Regeneration and molting effects on a proprioceptor organ in the Dungeness crab, Cancer magister

The effects of tricaine mesylate on arthropods: crayfish, crab and Drosophila

Tricaine mesylate, also known as MS-222, was investigated to characterize its effects on sensory neurons, synaptic transmission at the neuromuscular junction, and heart rate in invertebrates. Three species were examined: Drosophila melanogaster, blue crab (Callinectes sapidus), and red swamp crayfish (Procambarus clarkii). Intracellular measures of action potentials in motor neurons of the crayfish demonstrated that MS-222 dampened the amplitude, suggesting that voltage-gated Na + channels are blocked by MS-222. This is likely the mechanism behind the reduced activity measured in sensory neurons and depressed synaptic transmission in all three species as well as reduced cardiac function in the larval Drosophila. To address public access to data, a group effort was used for analysis of given data sets, blind to the experimental design, to gauge analytical accuracy. The determination of a threshold in analysis for measuring extracellular recorded sensory events is critical and is not easily performed with commercial software.

The effects of potassium and muscle homogenate on proprioceptive responses in crayfish and crab

Proprioception of limbs and joints is a basic sensory function throughout most of the animal kingdom. It is important to understand how proprioceptive organs and the associated sensory neurons function with altered environments such as increased potassium ion concentrations ([K⁺]) from diseased states, ionic imbalances, and damaged tissues. These factors can drastically alter neuronal activity. To assess this matter, we used the chordotonal organ in a walking leg of a blue crab (Callinectes sapidus) and the muscle receptor organ of the crayfish (Procambarus clarkii). These organs serve as tractable models for the analysis of proprioception. The preparations can help serve as translational models for these effects, which may be observed in other invertebrate species as well as mammalian species (including humans). When extracellular potassium concentration ([K⁺]_o) is increased to 20 mM in both preparations, mixed results are observed with activity increasing in some preparations and decreasing in others after mechanical displacement. However, when [K⁺]_o is increased to 40 mM, activity drastically decreases in all preparations. Additionally, proprioceptor sensory activity declines upon exposure to a diluted muscle homogenate, which contains a host of intracellular constituents. The robust effects of altered [K⁺] on proprioception in these models illuminate the potential detriments on neuronal function in cases of severe tissue damage as well as altered [K⁺]_o.

Proprioception and tension receptors in crab limbs: student laboratory exercises

The primary purpose of these procedures is to demonstrate for teaching and research purposes how to record the activity of living primary sensory neurons responsible for proprioception as they are detecting joint position and movement, and muscle tension. Electrical activity from crustacean proprioceptors and tension receptors is recorded by basic neurophysiological instrumentation, and a transducer is used to simultaneously measure force that is generated by stimulating a motor nerve. In addition, we demonstrate how to stain the neurons for a quick assessment of their anatomical arrangement or for permanent fixation. Staining reveals anatomical organization that is representative of chordotonal organs in most crustaceans. Comparing the tension nerve responses to the proprioceptive responses is an effective teaching tool in determining how these sensory neurons are defined functionally and how the anatomy is correlated to the function. Three staining techniques are presented allowing researchers and instructors to choose a method that is ideal for their laboratory.

Muscle receptor organs in the crayfish abdomen: a student laboratory exercise in proprioception

The primary purpose of this experiment is to demonstrate primary sensory neurons conveying information of joint movements and positions as proprioceptive information for an animal. An additional objective of this experiment is to learn anatomy of the preparation by staining, dissection and viewing of neurons and sensory structures under a dissecting microscope. This is performed by using basic neurophysiological equipment to record the electrical activity from a joint receptor organ and staining techniques. The muscle receptor organ (MRO) system in the crayfish is analogous to the intrafusal muscle spindle in mammals, which aids in serving as a comparative model that is more readily accessible for electrophysiological recordings. In addition, these are identifiable sensory neurons among preparations. The preparation is viable in a minimal saline for hours which is amenable for student laboratory exercises. The MRO is also susceptible to neuromodulation which encourages intriguing questions in the sites of modulatory action and integration of dynamic signals of movements and static position along with a gain that can be changed in the system.

Exploring with damaged antennae: do crayfish compensate for injuries?

Appendages are important sources of sensory information for all animals that possess them but they are commonly damaged in nature. We describe how the tactile system of the crayfish Cherax destructor functioned when subjected to the kind of damage found in wild-caught or cultured animals. Touch information was methodically varied by the removal of antennae and chelae. The resulting behaviour was analysed in a T-maze. Crayfish with a single antenna ablated turned toward the intact appendage, however, those with only a partial ablation did not, suggesting that a tactile information threshold exists for normal behaviour. When exposed to the same environment after an antennal ablation but with no prior experience in that terrain, crayfish also turned toward the side of the intact antenna. By contrast, when animals with experience obtained in a previous trial with intact antennae were tested after ablation of one antenna, they did not turn into one arm of the maze more than the other. These two outcomes indicate that behaviour is affected by an interaction between the time at which an injury occurs and an animal's knowledge of the topography, and that an injury may affect learning. We also tested to see if other appendages could provide tactile information to compensate for antennal loss. Input from the chelae did not affect the turning behaviour of crayfish in the maze.

Quantification of responses from proprioceptive neurons in the limbs of the crab, Cancer magister

In the limbs of crustaceans, proprioception is monitored by chordotonal organs. One in particular, MC1, is arranged in a manner that is accessible for single unit recording of primary sensory neurons while simulating joint movement. The movement-sensitive cells are of two types, those sensitive to relaxation or to elongation of the chordotonal strand which corresponds to flexion or extension of the meropodite-carpopodite joint, respectively. A statistical method for the quantification of these movement-sensitive proprioceptive neuronal responses was implemented. This statistical index, eta(2), should allow neuronal responses recorded in different laboratories to be easily and quantitatively compared. In addition, an eta(2) value can be assigned to individual cells which represents a cell's consistency and degree to which the response is related to the stimulus. We found some cells to have a high eta(2) and to be consistent in their activity while other cells had a high degree of variability with low eta(2) values. J. Exp. Zool. 284:629-636, 1999.