1% saponin in PBS overnight at 4 °C After washing of the cells t

1% saponin in PBS overnight at 4 °C. After washing of the cells twice with 0.5% NGS/0.1% saponin in PBS they were incubated with secondary antibody goat anti-mouse IgG (H + L) (FITC) (1:50; cat #: ab6785-1; Abcam) in 1% NGS/0.1% saponin for 1 h at RT. The cells were washed and resuspended in 0.5% NGS/0.1% saponin in 1xPBS and FACS analysis was performed using a FACS Calibur (Becton Dickinson). Human Rapamycin order and rat 3D liver cultures or hepatocyte monolayer cultures were incubated for 1 to 15 days with various concentrations of different compounds (Table 1) in culture medium containing serum. The concentrations of the various test compounds

were chosen around the in vivo plasma concentration (Cmax) observed at pharmacological doses, ranging from about 10-fold below to 10-fold above the human Cmax. The treatment of human and rat 3D liver cells or hepatocytes www.selleckchem.com/products/abt-199.html with different compounds and the collection of the media was performed on a daily basis or every other day. The cytotoxicity of the tested drugs was assessed as the release of lactate dehydrogenase (LDH) and alanine aminotransferase (ALT) from cells into the media. The amount of viable and metabolically active cells was determined via quantitation of ATP using the CellTiter-Glo

luminescent cell viability assay (cat. # G7571; Promega) at the end of the drug-treatment periods. Cytotoxicity, cell viability and caspase 3/7 activation were in some experiments determined simultaneously using the ApoTox-Glo-triplex assay kit (cat. #: G6320; Promega). Cell toxicity and viability were detected based on measurement of dead-cell and live-cell protease

activities using fluorogenic cell-impermeant or cell-permeant peptide substrate respectively. The caspase 3/7 activity was measured by luminogenic buy Bortezomib substrate, which is cleaved by caspase 3/7. After isolation and expansion of rat and human NPC in monolayer culture cells were inoculated into two nylon scaffolds placed above a porous membrane of inserts of 24-well plates (Fig. 1A). Two days later microscopic examination was performed to check whether the NPC were attached and uniformly distributed over the scaffold. Hepatocytes were seeded later only if the cultures containing NPC uniformly covered the scaffold. One week after NPC were seeded hepatocytes were inoculated into the screens allowing interactions with the other cell types and ECM. Cells differentiated properly forming liver tissue consisting of 7–9 layers of cells (tissue thickness around 200 μm, Fig. 1A). The three-dimensionality of the scaffold provides increased surface area for cell growth and allows NPC and PC to form a microenvironment conducive to cellular proliferation, maturation and migration (Naughton et al., 1994 and Naughton et al., 1995). We performed for each 3D liver culture quality control including microscopic examination and quantitative functionality measurements.

All were characterized by a similar lithology and geochemical com

The main geochemical features of this zone were the high content of terrigenous silica (88%) and large Mg/Ca, Na/K and Fe/Mn ratios. We examined three

sediment cores taken from Tromper Wiek (Figure 1). All were characterized by a similar lithology and geochemical composition. The shallowest (core 233230) was taken at a depth of 28.7 m b.s.l. (Figure 5). The sediments could be divided into two zones (Figure 6). The lower zone (E; 132–423 cm) MS 275 contained olive-grey silt with fine humus particles in the lower portion, and fine sand with plant remains in the upper portion. The sediment of zone E had the highest content of terrigenous silica (97%) and a low content of biogenic silica (2%), loss on ignition (2%) and ratios of Mg/Ca

(0.2), and Fe/Mn (40). The Na/K ratio was less than 1. The upper zone (F; 0–132 cm) consisted of olive-grey mud with some shell remains. It was indistinctly laminated below 96 cm and slightly darker and sandy below 127 cm. The base of zone F had the lowest content of terrigenous silica (70%), which gradually increased in the upper portion of the core. This zone had a higher content of biogenic silica (7.3%) than zone E, a higher loss on ignition (7.4%) and greater ratios of Mg/Ca (0.8), Na/K (1.5) and Fe/Mn (100). Core 233240 was taken at a depth of 29.5 m b.s.l., 2 km north-west of core 233230 (Figures 1, 5). The sediments of this core were divided Antiinfection Compound Library datasheet into the same two zones as in core 233230 (Figure 6). The lower Selleckchem Atezolizumab zone (E; 132–328 cm) consisted of fine, pale-olive sand with a thin silty layer at 160 cm and olive-grey silt with a 1 cm layer of peat gyttja at 141 cm. The geochemical composition of zone E had the highest content in the core of terrigenous

silica (96%) and low biogenic silica content (1%), loss on ignition (1.5%) and ratios of Mg/Ca (0.1) and Fe/Mn (55). The Na/K ratio increased gradually to a value of 2 in the upper levels of zone E. The upper zone (F; 0–132 cm) consisted of fine, olive-grey sandy mud with a large broken Arctica shell at 119 cm. The geochemical composition of this zone had the lowest content of terrigenous silica (70%) in the core and a higher contribution of biogenic silica (5.5%), loss on ignition (6%) and ratios of Mg/Ca (0.7), Na/K (1.5) and Fe/Mn (120). The deepest core from Tromper Wiek (core 233250) was taken at a depth of 30.7 m b.s.l., 10 km north-west of core 233240 (Figures 1, 5). This core consisted of two sediment zones (Figure 6). The lower zone (E; 233–431 cm) consisted of fine, dark-grey sand with a downward decreasing number of humus particles. The main features of the geochemical composition were the high content of terrigenous silica (99%), and the low biogenic silica content (1%), low loss on ignition (1.5%) and low ratios of Mg/Ca (0.2) and Fe/Mn (50). The Na/K ratio exhibited poor variability along the core.

Unlike CdCl2 or CdS, Cd(CH3)2 is a volatile compound (bp 105 5 °C

Unlike CdCl2 or CdS, Cd(CH3)2 is a volatile compound (bp 105.5 °C), which readily reacts with water to yield cadmium hydroxide but does not oxidize spontaneously in air. In fact, there is a gradation in stability among the Group 12 methyl derivatives, with Cd(CH3)2 ranking in an intermediate position between dimethylmercury, quite stable and dimethylzinc, AZD6244 very reactive toward oxygen and water [122]. Indicative of its stability, Cd(CH3)2 toxicity could be assessed, including through animal inhalation

studies, and a maximum 8-h work-place exposure has been set at 1 μg/m3[123]. While CH3 is the most abundant alkyl radical generated in the high temperature zone, homologue radicals with higher carbon content are also present that could react in the same way. In fact many other radicals present

in smoke could be expected to react with Cd(0) but very little information is available on such reactions. Thus, the following discussion is focused on Cd(CH3)2, since its reactivity is well documented and it is epitomical when discussing the consequences of the transitory formation of a volatile and reactive cadmium derivative. It should however be understood that Cd(CH3)2 may not be the main cadmium volatile intermediate that is actually formed in smoke. Cd(CH3)2 could certainly move to the filter during a puff, and exit the cigarette with mainstream smoke. Because of its reactivity, Cd(CH3)2 will deposit onto the unburnt tobacco downstream with C59 wnt order a high efficiency; yet, elements captured on the unburnt tobacco Adenosine during a puff can be mobilized in subsequent puffs, so that this capture

is not incompatible with the observed cadmium transfer to mainstream smoke (only 5–10%). The consequence of this high capture is a yield per puff that increases with puff number, which has indeed been observed [78]. Moreover, in such a case it is expected that a higher smoke flow rate through the tobacco rod would decrease the retention of gas-phase cadmium since it is diffusion-controlled. This was also observed. Compared to the ISO yields, cadmium yield was found to be more increased under HCI than nicotine was, whereas lead yield remains to a constant ratio to nicotine (Table 6 and Table 8). Specifically, a high and flow rate-sensitive capture of cadmium by the tobacco filler was evidenced by studies where the deposited cadmium was separately assessed in the unburnt tobacco and in the filter plug after machine-smoking the cigarettes using both ISO conditions and undefined “heavy” puffing conditions [82]. The fact that elements captured on the unburnt tobacco during a puff can be mobilized by subsequent heating also increases the possibility of transfer to sidestream smoke. Hot gases can diffuse out of a smoldering cigarette as sidestream emission, the temperature of this gas stream is about 350 °C [116]. Cadmium can diffuse out as CdCl2, which would be gaseous.

Furthermore, by choosing our study period, we have ensured no sys

Furthermore, by choosing our study period, we have ensured no systematic changes in coding because the ICD-10 coding system has been in continuous use in HES from 1995 to present. This, of course, does not exclude variation in rates of coding over the study period affecting our

estimates. For example, if the potential error in coding was systematically changing over time with increased coding of patients’ comorbidity rather than patients having more comorbidity, then clearly that could bias our results. However, the different trends ABT-199 nmr in comorbidity for variceal and nonvariceal bleed admissions and different trends in mortality in different age and comorbidity strata suggest that there was no systematic change in comorbidity coding over the time period of our study. Under-reporting of the comorbidities in the Charlson index may have resulted in incomplete adjustment for comorbidity. However, although the alternative Elixhauser index assessed almost twice the number of comorbidities, it did not alter the adjustment of comorbidity in the

model. Comorbidity adjustment by either index increased the magnitude of the mortality reduction, and, therefore, any residual confounding in this regard would only, we believe, cause an underestimate of the real mortality trend in our study. A PubMed search, to October 2010, found the largest comparable population-based study for nonvariceal hemorrhage mortality trends used a Canadian hospital discharge database with ICD-10 and ICD-9 codes. However, it identified less than one-third of the number of bleeds used for Enzalutamide price this study (n = 142,363) and was not able to identify a reduction in case fatality for nonvariceal hemorrhage between 1993 Carnitine palmitoyltransferase II and 2003.3 The researchers adjusted for changes in age but not for changes in comorbidity. They

also only identified deaths that occurred before discharge. The low mortality identified in this study (3.5%) is similar to other North American20 and Mediterranean1 and 21 studies but is much lower than other European studies.2, 22 and 23 However, a study of Medicare patients in the United States found that the proportion being managed as outpatients varied between states from 18.6% to 45.3%.24 These differences in practice would lead to differences in inpatient study populations and confound comparisons with countries such as England where outpatient management is not routine. Although the most recent report from the US National Inpatient Sample showed a 23% reduction in upper gastrointestinal hemorrhage mortality from 1998 to 2006 (n = unreported because only extrapolated estimates from the 20% sample are provided),20 this was a global figure for the reduction seen at the end of the study rather than year on year, and it did not distinguish variceal and nonvariceal hemorrhage. Another report from the US National Inpatient Sample noted an adjusted reduction in variceal hemorrhage from 18% to 12%.

The organotypic brain slice model is well-established

in

The organotypic brain slice model is well-established

in our working group and serves as a validated tool to study toxic, degenerative and developmental changes as well as synaptic recovery, survival and cell death of neurons (Gähwiler et al., 1997, Humpel and Weis, 2002, Moser et al., 2003, Moser et al., 2006, Stoppini et al., 1991, Weis et al., 2001 and Zassler et al., 2003). In this SP600125 in vivo model cholinergic neurons are axotomized, however, the normal cytoarchitecture is retained similar to the in vivo situation and functional connections including transport and diffusion probabilities are maintained. The brain tissue is derived from postnatal day 10 brains and therefore it is not completely comparable to adult brains, which is a limitation of the present study. In further studies it would be of particular interest to investigate the effects of EtOH in adult nbM slices and thus to compare with the neuropathological changes in adult brains. In fact, culturing of adult brain slices has been reported (Bickler et al., 2010, Hassen et al., 2004 and Xiang et al., 2000), although this technique is not trivial and such slices are not easy to culture for long time. Adolescent DNA Damage inhibitor brains distinctively response to EtOH exposure compared to adult brains (Smith,

2003) and the context of ongoing plasticity in the adolescence faces the continuous production of new neurons during adult neurogenesis (Nixon et al., 2010). Indeed, adolescents are more prone to the neurotoxic effects of EtOH than adults (Crews et al., 2007). before In the present model brain slices are normally cultured for 2 weeks before staining in experiments correlating to adolescent age. In fact the basal forebrain cholinergic neurogenesis is already completed before birth (E17) (Semba and Fibiger, 1988). In the present study detection of cholinergic neurons was performed using the immunohistochemical marker for the enzyme ChAT, which is expressed in cell bodies and nerve fibers of cholinergic neurons. In our experiments control slices displayed around

120 ChAT-positive neurons, which is in line with previous work (Weis et al., 2001). ChAT serves as a marker for the functional activity of cholinergic neurons (Oda, 1999) and a decreased number directly correlates with cognitive impairment (Counts and Mufson, 2005). Indeed, a dysfunction of the cholinergic system and the loss of cholinergic neurons is in concert with low levels of acetylcholine in the cortex and resulted in cognitive impairment (Mesulam, 2010). Interestingly, an impairment of the cholinergic system (Floyd et al., 1997) and cognitive decline has also been reported after long-term EtOH treatment in vivo (Arendt et al., 1988 and Ehrlich et al., 2012). Accordingly, the activity of cholinergic neurons after EtOH exposure possibly represents a depression of the enzyme ChAT and not cell death.

5 3 1) is reported to be about pH 10 in horse, pH 9 8 in rat and

5.3.1) is reported to be about pH 10 in horse, pH 9.8 in rat and pH 11 in Bacillus brevis. Those working with mammalian systems might favour an assay pH of about 7.2 which is believed to be around the physiological pH within the cell, but clearly this would be unphysiological for gastrointestinal enzymes, such, as pepsin and trypsin, or for lysosomal enzymes. Furthermore, the oxidation of ethanol by liver alcohol dehydrogenase (EC 1.1.1.1) is often followed at higher pH values because the equilibrium of the reaction greatly favours ethanol formation at neutral

pH. Naturally it would be appropriate to use physiological substrates for enzyme assays. However, many studies have used selleck chemicals unphysiological substrates for ease of manipulation and assay. For

example acetylthiocholine is frequently used to assay acetylcholinesterase (EC 3.1.1.7) because the thiocholine produced can be readily detected by reaction with sulfydryl reagent 5, http://www.selleckchem.com/products/ganetespib-sta-9090.html 5′-dithiobis-2-nitrobenzoate (Nbs2) releasing a yellow coloured compound whose formation can be followed spectrophotometrically at 412 nm (Ellman et al., 1961). Other examples include the use of 4-nitrophenyl phosphate to assay alkaline phosphatase (EC 3.1.3.1) (Schumann et al., 2011). The use of synthetic dyes as electron acceptors in oxidoreductase assays has been common and in some cases the physiological acceptor remains unknown. The demand for higher assay sensitivity and high-throughput procedures has resulted in the development of an increasing number of chromogenic and fluorogenic substrates (Goddard and Reymond, 2004 and Reymond et al., 2009). Clearly, in such cases a considerable amount of work would be necessary to show whether the enzyme behaves identically towards such substrates as it does towards its physiological substrates. It is often recommended that saturating substrate concentrations should be used (i.e. >10Km, for all substrates), as discussed Amino acid by Bisswanger

(2014). This, of course, assumes that the Km values have already been determined, at least approximately. Furthermore, this might not always be practicable because of factors such as solubility, the occurrence of high-substrate inhibition or a high absorbance of the assay mixture affecting the behaviour of optical assays ( Dixon et al., 1979 and McDonald and Tipton, 2002). It should also be remembered that any change in the assay conditions (e.g., pH, temperature, ionic strength) may affect the Km values. The buffers and ionic strengths and used in enzyme assays vary widely and are often far from physiological. It might be helpful if it were possible to recommend a simple standard buffer for use in all enzyme assays. Unfortunately, this goal appears to be unobtainable, because at least some enzymes are unhappy in one or other of the common buffers (see e.g., Boyce et al., 2004).

To understand how the arrangement of TF binding sites relates to

To understand how the arrangement of TF binding sites relates to their functional output, we analyzed the TRN controlling the zygotic expression of the gene hunchback, a transcription factor that is, partly, regulated by bicoid [Wunderlich et al., submitted]. Using a quantitative selleck inhibitor in situ hybridization pipeline [ 20], we measured the relative mRNA levels controlled by a

hunchback cis-regulatory element (CRE) and its five regulators at cellular resolution. This allowed us to model the relationship between TF mRNA concentrations (inputs) and mRNA expression directed by the hunchback CRE (output) in individual cells. We first measured both input levels and output levels in transgenic D. melanogaster lines that express a reporter under

the control of the hunchback zygotic CRE from six different Drosophila species. We then measured the inputs and outputs in the endogenous settings of three Drosophilids [[ 20], Fowlkes et al. PLoS Genetics, in press]. Using these data, we fit a simple linear function connecting the inputs to the output of one CRE and used this function to predict expression for orthologous CREs, with and without a calculated value for the cis-regulatory contributions to output. We found that predicted TF binding site occupancy summed across selleck antibody the CRE is an effective measure of relative cis-regulatory function. This is surprising given that the calculation does not account for cooperative or mutually exclusive TF binding. This is likely because orthologous CREs have been selected for functional TF binding site arrangements, allowing a simple measure of overall site strength to capture functional differences between sequences. This result underscores the flexibility of CRE sequences with respect to TF binding strength and arrangement, which is known to

vary between individuals and species [ 33 and 34]. Often a single TRN with a small number of TFs can specify several different cell types. Zinzen et al. used see more ChIP-chip binding data and tissue-level CRE activity data to investigate how a TRN specifies several different mesodermal cell types [ 35••]. They measured the genome-wide binding of five TFs involved in mesodermal specification and differentiation at several time points over ten hours of development, beginning before gastrulation. Though there are other TFs that also contribute to this process, the study was limited to the five TFs essential for mesodermal specification and differentiation. The goal of the study was to predict the expression patterns driven by candidate CREs identified by ChIP-chip. The strategy used was to make a statistical model that correlates ChIP-chip binding patterns with tissue-level expression patterns.

073) and a trend of cytotoxicity of SiNP-2 in A549 cells ( Fig 4

073) and a trend of cytotoxicity of SiNP-2 in A549 cells ( Fig. 4A) which contrasted with the pattern of effects in J774A.1 cells ( Fig. 4B), in which SiNP-1 and SiNP-2 were both cytotoxic. Contrasts in potencies were also observed among the CNTs, with CNT-1 and CNT-3 being relatively non-cytotoxic

by CTB assay, while CNT-2 and CNT-4 were clearly cytotoxic in both cell lines. The apparent higher cytotoxicity of CNT-4 by comparison to CNT-2 (decreased rate of reduction of resazurin to resorufin) is attributable in part to its chemical interference in the assay, probably through re-oxidation of resorufin or hyper-reduction of resorufin to non-fluorescent hydroresorufin. The magnitude of this interference can be assessed easily in Target Selective Inhibitor Library ic50 an acellular assay, either by correcting dose by dose,

or by fitting data in our potency model Forskolin (βINT; Table 1). Once corrected for βINT, potency of CNT-4 was more comparable to that of CNT-2, notably in A549 cells. In the present report, we describe the potential for interaction of the CNTs with both single-wall CNTs and multi-wall CNTs with the resazurin assay in two cell lines, A549 lung epithelial cells and J774A.1 murine macrophages. Our results indicate that all CNTs tested caused physical/optical interference with the fluorescence quantitation of reduced resazurin (resorufin) when wells were read directly with the test material (CNTs) present. This physical quench was particularly intense for the CNTs and for other carbonaceous materials such as carbon black and diesel emission particles (data not shown), and less pronounced for TiO2, SiO2 and SiNPs. As indicated by Oostingh et al. (2011), this type of interference is expected for highly optically dense materials such as CNTs, preventing the transmitted/emitted light from reaching the detector, or physically adsorbing the assay dye. Casey et al. (2007) have observed a total quenching of fluorescence and a complete loss of the pink color of the reduced dye resorufin, at concentrations as low as 0.08 mg/mL

of single-wall CNTs. Similarly, Monteiro-Riviere et al. (2009) have shown fluorescence quenching in the form of decreased Immune system fluorescence of HEK cell-reduced resazurin in the presence of single-wall CNTs (>0.1 mg/mL) and carbon black. Other NMs such as quantum dots and C60 fullerene did not interact with the resazurin fluorimetric assays. In addition to the optical interference, here we detected some chemical quenching of fluorescence by CNT-2 and CNT-4 particles, accompanied by visually observed decrease in pink color intensity. The decrease of fluorescence signal may result from the re-oxidation of resorufin (pink) back to non-fluorescent resazurin (blue) in the presence of CNTs (Monteiro-Riviere et al., 2009), or from hyper-reduction of resorufin (pink) to a the non-fluorescent hydroresorufin (colorless), a phenomenon described before (O’Brien et al.

Some of the risks described in the next two sections may be espec

Some of the risks described in the next two sections may be especially acute as people and animals habituate to the presence of commercial ships, even as other risks increase with the volume of traffic over time. The Bering Strait region is ecologically rich with high species diversity

due in part to the overall productivity of the area, in part because it is a corridor between the Bering and Chukchi seas, and in part because it sits on the Arctic-subarctic ecotone (boundary between ecosystems) [4], [6], [20], [21], [22] and [23]. Vessels navigating the Bering Strait region pose numerous environmental threats including collisions with marine check details mammals (ship strikes), disturbance of seabirds and marine mammals, increased noise, and contamination of the marine environment (e.g., discharges, air pollution, waste, or ballast water that contains invasive species). Other threats include the potential for an accident such as grounding or sinking of a vessel, which would endanger

Nivolumab order the crew and rescue personnel in addition to threatening an environmental disaster. In light of the lack of capacity to respond due to remoteness and challenging conditions, most worrisome is the prospect of an oil spill, either from a tanker or of fuel oil from any vessel transiting the area. Direct collisions between vessels and marine mammals can result in mortality through massive trauma. Worldwide records of ship strikes on whales show that all large whales are at risk [24] and [25], with bowhead whales most likely to be at risk in the Bering Strait region. Bowheads seasonally congregate in the Bering Sea and the entire population of the Bering/Chukchi stock transits the Bering Strait twice a year. The period of greatest concern is in the fall (October through November) as bowheads move

south along the Chukotka coast into the Strait at a time when vessel traffic remains high [26]. During spring, whales, walrus, and seals migrate north when sea ice is still present, so the risk of ship strikes is reduced due to lower levels of vessel traffic. Icebreakers, however, have Bcl-w the potential to disturb animals and habitat during spring migration. Ice-dependent seals are potentially at risk of displacement during spring and early summer (April through June) when they use ice for pupping and for molting. Sound is vital to survival of marine mammals as they use it to detect their environment and communicate with one another [27] and [28]. Persistent or increasing noise disturbance could alter health, behavioral and migratory patterns [29]. Responses to vessels (e.g., disturbance) have been documented in a wide variety of marine mammal species and primarily include avoidance behavior and increased stress.

D below the population average, although the discrepancy between

D. below the population average, although the discrepancy between verbal intelligence quotient and performance intelligence quotient was more limited than that described in some previous studies [5], [9] and [14]. Our control group of patients with

spinal muscular atrophy and osteogenesis Selleck NVP-BGJ398 imperfecta was severely motor impaired but did not exhibit any cognitive deficits, thus confirming that motor impairment does not influence intellectual abilities, as already demonstrated by Billard et al. [10]. Separate analyses taking into account the genetic alterations in the dystrophin gene (Duchenne muscular dystrophy distal and Duchenne muscular dystrophy proximal) indicated that the verbal intelligence quotients in both groups were significantly lower than those of control children, whereas only children in the distally mutated Duchenne muscular dystrophy group showed significantly lower performance intelligence quotients. Patients with distal mutations were generally more severely

affected and manifested different patterns of strengths and impairments, in comparison to patients with proximal mutations. In particular, distal mutations seem to produce greater deficits in verbal short-term memory, as expressed by low Digit Span scores (and possibly working memory, which may also be responsible for the Trametinib price low performances in the Picture Arrangement subtest), in visual memory, and in visuospatial organization, as expressed by lower scores on the Performance subtests of the Wechsler Intelligence Scale for Children-Revised, especially in Object Assembly, Branched chain aminotransferase and also in logical sequencing

(Picture Arrangement). On the other hand, patients with mutations in the proximal portion of the dystrophin gene demonstrated relative strengths in verbal short-term memory (as measured by the Digit Span subtest) and in the Performance subtests of the Wechsler scales, especially Object Assembly, Mazes, and Picture Arrangement (requiring visuospatial organization and planning), whereas they exhibited some difficulties in social judgment and the critical appreciation of general statements (as measured by the Comprehension subtest). Furthermore, dystrophic children with distal mutations manifested clear difficulties in syntactic processing, as expressed by both Token Test and Grammatical Comprehension scores. Finally, lower scores in Visual Memory were also an exclusive characteristic of patients with distal mutations, whereas deficits in Visual Attention were common to both subgroups. Analyses controlling for the influence of general intellectual deficits on specific linguistic, neuropsychologic, and academic functions revealed that most of the deficits were substantially explained by variations in intelligence quotients.