1. Nicotine and its main derivative. cotinine, are reported to have distinct central activities in mammals. In this study, the cotinine receptor was separated by biochemical procedures including radio receptor, affinity-chromatography, SDS-PAGE, and N-terminal sequencing assays. 2. Consistently, the results showed that distinctive cotinine receptors exist in different tissues of mammals. In rat brain, the affinity chromatography and [125I]cotinine receptor essays were used to isolate a 40-kDa protein (p40) with higher affinity for cotinine than alpha-bungarotoxin and nicotine. The N-terminus amino acid sequences of the p40 and its internal tryptic peptides showed no identity to recently described protein sequences, with the exception of homology to the human p205 synovial fluid protein. 3. These results, in agreement with other behavioral studies, are the first molecular evidence for distinctive nicotine and cotinine receptors in mammals.
1. Nicotine and its main metabolite, cotinine, were reported to have distinct behavioral activities in mammals. 2. In this study, cotinine was synthesized without detectable nicotine contamination to compare the ability of nicotine and cotinine to pass the blood-brain barrier (BBB) in rats. 3. The alkaloids were extracted from plasma and brain tissues by methanol, identified by thin-layer chromatography, and quantified by high-pressure liquid chromatography and radioimmunoassays. 4. Consistently, the three methods showed that the passage of cotinine was time, route of administration, and dose dependent and that nicotine was more efficient than cotinine to pass the BBB. 5. The results suggest that these alkaloids may have central activities that probably result from their actions at distinct molecular levels.
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