NEURAL REGENERATION RESEARCH
Volume 7, Issue 18, June 2012
Cite this article as: Neural Regen Res. 2012;7(18):1378-1385.
1378 Qiuling Xu☆, M.D., Associate professor, Hainan Medical University, Haikou 571101, Hainan Province, China
Corresponding author: Junling Liu, Professor, Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China
junling_liu@https://www.doczj.com/doc/712598215.html,
Received: 2012-02-22 Accepted: 2012-05-03
(N20110419003/WJ)
Xu QL, Liu T, Chen SP, Gao YH, Wang JY, Qiao LN, Liu JL. The cumulative analgesic effect of repeated electroacupuncture involves synaptic remodeling in the hippocampal CA3 region. Neural Regen Res.
2012;7(18):1378-1385.
https://www.doczj.com/doc/712598215.html,
https://www.doczj.com/doc/712598215.html,
doi:10.3969/j.issn.1673-5374. 2012.18.003
The cumulative analgesic effect of repeated electroacupuncture involves synaptic remodeling in the hippocampal CA3 region******☆
Qiuling Xu1, Tao Liu1, Shuping Chen2, Yonghui Gao2, Junying Wang2, Lina Qiao2, Junling Liu2
1Hainan Medical University, Haikou 571101, Hainan Province, China
2Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China Abstract
In the present study, we examined the analgesic effect of repeated electroacupuncture at bilateral
Zusanli (ST36) and Yanglingquan (GB34) once a day for 14 consecutive days in a rat model of
chronic sciatic nerve constriction injury-induced neuropathic pain. In addition, concomitant changes
in calcium/calmodulin-dependent protein kinase II expression and synaptic ultrastructure of neurons
in the hippocampal CA3 region were examined. The thermal pain threshold (paw withdrawal latency)
was increased significantly in both groups at 2 weeks after electroacupuncture intervention
compared with 2 days of electroacupuncture. In ovariectomized rats with chronic constriction injury,
the analgesic effect was significantly reduced. Electroacupuncture for 2 weeks significantly
diminished the injury-induced increase in synaptic cleft width and thinning of the postsynaptic
density, and it significantly suppressed the down-regulation of intracellular calcium/
calmodulin-dependent protein kinase II expression in the hippocampal CA3 region. Repeated
electroacupuncture intervention had a cumulative analgesic effect on injury-induced neuropathic
pain reactions, and it led to synaptic remodeling of hippocampal neurons and upregulated
calcium/calmodulin-dependent protein kinase II expression in the hippocampal CA3 region.
Key Words
chronic neuropathic pain; acupuncture analgesia; cumulative effect; synaptic plasticity;
hippocampal CA3 region; calcium/calmodulin-dependent protein kinase II; neurobiology;
electroacupuncture; neural regeneration
Abbreviations
CaMKII, calcium/calmodulin-dependent kinase II; CCI, chronic constrictive injury; OVX,
ovariectomized; PWL, paw withdrawal latency
INTRODUCTION
Functional changes in pain states have been a focus of many studies[1-3], but little attention has been paid to the fact that tremendous potential for plasticity exists in the pathways for pain at the structural and representational levels. The hippocampus is a target of stress-induced hormones, such as adrenal glucocorticoids, which modulate changes in synapse formation and dendritic structure, acutely and over the long-term[4-6]. Clinical studies revealed that the
hippocampus is involved in processing
physiological pain and also in the
development of pain syndromes[7-8].
Furthermore, experimental studies have
demonstrated that hippocampal synaptic
plasticity is associated with learning,
memory and adaptive processes, and is
accompanied by changes in expression of a
variety of genes and proteins[9-10]. For
example, calcium/calmodulin-dependent
kinase II (CaMKII) is a multifunctional
serine/threonine protein kinase in neurons
https://www.doczj.com/doc/712598215.html,
and functions in regulating neurotransmission, memory and synaptic plasticity in response to calcium signaling produced by neuronal activity[11-13]. Hippocampal CaMKII is also involved in the development of persistent pain in both mice and rats[14-15].
It has been demonstrated that repeated electroacupuncture at Zusanli (ST36) and Baihui (GV20) significantly increases the number of well-developed (tertiary) dendrites in the subgranular zone of the dentate gyrus and promotes neuroblast differentiation via phosphorylated cAMP response element binding protein and brain-derived neurotrophic factor activation in the dentate gyrus in normal rats[16-17]. Electroacupuncture also mitigates the cerebral ischemia-induced decrease in amplitude and slope rate of population spikes in the hippocampal CA1 region in rats with diabetes mellitus[18]. However, no study has determined whether hippocampal CaMKII plays a role in acupuncture analgesia, particularly as Zusanli and Yanglingquan (GB34) are clinically frequently used to treat sciatica[19-20].
Our previous studies[21-23] demonstrated that, in chronic constrictive injury (CCI) of the sciatic nerve in rats, repeated electroacupuncture intervention effectively relieved neuropathic pain. Concomitantly, upregulation of plasma cortisol, beta-endorphin and adrenocorticotropin hormone levels, and increased expression of hippocampal intracellular protein kinase A were found. In ovariectomized (OVX) + CCI rats, the analgesic effect of repeated electroacupuncture was significantly weakened, suggesting a close association between analgesic effect and estrogen levels. Thus, repeated electroacupuncture-induced pain relief may involve modulation of hippocampal neuronal plasticity by various hormones and neurotransmitters.
Biologically, functional activity and structure are closely related. Thus, functional changes are often accompanied by structural alterations. However, the relationship between the analgesic effects of electroacupuncture and changes in neuronal plasticity in the hippocampus remains poorly understood. The present study was designed to analyze the relationship between the analgesic effect of repeated electroacupuncture and hippocampal synaptic plasticity in ovariectomized rats with CCI of the sciatic nerve.
RESULTS
Quantitative analysis of experimental animals
A total of 98 female Wistar rats were randomized into normal control, CCI (ligation of the sciatic nerve), CCI + electroacupuncture 2 days, CCI + electroacupuncture 2 weeks, OVX + CCI, OVX + CCI + electroacupuncture 2 days and OVX + CCI + electroacupuncture 2 weeks groups, with 14 animals in each group. T en rats from each group were used for behavioral and immunohistochemistry experiments, and four were used for electron microscopy.
The CCI model of chronic neuropathic pain was employed in the CCI, CCI + electroacupuncture 2 days, CCI + electroacupuncture 2 weeks, CCI + OVX, CCI + OVX + electroacupuncture 2 days and the CCI + OVX + electroacupuncture 2 weeks groups. The OVX model of learning and memory impairment was applied in the
CCI + OVX, CCI + OVX + electroacupuncture 2 days and the CCI + OVX + electroacupuncture 2 weeks groups before establishment of chronic neuropathic pain. Rats in the electroacupuncture 2 days and electroacupuncture 2 weeks groups were subjected to electroacupuncture at Zusanli and Yanglingquan from the 16th day and 4th day after surgery, respectively (i.e. electroacupuncture lasted for 2 days and 2 weeks, respectively). Three rats in the CCI + OVX group died during ovariectomization. Therefore, 98 rats were included in the final analysis following supplementation.
Electroacupuncture decreases pain reaction after CCI
The pain threshold was measured as paw withdrawal latency (PWL; PWL of the healthy limb - PWL of the affected limb). Pain scores were significantly greater in the CCI and OVX + CCI rat groups compared with the normal control group (P < 0.05), suggesting a decreased pain threshold. The pain scores were significantly less in the CCI + electroacupuncture 2 weeks group and OVX + CCI + electroacupuncture 2 weeks group compared with the CCI and OVX + CCI groups (P < 0.05). The pain score was significantly increased in the OVX + CCI + electroacupuncture 2 weeks group compared with the CCI + electroacupuncture 2 weeks group (P < 0.05;
T able 1).
Electroacupuncture reduces synaptic cleft width between hippocampal neurons
Compared with the normal control group, the synaptic cleft width was significantly increased in the CCI and OVX + CCI groups (P < 0.05). The synaptic cleft width was significantly decreased in the CCI + electroacupuncture 2 weeks group compared with the CCI group (P < 0.05), but the width remained unchanged in the CCI + electroacupuncture 2 days group. Compared with the OVX + CCI group, synaptic cleft width was reduced remarkably in the OVX + CCI + electroacupuncture 2 weeks group (P < 0.05). The synaptic cleft width was significantly increased in the OVX + CCI + electroacupuncture 2 weeks group compared with the CCI + electroacupuncture 2 weeks group (P < 0.05; Figure 1).
1379
1380
Electroacupuncture increases postsynaptic density of hippocampal neurons Postsynaptic density values were significantly decreased in the CCI and OVX + CCI groups compared with the normal control group (P < 0.05), suggesting deterioration of excitatory signal transmission. The postsynaptic density value was significantly increased in the CCI +
electroacupuncture 2 weeks group compared with the CCI group (P < 0.05), and it was significantly increased
in the OVX + CCI + electroacupuncture 2 weeks group
compared with the OVX + CCI group (P < 0.05). No
significant differences were found between the CCI and CCI + electroacupuncture 2 days groups or between the OVX + CCI and OVX + CCI + electroacupuncture 2 days groups (P > 0.05). The postsynaptic density value was
significantly less in the OVX + CCI + electroacupuncture
2 weeks group than in the CCI + postsynaptic 2 weeks group (P < 0.05; Figure 2).
Electroacupuncture increases synaptic active zone length in hippocampal neurons Compared with the control group, the active zone length values for the CCI and OVX + CCI groups were significantly decreased (P < 0.05). The synaptic active zone length was significantly longer in the CCI + electroacupuncture 2 weeks group compared with the CCI group, and in the OVX + CCI + electroacupuncture 2 weeks group compared with the OVX + CCI group (both P < 0.05), suggesting an improvement of synaptic efficacy after repeated electroacupuncture. The active
zone length was significantly greater in the CCI +
electroacupuncture 2 weeks group compared with the OVX + CCI + electroacupuncture 2 weeks group (P < 0.05). No significant differences were found between the CCI and CCI + electroacupuncture 2 days groups or between the OVX + CCI and OVX + CCI + electroacupuncture 2 days groups in active zone length (both P > 0.05; Figure 3).
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Electroacupuncture upregulates CaMKII expression in the hippocampal CA3 region
CaMKII is an important calcium messenger regulating hippocampal synaptic plasticity and learning. The integral grey values of CaMKII expression were
significantly increased in the CCI and OVX + CCI groups compared with the normal control group (P < 0.05), a downregulation of this protein in CCI and OVX + CCI rats. Compared with the CCI group, the integral grey value was significantly lower in the CCI + electroacupuncture 2 weeks group compared with the CCI group (P < 0.05), but remained unchanged in the CCI +
electroacupuncture 2 days group. The change in CaMKII expression in CCI rats was similar to that in OVX + CCI rats. The integral grey value of CaMKII immunoreactivity was significantly higher in the OVX + CCI +
electroacupuncture 2 weeks group compared with the CCI + electroacupuncture 2 weeks group (P < 0.05). Collectively, these results indicate that
electroacupuncture upregulates CaMKII expression in the hippocampal CA3 region (Figure 4).
DISCUSSION
Synaptic plasticity, including changes in synapse number, structure and transmission efficacy, is the basis of neural plasticity. Sensory neurons undergo functional, chemical and structural changes (activity and signaling
molecule-dependent) in response to changes in their environment (including chronic nociceptive pain) that modify transduction, conduction and transmission efficiency [24]. McEwen [25] observed that after chronic constriction injury of the sciatic nerve in rats, the hippocampus exhibits structural plasticity, involving
ongoing neurogenesis of the dentate gyrus,
synaptogenesis under control of estrogens in the CA1 region and dendritic remodeling caused by repeated stress or elevated levels of exogenous glucocorticoids in the CA3 region. Peripheral nerve injury (e.g . CCI) may also increase hippocampal postsynaptic density and synaptic cleft area [26] or decrease hippocampal synaptic interface curvature in the rat [27]. Chronic pain is also a type of chronic stress. Under chronic stress conditions, significant decreases in hippocampal synaptic density and surface density were found [28].
At the spinal level, peripheral nerve injury may result in higher synaptic density or number and increase the percentage of positively curved synapses [29-30]. It may also lead to synaptic interface curvature and synaptic perforation in the dorsal horn of the spinal cord [31]. This morphological rearrangement may alter the organism’s capacity for pain perception or result in abnormal sensory processing (as in tactile allodynia) as an
adaptive and protective response [25, 32-33]. CaMKII plays an important role in peripheral stimulation-induced neural plasticity in the hippocampus [34-35].
The synaptic cleft (a space between the presynaptic terminals and postsynaptic membrane) is a space for transmitting action potentials and chemical transmitters. The postsynaptic density is a protein-dense
specialization attached to the postsynaptic membrane, serving as a signaling apparatus. The synaptic active zone is a unique presynaptic membrane specialization that is believed to be the site of neurotransmitter release. Our present results revealed that, in chronic neuropathic pain rats, the pain threshold was decreased significantly. Concomitantly, hippocampal synaptic cleft area was increased significantly, while synaptic postsynaptic
1382 density and active zone length were significantly decreased. These results are indicative of abnormal changes in plasticity and disruption of normal synaptic transmission. Moreover, hippocampal CaMKII
expression was significantly downregulated in CCI rats. Acupuncture can effectively alleviate both acute and chronic pain. Generally, one acupuncture treatment
session for acute disease may produce a substantial and immediate therapeutic effect. In order to obtain robust and reliable clinical efficacy, repeated treatment is necessary, particularly for chronic conditions. Our
present results revealed that compared with simple CCI rats, the pain threshold after electroacupuncture for 2 weeks was significantly increased and its effect was markedly superior to that of electroacupuncture for 2 days. This outcome is similar to previous results that electroacupuncture at Huantiao (GB30) and Weizhong (BL40) for one week alleviates neuropathic pain in CCI rats [36].
Acupuncture is an effective method for stimulating the central nervous system. Acupuncture plays an important role in brain functional reorganization and compensation. Shou et al [37] observed that repeated electroacupuncture could upregulate the expression of cannabinoid
receptor-1 mRNA and dopamine 1 receptor mRNA in the nucleus accumbens-caudate nucleus region in rats with inflammatory pain. Xing et al [38] found that, in rats with neuropathic pain, electroacupuncture treatment had a modulatory effect on long-term synaptic plasticity in the spinal dorsal horn. In addition, acupuncture could reduce the decline in the amplitude and slope rate of population spikes induced by diabetes mellitus and cerebral
ischemia, which may help improve memory by regulating hippocampal synaptic plasticity [18]. The mechanism of action of acupuncture was hypothesized to involve dendritic or synaptic plasticity in the ipsilateral hippocampal CA3 region.
Our present results indicate that the cumulative
analgesic effect of electroacupuncture is associated with the following: (1) significant increases in CaMKII
expression, postsynaptic density area and active zone length in the hippocampal CA3 region; and (2) a
significant reduction in synaptic cleft width. In OVX rats, the synaptic plasticity of neurons in the hippocampal CA3 region and the cumulative effect of acupuncture
analgesia were diminished. These results suggest that repeated electroacupuncture-induced pain relief is accompanied by improvement of hippocampal neural synaptic plasticity.
A number of studies have examined the effects of
repeated electroacupuncture [39-40], but a systematic study of the underlying mechanisms is needed. Our present study is the first attempt to reveal the mechanisms behind the analgesic effect of repeated
A randomized and controlled animal experiment.
Time and setting
The study was performed at the Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, China, from November 2007 to April 2009.
Materials
A total of 98 clean-grade, female Wistar rats, aged 3-4 months, weighing 240-250 g, were purchased from the Experimental Animal Center of Chinese Academy of Medical Sciences (License No. SCXX-Army 2007-004). Animal care and experimental process were performed in accordance with the Guidelines for the Care and Use of Laboratory Animals, formulated in 2005 by our institute and the Guidance Suggestions for the Care and Use of Laboratory Animals , issued by the Ministry of Science and T echnology of China [41].
Methods
Establishment of the CCI model
A model of chronic neuropathic pain was established by ligation of the sciatic nerve, based on a modification of the Bennett and Xie method [42]. Under anesthesia by intraperitoneal injection with a solution of 28 mg/100 g urethane (Beijing Chemistry Reagent, Beijing, China) and 3.3 mg/100 g chloralose (Sigma-Aldrich, St. Louis, MO, USA), followed by routine sterilization, the rat’s left sciatic nerve was exposed at the mid-thigh level by blunt dissection through the biceps femoris muscle. Four constrictive ligatures (4-0 surgical suture) were tied around the nerve at the distal end close to the nerve bifurcation at spaces about 1.0 mm apart. The ligature was considered to be suitable if local and moderate muscular contraction of the leg was clearly observed. Following local application of antibiotics (sodium
penicillin, 9 000–10 000 U/rat), the muscle and skin tissues were sutured in layers. In order to reduce experimental variability, all surgeries were performed by the same operator. For OVX + CCI rats, CCI surgery was performed following Morris water maze testing.
Establishment of memory impairment model
After anesthesia, rats in the CCI + OVX, CCI + OVX + electroacupuncture 2 days, and CCI + OVX + electroacupuncture 2 weeks groups underwent ovariectomy (OVX). Briefly, bilateral mid-abdominal dorsolateral incisions (about 2 cm long) were made, and both ovaries were removed. Four weeks after OVX, four animals from each group (CCI, CCI + electroacupuncture 2 days, CCI + electroacupuncture 2 weeks, CCI + OVX, CCI + OVX + electroacupuncture 2 days and CCI + OVX + electroacupuncture 2 weeks) were subjected to a vaginal smear test for verifying OVX success. Forty-five days after OVX, the rats’ learning-memory ability was analyzed by escape latency (place navigation test), swimming distance in the target quadrant and target quadrant crossing times (spatial probe test) in the Morris water maze test for 7 days using a Morris water maze apparatus (DigBehv-MWM Morris Water Maze Video Analysis System, Shanghai Jiliang Company Ltd, China) with reference to Nunez’s article [Nunez J. Morris Water Maze Experiment. https://www.doczj.com/doc/712598215.html,/index/details. stp?ID=897.].
Electroacupuncture
Bilateral Zusanli (5 mm beneath the capitulum fibulae and lateral posterior to the knee-joint) and Yanglingquan (about 5 mm superior-lateral to Zusanli) were punctured with filiform needles (Gauge 28), respectively, and electrically stimulated using a HANS Electroacupuncture Apparatus (LH202, Beijing Huawei Industrial Developing Company, Beijing, China). Electroacupuncture (2/15 Hz, 1 mA) intervention was administered for 30 minutes, once daily from the 4th day on after CCI surgery for 2 weeks for rats of the CCI + electroacupuncture 2 weeks and OVX + CCI + electroacupuncture 2 weeks groups, and from the 16th day on after CCI surgery for two sessions for rats of the CCI + electroacupuncture 2 days and OVX + CCI + electroacupuncture 2 days groups.
Thermal pain threshold detection
Each rat was placed into a black cloth bag with the hindlimbs and tail exposed for mobility. A mobile radiant heat source (high-intensity light beam with radiant heat dolorimeter) was focused on the plantar surface of the hind paw. Paw withdrawal latency (i.e. pain threshold) of the bilateral footplates was measured three times with an interval of 3-5 minutes between detections. T o avoid potential tissue damage, the cutoff time of the radiant heat was set to 20 seconds. Thermal pain threshold detection was conducted prior to, as well as 4, 8, 12, 16 and 18 days after CCI. Pain thresholds were measured
in rats from the CCI + electroacupuncture and CCI + OVX + electroacupuncture groups on the following day morning.
Transmission electron microscopy observation of the morphology of the hippocampal CA3 region
At the end of each experiment, under deep anesthesia, rats were perfused transcardially with a solution of 2% paraformaldehyde + 2% glutaraldehyde. Then, brain tissue containing the hippocampal CA3 region was cut into small cubes (about 1 mm3), fixed with 3% glutaraldehyde (EMS Company, Shanghai, China) and 1% osmium tetroxide, respectively, for 2 hours, dehydrated with ethanol, infused in acetone, embedded in 812 Epon-Araldite, sectioned into 250-nm-thick slices, and stained using uranyl acetate and lead citrate. The brain sections were then examined under a JEM-1230 transmission electron microscope (JEOL Ltd., T okyo, Japan) and areas of interest which contained synapses were imaged using a NIS-Elements BR2.30 (Nikon,
T okyo, Japan) operated at 200 KeV and a Gatan 2K × 2K CCD camera at a magnification of 50 000×. The average synaptic cleft width, the thickness of the postsynaptic densities and the lengths of active zones in 10 random visual fields of sections of each brain (4 rats/group) were examined according to a previously described method[43]. The length and thickness of the postsynaptic density and the synaptic cleft were assessed separately as previously described[43].
Immunohistochemical staining for CaMKII
The animals were deeply anesthetized with the same anesthetics mentioned above and transcardially perfused with saline, followed by 4% paraformaldehyde in 0.1 M PBS (pH 7.4). The brain (without the cerebellum) was removed and post-fixed in 30% sucrose solution (containing 4% paraformaldehyde) at 4°C. Serial coronal sections (60 μm) were cut on a cryostat (whole body slicing microtome Leitz 400 with a chest mobile freezer; Leitz OM, Leica, Germany) and stored in 0.01 M PBS solution at 4°C.
The brain sections containing the hippocampal CA3 region were mounted onto glass slides, immersed in PBS for 5 minutes, and incubated in 3% H2O2/deionized water for 15 minutes. Excess fluid was removed and the sections were incubated in 5% normal goat serum at room temperature for 15 minutes, followed by rabbit
anti-CaM kinase II polyclonal antibody (1:1 000; Santa Cruz Biotechnology, Santa Cruz, CA, USA) at 37°C for 24 hours. The sections were then washed three times in
1383
PBS for 5 minutes each, incubated with goat anti-rabbit
IgG (1:300; Zhongshan Golden Bridge Biotechnology, Beijing, China) at room temperature for 2 hours, washed three times in PBS, incubated in
avidin-biotin-horseradish peroxidase (1:300; Zhongshan Golden Bridge Biotechnology) at room temperature for 2 hours, washed three times with PBS for 5 minutes each, and stained with 3,3’-diaminobenzidine. The sections were then washed in running water, counterstained with 0.01% cresyl fast violet at 37°C for 15 minutes, incubated in a mixture of 100% alcohol:ether:chloroform (1:1:1) for 10 minutes, rinsed 2 minutes in water, dehydrated in alcohol, and then immersed twice in dimethyl benzene for 10 minutes. The slides were sealed with neutral gel and dried at room temperature. The immunostained structure (grey scale values) of the CA3 region was analyzed using NIS-Elements BR2.30 image analysis system (Nikon). Two sections were selected from each rat, and three areas of the hippocampal CA3 region of each slice were selected for determining the average grey scale value.
Statistical analysis
Data were expressed as mean ± SD. Differences in paw withdrawal latency were assessed using one-way analysis of variance with repeated measures when appropriate. Least significant difference-t test was used to compare data between two different groups. A value of P < 0.05 was considered statistically significant.
Acknowledgments: We thank Yuanshen Wang and Qing Cai from the Capital Medical University for their technical assistance.
Funding: This work was supported by the National Natural Science Foundation of China, No. 30472241, 90709031 and 30973796, and the Ministry of Science and Technology of China (“973” Project), No. 2007CB512505. Funding was also provided by the Foundation of Hainan Province, No. 310054 and the Health Department of Hainan Province,
QiongWei-45.
Author contributions: Qiuling Xu was responsible for animal experiments, data analysis and drafting of the manuscript in Chinese and English. T ao Liu was responsible for data analysis and figures. Shuping Chen and Yonghui Gao participated in the behavioral experiments and immunohistochemical staining technique consultation. Junying Wang and Lina Qiao participated in immunohistochemistry experiments. Junling Liu designed the study and provided research funding, and finished the manuscript in English.
Conflicts of interest: None declared.
Ethical approval: All procedures were approved by the Institute of Acupuncture and Moxibustion of China Academy of Chinese Medical Sciences. REFERENCES
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神经系统由大量的神经元构成。这些神经元之间在结构上并没有原生质相连，仅互相接触， 其接触的部位称为突触 细胞突起是由细胞体延伸出来的细长部分，又可分为树突和轴突。 树突棘是树突表面的棘状突起，也就是形成突触的部位 一般认为，NMDA受体主要分布在神经细胞的突触后膜。在兴奋性神经元，NMDA受体主要 分布在树突棘头的突触后膜，且主要分布在突触后致密区（postsynaptic density, PSD） 突触可塑性：突触在形态和传递效能上的改变 突触后致密区（PSD）：在电镜下所见的突触后膜胞质面聚集的一层均匀而致密的物质，见 于cns中所有树突棘突触的突触后膜上。主要功能是细胞粘附性的调节，受体集聚的控制和 受体功能的调节。 旷场试验：用来观察小鼠自发性探索运动活性和焦虑行为 反应实验动物在陌生环境中的自主行为与探究行为，以尿便次数反应其紧张度。 开场实验，open field test，这个测的是5min内，动物在一个开阔环境中的行为学变化，我 们用一个强光打在开场中央，开场有方形和圆形两种。圆形是一个大缸，白色的，具体尺寸 我忘记了。需要用的指标是：跨格数、站立数、排便数和梳理数（也就是理毛次数），前两 个指标为主。这个实验可以用中央场次数作为焦虑样行为的观察指标。 运动能力(locomotion， open field test 主要是评价动物的焦虑状态，它主要以动物进入中央区的时间百分率来评价焦虑状态，它也可以度等。 物在一个开放的新的地方会很小心，rodent动物喜暗而避明的特性会让自己躲在暗处，也会 对开阔地方有探索行为（好奇心），同时又有害怕紧张担心和焦虑心理，具有一定的新奇性 同时又具有一定的害怕。如果动物焦虑少，停留在中间等位置时间长久一些，不然反之。比 较这些特性可以比较动物的焦虑程度。具有抗焦虑作用的药物会让动物有更多的对开阔地方 有探索行为，焦虑紧张的动物更喜欢停留在开场的边缘和暗处。 LTP定义：给突触前纤维一个短暂的高频刺激后，突触传递效率和强度增加几倍且能持续数 小时至几天保持这种增强的现象。按LTP的时程分①PTP，强直后增强，一般5分钟后衰减； ②STP，短时程增强，持续半小时左右；③，LTP长时程增强，持续一小时以上 CaMKII这个蛋白是个很特殊的蛋白，在脑内含量非常高，大约占总蛋白量的1-2%。在突触 部位的含量很高，并且是PSD（postsynaptic density）主要蛋白。但这个蛋白最特殊之处是 其具有自身调节能力，仿佛自己本身就是一个具有学习记忆的功能。 因为把随着神经等器官、组织的兴奋所产生的动作电位作为其活动指标是最容易记录的现 象，所以常常用记录动作电位来深入研究神经系统等的机能。 高频刺激可引发突触后细胞的持久增强反应——最初被称为“持久增强作用”（
电针对脑功能障碍大鼠海马物质影响的 研究进展 （作者： _________单位：____________ 邮编：___________ ） 【摘要】目前，电针对脑缺血模型大鼠海马细胞影响的研究报道很多，对海马与学习记忆关系的研究已成为国内研究的重 点。本文就电针对脑功能障碍大鼠海马物质影响的研究作简要综述。 【关键词】电针海马物质 海马的生理功能目前仍在探讨之中.大量的动物模型研究表明，海马与学习记忆有关。当脑缺血等致海马受损时，可引起学习记忆功能的严重障碍。电针刺特定穴位可影响脑功能障碍大鼠海马物质的表达。现就目前电针对脑功能障碍大鼠海马物质影响的研究作一综述。 1电针对海马细胞凋亡相关蛋白表达的影响 1.1 Bel ]2是功能最为明确的细胞凋亡拮抗基因Bcl[2蛋白基本生物学功能为延长细胞的生命期限、增加细胞对多种凋亡刺激因素的抗性。Bax与Bcl]2作用相反，能够促进凋亡，Bcl〕2表达水平较高时，形成Bcl[2/Bcl[2同源二聚体，抑制细胞凋亡；Bax表达水平较高时，形成
Bax/Bax同源二聚体，加速细胞凋亡；BcL2和Bax水平相当 时，则形成Bcl[2/Bax异源二聚体，终止细胞凋亡。近年的研究提示 Bcl[2与Bax调节细胞凋亡，不仅取决于自身表达的高低，还与 Bax/Bcl_2比率有关，当比率增大时，细胞趋于凋亡[1 ]o caspase ]3 激活是触发凋亡的关键（有“分子开关”之称是凋亡的最终执行蛋白。Bcl]2家族基因在调节线粒体通透性上发挥重要作用，Bcl]2或其他 抗凋亡Bcl_2家族成员下调，或促凋亡Bcl_2家族成员如Bax在线粒体膜上过度表达和移位，均导致线粒体通透性增加，使细胞色素C 从线粒体释放入胞浆，与Apaf”、dADP形成复合体，再与胞浆中的caspase ]9前体形成凋亡小体，导致caspase[9被裂解激活，随后再裂解caspase家族其他成员包括caspase[3,引发凋亡。赵建新等[2] 报告电针刺激脑缺血小鼠“肾俞”膈腧”百会；各观察时点均可上调小鼠海马细胞Bcl[2表达，下调Bax表达，降低凋亡率。故电针可起到抑制凋亡、保护神经元的作用电针可显著上调内源性海马Bcl[2表达，降低Bax表达，有可能进一步抑制caspase [3的激活，或影响神经生长因子、过氧化物歧化酶、CHAT等促神经细胞存活相关基因的表达而发挥抗凋亡作用，有待今后动物实验验证。Noxa为BH3only 亚家族成员]3]，脑缺血研究发现，Noxa在脑缺血引起的细胞凋亡中起重要作用[4 ]。朱燕珍等]5]报告，电针刺激血管性痴呆模型大鼠“大椎百会：海马CA1区的Noxa阳性细胞数增加，Caspase ]3 阳性细胞数增加，提示Noxa调节的线粒体凋亡途径促进血管性痴呆的发展；电针治疗抑制
大脑的解剖结构和功能——布罗德曼分区系统 布罗德曼分区是一个根据细胞结构将大脑皮层划分为一系列解剖区域的系统。神经解剖学中所谓细胞结构（Cytoarchitecture），是指在染色的脑组织中观察到的神经元的组织方式。 布罗德曼分区1909年由德国神经科医生科比尼安·布洛德曼（Korbinian Brodmann）提出。根据皮质细胞的类型及纤维的疏密把大脑皮质分为52个区，并用数字给予表示。Brodmann Area 1, BA1 Brodmann Area 2, BA2 Brodmann Area 3, BA3 位置：位于中央后回 (postcentral gyrus) 和前顶叶区。 功能：分别为体感皮层内侧、末尾和前端区,BA1、BA2、BA3共同组成体感皮层； 具备基本体感功能（first somatic sensory area）接受对侧肢体的感觉传入。Brodmann Area 4, BA4 位置：位于中央前回(precentral gyrus)，中央沟(central sulcus)的内侧面 功能：初级运动皮层（first somatic motor area)，包含“运动小人”（motor homunculus ）。 控制行为运动，与BA6 （前）和BA3 、BA2 、BA1、（后）相连，同时与丘脑腹外侧核相连。 体感小人（Somatosensory Homunculus ） 传入体感信息较多的身体区域获得的皮层代表区域较大。比如手部在初级体感皮层中的代表区域比背部的大。体感皮质定位可用“体感小人”（Somatosensory homunculus）来表示。 Brodmann Area 5, BA5 位置：位于顶叶前梨状皮质区（梨状皮质piriform cortex为下边缘皮质的组成部分）。功能：与BA7形成体感联合皮层。 Brodmann Area 7, BA7 位置：位于顶叶皮质顶部，体感皮层后方，视觉皮层（visual area)上方。 功能：将视觉和运动信息联合起来；与BA5形成体感联合皮层；视觉-运动协调功能。 Sensory Areas---------Somatosensory Association Area 位置：位于初级躯体感觉皮层后方（BA5、BA7）
海马结构,希望有所帮助 海马结构(hippocampal formation，HF)属于脑的边缘系统(1imbic system)中的重要结构，与学习、记忆、认知功能有关，尤其是短期记忆与空间记忆。海马皮质从海马沟至侧脑室下角依次为分子层、锥体层和多形层。齿状回也分三层：分子层、颗粒细胞层和多形层。依据细胞形态、不同皮质区的发育差异以及纤维排列的不同，将海马分为4个区，即CAl、CA2、CA3、CA4区。海马结构是大脑边缘系统的重要组成部分．在进化上是大脑的古皮质，位于大脑内侧面颞叶的内侧深部，左右对称。一般认为海马结构由海马或称Ammon角、齿状回、下托及海马伞组成，结构比较复杂。在功能和纤维联系上，不仅与嗅觉有关，更与内脏活动．情绪反应和性活动有密切关系。细胞学研究表明，海马头部主要是由CAI区折叠而成，而CAI区对缺氧等损伤最为敏感，也被称为易损区，因此海马头部也是最易发生病变的部位。 海马结构由海马(hippoeampus)、齿状回(dentate gyrls)、下托(subiculum)和围绕胼胝体的海马残体(hippoeampal rudimerit)组成，其中海马为体积最大最主要的部分。 大脑海马（hippocampus）是位于脑颞叶内的一个部位的名称，人有两个海马，分别位于左右脑半球. 它是组成大脑边缘系统的一部分，担当着关于记忆以及空间定位的作用. 名字来源于这个部位的弯曲形状貌似海马(希腊语hippocampus). 在阿兹海默病中,海马是首先受到损伤的区域; 表现症状为记忆力衰退以及方向知觉的丧失。大脑缺氧(缺氧症)以及脑炎等也可导致海马损伤 . 在动物解剖中, 海马属于脑的演化过程中最古老的一部分。来源于旧皮质的海马在灵长类以及海洋生物中的鲸类中尤为明显。虽然如此, 与进化树上相对年轻的大脑皮层相比灵长类动物尤其是
海马结构 一．形态 海马结构（hippocampal formation）包括海马（hippocampus）又称安蒙角（Ammon’s born）,齿状回（dentate gyrus）和围绕胼胝体形成一圈的海马残件（灰被indusium grisem）.齿状回随海马伞向后，至胼胝体压部，它与海马伞分开，改为束状回，束状回向前上与覆盖在胼胝体上面的灰质称胼胝体上回（ssupracallosal gyrus）（灰被）相连续，灰被中埋有一对纵纹，分别为内侧纵纹和外侧纵纹。灰被与纵纹就是海马及其白质的残件，它们向前经胼胝体膝与胼胝体下回连续。 （一）海马 海马形似中药海马，故得名。其位于侧脑室下角的底和内侧壁，全长约5cm,前段较膨大，称海马角，他被2-3个浅沟分开，沟间隆起，称海马趾；海马表面被室管膜上皮覆盖，室管膜上皮下面一层有髓鞘纤维称室床，室床纤维沿海马背内侧缘集中，形成白色扁带称海马伞，构成穹窿系统的起始步，它自海马趾伸向压部，续于穹窿角。 海马内的细胞构筑分为三层，从海马裂到脑室依次为①分子层；②椎体细胞层；③多形层。根据细胞形态和皮质区发育差异等特点，在横断面上海马又可分为CA1、CA2、CA3和CA4四个区。CA4位于齿状回门内，内有大的椎体细胞；CA3有来自齿状回颗粒细胞的轴突（即苔状纤维）；CA2内有少量轴突；CA1内含有小的椎体细胞。 （二）齿状回 齿状回是一条灰皮质，由于血管进入形成沟而成齿状，故名。它位于海马的内侧，海马裂与海马伞之间，齿状回向后与束装回相连，其前端抵海马回钩和海马回之间。 海马接受扣带回来的纤维经扣带直接或间接地终止于海马，从隔核发出的纤维经穹窿，海马伞终止于海马CA3、CA4区和齿状回。一侧的海马也可经同侧海马伞，穹窿脚，通过海马联合投射至对侧的海马和齿状回，海马还可经室床通路接受内嗅区外侧份的传出纤维，这些纤维主要分布于CA1区和下托的深层，内侧份纤维则经穿通道、下托进入海马CA1-CA3斜角带核，在穹窿的行程中发出纤维至丘脑前核和板内核的吻部，部分纤维可向尾侧进入中脑被盖和中央灰质。 二．海马的功能 海马具有多方面的生理功能，50年代不少实验已经证明海马可接受来自外周的视觉、听觉、触觉、痛觉、本体感受性和内感受性刺激，感受性冲动经过脑干网状结构传递至海马，引起海马电活动的变化。近年来，由于神经科学的迅速发展，不少学者认为海马是情感和学习记忆等高级神经活动的重要部位。 （一）行为反应 毁损海马后，动物的行为发生一系列变化，最重要的是更乐于从事新的活动，在恐惧或应激的情况下，动物好动反应灵活，热衷于进行新的活动，有时也会出现“幻觉”，但很少出现攻击性动作。这些反应对动物具有一定的生理意义，如毁损海马的鼠，当遇到猫时，其表现为饥饿情绪反应增强，食欲亢进，性活动异
抑郁模型大鼠海马内环境的研究 发表时间：2011-07-13T16:28:59.267Z 来源：《中外健康文摘》2011年第16期供稿作者：郑晓霓1 单德红2 [导读] 海马神经元所处的细胞外液属于机体内环境，其成分和理化特性相对稳定是神经元发挥功能的前提。 郑晓霓1 单德红2 （1辽宁省沈阳市沈和区第二中医院110015；2辽宁省沈阳市中医药大学基础医学院110032）【中图分类号】R74【文献标识码】A【文章编号】1672-5085 (2011)16-0144-02 【摘要】目的研究海马内环境稳态在抑郁症中的作用。方法20只雌性Wistar大鼠分为对照组、模型组。ELISA法检测血清皮质醇、雌二醇，光镜和电镜观察海马CA3区形态学变化，免疫组化法检测海马脑源性神经生长因子和血管内皮生长因子表达。结果与对照组比较，模型组皮质醇水平显著升高，雌二醇水平明显下降，海马CA3区神经元损伤严重，脑源性神经生长因子和血管内皮生长因子表达明显降低。结论抑郁状态下，海马内环境稳态被破坏。【关键词】抑郁症海马内环境稳态脑源性神经生长因子血管内皮生长因子【Abstract】 Objective: To study the action of hippocampal internal enviroment in deprssion. Methods: 20 femal wistar rats were divided into the control, model group. Serum cortisol and estradiol were measured with ELISA. Hippocampal CA3 morphology were observed by light and electron miroscope. BDNF and VEGF expressions were detected by immunohistochemistry. Results: compared with those in the control, in the model group, the serum cortisol level increased obviously, serum estradiol level decreased significantly, and the CA3 neurons had severious structure damage, and the expressions of BDNF and VEGF decreased markedly. Conclusion: The homeostasis of hippocampal internal enviroment is disrupted in depression. 【Key words】 depression hippocampal internal enviroment homeostasis brain-derived neurotrophtic factor vascular endothelial growth factor 海马内环境指海马神经元的细胞外液，其理化性质和各种成分应保持相对稳定的状态，即稳态。海马内环境的理化特性包括温度、渗透压、酸碱度等，成分有各种离子、激素、递质、细胞因子等。海马内环境稳太破坏均会损伤海马功能和结构，进而影响行为、情绪和内脏功能。现代医学认为海马损伤在抑郁症发病中起重要作用[1-2]，但抑郁状态下，海马内环境出现何种变化目前尚没有系统研究，这就是本课题的研究目标，而本文主要对海马内环境中相关成分进行初步观察。 1 材料和方法 1.1实验动物的选取和分组健康Wistar雌性大鼠，清洁级，体重226±20g,中国医科大学动物实验中心提供，合格证号：医大动物合格证SCXK(辽)2008-0005。适应性饲养1周后，选择行为学得分相近的20只大鼠，随机分为对照组、抑郁症模型组（模型组），每组10只。室温20℃～25℃，湿度40%～50%。 1.2抑郁症模型的建立模型组大鼠建立慢性不可预见性应激模型，即在21d内随机施加电击足底（36V交流电，5min）、冰水游泳（4℃,5min）、摇晃（1min）、夹尾（1min）、禁水（24h）、禁食(24h)等刺激，每种刺激4次。 1.3血清雌二醇和皮质醇检测在实验的d22，2组大鼠均腹腔注射20%氨基甲酸乙酯（0.4mL/100g）麻醉后，腹主动脉取血，离心后取血清，低温冻存。采用ELISA方法检测皮质醇和雌二醇(Estradiol，E2)，此项工作由沈阳军区总医院内分泌实验室完成。 1.4海马组织学观察首先是HE染色：取完成1.3后2只大鼠，立即断头取双侧海马，置于10%甲醛中固定，石蜡切片，HE染色，观察海马CA3区神经元的形态学变化。其次电镜观察：取完成1.3后的2只大鼠，升主动脉插管，150ml生理盐水快速冲去血液，快速灌入4℃ 2.5%戊二醛固定液，取双侧海马，修块，再于戊二醛中固定2h，PBS反复清洗后，再经1%锇酸固定2h，双蒸水冲洗，梯度乙醇脱水，临界点干燥，离子溅射真空渡膜，扫描电镜下观察超微结构。 1.5脑源性神经生长因子和血管内皮生长因子表达取完成1.3的6只大鼠开胸，升主动脉插管，生理盐水快速冲去血液，取双侧海马，4%多聚甲醛固定4～6h，30%蔗糖溶液沉底。做海马石蜡冠状切片，片厚25μm，隔4片取1片，采用免疫组化SABC法检测脑源性神经生长因子(Brain-derived neurotrophtic factor，BDNF)和血管内皮生长因子(Vascular endothelial growth factor ,VEGF)表达，相关抗体和试剂盒均购于武汉博±德试剂公司，阴性对照选用PBS。利用BI-2000医学图像分析系统，测定海马CA3区BDNF和VEGF表达的平均灰度值。 1.6数据处理数据以x-±s表示，采用SPSS13.0中ANOVA检验进行统计学处理。 2 实验结果 实验过程中没有实验动物死亡及脱失现象。 2.1海马形态学变化 光镜下，对照组CA3区有大量致密锥体细胞，排列整齐，细胞完整，边缘清晰；模型组细胞层次减少、稀疏、排列紊乱，大量细胞坏死。电镜下，对照组细胞器丰富，轮廓清晰，细胞核呈圆形，核膜清晰光滑完整，核染色质分布均匀；模型组细胞器减少，线粒体空泡化，细胞核变小，不规则，且核膜增厚，核周电子密度降低。 2.2海马内环境相关成分变化 与对照组比较，模型组皮质醇显著升高，E2明显下降。BDNF和VEGF免疫阳性反应产物呈棕黄色，前者分布神经元胞浆内，后者主要分布于血管内皮细胞内。对照组BDNF和VEGF表达较多，模型组较少，二者灰度值均升高。具体数据见表1。表1 各组海马内环境相关成分的变化 注：与对照组比较：a P<0.05, b P<0.01
海马的两个记忆回路 海马→穹窿→乳头体→乳头丘脑束→丘脑前核→扣带回→海马，这条环路是30年代就认识到的边缘系统的主要回路，称为帕帕兹环。在这条环路中，海马结构是中心环节。所以，在40-50年代曾认为海马结构与情绪体验有关。近些年发现，内侧嗅回与海马结构之间存在着三突触回路，它与记忆功能有关。三突触回路始于内嗅区皮层，这里神经元轴突形成穿通回路，止于齿状回颗粒细胞树突，形成第一个突触联系。齿状回颗粒细胞的轴突形成苔状纤维(Mossy fibers)与海马CA3区和锥体细胞的树突形成第二个突触联系。CA3区锥体细胞轴突发出侧支与CA，区的锥体细胞发生第3个突触联系，再由CAi锥体细胞发出向内侧嗅区的联系。这种3突触回路是海马齿状回内嗅区与海马之间的联系，具有特殊的机能特性，成为支持长时记忆机制的证据。 1966年，罗莫(T. Lomo)首先报道了他称之谓长时程增强(Long-term potentiation，LTP)的现象，即电刺内嗅区皮层向海马结构发出的穿通回路时，在海马齿状回可记录出细胞外的诱发反应。如果电刺激由约100个电脉冲组成，在1-10秒内给出，则齿状回诱发性细胞外电活动在5-25分钟之后增强了2.5倍，说明电刺激穿通回路引起齿状回神经元突触后兴奋电位的LTP，因而这些神经元单位发放的频率增加。后来他们又报道，海马齿状回神经元突触电活动的LTP现象可持续散月的时间。他们认为，由短 暂电刺激穿通回路所引起的三突触神经回路持续性变化，可能是记忆的重要基础。 每侧的海马齿状回都接受两侧内侧嗅区来的穿通纤维，但以同侧性联系为主，对侧性联系较少。如果在单侧刺激内嗅区，则发现在同侧海马齿状回内很容易引起LTP现象，而在对侧海马齿状回内，则很难引起这种现象。如果用建立经典条件反射的程序对两侧内嗅区施以刺激时，就会发现LTP效应的呈现也符合经典条件反射建立的基本规律，从而证明LTP 现象可能是一种学习的脑机制。这种实验是这样进行的，如果先刺激对侧内嗅区，随后以不到20毫秒的间隔期施用同侧内嗅区刺激，这样处理重复几次以后就会发现，单独应用对侧内嗅区的刺激，也会很容易引起同侧海马齿状回的LTP现象。 这就是说，把对侧内嗅区刺激当作条件刺激，同侧内嗅区刺激作为非条件刺激（强化），可以建立海马齿状回的LTP现象条件反射。如果把条件刺激和非条件刺激呈现的顺序颠倒过来，或者延长条件刺激与非条件刺激呈现间的时间间隔至200毫秒以上，则发现齿状回的
海马结构 2010-06-18 10:19:05| 分类：专业相关| 标签：|字号大中小订阅 概述 海马结构（hippocampal formation）包括海马（又称安蒙角cornu AmmonisCA）、下托、齿状回和围绕胼胝体形成一圈的海马残件。齿状回至胼胝体压部，消失齿状外形，改称束状回，束状回向前上与覆盖胼胝体上面的深层灰质称灰被（又称胼胝体上回）相连续。灰被中埋有一对纵纹，分别为内侧纵纹与外侧纵纹。灰被与纵纹就是海马及其白质的残件。它们向前经胼胝体膝与终板旁回连续。 位置与外型 海马（hippocampus）形如中药海马故名。位于侧脑室下角底兼内侧壁，全长5 cm。海马前端较膨大称海
马足，它被2－3个浅沟分开，沟间隆起称海马趾。海马是一条镰状隆嵴，自胼胝体压部向前到侧脑室的颞端。海马至胼胝体压部时，从齿状回和海马旁回间翻出称Retzius回。 海马结构的位置 海马表面被室管膜上皮覆盖。室管膜上皮下面有一层有髓纤维称为海马槽（又称室床alveus）。室床纤维沿海马背内侧缘集中，形成白色扁带称海马伞（fimbria of hippocampus），它自海马趾伸向压部，续于穹隆脚（crus of fomix）。海马伞的游离缘直接延续于其上方的脉络丛，两者间隔以脉络裂。
海马结在下角的发育 齿状回（dentate gyms）是一狭条皮质；由于血管进入被压成许多横沟呈齿状，故名。它位于海马的内侧，介于海马沟与海马伞之间。齿状回向前伸展至钩的切迹，在此急转弯，成光滑小束横过钩的下面，这横行段称齿状回尾。齿状回尾将钩分成前部的前钩回，后部的边叶内回。齿状回向后与束状回（fasciolar gyrus） 相连。 在海马结构发育较好的颞中平面，作一个大脑半球的冠状切面，海马结构呈双重“C”形环抱的外形，大C锁住小C。大C代表海马，它开口向腹内侧。小C代表齿状回，位于海马沟的背内侧，开口朝向背侧。海马 沟的腹侧为下托（subiculum）。 海马结构的位置与安排，从发育过程来理解比较清楚。 在胚胎3个月，两个半球内侧壁上各显出一条纵行加厚部分称海马嵴（hippocampal ridge），这是海马结构的原基。此嵴的上方为海马沟。此嵴以下，内侧壁很薄弱，而有血管分支伸入形成一纵褶称脉络襞，它突入侧脑室，形成侧脑室脉络丛，突入处称脉络裂（choroid fissure）。伴随着大脑皮质的扩展，因胼胝体纤维的急剧发展，以致海马结构的各部发展不均匀。背侧部分很少分化。在成人它形成一个残余的薄层灰质称灰被（indusium griseum）覆盖在胼胝体上方。海马结构的腹侧部分（颞叶部分）未受胼胝体发展的影响，而较好发育，形成海马和齿状回。海马嵴和原来皮质的分界沟——海马沟（裂），将海马结构与相邻皮质分开，在颞叶它插入海马旁回与海马结构之间；在胼胝体上方，它插入扣带回与灰被之间改称胼胝体沟（callosal sulcus）。脉络裂在大脑半球内侧面形成弯曲，前起自室间孔，沿穹隆上外侧与胼胝体下方 弯曲向下，至颞叶行于海马的上内侧。 又由于颞叶皮质的高度扩展，将其内侧由海马嵴衍化的皮质带推向侧脑室下角的底与内侧壁。随着海马沟的加深，内陷部分的皮质突出于侧脑室下角的底，形成海马。海马向背内侧弯曲，到达半球内面，其内侧端又受脉络裂的制约，内侧份再向里弯，形成一个半月形的齿状回。如此海马沟的上唇为齿状回，下唇为下托。下托与海马结构间的过渡区称副下托。皮质区从内嗅区经旁下托、前下托、下托、副下托至海马与 齿状回，逐渐由原始型6层变到3层细胞结构。 内部结构
各类突触的结构、功能以及传递过程: 电突触（electrical synapse）是普遍存在于无脊椎动物和脊椎动物的神经系统中的一种直接通过电信号进行细胞间信息传递的突触，在动物的逃避反射中发挥重要作用。在哺乳动物的神经系统中，也存在着电突触，例如大鼠中脑核团中的感觉神经元间、海马锥体神经元间等需要高度同步化的神经元群之间。其结构基础为缝隙连接（gap junction），如图2-47所示，（a）为电突触的结构模式图，而（b）为缝隙连接示意图。可以看到两个相邻细胞间的距离特别小，只有3.5nm，并且两侧的神经元膜上都存在一些规则排列贯穿质膜的蛋白，称为连接子，每个连接子都由6个相同的亚基构成，中间形成一个通道可允许小的水溶性分子通过（分子量小于1.0~1.5kD或直径小于1 nm）。通过连接子，许多带电离子可以从一个细胞直接流入另一个细胞，形成局部电流和突触后电位，这种传递的特点是可以双向进行，并且迅速，耗时耗能少。但是电突触的连接子通道并非持续开放的，它受胞质中的pH值或Ca2+浓度的调节，因为这些因素会对细胞造成伤害。 图2-47电突触及缝隙连接模式图 2.2.2.2化学性突触传递 在中枢神经系统中，大多数的突触传递都是化学性的，是历来被研究的最多、最详细和最重要的突触。图2-48所示为化学性突触的电镜图，可以明显的观察到突触部位的膜厚度增厚。我们将发出信号的神经元称为突触前神经元，而接受信号的神经元叫做突触后神经元，两者之间的狭窄区间称为突触间隙。
图2-48电镜下的突触结构 1、定向突触传递 根据突触前、后的神经元之间是否存在紧密的解剖学关系，又可以将化学性突触分为定向突触（directed synapse）和非定向突触（non-directed synapse）。其中定向突触被认为是经典的化学性突触。定向突触的结构成分包括，突触前膜、突触间隙和突触后膜三部分。 （1）分类 除了上述介绍的几种分类，还有一种常用分类是根据神经元相互接触的部 图2-49突触类型模式图 位，可以分为轴突-树突式突触、轴突-胞体式突触、轴突-轴突式突触以及树突-树突式突触，其中最常见的是前两种（图2-49）。根据神经元功能又可以将其分为兴奋性突触和抑制性突触两种，关于这两种突触将在后叙的内容中详细介绍。（2）结构 如图2-50所示，突触前神经元末端膨大形成突触小体（synaptic knob），其轴浆内含有大量的线粒体和突触小泡（synaptic vesicle）还有负责轴浆运输的微