Selected line difference in sensitivity to a GABAergic neurosteroid during ethanol withdrawal

Abstract

The neurosteroid allopregnanolone (ALLO) is a potent positive modulator of g -aminobutyric acid A (GABA A ) receptors. Earlier work indicates that sensitivity to the anticonvulsant effect of ALLO was enhanced during ethanol (EtOH) withdrawal in rats and in C57BL/6 mice, an inbred strain with mild EtOH withdrawal. In contrast, ALLO sensitivity was reduced during EtOH withdrawal in DBA/2 mice, an inbred strain with severe EtOH withdrawal. Thus, the present studies examined ALLO sensitivity during EtOH withdrawal in another animal model of EtOH withdrawal severity, the Withdrawal SeizureProne (WSP) and Withdrawal Seizure-Resistant (WSR) selected lines. Male mice were exposed to EtOH vapor or air for 72 h. During peak withdrawal, animals were injected with ALLO [0, 3.2, 5, 10 or 17 mg/kg, intraperitoneally (i.p.)] and tested for their sensitivity to the anticonvulsant effect. In separate studies, potentiation of GABA-stimulated chloride uptake by ALLO (10 nM to 10 mM) was assessed in microsacs prepared from mouse brain mice during peak withdrawal. Notably, WSP mice were cross-tolerant to the anticonvulsant effect of ALLO during EtOH withdrawal (i.e. significant decrease in the efficacy of ALLO) when compared with values in airexposed mice. In contrast, sensitivity to the anticonvulsant effect of ALLO was unchanged during EtOH withdrawal in the WSR line. Functional sensitivity of GABA A receptors to ALLO was significantly decreased during EtOH withdrawal in WSP mice in a manner consistent with the change in behavioral sensitivity to ALLO. These findings suggest that mice selectively bred for differences in EtOH withdrawal severity are differentially sensitive to ALLO during EtOH withdrawal.

Decreased anticonvulsant efficacy of allopregnanolone during ethanol withdrawal in female Withdrawal Seizure-Prone vs. Withdrawal Seizure-Resistant mice

“…However, based on our a priori hypothesis that WSP and WSR mice would be differentially sensitive to ALLO during ethanol withdrawal (from results in male WSP and WSR mice; Finn et al, 2006), simple main effects analyses followed by Tukey's or Dunnett's post hoc tests also were conducted to examine significant treatment and steroid effects within each selected line. Pearson product-moment correlation coefficients were calculated to examine the relationship between progesterone, estradiol and corticosterone levels and each convulsion endpoint.…”

“…Details are provided in Finn and Crabbe (1999) and Finn et al (2006). Briefly, the ethanol-exposed animals were weighed and injected with a loading dose of ethanol (20% w/v, 1.5 g/kg; Pharmco Products, Brookfield, CT) and pyrazole hydrochloride (pyrazole; 68.1 mg/kg; Sigma Chemical Company, St. Louis, MO), an alcohol dehydrogenase inhibitor used to stabilize blood ethanol concentrations (BECs), prior to ethanol vapor exposure (8-10 mg ethanol/L air) inside inhalation chambers for 72 hrs.…”

“…The supernatant, obtained from processing the blood sample (see Finn et al, 2006), was transferred to a crimp top glass vial and analyzed by gas chromatography (Model 6890N, Agilent Technologies, Palo Alto, CA) with flame ionization detection. Seven pairs of ethanol standards (0.25 -4.0 mg/mL) were used to establish a standard curve.…”

“…The apparatus and procedure for timed tail vein infusion of PTZ have been described in detail (Finn and Crabbe, 1999;Finn et al, 2000Finn et al, , 2006. Briefly, mice were hand-held in a large Plexiglas container, a 27 gauge butterfly needle (Abbott Laboratories, North Chicago, IL) was inserted into a lateral vein, and PTZ was delivered at a rate of 2.5 mg/min (5.0 mg/mL in saline, 0.5 mL/min infusion rate) by one of two syringe pumps (Kd Scientific, Holliston, MA, Model 100; Sage Instruments, Freedom, CA, Model 355).…”

“…This observation is consistent with the finding that manipulation of endogenous ALLO levels produced the predicted change in GABA A receptor mediated inhibition (Belelli & Herd, 2003). However, with regard to ALLO sensitivity, the change in sensitivity to the anticonvulsant effect of alphaxalone or ALLO during ethanol withdrawal was enhanced in rats Devaud et al, 1996) and C57BL/6 mice that exhibit mild withdrawal (Finn et al, 2000) but was reduced in mouse genotypes with severe withdrawal (DBA/2 and WSP; Finn et al, 2000Finn et al, , 2006. Thus, the results in seizure-prone mouse genotypes during ethanol withdrawal suggest that a reduction in ALLO to levels that could decrease GABAergic inhibition in vivo, in conjunction with decreased sensitivity of GABA A receptors to ALLO, may contribute to their increased withdrawal severity (discussed in Finn et al, 2004a).…”