RAPID COMMUNICATION Calcium-Dependent Spike-Frequency Accommodation in Hippocampal CA3 Nonpyramidal Neurons

Chitwood, Raymond A. and David B. Jaffe. Calcium-dependent properties of interneurons, such as the expression of SFA, spike-frequency accommodation in hippocampal CA3 nonpyramicould therefore have significant effects on an inhibitory neudal neurons. J. Neurophysiol. 80: 983–988, 1998. Interneurons of ral network’s properties. For example, inconsistent synchrothe hippocampal formation are traditionally identified electrophysinization or even multiple frequencies of synchronization ologically as those cells that fire trains of weakly accommodating might result from networks of accommodating interneurons action potentials in response to depolarizing current injection. We (unpublished results) . Furthermore, differences in the firing studied the firing properties of nonpyramidal neurons in the five properties of nonpyramidal neurons would reflect variations substrata of the CA3b region of hippocampus. With the use of in their active membrane properties and the potential for whole cell recording methods we found that nonpyramidal neurons significant differences in their nonlinear membrane refired in a range from weak to strong spike-frequency accommodation (SFA) that was calcium dependent. Slow afterhyperpolarizasponses. tions were not associated with strong SFA. In addition a subset of Here we report that a significant proportion of interneuinterneurons (Ç20%) fired with an irregular firing pattern that was rons of the CA3b region of the hippocampal formation exgenerally calcium independent. These results suggest a calciumhibit calcium-dependent SFA in response to depolarizing dependent mechanism for SFA in nonpyramidal neurons that is current injection. In addition, we found that a subset of nondistinct from pyramidal cells and further demonstrates the heteropyramidal cells fire in an irregular pattern that was calcium geneity of hippocampal interneurons. independent. This work was previously presented in abstract form (Chitwood and Jaffe 1997).