الفهرس 
Subventricular zone (SVZ)Only 14 pages are availabe for public view
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Abstract
ackground: Neurogenesis is the production of new neurons from neural
stem cells. It can occur in postnatal life in all mammals in two main areas; the
subgranular zone of hippocampus from which newly formed neurons migrate
into the granule cell layer of the dentate gyrus and the subventricular zone of
lateral ventricle from which newly formed neurons migrate along the rostral
migratory stream to the olfactory bulb. The aim of this histological study was
the evaluation of the effect of enriched environment on the postnatal and
adult neurogenesis in the subventricular zone (SVZ) of the lateral ventricle in
male albino rat. In addition, this work traced the newly formed neurons
through the rostral migratory stream (RMS) to the olfactory bulb (OB).
Material and methods: Sixty male albino rats of different ages were
used in the present study and were divided into two groups; control group
and enriched environment group. Control group included 30 rats which were
put in standard cages all over the experiment and was subdivided according
to their ages into three subgroups (n=10 each). Postnatal control subgroup
(IA) one-day age were put in standard cages for three weeks. Adult control
subgroup (IB) three months’ age were put in standard cages for another three
months. Old age control subgroup (IC); ten months’ age were put in standard
cages for another ten months. Enriched environment group (included 30 rats)
was subdivided according to their ages into three subgroups IIA, IIB, IIC
(n=10 each) with the same ages of control subgroups and were put in
enriched environment cages with larger dimensions for the same periods as
the control ones.
For detection of proliferating cells in SVZ, rats were injected 2 hours before
scarification with BrdU and for detection of migrating cells in RMS and
differentiating cells in OB; rats were injected with BrdU labelling for 3consecutive days then sacrificed 10-12 days after the last injection. Tissue
specimens were collected and processed for histological study (by light and
transmission electron microscopes) and immunohistochemical study (by
GFAP and Anti BrdU stains). The collected data in the control and enriched
environment subgroups were statistically analysed for comparison.
Results: Histological and electron microscopic examination of the SVZ
revealed its site inferolateral to the lateral ventricle. It occupied smaller area
with reduced cellular density in adult than postnatal control subgroup and
appeared as narrow faint area with great reduction in cellular density in old
age control subgroup. However, it represented larger area in each enriched
subgroup when compared with its control one. Degenerative changes were
observed in all cells of SVZ with aging in the form of flattening of
ependymal cells with reduced cilia, small darkly stained nuclei, destructed
cristae of mitochondria, reduced cytoplasmic volume and increased
extracellular spaces between type A cells which were smaller in size and
fewer in number. Some nuclei of type A neuroblasts exhibited pyknosis and
type C transit amplifying cells revealed small irregular nuclei and vacuolated
cytoplasm. Whereas, type B astrocytes exhibited heterochromatic nuclei with
perinuclear halos and destructed mitochondria with absent cristae. All these
findings were more obvious in old age control subgroup. Whereas, enriched
subgroups showed increased number of all types of SVZ cells with less
degenerative changes as compared with their control ones.
GFAP stained sections showed strong reaction in postnatal subgroup
that appeared weaker in adult and old age control subgroups as there was
highly significant decrease in the number of GFAP +ve cells in old age
control subgroup when compared with postnatal and adult control subgroups.
Whereas, adult control subgroup revealed significant decrease in the number
of GFAP +ve cells in comparison to postnatal control one.