Effects of tetanus toxin on spontaneous and evoked transmitter release at inhibitory and excitatory synapses in the rat SDCN neurons

We observed the effects of tetanus toxin (TeNT) on spontaneous miniature and evoked postsynaptic currents at inhibitory (glycinergic) and excitatory (glutamatergic) synapses in SDCN of rat spinal cord, by use of ‘synaptic bouton’ preparations, under voltage clamp condition. TeNT (>10 pM) dose-dependently decreased the frequency without affecting amplitude of glycinergic spontaneous miniature IPSCs. However, TeNT (100 pM) had no effect on frequency or amplitude of glutamatergic spontaneous EPSCs. Focal paired electrical stimulation of ‘synaptic boutons’ elicited two consecutive glycinergic eIPSCs or glutamatergic eEPSCs with large amplitude and low failure rate (Rf). TeNT (100 pM) reduced the amplitude and increased the failure rate of the first glycinergic eIPSCs and greatly enhanced the ratio of the second to first (P2/P1) eIPSCs. Application of 4-AP restored glycinergic eIPSCs suppressed by TeNT (100 pM). However, TeNT (100 pM) had no effect on the amplitude, Rf or P2/P1 ratio of glutamatergic eEPSCs. These results show that TeNT pre-synaptically affects spontaneous and evoked, and inhibitory and excitatory neurotransmitter release differentially, thereby suggesting that molecular events underlying spontaneous and evoked, inhibitory and excitatory neurotransmitter release may be different in CNS, and that the release machinery becomes less sensitive to Ca2+ in TeNT poisoned ‘synaptic boutons’.

► Effects of TeNT on fast neurotransmission in SDCN neuron of rat spinal cord.
► 100 pM TeNT decreased the frequency without affecting amplitude of spontaneous glycinergic mIPSCs.
► However, 100 pM TeNT had no effect on frequency or amplitude of spontaneous glutamatergic mEPSCs.
► 100 pM TeNT reduced the amplitude and increased the Rf of glycinergic eIPSCs and enhanced the ratio of the P2/P1 eIPSCs.
► However, 100 pM TeNT had no effect on the amplitude, Rf or P2/P1 ratio of glutamatergic eEPSCs.