High environmental salinity induces memory enhancement and increases levels of brain angiotensin-like peptides in the crab Chasmagnathus granulatus

Previous work on the brackish-water crab Chasmagnathus granulatus demonstra ted that an endogenous peptide similar to angiotensin II plays a significan t role in enhancing long-term memory that involves an association between c ontext and an iterative danger stimulus (context-signal memory). The presen t results show that this memory enhancement could be produced by moving cra bs from brackish water to sea water (33.0 parts per thousand) and keeping t hem there for at least 4 days. The possibility that such a facilitatory eff ect is due to osmotic stress is ruled out. Coincidentally, the level of ang iotensin-II-like peptides in crab brain, measured by radioimmunoassay, incr eases with the length of exposure to sea water, reaching a significantly di fferent level at the fourth day. The presence of angiotensin-II-like immuno reactive material in neural structures of the supraoesophageal and eyestalk ganglia was confirmed by immunohistochemical analysis. The results are int erpreted as supporting the hypothesis that exposure to water of high salini ty is an external cue triggering a process mediated by angiotensins that le ads to enhanced memory in these crabs.