Internalizing problems before and during the COVID-19 pandemic in independent samples of Dutch children and adolescents with and without pre-existing mental health problems.

The aim of the study was to assess internalizing problems before and during the pandemic with data from Dutch consortium Child and adolescent mental health and wellbeing in times of the COVID-19 pandemic, consisting of two Dutch general population samples (GS) and two clinical samples (CS) referred to youth/psychiatric care. Measures of internalizing problems were obtained from ongoing data collections pre-pandemic (NGS = 35,357; NCS = 4487) and twice during the pandemic, in Apr-May 2020 (NGS = 3938; clinical: NCS = 1008) and in Nov-Dec 2020 (NGS = 1489; NCS = 1536), in children and adolescents (8-18 years) with parent (Brief Problem Monitor) and/or child reports (Patient-Reported Outcomes Measurement Information System®). Results show that, in the general population, internalizing problems were higher during the first peak of the pandemic compared to pre-pandemic based on both child and parent reports. Yet, over the course of the pandemic, on both child and parent reports, similar or lower levels of internalizing problems were observed. Children in the clinical population reported more internalizing symptoms over the course of the pandemic while parents did not report differences in internalizing symptoms from pre-pandemic to the first peak of the pandemic nor over the course of the pandemic. Overall, the findings indicate that children and adolescents of both the general and clinical population were affected negatively by the pandemic in terms of their internalizing problems. Attention is therefore warranted to investigate long-term effects and to monitor if internalizing problems return to pre-pandemic levels or if they remain elevated post-pandemic.

A common arthropod from the Late Ordovician Big Hill Lagerstätte (Michigan) reveals an unexpected ecological diversity within Chasmataspidida.

BACKGROUND: Chasmataspidids are a rare group of chelicerate arthropods known from 12 species assigned to ten genera, with a geologic range extending from the Ordovician to the Devonian. The Late Ordovician (Richmondian) fauna of the Big Hill Lagerstätte includes a new species of chasmataspidid represented by 55 specimens. This taxon is only the second chasmataspidid described from the Ordovician and preserves morphological details unknown from any of the previously described species. RESULTS: The new chasmataspidid species is described as Hoplitaspis hiawathai gen. et sp. nov.. Comparison with all other known chasmataspidids indicates that Hoplitaspis occupies an intermediate morphological position between the Ordovician Chasmataspis and the Silurian-Devonian diploaspidids. While the modification of appendage VI into a broad swimming paddle allies Hoplitaspis to the Diploaspididae, the paddle lacks the anterior 'podomere 7a' found in other diploaspidids and shows evidence of having been derived from a Chasmataspis-like chelate appendage. Other details, such as the large body size and degree of expression of the first tergite, show clear affinities with Chasmataspis, providing strong support for chasmataspidid monophyly. CONCLUSIONS: The large body size and well-developed appendage armature of Hoplitaspis reveals that chasmataspidids occupied a greater breadth of ecological roles than previously thought, with the abundance of available specimens indicating that Hoplitaspis was an important component of the local community. The miniaturization and ecological limiting of diploaspidids potentially coincides with the major radiation of eurypterids and may suggest some degree of competition between the two groups. The geographic distribution of chasmataspidid species suggests the group may have originated in Laurentia and migrated to the paleocontinents of Baltica and Siberia as tectonic processes drew the paleocontinents into close proximity.

Effects of altered pyruvate dehydrogenase activity on contracting skeletal muscle bioenergetics.

During aerobic exercise (>65% of maximum oxygen consumption), the primary source of acetyl-CoA to fuel oxidative ATP synthesis in muscle is the pyruvate dehydrogenase (PDH) reaction. This study investigated how regulation of PDH activity affects muscle energetics by determining whether activation of PDH with dichloroacetate (DCA) alters the dynamics of the phosphate potential of rat gastrocnemius muscle during contraction. Twitch contractions were induced in vivo over a broad range of intensities to sample submaximal and maximal aerobic workloads. Muscle phosphorus metabolites were measured in vivo before and after DCA treatment by phosphorus nuclear magnetic resonance spectroscopy. At rest, DCA increased PDH activation compared with control (90 ± 12% vs. 23 ± 3%, P < 0.05), with parallel decreases in inorganic phosphate (Pi) of 17% (1.4 ± 0.2 vs. 1.7 ± 0.1 mM, P < 0.05) and an increase in the free energy of ATP hydrolysis (ΔGATP) (-66.2 ± 0.3 vs. -65.6 ± 0.2 kJ/mol, P < 0.05). During stimulation DCA increased steady-state phosphocreatine (PCr) and the magnitude of ΔGATP, with concomitant reduction in Pi and ADP concentrations. These effects were not due to kinetic alterations in PCr hydrolysis, resynthesis, or glycolytic ATP production and altered the flow-force relationship between mitochondrial ATP synthesis rate and ΔGATP. DCA had no significant effect at 1.0- to 2.0-Hz stimulation because physiological mechanisms at these high stimulation levels cause maximal activation of PDH. These data support a role of PDH activation in the regulation of the energetic steady state by altering the phosphate potential (ΔGATP) at rest and during contraction.

Inactivating mutations of RNF43 confer Wnt dependency in pancreatic ductal adenocarcinoma.

A growing number of agents targeting ligand-induced Wnt/ß-catenin signaling are being developed for cancer therapy. However, clinical development of these molecules is challenging because of the lack of a genetic strategy to identify human tumors dependent on ligand-induced Wnt/ß-catenin signaling. Ubiquitin E3 ligase ring finger 43 (RNF43) has been suggested as a negative regulator of Wnt signaling, and mutations of RNF43 have been identified in various tumors, including cystic pancreatic tumors. However, loss of function study of RNF43 in cell culture has not been conducted, and the functional significance of RNF43 mutations in cancer is unknown. Here, we show that RNF43 inhibits Wnt/ß-catenin signaling by reducing the membrane level of Frizzled in pancreatic cancer cells, serving as a negative feedback mechanism. Inhibition of endogenous Wnt/ß-catenin signaling increased the cell surface level of Frizzled. A panel of 39 pancreatic cancer cell lines was tested for Wnt dependency using LGK974, a selective Porcupine inhibitor being examined in a phase 1 clinical trial. Strikingly, all LGK974-sensitive lines carried inactivating mutations of RNF43. Inhibition of Wnt secretion, depletion of ß-catenin, or expression of wild-type RNF43 blocked proliferation of RNF43 mutant but not RNF43-wild-type pancreatic cancer cells. LGK974 inhibited proliferation and induced differentiation of RNF43-mutant pancreatic adenocarcinoma xenograft models. Our data suggest that mutational inactivation of RNF43 in pancreatic adenocarcinoma confers Wnt dependency, and the presence of RNF43 mutations could be used as a predictive biomarker for patient selection supporting the clinical development of Wnt inhibitors in subtypes of cancer.

Abrogation of ß-catenin signaling in oligodendrocyte precursor cells reduces glial scarring and promotes axon regeneration after CNS injury.

When the brain or spinal cord is injured, glial cells in the damaged area undergo complex morphological and physiological changes resulting in the formation of the glial scar. This scar contains reactive astrocytes, activated microglia, macrophages and other myeloid cells, meningeal cells, proliferating oligodendrocyte precursor cells (OPCs), and a dense extracellular matrix. Whether the scar is beneficial or detrimental to recovery remains controversial. In the acute phase of recovery, scar-forming astrocytes limit the invasion of leukocytes and macrophages, but in the subacute and chronic phases of injury the glial scar is a physical and biochemical barrier to axonal regrowth. The signals that initiate the formation of the glial scar are unknown. Both canonical and noncanonical signaling Wnts are increased after spinal cord injury (SCI). Because Wnts are important regulators of OPC and oligodendrocyte development, we examined the role of canonical Wnt signaling in the glial reactions to CNS injury. In adult female mice carrying an OPC-specific conditionally deleted ß-catenin gene, there is reduced proliferation of OPCs after SCI, reduced accumulation of activated microglia/macrophages, and reduced astrocyte hypertrophy. Using an infraorbital optic nerve crush injury, we show that reducing ß-catenin-dependent signaling in OPCs creates an environment that is permissive to axonal regeneration. Viral-induced expression of Wnt3a in the normal adult mouse spinal cord induces an injury-like response in glia. Thus canonical Wnt signaling is both necessary and sufficient to induce injury responses among glial cells. These data suggest that targeting Wnt expression after SCI may have therapeutic potential in promoting axon regeneration.

Maintenance of adenomatous polyposis coli (APC)-mutant colorectal cancer is dependent on Wnt/beta-catenin signaling.

Persistent expression of certain oncogenes is required for tumor maintenance. This phenotype is referred to as oncogene addiction and has been clinically validated by anticancer therapies that specifically inhibit oncoproteins such as BCR-ABL, c-Kit, HER2, PDGFR, and EGFR. Identifying additional genes that are required for tumor maintenance may lead to new targets for anticancer drugs. Although the role of aberrant Wnt pathway activation in the initiation of colorectal cancer has been clearly established, it remains unclear whether sustained Wnt pathway activation is required for colorectal tumor maintenance. To address this question, we used inducible ß-catenin shRNAs to temporally control Wnt pathway activation in vivo. Here, we show that active Wnt/ß-catenin signaling is required for maintenance of colorectal tumor xenografts harboring APC mutations. Reduced tumor growth upon ß-catenin inhibition was due to cell cycle arrest and differentiation. Upon reactivation of the Wnt/ß-catenin pathway colorectal cancer cells resumed proliferation and reacquired a crypt progenitor phenotype. In human colonic adenocarcinomas, high levels of nuclear ß-catenin correlated with crypt progenitor but not differentiation markers, suggesting that the Wnt/ß-catenin pathway may also control colorectal tumor cell fate during the maintenance phase of tumors in patients. These results support efforts to treat human colorectal cancer by pharmacological inhibition of the Wnt/ß-catenin pathway.

Changes in child and adolescent mental health across the COVID-19 pandemic (2018-2023): Insights from general population and clinical samples in the Netherlands.

Background: The COVID-19 pandemic negatively affected child and adolescent mental health and at the end of the pandemic (April 2022) child mental health had not returned to pre-pandemic levels. We investigated whether this observed increase in mental health problems has continued, halted, or reversed after the end of the pandemic in children from the general population and in children in psychiatric care. Methods: We collected parent-reported and child-reported data at two additional post-pandemic time points (November/December 2022 and March/April 2023) in children (8-18 years) from two general population samples (N = 818-1056 per measurement) and one clinical sample receiving psychiatric care (N = 320-370) and compared these with data from before the pandemic. We collected parent-reported data on internalizing and externalizing problems with the Brief Problem Monitor and self-reported data on Anxiety, Depressive symptoms, Sleep-related impairments, Anger, Global health, and Peer relations with the Patient-Reported Outcomes Measurement Information System (PROMIS®). Results: In the general population, parents reported no changes in externalizing problems but did report higher internalizing problems post-pandemic than pre-pandemic (p < 0.001). Children also reported increased mental health problems post-pandemic, especially in anxiety and depression, to a lesser extent in sleep-related impairment and global health, and least in anger (all ps < 0.01). In the clinical sample, parents reported higher internalizing (p < 0.001), but not externalizing problems post-pandemic compared to the start of the pandemic. Children reported greatest increases in problems in anxiety, depression, and global health, to a lesser extent on sleep-related impairment, and least on anger (all ps < 0.05). Conclusions: Child mental health problems in the general population are substantially higher post-pandemic compared to pre-pandemic measurements. In children in psychiatric care mental health problems have increased during the pandemic and are substantially higher post-pandemic than at the start of the pandemic. Longitudinal and comparative studies are needed to assess what the most important drivers of these changes are.

N-methyl-D-aspartate receptors strongly regulate postsynaptic activity levels during optic nerve regeneration.

During development, neuronal activity is used as a cue to guide synaptic rearrangements to refine connections. Many studies, especially in the visual system, have shown that the N-methyl-D-aspartate receptor (NMDAr) plays a key role in mediating activity-dependent refinement through long-term potentiation (LTP)-like processes. Adult goldfish can regenerate their optic nerve and utilize neuronal activity to generate precise topography in their projection onto tectum. Although the NMDAr has been implicated in this process, its precise role in regeneration has not been extensively studied. In examining NMDAr function during regeneration, we found salient differences compared with development. By using field excitatory postsynaptic potential (fEPSP) recordings, the contribution of the NMDAr at the primary optic synapse was measured. In contrast to development, no increase in NMDAr function was detectable during synaptic refinement. Unlike development, LTP could not be reliably elicited during regeneration. Unexpectedly, we found that NMDAr exerted a major effect on regulating ongoing tectal (postsynaptic) activity levels during regeneration. Blocking NMDAr strongly suppressed spontaneous activity during regeneration but had no significant effect in the normal projection. This difference could be attributed to an occlusion effect of strong optic drive in the normal projection, which dominated ongoing tectal activity. During regeneration, this optic drive is largely absent. Optic nerve stimulation further indicated that the NMDAr had little effect on the ability of optic fibers to evoke early postsynaptic impulse activity but was important for late network activity. These results indicate that, during regeneration, the NMDAr may play a critical role in the homeostatic regulation of ongoing activity and network excitability.

The effects of COVID-19 on child mental health: Biannual assessments up to April 2022 in a clinical and two general population samples.

Background: The COVID-19 pandemic has had an acute impact on child mental and social health, but long-term effects are still unclear. We examined how child mental health has developed since the start of the COVID-19 pandemic up to 2 years into the pandemic (April 2022). Methods: We included children (age 8-18) from two general population samples (N = 222-1333 per measurement and N = 2401-13,362 for pre-covid data) and one clinical sample receiving psychiatric care (N = 334-748). Behavioral questionnaire data were assessed five times from April 2020 till April 2022 and pre-pandemic data were available for both general population samples. We collected parent-reported data on internalizing and externalizing problems with the Brief Problem Monitor and self-reported data on Anxiety, Depressive symptoms, Sleep-related impairments, Anger, Global health, and Peer relations with the Patient-Reported Outcomes Measurement Information System (PROMIS®). Results: In all samples, parents reported overall increased internalizing problems, but no increases in externalizing problems, in their children. Children from the general population self-reported increased mental health problems from before to during the pandemic on all six PROMIS domains, with generally worst scores in April 2021, and scores improving toward April 2022 but not to pre-pandemic norms. Children from the clinical sample reported increased mental health problems throughout the pandemic, with generally worst scores in April 2021 or April 2022 and no improvement. We found evidence of minor age effects and no sex effects. Conclusions: Child mental health in the general population has deteriorated during the first phase of the COVID-19 pandemic, has improved since April 2021, but has not yet returned to pre-pandemic levels. Children in psychiatric care show worsening of mental health problems during the pandemic, which has not improved since. Changes in child mental health should be monitored comprehensively to inform health care and policy.

Similar mitochondrial activation kinetics in wild-type and creatine kinase-deficient fast-twitch muscle indicate significant Pi control of respiration.

Past simulations of oxidative ATP metabolism in skeletal muscle have predicted that elimination of the creatine kinase (CK) reaction should result in dramatically faster oxygen consumption dynamics during transitions in ATP turnover rate. This hypothesis was investigated. Oxygen consumption of fast-twitch (FT) muscle isolated from wild-type (WT) and transgenic mice deficient in the myoplasmic (M) and mitochondrial (Mi) CK isoforms (MiM CK(-/-)) were measured at 20°C at rest and during electrical stimulation. MiM CK(-/-) muscle oxygen consumption activation kinetics during a step change in contraction rate were 30% faster than WT (time constant 53 ± 3 vs. 69 ± 4 s, respectively; mean ± SE, n = 8 and 6, respectively). MiM CK(-/-) muscle oxygen consumption deactivation kinetics were 380% faster than WT (time constant 74 ± 4 s vs. 264 ± 4 s, respectively). Next, the experiments were simulated using a computational model of the oxidative ATP metabolic network in FT muscle featuring ADP and Pi feedback control of mitochondrial respiration (J. A. L. Jeneson, J. P. Schmitz, N. A. van den Broek, N. A. van Riel, P. A. Hilbers, K. Nicolay, J. J. Prompers. Am J Physiol Endocrinol Metab 297: E774-E784, 2009) that was reparameterized for 20°C. Elimination of Pi control via clamping of the mitochondrial Pi concentration at 10 mM reproduced past simulation results of dramatically faster kinetics in CK(-/-) muscle, while inclusion of Pi control qualitatively explained the experimental observations. On this basis, it was concluded that previous studies of the CK-deficient FT muscle phenotype underestimated the contribution of Pi to mitochondrial respiratory control.

The impact of statin therapy and aerobic exercise training on skeletal muscle and whole-body aerobic capacity.

BACKGROUND: Statin use is widely recognized for improving cardiovascular health, but questions remain on how statin use influences skeletal muscle, particularly mitochondrial function. STUDY OBJECTIVE DESIGN AND PARTICIPANTS: The influence of statin therapy and exercise (EX) on aerobic capacity was determined. In Study1, skeletal muscle aerobic capacity was measured before and after 80 mg atorvastatin therapy. In Study2, aerobic capacity (skeletal muscle and whole body) was measured before and after a 12-week exercise randomized control trial in older adults (age = 67 ± 5 yrs.), a subset of which were on chronic low-moderate intensity statin therapy. MAIN OUTCOME MEASURES: Muscle oxidative capacity was determined from the phosphocreatine recovery rate constant (kPCr) using 31P Magnetic Resonance Spectroscopy. Whole body peak oxygen uptake (VO2 peak) was measured during a graded exercise test with indirect calorimetry. RESULTS: High dose statin therapy resulted in a 12% reduction in muscle oxidative capacity (pre = 1.34 ± 0.34 min-1, post = 1.17 ± 0.25 min-1, p = 0.004). Similarly, chronic low-moderate dose statin therapy was associated with lower muscle oxidative capacity at baseline (1.50 ± 0.35 min-1) compared to non-statin users (1.88 ± 0.047 min-1, p = 0.019). Following EX, muscle oxidative capacity increased by 35-40% (statin: Pre: 1.39 ± 0.44 vs. Post: 1.88 ± 0.47 min-1, no statin Pre: 1.86 ± 0.58 vs. Post: 2.58 ± 0.85 min-1) compared to control groups (Pre: 1.74 ± 0.27 vs Post: 1.75 ± 0.49 min-1, p = 0.001). VO2 peak increased by 11% for EX groups (Pre: 18.8 ± 2.8 vs. Post: 20.8 ± 3.0 ml·kg-1·min-1) following training compared to a small decline in controls (Pre: 21.8 ± 3.7 vs. Post: 20.8 ± 3.04 ml·kg-1·min-1, p = 0.001). CONCLUSIONS: Statin therapy resulted in reduced muscle oxidative capacity. Aerobic exercise improved skeletal muscle oxidative capacity and whole-body aerobic capacity during statin therapy.

A Proof of Concept for Biomarker-Guided Targeted Therapy against Ovarian Cancer Based on Patient-Derived Tumor Xenografts.

Advanced ovarian cancers are a leading cause of cancer-related death in women and are currently treated with surgery and chemotherapy. This standard of care is often temporarily successful but exhibits a high rate of relapse, after which, treatment options are few. Here we investigate whether biomarker-guided use of multiple targeted therapies, including small molecules and antibody-drug conjugates, is a viable alternative. A panel of patient-derived ovarian cancer xenografts (PDX), similar in genetics and chemotherapy responsiveness to human tumors, was exposed to 21 monotherapies and combination therapies. Three monotherapies and one combination were found to be active in different subsets of PDX. Analysis of gene expression data identified biomarkers associated with responsiveness to each of the three targeted therapies, none of which directly inhibits an oncogenic driver. While no single treatment had as high a response rate as chemotherapy, nearly 90% of PDXs were eligible for and responded to at least one biomarker-guided treatment, including tumors resistant to standard chemotherapy. The distribution of biomarker positivity in The Cancer Genome Atlas data suggests the potential for a similar precision approach in human patients. SIGNIFICANCE: This study exploits a panel of patient-derived xenografts to demonstrate that most ovarian tumors can be matched to effective biomarker-guided treatments.

The postprandial increase in blood triglycerides has no direct effect on the brain BOLD response.

A previous study showed that ingestion of a liquid meal high in polyunsaturated lipids decreased the blood-oxygenation-level-dependent (BOLD) response measured by functional magnetic resonance imaging (fMRI) during a finger-tapping motor task, and suggested that this effect was due to a direct effect of blood lipids on the cerebral vasculature. This study compared the time course and magnitude of the BOLD response in fixed anatomic locations before and 3 h after ingestion of high versus low lipid content liquid meals (235 ml Ensure Plus [Abbot Labs] with or without 50 ml added canola oil). Blood triglyceride content peaked 3 h after the high lipid meal and was elevated by 33% compared with the low lipid meal. There was no significant effect of meal composition on the time course or magnitude of the BOLD response in fixed-location clusters of voxels which were activated during either a motor (finger-tapping), a visual (flashing checkerboard), or an integrative/cognitive (number addition) block-design task paradigm. The results indicate that increased blood total triglyceride content after a meal with relatively high polyunsaturated fat does not directly alter the hemodynamic BOLD response to neural activity. However, the postprandial effect on BOLD response of other meals with varying fat types and amounts, as well as other nutrients and phytochemicals, remains to be determined.

Comparison of oxidative capacity among leg muscles in humans using gated 31P 2-D chemical shift imaging.

In many small animals there are distinct differences in fiber-type composition among limb muscles, and these differences typically correspond to marked disparities in the oxidative capacities. However, whether there are similar differences in the oxidative capacity among leg muscles in humans is less clear. The purpose of this study was to compare the rate of phosphocreatine (PCr) recovery, a functional in vivo marker of oxidative capacity, in the lateral and medial gastrocnemius, soleus, and the anterior compartment of the leg (primarily the tibialis anterior) of humans. Subjects performed plantar flexion and dorsiflexion gated exercise protocols consisting of 70 sets of three rapid dynamic contractions (<2.86 s) at 20 s intervals (total: 23.3 min). Starting after the sixth set of contractions, (31)P 2-D CSI (8 x 8 matrix, 14-16 cm FOV, 3 cm slice, TR 2.86 s) were acquired via a linear transmit/receive surface coil using a GE 3T Excite System. The CSI data were zero-filled (32 x 32) and a single FID was produced for each time point in the lateral and medial gastrocnemius, soleus, and anterior compartment. The time constant for PCr recovery was calculated from tau = -Deltat/ln[D/(D + Q)], where Q is the percentage change in PCr due to contraction during the steady-state portion of the protocol, D the additional drop in PCr from rest, and Deltat is the interval between contractions. The tau of PCr recovery was longer (p < 0.05) in the anterior compartment (32 +/- 3 s) than in the lateral (23 +/- 2 s) and medial gastrocnemius muscles (24 +/- 3 s) and the soleus (22 +/- 3 s) muscles. These findings suggest that the oxidative capacity is lower in the anterior compartment than in the triceps surae muscles and is consistent with the notion that fiber-type phenotypes vary among the leg muscles of humans.

Aerobic Exercise Improves Microvascular Function in Older Adults.

Microvascular function is reduced with age, disease, and inactivity. Exercise is well known to improve vascular health and has the potential to improve microvascular function in aging and disease. PURPOSE: The study aimed to assess changes in peripheral microvascular function in sedentary older adults after aerobic exercise training. METHODS: Twenty-three sedentary older adults (67 ± 5 yr, body mass index = 29 ± 5, mean ± SD) successfully completed a randomized 12-wk graded treadmill walking intervention. The exercise group (EX) performed 40 min of uphill walking 4 d·wk at 70% heart rate reserve. The control group (CON) maintained a sedentary lifestyle for 12 wk. Blood oxygen level-dependent (BOLD) responses of the soleus measured by magnetic resonance imaging were used to evaluate microvascular function; brief (1 s) maximal plantarflexion contractions were performed. Separately, blood flow in the popliteal artery was measured by ultrasound after brief contraction. Phosphorus magnetic resonance spectroscopy of the calf was used to examine muscle oxidative capacity, and whole-body peak oxygen consumption (V˙O2peak) was used to confirm training-induced cardiorespiratory adaptations. RESULTS: Peak postcontraction BOLD response increased by 33% in EX (PRE, 3.3% ± 1.0%; POST, 4.4% ± 1.4%) compared with CON (PRE, 3.0% ± 1.3%; POST, 3.2% ± 1.5%), P < 0.05. EX with hypertension tended to show a blunted peak BOLD increase (n = 6, 15%) compared with EX normotensive (n = 7, 50%), P = 0.056. Peak postcontraction blood flow increased by 39% in EX (PRE, 217 ± 88 mL·min; POST, 302 ± 167 mL·min) compared with CON (PRE, 188 ± 54 mL·min; POST, 184 ± 44 mL·min), P < 0.05. EX muscle oxidative capacity (kPCr) improved by 40% (PRE, 1.60 ± 0.57 min; POST, 2.25 ± 0.80 min) compared with CON (PRE, 1.69 ± 0.28 min; POST, 1.76 ± 0.52 min), P < 0.05. V˙O2peak increased by 9% for EX (PRE, 19.0 ± 3.1 mL·kg·min; POST, 20.8 ± 2.9 mL·kg·min) compared with a 7% loss in CON (PRE, 21.9 ± 3.6 mL·kg·min; POST, 20.4 ± 3.5 mL·kg·min), P < 0.05. CONCLUSION: Moderate aerobic exercise significantly improved microvascular function of the leg in older adults.

Rapid homeostatic plasticity in the intact adult visual system.

Neurons may possess activity-dependent homeostatic mechanisms that permit them to globally alter synaptic strength as activity varies. We used the retinotectal projection of goldfish to test this idea in the intact adult CNS. We first altered tectal neuron activity by selectively manipulating excitatory input. When excitatory synaptic drive to tectal neurons was eliminated by blocking optic fibers, current evoked at optic synapses increased by 183% within 90 min. With partial activity blockade, the increase in synaptic strength scaled with the magnitude of activity depression. This silence-induced potentiation was also rapidly reversible. Conversely, an increase in optic input was followed by a decrease in evoked synaptic current. When optic drive was not altered and tectal neuronal activity was instead increased or decreased pharmacologically via GABA(A) receptors, synaptic strength again changed inversely with activity, indicating that synaptic strength changed in response to neuronal activity and not excitatory drive. Furthermore, altered synaptic strength tended to return ongoing activity to baseline. Changes in synaptic strength could also be detected in heterosynaptic pathways, indicating a global response. Finally, changes in synaptic strength were associated with corresponding changes in ongoing and evoked firing rates, indicating that the responsivity of tectal neurons was altered. Thus, tectal neurons exhibit archetypical homeostasis, one of the first robust examples in the intact adult CNS.

Immunohistochemical localization of CNTFRalpha in adult mouse retina and optic nerve following intraorbital nerve crush: evidence for the axonal loss of a trophic factor receptor after injury.

Ciliary neurotrophic factor (CNTF) is important for the survival and outgrowth of retinal ganglion cells (RGCs) in vitro. However, in vivo adult RGCs fail to regenerate and subsequently die following axotomy, even though there are high levels of CNTF in the optic nerve. To address this discrepancy, we used immunohistochemistry to analyze the expression of CNTF receptor alpha (CNTFRalpha) in mouse retina and optic nerve following intraorbital nerve crush. In normal mice, RGC perikarya and axons were intensely labeled for CNTFRalpha. At 24 hours after crush, the immunoreactivity normally seen on axons in the nerve was lost near the lesion. This loss radiated from the crush site with time. At 2 days postlesion, labeled axons were not detected in the proximal nerve, and at 2 weeks were barely detectable in the retina. In the distal nerve, loss of axonal staining progressed to the optic chiasm by 7 days and remained undetectable at 2 weeks. Interfascicular glia in the normal optic nerve were faintly labeled, but by 24 hours after crush they became intensely labeled near the lesion. Double labeling showed these to be both astrocytes and oligodendrocytes. At 7 days postlesion, darkly labeled glia were seen throughout the optic nerve, but at 14 days labeling returned to normal. It is suggested that the loss of CNTFRalpha from axons renders RGCs unresponsive to CNTF, thereby contributing to regenerative failure and death, while its appearance on glia may promote glial scarring.

Axonal rearrangement without reexpression of a growth associated marker: evidence from the compression of the retinotectal system in adult goldfish.

PURPOSE: Growing axons express a number of proteins associated with axonal growth which are thought to be critical for regeneration and sprouting. Whether these proteins are expressed during injury-induced axonal remodeling is tested in this paper. METHODS: The posterior half of the adult goldfish tectum was removed leaving the anterior half intact. This causes optic fibers from nasal retina, which project to posterior tectum, to displace temporal fibers from the anterior remnant and form a compressed retinotopic projection of the entire retina onto the anterior tectum. Immunohistochemistry using an antibody shown here to recognize growing and regenerating fibers in goldfish was used to monitor optic fibers. RESULTS: As expected, surgery induced reactivity in the axotomized nasal axons peaking at 1 month which returned to normal at 2 months when compression was completed. Unexpectedly, axons from temporal retina showed no detectable reactivity even though they were induced to grow anteriorly by the invading nasal fibers. CONCLUSIONS: Extensive axonal remodeling and synaptic rearrangement can occur without reentering the growth state associated with axonal growth and regeneration.

Age Reduces Microvascular Function in the Leg Independent of Physical Activity.

The microvasculature is critical in the control of blood flow. Aging and reduced physical activity (PA) may both decrease microvascular function. PURPOSE: The primary aim was to evaluate the influence of age on microvascular function in adults with similar PA levels. Secondary aims were to assess the reliability of muscle functional magnetic resonance imaging in older adults (OA) and the relationship between PA and microvascular function in OA. METHODS: Microvascular blood-oxygen-level dependent (BOLD) responses were measured in young adults (YA, n = 12, mean ± SD age = 21 ± 1 yr old, PA = 239 ± 73 × 10 counts per day) and OA (n = 13, 64 ± 4 yr old, PA = 203 ± 48 × 10 counts per day). Functional magnetic resonance images (3T, echo planar BOLD) of the leg were acquired after brief (1 s) maximal voluntary isometric contractions. The test-retest reliability of BOLD responses and the Pearson correlation between peak BOLD and PA were assessed in a group of OA (OA-r) with a broad range of PA (66 ± 5 yr old, n = 9, PA range = 54 × 10 to 674 × 10 counts per day). RESULTS: Peak BOLD microvascular responses were reduced for OA compared with YA. OA peak BOLD was 27% lower in the soleus (3.3% ± 0.8% OA vs 4.5% ± 1.4% YA; P = 0.017) and 40% lower in the anterior compartment (1.6% ± 0.6% OA vs 2.7% ± 1.1% YA; P = 0.006). Coefficients of variation were 8.6% and 11.8% for peak BOLD in the soleus and anterior compartment, respectively, with an intraclass correlation of 0.950 for both muscle regions. The correlation between peak BOLD and PA was r ≥ 0.715, P ≤ 0.030. CONCLUSIONS: Aging was associated with reduced microvascular function in leg muscles, independent of PA. The findings also revealed good reliability for BOLD magnetic resonance imaging in OA for the soleus and anterior compartment muscles.

Axonal protein synthesis and degradation are necessary for efficient growth cone regeneration.

Axonal regeneration can occur within hours of injury, the first step being the formation of a new growth cone. For sensory and retinal axons, regenerative ability in vivo correlates with the potential to form a new growth cone after axotomy in vitro. We show that this ability to regenerate a new growth cone depends on local protein synthesis and degradation within the axon. Axotomy in vitro leads to a fourfold to sixfold increase in 3H-leucine incorporation in both neurones and axons, starting within 10 min and peaking 1 h after axotomy. Application of protein synthesis inhibitors (cycloheximide and anisomycin) to cut axons, including axons whose cell bodies were removed, or proteasome inhibitors (lactacystin and N-acetyl-Nor-Leu-Leu-Al) all result in a reduction in the proportion of transected axons able to reform growth cones. Similar inhibition of growth cone formation was observed on addition of target of rapamycin (TOR), p38 MAPK (mitogen-activated protein kinase), and caspase-3 inhibitors. Comparing retinal and sensory axons of different developmental stages, levels of ribosomal protein P0 and phosphorylated translation initiation factor are high in sensory axons, lower in embryonic axons, and absent in adult retinal axons. Conditioning lesions, which increase the regenerative ability of sensory axons, lead to increases in intra-axonal protein synthetic and degradative machinery both in vitro and in vivo. Collectively, these findings suggest that local protein synthesis and degradation, controlled by various TOR-, p38 MAPK-, and caspase-dependent pathways, underlie growth cone initiation after axotomy.