Crayfish Learning: Addiction and the Ganglionic Brain

Abstract

Recognizing addiction as a phenomenon with deep evolutionary roots grants valuable new perspectives into understanding its behavioral features, as well as its underlying neural mechanisms and genetic architecture. Although now generally misbranded as "human drugs of abuse," addictive plant alkaloids originally arose as potent chemical defenses against insect herbivory. The products of this evolutionary arms race, compounds such as nicotine, cathinone, or morphine, target essential biological mechanisms for motivation and learning and act as weaponized disruptors. Human vulnerabilities to these addictive drugs may thus represent little more than collateral damage arising from deep homology, i.e., shared biological implementation of behavioral functions with taxa that trace back to the early divergence of bilateral metazoans. Consistent with such a view, invertebrate preparations exhibit a rich spectrum of behavioral and neural consequences in response to drug exposure. Although there is certainly evidence for addiction-like phenomena in many invertebrate lineages, the present review focuses attention primarily on our recent work in crayfish. Using this decapod crustacean model, we have characterized a range of amphetamines, cathinones, and opioids for evidence of unconditioned intoxication, sympathomimetic properties, psychostimulant sensitization, conditioned cue learning, and operant selfadministration. Overall, our findings on drug-sensitive reward in crayfish bear striking similarities to equivalent phenomena illustrated in mammals. Experimentally tractable invertebrate models may thus provide fundamental insights into the homo-and paralogous mechanisms mediating responses to addictive drugs, while illuminating the limits of such contrasts.

Synaptic Mechanisms of Ethanol Tolerance and Neuroplasticity: Insights from Invertebrate Models

“…Invertebrates such as Caenorhabditis elegans (nematodes) and Drosophila melanogaster (fruit/vinegar flies) are valuable research models for investigating the roles of individual genes and proteins in neurotransmission, particularly those associated with alcohol-induced behaviors and neuroplasticity [30,31]. Other invertebrate models such as Schmidtea mediterranea, Giradia tigrina (planaria), Apis mellifera (honey bees), and Orconectes rusticus (crayfish) have also been used as promising models to study alcohol-related behaviors; however, they have been studied more sporadically and with lesser molecular and mechanistic amenability [32][33][34]. Therefore, this review will focus on the studies in Drosophila and C. elegans.…”

The Streetlight Effect: Reappraising the Study of Addiction in Light of the Findings of Genome-wide Association Studies

“…As just one example, a variant of the fatty acid amide hydrolase gene that is associated with drug dependence is estimated to be around 150,000 years old [Flanagan et al, 2006]. Moreover, many of the mechanisms that underlie drug dependence have much older evolutionary roots than that, far older than even just the mammalian lineage [van Staaden and Huber, 2018]. These roots may lie more in the common and deep evolutionary roots for motivation and its role in learning rather than for addiction per se.…”

Cardiac and Locomotor Responses to Acute Stress in Signal Crayfish Pacifastacus leniusculus Exposed to Methamphetamine at an Environmentally Relevant Concentration

“…Drug residues may be integrated into the tissue of aquatic invertebrates [16] and vertebrates [17], and can modify the physiology of invertebrates, i.e., zebra mussels [18][19][20]. Planarians [21,22] and crayfish [23][24][25][26][27] showed, similarly like target organism, reinforcing effect to higher concentrations of dopaminergic drugs. Impact of drugs to physiology and behaviour were reported by Liao et al (2015) [28] on aquatic vertebrates such as fish Oryzias latipes and European eel Anguilla anguilla [29].…”