Laboratories, West Grove, PA http://www.jacksonimmuno.com; 1:200) and fluorescein isothiocyanate-conjugated pig anti-mouse IgG (Vector Laboratories Burlingame, CA http://www.vectorlabs.com; 1:200). Nuclei were counterstained with 4′,6-diamidino-2-phenylindole using proLong Gold antifade reagent (Invitrogen, Carlsbad, CA http://www.invitrogen.com). To quantitatively analyze double-labeled neurons in the striatum, fluorescence signals were detected with an LSM 510 NLO Confocal Scanning System mounted on an Axiovert 200 inverted microscope (Carl Zeiss Ltd Maple Grove, MN http://www.zeiss.com) equipped with a two-photon Chameleon laser (Coherent Inc Santa Clara, CA http://www.coherent.com). Three-color images were scanned using Argon and 543 HeNe lasers. IMARIS (Bitplane AG, Zurich Switzerland, http://www.bitplane.com) imaging software was used for three-dimensional image reconstruction. Images were acquired using LSM 510 Imaging Software (Carl Zeiss Ltd Maple Grove, MN http://www.zeiss.com) as described previously [15]. The specificity of each label was first verified using single-channel scans that were then merged into multiple-channel views. Neurons were considered double-labeled if colabeling with relevant morphology was seen throughout the extent of the nucleus for nuclear markers or if a cytoplasmic marker surrounds a nuclear marker when viewed in x-y cross section as well as in x-z and y-z cross-sections produced by orthogonal reconstructions from z-stacks taken at ×400 magnification. Human antigen single-labeled neurons and neurons double-labeled for
