Identification of different putative neuronal subtypes in cultures of the superior region of the hippocampus using electrophysiological parameters

Cultured neurons offer many advantages over a slice preparation for whole-c ell patch-clamp studies, such as better control over the environment and sp ace clamp control. However, heterogeneous cultures of neurons present probl ems in distinguishing the cell type from which recordings are made. The pre sent study uses correlations with data obtained in the hippocampal slice pr eparation to determine the feasibility of "identifying" different neuronal subtypes in cultures obtained from the superior region of postnatal two- to 13-day-old rat hippocampus. Whole-cell patch-clamp recording in the curren t-clamp mode after 24-96 h in culture was used to determine if the action p otential duration would be a useful criterion in distinguishing cell types. Single action potentials were elicited by a 0.1-0.2 ms, 2-4 nA depolarizin g pulse. The average membrane potential and input resistance were -46.8 +/- 1.2 mV (n = 58) and 576 +/- 56 M Omega (n = 57), respectively. A frequency distribution of the action potential duration measured at half-maximal amp litude showed four distinct groups of neurons (group 1, 1.36 +/- 0.03 ms, n = 17; group 2, 2.19 +/- 0.05 ms, n = 20; group 3, 3.17 +/- 0.10 ms, n = 16 ; group 4, 4.36 +/- 0.13, n = 5). Based on correlations with previous studi es using intracellular recording in identified cells in slices, the data su ggest that group 1 represents basket cells, group 2 represents vertical cel ls, group 3 represents a combination of stellate cells and pyramidal cells, and group 4 represents another unidentified class of cells. Further analysis of the fast afterhyperpolarization allows distinction betw een pyramidal cells and stellate cells in group 3. In contrast to the inter neurons in a slice preparation, these cells offer good voltage control and environmental control. Future studies will record from these cells in curre nt-clamp mode to quickly characterize the action potential before switching to voltage-clamp recording to characterize the currents present in the dif ferent types of interneurons. (C) 1999 IBRO. Published by Elsevier Science Ltd.