Parametric studies of the response decrement produced by mechanical stimuli in the protozoan, Stentor coeruleus

A decrement in the probability of eliciting a response is observed during the course of repetitive stimulation in many response systems of both metazoa and protozoa. Those forms of metazoan response decrement called habituation have recently been characterized behaviorally. In the studies reported here, the response decrement of the contractile protozoan, Stentor coeruleus , to repeated mechanical stimulation was systemically characterized to provide a comparison with metazoan habituation. This change in response probability was closely approximated by a negative exponential function after the first few stimuli. Animals responded to parametric variations of stimulus amplitude, interstimulus interval and retention period in a manner paralleling that observed in metazoa. However, neither interpolated large amplitude mechanical stimuli nor suprathreshold electrical stimuli produced dishabituation in Stentor though these stimuli are among the most effective dishabituating stimuli for metazoan tactile response systems. Behavioral analysis of the response decrement proceeded on the assumption that Stentor contains receptor and effector mechanisms only. Since the response decrement was not correlated with a change in responsiveness to electrical stimuli, the ability of the animal to contract appears to be unaltered by the process producing the response decrement. On the other hand, weak mechanical prestimuli were found to increase the rate of the response decrement which suggests that a process of receptor adaption is operative.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50071/1/480010309_ftp.pd