DEVELOPMENTAL EMERGENCE OF LONG-TERM-MEMORY FOR SENSITIZATION IN APLYSIA

Adult Aplysia exhibit both short-term and long-term memory for sensiti zation in the gill and siphon withdrawal reflex. Previous developmenta l studies showed that short-term memory for sensitization emerges late in juvenile development (stage 12; Rankin and Carew, 1988; Wright et al., 1991). In the present study, we examined the development of long- term memory for sensitization. Long-term sensitization of the siphon w ithdrawal reflex was quantified as an increase in mean response durati on observed 20-24 h after receiving a training regime of one or more 9 0-min sessions of electrical shock to the tail. In the first three exp eriments we assessed the capacity for long-term sensitization in adult s and in juveniles of stages late 12 and early 12. Animals in all thre e age classes showed long-term sensitization. In a fourth experiment w e simultaneously trained and tested both early stage 12 animals and st age 11 animals with identical stimulus parameters that were scaled dow n to a level appropriate to the smaller stage 11 animals. Under these conditions, the early stage 12 animals demonstrated long-term sensitiz ation, while the stage 11 animals still showed no evidence of long-ter m sensitization. These results indicate that long-term sensitization f irst emerges at early stage 12, which is the same developmental stage in which short-term sensitization first emerges. Although these behavi oral data do not elucidate underlying mechanisms, the fact that short- term and long-term memory emerge according to the same developmental t imetable is consistent with the possibility that these two forms of me mory may share at least some common mechanistic features. (C) 1996 Aca demic Press, Inc.