Cortical axon sub-population maintains density, but not turnover, of en passant boutons in the aged APP/PS1 amyloidosis model.

Synaptic dysfunction is one of the key mechanisms associated with cognitive deficits observed in Alzheimer's disease (AD), yet little is known about the presynaptic axonal boutons in AD. Focusing on cortical en passant boutons (EPBs) along axons located in the motor, sensory and prefrontal regions of the cerebral cortex in the APP/PS1 mouse model of AD, we investigated structural properties of EPBs over the lifespan and in response to a midlife environmental enrichment (EE) intervention. At 3, 12, and 18-22 months and following 6 months of midlife EE, we found that EPBs showed remarkable resilience in preserving overall synaptic output, as evidenced by the maintained density of EPBs along the axon shaft across all experimental conditions. Using cranial window imaging to monitor synaptic changes in real time, we report that despite maintaining a stable synaptic density, the dynamic fraction (gains and losses) of EPBs was significantlyreduced at 10-13 months of age in APP/PS1 axons compared to age matched controls.

Synaptic elimination and protection after minimal injury depend on cell type and their prelesion structural dynamics in the adult cerebral cortex.

The axonal and synaptic mechanisms underlying dysfunction and repair of the injured CNS are poorly understood. Unresolved issues include to what degree, when, and how the surviving neurons degenerate and the extent of synaptic remodeling both along the severed axon and in the nearby area. One of the main reasons is the lack of tools to study the complex asynchronous and dynamic features of individual lesioned axon responses in the intact brain. To address these issues, we combined two-photon microscopy and laser microsurgery to image the real-time reorganization of cortical circuitry at synaptic resolution for periods of up to 1 year in the brain of living mice. Injured cortical axons were eliminated proximally through a two-phase retraction process, which continued for at least 3 months postlesion and was independent of the presence of scar tissue. Remarkably, axons which later attempt to regenerate in both the mature and juvenile brain retracted less, raising the possibility that targeting retraction may improve the chances of axon regrowth after axotomy. Comparing prelesion and postlesion dynamics on the same axons over several days and weeks revealed that, although synapse formation rates were unaffected, boutons on injured axons were either rapidly and persistently lost, or extremely resistant, depending on cell-type and their prelesion structural dynamics. Our data suggest a lasting deficiency in synaptic output on surviving injured cortical axons and a surprising difference in the vulnerability of synaptic boutons after axotomy, which depend on cell-type and their recent history.

In-vivo single neuron axotomy triggers axon regeneration to restore synaptic density in specific cortical circuits.

To what extent, how and when axons respond to injury in the highly interconnected grey matter is poorly understood. Here we use two-photon imaging and focused ion beam-scanning electron microscopy to explore, at synaptic resolution, the regrowth capacity of several neuronal populations in the intact brain. Time-lapse analysis of >100 individually ablated axons for periods of up to a year reveals a surprising inability to regenerate even in a glial scar-free environment. However, depending on cell type some axons spontaneously extend for distances unseen in the unlesioned adult cortex and at maximum speeds comparable to peripheral nerve regeneration. Regrowth follows a distinct pattern from developmental axon growth. Remarkably, although never reconnecting to the original targets, axons consistently form new boutons at comparable prelesion synaptic densities, implying the existence of intrinsic homeostatic programmes, which regulate synaptic numbers on regenerating axons. Our results may help guide future clinical investigations to promote functional axon regeneration.

Molecular mechanisms of axon guidance in the developing corticospinal tract.

The great repertoire of movements in higher order mammals comes courtesy of the corticospinal tract (CST) which is able to initiate precise movement of the entire musculature of the axial and limb muscle groups. It forms the longest axonal trajectory in the mammalian central nervous system and its axons must navigate the entire length of the central nervous system--from its origins in the deeper layers of the cerebral cortex down through the cerebral peduncles and brainstem and along the entire length of the spinal cord. This period of navigation is incredibly complex, and relies upon the coordinated regulation of a collection of molecular guidance cues - coming from all of the known major families of guidance cues - the ephrins, slits, Netrins and Semaphorins - that work together to steer the growing axonal tips through the brain and spinal cord. As such a long tract, the CST forms an excellent experimental model to investigate the nature of molecular cues that sequentially guide axons through the central nervous system. Using the rodent as a model system, this review discusses each step of axonal guidance through the major brain regions--starting from the decision to grow ventrally out of the cortical plate to the eventual activity-dependent refinement of circuitry in the spinal grey matter. In recent years, the identification of these guidance cues and their proposed mode of action is beginning to give us a picture at a molecular level of how the CST is guided so accurately over such a long distance.

Alterations in neurofilaments associated with reactive brain changes and axonal sprouting following acute physical injury to the rat neocortex.

In order to study the changes in axons related to acute localized physical trauma, a 25 gauge needle was inserted into the somatosensory cortex of anaesthetized adult rats. Animals were examined over 11 time points, from 30 min to 14 days postinjury. Initially, the central needle tract was surrounded by 'reactive' abnormal axons characterized by their bulb- or ring-like immunoreactivity for neurofila ments. Quantification demonstrated that these structures reached a peak density at 24 h postinjury, followed by a gradual decrease over 2 weeks. By 5 days postinjury, long axons showing high levels of neurofilament labelling were localized to the lesion area, either aligned parallel to the tract edges or extending into the bridge of tissue forming between the tract edges. Double-labelling demonstrated a close association between sprouting axons and ferritin-labelled microglia. Immunolabelling for GAP43 also demonstrated the presence of sprouting axons within this tissue bridge. Ultrastuctural examination showed that sprouting axons contained a high density of neurofilaments, with a leading edge lacking these filaments. Injury to the adult neocortex is associated with reactive and sprouting changes within axons, coordinated with the proliferation of microglia and wound healing. These data also support a role for neurofilaments in axonal sprouting following brain injury.

GDNF is a chemoattractant for enteric neural cells.

In situ hybridization revealed that GDNF mRNA in the mid- and hindgut mesenchyme of embryonic mice was minimal at E10.5 but was rapidly elevated at all gut regions after E11, but with a slight delay (0.5 days) in the hindgut. GDNF mRNA expression was minimal in the mesentery and in the pharyngeal and pelvic mesenchyme adjacent to the gut. To examine the effect of GDNF on enteric neural crest-derived cells, segments of E11.5 mouse hindgut containing crest-derived cells only at the rostral ends were attached to filter paper supports and grown in catenary organ culture. With GDNF (100 ng/ml) in the culture medium, threefold fewer neurons developed in the gut explants and fivefold more neurons were present on the filter paper outside the gut explants, compared to controls. Thus, in controls, crest-derived cells colonized the entire explant and differentiated into neurons, whereas in the presence of exogenous GDNF, most crest-derived cells migrated out of the gut explant. This is consistent with GDNF acting as a chemoattractant. To test this idea, explants of esophagus, midgut, superior cervical ganglia, paravertebral sympathetic chain ganglia, or dorsal root ganglia from E11.5-E12.5 mice were grown on collagen gels with a GDNF-impregnated agarose bead on one side and a control bead on the opposite side. Migrating neural cells and neurites from the esophagus and midgut accumulated around the GDNF-impregnated beads, but neural cells in other tissues showed little or no chemotactic response to GDNF, although all showed GDNF-receptor (Ret and GFRalpha1) immunoreactivity. We conclude that GDNF may promote the migration of crest cells throughout the gastrointestinal tract, prevent them from straying out of the gut (into the mesentery and pharyngeal and pelvic tissues), and promote directed axon outgrowth.

Expression of Ret-, p75(NTR)-, Phox2a-, Phox2b-, and tyrosine hydroxylase-immunoreactivity by undifferentiated neural crest-derived cells and different classes of enteric neurons in the embryonic mouse gut.

Cells of the enteric nervous system are derived from the neural crest. Probes to a number of molecules identify neural crest-derived cells within the gastrointestinal tract of embryonic mice prior to their differentiation into neurons and glial cells. However, it is unclear whether the different markers are identifying all neural crest-derived cells. In this study the distribution of p75(NTR)-immunoreactivity was compared with that of Ret-, Phox2a-, Phox2b-, and tyrosine hydroxylase (TH) in undifferentiated neural crest-derived cells in the E10.5-E13.5 mouse intestine. Neural crest-derived cells colonise the embryonic mouse gut in a rostral-to-caudal wave between E9.5-E14, and differentiation into enteric neurons also occurs in a rostral-to-caudal wave. Thus, the most caudal neural crest-derived cells within the gut are undifferentiated. These most caudal neural crest-derived cells co-expressed p75(NTR)-, Phox2b- and Ret-immunoreactivity; at E10.5 a sub-population was also TH-positive. The most caudal cells did not show Phox2a-immunoreactivity at any stage. However, a sub-population of cells, which was rostral to the undifferentiated neural crest-derived cells, was Phox2a-positive, and these are likely to be cells beginning to differentiate along a neuronal lineage. The expression of Ret-, Phox2a-, Phox2b- and p75(NTR)-immunoreactivity by two classes of enteric neurons that differentiate prior to birth was also examined. Nitric oxide synthase (NOS) neurons showed Phox2b and Ret immunoreactivity at all ages, and Phox2a and p75(NTR) immunoreactivity only transiently. Calcitonin gene-related peptide (CGRP) neurons showed Phox2b and Ret-immunoreactivity, but not Phox2a immunoreactivity. It is concluded that all undifferentiated neural crest-derived cells initially express Phox2b, Ret, and p75(NTR); a sub-population of these cells also expresses TH transiently. Those cells that are beginning to differentiate along a neuronal lineage maintain their expression of Phox2b and Ret, and they start to express Phox2a, but down-regulate p75(NTR); those cells that differentiate along a glial lineage down-regulate Ret and maintain their expression of p75(NTR). Dev Dyn 1999;216:137-152.

Identification of managerial behavior dimensions in a federal health-care agency.

Understanding the behavior of managers provides an opportunity to assess congruencies between organizational needs and managerial skills. This assessment is critical in federal health-care wherein the environment is rapidly changing. In the current investigation, dimensions of managerial behavior for 267 managers in a federal health-care agency were identified. Recommendations are provided with respect to the relevance of using these dimensions for organizational training and development activities.

Back school programs. The pregnant patient and her partner.

We believe that couples contemplating pregnancy should consider it to be a 12-month experience, taking 3 months prior to conception to change diets, lifestyles, and exercise routines, so as to maximize overall health. We encourage expectant parents to use the information and approach presented in back school in purchasing car seats and other equipment for child care activities. The Alexander Technique approach to posture and body mechanics can be a powerful adjunct to back school. It is being taught privately, in clinical settings, and in universities throughout the United States. Benefits range from relieving neck and back pain to improving body mechanics in child care activities. This approach to working with the mind and body as a whole enables patients to further help themselves without having to depend on long-term therapy in the reduction of overall musculoskeletal problems. Health care practitioners, working as a team, have an important role to play in the prevention and control of back pain in expectant women and their partners. Patient education, in individual or group form, can help to prepare patients and their partners to handle the stresses and strains of pregnancy, birth, and child care activities.

A discrepancy between the instantaneous and the overall collection efficiency of the Fenwal CS3000 for peripheral blood stem cell apheresis.

The collection efficiency (CE) of the Fenwall CS3000 continuous flow blood cell separator in the apheresis of peripheral blood stem cells during haemopoietic recovery following myelosuppressive chemotherapy was analysed. Ninety-three apheresis were performed in 19 patients using procedure 3 on the Fenwal CS3000. The overall CE was calculated from the pre-apheresis cell counts and the stated blood volume processed. Instantaneous CE was calculated from cell counts in the inlet and return lines. The overall mononuclear cell and granulocyte-macrophage colony forming unit CE were 64.0% and 55.8%, respectively, significantly lower than the instantaneous CEs of 94.5% and 95.4%, respectively (P = 0.0001, t test, for both comparisons). Three factors unrelated to machine performance contributed to the lower overall CE despite a high instantaneous CE: (1) A fall in the patient's mononuclear cell counts during apheresis leading to an overestimation of the cells available for collection, (2) dilution of blood by anti-coagulant, and (3) the operational dead space of the Fenwal CS3000. The overall CE corrected for these 3 factors approximated the instantaneous CE closely. Thus there is little room for further enhancement of machine performance because the Fenwal CS3000 is already operating with a very high instantaneous CE. To achieve major improvement in the yield of peripheral blood stem cell harvests, more effective mobilization protocols and better timing of apheresis are required.

Octanol/water partition coefficients as a model system for assessing antidotes for methylmercury(II) poisoning, and for studying mercurials with medicinal applications.

1-Octanol/water partition coefficients, [HgII]octanol/[HgII]water, provide a simple but limited model system for aspects of the biological behavior of methylmercury(II) and commonly used organomercury(II) medicinal compounds. In an octanol/water system some widely studied antidotes for mercury poisoning at least partly displace the biological thiols L-cysteine and glutathione from binding to MeHgII at pH 6.9. Addition of the antidote meso-dimercaptosuccinic acid to MeHgII in the presence of glutathione results in formation of metallic mercury. For RHgII derivatives of L-cysteine and glutathione, octanol/water partition coefficients follow the order Ph greater than Et greater than Me. An exceptionally high value for diphenylmercury, compared with PhHgII derivatives of L-cysteine and glutathione, is consistent with reported results of the distribution of mercury compounds in rats. Ethylmercury(II) is partly displaced from thimerosal by L-cysteine and glutathione in the octanol/water system, indicating that the active form of thimerosal in vivo may involve binding of EtHgII to biological ligands.

Chelation therapy for methylmercury(II) poisoning. Synthesis and determination of solubility properties of MeHg(II) complexes of thiol and dithiol antidotes.

Methylmercury(II) complexes of the most widely studied antidotes for mercury poisoning have been prepared, and both the water solubility and 1-octanol/water partition coefficients determined for these complexes and the L-cysteine complex. New complexes of N-acetyl-D,L-penicillamine, 2-mercaptosuccinic acid, meso-dimercaptosuccinic acid, and Unithiol have been synthesized and characterized, and are found to have the formulations MeHgSCMe2CH(NHCOMe)CO2H, MeHgSCH(CO2H)CH2CO2H, MeHgSCH(CO2H)CH(CO2H)SHgMe, and Na[MeHgSCH2CH-(SHgMe)CH2SO3], respectively. Trends in octanol/water partition coefficients are consistent with reported studies of the effectiveness of antidotes for MeHg(II) poisoning and redistribution of MeHg(II) on administration of antidotes, particularly for British anti-Lewisite, Unithiol, and meso-dimercaptosuccinic acid.

The natural history of chronic middle ear disease in Australian Aboriginals: a cross-sectional study.

One hundred and sixty-three Australian Aboriginals, who were aged from four months to 60 years, were examined clinically and otologically. Audiometric tests were completed on 110 of these subjects. On the assumptions that the aural health of these people has remained stable for many years, the cross-sectional data which were obtained have been used to infer the natural history of ear disease. Seromucinous otitis media is manifest as a disease of early childhood, which recovers spontaneously in most cases and has no obvious sequelae. Perforated tympanic membranes likewise seem to heal spontaneously in the majority of cases. The evidence suggests that hearing loss is the main problem and treatment should be directed towards the level of hearing loss and its effects.