The hypothalamo-hypophysial system of the frog Rana temporaria

Summary The median eminence (ME) of the adult frog, Rana temporaria, was studied by means of electron microscopy including quantitative electron-microscopic autoradiography. In frogs captured in May and June numerous peptidergic neurosecretory fibres extending via the internal zone to the pars nervosa display large swellings containing few granules, mitochondria, neurotubules and cisternae of the smooth endoplasmic reticulum. In addition, few secretory globules up to 1.5 m in diameter occur in these varicosities. In animals collected during the autumn period many of these neurosecretory swellings filled with neurosecretory granules and polymorphic inclusions resemble Herring bodies. Three types of granule-containing neurosecretory fibres were observed in the external zone (EZ) of the ME of adult R. temporaria. Peptidergic A₁- and A₂-type fibres are characterized by granules 150–220 nm and 100–160 nm in diameter, respectively. Monoaminergic fibres of type B with granules approximately 100 nm in diameter represent 50% of all neurosecretory elements in the EZ of the frog ME; 12% of the total number of granule-bearing axons in the EZ actively taking up radiolabelled 5-hydroxytryptophan are thought to be serotoninergic terminals. Neurosecretory terminals of all types and glial vascular endfeet establish direct contacts with the perivascular space of the primary portal capillaries. Some neurosecretory terminals are separated from the lumen of the third ventricle by a thin cytoplasmic lamella of tanycytes. The possible physiological significance of this structural pattern is discussed.     

The hypothalamo-hypophysial system in Acipenseridae

Summary The proximal neurosecretory contact region (PCR) of Acipenseridae, a homologue of the tetrapod median eminence, has been studied by light, fluorescence and electron microscopy. It occupies the rostral and chiefly the ventral surfaces of the hypothalamic tuber cinereum. PAF-positive fibres occur in the zone of the preoptico-hypophysial tract but their terminal enlargements are concentrated mainly in the external zone. They make contact with the primary portal capillaries situated in the pia mater. Monoaminergic fibres and terminals with an intense green fluorescence are localized in the same regions. The fibres of some bipolar monoaminergic neurons of the PCR make contact both with the third ventricle and the primary portal capillaries.Three types of granule-containing neurosecretory fibres and terminals have been recognized in the PCR. Fibres of types A₁ (d=120–300 nm) and A₂ (d=100–170 nm) are peptidergic PAF-positive, although some fibres, including some of type A₁; belong possibly to PAF-negative type. Monoaminergic type B fibres have granules 80–100 nm in diameter. Neurosecretory terminals and vascular endfeet of tanycytes make contact with the 70 nm thick outer basement membrane of the primary portal capillaries. Several laminae of thin horizontally oriented tanycyte processes form a boundary between the external zone and the preoptico-hypophysial tract. Few neuroglial cells with pale cytoplasm, numerous lysosomes and lipofuscin granules are seen in this region. It is hypothesized that, as in other vertebrates, both peptide hypophysiotropic neurohormones and monoamines are discharged from the PCR into the portal circulation and affect the activity of the glandular cells of the pars distalis.Dedicated to Prof. Dr. Drs. h.c. W. Bargmann on the occasion of his 70th birthday     

The hypothalamo-hypophysial system of the wild carp,Cyprinus carpio L.

Summary The posterior neurohypophysis (PNH)-pars intermedia complex of the wild and pond carp, Cyprinus carpio L., has been studied by light, fluorescence and electron microscopy. Gomori-positive neurosecretory fibres are abundant in the main trunk of the neurohypophysis as well as its roots penetrating the pars intermedia. Terminals of these fibres are in contact with capillaries of the general circulation and with glandular cells of the pars intermedia. Monoaminergic fibres with a weak green fluorescence, somewhat increasing after injection of nialamide into the pond carp, have largely the same distribution. Three types of neurosecretory fibres and their terminals have been recognized in the PNH-pars intermedia complex. Types-A₁ and -A₂ fibres, containing granules of 140–180 nm and 100–160 nm in diameter respectively, are peptidergic Gomori-positive. Type-A₂ fibres predominate in the PNH. The least frequent monoaminergic type-B fibres have granules of 60–100 nm in diameter. Numerous peptidergic and few monoaminergic neurosecretory terminals make contact with the capillaries located within the roots of the PNH as well as at the border between them and the pars intermedia. Both peptidergic and monoaminergic terminals make direct synaptoid contacts with the gland cells or end close to connective tissue septa, basal lamina or pituicytes. The PAS-positive gland cells and to a lesser degree the leadhaematoxylin-positive gland cells show these relationships with neurosecretory terminals. The question concerning the mode of interaction between peptidergic and monoaminergic structures in the dual control of the gland cells of the pars intermedia of teleosts is discussed.     

Immunohistochemical localization of urotensin I and other neuropeptides in the caudal neurosecretory system of three species of teleosts and two species of elasmobranchs

Summary In three species of teleosts — carp Cyprinus carpio; grass carp Ctenopharyngodon idella; and crucian carp Carassius auratus — the caudal neurosecretory system displays small, medium-sized and large neurons. Urotensin I (UI)-immunoreactive and UI-nonreactive neurons were found in all three groups; in general, the number of the latter neurons exceeded that of the former. Noteworthy are: (i) UI-immunoreactive fibers in the caudal spinal cord and (ii) dense accumulations of UI-immunoreactive product around the capillaries of the urophysis. In two species of elasmobranchs — cat shark Heterodontus japonicas and swell shark Cephaloscyllium umbratile — neurosecretory neurons decreased in size in rostro-caudal direction. Most of the neurosecretory perikarya, their axons and the corresponding neurohemal areas were UI-immunoreactive, but a small number of secretory neurons was devoid of immunoreaction. Oxytocin, arginine vasopressin, substance P, somatostatin, neurotensin, vasoactive intestinal polypeptide and gastrin-releasing peptide were not detected in the caudal neurosecretory system of the carp.     

Electron microscopic study of monoaminergic fibers in the posterior lobe of the rat hypophysis]

Monoaminergic fibers and their swellings containing dense core vesicles, 700-1000 A in diameter, were found by electron microscopic studies in the posterior pituitary of rat. Most of them are situated far from capillaries and are surrounded by neurosecretory fibers and pituicytes. There are usually no specialized structures at the sites of contact between them. Single monoaminergic fibers come in contact with the capillaries and even penetrate the pericapillary space. Large swelling of these fibers which sometimes occur contain different polymorphous inclusions, degenerating mitochondria and numerous small tubules along with the dense core vesicles.     

Electron microscopy of neurosecretory nerve fibres in the neural lobe of the embryonic mouse

Summary Nerve fibres of the neurosecretory hypothalamo-hypophyseal tract were studied in embryonic C3H mouse neural lobes; at least four glands at each gestational day 15–19 were examined.Single axons and small bundles of fibres are visible at gestational days 15 and 16. By day 17 large fibre bundles penetrate between glial cells. They increase in number during the next two days.Electron-lucent and electron-dense vesicles are seen in the fibres of the 15th and 16th gestational days. In the 17–19 day-old embryos development is characterized by a successive rise in the number of the two types of vesicles. The mean diameter of the electron-lucent vesicles is approximately unchanged in all the stages examined (50 nm). The electron-dense vesicles increase in size from approximately 80–90 nm at days 15–16 to 140 nm at the 19th gestational day.By day 19 contacts between neurosecretory fibre terminals and the outer basement membrane of internal and peripheral capillaries are occasionally observed. The possibly adrenergic nature of a few terminals contacting peripheral vascular structures in 17 and 18 day-old embryos is suggested.This investigation was supported by grant No. 2180-020 from the Swedish Natural Science Research Council. The skilful technical assistance of Mrs. Ulla Wennerberg is gratefully acknowledged.     

Terminal processes of serotonin neurons in the caudal spinal cord of the molly,Poecilia latipinna,project to the leptomeninges and urophysis

Summary The caudal neurosecretory complex of poeciliids has previously been shown to be innervated by extranuclear and intrinsic serotonergic projections. In the present study, immunohistochemical techniques were used to characterize fibers originating from serotonin neurons intrinsic to the caudal spinal cord. Bipolar and multipolar neurons were oriented ventromedially, and contained numerous large granular vesicles. Three types of serotonergic fibers were distinguished based on their distribution and morphology. Intrinsic Type-A fibers branched into varicose segments near the ventrolateral surface of the spinal cord and contacted the basal lamina beneath the leptomeninges. Type-B fibers coursed longitudinally to enter the urophysis, where they diverged and terminated around fenestrated capillaries. Labelled vesicles in Type-A and Type-B terminals were the same size as those in labelled cells and in unlabelled neurosecretory terminals in the urophysis. Type-C small varicose fibers branched within the neuropil of the caudal neurosecretory complex. Serotonin may be secreted into the submeningeal cerebrospinal fluid, the urophysis, and the caudal vein by Type-A and Type-B fibers, whereas, Type-C fibers may be processes of serotonergic interneurons in the neuroendocrine nucleus. The possibility that urotensins I and II or arginine vasotocin were colocalized in the processes of the intrinsic serotonin neurons was investigated immunohistochemically. The negative results of these experiments suggest that serotonin-containing neurons may represent a neurochemically distinct subpopulation in the caudal neurosecretory complex.     

The hypothalamo-hypophysial system in acipenseridae

Summary The neurohypophysis of sexually mature male and female Acipenser güldenstädti Brandt and Acipenser stellatus Pallas was studied light and electron microscopically. The recessus hypophysei lined with ependymal cells of two main types, narrow and wide, are in the center of the neurohypophysial roots. Processes from both cell types run radially to the basement membrane of the connective tissue layers abutting on the hypophysial intermediate lobe. Protrusions penetrating deep into the recessus hypophyseus are found in the apical parts of the wide cells. Pituicytes are rare in the neurohypophysis. The ultrastructure of both ependymal cell types and of the pituicytes is described. Nonmyelinated Gomori-positive (peptidergic) neurosecretory A₁ and A₂ type fibres and their terminals containing elementary neurosecretory granules (1400–1800 Å and 1000–1400 Å respectively) are the main structural elements of the neurohypophysis. Some dark and single myelinated neurosecretory fibres have been found. The adrenergic fibres (type B) were described earlier (Polenov et al., 1972a). The structural peculiarities of the neurohypophysis are discussed in functional and comparative-morphological terms.     

Localization of monoamines in the forebrain of two salmonid species,with special reference to the hypothalamo-hypophysial system

Summary In the salmon and trout aminergic cell bodies were found in the nucleus recessus lateraralis (NRL) and the nucleus recessus posterioris (NRP), both of which are situated near the third ventricle. Three cell types could be distinguished. Type 1 produces a green and type 2 a yellow fluorescence. The former type probably contains dopamine and the latter 5-hydroxytryptamine. Both types possess intraventricular protrusions in contact with the cerebrospinal fluid. The third cell type produces a less intense blue-green fluorescence; relatively few cells of this type have thick processes in contact with the ventricle. In addition, large fluorescent cells were found in the salmon, dorsal from the caudal part of the NRL. The various parts of the NRL and NRP are interconnected by thick bundles of nerve fibers; tracts leaving the nuclei could be traced for short distances only. The cells of the nucleus praeopticus (NPO), those of the medial part and to a much lesser extent also of the lateral part of the nucleus lateralis tuberis (NLT) have an aminergic innervation which probably originates from the NRL and/or NRP. All parts of the neurohypophysis contain many monoaminergic fibers, with aminergic material concentrated at the neuro-adenohypophysial interface. Fibers were not observed to penetrate the basal lamina. In the salmon and trout the fibers have a similar distribution, but differ in the intensity of fluorescence, being high in the salmon and low in the trout. Only in the trout have fluorescent cells been found in the adenohypophysis and very occasionally in the neurohypophysis. A number of these cells are basophilic and show a PAS-positive reaction.     

Afferent activity in thin myelinated and unmyelinated cutaneous nerve fibers during mechanical stimulation of skin receptors

Afferent activity in thin myelinated and unmyelinated cutaneous nerve fibers was analyzed by an impulse collision method and by methods improving the signal-to-noise ratio in the record of the antidromic action potential. The following groups were distinguished among the thin myelinated and unmyelinated nerve fibers on the basis of the results of investigation of conduction velocities, thresholds of electrical excitation, and response to mechanical stimulation: A ₁ (conduction velocity 30-14 m/sec) — a relatively larger number of these fibers conducts excitation in response to weak mechanical stimulation; A ₂ (14–4.0 m/sec) — the receptors of these fibers are more easily excited by a strong stimulus; a group of "mixed" fibers, containing myelinated and unmyelinated nerve fibers (4–2 m/sec), conducting excitation in response to both types of mechanical stimulation; C₁ (2.0–1.0 m/sec) — a fairly large number of these unmyelinated fibers conducts impulses in response to weak mechanical stimulation; C₂ (1.0–0.15 m/sec) the majority of fibers of this group is connected with receptors requiring strong mechanical stimulation for their excitation.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 67–75, January–February, 1976.     

Ultrastructural demonstration of neurohaemal contacts in the internal zone of the median eminence of the Mongolian gerbil (Meriones unguiculatus): correlation with synaptophysin immunohistochemistry

Summary Electron microscopy of the median eminence (ME) of the Mongolan gerbil (Meriones unguiculatus) revealed that, unlike most other mammalian species, abundant neurohaemal contacts were present not only in the external zone (EZ), but also in the internal zone (IZ) up to the subependymal layer. In the IZ, nerve terminals with dense core vesicles and/or small clear vesicles abutted on the outer basal lamina of the perivascular space of portal capillaries, alternating with tanycyte processes. In addition to these neurohaemal contacts, several layers of vesicle-filled varicosities surrounded the portal vasculature. An analysis of serial thin sections showed that the latter varicosities could also reach the perivascular basal lamina or contact it through small extensions in other planes of section. Apparently at least some of the nerve terminals making neurohaemal contacts were en passant in nature. A correlative investigation of synaptophysin (a major integral membrane protein of small synaptic vesicles) immunoreactivity at the light microscopical level demonstrated a conspicuously dense immunostaining around portal capillaries in both EZ and IZ of the proximal and distal ME (neural stalk). Since this perivascular accumulation of immunoreactivity coincides precisely with the ultrastructural accumulation of vesicle-filled axons which establish numerous neurohaemal contacts, it is concluded that this pattern of synaptophysin immunostaining indicates sites of neurohaemal contacts at the light microscopical level. During postnatal development, the perivascular concentration of synaptophysin immunoreactivity in the IZ appeared concomitantly with the early postnatal expansion of long portal capillary loops into the IZ. By direct electron-microscopical demonstration and indirect immunohistochemical evidence, the present study of the gerbil ME reveals that the whole extent of portal capillaries up to the subependymal layer constitutes an area for numerous neurohaemal contacts. Hence, the common view that neurohaemal contacts are restricted to the EZ of the mammalian ME is not generally valid.     

Electron transfer in deuterated reaction centers of Rhodobacter sphaeroides at 90 K according to femtosecond spectroscopy data

The primary act of charge separation was studied in P⁺B_A ^– and P⁺H_A ^– states (P, primary electron donor; B_A and H_A, primary and secondary electron acceptor) of native reaction centers (RCs) of Rhodobacter sphaeroides R-26 using femtosecond absorption spectroscopy at low (90 K) and room temperature. Coherent oscillations were studied in the kinetics of the stimulated emission band of P* (935 nm), of absorption band of B_A ^– (1020 nm) and of absorption band of H_A (760 nm). It was found that in native RCs kept in heavy water (D₂O) buffer the isotopic decreasing of basic oscillation frequency 32 cm ^–1 and its overtones takes place by the same factor 1.3 in the 935, 1020, and 760 nm bands in comparison with the samples in ordinary water H₂O. This suggests that the femtosecond oscillations in RC kinetics with 32 cm ^–1 frequency may be caused by rotation of hydrogen-containing groups, in particular the water molecule which may be placed between primary electron donor P_B and primary electron acceptor B_A. This rotation may appear also as high harmonics up to sixth in the stimulated emission of P*. The rotation of the water molecule may modulate electron transfer from P* to B_A. The results allow for tracing of the possible pathway of electron transfer from P* to B_A along a chain consisting of polar atoms according to the Brookhaven Protein Data Bank (1PRC): Mg(P_B)-N-C-N(His M200)-HOH-O = B_A. We assume that the role of 32-cm ^–1 modulation in electron transfer along this chain consists of a fixation of electron density at B_A ^– during a reversible electron transfer, when populations of P* and P⁺B_A ^– states are approximately equal.     

Formation of the external zone of the median eminence of rats in the perinatal period

The formation of interrelations of the axons of neurosecretory cells and of ependyme cells with the capillaries of primary portal plexus in rats from the 14th day of embryogenesis till the 9th day of postnatal life was studied using the light and electron microscope methods. During the whole period under study, the basal processes of the ependyme cells reach the primary portal plexus of the capillaries. The terminals of the basal processes are usually separated from the endothelium of the capillaries by two basal membranes and enclosed pericapillary space. After the birth, some basal process penetrate in the pericapillary space and terminate on the endothelium. The surface of contact of the ependyme cell processes with the external basal membrane increases with the age, this being accompanied by the increase of pinocytotic activity. The neurosecretory axons are found in the median eminence already on the 14th day of embryogenesis, but by the 20th day only they reach the external basal membrane and penetrate sometimes in the pericapillary space. After the birth, the number of axons reaching the external basal membrane and the surface of contact between them increase gradually with, apparently, a concomitant intensification of the transport of neurohormones in the portal circulatory system of the hypophysial-hypothalamic complex.     

The effect of ageing on the SIF-cells in the hypogastric (main pelvic) ganglion of the rat

Summary The effect of ageing on SIF-cells was studied by the formaldehyde-induced fluorescence (FIF) method and by electron microscopy (EM). Microspectrofluorimetry was used to record emission spectra in FIF preparations. In newborn and in young adult (8–12 weeks) rats a single type of SIF-cell emitting greenish-yellow FIF was found while in aged rats a second type of SIF-cell emitting yellowish-brown granular FIF was also present. The intensity of the yellowish-brown FIF was lower than that of the greenish-yellow FIF. Also a few bright cytoplasmic fluorescent areas were occasionally found in some SIF-cells. The distribution of the SIF-cells through the ganglion did not change remarkably with age.In EM after glutaraldehyde-fixation in newborn and in young adult rats two types of small granule-containing (SGC) cells were distinguished according to the size of the dense cored vesicles, 1) 50–150 nm and 2) 50–250 nm. In aged rats, a third type of SGC-cells containing 50×250 nm elongated dense core vesicles could also be distinguished. After KMnO₄-fixation in newborn and in young adult rats the classification was identical with glutaraldehyde-fixation. In aged rats three types of storage granules were found after KMnO₄, 1) 100–300 nm empty vesicles and 2) 100–300 nm vesicles with small dense core, 3) 100–500 nm irregular in shape and filled with electron opaque material with a more dense core.     

Influence of neurosecretion on the activity of median eminence and pars intermedia in hereditary nephrogenic diabetes insipidus mice with bilateral supraoptic lesions

Summary The extremely hypertrophied hypothalamo-hypophysial neurosecretory system of the hereditary nephrogenic diabetes insipidus (DI Os/+) mice, shows distinctly hypertrophied median eminence (ME) indicated by the hypertrophied ependymal cells, increased number of Herring bodies and a great number of neurosecretory fibers loaded with secretion converged towards blood capillaries and towards pars tuberalis. The other distinct feature of the DI Os/+ mice is the marked hypertrophy and hyperplasia of the pars intermedia (PI) infiltrated with many beaded neurosecretory fibers. The majority of the PI glandular cells are of the large light type rather than the small type, the latter being comparatively numerous in normal mice. Very often these large light glandular cells and the marginal cuboidal epithelial cells of the hypophysial cleft contain or are surrounded by AF⁺ granules and/or colloid.When the SON is destroyed bilaterally by means of electrolytic lesions, loss of NSM from the ME, infundibulum and the pars nervosa, is accompanied by the disappearance of AF⁺ granules in the PI, and the shrinkage of all the above mentioned parts. The changes also occur in the three glandular cell types. The large light glandular cells, decrease in number as well as in size, while the granularity of the dark cells increases. The marginal cuboidal cells of the hypophysial cleft and the large light glandular cells loose most of the AF⁺ material from the cells as well as from the surroundings. Wherever the AF⁺ material does not disappear in the PI, the PI cells remain much big, as in the controls. The colloidal secretion on the margin of the PI and from the cleft may be the secretion of PI glandular cells, as a result of the stimulation of the neurosecretory fibers in the PI of DI Os/+ mice. This colloid disappears when the neurosecretory fibers are destroyed from the PI as a result of lesioning. Therefore, it suggests that this secretory material may belong to SON, or possibly to some other secretory cells residing in the anterior hypothalamic region. Or more probable explanation could be that with the disappearance of supraoptic neurons and/or anterior hypothalamic neurons due to electryolytic lesions, the secretory activity of the PI cells and its AF⁺ material, might have been hampered due to lack of stimulation of these fibers in PI.Therefore, from the previous work and from the present one, it is suggested that the NSM may contain some substance which stimulates the glandular cells of the PI and this substance may be either vasopressin and/or a type of CRF. However, it is concluded that the activated neurosecretory system plays an important role in the hypertrophy of the ME and PI and certain changes in PI cell types. The impairment of catecholamine fibers and their lack of influence on synthesis and/or release in PI parenchyma cells is discussed.This study was supported by MRC of Canada Grant No. MA-3759. A preliminary report on a part of this work appeared (Naik, 1970b) in Proc. Can. Fed. Biol. 13, 147.     

Synganglial and neurosecretory morphology of the chicken mite Dermanyssus gallinae (DeGeer) (Mesostigmata: Dermanyssidae)

Histological techniques and paraldehyde-fuchsin (PAF) staining were used to study the synganglion and to locate neurosecretory regions and neurosecretion within the synganglion of the chicken mite, Dermanyssus gallinae. The synganglion, which is formed internally by neuropilar ganglia, gives rise to a single esophageal and paired cheliceral, palpal, pedal (I-IV), and opisthosomal nerves. The neuropilar ganglia are interconnected by commissures and connectives within the synganglion. Twelve PAF-positive neurosecretory regions are present in unfed protonymphs, unfed deutonymphs, virgin males and females, and mated males. There are 11 PAF-positive neurosecretory regions in larvae, 24–72 hours post-fed deutonymphs and mated females. Neurosecretory regions in these developmental stadia are described in relation to their positions adjacent to individual neuropilar ganglia.     

Ability of growth hormone fragments to compete with I-iodinated human growth hormone for specific binding to isolated adipocytes of hypophysectomized rats

Several noncovalent complexes of large fragments of human GH, which are less active than native human GH in stimulating glucose metabolism in adipose tissue of hypophysectomized rats, were tested for their ability to compete with ¹²⁵I-iodinated human GH for specific binding to isolated adipocytes of hypophysectomized rats. The complexes tested were A (residues 1–134 + residues 141–191; S-carbamidomethylated), B (residues 1–134 + residues 135–191; S-carbamidomethylated) and C (residues 1–134 + residues 135–191; S-carboxymethylated). When compared to native human GH, the complexes were less active in competing with ¹²⁵I-iodinated human GH for specific binding to adipocytes, and their order of potency in the binding assay (A > B > C) was similar to that of their respective activities in stimulating glucose metabolism in isolated adipose tissue of hypophysectomized rats.     

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     

The hypothalamo-hypophysial system in acipenseridae

Summary The percentage of peptidergic (A₁ and A₂) and adrenergic (B) neurosecretory terminals was studied in the neurohypophysis of sexually mature female sturgeons. Neurosecretory terminals of the A₂ type prevail in the neurohypophysis, whereas A₁ and B terminals are rare. The activity of these types of terminals was established (1) during upstream migration, (2) shortly after spawning, and (3) three to six weeks after spawning. Terminals of B type are the most active elements during all the periods studied. These elements become strongly activated in sturgeons during upstream migration, i.e., earlier than the peptidergic neurosecretory terminals. Peptidergic terminals, especially elements of type A₂, become synchronously and strongly activated in fish shortly after spawning. In the late postspawning period neurosecretory terminals of all three types become synchronously inactive, persisting in a quiescent state in comparison to the two previous periods. The appearance of neurosecretory material discharged into the intercellular clefts by exocytosis correlates on the whole with the activity level of the A₁ and A₂ terminals in each individual studied. A functional correlation exists between the activity of the peptidergic and adrenergic neurosecretory terminals in the neurohypophysis. The data obtained are discussed with reference to a concept regarding spawning in some fish species as a physiological stress (Polenov et al., 1976). A possible dual control (peptide and monoamine neurohormones) over the function of visceral organs and glandular cells of the intermediate lobe of the hypophysis is also suggested (Polenov, 1970, 1975, 1978; Polenov and Belenky, 1973).Dedicated to the memory of Professor Wolfgang Bargmann, a great scientist and a generous friend