Structural organization of the retina in the tree shrew (Tupaia glis).

This investigation was undertaken to establish the gross and ultrastructural organization of the photoreceptors and retina in the Malayan tree shrew (Tupaia glis). Photographs of the fundus revealed no specialization or differentiation of a central foveal region. Histologic sections revealed a single row of relatively short and thick cones distributed uniformly throughout the retina. Electron micrographs of the retina indicated that the receptor outer segments are closely invested by pigment-filled epithelial processes and an amorphous interstitial material. The internal fine structure of the receptor outer segments revealed the characteristic stacks or arrays of bimembranous discs. The ellipsoid portions of the cone inner segments include tightly packed and extraordinarily large mitochondria. These mitochondria consist of unique patterns of concentric cristae arranged in highly ordered whorls of lamellar configurations. The cone synaptic pedicles contain a unique system of tubules not previously described in synaptic endings. Histologic sections indicated that only cone populations are located in the central region of the retina, whereas histologic, histochemical, and ultrastructural comparisons suggested that photoreceptors with some "rodtype" features are located more peripherally. The relatively small proportion of these rodtype receptors among the great preponderance of cone populations is in general accord with the tree shrew's diurnal habits as well as its great reliance on photopic vision and its visually guided behavior.

Age-related changes in rat brain capillaries.

We have measured several morphological parameters by electron microscopy of the frontal cortex (FC) and hippocampal CA1 (HC) capillaries in male Fischer 344 rats 3-, 9- and 24-months old. The results indicate that with increasing age there is an increase in the cross-sectional area of the basement membrane, increase in the fraction of endothelial cell and pericyte cytoplasmic area occupied by mitochondria in the FC, increase in the size of the pericyte mitochondria in both the FC and HC, increased capillary lumen area in the FC and decreased capillary lumen area in the HC. Also, the cytoplasmic area occupied by mitochondria in capillary pericytes is larger than in the endothelial cells of both FC and HC. These results suggest that there is regional variation in the age-associated changes in capillary morphometrics.

Effect of exercise on longevity, body weight, locomotor performance, and passive-avoidance memory of C57BL/6J mice.

Studies of human and animal subjects have suggested that exercise may retard aging, help prevent age-related diseases, and prolong life span. Earlier studies focused on the effects of exercise on the heart, skeletal muscles, lungs, metabolism, and longevity. Researchers recently have begun to direct their attention to possible benefits of exercise on the brain. The goals of this study were to examine the effects of voluntary wheel-running exercise on life span, body weight, food and water intake, locomotor performance, and one-trial passive-avoidance memory of mature (10-14 month), middle-aged (20-24 month), and old (28-30 month) C57BL/6J male mice. No significant differences in life span, expressed in months, were found between control and exercised mice when exercise was carried out during maturity, senescence, intermittently across both periods, or continuously throughout maturity and senescence. Exercised adult mice maintained body weight compared to adult controls, an effect not apparent in old mice. Locomotor performance was reduced in old mice, and exercise increased performance much more in adult than in old mice. In the passive avoidance test of recent memory, exercise significantly increased latency, that is, it improved retention, in adult, middle-aged, and old mice. The effect was greatest in middle-aged, next in old, and lowest in adult mice. The findings indicate that exercise may be an important modulator of the rate of aging.

Late ultrastructural changes in neuronal mitochondria after lonizing radiation of the brain.

Brain tissue was examined for morphological changes at 12 and 16 months after focal irradiation of the brain in female mice. Irradiation was performed with deuteron beams derived from the 60-inch Brookhaven cyclotron at a rate of 1925 rad second -minus 1 though an anti-Bragg device which produced uniform exposure. Experimental animals received a dose of 10,000 rad, covering a 9 by 5 mm area over the skull and extending into the brain from a depth of about 2 mm. An additional group of animals served as sham-irradiated controls. Histological studies revealed extensive cell loss, vacuolation, and prominent vascular changes in irradiated regions of the brain at 16 months post-irradiation. Ultrastructural examination of brain tissue at 12 and 16 months after irradiation revealed the presence of unusual elongated mitochondria with parallel arrays of cristae. Altered mitochondria were more prevalent at the longer post-irradiation interval.

Nerve fiber hypertrophy in posterior tibial nerves of mice in response to voluntary running activity during aging.

Three-month-old male C57BL/10 mice were exercised by voluntary running activity in vertically revolving wheels for two hours each day until 24 months of age. Activity scores were recorded each day and the animals were regularly weighed and inspected for abnormalities. Control animals were similarly treated except that the activity wheels were immobilized. At the end of the exercise period, survival was 84% for the exercise group and 64% for the controls. Light microscopic examination of the posterior tibial nerve of the surviving animals showed a significant fiber hypertrophy in response to the exercise. The number of myelinated fibers in nerves from exercised animals did not differ from those of the controls. On the basis of these data, it is suggested that prolonged exercise does not prevent the loss of peripheral nerve fibers associated with age but rather, may exert an effect on the nervous system by modifying the surviving cells.

Voluntary wheel running exercise and monoamine levels in brain, heart and adrenal glands of aging mice.

The goals of this study were to examine the effects of three months of voluntary wheel-running exercise on life span, whole body and brain, heart and adrenal weights and biogenic amine content (norepinephrine, dopamine, epinephrine and serotonin) in three age groups of male mice. The three groups consisted of mature (9 months), middle-aged (19 months), and old (27-29 months) mice. No significant differences in weight were found between control and exercise or age. The oldest mice had a survival rate of 69% for the exercise group and 43% for the age matched controls when the exercise phase was completed. Locomotor activity was significantly reduced for the old mice compared to the middle-age and mature mice. Only the mature (12 months of age at sacrifice) exercised mice showed a cardiac and adrenal hypertrophy (about 10%). There was a moderate increase in norepinephrine content in the ventral hypothalamus of the brain with exercise (significant at 12 months of age). Biogenic amine content in other regions of the brain (brain stem and forebrain minus hypothalamus) was not affected by age and/or exercise. There was a significant decrease in heart norepinephrine content with exercise in old mice (30-32 months). Adrenal gland norepinephrine content was significantly increased by exercise at 12 months of age and decreased at 22 months of age. Our results suggest that an increase in norepinephrine content in the hypothalamus might be a manifestation of an adaptation to the increased demands upon hypothalamic noradrenergic terminals imposed by prolonged exercise. It is also apparent that aging and exercise alters the amounts of sympathetic transmitter of the heart and adrenal glands. Such alteration may be beneficial to the aging brain by retaining norepinephrine stores that normally decline with age.

How the human brain responds to aging.

The characteristic morphologic changes frequently observed in the brain of an old adult include a decrease in weight and volume, a change in the pattern of cerebral cortical convolutions, and an increase in ventricular size. Cell loss varies from region to region in the brain, and may be intensified in Alzheimer's disease and other disorders associated with senile dementia. Among the neuroglial cells, the microglia undergo the most significant changes with age. Although senile brain disease previously has been regarded as secondary to atherosclerosis, recent neuropathologic studies indicate that only 30 to 40 percent of senile brain disease arises from cerebrovascular pathologic lesions. The dilemma remains, however, of how much of the deterioration observed in the aged is related to disease and how much to senescence. The interaction between gene expression and environmental conditions in aging is another important question for the geriatrician. Progress in the control and treatment of disorders associated with old age depends upon further research into the mechanisms that underlie the process of aging in the brain.

Central neurotransmitter substances and aging: a review.

Available evidence suggests that age is an important determinant of the levels of neurotransmitters and their associated enzymes and metabolites in some regions of the brain. Alterations at the synaptic level, or selective cell death in the brain, or both, may be implicated in progressive loss of function, behavioral changes and the onset of age-related diseases. Stimulation of hypothalamic neuroendocrine transducer cells by agents that alter neurotransmitter metabolism might provide some measure of control of the process of aging.

Alcoholism in the geriatric population.

Alcohol abuse by elderly persons may be overlooked by clinicians because the effects of alcoholism on intellectual processes may be attributed to advancing age. In older patients, in whom liver and other organ functions may be reduced, even modest social drinking will impair cognitive abilities. Alcoholism is especially detrimental to older persons because 1) their blood levels of ethanol are higher than those in younger persons, and brain neurons may be more sensitive to the drug; 2) ethanol can disturb their sleep and sexual performance; 3) their cognitive functions may be significantly impaired by ethanol; and 4) for elderly patients, who commonly take a variety of drugs, ethanol and drug interactions are particularly hazardous.

Behavioral evidence for supersensitivity after chronic bromocriptine administration.

Behavioral evidence for tolerance and supersensitivity during and after chronic (30 day) administration of bromocriptine (BRC) or bromocriptine + L-dopa in mice was assessed by measuring wheel running (WR) behavior during and after chronic drug administration, and apomorphine- and methylphenidate-(MP-)induced stereotyped gnawing after termination of chronic injections. In both BRC and BRC + L-dopa groups, tolerance developed fairly quickly to the depressing effect of BRC on WR seen on day 1 of drug administration. Mice receiving BRC showed significant increases in WR by week 2 of chronic drug administration, which persisted for at least two days after the termination of chronic injections. During the first week after termination of chronic injections, low doses of both apomorphine and MP induced significantly more stereotyped gnawing in BRC and BRC + L-dopa mice than in the control mice or the mice treated with L-dopa alone. This behavioral evidence for dopaminergic supersensitivity after chronic BRC administration may have relevance for the clinical use of BRC in combination with L-dopa or other dopamine agonists.

A morphometric analysis of pyramidal tract structures during postnatal undernourishment and recovery.

Rats were postnatally undernourished during the suckling period (up to 20 days) and the brainstems of the perfused rats were dissected and prepared for electronmicroscopy at 21, 35 and 63 days of age. The effects on myelin were relatively mild and consisted primarily of a slight reduction in the relative numbers of myelinated fibers, most likely caused by a lag in the rate of loss of non-myelinated fibers, and fewer lamellae in myelinated axons of less than 2.5 micron circumference. Organelles were examined in the interfasicular oligodendroglia and in paragigantocellular reticular neurons immediately dorsal to the pyramidal tract. The numbers of mitochondrial particles in neuronal perikarya were significantly increased by postnatal undernourishment, although the numbers of other organelles appeared normal. Increased numbers of mitochondria persisted in nutritionally rehabilitated rats. Mitochondrial particles in oligodendroglia were not altered.

The corpus callosum during postnatal undernourishment and recovery: a morphometric analysis of myelin and axon relationships.

This study was designed to compare morphometric relationships between myelin lamellae and axons in undernourished and well nourished developing rats, and in rats nutritionally rehabilitated for two weeks. Although sampling techniques employed in this study were not specifically designed to compare numbers of myelinated fibers in test and control populations, we did observe a trend indicating a reduction in the numbers of myelinated fibers. The mean numbers of myelin lamellae, from an average of all myelinated axons, were not different in control and test population. However, regression analysis of axon sizes by numbers of myelin lamellae revealed significant differences from the normal in 21-day-old undernourished rats. For callosal axons of any size, there were too few myelin lamellae in the undernourished rats. A partial recovery was observed in relatively small fibers by 35 days of age, but no recovery was observed in larger sized fibers. Comparison of the frequency distribution of axon circumferences of myelinated fibers revealed an increase in average axonal caliber. Computation shows that although mean numbers of lamellae were not altered by undernourishment, the axons themselves are increased in size by about 10%. This unexpected result indicates that the relationship normally governing the numbers of myelin lamellae is altered by postnatal nutritional deprivation, and that the relatively larger axon calibers do not produce in the ensheathing oligodendroglia any compensatory increase in the layers of myelin.

Opiate antinociception is altered by immunemodification: the effect of interferon, cyclosporine and radiation-induced immune suppression upon acute and long-term morphine activity.

It has recently been demonstrated that various forms of immune modification result in a profound attenuation of the opiate withdrawal syndrome. Herein we investigate the extent to which some of the immune modifiers active in withdrawal attenuation affect other opiate related behaviors, namely antinociception and the development of tolerance to this effect. The observations demonstrate that immune modification by cyclosporine and irradiation exposure result in an alteration of the acute antinociceptive effect of morphine; while none of these treatments modify the development of tolerance to this property of morphine.

Myelination of the rat optic nerve during postnatal undernourishment and recovery: a morphometric analysis.

Newborn rats were undernourished from the second postnatal day through 20 days of age and weaned to a diet of laboratory chow ad libitum. Optic nerve development was examined by various light and electron microscopic techniques at 14, 21, 35 and 63 days of age. The degree of undernourishment achieved resulted in body growth lag comparable to results obtained in our previous studies. Although cellularity (cells per photomicrograph area) of the oligodendroglia was unaffected, there was an apparent significant relative reduction in the total number of myelinated fibers by 21 days of age, as determined by light microscopic sampling. Ratios of unmyelinated-to-myelinated fibers were thus estimated by electron microscopy, and results indicated an early increase in the ratio (14 days). Either as the result of catch up in a developmental lag, or as a result of possible restorative effects of rehabilitation, these differences were significant by 35 days of age. The relationship between axon circumference and numbers of myelin lamellae was determined by regression analysis, which revealed a significant reduction in numbers of lamellae over axons of all sizes at 14 days. By 21 days, only fibers in the size range of 1-2 micron of circumference showed a difference, and by 35 days there were no significant differences. These results all indicate that there is a significant myelin reduction in optic nerve of the undernourished rat.

The synthesis of myelin and brain subcellular membrane proteins in the offspring of rats fed ethanol during pregnancy.

Pregnant Long-Evans rats received either: (1) liquid diet containing 5.15% ethanol; (2) liquid diet pair fed to (1) for total calories; or (3) liquid diet ad libitum. These special diets were administered from the 5th through the 18th days of gestation. Dams received standard laboratory chow and water ad libitum before and after the test interval. Additional dams received standard chow and water throughout the study. Birth weights of offspring in the ethanol group were lower than for offspring of the pair-fed or control groups, and their subsequent growth lagged behind the other groups. Neonate deaths in the ethanol group outnumbered other deaths. Eye opening was delayed, and brain weights appeared low from 16 to 30 days postnatal age, The onset of myelin synthesis was delayed by several days; however, by 30 days of age, the rate of myelin synthesis and net accumulation was comparable to the offspring of pair-fed controls. Thus, the effect of ethanol on brain myelination in the offspring of subject females appears as a delay in myelin initiation and cannot be fully explained by caloric undernourishment. An unexpected observation involved offspring of females fed standard chow throughout the study. The brain myelin concentration in this group was lower than for any of the other groups, which may relate to the higher fat content of the liquids diets and/or the comparatively slow weight gain of pregnant rats on standard chow.

Synaptic density of caudate-putamen and visual cortex following exposure to ethanol in utero.

Pregnant Long-Evans rats were fed a liquid diet containing ethanol (30% of total calories) during days 3-19 of gestation. Controls were given ad libitum access to liquid diet lacking ethanol, or pair-fed isocaloric amounts based on consumption by the animals in the ethanol group. Brain development of female offspring was evaluated by analysis of electron micrographs of caudate-putamen and visual cortex. Numbers of presynaptic terminals and synaptic junctions (synaptic density) per unit area were compared for 14- and 28-day-old offspring of dams from the three treatment groups. Synaptic density of the caudate-putamen and visual cortex was not affected by ethanol at 14 or 28 days. Although exposure to ethanol during a period comparable to the first two trimesters of human development with minimal or no undernutrition did not affect numerical density of synapses in visual cortex or caudate-putamen, synaptogenesis of caudate-putamen was altered in offspring of pair-fed animals.

Fetal ethanol exposure: a morphometric analysis of myelination in the optic nerve.

Pregnant Long-Evans rats were fed a liquid diet containing ethanol during gestation. Controls consisted of both pair-fed dams and dams fed ad libitum with an equivalent, iso-caloric diet lacking ethanol. Subsequent effects of ethanol measured in the offspring include a significant lag in the rate at which non-myelinated axons are lost in association with the initial overproduction of neurons. Additionally, there was a slight lag in the rate of acquisition of myelinated axons; and altogether there was a large increase in the ratio of non-myelinated to myelinated axons. Frequency spectra of myelinated and non-myelinated axons by size were normal, and the relationship between axon size and myelin lamellae was also normal. Measured against the dynamic, normal background of rapid cell-loss and the progressive development of myelin, morphometric demonstration and evaluation of the comparatively small divergences associated with fetal alcohol exposure are difficult: nevertheless, these results are consistent with and help account for the marginal hypomyelination previously observed by quantitative neurochemistry.

Development of axonal-oligodendroglial relationships and junctions during myelination of the optic nerve.

The early stages of myelination were examined in optic nerves of rats aged 12-15 days. The initial association between oligodendroglial processes and bare axons involves no junctional specialization, as the axoglial extracellular space remains unaltered. Following ensheathment by a collar of glial cytoplasm, at least one full rotation of mesaxon was evident before compact myelin formed. Furthermore, myelin was generally evident before a second rotation was completed. In longitudinal sections, an axoglial junction was always observed beginning on the first paranodal loop, continuing through to the last (or outermost) loop. Thus, the formation of myelin and elaboration of a junctional complex in the paranodal region follow a promyelination phase and appear to be synchronous (and possibly related) events. Although the paranodal plasmalemma and axolemma are in close apposition, there is a material in the extracellular space that precipitates phosphotungstic acid, a characteristic that appears to be featured in a number of different types of cell junctions.

A metabolism chamber for measuring oxygen consumption in the laboratory rat and mouse.

Details are given for the construction and use of an inexpensive metabolism chamber to measure oxygen consumption in a relatively large group of laboratory rodents in a brief time. Metabolic rates (MR) were measured regularly in male and female Sprague Dawley rats, 11-114 days old, and mice, 100 days old. Adult mice had higher MR than rats of approximately the same age. Female rats and mice had higher MR than males at all times. To demonstrate the versatility of the metabolism chambers adult rats were injected once or for 9 consecutive days with 6-n-propyl-2-thiouracil (PTU) to inhibit thyroid function and reduce MR, or with the carboxymethylcellulose (CMC) vehicle. PTU failed to lower MR in the animals most probably because CMC vehicle tended to increase MR, an effect more prominent in males than females.