The role of the pontis oralis in the generation of RSA activity in the hippocampus of the guinea pig

The relationship between field activity in the nucleus pontis oralis (PnO) and the hippocampus was examined in the guinea pig. Rhythmical slow activity (RSA or theta activity) could be recorded from both the pontis oralis and the hippocampus. RSA recorded in the pontis oralis was of the same principal frequency as that found in the hippocampus, but had a much lower amplitude. Behavioral correlates of PnO RSA were the same as the behavioral correlates of hippocampal RSA. The effects of atropine sulfate on RSA were the same at each site. Stimulation of the PnO produced RSA in the hippocampus. Lesions of the PnO had no effect on RSA recorded from the hippocampus or on the behavioral correlates of this RSA. Lesions of the medial septum abolished RSA in both sites. Cross-correlations between field activity recorded from both the hippocampus and PnO showed the same time lag before and after septal lesions. These results indicate that while the PnO is not instrumental in the production of hippocampal RSA, an intact septum is necessary for the production of RSA in both sites. They also indicate that there is a common projection to these sites which does not pass through the medial septum.