Electrophysiological properties of single units in dopamine-rich mesencephalic transplants in rat brain.

Electrophysiological recordings were made from grafts of embryonic ventral mesencephalon transplanted into the neocortex, overlying the host neostriatum of rats in which the intrinsic striatal dopamine (DA) innervation had been removed by a unilateral 6-hydroxydopamine (6-OHDA) lesion. Whereas all rats had surviving grafts, half of the rats showed recovery from amphetamine-induced rotational asymmetry induced by the 6-OHDA lesions ('compensation'), indicating a functional dopaminergic reinnervation of the host striatum by the graft. The electrophysiological recordings revealed: neurons within all grafts which could be antidromically activated from host striatum, and which had faster conduction velocities and narrower action potentials than is characteristic of DA neurons in the intact substantia nigra, neurons only within the grafts of compensated rats which had properties characteristic of normal nigral DA neurons, and neurons within the grafts which responded to stimulation of the frontal cortex and lower brainstem of the host. The data support the view that the grafts can establish physiologically functional afferent and efferent connections with the host brain.