Behavioral consequences of intraperitoneal carbon monoxide administration in rats

Blood carboxyhemoglobin (HbCO) was determined 15, 30, 45, 60, 90, and 120 min following ip injection of 2.5, 5, 10, 20, and 40 ml pure carbon monoxide (CO)/kg body wt in rats. These CO doses produced HbCO concentrations of 12, 24, 35, 45, and 60%, respectively, at 30 min postinjection. Once these normative data were obtained, a group of eight naive rats were trained to produce a rapid sequence of responses in a stimulus-tracking task, then they were exposed to each of the doses of CO. The 10-ml/kg dose produced a slight decrement in performance, the 20-ml/kg dose reduced correct responses by nearly half, and the 40-ml/kg dose resulted in virtually complete cessation of responding. CO exposure resulted in longer pauses in responding with increasing dose, but the distribution of errors produced in the stimulus-tracking task remained relatively parallel across the range of CO exposures. Thus CO exposure impaired tracking performance but had relatively little effect on the pattern of errors rats produced during the stimulus-tracking test. Taken together these results contradict previous reports purporting to show that CO by ip administration has no behavioral effects; instead, the results indicate that CO administration via the ip route has very similar effects to inhaled CO on behavior.