Atipamezole hydrochloride is a synthetic α₂-adrenoceptor antagonist with a K_i of 1.6 nM. IC50 & Target: Ki: 1.6 nM^[1] In Vitro: The affinity of atipamezole for α₂-adrenoceptors and its α₂/α₁ selectivity ratio are considerably higher than yohimbine. Atipamezole is not selective for subtypes of α₂-adrenoceptors. It has negligible affinity for 5-HT₁, 5-HT2 and I2 bindings sites^[1]. In Vivo: Atipamezole is well tolerated in rodents. In anesthetized, normotensive rats, the cardiovascular effects of atipamezole (0.01–1 mg/kg, i.v.) are rather modest. Atipamezole is commonly used by veterinarians to awaken animals from sedation or anesthesia. Atipamezole increases sexual activity in rats and monkeys. In animals with sustained nociception, atipamezole increases pain-related responses by blocking the noradrenergic feedback inhibition of pain. Atipamezole at low doses has beneficial effects on alertness, selective attention, planning, learning, and recall in experimental animals, but not necessarily on short-term working memory^[1].