The Fuzzy Kinetics Index: an indicator conflating cardiorespiratory kinetics during dynamic exercise.

PURPOSE: The aim of the present study was to develop a novel index using fuzzy logic procedures conflating cardiorespiratory and pulmonary kinetics during dynamic exercise as a representative indicator for exercise tolerance. METHODS: Overall 69 data sets were re-analyzed: (age: 29 ± 1.2 y [mean ± SEM], height: 179 ± 1.0 cm; body mass: 78 ± 1.4 kg; peak oxygen uptake ([Formula: see text]̇O2peak): 48 ± 1.1 ml·min-1·kg-1), that comprised pseudo random binary sequence work rate (WR) changes between 30 and 80 W on a cycle ergometer, with additional voluntary exhaustion to estimate [Formula: see text]O2peak. Heart rate (HR), stroke volume (SV) and gas exchange (pulmonary oxygen uptake ([Formula: see text]O2pulm)) were measured beat-to-beat and breath-by-breath, respectively. For estimation of muscle oxygen uptake ([Formula: see text]O2musc) kinetics and for the analysis of kinetic responses of the parameters of interest (perfusion ([Formula: see text] = HR·SV), [Formula: see text]O2pulm, [Formula: see text]O2musc) the approach of Hoffmann et al. (2013) was applied. For calculation of the Fuzzy Kinetics Index [Formula: see text], [Formula: see text]O2pulm, and [Formula: see text]O2musc were used as input variables for the subsequent fuzzy- and defuzzyfication procedures. RESULTS: For both absolute and relative [Formula: see text]O2peak a significant correlation has been observed with FKI, whereas the correlation coefficient is higher for relative (r = 0.430; p < 0.001; n = 69) compared to absolute [Formula: see text]O2peak (r = 0.358; p < 0.01; n = 69). No significant correlations have been found between FKI and age, height or body mass (p > 0.05 each). CONCLUSIONS: The significant correlations between FKI and [Formula: see text]O2peak represent a physiological connection between the regulatory and the capacitive system and its exercise performance. In turn, the application of FKI can serve as an indicator for healthy participants to assess exercise tolerance and sport performance.

Time-series analysis of heart rate and blood pressure in response to changes in work rate before and after 60 days of 6° head down tilt bed rest.

PURPOSE: Cardiovascular regulation during exercise, described using time series analysis, is expected to be attenuated after bed rest (BR) and this effect will be dampened by a reactive jumps countermeasure. METHODS: Twenty subjects (29 ± 6 years, 23.6 ± 1.7 kg m-2) were tested on a cycle ergometer 9 days (BDC-9) before the beginning of BR as well as 2 (R + 2) and 13 days (R + 13) after the end of BR, applying moderate pseudo-random binary (PRBS) work rate changes. Heart rate (HR) and mean arterial blood pressure (mBP) were measured beat-to-beat and interpolated to 1 s intervals. HR and mBP were cross-correlated [CCF(HR-mBP)] during the PRBS. Eleven subjects participated in a reactive jump countermeasure (JUMP) during the BR period, the other part of the group served as control group (CTRL). RESULTS: In the CTRL group, significantly lower CCF(HR-mBP) values during BDC-9 were observed compared to R + 2 during the lags 20-25 s and significantly higher values during the lags - 39 s to - 35 s. In the JUMP group, significantly lower CCFs were only observed at R + 2 compared with BDC-9 during the lags 23 s and 24 s, whereas the CCFs for BDC-9 were significantly higher at several lags compared with R + 13. CONCLUSION: Attenuations in the regulation of the cardiovascular system during cycling exercise after BR were found in the CTRL group of the RSL study. Cardiovascular regulation in the JUMP group was improved compared to values before the beginning of BR, suggesting the effectiveness of the reactive jumps countermeasure to mitigate the deleterious effects of prolonged BR.

Cardiovascular regulation: associations between exercise and head-up tilt.

It was hypothesized that faster cardiorespiratory kinetics during exercise are associated with higher orthostatic tolerance. Cardiorespiratory kinetics of 14 healthy male subjects (30 ± 4 years, 179 ± 8 cm, 79 ± 8 kg) were tested on a cycle ergometer during exercise with changing work rates of 30 and 80 W. Pulmonary oxygen uptake ( ) was measured breath-by-breath and heart rate (HR), mean arterial blood pressure (MAP), and total peripheral resistance (TPR) were measured beat-to-beat. Muscular oxygen uptake ( ) was estimated from HR and . Kinetic parameters were determined by time-series analysis, using cross-correlation functions (CCFmax(x)) between the parameter and the work rate. Cardiovascular regulations of MAP, HR, and TPR during orthostatic stress were measured beat-to-beat on a tilt seat. Changes between the minima and maxima during the 6° head-down tilt and the 90° head-up tilt positions were calculated for each parameter (Δtilt-up). correlated significantly with ΔTPRtilt-up (r = 0.790, p ≤ 0.001). CCFmax(HR) was significantly correlated with ΔHRtilt-up (r = -0.705, p = 0.002) and the amplitude in HR from 30 to 80 W (rSP = -0.574, p = 0.016). The observed correlations between cardiorespiratory regulation in response to exercise and orthostatic stress during rest might allow for a more differential analysis of the underlying mechanisms of orthostatic intolerance in, for example, patient groups.

Impact of 60 days of 6° head down tilt bed rest on muscular oxygen uptake and heart rate kinetics: efficacy of a reactive sledge jump countermeasure.

PURPOSE: The effects of 60 days of head down tilt bed rest (HDBR) with and without the application of a reactive jump countermeasure were investigated, using a method which enables to discriminate between pulmonary ([Formula: see text]O2pulm) and muscular ([Formula: see text]O2musc) oxygen uptake kinetics to control for hemodynamic influences. METHODS: 22 subjects were randomly allocated to either a group performing a reactive jumps countermeasure (JUMP; n = 11, male, 29 ± 7 years, 23.9 ± 1.3 kg m- 2) or a control group (CTRL; n = 11, male, 29 ± 6 years, 23.3 ± 2.0 kg m- 2). Heart rate (HR) and [Formula: see text]O2pulm were measured in response to repeated changes in work rate between 30 and 80 W before (BDC-9) and two times after HDBR (R+ 2, R+ 13). Kinetic responses of HR, [Formula: see text]O2pulm, and [Formula: see text]O2musc were assessed applying time series analysis. Higher maxima in cross-correlation functions (CCFmax(x)) between work rate and the respective parameter indicate faster kinetics responses. Statistical analysis was performed applying multifactorial analysis of variance. RESULTS: CCFmax([Formula: see text]O2musc) and CCFmax([Formula: see text]O2pulm) were not significantly different before and after HDBR (P > 0.05). CCFmax(HR) decreased following bed rest (JUMP: BDC-9: 0.30 ± 0.09 vs. R+ 2: 0.28 ± 0.06 vs. R+13: 0.28 ± 0.07; CTRL: 0.35 ± 0.09 vs. 0.27 ± 0.06 vs. 0.33 ± 0.07 P = 0.025). No significant differences between the groups were observed (P > 0.05). Significant alterations were found for CCFmax of mean arterial blood pressure (mBP) after HDBR (JUMP: BDC-9: 0.21 ± 0.07 vs. R+ 2: 0.30 ± 0.13 vs. R+ 13: 0.28 ± 0.08; CTRL: 0.25 ± 0.07 vs. 0.38 ± 0.13 vs. 0.28 ± 0.08; P = 0.008). CONCLUSIONS: Despite hemodynamic changes, [Formula: see text]O2 kinetics seem to be preserved for a longer period of HDBR, even without the application of a countermeasure.

Temporal dissociation between muscle and pulmonary oxygen uptake kinetics: influences of perfusion dynamics and arteriovenous oxygen concentration differences in muscles and lungs.

PURPOSE: The aim of the study was to test whether or not the arteriovenous oxygen concentration difference (avDO2) kinetics at the pulmonary (avDO2pulm) and muscle (avDO2musc) levels is significantly different during dynamic exercise. METHODS: A re-analysis involving six publications dealing with kinetic analysis was utilized with an overall sample size of 69 participants. All studies comprised an identical pseudorandom binary sequence work rate (WR) protocol-WR changes between 30 and 80 W-to analyze the kinetic responses of pulmonary ([Formula: see text]) and muscle ([Formula: see text]) oxygen uptake kinetics as well as those of avDO2pulm and avDO2musc. RESULTS: A significant difference between [Formula: see text] (0.395 ± 0.079) and [Formula: see text] kinetics (0.330 ± 0.078) was observed (p < 0.001), where the variables showed a significant relationship (rSP = 0.744, p < 0.001). There were no significant differences between avDO2musc (0.446 ± 0.077) and avDO2pulm kinetics (0.451 ± 0.075), which are highly correlated (r = 0.929, p < 0.001). CONCLUSION: It is suggested that neither avDO2pulm nor avDO2musc kinetic responses seem to be responsible for the differences between estimated [Formula: see text] and measured [Formula: see text] kinetics. Obviously, the conflation of avDO2 and perfusion ([Formula: see text] ) at different points in time and at different physiological levels drive potential differences in [Formula: see text] and [Formula: see text] kinetics. Therefore, [Formula: see text] should, in general, be considered whenever oxygen uptake kinetics are analyzed or discussed.

Oxygen uptake kinetics following six weeks of interval and continuous endurance exercise training - An explorative pilot study.

PURPOSE: The aim of the study was to compare the responses of pulmonary (V˙O2pulm) and muscle (V˙O2musc) oxygen uptake kinetics before (PRE) and after (POST) six weeks of endurance exercise training. METHODS: Nine untrained individuals performed pseudo-random binary sequences work rate changes between 30W and 80W at PRE and POST training intervention. Heart rate (HR) and V˙O2pulm were measured beat-to-beat and breath-by-breath, respectively. V˙O2musc was estimated applying the approach of Hoffmann et al. (Eur J Appl Physiol 113: 1745-1754, 2013). RESULTS: Maximal oxygen uptake showed significant increases from PRE (3.2±0.3Lmin-1) to POST (3.7±0.2Lmin-1; p<0.05). For HR, V˙O2pulm and V˙O2musc kinetics no significant changes from PRE to POST training intervention were observed (p>0.05). CONCLUSIONS: Discrepancies in the adaptations of the involved exercise induced physiological systems seem to be responsible for the observed significant alterations in maximal V˙O2 after six weeks of the training intervention in contrast to no changes in the kinetics responses.

Analysis of heart rate and oxygen uptake kinetics studied by two different pseudo-random binary sequence work rate amplitudes.

PURPOSE: The aim of the study was to compare the kinetics responses of heart rate (HR), pulmonary (V˙O2pulm) and predicted muscular (V˙O2musc) oxygen uptake between two different pseudo-random binary sequence (PRBS) work rate (WR) amplitudes both below anaerobic threshold. METHODS: Eight healthy individuals performed two PRBS WR protocols implying changes between 30W and 80W and between 30W and 110W. HR and V˙O2pulm were measured beat-to-beat and breath-by-breath, respectively. V˙O2musc was estimated applying the approach of Hoffmann et al. (Eur J Appl Physiol 113: 1745-1754, 2013) considering a circulatory model for venous return and cross-correlation functions (CCF) for the kinetics analysis. RESULTS: HR and V˙O2musc kinetics seem to be independent of WR intensity (p>0.05). V˙O2pulm kinetics show prominent differences in the lag of the CCF maximum (39±9s; 31±4s; p<0.05). CONCLUSIONS: A mean difference of 14W between the PRBS WR amplitudes impacts venous return significantly, while HR and V˙O2musc kinetics remain unchanged.

Gas exchange kinetics following concentric-eccentric isokinetic arm and leg exercise.

PURPOSE: To evaluate the effects of exercise velocity (60, 150, 240deg∙s-1) and muscle mass (arm vs leg) on changes in gas exchange and arterio-venous oxygen content difference (avDO2) following high-intensity concentric-eccentric isokinetic exercise. METHODS: Fourteen subjects (26.9±3.1years) performed a 3×20-repetition isokinetic exercise protocol. Recovery beat-to-beat cardiac output (CO) and breath-by-breath gas exchange were recorded to determine post-exercise half-time (t1/2) for oxygen uptake (V˙O2pulm), carbon dioxide output (V˙CO2pulm), and ventilation (V˙E). RESULTS: Significant differences of the t1/2 values were identified between 60 and 150deg∙s-1. Significant differences in the t1/2 values were observed between V˙O2pulm and V˙CO2pulm and between V˙CO2pulm and V˙E. The time to attain the first avDO2-peak showed significant differences between arm and leg exercise. CONCLUSIONS: The present study illustrates, that V˙O2pulm kinetics are distorted due to non-linear CO dynamics. Therefore, it has to be taken into account, that V˙O2pulm may not be a valuable surrogate for muscular oxygen uptake kinetics in the recovery phases.

Cardiorespiratory Kinetics Determined by Pseudo-Random Binary Sequences - Comparisons between Walking and Cycling.

This study aims to compare cardiorespiratory kinetics as a response to a standardised work rate protocol with pseudo-random binary sequences between cycling and walking in young healthy subjects. Muscular and pulmonary oxygen uptake (V̇O2) kinetics as well as heart rate kinetics were expected to be similar for walking and cycling. Cardiac data and V̇O2 of 23 healthy young subjects were measured in response to pseudo-random binary sequences. Kinetics were assessed applying time series analysis. Higher maxima of cross-correlation functions between work rate and the respective parameter indicate faster kinetics responses. Muscular V̇O2 kinetics were estimated from heart rate and pulmonary V̇O2 using a circulatory model. Muscular (walking vs. cycling [mean±SD in arbitrary units]: 0.40±0.08 vs. 0.41±0.08) and pulmonary V̇O2 kinetics (0.35±0.06 vs. 0.35±0.06) were not different, although the time courses of the cross-correlation functions of pulmonary V̇O2 showed unexpected biphasic responses. Heart rate kinetics (0.50±0.14 vs. 0.40±0.14; P=0.017) was faster for walking. Regarding the biphasic cross-correlation functions of pulmonary V̇O2 during walking, the assessment of muscular V̇O2 kinetics via pseudo-random binary sequences requires a circulatory model to account for cardio-dynamic distortions. Faster heart rate kinetics for walking should be considered by comparing results from cycle and treadmill ergometry.

Analysis of cardio-pulmonary and respiratory kinetics in different body positions: impact of venous return on pulmonary measurements.

PURPOSE: The aim of the study was to compare the kinetics responses of heart rate (HR), pulmonary ([Formula: see text]O2pulm), and muscular ([Formula: see text]O2musc) oxygen uptake during dynamic leg exercise across different body positions (-6°, 45°, and 75°). METHODS: Ten healthy individuals [six men, four women; age 23.4 ± 2.8 years; height 179.7 ± 8.3 cm; body mass 73 ± 12 kg (mean ± SD)] completed pseudo-random binary sequence (PRBS) work rate (WR) changes between 30 and 80 W in each posture. HR was measured beat-to-beat by echocardiogram and [Formula: see text]O2pulm by breath-by-breath gas exchange. [Formula: see text]O2musc kinetics were assessed by the procedure of Hoffmann et al. (Eur J Appl Physiol 113:1745-1754, 2013) applying a circulatory model and cross-correlation functions (CCF). RESULTS: For [Formula: see text]O2pulm kinetics significant differences between -6° (CCF-values: 0.292 ± 0.040) and 45° (0.256 ± 0.034; p < 0.01; n = 10) as well as between -6° and 75° (0.214 ± 0.057; p < 0.05; n = 10) were detected at lag '40 s' of the CCF course as interaction effects (factors: Lag × Posture). HR and [Formula: see text]O2musc kinetics yield no significant differences across the postures. CONCLUSIONS: The analysis of cardio-dynamic and respiratory kinetics, especially with an emphasis on muscular and cellular level, has to consider venous return and cardiac output distortions. Simplified observations of kinetics responses resulting in time constants and time delays only should be replaced by the time-series analysis for a more sophisticated evaluation. The results illustrate that isolated [Formula: see text]O2pulm measurements without cardio-dynamic influences may not represent the kinetics responses originally revealed at muscular level.

Muscular Oxygen Uptake Kinetics in Aged Adults.

Pulmonary oxygen uptake (V˙O2) kinetics and heart rate kinetics are influenced by age and fitness. Muscular V˙O2 kinetics can be estimated from heart rate and pulmonary V˙O2. In this study the applicability of a test using pseudo-random binary sequences in combination with a model to estimate muscular V˙O2 kinetics was tested. Muscular V˙O2 kinetics were expected to be faster than pulmonary V˙O2 kinetics, slowed in aged subjects and correlated with maximum V˙O2 and heart rate kinetics. 27 elderly subjects (73±3 years; 81.1±8.2 kg; 175±4.7 cm) participated. Cardiorespiratory kinetics were assessed using the maximum of cross-correlation functions, higher maxima implying faster kinetics. Muscular V˙O2 kinetics were faster than pulmonary V˙O2 kinetics (0.31±0.1 vs. 0.29±0.1 s; p=0.004). Heart rate kinetics were not correlated with muscular or pulmonary V˙O2 kinetics or maximum V˙O2. Muscular V˙O2 kinetics correlated with maximum V˙O2 (r=0.35; p=0.033). This suggests, that muscular V˙O2 kinetics are faster than estimates from pulmonary V˙O2 and related to maximum V˙O2 in aged subjects. In the future this experimental approach may help to characterize alterations in muscular V˙O2 under various conditions independent of motivation and maximal effort.

V̇O2 and HR kinetics before and after International Space Station missions.

PURPOSE: Heart rate (HR), pulmonary and muscle oxygen uptake ([Formula: see text]O2pulm, [Formula: see text]O2musc) kinetics after changes of work rate (WR) indicate regulatory characteristics related to aerobic metabolism. We analysed whether the kinetics of HR, [Formula: see text]O2pulm and [Formula: see text]O2musc are slowed after missions to the International Space Station (ISS). The changes of the kinetics were correlated with [Formula: see text]O2peak data. METHODS: 10 astronauts [4 females, 6 males, age: 48.0 ± 3.8 years, height: 176 ± 7 cm, mass: 74.5 ± 15.9 kg (mean ± SD)] performed an incremental test to determine [Formula: see text]O2peak (before missions on L-110 days, after return on R+1/+10/+36 days), and a cardio-respiratory kinetics test (CRKT) with randomized 30-80 W WR changes to determine HR, [Formula: see text]O2pulm and [Formula: see text]O2musc kinetics by time-series analysis (L-236/-73, R+6/+21). Kinetics were summarized by maximum and related lag of cross-correlation function (CCFmax, CCFlag) of WR with the analysed parameter. RESULTS: Statistically, significant changes were also found for CCFmax([Formula: see text]O2musc) between L-236 and R+6 (P = 0.010), L-236 and R+21 (P = 0.030), L-72 and R+6 (P = 0.043). Between pre-to-post mission change in [Formula: see text]O2peak and CCFmax(HR), a correlation was shown (r SP = 0.67, P = 0.017). CONCLUSION: The [Formula: see text]O2musc kinetics changes indicate aerobic detraining effects which are present up to 21 days following space flight. The correlations between changes in [Formula: see text]O2peak and HR kinetics illustrate the key role of cardiovascular regulation in [Formula: see text]O2peak. The addition of CRKT to ISS flight is recommended to obtain information regarding the potential muscular and cardiovascular deconditioning. This allows a reduction in the frequency of higher intensity testing during flight.

Essential Hypertension: Cardiovascular Response to Breath Hold Combined with Exercise.

Essential hypertension (EH) is a widespread disease and might be prevalent in apnea divers and master athletes. Little is known about the influence of EH and the antihypertensive drugs (AHD) on cardiovascular reactions to combined breath hold (BH) and exercise. In this pilot study, healthy divers (HCON) were compared with treated hypertensive divers with regard to heart rate (HR) and mean blood-pressure (MAP) responses to BH, exercise and the combination of both. Ten subjects with EH and ten healthy divers were tested. 3 different 20 s stimuli were applied: BH combined with 30 W or 150 W and 150 W without BH. The time-charts during the stress intervals and during recovery were compared. Subjects treated with an angiotensin-converting enzyme (ACE) inhibitor showed higher changes for MAP values if breath hold was performed. HR responses were obviously changed if a ß-blocker was part of the medication. One subject showed extreme MAP responses to all stimuli and conspicuous HR if BH was involved. The modulation of HR-/MAP-response in EH subjects depends on the mechanisms of antihypertensive agents. The combination of an ACE inhibitor and a ß-blocker may give the best protection. It is recommended to include short apnea tests in the fitness-to-dive examination to individually predict potential endangerment.

Oxygen uptake and heart rate kinetics during dynamic upper and lower body exercise: an investigation by time-series analysis.

PURPOSE: The study compared the kinetic responses of heart rate (HR), pulmonary ([Formula: see text]O2pulm) and muscular oxygen uptake ([Formula: see text]O2musc) for upper (UpBody) and lower body (LoBody) exercise. METHODS: Eleven healthy men (24 ± 2 years, 184 ± 8 cm, 79 ± 7 kg) performed pseudo-random binary sequence (PRBS) work rate (WR) changes on a semi-recumbent cycle ergometer (30 and 80 W) and an arm cranking exercise device (20 and 50 W); followed by stepwise increases in WR (UpBody: 20 W 5 min(-1); LoBody: 50 W 5 min(-1)). [Formula: see text]O2pulm was measured breath-by-breath and HR beat-to-beat. [Formula: see text]O2musc was estimated by the approach as reported by Hoffmann et al. (Eur J Appl Physiol 113:1745-1754, 2013), accounting for circulatory distortions. Time constants (τ) for HR (τHR), [Formula: see text]O2pulm (τ [Formula: see text]O2pulm) and [Formula: see text]O2musc (τ [Formula: see text]O2musc) were estimated during the PRBS phases by time-series analysis. RESULTS: Peak oxygen uptake differed significantly between UpBody (37.8 ± 5.0 ml min(-1) kg(-1)) and LoBody exercises (56.1 ± 7.4 mL min(-1) kg(-1); p < 0.001). Significant differences were observed for τ [Formula: see text]O2musc (UpBody: 41.1 ± 11.3 s vs LoBody: 29.5 ± 5.2 s; p < 0.05), but not for τ [Formula: see text]O2pulm (49.1 ± 17.1 s vs 39.6 ± 11.2 s; p > 0.05) and τHR (29.1 ± 15.6 s vs 25.6 ± 8.0 s; p > 0.05). CONCLUSIONS: Meaningful dissociations between [Formula: see text]O2pulm and [Formula: see text]O2musc kinetics exist for both UpBody and LoBody exercise during rapid work rate changes. Therefore, isolated [Formula: see text]O2pulm kinetic estimations without the consideration of the circulatory distortions may not allow a reliable assessment of [Formula: see text]O2musc kinetics.

Skeletal muscle VO2 kinetics from cardio-pulmonary measurements: assessing distortions through O2 transport by means of stochastic work-rate signals and circulatory modelling.

During non-steady-state exercise, dynamic changes in pulmonary oxygen uptake (VO2pulm) are dissociated from skeletal muscle VO2 (VO2musc) by changes in lung and venous O2 concentrations (CvO2), and the dynamics and distribution of cardiac output (CO) between active muscle and remaining tissues (Qrem). Algorithms can compensate for fluctuations in lung O2 stores, but the influences of CO and CvO2 kinetics complicate estimation of VO2musc from cardio-pulmonary measurements. We developed an algorithm to estimate VO2musc kinetics from VO2pulm and heart rate (HR) during exercise. 17 healthy volunteers (28 ± 7 years; 71 ± 12 kg; 7 females) performed incremental exercise using recumbent cycle ergometry (VO2peak 52 ± 8 ml min(-1) kg(-1)). Participants completed a pseudo-random binary sequence (PRBS) test between 30 and 80 W. VO2pulm and HR were measured, and CO was estimated from HR changes and steady-state stroke volume. VO2musc was derived from a circulatory model and time series analyses, by solving for the unique combination of venous volume and the perfusion of non-exercising tissues that provided close to mono-exponential VO2musc kinetics. Independent simulations showed that this approach recovered the VO2musc time constant (τ) to within 7% (R(2) = 0.976). Estimates during PRBS were venous volume 2.96 ± 0.54 L; Qrem 3.63 ± 1.61 L min(-1); τHR 27 ± 11 s; τVO2musc 33 ± 8 s; τVO2pulm 43 ± 14 s; VO2pulm time delay 19 ± 8 s. The combination of stochastic test signals, time series analyses, and a circulatory model permitted non-invasive estimates of VO2musc kinetics. Large kinetic dissociations exist between muscular and pulmonary VO2 during rapid exercise transients.

Graded expression patterns of ephrin-As in the superior colliculus after lesion of the adult mouse optic nerve.

The idea has been put forward that molecules and mechanisms acting during development are re-used during regeneration in the adult, for example in response to traumatic injury in order to re-establish the functional integrity of neuronal circuits. Members of the Eph family of receptor tyrosine kinases and their 'ligands', the ephrins, play a prominent role during development of the retinocollicular projection in rodents, where EphA receptors and ephrin-As are expressed in gradients in both the retina and the superior colliculi (SC). We were interested in investigating whether EphA family members are also expressed or re-expressed in the adult after optic nerve lesion, since the presence of axon guidance information is an important prerequisite for a topographically appropriate re-connection by retinal ganglion cell (RGC) axons. This analysis was encouraged by results showing that RGC axons do not exert guidance preferences in response to membranes from adult unlesioned SC, but in response to membranes from the adult deafferented SC. We found a graded expression pattern of ephrin-As in the SC both before and after deafferentation, which was remarkably similar to those found during development. EphA receptor levels were reduced in the SC after deafferentation and the expression patterns of the EphB family were not changed. In particular, the presence of a graded ephrin-A expression in the deafferented SC suggests that - if robust regeneration of RGC axons can be achieved - topographic guidance information as a likely requirement for a functionally successful re-establishment of the retinocollicular projection is available.

Analysis of ephrin-A2 in the chick retinotectal projection using a function-blocking monoclonal antibody.

Eph receptor tyrosine kinases and their ligands have been shown to be involved in processes of cell migration and axon guidance during embryonic development. Here we describe the development of a function-blocking monoclonal antibody against chick ephrin-A2, and its effect on retinal ganglion cell axons studied both in vitro and in vivo. In the stripe assay, the blocking antibody completely abolished the repulsive effect of posterior tectal membranes. In vivo, in a loss-of-function approach, hybridoma cells secreting the antiephrin-A2 antibody were applied to chick embryos from embryonic day 3 (E3) on, and the retinotectal projection was subsequently analyzed at E16. DiI tracing analyses showed that although the projection of both temporal and nasal retinal ganglion axons in the tectum was, overall, normal, occasionally diffuse and extra termination zones were observed, in addition to axons over-shooting their termination zones. These data support the idea that ephrin-A2 contributes to the establishment of the chick retinotectal projection.

A role for the EphA family in the topographic targeting of vomeronasal axons.

We have investigated the role of the Eph family of receptor tyrosine kinases and their ligands in the establishment of the vomeronasal projection in the mouse. Our data show intriguing differential expression patterns of ephrin-A5 on vomeronasal axons and of EphA6 in the accessory olfactory bulb (AOB), such that axons with high ligand concentration project onto regions of the AOB with high receptor concentration and vice versa. These data suggest a mechanism for development of this projection that is the opposite of the repellent interaction between Eph receptors and ligands observed in other systems. In support of this idea, when given the choice of whether to grow on lanes containing EphA-F(c)/laminin or F(c)/laminin protein (in the stripe assay), vomeronasal axons prefer to grow on EphA-F(c)/laminin. Analysis of ephrin-A5 mutant mice revealed a disturbance of the topographic targeting of vomeronasal axons to the AOB. In summary, these data, which are derived from in vitro and in vivo experiments, indicate an important role of the EphA family in setting up the vomeronasal projection.

An ephrin-A-dependent signaling pathway controls integrin function and is linked to the tyrosine phosphorylation of a 120-kDa protein.

The Eph family of receptor tyrosine kinases and their ligands, the ephrins, have been implicated in the development of the retinotectal projection. Here, glycosylphosphatidylinositol-anchored A-ephrins are not only expressed in the tectum but also on retinal axons, raising the possibility that they function in this context as receptors. We now show that activation of ephrin-A2 or ephrin-A5 by one of their receptors, ephA3, results in a beta 1-integrin-dependent increased adhesion of ephrin-A-expressing cells to laminin. In the search for an ephrin-A-dependent signaling pathway controlling integrin activation, we identified a 120-kDa raft membrane protein that is tyrosine-phosphorylated specifically after ephrin-A activation. Tyrosine phosphorylation of this protein is not seen after stimulating ephrin-A2-expressing cells with basic fibroblast growth factor, epidermal growth factor, insulin growth factor, or fetal calf serum containing a large set of different growth factors. The role of p120 as a mediator of an ephrin-A-integrin coupling is supported by the finding that inhibiting tyrosine phosphorylation of p120 correlates with an abolishment of the beta 1-dependent cell adhesion.