Evidence suggests that noradrenergic signaling may play a role in mediating alcohol-drinking behavior in both rodents and humans. We have investigated this possibility by administering
clonidine to alcohol-drinking rats selectively bred for alcohol preference (P line).
Clonidine is an α2-adrenergic receptor agonist which, at low doses, inhibits noradrenergic signaling by decreasing
norepinephrine release from presynaptic noradrenergic neurons. Adult male P rats were given 24 h access to food and water and scheduled access to a 15% (v/v) alcohol
solution for 2 h daily. Rats received intra-peritoneal (IP)
injections with
clonidine (0, 10, 20, 40, or 80 μg/kg
body weight [
BW], 10-11 rats/treatment group) once/day at 30 min prior to onset of the daily 2 h alcohol access period for 2 consecutive days.
Clonidine, in doses of 40 or 80 μg/kg BW, significantly reduced alcohol intake on both days of treatment (p<0.001). Two weeks later, rats were treated with
clonidine for 5 consecutive days and
clonidine, in doses of 40 or 80 μg/kg BW, reduced alcohol intake on all 5 treatment days (p < 0.001).
Clonidine did not alter water consumption during the daily 2 h free-choice between alcohol and water. In a separate group of male P rats,
clonidine (40 μg/kg BW) suppressed intake of a
saccharin solution (0.04 g/L). These results are consistent with and
complement our previous findings that the α1-adrenergic receptor antagonist,
prazosin, decreases voluntary alcohol drinking in alcohol-preferring rats, but suggests that effects of
clonidine may not be specific for alcohol. The results suggest that although activation of the noradrenergic system plays an important role in mediating voluntary alcohol drinking, care is needed in selecting which drugs to use to suppress central noradrenergic signaling in order to maximize the selectivity of the drugs for treating
alcohol-use disorders.