Ultrastructure of the corpus cardiacum and corpus allatum of the house cricket Acheta domesticus

Summary The ultrastructure of the corpus cardiacum (CC) and corpus allatum (CA) of the house cricket, Acheta domesticus, is described. Axon profiles within the CC contain neurosecretory granules 160–350 nm in diameter which are indistinguishable from those found in type I neurosecretory cells of the pars intercerebralis and in the nervus corporis cardiaci I. The CC itself contains two cell types: intrinsic neurosecretory cells and glial cells. Intrinsic NSC cytoplasm contains Golgi bodies and electron dense neurosecretory granules 160–350 nm in diameter. Synaptoid configurations with 20–50 nm diameter electron lucent vesicles were observed within axon profiles of the CC. The structure of the CA is relatively uniform with one cell type predominating. Typical CA cells possess large nucleoli, active Golgi complexes, numerous mitochondria, and occassional microtubules. Groups of dark staining cells scattered throughout the CA of some animals were interpreted as evidence of cellular death.This work was done while JTB was supported by USPHS Training Grant HD-0266 from NICHDI wish to express my thanks to Dr. Richard A. Cloney for sharing his expertise in electron microscopy     

Identification of adenohypophysiotropic neurohormone producing neurosecretory cells in Rana temporaria

Summary By means of electron microscopy, in the median eminence of Rana temporaria, the terminal arborizations of axons of six different types of neurosecretory cells, located in the pars ventralis of the tuber cinereum, were identified. In addition, phenomena connected with the release of neurosecretory material from the axon terminals of these neurosecretory cells into the blood capillaries of the median eminence are described.Preliminary results suggested the existence, in the median eminence, of additional different neurosecretory axon types which could also belong to corresponding neurosecretory cell types probably located in the apical part of the pars ventralis of the tuber cinereum. Moreover, in the external region of the normal median eminence, separate monoaminergic nerve fibres were tentatively identified. Arguments are adduced which plead (1) against the assumption that the ependyma or the pituicytes of the median eminence could produce adenohypophysiotropic hormones; (2) against the inference that the ependymal cells of the median eminence might be involved in the transport of adenohypophysiotropic hormones from the cerebrospinal fluid into the blood capillaries of the median eminence.     

The hypothalamo-hypophysial system of the lamprey,Lampetra fluviatilis L.

The proximal neurosecretory contact region (PNCR) of the lamprey, a homologue of the median eminence of tetrapods, was studied by light, fluorescence and electron microscopy. Paraldehyde fuchsin-positive neurosecretory fibers are seen mainly in the central part of the rostral subdivision of the PNCR. The Falck-Hillarp technique reveals a weak, mainly diffuse yellow-green fluorescence in the PNCR. The ultrastructure of the tanycyte layer of the PNCR is very similar to that in the neurohypophysis of the same species, although the funnel-shaped protrusions of the third ventricle in the rostral part of the PNCR are more frequent than in the neurophypophysis. Peptidergic A1 and A2 neurosecretory fibers are characterized by neurosecretory granules of 120-200 nm and 100-150 nm in diameter, respectively. Monoaminergic B type fibers contain granules 80-100 nm in diameter. Neurosecretory terminals and the vascular endfeet of tanycytes make contact with the basement membrane of the avascular connective tissue layer separating the PNCR from the hypophysial pars distalis. It is suggested that both peptide and monoamine neurohormones diffuse through the thick connective tissue septa into the underlying blood vessels which supply the pars distalis and thus affect the function of its glandular cells.     

Fine structure of the median eminence and the pars nervosa of the bullfrog,Rana catesbeiana

Summary The hypothalamic neurosecretory system of the bullfrog, Rana catesbeiana, was studied with light- and electron microscopy. The median eminence is roughly divided into two portions. The upper portion mostly consists of ependymal cells, glial cells and preoptico-hypophysial nerve tract, whereas in the lower portion, neurosecretory axons, glial cells, processes of glial and ependymal cells, and fine blood vessels of the hypothalamic portal vein are located. A part of the neurosecretory axons of the preoptico-hypophysial tract proceeds to the lower portion of the median eminence. These axons are arranged perpendicularly to the capillaries of the hypothalamic portal vein. The glial cells are densely located in the area of the median eminence where neurosecretory material is abundant. The neurosecretory material in the neurosecretory cells, their axons, the median eminence and the pars nervosa of the bullfrog shows a positive reaction to PAS treatment.The neurohemal area of the median eminence is occupied by many neurosecretory and non-neurosecretory axons, containing neurosecretory granules and/or synaptic vesicles. The axonal portions with the synaptic vesicles which are considered to be the nerve endings abut on the capillaries of the portal system. The size of synaptic vesicles in the axon terminals containing few neurosecretory granules is larger than those in the endings with many neurosecretory granules. Infrequently glial and ependymal processes are interposed between the nerve endings and the capillary wall.In the hilar region of the infundibulum, synapses are frequently observed between the thin fibers with or without neurosecretory granules and dendrites of non-neurosecretory neurons. The probable functions of these synapses are briefly discussed on the basis of our findings. Both in the hilar region of the infundibulum and in the pars nervosa, electron-dense neurosecretory granules of two different sizes were observed. The median eminence contains only one type of granules.The fine structure of the pars nervosa shows similar structures to those of the median eminence. Both in the median eminence and the pars nervosa, the fenestrated endothelium of the capillaries was frequently observed. The thick perivascular connective tissue space containing fibroblasts and collagen fibrils was observed both in the median eminence and the pars nervosa. Vesicles in the cytoplasm of the endothelial cells which appear to take a part in the transendothelial transport were observed.This investigation was supported in part by United States Public Health Service Research Grant, No. A-3678, to Hideshi Kobayashi from the National Institute of Arthritis and Metabolic Diseases and partly by a grant for Fundamental Scientific Research from the Ministry of Education of Japan. The authors wish to express their thanks to Prof. K. Takewaki for his kind encouragement.     

Immunofluorescence of somatostatin-producing sites in the hypothalamus of the tadpole,Alytes obstetricans Laur.

Summary Three sites of somatostatin-synthesizing perikarya, or a related antigen, were determined by immunofluorescence in the hypothalamus of the tadpole, Alytes obstetricans (Amphibia, Anura). Two sites of neurosecretory perikarya were localized in the preoptic nuclei of the anterior hypothalamus; the axons extended either to the anterior diencephalon or to the median eminence and the pituitary. The third site was found in the posterior hypothalamus. These neurosecretory cells showed a strong immunofluorescent reaction; their axons all terminated at the level of the median eminence. Somatostatin cells were only found in intact or hypophysectomized tadpoles given somatotropin (STH). The strong reaction observed in hypophysectomized tadpoles was possibly due to the loss of the terminal portion of the neurosecretory pathway (median eminence and pituitary) by which the agent is transported to the site of discharge.     

Ultrastructural studies on the localization of neurohypophysial hormones and their carrier proteins.

Neurophysin, vasopressin and oxytocin were localized in different portions of the supraopticohypophysial tract (SHT) using the unlabeled antibody enzyme technique at the ultrastructural level. In vasopressin-positive supraoptic perikarya, vasopressin and neurophysin were present in all neurosecretory granules. Within the zona interna of the median eminence, vasopressin and neurophysin were present in two populations of axons, one with granules of 1300-1500 A and one with granules of 900-1300 A. Following exposure of thin sections of median eminence to antiserum to neurophysin, reaction products were present in granules and in the extragranular cytoplasm in the axons with larger granules; in all other cases reaction product was confined to the granules. Vasopressin-positive fibers were also presented in large numbers of the zona externa of the median eminence and many terminated on the pituitary primary portal plexus. A few oxytocin fibers were present on the portal capillaries in the infundibular stalk. In the posterior pituitary all axon profiles were neurophysin positive. Neurophysin was present as both a granular and cytoplasmic pool. Vasopressin-containing axons account for 90% of the neuronal elements in the posterior pituitary and oxytocin for the remaining 10%. Findings on the subcellular distribution of these peptides are related to current theories on transport and release of neurohormones.     

Ultrastructural changes in the median eminence of the rat following deafferentation of the basal hypothalamus

Summary This report concerns a light and electron microscopic investigation of the median eminence and dorsal infundibular stem of the rat following surgical isolation (deafferentation). Using a modification of the Halász technique, the basal hypothalamus, including the arcuate nucleus and median eminence were surgically isolated from surrounding structures. Special attention was directed to the contact (external) zone of the median eminence and rostral infundibulum where tuberohypophyseal axons as well as ependymal cell processes abut upon the abluminal basement membrane of the portal perivascular space. The results of this study to date suggest that 9, 20, and 40 days following surgical isolation, there is a distinct increase in the population of tuberohypophyseal dense core vesicles. It is suggested that deafferentation abolishes inhibitory and excitatory input that serves to modify the cellular dynamics of tuberohypophyseal neurosecretory elements. Comments are also made on the presence of cistern-like structures in the lateral median eminence; the presence of vesicle-like inclusions in terminal ependymal processes is discussed in relationship to the role that ependyma may play in linking the third ventricle with the adenohypophysis.This research was supported by USPHS Grants NB 08171 and AM 10002. The authors are indebted to the excellent technical assistance provided by G. Krobisch Dudley. Further, the authors wish to express their thanks to Dr. Adolph Weindl for his valuable advice and criticism, and to Matilde Holzwarth for her helpful assistance.     

Immunocytochemical study of the hypothalamic magnocellular neurosecretory nuclei of the snake Natrix maura and the turtle Mauremys caspica

Summary An immunocytochemical study of the magnocellular neurosecretory nuclei was performed in the snake Natrix maura and the turtle Mauremys caspica by use of antisera against: (1) a mixture of both bovine neurophysins, (2) bovine oxytocin-neurophysin, (3) arginine vasotocin, and (4) mesotocin. Arginine vasotocin- and mesotocin-immunoreactivities were localized in individual neurons of the supraoptic and paraventricular nuclei, with a distinct pattern of distribution in both species. The same cells appeared to be stained by the anti-oxytocin-neurophysin and anti-mesotocin sera. The supraoptic nucleus can be subdivided into rostral medial and caudal portions. In N. maura, but not in M. caspica, neurophysin-immunoreactive neurons were found in the retrochiasmatic nucleus. No immunoreactive elements were seen in the suprachiasmatic nucleus of both species after the use of any of the antisera. A dorsolateral aggregation of neurophysin-containing cells, localized over the lateral forebrain bundle, was present in both species. Magnocellular and parvocellular neurophysin-immunoreactive neurons were present in the paraventricular nucleus of both species. In the turtle, the paraventricular neurons were arranged into four distinct layers parallel to the ependyma; these neurons were bipolar with the major axis perpendicular to the ventricle, and many of them projected processes toward the cerebrospinal-fluid compartment. In N. maura a group of large neurons of the paraventricular nucleus was found in a very lateral position. The posterior lobe of the hypophysis and the external zone of the median eminence contained arginine vasotocin- and mesotocin-immunoreactive nerve fibers. The lamina terminalis of both species was supplied with a dense bundle of fibers containing immunoreactive neurophysin. Neurophysin-immunore-active fibers were also present in the septum, some telencephalic regions, including the cortex and the olfactory tubercule, in the paraventricular organ, and the periventricular and periaqueductal gray of the brainstem.This work was partially supported by a Grant S-85-39 from the Direccion de Investigaciones, Universidad Austral de Chile to E.M. Rodriguez     

Ultrastructural immunocytochemical localization of neurophysin and vasopressin in the median eminence and posterior pituitary of the guinea pig

Summary With the use of tissue prepared by freeze-substitution and the unlabelled antibody enzyme technique, neurophysin and vasopressin were localized at the ultrastructural level in the posterior pituitary and median eminence of the guinea pig. In the posterior pituitary neurophysin was found in the large neurosecretory granules (1300–1500 Å) of axons, Herring bodies, and nerve terminals. In some of these axons immunoreactive neurophysin was found outside of granules in the axoplasm. By light microscopy neurophysin was found in both the zona interna and zona externa of the median eminence; this was confirmed by electron microscopy. In the zona interna as in the posterior pituitary, neurophysin was localized both inside and outside the large neurosecretory granules. In the zona externa, immunoreactive deposit was primarily located in granules with a diameter of 900–1100 Å in nerve terminals abutting on the primary portal plexus. The distribution of vasopressin paralleled that of neurophysin except that the hormone was rarely extragranular. These results demonstrate for the first time that both neurophysin and vasopressin are present in granules of axons that are in contact with the hypophysial portal vasculature.The authors wish to thank Dr. Alan Robinson for the gifts of antiserum to bovine neurophysin I and for purified bovine neurophysin I; Dr. Ludwig Sternberger for the peroxidase-anti-peroxidase complex; and Dr. Robert Utiger for antiserum to lysine vasopressinSupported in part by U.S. Public Health Service grant RR-00167 to the Wisconsin Regional Primate Research Center from the National Institutes of Health. Primate Center publication No. 14-017.Recipient of NIH, NINDS Teacher-Investigator Award NS-1108.     

In vitro peptidergic neurons from the adult locust pars intercerebralis: Morphological and immunocytological studies

Primary cell cultures were prepared from a major neurosecretory center of the adult locust brain, the pars intercerebralis, in order to characterize neurosecretory cells growingin vitro. Individual pars intercerebralis could be removed free of surrounding tissue and dissociated by mechanical treatment. Mature neurosecretory neurons of different sizes regenerate new neurites during the initial three daysin vitro in serum-free medium. They show a tendency to sprout one primary neurite from which fine processes develop. By means of electron microscopy, we observed the integrity of the cellular organelles, indicating that cultured neurons are healthy, and we were able to distinguish three types of neurosecretory neurons on the basis of the ultrastructural aspects of the neurosecretory material. These three types have the same ultrastructural characteristics asin situ neuroparsin, ovary maturing parsin and locust insulin related peptide neurons. Immunogold labelling at the electron microscopic level, using the two available specific antibodies, anti-neuroparsin and anti-ovary maturing parsin, confirms the morphological characterization of neuroparsin and ovary maturing parsin cells. These results show for the first time that cultured locust neurosecretory neurons behave like thosein vivo, in terms of their ultrastructure and immunocytochemistry. Moreover, the presence of recently-formed neurosecretory material both in the Golgi zone of the perikaryon and in the neuronal processes indicates that cultured neurons have functional capacity since they are able to synthesizede novo and to transport the neurosecretory material along the neurite. Thus our well-characterized culture system provides a suitable invitro model to investigate the secretory mechanism of locust neurosecretory neurons.     

Effect of transection at different levels of hypothalamus on the hypothalamo-hypophysial system of the toad,Bufo bufo,with particular reference to the ultrastructure of the zona externa of the median eminence

Summary The ultrastructural changes taking place in the median eminence of Bufo bufo 3 hours to 4 months after transection of the brain at different levels, are described.5 types of neurons in the zona externa of the median eminence of normal toads are described. All types of neurons degenerate, and profound changes of the ultrastructure of the capillaries are observed after transection just behind, or immediately in front of the optic chiasma. A few neurons containing dense granules with a diameter of about 1,000–1,300 Å remain intact, however. The degeneration following denervation in front of the optic chiasma was considerably delayed compared to degeneration after denervation behind the optic chiasma.After transection more rostral to the optic chiasma, no significant degeneration of the median eminence was observed.The results are discussed with regard to degenerative dynamics and origin of the different nerve types. It is concluded, that all types of neurons terminating in the median eminence, originate at a level between the caudal and rostral parts of the preoptic nucleus, some fibres, however, containing dense, 1,000–1,300 Å granules, originate caudally to the optic chiasma, in the posterior hypothalamus.Part of this study was presented at the Vth International Symposium on Neurosecretion, Kiel, Germany, August 1969.     

The hypothalamo-hypophysial system of hypophysectomized rats

Summary The median eminence (ME) of hypophysectomized rats was studied by means of light and electron microscopy. Paraldehyde-fuchsin (PAF)-positive material is seen in the external zone (EZ) of the ME 2–5 days after the operation. Its amount gradually increases especially in the caudal part of the ME during the following few days. Some PAF-positive fibers make contact with the subependymally located blood capillaries. In the most caudal region of the recessus infundibuli they penetrate into the third ventricle. PAF-positive material decreases markedly from the ME of rats two months after hypophysectomy and exposure to a 1% salt load. Fibers of types A₁, A₂ and B containing granules of 120–220 nm, 100–150 nm and 80–100 nm in diameter, respectively, are seen in the EZ of the ME in hypophysectomized rats, although almost exclusively A₂- and B-type structures make contact with the primary portal capillaries in intact animals. All types of neurosecretory fibers establish contact with the subependymal nonfenestrated blood capillaries and penetrate the recessus infundibuli. Some neurosecretory terminals of different types make direct contact with the glandular cells of the pars tuberalis or are separated from them by a thin basal lamina. It is assumed that mainly neurosecretory fibers of types A₂ and B are permanently connected with the primary portal capillaries in the EZ of the ME in intact mammals, while the overwhelming majority of fibers of A₁-type shows ingrowth during the course of postoperative reparation. The possible physiological significance of the described changes is discussed.     

The development of the corticoliberin- and vasopressinergic elements of the rat hypothalamus during postnatal ontogeny

In 10--81-day and adult Wistar rats, neurosecretory cells were revealed which react with antisera to corticoliberin and vasopressin. Morphometric analysis of these cells in the supraoptic, paraventricular and anterior commissural nuclei shows that in the latter vasopressinergic cells develop somewhat later than in the supraoptic and paraventricular nuclei. Complete differentiation of neurosecretory cells in all the centres investigated is observed in 2-month animals. Studies were also made on the amount of corticoliberin- and vasopressinergic terminals in the external zone of the median eminence. Vasopressin-immunoreactive fibers are more numerous in young rats than in adult ones. Corticoliberin-positive neurosecretory fibers are more abundant in adult animals. Earlier development of vasopressinergic elements corresponds to a hypothesis of a more ancient origin of nonapeptidergic structures as compared to those producing liberins and statins.     

Immunocytochemical study of the GABAergic innervation of the mouse pituitary by use of antibodies against gamma-aminobutyric acid (GABA)

Summary The GABAergic innervation of the mouse pituitary, including the median eminence, was studied at light microscopic and ultrastructural levels by use of a pre-embedding immunocytochemical technique with antibodies directed against GABA. In the median eminence, a high density of GABA-immunoreactive fibers was found in the external layer where the GABAergic varicosities were frequently observed surrounding the blood vessels of the primary capillary plexus. In the internal and subependymal layers, only few fibers were immunoreactive. The intense labeling of the external layer was observed in the entire rostro-caudal extent of the median eminence. In the pituitary proper, a dense network of GABA-immunoreactive fibers was revealed throughout the neural and intermediate lobes, entering via the hypophyseal stalk. The anterior and tuberal lobes were devoid of any immunoreactivity. The GABA-immunoreactive terminals were characterized in the median eminence, and in the intermediate and posterior lobes at the electron-microscopic level. They contained small clear vesicles, occasionally associated with dense-core vesicles or neurosecretory granules. In the intermediate lobe they were seen to be in contact with the glandular cells. In the posterior lobe and in the median eminence, GABA-immunoreactive terminals were frequently located in the vicinity of blood vessels. These results further support the concept of a role of GABA in the regulation of hypophyseal functions, via the portal blood for the anterior lobe, directly on the cells in the intermediate lobe, and via axo-axonic mechanisms in the median eminence and posterior lobe.     

Localization of corticotropin-releasing hormone (CRF)-like immunoreactivity in the central nervous system of the elasmobranch fish,Scyliorhinus canicula

Summary The occurrence and localization of immunoreactive corticotropin-releasing factor (CRF) in the brain and pituitary of the elasmobranch fish Scyliorhinus canicula, were studied by means of specific radioimmunoassay and immunohistochemistry using the indirect immunofluorescence method. Brain and pituitary extracts showed a good cross-reactivity with the ovine CRF antiserum, but serial dilutions of tissue samples did not completely parallel the standard curve. Relatively high concentrations of CRF-like material were found within the pituitary, diencephalon, and telencephalon. CRF-like immunoreactive perikarya were observed in the preoptic nucleus and in the nucleus lateralis tuberis. Numerous immunoreactive cells appeared to be of the CSF-contacting type. CRF-like immunopositive fibers were seen to run through the hypothalamus within the ventro-medial floor of the infundibular region. A dense plexus of immunoreactive nerve endings terminated in the median eminence and the neurointermediate lobe of the pituitary. These results indicate that a neurosecretory system containing CRF-like immunoreactivity exists in the brain of elasmobranchs, a group of vertebrates which has diverged early from the evolutionary line leading to mammals. In addition, our data support the notion that a CRF-like molecule is involved in the regulation of corticotropic and melanotropic cell activity in this primitive species of fish.     

The distribution of monoamine oxidase and acetylcholinesterase in the hypothalamus and its relation to the hypothalamo-hypophysial neurosecretory system in the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary The distribution of monoamine-oxidase and acetylcholinesterase activities in the hypothalamus of the White-crowned Sparrow has been studied in relation to the hypothalamohypophysial neurosecretory system. The enzyme activities, as revealed by the methods employed, are unaffected during photoperiodically induced testicular growth. Monoamine oxidase has a distribution distinctly different from that of the aldehyde-fuchsin positive neurosecretory material in that there is high activity in the peripheral palisade layers of both the anterior and posterior divisions of the median eminence. Intimate contact is made between these areas with the primary vessels of the hypophysial portal system. A second concentration of activity lies in a layer between the ependymal cells and the neurosecretory material of the fiber tract. In general, monoamine oxidase appears to be associated with glial elements and non-neurosecretory axons. The pars nervosa has little or no monoamine-oxidase activity. The distribution of acetylcholinesterase activity in the anterior division of the median eminence is very similar to that of the aldehyde-fuchsin positive neurosecretory neurons; however, acetylcholinesterase also occurs in the posterior division without associated neurosecretory fibers. These distribution of enzyme activities are considered in relation to possible adrenergic and cholinergic mechanisms in the median eminence.Dedicated to Professor Berta Scharrer in honor of her 60th birthday.Supported by grant NB-01353 from the National Institutes of Health to Professor Farner. This investigation was conducted while Doctor Kobayashi was a National Science Foundation Senior Foreign Scientist at Washington State University. We are indebted to Doctor Christian Da Lage, Laboratoire de Histologie, Falculté de Médecine de Paris, for the preliminary development of some of the techniques used in these investigations.     

A double sequential immunofluorescence method demonstrating the co-localization of urotensins I and II in the caudal neurosecretory system of the teleost,Gillichthys mirabilis

Summary A double immunofluorescence method was devised to localize simultaneously urotensin-I (UI) and -II (UII) immunoreactivities in the caudal neurosecretory system of the goby, Gillichthys mirabilis. In a sequential fashion, sections of the posterior spinal cord and urophysis were treated with antiserum to corticotropin-releasing factor (CRF) that cross-reacts with UI, fluorescein-conjugated sheep anti-rabbit IgG, biotinylated anti-UII and rhodamine-conjugated avidin. UI and UII immunoreactivities appeared to coexist in some neurons and in most fibers and urophysial tissue; the remainder of the fibers and urophysis and the majority of neurons were immunoreactive for CRF/ UI only. No convincing evidence of immunoreactivity for UII only was found. A few nonreactive cells were seen, but these may not be neurosecretory neurons. The two immunoreactive cell types were not segregated topographically, and the intensity of perikaryal immunofluorescence for CRF/UI was variable. To explain these results a hypothesis that all caudal neurosecretory cells may synthesize both UI and UII and that immunoreactive differences may reflect different states of cellular activity, is suggested. This sequential double immunofluorescence method offers several advantages over other techniques and is especially useful for co-localization studies when primary antisera from different species are not available.     

Ultrastructure and hormonal content of the proximal stump of the transected hypothalamo-hypophysial tract of the frog (Rana pipiens)

Summary Several types of neurosecretory fibers were observed in the normal infundibulum of the frog. After transection of the median eminence, these neurosecretory fibers of the proximal stump reacted asynchronously, but followed approximately the same pattern: a passive accumulation of granules observed early after the transection was followed by an active axonal reaction with the appearance of numerous tubular formations which are thought to be related to the Golgi apparatus. They filled the axon almost completely, and then became dilated and filled with an electron dense material. Subsequently these dilatations pinched off and gave origin to new neurosecretory granules. These locally packed granules plus others which were probably formed in more proximal parts of the axon, and the perikaryon and then transported distally, accumulated in the proximal axonal stumps and started to fill the fibers retrogradely.There was a parallelism between the increase of tubular formations and neurosecretory granules larger then 1,500 Å in diameter, on one side, and the vasopressor activity of the proximal stump, on the other. The latter increased at an approximate rate of 1 mU/stump/day.The regeneration of the fibers of the hypothalamo-median eminence system is suggested by the presence in the proximal stump of fibers filled with granules smaller than 1,000 Å in diameter (normally seen in the median eminence) and the fact that 40% of the vasopressor activity of the extracts was not abolished by the thioglycollate treatment, which could be due to the presence of vasopressor amines other than adrenaline. The appearance towards the end of the observation period of a few nerve endings of several types contacting the perivascular basement membrane of vessels of the proximal stump would indicate that the neural lobe and median eminence functions were being reestablished, at least partially.This investigation was supported by grants 5RO1 NB 06641 NEUA and 5RO1 NB 07492 NEUA from the National Institute of Health and by the Space Sciences Research Center of the University of Missouri. The authors wish to thank Mrs. G. Clark, Mr. G. Ribas and Mr. R. Faup for their valuable technical help.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.     

Ultrastructure of the neurosecretory cells of the anterior commissural nucleus of the hypothalamus in rats

The ultrastructure of neurosecretory cells of the anterior commissural nucleus of rat hypothalamus is similar to that of the supraoptic nucleus and of the "magnocellular" part of the paraventricular nucleus. The only difference is a less expressed granular endoplasmatic reticulum and a smaller diameter of elementary neurosecretory granules (80-150 nm in diameter). Such elementary granules are characteristic of neurosecretory terminals located in the external zone of the median eminence. It is suggested that neurosecretory cells of the anterior commissural nucleus project to this neurohemal region.     

Ovipositor ultrastructure of the striped bitterling Acheilognathus yamatsutae (Teleostei: Acheilognathinae) during spawning season

The ovipositor of striped bitterling Acheilognathus yamatsutae was subjected to ultrastructure and histochemical analysis during spawning season using light and electron microscopy. Although the ovipositor of A. yamatsutae is a long cylindrical tube with smooth external surface, it was possible to confirm the presence of well-developed fingerprint structure using scanning electron microscopy. Internal aspect analysis of ovipositor revealed formation of 5–8 longitudinal folds. Cross section analysis revealed that the ovipositor is composed of an outer epithelial layer, a mid connective tissue layer, and an inner epithelial layer. The outer epithelial layer contains 7–9 cell layers composed mainly of epithelial and mucous cells. Result of AB–PAS (pH 2.5) and AF–AB reaction showed that mucous cells contained mainly acidic carboxylated mucosubstances. The connective tissue layer was loose and made mainly of collagen fibers and some muscle fibers, along with blood vessels and a small number of chromatophores. The inner epithelial layer, which is a single layer, is composed of columnar epithelia. Observation under transmission electron microscope enabled distinction of the outer epithelial layer into superficial, intermediate and basal layers. Although the types of cells in the superficial tissue layer were diverse, they all shared the development of glycocalyx covered microridges. The majority of epithelial cells in the intermediate layer were cuboidal shaped, while those in the basal layer were columnar. Two types (A and B) of secretory cells were observed in the outer epithelial layer. The connective tissue layer had two types of chromatophores including xantophore and melanophore, in addition to a well-developed nerve fiber bundles. Columnar epithelial cells, mitochondria-rich cells and rodlet cells were observed in the inner epithelial layer. Microvilli were well developed on the free surface of columnar epithelial cells.