Effects of Bacterial Endotoxin Lipopolysaccharides (LPS) on Synaptic Transmission at Neuromuscular Junction in an Amphibian

Lipopolysaccharides (LPS) are found in the outer membrane of gram-negative bacteria and can elicit direct cellular responses in addition to inflammatory immune responses in an infected organism. The purpose of this study was to investigate the effect of LPS on synaptic transmission at the neuromuscular junction (NMJ) of a model amphibian preparation. The cutaneous pectoris muscle of Lithobates pipiens was dissected and maintained in a physiological saline to acutely expose the preparation to LPS from Serratia marcescens. The evoked excitatory junction potentials (EJPs) completely diminished after 10 min (n = 6, p<0.05 paired t-test). These EJPs were able to be partially recovered after removal of LPS. The frequency and amplitude of the spontaneous miniature excitatory junction potentials (mEJPs) did not change with LPS exposure (n = 6, p>0.05 paired t-test). These findings suggest that LPS acts in frogs by inhibiting the activity of the voltage-gated Ca2+ channels in presynaptic motor neurons and not by blocking the acetylcholine receptors on the skeletal muscle fibers. These findings imply the acute action of LPS in mammals is presynaptic at the NMJs and can suppress synaptic transmission independent of initiating a systemic immune response.