抄録
The afferent fibers in the vagus nerve transmit visceral information encoded as varying firing frequency to the second-order neurons in the solitary complex (SC). We have demonstrated that efficiency and frequency-dependency of the synaptic transmission from the primary afferent fibers in the solitary tract (TS) to distinct types of second-order neurons (the nucleus of the solitary tract, NTS, and the dorsal motor nucleus of the vagus nerve, DMX) critically depends on the type of postsynaptic neurons, but mostly through differences in the presynaptic mechanisms. Here we analyzed the mechanism underlying distinct types of transmission by evaluating the effects of manipulations that affect release probability on the paired-pulse ratio (PPR) of EPSC amplitudes evoked by two TS stimuli separated by 100 ms in the brainstem slices from young Wistar rats.. Reducing [Ca 2+]o from 2.0 to 0.5 mM significantly increased the PPR of TS-NTS synapses from 0.4±0.2 to 1.1±0.2 (n=6; mean ± SD) but did not significantly affect that of TS-DMX synapses (type I-DMX neurons, from 0.7±0.2 to 0.7±0.2; n=8; type II-DMX neurons, from 0.4±0.1 to 0.7±0.3; n=8). Whereas the PPR of TS-NTS synapse was significantly increased by adenosine (100 μM) to 0.5±0.2 (n=7), that of TS-DMX-type II synapse was not affected (0.5±0.1 with adenosine). These results suggest that distinct presynaptic mechanisms are involved in the distinct short-term plasticity of the SC synapses depending on the function of each postsynaptic target. [J Physiol Sci. 2007;57 Suppl:S149]
