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Steroid-sensitive, vocal courtship behavior is a function of a specific, hypothalamic nucleus, the sexually dimorphic area pars compacta (SDApc) in the male adult gerbil. Gender-related differences in the number of neurons in this nucleus are evident immediately after birth. By using unbiased stereological estimates of cell numbers in Nissl-stained, paraffin-wax sections of brain, we investigated the mechanisms differentiating cell number between the sexes in the SDApc on postnatal days 0, 3, 6, and 15. Cell death, identified by pyknosis, was greatest in the SDApc between days 0-3 in males, whereas in females, maximum values were reached between days 3-6. Similarly, the ratio of pyknotic to normal neurons peaked between days 0-3 in males and 3-6 in females but then declined in both sexes. Pyknotic cells were seldom seen in either sex by day 15. Morphological characteristics of apoptosis including chromatin condensation, cell fragmentation, and ingestion of apoptic bodies by macrophages were all demonstrated by transmission electron microscopy. Macrophages showed specific morphological characteristics of microglia. Cell division (mitosis) was identified in the SDApc during postnatal days 0, 3, and 6 but the numbers of mitotic figures were low, negligible on day 15, and similar between the sexes. These results demonstrate that cell death and proliferation occur simultaneously in the neonatal gerbil brain. The stereological estimates of cell death in the developing SDApc indicated a lower incidence of neuronal death occurring earlier in males than in females. (C) 1996 Wiley-Liss, Inc
Adult. --- Androgens. --- Area. --- Behavior. --- Birth. --- Brain. --- Cell-death. --- Courtship behavior. --- Cytoarchitecture. --- Death. --- Degeneration. --- Development. --- Differentiation. --- Female. --- Females. --- Function. --- Gerbil. --- Gerbils. --- Male. --- Males. --- Mechanisms. --- Medial preoptic area. --- Mitosis. --- Neonatal. --- Nervous-system. --- Neuronal death. --- Neuronal. --- Neurons. --- Nucleus. --- Pars compacta. --- Postnatal-development. --- Pyknosis. --- Rat-brain. --- Sex-differences. --- Sex. --- Sexes. --- Sexually dimorphic area. --- Time. --- Transmission. --- Vocal function.
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The mammalian brain has a high degree of plasticity, with dentate granule cell neurogenesis(1) and glial(2,3) proliferation stimulated by an enriched environment combining both complex inanimate and social stimulation. Moreover, rodents exposed to an enriched environment both before and after a cerebral insult show improved cognitive performance(1,4). One of the most robust associations of environmental enrichment is improved learning and memory in the Morris water maze, a spatial task that mainly involves the hippocampus(5). Furthermore, clinical evidence showing an association between higher educational attainment and reduced risk of Alzheimer(6) and Parkinson-related dementia(7) indicates that a stimulating environment has positive effects on cerebral health that may provide some resilience to cerebral insults. Here we show that in addition to its effects on neurogenesis, an enriched environment reduces spontaneous apoptotic cell death in the rat hippocampus by 45%. Moreover, these environmental conditions protect against kainate-induced seizures and excitotoxic injury. The enriched environment induces expression of glial-derived neurotrophic factor and brain-derived neurotrophic factor and increases phosphorylation of the transcription factor cyclic-AMP response element binding protein, indicating that the; influence of the environment on spontaneous apoptosis and cerebral resistance to insults may be mediated through transcription factor activation and induction of growth factor expression
Activation. --- Adult-rat. --- Association. --- Brain. --- Cell-death. --- Death. --- Enriched environment. --- Enriched. --- Enrichment. --- Environment. --- Environmental enrichment. --- Expression. --- Fibroblast growth-factor. --- Generated granule cells. --- Growth. --- Health. --- Hippocampal-neurons. --- Hippocampus. --- Increase. --- Increases. --- Induction. --- Injuries. --- Injury. --- Learning. --- Memory. --- Morris water maze. --- Neurogenesis. --- Neurotrophic factor. --- Nmda receptor activation. --- Phosphorylation. --- Plasticity. --- Progenitor cells. --- Protein. --- Rat dentate gyrus. --- Rat hippocampus. --- Rat. --- Resistance. --- Response. --- Risk. --- Rodent. --- Rodents. --- Seizure. --- Seizures. --- Social. --- Spatial task. --- Spatial. --- Stimulation. --- Task. --- Transcription.
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