Role of s-nitrosylation in learning-induced in-vitro neuronal plasticity in the mollusk aplysia

In Aplysia, in vivo exposure to aversive stimuli (i.e., electrical shocks) causes feeding suppression and a reduction in excitability of B51, a neuron linked to biting decision-making (Shields-Johnson et al. 2013). A short-term (15 min) decrease of B51 excitability can be induced in a preparation of the isolated Aplysia ner- vous system in which electrical stimulation of afferent nerves is used as in vitro training (Weisz et al. 2017). Previous studies have revealed that the gaseous neurotransmitter nitric oxide (NO) is necessary for short- term B51 decreased excitability (Farruggella et al. 2019). However, when the downstream targets of NO modulation guanylyl cyclase (sGC) and protein kinase G (PKG) are pharmacologically blocked, short-term B51 decreased excitability is only partially prevented, suggesting the contribution of another NO-dependent biochemical cascade. In this ongoing study, we are examining the role of S-nitrosylation in the expres- sion of training-induced short-term B51 decreased excitability by blocking this process with the selective inhibitor TEMPOL. Four groups of preparations are being used: untrained/vehicle (artificial seawater), trained/vehicle, untrained/TEMPOL, and trained/TEMPOL. Each preparation is initially incubated for 30 minutes with either TEMPOL or vehicle. Following incubation, the excitability of B51 is measured be- fore (pre-test) and 15 minutes (post-test) after the training or untraining protocol. For each excitability measurement, the percent change is calculated as (𝑝𝑜𝑠𝑡 − 𝑝𝑟𝑒/𝑝𝑟𝑒)𝑥100, and the Kruskal-Wallis test, followed by the Dunn’s post-hoc comparisons, are conducted to isolate the sources of significance. Although statistical significance has not been achieved yet, current results show a trend that short-term B51 decreased excitability is partly blocked in the trained group incubated with TEMPOL. If confirmed, this result would demonstrate a contribution of S-nitrosylation in short-term B51 decreased excitability and would indicate that two NO-dependent biochemical cascades sustain this learning- induced plasticity: one mediated by a sGC-PKG pathway, and one regulated by a S-nitrosylation process.