Fine mapping of QTL for prepulse inhibition in LG/J and SM/J mice using F2 and advanced intercross lines

Prepulse inhibition (PPI) of the startle response is a measure of sensorimotor gating, a process that filters out extraneous sensory, motor and cognitive information. Humans with neurological and psychiatric disorders, including schizophrenia, obsessive‐compulsive disorder and Huntington's disease, exhibit a reduction in PPI. Habituation of the startle response is also disrupted in schizophrenic patients. In order to elucidate the genes involved in sensorimotor gating, we phenotyped 472 mice from an F₂ cross between LG/J × SM/J for PPI and genotyped these mice genome‐wide using 162 single nucleotide polymorphism (SNP) markers. We used prepulse intensity levels that were 3, 6 and 12 dB above background (PPI3, PPI6 and PPI12, respectively). We identified a significant quantitative trait locus (QTL) on chromosome 12 for all three prepulse intensities as well as a significant QTL for both PPI6 and PPI12 on chromosome 11. We identified QTLs on chromosomes 7 and 17 for the startle response when sex was included as an interactive covariate and found a QTL for habituation of the startle response on chromosome 4. We also phenotyped 135 mice from an F₃₄ advanced intercross line (AIL) between LG/J × SM/J for PPI and genotyped them at more than 3000 SNP markers. Inclusions of data from the AIL mice reduced the size of several of these QTLs to less than 5 cM. These results will be useful for identifying genes that influence sensorimotor gaiting and show the power of AIL for fine mapping of QTLs.     

Two quantitative trait loci for prepulse inhibition of startle identified on mouse chromosome 16 using chromosome substitution strains

Prepulse inhibition (PPI) of acoustic startle is a genetically complex quantitative phenotype of considerable medical interest due to its impairment in psychiatric disorders such as schizophrenia. To identify quantitative trait loci (QTL) involved in mouse PPI, we studied mouse chromosome substitution strains (CSS) that each carry a homologous chromosome pair from the A/J inbred strain on a host C57BL/6J inbred strain background. We determined that the chromosome 16 substitution strain has elevated PPI compared to C57BL/6J (P = 1.6 x 10(-11)), indicating that chromosome 16 carries one or more PPI genes. QTL mapping using 87 F(2) intercross progeny identified two significant chromosome 16 loci with LODs of 3.9 and 4.7 (significance threshold LOD is 2.3). The QTL were each highly significant independently and do not appear to interact. Sequence variation between B6 and A/J was used to identify strong candidate genes in the QTL regions, some of which have known neuronal functions. In conclusion, we used mouse CSS to rapidly and efficiently identify two significant QTL for PPI on mouse chromosome 16. The regions contain a limited number of strong biological candidate genes that are potential risk genes for psychiatric disorders in which patients have PPI impairments.     

Complex genetic architecture revealed by analysis of high-density lipoprotein cholesterol in chromosome substitution strains and F2 crosses

Intercrosses between inbred lines provide a traditional approach to analysis of polygenic inheritance in model organisms. Chromosome substitution strains (CSSs) have been developed as an alternative to accelerate the pace of gene identification in quantitative trait mapping. We compared a classical intercross and three CSS intercrosses to examine the genetic architecture underlying plasma high-density lipoprotein cholesterol (HDL) levels in the C57BL/6J (B) and A/J (A) mouse strains. The B x A intercross revealed significant quantitative trait loci (QTL) for HDL on chromosomes 1, 4, 8, 15, 17, 18, and 19. A CSS survey revealed that many have significantly different HDL levels compared to the background strain B, including chromosomes with no significant QTL in the intercross and, in some cases (CSS-1, CSS-17), effects that are opposite to those observed in the B x A intercross population. Intercrosses between B and three CSSs (CSS-3, CSS-11, and CSS-8) revealed significant QTL but with some unexpected differences from the B x A intercross. Our inability to predict the results of CSS intercrosses suggests that additional complexity will be revealed by further crosses and that the CSS mapping strategy should be viewed as a complement to, rather than a replacement for, classical intercross mapping.     

A major QTL on chromosome 11 influences psychostimulant and opioid sensitivity in mice

The identification of genes influencing sensitivity to stimulants and opioids is important for determining their mechanism of action and may provide fundamental insights into the genetics of drug abuse. We used a panel of C57BL/6J (B6; recipient)× A/J (donor) chromosome substitution strains (CSSs) to identify quantitative trait loci (QTL) for both open field activity and sensitivity to the locomotor stimulant response to methamphetamine (MA). Mice were injected with saline (days 1 and 2) and MA (day 3; 2 mg/kg i.p.). We analyzed the total distance traveled in the open field for 30 min following each injection. CSS-8, -11 and -16 showed reduced MA-induced locomotor activity relative to B6, whereas CSS-10 and -12 showed increased MA-induced locomotor activity. Further analysis focused on CSS-11 because it was robustly different from B6 following MA injection, but did not differ in activity following saline injection and because it also showed reduced locomotor activity in response to the mu-opioid receptor agonist fentanyl (0.2 mg/kg i.p.). Thus, CSS-11 captures QTLs for the response to both psychostimulants and opioids. Using a B6 × CSS-11 F₂ intercross, we identified a dominant QTL for the MA response on chromosome 11. We used haplotype association mapping of cis expression QTLs and bioinformatic resources to parse among genes within the 95% confidence interval of the chromosome 11 QTL. Identification of the genes underlying QTLs for response to psychostimulants and opioids may provide insights about genetic factors that modulate sensitivity to drugs of abuse.     

Prepulse inhibition （PPI） of tactile startle response in recombinant congenic strains of mice： QTL mapping and comparison with acoustic PPI

Prepulse inhibition (PPI) of the startle response is a psychophysiological measure of sensorimotor gating believed to be cross-modal between different sensory systems.We analyzed the tactile startle response (TSR) and PPI of TSR (tPPD,using light as a prepulse stimulus,in the mouse strains A/J and C57BL/6J and 36 recombinant congenic strains derived from them.Parental strains were significantly different for TSR,but were comparable for tPPI.Among the congenic strains,variation for TSR was significant in both genetic backgrounds,but that of tPPI was significant only for the C57BL/6J background.Provisional mapping for loci modulating TSR and tPPI was carded out.Using mapping data from our previous study on acoustic startle responses (ASR) and PPI of ASR (aPPI),no common markers for aPPI and tPPI were identified.However,some markers were significantly associated with both ASR and TSIL at least in one genetic background.These results indicate cross-modal genetic regulation for the startle response but not for PPI,in these mouse strains.     

Habituation and prepulse inhibition of acoustic startle in rodents

The acoustic startle response is a protective response, elicited by a sudden and intense acoustic stimulus. Facial and skeletal muscles are activated within a few milliseconds, leading to a whole body flinch in rodents(1). Although startle responses are reflexive responses that can be reliably elicited, they are not stereotypic. They can be modulated by emotions such as fear (fear potentiated startle) and joy (joy attenuated startle), by non-associative learning processes such as habituation and sensitization, and by other sensory stimuli through sensory gating processes (prepulse inhibition), turning startle responses into an excellent tool for assessing emotions, learning, and sensory gating, for review see( 2, 3). The primary pathway mediating startle responses is very short and well described, qualifying startle also as an excellent model for studying the underlying mechanisms for behavioural plasticity on a cellular/molecular level(3). We here describe a method for assessing short-term habituation, long-term habituation and prepulse inhibition of acoustic startle responses in rodents. Habituation describes the decrease of the startle response magnitude upon repeated presentation of the same stimulus. Habituation within a testing session is called short-term habituation (STH) and is reversible upon a period of several minutes without stimulation. Habituation between testing sessions is called long-term habituation (LTH)(4). Habituation is stimulus specific(5). Prepulse inhibition is the attenuation of a startle response by a preceding non-startling sensory stimulus(6). The interval between prepulse and startle stimulus can vary from 6 to up to 2000 ms. The prepulse can be any modality, however, acoustic prepulses are the most commonly used. Habituation is a form of non-associative learning. It can also be viewed as a form of sensory filtering, since it reduces the organisms' response to a non-threatening stimulus. Prepulse inhibition (PPI) was originally developed in human neuropsychiatric research as an operational measure for sensory gating(7). PPI deficits may represent the interface of "psychosis and cognition" as they seem to predict cognitive impairment(8-10). Both habituation and PPI are disrupted in patients suffering from schizophrenia(11), and PPI disruptions have shown to be, at least in some cases, amenable to treatment with mostly atypical antipsychotics(12, 13). However, other mental and neurodegenerative diseases are also accompanied by disruption in habituation and/or PPI, such as autism spectrum disorders (slower habituation), obsessive compulsive disorder, Tourette's syndrome, Huntington's disease, Parkinson's disease, and Alzheimer's Disease (PPI)(11, 14, 15) Dopamine induced PPI deficits are a commonly used animal model for the screening of antipsychotic drugs(16), but PPI deficits can also be induced by many other psychomimetic drugs, environmental modifications and surgical procedures.     

Independent genetic loci for sensorimotor gating and attentional performance in BXD recombinant inbred strains

A startle reflex in response to an intense acoustic stimulus is inhibited when a barely detectable pulse precedes the startle stimulus by 30-500 ms. It has been theorized that this phenomenon, named prepulse inhibition (PPI) of a startle response, is an automatic early-stage gating process contributing to the ability to focus attention. Deficits in PPI may therefore contribute to deficits in attentional processing. Both deficits are observed in schizophrenia spectrum disorders. Here, we investigated whether there is overlap in genetic control of PPI and attentional processing phenotypes in the panel of BXD recombinant inbred strains of mice. Using an individually titrated prepulse intensity to handle differences in perceived prepulse intensities among strains, we identified a significant quantitative trait locus (QTL) for PPI at the mid-distal end of chromosome 17. A measure of attentional processing in the five-choice serial reaction time task, response variability, mapped to a different locus on proximal-mid chromosome 16. In addition, the estimated genetic and environmental correlations between PPI and several attentional phenotypes were low and not significant. Taken together, the observation of separate genetic loci for PPI and attention and the absence of genetic and environmental correlations indicate that differences in sensorimotor gating do not contribute to differences in attentional performance. Therefore, it is worth pursuing the causative genes residing in both attention and PPI QTL, as these may contribute to separate molecular pathways implicated in neuropsychiatric diseases, such as schizophrenia.     

Foraging strategy switching in an antlion larva

Prepulse inhibition (PPI) refers to the process wherein startle responses to salient stimuli (e.g., startling sound pulses) are attenuated by the presentation of another stimulus (e.g., a brief pre-pulse) immediately before the startling stimulus. Accordingly, deficits in PPI reflect atypical sensorimotor gating that is linked to neurobehavioral systems underlying responsivity to emotionally evocative cues. Little is known about the effects of changes in visual contextual information in PPI among humans. In this study, the effects of introducing unexpected changes in the visual scenes presented on a computer monitor on the human auditory startle response and PPI were assessed in young adults. Based on our animal data showing that unexpected transitions from a dark to a light environment reduce the startle response and PPI in rats after the illumination transition, it was hypothesized that novel changes in visual scenes would produce similar effects in humans. Results show that PPI decreased when elements were added to or removed from visual scenes, and that this effect declined after repeated presentations of the modified scene, supporting the interpretation that the PPI reduction was due to novel information being processed. These findings are the first to demonstrate that novel visual stimuli can impair sensorimotor gating of auditory stimuli in humans.     

Whole-Body Prepulse Inhibition Protocol to Test Sensorymotor Gating Mechanisms in Monkeys

Prepulse inhibition (PPI) is the decrease of startle reflex amplitude when a slight stimulus is previously generated. This paradigm may provide valuable information about sensorimotor gating functionality. Here we aimed at determining the inhibited and uninhibited startle response of capuchin monkeys (Sapajus spp.), and to evaluate the role of the superior colliculus in PPI. Capuchin monkeys were tested in a whole-body protocol, to determine the best startle amplitude and interstimuli interval. Additionally we tested two subjects with bilateral superior colliculus damage in this protocol. Results show that 115 dB auditory pulse has induced the best startle response. In contrast to reports in other species, no habituation to the auditory stimuli was observed here in capuchins. Also, startle reflex inhibition was optimal after 120 msec interstimuli interval. Finally, there was a downward tendency of percentage inhibition in superior colliculus-lesioned monkeys. Our data provides the possibility of further studies with whole-body protocol in capuchin monkeys and reinforces the importance of the superior colliculus in PPI.     

Effects of repeated maternal separation on prepulse inhibition of startle across inbred mouse strains

A growing body of research implicates genetic factors and childhood trauma in the etiology of neuropsychiatric diseases such as schizophrenia. However, there remains little understanding of how genetic variation influences early life stress to affect later disease susceptibility. Studies in rats have shown that postnatal maternal separation (MS) results in later deficits in prepulse inhibition of the acoustic startle response (PPI), an impairment in sensorimotor gating found in schizophrenic patients. In the present study, genetic differences in the effects of repeated MS on PPI were examined in eight inbred strains of mice (129S1/SvImJ, 129P3/J, A/J, BALB/cJ, BALB/cByJ C57BL/6J, DBA/2J and FVB/NJ). Mice were assigned to either MS (180 min/day on postnatal days P0-P13), 'handling' (15 min/day, P0-P13) or facility-reared conditions and tested for PPI at 12 weeks of age. Results demonstrated major strain differences in the production of viable offspring irrespective of MS, leading to the exclusion of 129P3/J, A/J and BALB/cJ from the study. Pups from the five remaining strains exhibited marked differences in the acoustic startle response and PPI, confirming previous strain comparisons. However, MS produced no significant effects on PPI in any of the strains tested. A second form of postnatal stress (repeated footshock) also failed to alter PPI in the one strain studied, C57BL/6J. Present results demonstrate that the form of MS studied herein does not provide a robust model of early life stress effects on PPI in the mouse strains tested. The development and validation of a reliable mouse model of early life stress remains an important research goal.     

Sensorimotor gating and spatial learning in α7‐nicotinic receptor knockout mice

The role of acetylcholine and specific nicotinic receptors in sensorimotor gating and higher cognitive function has been controversial. Here, we used a commercially available mouse with a null mutation in the Chrna7^tm1Bay gene [α7‐nicotinic acetylcholine receptor (nAChR) knockout (KO) mouse] in order to assess the role of the α7‐nAChR in sensorimotor gating and spatial learning. We examined prepulse inhibition (PPI) of startle and nicotine‐induced enhancement of PPI. We also tested short‐ and long‐term habituation of the startle response as well as of locomotor behaviour in order to differentiate the role of this receptor in the habituation of evoked behaviour (startle) vs. motivated behaviour (locomotion). To address higher cognition, mice were also tested in a spatial learning task. Our results showed a mild but consistent PPI deficit in α7‐nAChR KO mice. Furthermore, they did not show nicotine‐induced enhancement of startle or PPI. Short‐ and long‐term habituation was normal in KO mice for both types of behaviours, evoked or motivated, and they also showed normal learning and memory in the Barnes maze. Thorough analysis of the behavioural data indicated a slightly higher degree of anxiety in α7‐nAChR KO mice; however, this could only be partially confirmed in an elevated plus maze test. In summary, our data suggest that α7‐nAChRs play a minor role in PPI, but seem to mediate nicotine‐induced PPI enhancement. We found no evidence to suggest that they are important for habituation or spatial learning .     

Gating deficits in isolation-reared rats are correlated with alterations in protein expression in nucleus accumbens

The isolation-rearing (IR) paradigm, consisting of the social deprivation for 6–9 weeks after weaning, induces a spectrum of aberrant behaviors in adult rats. Some of these alterations such as sensorimotor gating deficits are reminiscent of the dysfunctions observed in schizophrenia patients. Although gating impairments in IR rats have been linked to impairments in the cortico-mesolimbic system, the specific molecular mechanisms underlying this relation are unclear. To elucidate the neurochemical modifications underlying the gating disturbances exhibited by IR rats, we compared their pre-pulse inhibition (PPI) of the acoustic startle reflex with that of socially reared (SR) controls, and correlated this index to the results of proteomic analyses in prefrontal cortex and nucleus accumbens from both groups. As expected, IR rats exhibited significantly lower startle amplitude and PPI than their SR counterparts. Following behavioral testing, IR and SR rats were killed and protein expression profiles of their brain regions were examined using two-dimensional electrophoresis based proteomics. Image analysis in the Coomassie blue-stained gel revealed that three protein spots were differentially expressed in the nucleus accumbens of IR and SR rats. Mass spectrometry (matrix-assisted laser desorption ionization-time of flight and MS/MS) identified these spots as heat shock protein 60 (HSP60), α-synuclein (α-syn), and 14-3-3 protein ζ/δ. While accumbal levels of HSP60 was decreased in IR rats, α-syn and 14-3-3 proteins were significantly increased in IR in comparison with SR controls. Notably, these two last alterations were significantly correlated with different loudness intensity-specific PPI deficits in IR rats. In view of the role of these proteins in synaptic trafficking and dopaminergic regulation, these findings might provide a neurochemical foundation for the gating alterations and psychotic-like behaviors in IR rats.     

Further mapping of quantitative trait loci for postnatal growth in an inter-sub-specific backcross of wild Mus musculus castaneus and C57BL/6J mice

We performed a quantitative trait locus (QTL) analysis of eight body weights recorded weekly from 3 weeks to 10 weeks after birth and two weight gains recorded between 3 weeks and 6 weeks, and between 6 weeks and 10 weeks in an inter-sub-specific backcross population of wild Mus musculus castaneus mice captured in the Philippines and the common inbred strain C57BL/6J ( M. musculus domesticus ), to elucidate the complex genetic architecture of body weight and growth. Interval mapping identified 17 significant QTLs with main effects on 11 chromosomes. In particular, the main effect of the most potent QTL on proximal chromosome 2 increased linearly with age, whereas other QTLs exerted effects on either the early or late growth period. Surprisingly, although wild mice displayed 60% of the body size of their C57BL/6J counterparts, the wild-derived allele enhanced growth at two QTLs. Interestingly, five of the 17 main-effect QTLs identified had significant epistatic interaction effects. Five new epistatic QTLs with no main effects were identified on different chromosomes or regions. For one pair of epistatic QTLs, mice that were heterozygous for the wild-derived allele at one QTL and homozygous for that allele at another QTL exhibited the most rapid growth in all four possible genotypic combinations. Out of the identified QTLs, several showed significant sex-specific effects.     

Expanded characterization of the social interaction abnormalities in mice lacking Dvl1

Dvl1 is one of three murine Dishevelled genes widely expressed in embryonic development and in the adult central nervous system. Dishevelled proteins are a necessary component of the Wnt and planar cell polarity developmental signaling pathways. We reported previously that mice deficient in Dvl1 exhibited abnormal social interaction and sensorimotor gating. To assess the validity of our earlier findings, we replicated the previous behavioral tests and included several new assays. The behaviors assessed included: social interaction, sensorimotor reflexes, motor activity, nociception, prepulse inhibition of acoustic startle (PPI) and learning and memory. Assessments with an explicit social component included: social dominance test, whisker trimming, nest building, home-cage huddling and ultrasonic vocalization rate analysis in pups. In addition, separate cohorts of wildtype and Dvl1 -null mice were assessed for social recognition of a conspecific. Replicating the original report, Dvl1 -null mice were impaired in several tasks containing an explicit social component. However, no impairment was obser‐ ved in the social memory task. A previously observed deficit in PPI did not replicate in two institutions. In conclusion, we provide evidence that the social interaction phenotype of Dvl1 -deficient mice has a strong genetic influence, but the sensorimotor gating deficit was subject to environmental influences. The specificity of observed social interaction deficits also suggests that lack of Dvl1 is associated with deficits in the recognition of social hierarchy and dominance.     

Genetic resistance to diet-induced obesity in chromosome substitution strains of mice

Discovery of genes that confer resistance to diseases such as diet-induced obesity could have tremendous therapeutic impact. We previously demonstrated that the C57BL/6J-Chr^A/J/NaJ panel of chromosome substitution strains (CSSs) is a unique model for studying resistance to diet-induced obesity. In the present study, three replicate CSS surveys showed remarkable consistency, with 13 A/J-derived chromosomes reproducibly conferring resistance to high-fat-diet-induced obesity. Twenty CSS intercrosses, one derived from each of the 19 autosomes and chromosome X, were used to determine the number and location of quantitative trait loci (QTLs) on individual chromosomes and localized six QTLs. However, analyses of mean body weight in intercross progeny versus C57BL/6J provided strong evidence that many QTLs discovered in the CSS surveys eluded detection in these CSS intercrosses. Studies of the temporal effects of these QTLs suggest that obesity resistance was dynamic, with QTLs acting at different ages or after different durations of diet exposure. Thus, these studies provide insight into the genetic architecture of complex traits such as resistance to diet-induced obesity in the C57BL/6J-Chr^A/J/NaJ CSSs. Because some of the QTLs detected in the CSS intercrosses were not detected using a traditional C57BL/6J × A/J intercross, our results demonstrate that surveys of CSSs and congenic strains derived from them are useful complementary tools for analyzing complex traits.     

Four additional mouse crosses improve the lipid QTL landscape and identify Lipg as a QTL gene

To identify genes controlling plasma HDL and triglyceride levels, quantitative trait locus (QTL) analysis was performed in one backcross, (NZO/H1Lt × NON/LtJ) × NON/LtJ, and three intercrosses, C57BL/6J × DBA/2J, C57BL/6J × C3H/HeJ, and NZB/B1NJ × NZW/LacJ. HDL concentrations were affected by 25 QTL distributed on most chromosomes (Chrs); those on Chrs 1, 8, 12, and 16 were newly identified, and the remainder were replications of previously identified QTL. Triglyceride concentrations were controlled by nine loci; those on Chrs 1, 2, 3, 7, 16, and 18 were newly identified QTL, and the remainder were replications. Combining mouse crosses with haplotype analysis for the HDL QTL on Chr 18 reduced the list of candidates to six genes. Further expression analysis, sequencing, and quantitative complementation testing of these six genes identified Lipg as the HDL QTL gene on distal Chr 18. The data from these crosses further increase the ability to perform haplotype analyses that can lead to the identification of causal lipid genes.     

Relationship between PPI and baseline startle response

Prepulse inhibition (PPI) of the startle response to a sudden noise is the reduction in startle observed when the noise is preceded shortly by a mild sensory event, which is often a tone. A part of the literature is based on the assumption that PPI is independent of the baseline startle. A simple model is presented and experimental validation provided. The model is based on the commonly accepted observation that the neuronal circuit of PPI differs from that of startle. But, by using a common output, the measures of both phenomena become linked to each other. But, how can we interpret the numerous experimental data showing PPI to be independent of the startle level? It is suggested that in a number of such cases the baseline startle would have been stabilized by a ceiling effect in the startle/PPI neuronal networks. Reducing the startle level, for example in a PPI evaluation procedure, may disclose properties of startle masked by this ceiling effect. Disclosure of habituation to the startle eliciting noise produced an increase of PPI along its initial measurements. Taken together, even if the neuronal process that sustains startle and PPI are distinct, separating them experimentally requires careful parametric methods and caution in the interpretation of the corresponding observations.     

Genetic Dissection of Quantitative Trait Loci for Hemostasis and Thrombosis on Mouse Chromosomes 11 and 5 Using Congenic and Subcongenic Strains

Susceptibility to thrombosis varies in human populations as well as many inbred mouse strains. Only a small portion of this variation has been identified, suggesting that there are unknown modifier genes. The objective of this study was to narrow the quantitative trait locus (QTL) intervals previously identified for hemostasis and thrombosis on mouse distal chromosome 11 (Hmtb6) and on chromosome 5 (Hmtb4 and Hmtb5). In a tail bleeding/rebleeding assay, a reporter assay for hemostasis and thrombosis, subcongenic strain (6A-2) had longer clot stability time than did C57BL/6J (B6) mice but a similar time to the B6-Chr11^A/J consomic mice, confirming the Hmtb6 phenotype. Six congenic and subcongenic strains were constructed for chromosome 5, and the congenic strain, 2A-1, containing the shortest A/J interval (16.6 cM, 26.6 Mbp) in the Hmtb4 region, had prolonged clot stability time compared to B6 mice. In the 3A-2 and CSS-5 mice bleeding time was shorter than for B6, mice confirming the Hmtb5 QTL. An increase in bleeding time was identified in another congenic strain (3A-1) with A/J interval (24.8 cM, 32.9 Mbp) in the proximal region of chromosome 5, confirming a QTL for bleeding previously mapped to that region and designated as Hmtb10. The subcongenic strain 4A-2 with the A/J fragment in the proximal region had a long occlusion time of the carotid artery after ferric chloride injury and reduced dilation after injury to the abdominal aorta compared to B6 mice, suggesting an additional locus in the proximal region, which was designated Hmtb11 (5 cM, 21.4 Mbp). CSS-17 mice crossed with congenic strains, 3A-1 and 3A-2, modified tail bleeding. Using congenic and subcongenic analysis, candidate genes previously identified and novel genes were identified as modifiers of hemostasis and thrombosis in each of the loci Hmtb6, Hmtb4, Hmtb10, and Hmtb11.     

Behavior and mutagenesis screens: the importance of baseline analysis of inbred strains

Random mutagenesis as a means of identifying the function of genes has been used extensively in a variety of model organisms. Until recently it has been used primarily in the identification of single-gene traits that cause visible and developmental mutations. However, this genetic approach also has the power to identify genes that control complex biological systems such as behavior. Mutagenesis screens for behavioral mutations require careful consideration of many factors, including choice of both assays and background strains for use in mutagenesis and subsequent mapping of the affected gene or genes. This paper describes behavioral assays for monitoring motor coordination on the accelerating rotarod, anxiety-related behaviors in the elevated zero maze and sensorimotor reactivity, gating, and habituation of acoustic startle. These five physiological or neurological behaviors can represent potential endophenotypes for a variety of neurological and psychiatric disorders. The significant degree of strain- and sex-specific differences in the performance of four inbred strains of mice (C57BL/6J, C3HeB/FeJ, DBA/2J, and 129/SvlmJ) in these behavioral assays illustrates the importance of performing baseline analysis prior to behavioral mutagenesis screens and genetic mapping of selected mutations. Received: 16 December 1999 / Accepted: 17 December 1999