Relationships of nucleus reticularis pontis oralis neuronal discharge with sensory and carbachol evoked hippocampal theta rhythm.

The activity of 72 neurons recorded in the reticularis pontis oralis nucleus (RPO) was examined in anesthetized and curarized rats during hippocampal theta (theta) rhythm elicited by either sensory stimulation or carbachol microinjections. During hippocampal theta rhythm evoked by sensory stimulation, 63.9% of RPO neurons increased their discharge rate while the firing rate decreased in 20.8%. In all cases, the RPO neurons maintained a non-rhythmic discharge pattern. In 44% of the neurons the discharges tended to occur on the positive wave of the theta rhythm. Similar firing patterns were seen in 18 RPO neurons recorded during theta rhythm elicited by both, sensory stimulation and a carbachol microinjection; this effect was blocked by atropine. These results indicate that the RPO region contributes to the generation of hippocampal theta rhythm with a tonic and nonrhythmic outflow through a cholinergic system which may be muscarinic.