Semax Peptide Enhances Synaptic Communication in Spinal Cord Pain Pathways

The synthetic peptide Semax is widely recognized for its neuroprotective and nootropic properties, often explored for its cognitive-enhancing effects. While its benefits in various neurological contexts are acknowledged, the precise mechanisms by which it influences fundamental neuronal communication, particularly within the intricate pain processing pathways of the spinal cord, have remained less clear. This study aimed to elucidate the direct impact of Semax on the synaptic activity and short-term plasticity of glutamatergic synapses between co-cultured dorsal root ganglion (DRG) and dorsal horn neurons (DHN), which are crucial components for transmitting and modulating pain signals.

The study revealed that Semax significantly and positively modulated synaptic transmission within the co-culture model. Treatment with Semax led to a robust increase in the frequency of spontaneous excitatory postsynaptic currents (sEPSCs), indicating a ~35% enhancement in presynaptic glutamate release compared to untreated controls. Furthermore, Semax notably improved short-term synaptic plasticity, specifically enhancing paired-pulse facilitation (PPF) by approximately 28% at a 50 ms inter-stimulus interval, suggesting more efficient and adaptable synaptic responses. This enhancement was observed across multiple tested concentrations, with optimal effects noted around 100 nM.