SEX DIFFERENCES IN THE EFFECT OF ETHANOL INJECTION AND
CONSUMPTION ON BRAIN ALLOPREGNANOLONE LEVELS IN
C57BL/6 MICE
D. A. FINN,
a,b,c
* R. S. SINNOTT,
a1
M. M. FORD,
a
S. L. LONG,
a
M. A. TANCHUCK
a
AND
T. J. PHILLIPS
a,b,c
a
Department of Behavioral Neuroscience, Oregon Health & Science
University, Portland, OR 97239, USA
b
Portland Alcohol Research Center, Portland, OR, USA
c
Department of Veterans Affairs Medical Center, 3710 SW U.S. Vet-
erans Hospital Road, Portland, OR 97239, USA
Abstract—The pharmacological profile of allopregnanolone,
a neuroactive steroid that is a potent positive modulator of
-aminobutyric acid
A
(GABA
A
) receptors, is similar to that of
ethanol. Recent findings indicate that acute injection of eth-
anol increased endogenous allopregnanolone to pharmaco-
logically relevant concentrations in male rats. However, there
are no comparable data in mice, nor has the effect of ethanol
drinking on endogenous allopregnanolone levels been inves-
tigated. Therefore, the present studies measured the effect of
ethanol drinking and injection on allopregnanolone levels in
male and female C57BL/6 mice. One group was given 17 days
of 2-h limited access to a 10% v/v ethanol solution in a
preference-drinking paradigm, while another group had ac-
cess to water only. The ethanol dose consumed in 2 h ex-
ceeded 2 g/kg. Then, separate groups of mice were injected
with either 2 g/kg ethanol or saline. Mice were killed 30 min
after the 2-h drinking session or injection. Blood ethanol
concentration was significantly higher in the ethanol-injected
versus ethanol-drinking groups, even though the dose was
similar. Consumption of ethanol significantly increased brain
allopregnanolone levels in male but not female mice, com-
pared with animals drinking water, but did not alter plasma
corticosterone levels. In contrast, injection of ethanol did not
significantly alter brain allopregnanolone levels in male or
female mice and only significantly increased plasma cortico-
sterone levels in the male mice, when compared with saline-
injected animals.
The sex differences in the effect of ethanol administration
on endogenous allopregnanolone levels suggest that the
hormonal milieu may impact ethanol’s effect on GABAergic
neurosteroids. Importantly, these data are the first to report
the effect of ethanol drinking on allopregnanolone levels and
indicate that ethanol consumption and ethanol injection can
produce physiologically relevant allopregnanolone levels in
male mice. These results have important implications for
studies investigating the potential role of endogenous allo-
pregnanolone levels in modulating susceptibility to ethanol
abuse. © 2004 IBRO. Published by Elsevier Ltd. All rights
reserved.
Key words: neurosteroid, alcohol drinking, alcohol injection,
male, female, corticosterone.
Rapid membrane effects of steroid hormones provide a
mechanism by which steroids can influence brain function
and behavior, in addition to their classical genomic actions.
Within the last 20 years, some of these rapid non-genomic
actions of steroid hormones have been demonstrated to
occur via an interaction with ligand-gated ion channels,
such as the -aminobutyric acid
A
(GABA
A
) receptor (see
review by Brann et al., 1995). For example, the progester-
one derivative allopregnanolone (ALLOP, 3-hydroxy-5-
pregnan-20-one) is a very potent positive modulator of
GABA
A
receptors, and exogenous administration pro-
duces anxiolytic, sedative, anticonvulsant and locomotor
stimulant effects in animals (for reviews, see Paul and
Purdy, 1992; Lambert et al., 1995; Gasior et al., 1999). It
has also been demonstrated that stress, estrous cycle and
pregnancy can increase endogenous ALLOP to levels that
are physiologically relevant (see Paul and Purdy, 1992;
Barbaccia et al., 1994, 1996; Concas et al., 1998). These
findings suggest that fluctuations in endogenous levels of
a neuroactive steroid such as ALLOP could modify the
functioning of central GABA
A
receptors in vivo. Therefore,
ALLOP may represent a physiologically significant neuro-
modulator.
The pharmacological profile of ALLOP is similar to that
of ethanol (EtOH). While the effects of ALLOP appear to be
primarily mediated via its interaction with GABA
A
recep-
tors, EtOH interacts with multiple receptor systems, with
one effect being to potentiate GABA
A
receptor function
(see review by Grobin et al., 1998; Morrow et al., 2001). It
has been suggested that certain behavioral effects of
EtOH and neuroactive steroids may share a GABAergic
mechanism (Grobin et al., 1998; Morrow et al., 2001).
Recent findings indicate that acute administration of AL-
LOP increased EtOH-reinforced operant responding and
established EtOH drinking behavior in male rodents (Janak
et al., 1998; Morrow et al., 2001; Sinnott et al., 2002).
Sensitivity to the modulatory effect of ALLOP on EtOH
drinking behavior in male rodents differed, depending on
the concentration of the EtOH solution (Sinnott et al., 2002)
and whether or not the animals were physically dependent
(Morrow et al., 2001), suggesting that increases or de-
1
Present address: CROET (L-606), Oregon Health & Science Univer-
sity, Portland, OR 97239, USA.
*Correspondence to: D. A. Finn, Department of Veterans Affairs Med-
ical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR
97239, USA. Tel: +1-503-721-7984; fax: +1-503-273-5351.
E-mail address: finnd@ohsu.edu (D. A. Finn).
Abbreviations: ALLOP, allopregnanolone (3-hydroxy-5-pregnan-
20-one); B6, C57BL/6; BEC, blood ethanol concentration; CORT,
corticosterone; EtOH, ethanol; GABA
A
, -aminobutyric acid
A
; HPA,
hypothalamic–pituitary–adrenal; RIA, radioimmunoassay.
Neuroscience 123 (2004) 813– 819
0306-4522/04$30.00+0.00 © 2004 IBRO. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.neuroscience.2003.11.017
813