Berkeley Scientific Journal

Glutamatergic synapses are highly modifiable, making them key targets in processes such as learning and memory. In crayfish glutamatergic neuromuscular junctions, hyperpolarization and cyclic nucleotide-activated (HCN) channels and actin cytoskeleton dynamics are critical intermediate factors in hormonal modulation of glutamatergic synapses which lead to cAMP (3’-5’-cyclic adenosine monophosphate)-dependent enhancement of synaptic transmission. Although models have been proposed, there has been a lack of experimental evidence on the relationship between HCN channels and the integrity of the actin cytoskeleton during cAMP-dependent enhancement. The specific goal of this study is to test the sequence of activation of the aforementioned mediators in synaptic enhancement via precisely controlled pharmacological experiments. At glutamatergic neuromuscular junctions of crayfish limb muscles, HCN channel activator, lamotrigine (50 μM), enhanced synaptic transmission about 20%. This enhancement was completely blocked with actin depolymerizer, latrunculin B (3 μM). These results support previous models of the temporal arrangement of events leading to synaptic enhancement, specifically that changes in actin cytoskeleton follow HCN channel activation. Concurrently, we are also using a spatio-temporal marker called phalloidin, a toxin which binds actin filaments, to further test the hypothesis that activation of HCNCs precedes actin cytoskeleton polymerization. This allows for manipulation of HCN channels and visualization of actin that could propose the associated molecular mechanisms. Preliminary evidence suggests actin reorganization.