Attention and habituation: catecholamine interactions and sex differences

Norepinephrine (NE)-dopamine (DA) interactions in mediation of long-term habituation were tested using the stimulus-elicited investigation paradigm. Systemic injections of clonidine hydrochloride (CLON), an alpha-adrenergic receptor agonist, given before apomorphine (APO) (1 mg/kg SC), a DA receptor agonist, prevented APO-induced disruption of the duration measure of habituation 25-hr later. A lower dose was effective in female gerbils than that required for male gerbils, suggesting that females are more sensitive to the effects of clonidine. In addition, apomorphine, with or without CLON (0.01 mg/kg), increased locomotor activity in male gerbils but reduced activity in female gerbils. The same dose of CLON that prevented APO-induced disruption of 24-hr habituation did not reverse APO-induced reduction of investigation of an object or an odor, or APO-induced changes in activity. Neither CLON nor desmethylimipramine, a blocker of NE reuptake, had any selective effects on investigation of novel stimuli or short-term habituation showing that relative NE-DA activity can be disrupted without interfering with the behavior, However, CLON interfered with the frequency measure of long-term habituation in male gerbils but not in female gerbils at any dose used (0.0100.3 mg/kg). THe data suggest important sex dependent NE-DA interactions in mediation of long-term habituation.