies Research Articles

Morphology of kisspeptin-producing nuclei in the rat hypothalamus

ВACKGROUND: The article is devoted to the stereo-morphological analysis of the nuclei of the hypothalamus, synthesizing proteins of the kisspeptin family, regulating sexual differentiation various parts of the extended kisspeptin-producing nuclei of the hypothalamus and the features of their asymmetry in mature rats. The morphology of various parts of extended kisspeptin-producing nuclei of the hypothalamus remains poorly understood, which significantly complicates the choice of their reference zone, from which planning and implementation of morphological studies should begin, related to the evaluation of the effectiveness of therapeutic correction of various forms of hypogonadism.
 AIM: Determination of the main source of regulatory peptides of the kisspeptin family based on the analysis of the number, area of neuron bodies and volumetric characteristics of the kisspeptin-producing nuclei of the hypothalamus.
 MATERIALS AND METHODS: We studied 50 frontal paraffin sections of KPNs of 8 intact sexually mature male rats obtained as a result of a standard technique for their preparation and staining by the Nissl method. As a result, we carried out volumetric reconstruction of the largest nucleus of the arcuate complex the medial arcuate nucleus and the large periventricular nucleus, after which the number and area of neurosecretory cell bodies were determined in 5 frontal planes of these nuclei. To determine the proportion of kisspeptin-producing neurons in the total number of neurons in the kisspeptin-producing nuclei of the hypothalamus, we also performed the subsequent quantitative and morphometric characterization of their kisspeptin-producing neurons (after immunohistochemical staining, the identification of kisspeptin-kisspeptin granules. Statistical data processing was performed using the GraphPad PRISM 6.0 program, determining and lower quartiles. Differences were considered significant at p 0.01.
 RESULTS: Subdivisions of the nuclei, which are the main source of these regulatory proteins, have been identified. The caudal part of the medial arcuate nucleus (at the level of bregma 3.6 mm) and the anterior part of the periventricular nucleus (at the level of bregma 0.2 mm) are subdivisions of the corresponding kisspeptin-producing nuclei of the hypothalamus of the kisspeptin-producing nuclei of the hypothalamus, containing the largest number of neurosecretory cells and the bodies of their largest largest area. The number and area of neurons in the left-sided and right-sided parts of the hypothalamic kisspeptin-producing nuclei of the hypothalamus did not differ significantly. In this regard, the listed left-sided and right-sided subdivisions of the kisspeptin-producing kisspeptin-producing nuclei of the hypothalamus of the were proposed as standards for their subsequent morphological studies, which are important for assessing the effectiveness of therapeutic correction of various forms of hypogonadism.
 CONCLUSIONS: The left-sided and right-sided caudal parts of the medial arcuate hypothalamic nucleus and the anterior parts of the periventricular hypothalamic nucleus are proposed as a reference for their subsequent morphological studies related to the evaluation of the effectiveness of therapeutic correction of various forms of hypogonadism. as the main sources of regulatory proteins of the kisspeptin family.

Localization and identification of crustacean hyperglycemic hormone producing neurosecretory cells in the eyestalk of blue swimmer crab, Portunus pelagicus.

This study intensely focuses on to the localization and identification of crustacean hyperglycemic hormone (CHH) producing neurosecretory cells in the eyestalk of the blue swimmer crab Portunus pelagicus. Anti-Carcinus maenas-CHH was used to identify the location of CHH neurosecretory cells by immunohistochemistry. Ten pairs of eyestalks were collected from intact adult intermoult female crab and fixed in Bouin's fixative. Eyestalks were serially sectioned and stained with chrome-hematoxylin-phloxine stain. Histological studies show the presence of different types of neurosecretory cells namely A (multipolar), B (tripolar), C (bipolar), D (unipolar), E (oval), and F (spherical) in the medulla interna, externa, and terminalis regions based on their size, shape, and tinctorial properties. The neurohemal organ, sinus gland (SG) was observed laterally between medulla interna and terminalis regions. Immunohistochemical studies showed the presence of distinct CHH-like immunoreactivity in the optic ganglia. Divergent group of neurosecretory cells with varying degree of immunoreactivity with Anti-Carcinus maenas-CHH (low, moderate, and intense reactivity) were identified in medulla terminalis, medulla interna, medulla externa, and sinus gland. The present study maps the various types of neurosecretory cells in the optic ganglia and also shows the presence of CHH-like immunoreactivity in various regions of optic ganglia in P. pelagicus. The presence of these unique neurosecretory cell types with larger cell diameter in medulla terminalis, a region that bears the neurosecretory cell bodies, suggest high secretory activity.

Effect of apoptotic proteins on function of rat vasopressin-and dopaminergic hypothalamic neurons

To study character of effect of apoptosis signal proteins on activities of neurosecretory cells and neurons of rat hypothalamus, pharmacologic inhibitors of proapoptotic protein p53 Pifithrin-alpha and antiapoptotic protein Bcl-2 HA14-1 were injected into the hypothalamus. Activation of vasopressinergic neurosecretory cells at administration of the blocker Bcl-2 HA14-1 was shown: there were observed an increase of vasopressin mRNA in neurons of hypothalamus supraoptical and paraventricular nuclei, a decrease of the immunoreactive vasopressin content in posterior pituitary, and reduction of diuresis. Inactivation of p53 inhibited release of vasopressin from hypothalamus cell bodies, which is indicated by an elevated content of immunoreactive vasopressin in neurosecretory cell bodies with its unchanged synthesis, a decrease of the neurohormone content in the posterior pituitary, and an increase of diuresis rate. Activation of vasopressinergic neurons of the suprachiasmatic nucleus was also shown. Administration of the blocker Bcl-2 has been revealed to decrease functional activity both of dopaminergic neurons (Zona Incerta) and of dopaminergic neurosecretory cells (arcuate nucleus), in which a decrease of the tyrosine hydroxylase content was observed. The p53 inactivation also led to a decrease of activity of dopaminergic neurosecretory cells of arcuate nucleus, whereas activity of the proteins Zone Incerta did not change. Thus, it has been shown that a change of the apoptotic protein content in vasopressinergic and dopaminergic neurons and neurosecretory cells leads to a change of their functional activity, the character and possibly mechanisms of effects of apoptotic proteins on activities of vasopressin- and dopaminergic cells being different.

Brain‐derived neurotrophic factor‐like neuropeptide is secreted as a neurohormone from specific brain neurons into the corpus allatum in the silkworm Bombyx mori

AbstractThe aim of this study was to investigate the secretion of brain‐derived neurotrophic factor (BDNF)‐like neuropeptide in the silkworm, Bombyx mori , by using immunocytochemical techniques on the brain and retrocerebral complex of fifth instar larvae. In the brain, four pairs of median neurosecretory cell (MNC) bodies and six pairs of lateral neurosecretory cell (LNC) bodies had distinct immunoreactivities to this peptide, suggesting that this peptide is produced from two types of brain neuron. These reactivities were much stronger in the MNC than in the LNC. Labeled MNC projected their axons into the contralateral corpora allata, to which axons of labeled MNC were eventually innervated, through decussation in the median region, contralateral nerve corporis cardiaci I and nerve corpora allata I. Labeled LNC extended their axons into the ipsilateral corpora allata to be innervated through the ipsilateral nerve corporis cardiaci II and nerve corpora allata I. These results suggest that BDNF is secreted as a neurohormone from MNC and LNC of the brain into the corpora allata.

Antipeptide antibodies for detecting crab ( Callinectes sapidus) molt-inhibiting hormone

In crustaceans, the synthesis of ecdysteroid molting hormones is regulated by molt-inhibiting hormone (MIH), a neuropeptide produced by an eyestalk neuroendocrine system, the X-organ/sinus gland complex. Using sequence analysis software, two regions of the blue crab ( Callinectes sapidus) MIH peptide were selected for antibody production. Two 14-mer peptides were commercially synthesized and used to generate polyclonal antisera. Western blot analysis revealed that each antiserum bound to proteins of the predicted size in extracts of C. sapidus sinus glands, and lysates of insect cells containing recombinant MIH. Thin section immunocytochemistry using either antiserum showed specific immunoreactivity in X-organ neurosecretory cell bodies, their associated axons and collaterals, and their axon terminals in the sinus gland.

Molt-inhibiting hormone immunoreactive neurons in the eyestalk neuroendocrine system of the blue crab, Callinectes sapidus

The production of ecdysteroid molting hormones by crustacean Y-organs is negatively regulated by a neuropeptide, molt-inhibiting hormone. It is generally agreed that molt-inhibiting hormone is produced and released by the eyestalk neuroendocrine system. In the present study, immunocytochemical methods were used to detect molt-inhibiting hormone immunoreactive neurons in eyestalk ganglia of the blue crab, Callinectes sapidus. The primary antiserum used was generated against molt-inhibiting hormone of the green shore crab, Carcinus maenas. A preliminary Western blot analysis indicated the antiserum binds molt-inhibiting hormone of Callinectes sapidus. Using confocal and conventional immunofluorescence microscopy, molt-inhibiting hormone immunoreactivity was visualized in whole mounts and thin sections of Callinectes sapidus eyestalk ganglia. Immunoreactivity was detected in 15–25 neurosecretory cell bodies in the medulla terminalis X-organ, their associated axons and collateral branches, and their axon terminals in the neurohemal sinus gland. The cellular organization of molt-inhibiting hormone immunoreactive neurons in blue crabs is generally similar to that reported for other crab species. The combined results suggest the cellular structure of the molt-inhibiting hormone neuroendocrine system is highly conserved among brachyurans.

Immunoreactivity to P2X 6 receptors in the rat hypothalamo-neurohypophysial system: an ultrastructural study with extravidin and colloidal gold-silver labelling

The distribution of the purine receptor P2X 6 subtype was studied in the rat hypothalamo-neurohypophysial system at the electron microscope level. Receptors were visualised with ExtrAvidin peroxidase conjugate and immunogold-silver pre-embedding immunocytochemistry using a polyclonal antibody against an intracellular domain of the receptor. Application of ExtrAvidin labelling revealed P2X 6 receptors in subpopulations of: (i) neurosecretory cell bodies, neurosecretory and non-neurosecretory axons and dendrites of neurones in the paraventricular and supraoptic nuclei; and (ii) pituicytes and neurosecretory axons of the neurohypophysis. Some of the neurosecretory granules observed in the supraoptic and paraventricular nuclei neurone cell bodies, dendrites and axons as well as those in neurohypophysial axons were also positive for the P2X 6 receptors. In the paraventricular nucleus, some axons and dendrites of non-neurosecretory neurones positive for P2X 6 receptors formed synapses between themselves. Using the immunogold-silver method, the electron-dense particles labelling P2X 6 receptors were found in neurosecretory cell bodies of the supraoptic and paraventricular nuclei, in relation to the cytoplasm, endoplasmic reticulum, Golgi complex and neurosecretory granules. The particles indicative of P2X 6 receptors were also located in neurosecretory and non-neurosecretory axons including axonal buttons making synapses with P2X 6-negative dendrites. In the neurohypophysis, the electron-dense particles were localised in a subpopulation of pituicytes and neurosecretory axons. In neurohypophysial axons, particles were at times seen over the membrane of some neurosecretory granules (immunogold label) or microvesicles (immunoperoxidase label). We speculate that the P2X 6 receptors at the neurohypophysial level may be implicated not only in hormone release from the axon terminals, but also in membrane recycling of the granular vesicles and microvesicles.

Nitric oxide synthase in the caudal neurosecretory system of the teleost Oreochromis niloticus

This study provides evidence that, within the caudal neurosecretory system of the teleost Oreochromis niloticus, neurons express nitric oxide synthase (NOS)-like molecules. The presence of NOS-like molecules was demonstrated by means of NADPH-diaphorase (NADPHd) staining and NOS immunohistochemistry. In the caudal spinal cord, NOS-positive neurosecretory cell bodies and neurosecretory fibers were observed. In addition, NOS-positive structures were found in the urophysis which correspond to neurosecretory axon terminals. Cellular co-localization of NOS and ovine corticotropin-releasing factor (oCRF) immunoreactivities confirmed that the NOS-positive structures belong to the caudal neurosecretory system. The present results suggest that NO may participate in the caudal neuroendocrine function.

Responsiveness to D-glucose in neurosecretory cells of crustaceans.

1. An electrophysiological study of the D-glucose sensitivity of X-organ (XO) neurosecretory cell bodies in crayfish was carried out with the use of microelectrodes, perforated, and cell-attached patch-clamp techniques. 2. Glucose depolarizes the membrane potential of XO cells in a concentration-dependent manner. 3. Depolarization produced by glucose initiates a change in the pattern of electrical activity. Silent cells began to discharge action potentials. When bursting cells are depolarized by glucose, their action potentials are no longer grouped in bursts or disappear entirely. 4. Although the membrane potential returns to its initial value after removing glucose from the bath, discharge patterns of the cells may remain different. This suggests that besides the depolarizing effect, once the cells have been exposed to glucose, the sugar switches on a process that is maintained for a long time. 5. Glucose produced a reduction of membrane steady-state conductance, and a shift of reversal potential of membrane currents to a more positive value. 6. Depolarization induced by D-glucose appears to be related with a closure of potassium channels. 7. Glucose effect was thought to be generated by a product of metabolism that would act as intracellular mediator.

Ultrastructural morphology of neurosecretory neurons in the barnacle Balanus amphitrite

Barnacles are very specialized Crustacea, with strongly reduced head and abdomen. Their nervous system is rather simple: the brain or supra-oesophageal ganglion (SG) is a small bilobed structure and the toracic ganglia are fused into a single ventral mass, the suboesophageal ganglion (VG). Neurosecretion was shown in barnacle nervous system by histochemical methods and numerous putative hormonal substances were extracted and tested. Recently six different types of dense-core granules were visualized in the median ocellar nerve of Balanus hameri and serotonin and FMRF-amide like substances were immunocytochemically detected in the nervous system of Balanus amphitrite. The aim of the present work is to localize and characterize at ultrastructural level, neurosecretory neuron cell bodies in the VG of Balanus amphitrite.Specimens of Balanus amphitrite were collected in the port of Genova. The central nervous system were Karnovsky fixed, osmium postfixed, ethanol dehydrated and Durcupan ACM embedded. Ultrathin sections were stained with uranyl acetate and lead citrate. Ultrastructural observations were made on a Philips M 202 and Zeiss 109 T electron microscopy.

Flight-induced inhibition of the cerebral median peptidergic neurosecretory system in Locusta migratoria

This study discusses the effects of a 1-hr period of flight on the peptidergic pars intercerebralis (PI)-corpus cardiacum storage part (CCS) system in male Locusta migratoria, particularly the effects on material in this system stained by a histochemical method for peptidergic neurosecretory material (NSM) or labeled by in vivo incorporation of radioactive amino acid molecules. By use of an automatic image analysis system a number of parameters of the stained or radioactively labeled substances were measured to quantify the flight-induced effects and to get information on the manner in which the neurosecretory cell bodies in the PI and their axonal endings in the CCS accommodate changing amounts of NSM. The CCS of flown locusts contained distinctly more stained and radioactively labeled substances than the CCS of unflown locusts. A tendency to similar differences was observed in the cluster of neurosecretory cell bodies in the PI. The results indicate that 1 hr flight inhibited the release of NSM by the PI-CCS system. After the onset of reduced release activity by flight, some NSM continued to be synthesized and transported from the PI to the CCS, gradually filling up and expanding the entire PI-CCS system, the NSM at the same time becoming more and more densely packed. It is concluded that the peptidergic PI-CCS system is not actively involved in the control of flight metabolism or flight behavior.

Evidence for neurosecretory control of the optic gland in terrestrial pulmonates

The optic gland in terrestrial pulmonates secretes gonadotropic hormone. The present study investigates the fine structure of the optic gland to clarify the control of secretion. Animals used were the slug, Limax marginatus, and the snail, Euhadra peliomphala. The optic gland cell has a process and the cytoplasm is filled with large granules about 750–1300 nm in diameter with a thin corfex in L. marginatus and 800–1700 nm delimited by a thick peripheral layer in E. peliomphala. These gland cells are characterized by well-developed granular endoplasmic reticulum. Granule formation was seen in the region of the Golgi apparatus. During the breeding season, the medial neurosecretory cells of the brain are active in the production and release of secretory materials. Although no neurosecretory cell bodies occur in the tentacular ganglion, neurosecretory axons penetrate into the optic gland cells. Cobalt filling reveals that axons of the medial neurosecretory cells project to the tentacular ganglion, near the optic gland. These results suggest that the optic gland is controlled by a neurohormone originating from the medial neurosecretory cells of the brain.

Immunocytochemical identification of dynorphin-containing vesicles in brattleboro rats

Vasopressin and its carrier protein, vasopressin-associated neurophysin, are co-packaged together with an opioid peptide, dynorphin, into 160 nm diameter neurosecretory vesicles in the normal rat hypothalamo-neurohypophysial system. The homozygous Brattleboro rat lacks vasopressin and vasopressin-associated neurophysin, but contains substantial amounts of dynorphin in the vasopressin-deficient neurosecretory cells. We used post-embedding electron microscopic immunocytochemistry to determine the subcellular location of dynorphin in Brattleboro rats. The results show that dynorphin is present within 100 nm neurosecretory vesicles in homozygous Brattleboro cell bodies and axons, and within 160 nm vesicles in heterozygous (control) neurosecretory cell bodies and axons. Oxytocin-associated neurophysin is present in a separate population of magnocellular neurons in both homozygous and heterozygous rats, and is contained within 160 nm vesicles in both cases. Therefore, the absence of synthesis of the vasopressin prohormone results in a dramatic reduction of neurosecretory vesicle size, despite the continued synthesis and packaging of dynorphin peptides.

The effects of transverse cuts caudal to the preoptic recess on the fine structure of paraventricular nuclei in rats

Lesions of the tissue surrounding the preoptic recess (anteroventral third ventricle (AV3V) region) have been shown to severely impair normal mechanisms of body fluid homeostasis, including the antidiuretic response. In an earlier investigation of the pathways affected by these lesions, coronal cuts were placed between the level of the organum vasculosum lamina terminalis in the AV3V region and the level of the supraoptic nuclei. Rats with such cuts exhibited hyperdipsia and polyuria, but their plasma levels of antidiuretic hormone (ADH) were elevated. The fine structure of the supraoptic nucleus, a major site of ADH production, and of the neural lobe of the hypophysis, where ADH is released, were observed in rats with similar cuts. Although neural lobes showed evidence of hormone depletion and degenerating axons and terminals were present in supraptic nuclei, there was no morphological evidence that neurosecretory cell bodies in supraoptic nuclei were affected by these cuts. Therefore, in this investigation we observed the ultrastructural effects of such cuts on paraventricular nuclei, which are the other major source of ADH. Degenerating axons and terminals were common in paraventricular nuclei of lesioned rats, both in the major magnocellular subnucleus and in the periventricular region. Cell bodies and nuclei of neurosecretory cells were not significantly larger in lesioned animals, but morphometric evaluations revealed dispersion of the Golgi complex and alterations in the rough endoplasmic reticulum of the cells. In addition, more multiple nucleoli were present, and nucleoli tended to lie adjacent to the nuclear envelope more frequently. We conclude that the neurosecretory cells in the paraventricular nuclei become more active in rats with these knife cuts.

The neuronal endoplasmic reticulum: its cytochemistry and contribution to the endomembrane system. II. Axons and terminals.

The morphology and cytochemistry of the endoplasmic reticulum (ER) in axons and terminals of a number of different types of neurons in brains from mice were investigated ultrastructurally. The neurohypophysis received particular attention because the morphology and enzyme cytochemical activities of many of the preterminal swellings of hypothalamo-neurohypophysial axons are altered by chronic salt-stress. Membrane contrast and enzyme cytochemical staining techniques were employed to characterize the axonal reticulum and to determine if organelles representing the lysosomal system in the axon and the tubular profiles participating in the anterograde axonal transport of native horseradish peroxidase (HRP) are associated with the ER. Potential enzyme cytochemical markers for the axonal ER included glucose-6-phosphatase (G6Pase), thiamine pyrophosphatase, nucleoside diphosphatase, and acid hydroxylase activities. The anterograde transport of HRP was analyzed in undamaged hypothalamo-neurohypophysial neurons and in facial and hypoglossal motoneurons of mice receiving the protein in the lateral cerebral ventricle. The ER pervaded the axon and appeared as parallel, 20-40-nm-wide tubules interconnected by oblique anastomoses. Membrane thickness of the axonal reticulum measured 60-100 A, which is similar to that of the perikaryal ER. Enzyme cytochemical activities associated with the ER or lysosomes were not conspicuous in axons and terminals under normal conditions but became prominent in some axons and preterminal swellings manifesting an autophagic appearance within neurohypophyses from salt-stressed mice. Only G6Pase activity was a marker for the ER in these axons and preterminals. Many ER profiles in non-incubated sections and in G6Pase cytochemical preparations of salt-stressed neurohypophyses were wrapped around or interspersed among secretory granules, multilamellar bodies, and vacuoles that may represent forms of lysosomes involved in autophagy and crinophagy. Acid hydrolase activities were localized within the vacuoles as well as within 80-130-nm-wide, blunt-ended tubules in pituitary stalk axons; similar reactive tubules were confluent with large secondary lysosomes in neurosecretory cell bodies and may be derived from these lysosomes. Morphologically identical tubules transporting HRP in the anterograde direction were observed only in the salt-stressed hypothalamo-neurohypophysial neuron. The HRP-positive tubules very likely are affiliated with the lysosomal system.

The Subgenus Persicargas (Ixodoidea: Argasidae: Argas): A. (P.) arboreus Central Nervous System Anatomy and Histology

The anatomy and histology of the adult Argas (Persicargas) arboreus central nervous system are described and compared with these properties in other ticks. The single, integrated, central nerve mass (CNM) is formed by a fused supra-esophageal part (protocerebrum, cheliceral ganglia, palpal ganglia, and stomodeal pons) and a subesophageal part (4 pairs of pedal ganglia and the complex opisthosomatic ganglion). Single peripheral nerves (pharyngeal and recurrent) and paired peripheral nerves (compound protocerebral, cheliceral, palpal, pedal and opisthosomatic) extend from the CNM to body organs and appendages. Optic nerves, described in other Argas species, are not found in A. (P.) arboreus. Histologically, the CNM is enclosed by a thin-walled periganglionic blood sinus and invested by a collagenous neural lamella followed by a perineurial layer composed of glial cells and containing fine reticular spaces, a cortical layer of association, motor and neurosecretory cell bodies and glial cells, and inner neuropile regions of fiber tracts forming 5 horizontal levels of connectives and commissures.

Long term effects on the supraoptic nuclei and neural lobe produced by ablation of the tissue surrounding the preoptic recess (AV3V)

In previous investigations, lesions of the AV3V region surrounding the preoptic recess in the rat caused acute loss of the antidiuretic response to severe dehydration. Ultrastructural study of the supraoptic nuclei and neural lobes following several days of adipsia revealed a lack of response in neurosecretory cell bodies, which would normally show hypertrophy, and engorgement of axon terminals in the neural lobe with unreleased hormone, which would normally be depleted. When rats with such lesions were sustained through the acute phase, they regained their ability to concentrate their urine maximally in response to water deprivation, but their antidiuretic responses to angiotensin II or centrally injected hypertonic saline were still impaired. In this study we compared the fine structure of supraoptic nuclei and neural lobes of rats with AV3V lesions and rats with sham lesions after a recovery period of 5 weeks. We also compared responses to 5 days of water deprivation in lesioned and sham lesioned rats. Neurosecretory cell bodies in lesioned rats were smaller and contained fewer neurosecretory granulated vesicles, and axon terminals in the neural lobe contained more neurosecretory granulated vesicles compared to controls. In addition, the basal lamina surrounding fenestrated capillaries was covered to a greater degree by pituicyte processes in neural lobes of lesioned rats. Lesioned rats deprived of water for 5 days had changes in supraoptic nuclei and neural lobes which in general were qualitatively similar to those of controls. However, AV3V lesions blocked the increase in neurosecretory granulated vesicles in cell bodies in supraoptic nuclei and significantly inhibited depletion of neurosecretory granulated vesicles from axon terminals in the neural lobe of water deprived rats. We conclude that after 5 weeks of recovery the neurosecretory system had regained its ability to respond to dehydration, but the response was chronically affected by AV3V lesions.

Possible morphological bases for synchronisation of neuronal firing in the rat supraoptic nucleus during lactation

Oxytocin-containing neurones in the supraoptic and paraventricular nuclei of lactating rats display a periodic activation which results in a pulsatile release of hormone before each reflex milk ejection induced by suckling. This electrical activity occurs in an all-or-none fashion and is synchronised in the whole population of oxytocin neurones in both nuclei. The present report describes changes in the ultrastructure of the supraoptic nucleus of lactating animals which may serve as morphological bases for such a functional synchronisation. In the supraoptic nuclei of normal rats, neurosecretory neurones are usually separated by elements of the neuropil, particularly glial processes. At rare intervals, adjacent neurosecretory somata, and dendrites, are seen to be in direct apposition. The only specialisations apparent between the contiguous membranes are occasional attachment plates. In nuclei of lactating rats, quantitative analysis indicated that 34% of profiles of the sectioned neurosecretory cell bodies were in direct contact with each other and 22% with profiles of dendrites, a 5-fold increase over the corresponding frequencies observed in normal male and virgin female animals. Such contacts involved 10% of the total measured soma surface membrane (compared to 1.5% in the controls). The number of attachment plates supporting the apposing membranes also increased significantly as did the mean size of the individual appositions. There was also a higher incidence of presynaptic terminals contacting more than one post-synaptic element (soma or dendrite) in the same plane of section, a rare phenomenon in the normal nucleus. No further increases were evident in these appositional relations in virgin female and lactating rats deprived of water for one day, a stimulus which enhances vasopressin release. It is postulated that the structural reorganisation observed in the nuclei of lactating animals may lead to electrical interactions between the neurosecretory cells and may thus be one of the factors supporting the synchronisation of neuronal activity during the episodic release of oxytocin.

Cytochemistry of undamaged neurons transporting exogenous protein in vivo.

AbstractThe uptake, transport and fate of exogenous protein in undamaged cranial motor and neurosecretory neurons in mice have been investigated using enzyme cytochemical techniques for horseradish peroxidase (HRP) and lysosomal acid hydrolases. Labeling of these neuronal perikarya with HRP is accomplished by retrograde axoplasmic transport from their axon terminals following vascular injection of the protein or by direct somal‐dendritic uptake subsequent to cerebral ventriculo‐cisternal perfusion of peroxidase. Axon terminals of neurosecretory neurons innervating the posterior pituitary gland and those of cranial motoneurons can remain unexposed to HRP administered intraventricularly and, therefore, cannot directly incorporate the protein.Perikaryal organelles containing HRP reaction product include multivesicular bodies, small vacuoles, membrane‐delimited cisterns and dense bodies. The concentrations of these different types of peroxidase‐positive organelles are consistently greater in retrogradely labeled cell bodies than in perikarya which have pinocytosed the protein from the perisomal clefts, even though the amount of HRP bathing the cell bodies is much greater than the amount exposed to the axon terminals. Since the same groups of dense bodies contain lysosomal acid hydrolases as well as exogenous peroxidase, the HRP‐labeled dense bodies are indeed lysosomes. Exogenous peroxidase does not stimulate lysosome proliferation; the concentration of acid hydrolase‐positive lysosomes appears to remain the same whether or not the cells are labeled with HRP.Despite peroxidase labeling of cranial motor and neurosecretory cell bodies after intraventricular injection, the anterograde axonal transport of peroxidase in these neurons is negligible. This transport can be demonstrably increased in the neurosecretory system, but not in cranial motor nerves, in response to hyperosmolarity induced in the animals by salt loading. Under such a stimulus many axons and Herring bodies in the posterior pituitary gland contain HRP‐labeled cisterns and 1,200–2,000 Å wide dense bodies. Both types of organelles also contain acid hydrolase activity and are confluent with each other. When compared to normal controls, the concentration of acid hydrolase‐positive organelles in pituitary stalk axons and Herring bodies from osmotically stressed mice is noticeably increased. Axonal cisterns with acid hydrolase activity and those transporting peroxidase in an anterograde or a retrograde direction appear similar morphologically.Our results indicate that peroxidase pinocytosed by the neuron is eventually sequestered within perikaryal lysosomes for enzymatic degradation. Under normal conditions acid hydrolase activity and the majority of lysosomes are confined largely to dendrites and the cell body, and anterograde axonal transport of HRP is minor. In the osmotically stressed neurosecretory system, HRP appears to be carried coincidentally and anterogradely along with the movement of acid hydrolases, most likely from secondary lysosomes in the cell body. The movement of acid hydrolases down the axon is presumably increased for degradative purposes in the posterior pituitary gland. A part of the cisternal network conveying acid hydrolases and transporting peroxidase in anterograde and retrograde directions may represent a special compartment of agranular reticulum specifically involved with the lysosomal system of organelles and important in the segregation of exogenous macromolecules within the neuron for transport to or from lysosomes.

Changes in hormone activity of single neurosecretory cell bodies during a physiological secretion cycle

Single neurosecretory cell bodies were dissected from the ventral ganglionic mass of Rhodnius prolixus, lysed in distilled water, and bioassayed for diuretic hormone (DH) activity on isolated malpighian tubules. DH was found in at least 10 somata within the ganglion; electron micrographs of isolated cells show a large population of elementary neurosecretory granules. Quantitative measures of hormone activity were made by bioassaying somata from unfed 5th instar larvae, and at the following times after feeding: 1 h, 4 h (near the end of DH-mediated diuresis), 1 day, 5 days, 10 days, 17 days and 21 days (just after the moult to adult). DH activity in cell bodies drops significantly within 1 h after feeding, and remains low long after hormone secretion ceases. Restocking of the soma with active hormone occurs during the period 10–21 days after feeding.