Perfusion with lithium modifies neurophysiological responses in the CA1 region of the hippocampal slice preparation

The effects of acute lithium exposure on extracellular electrophysiological responses in the CA1 region of the in vitro hippocampus were investigated. Field potentials were assessed while perfusing slices with normal media or media in which LiCl was substituted for NaCl in 30, 20, 10 and 2 mM amounts. Lithium concentration in the slice following 20 min perfusion with 20 mM lithium was determined to be about 14 mM. At the higher concentrations, lithium exposure depressed the presynaptic fiber volley and antidromic population spike. On the other hand, the population EPSP and orthodromic population spike were enhanced. No significant changes were found at 2 mM. The findings are compatible with one action of lithium being on the excitability of axons and synaptic terminals. Comparisons were drawn between previous studies involving chronic lithium exposure and the present results. In this acute preparation lithium effects, as reflected in the population EPSP, were in opposition to those found with chronic lithium exposure. Changes demonstrated in this preparation in fiber volley and antidromic population spike paralleled those found with chronic lithium exposure.