Chimeric Studies of the Extracellular Domain of the Rat Thyrotropin (TSH) Receptor: Amino Acids (268-304) in the TSH Receptor are involved in Ligand High Affinity Binding, but not in TSH Receptor-Specific Signal Transduction.:Amino Acids (268-304) in the TSH Receptor are involved in Ligand High Affinity Binding, but not in TSH Receptor-Specific Signal Transduction