Radioisotopes as Tools in Neurobiological Studies of Mammalian Receptor Sites
Bredau, Beth S.
MetadataShow full item record
Recent evidence has revealed that radioactive chemicals are useful for qualitative measurements and the localization of receptor interactions within the neurological system. The present experiments demonstrate that radioactive (125-I) compounds successfully measure these boundaries in specific vasopressin (AVP) and Substance P (SP) interactions. Radioimmunoassays (RIA) for cAMP were performed with heterogeneous kidney tissue (sprague-Dawley rats) samples as a means of measuring AVP receptor interactions. Since there is no known radiolabeled ligand around to measure AVP receptor sites, measurements are taken by comparing the amount of unlabeled cAMP to experimentally controlled levels of labeled cAMP. AVP reacts with adenylate cyclase to catalyze the formation of cAMP; thus, the ratio of bound to free cAMP can reveal the presence of AVP receptors. SP receptor localization and affinity was investigated by incubating in vitro spinal cord cultures and fresh brain tissue slices with labeled and unlabeled SP. Some cultures were counted to detect the amount of radioactive uptake in the tissue. Other tissue was then allowed close contact with photographic emulsion. When these substances are exposed to material containing radioactive material, a photographic image is made upon development. This method provides visualization and localization of the radioactive uptake in the sample. Reliable photographs of SP receptors were obtained from both in vitro cultures and frozen tissue slices. Localization of SP receptors in the brain appeared to be generalized in certain areas of the brain. Further study is being conducted to identify which cells in the spinal cord contain SP receptors. Radiolabeled derivatives of cAMP and SP have been used successfully to demonstrate specific interactions at receptor sites. These results indicate that careful use of radioisotopes can aid greatly neurobiological research.