Action of norepinephrine in the dentate gyrus. I. Stimulation of locus coeruleus.

The effect of stimulating locus coeruleus (LC) on the response of dentate gyrus granule cells to medial perforant pathway stimulation was studied in anesthetized rats. Field responses were recorded simultaneously at the mid-dendritic and granule cell levels. Two types of responses were recorded: those due to the synchronous firing of granule cell action potentials (population spikes) and those produced by excitatory synaptic activity (evoked synaptic potentials or ESPs). Stimulation of LC prior to stimulating the perforant pathway resulted in a decrease in the ESP (inward current) measured at the dendrites and, in most animals, an increase of the population spike measured at the granule cell level. Although LC stimulation decreased the ESP at the dendrites, the ESP at the granule cell body level (outward current) was not affected. The changes in granule cell responses following LC stimulation are discussed in relation to previous findings in freely moving rats.