Neurofilaments are nonessential to the pathogenesis of toxicant-induced axonal degeneration.

Axonal neurofilament (NF) accumulations occur before development of symptoms and before other pathological changes among idiopathic neurodegenerative diseases and toxic neuropathies, suggesting a cause-effect relationship. The dependence of symptoms and axonal degeneration on neurofilament accumulation has been tested here in a transgenic mouse model (Eyer and Peterson, 1994) lacking axonal NFs and using two prototypic toxicant models. Chronic acrylamide (ACR) or 2,5-hexanedione exposure resulted in progressive and cumulative increases in sensorimotor deficits. Neurobehavioral tests demonstrated similar expression of neurotoxicity in transgenic (T) mice and their nontransgenic (NT) littermates (containing normal numbers of axonal NFs). Axonal lesions were frequently observed after exposure to either toxicant. Quantitation of ACR-induced lesions demonstrated the distal location of pathology and equal susceptibility of T and NT axons. We conclude that axonal NFs have no effect on neurotoxicity and the pattern of pathology in these mammalian toxic neuropathies. These results also suggest that the role of neurofilament accumulation in the pathogenesis of neurodegenerative diseases requires careful evaluation.

Neurofilaments are non-essential elements of toxicant-induced reductions in fast axonal transport: pulse labeling in CNS neurons.

Acrylamide (ACR) and g-diketones (g-DK) produce distal sensory-motor neuropathy in a variety of species, including humans. The specific molecular site and mechanism of toxicant action leading to specific morphological and behavioral abnormalities requires definition. The relative roles of fast anterograde axonal transport and neurofilaments (NF) are investigated using optic nerves of mice, with and without axonal neurofilaments. Segmental analysis, following pulse labeling with 3H-leucine into the vitreous body, was used to detect changes in fast anterograde transport in the optic nerve and tract. Single injections of ACR significantly reduced the quantity of radiolabeled proteins transported in both transgenic (lacking NF) and non-transgenic (containing NF) mice by 68.4% and 46.2%, respectively. Similarly, single injections of 2,5-hexanedione (2,5-HD) reduced the quantity of radiolabeled transport in transgenic and non-transgenic mice by 55.2% and 47.1%, respectively. Equimolar doses of propionamide and 3,4-hexanedione (non-neurotoxic analogues of ACR and 2,5-HD, respectively) produced no changes in the quantity or apparent rate of optic nerve transport. Additionally, no differences in quantity or apparent rate of transport between transgenic and non-transgenic animals were observed under control or experimental conditions. Therefore, ACR and 2,5-HD reduce the quantity of fast anterograde axonal transport in mouse CNS axons in a comparable amount to previously reported reductions in rat PNS axons. The absence of axonal neurofilaments had no effect on normal fast transport. Furthermore, the presence or absence of neurofilaments did not alter the effect of these toxicants on fast axonal transport. We conclude that toxicant-induced reductions in fast axonal transport are unrelated to ACR and g-diketone effects on NF or their accumulation.

Axonal neurofilaments are nonessential elements of toxicant-induced reductions in fast axonal transport: video-enhanced differential interference microscopy in peripheral nervous system axons.

Neurofilament modification and accumulation, occurring in toxicant-induced neuropathies, has been proposed to compromise fast axonal transport and contribute to neurological symptoms or pathology. The current study compares the effects of the neurotoxicants acrylamide (ACR) and 2,5-hexanedione (2,5-HD) on the quantity of fast, bidirectional vesicular traffic within isolated mouse sciatic nerve axons from transgenic mice lacking axonal neurofilaments (Eyer and Peterson, Neuron 12, 1-20, 1994) and nontransgenic littermates possessing neurofilaments. Fast anterograde and retrograde membrane bound organelle (MBO) traffic was quantitated within axons, before and after toxicant exposure, using video-enhanced differential interference contrast (AVEC-DIC) microscopy. Addition of 0.7 mM ACR to the buffer bathing the nerve produced a time-dependent reduction in bidirectional transport with a similar time to onset and magnitude in both transgenic and nontransgenic mice. 2,5-HD (4 mM) exposure reduced bidirectional vesicle traffic by a similar amount in both transgenic and nontransgenic animals. The time to onset of the transport reduction was less and the magnitude of the reduction was greater with 2,5-HD compared to ACR. A single 10-min exposure to ACR or 2,5-HD produced a similar reduction in transport to that produced by prolonged (1 h) exposure. Nonneurotoxic propionamide or 3,4-hexanedione (3,4-HD) produced no changes in bidirectional transport in either transgenic or nontransgenic animals. We conclude that ACR or 2,5-HD produces a rapid, saturable, nonreversible, neurotoxicant-specific reduction in fast bidirectional transport within isolated peripheral nerve axons. These actions are mediated through direct modification of axonal component(s), which are independent of toxicant-induced modifications of, or accumulations of, neurofilaments.

Fetal lung maturity assessed by fluorescence polarization: evaluation of predictive value, correction for endogenous fluorescence, and comparison with L/S ratio.

The steady-state polarization (or anisotropy) of the fluorescent dye 1,6-diphenyl-1,3-5-hexatriene in amniotic fluid samples and the lecithin/sphingomyelin ratio of the samples were correlated with development of respiratory distress syndrome in newborns. We found that clinical samples have a variable endogenous fluorescence that reduces the observed polarization (or anisotropy). This background is a major interference in the assessment of fetal lung maturity by the polarization method. Correction for this interference, by also measuring the blank fluorescence and anisotropy of the sample, provides a clinical tool with a lower coefficient of variation than that of the more time-consuming lecithin/sphingomyelin ratio. The clinical correlation for 17 cases of respiratory distress syndrome in a high-risk population (60 births; twins counted as a single birth) indicates that the two methods are equivalent for predicting immature fetal lung status.

Glucocorticoid receptors in normal human eosinophils: comparison with neutrophils.

Saturation analysis with [3H]-dexamethasone was employed to measure glucocorticoid binding in purified preparations of human eosinophils and neutrophils. Eosinophils contained 10.8 +/- 1.3 x 10(3) high-affinity receptor sites per cell, with a dissociation constant (Kd) of 15.3 +/- 0.6 nM dexamethasone. Cortisol was capable of competing with [3H]-dexamethasone in the binding reaction, whereas progesterone, estradiol, estriol, and testosterone were less effective. Saturable glucocorticoid binding in neutrophils had a Kd of 17.7 +/- 0.8 nM dexamethasone with 11.1 +/- 0.8 x 10(3) sites per cell and displayed similar steroid specificity. These data indicate that normal human eosinophils have glucocorticoid receptors with characteristics similar to those in neutrophils and that in these cells ligand-receptor interaction can occur at physiologic glucocorticoid concentrations. Furthermore, these results suggest that certain glucocorticoid effects on eosinophils and neutrophils may be mediated through specific receptors.

Respiratory drives and exercise in menstrual cycles of athletic and nonathletic women.

To investigate the influence of the midluteal and midfollicular phases of the menstrual cycle on exercise performance and ventilatory drives, we studied six outstanding female athletes, six controls with normal menstrual cycles, and six outstanding athletes who were amenorrheic. In all menstruating subjects resting minute ventilation (Ve) and mouth occlusion pressures (P0.1) were higher in the luteal phase (p less than k0.0001 and p less than 0.02, respectively),. Hypoxic (expressed as the hyperbolic shape parameter A) and hypercapnic (expressed as S, deltaVE/delta PAco2) ventilatory responses were increase in the luteal phase (p less than 0.01). The athletes had lower A values during the luteal phase than the nonathletes (p less than 0.001). Maximal exercise response, expressed either as total exercise time or maximum O2 consumption or CO2 production (VO2 max or Vco2 max) was decreased during the luteal phase but was significantly different at a p less than 0.05 level only among the nonathletes. Ventilatory equivalent (VE/VO2) during progressive exercise on a bicycle ergometer was significantly increased during the luteal phase. The amenorrheic athletes showed no changes between the two test periods. The luteal phase of the menstrual cycle induced increases in ventilatory drives and exercise ventilation in both athletes and controls, but the athletes, in contrast to controls, demonstrated no significant decrease in exercise performance in the luteal phase.