เรื่องสีเทา prefrontal Smaller prefrontal gray matter volumes in individuals diagnosed
ขนาดเล็กปริมาณในบุคคลที่ได้รับการวินิจฉัยว่าเป็นโรคจิตเภทปรากฏจะเป็นเพราะneuropil เยื่อหุ้มสมองน้อย with schizophrenia appear to be due to less cortical neuropil (i.e. small
(เช่นขนาดเล็กเพลาdendritic เงี่ยง dendritic, ซอนและอาคารซอน; Selemon dendritic shafts, dendritic spines, axons and axon terminals; Selemon
และโกลด์แมน-Rakic, 1999) และไม่ให้เซลล์เยื่อหุ้มสมองน้อย (Akbarian & Goldman-Rakic, 1999), and not to fewer cortical neurons (Akbarian
et อัล, 1995;.. Thune, et al, 2001) neuropil ลดลงใน DLPFC ปรากฏขึ้นเพื่อสะท้อนให้เห็นน้อยลงขั้วซอนที่แนะนำโดยผลการวิจัยในการศึกษาชันสูตรของโรคจิตเภทของระดับที่ต่ำกว่าของโปรตีนที่อยู่ในขั้วซอน(Glantz และลูอิส 1997) และน้อยเงี่ยงdendritic (Garey et al, , 1998; Glantz และลูอิส, 2000) et al., 1995; Thune et al., 2001). The reduced neuropil in the DLPFC
appears to reflect fewer axon terminals, as suggested by findings in
post mortem studies of schizophrenia of lower levels of proteins
present in axon terminals (Glantz & Lewis, 1997), and of fewer
dendritic spines (Garey et al., 1998; Glantz & Lewis, 2000). These
alterations appear to be particularly pronounced in layer 3. For
example, in the DLPFC of subjects with schizophrenia, basilar
dendritic spine density was significantly lower on deep layer 3
pyramidal cells relative to both normal and psychiatrically ill
comparison subjects, but spine density was only modestly lower on
superficial layer 3 pyramidal neurons and unchanged on pyramidal
neurons in layers 5 and 6 (Glantz & Lewis, 2000; Kolluri et al., 2005).
Consistent with these findings, the mean somal volume of layer 3
pyramidal neurons was smaller in subjects with schizophrenia in the
DLPFC and in other cortical regions (Arnold et al., 1995; Rajkowska
et al., 1998; Pierri et al., 2001; Sweet et al., 2003), whereas the
volume of layer 5 pyramidal neurons was unchanged (Sweet et al.,
2004). Importantly, none of these findings appeared to be attributable
to medication use or length of illness (Lewis & Gonzalez-Burgos,
2008).
In addition to these alterations in excitatory pyramidal neurons,
multiple studies have reported alterations in markers of inhibitory caminobutyric
acid (GABA) neurotransmission. For example, lower
levels of the mRNA for the 67-kDa isoform of the GABA synthesizing
enzyme glutamic acid decarboxylase (GAD67) have
been consistently found in the DLPFC of subjects with schizophrenia
(Gonzalez-Burgos et al., 2010). This deficit in GAD67 mRNA
appears to be particularly pronounced in the subset of DLPFC GABA
neurons that express the calcium-binding protein parvalbumin (PV), as
about 50% of PV neurons lacked detectable levels of GAD67 mRNA
in individuals with schizophrenia (Hashimoto et al., 2003). Importantly,
the number of PV neurons in the DLPFC appears to be
unchanged (Lewis et al., 2005), although the expression of PV mRNA
per neuron is decreased (Hashimoto et al., 2003). The latter finding, in
addition to methodological confounds, appears to explain the reports in some studies of a lower density of cortical PV-immunoreactive
neurons in schizophrenia (Stan & Lewis, 2012).
PV neurons can be subdivided into two major classes based on the
principal target of their axon terminals. The axon terminals from the
basket cell class of PV neurons target the cell body and proximal
dendrites of pyramidal neurons. Both pre- and postsynaptic alterations
in PV basket cell–pyramidal cell connectivity in the DLPFC,
especially in layer 3, appear to be present in schizophrenia. First,
the density of PV-labeled axon terminals, presumably from basket
neurons, is reduced in DLPFC layer 3 in schizophrenia (Lewis et al.,
2012). Second, the level of GAD67 protein is markedly lower in these
terminals (Curley et al., 2011), suggesting that basket cells represent
the population of PV neurons with undetectable levels of GAD67
mRNA (Hashimoto et al., 2003). Third, mRNA expression of the
GABAA receptor a1 subunit, which is postsynaptic to PV basket cell
inputs, is preferentially lower in layer 3 in schizophrenia (Beneyto
et al., 2011), and this deficit is selective for pyramidal neurons and is
not present in GABA neurons (Glausier & Lewis, 2011).
The other major class of PV neurons, chandelier cells, gives rise to
axon terminals that form distinctive vertical arrays, termed cartridges,
which exclusively target the axon initial segments (AIS) of pyramidal
neurons. In the DLPFC of subjects with schizophrenia, the density of
cartridges immunoreactive for the GABA membrane transporter
(GAT1) is lower than comparison subjects (Woo et al., 1998),
whereas the density of pyramidal cell AIS immunoreactive for the
GABAA receptor a2 subunit, the dominant GABAA receptor a subunit
present in pyramidal cell AIS in layer 3, is markedly increased (Volk
et al., 2002). In addition, the density of AIS immunoreactive for
ankyrin-G, a protein that plays a key role in the structure and plasticity
of the AIS, is also lower in the DLPFC in schizophrenia (Cruz et al.,
2009). Importantly, both the chandelier and PV basket cell alterations
appear to be specific to the disease process of schizophrenia as they
are not observed in individuals with other psychiatric disorders or in
monkeys exposed chronically to antipsychotic medications (Lewis
et al., 2012).
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