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.     

Cellular localization of somatolactin in the pars intermedia of some teleost fishes

Summary We report here on the cellular localization in the fish pituitary of somatolactin (SL), a putative new pituitary hormone related to growth hormone and prolactin, which has been recently identified in the piscine pituitary gland. Immunocytochemical staining, using anti-cod SL serum, revealed that in the cod pituitary gland, SL is produced by cells in the intermediate lobe, bordering the neural tissue. These cells, staining weakly with periodic-acid-Schiff (PAS), are distinct from the melanocyte stimulating hormone (MSH) cells which, as in all teleosts, are PAS-negative. SL-immunoreactivity was observed in the same location in all other teleost species examined: flounder, rainbow trout, killifish, molly, catfish and eel. In most fish the SL-immunoreactive cells are either strongly or weakly PAS-positive but in rainbow trout are chromophobic, indicating that the SL protein can probably exist in glycosylated and non-glycosylated forms. Thus, in demonstrating the cellular localization of SL, this study provides the first identification of the enigmatic, second cell-type of the fish pars intermedia.     

2-Arachidonoyl glycerol sensitizes the pars distalis and enhances forskolin-stimulated prolactin secretion in Syrian hamsters

2-Arachidonoyl glycerol (2-AG) is a major endocannabinoid and an important regulator of neuroendocrine system. In Syrian hamster and human, we found that 2-AG is synthesized in the hypophysial pars tuberalis (PT), an interface between photoperiodic melatonin signals and neuroendocrine output pathways. The target of 2-AG produced in the PT is likely to be the pars distalis (PD). Here we demonstrate that 2-AG in combination with forskolin stimulated prolactin secretion from PD organ cultures of Syrian hamsters, whereas incubation with 2-AG alone had no effect. Forskolin-induced prolactin secretion was also significantly enhanced when cultured PD tissue was preincubated with 2-AG. The stimulatory effects of 2-AG on prolactin secretion were blocked by AM251, a selective CB1 antagonist, and were still observed in the presence of quinpirole, a D2-class dopamine receptor agonist. 2-AG also enhanced prolactin secretion in the presence of adenosine, while it had little effect when applied together with adenosine diphosphate (ADP) and adenosine triphosphate (ATP). Moreover, the effect of forskolin was mimicked by adenosine in a dose-dependent manner. In conclusion, our data suggest that 2-AG sensitizes the PD tissue to potentiate the stimulating effects of forskolin and adenosine on prolactin secretion and thus provide novel insight into the mode of action of 2-AG in the PD.     

Analyses of Oviductal Pars Recta-Induced Fertilizability of Coelomic Eggs in Xenopus laevis

The acquisition of fertilizability in coelomic eggs of Xenopus laevis has been shown to be correlated with the physical, biochemical, and ultrastructural alterations of the egg envelope [coelomic envelope (CE)] induced during the passage of eggs through the pars recta portion of the oviduct. However, no direct evidence that the pars recta renders eggs fertilizable has yet been presented. In this study, we show that coelomic eggs are highly fertilizable when they are incubated with continuous shaking for 4 h at 15 degrees C in pars recta extract (PRE) derived from females prestimulated by pregnant mare serum gonadotropin. The PRE from pituitary-stimulated Bufo japonicus was as potent as homologous PRE in rendering Xenopus eggs fertilizable. Incubation of coelomic eggs in PRE for 30 min induced a dramatic increase in the rates of sperm binding to the envelope to a level equivalent to that exhibited by the envelope from uterine eggs (VEs). The CE-to-VE ultrastructural conversion and a 43k-to-41k hydrolysis of the envelope glycoprotein component started 5 min after, and were completed by 15 min after, the start of incubation in PRE and were accompanied by an exposure of a new N-terminal sequence typical to gp41. Thus, the biochemical and ultrastructural conversions and the sperm-binding activity of the envelope induced by PREs, although being prerequisite, were not sufficient to render coelomic eggs fully accessible to fertilizing sperm.     

Occurrence of colloid-containing follicles in the pars distalis of pituitary glands from aging guinea pigs

Summary Colloid-containing follicles in the pars distalis of pituitary glands from guinea pigs at various ages ranging from 5 days to 36 months were examined by the periodic acid-Schiff (PAS) reaction, immunohistochemistry, and electron microscopy. The follicles storing PAS-positive colloid were first detected in 6-month-old animals, in which only a few follicles were present and mean diameters of colloid deposits were small: 4.3±1.0 m in males and 4.1±0.4 m in females. Thereafter, the follicles gradually increased in number and size with age. The largest number of follicles was observed in the senile groups: 410.5±92.3 in males, 454.7±84.7 in females. Mean diameters of colloid masses in the senile groups were more than 2 times larger than those in 6-month-old animals: 10.0±0.1 m in males, 9.7±0.1 m in females. These findings suggest that the formation of colloidcontaining follicles in the guinea-pig pars distalis is an aging phenomenon. The follicular lumina were mainly surrounded by thin cytoplasmic processes or cell bodies of folliculo-stellate cells immunoreactive for S-100 protein. The lining folliculo-stellate cells showed aggregations of intermediate-sized filaments, numerous lysosomes and colloid-like inclusions. Granulated cells in contact with colloid were occasionally encountered. Intracellular cavities storing colloid-like and fibrous materials were detected in the syncytial formation of GH cells.     

Synthesis and evaluation of biaryl derivatives for structural characterization of selective monoamine oxidase B inhibitors toward Parkinson’s disease therapy

Benzyloxyphenyl moiety is a common structure of highly potent, selective and reversible inhibitors of monoamine oxidase B (MAO-B), safinamide and sembragiline. We synthesized 4-(benzyloxy)phenyl and biphenyl-4-yl derivatives including halogen substituents on the terminal aryl unit. In addition, we modified the carbon linker between amine group and the biaryl linked unit. Among synthesized compounds, 12c exhibited the most potent and selective MAO-B inhibitory effect (hMAO-B IC₅₀: 8.9?nM; >10,000-fold selectivity over MAO-A) as a competitive inhibitor. In addition, 12c showed greater MAO-B inhibitory activity and selectivity compared to well-known MAO-B inhibitors such as selegiline, safinamide and sembragiline. In the MPTP-induced mouse model of Parkinson’s disease (PD), 12c significantly protected the tyrosine hydroxylase (TH)-immunopositive DAergic neurons and attenuated the PD-associated behavioral deficits. This study suggests characteristic structures as a MAO-B inhibitor that may provide a good insight for the development of therapeutic agents for PD.     

燕雀上纹状体腹侧尾核对发声和呼吸的调制效应及其纤维联系

在乌拉坦麻醉的鸣禽燕雀（Ｆｒｉｎｇｉｌｌａｍｏｎｔｉｆｒｉｎｇｉｌｌａ）上,观察电刺激上纹状体腹侧尾核（ＨＶｃ）对发声和呼吸的影响,随后在ＨＶｃ内注入ＣＢ－ＨＲＰ溶液,研究ＨＶｃ的中枢联系。结果如下：（１）电刺激ＨＶｃ的不同区域都引起鸣叫反应。（２）长串电脉冲刺激ＨＶｃ,产生明显的呼吸易化效应,表现为增频增幅的呼吸。（３）吸气期用短串电脉冲刺激ＨＶｃ,产生吸气切断效应;刺激落位于呼气相,可使该呼气时程明显延长,以配合鸣叫,然后转变为增频增幅的呼吸。（４）ＣＢＨＲＰ法表明,ＨＶｃ投射到古纹状体粗核和嗅叶Ｘ区,ＨＶｃ接受新纹状体前部大细胞核内侧部、新纹状体中部界面核、端脑听核－Ｌ区、丘脑葡萄形核及脑桥蓝斑核的传入投射。提示ＨＶｃ除控制发声外,尚参与呼吸易化的调制。ＨＶｃ对发声及呼吸的特异性影响,可能在鸣叫与呼吸的协调机制中起重要作用。     

Regulation of axotomy-induced dopaminergic neuron death and c-Jun phosphorylation by targeted inhibition of cdc42 or mixed lineage kinase

Mechanical transection of the nigrostriatal dopamine pathway at the medial forebrain bundle (MFB) results in the delayed degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). We have previously demonstrated that c-Jun activation is an obligate component of neuronal death in this model. Here we identified the small GTPase, cdc42, and mixed lineage kinases (MLKs) as upstream factors regulating neuronal loss and activation of c-Jun following MFB axotomy. Adenovirus-mediated expression of a dominant-negative form of cdc42 in nigral neurons blocked MFB axotomy-induced activation (phosphorylation) of MAP kinase kinase 4 (MKK4) and c-Jun, resulting in attenuation of SNpc neuronal death. Pharmacological inhibition of MLKs, MKK4-activating kinases, significantly reduced the phosphorylation of c-Jun and abrogated dopaminergic neuronal degeneration following MFB axotomy. Taken together, these findings suggest that death of nigral dopaminergic neurons following axotomy can be attenuated by targeting cell signaling events upstream of c-Jun N-terminal mitogen-activated protein kinase/c-Jun.     

Response of pituitary thyrotrophs to thyrotrophin-releasing hormone in Snell dwarf mice

Summary The effect of thyrotrophin-releasing hormone (TRH) on pituitary thyrotrophs was investigated in Snell dwarf mice (dw/dw) that are genetically deficient in thyrotrophin (TSH) and in normal animals of the same strain. The normal animals were treated with either saline or 10 g TRH per day for 2 weeks, while the dwarf mice were given daily injections of saline, 10 g TRH for 2 weeks or 10 g for 6 weeks. At the end of each experimental period, the pituitary glands were removed and fixed for light-microscopic analysis using immunocytochemistry, or for transmission electron-microscopic study. Compared to thyrotrophs observed in the pituitary glands of untreated normal mice, thyrotrophs in TRH-treated normal mice appeared to be more numerous by immunocytochemistry and showed signs of stimulation by electron microscopy. In contrast, immunostainable thyrotrophs could not be identified in the pituitary glands of untreated or TRH-treated dwarfs. However, a few cells exhibiting ultrastructural features of stimulated thyrotrophs, were noticeable in the dwarfs following TRH administration. Thus, while failing to induce the synthesis of immunoreactive TSH under the applied experimental conditions, exogenous TRH appeared to elicit differentiation of thyrotroph precursors into ultrastructurally recognizable thyrotrophs. The discrepancy between the immunocytochemical and ultrastructural findings remains unresolved; more work is required to clarify the question as to why ultrastructural maturation of thyrotrophs was unaccompanied by the production of immunoreactive TSH.