Biphasic effects of clonidine on conflict behavior: involvement of different alpha-adrenoceptors.
The effect of the alpha-2-adrenoceptor agonist clonidine on anxiety-related behavior was investigated using two different rat anxiety models: a modified Vogel's drinking conflict model and Montgomery's elevated plus-maze. In both models biphasic dose-response curves were obtained; in a narrow low-dose range (6.25-10.0 micrograms/kg) the drug produced anxiolytic-like effects, while anxiogenic-like properties were found after higher doses (12.5-80.0 micrograms/kg). Attempts to block the effects obtained were made in Montgomery's elevated plus-maze. The specific alpha-2-adrenoceptor antagonist idazoxan blocked the anxiolytic-like effect but did not influence the anxiogenic-like activity. Conversely, the specific alpha-1-adrenoceptor antagonist prazosin blocked the anxiogenic-like effect but did not alter the anxiolytic-like activity. These findings may suggest that alpha-1- and alpha-2-adrenergic receptor mechanisms are reciprocally involved in anxiety-related behavior.
Söderpalm
B
B
Department of Pharmacology, University of Göteborg, Sweden.
Engel
J A
JA
D000818:Animals; D001007:Anxiety; D003000:Clonidine / Q000494:pharmacology*; D003220:Conflict, Psychological; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*
D011942:Receptors, Adrenergic, alpha; D003000:Clonidine