The possible participation of a dopaminergic system in mutilating behavior in rats with forelimb deafferentation

Partial rhizotomy (section of dorsal roots C5 to Th 1 included) leads to abnormal mutilating behavior in the rat, presumably due to pain sensation in the deafferented limb. As dopamine (DA) has been shown to play a role in analgesia, destruction and stimulation of the ventral tegmental area (VTA) were used to check whether they induced an increase or a decrease in the mutilating behavior respectively. Destruction of DA neurons located in the VTA was performed by local administration of 6-hydroxydopamine whereas activation was achieved either by imposed electrical stimulation or by chronic oral administration of D-amphetamine sulfate. These 3 treatments accelerated the onset of the mutilating behavior and induced an extension of the mutilating wounds, D-amphetamine sulfate producing the most pronounced acceleration in their development. The results obtained after destruction of DA-VTA neurons fit well with the working hypothesis. The increase of the mutilating behavior rather than a decrease subsequent to the other treatments could have been caused by the hyperactivity and increase of chewing behavior induced by the less specific stimulating techniques.