Activity-related calcium dynamics in motoneurons of the nucleus hypoglossus from mouse

A quantitative analysis of activity-related calcium dynamics was performed in motoneurons of the nucleus hypoglossus in the brain stem slice preparation from mouse by simultaneous patch-clamp and microfluorometric calcium measurements. Motoneurons were analyzed under in vitro conditions that kept them in a functionally intact state represented by rhythmic, inspiratory-related bursts of excitatory postsynaptic currents and associated action potential discharges. Bursts of electrical activity were paralleled by somatic calcium transients resulting from calcium influx through voltage-activated calcium channels, where each action potential accounted for a calcium-mediated charge influx around 2 pC into the somatic compartment. Under in vivo conditions, rhythmic-respiratory activity in young mice occurred at frequencies up to 5 Hz, demonstrating the necessity for rapid calcium elevation and recovery in respiratory-related neurons. The quantitative analysis of hypoglossal calcium homeostasis identified an average extrusion rate, but an exceptionally low endogenous calcium binding capacity as cellular parameters accounting for rapid calcium signaling. Our results suggest that dynamics of somatic calcium transients 1) define an upper limit for the maximum frequency of respiratory-related burst discharges and 2) represent a potentially dangerous determinant of intracellular calcium profiles during pathophysiological and/or excitotoxic conditions.     

Localization of motoneurons innervating the stylopharyngeus muscle in the cat

Recent investigations of the nucleus ambiguus (NA) have attempted to identify motoneurons associated with muscles of the larynx and pharynx. However, relatively little attention has been directed to the stylopharyngeus muscle, which is important in elevation of the pharynx in swallowing and speech. The present study was designed to identify the specific location of stylopharyngeus motoneurons within the brainstem. Horseradish peroxidase or fluorescent dye was injected into the stylopharyngeus muscle of 12 cats. Retrogradely labeled cells were located ipsilateral in the rostral NA and retrofacial nucleus. This is the first report to definitively localize stylopharyngeus motoneurons.     

X-ray determination of crystalline hydroxyapatite to amorphous calcium-phosphate ratio in plasma sprayed coatings

A method to measure the amorphous calcium phosphate (ACP) content of plasma sprayed hydroxyapatite (HA) coatings is presented. The areas of the crystalline peaks and the broad amorphous "hump" in an X-ray diffraction scan of a mixture of crystalline and amorphous HA can be fitted using conventional nonlinear least-squares methods. The weight fraction of the amorphous component in a mixture of unknown proportions is obtained from the measured hump fraction using a linear expression requiring a single calibration constant. This calibration constant may be determined by applying the same sample preparation, X-ray measurement, and least-squares fitting methods to a single standard of known (weighed) proportions as used to measure the unknown(s). Application of this method to a set of 12 samples yields an "index of crystallinity" for plasma sprayed HA coatings with an estimated standard deviation of 1 wt % ACP across the entire compositional range.     

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Strain-specific development of the mossy fiber system in organotypic cultures of the mouse hippocampus

The postnatal development of the hippocampus of the inbred mice strains BALB/c, C57BL/6, and DBA/2 was studied in organotypic explant cultures using the roller-tube technique. In vivo, mice exhibit strain-specific mossy fiber distribution patterns. As a main result we found, that after cultivation of 3-4 weeks, similar strain-specific patterns became apparent in vitro, as visualized by a modified Timm staining. From this experiment we can conclude that a postnatal extrinsic influence cannot be the cause of the strain-specific hippocampal features.     

The cauliflower mosaic virus translational transactivator interacts with the 60S ribosomal subunit protein L18 of Arabidopsis thaliana

The cauliflower mosaic virus (CaMV) open reading frame VI product (P6) is involved in several aspects of the infectious cycle. P6 specifically controls the synthesis of other CaMV proteins by transactivating their expression from the polycistronic 35S RNA. By far-Western assays, we have demonstrated that P6 interacts with proteins from both healthy and CaMV-infected leaves of Arabidopsis thaliana. These proteins are found in ribosome-enriched extracts, suggesting that they participate in the translation process. One of these proteins, identified by microsequencing, corresponds to the 60S ribosomal subunit protein L18 (RPL18). Its cDNA was cloned and expressed in Escherichia coli, and the resulting RPL18 protein was shown to interact with the minimal region required for translational transactivation, designated the miniTAV domain of P6.