Neurophysiological changes in the in vitro rat hippocampus following chronic lithium administration

The effect of chronic lithium exposure on the electrophysiological responses of the Schaffer collateral-commissural (SCC) input to the CA1 pyramidal neurons in the in vitro hippocampus was investigated. Experimental animals were intubated intragastrically with lithium carbonate (150 mg/kg) for 3-4 weeks. This treatment produced lithium levels in serum and hippocampus of 0.3-1.3 mM. During the recording period, the hippocampal slice retained a stable lithium concentration of 53% of the initial value. Chronic lithium exposure had a depressive effect on input/output relationships, paired-pulse facilitation and strength of orthodromic inhibition. The antidromic inhibition was virtually intact. No obvious differences were found between control and lithium slices in amplitude, latency or waveforms, of synaptic and antidromic extracellular potentials. These findings are compatible with a major action of lithium on the excitability of SCC axons and synaptic terminals.