SPERMINE INCREASES PAIRED-PULSE FACILITATION IN AREA CA1 OF HIPPOCAMPUS IN A CALCIUM-DEPENDENT MANNER

The effect of spermine on neurotransmission was studied in area CA1 of the hippocampal slice preparation. Paired-pulse stimulation (20 ms in terpulse interval) was delivered to stratum radiatum; the evoked field potential responses were recorded simultaneously from stratum radiatu m and from stratum pyramidale. At mM and sub-mM concentrations, spermi ne decreased the slope of pEPSP in stratum radiatum and the area of th e conditioning population spike in stratum pyramidale. Short-latency p aired-pulse inhibition of the population spike was converted to facili tation by spermine. These effects of spermine resembled those observed at low calcium concentration. In addition, dose-response and input-ou tput curves determined at various Ca2+ concentrations demonstrated tha t the depressant effects of spermine were larger at low Ca2+ levels. T he results support the notion that spermine competitively blocks presy naptic voltage-sensitive Ca2+ channels, thus causing a decreased relea se of neurotransmitter. Since spermine is present in brain, it is like ly that it is a natural modulator of Ca2+ channels.