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Biomedical subjects

B Borg

Publications and source records attributed to B Borg.

14 recordsLinked to original sources
PubMed1992

Activation of polyphosphoinositide metabolism at artificial maturation of Patella vulgata oocytes.

The metabolism of polyphosphoinositides (PPI) has been investigated during the meiosis reinitiation of the oocytes of a prosobranch mollusk, the limpet Patella vulgata. Meiosis reinitiation which leads to germinal vesicle breakdown (GVBD) and metaphase-1 spindle formation was artificially induced by treating the prophase-blocked oocytes with 10 mM NH4Cl, pH 8.2. This treatment, which results in a rise in intracellular pH, triggered a general increase in polyphosphoinositide synthesis. Determinations of phosphorus content showed that maturation induced a 30 to 50% increase in both phosphatidylinositol (PI) and phosphatidylinositol-1 monophosphate (PIP) concentrations. Incorporations of 32PO4 and [3H]inositol have been measured in three classes of polyphosphoinositides: PI, PIP, and phosphatidylinositol 4,5-bisphosphate (PIP2). By comparing incorporation rates of the radiolabeled precursors into PPI before and after meiosis reinitiation, we found that artificial maturation by ammonia induced a 50-fold increase in the turnover of these lipids. No significant burst of inositol 1,4,5-trisphosphate (IP3) was observed after maturation. We suggest that modifications in PPI metabolism occurring at maturation of Patella oocytes might ensure the formation of an important stock of PPI that would be available for the profuse production of IP3, the messenger responsible for the Ca2+ signal at fertilization.

Ammonia↗
PubMed1992

Metabolism of androstenedione and 11-ketotestosterone in the kidney of the three-spined stickleback, Gasterosteus aculeatus.

Stickleback kidneys were incubated with tritiated androstenedione (A4) or 11-ketotestosterone (OT). After the A4 incubations the following steroids were found, testosterone (T), 5 beta-androstane-3,17-dione (5 beta Ad), etiocholanolone (Et), 5 beta-dihydrotestosterone (5 beta DHT), 5 beta-androstane-3 alpha,17 beta-diol (5 beta A3 alpha 17 beta diol), androsterone, 5 alpha-androstane-3,17-dione, 5 alpha-androstane-3 alpha,17 beta-diol (5 alpha A3 alpha 17 beta diol), as well as glucuronides of T, Et, 5 beta DHT, 5 beta A3 alpha 17 beta diol, and 5 alpha A3 alpha 17 beta diol. The metabolites found in the largest amounts were usually T, 5 beta Ad, Et, and the glucuronides of T, Et, and especially of 5 beta A3 alpha 17 beta diol. These results suggest the main pathway to be A4-5 beta Ad-Et-5 beta A3 alpha 17 beta diol-5 beta A3 alpha 17 beta diol-glucuronide or Et-Et-glucuronide-5 beta A3 alpha 17 beta diol-glucuronide. The formation of 5 beta-reduced compounds was larger in postbreeding males and females than in breeding males. The opposite was the case for 5 alpha-reduced compounds. The total formation of glucuronides was lower in the breeding males than in the other groups. After the OT incubations 11-ketoandrostenedione, 17 beta-hydroxy-5 beta-androstane-3,11-dione (tentatively identified), and OT-glucuronide were found. 17 beta-Hydroxy-5 alpha-androstane-3,11-dione was not present.

Androstane-3,17-diol↗
PubMed1992

Temperature, but not photoperiod, influences gonadotropin-releasing hormone binding in the pituitary of the three-spined stickleback, Gasterosteus aculeatus.

Gonadotropin-releasing hormone (GnRH) binding characteristics in pituitaries of stickle-backs under different physiological conditions were studied using D-Arg6-Pro9-salmonGnRH-NEt as labeled ligand. Both males and females displayed marked seasonal changes in the capacity of high-affinity GnRH binding sites; there was a high content in the breeding season (summer) (800-1500 pmol/pituitary) and no detectable high affinity (< 150 pmol) binding in late winter-early spring. The binding capacity was lower in postbreeding fish (ca. 400 pmol/pituitary in females, ca. 900 pmol in males) than in breeding fish (females: ca. 1850, males ca. 1400 pmol). GnRH binding sites were also studied in fish exposed to long and short photoperiod in combination with high and low temperature in winter. Only long photoperiod in combination with high temperature stimulated sexual maturation. The capacity of the GnRH binding sites was similar in fish exposed to long (females 1550 pmol, males 1000 pmol) and short (females 1800, males 900) photoperiod in combination with high temperature. In fish exposed to low temperature, binding was nondetectable irrespective of the photoperiod.

Amino Acid Sequence↗
PubMed1992

Polyphosphoinositide metabolism during the fertilization wave in sea urchin eggs.

A transient increase in intracellular free calcium is believed to be the signal responsible for the stimulation of the egg metabolism at fertilization and the resumption of the cell cycle. We have studied how the polyphosphoinositides (PPI) turn over at fertilization in sea urchin eggs, in order to determine the relationship between the metabolism of these lipids and the calcium signal. We compare the patterns of PPI turnover that occur during the first minute following fertilization in eggs in which PPI are labelled to steady state with [3H]inositol or [3H]arachidonate with that in which PPI are labelled for a shorter period with [3H]inositol. When eggs are labelled to apparent isotopic equilibrium with either [3H]inositol or [3H]arachidonate, no early increase in [3H]PtdInsP2 occurs while PtdIns decreases slightly. On the contrary, when not labelled to isotopic equilibrium, all [3H]PPI increase during the first 15 seconds following fertilization. We find that, within seconds, fertilization triggers a 600-fold increase in the turnover of PPI, producing an amount of InsP3 apparently sufficient to trigger calcium release. We suggest that phosphoinositidase C and PtdInsP kinase, responsible respectively for the hydrolysis and synthesis of PtdInsP2, are both stimulated to a comparable degree in the first 30 seconds following fertilization and that net changes in the amount of PtdInsP2 at fertilization are very sensitive to the relative levels of activation of the two enzymes. Activating the eggs with the calcium ionophore A23187 showed that both these enzymes are sensitive to calcium, suggesting that calcium-dependent InsP3 production might play a role in the initiation and/or the propagation of the fertilization calcium wave.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Phosphatidylinositol 4-Kinase↗
PubMed1991

Effects of castration and androgen treatment on aromatase activity in the brain of mature male Atlantic salmon (Salmo salar L.) parr.

Brain homogenates from male Atlantic salmon parr aromatized tritiated androstenedione to estrogens. The aromatase activity in homogenates of whole brains from castrated male parr was lower than that in homogenates from sham-operated male parr in autumn. This was also found in homogenates of the telencephalon and diencephalon, but not in homogenates of the tectum opticum. Treatment of castrated males with testosterone (T) and 11-ketoandrostenedione (OA) increased the aromatase activity in whole brains. T, but not OA, also significantly increased aromatase activity in all brain parts. In spring, half a year after the peak breeding period, mature parr males had a lower aromatase activity in telencephalon, diencephalon and tectum than that found in castrated males in autumn, whereas immature males displayed an even lower level of activity.

Androgens↗
PubMedDate not supplied

Development of tyrosine hydroxylase-, dopamine- and dopamine beta-hydroxylase-immunoreactive neurons in a teleost, the three-spined stickleback.

The development of catecholaminergic neuronal systems in the brain of a teleost, the three-spined stickleback, was studied through embryonic to early larval stages by immunocytochemistry using specific antibodies against dopamine, tyrosine hydroxylase and dopamine beta-hydroxylase. By analysing the spatiotemporal patterns of development for the catecholaminergic nuclei, possible homologies with nuclei in amniote brains have been identified. The noradrenergic neurons in the isthmus region of the rostral rhombencephalon originate in the same manner as the A4-A7 + subcoeruleus group in mammals. Their developmental characteristics show the largest similarities with the subcoeruleus group of birds and mammals, although some features are shared with developing A6 (locus coeruleus) neurons. Catecholaminergic neurons never appear during development in the ventral mesencephalon of the three-spined stickleback. A group of large dopaminergic neurons that accompany the cerebrospinal fluid (CSF)-contacting neurons follows the border between the hypothalamus and the ventral thalamus into the caudal hypothalamus, where they are continuous with the dopaminergic neurons in the posterior tuberculum. They are thus topologically comparable with the dopaminergic neurons of the zona incerta in mammals. The dopaminergic CSF-contacting neurons that line the median, lateral and posterior recesses of the third ventricle do not contain tyrosine hydroxylase-immunoreactivity at any developmental stage. This indicates that they take up and accumulate exogenous dopamine or L-dihydroxyphenylalanine, and do not synthesize dopamine from tyrosine at any developmental stage. Tyrosine hydroxylase-immunoreactive neurons appear in the pineal organ on the day of hatching (120 h post-fertilization). They were still observed in 240-h-old larvae, but are absent in the pineal organ of adult sticklebacks. The initial appearance and subsequent differentiation of catecholaminergic neurons in the stickleback embryo follow essentially the same spatial and temporal pattern as in amphibian, avian and mammalian embryos. This observation supports the hypothesis that morphologically, topologically and chemically similar monoaminergic neurons in different vertebrate classes are homologous.

Animals↗