Fig. 4. Bicuculline antagonized the nitrogen pressure-induced sedative action. (A ) Total locomotor activity expressed in arbitrary units (mean ± SEM) during the 30-min period of recording. Pretreatment with bicuculline at 1, 2.5, or 5 nmol (n = 4 per dose), 10 min before nitrogen was applied, inhibited nitrogen sedation (n = 4) in a dose-dependent manner. +P < 0.05, ++P < 0.001 versus  control records; *P < 0.01, **P < 0.001 versus  nitrogen pressure when applied alone. Note that bicuculline at 5 nmol had no effect on basal locomotor activity. (B ) The nitrogen sedation dose–response curve is shifted to the right by bicuculline at 1, 2.5, and 5 nmol, leading to an increase of half-maximal effective nitrogen pressure (EP⁵⁰) from 1.52 to 1.66 (B1 ), 1.93 (B2 ), and 2.46 MPa (B3 ), respectively. (C ) Schild plot analysis yields a linear regression of high reliability (r²= 0.994) with a slope of 1.183 and a bicuculline pA2 value of 8.12 that corresponds to a Ki value of 7.59 nmol.