Grafts to embryonic rat striatal tissue placed into the striatum of adult rats will be studied using anatomical and neurophysiological methods. The goal of these studies is to determine the extent to which the grafted neurons posses the characteristic phenotypic features of striatal neurons, and whether they resemble mature or immature striatal cells. Neurons in the graft will be identified as located in one of two major tissue compartments that are known to form there, called P and NP. Dopamine-innervated neurons of the P region will be identified by their projections to globus pallidus and/or cytochemical identification of the dopaminergic fibers. Morphological studies will employ intracellular staining of P and NP cells to determine whether these neurons show the characteristics morphological features of adult or immature striatal neurons, whether they have dendritic or axonal projects into the other tissue compartments, and whether these are related to the presence of axonal projections to the globus pallidus. Neurophysiological studies will concentrate on the characteristic set of ion conductances of striatal neurons. Developmentally-regulated ion channels, including a group responsible for transient potassium conductances (A-channels), inwardly-rectifying potassium conductances, and both high and low- threshold calcium conductances will have the highest priority. These conductances, as well as helping to specify the functional properties of the graft neurons, can also be used to access the maturational state of the cells in the grafts. Ionic conductances will be assessed using whole-cell voltage clamp recordings using acutely dissociated striatal graft neurons. The function of these channels will be confirmed using conventional intracellular recording in slices from striatal grafts. Neurons identified as P or NP cells based upon their projects to the globus pallidus will also be studied using single-cell mRNA amplification methods to determine the presence of specific ion channel mRNAs related to the neurophysiological experiments and to allow comparison of the constellation of cell-type specific mRNAs expressed in normal adult, immature, and grafted striatal projection neurons.
