The effect of chronic administration and withdrawal of amphetamine on cerebral dopamine receptor sensitivity

Mice with a 6-hydroxydopamine induced unilateral nigro-striatal lesion received (+)-amphetamine sulphate (2.5-20 mg/kg) over a 3-month period by daily incorporation into the drinking water. Druing this period the circling response to apomorphine hydrochloride (0.01-0.5 mg/kg, s.c.) was increasingly suppressed in comparison to control animals, while spontaneous locomotor activity increased. Following drug withdrawal the circling response to apomorphine remained suppressed two months later. However, spontaneous locomotor activity was also reduced up to 1 month following drug removal. The dopamine content of the lesioned side of the forebrain was 25% of the intact side in control animals and was not further reduced by amphetamine administration. The dopamine content of the intact forebrain was reduced by 43% during amphetamine administration and remained 18% depressed 1 month following drug withdrawal. No changes in 5-hydroxytryptamine or noradrenaline concentrations were observed in either the intact or lesioned side. This data, while showing that chronic amphetamine treatment can induce persistent changes in dopamine receptor sensitivity, can be interpreted in terms of increased striatal receptor sensitivity or as a decreased response of dopamine receptors in the nucleus accumbens.