Volume 17, Number 22,
Issue of November 15, 1997
pp. 8856-8866
An Initial, Three-Day-Long Treatment with Alcohol Induces a
Long-Lasting Phenomenon of Selective Tolerance in the Activity of the
Rat Hypothalamic-Pituitary-Adrenal Axis
Received June 2, 1997; revised Aug. 26, 1997; accepted Aug. 27, 1997.
Soon Lee and
Catherine Rivier
The Clayton Foundation Laboratories for Peptide Biology, The Salk
Institute, La Jolla, California 92037
We determined whether an initial alcohol challenge induced
long-lasting changes in the activity of the
hypothalamic-pituitary-adrenal (HPA) axis. Adult male rats received
intragastric injections of the vehicle or a moderately intoxicating
dose of alcohol (3.0 gm/kg) daily for 3 d. When animals were
acutely challenged with alcohol 3-12 d later, their ACTH and
corticosterone responses were significantly blunted, compared with that
of vehicle-pretreated rats. In contrast, exposure to mild electric foot
shocks induced a pattern of ACTH secretion that was comparable in
animals administered alcohol or the vehicle previously, indicating a
lack of cross-tolerance. No significant differences were observed in
pituitary responsiveness to corticotropin-releasing factor or
vasopressin in rats pretreated with the vehicle or alcohol. The
influence of the initial drug treatment was not mimicked by exposure to
foot shocks, nor was it prevented by administering a potent
corticotropin-releasing factor antagonist to block the elevations in
plasma ACTH and corticosterone induced by this initial treatment.
Finally, we found that rats injected initially with the vehicle and
challenged subsequently with alcohol exhibited the expected increased
neuronal activation (measured by the upregulation of steady-state mRNA
and protein levels of immediate early genes) in the paraventricular
nucleus of their hypothalamus. In contrast, this response was markedly decreased in animals exposed previously to the drug.
To our knowledge, this is the first report that exposure to a stress
(i.e., alcohol), although not immediately altering the response of the
HPA axis to this particular signal, induces a selective tolerance that
is both slow to develop and long-lasting. The primary mechanism
mediating the ability of an initial drug treatment to decrease
subsequent responses of the HPA axis to a second drug challenge seems
to be the inability of hypothalamic neurons to respond adequately to
this second challenge.
Key words:
alcohol;
ACTH;
corticosterone;
c-fos;
NGFI-B;
PVN;
rat