Significant Effect Of Position Research Articles

Genome-wide landscape of position effects on heterogeneous gene expression in Saccharomyces cerevisiae

BackgroundIntegration of heterogeneous genes is widely applied in synthetic biology and metabolic engineering. However, knowledge about the effect of integrative position on gene expression remains limited.ResultsWe established a genome-wide landscape of position effect on gene expression in Saccharomyces cerevisiae. The expression cassette of red fluorescence protein (RFP) gene was constructed and inserted at 1044 loci, which were scattered uniformly in the yeast genome. Due to the different integrative loci on the genome, the maximum relative intensity of RFP is more than 13-fold over the minimum. Plots of the number of strains to RFP relative intensity showed normal distribution, indicating significant position effect on gene expression in yeast. Furthermore, changing the promoters or reporter genes, as well as carbon sources, revealed little consequences on reporter gene expression, indicating chromosomal location is the major determinant of reporter gene expression.ConclusionsWe have examined the position effects to integration genes expression in large number loci around whole genome in S. cerevisiae. The results could guide the design of integration loci for exogenous genes and pathways to maximize their expression in metabolic engineering.

Domain-general neural correlates of dependency formation: Using complex tones to simulate language

There is an ongoing debate whether the P600 event-related potential component following syntactic anomalies reflects syntactic processes per se, or if it is an instance of the P300, a domain-general ERP component associated with attention and cognitive reorientation. A direct comparison of both components is challenging because of the huge discrepancy in experimental designs and stimulus choice between language and ‘classic’ P300 experiments. In the present study, we develop a new approach to mimic the interplay of sequential position as well as categorical and relational information in natural language syntax (word category and agreement) in a non-linguistic target detection paradigm using musical instruments. Participants were instructed to (covertly) detect target tones which were defined by instrument change and pitch rise between subsequent tones at the last two positions of four-tone sequences. We analysed the EEG using event-related averaging and time-frequency decomposition. Our results show striking similarities to results obtained from linguistic experiments. We found a P300 that showed sensitivity to sequential position and a late positivity sensitive to stimulus type and position. A time-frequency decomposition revealed significant effects of sequential position on the theta band and a significant influence of stimulus type on the delta band. Our results suggest that the detection of non-linguistic targets defined via complex feature conjunctions in the present study and the detection of syntactic anomalies share the same underlying processes: attentional shift and memory based matching processes that act upon multi-feature conjunctions. We discuss the results as supporting domain-general accounts of the P600 during natural language comprehension.

Effects of foot rotation positions on knee valgus during single-leg drop landing: Implications for ACL injury risk reduction

BackgroundNon-contact anterior cruciate ligament (ACL) injuries commonly occur when athletes land in high risk positions such as knee valgus. The position of the foot at landing may influence the transmission of forces from the ankle to the knee. Using an experimental approach to manipulate foot rotation positions, this study aimed to provide new insights on how knee valgus during single-leg landing may be influenced by foot positions. MethodsEleven male recreational basketball players performed single-leg drop landings from a 30-cm high platform in three foot rotation positions (toe-in, toe-forward and toe-out) at initial contact. A motion capture system and a force plate were used to measure lower extremity kinematics and kinetics. Knee valgus angles at initial contact (KVA) and maximum knee valgus moments (KVM), which were known risk factors associated with ACL injury, were measured. A one-way repeated measures Analysis of Variance was conducted (α=0.05) to compare among the three foot positions. ResultsFoot rotation positions were found to have a significant effect on KVA (p<0.001, η2=0.66) but the difference between conditions (about 1°) was small and not clinically meaningful. There was a significant effect of foot position on KVM (p<0.001, η2=0.55), with increased moment observed in the toe-out position as compared to toe-forward (p=0.012) or toe-in positions (p=0.002). ConclusionsWhen landing with one leg, athletes should avoid extreme toe-out foot rotation positions to minimise undesirable knee valgus loading associated with non-contact ACL injury risks.

SA67. Deficient Predictive Coding During a Visual Oddball Task in Early Illness Schizophrenia

Background: The P300 event-related potential component is typically elicited during an “oddball” task by infrequent target stimuli (P3b) and infrequent novel distractor stimuli (P3a) that are randomly interspersed among frequent standard stimuli. Although standards do not generally elicit a P300, they can elicit a P3a when their appearance late in a local series of repeating standards is improbable. In a typical oddball task, local sequences of repeating standards end with the appearance of a deviant (target or novel) stimulus. Toward the end of such local sequences, the probability that a standard will appear decreases, and the probability that a deviant will appear increases. Previously, using an auditory oddball task, we showed that healthy subjects generated a P3a in response to late appearing standards within local sequences of repeating standards, suggesting that they implicitly recognized the conditional improbability of a standard following a local sequence of multiple repeating standards, likely in the service of predictive coding. However, chronic schizophrenia (SZ) patients failed to generate this P3a response to late appearing standards. Here, we examined whether similar P3a effects are present using a visual oddball task and whether similar deficits in P3a generation are evident early in the course of SZ. Methods: ERPs were recorded from 19 early illness SZ patients (ESZ; mean illness duration = 2.5 years) and 43 healthy controls (HC) during a visual oddball task containing frequent (80%) standard stimuli and infrequent deviant stimuli (10% targets requiring a response; 10% novel distractors). Consecutively presented standards (S) following deviant (D) stimuli ranged in conditional probability, (P(S|D) = 1.0, P(S|DS) = .97, P(S|DSS) = .97, P(S|DSSS) = .69, P(S|DSSSS) = .41, P(S|DSSSSS) = .29), with late appearing repeated standards being less probable than early ones. ERPs to standards based on their position within local sequences of repeating standards were generated, and the amplitude of the P3a was measured. Results: There was a significant main effect of Standard Position (P < .001) and a significant Standard Position × Group interaction (P = .027). Follow-up analyses showed that late appearing, relative to early appearing, standards within local sequences of repeating standards, elicited a larger P3a in HC (P < .001), but not in ESZ (P = .133). Conclusion: These results suggest that the previously observed P3a elicited by late appearing standards in local sequences of repeating standards during an auditory oddball task is also evident in healthy subjects performing a visual oddball task. The failure to implicitly process the local sequential stimulus probabilities previously observed in chronic SZ was also evident in ESZ, consistent with the presence of deficient task-based predictive coding early in the illness.

Dynamics of male meiotic recombination frequency during plant development using Fluorescent Tagged Lines in Arabidopsis thaliana

Meiotic homologous recombination plays a central role in creating genetic variability, making it an essential biological process relevant to evolution and crop breeding. In this study, we used pollen-specific fluorescent tagged lines (FTLs) to measure male meiotic recombination frequency during the development of Arabidopsis thaliana. Interestingly, a subset of pollen grains consistently shows loss of fluorescence expression in tested lines. Using nine independent FTL intervals, the spatio-temporal dynamics of male recombination frequency was assessed during plant development, considering both shoot type and plant age as independent parameters. In most genomic intervals assayed, male meiotic recombination frequency is highly consistent during plant development, showing no significant change between different shoot types and during plant aging. However, in some genomic regions, such as I1a and I5a, a small but significant effect of either developmental position or plant age were observed, indicating that the meiotic CO frequency in those intervals varies during plant development. Furthermore, from an overall view of all nine genomic intervals assayed, both primary and tertiary shoots show a similar dynamics of increasing recombination frequency during development, while secondary and lateral shoots remain highly stable. Our results provide new insights in the dynamics of male meiotic recombination frequency during plant development.

A general catch comparison method for multi-gear trials: application to a quad-rig trawling fishery for Nephrops

Expeditious uptake of quad-rig trawling in the economically important Irish fishery for Nephrops norvegicus outpaced technical understanding of this newly introduced gear. The main driver for its introduction is increased catch rates of Nephrops. Higher Nephrops discard rates associated with quad-rig trawling are likely to be problematic under the landing obligation unless size selectivity can be improved. Catch comparison methods are suitable for assessing the performance of fishing gear modifications to reduce discards. Utilizing a quad-rig potentially increases the number of gears that can be included in a catch comparison study to four but current modeling methods are limited to two gears. Our study provides a new general multinomial mixed effects modeling framework that can be applied to two or more gears, elucidates how case-specific and choice-specific covariates may influence catch at length, and facilitates discussion on appropriate gear based management measures. Application of the method to catches from four different cod-end mesh sizes revealed significant effects of carapace length, catch weight and net position, on the numbers of Nephrops retained in each cod-end. Results suggest that management measures which specifically address different catch profiles associated with different numbers of trawling rigs are required to optimize Nephrops size selectivity.

Anteroposterior perception of the trunk position while seated without the feet touching the floor.

[Purpose] The purpose of this study was to investigate the trunk position perception in the anteroposterior direction in young participants sitting without their feet touching the floor to avoid the influence of the hamstrings tension and the feet pressure on the perception. [Subjects and Methods] Fourteen healthy volunteers were seated on a chair fitted with an original manual goniometer. There were 7 reference positions set at 5° increments, from −15° to 15°, and reproductions of each position were conducted 5 times. Trunk position perception was evaluated by the absolute error between the reproduced trunk angle and the reference position angle. [Results] The results revealed a significant effect of reference position on the absolute error. The absolute error at the −5° reference position was significantly larger than at the −15° and 15° positions, and the absolute error at the 0° position was significantly larger than at the −15°, 10°, and 15° positions. [Conclusion] These results suggest that the perception of extreme forward- and backward-leaning trunk positions while sitting without the feet touching the floor would be higher than in a neutral sitting position. The relationship between the stability of the posture and the perception may be involved in the sitting position.

Cone-beam computed tomography in children with cochlear implants: The effect of electrode array position on ECAP

ObjectivesTo assess the feasibility of using cone-beam computed tomography (CBCT) in young children with cochlear implants (CIs) and study the effect of intracochlear position on electrophysiological and behavioral measurements. MethodsA total of 40 children with either unilateral or bilateral cochlear implants were prospectively included in the study. Electrode placement and insertion angles were studied in 55 Cochlear® implants (16 straight arrays and 39 perimodiolar arrays), using either CBCT or X-ray imaging. CBCT or X-ray imaging were scheduled when the children were leaving the recovery room. We recorded intraoperative and postoperative neural response telemetry threshold (T-NRT) values, intraoperative and postoperative electrode impedance values, as well as behavioral T (threshold) and C (comfort) levels on electrodes 1, 5, 10, 15 and 20. ResultsCBCT imaging was feasible without any sedation in 24 children (60%). Accidental scala vestibuli insertion was observed in 3 out of 24 implants as assessed by CBCT. The mean insertion angle was 339.7°±35.8°. The use of a perimodiolar array led to higher angles of insertion, lower postoperative T-NRT, as well as decreased behavioral T and C levels. We found no significant effect of either electrode array position or angle of insertion on electrophysiological data. ConclusionCBCT appears to be a reliable tool for anatomical assessment of young children with CIs.Intracochlear position had no significant effect on the electrically evoked compound action potential (ECAP) threshold. Our CBCT protocol must be improved to increase the rate of successful investigations.

Improving Food Labels for Health and Safety

Finding the ingredients on food product labels can be critical for safety and health. This study examines whether the amount of time it takes to locate an ingredients list on a food product label depends on its physical location, or its position relative to a conspicuous landmark, the nutrition facts panel (NFP). The position of the ingredients list was manipulated with respect to 6 potential label locations and its position relative to the NFP, yielding 30 possible combinations of locations for the ingredients list and NFP. Participants were shown the set of 30 layouts in random order, with instructions to find the ingredients list on each layout. Response time (ms) for finding the ingredients list was recorded. Analyses indicated a significant vertical position effect, with placement on the bottom producing longer response times than the top or middle positions. Other analyses examined the relative distance between the ingredients and the NFP, which showed that participants found the ingredients list faster when it were located near the NFP, as opposed to placements furthest away. Implications for the understanding search times on relatively complex labels are discussed. Benefits for health and safety through better food labeling are described.

Spatial-Numerical and Ordinal Positional Associations Coexist in Parallel.

There is evidence for a systematic association of numbers and space. A prominent finding supporting this notion is the spatial-numerical association of response codes (SNARC) effect describing relatively faster responses to smaller numbers using a left-hand key and to larger numbers using a right-hand key. However, the assumption of the SNARC effect reflecting spatial-numerical associations was challenged recently. A working memory account was proposed suggesting that not numbers per se but their position in a memorized sequence is associated with space. Yet, there is also first evidence suggesting that this ordinal position and the SNARC effect may not be mutually exclusive. In the present study, we further examined the relationship between the ordinal position and the SNARC effect. We manipulated the number of items in the memorized ordered sequence and the number range employed. Results revealed both a significant ordinal position effect, but also a significant SNARC effect, substantiating the view that both effects are not mutually exclusive but may co-exist. Furthermore, we found that the SNARC effect was reduced when numbers ranging from 1 to 10 versus numbers ranging from 1 to 9 were employed. Thus, our results question a pure working memory account for the SNARC effect. Additionally, they highlight the critical role of the number range employed in research about the SNARC effect.

Determining item position effects in a computer-based test

If items become more or less difficult or discriminating depending on their position within a test form, and if different examinees respond to the same items in different positions, the fairness of test scoring for examinees is undermined. Such context effects have been investigated in the past with mixed results. This study investigates whether item position effects are present in a computer-administered certification test in which items are presented in random order. The results showed few consistent significant position effects for either item difficulty or discrimination for the entire test. However, there was a tendency for items to be slightly more difficult when they were administered in the last five positions at the end of each test form. For individual items, there was no obvious position effect for either item difficulty or discrimination. For practitioners working in computer-based testing programs, the findings support the use of random item ordering, but it is still recommended that each testing program conduct an item position investigation for items.

The effects of forward rotation of posture on heavy intensity cycling: Implications of UCI rule 1.3.013

UCI rule 1.3.013 limits the forward displacement of the nose of the saddle to 5cm rearward of the centre of the bottom-bracket. This study tests the effects of contravening this rule on 4km laboratory time trials and highlights biomechanical and physiological responses that could be of interest to coaches and bike fitters. Ten competitive male cyclists age 26±2 (mean±SD) yrs, height 180±5 cm, body mass 71±6 kg; V I‡ O 2max 70.9±8.6 ml·kg -1 ·min -1 ) completed 4km time trials and heavy intensity bouts. Riding posture was rotated forward where the nose of the saddle was 0, 2, 4, and 6cm to the rear of the bottom bracket (P 0 , P 2 , P 4 and P 6 ). End time, power, cardiorespiratory responses, lower appendage kinematics and crank torque kinetics were measured. There was no significant effect of position on 4 km time trials completion time or power. During 4 km time trials and heavy intensity bouts , gas exchange variables and lower limb range of motion were unchanged ( P >0.05). Trunk lean angle, cardiac output and stroke volume were greater at P 6 than other positions ( P 0.05). Results indicate, contravening rule 1.3.013 does not bring about improvements to 4km laboratory TTs. The rearward shift in peak crank torque most likely occurs as a function of altered muscle activation. Haemodynamic variations are possibly related to changes in peripheral resistance at the most forward position. Further work is necessary to allude to probable improvements in aerodynamics. Â

Syllable Structure Universals and Native Language Interference in Second Language Perception and Production: Positional Asymmetry and Perceptual Links to Accentedness.

The present study investigated how syllable structure differences between the first Language (L1) and the second language (L2) affect L2 consonant perception and production at syllable-initial and syllable-final positions. The participants were Mandarin-speaking college students who studied English as a second language. Monosyllabic English words were used in the perception test. Production was recorded from each Chinese subject and rated for accentedness by two native speakers of English. Consistent with previous studies, significant positional asymmetry effects were found across speech sound categories in terms of voicing, place of articulation, and manner of articulation. Furthermore, significant correlations between perception and accentedness ratings were found at the syllable onset position but not for the coda. Many exceptions were also found, which could not be solely accounted for by differences in L1–L2 syllabic structures. The results show a strong effect of language experience at the syllable level, which joins force with acoustic, phonetic, and phonemic properties of individual consonants in influencing positional asymmetry in both domains of L2 segmental perception and production. The complexities and exceptions call for further systematic studies on the interactions between syllable structure universals and native language interference with refined theoretical models to specify the links between perception and production in second language acquisition.

Charge-Transfer Emission in Organoboron-Based Biphenyls: Effect of Substitution Position and Conformation.

A series of organoboron-based biphenyls o,o'-NMe2, o,p'-NMe2, p,p'-NMe2, which contain an electron-donating NMe2 and an electron-accepting BMes2 groups at o,o'-, o,p'-, p,p'-positions of biphenyl skeleton, respectively, as well as o,o'-NBn2, which contains more bulky NBn2 rather than NMe2, were fully characterized to explore the effect of structural modification on the intramolecular charge-transfer emissions. In addition to significant effect of substitution position on photophysical properties, remarkable influence of conformation was also observed for o,o'-substituted compounds. The emission is substantially blue-shifted as conformation changes from the location of NMe2 and BMes2 at same side of biphenyl axis with a close B···N distance, and thus direct B···N electronic interaction in o,o'-NMe2, to the location of NBn2 and BMes2 on two opposite sides in o,o'-NBn2. And o,o'-NMe2 exhibits the longest emission wavelength, but the shortest absorption wavelength, and thus largest Stokes shift among these four organoboron-based biphenyls in both solution and solid state. The theoretical calculations demonstrated that the unique structure of o,o'-NMe2, in which boryl and amino located at the same side of biphenyl axis with close B···N distance and direct B···N electronic interaction, is helpful to stabilize the lowest singly occupied orbital in the exited state.

Effect of body position on vocal tract acoustics: Acoustic pharyngometry and vowel formants

The anatomic basis and articulatory features of speech production are often studied with imaging studies that are typically acquired in the supine body position. It is important to determine if changes in body orientation to the gravitational field alter vocal tract dimensions and speech acoustics. The purpose of this study was to assess the effect of body position (upright versus supine) on (1) oral and pharyngeal measurements derived from acoustic pharyngometry and (2) acoustic measurements of fundamental frequency (F0) and the first four formant frequencies (F1-F4) for the quadrilateral point vowels. Data were obtained for 27 male and female participants, aged 17 to 35 yrs. Acoustic pharyngometry showed a statistically significant effect of body position on volumetric measurements, with smaller values in the supine than upright position, but no changes in length measurements. Acoustic analyses of vowels showed significantly larger values in the supine than upright position for the variables of F0, F3, and the Euclidean distance from the centroid to each corner vowel in the F1-F2-F3 space. Changes in body position affected measurements of vocal tract volume but not length. Body position also affected the aforementioned acoustic variables, but the main vowel formants were preserved.

Topographic controls on soil nitrogen availability in a lowland tropical forest

Geomorphic position often correlates with nutrient cycling across landscapes. In tropical forests, topography is known to influence phosphorus (P) availability, but its effect on nitrogen (N) cycling has received less exploration, especially in lowland forests where widespread N richness is frequently assumed. Here, we report significant effects of topographic slope and landscape position on multiple aspects of the N cycle across a highly dissected lowland tropical forest on the Osa Peninsula, Costa Rica. A suite of N cycle metrics measured along a topographic sequence revealed a distinct gradient in N availability. Values of soil δ15N, inorganic N pools, net nitrification rates, and nitrification potentials were all substantially lower on a flanking steep hillslope (~28°) compared to a relatively flat ridge top (~6°), indicating lower N availability and a less open N cycle in steep parts of the landscape. Slope soils also hosted smaller total carbon and nitrogen stocks and notably less weathered soil minerals than did ridge soils. These latter findings suggest that elevated N loss resulting from high rates of soil and particulate organic matter erosion could underpin the spatial variation in N cycling and availability. Expanding our analysis to the larger study landscape, a strong negative linear relationship between soil δ15N values and surface slope angles was observed. N isotope mass balance models suggest that this pattern is most plausibly explained by an increase in N loss via erosive, non‐fractioning pathways from steep zones, as most other variables commonly assumed to affect soil δ15N values (such as temperature, precipitation, and vegetation type) did not vary across the sampled region. Together, these results reveal notable hillslope‐scale variation in N richness and suggest an important role for non‐fractionating N loss in the maintenance of this pattern. Such findings highlight the importance of geomorphology and the significant capacity of erosion to influence N availability in steepland ecosystems.

The Bradyrhizobium-legume symbiosis is dominant in the shrubby ecosystem of the Karst region, Southwest China

Nodulation symbiosis is a key component of natural ecosystems, and the nitrogen-fixing ability of such symbioses can have a significant impact on the restoration of degraded ecosystems. Here, we investigated the diversity of legume-rhizobium symbioses, compared the N2-fixing efficiency of legume-rhizobium symbioses, and clarified the relationship of rhizobia, host species, and microhabitat. Eighteen potential N2-fixing species were surveyed, and only nine of them were found to be nodulated. Most of wild legumes were found to be associated with rhizobia belonging to the genus Bradyrhizobium, except for Callerya nitida, which formed associations with the genus Mesorhizobium. δ15N signatures of Derris fordii were significantly closer to zero than all the other plants tested, suggesting that the D. fordii-ISA2507 (Bradyrhizobium elkanii) symbiosis might have the highest N2-fixing efficiency of all the associations. D. fordii and its rhizobial symbionts may have potential for application in ecological restoration and agricultural production. Host species selection was the major factor, and there was no significant effect of slope position on nodulation-legume symbioses in our study area, in which altitudes ranged from 287 m to 521 m at the small scale. The Shannon diversity and the evenness of N2-fixing species (nodulated legumes) were significantly positively correlated (P < 0.05) with the Shannon and evenness across non-N2-fixing plants (non-nodulated plants), suggesting that the Bradyrhizobium-legume nodulation symbiosis plays an important role in maintaining plant community structure in this degraded ecosystem.

The role of fracture reduction and plate position in the aetiology of flexor pollicis longus tendon rupture after volar plate fixation of distal radius fractures.

Flexor pollicis longus (FPL) rupture has been described as complication following volar plating for distal radius fractures. It has been hypothesised that this is due to plate prominence. The aim of the study was to investigate the relationship between sub-optimal plate position and fracture reduction on plate prominence. Plate prominence was measured in two experimental models. In the first, the effect of plate position was investigated using 18 fresh frozen cadavers with prominence being measured using a micrometer. In the second study, the effect of fracture reduction on plate prominence was investigated using similar methodology with simulated mal-reductions on dry bone models. The results of the first study showed a significant increase in lift-off for three plates (DVR, Synthes Universal and Acu-Loc), if the plates were moved distally or proximally from the anatomical position. Similar increases in prominence were also seen with rotational mal-positions. The results of the second study showed a statistically significant effect on plate prominence for even a 5° mal-reduction (p = 0.001) with worsening lift-off with increasing mal-reduction. These changes are significantly different from baseline and also significantly different to the lift-off recorded with mal-reductions 5° better and worse. Mal-reductions also necessitate more proximal placement of the plate to avoid screw penetration of the articular surface, and each 5° increment is significantly different from baseline. The results show a statistically and clinically significant effect of both plate position and fracture reduction on plate prominence and support the theory that both contribute to the aetiology of post-operative FPL rupture.

Metacarpophalangeal Joint Angle Measurement in Equine Forelimbs

The objective of the present study was to identify a consistent method for measuring the equine metacarpophalangeal joint (MCPJ) angle in a standing horse; and investigate effects of lifting the contralateral limb, changing head position and treadmill exercise on that angle. A circle circumference was best fit onto lateromedial radiographs of the dorsal region of the lateral condyle of three MCPJs with radio-opaque markers fixed on the bony prominences. The circle center was assumed to approximate the center of MCPJ motion and the bony eminence at this point was used to position the goniometer in subsequent tests. MCPJ dorsal angles of ten vertically-fixed cadaver forelimbs were measured with a goniometer five times by rater A, and once by rater B. MCPJ angles of fourteen horses were measured before and after lifting the contralateral limb. Five (standing) and eight (limb lifted) horses were measured six and five times in random order respectively. Skin marked MCPJ of five horses were filmed in five different head positions (forward, right, left, raised, and lowered). Duplicate MCPJ angles of 6 control and 6 exercised horses were measured before and after treadmill exercise. The goniometer repeatability coefficient was 4.7° (95%CI 3.9° to 6.0°) and was similar in horses standing squarely and with the contralateral limb lifted. There was no significant difference in MCPJ measurements between raters. MCPJ dorsal angles were significantly less with the contralateral limb lifted. There was no significant effect of head position. The right MCPJ dorsal angle decreased with exercise. In conclusion, the goniometer can be used to measure MCPJ angles in live horses, either standing squarely or with the contralateral limb lifted. Recent exercise, but probably not head position may affect the angle.

Polytocus focus: Uterine position effect is dependent upon horn size

Understanding the variability caused by uterine position effects in polytocus species, such as rats, may enhance prenatal animal models for the study of drug and environmental agents. The primiparous litters of 42 intact female Sprague-Dawley rats were studied. Uterine position, fetal body weight, and fetal brain (wet) weight were recorded on gestation day (GD) 20 (GD 0=sperm positive). Uterine position effect for brain and body weight varied depending upon horn size. Furthermore, an inverse relationship between horn size (and, to a lesser extent, litter size) and fetal weight applied to both body and brain weight measures. There were no statistical differences in brain and body weights between the left and right uterine horns. The position of the uterine horn (left vs. right) and litter size did not influence the uterine position effect in the rat. Collectively, the present data suggest the presence of a significant uterine position effect. Prenatal differences based on uterine position provide an untapped opportunity to increase our understanding of developmental neurotoxicological and teratological studies that employ a polytocus species as an animal model.