Neurobiology C.Elegans

Abstract:

Evolution is known as the way species become fit over many generations, however individuals can also learn new behaviors within their lifetime that increase their chances of survival. In order to accomplish this, organisms need to be able to anticipate and respond to the current state of their environment. In this experiment it is expected that wild type and mutant C.elegans will form non-associative memories (habituate), measured by decreased number of reversals, when presented with a tap stimulus over multiple trials. The C.elegans tested were placed under a microscope and given a tap stimulus over several training and test trials. During each of these trials the movement of the C.elegans was measured before and after stimulus. This was repeated with C.elegans with a mutation in the Nmr-1 gene. It was observed that wild type and Nmr-1 mutant C.elegans had and positive average savings (0.8 and 0.6 reversals) trials for both wild type and Nmr-1 mutants. Nmr-1 mutants showed a greater amount of reversals during training compared to wild type. We concluded that C.elegans are able to habituate in both wild type and Nmr-1 mutants. The Nmr-1 gene appears to cause a decrease in ability of the creatures to continue in one direction for long periods of time.

Introduction:

The association between learned associations and environment is a crucial factor in many aspects of an organism's life. These aspects include survival all the way down to simple daily activities such as moving. One of the most common forms of association, and also the one which was studied in this lab with C.elegans, is habituation. Habituation is an example of non-associative memory, which is when a response behavioral response diminishes when given repeated stimuli. An organism will first respond to a stimulus, however, if it is neither harmful nor beneficial then subsequent responses will be diminished. This differs from the classical conditioning (associative learning), in which an association between two stimuli (unconditioned stimulus and conditioned stimulus) is learned. Habituation has been recorded in all organisms that have been tested, from protozoa to humans (Rankin and Rose, 2001).

In this lab, the memory of C.elegans was tested by measuring the changes in behavioral responses over several trials. The lab focused on measuring habituation in the C.elegans, which would show the formation of non-associative memory. This was done by presenting a conditioned stimulus repeatedly without any unconditioned stimulus. During these repeated trials the C.elegans should show a decreased response to the CS, as it does not positively or negatively affect them. C.elegans are a good model organism for this habituation experiment. C.elegans have a simple morphology, and we have been able to diagram the entirety of their neuronal