Brain Development: Normal Processes and the Effects of Alcohol ...

12 NORMA L DEVELOPMENT
and apparentl y permanen t precurso r poo l calle d th e
subgranular, or intrahilar zone (IHZ) (Angevine, 1965 ;
Stanfield an d Cowan , 1979 ; Altman and Bayer , 1990) .
The IH Z is the sourc e o f the majorit y of granule neu -
rons of the dentate gyru s later in development, including
adult life (Angevine , 1965 ; Bayer , 1982 ; Camero n
et al, 1993 ; Gag e et al, 1998 ; va n Praag et al, 2002 ;
Kempermann et al., 2004).
Although th e architectoni c an d cytokineti c subdivisions
mentioned above appea r i n nearly all parts of
the developin g telencephalon , considerable regiona l
variation occur s i n term s o f the siz e o f the differen t
FIGURE 2- 2 Regiona l difference s i n the siz e of the cytoarchitectoni c compart -
ments i n th e developin g brain . A histologica l sectio n i n th e corona l plan e
though th e hea d o f an 11-day-ol d mouse fetus is shown. The fetu s was exposed
to th e S-phas e marke r bromodeoxyuridine (BrdU ) fo r 6 hours; Brd U was injected
int o th e pregnan t da m an d th e fetu s wa s harvested 6 hours later . Th e
section wa s processe d immunohistochemicall y t o revea l th e distributio n o f
BrdU i n proliferatin g cells. BrdU-labele d cell s appear dar k and surroun d th e
ventricular cavities of the brain (empty space at the center o f the micrograph).
The compartment s o f the telencephalo n visibl e a t thi s corona l leve l ar e th e
hippocampus (HIP) , cerebra l neocortica l wal l (CX) , latera l ganglioni c emi -
nence (LGE) , and medial ganglionic eminence (MGE) . O n the left-hand side ,
the broken line marks the approximate boundar y between th e ventricular zon e
(VZ) and the subventricular zone (SZ), and the solid line marks the boundary
between th e S Z and the intermediat e zon e (IZ) . The broke n line i s drawn on
the basi s of difference s i n th e packin g densit y and dispositio n o f the BrdU -
labeled cell s (highe r densit y i n th e VZ , aligne d i n compariso n t o th e SZ ,
which has a lower density of BrdU-labeled cell s that are randomly distributed) .
The soli d line is at the boundary between BrdU-labele d (precursor ) and unla -
beled (nonproliferatin g or differentiating) cells . A relatively large VZ, SZ , and
IZ area i s in the ganglioni c regio n (LG E an d MGE ) compare d t o that i n th e
dorsal C X an d hippocampa l anlag e (HIP) , eve n a t thi s earl y stage o f brain
development. Th e higher-magnificatio n image s (right ) sho w th e histolog -
ical divisions of VZ, SZ, and PPZ in the different telencepahlic compartments .
The primordi a of eyes (EYE) are also visible in this section. (Source: Modifie d
from Shet h and Bhide, 1997 )