text on bottom of page 7 of paper handout

Caenorhabditis elegans
a thread worm

See Habituation refs Broster and Rankin (1994), Wicks and Rankin (1996) and Staddon & Higa (1996), plus the references below, particularly Rose and Rankin (2001) for long-term habituation.

Many biologists work on this species because it is a simple animal, which matures in 3 days and lives only 3 or 4 weeks.

The project to determine the exact sequence of all its DNA was one of the first of this kind and was completed in 1998. (Hodgkin, Jasny and Kimble, Science, Dec 11th, 1998 | summary ot the introduction to the special issue of Science) gif

It is a thread worm, only 1 mm long that lives in soil.

Its body is made up of 959 cells, of which 81 are muscle cells and 302 are neurons
(In the rare males, 1031 cells of which 381 are neurons.)

Although habituation of its “reverse-swimming” response varies according to the Inter-Stimulus-Interval (ISI) the data can be modelled by “a remarkably simple process” (Staddon and Higa, 1996), which corresponds to two habituating neurons in the S-R (stimulus-response) pathway (cf Groves and Thompson, 1970: sheet 8 of handout )

Hobert, O. (2003). Behavioral plasticity in C-elegans: Paradigms, circuits, genes. Journal of Neurobiology, 54(1), 203-223.

Life in the soil is an intellectual and practical challenge that the nematode Caenorhabditis elegans masters by utilizing 302 neurons. The nervous system assembled by these 302 neurons is capable of executing a variety of behaviors, some of respectable complexity. The simplicity of the nervous system, its thoroughly characterized structure, several sets of well- defined behaviors, and its genetic amenability combined with its isogenic background make C. elegans an attractive model organism to study the genetics of behavior. This review describes several behavioral plasticity paradigms in C. elegans and their underlying neuronal circuits and then goes on to review the forward genetic analysis that has been undertaken to identify genes involved in the execution of these behaviors. Lastly, the review outlines how reverse genetics and genomic approaches can guide the analysis of the role of genes in behavior and why and how they will complement the forward genetic analysis of behavior. (C) 2003 Wiley Periodicals, Inc.

Rose, J. K., & Rankin, C. H. (2001). Analyses of habituation in Caenorhabditis elegans. Learning & Memory, 8(2), 63-69.

Although the nonassociative form of learning, habituation, is often described as the simplest form of learning, remarkably little is known about the cellular processes underlying its behavioral expression. Here, we review research on habituation in the nematode Caenorhabditis elegans that addresses habituation at behavioral, neural circuit, and genetic levels. This work highlights the need to understand the dynamics of a behavior before attempting to determine its underlying mechanism. In many cases knowing the characteristics of a behavior can direct or guide a search for underlying cellular mechanisms. We have highlighted the importance of interstimulus interval (ISI) in both short- and long-term habituation and suggested that different cellular mechanisms might underlie habituation at different ISIs. Like other organisms, C. elegans shows both accumulation of habituation with repeated training blocks and long-term retention of spaced or distributed training, but not for massed training. Exposure to heat shock during the interblock intervals eliminates the long-term memory for habituation but not the accumulation of short-term habituation over blocks of training. Analyses using laser ablation of identified neurons, and of identified mutants have shown that there are multiple sites of plasticity for the response and that glutamate plays a role in long-term retention habituation training.

Schafer, W. R. (2005). Deciphering the neural and molecular mechanisms of C-elegans behavior. Current Biology, 15(17), R723-R729.

Because of its small and well-characterized nervous system and amenability to genetic manipulation, the nematode Caenorhabditis elegrans offers the promise of understanding the mechanisms underlying a whole animal's behavior at the molecular and cellular levels. In fact, this goal was a primary motivation behind the development of C. elegans as an experimental organism 40 years ago. Yet it has proven surprisingly difficult to obtain a mechanistic understanding of how the C. elegans nervous system generates behavior, despite the existence of a 'wiring diagram' that contains a degree of information about neural connectivity unparalleled in any organism. This review describes three types of information - molecular data on cellular neurochemistry, temporal information about neural activity patterns, and behavioral data on the consequences of neural ablation and manipulation - that, along with genetic analysis, may ultimately lead to a complete functional map of the C. elegans nervous system.