bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear and Cytoplasmic Triiodothyronine‐Binding Sites in Primary Sensory Neurons and Schwann Cells: Radioautographic Study During Development
Authors: Walter I. Barakat , Droz B.
Published: September 2006

The effects of the thyroid hormones on target cells are mediated through nuclear T3 receptors. In the peripheral nervous system, nuclear T3 receptors were previously detected with the monoclonal antibody 283 rnAb in all the primary sensory neurons throughout neuronal life and in peripheral glia at the perinatal period only (Eur. J. Neurosci. 5, 379, 7993). To determine whether these nuclear T3 receptors correspond to functional ones able to bind T3, cryostat sections and in vitro cell cultures of dorsal root ganglion (DRG) or sciatic nerve were incubated with 0.1 nM [1251]‐labeled T3, either alone to visualize the total T3‐binding sites or added with a lo3 fold excess of unlabeled T3 to estimate the part due to the non‐specific T3‐binding. After glutaraldehyde fixation, radioautography showed that the specific T3‐binding sites were largely prevalent. The T3‐binding capacity of peripheral glia in DRG and sciatic nerve was restricted to the perinatal period in vivo and to Schwann cells cultured in vitro. In all the primary sensory neurons, specific T3‐binding sites were disclosed in foetal as well as adult rats. The detection of the T3‐binding sites in the nucleus indicated that the nuclear T3 receptors are functional. Moreover the concomitant presence of both T3‐binding sites and T3 receptors CI isoforms in the perikaryon of DRG neurons infers that: 1) [1251]‐labeied T3 can be retained on the T3‐binding ‘E’ domain of nascent CI, isoform molecules newly‐synthesized on the perikaryal ribosomes; 2) the CI isoforms translocated to the nucleus are modified by posttranslational changes and finally recognized by 2B3 rnAb as nuclear T3 receptor. In conclusion, the radioautographic visualization of the T3‐binding sites in peripheral neurons and glia confirms that the nuclear T3 receptors are functional and contributes to clarify t h e discordant intracellular localization provided by the immunocytochemical detection of nuclear T3 receptors and T3 receptor CI isoforms.
Androgen and Estrogen Effects on Vasopressin Messenger RNA Expression in the Medial Amygdaloid Nucleus in Male and Female Rats
Authors: Wang Zuoxin , De Vries Geert J.
Published: September 2006

Vasopressin messenger RNA (AVP mRNA) expression in the medial amygdala and bed nucleus of the stria terminalis (BST) is almost completely dependent on gonadal steroids. In the BST, the effects of gonadal steroids on AVP mRNA expression are sexually dimorphic. Males have more cells that express AVP mRNA and more AVP mRNA per cell than females. Here we test whether this is also true for the MA.

In gonadectomized rats that were treated with testosterone, males had more cells that were labeled for AVP mRNA than females. However, the labeling per cell did not differ between males and females. To assess contribution of testosterone metabolites to these differences, male and female rats were gonadectomized and implanted with empty tubing, or tubing filled with dihydrotestosterone (DHT), estradiol (E), or E plus DHT (E + DHT). The pattern of steroid effects on AVP mRNA expression in the MA was similar in both sexes. Hardly any labeled cells were found in rats with empty implants or rats treated with DHT. Significantly more labeled cells were found in rats treated with E, and even more cells in rats treated with E + DHT. The number of AVP mRNA‐labeled cells was higher in males than in females for E as well as E + DHT treatment, but the labeling per cell did not differ between sexes. These data suggest that the number of MA cells that can express AVP mRNA is higher in males than in females, but the estrogen and androgen responsiveness of individual AVP mRNA‐expressing cells in the MA does not differ between sexes.
Withdrawal of Somatostatin Augments L‐type Ca2+ Current in Primary Cultured Rat Somatotrophs
Authors: Kato Masakatsu
Published: September 2006

It is known that withdrawal of somatostatin (SRIF) augments the growth hormone (GH) releasing hormone (GRF)‐induced GH secretion. To investigate the mechanism of this augmentation in GH secretion, effects of GRF and SRIF on L‐type Ca2+ current (Ba2+ was used as a charge carrier) of primary cultured rat somatotroph were studied by perforated patch clamp technique. The reason is that GRF‐induced GH secretion is thought to be causally related to the influx of Ca2+ through L‐type Ca2+ channels. 10 mM GRF augmented maximum amplitude of L‐type Ba2+ current by 12.2% (n = 12). Subsequent application of SRIF slightly suppressed the currents but the suppression never exceeded the control level of the current. Removal of SRIF, however, promptly augmented the L‐type Ba2+ current by 26.8%. Such off‐response of SRIF was not observed in cells treated overnight with 100 ng/ml pertussis toxin. Further, specific inhibitor of protein kinase A, H‐89 at 1 μM reversibly suppressed the augmentation of L‐type Ba2+ current to control level. At 10 μM, H‐89 suppressed L‐type Ba2+ current by more than 40% from control level.

These results suggest that (1) L‐type Ca2+ channel of somatotroph is probably phosphorylated in a basal condition and may be slightly modulated by GRF through increased level of CAMP; (2) SRIF only slightly suppress the channel activity; (3) Withdrawal of SRIF facilitates the activity of L‐type Ca2+ channel via PTX‐sensitive G‐protein, although the precise mechanism of this facilitation is unknown. The augmentation by SRIF‐pretreatment of GRF‐induced GH secretion may be at least partly due to the facilitation of the activity of L‐type Ca2+ channel.
The Photoperiodic Response in Syrian Hamster Depends upon a Melatonin‐Driven Circadian Rhythm of Sensitivity to Melatonin
Authors: Pitrosky B. , Kirsch R. , Vivien‐Roels B. , Georg‐Bentz I. , Canguilhem B. , Pevet P.
Published: September 2006

The pineal gland, via the daily pattern of melatonin (MEL) secretion, is directly involved in the conduction of photoperiodic information. The duration of MEL secretion is proportional to the duration of the dark period and, whatever the photoperiod is, MEL synthesis occurs 3 or 4 h after the dark onset in Syrian hamsters. In order to determine the relative importance of the duration or the coincidence hypothesis, a daily infusion protocol was used in sexually active pinealectomized hamsters. Long duration of MEL infusion (10 h) completely inhibit testes whereas short duration infusion (5 h) had no effect. When the animals were infused twice within 2 h 30 min separated by 3 h, they presented a complete gonadal atrophy, similar to the one observed with the 10 h infusion. Measurement of plasma MEL during the infusion and seperation periods revealed that MEL reached physiological nighttime values during the infusion period and fell to daytime values 1 h after the end of an infusion period. Thus, the results could not be due to a time additive action of the two MEL pulses. An intermediate response was observed when the 2 signals were applied across the light/dark transition. Gonadal regression did not occur when the 2 periods of infusion were separated by 5 h 30 min. The efficiency of this type of infusion was not dependent on the ambiant photoperiod since similar results were obtained in long and short photoperiods. The infusion was also as effective during the day as well as during the night. These results suggest that there is a rhythm of sensitivity to MEL, based on the coincidence hypotheses, that are important for transmission of photoperiodic information. This rhythm of sensitivity to MEL seems to be entrained by MEL itself, since the efficiency of the two pulses of MEL is not dependent of time of application and/or of photoperiod.
Localization of mRNA Coding for the Three Subtypes of Atrial Natriuretic Factor (ANF) Receptors in Rat Anterior Pituitary Gland Cells
Authors: Grandclément Béatrice , Brisson Christine , Bayard Francis , Tremblay Johanne , Gossard Francis , Morel Gerard
Published: September 2006

Atrial Natriuretic Factor (ANF) action is mediated by highly selective and specific receptors. Three subtypes have been characterized and cloned: ANF receptor‐A, ‐B and ‐C. These subtypes are all expressed in the anterior pituitary of the rat. In the present study, the mRNA for each subtype was detected by in situ hybridization. The amounts of ANFR‐A and ‐B mRNA were found to be similar, and to be twice that of ANFR‐C mRNA. At the ultrastructural level, the three types of ANFR mRNA were expressed in three anterior pituitary cell types, namely lactotrophs, corticotrophs, and gonadotrophs, identified by their hormonal content. No signal was revealed in somatotrophs or thyrotrophs. The different forms of mRNA were similar in terms of subcellular localization: in the cytoplasmic matrix and the nuclear euchromatin.

These data indicate that the anterior pituitary is an important target tissue for ANF action.
Dexamethasone Regulates the Expression of Neuronal Properties of a Rat Insulinoma Cell Line
Authors: Atouf Fouad , Tazi Abdelali , Polak Michel , Czemichow Paul , Scharfmann Raphael
Published: September 2006

Insulin producing cells of the pancreas (beta cells) and neuronal cells share a large number of similarities. For example, different molecules, thought to be specific of neuronal cells, are expressed by beta cells. The factors regulating the expression of these molecules in beta cells are poorly understood. In the present work, we have studied the effect of dexamethasone, a synthetic glucocorticoid, on the expression of three different neuronal traits expressed by INS‐1 cells, a highly differentiated beta cell line. We demonstrate that dexamethasone treatment decreases the steady state levels of mRNAs coding for both the low‐and the high‐affinity NGF receptors and of mRNA coding for NF‐H, an intermediate neurofilament specific of neurons. This effect was time‐dependent, the decrease being detectable after 4–8 h treatment. The decrease in NGF receptors mRNAs steady state levels was paralleled by a decrease in the number of NGF binding sites as demonstrated after Scatchard analysis. We further focused on the mechanisms by which dexamethasone affects the expression of the low affinity NGF receptor. The effect is countered by the glucocorticoid antagonist RU486, indicating that it is mediated by the glucocorticoid receptor. Finally, the decrease in the low‐affinity nerve growth factor receptor mRNA steady state level after dexamethasone treatment is not due to mRNA destabilization but can be rather explained through a change in gene transcription.
Effects of Growth Hormone‐Releasing Peptide‐2 (GHRP‐2) on Membrane Ca2+ Permeability in Cultured Ovine Somatotrophs
Authors: Chen Chen , Clarke Iain J.
Published: September 2006

The newly synthesized GH‐releasing peptide, GHRP‐2 (D‐Ala‐D‐βNal‐Ala‐Trp‐D‐Phe‐Lys‐NH2), was studied in somatotroph‐enriched populations of ovine pituitary cells in primary culture. Nystatin‐perforated whole‐cell recordings were made on identified somatotrophs after 4–14 days of culture. Using a standard bath solution (containing Na+, Ca2+) and an electrode solution containing K+ in current‐clamp recordings, GHRP‐2 (10 nM) depolarized the membrane potential of the cells triggering a burst of action potentials. Voltage‐clamp recordings indicated that GHRP‐2 produced a slowly inactivated inward current with a slight reduction in outward current. The inward current was blocked by the Ca2+ channel blocker, Co2+ (0.5 mM). Ca2+ currents were then isolated using tetraethylammonium bath solution and an electrode solution containing Cs+. Ovine somatotrophs possess transient (T type) and long lasting (L type) Ca2+ currents. The L type current was abolished by addition of nifedipine (3 μM) to the bath solution and T type current was isolated on this basis. Current‐voltage relationships indicated an increase in both T and L type Ca2+ currents in response to GHRP‐2. The voltage‐dependent inactivation curve for T type Ca2+ current was shifted towards a less negative level by the peptide. Intracellular free Ca2+ concentration ([Ca2+]i) in somatotroph‐enriched populations was specifically increased by GHRP‐2 but this effect was totally abolished by blockade of membrane Ca2+ channels. These data show that GHRP‐2 causes an influx of Ca2+ leading to an increase in [Ca2+]i in ovine somatotrophs. The Ca2+ currents were both L type and T type with a shift in the inactivation curve of the latter by the releasing peptide.
Effect of Sustained Physiological Hyperinsulinaemia on Hypothalamic Neuropeptide Y and NPY mRNA Levels in the Rat
Authors: Cusin Isabelle , Dryden Simon , Wang Qiong , Rohner‐Jeanrenaud Francoise , Jeanrenaud Bernard , Williams Gareth
Published: September 2006

Neuropeptide Y (NPY) synthesized in the arcuato‐paraventricular projection in the rat hypothalamus is thought to play an important role in controlling energy homeostasis. The factors that regulate hypothalamic NPY are not known but, amongst others, insulin has been postulated as an inhibitory modulatory agent. To test this hypothesis, normal male rats were given either insulin (2 units/day) or saline via subcutaneous osmotic minipumps for 3 days. Euglycaemia was maintained by a concomitant glucose infusion in insulin‐infused rats which had peripheral insulin levels 5–8 times higher than saline‐infused controls. Hyperinsulinaernic rats ate 42% less than controls, but their total energy intake (food intake plus glucose infusion) was higher than that of controls, and they gained more weight than controls during the experimental period. Hyperinsulinaemia had no significant effect on hypothalamic NPY mRNA or NPY levels in the arcuate nucleus. NPY concentrations in the paraventricular nucleus were, however, significantly increased by 73% in hyperinsulinaemic rats, but were closely similar to controls in all other areas. Insulin may act as a satiety factor in that hyperinsulinaemic rats ate less, but the fact that these animals had increased total energy intake and gained excessive weight suggests that insulin may not function as an overall regulator of energy balance. In addition, physiological hyperinsulinaemia does not apparently inhibit NPY gene expression in the arcuate nucleus. Due to the lack of effect of hyperinsulinaemia on NPY synthesis in the arcuate nucleus, the elevated NPY concentrations in the paraventricular nucleus could result from a reduction of its release, which would be in keeping with the reduction in food intake.
The Neuroactive Steroid 5α‐Tetrahydrodeoxycorticosterone Increases GABAergic Postsynaptic Inhibition in Rat Neocortical Neurons in vitro
Authors: Teschemacher Anja , Zeise Marc L. , Holsboer Florian , Zieglgänsberger Walter
Published: September 2006

The neuroactive steroid 5α‐pregnane‐3α,21‐diol‐20‐one (5α‐tetrahydrodeoxycorticosterone; 5α‐THDOC) has been shown to potentiate GABA‐induced chloride currents in cell cultures and subcellular preparations.

In this study, we recorded from pyramidal neurons in an in vitro slice preparation of the adult rat frontal neocortex using intracellular microelectrodes. 5α‐THDOC (10 μM) increased and prolonged the inhibitory postsynaptic potential (IPSP). The mean maximal synaptic conductance of the early, GABAA receptor‐mediated, IPSP was enhanced to more than 700%, the one at the maximum of the late, partially GABAA receptor‐mediated, IPSP to approximately 400%. The progesterone/glucocorticoid receptor antagonist RU 38486 did not prevent the IPSP increase. At a concentration of 1 μM 5α‐THDOC increased only the early IPSP to about 125%.

Responses to the iontophoretically applied specific GABAA receptor agonist muscimol but not to the specific GABAB receptor agonist L‐baclofen were enhanced by 5α‐THDOC (10 μM). In the giga‐seal whole‐cell configuration when the GABAB receptor‐mediated IPSP component was absent due to intracellular perfusion, 5α‐THDOC (10 μM) increased IPSPs to a similar extent as in the conventional microelectrode recordings. Excitatory postsynaptic potentials, resting membrane potential, input resistance and action potential amplitude were not affected by 5α‐THDOC (10 μM).

These data demonstrate that in neocortical tissue of the rat 5α‐THDOC enhances GABAergic inhibition by interacting with postsynaptic GABAA receptors while synaptic excitation and parameters of electric excitability remain unchanged.
The C‐Type Natriuretic Peptide Receptor is the Predominant Natriuretic Peptide Receptor mRNA Expressed in Rat Hypothalamus
Authors: Langub M. C. , Dolgas C. M. , Watson R. E. , Herman J. P.
Published: September 2006

The natriuretic peptide receptors (NPR) are membrane‐bound guanylate cyclases with extracellular binding domains specific for particular members of the natriuretic peptide family. NPR‐A binds atrial natriuretic peptide (ANP) with high affinity, whereas the NPR‐B appears to be specific for C‐type natriuretic peptide (CNP). Previous data indicating extensive overlap between localization of ANP and CNP in hypothalamic neuroendocrine circuits suggest the importance of determining whether specificity of natriuretic peptide action may be conferred via receptor type present on target cells. To address this issue, we used in situ hybridization histochemistry to localize NPR‐A and NPR‐B mRNA in the hypothalamus. NPR‐A mRNA was not found in substantial abundance in any hypothalamic nucleus; however, detectable NPR‐A signal was observed in other brain regions, including the subfornical organ and medial habenula. In contrast, NPR‐B mRNA was expressed throughout the hypothalamus, including neurons of the magnocellular and parvocellular paraventricular, the arcuate, and the supraoptic nuclei. Expression was also seen in other nuclei essential to neuroendocrine control, including the median preoptic, anteroventral periventricular, tuberomammillary, ventromedial and suprachiasmatic nuclei. NPR‐B mRNA was also observed in the neural lobe of the pituitary gland, suggesting expression by pituicytes. The results suggest that NPR‐B is the primary natriuretic peptide receptor in hypothalamus, and by inference indicate that CNP is the primary active natriuretic peptide in neuroendocrine regulation.
Influence of Environmental Colour and Diurnal Phase on MCH Gene Expression in the Trout
Authors: Suzuki Masakazu , Narnaware Y. K. , Baker Bridget I. , Levy Andy
Published: September 2006

Melanin‐concentrating hormone (MCH) gene expression in the brain of rainbow trout, reared and maintained in either pale or black‐coloured tanks, was studied using in situ hybridization histochemistry. MCH transcripts were most prevalent in the magnocellular neurones of the nucleus lateralis tuberis (NLT), which project to the pituitary gland. They were also present, although at much lower levels, in dorsally projecting parvocellular neurones, sited more posteriorly above the lateral ventricular recess (LVR). In the NLT the most intense hybridization signal was seen over the pituitary stalk; above the LVR, the most active neurones were located caudally. In both the NLT and above the LVR, MCH hybridization signal was 4‐fold stronger in white‐reared fish than in black‐reared fish. There was also a marked diurnal variation in MCH expression in both sites, with high levels at 16.00 h and lower levels at 04.00 h. The results show that gene activity in both hormonal (NLT) and neuromodulator/neurotransmitter (LVR) MCH neurones is induced by pale environmental colour and that MCH gene activity is subject to pronounced diurnal variation.
Resistance of Growth Hormone Secretion to Hypoglycemia in the Mouse
Authors: Tamaki Miho , Sato Makoto , Niimi Michio , Takahara Jiro
Published: September 2006

Although previous studies have demonstrated that acute hypoglycemia inhibits growth hormone (GH) secretion due to stimulation (hypothalamic somatostatin (SS) neurones in the rat, the effect of hypoglycemia on GH secretion has not yet been elucidated in the mouse In this study, the effects of insulin‐induced hypoglycemia on mouse GH secretion, hypothalamic c‐fos expression, GH‐releasing hormon (GRH) and SS mRNA levels were investigated in conscious male mice. Seven days after implantation of chronic atrial catheters, bloo samples were taken every 20 min from 1200–1600 h under unrestrained conditions. Insulin was administered iv every 20 min fro1 1200‐1240 h to induce moderate hypoglycemia (MH) and severe hypoglycemia (SH), respectively. Expression of hypothalamic c‐fos protei was examined 30 min and 60 min after induction of hypoglycemia by immunohistochemistry. Hypothalamic GRH and SS mRNA level were examined 1 h and 3 h after induction of hypoglycemia by Northern blot analysis. The lowest mean plasma glucose levels after insuli injections were 49.1 ± 4.1 mg/dl and 34.2 ± 5.6 mg/dl in conscious mice, respectively. However, pulsatile GH secretion was no significantly altered in either group. Although both MH and SH markedly stimulated c‐fos expression in specific hypothalamic nuclc including the paraventricular nucleus, they did not induce c‐fos protein in the periventricular nucleus. Neither MH nor SH altere hypothalamic GRH or SS mRNA levels. These results suggest that hypoglycemia does not activate SS neurons which inhibit GH secretio in the mouse.
Sex‐Steroid Control of Galanin in the Rat Hypothalamic‐Pituitary Axis
Authors: Selvais Philippe L. , Denef Jean‐François , Adam Evelyne , Maiter Dominique M.
Published: September 2006

To further investigate how sex steroids regulate galanin (GAL) in the rat pituitary and hypothalamus, we examined the effects of prepubertal gonadectomy (Gx) and long‐term (9 weeks) replacement with estradiol (E2) or testosterone (T) on pituitary and hypothalamic GAL concentrations in Wistar rats (5–6/group). Sham‐operated animals served as controls (CTR). Pituitary GAL concentration was markedly higher in random‐cycling CTR‐females than in CTR‐males (1391 ± 247 vs 39 ± 5 pg/mg protein, P<0.01) and decreased after Gx only in females (20 ± 3 pg/mg protein, P<0.01). E2 strongly increased pituitary GAL in Gx‐females and Gx‐males (4470 ± 365 and 3853 ± 347 pg/mg protein, P<0.01), whereas T had no effect. Inversely, hypothalamic GAL was higher in CTR males than in CTR females (5.4 ± 0.3 vs 4.0 ± 0.5 ng/mg protein, P<0.05), and decreased significantly after gonadectomy in males (3.7 ± 0.2 ng/mg protein, P<0.01). The only steroid treatment that significantly modified hypothalamic GAL in Gx animals was administration of E2 to females (5.7 ± 0.4 ng/mg protein, P<0.01 vs non‐treated Gx). We also studied in hypophysectomized (Hx) rats (8/group) the effects of sex steroids on hypothalamic GAL concentration and distribution. The low hypothalamic GAL concentration observed in male and female Hx rats (1.0 ± 0.1 ng/mg protein) was significantly increased by T in males and in females (respectively, by 40% and by 50%, P<0.02) and by E2 in males (by 60%, P<0.02). Immunohistochemistry showed that both E2 and T increased GAL labeling in fibers restricted to the lateral regions of the median eminence of male and female Hx rats, a distribution corresponding to that of GnRH‐immunoreactive fibers. In conclusion, in addition to the marked stimulatory effect of estradiol on pituitary GAL, endogenous and exogenous sex steroids also modulate hypothalamic GAL in male and female rats. Both E2 and T may exert a stimulatory influence on hypothalamic GAL concentration and histochemical analysis shows that sex steroids enhance GAL immunoreactivity in a subset of neurons that closely overlaps the distribution of GnRH neurons.
Disruption of Reproductive Rhythms and Patterns of Melatonin and Prolactin Secretion Following Bilateral Lesions of the Suprachiasmatic Nuclei in the Ewe
Authors: Scott Christopher J. , Jansen Heiko T. , Kao Chen‐Chih , Kuehl David E. , Jackson Gary L.
Published: September 2006

To determine whether the photoperiodic responses of reproductive and prolactin (PRL) rhythms in the ewe requires an intact suprachiasmatic nucleus (SCN) driving the pineal rhythm of melatonin secretion, four groups of ovary‐intact ewes over a 6‐year period were subjected to bilateral (n = 40) or sham lesions (n = 15) of the SCN. Animals were exposed to an alternating 90–120 day photoregimen of 9L:15D and 16L: 8D photoperiods. Blood samples taken twice weekly were assayed for prolactin and for progesterone to monitor oestrous cycles. On several occasions blood samples also were taken at hourly intervals for 24 h and analyzed for melatonin. Melatonin concentrations in sham lesioned ewes were basal during the lights‐on period and rose robustly during darkness. Those sheep bearing unilateral lesions of the SCN (n = 13) or where the lesion spared the SCN entirely (n = 8) had patterns of melatonin secretion similar to sham ewes. The remaining ewes, having complete (n = 9) or incomplete bilateral (n = 8) destruction of the SCN, with one exception, had disrupted patterns of melatonin secretion. The nature of this disruption varied from complete suppression to continuously elevated levels. In lesioned ewes where melatonin secretion was not affected the onset and cessation of ovarian cycles were similar to sham ewes; stimulation of oestrous cycles under 9L:15D and cessation of oestrous cycles under 16L:8D. In contrast, 13 of 17 ewes with disrupted melatonin secretion also exhibited disrupted patterns of ovarian activity. In these animals oestrous cycles were no longer entrained by photoperiod but still occurred in distinct clusters, that is, groups of cycles began and ended spontaneously. Sheep with normal melatonin patterns showed low levels of PRL secretion during short days and elevated PRL levels during long days. However, 8 of 13 ewes with disrupted melatonin showed patterns of PRL secretion that were no longer entrained by photoperiod. A minority of ewes with disrupted melatonin patterns still showed reproductive (n = 4) and PRL (n = 5) responses similar to those of sham‐lesioned ewes. These results show that bilateral destruction of the SCN in the ewe disrupts the circadian pattern of melatonin secretion and that this disruption usually, but not always, is associated with altered photoperiodic responses. These results strongly suggest that the SCN are important neural elements within the photoperiod time–keeping system in this species. A role for the SCN in the generation of endogenous transitions in reproductive activity (refractoriness) and prolactin secretion is not supported.
Differential Melanin‐Concentrating Hormone Gene Expression in Two Hypothalamic Nuclei of the Teleost Tilapia in Response to Environmental Changes
Authors: Gröneveld Diet , Balm Paul H.M. , Martens Gerard J.M. , Bonga Sjoerd E. Wendelaar
Published: September 2006

For some teleosts, a role has been established for melanin‐concentrating hormone (MCH) background adaptation and stress response. In teleost fishes, prepro‐MCH (ppMCH) rnRNA is expressed in the hypothalamus, predominantly in neurons of the nucleus lateralis tuberis (NLT) and in scattered cells of the nucleus recessus lateralis (NRL). The response of mature tilapia to different environmental challenges was studied by assessing ppMCH rnRNA levels in these two hypothalamic nuclei by quantitative dot blot analysis. Changes in background colour induced pronounced differences in ppMCH mRNA expression in the NLT, but not in the NRL. The NLT of tilapia adapted to a white background contained 2.5 to 3 times more ppMCH mRNA than the NLT of black‐adapted fish. The NLT of fish kept on neutral background contained intermediate levels of ppMCH mRNA, which were significantly lower than the levels in white‐adapted fish. Oral administration of dexamethasone lowered plasma cortisol concentrations, but had no effect on ppMCH mRNA levels in white‐ and black‐adapted fish. In tilapia exposed to strongly acidified water (pH 3.5), plasma cortisol and ACTH concentrations were highly elevated, and plasma chloride concentrations considerably lower than in controls. These fish responded with a 70% rise in ppMCH mRNA levels in the NLT, which is most probably associated with a stress response evoked by inadequate osmoregulation. After exposure to a milder acidification (pH 4.0) or to seawater no significant changes in ppMCH mRNA levels occurred in either the NLT or the NRL, nor in plasma chloride, cortisol and ACTH levels. A specific increase of ppMCH mRNA levels in the NRL was observed in repeatedly disturbed tilapia. We conclude that MCH neurons in the NLT and NRL of this teleost differentially respond to background colour, acidification and disturbance stress, and that this response is not strictly associated with changes in plasma ions and activity of the pituitary‐interrenal axis.
Regulation of Melatonin Secretion by Light in the Isolated Pineal Organ of the White Sucker (Catostomus commersoni)
Authors: Bolliet Valérie , Falcón Jacky , Ali M. Ather
Published: September 2006

The effects of different lighting conditions and physical parameters of light were investigated in the isolated pineal organ of the white sucker kept under static or superfusion culture. The secretion of pineal melatonin is directly controlled by the photoperiod and completely suppressed under constant illumination. When pineal organs are exposed to unexpected light at night, the secretion of melatonin is significantly reduced within 15 min and reaches basal value after 30–35 min of light treatment. The inhibition of melatonin secretion by unexpected light at night depends on the irradiance, duration, timing of the treatment and the lighting history of the pineal organ.
Leukaemia Inhibitory Factor Expression in Cultured Rat Anterior Pituitary is Regulated by Glucocorticoids
Authors: Carter David A.
Published: September 2006

Leukaemia inhibitory factor (LIF) is the generally recognized nomenclature for a pleiotropic cytokine that exerts multiple biological effects in different systems. However, its role in the neuroendocrine system is relatively unexplored, with the exception of one report indicating that LIF may act to determine the unique vascular organization of the pituitary gland. In the present study the expression of LIF mRNA has been demonstrated for the first time in the pituitary gland of the rat, in all three pituitary lobes. However, LIF gene expression is restricted to tissues in explant culture where LIF transcripts are readily detectable by Northern Techniques. Similar studies using the reverse transcriptase‐polymerase chain reaction (RT‐PCR) technique also failed to detect LIF transcripts in fresh tissue from adult animals. These results are consistent with the hypothesis that LIF acts to mediate the response to trauma, a response that may include the induction of neuropeptide expression in the anterior pituitary.

In further studies it has also been shown that anterior pituitary LIF mRNA is super‐induced in the presence of protein synthesis inhibitors, a response that indicates a role for a labile protein in the attentuation of LIF expression. Both the explantation response, and the response to protein synthesis inhibitory drugs are decreased in the presence of dexamethasone indicating that a glucocorticoid receptor mechanism acts as a general modulatory influence on LIF mRNA levels. These findings are consistent with the presence of multiple regulatory controls on the expression of LIF that serve to restrict its expression to pathological conditions, and indicate that LIF does not participate in normal endocrine physiology.
Comparison of the Number of Vasopressin‐Producing Hypothalamic Neurons in Rats and Humans
Authors: Harding A. J. , Ng J. L. F. , Halliday G. M. , Oliver J.
Published: September 2006

The aim of this study was to assess the number and proportion of vasopressin‐producing neurons in the hypothalamic magnocellular nuclei in rats and humans. Accurate and unbiased neuronal counts were estimated using the optical disector method. Arginine vasopressin‐containing neurons were immunohistochemically visualized in formalin‐fixed tissue sections. The magnocellular neurons were similar in size and morphology in both species. While the human hypothalamus contained significantly more vasopressin‐containing neurons compared with the rat (36‐fold increase), the proportion of vasopressin‐containing neurons between species was similar. In both species, the majority of supraoptic neurons contained vasopressin, however the proportion of vasopressin‐containing neurons in the human paraventricular nucleus was double that of the rat (nearly a 100‐fold increase in number). These results suggest that the paraventricular nucleus contributes significantly to the release of vasopressin from the posterior pituitary in humans, whereas in rats vasopressin is mainly released by supraoptic neurons.
Effects of Activin‐A on Neurons Acutely Isolated from the Rat Supraoptic Nucleus
Authors: Oliet Stephane H. R. , Plotsky Paul M. , Bourque Charles W.
Published: September 2006

Nerve fibers containing activin‐like immunoreactivity have been shown to be present within the area of the supraoptic nucleus. In this study, whole‐cell patch‐clamp recordings from supraoptic magnocellular neurosecretory cells were used to characterize the electrophysiological effects of this peptide. Nanomolar concentrations of recombinant activin‐A caused the appearance of a voltage‐independent current reversing near –40 mV. At resting potential, membrane depolarization caused by this current was sufficient to accelerate action potential discharge, suggesting that activin receptors expressed on magnocellular neurosecretory cells may play a role in the control of neurohypophysial hormone release.
Annual Variations of in vitro GNRH Release by Hypothalamic Explants in Intact and Castrated Male Mink: Relations with LH, FSH and Testosterone Circulating Serum Levels
Authors: Caillol M. , Mondain‐Monval M. , Rossano B. , Solari A. , Martinet L.
Published: September 2006

In mink, a short‐day breeder, testis growth begins in autumn (November), reaches a maximum in February, before matings occur, and decreases from March to very low volumes during spring and summer. To study the effects of season and testosterone feedback on gonadotrophin and GnRH secretion, the annual variations of LH, FSH, testosterone and GnRH were studied in intact and castrated mink. As portal blood sampling raised serious difficulties, an in vitro static incubation system was used for studying GnRH variations. In intact mink, serum LH concentrations did not vary significantly throughout the year, whereas FSH concentrations increased significantly between September and November then decreased to a minimum in January. Testosterone values rose significantly from November to a maximum from January to March, decreased very rapidly thereafter. Castration in November resulted in a significant increase in LH and FSH concentrations which remained higher than the values measured in intact males throughout the year. In long‐term castrated mink, FSH concentrations did not fluctuate during the year, whereas LH concentrations showed an annual variation, with high values in April and August. For the study of in vitro GnRH liberation, medio‐basal hypothalamic explants were incubated in Krebs‐Ringer phosphate buffer for 3 periods of 15 min, and stimulated with copper complexed equimolarly with histidine (Cu/His, 200 pM) and prostaglandin E2 (PGE2, 10 μM). After Cu/His, the release of GnRH was 1 to 4 fold the basal release; after PGE2, the increase was 4–7 fold the basal release. The basal release of GnRH increased significantly between September and October to reach a maximum in November, decreased significantly in December to a minimum in February then increased progressively from May. The release of GnRH stimulated by Cu/His and PGE2 showed the same seasonal variation as the basal release. Castration 8 days before the sacrifice did not alter the release of GnRH, except in December: the release stimulated by PGE2 was then higher in intact than in castrated mink. Taken together, these results indicate that, with an in vitro static incubation system, it is possible to study the annual variations of GnRH release and to correlate these variations with those of serum gonadotrophin and testosterone concentrations. The synthesis and release of GnRH increased slightly from May, under long days, then more rapidly from September, resulting in an increased secretion of FSH in October, responsible for testis recrudescence. The annual pattern of basal and stimulated GnRH release was similar in intact and castrated mink, suggesting a direct effect of the season on the hypothalamus, rather than a negative feedback effect of the testis; however, testosterone seemed to feedback mainly at the pituitary level.
Response of Interleukin‐1β in the Magnocellular System to Salt‐Loading
Authors: Summy‐Long J. Y. , Hu S. , Pruss A. , Chen X. , Phillips T. M.
Published: September 2006

Drinking 2% NaCl decreases interleukin (IL)‐1β in the neural lobe and enhances IL‐1 Type 1 receptor expression in magnocellular neurones and pituicytes. To quantify cytokine depletion from the neural lobe during progressive salt loading and determine whether the changes are reversible and correspond with stores of vasopressin (VP) or oxytocin (OT), rats were given water on day 0 and then 2% NaCl to drink for 2, 5, 8 or 5 days followed by 5 days of water (rehydration). Control rats drinking only water were pair‐fed amounts eaten by 5‐day salt‐loaded animals. Animals were decapitated on day 8, the neural lobe frozen and plasma hormones analysed by radioimmunoassay (OT, VP) or enzyme‐linked immunosorbent assay (IL‐1β). IL‐1β, VP and OT in homogenates of the neural lobe were quantified by immunocapillary electrophoresis with laser‐induced fluorescence detection. Differences were determined by anova, Tukey's t‐test, Dunnett's procedure, Fisher's least significant difference and linear regression analysis. In response to salt‐loading, rats lost body weight similar to pair‐fed controls, drank progressively more 2% NaCl and excreted greater urine volumes. Plasma VP increased at days 2 and 8 of salt‐loading, whereas osmolality, OT and cytokine were enhanced after 8 days with IL‐1β remaining elevated after rehydration. In the neural lobe, all three peptides decreased progressively with increasing duration of salt‐loading (IL‐1β, r2 = 0.98; OT, r2 = 0.94; VP, r2 = 0.93), beginning on day 2 (IL‐1β; VP) or 5 (OT), with only VP replenished by rehydration. IL‐1β declined more closely (P < 0.0001; anova interaction analysis) with OT (r2 = 0.96) than VP (r2 = 0.86), indicative of corelease from the neural lobe during chronic dehydration. Local effects of IL‐1β on magnocellular terminals, pituicytes and microglia in the neural lobe with activation of forebrain osmoregulatory structures by circulating cytokine may sustain neurosecretion of OT and VP during prolonged salt‐loading.
Cyclic‐di‐GMP‐mediated signalling within the σS network of Escherichia coli
Authors: Weber Harald , Pesavento Christina , Possling Alexandra , Tischendorf Gilbert , Hengge Regine
Published: September 2006

Bis‐(3′−5′)‐cyclic‐di‐guanosine monophosphate (c‐di‐GMP) is a bacterial signalling molecule produced by diguanylate cyclases (DGC, carrying GGDEF domains) and degraded by specific phosphodiesterases (PDE, carrying EAL domains). Neither its full physiological impact nor its effector mechanisms are currently understood. Also, the existence of multiple GGDEF/EAL genes in the genomes of most species raises questions about output specificity and robustness of c‐di‐GMP signalling. Using microarray and gene fusion analyses, we demonstrate that at least five of the 29 GGDEF/EAL genes in Escherichia coli are not only stationary phase‐induced under the control of the general stress response master regulator σS (RpoS), but also exhibit differential control by additional environmental and temporal signals. Two of the corresponding proteins, YdaM (GGDEF only) and YciR (GGDEF + EAL), which in vitro show DGC and PDE activity, respectively, play an antagonistic role in the expression of the biofilm‐associated curli fimbriae. This control occurs at the level of transcription of the curli and cellulose regulator CsgD. Moreover, we show that H‐NS positively affects curli expression by inversely controlling the expression of ydaM and yciR. Furthermore, we demonstrate a temporally fine‐tuned GGDEF cascade in which YdaM controls the expression of another GGDEF protein, YaiC. By genome‐wide microarray analysis, evidence is provided that YdaM and YciR strongly and nearly exclusively control CsgD‐regulated genes. We conclude that specific GGDEF/EAL proteins have very distinct expression patterns, and when present in physiological amounts, can act in a highly precise, non‐global and perhaps microcompartmented manner on a few or even a single specific target(s).
Inward rectification of the AKT2 channel abolished by voltage‐dependent phosphorylation
Authors: Michard Erwan , Dreyer Ingo , Lacombe Benoît , Sentenac Hervé , Thibaud Jean‐Baptiste
Published: September 2006

The Arabidopsis K+ channel AKT2 possesses the remarkable property that its voltage threshold for activation can be either within the physiological range (gating mode 1), or shifted towards considerably more positive voltages (gating mode 2). Gating mode 1 AKT2 channels behave as delayed K+‐selective inward rectifiers; while gating mode 2 AKT2 channels are K+‐selective ‘open leaks’ in the physiological range of membrane potential. In the present study we have investigated modulation of AKT2 current by effectors of phosphatases/kinases in COS cells and Xenopus oocytes. These experiments show that (i) dephosphorylation can result in AKT2 channel silencing; and (ii) phosphorylation by protein kinase A (PKA) favors both recruitment of silenced AKT2 channels and transition from gating mode 1 to gating mode 2. Interestingly, phosphorylation of AKT2 by PKA in COS cells and Xenopus oocytes is favored by hyperpolarization. Two PKA phosphorylation sites (S210 and S329) were pinpointed in the region of the pore inner mouth. The role of these phosphorylation sites in the switch between the two gating modes was assessed by electrophysiological characterization of mutant channels. The molecular aspects of AKT2 regulation by phosphorylation, and the possible physiological meaning of such regulation in the plant context, are discussed.
Tobacco aquaporin NtAQP1 is involved in mesophyll conductance to CO2in vivo
Authors: Flexas Jaume , Ribas‐Carbó Miquel , Hanson David T. , Bota Josefina , Otto Beate , Cifre Josep , McDowell Nate , Medrano Hipólito , Kaldenhoff Ralf
Published: September 2006

Leaf mesophyll conductance to CO2 (gm) has been recognized to be finite and variable, rapidly adapting to environmental conditions. The physiological basis for fast changes in gm is poorly understood, but current reports suggest the involvement of protein‐facilitated CO2 diffusion across cell membranes. A good candidate for this could be the Nicotiana tabacum L. aquaporin NtAQP1, which was shown to increase membrane permeability to CO2 in Xenopus oocytes. The objective of the present work was to evaluate its effect on the in vivo mesophyll conductance to CO2, using plants either deficient in or overexpressing NtAQP1. Antisense plants deficient in NtAQP1 (AS) and NtAQP1 overexpressing tobacco plants (O) were compared with their respective wild‐type (WT) genotypes (CAS and CO). Plants grown under optimum conditions showed different photosynthetic rates at saturating light, with a decrease of 13% in AS and an increase of 20% in O, compared with their respective controls. CO2 response curves of photosynthesis also showed significant differences among genotypes. However, in vitro analysis demonstrated that these differences could not be attributed to alterations in Rubisco activity or ribulose‐1,5‐bisphosphate content. Analyses of chlorophyll fluorescence and on‐line 13C discrimination indicated that the observed differences in net photosynthesis (AN) among genotypes were due to different leaf mesophyll conductances to CO2, which was estimated to be 30% lower in AS and 20% higher in O compared with their respective WT. These results provide evidence for the in vivo involvement of aquaporin NtAQP1 in mesophyll conductance to CO2.
The maize Mucronate mutation is a deletion in the 16‐kDa γ‐zein gene that induces the unfolded protein response1
Authors: Kim Cheol Soo , Gibbon Bryan C. , Gillikin Jeffrey W. , Larkins Brian A. , Boston Rebecca S. , Jung Rudolf
Published: September 2006

Mucronate (Mc) was identified as a dominant maize (Zea mays L.) opaque kernel mutation that alters zein storage protein synthesis. Zein protein bodies in Mc endosperm are misshapen and are associated with increased levels of ER Lumenal Binding Protein (BiP). Using GeneCallingTM to profile endosperm RNA transcripts, we identified an aberrant RNA in Mc that encodes the 16‐kDa γ‐zein protein. The transcript contains a 38‐bp deletion (nucleotides 406–444 after the initiation codon) that creates a frame‐shift mutation and an abnormal sequence for the last 63 amino acids. Genetic mapping revealed the Mc mutation is linked with the locus encoding the 16‐kDa γ‐zein, and two‐dimensional gel electrophoresis confirmed the 16‐kDa γ‐zein protein is altered in Mc. The mutant protein exhibited changes in solubility properties and co‐immunoprecipitated with the molecular chaperone, BiP. Transgenic maize plants expressing the Mc 16‐kDa γ‐zein manifested an opaque kernel phenotype with enhanced levels of BiP in the endosperm, similar to the Mc mutant. Unlike the wild‐type protein, the Mc 16‐kDa γ‐zein interacted only weakly with the 22‐kDa α‐zein when expressed in the yeast two‐hybrid system. These results indicate that the Mc phenotype results from a frame‐shift mutation in the gene encoding the 16‐kDa γ‐zein protein, leading to the unfolded protein response in developing endosperm.
The efficacy of photochemical treatment with methylene blue and light for the reduction ofTrypanosoma cruziin infected plasma
Authors: Gironés N. , Bueno J. L. , Carrión J. , Fresno M. , Castro E.
Published: September 2006

Background and Objectives Chagas disease is a transfusion‐transmitted infection. This study evaluates the efficacy of a methylene blue (MB) and light system for reducing the viability ofTrypanosoma cruziin plasma.

Materials and Methods Trypanosoma cruzistrains were spiked in plasma pools. Treatment arms included combined filtration, MB, light and freezing. Post‐treatment parasite viability was assayed throughin vitrocultures andin vivoinoculation in inducible nitric oxide synthase‐ and interferon‐γ‐receptor‐deficient mice.

Results The filtration, MB and light combined treatment showed a log reduction of > 3·4 inin vitrocultures, and log reductions that ranged from > 4·9 to > 5·8 in deficient mice inoculated with differentT. cruzistrains.

Conclusion The treatment of plasma units with the MB and light system reduces theT. cruziburden and could be useful in preventing transfusion‐transmitted Chagas disease.
Ultrastruktur‐Merkmale zur Definition der Begriffe ‘Hefezelle’, ‘Pseudomyzel’ und ‘echtes Myzel’ bei Candida albicans
Authors: Müller J. , Melchinger W.
Published: September 2006

Die Unterscheidung der Gestaltformen ‘Hefezelle’, ‘Pseudomyzel’ und ‘echtes Myzel’ ist in der mykologischen und histopathologischen Diagnostik von Candida albicans‐Mykosen unverzichtbar. Präzise definierte Unterscheidungskriterien fehlen allerdings in der medizinisch‐mykologischen Literatur. Diese Kriterien, basierend auf elektronenmikroskopischen Studien der Zellwand, werden nachfolgend beschrieben.