EFFECTS OF THE RETRORUBRAL FIELD STIMULATION ON THE EXCITABILITY OF THE RAT HIPPOCAMPUS IN-VIVO

We studied in vivo the influences exerted by the retrorubral field (RR F) on the on commissural-evoked CA1 pyramidal cell excitability in the rat hippocampal formation (HF). The stimulation of RRF before the act ivation of the contralateral CA3 area evoked in all the studied rats a reduction in amplitude of the evoked population spike in the CA1 pyra midal cell body layer of both the dorsal and the ventral HF. No signif icant differences in the intensity of the inhibitory effect were obser ved between dorsal and ventral parts of the HF. The stimulation of the ipsilateral RRF reduced the amplitude of the evoked population spike in a higher degree with respect to the contralateral side. Since these side-to-side differences were significant, it can be concluded that t he RRF-induced inhibitory effect is stronger on the ipsilateral CA1 py ramidal cells. The inhibitory effect appears within 0.1 s of stimulati ng the RRF, reaches its maximal effect around 0.4-0.5 s following the conditioning train and returned to its control size after 5 s.