Figure 2

Effects of amphetamine on locomotor activity and mu receptor activity in the nucleus accumbens. (A) When challenged with amphetamine, rats pretreated with repeated administration of saline solution (SA) or amphetamine (AA) had higher locomotor responses than rats pretreated and challenged with saline solution (SS). Locomotor activity is expressed in arbitrary units. (B) As assessed immediately after being challenged with amphetamine, rats pretreated with repeated injection of saline solution (SA) or amphetamine (AA) had higher mu receptor activity in the nucleus accumbens than rats pretreated and challenged with saline solution (SS). The ratio of the dissociation constant (Kd) to the maximal number of binding sites (Bmax) was calculated to assess the activity of mu receptors in the nucleus accumbens; mu receptor activity in controls rats pretreated and challenged with amphetamine was taken as a 100 % value. SS: pretreatment with saline + challenge with saline; SA: pretreatment with saline + challenge with amphetamine; AA: pretreatment with amphetamine + challenge with amphetamine. * P < 0.001 vs SS + Air; ^#P < 0.001 vs SA + Air.