Modulating Effect of Peptide Semax on the Level of Synaptic Activity and Short-Term Plasticity in Glutamatergic Synapses of Co-Cultured Dorsal Root Ganglion and Dorsal Horn Neurons of Rats

Abstract

The effects of a long-term culturing (12 days, in vitro) of the dorsal root ganglion (DRG) and the dorsal horn (DH) neurons with peptide Semax on the level of synaptic activity in co-cultures, as well as short-term plasticity in sensory synapses were studied. It has been revealed that neuronal culturing with peptide at concentrations of 10 and 100 µM leads to increasing the frequency of spontaneous glutamatergic postsynaptic currents in DH neurons by 71.7 ± 1.8% and 93.9 ± 3.1% (n = 6; P < 0.001). Semax does not exert a pronounced effect on the amplitude and frequency of miniature glutamatergic currents, but it causes an increase of the amplitudes of spontaneous postsynaptic currents and an elevation of the quantum content. The data obtained indicate the increase in multivesicular glutamate release efficiency in neural networks of co-cultures following incubation with the peptide. Moreover, Semax (10 and 100 µM) induces changes in the basic parameters of short-term plasticity of sensory synapses, namely, i) an increase in the paired-pulse ratio from (0.53 ± 0.028) (n = 8) to (0.91 ± 0.072) (n = 6, P < 0.01) and (0.95 ± 0.026) (n = 7; P < 0.001); ii) reduced coefficients of variation ratio (CV2/CV1) from (1.49 ± 0.11) (n = 8) to (1.02 ± 0.09) (n = 6; P < 0.05) and (1.11 ± 0.13) (n = 7; P < 0.01) respectively. The results indicate a stimulating effect of Semax on the activity of glutamatergic synapses in neural networks of co-cultures, as well as the ability of the peptide to modulate effectively short-term plasticity of sensory synapses.