Showing posts with label learning. Show all posts
Showing posts with label learning. Show all posts

Saturday, January 28, 2017

Molluscan Memory of Injury: Evolutionary Insights into Chronic Pain

 Brain Behav Evol 2009; 74: 206-218

Edgar T. Walters and Leonid L. Moroz

In this paper, the authors raise an interesting hypothesis that the plasticity mechanisms underlying learning and memory in higher organisms may have evolved from adaptive responses that repair damaged neuronal processes or body parts. Persistent nociceptive sensitization in Aplysia nervous system displays many functional similarities to alterations in mammalian nociceptors associated with the clinical problem of chronic pain. The original responses induced regrowth of damaged axon, increased excitability, enhanced release of transmitter, and reorganization of cellular network. Such compensatory responses would be critical for survival in the early age.

Before discussing about the origin of chronic pain and synaptic plasticity, the authors also described how great Aplysia is. They compared molluscs with other model systems like arthropod and nematode by comparing the number of gene homologues that are shared by mammals, and their evolutionary distances from mammals. Mollucs are closer to mammals because they split earlier. Slower rate of gene evolution provided molluscs more homologous genes associated with human disease than Drosophila or C. elegans. DNA methylation can also be seen in molluscs. Thus, integration of genomics and physiological studies in molluscan neurons offers a powerful comparative approach to address molecular and cellular aspects of selected neurological problems.

Altogether, molluscan preparations should become increasingly useful for comparative studies across phyla that can provide insight into cellular functions of clinically important genes.

Thursday, December 29, 2016

Journal club: Evolution of highly diverse forms of behavior in molluscs

Current Biology 26, R965-71 (2016)
Binyamin Hochner and David L. Glanzman
DOI: http://dx.doi.org/10.1016/j.cub.2016.08.047

This short review paper starts off with the comparative anatomy of the nervous system.  The authors discuss the diversity of the nervous system and its co-evolution with body plan by showing a variety of nervous systems from Solenogastres to cephalopods. Then, cellular mechanisms of synaptic plasticity underlying learning in the gastropod Aplysia and the cephalopod Octopus were discussed.

The first part was fun to read.
Comparative anatomy of the nervous system is a good reminder that the molluscan nervous system, or the medullary cord, is organized in a ladder-like fashion. The loss of collinear pattern of gene expression may explain their simple body plans. The supremacy of Octopus in the motor and cognitive abilities can be due to the high expansion of two developmentally important gene families, extensive transposable element activity, and genome rearrangements.

The second part was somewhat boring.
The title says the diversity of behavior, but this part actually covers just synaptic plasticity in Aplysia (serotonin-mediated long-term facilitation) and Octopus (long-term potentiation). The mechanisms underlying the serotonergic enhancement of synaptic strength has already been described five hundred times elsewhere.  Plus, I don't think this is a valid comparison to discuss about the evolutional process, because the gill-withdrawal reflex and the higher-order learning are completely different brain functions. Such comparison merely shows different types of learning regardless of species, not actually explains the species-dependent differences or the evolution. This is like comparing the spinal reflex and motor learning in two different vertebrate species. No wonder they are different; synaptic plasticity has little to do with the diversity of behavioral expressions.