N-Acetylaspartylglutamate Stimulates Metabotropic Glutamate Receptor 3 to Regulate Expression of the GABAAα6 Subunit in Cerebellar Granule Cells

Abstract: We have shown that the vertebrate neuropeptide N-acetylaspartylglutamate (NAAG) meets the criteria for a neurotransmitter, including function as a selective metabotropic glutamate receptor (mGluR) 3 agonist. Short-term treatment of cerebellar granule cells with NAAG (30 µM) results in the transient increase in content of GABA_Aα6 subunit mRNA. Using quantitative PCR, this increase was determined to be up to 170% of control values. Similar effects are seen following treatment with trans-1-aminocyclopentane-1,3-dicarboxylate and glutamate and are blocked by the mGluR antagonists (2S,3S,4S)-2-methyl-2-(carboxycyclopropyl)glycine and (2S)-α-ethylglutamic acid. The effect is pertussis toxin-sensitive. The increase in α6 subunit mRNA level can be simulated by activation of other receptors negatively linked to adenylate cyclase activity, such as adenosine A1, α2-adrenergic, muscarinic, and GABA_B receptors. Forskolin stimulation of cyclic AMP (cAMP) levels abolished the effect of NAAG. The change in α6 levels induced by 30 µM NAAG can be inhibited in a dose-dependent manner by simultaneous application of increasing doses of the β-adrenergic receptor agonist isoproterenol. The increase in α6 mRNA content is followed by a fourfold increase in α6 protein level 6 h posttreatment. Under voltage-clamped conditions, NAAG-treated granule cells demonstrate an increase in the furosemide-induced inhibition of GABA-gated currents in a concentration-dependent manner, indicating an increase in functional α6-containing GABA_A receptors. These data support the hypothesis that NAAG, acting through mGluR3, regulates expression of the GABA_Aα6 subunit via a cAMP-mediated pathway and that cAMP-coupled receptors for other neurotransmitters may similarly influence GABA_A receptor subunit composition.     

Human Platelet Sulfotransferase Shows Seasonal Rhythms

Our study aimed to investigate the possible presence of seasonal changes in platelet phenolsulfotransferase (ST) in a group of 20 healthy, drug-free subjects of both sexes and between 24 and 37 years of age. Blood samples were taken four times a year in the period immediately following the equinoxes and the solstices. The results showed that both STs underwent seasonal changes: the lowest values were found in autumn and in winter, and the highest in the summer. A positive correlation between the two STs and the length of the photoperiod was observed in winter, whereas in the spring we detected a negative correlation between the TL ST and the photoperiod length. Future studies should clarify whether platelet ST of patients with mood disorders shows a similar seasonality.     

Changes in the surface morphology of the rabbit endometrium related to the estrous and progestational stages of the reproductive cycle

Summary Changes occurring on the surface of the uterine luminal epithelium of the rabbit during the estrous and progestational stages of the reproductive cycle were examined by scanning and transmission electron microscopy. The findings demonstrate that the uterine epithelium, or endometrium, contains two cell types: ciliated cells and nonciliated, microvillous cells. In estrous animals, ciliated cells, although not very numerous, were usually observed in small groups. However, at increasing intervals of time following mating, ciliated cells progressively disappeared from the endometrium until approximately eight to ten days post coitum, when they became scare. From several hours to four to five days following mating, extensive changes occurred on the surfaces of microvillous cells. When observed by TEM, these elements contained organelles typical of cells involved in the synthesis and secretion of glycoproteins. Furthermore, microvillous cells during this period displayed numerous apical protrusions of different sizes and shapes and containing material of varying electron density. Parallel SEM examinations of the same material confirmed the presence of these protrusions. Some of the protrusions appeared as spheroidal masses attached to the cytoplasm by means of a cytoplasmic strand. Other surface masses were clearly unattached to the cell surface and were distributed (1) on the surface of microvillous cells, (2) on the cilia of adjacent ciliated cells, and (3) on the surface of spermatozoa.Changes occurring on the luminal surface during the early postcoital period are interpreted as an expression of morphodynamic processes likely involving coupled secretion (exocytosis) and resorption (endocytosis) of luminal material. The observations presented here also demonstrate that between six and ten days post coitum, the rabbit endometrium contained increasing numbers of enlarged, nonciliated cells that probably arose by the fusion of smaller, microvillous elements.The work reported here was supported by C.N.R. contracts No. CT 760128809 and CT 77014239 (to P.M.) and NIH. Grant HD-04274 (to J.V.B.)     

Basal metabolism and dynamic activity of food in obesity

Metabolic rate of obese patients is reported, recorded to cellular active mass. The metabolic rate is higher in obese patients and the value is diucthy related to individual actual weight. The dinamic-specific action of proteins is normal.     

The generation of the proton electrochemical potential and its role in energy transduction

Summary The evidence that all energy transducing membranes can generate a proton electrochemical potential difference, _H, across the membrane and that this potential can be used to transfer energy among energy transducing units and to generate ATP, has increased the interest for the view that _H plays an obligatory role in energy transduction and ATP synthesis. In the present article we shall concentrate on two experimental questions related with the generation and role of _H: (a) the charge/site ratio; (b) the relation between the proton electrochemical potential on one side and the cation electrochemical potential, the phosphate potential and the redox potential on the other. We shall then discuss the view that energy transduction corresponds to a molecular energy machine rather than to a fuel cell.     

Steroid modulation of oxytocin/vasopressin receptors in the uterus

Oxytocin (OT) and V1 vasopressin (VP) receptors are present simultaneously in several tissues, including the uterus. In myometrium these receptors mediate contractility, while in endometrium they mediate the release of other uterotonic substances as endothelin (ET). In rabbit myometrium, estrogens increase, while progesterone blunts neurohypophysial hormone receptors. However, the action of sex steroids on OT and V1 VP receptors differs in terms of the ED₅₀ and maximal effect. Therefore, at parturition, only OT receptors show a dramatic rise, while V1 VP receptors do not change, suggesting a major role for OT in labor. ET is a potent stimulator of uterine activity acting through specific receptors present on myometrial cells. These receptors as well as the endometrial localization of ET are modulated by sex steroids, indicating that ET might represent a paracrine regulator of uterine activity. In humans, OT but not V1 VP receptors increase as pregnancy progresses, confirming the primary relevance of OT in timing delivery.     

Maitotoxin-Induced Intracellular Calcium Rise in PC 12 Cells: Involvement of Dihydropyridine-Sensitive and ω-Conotoxin-Sensitive Calcium Channels and Phosphoinositide Breakdown

The biological activities of maitotoxin are strictly dependent on the extracellular calcium concentration and are always associated with an increase of the free cytosolic calcium level. We tested the effects of voltage-sensitive calcium channel blockers (nicardipine and omega-conotoxin) on maitotoxin-induced intracellular calcium increase, membrane depolarization, and inositol phosphate production in PC12 cells. Maitotoxin dose dependently increased the cytosolic calcium level, as measured by the fluorescent probe fura 2. This effect disappeared in a calcium-free medium; it was still observed in the absence of extracellular sodium and was enhanced by the dihydropyridine calcium agonist Bay K 8644. Nicardipine inhibited the effect of maitotoxin on intracellular calcium concentration in a dose-dependent manner. The maitotoxin-induced calcium rise was also reduced by pretreating cells with omega-conotoxin. Pretreatment of cells with maitotoxin did not modify 125I-omega-conotoxin and [3H]PN 200-110 binding to PC12 membranes. Nicardipine and omega-conotoxin inhibition of maitotoxin-evoked calcium increase was reduced by pertussis toxin pretreatment. Maitotoxin caused a substantial membrane depolarization of PC12 cells as assessed by the fluorescent dye bisoxonol. This effect was reduced by pretreating the cells with either nicardipine or omega-conotoxin and was almost completely abolished by the simultaneous pretreatment with both calcium antagonists. Maitotoxin stimulated inositol phosphate production in a dose-dependent manner. This effect was reduced by pretreating the cells with 1 microM nicardipine and was completely abolished in a calcium-free EGTA-containing medium. The findings on maitotoxin-induced cytosolic calcium rise and membrane depolarization suggest that maitotoxin exerts its action primarily through the activation of voltage-sensitive calcium channels, the increase of inositol phosphate production likely being an effect dependent on calcium influx. The ability of nicardipine and omega-conotoxin to inhibit the effect of maitotoxin on both calcium homeostasis and membrane potential suggests that L- and N-type calcium channel activation is responsible for the influx of calcium following exposure to maitotoxin, and not that a depolarization of unknown nature causes the opening of calcium channels.     

To lek or not to lek: mating strategies of male fallow deer

We studied the mating system of fallow deer (Dama dama) for6 years in central Italy. Males in this population could defendterritories that were either single, clumped in leks, or satelliteto leks. The most highly successful males in our study werein leks. When we considered all males, there were no significantdifferences in average copulatory success according to territorytype because many lek males did not achieve any copulations,which were seen in only a few lek territories. The variancein copulatory success, however, was much greater for leks thanelsewhere. Single territories were occupied for shorter timesduring the rut than lek territories. Fighting among males wasmore frequent in the lek, even when we excluded highly successfullek males from the analysis. Chases of nonterritorial malesand harem size were correlated with the number of copulationsachieved by individual males, but did not vary according toterritory type. Copulatory success of some individuals increasedwith age, but there were no age differences among males holdingdifferent types of territories. Satellite males switched tolek territoriality in the course of one rut, but switches fromsingle territory to lek territory were rare. We suggest thatmales in single territories are inferior competitors that selecta low-risk, lowbenefit strategy, whereas those in lek territorieswhere no copulations were seen may be attempting to establishthemselves on the lek to increase their copulatory success infuture years.