Ultrastructural localization of thyrotropin (TSH)-like immunoreactivity in specific secretory cells of the hypophyseal pars tuberalis in the Djungarian hamster,Phodopus sungorus

Summary Specific secretory cells in the hypophyseal pars tuberalis of Djungarian hamsters maintained under different photoperiods were investigated immunocytochemically by means of the colloidal gold technique using antibodies against rat thyrotropin (TSH). Secretory cells of animals kept under long photoperiods (LD16:8) showed positive staining of secretory granules (diameters 90–130 nm), whereas other intracellular structures were free of immunoreactivity. In animals kept under short photoperiods (LD8:16) secretory cells displayed increased numbers of secretory granules, but these organelles were devoid of immunoreactivity. In contrast, immunoreactivity of thyrotropes in the pars distalis did not differ between the two groups of animals investigated. The present results confirm earlier light-microscopical studies that in the pars tuberalis specific secretory cells show TSH-like immunoreactivity; however, they differ in their reactivity pattern from classical thyrotropes in the pars distalis.     

Photoperiod-dependent changes in exocytotic activity in the hypophyseal pars tuberalis of the Djungarian hamster,Phodopus sungorus

The pars tuberalis of the hypophysis of the Djungarian hamster, Phodopus sungorus, was investigated with regard to secretory activity by applying the tannic acid-Ringer perfusion technique. Two groups were maintained under long photoperiods (16 h light: 8 h dark) or short photoperiods (8 h light: 16 h dark), respectively. Perfusion with tannic acid showed that specific pars tuberalis cells release some of their secretory granules as indicated by typical exocytotic figures. The percentage of cells displaying exocytotic activity was significantly higher in the pars tuberalis of hamsters kept under long photoperiods. The number of exocytotic figures per single cell was not increased. These results provide further evidence for a secretory activity of the pars tuberalis and support the hypothesis of its involvement as a mediator between photoperiodic stimuli and the endocrine system.     

Stereological analysis of daily variation in the ultrastructure of the pars intermedia of the pituitary gland of the Djungarian hamster (Phodopus sungorus)

Summary A Stereological analysis has been made of the daily changes occurring in the ultrastructure of the melanotrophs of the pars intermedia of the pituitary gland of the Djungarian or Siberian hamster, Phodopus sungorus, maintained in long day photoperiods. The rough endoplasmic reticulum, Golgi apparatus and lysosomes all declined in fractional volume throughout the photophase reaching minima at mid-scotophase and rising to reach their maxima at about the time of onset of the photophase. The mitochondria reached their peak fractional volume just before the cessation of the photophase but then also declined to a minimum at mid-scotophase. No significant changes were found to occur in the fractional volumes of the nucleus or the secretory granules. These morphological findings are compared with the changes in plasma and pituitary -melanocyte-stimulating hormone levels found in the rat.Supported in part by the Medical Research Council (Project Grant G978-398/C to BW)     

Fine structural studies of the islets of Langerhans in the Djungarian hamster (Phodopus sungorus)

Summary A study of the pancreatic islets of Langerhans in the Djungarian hamster (Phodopus sungorus) was initiated by the observation that 98 percent of the animals of a recently established colony showed ketoacidosis soon after birth, about ten percent of which later developed persistent hyperglycemia. The islets are made up of a centrally located mass of insulin-producing B-cells surrounded by a peripheral rim of A-and D-cells. Most islets are richly supplied by unmyelinated nerve fibers which terminate on all three cell types with cholinergic synaptic endings. Early changes in islet fine structure due to ketosis comprise degranulation of A-cells combined with signs of crinophagia of -granules. After the manifestation of hyperglycemia, degranulation of B-cells is followed by deposition of glycogen which in the late phase of the diabetic syndrome forms large masses obscuring the regular cellular organelles. In six-to nine-month hyperglycemic animals degenerative changes are also observed in D-cells in the form of autophagic vacuoles.Dedicated to Professor Dr. Helmut Ferner, Vienna on the occasion of his 65th birthday     

Distributional pattern of oxytocin- and vasopressin-immunoreactivity in the neurohypophysis of the Djungarian hamster (Phodopus sungorus)

Summary The topography of oxytocin (OT)- and vasopressin (VP)-containing axons of the hypothalamo-neurohypophyseal system was studied in the neurohypophysis of the Djungarian hamster (Phodopus sungorus) by means of immunohistochemistry. Compared with other mammalian species, the neurohypophysis of Phodopus shows some peculiarities. Accumulations of OT-immunoreactivity around the distal vessels of the primary portal plexus can be observed in the distal median eminence and neural stem. This staining pattern indicates that OT is secreted into portal blood. In the neural lobe, OT- and VP-immunopositive fibers terminate in different areas. The vast majority of the OT-containing axons is distributed in the dorsal part of the neural lobe. In contrast, VP-containing axons are mainly found in the centre of the neural lobe up to the pars intermedia.     

Glial cells positive for glial fibrillary acidic protein in the neurohypophysis of the Djungarian hamster (Phodopus sungorus)

Summary The presence and distribution of the glial fibrillary acidic protein (GFAP; an astrocytic marker protein associated with glial filaments) in the neurohypophysis of the Djungarian hamster (Phodopus sungorus) were investigated immunohistochemically. Our study revealed characteristic GFAP-staining patterns within the median eminence, infundibular stem and neural lobe. In the whole neurohypophysis, few glial cells showed immunoreactivity. In the neural lobe, immunopositive pituicytes appeared preferentially in the periphery. At the ultrastructural level, we found some pituicytes containing filaments, most notably in their processes. We thus demonstrated that, in contrast to the GFAP-immunoreactivity of cultured pituicytes, pituicytic GFAP-expression in vivo coincides with the presence of electron-microscopically detectable filaments.     

Ultrastructure of melatonin-responsive cells in the ovine pars tuberalis

Summary Functional receptors for melatonin have been localized and characterized on the pars tuberalis (PT) of a number of mammalian species, but the cell-type responsive to melatonin is unknown. The ultrastructure of the ovine pars tuberalis has been examined and these findings correlated with the functional response of the gland to melatonin. This study revealed that two secretory cell types predominate in the ovine PT, which differ in the abundance of dense-core granules. The most abundant of the cells are either agranular or very sparsely granulated and represent 90% of the total population, with the remaining 10% being composed of cells with abundant dense-core vesicles. Few follicular cells were observed. This ratio of secretory cell-types persisted in primary culture, with the two types non-separable by Percoll gradient centrifugation. Using forskolin, as a non-specific stimulant of adenylate cyclase, melatonin was shown to inhibit the formation of cyclic AMP by 80–90% in cells both before and after Percoll centrifugation. The results demonstrate that the agranular secretory cells of the ovine pars tuberalis are the melatonin responsive cell-type of this gland.     

The impact of dietary fats,photoperiod, temperature and season on morphological variables,torpor patterns,and brown adipose tissue fatty acid composition of hamsters,Phodopus sungorus

We investigated how dietary fats and oils of different fatty acid composition influence the seasonal change of body mass, fur colour, testes size and torpor in Djungarian hamsters, Phodopus sungorus, maintained from autumn to winter under different photoperiods and temperature regimes. Dietary fatty acids influenced the occurrence of spontaneous torpor (food and water ad libitum) in P. sungorus maintained at 18°C under natural and artificial short photoperiods. Torpor was most pronounced in individuals on a diet containing 10% safflower oil (rich in polyunsaturated fatty acids), intermediate in individuals on a diet containing 10% olive oil (rich in monounsaturated fatty acids) and least pronounced in individuals on a diet containing 10% coconut fat (rich in saturated fatty acids). Torpor in P. sungorus on chow containing no added fat or oil was intermediate between those on coconut fat and olive oil. Dietary fatty acids had little effect on torpor in animals maintained at 23°C. Body mass, fur colour and testes size were also little affected by dietary fatty acids. The fatty acid composition of brown fat from hamsters maintained at 18°C and under natural photoperiod strongly reflected that of the dietary fatty acids. Our study suggests that the seasonal change of body mass, fur colour and testes size are not significantly affected by dietary fatty acids. However, dietary fats influence the occurrence of torpor in individuals maintained at low temperatures and that have been photoperiodically primed for the display of torpor.Abbreviations BAT brown adipose tissue - bm body mass - FA fatty acid(s) - MR metabolic rate - MUFA monounsaturated fatty acid(s) - PUFA polyunsaturated fatty acid(s) - SFA saturated fatty acid(s) - T _a air temperature - T _b body temperature - T_s body surface temperature(s) - TNZ thermoneutral zone - UFA unsaturated fatty acid(s)     

Microfibrils are a major component of the mesangial matrix in the glomerulus of the rat kidney

Summary Certain secretory cells in the hypophysial pars tuberalis of the Djungarian hamster display marked circannual structural alterations. The present investigation deals with the immunohistochemical properties of this cell group. A distinct TSH-like immunoreactivity was found in secretory cells of this type in the pars tuberalis of animals exposed to long photoperiods, whereas under short photoperiods the TSH-like immunoreactivity was nearly absent. In the pars distalis, the number and distribution of TSH-positive cells did not differ significantly between animals maintained under long and under short photoperiods. LH-and FSH-positive cells could not be detected in the pars tuberalis, but they are clearly present in the pars distalis of both groups of hamsters. Our immunocytochemical results suggest that photoperiodic stimuli influence the secretory activity of TSH-like immunoreactive cells in the pars tuberalis. A connection with the neuroendrocrine-thyroid axis is discussed.The study was supported by the Deutsche Forschungsgemeinschaft (Wi 558/3-1, Pe 134/2-4)     

Maximum energy assimilation rates in the Djungarian hamster (Phodopus sungorus)

Summary Physiological limits to energy budgets were estimated in Djungarian hamsters (Phodopus sungorus) using food balance and respirometric methods. The summer acclimatized, reproductively inactive hamsters could balance their energy budget at-2° C, assimilating 91.1 kJ·animal^-1· day^-1 after gradual cold acclimation, whereas non-acclimated hamsters showed negative energy balance assimilating only 54.4 kJ·animal^-1·day^-1. At the same ambient temperature, multiparous females (although neither pregnant nor lactating at the time) maintained positive energy balance assimilating 81.6 kJ·animal^-1·day^-1. Hamsters are capable of rapid adjustments of their maximum assimilation rates to meet their current energy demands, but only up to the value of about 3.5xBMR. It is concluded, that the actual energy budgets of small mammals keep, all the time, fairly near the upper physiological limit, with body reserves ready to buffer short-term oscillations.     

Modulation of leptin sensitivity by short photoperiod acclimation in the Djungarian hamster, Phodopus sungorus

During seasonal acclimation, Djungarian hamsters spontaneously exhibit a reduction in food intake, body mass and body fat stores, which is externally cued by shortening of day length in autumn and controlled by a sliding set-point. We investigated the function of the leptin adipostatic feedback system in the photoperiodic control of seasonal acclimation. In response to mouse recombinant leptin injections for 10 days, long day photoperiod (LD) and short day photoperiod (SD)-acclimated hamsters decreased food intake and body mass. The reduction of body mass was due to the depletion of body fat, as revealed by carcass composition analysis. In SD hamsters, leptin caused a larger reduction of body fat mass than observed under LD conditions, whereas the anorectic effect was similar in both photoperiods. The serum leptin concentration was 9.3 ± 1.2 ng/ml in LD-acclimated hamsters and decreased significantly to 4.2 ± 0.8 ng/ml and 2.1 ± 0.6 ng/ml in hamsters exposed to SD for 66 days and 116 days, respectively (P < 0.001). A strong positive correlation between total body fat mass and serum leptin concentration was found (r _S=0.935, P < 0.0001, n=70). Despite the anorectic action of exogenous leptin, higher endogenous leptin levels in LD hamsters were paralleled by higher food intake in LD hamsters as compared to SD hamsters. This paradoxical finding further supports the increased leptin sensitivity in SD hamsters as judged from leptin treatment experiments. We tested the functional significance of leptin for the controlled down-regulation of food intake and body mass induced by short photoperiod. Food restriction for 10 days during the transition phase decreased body mass below the desired sliding set-point, which was recovered in control hamsters following ad libitum refeeding. Treatment with mouse recombinant leptin during ad libitum refeeding inhibited the recovery of body mass and blunted the increase of food intake observed in controls, indicating that the sliding set-point utilizes leptin as a signal for the adjustment of the appropriate body mass level. Accepted: 15 October 1999     

Seasonal changes of the ultrastructure of the pars tuberalis of the hypophysis of Rana temporaria

Summary In the pars tuberalis of the hypophysis of Rana temporaria, which shows the ultrastructural characteristics of a polypeptide hormone secreting endocrine gland, seasonal changes of the ultrastructure are described. In accordance with the literature, these seasonal changes of ultrastructure are interpreted as the morphological expression of seasonal changes of endocrine activity of the pars tuberalis.     

Cellular composition of the human pituitary pars tuberalis as revealed by immunocytochemistry

Summary An attempt was made to determine if any of the specialized secretory cell types common to the pars distalis also occur in the pars tuberalis of the human hypophysis. Available for study were 18 specimens of the inferior pars tuberalis, which partially surrounds the infundibular stem, and 3 specimens of the superior pars tuberalis that is attached to the median eminence. Antisera to human somatotropin, mammotropin, chorionic gonadotropin, follicle-stimulating hormone, FSH , luteinizing hormone, LH , thyrotropin, TSH , as well as to ^1–24-corticotropin, porcine ^17–39-corticotropin, and ovine LH were used with the Sternberger peroxidase-antiperoxidase immunocytochemical procedure to identify the probable cells of origin for these hormones.The evidence indicated that gonadotropic cells constitute the major portion of the parenchymal cell population in the pars tuberalis. They occurred throughout all of the pars tuberalis and were usually arranged in clusters. Somatotropic, mammotropic, corticotropic, and thyrotropic cells were rare and not found in all specimens. When present, they often formed a common group suggesting that their occurrence in the pars tuberalis resulted from displacement of primordial tissue of the pars distalis during embryogenesis.Supported in part by research grants HD-03159 and HD-08333 from the National Institute for Child Health and Human DevelopmentWe thank Dr. L.A. Sternberger for providing the PAP complex and others for antisera (Table 2) and hormones (Footnote 2) as listed     

Annual cycle of activity in the nucleus tuberis hypothalami and the pars tuberalis of the hypophysis in the frog Rana esculenta

Abstract

A very distinct annual cycle of activity, as judged from nuclear volume changes, has been found in glandular cells of the pars tuberalis of the hypophysis and neurons in the nucleus tuberis hypothalami of adult green frogs (Rana esculenta). The changes are very similar at both sites, a single maximum in April and a single minimum in September being observed. Ependymal tanycy tes of the region which was investigated showed only very moderate activity changes. No sex differences were found with regard to the character of the cycle and the amplitude of changes. Only quantitative differences in absolute nuclear volume were found between the two sexes.     

Nucleolus-like bodies in the pineal gland of the Djungarian hamster (Phodopus sungorus)

Summary Light- and electron-microscopic observations on the pineal gland of Phodopus sungorus revealed intracytoplasmic inclusions resembling nucleolus-like bodies similar to those found in other regions of the central nervous system. Bernhard's EDTA method was used to confirm that these inclusions were nucleolus-like bodies. These structures were rarely found in pinealocytes of sexually active longday animals, whereas large numbers of them were observed in pinealocytes of sexually quiescent short-day animals. Nucleolus-like bodies may therefore be involved in pineal secretion.     

Cold prevents the light induced inactivation of pineal N-acetyltransferase in the Djungarian hamster,Phodopus sungorus

Summary In the Djungarian hamster seasonal acclimatization is primarily controlled by photoperiod, but exposure to low ambient temperature amplifies the intensity and duration of short day-induced winter adaptations. The aim of this study was to test, whether the pineal gland is involved in integrating both environmental cues. Exposure of hamsters to cold (0 °C) reduces the sensitivity of the pineal gland to light at night and prevents inactivation of N-acetyltransferase (NAT). The parallel time course of NAT activity and plasma norepinephrine content suggests that circulating catecholamines may stimulate melatonin synthesis under cold load.Abbreviations NAT N-acetyltransferase - NE norepinephrine - T _a ambient temperature     

Effects of pimozide on the ultrastructure of the pars intermedia in the rat

Summary The effects of pimozide, a dopamine receptor-blocking agent, were studied in the pars intermedia of the rat. The animals received 100 g/100 g pimozide daily for 2, 5, 10, 15, and 20 days. Pimozide induces ultrastructural changes after 5 days of treatment. About 50% of the MSH-cells display characteristics of stimulation. Their cytoplasm is partially or totally depleted of secretory granules. The rough endoplasmic reticulum displays a network of interconnecting cisternae and ribbon-like structures. The well-developed Golgi complexes exhibit numerous dilatations of their cisternae, which contain electron-dense material. The nerve endings are not altered. Twenty days after treatment, the above-described changes have not decreased in magnitude. The present findings suggest that pimozide stimulates the mechanism of synthesis and release in some MSH-cells, most probably the elements underlying an inhibitory dopaminergic control.Supported by CONICET and CIUNC of ArgentinaMember of the Research Career of CONICET, ArgentinaFellow of CONICET, Argentina     

Photoperiodic influence on the innervation of the ductus epididymidis and ductus deferens of the Djungarian hamster,Phodopus sungorus: electron-microscopic and biochemical results

Summary The influence of long (light: dark 168) and short (light:dark 816) photoperiods on the autonomic innervation of the ductus epididymidis and the ductus deferens of Phodopus sungorus was studied using electron microscopy with morphometric analyses, and biochemical methods. At short photoperiods, only the large smooth muscle cells in the ductus deferens became atrophic, the number of mainly adrenergic varicosities in the smooth muscle layer decreased, and the mean distance between varicosity and smooth muscle cells increased. The content of noradrenaline was determined by high-performance liquid chromatography with electrochemical detection. For the ductus deferens, the noradrenaline content was reduced at LD 816 to less than 10% of the initial value. Short photoperiods are proposed to influence only the adrenergic innervation of the large smooth muscle cells of the ductus deferens. These cells are believed to exert a trophic influence on their nerves.     

Effects of pimozide on the ultrastructure of the pars distalis in the rat

Summary The effects of pimozide, a dopamine receptor-blocking agent, were studied in the pars distalis of the rat. The animals received 100g/100 g pimozide daily for 5, 10, 15, and 20 days. Pimozide induces striking ultrastructural changes after 5 days of treatment. The number of luteotroph (LTH) cells is significantly increased; they display characteristics of stimulation. The extrusion of granules into the intercellular space via exocytosis is frequently observed. The intercellular spaces are highly dilated, forming a lacunar system filled with an amorphous material, erythrocytes and involuted LTH cells. Transitional stages in the process of involution are observed in LTH cells. Luteotroph cells also form a syncytium. Twenty days after treatment the abovedescribed changes decrease in magnitude. The present findings suggest that pimozide stimulates the mechanism of synthesis and release in the luteotroph cells, an effect that is less evident with longer treatment.Supported by CONICET and CIUNC of ArgentinaMember of the Research Career of CONICET, ArgentinaFellow of CONICET, Argentina     

The structure and vascularization of the pars tuberalis of the hypophysis of Rana temporaria

Summary The pars tuberalis of the hypophysis of Rana temporaria presents the general structural and the cytological characteristics of an endocrine gland. It is composed of elongated cells with long, branching processes ending on the external basement membrane of the pericapillary space. The pars tuberalis cells produce secretory granules which are accumulated in the pericapillary endings of the processes.Corresponding to its separate localization, the pars tuberalis of Rana temporaria has a separate vascularization of which the efferent capillaries anastomose with the capillary plexus of the median eminence. The general direction of the blood flow of the pars tuberalis is towards the capillaries of the median eminence. Also, the secretory products of the pars tuberalis pass into the blood stream of the hypophysial portal system.Several characteristics of the pars tuberalis show that its function must be different from that of the pars distalis of the hypophysis. Moreover, in contrast with the pars distalis, the activity of the pars tuberalis is not regulated by neurohumoral factors.The results show that a role of the pars tuberalis in the regulation of the activity of the pars distalis of the hypophysis is not excluded.