The Nishikawa Lab

Research Program & Projects

Fields of Research

Elastic properties of muscles
   During natural movements, muscles exhibit a variety of functions; they serve not only as motors, but also as springs, brakes, and struts. Our lab seeks to understand the mechanisms underlying the spring properties exhibited by muscles during active lengthening and shortening.

Neuromechanics of prey capture in frogs
   Feeding in frogs consists of coordinated head, jaw, and tongue movements that serve as an excellent model for studying the relationship between biomechanics and control in vertebrates. We have been focusing on feeding studies in the following anuran genera: Bufo, Rana, Litoria, Hemisus.

Diversity of form, function, and control
   While herps represent a dizzying range of forms used in an equally diverse functions, we also enjoy comparing the biomechanics of these animals to the truly astonishing diversity represented by invertebrate organisms. As such, we've looked at the muscle mechanical properties of orthopterans and are now developing a research project looking at structure and function of dynamic compliance in cephalopod vasculature.

Current Research Projects (2007-2008)

   Listed below are abstracts describing specific research projects being currently undertaken by the lab members.

Spring properties of muscle during active shortening and lengthening
Jenna Monroy, Jim Hokanson, & Kiisa Nishikawa
   When its load is reduced, an active muscle will recoil elastically to a shorter length. When its load increases, an active muscle will lengthen. In this study, we describe and compare the spring properties of mouse soleus muscle during active shortening and lengthening. Using load-clamp and dynamic stiffness experiments performed on a servo-motor force-lever, we measured the changes in muscle length that resulted from changes in muscle force. Using these data, we calculated muscle stiffness across a range of muscle forces and lengths. Our results show that muscle stiffness increases with force (i.e., up to maximum isometric force) and is greatest when changes in load are small (i.e., isotonic shortening). The relationship between change in length and force is exponential during active shortening. Thus, muscle stiffness decreases non-linearly as the change in load increases. Minimum stiffness, reached during unloaded shortening, is independent of the initial force. As active muscles are lengthened, both peak and steady-state forces increase linearly, so that muscle stiffness remains constant and is likewise independent of the initial force. Remarkably, the steady-state stiffness of actively lengthening muscle approaches the minimum stiffness observed during active shortening at zero load. These observations support the hypothesis that titin plays a role in elastic recoil of actively shortening muscle as well as in steady-state enhancement of force with stretch. Supported by NSF IOS-0623791, IOS-0732949, NIH R25-GM56931, the TRIF Fund for Biotechnology and Science Foundation Arizona.

More boing for your buck: spring properties of muscle at and beyond optimal length
Leslie Gilmore, Jenna Monroy, Jim Hokanson, & Kiisa Nishikawa
   A muscle produces maximal force when activated at its optimal length. If the muscle is rapidly unloaded at this length, it exhibits a fast recoil phase and then a slow phase of shortening. Distance and speed of recoil during the initial phase are determined by the elastic properties of the muscle, while the slow phase of shortening is a function of the cycling of the crossbridges with the thin filament. In this study, we investigated the effects of increases in muscle length on the fast recoil phase. We used a servo motor force lever system to perform load clamp experiments on mouse soleus and EDL muscles. Prior to activation, muscle lengths were increased 5-25% beyond optimal lengths in order to measure the distance of shortening during the fast phase. Preliminary results show that, for a given change in load, as muscle length increases the distance shortened during the fast phase is greater. Remarkably, the stiffness decreases as the muscle length increases beyond the optimal length. These preliminary results appear to be consistent with the hypothesis that the viscoelastic titin protein contributes to both force enhancement with stretch and elastic recoil during rapid unloading in active muscle. Supported by NSF IOS-0623791, IOS-0732949, NIH R25-GM56931, the TRIF Fund for Biotechnology and Science Foundation Arizona.

Don't call me a stiff: changes in performance and histology with age
Morgan Burnette, Jenna Monroy, Bud Lindstedt, & Kiisa Nishikawa
   As many of us can feel, muscles get stiffer and weaker as we age. Stiffness is dependent on the force generated by the muscle as well as the external load. This is true for muscles during both active shortening and lengthening. Our study investigates the histology underlying changes in stiffness and force during active shortening. Mouse soleus and EDL muscles were serially sectioned and stained for ATPase activity and oxidative capacity. We measured whole muscle cross-sectional area, fiber cross sectional area, fiber density, fiber-type (fast or slow), fiber-type ratio and distribution. Relative to old muscles, young muscles are larger in cross-sectional area and mass. In young EDL and soleus muscles, low oxidative fibers have greater cross-sectional area and diameter than high oxidative fibers. Furthermore, the ratio of fast to slow fibers was 60:40 in EDL and 50:50 in soleus. Preliminary results indicate that old EDL and soleus muscles have relatively fewer high oxidative fast fibers. As such, muscles that produce less force have increased stiffness. These results suggest an increased importance of maintaining muscle force to ensure more compliant muscles as we age.

It's in the way that you use it: how activation patterns affect anuran feeding behavior
Eric Zepnewski, Carrie Carreno, Kris Lappin, & Kiisa Nishikawa
   Most frogs and toads capture prey by protracting their tongues. More than 90% of the power for this movement is generated by a single pair of jaw opening (depressor) muscles. In species of Bufo, the depressor muscles are pre-loaded to achieve the relatively high forces necessary for ballistic tongue protraction. When the depressor muscles are pre-loaded, elastic energy is stored and then recovered during mouth opening. As such, the spring properties of the depressor muscles are thought to play an important role. In comparison, Ceratophrys cranwelli exhibits non-ballistic tongue protraction. Simultaneous EMG and high-speed video recordings show that the depressor muscles are not pre-loaded prior to tongue protraction. In situ muscle lever experiments in Ceratophrys demonstrated that active depressor muscle stiffness during shortening resembled stiffness values of Bufo when they were loaded similarly. Thus, behavioral differences may be explained by different morphologies. Morphological measurements showed differences in mechanical advantage between species. These results suggest that muscle is an adaptable tissue that, by virtue of common intrinsic elastic properties, may exhibit extremely different behaviors under varying conditions of activation, load, and mechanical advantage. Supported by NSF IOS-0623791, IOS-0732949, NIH R25-GM56931, the TRIF Fund for Biotechnology and Science Foundation Arizona.

Response of Herpetofauna to Ponderosa Pine Forest Treatments Prescribed by the National Fire and Fire Surrogate Study
Jean Block & Kiisa Nishikawa
   Ponderosa pine forests across the southwestern United States are being treated by thinning and burning to reduce fuel loads and the risk of catastrophic wildfire and to reintroduce fire regimes that were known to occur prior to European settlement. However, little is known about how these treatments influence herpetofauna populations. Compared to bird and mammal studies, herpetofauna are underrepresented in the literature. Studying their response to forest treatments is especially important given their general decline worldwide. I compared post-treatment occupancy rates, abundance, sex and age ratios and survival of herpetofauna between four different forest treatments prescribed by the National Fire and Fire Surrogate Study in northern Arizona. Additionally, I examined associations between habitat and occupancy rate in each treatment. Treatments were prescribed in three replicated blocks and included an untreated control, a burned area, a thinned area and a thinned and burned area. Results from my study revealed several significant patterns. The southern plateau lizard (Sceloporus undulates tristichus) was the dominant species detected and was the only species that provided a sufficient sample size to perform statistical analyses. Occupancy rate of these lizards was significantly greater in the thin/burn treatment and across one replicate. The proportion of hatchlings was significantly lower in the untreated control. Habitat features associated with late successional forest stages were negatively correlated with occupancy while those associated with early successional forest stages were positively correlated with occupancy. My study suggests that southern plateau lizards select habitat associated with early to middle successional forest stages, especially habitat disturbed by the combination of thinning and burning. Additionally, untreated, dense, fire-suppressed forests restrict juvenile recruitment of this species. Increased presence of both adult and juvenile lizards in thinned and burned forest areas indicates increased diversity of other species. Hence, thinning and burning ponderosa pine forests to some degree is recommended. However, in the interest of other species, it is important to maintain patches of middle to late successional forest habitat. Finally, further studies of other herpetofauna species in treated and untreated ponderosa pine forests are recommended since very few of these species were detected.

The biomechanics of cephalopod branchial hearts: an interdisciplinary approach to a novel inspiration for the treatment of peripheral arterial disease
Ted Uyeno, Scott Nichols & Kiisa Nishikawa
   Peripheral Arterial Disease concerns Arizona because of its prevalence and debilitating symptoms. Caused by reduced blood flow through peripheral arteries, surgical treatment may involve implanting synthetic vascular grafts. Because these rigid implants tend to buckle and plug with clots, new designs are of great value. Our goal is to develop novel design principles using a biologically inspired approach: as active cephalopods evolved efficient, closed-circuit, and high-pressure circulatory systems with elastic arteries and accessory hearts, from open and low-pressure ancestral precursors, biomechanical analyses may inspire useful structural designs. To identify principles of function, we will describe cephalopod accessory heart morphology using microscopy, histology, and corrosion casts; we will test vascular wall mechanical properties using force lever and material properties testing; and electromyography, cinematography, and pressure measurements will be used to test the resultant functional postulates. These data will enhance future grant proposals to develop proof of concepts for novel implant designs.