THE EXISTENCE of intralamino-striatal fibers, previously suggested by different workers,1-3 has been more firmly established by recent studies involving both morphological4-6 and electrophysiological7 criteria. The fact that the electrical stimulation of nucleus centrum medianum (CM) induces the release of minute amounts of dopamine from the caudate nucleus led to the suggestion that the intralamino-striatal fibers are dopaminergic.8 This hypothesis is supported by the fact that the inhibition of unit activity in the caudate nucleus produced by electrical stimulation of nucleus centrum medianum is similar to the inhibitory effect obtained by applying dopamine on the surface of the caudate nucleus.9 On the other hand, it has been shown that lesions of the ventromedial tegmental area of the midbrain are associated with an almost complete depletion of dopamine and serotonin in the corresponding striatum in the monkey10 and the cat.11 Therefore it was considered