Abstract
INTRODUCTION: Aplysia californica has been a useful model system for studies of the neural basis of behavior, learning, and aging. While the latter topic has been explored with respect to several of its simple reflex behaviors, this study represents the first examination of how one of Aplysia's more complex behaviors, escape locomotion, is affected in animals nearing the end of their natural lifespan. METHODS: Middle-aged (5-7 mo) and elderly (12-13 mo) Aplysia were subjected to an experimental or control stimulus protocol (n = 16 each group). Head reach latency, gallop share, and cycle number were calculated for each animal. Voltage-sensitive dye (VSD) imaging was performed on the isolated brains of middle-aged or elderly animals (n = 6 each group) under an experimental or control fictive locomotion stimulus protocol. Onset latency, cycle number, and average spikes/cell were calculated for each recording. VSD imaging was also done on middle-aged and elderly brains at rest (n = 7 each group), and average # of spikes/cell as well as burst duration, intraburst frequency, and cycle/min were calculated for each recording. RESULTS: Elderly Aplysia showed greatly reduced gallop response, and a loss in head reach latency sensitization in both intact animals and isolated brains. Onset latency sensitization was also more transient in middle-aged isolated brains than in middle-aged intact animals. Repeated stimulation in middle-aged isolated brains increased average spikes/cell, but elderly brains saw decreased average spikes/cell under the same protocol. Resting state activity was also weaker and slower in elderly isolated brains. DISCUSSION: This study provides the first evidence of how aging changes behavioral and network parameters of Aplysia escape locomotion, including a potential early indicator of age-related dysfunction present in middle-aged brains that has yet to emerge in the behavior. This supports future work investigating compensatory mechanisms and opportunities for future therapeutic interventions.