Chronic and acute applications of lithium have similar depressive effects on EPSPs in the medial bundles of fast extensor muscles at the crayfish

Abstract

It is currently unknown how lithium, a drug commonly used to treat bipolar disorder, biologically affects synaptictransmission in the brain. This investigation aimed to determine the effects of chronic lithium exposure and acute lithium exposure on synaptic transmission. In our experiment, we measured the excitatory postsynaptic potentials at the neuromuscular junctions in three groups of crayfish: crayfish with chronic exposure to sodium (5 mM), crayfish with acute exposure to lithium (5 mM), and crayfish with chronic exposure to lithium (5 mM). When we compared the three groups average EPSPs, we found that acute and chronic exposure to lithium similarly decrease EPSP magnitude relativeto the EPSP magnitude of the crayfish muscles with sodium exposure. Because we know that therapeutic effects of lithium in the treatment of bipolar disorder are delayed, but EPSP magnitudes are affected immediately, we have determined that the decrease in EPSP magnitude is not the sole cause of lithiums therapeutic effects for bipolar disorder. Therefore, another physiological mechanism must exist that causes lithiums therapeutic effects.