Semantic segmentation of pyramidal neuron skeletons using geometric deep learning

Neurons can be abstractly represented as skeletons due to the filament nature of neurites.With the rapid development of imaging and image analysis techniques,an increasing amount of neuron skeleton data is being produced.In some scienti fic studies,it is necessary to dissect the axons and dendrites,which is typically done manually and is both tedious and time-consuming.To automate this process,we have developed a method that relies solely on neuronal skeletons using Geometric Deep Learning(GDL).We demonstrate the effectiveness of this method using pyramidal neurons in mammalian brains,and the results are promising for its application in neuroscience studies.

Takeda G protein-coupled receptor 5 modu⁃lates depression-like behaviors via hippocam⁃pal CA3 pyramidal neurons afferent to dorso⁃lateral septum

OBJECTIVE Takeda G protein-coupled receptor 5(TGR5)is recognized as a promising target for type 2 diabetes and metabolic syndrome;its expression has been demonstrat⁃ed in the brain and is thought to be neuroprotec⁃tive.Here,we hypothesize that dysfunction of central TGR5 may contribute to the pathogene⁃sis of depression.METHODS In well-established chronic social defeat stress(CSDS)and chronic restraint stress(CRS)models of depression,we investigated the functional roles of TGR5 in CA3 pyramidal neurons(PyNs)and underlying mech⁃anisms of the neuronal circuit in depression(for in vivo studies,n=10;for in vitro studies,n=5-10)using fiber photometry;optogenetic,chemoge⁃netic,pharmacological,and molecular profiling techniques;and behavioral tests.RESULTS Both CSDS and CRS most significantly reduced TGR5 expression of hippocampal CA3 PyNs.Genetic overexpression of TGR5 in CA3 PyNs or intra-CA3 infusion of INT-777,a specific agonist,protected against CSDS and CRS,exerting sig⁃nificant antidepressant-like effects that were mediated via CA3 PyN activation.Conversely,genetic knockout or TGR5 knockdown in CA3 facilitated stress-induced depression-like behav⁃iors.Re-expression of TGR5 in CA3 PyNs rather than infusion of INT-777 significantly improved depression-like behaviors in Tgr5 knockout mice exposed to CSDS or CRS.Silencing and stimula⁃tion of CA3 PyNs→somatostatin-GABAergic(gamma-aminobutyric acidergic)neurons of the dorsolateral septum circuit bidirectionally regulat⁃ed depression-like behaviors,and blockade of this circuit abrogated the antidepressant-like effects from TGR5 activation of CA3 PyNs.CON⁃CLUSION TGR5 can regulate depression via CA3 PyNs→somatostatin-GABAergic neurons of dorsolateral septum transmission,suggesting that TGR5 could be a novel target for developing antidepressants.

Dual face of axonal inhibitory inputs in the modulation of neuronal excitability in cortical pyramidal neurons

Limited by the tiny structure of axons,the effects of these axonal hyperpolarizing inputs on neuronal activity have not been directly elucidated.Here,we imitated these processes by simultaneously recording the activities of the somas and proximal axons of cortical pyramidal neurons.We found that spikes and subthreshold potentials propagate between somas and axons with high fidelity.Furthermore,inhibitory inputs on axons have opposite effects on neuronal activity according to their temporal integration with upstream signals.Concurrent with somatic depolarization,inhibitory inputs on axons decrease neuronal excitability and impede spike generation.In addition,following action potentials,inhibitory inputs on an axon increase neuronal spike capacity and improve spike precision.These results indicate that inhibitory inputs on proximal axons have dual regulatory functions in neuronal activity（suppression or facilitation）according to neuronal network patterns.

Myricetin protects hippocampal CA3 pyramidal neurons and improves learning and memory impairments in rats with Alzheimer's disease

There is currently no treatment for effectively slowing the progression of Alzheimer＇s disease, so early prevention is very important. Numerous studies have shown that flavonoids can improve memory impairment. The present study investigated the effects of myricetin, a member of the flavonoids, on intracerebroventricular streptozotocin induced neuronal loss and memory impairment in rat models of Alzheimer＇s disease. Myricetin at 5 or 10 mg/kg was intraperitoneally injected into rats over 21 days. Control rats were treated with 10 m L/kg saline. Behavioral test（the shuttle box test） was performed on day 22 to examine learning and memory in rats. Immediately after that, hematoxylin-eosin staining was performed to observe the morphological change in hippocampal CA3 pyramidal neurons. Myricetin greatly increased the number of hippocampal CA3 pyramidal neurons and improved learning and memory impairments in rats with Alzheimer＇s disease. These findings suggest that myricetin is beneficial for treatment of Alzheimer＇s disease.

Neuroprotective effects of ischemic preconditioning on hippocampal CA1 pyramidal neurons through maintaining calbindin D28k immunoreactivity following subsequent transient cerebral ischemia

Ischemic preconditioning elicited by a non-fatal brief occlusion of blood flow has been applied for an experimental therapeutic strategy against a subsequent fatal ischemic insult. In this study, we investigated the neuroprotective effects of ischemic preconditioning（2-minute transient cerebral ischemia） on calbindin D28k immunoreactivity in the gerbil hippocampal CA1 area following a subsequent fatal transient ischemic insult（5-minute transient cerebral ischemia）. A large number of pyramidal neurons in the hippocampal CA1 area died 4 days after 5-minute transient cerebral ischemia. Ischemic preconditioning reduced the death of pyramidal neurons in the hippocampal CA1 area. Calbindin D28k immunoreactivity was greatly attenuated at 2 days after 5-minute transient cerebral ischemia and it was hardly detected at 5 days post-ischemia. Ischemic preconditioning maintained calbindin D28 k immunoreactivity after transient cerebral ischemia. These findings suggest that ischemic preconditioning can attenuate transient cerebral ischemia-caused damage to the pyramidal neurons in the hippocampal CA1 area through maintaining calbindin D28k immunoreactivity.

MDGA2 Constrains Glutamatergic Inputs Selectively onto CA1 Pyramidal Neurons to Optimize Neural Circuits for Plasticity,Memory,and Social Behavior

Synapse organizers are essential for the development,transmission,and plasticity of synapses.Acting as rare synapse suppressors,the MAM domain containing glycosylphosphatidylinositol anchor(MDGA)proteins contributes to synapse organization by inhibiting the formation of the synaptogenic neuroligin-neurexin complex.A previous analysis of MDGA2 mice lacking a single copy of Mdga2 revealed upregulated glutamatergic synapses and behaviors consistent with autism.However,MDGA2 is expressed in diverse cell types and is localized to both excitatory and inhibitory synapses.Differentiating the network versus cell-specific effects of MDGA2 loss-of-function requires a cell-type and brain region-selective strategy.To address this,we generated mice harboring a conditional knockout of Mdga2 restricted to CA1 pyramidal neurons.Here we report that MDGA2 suppresses the density and function of excitatory synapses selectively on pyramidal neurons in the mature hippocampus.Conditional deletion of Mdga2 in CA1 pyramidal neurons of adult mice upregulated miniature and spontaneous excitatory postsynaptic potentials,vesicular glutamate transporter 1 intensity,and neuronal excitability.These effects were limited to glutamatergic synapses as no changes were detected in miniature and spontaneous inhibitory postsynaptic potential properties or vesicular GABA transporter intensity.Functionally,evoked basal synaptic transmission and AMPAR receptor currents were enhanced at glutamatergic inputs.At a behavioral level,memory appeared to be compromised in Mdga2 cKO mice as both novel object recognition and contextual fear conditioning performance were impaired,consistent with deficits in long-term potentiation in the CA3-CA1 pathway.Social affiliation,a behavioral analog of social deficits in autism,was similarly compromised.These results demonstrate that MDGA2 confines the properties of excitatory synapses to CA1 neurons in mature hippocampal circuits,thereby optimizing this network for plasticity,cognition,and social behaviors.

Projection-Specific Heterogeneity of the Axon Initial Segment of Pyramidal Neurons in the Prelimbic Cortex

The axon initial segment(AIS)is a highly specialized axonal compartment where the action potential is initiated.The heterogeneity of AISs has been suggested to occur between interneurons and pyramidal neurons(PyNs),which likely contributes to their unique spiking properties.However,whether the various characteristics of AISs can be linked to specific PyN subtypes remains unknown.Here,we report that in the prelimbic cortex(PL)of the mouse,two types of PyNs with axon projections either to the contralateral PL or to the ipsilateral basal lateral amygdala,possess distinct AIS properties reflected by morphology,ion channel expression,action potential initiation,and axo-axonic synaptic inputs from chandelier cells.Furthermore,projection-specific AIS diversity is more prominent in the superficial layer than in the deep layer.Thus,our study reveals the cortical layer-and axon projection-specific heterogeneity of PyN AISs,which may endow the spiking of various PyN types with exquisite modulation.

Effect of etomidate on voltage-dependent potassium currents in rat isolated hippocampal pyramidal neurons

Background Previous studies demonstrated general anesthetics affect potassium ion channels, which may be one of the mechanisms of general anesthesia. Because the effect of etomidate on potassium channels in rat hippocampus which is involved in memory function has not been studied, we investigated the effects of etomidate on both delayed rectifier potassium current （IK（DR）） and transient outward potassium current （I_K（A）） in acutely dissociated rat hippocampal pyramidal neurons.Methods Single rat hippocampal pyramidal neurons from male Wistar rats of 7-10 days were acutely dissociated by enzymatic digestion and mechanical dispersion according to the methods of Kay and Wong with slight modification. Voltage-clamp recordings were performed in the whole-cell patch clamp configuration. Currents were recorded with a List EPC-10 amplifier and data were stored in a computer using Pulse 8.5. Student＇s paired two-tail t test was used for data analysis. Results At the concentration of 100 μmol/L, etomidate significantly inhibited IK（DR） by 49.2% at ＋40 mV when depolarized from -110 mV （P 〈0.01, n=8）, while did not affect IK（A） （/1=8, P 〉0.05）. The IC50value of etomidate for blocking IK（DR）was calculated as 5.4 μmol/L, with a Hill slope of 2.45. At the presence of 10 μmol/L etomidate, the V1/2 of activation curve was shifted from （17.3±1.5） mV to （10.7±9.9） mV （n=8, P 〈0.05）, the V1/2 of inactivation curve was shifted from （-18.3±2.2） mV to （-45.3±9.4） mV （n=8, P 〈0.05）. Etomidate 10 μmol/L shifted both the activation curve and inactivation curve of IK（DR））to negative potential, but mainly affected the inactivation kinetics.Conclusions Etomidate potently inhibited IK（DR） but not IK（A） in rat hippocampal pyramidal neurons. IK（DR） was inhibited by etomidate in a concentration-dependent manner, while IK（A） remained unaffected.

Protein Kinase C Controls the Excitability of Cortical Pyramidal Neurons by Regulating Kv2.2 Channel Activity

The family of voltage-gated potassium Kv2 channels consists of the Kv2.1 and Kv2.2 subtypes.Kv2.1 is constitutively highly phosphorylated in neurons and its function relies on its phosphorylation state.Whether the function of Kv2.2 is also dependent on its phosphorylation state remains unknown.Here,we investigated whether Kv2.2 channels can be phosphorylated by protein kinase C(PKC)and examined the effects of PKC-induced phosphorylation on their activity and function.Activation of PKC inhibited Kv2.2 currents and altered their steadystate activation in HEK293 cells.Point mutations and specific antibodies against phosphorylated S481 or S488 demonstrated the importance of these residues for the PKC-dependent modulation of Kv2.2.In layer Ⅱ pyramidal neurons in cortical slices,activation of PKC similarly regulated native Kv2.2 channels and simultaneously reduced the frequency of action potentials.In conclusion,this study provides the first evidence to our knowledge that PKC-induced phosphorylation of the Kv2.2 channel controls the excitability of cortical pyramidal neurons.

Postsynaptic Excitation of Prefrontal Cortical Pyramidal Neurons by Hypocretins/Orexins

Hypocretins/orexins are crucial for the regulation of wakefulness by the excitatory actions on multiple subcortical arousal systems. In prefrontal cortex,

Regulation of specific abnormal calcium signals in the hippocampal CA1 and primary cortex M1 alleviates the progression of temporal lobe epilepsy

Temporal lobe epilepsy is a multifactorial neurological dysfunction syndrome that is refractory,resistant to antiepileptic drugs,and has a high recurrence rate.The pathogenesis of temporal lobe epilepsy is complex and is not fully understood.Intracellular calcium dynamics have been implicated in temporal lobe epilepsy.However,the effect of fluctuating calcium activity in CA1 pyramidal neurons on temporal lobe epilepsy is unknown,and no longitudinal studies have investigated calcium activity in pyramidal neurons in the hippocampal CA1 and primary motor cortex M1 of freely moving mice.In this study,we used a multichannel fiber photometry system to continuously record calcium signals in CA1 and M1 during the temporal lobe epilepsy process.We found that calcium signals varied according to the grade of temporal lobe epilepsy episodes.In particular,cortical spreading depression,which has recently been frequently used to represent the continuously and substantially increased calcium signals,was found to correspond to complex and severe behavioral characteristics of temporal lobe epilepsy ranging from gradeⅡto gradeⅤ.However,vigorous calcium oscillations and highly synchronized calcium signals in CA1 and M1 were strongly related to convulsive motor seizures.Chemogenetic inhibition of pyramidal neurons in CA1 significantly attenuated the amplitudes of the calcium signals corresponding to gradeⅠepisodes.In addition,the latency of cortical spreading depression was prolonged,and the above-mentioned abnormal calcium signals in CA1 and M1 were also significantly reduced.Intriguingly,it was possible to rescue the altered intracellular calcium dynamics.Via simultaneous analysis of calcium signals and epileptic behaviors,we found that the progression of temporal lobe epilepsy was alleviated when specific calcium signals were reduced,and that the end-point behaviors of temporal lobe epilepsy were improved.Our results indicate that the calcium dynamic between CA1 and M1 may reflect specific epileptic behaviors corresponding to different grades.Furthermore,the selective regulation of abnormal calcium signals in CA1 pyramidal neurons appears to effectively alleviate temporal lobe epilepsy,thereby providing a potential molecular mechanism for a new temporal lobe epilepsy diagnosis and treatment strategy.

Delayed hippocampal neuronal death in young gerbil following transient global cerebral ischemia is related to higher and longer-term expression of p63 in the ischemic hippocampus

The tumor suppressor p63 is one of p53 family members and plays a vital role as a regulator of neuronal apoptosis in the development of the nervous system. However, the role of p63 in mature neuronal death has not been addressed yet. In this study, we first compared ischemia-induced effects on p63 expression in the hippocampal regions （CA1-3） between the young and adult gerbils subjected to 5 minutes of transient global cerebral ischemia. Neuronal death in the hippocampal CA1 region of young gerbils was significantly slow compared with that in the adult gerbils after transient global cerebral ischemia, p63 immunoreactivity in the hippocampal CA1 pyramidal neurons in the sham-operated young group was significantly low compared with that in the sham-operated adult group, p63 immunoreactivity was apparently changed in ischemic hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. In the ischemia-operated adult groups, p63 immunoreactivity in the hippocampal CA1 pyramidal neurons was significantly decreased at 4 days post-ischemia; however, p63 immunoreactivity in the ischemia-operated young group was significantly higher than that in the ischemia-operated adult group. At 7 days post-ischemia, p63 immunoreactivity was decreased in the hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. Change patterns of p63 level in the hippocampal CA1 region of adult and young gerbils after ischemic damage were similar to those observed in the immunohistochemical results. These findings indicate that higher and longer-term expression of p63 in the hippocampal CA1 region of the young gerbils after ischemia/reperfusion may be related to more delayed neuronal death compared to that in the adults.

Hippocampal CA1 pyramidal cells and neurotrophic factors in a rat model of vascular dementia following Xiongma drop pill versus Ginkgo leaf tablets

BACKGROUND： Previous studies have demonstrated the neuroprotective effects of Xiongma drop pill （XMDP） in a mouse model of vascular dementia. Neurotrophic factors play an important role in repair and regeneration of injured neurons. OBJECTIVE： To compare the effects of XMDP and Ginkgo leaf tablets on the appearance and number of hippocampal CA1 pyramidal neurons, as well as neurotrophic factor content in brain tissues, during vascular dementia formation to explore the neuroprotective mechanisms of XMDP. DESIGN, TIME AND SETTING： A randomized, controlled, animal experiment was performed at the Laboratory of Pharmacology, College of Pharmacy, Harbin University of Commerce between April 2007 and December 2008. MATERIALS： XMDP was prepared by the College of Pharmacy, Harbin University of Commerce, with each 40 mg pill containing ferulic acid （≥ 0.149 mg） and gastrodin （≥ 0.171 mg）. Ginkgo leaf tablets were purchased from Taiyuan Qianyuan Pharmacy, China. METHODS： Healthy, adult, male, Wistar rats were randomly assigned to 6 groups： sham-operation, model, XMDP （high-, middle-, and low- dose）, and Ginkgo leaf tablets. The 6 groups were subdivided into two subgroups according to administration days, i.e., 30 and 60 days, with 8 animals in each subgroup. Rats in the model, XMDP, and Ginkgo leaf tablets groups were subjected to permanent bilateral ligation of the common carotid artery to establish a vascular dementia model. At 8 days after model establishment, all groups received intragastric administration once daily of the following： 10 mL/kg normal saline in the sham-operation and model groups; 0.4, 0.2, and 0.1 g/kg XMDP in the high-, middle-, and low-dose XMDP groups, respectively; and 50 mg/kg Ginkgo leaf tablets in the Ginkgo leaf tablets group. MAIN OUTCOME MEASURES： Hematoxylin-eosin staining was used to observe appearance and to quantify the number of hippocampal CA1 pyramidal neurons. Brain-derived neurotrophic factor and nerve growth factor concentrations in brain tissues were detected by enzyme-linked immunosorbent assay. RESULTS： Following model establishment, hippocampal CA1 neurons exhibited pathological changes. Compared with the sham-operation group, the number of pyramidal neurons significantly decreased （P 〈 0.05 or P 〈 0.01）, and neurotrophic factor concentration increased in the model rats （P 〈 0.05 or P 〈 0.01）. XMDP attenuated neuronal injury in a dose-dependent manner： the number of pyramidal neurons and neurotrophic factor concentrations were significantly increased compared with the model group （P〈 0.05 or P〈 0.01）. High- and middle-dose XMDP resulted in equivalent effects to Ginkgo leaf tablets. In addition, neurotrophic factor concentrations in all XMDP groups, after 60 days of administration, were remarkably greater than corresponding concentrations at 30 days （P 〈 0.05 or P 〈 0.01 ）. CONCLUSION： Hippocampal CA1 pyramidal cells exhibited pathological injury following establishment of the vascular dementia model. Middle- and high-dose XMDP increased neurotrophic factor expression in the brain of vascular dementia rats, which suggested neuroprotection equivalent to Ginkgo leaf tablets.

大鼠海马CA1区神经元在衰老过程中的形态学变化

对不同年龄组雄性ＳＤ大鼠海马ＣＡ１区锥体层神经元分别做光学和电镜观察与测定，结果表明ＣＡ１区锥体层单位面积内神经元数目随增龄下降达３３％（Ｐ＜０． ００１），同时伴有锥体层厚度的增加（Ｐ＜０. ００１）；ＣＡ１区部分锥体神经元细胞器与胞突在老化过程中出现一系列形态学变化。本文对上述结果及其意义进行了讨论。

Neuroprotection of Chrysanthemum indicum Linne against cerebral ischemia/reperfusion injury by anti-inflammatory effect in gerbils

In this study, we tried to verify the neuroprotective effect of Chrysanthemum indicum Linne（CIL） extract, which has been used as a botanical drug in East Asia, against ischemic damage and to explore the underlying mechanism involving the anti-inflammatory approach. A gerbil was given CIL extract for 7 consecutive days followed by bilateral carotid artery occlusion to make a cerebral ischemia/reperfusion model. Then, we found that CIL extracts protected pyramidal neurons in the hippocampal CA1 region（CA1） from ischemic damage using neuronal nucleus immunohistochemistry and Fluoro-Jade B histofluorescence. Accordingly, interleukin-13 immunoreactivities in the CA1 pyramidal neurons of CIL-pretreated animals were maintained or increased after cerebral ischemia/reperfusion. These findings indicate that the pre-treatment of CIL can attenuate neuronal damage/death in the brain after cerebral ischemia/reperfusion via an anti-inflammatory approach.

Subjective tinnitus: lesion-induced pathological central homeostasis remodeling

Subjective tinnitus is the most common type of tinnitus, which is the manifestation of pathologicalactivities in the brain. It happens in a substantial portion of the general population and brings significantburden to the society. Severe subjective tinnitus can lead to depression and insomnia and severely affectspatients’ quality of life. However, due to poor understanding of its etiology and pathogenesis, treatmentof subjective tinnitus remains challenging. In recent decades, a growing number of studies have shownthat subjective tinnitus is related to lesion-induced neural plasticity of auditory and non-auditory centralsystems. This article reviews cellular mechanisms of neural plasticity in subjective tinnitus to providefurther understanding of its pathogenesis.

老年大鼠海马CA1区锥体神经元的“空泡变性”的观察

目的：观察老年大鼠海马ＣＡ１区锥体神经元的超微结构变化，以期探讨大鼠老化的形态学机理。方法：电子显微镜。结果：在老年大鼠海马ＣＡ１区锥体神经元的核周体、核及树突中均存在一种特殊的空泡，且与以往学者所述的“颗粒空泡变性”现象不同。结论：我们认为是一种较为特殊的变化，称其为“空泡变性”（Ｖａｃｕｏｌａｔｉｏｎ），并推测此种“空泡变性”现象可能是大鼠老化的形态学标志之一。

Effects of diazepam on glutamatergic synaptic transmission in the hippocampal CA1 area of rats with traumatic brain injury

The activity of the Schaffer collaterals of hippocampal CA3 neurons and hippocampal CA1 neurons has been shown to increase after lfuid percussion injury. Diazepam can inhibit the hy-perexcitability of rat hippocampal neurons after injury, but the mechanism by which it affects excitatory synaptic transmission remains poorly understood. Our results showed that diazepam treatment signiifcantly increased the slope of input-output curves in rat neurons after lfuid per-cussion injury. Diazepam signiifcantly decreased the numbers of spikes evoked by super stimuli in the presence of 15 μmol/L bicuculline, indicating the existence of inhibitory pathways in the injured rat hippocampus. Diazepam effectively increased the paired-pulse facilitation ratio in the hippocampal CA1 region following fluid percussion injury, reduced miniature excitatory postsynaptic potentials, decreased action-potential-dependent glutamine release, and reversed spontaneous glutamine release. These data suggest that diazepam could decrease the lfuid per-cussion injury-induced enhancement of excitatory synaptic transmission in the rat hippocampal CA1 area.

Hippocampal ultrastructural changes and apoptotic cell death in rats following endurance training and acute exhaustive exercise

BACKGROUND： Exhaustive exercise can lead to apoptosis of skeletal muscle cells and myocardial cells as a result of pathological changes in the corresponding cellular ultrastructure. It is hypothesized that such changes could also occur in neurons. OBJECTIVE： To observe brain cell apoptosis and ultrastructural changes in hippocampal neurons in rats following endurance training and acute exhaustive exercise. DESIGN, TIME AND SETTING： A randomized, controlled, morphological analysis was performed at the Medical Laboratory Center of Zhengzhou University between July and November 2007. MATERIALS： Forty male, 8-week-old, Sprague Dawley rats were included in this study. METHODS： Endurance training consisted of treadmill running once a day, 6 days a week, for 4. weeks. For acute exhaustive exercise, graded treadmill running was conducted. Rats were exposed to exercise at an increasing speed （10 m/min, increasing to 20 and 36 m/min for moderate- and high-intensity exhaustive exercise, respectively, and then was continued until exhaustion）. A total of 40 rats were evenly distributed into the following 4. groups： Group A rats were not exercised; Group B rats were not trained but sacrificed 24 hours after acute exhaustive treadmill running exercise; Group C-rats were subjected to endurance training and sacrificed immediately after acute exhaustive treadmill running exercise; Group D rats were subjected to endurance training and sacrificed 24 hours after acute exhaustive treadmill running exercise. MAIN OUTCOME MEASURES： Apoptotic cell death was detected by the TUNEL method and hippocampal neuronal ultrastructural change was observed through using transmission electron microscopy. RESULTS： All 40 rats were included in the final analysis. Subsequent to exhaustive exercise, rat cerebral cortex and hippocampal neurons appeared contracted and degenerated. In addition, high amount of lipofuscin was visible in the hippocampal region, Necrotic neurons encased by glial cells appeared in the cerebral cortex and hippocampus. Glial cells exhibited different degrees of swelling. Subsequent to exhaustive exercise, brain cell apoptosis rate significantly increased, and reached over 30% in some regions, compared with group A （P 〈 0.05）. No significant difference in apoptosis rate existed between groups B, C, and D （P 〈 0.05）. CONCLUSION： Endurance training and acute exhaustive exercise cause, to some degree, injuries to glial cells, resulting in apoptosis of numerous brain cells. Subsequent to exhaustive exercise, high amounts of lipofuscin appear in the hippocampus, indicating that exhaustive exercise possibly contributes to neural cell aging or dysmetabolism.

Monocarboxylate transporter 4 plays a significant role in the neuroprotective mechanism of ischemic preconditioning in transient cerebral ischemia

Monocarboxylate transporters（MCTs）, which carry monocarboxylates such as lactate across biological membranes, have been associated with cerebral ischemia/reperfusion process. In this study, we studied the effect of ischemic preconditioning（IPC） on MCT4 immunoreactivity after 5 minutes of transient cerebral ischemia in the gerbil. Animals were randomly designated to four groups（sham-operated group, ischemia only group, IPC ＋ sham-operated group and IPC ＋ ischemia group）. A serious loss of neuron was found in the stratum pyramidale of the hippocampal CA1 region（CA1）, not CA2/3, of the ischemia-only group at 5 days post-ischemia; however, in the IPC ＋ ischemia groups, neurons in the stratum pyramidale of the CA1 were well protected. Weak MCT4 immunoreactivity was found in the stratum pyramidale of the CA1 in the sham-operated group. MCT4 immunoreactivity in the stratum pyramidale began to decrease at 2 days post-ischemia and was hardly detected at 5 days post-ischemia; at this time point, MCT4 immunoreactivity was newly expressed in astrocytes. In the IPC ＋ sham-operated group, MCT4 immunoreactivity in the stratum pyramidale of the CA1 was increased compared with the sham-operated group, and, in the IPC ＋ ischemia group, MCT4 immunoreactivity was also increased in the stratum pyramidale compared with the ischemia only group. Briefly, present findings show that IPC apparently protected CA1 pyramidal neurons and increased or maintained MCT4 expression in the stratum pyramidale of the CA1 after transient cerebral ischemia. Our findings suggest that MCT4 appears to play a significant role in the neuroprotective mechanism of IPC in the gerbil with transient cerebral ischemia.