A neuromechanical model for the neuronal basis of curve walking in the stick insect.

The coordination of the movement of single and multiple limbs is essential for the generation of locomotion. Movement about single joints and the resulting stepping patterns are usually generated by the activity of antagonistic muscle pairs. In the stick insect, the three major muscle pairs of a leg are the protractor and retractor coxae, the levator and depressor trochanteris, and the flexor and extensor tibiae. The protractor and retractor move the coxa, and thereby the leg, forward and backward. The levator and depressor move the femur up and down. The flexor flexes, and the extensor extends the tibia about the femur-tibia joint. The underlying neuronal mechanisms for a forward stepping middle leg have been thoroughly investigated in experimental and theoretical studies. However, the details of the neuronal and mechanical mechanisms driving a stepping single leg in situations other than forward walking remain largely unknown. Here, we present a neuromechanical model of the coupled three joint control system of the stick insect's middle leg. The model can generate forward, backward, or sideward stepping. Switching between them is achieved by changing only a few central signals controlling the neuromechanical model. In kinematic simulations, we are able to generate curve walking with two different mechanisms. In the first, the inner middle leg is switched from forward to sideward and in the second to backward stepping. Both are observed in the behaving animal, and in the model and animal alike, backward stepping of the inner middle leg produces tighter turns than sideward stepping.

[Navigation-assisted nailing of femoral shaft fractures--experimental and clinical results]. / Navigationsgestützte Marknagelung von Femurschaftfrakturen - experimentelle und klinische Ergebnisse.

AIM: The aim of the study was to evaluate the application of a navigation system (Brainlab) to control length and torsion intraoperatively while nailing a femoral shaft fracture. METHOD: At first the system was tested with 10 fractured synthetic bones. The postoperatively reached length and torsion were measured and the difference to the envisioned values statistically evaluated. Clinically we used the navigation system for patients with complex femoral shaft fractures. We always performed a preoperative computed tomography of the opposite leg to analyse the axis and fixed the fractured leg on these parameters using the navigation system. We noticed as improvement opportunities, the duration of the operative steps and the radiation exposure. The operative result was radiologically controlled and the torsion and length differences to the intraoperative measurement evaluated. Furthermore, we analysed the duration of the operation steps including the additional radiation exposure. RESULTS: There were no technical problems during operations on the synthetic bones. The accuracy was with +/- 5 degrees or +/- 2 mm good enough to use the already approved system clinically. The navigation system was used for 17 operations. All navigation-assisted operations were completed successfully. It took an average time of 32 min to install the navigation system and required an additional X-ray time of 44 sec. The average postoperative rotational deviation was 5.5 degrees . The average difference in length was 2 mm. CONCLUSION: The application of a navigation system for repositioning of femoral shaft axes and controlling the length and torsion while nailing complex femoral shaft fractures is associated with some additional work. Nevertheless, in our study a relevant rotational deviation can be avoided by using the navigation system. To prove the advantage of the navigation system over the conventional technique, clinical studies with larger number of cases are necessary.

Wide distribution of the cysteine string proteins in Drosophila tissues revealed by targeted mutagenesis.

The "cysteine string protein" (CSP) genes of higher eukaryotes code for a novel family of proteins characterized by a "J" domain and an unusual cysteine-rich region. Previous studies had localized the proteins in neuropil and synaptic terminals of larval and adult Drosophila and linked the temperature-sensitive paralysis of the mutants described here to conditional failure of synaptic transmission. We now use the null mutants as negative controls in order to reliably detect even low concentrations of CSPs by immunohistochemistry, employing three monoclonal antibodies. In wild-type flies high levels of cysteine string proteins are found not only in apparently all synaptic terminals of the embryonic, larval, and adult nervous systems, but also in the "tall cells" of the cardia, in the follicle cells of the ovary, in specific structures of the female spermatheca, and in the male testis and ejaculatory bulb. In addition, low levels of CSPs appear to be present in all tissues examined, including neuronal perikarya, axons, muscles, Malpighian tubules, and salivary glands. Western blots of isolated tissues demonstrate that of the four isoforms expressed in heads only the largest is found in non-neural organs. The wide expression of CSPs suggests that at least some of the various phenotypes of the null mutants observed at permissive temperatures, such as delayed development, short adult lifespan, modified electroretinogram, and optomotor behavior, may be caused by the lack of CSPs outside synaptic terminals.

Selective histamine uptake rescues photo- and mechanoreceptor function of histidine decarboxylase-deficient Drosophila mutant.

In insects, histamine is found both in the peripheral nervous system (PNS) and in the CNS and is known to function as a fast neurotransmitter in photoreceptors that have been shown to express selectively the hdc gene. This gene codes for histidine decarboxylase (HDC), the enzyme for histamine synthesis. Fast neurotransmission requires the efficient removal of the transmitter from the synaptic cleft. Here we identify in Drosophila photo- and mechanoreceptors a histamine uptake mechanism that can restore the function of these receptors in mutants unable to synthesize histamine. When apparent null mutants for the hdc gene imbibe aqueous histamine solution or are genetically "rescued" by a transgene ubiquitously expressing histidine decarboxylase under heat-shock control, sufficient amounts of histamine selectively accumulate in photo- and mechanoreceptors to generate near-normal electrical responses in second-order visual interneurons and qualitatively to restore wild-type visual and mechanosensory behavior. This strongly supports the proposal that histamine functions as a fast neurotransmitter also in a certain class of mechanoreceptors. A set of CNS-intrinsic neurons that in the wild type contain high concentrations of histamine apparently lacks this uptake mechanism. We therefore speculate that histamine of intrinsic neurons may function as a neuromodulator rather than as a fast transmitter.

Co-localization of NADPH-diaphorase and myomodulin in synaptic glomeruli of Aplysia.

We used NADPH-diaphorase staining as a marker for nitric oxide synthase to identify neurons and synapses in the nervous system of the mollusc Aplysia californica in which nitric oxide may be used as a transmitter. About 30 bilaterally paired neurons in the cerebral ganglion and a few neurons in other major ganglia were stained, as well as specific fiber tracts, neuropil and the lateral terminus, a synaptic glomerulus of the optic tract. The glomerulus was also stained by antisera to myomodulin, a peptide co-transmitter. The co-localization of myomodulin immunoreactivity and NADPH-diaphorase staining in the synaptic glomerulus, and the staining of select neurons and synaptic structures strongly suggests that nitric oxide functions in interneuronal communication.