Tonic immobility and the alpha-adrenergic system in chickens

Abstract

In two experiments, groups of 2 1 2 to 3 1 2 week old chickens were injected with various adrenergic agonists. The relatively low potency alpha agonists (methoxamine, phenylephrine) produced significant decreases in the duration of tonic immobility, while more potent alpha agonists (norepinephrine, methyldopa, clonidine, epinephrine) produced increases in the duration of immobility. Isoproterenol, a beta agonist, had no apparent effect on immobility. These results clearly support the involvement of the alpha-adrenergic system with the immobility response and are discussed in terms of the importance of the adrenergic system for other predator responses such as fight or flight, and the possible differential relations of tonic immobility to alpha 1 and alpha 2 receptors.