Date

December 2009

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Behavioral Neuroscience

Institution

Oregon Health & Science University

Abstract

The alcohol (Ethanol; EtOH) withdrawal syndrome is a hallmark of EtOH dependence, and withdrawal avoidance is one reason that alcoholics relapse. Elucidating the mechanisms underlying EtOH withdrawal may result in improved pharmacotherapy for EtOH dependence. One neural substrate underlying the acute and chronic effects of EtOH is the γ-aminobutyric acidA (GABAA) receptor system. Neuroactive steroids (NAS) are potent allosteric agonists at GABAA receptors, and previous work has indicated that a single, acute administration of EtOH increased levels of NAS and that these levels were decreased during EtOH withdrawal. However, the contribution of NAS to the symptoms of EtOH withdrawal is not known. The main purpose of this dissertation was to elucidate the contributions of endogenous GABAergic NAS to the expression of the acute EtOH withdrawal profile in male and female mice. To accomplish this, the peripheral sources of NAS were removed (through adrenalectomy, ADX; gonadectomy, GDX; and ADX/GDX surgery) in both male and female DBA/2J (D2) and C57BL/6J (B6) mice. Rebound hyperactivity after a 4 g/kg dose of EtOH was measured with handling-induced convulsions (HICs) versus animals with SHAM surgery. I predicted that ADX/GDX surgery would increase the severity of neuronal rebound hyperactivity versus SHAM surgery, indicating that an endogenous anticonvulsant NAS was an important modulator of the neural rebound hyperactivity seen during EtOH withdrawal in intact animals. Acute EtOH withdrawal was increased in male D2 and B6 that had undergone ADX or ADX/GDX surgery and in female D2 mice following ADX/GDX, when compared to respective SHAM mice. In contrast, surgical status did not alter EtOH withdrawal severity in female B6 mice. These results suggested that progesterone (PROG) or deoxycorticosterone (DOC), but not a testosterone derived NAS, was involved in modulating acute EtOH withdrawal severity. In order to further examine the contributions of NAS to acute EtOH withdrawal severity, male and female D2 mice underwent ADX/GDX or SHAM surgery. After recovery, separate groups of animals were administered steroids in the NAS biosynthetic pathway or steroids plus the 5α-reductase inhibitor finasteride (FIN). HICs were the index of withdrawal severity after a 4 g/kg dose of EtOH. The results indicate that replacement with PROG and DOC restored the withdrawal profile in ADX/GDX animals to SHAM levels, and that this effect was blocked with co-administration of FIN. These findings indicate that the increase in acute withdrawal severity after ADX/GDX may be due to the loss of GABAergic NAS, providing insight into the contribution of endogenous GABAergic NAS to EtOH withdrawal severity. A final experiment attempted to elucidate a mechanism for the effect of ADX/GDX and steroid replacement on acute EtOH withdrawal severity. I measured the expression of eight GABAA receptor subunits and steroidogenic acute regulatory (StAR) protein in the hippocampus of the animals just described using quantitative Real-Time reverse transcriptase polymerase chain reaction. It was found that expression of the GABAA receptor α1 subunit in male and female ADX/GDX mice was decreased in all groups that had received pretreatments that did not restore the withdrawal profile to that in intact animals. A similar finding was revealed in ADX/GDX female mice when expression of StAR protein mRNA was analyzed. These results suggest that expression levels of the GABAA receptor α1 subunit and StAR protein may be important in modulating some of the effects seen during acute EtOH withdrawal.

Identifier

doi:10.6083/M4057CWD

School

School of Medicine

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