These might include a 30kDa surface receptor, or macrophage scavenger receptors. HBII-52 regulates the splicing of serotonin receptor 2C. Buspirone acts as an agonist of the serotonin 5-HT receptor with high affinity. Codeine is an opioid and an agonist of the mu opioid receptor. Acetylcholine binds to a post-synaptic nicotinic acetylcholine receptor. A competitive antagonist competes with an agonist for binding to the receptor. Glucocorticoids affect cells by binding to the glucocorticoid receptor. Aripiprazole is also a partial agonist of the serotonin 5-HT receptor (intrinsic activity = 68%). Azapirones are a class of 5-HT receptor agonists. Affinity is a measure of the tendency of a ligand to bind to its receptor. It exerts its action through binding to and activation of the androgen receptor. These ligands bind to the pregnane X receptor (PXR). Xenon is a competitive inhibitor of the serotonin 5-HT receptor. They have some of the characteristics of true steroids as receptor ligands. Propene acts as a central nervous system depressant via allosteric agonism of the GABA receptor.