en Experimental research article Experimental research article Introduction: The functional effects of orexin-B on the calcium spikes and excitability of the neuronal soma membrane of garden snail, Helix aspersa were studied. Methods: Conventional intracellular recording, under the current clamp conditions was performed to examine the effects of orexin-B on the configuration and electrophysiological properties of calcium spikes. Results: Application of orexin-B (300 nM) led to a membrane depolarization and thereby the increase in excitability of neurons. It also decreased the duration and the amplitude of calcium spikes. On the other hand, orexin-B had a dual effect on the amplitude of afterhyper polarization (AHP) in a time dependent manner. The maximum reduction of the amplitude of AHP was recorded within 10 min of orexin-B exposure. However a maximum increase in AHP amplitude was observed later (15 min after exposure to orexin-B). Inactivation of G-proteins by pertussis toxin (100 nM) was used to test the involvement of Gi/Go in the orexin-B induced modulation of calcium channels. Pre-incubation of ganglia for 3-6 h with PTX blocked the depolarization effect of orexin-B on the resting membrane potential. Orexin-B on pretreated neuronal cells with PTX did not statistically change the calcium spike parameters, unless the peak amplitude of AHP increased remarkably. Conclusion: In conclusion, these data suggest that orexin-B (300 nM) may affect the membrane excitability and modulates the activity of calcium and calcium activated potassium channels in snail neurons. Orexin-B, Pertussis toxin, Calcium spike, Neuronal excitability, Snail, Electrophysiology. 191 200 http://ppj.phypha.ir/browse.php?a_code=A-10-25-44&slc_lang=en&sid=1