Binge alcohol exposure distorts the formation and regulation of immature GABAergic synapses in medial septum/diagonal band of broca : a dissertation /
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| Format: | Thesis Book |
| Language: | English |
| Published: |
[College Station, Tex.] :
[Texas A&M University System Health Science Center],
[2008]
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| Subjects: |
| Abstract: | ABSTRACT: Septal neurons isolated from rat pups on embryonic day (ED) 20 undergo synaptogenesis and show time-dependent maturation of synaptic GABA[subscriptA] receptors (GABA[subscriptA]R[subscriptS] in primary cell cultures over days in vitro (DIV) 1-30. This maturation is characterized, in whole cell recordings, by increased frequency, an accelerated rate of decay and enhanced zolpidem potentiation of GABAergic miniature postsynaptic currents (mPSCs) (Dubois D.W. et al., 2004, 2006). The maturation of GABA synapses in this in vitro model is disrupted by an exposure to ethanol that mimics binge-like ethanol exposure in vivo on postnatal day (PD) 4-9, which models binge drinking during a period of brain development in human third trimester, would cause injury to developing GABA synapses in the medial septum/diagonal band (MS/DB). MS/DB neurons displayed a parallel age-dependent acceleration of GABA MPSC kinetics in acute cut brain slices studies over PD 4-16. This maturation pattern continued until late in the first postnatal month (PD 25) when kinetic parameters stabilized through early adulthood (PD 60-120). This maturational pattern was similar for male and female rats. Zolpidem (0.03-100[micromolar]M) caused an increasing age-dependent prolongation to GABA mPSC decay during PD 4-16, which paralleled an increase [alpha] 1 protein level in MS/DB tissue between ED 20 and adulthood. Chronic binge-like ethanol exposure during PD 4-9 blunted GABAergic mPSC maturation of MS/DB neurons in slices prepared on PD 11-16, significantly decreased frequency, amplitude and substantially slowed decay. Zolpidem potentiation of mPSC decay was strikingly attenuated after ethanol binge exposure. These changes were accompanied by up-regulation of GABA[subscript capital A]R [alpha]4 subunit protein expression in the MS/DB and a higihly exaggerated potentiation of GABA MPSC decay kinetics by allopregnanolone (Allo) (0.03-1 [micromolar]M). GABA synaptic distortions including attenuated zolpidem sensitivity and enhanced Allo sensitivity ware partially prevented when binge-like ethanol exposure was combined with a co-treatment of finasteride 100mg/kg/day, a 5[alpha]-reductase inhibitor that blocks endogenous Allo sysnthesis. Overall, these ethanol-induced changes in MS/DB neurons were quite similar to earlier findings in primary septal neurons exposed to ethanol. Additional studies further characterized maturation of GABA synapses and ethanol induced synaptic injury in MS/DB neurons. Acute application of finasteride directly to brain slices during PD 4-16 did not change GABA mPSC decay, suggesting a lack of local neurosteroid tone early in synaptic development. L655,708 (100[micromolar]M), an [alpha]5 subunit selective allosteric inhibitor, significantly modified GABA mPSC kinetics across PD 4-9, in control and binge ethanol exposed groups, suggesting changes in receptors containing [alpha]5 subunit may have occurred during maturation or ethanol injury. In an effort to determine whether GABA[subscript capital A]Rs containing [alpha]4 subunits played a role in synaptic maturation and/or ethanol induced injury, the antagonist furosemide, and the allosteric modulators RO15-4513 and bretazenil were tested on MS/DB neurons. The results suggested that [alpha]4 subunits were unlikely to be important in PD 4-9 untreated synapses but might play an enhanced role in Control synapse by PD 11-16 and likely participate to an even greater extent after ethanol injury. Finally, a role for [alpha]2/3 subunit containing GABA[subscript capital A]Rs was tested with allosteric modulator, SB 205348. Results suggested a role for [alpha]2/3 receptors in immature synapses on PD 4-9, which decresed with maturation, but which was exaggerated after ethanol injury. In summary, these results showed that synaptogenesis and synaptic maturation in MS/DB neurons acutely prepared brain slices progress in a manner remarkably similar to that described previously for septal cells in primary cultures. In addition, this work shows that signs of the ethanol injury to GABA synapses are equivalent in males and females, and that the damage can persist well into adulthood. Furthermore, this work suggests that ethanol likely disrupts normal maturation of GABA synpses in part by changing the expected complement of postsynaptic GABA[subscript capital A]Rs. Together these results lead to the conclusion that long lasting synaptic dysfunction occurs in response to an ethanol-induced distortion in developing GABAergic circuits and that this injury could contribute to cognitive deficits identified in fetal alcohol spectrum disorders. |
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| Item Description: | Vita. "Major Subject: Medical Sciences". "Submitted to the Office of Research and Graduate Studies of The Texas A&M University System Health Science Center in partial fulfillment for the requirements for the degree of Doctor of Philosophy December 2008." Approved as to style and content by: Gerald D. Frye, William H. Griffith II, Ursula H. Winzer-Serhan, Farida Sohrabji, Hilliam H. Griffith III. |
| Physical Description: | xvi, 196 leaves : illustrations ; 28 cm. |
| Bibliography: | Includes bibliographical references (leaves 154-193). |