Mistry, V. K. | bioRxiv Science

bioRxiv2025

Age-related degradation of behavioral and network features of Aplysia escape locomotion

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 Aplysias more complex behaviors, escape locomotion, is affected in animals nearing the end of their natural lifespan. Old animals (12-13mo) showed a greatly reduced gallop response compared with middle-aged adults (5-7mo), together with a loss of locomotion onset latency sensitization. Large-scale VSD imaging was used to record motor programs in isolated brain preparations from middle-aged vs. elderly animals. Old brains displayed the same loss of onset latency sensitization seen in the intact old animal behavior, and also a reduced number of cycles per locomotion episode. Brains from middle-aged animals showed an unchanged number of motor program cycles from that observed in intact animals, but a much more transient motor program onset latency sensitization. A further age-related finding was that while in middle-aged brains repeatedly eliciting the motor program led to progressively increasing cumulative activity across trials, in old brains this same procedure led to progressively decreasing activity. Some of our results are consistent with peripheral processes working in concert with the CNS as animals age to support healthy locomotion behavior and its modification by learning, or with early changes in the brain that are not yet expressed in behavior.

neuroscience↗

bioRxiv2025

Strategies used by two memories to share space in a common neural network

How distinct memories are encoded into the same network space without destructive interference is not well-understood. Here, we utilized Tritonia diomedeas escape swim network to explore how two sequentially acquired forms of non-associative learning, sensitization and habituation, are encoded into the same network. Behavioral experiments showed them to alter non-identical sets of behavioral features, suggesting they utilize somewhat independent sites of plasticity within the network. Large-scale voltage-sensitive dye recordings revealed two findings. First, both forms of learning, which occur sequentially in the 10-trial training protocol used, act to produce a change in the number of pedal neurons firing during the dorsal phase of the motor program, with sensitization producing an increase, and habituation a decrease in their number. The number of neurons participating in the ventral phase was unaffected. Second, sensitization produced an enhancement of burst intensity specific to the ventral phase neurons, while habituation was associated with a decrease in burst intensity in both phases. Using injected current pulses, intracellular recordings revealed that sensitization acted to increase the excitability of neurons firing in both phases, whereas habituation only acted to reduce excitability in ventral phase neurons. These excitability changes were associated with different mechanisms - reduced spike frequency accommodation in the ventral phase neurons, and depolarization of the resting potential in the dorsal phase neurons. These findings of partially different storage sites and mechanisms for two different non-associative memories illuminate a potential network strategy for minimizing destructive interference when storing multiple memories into the same network.

neuroscience↗