Serotonin transporter gene
Most of the 5-HTmolecules released into the synaptic cleft are
inactivated functionally by active transport of 5-HT from the
extracellular space into 5-HT terminals. The reuptake
mechanism allowing the same 5-HT molecule to be used
repeatedly is mediated by plasma membrane5-HT transporter
(SERT), which is expressed selectively on 5-HT neurons.
SERT terminates 5-HT action at the synapse and represents
one of the key regulators of 5-HT-ergic activity providing
effective control over the intensity 5-HT-mediated signaling.(
52,53) Deletion of SERT in knockout mice produces a
reduction in aggressive behavior: SERT-knockout males in
resident-intruder test have longer latency before attacking the
intruder and the number of attacks was decreased compared
to control mice.(54)
5-HT receptor genes and aggressive behavior
Another group of proteins that belong to the brain 5-HTsystem
is the 5-HT receptor superfamily. In recent decades, 14
different subtypes of 5-HT receptors were described, which
were subdivided in seven families based on operational (drugrelated),
transductional (receptor coupling), and structural
(primary amino acid sequence) characteristics. All 5-HT
receptors except one (5-HT3 type) are metabotropic Gprotein-
coupled receptors; structurally and functionally distinct
from all the other 5-HTreceptor types, the 5-HT3 receptor is an
ionotropic ligand-gated ion-channel receptor.
Among an impressive variety of cloned and identified 5-HT
receptors, particular attention has focused on the 5-HT1A
receptor. This attention has been due to the available selective
agonists and antagonists of the 5-HT1A receptor and the data
on its involvement in the control of (i) anxiety and depression,(
55–58) (ii) the autoregulation of 5-HT neurons in the
brain(59) and (iii) pharmacological data suggesting that 5-HT1A
receptor function is linked to aggression. An inhibitory effect of
5-HT1A receptor agonists on agonistic and social behavior in
mice and rats was shown.(60–64)
Considerable differences in 5-HT1A receptorswere found in
Norway rats bred for high aggression and for lack of aggressive
reactions to man.(65) 5-HT1A receptor density, the receptor
mRNAexpression in brain structures and functional correlates
for 5-HT1A receptors identified as 5-HT1A agonist 8-OH-DPATinduced
hypothermia and lower lip retraction (LLR) were
studied. A significant decrease in Bmax of specific receptor
binding of [3H]8-OH-DPAT in the frontal cortex, hypothalamus
and amygdala as well as a reduction in 5-HT1A receptor mRNA
expression in the midbrain of aggressive rats were found. 5-
HT1A receptor agonist 8-OH-DPAT (0.5 mg/kg, i.p.) produced a
distinct hypothermic reaction in nonaggressive rats and did not
affect significantly the body temperature in aggressive rats.
Similar differences were revealed in 8-OH-DPAT-induced LLR:
LLR was much more strongly expressed in nonaggressive
than in aggressive animals.
Hence, genetically defined low aggressiveness was shown
to be associated both with increased expression of 5-HT1A
receptor mRNA in the midbrain, their density in some brain
regions and functional activity of 5-HT1A receptors, suggesting
an important role of the 5-HT1A receptor in the aggressive
behavior suppression. This suggestion is in good agreement
with pharmacological studies demonstrating inhibitory effects
of 5-HT1A receptor agonists on different models of aggressive
behavior in mice and rats. Moreover, our data are consistent
with the studies carried out in man:
* an inverse correlation between response to 5-HT1A
receptor agonist ipsapirone and aggression in man was
shown: the subjects with a blunted neuroendocrine
response to ipsapirone challenge had significantly higher
self-ratings of aggressivity/(66). Furthermore, there was a
significant negative correlation found between binding
potential of 5-HT1A receptors measured by positron
emission tomography and lifetime aggression;(67)a correlation
of reduced 5-HT1A receptor binding in temporal cortex
with aggressive behavior in Alzheimer disease has
been described by Lai et al.(68) These authors suggested
that 5-HT1A receptor Bmax represented the best predictor
for aggression.
The decreased sensitivity of 5-HT1A receptors and the
decreased 5-HT1A receptor density in the limbic system of
aggressive rats found in our experiments are to some extent in
accordance with similar results obtained on displaying
aggressive phenotype MAO A-knockout mice.(45)
Taken together, the evidence reviewed above suggests that
5-HT1A receptors in the limbic system of the brain may fulfill a
significant role in the expression of aggressiveness, and
inherited high or low aggressiveness may be determined, at
least partly, by the expression and density of 5-HT1A receptors
in the limbic system.
At the same time, 5-HT1A receptor knockout mice display
anxiety-related behavior,(57) but there are no indications of
increased aggression.(69) Among the possible explanations of
this apparent discrepancy is the fact that the gene knockout
technique is excellent for animal models of human hereditary
disease but itmay have some limitations for studying the role of
the gene in the physiology or behaviour of adult animals. There
are two reasons for this. (i) The genetic defect is present from
the earliest stage of ontogeny, throughout the growth of the
nervous system. Compensatory genes may take over the
function of the mutated gene, during the course of development;(
70) Therefore, at least some of the changes observed in
adult mice with genetic knockout may be caused by
disturbances of developmental processes and are not
associated with the functional role of the given gene in adult
organism. ((ii)The deficiency of the 5-HT1A-receptor gene in
knockout mice results in a complete elimination of functionally
distinct 5-HT1A receptors. It is well known that 5-HT1A
receptors are localized both presynaptically and postsynaptically,
and according to their localization, they exert different
effect on the functional state of the 5-HT system. The
stimulation of presynaptic receptors inhibits this system,
whereas stimulation of postsynaptic receptors produces
effects typical of the functional activation of the 5-HT system.
The greatest differences between aggressive and nonaggressive
rats are found in the brain areas where postsynaptic 5-
HT1A receptors are predominantly located, i.e. in the frontal
cortex, hypothalamus and amygdala. In these structures, the
density of 5-HT1A receptors was decreased in highly aggressive
rats. Thus, it can be proposed that, in mutant mice lacking
both types of 5-HT1A receptor, the deficiency of postsynaptic 5-
HT1A receptors in the limbic system can be counteracted by
the deficiency of presynaptic 5-HT1A receptors.
Enhanced aggressive behavior was revealed in 5-HT1B
receptor knockout mice.(71,72) Mice lacking the 5-HT1B
receptor attacked the intruder faster and more intensely than
wild-type mice: the attack latency decreased, and number of
attacks increased in 5-HT1B knockout mice. These findings
are supported by preclinical studies showing the attenuating
effect of 5-HT1B receptor agonists on aggression heightened
by social instigation, frustration or alcohol.(73–76) Importantly,
a linkage of aggressive and impulsive behavior due to
alcoholism with the 5-HT1B receptor gene was revealed in
two human populations—in Finnish alcoholic criminal offenders
and in a large multigenerational family from an American
Indian tribe.(77)
The data on other 5-HT receptors are rather scarce. A
selective 5-HT7-receptor agonist SB 269970 did not produce
any significant changes in isolation-induced agonistic encounters
between male mice, suggesting that 5-HT7-receptor
might not be involved in the modulation of aggression.(78) The
results of pharmacological analysis implicate 5-HT3 receptor
in the regulation of aggressive behavior and alcohol-heightened
aggression in mice,(79) and a cocaine-induced aggressive
response in hamsters.(80) At the same time, no changes
were found in alcohol-induced intermale aggression in HT3-
overexpressing mice (TG), and 5-HT3 antagonist zacopride
reduced aggression in both TG and wild-type mice.(79) It was
shown that 5-HT2A/2C receptor agonist a-methyl-5-hydroxytryptamine
microinjected into the periaqueductus gray matter
decreased maternal aggression in rats.(81) However, to date
there is no evidence concerning the role of these receptors in
genetic regulation of aggressive behavior.
Serotonin ขนส่งยีน5-HTmolecules ปล่อยเพดาน synaptic มียกเลิกฟังก์ชัน โดยการขนส่งการใช้งานของเอชที 5 จากการพื้นที่ extracellular เป็นเทอร์มินัลเอชที 5 การ reuptakeกลไกที่ทำให้โมเลกุล 5 เอชทีเดียวจะใช้ซ้ำ ๆ mediated โดยขนส่ง membrane5 เอชทีพลาสม่า(SERT), ซึ่งจะแสดงเรียงบน neurons เอชที 5ยุติการดำเนินการ 5 เอชทีที่ไซแนปส์ SERT และแสดงถึงเร็คกูเลเตอร์หลักกิจกรรม 5-เอชที-ergic ให้อย่างใดอย่างหนึ่งควบคุมที่มีประสิทธิภาพกว่าความเข้ม 5-เอชที-mediated ตามปกติ (สร้าง 52,53) การลบของ SERT ในหนูชนะน็อกโดยเทคนิคการลดพฤติกรรมก้าวร้าว: SERT น่าพิศวงชายในทดสอบผู้บุกรุกอาศัยมีแฝงยาวก่อนที่จะโจมตีการงานและจำนวนการโจมตีลดลงเมื่อเทียบการควบคุมหนู (54)ยีนตัวรับเอชที 5 และพฤติกรรมก้าวร้าวกลุ่มอื่นของโปรตีนที่อยู่ในสมอง 5-HTsystemsuperfamily เอชที 5 ตัวรับได้ ในทศวรรษล่าสุด 14subtypes ที่แตกต่างกันของ 5 เอชที receptors ได้อธิบาย ที่มีปฐมภูมิในครอบครัวเจ็ดตามปฏิบัติ (drugrelated),transductional (ตัวรับคลัป), และโครงสร้าง(กรดอะมิโนหลักลำดับ) ลักษณะการ ทั้งหมด 5-เอชทีreceptors ยกเว้นหนึ่ง (5 HT3 ชนิด) มี metabotropic Gprotein-receptors ควบคู่ แตกต่างกัน structurally และฟังก์ชันจากทั้งหมด 5 HTreceptor ชนิดอื่น ตัวรับ 5-HT3 เป็นการionotropic gated ลิแกนด์ไอออนช่องตัวรับในการโคลน และระบุ 5-เอชทีหลากหลายน่าประทับใจreceptors ความสนใจเฉพาะได้เน้น 5-HT1Aตัวรับ ความสนใจนี้ได้เนื่องจากการว่างงานagonists และตัวของข้อมูลและตัวรับ 5-HT1Aในการมีส่วนร่วมในการควบคุม (i) ความวิตกกังวล และภาวะซึมเศร้า (55-58) neurons (ii) autoregulation ของเอชที 5 ในการbrain(59) และ (iii) pharmacological ข้อมูลแนะนำที่ 5 HT1Aมีการเชื่อมโยงฟังก์ชันของตัวรับการรุกราน ลิปกลอสไขลักษณะพิเศษของ5 HT1A ตัวรับ agonists ในลักษณะ agonistic และสังคมในหนูและหนูที่แสดง (60 – 64)พบความแตกต่างมากใน receptorswere 5 HT1Aหนูนอร์เวย์ bred และ ขาดการก้าวร้าวรุกรานสูงปฏิกิริยากับมนุษย์ (65) 5 HT1A ตัวรับความหนาแน่น ตัวรับการคู่ mRNAexpression ในโครงสร้างของสมอง และการทำงานสำหรับ 5 HT1A receptors เป็น 5 HT1A อะโกนิสต์ 8-OH-DPATinducedhypothermia และล่าง lip retraction (LLR)ศึกษา ลดลงอย่างมีนัยสำคัญใน Bmax ของตัวรับเฉพาะการมัด [3H] 8-OH-DPAT ในคอร์เทกซ์หน้าผาก hypothalamusและ amygdala เป็นลดตัวรับ 5-HT1A mRNAนิพจน์สมองส่วนกลางของหนูก้าวร้าวพบ 5-HT1A ตัวรับอะโกนิสต์ 8-OH-DPAT (0.5 mg/kg, i.p.) ผลิตเป็นปฏิกิริยาแตกต่าง hypothermic ที่ nonaggressive หนู และไม่ผลอุณหภูมิร่างกายในหนูที่ก้าวร้าวมากความแตกต่างคล้ายถูกเปิดเผยใน LLR 8-OH-DPAT-เกิด:LLR was much more strongly expressed in nonaggressivethan in aggressive animals.Hence, genetically defined low aggressiveness was shownto be associated both with increased expression of 5-HT1Areceptor mRNA in the midbrain, their density in some brainregions and functional activity of 5-HT1A receptors, suggestingan important role of the 5-HT1A receptor in the aggressivebehavior suppression. This suggestion is in good agreementwith pharmacological studies demonstrating inhibitory effectsof 5-HT1A receptor agonists on different models of aggressivebehavior in mice and rats. Moreover, our data are consistentwith the studies carried out in man:* an inverse correlation between response to 5-HT1Areceptor agonist ipsapirone and aggression in man wasshown: the subjects with a blunted neuroendocrineresponse to ipsapirone challenge had significantly higherself-ratings of aggressivity/(66). Furthermore, there was asignificant negative correlation found between bindingpotential of 5-HT1A receptors measured by positronemission tomography and lifetime aggression;(67)a correlationof reduced 5-HT1A receptor binding in temporal cortexwith aggressive behavior in Alzheimer disease hasbeen described by Lai et al.(68) These authors suggestedthat 5-HT1A receptor Bmax represented the best predictorfor aggression.The decreased sensitivity of 5-HT1A receptors and thedecreased 5-HT1A receptor density in the limbic system ofaggressive rats found in our experiments are to some extent in
accordance with similar results obtained on displaying
aggressive phenotype MAO A-knockout mice.(45)
Taken together, the evidence reviewed above suggests that
5-HT1A receptors in the limbic system of the brain may fulfill a
significant role in the expression of aggressiveness, and
inherited high or low aggressiveness may be determined, at
least partly, by the expression and density of 5-HT1A receptors
in the limbic system.
At the same time, 5-HT1A receptor knockout mice display
anxiety-related behavior,(57) but there are no indications of
increased aggression.(69) Among the possible explanations of
this apparent discrepancy is the fact that the gene knockout
technique is excellent for animal models of human hereditary
disease but itmay have some limitations for studying the role of
the gene in the physiology or behaviour of adult animals. There
are two reasons for this. (i) The genetic defect is present from
the earliest stage of ontogeny, throughout the growth of the
nervous system. Compensatory genes may take over the
function of the mutated gene, during the course of development;(
70) Therefore, at least some of the changes observed in
adult mice with genetic knockout may be caused by
disturbances of developmental processes and are not
associated with the functional role of the given gene in adult
organism. ((ii)The deficiency of the 5-HT1A-receptor gene in
knockout mice results in a complete elimination of functionally
distinct 5-HT1A receptors. It is well known that 5-HT1A
receptors are localized both presynaptically and postsynaptically,
and according to their localization, they exert different
effect on the functional state of the 5-HT system. The
stimulation of presynaptic receptors inhibits this system,
whereas stimulation of postsynaptic receptors produces
effects typical of the functional activation of the 5-HT system.
The greatest differences between aggressive and nonaggressive
rats are found in the brain areas where postsynaptic 5-
HT1A receptors are predominantly located, i.e. in the frontal
cortex, hypothalamus and amygdala. In these structures, the
density of 5-HT1A receptors was decreased in highly aggressive
rats. Thus, it can be proposed that, in mutant mice lacking
both types of 5-HT1A receptor, the deficiency of postsynaptic 5-
HT1A receptors in the limbic system can be counteracted by
the deficiency of presynaptic 5-HT1A receptors.
Enhanced aggressive behavior was revealed in 5-HT1B
receptor knockout mice.(71,72) Mice lacking the 5-HT1B
receptor attacked the intruder faster and more intensely than
wild-type mice: the attack latency decreased, and number of
attacks increased in 5-HT1B knockout mice. These findings
are supported by preclinical studies showing the attenuating
effect of 5-HT1B receptor agonists on aggression heightened
by social instigation, frustration or alcohol.(73–76) Importantly,
a linkage of aggressive and impulsive behavior due to
alcoholism with the 5-HT1B receptor gene was revealed in
two human populations—in Finnish alcoholic criminal offenders
and in a large multigenerational family from an American
Indian tribe.(77)
The data on other 5-HT receptors are rather scarce. A
selective 5-HT7-receptor agonist SB 269970 did not produce
any significant changes in isolation-induced agonistic encounters
between male mice, suggesting that 5-HT7-receptor
might not be involved in the modulation of aggression.(78) The
results of pharmacological analysis implicate 5-HT3 receptor
in the regulation of aggressive behavior and alcohol-heightened
aggression in mice,(79) and a cocaine-induced aggressive
response in hamsters.(80) At the same time, no changes
were found in alcohol-induced intermale aggression in HT3-
overexpressing mice (TG), and 5-HT3 antagonist zacopride
reduced aggression in both TG and wild-type mice.(79) It was
shown that 5-HT2A/2C receptor agonist a-methyl-5-hydroxytryptamine
microinjected into the periaqueductus gray matter
decreased maternal aggression in rats.(81) However, to date
there is no evidence concerning the role of these receptors in
genetic regulation of aggressive behavior.
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