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Tyler Janicke
Normal volunteers, aged 30 to 99 years, were studied with MRI. Age was related to estimated volumes of: gray matter, white matter, and CSF of the cerebrum and cerebellum; gray matter, white matter, white matter abnormality, and CSF within each cerebral lobe; and gray matter of eight subcortical structures. The results were: 1) Age-related losses in the hippocampus were significantly accelerated relative to gray matter losses elsewhere in the brain. 2) Among the cerebral lobes, the frontal lobes were disproportionately affected by cortical volume loss and increased white matter abnormality. 3) Loss of cerebral and cerebellar white matter occurred later than, but was ultimately greater than, loss of gray matter. It is estimated that between the ages of 30 and 90 volume loss averages 14% in the cerebral cortex, 35% in the hippocampus, and 26% in the cerebral white matter. Separate analyses were conducted in which genetic risk associated with the Apolipoprotein E epsilon4 allele was either overrepresented or underrepresented among elderly participants. Accelerated loss of hippocampal volume was observed with both analyses and thus does not appear to be due to the presence of at-risk subjects. MR signal alterations in the tissues of older individuals pose challenges to the validity of current methods of tissue segmentation, and should be considered in the interpretation of the results.
The largest part of the vertebrate brain, filling most of the skull and consisting of two cerebral hemispheres divided by a deep groove and joined by the corpus callosum, a transverse band of nerve fibers. The cerebrum processes complex sensory information and controls voluntary muscle activity. In humans it is the center of thought, learning, memory, language, and emotion.
The largest part of the brain, consisting of two lobes, the right and left cerebral hemispheres. The cerebrum controls thought and voluntary movement. (See cerebral cortex, left brain, and right brain.)
The cerebrum is a paired neural structure composed of the two cerebral hemispheres (left and right) each containing a central space, the lateral ventricle. It develops from the telencephalon.
The cerebrum (right and left) is the upper, front portion of the brain and consists of two hemispheres, or halves. The two hemispheres are connected by the corpus callosum, which is a large bundle of nerve fibers. The cerebrum can be divided into four lobes: frontal lobe, parietal lobe, occipital lobe, and temporal lobe.
The cerebrum is the largest portion of the brain. It oversees many everyday activities. These include motor function, cognitive abilities (thinking and reasoning), sensory impulse interpretation, speech and language, bowel and bladder control, sexual desire, and emotional control.
C57Bl/6J mice were infected with 2000 embryonated T. canis and T. cati eggs, respectively as well as Balb/c mice infected with T. cati eggs only. On 8 time points post infection, organs were removed and microscopically examined for respective larvae. Special focus was put on the CNS, including analysis of larval distribution in the cerebrum and cerebellum, right and left hemisphere as well as eyes and spinal cord. Additionally, brains of all infection groups as well as uninfected controls were examined histopathologically to characterize neurostructural damage.
On day 2 pi, the brain recovery rate (Figure 2) for all infection groups was low resulting on average in 2.4% and 1.8% in Balb/c and B6 T. cati infected mice as well as 0.3% in B6 T. canis infected mice. On day 7 pi, the recovery rate of T. cati larvae in Balb/c mice was rather high with 16.5% when compared to B6 T. cati infected mice (4.5%); however, no significant difference was observed. In contrast, 46.6% of recovered T. canis larvae were found in the brain at day 7 pi. In Balb/c as well as B6 T. cati infected mice, recovery rates in the brain remained rather low during the remaining course of infection (4.5% on average in Balb/c mice and 2.73% on average in B6 T. cati infected mice). In Balb/c T. cati infected mice, recovery rates differed significantly on day 7 pi vs. day 21 and 28 pi, at which larval counts dropped to a minimum. No significant differences during the course of infection were found in B6 T. cati infected mice. T. canis infected mice revealed a rather high recovery rate in the brain with an average of 32.57%. Significant differences were observed on day 2 pi vs. the succeeding time points, as well as day 7 pi vs. day 28 and 42 pi, respectively. Larval distribution in the cerebrum compared to the cerebellum revealed significant differences between T. cati and T. canis infected mice with statistically significantly higher larval recovery rates in the cerebra of T. canis than in T. cati infected mice beginning from day 14 throughout day 98 pi. In contrast, significantly higher recovery rates were observed in cerebella of T. cati infected mice on day 28, 35 and 98 pi when compared to T. canis infected mice. Between both T. cati infection groups, no statistically significant differences were observed. Larval recovery rates from the cerebellum and cerebrum are graphically displayed in Figures 3 and 4. Concerning larval distribution in the right and left hemisphere, no significant differences were found between left and right parts of the brain within the infection groups at the different time points post infection. Significant differences between infection groups over the course of infection for cerebellum and cerebrum as well as right and left hemisphere are provided in Table 2.
Larval recovery rates in the cerebrum. Recovery rates in [%] of T. cati and T. canis larvae from the cerebrum based on the total larval number found in the brain of experimentally infected mice during different time points pi. Error bars indicate standard errors of the mean (SEM).
No changes were observed macroscopically or microscopically on day 2 pi in any of the brains. Starting day 7 pi, severe hemorrhages (Figure 5) were observed macroscopically in the brains of both T. canis and T. cati infected mice (Balb/c T. cati infected: 2/7 mice, 28.57%; B6 T. cati infected: 1/7 mice, 14.29%; B6 T. canis infected: 3/7 mice, 42.86%), which were also seen histopathologically (Figure 6a). Hemorrhages were mainly observed in the brain cortex and were more severe in T. canis than T. cati infected mice. As in lungs, hemorrhages were reabsorbed starting at day 14 pi and only observed sporadically during the subsequent course of infection. Histopathology revealed changes in brain structure in all infection groups; however, changes in T. canis infected mice were more severe than those in T. cati infected mice. From day 14 pi onwards, structural brain damage intensified in all infection groups, reaching a maximum of structural damage on the last study day 98 pi. It was apparent that structural damage was mainly observed in the cerebellum of T. cati infected mice whereas structural damage was also frequently observed in the cerebrum of T. canis infected mice. Histological changes included malacia (T. canis infected mice) with the presence of activated microglia and focal accumulation of gitter cells, which are phagocytic cells with the presence of myelin debris within the cytoplasm (myelinophages). Furthermore, occurrence of swollen axons (spheroids), indicative of axonal damage, was observed. Structural damage is shown exemplarily in Figure 6. The subjective impression was that T. canis infected mice started to exhibit slight balance problems starting around day 70 pi. Both T. canis and T. cati infected B6 mice seemed less aggressive day 98 pi when compared to earlier time points.
The frequent occurrence of T. cati larvae in the cerebellum as opposed to T. canis larvae in the cerebrum is rather surprising as previous studies demonstrated T. canis and T. cati larvae being predominantly present in the cerebellum [9, 10, 33, 38]. Eventually, different paratenic hosts could lead to the shift of distribution in the brain. Additionally, due to size difference, the cerebrum is supplied by a greater amount of blood compared to the cerebrum and therefore more T. canis larvae may arrest in the small cerebrum arteries. Nevertheless, data obtained correlate well with histopathology as several changes were found in cerebra of T. canis infected mice, however, most structural damage in T. cati infected mice was observed in the cerebellum. As the cerebellum controls complex motor functions, the predominant occurrence of T. cati larvae in the cerebellum may be explained by possible clinical consequences like an increase of immobility and behavioral alterations, e.g. spending more time in open areas. Consequently, paratenic hosts are an easier prey for final hosts of Toxocara spp. [26, 29, 44, 45].
The cerebrum -- which is just Latin for "brain" -- is thenewest (evolutionarily) and largest part of the brain as a whole. It is herethat things like perception, imagination, thought, judgment, anddecisionoccur.
The surface of the cerebrum -- the cerebral cortex -- iscomposedof six thin layers of neurons, which sit on top of a largecollection of white matterpathways. The cortex is heavily convoluted, so that if you were to spread itout, it would actually take up about 2 1/2 square feet (2500 sqcm). It includes about 10 billion neurons, with about 50 trillionsynapses!
The convolutions have "ridges" which are called gyri(singular:gyrus), and "valleys" which are called sulci (singular: sulcus). Someofthesulciarequitepronounced and long, and serve asconvenientboundaries between four areas of the cerebrum called lobes.
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