The purpose of this study was to examine the effect of blockade of GABAA receptors by Bicuculline (BIC) on the spectrum of phrenic nerve discharge. To assess this, an arterially perfused adult rat preparation was used. The aorta was cannulated to allow for arterial perfusion and then the phrenic nerves were isolated and connected to electrodes to send a signal for recording. Baseline activity was first recorded and then BIC was added in progressive doses, with ten minutes of recording for each dose. The doses used were 0.1µM, 0.2µM, 1µM, 5µM, 10µM and 20µM. The spectrum analyzed was from the average of 10 phrenic bursts from each minute. The data was down sampled at 500Hz and filtered at 20Hz and 250Hz before analysis began. Spectral analysis was performed using Blackman and Tukey's Power Spectral Density for analysis. The spectrum was calculated and then plotted for each minute of the experiment. It was seen in the experiments analyzed thus far that MFO power increased while the dosage was increased, but then capped off at about one 1.5 times the baseline power. It was also seen that the smaller concentrations (0.1µM and 0.2µM) had no significant effect on the spectrum while in one experiment, the 20µM concentration created a drastic change in the spectrum that was not seen with any other dose. The MFO and HFO powers were similar to the previous doses, but at the higher frequencies (150Hz~250Hz), increased oscillations were seen that were not seen with the smaller doses. Specifically, there was a peak seen in the 160Hz-175Hz range and another peak seen in the 210Hz-225Hz range. It is not known what these two new oscillations mean in the respiratory system, but it may be due to the large dose that was given which may have the power to completely block all GABAA receptors. In another experiment, the HFO power sharply decreased with a 5µM dose while the MFO power increased significantly. The 10µM and 20µM doses for this experiment completely knocked out the HFO and significant power was seen at the MFO. This primary research shows that blockade of GABAA receptors changes the spectrum of phrenic nerve discharge by reducing HFO and increasing MFO. This study was supported by NIH Grant HL63175 and the Simons Summer Research Fellowship.