Differences In Brain Weight Research Articles

Development of learning and memory in mice genetically selected for differences in brain weight

Mice selected for high (H), medium (M), and low (L) brain weight were trained to the goal arm opposite their preference in a shock-escape T-maze at 7, 9, 11, or 13 days of age. Twenty-four hours later, half of the trained groups at each age received additional training to the original goal, whereas the other half was trained to the opposite goal. Maturational control groups without prior training were trained on the selected retest days for the previously trained groups. Improvement in correct choice-point turns during training was suggested for the H-line by 9 days of age and by 11 days of age for the M- and L-lines. During retraining, H-line mice demonstrated 24-hr retention effects by 10 days of age, whereas 24-hr memory was not indicated for M- and L-lines at any of the ages investigated. These results indicate that the onsets of learning and memory were influenced by genes affecting brain weight, in that H-line mice demonstrated more rapid brain growth as well as heavier brain weights at every age studied as compared with M- and L-line mice which showed similar brain growth functions.

Monamines in brain and urine of rats with hereditary hypothalamic diabetes insipidus.

Monoamine levels in brain and urine of homozygous and heterozygous diabetes insipidus (DI) rats (Brattleboro strain) were assessed. Homozygous DI rats had a higher whole brain content of serotonin than their heterozygous littermates. However, when corrected for differences in brain weight, homozygous DI also appeared to have higher brain concentrations of noradrenaline, tyrosine and GABA. The total 24 h excretion of all amines and their precursors was greater in the homozygous than in the heterozygous rats.

Direct contact with enriched environment is required to alter cerebral weights in rats.

To test the relative effectiveness of direct vs. indirect interaction with an enriched environment, some rats were housed in groups of 12 in large enriched condition (EC) cages while littermate "observer" (OC) rats were placed singly in small wire-mesh cages within EC. A third group was housed singly in an impoverished condition (IC) where stimulation was minimal. After 30 days, the animals were killed and the brains dissected. In both experiments the usual pattern of EC-IC differences in brain weights appeared, whereas OC showed no significant differences from IC. On measures of exploratory behavior taken during the last 2 days of the second experiment, IC fell significantly below EC, and OC was somewhat below IC. Thus EC differen from both IC and OC in brain and in behavior. Active contact with an enriched environment appears necessary for development of EC effects.

Effects of successive environments on brain measures

To test the persistence of cerebral effects induced by differential experience, littermate rats were placed in an enriched environment (EC) or an impoverished environment (IC) for either 30 or 80 days. Following this initial period, one rat of each litter was transferred from the EC to IC condition while its littermates remained in EC or IC. The second phase lasted either 7, 14, 21, 32 or 47 days. The cerebral differences induced by differential experience began to dissipate when the animals were placed in a common environment, but statistically significant differences still persisted weeks after the end of the inducing conditions. Greater persistence was found after 80 days of initial exposure than after 30 days. Following 80 days in EC, significant persistence of brain weight differences was found 21 days after removal from EC to IC; significant persistence of differences in acetylcholinesterase and cholinesterase activities were found 47 days later. Different brain regions and different measures showed somewhat different patterns of results. Three different kinds of environmental enrichment — devised in three laboratories — were compared for their effects on brain weights and brain enzymes.

Behavioral development in mice selected for differences in brain weight.

AbstractMouse pups from the SEL‐16 lines which have been selected for high or low brain weight differed from unselected controls in body size and intensity of some behaviors, particularly between 4 and 10 days of age. The differences were not related in a simple manner to brain size nor to brain growth patterns previously described by the authors. A hypothesis of pleiotropic effects of “brain weight genes” upon behavior is not supported by the data.

Environmentally-induced Changes in the Brains of Elderly Rats

ANIMALS that have been exposed to environmental stimulation develop marked differences in brain structure and biochemistry when compared with animals that have not been exposed in this way1–4. Factors influencing the magnitude of these changes are the duration of rearing and the age of the animals when the environmental separation takes place. Most studies have focused on young animals because the brain is thought to be more plastic at this stage. As a result, temporal analyses of the induced changes have usually been limited to fairly short periods of environmental exposure early in the animal's life. Rosenzweig et al.3 have suggested that, in rats differentially reared from weaning, the induced differences in brain weight reach a maximum during the first 30 d of separation, after which they decrease. But the evidence for this biphasic response has been based on relatively short periods of differential rearing (15–160 d).

Age and Regional Differences in the Chemical Composition of Brains of Mice, Monkeys and Humans

This chapter investigates how closely regional changes occur with age in the brain of mice and monkeys parallel those occurring in human brain. The specific purpose is to examine age differences in brain weight, water content, nucleic acid, neurotransmitters, some enzymes, and myelin phospholipids at different age levels in cortical and subcortical regions of the brain of C57BL/10 mice, rhesus monkeys, and humans. One of the long range goals of research on aging is to provide experimental methods for preventing, delaying or ameliorating detrimental factors in senescence. The complex relationships between the various anatomical and chemical compartments of developing brain are continuously changing because of a consequence of many processes, reaching their peak activity during early adult life and declining at different rates during the periods of old age and senescence. Consequently, specific biologic or biochemical mechanisms which may play a key role in aging have remained relatively unexplored, and human aging is usually characterized only in general descriptive or actuarial terms.

Changes in neurochemistry and neuronal morphology after exposure of the mouse brain to lethal levels of focal irradiation.

AbstractThe brains of normal and irradiated C57BL/J6 adult female mice were studied for morphologic and biochemical differences at four and six hours after focal brain irradiation when the animals first experienced seizures and, at the terminal phase just prior to death. Focal irradiation of the brain was performed under stereotaxic conditions with microbeams delivered through a 5.0 × 9.0 mm aperture to the dorsal surface of the brain at an adsorbed surface dose of 50,000 rad.An analysis of variance did not indicate any difference in brain weight or in DNA, RNA, or protein concentration due to irradiation. There was a significant increase in 5‐HT and NE concentration, and in AChE activity in the brains of the irradiated groups. Histochemical observations failed to show differences in the localization of alkaline and acid phosphatase activity. However, localization of ATPase activity associated with the blood vessels was more diffuse in the irradiated regions of the brain. Biochemical comparisons of ATPase activity indicated that there was a change in the subcellular distribution of ATPase enzyme following irradiation. Light and electron microscopic comparisons revealed a selective damage to astrocytes and dendritic processes in irradiated regions of the cortex.

Studies of brain weight and RNA content after short periods of exposure to environmental complexity

Rats in Environmental Complexity (EC) were compared with litter mates maintained in Impoverished Conditions (IC) for various times. An initial relatively fast onset of the difference between the cerebral weight of the EC and IC rats was observed. This phase was followed by another in which this difference was not statistically significant. The third period was characterized by a slow increase of the difference in cerebral weight of the EC and IC rats. The RNA content per gram of wet tissue was higher in the EC than in the IC animals in the period of fast acquisition of difference in brain weight, but in the successive periods (60 days in total) no definite indications of differences in the RNA/gram of wet tissue were found. The differences of RNA content per cerebrum followed a pattern similar to the differences of cerebral weight. Body and hypophysis weights were higher in IC than in EC animals after 2 days in their respective conditions and throughout the rest of the experiment.