The effects of brainstem priming stimulation on interhemispheric hippocampal responses in the awake rat.

Evoked hippocampal responses to stimulation of the contralateral hippocampus were recorded in the awake rat. The effects of priming stimulation applied to the nucleus locus coeruleus and the raphe nuclei on averaged evoked hippocampal responses to the interhemispheric stimulation were measured. It was found that priming stimulation of these monoamine-containing nuclei caused the formation of a late component in the interhemispheric potential without affecting the magnitude of the initial response component. Drugs which selectively interfere with noradrenergic or serotonergic transmission, antagonized the locus coeruleus or raphe primed late response component, respectively. Parenteral administration of d-amphetamine or l-amphetamine caused the appearance of a late response component which was similar to that seen after brainstem priming stimulation. It is suggested that the monoamines modify responses to afferent stimulation of particular pathways in the brain.