PHYSIOLOGICAL AND MORPHOLOGICAL HETEROGENEITY OF DENTATE GYRUS-HILUS INTERNEURONS IN THE GERBIL HIPPOCAMPUS IN-VIVO (VOL 7, PG 1393, 1995)

A variety of morphological types of dentate gyrus/hilus interneurons h ave been described, but little is known about their corresponding phys iological characteristics. To address this issue, intracellular respon ses to current injection and perforant path stimulation were obtained from putative dentate interneurons in anaesthetized adult gerbils. Our sample of interneurons showed heterogeneity in their intrinsic physio logical characteristics and spike thresholds to perforant path stimula tion, suggesting the existence of distinct physiologically-defined cla sses. 'Fast-spiking' interneurons had a low threshold to perforant pat h stimulation, whereas 'slow-spiking' interneurons responded with pred ominantly inhibitory potentials. In several cases, cells were intracel lularly labelled with biocytin for visualization. Interneurons with di fferent physiological traits had distinct morphological features. Thes e results confirm that, as in hippocampus proper, morphologically iden tifiable interneurons in the dentate hilus show electrophysiological f eatures that are likely to reflect functionally specific roles in info rmational processing.