Chronic stimulation increases acetylcholinesterase activity in old Aplysia

In the marine mollusc Aplysia, a reduced level of activity of circulating AChE (acetylcholinesterase) signals the onset of aging [28], as it does in mammals [23,25]. In old Aplysia, coincident with the reduced AChE activity is impaired neuron function [17], which chronically applied sensory stimulation (CSS) improves [35]. As a first step to establish the link between the CSS and improved neuronal function, we investigated if CSS alters the level of AChE activity in old Aplysia. Before and after 4 weeks of CSS of the siphon-gill withdrawal reflex (S/GWR), we measured circulating and neural levels of AChE and behaviors involving the gill in freely moving mature and old Aplysia. Only in old animals did the CSS produce increased AChE activity levels in both the CNS and serum, and the increased levels were correlates of a change in the S/GWR, the behavior elicited by the CSS. This result shows that aging animals are able to up regulate enzymatic activity in response to specific sensory input. It also suggests that age influences how the level of AChE activity responds to persistent changes in sensory input. Parallels exist between the results here and those in higher vertebrates and are discussed.