A lpha2 adrenergic agonists are used in the anesthetic management of the surgical patient for their sedative/hypnotic properties although the alpha2 adrenoceptor subtype responsible for these anesthetic effects is not known. Using a gene-targeting strategy, it is possible to specifically reduce the expression of the individual adrenoceptors expressed in the central nervous system and to thereby determine their role in hypnotic action. Stably transfected cell lines (PC 124D for rat alpha2A; NIH3T3 for rat alpha2C adrenoceptors) were exposed to 5 microM antisense oligodeoxynucleotides (ODNs) for alpha2A and alpha2C adrenergic receptor subtypes for 3 d. Individual receptor subtype expression, as determined by radiolabeled ligand binding, was selectively decreased only by the appropriate antisense ODNs and not by the "scrambled" ODNs. These antisense ODNs were then administered three times, on alternate days, into the locus coeruleus of chronically cannulated rats and their hypnotic response to dexmedetomidine (an alpha2 agonist) was determined. Only the alpha2A antisense ODNs significantly change the hypnotic response causing both an increase in latency to, and a decrease in duration of, the loss of righting reflex following dexmedetomidine; hypnotic response had normalized 8 d after stopping the ODNs. Therefore, the alpha2A adrenoceptor subtype is responsible for the hypnotic response to dexmedetomidine in the locus coeruleus of the rat.