Effects of intraperitoneal carbon monoxide on fixed-ratio and screen-test performance in the mouse

The behavioral effects of carbon monoxide (CO) administered via IP injection were investigated in the mouse. Mice were trained to lever press under a fixed-ratio (FR) 100 schedule of water reinforcement. Thirty-min test sessions were conducted either immediately or 30 min following IP injections of air (100 ml/kg) or CO (7.5, 15, 30, 50 or 100 ml/kg). CO produced a decrease in rates of responding which was exhibited earlier and lasted longer with increasing doses. Motor performance was also measured with the inverted-screen test following the same doses of CO at either 5, 15, 30, 60, 120 min or 24 hr post-injection. Performance was affected in a dose- and time-dependent fashion. Peak carboxyhemoglobin (COHb) levels were observed at 15 or 30 min and were 20%, 32%, 42%, 51% and 60% for 7.5, 15, 30, 50 and 100 ml/kg CO, respectively. COHb saturation alone was not always a good predictor of behavioral effects since both level and duration of exposure contributed to behavioral impairment. The results also show that the IP route can be used to study the toxicity of CO.