1. This paper describes two novel population patterns in the dentate gyrus of the
awake rat, termed type 1 and type 2 dentate spikes (DS1, DS2). Their cellular generation
and spatial distribution were examined by simultaneous recording of field potentials
and unit activity using multiple-site silicon probes and wire electrode arrays. 2.
Dentate spikes were large amplitude (2-4 mV), short duration (<30 ms) field potentials
that occurred sparsely during behavioral immobility and slow-wave sleep. Current-source
density analysis revealed large sinks in the outer (DS1) and middle (DS2) thirds of
the dentate molecular layer, respectively. DS1 and DS2 had similar longitudinal, lateral,
and interhemispheric synchrony. 3. Dentate spikes invariably were coupled to synchronous
population bursts of putative hilar interneurons. CA3 pyramidal cells, on the other
hand were suppressed during dentate spikes. 4. After bilateral removal of the entorhinal
cortex, dentate spikes disappeared, whereas sharp wave-associated bursts, reflecting
synchronous discharge of the CA3-CA1 network, increased several fold. 5. These physiological
characteristics of the dentate spikes sug gest that they are triggered by a population
burst of layer II stellate cells of the lateral (DS1) and medial (DS2) entorhinal
cortex. 6. We suggest that dentate spike-associated synchronized bursts of hilar-region
interneurons provide a suppressive effect on the excitability of the CA3-CA1 network
in the intact brain.
