Developmental expression of monoamine oxidases A and B in the central and peripheral nervous systems of the mouse.

Monoamine oxidases A (MAOA) and B (MAOB) are key players in the inactivation pathway of biogenic amines. Their cellular localization has been well established in the mature brain, but nothing is known concerning the localization of both enzymes during development. We have combined in situ hybridization and histochemistry to localize MAOA and MAOB in the developing nervous system of mice. Our observations can be summarized as five key features. (1) MAOA is tightly linked to catecholaminergic traits. MAOA is expressed in all noradrenergic and adrenergic neurons early on, and in several dopaminergic cell groups such as the substantia nigra. MAOA is also expressed in all the neurons that display a transient tyrosine hydroxylase expression in the brainstem and the amygdala and in neurons with transient dopamine-beta-hydroxylase expression in the cranial sensory ganglia. (2) MAOA and MAOB are coexpressed in the serotoninergic neurons of the raphe from E12 to P7. During postnatal life, MAOA expression declines, whereas MAOB expression remains stable. (3) MAOA is transiently expressed in the cholinergic motor nuclei of the hindbrain, and MAOB is expressed in the forebrain cholinergic neurons. (4) MAOA- and MAOB-expressing neurons are also detected in structures that do not contain aminergic neurons, such as the thalamus, hippocampus, and claustrum. (5) Starting at birth, MAOB expression is found in a variety of nonneuronal cells, the choroid plexus, the ependyma, and astrocytes. These localizations are of importance for understanding the effects of monoaminergic transmission during development.

Alpha7-nicotinic receptor expression and the anatomical organization of hippocampal interneurons.

C3H and DBA/2 mice differ in their hippocampal inhibitory function, as measured by the inhibitory gating of pyramidal neuron response to repeated auditory stimulation. This functional difference appears to be related to differences in expression of the alpha7 nicotinic cholinergic receptor, which may be generally expressed by interneurons. This study examines the relationship between genetic variation in alpha7 receptor subunit expression and GABAergic interneuron distribution in various regions and layers of the hippocampus in the two mouse strains. Subpopulations of hippocampal interneurons in both mouse strains were found to bind [(125)I]alpha-bungarotoxin. However, the distribution of the [(125)I]alpha-bungarotoxin-positive hippocampal interneurons was significantly different between C3H and DBA/2 mice. In region CA1, and to a lesser extent in region CA3, DBA/2 mice had increased numbers of [(125)I]alpha-bungarotoxin-positive neurons in stratum lacunosum-moleculare and decreased numbers in stratum oriens. Similar differences in GABAergic neuron distribution were observed in region CA1 in the two strains. C3H/DBA/2 F1 animals were backcrossed to the C3H parental strain for six generations, with selection for either the DBA/2 or C3H allelic variant of the alpha7 receptor gene. The distribution of [(125)I]alpha-bungarotoxin labeling closely resembled the DBA/2 parental phenotype in animals retaining the DBA/2 allele of the alpha7 gene. These data suggest that the alpha7 receptor gene locus may influence the anatomical organization of at least a subset of hippocampal interneurons by an as yet unidentified mechanism. This difference in interneuron anatomy may also contribute to functional differences in inhibitory sensory gating between the two strains.

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.

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.

Electron-microscopic studies on the maturation of secretory cells in the mouse Harderian gland.

The porphyrins in the Harderian glands of mice are first detectable at 7-8 days of age in both sexes. Thereafter, the levels show a marked rise during the closed-eye period, reaching a peak around the time of eyelid disjunction and then decrease gradually until day 25. At onset of puberty, the level rises again and exhibits a sexual dimorphism. The development of the Harderian gland was examined by light and electron microscopy in the mouse. Although two types of secretory cells, designated as type A and type B, comprise the glandular epithelium in fully developed glands, the time of neonatal appearance is different between the two. Type A cells first appear on the 5th day of age, while type B cells appear around the 7th day corresponding to the time at which porphyrins are first detected. Results of the investigations suggest that the porphyrins in the Harderian gland of mice may be synthesized mainly by type B cells.

Mammary gland growth and response to hormones in mastomys compared with mice.

Mammary gland growth with or without hormone manipulation was examined in virgin mastomys (Praomys (mastomys) natalensis) and compared with C3H/He mice having a low mammary tumor incidence. Mammary glands of mastomys consisted mostly of duct systems even at 720 days of age, whereas conspicuous formation of normal end-buds and preneoplastic hyperplastic alveolar nodules were seen in the glands of mice after 180 days of age. Mammary glands of mastomys showed a higher response to estrogen or progesterone rather than prolactin, which is much different from other rodents.

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.

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.

Differential responses to adjuvants of macrophages from young virgin, aging virgin and aging breeder mice.

Age related differences in macrophage responsiveness to adjuvants seen previously with thioglycollate induced cells were also found with resident macrophages. Thus, activation of phagocytosis by lipopolysaccharide, polyadenylic-polyuridylic acid complexes and muramyl dipeptides occurred when exposed to macrophages removed from young but not aging C58 and C3H/He mice. However, breeding status differences were observed in that aging virgin mice were unresponsive to these adjuvants, while aging breeder mice responded similarly to young virgin mice. Analysis of any changes in membrane phospholipids was carried out to determine their association with the age related and breeding status differences observed. Significant differences occurred in 32P labelling of phosphatidyl inositol between unstimulated macrophages from young and aging C58 mice. No differences were evident, however, after LPS stimulation. Analysis of macrophage plasma membranes from young and aging mice for cholesterol revealed significant age related differences in their ability to undergo increases in cholesterol content after LPS activation.

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.

Effect on growth of prolactin deficiency induced in infant mice.

The effect of lowering PRL levels in blood during early infancy on subsequent growth and development was studied in mice. PRL was reduced by injecting either an antiserum raised against homologous PRL or a PRL-inhibiting drug, 2-chloro-6-methylergoline-8 beta-acetonitrile methanesulfonate (ergoline), into 4-day-old mice for a period of 4 or 5 days. Both the anti-PRL serum and ergoline rapidly killed some of the injected animals, but the effect of anti-PRL serum was much more severe than that of ergoline (39% vs. 8.7% mortality during the period of injection). Similar administration of an antiserum against mouse GH or the GH-inhibiting peptide somatostatin did not cause a significant number of deaths. The deaths from the anti-PRL serum largely ceased when the antiserum was neutralized with rat PRL (NIH-RP-1) before injection. The gain in body weight of baby mice was markedly retarded within 24 h of injecting anti-PRL serum and ergoline, in contrast to the anti-GH serum and somatostatin injections, which took 3--4 days to inhibit growth perceptibly. The anti-PRL serum, despite having only one eighth the titer of anti-GH serum, was by far the most effective of the two antisera in diminishing tibial epiphyseal cartilage width as well as weights of pituitary glands, testes, and adrenals and retarding sexual maturity. The more severe and generalized developmental abnormalities and the incidence of mortality as a result of anti-PRL serum administration suggest that PRL in mice may be involved in the maintenance of some vital function during infancy.

Tumour incidence, growth, reproduction and longevity in female C3H mice fed polyunsaturated ruminant-derived foodstuffs.

Earlier studies with the random-bred Quackenbush mouse strain showed that human-type diets based on linoleic acid-enriched foodstuffs derived from ruminants fed protected polyunsaturated oils have no detrimental effects on growth, reproduction or longevity. Tumour incidence and time of onset of tumour development have now been studied in the inbred, tumour-prone mouse strain C3H, in addition to growth, reproduction and longevity. Mice were fed a polyunsaturated human diet, a conventional human diet, or mouse cubes. The results with C3H mice tended to confirm those with Quackenbush strain mice-growth rates and reproductive productivities were very similar in the two groups eating human diets. Mice on the conventional human diet tended to survive better to about 60 weeks of age than mice on the polyunsaturated diet or the cube diet, after which the mortality rates of the mice on the three diets were similar. The degree of unsaturation of the dietary fat had no significant effect on the incidence of tumours. The tumour incidence was about 40% which, taken in conjunction with the average age of onset (about 80 weeks), suggested that the NIV virus rather than the MMTV virus was responsible. It would appear that the high-fat human diets had no effect on the incidence of mammary tumours caused by this virus.

Cellular characteristics of skeletal muscle in selected strains of pigs and mice and the unselected controls.

Skeletal muscle growth of swine differing in rate of growth and muscularity was studied by analysis of DNA, RNA, and protein in the semitendinosus muscle of fast growing domestic lean pigs (Yorkshire) and the slow-growing feral obese pigs (Ossabaw). Both lean and obese strains were fed ad libitum corn and soybean mean diet containing 14% protein. The pigs were slaughtered at 6 months of age. The Yorkshire pig had significantly greater body and muscle weights (P less than 0.005) Total DNA, RNA, and protein in semitendinosus muscles were significantly greater in the Yorkshire pigs (P less than 0.005). RNA/DNA and protein/DNA ratios were significantly different between the Yorkshire and Ossabaw pigs. These data suggest that the greater muscle growth in the Yorkshire pigs is achieved by greater cell numbers and size. The response of skeletal muscle cells and fiber characteristics to selection was studied in two strains of mice by analysis of DNA, RNA, and histological measurement of muscle fibers. Both strains were fed ad libitum on laboratory rat chow diet. They were sacrificed at 12 months of age. Leg muscle DNA and RNA were significantly greater in the mice selected for rapid growth rate as compared to the control (P less than 0.005 and P less than .10, respectively). Measurements of the semimembranosus muscle reveal that the growth strain had significantly greater muscle weight (P less than .01) and muscle length (P less than 0.005). Histological measurements of the same muscle showed that the growth strain had significantly greater fiber number (P less than 0.005) and larger fiber size (P less than 0.005) than the controls. It would appear that the greater muscle cellularity (DNA) in growth strain mice is accompanied by greater muscle length, fiber number, and fiber diameter.

Cyclic guanosine monophosphate: elevation in degenerating photoreceptor cells of the C3H mouse retina.

As a result of an early deficiency in cyclic nucleotide phosphodiesterase activity, guanosine 3',5'-monophosphate accumulates in retinal photoreceptor cells before they begin to degenerate. It is suggested that degeneration of the photoreceptor cells is related to an imbalance in their metabolism or function which is caused by the elevated levels of cyclic guanosine monophosphate.