Increased excitability of hippocampal unmyelinated fibres following conditioning stimulation

Unmyelinated fibres in the stratum radiatum (area CA1) were electrically stimulated in hippocampal slices from guinea pigs. The size of the evoked fibre volley was increased by a preceding conditioning stimulation to the same fibres, provided that the strength of the conditioning stimulus was larger than that of the test pulse. This facilitation was maximal for 20-30 ms interstimulus intervals and had a duration of about 200 ms. The results are compatible with an increased excitability (reduction in threshold) specific for fibres activated by the conditioning stimulation.