Morphine dependence in rats with medial forebrain bundle lesions

Rats with posterior medial forebrain bundle (PMFB) lesions and control rats were administered morphine chronically for 4 or 5 days via implanted subcutaneous silicone reservoirs. Following cessation of morphine administration after five days, PMFB rats showed less withdrawal-induced weight loss than control rats. Other PMFB and control rats were subjected to forced drinking of morphine solution for 9 days. PMFB rats consumed the morphine solution much more readliy than control rats, whereas intake of a quinine solution was similar in two other PMFB and control groups. These results suggest that the addictive and dependence properties of morphine may have separate mechanisms and based on previously reported neurochemical effects of PMFB lesions, that biogenic amines may be differentially involved in such mechanisms.