Piperoxan hydrochloride (Benodaine hydrochloride) is an α2 adrenoceptor antagonist. Piperoxan (benodaine) is a drug which was the very first antihistamine to be discovered.

When superfusing the medulla with Piperoxan (50 μM; 5 min) and the pons with artificial cerebrospinal fluid (ACSF), three inactive preparations exhibit low-frequency rhythmic phrenic bursts (2-4 c/min), with the phrenic burst frequency in 12 active preparations significantly increasing to 163±12% of the previous average frequency in the final 3 minutes of Piperoxan application. In active preparations, the impact of norepinephrine (NA) applications (25 μM; 5 min) is assessed under conditions of superfusion with either ACSF (n=8) or α2 adrenoceptor antagonist Piperoxan (50 μM; PIP-ACSF; n=5). Both scenarios of NA application (NA-ACSF alone or combined with PIP-ACSF+NA) lead to a marked increase in phrenic burst frequency. Notably, inhibiting medullary α2 adrenoceptors with Piperoxan significantly enhances this effect: during NA application's fifth minute, phrenic burst frequency escalates to 171±11% with ACSF alone and 234±21% under PIP-ACSF, compared to the baseline control values.