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Dopaminergic substrates of reward in the caudate-putamen of the rat Carter, David Alexander


An extensive mapping of the caudate-putamen in the rat for intracranial self-stimulation (ICS) sites »as undertaken to provide additional support for the role of dopamine in brain stimulation reward. Eighty-seven percent of the placements in the neostriatum supported ICS, with self-stimulation rates greater than 250/15 min at 56% of the sites. In a second experiment, animals were prepared with electrodes aimed at the lateral caudate-putamen. Those subjects displaying ICS subsequently received 6-hydroxydopamine lesions to the dopamine cell bodies in the substantia nigra pars compacta either ipsilateral or contralateral to the electrode. The destruction of the dopamine cell bodies attenuated ICS in both groups during the first post-lesion test sessions. However, the rates in the ipsilateral group declined to between 2-9% of control scores, whereas the rates in the contralateral group improved over testing to 72% of control values, 28 days after the lesion. On the basis of these data, it was concluded that unilateral destruction of the dopaminergic nigro-neostriatal (NSB) has two effects on ICS behaviour. First, unilateral reduction of neostriatal dopamine is accompanied by a loss of brain stimulation reward at sites normally innervated by the NSB, specifically the caudate-putamen. Secondly, lesions of the NSB produce a general disruption in bar pressing behaviour, as evidenced by the attenuation of ICS following contralateral lesions. The possible role of the NSB in natural reward is discussed.

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