Quantifying the Effects of Two Local Anesthetics on the Crayfish Stretch Receptor Organ: An Integrated Neurophysiology Lab.

The crayfish stretch receptor organ (SRO) preparation represents a robust experimental model for undergraduate laboratory experiences. For example, this preparation may be included as part of a course-based undergraduate research experience (CURE), where students work independently to plan and carry out their own experiments. In the current paper, we provide an example of how local anesthetics may be used to manipulate the SRO preparation and to perform quantitative analyses of SRO action potential firing rates. Local anesthetics provide interesting tools for manipulating physiological responses within the nervous system. A variety of inexpensive anesthetics are available for student use and each of these is expected to inhibit neurophysiological responses. While specific anesthetics exhibit subtle differences in chemical organization, they are generally understood to block voltage gated sodium channels. In the current study, we investigated the effects of two local anesthetics, MS-222 and procaine, on the action potential firing rate from the crayfish SRO. Using quantitative analyses of SRO action potential generation, we determined that each anesthetic has unique inhibitory effects on action potential firing rate that may be explained by their neuropharmacological properties. This manipulation may thus be utilized as an interesting experimental tool in undergraduate teaching laboratories. Local anesthetics applied to crayfish SRO preparations can thus be used to deepen student understanding of local anesthetics, exercise quantitative analyses, and provide experimental tools for independent experimental design.

Cuneate nucleus: The somatosensory gateway to the brain.

Much remains unknown about the transformation of proprioceptive afferent input from the periphery to the cortex. Until recently, the only recordings from neurons in the cuneate nucleus (CN) were from anesthetized animals. We are beginning to learn more about how the sense of proprioception is transformed as it propagates centrally. Recent recordings from microelectrode arrays chronically implanted in CN have revealed that CN neurons with muscle-like properties have a greater sensitivity to active reaching movements than to passive limb displacement, and we find that these neurons have receptive fields that resemble single muscles. In this review, we focus on the varied uses of proprioceptive input and the possible role of CN in processing this information.