Opiate and alpha 1-adrenergic receptors in mice responding to morphine with sedation or with running fit.

Two subpopulations of Albino Swiss mice were selected on the basis of their response to a dose of 20 mg/kg ip of morphine: individuals in which the drug constantly produced sedation, and those which responded with running fit. Both subpopulations of mice had cerebral opiate delta and mu receptors (defined as [3H]DADLE and [3H]naloxone binding sites) of similar Bmax and KD values but mice responding with sedation showed lower density of alpha 1-adrenoceptors (defined as [3H]prazosin binding sites) as compared both with mice reacting with running fit or randomly selected animals. Chronic administration of imipramine resulted in a significant increase in the density of [3H]prazosin binding sites in the mice responding with sedation, but not in the animals responding with running fit.