Serotonin (5HT) and its receptors are part of major neurotransmitter pathways in both the central and peripheral nervous systems. It is therefore important to know more about the receptors on which 5HT acts and the channels which they operate. for this purpose a multidisciplinary study will be made of the structure and function of 5HT receptors, using frog oocytes and recombinant DNA research. This will provide information about the neurotransmitter receptors and associated channels at all levels, from their genes to their mode of action. 5HT receptors will be 'transplanted' from the brain into the membrane of Xenopus oocytes by isolating messenger RNA from rat and human brains, and injecting it into the oocytes. Translation of the foreign mRNA by the oocyte causes it to acquire functional 5HT receptors, where they are made more amenable to study than if they were in their native brain cells. Furthermore, Xenopus oocytes are extremely sensitive detectors of mRNAs coding for neurotransmitter receptors and channels. Therefore, oocyst will be used for cloning the genes of the receptors and channels involved in the action of 5HT on brain cells. This will be done by a novel approach that avoids the difficult task of having first to purify the proteins. 5HT receptors, transplanted from the brain into the oocyte membrane, mediate at least three different types of responses; possibly involving different receptors. Two of the 5HT responses are caused by the opening of different types of Cl- channels, while the other is caused by the closing of K+-channels. Electrophysiological, biochemical and immunological techniques will be used to study the 5HT receptors and associated channels, as well as the intracellular receptor-channel coupling systems operated by 5HT. Apart from the Cl- channels activated by 5HT, a different Cl- channel is expressed in oocytes by mRNA from Torpedo electrocytes. This mRNA will be used to clone the electrocyte channel, and the clones obtained will then be used to clone other Cl- channels of brain cells. Chloride channels are a very important element in central and peripheral neurons as well as in muscle, secretory and epithelial cells. Accordingly 5HT receptors and Cl-channels have been implicated in a wide variety of human diseases; e.g., mental depression, schizophrenia, Down's syndrome, Cushing's, Huntington and Alzheimer diseases, myotonia and cystic fibrosis. Therefore, this study aims at cloning 5HT receptors and Cl- channels to study their structure and function because the results will undoubtedly help to understand and alleviate some human diseases.