Morphologic and electrophysiologic maturation in developing dentate gyrus granule cells

Dentate gyrus granule cells from immature (7-28 days) Sprague-Dawley mts we re examined with whole cell patch clamp recordings and biocytin filling in in vitro hippocampal slice preparations. Although recordings were confined to the middle third of the suprapyramidal limb of the dentate, the granule cells exhibited marked variability in their physiologic properties: input r esistance (IR) ranged from 250 M Omega to 3 G Omega, and resting membrane p otential (RMP) from -82 to -41 mV. Both IR and RMP were inversely correlate d with dendritic length, a morphometric indicator of cell maturity. Thus th e highest IR cells were the youngest, and maturation was characterized by a progressive decrease in IR, hyperpolarization of RMP, and elongation of th e dendritic arbor. When cells were grouped by IR, significant intergroup di fferences were found in RMP, dendritic length, and number of dendritic term inal branches. Although cells of all IR categories were examined throughout the age spectrum under study, none of the inter-IR group differences was a ge-dependent. These data suggest that IR provides a reasonable estimate: of granule cell maturity and that maturation entails predictable changes in c ell properties and morphology. These aspects of maturation correlate with e ach other, are independent of animal age, and most likely proceed according to a program related to cell bir th. (C) 2000 Published by Elsevier Scienc e B.V. All rights reserved.