Cellular Mechanisms of Intrinsic and Extrinsic Sensitization

Purdue University, West Lafayette IN

Investigators

Abstract

Burrell, Brian 0213458 Sensitization is a simple form of learning in which an animal's responses to environmental stimuli are enhanced. This form of behavioral plasticity is important because it contributes to processes of attention and arousal, as well as to more complex forms of learning such as classical (i.e. Pavlovian) conditioning. Typically, sensitization is induced by the delivery of a particularly strong or salient stimulus. This stimulus activates neurons that release modulatory neurotranmitters, which alter the neural circuit mediating the test behavior. Because the modulatory neurons are distinct from the neurons that mediate the test behavior, this process is referred to as extrinsic sensitization. However, there are many examples where sensitization is induced by a stimulus that is similar or identical to the stimulus that elicits the test behavior. In such situations, modulatory neurotransmitters are released by neurons within the circuit that mediates the test behavior. This is referred to as intrinsic or wind-up sensitization. Using the medicinal leech, the distinct physiological and cellular mechanisms of intrinsic and extrinsic sensitization will be examined. These experiments will combine electrophysiological recordings from single neurons with simultaneous monitoring of sensitization-induced changes in a defensive withdrawal reflex (shortening). Both forms of sensitization are observed in the leech shortening reflex and the leech nervous system is extremely well characterized, making it possible to record from single, identifiable neurons that are known to mediate this behavior.