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      Estrogen and Laryngeal Synaptic Strength in Xenopus laevis: Opposite Effects of Acute and Chronic Exposure

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          Synaptic transmission at the vocal synapse, the laryngeal neuromuscular junction, of Xenopus laevis has been shown to be regulated by long-term changes in circulating estrogen. In females, high levels of circulating estrogen also accompany gonadotropin-induced ovulation and oviposition and the switch from sexually unreceptive to receptive states, including changes in vocal behaviors (ticking to rapping). Here we examine the effects of gonadotropin injection on laryngeal synaptic strength and call type. Gonadotropin acutely reduced quantal content values of laryngeal synapses in intact, adult females; the lowest values were attained by 12 h post-injection. Estrogen and progesterone levels increased following human chorionic gonadotropin (hCG) injection; the time course was similar to, but negatively correlated with, changes in synaptic strength. In ovariectomized frogs, exogenous estrogen, but not progesterone or hCG, mimicked the acute effects of hCG in weakening laryngeal synapses of intact frogs. hCG injection suppressed ticking and sometimes induced rapping. Females could tick with either strong or weakened laryngeal synapses while rapping was only produced during the weakening action of hCG. The normally strong synapses of females may enable vocal production even when laryngeal synapses are weakened by hormones that induce ovulation. In contrast to the acute effect of estrogen on weakening laryngeal synapses, juveniles required more than 2 weeks of estrogen treatment to strengthen laryngeal synapses while at least 4 weeks postovariectomy were required to weaken synapses in adult females. We conclude that acute (hours) increases in circulating levels of estrogen weaken synapses while chronic (weeks) increases strengthen laryngeal synapses.

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          Most cited references 7

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          Yeast homologue of neuronal frequenin is a regulator of phosphatidylinositol-4-OH kinase.

          In metazoans, certain calmodulin-related calcium-binding proteins (recoverins, neurocalcins and frequenins) are found at highest levels in excitable cells, but their physiological roles are largely uncharacterized. Here we show that Saccharomyces cerevisiae contains a frequenin homologue, Frq1, and that its target is Pik1, a phosphatidylinositol-4-OH kinase. Frq1 binds to a conserved sequence motif in Pik1 outside Pik1's catalytic domain and stimulates its activity in vitro. N-myristoylated Frq1 may also assist in Pik1 localization.
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            Acute Activation of Maxi-K Channels (hSlo) by Estradiol Binding to the Subunit

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              • Abstract: not found
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              Rapping, a female receptive call, initiates male-female duets in the South African clawed frog


                Author and article information

                S. Karger AG
                July 2001
                06 July 2001
                : 74
                : 1
                : 22-32
                Department of Biological Sciences, Columbia University, New York, N.Y., USA
                54667 Neuroendocrinology 2001;74:22–32
                © 2001 S. Karger AG, Basel

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                Page count
                Figures: 7, References: 31, Pages: 11
                Reproductive Neuroendocrinology


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