Distribution of Elements in Rat Peripheral Axons and Nerve Cell Bodies Determined by X‐Ray Microprobe Analysis

Abstract

X-ray microprobe analysis was used to determine concentrations (millimoles of element per kilogram dry weight) of Na, P, Cl, K, and Ca in cellular compartments of frozen, unfixed sections of rat sciatic and tibial nerves and dorsal root ganglion (DRG). Five compartments were examined in peripheral nerve (axoplasm, mitochondria, myelin, extraaxonal space, and Schwann cell cytoplasm), and four were analyzed in DRG nerve cell bodies (cytoplasm, mitochondria, nucleus, and nucleolus). Each morphological compartment exhibited characteristic concentrations of elements. The extraaxonal space contained high concentrations of Na, Cl, and Ca, whereas intraaxonal compartments exhibited lower concentrations of these elements but relatively high K contents. Nerve axoplasm and axonal mitochondria had similar elemental profiles, and both compartments displayed proximodistal gradients of decreasing levels of K, Cl, and, to some extent, Na. Myelin had a selectively high P concentration with low levels of other elements. The elemental concentrations of Schwann cell cytoplasm and DRG were similar, but both were different from that of axoplasm, in that K and Cl were markedly lower whereas P was higher. DRG cell nuclei contained substantially higher K levels than cytoplasm. The subcellular distribution of elements was clearly shown by color-coded images generated by computer-directed digital x-ray imaging. The results of this study demonstrate characteristic elemental distributions for each anatomical compartment, which doubtless reflect nerve cell structure and function.

Ganglioside Treatment Modifies Abnormal Elemental Composition in Peripheral Nerve Myelinated Axons of Experimentally Diabetic Rats

“…The morphological characteristics of myelinated axons and Schwann cells in cryosections of rat peripheral nerve have been well documented in previous studies (LoPachin et al, 1988;1990;1992a,h). In the present study, no significant changes in axon or glial cell morphology were observed in cryosections from rats of either diabetic or ganglioside treatment groups.…”

“…Morphological criteria used to identify analytical compartments in frozen sections were confirmed in a previous parallel study of conventionally fixed control rat peripheral nerve (LoPachin et a]., 1988). Given the relative paucity of nodes of Ranvier in peripheral nerves, the majority of our axonal measurements in transverse cryosections were probably of internodal axoplasm.…”

“…At the end of the experimental period, rats from all treatment groups were anesthetized (ketamine, 44 mg/kg, and xylazine, 5 mg/kg i.p.). Distal tibia1 and proximal sciatic nerve samples (-I cm in length) were removed from separate legs of anesthetized animals (LoPachin et al, 1988;Lowery et al, 1990). Nerve samples were frozen immediately in melting Freon 22 and then stored in liquid nitrogen until analyzed.…”

“…The use of unfixed, unstained cryosections with low spatial resolution precludes absolute identification of mitochondria. Therefore, this compartment was identified according to both functional (e.g., differential response to injury and Ca sequestration) and gross structural (e.g., size, shape, and orientation) criteria (LoPachin et al, 1988(LoPachin et al, , 1991. Coincidental inclusion of adjacent axoplasm in mitochondrial analysis is also possible because the microscope beam diameter (0.1-0.15 pm), which is rastered over this compartment, is only slightly smaller than that of an average mitochondrion.…”

“…The elemental composition of myelinated axons and Schwann cells in nondiabetic, saline-treated control rat peripheral nerve is well characterized (LoPachin et al, 1988(LoPachin et al, , 1992aLowery et al, 1990), and only a brief description of data is provided. Potassium was the most abundant element present in axoplasm and mitochondria1 areas of all myelinated fibers.…”