The impact of tail tip amputation and ink tattoo on C57BL/6JBomTac mice

Genetic material for polymerase chain reaction (PCR) and Southern blot analysis on transgenic mice is normally obtained by tail biopsy. Additionally, it may be necessary to tattoo the mice, as it is essential to have a good and permanent identification. The aim of this study was to evaluate the effects of amputating the tip of the tail to obtain a biopsy for genetic analysis and of ink tattooing on welfare in C57BL/6J mice, a strain often used as genetic background for transgenes. The behaviour of the animals, fluctuating asymmetry (FA, a measure of developmental instability) and the level of restitution in the remaining part of the tail were evaluated and used for an assessment of the impact of these procedures on the welfare of the animals. One group of mice was marked by tail tattooing at various ages. Another group of mice were tail amputated at 12 or 20 days of age. Body weight and FA were followed, and at the end of the experiment, the level of fear/anxiety was assessed using a light–dark box. In the group of tail-amputated animals observation of climbing behaviour and a beam walking test for balance was performed. Seven weeks after tail amputation, the animals were euthanized. The remaining part of the tail was evaluated histopathologically. Body weight, behaviour in the light–dark box and balance test results were not influenced by tail amputation or tattooing. FA was only transiently increased by tattooing. Climbing behaviour was reduced just after tail amputation at 20 days of age. No signs of neuromas were found in the amputated tails, but seven weeks after amputation a significant number of mice did not have fully regenerated glandular tissue and hair follicles in the tail. It is concluded that both tail amputation and tail tattooing seem to have minor short-term negative effects on welfare and that the tissues on the tail probably do not regenerate fully after amputation.

Postnatal Development of the Craniofacial Skeleton in Male C57BL/6J Mice

C57BL/6J is one of the most commonly used inbred mouse strains in biomedical research, including studies of craniofacial development and teratogenic studies of craniofacial malformation. The current study quantitatively assessed the development of the skull in male C57BL/6J mice by using high-resolution 3D imaging of 55 landmarks from 48 male mice over 10 developmental time points from postnatal day 0 to 90. The growth of the skull plateaued at approximately postnatal day 60, and the shape of the skull did not change markedly thereafter. The amount of asymmetry in the craniofacial skeleton seemed to peak at birth, but considerable variation persisted in all age groups. For C57BL/6J male mice, postnatal day 60 is the earliest time point at which the skull achieves its adult shape and proportions. In addition, C57BL/6J male mice appear to have an inherent susceptibility to craniofacial malformation.

Effects of the physical form of the diet on food intake, growth, and body composition changes in mice

The present study investigated effects of the physical form of the diet on food intake, growth, and body composition in male C57BL/6 mice. Three-week-old mice were fed isocaloric diets (AIN93G or a modification containing 25% wheat) in powdered or pelleted form. In experiment 1, mice were assigned into 4 groups offered the AIN93G or the wheat-modified diet in powdered or pelleted form. In experiment 2, mice were pair-fed the powdered diets to the ad libitum level of food intake of those fed the pelleted form of the respective diets. Body weight, food intake, and fecal excretion were recorded, and body composition was assessed on mice 1 wk before termination of the experiment. Mice fed the powdered diets showed greater increases in body weight in 2 wk of feeding than did mice fed the pelleted diets. Compared with the pelleted diets, the powdered diets supported an approximately 85% increase in the fat-mass:body-mass ratio and a 2-fold increase in the abdominal-fat-weight:carcass-weight ratio. In addition, mice fed the powdered diet showed significantly greater plasma concentrations of insulin and leptin and significantly lower plasma adiponectin, compared with their pellet-fed counterparts. Food intake of mice fed the powdered diet was 11% greater for the AIN93G and 16% greater for the wheat diet compared with that of the respective pelleted diet. These results demonstrate that C57BL/6 mice responded to the physical form of these diets in terms of food intake, which affected their growth, body composition, and plasma concentrations of insulin and adipocytokines.

The water delivery system affects the rate of weight gain in C57BL/6J mice during the first week after weaning

Facility planners, IACUCs, veterinary staff, and researchers make choices on water delivery systems for rodents on the basis of cost effectiveness, water quality, risk of malfunction, and potential effect on animal health and welfare. Here we compare biometrics, including weight trends, of newly arrived mice unfamiliar with automated watering; weight trends of weanlings; fecundity of mice; and risk of malfunction among 3 water delivery techniques: water bottle only, combination of automated delivery and water bottle, and automated system only. There was no statistically significant difference among the 3 experimental groups with respect to fecundity, mortality, and delivery malfunction. On the basis of body weight trends, the health and wellbeing of the mice used in these studies were not affected by the water delivery system or housing density after the first week; however, there was a significant difference in the growth rate at 21 to 28 d of age among the 3 groups of pups. The mice receiving both automated delivery and water bottles experienced higher growth rates from 21 to 28 d of age than did the other experimental groups. However, after 35 d of age, weight trends did not differ among the groups. Our results suggest that mice weaned into the same method of water delivery as their respective dams thrive equally well among the 3 tested water delivery systems.

Adult but not aged C57BL/6 male mice are capable of using geometry for orientation

Geometry, e.g., the shape of the environment, can be used by numerous animal species to orientate, but data concerning the mouse are lacking. We addressed the question of whether mice are capable of using geometry for navigating. To test whether aging could affect searching strategies, we compared adult (3- to 5-mo old) and aged (20- to 21-mo old) C57BL/6 male mice. We established a water maze task in which spatial information is provided by one landmark proximal to the target (featural information) and by the rectangular shape of the maze (geometric information). By means of probe trials in which we manipulated the presence of these two kinds of information, we show that adult mice can use both geometry and landmark to orientate. By contrast, aged mice do not use geometry and rely exclusively on the landmark to locate the platform. This study provides the first evidence that mice are capable of using geometric information for orientation and that this ability declines in aged animals.

Abnormality in the cerebellar folial pattern of C57BL/6J mice

The characteristic folial pattern of the mouse cerebellum is formed during postnatal development. We observed this process in C57BL/6J (B6) mice in detail, and found an abnormal folial pattern in a specific region (lobules VIII and IX of the vermis) in a substantial number of B6 mice. The frequency of this abnormality increased during postnatal development and reached 55% in the adult. Thus, the present study showed an abnormality in the cerebellar folial pattern of B6 mice, a mouse widely used in knockout studies, and called for caution in the phenotypic analysis of knockout mice of the B6 genetic background.

Further mapping of quantitative trait loci for postnatal growth in an intersubspecific 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 intersubspecific 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.

Biotelemetry transmitter implantation in rodents: impact on growth and circadian rhythms

The implantation of a biotelemetry transmitter for core body temperature (T(c)) and motor activity (MA) measurements is hypothesized to have effects on growth and circadian rhythmicity depending on animal body-to-transmitter (B:T) size ratio. This study examined the impact of transmitter implantation (TM) on body weight, food intake (FI), water intake (WI), and circadian T(c) and MA rhythms in mice (23.8 +/- 0.04 g) and rats (311.5 +/- 5.1 g) receiving no treatment (NT), anesthesia, laparotomy (LAP), and TM. The B:T size ratio was 6:1 and 84:1 for mice and rats, respectively. In mice, body weight required 14 days to recover to presurgical levels and never attained the level of the other groups. FI recovered in 3 days, whereas WI never reached presurgical levels. Rat body weight did not decrease below presurgical levels. FI and WI recovered to presurgical levels in rats by day 2 postsurgery. Anesthesia decreased mouse body weight for 1 wk, but was without effect in rats. LAP significantly decreased body weight for 5 days in mice and 1 day in rats, showing a significant effect of the surgical procedure in the absence of TM in both species. Circadian T(c) and MA rhythms were evident within the first week in both species, indicating dissociation between circadian rhythmicity and recovery of growth variables. Cosinor analysis showed a TM effect on T(c) min, T(c) max, mesor, amplitude, and period of mice, whereas only the amplitude of the rhythm was affected in rats. These data indicate that a large B:T size ratio is associated with minimization of the adverse effects of surgical implantation. We recommend that B:T size ratio, recovery of presurgical body weight, and display of a robust circadian T(c) and MA rhythm be established before collection of biotelemetry data collection under an experimental paradigm.

Marked differences in olfactory sensitivity and apparent speed of forebrain neuroblast migration in three inbred strains of mice

In the adult forebrain, new neuroblasts constantly migrate from the subventricular zone along the rostral migratory stream to the olfactory bulb, where many become neurons. It is unclear whether this process is different in commonly used mouse strains and whether it is related to olfactory function. Adult male BALB/c, C57BL/6, and 129/S1 (formerly 129SV) mice were tested for olfactory sensitivity plus discrimination, using male mouse urine from the two other strains. BALB/c mice had the greatest olfactory sensitivity, followed by 129/S1, and C57BL/6 mice, by an order of magnitude each. Newly formed cells were pulse-labeled for 3 h with i.p. 5-bromo-2'-deoxyuridine (BrdU) injections and the animals analyzed 24 h later. In 129/S1 mice, a greater proportion of neuroblasts were present closer to the olfactory bulb than in BALB/c mice, followed by C57BL/6 mice. The total number of BrdU-labeled cells did not differ, suggesting differences in migration and not proliferation. The impaired olfactory function in C57BL/6 mice might be caused by the reduced number of neuroblasts that reach the olfactory bulbs. However, olfactory function in BALB/c and 129/S1 mice did not correlate with their putative migration speed, suggesting a more complex nature of cellular processes that contribute to olfactory function. These results caution against comparing studies of olfactory function or neural precursors that use different strains of mice, and question the use of C57BL/6 mice as a "normal" strain or as transgenic background. Perhaps more importantly, the results point to an opportunity to identify genes that regulate olfactory function and neuroblast behavior.

Developmental timing of hair follicle and dorsal skin innervation in mice

The innervation of hair follicles offers an intriguing, yet hardly studied model for the dissection of the stepwise innervation during cutaneous morphogenesis. We have used immunofluorescence and a panel of neuronal markers to characterize the developmental choreography of C57BL/6 mouse backskin innervation. The development of murine skin innervation occurs in successive waves. The first cutaneous nerve fibers appeared before any morphological evidence of hair follicle development at embryonic day 15 (E15). Stage 1 and 2 developing hair follicles were already associated with nerve fibers at E16. These fibers approached a location where later in development the follicular (neural) network A (FNA) is located on fully developed pelage hair follicles. Prior to birth (E18), some nerve fibers had penetrated the epidermis, and an additional set of perifollicular nerve fibers arranged itself around the isthmus and bulge region of stage 5 hair follicles, to develop into the follicular (neural) network B (FNB). By the day of birth (P1), the neuropeptides substance P and calcitonin gene-related peptide became detectable in subcutaneous and dermal nerve fibers first. Newly formed hair follicles on E18 and P1 displayed the same innervation pattern seen in the first wave of hair follicle development. Just prior to epidermal penetration of hair shafts (P5), peptide histidine methionine-IR nerve fibers became detectable and epidermal innervation peaked; such innervation decreased after penetration (P7- P17). Last, tyrosine hydroxylase-IR and neuropeptide Y-IR became readily detectable. This sequence of developing innervation consistently correlates with hair follicle development, indicating a close interdependence of neuronal and epithelial morphogenesis.

Expression pattern of alpha CaMKII in the mouse main olfactory bulb

Multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is highly enriched at synapses and has been implicated in regulating the formation and function of several sensory systems, including the visual and the somatosensory systems. Although there is evidence for CaMKII expression in the olfactory system, the cellular localization of CaMKII has not been well studied and its function remains unknown. In this study, we examined the normal expression patterns of the predominant alpha CaMKII in the mouse main olfactory bulb. We showed that alpha CaMKII expression levels were high in the olfactory bulb and were developmentally regulated. Immunoreactivity to alpha CaMKII was heavy in the external plexiform layer and the granule cell layer but minimal in the olfactory nerve layer and the glomerular layer. At the cellular level, alpha CaMKII was selectively expressed in the gamma-aminobutyric acid (GABA)ergic granule cells but not in the GABAergic periglomerular cells. Unexpectedly, alpha CaMKII was not detected in the glutamatergic mitral/tufted cells. At the ultrastructural level, alpha CaMKII immunoreactivity was positive in granule cell spines and dendrites, but negative in mitral/tufted cell dendrites. In contrast, in the piriform cortex, as in the majority of cortical regions, alpha CaMKII was expressed in the glutamatergic neurons but not in the GABAergic neurons. Our results set the stage for ongoing investigations of the roles of CaMKII in the formation and function of the olfactory system.

Expression and function of glycine receptors in striatal cholinergic interneurons from rat and mouse

Although glycine receptors are widely expressed in the forebrain their function is obscure. We studied their activation by two possible endogenous ligands, glycine and taurine, and demonstrate a different expression pattern of glycine receptors in neostriatal cholinergic interneurons from two rodent species. Single-cell-reverse transcription-polymerase chain reaction analysis of glycine receptor-subunit expression was combined with whole-cell recordings from acutely isolated cholinergic interneurons. All cells expressed the alpha2-glycine receptor subunit, the majority (72%) in mice but none in young and aged rats expressed the alpha3-subunit. The beta-subunit expression was associated with both a higher efficacy and a higher potency of the partial agonist taurine. Cells expressing the alpha3-subunit displayed a slower desensitization of taurine responses than of glycine responses, in contrast to cells expressing the alpha2-, beta-subunits where desensitization time constants were similar. Glycine responses were reduced by preapplication of taurine; this effect was more pronounced in cells lacking the alpha3-subunit. We demonstrate interspecies differences and heterogeneity in expression and function of glycine receptors within the same neuronal population in the neostriatum.

Mouse models for the analysis of myopia: an analysis of variation in eye size of adult mice

PURPOSE

To assess the relative importance of genetic and environmental factors that modulate eye growth, eyes, lenses, and retinas of 507 mice belonging to 50 strains were measured.

METHODS

Mice of both sexes and a wide range of ages (27 to 526 days) were perfused for electron microscopy and eyes, lenses, and retinas were dissected and measured. Our uniform fixation protocol was shown to cause a weight loss of 4 to 6%. Multiple linear regression methods were used to explore relations between eye and lens weight, retinal area, age, sex, body and brain weight, and retinal ganglion cell number.

RESULTS

The eye and lens of mice continue to grow long after sexual maturity is reached at 40 to 60 days of age. The pace of growth matches the logarithm of age. Despite their smaller bodies, females have eyes as large as those of males. The correlation of eye weight to brain weight is remarkably low (r = 0.19), whereas that to retinal area is high (r = 0.86). Surprisingly, the correlation between lens weight and the size of the posterior segment (eye minus lens weight) is only 0.5 to 0.6, and ratios of these parameters are highly variable. Heritability of all traits is between 25 to 50%.

CONCLUSIONS

The continued growth of eyes in adult mice provides an excellent system to test effects of genetic and molecular manipulations on the development and treatment of myopia. Heritability is sufficiently high to map genes that specifically modulate growth of different parts of the eye.

Aspen wood-wool is preferred as a resting place, but does not affect intracage fighting of male BALB/c and C57BL/6J mice

Aspen wood-wool, provided as nesting material, was evaluated as a possible improvement of cage environment for 10-14-week-old inbred male mice maintained in groups of six (BALB/c n = 72 and C57BL/6J n = 36). The daily behaviour of mice was video recorded and their body weight, food consumption, weights of some organs and serum corticosterone concentrations were measured. Aggressive interactions between cage mates and against a strange intruder as well as the number of wounds on the back of the animals was monitored in order to evaluate the effect of nesting material on intermale aggression. Nesting material did not affect the daily active/passive behaviour patterns of mice, although animals clearly preferred it as a resting place. BALB/c mice given nesting material showed less weight gain and smaller brown adipose tissue weights than animals without nesting material. The other characteristics measured were not affected by the presence of nesting material in either strain. The presence of nesting material had no effect on fighting in cages. C57BL/6J mice were more aggressive than BALB/c mice according to the number of wounded animals in a cage. Wounded BALB/c mice had enlarged spleens and decreased epididymal adipose tissue weights. In conclusion, the nesting material used in this study did not adversely affect the animals. On the other hand, the material was clearly preferred to conventional bedding as a resting place. These findings suggest that nesting material may improve the cage environment of laboratory mice. Furthermore, there was an indication of strain differences in aggressive behaviour. It could be suggested that C57BL/6J mice are less tolerant towards intruders and housing six mice per cage is not suitable for this strain.

Quantitative trait loci for growth traits in C57BL/6J x DBA/2J mice

Quantitative trait loci (QTLs) for body weight and tail length are mapped in an F2 population of 927 C57BL/6J x DBA/2J mice. We test the concordance between the locations of the mapped QTLs with those detected by changes of marker frequency under artificial selection in a previous experiment with the same base population. The directions of effects of the QTLs are generally in agreement, and in many cases significant QTLs are found in similar map positions, but there are also discrepancies between the two experiments. There are indications of age-specific QTL effects on growth. For body weight traits, the genetic variation in the F2 appears to result from many loci with relatively small effects. For tail length at 10 weeks, however, a single QTL on Chromosome (Chr) 1 with a peak LOD score of approximately 33 contributes most of the genetic variation detected, changes the trait value by about 6%, and explains about 20% of the phenotypic variance of the trait.

Morphological and immunocytochemical features of the pineal organ of C3H and C57BL mice at different stages of postnatal development

Considerable progress is currently being made in elucidating the molecular basis of the circadian (photoneuroendocrine) system by use of transgenic mice generated from the inbred strains C57BL and C3H. As in all other vertebrate species, the pineal organ is an important component of the photoneuroendocrine system in these mouse strains, but very little is known about its morphological and immunocytochemical features. We therefore investigated the pineal organ and the adjacent epithalamic region of adult, 10-, and 5-day-old C57BL and C3H mice for S-antigen, serotonin, and dopamine-ss-hydroxylase (DBH) immunoreactions. In adult animals, the pineal organ was more than 2 times bigger in C3H than in C57BL mice. In younger animals, this difference was already evident, but less pronounced. The S-antigen immunoreactivity was more intense in adult C3H than in C57BL mice. This difference developed with increasing age; it was not yet detectable in 5-day-old animals. The intensity of the serotonin immunoreaction was similar in both strains at all stages investigated. However, the serotonin immunoreaction was more pronounced in adult than in young animals. The relative DBH-immunoreactive area (used as a marker for the sympathetic innervation of the pineal organ) was much bigger in C3H than in C57BL mice; within each strain it remained relatively constant during postnatal development. Adult individuals of both strains contained S-antigen- and serotonin-immunoreactive cells in the habenular complex. Their number increased with age, but they were always more numerous in C3H. In conclusion, the study has shown considerable differences in pineal morphology between C3H and C57BL, which may be related to the well-known differen- ces in melatonin formation between these two strains.

The response of transgenic mice to beta-adrenergic agonist administration is different from that of normal mice

Eighteen transgenic mice carrying an ovine metallothionein la-ovine growth hormone (oMTla-oGH) transgene and 18 littermate normal mice were used to investigate the effects of transgene expression and clenbuterol administration on growth performance and skeletal muscle characteristics. The oGH transgene was activated from 21 d of age, and half of the mice were fed 15 ppm clenbuterol from 42 to 70 d of age. All mice were killed at 70 d of age after 4 wk of treatment, and organs and muscles were dissected, weighted, and analyzed. Transgenic mice (TM) gained 2.6 times more than normal mice (NM). However, TM had a significantly lower (-20%, P < .01) proportion of muscle, expressed as percentages of body weights, and a higher percentage of heart (+10%), liver (+26%, P < .01) and spleen (+64%, P < .01) than NM. Clenbuterol improved the weight gain of TM by 20%, compared with 10% for NM. The growth-promoting effect of clenbuterol was almost exclusively confined to skeletal muscle (24% increase) in NM, in contrast to a more generalized growth increase in all tissues including skeletal muscle (11% increase) in TM. The skeletal muscles of TM were longer but smaller in diameter due to 30% smaller muscle fiber cross-sectional area. Clenbuterol increased the muscle fiber size of all fiber types by 60% in NM, compared to 30% in TM. Muscle DNA concentrations and content were higher (P < .05) in TM than in NM, and clenbuterol administration decreased DNA concentrations but not total DNA content for both genotypes. Cathepsin B, C, and H activities were higher (P < .01) in TM muscle, but the significance is not clear at the present time, although it points to a potential for greater protein degradation and(or) turnover rates as suggested by smaller muscle weights.

Developmental differences in place-learning performance between C57BL/6 and DBA/2 mice parallel the ontogeny of hippocampal protein kinase C

This study determined the ontogenic changes in learning and hippocampal protein kinase C (PKC) in C57 and DBA mice. Mice were tested on the visible- or hidden-platform versions of the Morris water task starting at 17, 24, 31, or 60 days of age. Both strains learned to locate the visible platform at all ages. C57 mice learned to solve the hidden-platform task when they were 24 days old, whereas DBA mice never learned to solve this task. Using a [3H]-phorbol ester binding assay, the authors found that both strains had similar amounts of hippocampal PKC at 10 and 17 days of age but that C57 mice had significantly more PKC at 24, 31, and 60 days of age. Immunoblotting results revealed that C57 mice had more gamma-PKC, but not alpha-PKC, than DBA mice. Thus, the development of performance differences in spatial learning between C57 and DBA mice parallels the ontogeny of hippocampal PKC.

Melanogenesis is coupled to murine anagen: toward new concepts for the role of melanocytes and the regulation of melanogenesis in hair growth

Hair is actively pigmented only when it grows: the melanogenic activity of follicular melanocytes (MC) is strictly coupled to the anagen stage of the hair cycle. In catagen, melanin formation is switched off and is absent throughout telogen. The appearance of pigmentation is preceded, and further accompanied by, a time-frame - restricted, differential pattern of tyrosinase transcription, translation, and enzyme activities during the development of anagen follicles. In this speculative review, we argue that signals required for melanin synthesis and pigment transfer to bulb keratinocytes (KC) are intrinsic to the skin, rather than coming from the serum. First, the proopiomelanocortin (POMC) gene is expressed and translated during anagen, but is below the level of detectability in telogen; POMC is a precursor protein for adrenocorticotropin and melanotropins, which are potent regulators of MC proliferation and differentiation. Second, fibroblasts and KC produce factors that affect MC proliferation and differentiation. We suggest that signals regulating follicular MC activity partially derive from cutaneous cells expressing POMC. Vice versa, MC transfer to surrounding KC pigment granules with potent bioregulatory properties. MC also produce and secrete various signal molecules that can regulate mesenchymal and epithelial cell functions. Anagen-associated melanogenesis and the cyclic production of a pigmented hair shaft result from programmed and tightly coordinated epithelial-mesenchymal-neuroectodermal interactions, in which MC may act not only as pigmentary, but also as hair growth-regulatory cells.

In vivo effects of growth hormone on thymus function in aging mice

It is well demonstrated that the normal functioning of the thymus gland is under neuroendocrine control. Thus, steroid, thyroid, and pituitary hormones can affect distinct structural and/or functional thymic parameters. Particularly growth hormone (GH) was shown to be capable of restoring some thymus functions in old individuals. This prompted us to carry out a multiparametric analysis of the thymus in young, middle-aged, and old mice, subjected to GH treatment lasting 3 or 6 weeks. For that, we treated animals with daily injections of ovine GH (2 micrograms/g BW). Although the general microarchitecture of the thymus remained unchanged following in vivo GH treatment, there was a clearcut increase in thymulin production, independent of the age group analyzed. Regarding the lymphoid compartment, we could not find evidence of changes in total thymocyte numbers nor in the subsets phenotypically defined by the expression of CD3, CD4, and CD8 antigens. Nonetheless, in GH-treated middle-aged and old mice, the concanavalin A-dependent proliferative response of thymocytes, as well as IL-6 production were enhanced compared to age-matched controls. These findings support the notion that GH has a pleiotropic effect upon the thymus, functionally affecting both microenvironmental and lymphoid compartments of the organ.

Morphology of the dorsal cochlear nucleus in C57BL/6J and CBA/J mice across the life span

The morphology of the dorsal cochlear nucleus (DCN) was evaluated across the life span in inbred C57BL/6J (C57) and CBA/J (CBA) mice using 5 age groups (young adult to very old). C57 mice exhibit progressive cochlear sensorineural pathology and hearing loss during middle age; CBA mice have only modest sensorineural pathology late in life. DCN layers I, II, and III were evaluated histologically with serial sections stained for Nissl and fibers. DCN volume decreased with age in C57 mice, but the change began earliest and was most pronounced in layer III. In CBA mice, volume increased during the first year of life and decreased only in the oldest mice. All major DCN cell types were found in both strains at all ages. There was an age-related decrease in the mean size of neurons in C57 mice that was first observed in layer III. In CBA mice, only a nonsignificant trend toward smaller neurons was observed in the oldest mice. An age-related decline in the number of neurons in layer III (but not in layers I and II) occurred in C57 mice. Aged CBA mice exhibited no significant loss of DCN neurons. Thus, age-related changes in the DCN were much more pronounced in C57 mice than in CBA mice, and the changes in C57 mice were most pronounced in layer III. Because layer III receives most of the DCN's primary auditory input, it would be directly affected by age-related hearing loss and degeneration of spiral ganglion cells in C57 mice. This suggests that the age-related changes observed in DCN layer III of C57 mice are affected by progressive peripheral degenerative changes; when peripheral loss is minimal (CBA mice), less substantial age-related changes are observed.

The alpha 1, alpha 2, and alpha 3 subunits of GABAA receptors: comparison in seizure-prone and -resistant mice and during development

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in brain, opens chloride channels through actions on GABAA receptors. We now report base and amino acid sequences of the alpha 1, alpha 2, and alpha 3 subunits from GABAA receptors of audiogenic seizure-prone (DBA/2J) and -resistant (C57BL/6J) inbred strains of mice. Inbreeding had fixed different alleles of the alpha 1 subunit in the two strains, giving five base differences in the cDNAs. None of these affected amino acid sequence, but one did create a NsiI restriction site potentially useful in mapping genomic DNA. No base or amino acid sequence differences between the strains were detected for the other two subunits. Northern blots revealed no apparent strain differences in message levels for these three subunits in whole brains of the mice at 3 weeks of age, the peak of seizure susceptibility in DBA/2J, but did reveal distinct regional and developmental patterns of expression among the subunits in mouse brain.

Development of the paramedian lobule of the cerebellum in wild-type and tottering mice

The mutant mouse tottering, (tg/tg), and the compound heterozygote mouse (tg/tg1a) exhibit three neurological disorders: ataxia, petit mal-like absence seizures and myoclonic intermittent movement disorders which are independent of the absence seizures. The tottering mouse carries an autosomal recessive single gene mutation on chromosome 8, and behavioral symptoms are first observed in the 3rd to 4th week of age. Using an additional genetic marker, Oligosyndactyly (Os), it is possible to distinguish tg/tg and tg/tg1a mice from wild-type mice at birth; nonaffected heterozygous littermates carry the Os mutation while tottering and compound heterozygous mice do not carry the Os gene. Similar to neurons found elsewhere in the brain, cerebellar Purkinje cells in both the wild-type and mutant mice were found to decrease in diameter with maturation. Forebrain weight, hindbrain weight, Purkinje cell dimensions and the thickness of the molecular layer in the paramedian lobule of the cerebellum in mutant mice were found to be reduced in mutants after, but not prior to the onset of behavioral symptoms.

Developmental expression of glial fibrillary acidic protein and actin-encoding messages in quaking and control mice

Quaking is a neurological mutation leading to pleiotropic phenotypic expression, the most prominent being disturbed myelin formation in the central nervous system (CNS) with minor abnormalities in the peripheral nervous system. Previous immunochemical measurements of glial fibrillary acidic protein (GFAP) revealed a marked increase in the protein in several areas of the CNS. To further characterize the regulation parameters of GFAP synthesis, we analyzed the levels of GFAP mRNA in 5 regions of the CNS, some with elevated levels of GFAP and some without. This was compared to the developmental expression of GFAP transcripts in the same regions in normal mice. To establish the specificity of the variations observed with this astroglial specific message, we conducted a similar investigation with actin RNA which is expressed by several cell types in the CNS. Both the actin and the GFAP message were found to be increased in the adult mutant throughout the CNS. In 2-year-old normal mice the messengers for both cytoskeleton proteins were expressed in a higher amount than in young adults.

Effect of the energy density of non-purified diets on growth, gestation and lactation in mice

The effects of dietary energy density on the performance of growing, gestating and lactating C57BL/6J mice were determined in order to develop pelleted non-purified practical diets for use in all stages of the mouse life cycle. Experimental diets with 4 levels of energy at 24% crude protein (CP) were pelleted and the nutritional values were determined using adult rats. The nitrogen-corrected metabolizable energy (MEn) values ranged from 2.86 to 3.73 kcal/g and the digestive CP (DCP) contents ranged from 20.5 to 22.6% on a dry matter (DM) basis. Mice responded to decreased dietary energy by increasing their feed intake to maintain MEn intake levels, except for 1 week after weaning and during lactation periods. During these periods, mice fed lower energy diets could not consume as much MEn as those fed higher energy diets. The lowest energy diet, in comparison with the highest energy diet, resulted in approximately a 33% lower weaning weight of pups at 3 weeks of age, a 13.2 to 34.4% slower growth at 3 to 4 weeks of age, and a 9.3 day delay in the onset of vaginal opening in young females. Lower energy diets, however, did not affect the litter size or the birth weight of pups. The DCP intake usually increased with decreases in dietary energy but apparently this did not affect the performance of the mice. It was concluded that an optimal diet should have an MEn value of 3.73 kcal/g DM or more for both the one week post weaning growth period and during lactation, but a diet with an MEn value of 2.86 kcal/g DM was sufficient for growth after 4 weeks of age and during gestation.

Strain differences in mouse brain weight gain and spatial-location scores during postnatal development

Brain weight and performance on a spatial-location test were measured from birth to weaning on mouse strains CD1, Balb/c, and their F1 cross. For CD1, onsets of both the last rapid-brain-growth stage and nonzero scores on the spatial-location test were around age 17 days; asymptotes of both were reached about age 23 days. Balb/c and F1 had at least 5- to 6-day delays of both onsets and asymptotes. For the strains studied, onset of nonzero performance on the spatial-location test may be a provisional indicator of onset of significant and rapid brain growth after age 15 days. The delayed F1 brain growth stage could indicate that control of brain growth about age 20 days resides in an inhibitory factor present in Balb/c but not in CD1.

Acceleration of chromosome aberrations in senescence-accelerated strains of mice

Age-related changes in the frequency of chromosome aberrations were examined using bone marrow cells of senescence-accelerated strains of mice (SAM). An accelerated senescence-prone strain, SAM-P/1, showed a striking increase in the frequency of chromosome aberrations, from age 3 to 8 months, whereas an accelerated senescence-resistant strain, SAM-R/1, at the same ages showed only a slight increase. Both these strains were derived from the same ancestral strain (AKR/J). The rate of increase of chromosome aberration frequency paralleled the advancement of senescence in both strains. These observations suggest that there are genetic factors which closely relate to chromosomal instability and acceleration of the senescence processes.

Age-related monoclonal gammapathies: clinical lessons from the aging C57BL mouse

In this article the long-held notion that benign monoclonal gammapathy (BMG) is a premalignant stage in the development of multiple myeloma (MM) is attacked. Jiri Radl argues that clinical and experimental observations indicate that they are separate entities which may be distinguished in the laboratory and which should be managed in radically different ways.

Age-related cholinergic drug effects on analgesia in two inbred strains of mice

The two inbred strains of mice C57BL/6 and DBA/2 are characterized by a different behavioral reactivity to cholinergic agents during development. The present experiment revealed that the strain-dependent differences in cholinergic-mediated analgesia during development disappeared during adult life. In fact, oxotremorine administration (0.0025 and 0.005 mg/kg) exerted the same analgesic effect in both strains at 6 months of age, in contrast with the finding of the lack of any effect of the drug in C57 mice at two months of age in comparison with DBA.

Strain-dependent decrease in glutamate binding to the N-methyl-D-aspartic acid receptor during aging

Glutamate binding to the N-methyl-D-aspartic acid (NMDA) receptor decreases in two strains of aged mice. In BALB/c mice the Bmax values decline 16% by 10 months and 45% by 30 months of age when compared to 3 months. The Kd increased more by 10 months (+29%) than by 30 months (+14%). In the C57Bl strain the Bmax was unaltered by 10 months but decreased 17% by 30 months. The Kd values, however, increased 121% by 10 months and 283% by 30 months of age. These data suggest that the age-related decline in glutamate binding to the NMDA receptor may predict a strain-specific reduction in NMDA-mediated processes (e.g. long-term potentiation, postsynaptic calcium fluxes).

Evolution of some biochemical characteristics of the intestinal mucosa during the first postnatal weeks in C57 mice. Effects of thyroxine and putrescine

In C57 mice, during the third week after birth, there is a rapid conversion of the intestinal epithelium from fetal to mature adult status. Some characteristics (lactase, maltase, diamine oxidase, and sucrase activity; putrescine, spermine and spermidine concentrations; mitotic index) have been analyzed for the proximal, middle, and distal parts of the intestine in mice of different ages: 8, 15, 19, and 60 days. The most important observations recorded were as follows: (a) sucrase- and maltase-specific activities as well as spermine and spermidine contents increased abruptly on the 19th postnatal day and then decreased; (b) decrease of lactase and diamine oxidase-specific activity was recorded between the 15th and 19th postnatal days, (c) later, diamine oxidase-specific activity increased, whereas putrescine content decreased in the proximal part of the intestine; and (d) mitotic index was not significantly different when estimated for the crypts on days 11 and 19. No similar variations of these biochemical parameters were observed over a period of 3 days when mice were injected with thyroxine on the 8th day or when mice received putrescine per os on the 9th day, as explained in the text. Only a slight but significant variation in sucrase- or maltase-specific activity with thyroxine and a variation of the lactase or DAO-specific activity of the distal part of the intestine with putrescine were recorded.

Genetic and developmental defects of the mouse corpus callosum

Among adult BALB mice fewer than 20% usually have a small or absent corpus callosum (CC) and inheritance is polygenic. In the fetus at the time when the CC normally forms, however, almost all BALB mice show a distinct bulge in the interhemispheric fissure and grossly retarded commissure formation, and inheritance appears to result from two autosomal loci, provided the overall maturity of fetuses is equated. Most fetuses recover from the early defect when the CC axons manage to cross over the hippocampal commissure, and thus there is developmental compensation for a genetic defect rather than arrested midline development. The pattern of interhemispheric connections when the adult CC is very small is topographically normal in most respects, despite the unusual paths of the axons. The proportion of mice which fail to recover completely can be doubled by certain features of the maternal environment, and the severity of defects in adults can also be exacerbated by new genetic mutations which create new BALB substrains. The behavioral consequences of absent CC in mice are not known, nor have electrophysiological patterns been examined. The mouse provides an important model for prenatal ontogeny and cortical organization in human CC agenesis, because these data are not readily available for the human condition.

Age and strain dependence of O6-methylguanine DNA methyltransferase activity in mice

The activity of the DNA repair protein O6-methylguanine DNA methyltransferase (MT) was compared in liver extracts from female ICR and male C57BL/6 mice at various ages (3-130 weeks old). Similar patterns of overall enzyme activity were observed in both strains with O6-MT activity being relatively low in young mice (3 or 8 weeks old). However, the activity significantly increased after adolescence (middle age), thereafter decreasing with old age (over 100 weeks old) to a level equivalent to that found in young mice. In an additional strain difference study, O6-MT activities in liver extracts from 4 strains of mice were compared at 5 and 30 weeks of age. Although a similar age-associated increase of enzyme activity in adolescence was confirmed in all 4 strains investigated, the closed-colony ICR mice differed from the inbred strains in demonstrating significantly higher levels of O6-MT activity in females than in males. However, the same tendency was also observed in a comparison of the sexes in 30-week-old C3H/HeN, C57BL/6 and BALB/c mice.

Serotonin concentration and turnover in cerebellum and other brain regions of pcd mutant mice

The Purkinje cell degeneration (pcd) mutant mouse is characterized by a loss of Purkinje cells in the cerebellum. Loss of granule cells occurs and is severe in pcd mutants after 9 months of age. Since Purkinje cells and granule cells represent two groups of target cells for serotonin neurons projecting from raphe nuclei and other brain areas, the content and turnover of serotonin in the cerebellum were determined in pcd mice aged 3-15 months. The content of serotonin was not decreased in pcd mouse cerebellum but tended to be slightly increased after 7 months. The ratio of 5-hydroxyindoleacetic acid (5-HIAA) to serotonin was significantly decreased in cerebellum at 7-15 months but not at 3 or 6 months. The decrease in this ratio is indicative of decreased serotonin turnover. Similar changes were not seen in brainstem or hypothalamus in mice up to 14 months old, but slight decreases were observed at 15 months. Another index of turnover, the accumulation of 5-HIAA after administration of probenecid to block its efflux from brain, was decreased by 46% in 7-month-old pcd mice in the cerebellum but not in the brainstem or hypothalamus. The decrease in serotonin turnover in pcd mouse cerebellum occurs subsequent to and perhaps due to the loss of the target Purkinje and granule cells.

The mdx mouse skeletal muscle myopathy: II. Contractile properties

The contractile properties of soleus muscles from mdx and control mice aged between 26 and 350 days were compared with those of muscles from similarly aged control mice. Mdx mice were in general heavier (their individual soleus muscles were also heavier), of greater cross-sectional area and greater standard length than age-matched controls. Isometric forces produced by soleus muscles from young mdx mice (less than or equal to 100 days) were similar to controls, but were weaker when force was normalized for cross-sectional area. Conversely, although the absolute isometric forces produced by older (greater than 100 days) mdx muscles were greater than age-matched controls, when normalized for cross-sectional area they were similar. No differences were found between mdx and control muscles in terms of length-force or force-velocity relationships. Thus, young mdx control muscles produce similar absolute isometric force but mdx mouse muscles are larger. When muscle size is accounted for, in terms of cross-sectional area, younger mdx muscles are, therefore, weaker than controls. Inefficient contraction of young mdx muscles may result from lack of contractile fibres, physiological inefficiency of contractile fibres, or loss of tendon-fibre continuity during muscle fibre necrosis and regeneration. The striking supernormal size and strength of older mdx muscles reflects their considerable regenerative capacity; whether this is due to an increase in muscle fibre number rather than fibre hypertrophy remains unclear.

Effects of a hybrid maternal environment on brain growth and corpus callosum defects of inbred BALB/c mice: a study using ovarian grafting

The corpus callosum of many but not all BALB/c mice is either abnormally small or absent. The basis for the defect is hereditary, but the proportion of mice expressing the anomaly can be modified by changing the early environment. The present study investigated the effects of an F1 hybrid maternal environment, which is known to promote better fetal development than an inbred environment, on body and brain growth in BALB/c and on the incidence of the corpus callosal defect. Ovarian follicle cells from BALB/cWah (albino) mice were grafted into pigmented F1 hybrid, BALB/cWah, and pigmented BALB female hosts of comparable age which were subsequently mated to BALB/cWah males. Groups of unoperated BALB/cWah and pigmented BALB dams were included as controls. Data from 111 litters were analyzed. Results showed that BALB mice with F1 mothers had heavier bodies at birth, weaning, and 100 days of age and heavier brains at 100 days than those with either grafted or ungrafted BALB mothers. The effects at birth were evident across all litter sizes (2 to 11), but those at weaning and 100 days were seen only in litters of more than 5 or 6. Neither the F1 hybrid maternal environment nor the grafting procedure itself appeared to influence the incidence or expression of the corpus callosal defect. About 22% of the offspring from each of the three groups (ungrafted BALB, grafted BALB, and grafted F1) showed a defective corpus callosum.

Toward an analogue of alcoholism in mice: analysis of nongenetic variance in consumption of alcohol

Drinking behavior of the isogenic mouse strain C57BL/6J was analyzed into nongenetic components: stochastic fluctuations, responses to fluctuations in the current environment, and persistent differences between individual animals. The latter accounted for the major part of the variance. The variance was neither increased by differences in diet during the postweaning rapid growth period (prior to assay for drinking choice) nor diminished by uniformity of treatment during this period, suggesting that significant differentiation had occurred prior to weaning. The large variance between animals could be explained by assuming that the genetic role in consumption of alcohol by C57BL mice is permissive--a relative insensitivity to the aversive orosensory and pharmacological effects of 10% alcohol--rather than a specific drug-seeking predisposition.

Ontogenic variation in acute lethality of cadmium in C57BL/6J mice

Susceptibility of C57BL/6J mice to the lethal effects of parenterally administered Cd declined as a function of age at exposure. The 7-day LD50 increased from 1.65 mg Cd/kg body wt in 7-day-old mice to 4.08 mg/kg in adult mice. Survival time following treatment with Cd also increased as a function of age. High constitutive concentrations of metallothionein, a transition metal-binding protein, in livers of young mice did not protect against the lethality of Cd. These results suggest that, in the mouse, the interaction between Cd and this metal-binding protein may be affected by age at exposure to this toxic metal.

Friend virus replication as a function of age

We have investigated the effect of age on the replication of Friend spleen focus-forming virus (SFFV). Recovery of SFFV from the spleens of four strains of mice was determined following intravenous infection with NB-tropic Friend virus (FV) complex at ages ranging from 6 to 134 weeks. In C57BL/6 mice, the virus did not replicate in adults up to 40 weeks of age, but beyond that there was a steep exponential increase with age in the amounts of SFFV recoverable. In C3H/He mice, which replicate the virus as young adults, the amount of SFFV recovered was 6-fold greater in old than in young mice. Recovery of virus was biphasic with age in SJL mice; in A strain mice no consistent change with age was noted. In C57BL/6 mice, reconstitution of lethally irradiated recipients with syngeneic marrow cells, followed by i.v. infection with FV, showed that the amounts of SFFV recovered depended on the age of the recipient. The present work shows that Friend SFFV replication is a sensitive indicator and can be used as a tool for the investigation of aging processes. The mechanisms responsible for the age-dependent change in regulation of virus replication and for the polymorphism remain to be determined.

Efficiency of growth in mice with a major gene for rapid postweaning gain

Previous research in this laboratory demonstrated the existence of a major gene (hg), inherited as a homozygous recessive, which increases postweaning growth by 40 to 50% in C57Bl/6 mice (Ch) compared to the same genetic stock without the major gene (CH). Although its effect has not been previously evaluated, this single recessive allele is also in a line of mice selected for rapid postweaning gain for over 70 generations. Gh represents that line of mice with the major gene for growth (hg) in the growth-selected background and GH the growth-selected background without the major gene. Total body weight, daily weight gain, feed consumption and gain/feed, measured daily from 21 to 42 d of age, were all significantly greater (p less than .01) in the two lines with the hg/hg genotype (Ch and Gh) compared with their respective control lines (CH and GH). Differences in body composition at 42 d of age between CH compared with Ch and GH compared with Gh were accounted for by difference in body weight. Gross and net energetic efficiency, calculated assuming a similar maintenance energy requirement, were improved (P less than .01) in Ch and Gh compared to CH and GH, respectively. The results demonstrated that hg influences growth in growth-neutral and growth-selected backgrounds. The gene also alters energy metabolism by increasing energetic efficiency of growth and(or) decreasing maintenance energy requirement.

Testosterone-responsive mouse kidney glycosphingolipids: developmental and inbred strain effects

Mouse kidney and urinary glycosphingolipids from developing C57BL/6J and adults of several other inbred strains were analyzed by high performance liquid chromatographic techniques. Glycosphingolipids from male and female C57BL/6J kidneys were similar until the fifth week of age. Galactosylceramide containing nonhydroxy fatty acids and galabiglycosylceramide containing nonhydroxy fatty acids first appeared in male kidneys, followed by an increase in galabiglycosylceramide containing hydroxy fatty acids. Galabiglycosylceramide was observed in male urine from the earliest collection period (26 days of age). At 5 weeks, globotriglycosylceramides were present in male urine, and by 6 weeks, they became the major glycolipid species. Analysis of the glycosphingolipids from adult male and female DBA/2J, CBA/J, C3H/HeJ, and AKR/J kidneys revealed that galactosylceramides and galabiglycosylceramides which contain nonhydroxy fatty acids were absent in all females and present in all males. The globotriglycosylceramides were elevated in male kidneys of all strains. Galabiglycosylceramides and globotriglycosylceramides were present in male urine of all strains. Each strain exhibited a characteristic pattern of urinary glycosphingolipids which varied not only in the different levels of di- and triglycosylceramides but also in the ratio of components that are distinguished by their fatty acid and long chain base composition. These data provide evidence that in several inbred strains of mice, testosterone induces the production of specific di- and triglycosylceramides, which are components of lysosomal organelles that are normally excreted in the urine.

Auditory development in the mouse: structural maturation of the middle ear

The development of middle-ear structures in the mouse was examined in nine groups of pups between 1 and 45 days of age. The area of the tympanic membrane (pars tensa and pars flaccida), the length of the lever arms of the malleus and incus, the surface area of the oval window, and the volume of the bulla all showed systematic changes during neonatal life. The area of the oval window reached maturity first and the lever arms achieved 90% of their adult size on day 11. The tympanic membrane achieved the same criterion on day 18. These data help us further to understand the processes that contribute to the functional ontogeny of the middle ear.

[Changes in the intercellular contacts of hepatocytes in the ontogeny of inbred mouse strains with a high (CBA) and low (C57BL) frequency of spontaneous hepatomas]

Some parameters of cellular contacts between hepatocytes were studied in ontogenesis of the inbred mouse lines with the high (CBA) and low (C57BL) frequency of spontaneous hepatomas. In both the lines the force of intercellular linkage of the hepatocytes drops down by the end of the animal's life. But in the C57BL mice this characteristics increases sharply between the 5th and 10th days after birth, whereas in the CBA mice no such increase is observed. During the whole postnatal development the force of linkage in the CBA mouse liver is thrice lower than in the C57BL mouse liver. The stability of contacts between the hepatocytes in the C57BL mice is not affected during ontogenesis, as well as in the CBA mice, except in the males at the age of 15-24 months when the stability of contacts decreases. This parameter decreases still more in the tumour. Since the CBA males are characterized by a higher frequency of spontaneous hepatomas, a suggestion is put forward to the effect that the primary disturbance of the stability of contacts reflects the early changes characteristic for the spontaneous liver carcinogenesis.

Relationship between brain cortex and testis maturation rate in two inbred strains of mice

Two inbred strains of mice, SEC/1ReJ (SEC) and C57BL/6J (C57) showed significant differences in the maturation rate of two different anatomical districts: the brain cortex and the seminiferous epithelium. The cortical maturation rate, recorded by means of an electrocorticogram (ECoG), indicated that SEC mice are slower in the development of an adult wave pattern than C57 mice, which are more mature at birth. Furthermore, the C57 strain appears to have a faster maturation rate of the seminiferous epithelium. In fact, spermatogenesis in these mice shows the presence of spermatids in the seminiferous epithelium at 25 days, and mature spermatozoa in the epididymis at 40 days. Instead, the SEC strain, because of its slower development, shows a considerable delay of spermiogenesis and the epididymis is still empty at 40 days. These data, together with those on the ECoG differences of these strains, seem to indicate a relationship between brain and testis maturation.

Direct genetic and maternal influences on behavior and growth in two inbred mouse strains

Newborn male DBA/2 and C57BL/6 mice were either crossfostered, fostered within strains, or, after handling, left with their own dams and compared for nine behavioral compenents observed in single animals at an adult age and for body weight measured at 4 weeks and 3 months. Many strain differences between the unfostered control groups emerged and these remained largely unchanged in comparisons between the infostered and between the outfostered groups. In neither infostered group were significant influences of fostering per se found. Some variation due to foster strain was detected mainly in the DBA outfostered group, namely, for 4-week body weight, rearing frequency, and locomotor activity, but no resemblance to the alien strain was brought about by this. Effects of litter occurred rarely. Unlike the C57BL strain, the DBAs showed a clear pattern of interdependence among exploratory acts. In spite of problems that may be attached to the crossfostering method, it was concluded that postnatal genotype-dependent maternal influences were rather unimportant as a source of variation in behavior and growth as measured between these two strains, relative to direct genetic effects and, possibly, prenatal factors.

Aging and sister chromatid exchange. V. The effect of post-embryonic development on mutagen-induced sister chromatid exchanges in mouse and rat bone marrow cells

Induction of sister chromatid exchanges (SCE) was examined as a function of post-embryonic development in C57BL/6J mice and Wistar rat bone marrow cells. At low concentrations of three different mutagens, cyclophosphamide, mitomycin C, and doxorubicin, induced SCE levels were not altered with post-embryonic development. However, at higher mutagen concentrations, SCE induction was significantly reduced in growing (3- to 8-week-old) animals when compared to mature (7- to 9-month-old) animals. Studies of 1- to 8-month-old mice at these high doses revealed that mutagen-induced SCE frequencies increase gradually during this period. These results suggest that with post-embryonic development, changes occur in cellular response to mutagen-induced DNA damage.

Electron microscopic analysis of postnatal histogenesis in the cerebellar cortex of staggerer mutant mice

Postnatal development of the cerebellar cortex has been compared in staggerer mutant and unaffected littermate mice. From postnatal day 3 to about day 21 the external granular layer in staggerer mice is decreased in thickness and area, and the number of postmitotic granule cell neurons is reduced. Those granule cells that are generated seem to differentiate normally, with the remarkable exception that they form only primitive junctions with Purkinje cell dendritic shafts. These specialized junctions are not superseded by the normal parallel fiber:Purkinje spine synapses and disappear by the third week. Purkinje cell somata and dendrites are smaller than normal at all stages examined. The dendrites are not confined to the sagittal plane as in the normal and, unique among mutant or other animals described to date, they exhibit virtually no branchlet spines. All other cortical synaptic relations of granule and Purkinje cells, including climbing fiber:Purkinje spine synapses, appear qualitatively normal. However, by 28 days virtually all staggerer granule cells have degenerated. While the primary genetic defect remains unknown, we postulate that the morphological abnormalities may be attributable to a block in the normal developmental relationship between granule cells and Purkinje cells. The small cell size and failure to form branchlet spines suggest that the Purkinje cell abnormality may be closer to the primary effect of the mutant gene than the more flagrant hypoplasia and degeneration of granule cell neurons.

Effect of chronic restraint on open field activity of aging C57BL/6N mice

Eight, 20, and 31 month old male C57BL/6N mice were exposed to three 24-hour restraint sessions per week, or to a nontreatment condition. All mice received five 2-minute open field tests after 5 and after 6 weeks of treatment. The activity of restrained mice tended to be greater than that of nonrestrained animals. In general, 8 month old mice were more active than older subjects. Age related activity decrements were prominent in the first series of open field tests, while restraint effects were most pronounced in the second series.

Developmental profile of enzyme activity in several tissues of the C57BL/6 mouse between birth and 35 days of age

The activity of 19 liver enzymes as well as the level of activity of a lesser number of enzymes in brain, kidney and heart tissue was measured in C57BL/6 mice at various ages between birth and 35 days. Several enzymes were present at significant levels in the liver at earlier ages than reported for rat liver. The time course of the development, the magnitude of the charges and the direction of the changes are often significantly different from the profiles observed in rat tissues, thus the mouse may respond differently than other species to dietary alterations and/or hormonal stimulations during the developmental period.