Effects of activation and inhibition of cAMP-dependent protein kinase on long-term habituation in the crab Chasmagnathus

ROMANO A; LOCATELLI F; DELORENZI A; PEDREIRA ME; MALDONADO H

BRAIN RESEARCH

Elsevier

Lugar: La Jolla, CA, USA.; Año: 1996 vol. 735 p. 131 - 140

0006-8993

On sudden presentation of a danger stimulus, the crab Chasmagnathus elicits an escape response that habituates promptly and for a long period. We have previously reported that administration of a cAMP-permeable analog (CPT-cAMP) along with a phosphodiesterase inhibitor (IBMX) improves long-term habituation (LTH). In present experiments we studied the effect of systemic administration of the protein kinase A (PKA) activator Sp-5,6-DCI-cBIMPS and that of the PKA inhibitor Rp-8-CI-cAMPS on LTH tested 24 h after a weak training protocol (5 trials of danger stimulus presentation) or a strong training protocol (15-30 trials), respectively. A 50 txl pre-training injection of 75 txM Sp-5,6-DCI-cBIMPS, and to a lesser degree of 25 IxM, improved retention of the habituated response but not affect short-term habituation (STH). Like pre-training injection, post-training administration of Sp-5,6-DCI-cBIMPS proved to exert a facilitatory action on retention though with 75 IxM dose only. Conversely, both pre- and post-training injection of 25 txM Rp-8-CI-cAMPS impaired LTH without affecting STH. Thus, the PKA activator Sp-5,6-DCI-cBIMPS enables a weak training to produce LTH while the PKA inhibitor Rp-8-CI-cAMPS impairs LTH when a strong training is given. Activation of crab PKA by Sp-5,6-DCI-cBIMPS and its inhibition by Rp-8-CI-cAMPS were assessed using an in vitro PKA activity assay. These results provide independent evidences supporting the view that PKA plays a key role in long-term memory storage in this learning paradigm.