Abstract
A decade of studies on long-term habituation (LTH) in the crab Chasmagnathus is reviewed. Upon sudden presentation of a passing object overhead, the crab reacts with an escape response that habituates promptly and for at least five days. LTH proved to be an instance of associative memory and showed context, stimulus frequency and circadian phase specificity. A strong training protocol (STP) (> or = 15 trials, intertrial interval (ITI) of 171 s) invariably yielded LTH, while a weak training protocol (WTP) (< or = 10 trials, ITI = 171 s) invariably failed. STP was used with a presumably amnestic agent and WTP with a presumably hypermnestic agent. Remarkably, systemic administration of low doses was effective, which is likely to be due to the lack of an endothelial blood-brain barrier. LTH was blocked by inhibitors of protein and RNA synthesis, enhanced by protein kinase A (PKA) activators and reduced by PKA inhibitors, facilitated by angiotensin II and IV and disrupted by saralasin. The presence of angiotensins and related compounds in the crab brain was demonstrated. Diverse results suggest that LTH includes two components: an initial memory produced by spaced training and mainly expressed at an initial phase of testing, and a retraining memory produced by massed training and expressed at a later phase of testing (retraining). The initial memory would be associative, context specific and sensitive to cycloheximide, while the retraining memory would be nonassociative, context independent and insensitive to cycloheximide.
Highlights
A decade of studies on long-term habituation (LTH) in the crab Chasmagnathus is reviewed
Diverse results suggest that LTH includes two components: an initial memory produced by spaced training and mainly expressed at an initial phase of testing, and a retraining memory produced by massed training and expressed at a later phase of testing
With this theoretical reference framework we are presenting in this review the most salient results obtained over more than ten years using a basic model of memory, namely the long-term habituation (LTH) of the crab Chasmagnathus granulatus
Summary
Simple-system approaches using invertebrate species have led to considerable progress in our understanding of the mechanisms underlying learning and memory (e.g., the mollusks Aplysia [1,2] and Hermissenda [3,4], the fruit fly Drosophila [5], and the honey bee Apis [6]). It has been argued that the relevance to memory of these results should be tested in a behaving animal (an appropriate basic model), bringing the search for the cellular and molecular basis of memory back to the behaviors it was designed to explain [10]. With this theoretical reference framework we are presenting in this review the most salient results obtained over more than ten years using a basic model of memory, namely the long-term habituation (LTH) of the crab Chasmagnathus granulatus
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