Prior Conditioning Research Articles

Interactions between pairs of transcranial magnetic stimuli over the human left dorsal premotor cortex differ from those seen in primary motor cortex

A single TMS pulse (110% resting motor threshold, RMT) to the left dorsal premotor cortex (PMd) (CS2) suppresses the amplitude of motor evoked potentials (MEPs) from a test pulse (TS) over the right motor cortex (M1), and facilitates MEPs from the left motor cortex. We probed how this interaction was changed by a prior conditioning pulse over PMd (CS1) using a paired pulse TMS design. In the main experiments, the intensity of CS1 was 80% RMT. Basal suppression of right M1 was removed when CS1-CS2 was 1 ms or 5 ms with a similar tendency at 15 ms. Basal facilitation of left M1 was suppressed at CS1-CS2 of 5 ms. A similar time course was seen if CS2 was increased to 100% RMT, but there was no significant effect if CS1 was 70% RMT. Preconditioning PMd with continuous or intermittent theta burst repetitive TMS (cTBS, iTBS) abolished the basal CS2-TS interaction between premotor and motor cortices. Finally, if very short interstimulus intervals between CS1 and CS2 were explored to detect interactions similar to I-wave facilitation in M1, we found that the basal suppression of right M1 was abolished at CS1-CS2 intervals of 1.8 and 2.8 ms. We suggest that paired pulse TMS may be capable of investigating properties of intrinsic circuits in PMd and that their properties differ from those in the nearby M1. Paired TMS may be a useful method of studying the excitability of intrinsic circuits in non-primary areas of the motor system.

A CASE OF IMPLEMENTING ON-LINE ANALYSIS OF IRON ORE SLURRIES

An account is presented of the development and implementation of an on-line analyzer in an iron ore pelletizing plant. The analyzer uses Laser-Induced Breakdown Spectroscopy (LIBS) technology to interrogate the target material and determine the concentration of key elements. Following primary slurry sampling, prior conditioning is necessary to ensure reliable determinations. The instrument has proved to be a very sensitive detector of process perturbations of either chemical or physical origin and has enabled plant operators to exert tighter control over the chemistry of the final product.

The ontogeny of fear-potentiated startle: Effects of earlier-acquired fear memories.

Research has shown that learned fear emerges in a response-specific sequence. For example, freezing is observed at a younger age than is potentiated startle (P. Hunt & B. A. Campbell, 1997). The present study shows that the age at which a specific learned fear response emerges is influenced by the animal's early experiences. Specifically, fear potentiation of startle emerges earlier in development if the rat is given prior fear conditioning to a different stimulus. Some constraints of this "facilitation" effect are determined in follow-up experiments. This facilitation effect may provide a novel way of testing the development of the neural circuits underlying learned fear.

Military Training and Musculoskeletal Disorders

Objectives: This study examined the extent to which musculoskeletal disorders [MSD] affect military populations, as well as intrinsic and extrinsic factors associated with MSD and the relative contribution of training, sports, and manual handling. A search of published literature was conducted using PubMed-listed articles published up to February 2006. Findings: Although physical conditioning represents an important facet of military preparedness, up to half of all recruits may suffer an injury during their basic military training. Musculoskeletal disorders are a common occurrence for soldiers and represent an important source of morbidity for the military as a whole. Intrinsic risk factors linked to military training injuries include a diverse range of inherent variables such as the level of prior physical conditioning, psychological make up, age, height, weight, and gender. Extrinsic risk factors for military MSD include training surface, exercise when fatigued, progressive training in place of cyclical training, and the type of footwear usually worn. Other military-specific variables may also include drill methods, the arrangement of platoons, training technique, and the actual training distance. Conclusions: Overall, this review suggests that MSD are a common occurrence for military personnel and represent an important source of morbidity for the military as a whole. In meeting this problem, there is clearly an urgent need to target effective preventive measures, especially those involving military-specific training and sports activities.

Second-order conditioning during a compound extinction treatment

Two conditioned taste aversion experiments with rats were conducted to establish if a target taste that had received a prior pairing with illness could be subject to second-order conditioning during extinction treatment in compound with a flavor that also received prior conditioning. In these experiments, the occurrence of second-order conditioning was indicated by protection from extinction of the aversion elicited by the target taste. This possibility, although intuitive, deserves attention because current associative models [e.g., Rescorla, R. A., & Wagner, A. R. (1972). A theory of Pavlovian conditioning: variations in the effectiveness of reinforcement and nonreinforcement. In A. H. Black & W. F. Prokasy (Eds.), Classical conditioning II: Current research and theory (pp. 64–99). New York: Appleton-Century-Crofts.] predict exactly the opposite outcome, namely, that compound extinction of two CSs should result in enhanced extinction.

OxLDL immune complexes activate complement and induce cytokine production by MonoMac 6 cells and human macrophages

Oxidized low density lipoprotein (OxLDL) is immunogenic and induces autoimmune responses in humans. OxLDL antibodies are predominantly of the proinflammatory IgG1 and IgG3 isotypes. We tested the capacity of immune complexes prepared with copper-oxidized human LDL and affinity chromatography-purified human OxLDL antibodies [OxLDL-immune complexes (ICs)] to activate complement and to induce cytokine release by MonoMac 6 (MM6) cells and by primary human macrophages. The levels of C4d and C3a were significantly higher in human serum incubated with OxLDL-ICs than after incubation with OxLDL or OxLDL antibody, indicating complement activation by the classical pathway. MM6 cells and primary human macrophages were incubated with OxLDL-ICs, with or without prior conditioning with interferon-gamma. After 18 h of incubation, both MM6 cells and primary human macrophages released significantly higher levels of proinflammatory cytokines after incubation with OxLDL-ICs than after incubation with OxLDL or with OxLDL antibody, both in primed and unprimed cells. OxLDL-ICs were more potent activators of MM6 cells than keyhole limpet hemocyanin-ICs. Blocking Fc gamma receptor I (FcgammaRI) with monomeric IgG1 significantly depressed the response of MM6 cells to OxLDL-ICs. In conclusion, human OxLDL-ICs have proinflammatory properties, as reflected by their capacity to activate the classical pathway of complement and to induce proinflammatory cytokine release from MM6 cells and primary human macrophages.

Protective effect of prior physical conditioning on relaxing response of corpus cavernosum from rats made hypertensive by nitric oxide inhibition

The aim of this work was to evaluate the influence of run training on the responsiveness of corpus cavernosum (CC) from rats made hypertensive by treatment with nitric oxide (NO) synthesis inhibitor. Wistar rats were divided into sedentary control (C-SD), exercise training (C-TR), N(omega)-nitro-L-arginine methyl ester (L-NAME) sedentary (LN-SD) and L-NAME trained (LN-TR) groups. The run training program consisted in 8 weeks in a treadmill, 5 days/week, each session lasted 60 min. L-NAME treatment (2 and 10 mg/rat/day) started after 4 weeks of prior physical conditioning and lasted 4 weeks. Concentration-response curves were obtained for acetylcholine (ACh), sodium nitroprusside (SNP), sildenafil and BAY 41-2272. The effect of electrical field stimulation (EFS) on the relaxations responses of CC was evaluated. Run training prevented the arterial hypertension induced by L-NAME treatment (LN-SD: 135+/-2 and 141+/-2 mm Hg for both doses of L-NAME) compared to LN-SD groups (154+/-1 and 175+/-2 mm Hg, for 2 and 10 mg of L-NAME, respectively). Run training produced an increase in the maximal responses (E(max)) of CC for ACh (C-SD: 47+/-3; C-TR: 52+/-1; and LN-TR: 53+/-3%) and SNP (C-SD: 89+/-1; C-TR: 98+/-1; and LN-TR: 95+/-1%). Both potency and E(max) for ACh were reduced in a dose of 10 mg of L-NAME, and run training restored the reduction of E(max) for ACh. No changes were found for BAY 41-2271 and sildenafil. Relaxing responses to EFS was reduced by L-NAME treatment that was restored by prior physical conditioning. In conclusion, our study shows a beneficial effect of prior physical conditioning on the impaired CC relaxing responses in rats made hypertensive by chronic NO blockade.

Adhesion of glass/epoxy composites influenced by thermal and cryogenic environments

AbstractLittle information regarding the effects of prior thermal and cryogenic conditionings on hydrothermal and mechanical behavior, for varied volume fractions of constituent phases in polymer matrix fiber composites, has been published to date. The present experimental investigation uses flexural test to assess the effects of thermal and cryogenic treatments, and concurrently followed hydrothermal aging on quality of adhesion of multilayered laminates for 55, 60, and 65 wt % of E‐glass fiber‐reinforced epoxy composites. The specimens were conditioned at 80°C and −80°C temperatures for different time durations, and thereafter they were immediately immersed in boiling water for an hour. Water absorption rates were evaluated for those conditioned specimens in such environment. Absorption study in hydrothermal aging showed a remarkable variation for the two cases of prior conditionings. The shear strength values were compared with the test value of as‐cured samples. Degradation of mechanical property was found to be less prevalent during hydrothermal aging, with a prior conditioning at 80°C temperature compared to −80°C treated glass/epoxy composites. Improved shear strength for almost all conditions of thermal conditioning in the initial stages has highlighted better adhesion influenced by postcuring phenomena during thermal or cryogenic conditioning. It was also observed from water absorption data that high temperature conditioning contributed more strengthening effect and better adhesion at the interfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1943–1949, 2006

Nucleation and growth of the α′ martensitic phase in Pu–Ga alloys

In a Pu–2.0 at.% Ga alloy, it is observed experimentally that the amount of the martensitic α′ product formed upon cooling the metastable δ phase below the martensite burst temperature ( M b) is a function of the holding temperature and holding time of a prior conditioning (“annealing”) treatment. Before subjecting a sample to a cooling and heating cycle to form and revert the α′ phase, it was first homogenized for 8 h at 375 °C to remove any microstructural memory of prior transformations. Subsequently, conditioning was carried out in a differential scanning calorimeter apparatus at temperatures in the range between −50 and 370 °C for periods of up to 70 h to determine the holding time and temperature that produced the largest volume fraction of α′ upon subsequent cooling. Using transformation peak areas (i.e., the heats of transformation) as a measure of the amount of α′ formed, the largest amount of α′ was obtained following holding at 25 °C for at least 6 h. Additional time at 25 °C, up to 70 h, did not increase the amount of subsequent α′ formation. At 25 °C, the Pu–2.0 at.% Ga alloy is below the eutectoid transformation temperature in the phase diagram and the expected equilibrium phases are α and Pu 3Ga, although a complete eutectoid decomposition of δ to these phases is expected to be extremely slow. It is proposed here that the influence of the conditioning treatment can be attributed to the activation of α-phase embryos in the matrix as a beginning step toward the eutectoid decomposition, and we discuss the effects of spontaneous self-irradiation accompanying the Pu radioactive decay on the activation process. Subsequently, upon cooling, certain embryos appear to be active as sites for the burst growth of martensitic α′ particles, and their amount, distribution, and potency appear to contribute to the total amount of martensitic product formed. A modeling approach based on classic nucleation theory is presented to describe the formation of α-phase embryos during conditioning. The reasons why the holding times during conditioning become eventually ineffective in promoting more α′ formation on cooling are discussed in terms of the differences in the potency of the embryos created in the δ matrix during conditioning and in terms of growth-impeding volume strains in the matrix resulting from an increasing number of martensite particles, thus opposing further growth. It is suggested that the disparate amounts of the α′ formation reported in the literature following various studies may be in part a consequence of the fact that conditioning times at ambient temperatures are inevitably involved in any handling of radioactive samples prior to testing.

Effects of heat stress on Young's modulus of outer hair cells in mice

Intense sound exposure causes permanent hearing loss due to hair cell and cochlear damage. Prior conditioning with sublethal stressors, such as nontraumatic sound, heat stress and restraint protects the ear from acoustic injury. However, the mechanisms underlying conditioning-related cochlear protection remain unknown. In this paper, Young's modulus and the amount of filamentous actin (F-actin) of outer hair cells (OHCs) with/without heat stress were investigated by atomic force microscopy and confocal laser scanning microscopy, respectively. Conditioning with heat stress resulted in a statistically significant increase in Young's modulus of OHCs at 3–6 h after application, and such modulus then began to decrease by 12 h and returned to pre-conditioning level at 48 h after heat stress. The amount of F-actin began to increase by 3 h after heat stress and peaked at 12 h. It then began to decrease by 24 h and returned to the pre-conditioning level by 48–96 h after heat stress. These time courses are consistent with a previous report in which heat stress was shown to suppress permanent threshold shift (PTS). In addition, distortion product otoacoustic emissions (DPOAEs) were confirmed to be enhanced by heat stress. These results suggest that conditioning with heat stress structurally modifies OHCs so that they become stiffer due to an increase in the amount of F-actin. As a consequence, OHCs possibly experience less strain when they are exposed to loud noise, resulting in protection of mammalian hearing from traumatic noise exposure.

Acquisition of Nicotine Self-Administration in Adolescent Rats Given Prolonged Access to the Drug

As most human tobacco use begins during adolescence and ongoing development of the adolescent central nervous system could affect acquisition of nicotine self-administration (SA), our established rat SA procedure was modified to study adolescent acquisition of SA with prolonged access to nicotine (23 h/day). Postnatal age 43-45 female Lewis rats, without prior shaping, conditioning, or food deprivation, were housed in operant chambers equipped with two levers; pressing the active lever triggered an i.v. injection of nicotine. By the 10th day of SA, rats receiving 7.5, 15, 30, or 60 microg/kg/injection nicotine (free base) obtained 23+/-16, 50+/-8, 65+/-8, or 48+/-5 injections (mean+/-SE), respectively. In the 30 microg/kg/injection group, active : inactive ratio was greater than 2 after SA day 4; 92% of injections occurred during the 12-h active (dark) phase of the light cycle. Main effects (analysis of variance) were shown for day and lever (ie active vs inactive) (p<0.001). Adolescent males showed similar dose-dependent nicotine SA. With the increasing workload imposed by raising the fixed ratio (FR), less nicotine was self-administered at FR 5 and 7 compared to FR 1 and 3. In comparison to adult females self-administering 30 microg/kg/injection of nicotine at FR 1, adolescents acquired nicotine SA at an accelerated rate (p<0.05) and received a greater number of injections (p<0.05) by day 10. In conclusion, when given prolonged access to the drug, both female and male adolescent Lewis rats rapidly acquire nicotine SA within the dosage range and FR constraints previously observed in adult Lewis rats. However, adolescent females acquired the behavior more rapidly and attained higher levels of stable nicotine SA than adults.

A Postmigrational Switch among Skin-Derived Dendritic Cells to a Macrophage-Like Phenotype Is Predetermined by the Intracutaneous Cytokine Balance

Migration of dendritic cells (DC) to secondary lymphoid organs under proinflammatory conditions coincides with their maturation and acquisition of T cell stimulatory abilities. In contrast, impaired activation of DC, e.g., in tumor-conditioned environments, may hamper their activation and possibly their subsequent migration to lymph nodes, leading to either immunological tolerance or ignorance, respectively. In this study, the influence of cytokines in the peripheral skin microenvironment on the activation state of migrating cutaneous DC was assessed using an ex vivo human skin explant model. We observed a phenotypic shift from mature CD83(+) DC to immature CD14(+) macrophage-like cells within 7 days subsequent to migration from unconditioned skin. These macrophage-like cells displayed a poor T cell stimulatory ability and lacked expression of CCR7, thus precluding their migration to paracortical T cell areas in the lymph nodes. The balance of suppressive and stimulatory cytokines during the initiation of migration decided the postmigrational fate of DC with IL-10 accelerating and GM-CSF and IL-4 preventing the phenotypic switch, which proved irreversible once established. These observations indicate that, in immunosuppressed environments, a postmigrational DC-to-macrophage shift may hinder T cell activation, but also that it may be prevented by prior conditioning of the tissue microenvironment by GM-CSF and/or IL-4.

The interactive effects of colors and products on perceptions of brand logo appropriateness

This article explores the role that color can play in building brand meaning with two experiments. Without prior conditioning, we demonstrate how an appropriately chosen color for a brand name (logo) can bring inherent and immediate value to a brand. Experiment 1 explores the notion of congruity, showing that it is more appropriate for functional products to be presented in functional colors, and sensorysocial products in sensory-social colors. Experiment 2 examines the effect of red and blue on brands of products that can be classified as both functional and sensory-social, and the ability of color to enhance a brand's desired image. When people know how brands are attempting to position themselves, people consider colors congruent with those positions to be more appropriate.

NO is necessary and sufficient for the protection from contraction‐induced injury provided by passive‐stretch‐conditioning

Exposing skeletal muscle to repeated stretches without activation (passive stretches) reduces the severity of injury induced by subsequent exposure to lengthening contractions (LCs). Passive stretch leads to release of nitric oxide (NO) and overexpression of neuronal nitric oxide synthase (nNOS) reduces the inflammation and membrane damage of reloading injury. We hypothesized that the NO release is necessary for the protective effects of passive-stretch-conditioning and elevated NO is sufficient to reduce injury, even in the absence of prior conditioning. Mice were untreated or treated with either the nNOS inhibitor 1-(2-trifluoromethyl-phenyl)-imidazole (TRIM) or the NOS substrate L-arginine. Extensor digitorum longus (EDL) muscles underwent 75 LCs with or without exposure to 75 passive stretches 1 hour before. Maximum isometric force, damaged fibers, and infiltrating neutrophils were measured 3 days after LCs. The deficits in isometric force, the numbers of injured fibers, and the numbers of infiltrating neutrophils were not different for passive-stretch-conditioned muscles of TRIM-treated mice or unconditioned muscles of TRIM-treated or untreated mice. For L-arginine-treated mice, both unconditioned and passive-stretch-conditioned muscles had smaller deficits in isometric force, fewer injured fibers, and fewer neutrophils compared with unconditioned muscles of untreated mice. We conclude that NO is both necessary and sufficient to reduce contraction-induced injury and that the protective effects of NO may be due to a decrease in inflammation. Supported by AG-20591.

Increased resistance to free radical damage induced by low-level sound conditioning

Conditioning is the phenomenon where exposure to moderate-level acoustic stimuli can increase the ear’s resistance to subsequent more intense sound exposures. In recent years, research has shown that conditioning increases the availability of antioxidant enzymes which presumably protects the ear from oxidative stress induced by a traumatic noise exposure [Jacono, A.A., Hu, B., Kopke, R.D., Henderson, D., Van De Water, T.R., Steinman, H.M., 1998. Changes in cochlear antioxidant enzyme activity after sound conditioning and noise exposure in the chinchilla. Hear Res 117, 31–8]. The current study was designed to assess whether the increase in endogenous antioxidants seen following conditioning could provide protection from oxidative stress induced by Paraquat, a potent generator of superoxide. Chinchillas were exposed to a conditioning noise, 500 Hz OBN at 95 dB for 6 h/day for 10 days, followed 5 days later with Paraquat application to the round window. Controls underwent the Paraquat application surgery, without prior conditioning. Evoked potential thresholds were determined prior to conditioning, at day 1, 5 and 10 during conditioning, at day 15 (5 days after conditioning), and at day 17, 19, 23, and 35 (1, 3, 7, and 20 days post-Paraquat). The conditioned animals showed reductions in permanent threshold shift and reduced inner hair cell loss relative to controls. These results reinforce the hypothesis that antioxidants are primary mediators of the conditioning effect.

FULL-BODY EXERCISE TRAINING IMPROVES FITNESS AND QUALITY OF LIFE IN SURVIVORS OF BREAST CANCER

This study evaluated the safety and effectiveness of an 8-week full-body resistance and aerobic exercise program for 27 survivors of breast cancer (age, 57.7 ± 7.2 years; years posttreatment, 0.8–21.0) with prior upper-body conditioning. Physical fitness and quality-of-life (QOL) measures were obtained before and after the training period. Lymphedema, evaluated via arm volume measurement at baseline, was self-monitored throughout the trial. Sum of skinfolds, waist girth, and hip girth were significantly reduced posttraining (p < 0.01), although body weight did not change. Significant improvements (p < 0.01) were observed in upper-body strength (35.6 ± 16.4%) and endurance (167.4 ± 55.4%), lower-body strength (50.7 ± 32.3%) and endurance (273.1 ± 120.7%), O2peak, trunk flexibility, and flexibility of the ipsilateral (surgical) and contralateral shoulder joint. Psychological QOL and overall QOL, evaluated via the World Health Organization Quality of Life Assessment Scale–Abbreviated Version. Inventory also improved significantly (p < 0.01). No incidents of lymphedema or injury were reported. These findings suggest that survivors of breast cancer can safely benefit from engaging in a full-body exercise regimen.

The Effects of Exercise Conditioning on Protein Production in Rat Muscle Trauma

The effect of prior exercise conditioning, on the collagenous and non-collagenous protein contents of skeletal muscle of the lower limb during recovery from acute blunt trauma were investigated. One hundred and twelve, Sprague-Dawley rats were trained following a common eight week endurance training program, producing a significant (p<0.05) increase in citrate synthase activity of the skeletal muscle1). The training protocol was implemented to duplicate the reaction to injury and to follow-up recovery on muscle which had been pre-conditioned by exercise. Rats of the same weight were then randomly assigned to one of five experimental groups following the eight weeks of training. Muscle trauma was produced utilizing a humane and reproducible experimental device. After the different treatments for ten days, results indicated that animals in the exercise trauma, produced more collagen in traumatized lower limb muscles than rats in the exercise no trauma (ENT), exercise trauma, untreated (ET), and exercise trauma groups (p<0.05). The amount of non-collagenous contractile protein was significantly lower (p<0.05) in the ENT group compared to the ET. The results suggest that the exercise has a protective effect on muscle and on the production of collagen in traumatized skeletal muscle. Finally, prior experience conditioning protected against injury and improved muscle recovery.

Full-body Exercise Training Improves Fitness and Quality of Life in Survivors of Breast Cancer

This study evaluated the safety and effectiveness of an 8-week full-body resistance and aerobic exercise program for 27 survivors of breast cancer (age, 57.7 +/- 7.2 years; years posttreatment, 0.8- 21.0) with prior upper-body conditioning. Physical fitness and quality-of-life (QOL) measures were obtained before and after the training period. Lymphedema, evaluated via arm volume measurement at baseline, was self-monitored throughout the trial. Sum of skinfolds, waist girth, and hip girth were significantly reduced posttraining (p < 0.01), although body weight did not change. Significant improvements (p < 0.01) were observed in upper-body strength (35.6 +/- 16.4%) and endurance (167.4 +/- 55.4%), lower-body strength (50.7 +/- 32.3%) and endurance (273.1 +/- 120.7%), Vo(2peak), trunk flexibility, and flexibility of the ipsilateral (surgical) and contralateral shoulder joint. Psychological QOL and overall QOL, evaluated via the World Health Organization Quality of Life Assessment Scale-Abbreviated Version. Inventory also improved significantly (p < 0.01). No incidents of lymphedema or injury were reported. These findings suggest that survivors of breast cancer can safely benefit from engaging in a full-body exercise regimen.

Prior Thermal Spikes and Thermal Shocks on Mechanical Behavior of Glass Fiber-Epoxy Composites

Fiber-reinforced glass-epoxy composites with and without prior thermal history are subjected to hygrothermal conditioning for different exposure times. The prior thermal history is given in the form of thermal shocks and thermal spikes at three different temperatures. The effects of exposure time and prior thermal history on the moisture absorption kinetics are studied. The effects of prior conditioning parameters are also investigated. The variation of mechanical properties as a function of exposure time and prior conditioning parameters are assessed by the three-point short beam shear bend test. It has been observed that there is an initial improvement in the mechanical properties followed by a steady deterioration. Mechanical tests performed at different crosshead velocities show increasing brittleness of the composites and that is found to be a function of cross-head velocity.

Mobilization as a Preparative Regimen for Hematopoietic Stem Cell (HSC) Transplantation in Rhesus Macaques.

The myeloablative conditioning regimens currently used for hematopoietic stem cell (HSC) transplantation are associated with significant morbidity and mortality. Alternative strategies to promote engraftment of infused HSCs with increased safety warrant investigation. In a murine model, we previously demonstrated that, in absence of irradiation, mobilization with AMD3100 (a CXCR4 antagonist) before marrow transplantation vacated microenvironmental niches and resulted in higher levels of engraftment of transplanted HSCs compared to controls (no AMD3100 treatment before transplantation) (Abkowitz JL et al., Blood (ASH Annual Meeting Abstracts) 104 (11): 1187, 2004). In this study, we hypothesized that AMD3100 mobilization before transplantation could also promote HSC engraftment in a large animal model, eliminating the need for toxic myeloablative conditioning. Peripheral blood cells from two rhesus macaques were collected by apheresis 3 hours after administration of a single dose of AMD3100 1mg/Kg. CD34+ cells were enriched and transduced for four days in the presence of cytokines and fibronectin with non-expression Moloney murine leukemia virus-derived retroviral vectors (G1PLI) that carry a bacterial neomycin phosphotransferase resistance gene (neoR). The neoR-marked CD34+ cells were reinfused in the non-myeloablated animals, immediately after AMD3100 mobilization and apheresis repeated on the day of transplantation. NeoR-marking levels of approximately 0.1% were detected in both peripheral blood MNC and granulocytes at two months (animal 2RC102) and four months (animal RQ4791) after transplantation. Previous transplantation studies performed without prior myeloablative conditioning or mobilization preparative regimen resulted in no long-term in vivo gene marking. We mathematically confirmed that this observed level of gene marking is what can be expected when AMD3100 mobilization is used as a conditioning regimen. Previous studies have estimated the number of long-term repopulating HSCs at 6 per 105 CD34+ cells (Abkowitz JL et al, Blood 96: 3399, 2000). In animal RQ4791, approximately 4.5X107 CD34+ cells, and therefore 2700 HSCs, were mobilized after AMD3100 administration. The total number of HSCs per animal is thought to be conserved in mammals and has been estimated at 11,000 to 22,000 (Abkowitz JL et al, Blood 100: 2665, 2002). Hence, 12–24% of HSCs were mobilized after a single dose of AMD3100, consequently opening 12–24% of microenvironmental niches for engraftment. If 1% of engrafted HSCs are marked, 0.12–0.24% long-term marking levels are expected, correlating well with the observed marking level of 0.1%. These results imply that the number of available niches in large animals, as in murine models, regulates the number of HSCs that engraft. As importantly, mobilization with AMD3100 could provide a non-toxic preparative approach in large mammals, including humans, to improve HSC engraftment in transplantation for genetic and other nonmalignant disorders.