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

Abstract

Previous work on the brackish-water crab Chasmagnathus granulatus demonstrated that an endogenous peptide similar to angiotensin II plays a significant role in enhancing long-term memory that involves an association between context and an iterative danger stimulus (context-signal memory). The present results show that this memory enhancement could be produced by moving crabs from brackish water to sea water (33.0%) and keeping them there for at least 4 days. The possibility that such a facilitatory effect is due to osmotic stress is ruled out. Coincidentally, the level of angiotensin-II-like peptides in crab brain, measured by radioimmunoassay, increases with the length of exposure to sea water, reaching a significantly different level at the fourth day. The presence of angiotensin-II-like immunoreactive material in neural structures of the supraoesophageal and eyestalk ganglia was confirmed by immunohistochemical analysis. The results are interpreted as supporting the hypothesis that exposure to water of high salinity is an external cue triggering a process mediated by angiotensins that leads to enhanced memory in these crabs.