Dehydration affects synaptic transmission at flexor muscle in acute lead-treated mice

The effect of 24 hrs. water deprivation on spontaneous and evoked transmitter release was studied at flexor nerve terminals of control and lead-treated male C57BL mice. Miniature endplate potentials (MEPPs) and endplate potentials (EPPs) were recorded intracellularly from urethane-anesthetized (2 mg/g, i.p.) control and lead exposed mice in both hydrated and dehydrated conditions. Exposure to lead was made by i.p. injection of lead acetate (1.0 mg/kg) dissolved in a 5% glucose solution 24 hrs. prior to the experiment. Unimodal and bimodal MEPP frequencies decreased with dehydration, while small mode MEPPs remained unchanged and large mode MEPPs increased in frequency. EPP amplitude and quantal content were unchanged by dehydration. Lead treatment by itself reduced the frequency of unimodal and bimodal MEPPs but had no effect on the amplitude of EPPs or of quantal content. However a combination of dehydration and acute lead treatment reduced the frequency of unimodal, bimodal and large mode MEPPs and significantly reduced both EPP amplitude and quantal content. Dehydration apparently reveals an underlying neurotoxic action of lead at the neuromuscular junction. This raises a health concern that people subjected to both lead pollution and dehydration are at greater risk to lead poisoning of the neuromuscular junction.