Increased age affects properties characterizing behavioral plasticity in freely behaving Aplysia.
In the marine mollusc Aplysia, in vitro studies showed that the gill withdrawal reflex (GWR) and its neuronal substrates were altered by age. In contrast, age minimally affected the gill respiratory pumping movements (GPM) and its neuronal substrates. Based on the respective properties of the GWR- and GPM-pathways in vitro, we proposed that the more pronounced the effect of age, the greater the expression of plasticity in a pathway. This conclusion may hold for in vitro preparations, but it remained to be demonstrated in intact animals. Based on this conclusion, the GWR should exhibit greater plasticity than the GPM in intact animals. Using freely behaving Aplysia, we tested for plasticity of the GWR and the GPM in three age groups (young, mature, and old). The tests for behavioral plasticity were: Graded responses to varying stimulus strength, response decrement (or habituation) to repetitive stimulation, enhanced response to dishabituating stimuli, and the effect of the GWR stimulus on the GPM and the GPM stimulus on the GWR. The GWR in mature animals exhibited all four properties, but in old animals, graded responses and habituation were significantly altered and in young animals habituation and dishabituation were absent. The GPM exhibited fewer of the properties than the GWR, only graded responses and response decrement, both of which were generally the same in the three groups. We found that behavioral plasticity and age-induced plasticity are related in freely behaving animals and are consistent with in vitro findings. The effect of age on properties characterizing plasticity at both the behavioral and pathway levels is discussed.
Hallahan
B J
BJ
Department of Physiology and Biophysics, College of Medicine, University of Kentucky, Lexington 40536-0084.
Peretz
B
B
Skinner
T L
TL
D000375:Aging / Q000523:psychology*; D000818:Animals; D001048:Aplysia / Q000502:physiology*; D001522:Behavior, Animal / Q000502:physiology*; D005880:Gills / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D009434:Neural Pathways / Q000502:physiology; D012018:Reflex / Q000502:physiology