UCLA

Long-term Sensitization (LTS) and Long-term facilitation (LTF) are accompanied by an increase in the number of varicosities in the presynaptic sensory neurons in Aplysia (Bailey and Chen, 1983, 1988a; Glanzman et al., 1990). Both LTS and LTF are subject to erasure by inhibiting PKM Apl III, a PKM isoform in Aplysia, or by disrupting reconsolidation in Aplysia (Cai et al., 2011, 2012). To examine the effect of the two protocols of memory erasure on the morphological correlate of LTF, individual SN varicosities were tracked in confocal microscope images of a sensorimotor synapse that mediates the siphon/gill withdrawal reflex (SWR) in Aplysia. While the morphological correlate of LTF persisted up to 48 hours after 5X5-HT training, inhibiting PKM Apl III by chelerythrine or disrupting reconsolidation by reactivation with 1X5-HT immediately followed by protein synthesis inhibition with anisomycin (ANISO) at 24-hr reversed the presynaptic growth during 24-48 hr. Since chelerythrine did not change the number of SN varicosities in cocultures without prior 5X5-HT training, PKM Apl III inhibition selectively erased the structural growth underlying long-term memory. Furthermore, the abolition of the morphological correlate of LTF invariably resulted from inhibition of new growth during 24-48 hr as well as nonspecific removal of SN varicosities based on their formation history, suggesting that the engram for LTF is not localized to specific synapses.