Activation of 5-HT1B receptors suppresses low but not high frequency synaptic transmission in the rat subicular cortex in vitro.

We have shown previously that activation of 5-HT1B serotonin receptors mediates suppression of the amplitude of evoked potentials in the subiculum [2]. Here we show that after application of 5-HT (10 microM), excitatory postsynaptic potentials of subicular neurons have reduced amplitudes with no change in membrane potential, input resistance and presynaptic fiber volleys. These results suggest that activation of 5-HT1B receptors reduces the release of glutamate from incoming fibers originating from CA1 pyramidal cells. In presence of 5-HT (10 microM), theta patterned stimulation still induced LTP, similar to that observed in control slices. Application of similar concentrations of 5-HT during double pulse stimulation (interval 10-15 ms) reduced the response to the first pulse (repetition interval 30 s), but the response to the second pulse of the pair was unaffected. We propose that 5-HT1B receptor activity suppresses subicular transmission at low but not at high frequencies.