No abstract

The purpose of this study was to develop a scheme for classifying turtle motoneurons, such that their properties could be compared to those of other vertebrate species, including, in particular, the cat. A 130-cell sample of turtle motoneurons was provisionally classified into four groups (1-4) on the basis of a cluster analysis of the cells' intracellularly recorded input resistance, rheobase, and slope of their stimulus current-spike frequency relation. These measurements, using sharp microelectrodes and an in vitro spinal cord slice preparation, were particularly robust. It is argued that the cat counterpart of our turtle type 1, 2, and 3 motoneurons innervate slow-twitch muscle fibers, fast-twitch-oxidative fibers, and fast-twitch-glycolytic fibers, respectively. Our turtle type 4 motoneuron is thought analogous to a particularly high-threshold cat and human cell that innervates highly fatigable fast-twitch muscle fibers in both species. Our turtle type 1 category may include cells that innervate non-twitch muscle fibers, which are found in other non-mammalian vertebrates. To advance comparative spinal cord neurobiology, the present results invite comparison to the motoneurons of other vertebrate species, which have yet to be subjected to similar or other classification procedures.

<p></p><p>Molten mixtures of XeF₆ and Cr^VIOF₄ in 1:1 and 1:2 molar ratios undergo reduction to Cr(V) and Cr(IV) by means of F₂ elimination to form [XeF₅][Xe₂F₁₁][Cr^VOF₅]∙2Cr^VIOF₄ and [XeF₅]₂[Cr^IVF₆]∙2Cr^VIOF₄, respectively, as shown by low-temperature (LT) single-crystal X-ray diffraction (SCXRD). A LT Raman spectroscopic study of an equimolar mixture of solid XeF₆ and CrOF₄ and its melt showed that [Cr^VIOF₅]^– is formed as an intermediate. Reaction of [XeF₅]₂[Cr^IVF₆]∙2Cr^VIOF₄ with XeF₆ in a melt gave [Xe₂F₁₁]₂[Cr^IVF₆] and [XeF₅]₂[Cr^V₂O₂F₈]. Their LT crystal structures revealed that [XeF₅]⁺ and [Xe₂F₁₁]⁺ are coordinated to their respective [CrF₆]²⁻ and [Cr₂O₂F₈]²⁻ anions by means of Xe---F–Cr bridges to form infinite chain structures. The reactions of a 1:1 molar ratio of XeF₆ and CrOF₄ in anhydrous hydrogen fluoride (aHF) and in mixed CFCl₃/aHF solvents yielded [XeF₅]₂[Cr^V₂O₂F₈]∙2HF and a mixture of [XeF₅]₂[Cr^V₂O₂F₈]∙2HF and [XeF₅]₂[Cr^V₂O₂F₈]∙2XeOF₄, respectively. The SCXRD structures of the latter and aforementioned salts provide the first X-ray structures of [CrOF₅]^2– and [Cr₂O₂F₈]^2–. The [XeF₅]₂[Cr^V₂O₂F₈]∙2XeOF₄ and [XeF₅][Xe₂F₁₁][Cr^VOF₅]∙2Cr^VIOF₄ salts were also characterized by LT Raman spectroscopy. Quantum-chemical calculations were carried out to obtain the energy-minimized, gas-phase geometries and vibrational frequencies for [Cr^VIOF₅]^–, [XeF₅]₂[Cr^V₂O₂F₈]∙2XeOF₄, [Cr^V₂O₂F₈]^2–, [XeF₅][Xe₂F₁₁][Cr^VOF₅]∙2Cr^VIOF₄, [Cr^VOF₅]^2–, and to aid in the assignments of their vibrational frequencies.</p><br><p></p>