Classical aversive conditioning of heart rate in curarized rats at different blood gas levels

In an effort to examine whether normal blood gas tensions were essential for conditioning, paralyzed rats received a classical aversive heart rate (HR) conditioning session while respirated at different peak expired CO2 values. After the session, arterial blood was drawn for analysis. That peak expired CO2 was effective in manipulating PCO2 was indicated by a significant correlation (r=0.594, df=17, P less than 0.05). In addition, only rats with blood gas values similar to those of anesthetized controls displayed a discriminated HR CR. These animals also had lower baseline HRs and greater HR variability. Further, 7 of the 9 rats with normal blood gas values were respirated at peak expired CO2 values from 5.0-5.1 per cent, and no animal ventilated within this range displayed abnormal values. These findings suggest that previous difficulties in obtaining calssical and operant conditioning in paralyzed animals may, in part, be attributable to inadequate ventilation.