Hippocampal-dentate theta disturbance after selective CA1 pyramidal cell damage in the rat.

The contribution of the CA1 area of the dorsal hippocampus to both superficial and deep theta recorded from the dorsal hippocampal formation was assessed in rats anesthetized with ether. CA1 area cells were destroyed unilaterally by local injection of 2 micrograms of ibotenic acid dissolved in 0.1 microliters of phosphate buffer. Limited destruction of CA1 resulted in partial suppression of both superficial and deep theta, whereas extensive destruction resulted in almost total suppression of both theta's. A good correlation was found between the extent of the lesion and the theta disruption. Control preparations involving destructions by means of this neurotoxin of the hippocampal CA3 area or lower blade of the dentate gyrus failed to alter either superficial or deep theta. These data suggest that neuroanatomical integrity of the CA1 area of the dorsal hippocampus is a necessary condition for the normal appearance and maintenance of both superficial and deep theta as recorded from the dorsal hippocampal formation of the ether-anesthetized rat.