HIPPOCAMPUS 6:294-305 (1996) Physiological Properties of Anatomically Identified Basket and Bistratified Cells in the CAl Area of the Rat Hippocampus In Vitro Eberhard H. BuhV Tibor Szilagyi,l,2 Katalin Halasy, 1,3 and Peter Somogyi 1 IMRC Anatomical Neuropharmacology Unit, Oxford Uni vers ity, Oxford, England; 2Department of Physiology , Uni vers ity of Medicin e and Pharmacy, Tirgu Mures, Romania; 3Department of Zoology and Cell Biolog1j, f6zs ef Attila Uni versity, Szeged, Hungary ABSTRACT: Basket and bistratified cells form two anatomically distinct classes of GABAergic local-circuit neurons in the CA 1 region of the rat hippocampus. A physiological comparison was made of intracellularly recorded basket (n = 13) and bistratified neurons (n = 6), all of which had been anatomically defined by their efferent target profile (Halasy et al., 1996). Basket cells had an average resting membrane potential of -64.2 ± 7.2 vs. -69.2 ± 4.6 mV in bistratified cells. The latter had considerably higher mean input resistances (60.2 ± 42.1 vs. 31.3 ± 10.9 MU) and longer membrane time constants (18.6 ± 8.1 vs. 9.8 ± 4.5 ms) than bas- ket cells. Differences were also apparent in the duration of action po- tentials, those of basket cells being 364 ± 77 and those of bistratified cells being 527 ± 138 p.s at half-amplitude. Action potentials were generally followed by prominent, fast afterhyperpolarizing potentia Is which in bas- ket cells were 13.5 ± 6.7 mV in amplitude vs. 10.5 ± 5.1 in bistratified cells. The differences in membrane time constant, resting membrane po- tential, and action potential duration reached statistical significance (P < 0.05). Extracellular stimulation of Schaffer collateral/commissural afferents elicited short-latency ex citatory postsynaptic potentials (EPSPs) in both cell types. The average 10-90 % rise time and duration (at half-ampli- tude) of subthreshold EPSPs in basket cells were 1.9 ± 0.5 and 10.7 ± 5.6 ms, compared to 3.3 ± 1.3 and 20.1 ± 9.7 ms in bistratified cells, the difference in EPSP rise times being statistically significant. Ba sket and bi- stratified EPSPs were highly sensitive to a bath applied antagonist of non-N-methyl-D-aspartate (NMDA) receptors, whereas the remaining slow-rise EPSP could be abolished by an NMDA receptor antagonist. Increasing stimulation intensity elicited biphasic inhibitory postsynaptic potentials (IPSPs) in both basket and bistratified cells. In conclusion, basket and bistratified cells in the CA 1 area show promi- nent differences in several of their membrane and firing properties. Both cell classes are activated by Schaffer collateral/commissural axons in a feedforward manner and receive inhibitory input from other, as yet unidentified, local-circuit neurons. © 1996 Wiley-Liss, Inc. KEY WORDS: GABA, interneuron, inhibition, postsynaptic, feed for- ward Accepted for pub li cation May 1, 1996. Address correspondence and reprint requests to E.H. Buhl , MRC Anatomical Neuropharmacology Un it, Oxfo rd Un ive r si ty, Ma nsfie ld Rd ., Oxford OX 1 3TH, UK . © 1996 WlLEY -LISS, [Ne. INTRODUCTION Hippocampal interneurons, or non-principal cell s, sha re two common properties. First, they have a dense local axonal arbor whi ch may either target pr in ci pal ce ll s, other local -ci tcuit neurons, or a mixture of both (Somogyi et aI., 1983.; Schw.rrLkro in and Kunkel, 19 85; G ul yas et al. , 1993 b; Hal asy and Somogyi, 1993; Han et al., 1993; Buhl et al., 1994a,b). Second, it ap- pea rs that mos t interneurons investigated to date store the inhibito ry neurotransmittet l'-aminoburytic ac id (GABA) in their tetminals (Somogyi et al ., 1983b, 1984, 198 5; Sotiano and Frotschet, 19 89; Halasy and Somogyi, 1993; Halasy et al., 1996). Apart from th ese common characteri sti cs, however, interneurons must be tegatded as a conglomerate of heterogeneous, albeit di s- tinct, cell classes. With respect to their anato mi cal prop- erti es , non-ptincipal cells may be segregated into several ca tego ri es , differing with respect ro their content of pep- tide neuro transmittets (So mogyi et al., 1984; Kosab et al ., 1985; Sloviter and Ni lavet, 1987), calcium-binding proteins (N itsc h et al ., 1990; G ul yas et al ., 1991), and /or effe rent targe t profile (So mo gyi et al ., 1983a, 1985; Gulyas et al., 1993 b; Halasy and Somogyi, 1993; Buh/ et al., 1994a,b; Sik et al., 1995). However, these features are not necessarily mutually exclusi ve; on the contrary, for example, neu ro ns sll ch as the dentate gyrus hilat per- forant pathway-associated (HIPP) cell s (Han et al ., 1993) ptes umably corres pond to the class of so mato- statin-positive hilar neuron s. Wit h res pect to their physiological properties, how- ever, distinctions berween diffetent classes of GABAergic neuron are either blurred or are ye t to be established. As ye t, there is so me degt ee of ge ne ral co nse nsus that in - terneurons per se may differ from ptincipal cell s in many of theit inttinsic properti es , such as short-duration ac -