Lithium causes differential effects on postsynaptic stability in normal and denervated neuromuscular synapses

Abstract

Lithium chloride has been widely used as a therapeutic mood stabilizer. Although cumulative evidence suggests that lithium plays modulatory effects on postsynaptic receptors, the underlying mechanism by which lithium regulates synaptic transmission has not been fully elucidated. In this work, by using the advantageous neuromuscular synapse, we evaluated the effect of lithium on the stability of postsynaptic nicotinic acetylcholine receptors (nAChRs) in vivo. We found that in normally innervated neuromuscular synapses, lithium chloride significantly decreased the turnover of nAChRs by reducing their internalization. A similar response was observed in CHO-K1/A5 cells expressing the adult muscle-type nAChRs. Strikingly, in denervated neuromuscular synapses, lithium led to enhanced nAChR turnover and density by increasing the incorporation of new nAChRs. Lithium also potentiated the formation of unstable nAChR clusters in non-synaptic regions of denervated muscle fibres. We found that denervation-dependent re-expression of the foetal nAChR γ-subunit was not altered by lithium. However, while denervation inhibits the distribution of β-catenin within endplates, lithium-treated fibres retain β-catenin staining in specific foci of the synaptic region. Collectively, our data reveal that lithium treatment differentially affects the stability of postsynaptic receptors in normal and denervated neuromuscular synapses in vivo, thus providing novel insights into the regulatory effects of lithium on synaptic organization and extending its potential therapeutic use in conditions affecting the peripheral nervous system.

Functional regeneration of the murine neuromuscular synapse relies on long-lasting morphological adaptations

“…The NMJ morphometric analyses were performed as described [ 23 , 31 , 47 ]. Ectopic AChR aggregates were identified as plaque or oval morphologies and by their distribution within muscle fibers, as we have previously described [ 48 ]. To quantify poly-innervation as well as tSC number and projections, z-stacks were projected in 3D using the ImageJ software.…”

“…Pretzel-like structures were manually traced using the Image J software and the mean fluorescence intensity of BTX-1 and BTX-2 was quantified. In our working conditions, NMJs were classified as “unstable” when the BTX-2/BTX-1 ratio was ≥1.0 or as “stable” for values < 1.0, as we have previously described [ 48 ]. Data are expressed as the percentage of stable and unstable AChRs at denervated NMJs in both nerve injury protocols.…”