VENTRAL MESENCEPHALIC GRAFTS IN THE NEOSTRIATUM OF THE WEAVER MUTANT MOUSE - STRUCTURAL-MOLECULE AND RECEPTOR STUDIES

Mesencephalic cell suspensions were prepared from E12 wild-type (+/+) mouse embryos and stereotaxically implanted into the dorsal neostriatu m of weaver mutant mice (wv/wv), which have a genetic mesostriatal dop amine (DA) deficiency. Survival of DA neurons in the grafts was docume nted by tyrosine hydroxylase (TH) immunocytochemistry. Axon growth was monitored by immunocytochemistry using a battery of antibody markers, and the cellular localization of structural protein and receptor RNA transcripts was studied by in situ hybridization histochemistry using [P-32]oliognucleotide probes. The cell suspension grafts exhibited str ong immunoreactivity for neural cell adhesion molecule (N-CAM), growth -associated phosphoprotein GAP-43, microtuble-associated protein 2 (MA P2), beta-amyloid protein precursor (beta APP), and phosphorylated neu rofilament epitopes (clone SMI-31) intermediate-to-high levels of immu noreactivity were seen for synaptophysin. High levels of hybridization were found in the grafts for the RNA transcripts of GAP-43, MAP2, and isoforms beta APP(695), beta APP(714) and beta APP(751) of the beta A PP. No hybridization signal was detected in the grafts for DA D-2 or n eurotensin receptor mRNAs, both of which are normally expressed by nig ral DA neurons. DA receptor autoradiography using the D-2/D-3 agonist [H-3]CV 205-502 as a ligand showed no binding in the transplants, indi cating an apparent abnormality of grafted cells; neurotensin binding s ites, labeled with [I-125]neurotensin, were visualized int he suspensi ons, indicating the possibility that receptors could be present but th at RNA message levels might be too low to allow detection. These findi ngs offer a molecular correlate of axonal, dendritic and structural pr otein expression by transplanted mesencephalic neurons; further, they suggest that specific functional properties of grafted nigral cells ar e maintained after transplantation, while other aspects of their cellu lar biology may be compromised.