Class
Article
College
College of Science
Department
Biology Department
Faculty Mentor
Sara Freeman
Presentation Type
Poster Presentation
Abstract
Oxytocin is a neuropeptide that influences social behavior in animals and humans. One way to test the effects of oxytocin on social behavior is by blocking oxytocin receptors (OXTR) with an antagonist. The commercially-available OXTR antagonist L-368,899 (the “Merck compound”) is commonly used for such studies despite inadequate evidence of its affinity and selectivity for OXTR in the brain. The Freeman Lab has used the custom-synthesized antagonist ALS-III-61 (the “Smith compound”), which has high specificity and affinity for OXTR in the brain but is not commercially available. Due to our diminishing supply of the Smith compound, we sought evidence that the Merck compound has similar pharmacological properties as the Smith compound. We performed competitive-binding autoradiography to quantify the binding affinities of these two antagonists in competition with 1) the OXTR radioligand, 125I-ornithine vasotocin analog, and 2) the vasopressin 1a receptor (AVPR1a) radioligand, 125I-linear vasopressin antagonist. Autoradiography was conducted using previously mounted 20-micron sections of human brain tissue from the substantia nigra (source of OXTR; n=5) and the primary visual cortex (source of AVPR1a; n=5). We co-incubated six series of adjacent brain tissue sections from each specimen in increasing concentrations of the Smith and Merck antagonists with a constant radioligand concentration. After quantifying the receptor densities across our binding conditions, we generated competition curves, which demonstrated that as the concentration of the antagonist increases, the binding density of the radioligand decreases. Our data shows that the Merck compound has a slightly higher affinity for AVPR1a than OXTR. We also confirmed that Smith compound has a higher binding affinity to OXTR than does the Merck compound and a better binding selectivity to OXTR over AVPR1a. With such results, we recommend against using the Merck compound (L-368,899) as an OXTR-specific antagonist. Due to some unexpected assay results, we intend to replicate this study to confirm our findings. Presentation Time: Thursday, 2-3 p.m.
Location
Logan, UT
Start Date
4-9-2021 12:00 AM
Included in
Comparing L-368,899 and ALS-III-61 as Human-Selective Oxytocin Receptor Antagonists
Logan, UT
Oxytocin is a neuropeptide that influences social behavior in animals and humans. One way to test the effects of oxytocin on social behavior is by blocking oxytocin receptors (OXTR) with an antagonist. The commercially-available OXTR antagonist L-368,899 (the “Merck compound”) is commonly used for such studies despite inadequate evidence of its affinity and selectivity for OXTR in the brain. The Freeman Lab has used the custom-synthesized antagonist ALS-III-61 (the “Smith compound”), which has high specificity and affinity for OXTR in the brain but is not commercially available. Due to our diminishing supply of the Smith compound, we sought evidence that the Merck compound has similar pharmacological properties as the Smith compound. We performed competitive-binding autoradiography to quantify the binding affinities of these two antagonists in competition with 1) the OXTR radioligand, 125I-ornithine vasotocin analog, and 2) the vasopressin 1a receptor (AVPR1a) radioligand, 125I-linear vasopressin antagonist. Autoradiography was conducted using previously mounted 20-micron sections of human brain tissue from the substantia nigra (source of OXTR; n=5) and the primary visual cortex (source of AVPR1a; n=5). We co-incubated six series of adjacent brain tissue sections from each specimen in increasing concentrations of the Smith and Merck antagonists with a constant radioligand concentration. After quantifying the receptor densities across our binding conditions, we generated competition curves, which demonstrated that as the concentration of the antagonist increases, the binding density of the radioligand decreases. Our data shows that the Merck compound has a slightly higher affinity for AVPR1a than OXTR. We also confirmed that Smith compound has a higher binding affinity to OXTR than does the Merck compound and a better binding selectivity to OXTR over AVPR1a. With such results, we recommend against using the Merck compound (L-368,899) as an OXTR-specific antagonist. Due to some unexpected assay results, we intend to replicate this study to confirm our findings. Presentation Time: Thursday, 2-3 p.m.