Apical Dendritic Spine Density Research Articles

HIV-1 Tat reduces apical dendritic spine density throughout the trisynaptic pathway in the hippocampus of male transgenic mice

Nearly one-third of persons infected with HIV-1 (PWH) develop HIV-associated neurocognitive disorders (HAND), which can be exacerbated by exposure to opioids. The impact of opioids on HIV-induced alterations in neuronal plasticity is less well understood. Both morphine exposure and HIV have been shown to disrupt synaptic growth and stability in the hippocampus suggesting a potential site of convergence for their deleterious effects. In the present study, we examined the density of dendritic spines in CA1 and CA3 pyramidal neurons, and granule neurons within the dentate gyrus representing the hippocampal trisynaptic pathway after short-term exposure to the HIV transactivator of transcription (Tat) protein and morphine. We exposed inducible male, HIV-1 Tat transgenic mice to escalating doses of morphine (10–40 mg/kg, b.i.d.) and examined synaptodendritic structure in Golgi-impregnated hippocampal neurons. HIV-1 Tat, but not morphine, systematically reduced the density of apical, but not basilar, dendrites of CA1 and CA3 pyramidal neurons, and granule neuronal apical dendrites, suggesting the coordinated loss of specific synaptic interconnections throughout the hippocampal trisynaptic pathway.

APOE4 homozygotes are resistant to the mnemonic benefits of 17β-estradiol in the EFAD mouse model of Alzheimer's disease.

Loss of circulating estrogens at menopause may contribute to increased risk for Alzheimer's disease (AD) in females relative to males. APOE4, the greatest genetic risk factor for AD, acts synergistically with estrogens to increase risk in females. However, despite the relative contributions of APOE genotype and estrogen loss to sex differences in AD risk, these factors are rarely examined in concert in basic research. Hence, our knowledge of how APOE genotype may interact with estrogens to contribute to AD risk, or whether estrogens may be of benefit to particular genotypes, is limited. The present study was designed to test whether APOE genotype interacts with E2 to modulate cognition and dendritic spine density in a mouse model of AD. Effects of 17β-estradiol (E2 ) treatment on memory were examined in ovariectomized (OVXed) transgenic mice expressing 5 familial AD mutations (5XFAD) and two copies of human APOE3 (E3FAD), APOE4 (E4FAD), or one copy each of APOE3/APOE4 (E3/4FAD). OVXed female E3FAD, E3/4FAD, and E4FAD mice received bilateral dorsal hippocampal (DH) infusion of E2 immediately after training in object recognition (OR) and object placement (OP) tasks. Next, the effect of APOE genotype to modulate estrogenic effects on spines was examined. E3FAD, E3/4FAD, and E4FAD mice received DH infusion of E2 and brains were collected for Golgi impregnation and quantification of dendritic spine density 2 h later. DH infusion of E2 facilitated OR and OP memory in E3FAD and E3/4FADs, but not E4FADs. Similarly, DH infusion of E2 increased CA1 apical dendritic spine density in E3FADs and E3/4FADs, but not E4FADs. CA1 basal spine density was significantly reduced by E4FAD genotype. The significant benefit of E2 only in E3FAD and E3/4FAD mice suggests that having two copies of the APOE4 allele results in lower susceptibility to the memory-enhancing effects of E2 in the EFAD model. These findings provide novel evidence that E2 may be of clinical benefit to APOE3 and APOE3/4, but not homozygous APOE4, carriers.

Orexin (hypocretin) mediates light-dependent fluctuation of hippocampal function in a diurnal rodent.

Environmental lighting conditions play a central role in cognitive function, but the underlying mechanisms remain unclear. Utilizing a diurnal rodent model, the Nile grass rat (Arvicanthis niloticus), we previously found that daytime light intensity affects hippocampal function in this species in a manner similar to its effects in humans. Compared to animals housed in a 12:12 h bright light-dark (brLD) cycle, grass rats kept in a 12:12 h dim light-dark (dimLD) cycle showed impaired spatial memory in the Morris water maze (MWM) and reduced CA1 apical dendritic spine density. The present study explored the neural substrates mediating the effects of daylight intensity on hippocampal function focusing on the hypothalamic orexin (hypocretin) system. First, animals housed in dimLD were treated with daily intranasal administration of orexin A peptide over five training days of the MWM task. Compared to vehicle controls, this treatment led to superior spatial memory accompanied by increased phosphorylation of Ca2+ /calmodulin-dependent protein kinase II α and glutamate receptor 1 within the CA1. To assess the role of hippocampal orexinergic signaling, an adeno-associated viral vector (AAV) expressing an orexin receptor 1 (OX1R) shRNA was injected into the dorsal hippocampus targeting the CA1 of animals housed in brLD. AAV-mediated knockdown of OX1R within the hippocampus resulted in deficits in MWM performance and reduced CA1 apical dendritic spine density. These results are consistent with the view that the hypothalamic orexinergic system underlies the modulatory role of daytime illumination on hippocampal function in diurnal mammals.

Repeated victorious and defeat experiences induce similar apical dendritic spine remodeling in CA1 hippocampus of rats

In this study, apical dendritic spine density of neurons in hippocampal, amygdalar and prefrontal cortical areas was compared in rats that were repeatedly winning or losing social conflicts. Territorial male wild-type Groningen (WTG) rats were allowed multiple daily attacks (>20 times) on intruder males in the resident-intruder paradigm. Frequent winning experiences are known to facilitate uncontrolled aggressive behavior reflected in aggressive attacks on anesthetized males which was also observed in the winners in this study. Both winners and losers were socially housed during the experiments; winners with females to stimulate territorial behavior, and losers with two other losing male rats. Twenty-four hours after the last social encounter, brains from experienced residential winners and repeatedly defeated intruder rats were collected and neuronal morphology in selected brain regions was studied via Golgi-Cox staining. Results indicate that spine density in the apical dendrites of the hippocampal CA1 reduced similarly in both winners and losers. In addition, winners showed increased spine densities at the proximal segments (20−30 μm) of the basolateral amygdala neurons and losers tended to show a decreased spine density at the more proximal segments of the infralimbic region of prefrontal cortex neurons. No effect of winning and losing was observed in the medial amygdala. The atrophic effect of repeated defeats in hippocampal and prefrontal regions was anticipated despite the fact that social housing of the repeatedly losing intruder males may have played a protective role. The reduction of hippocampal spine density in the winners seems surprising but supports previous findings in hierarchical dominant males in rat colonies. The dominants showed even greater shrinkage of the apical dendritic arbors of hippocampal CA3 pyramidal neurons compared to the stressed subordinates.

Decreased Level of Exosomal miR-5121 Released from Microglia Suppresses Neurite Outgrowth and Synapse Recovery of Neurons Following Traumatic Brain Injury.

Activated microglia can suppress neurite outgrowth and synapse recovery in the acute stage following traumatic brain injury (TBI). However, the underlying mechanism has not been clearly elucidated. Exosomes derived from microglia have been reported to play a critical role in microglia-neuron interaction in healthy and pathological brains. Here, we aimed to investigate the role of microglia-derived exosomes in regulating neurite outgrowth and synapse recovery following TBI. In our study, exosomes derived from microglia were co-cultured with stretch-injured neurons in vitro and intravenously injected into mice that underwent fluid percussion injury (FPI) by tail vein injection in vivo. The results showed that microglia-derived exosomes could be absorbed by neurons in vitro and in vivo. Moreover, exosomes derived from stretch-injured microglia decreased the protein levels of GAP43, PSD-95, GluR1, and Synaptophysin and dendritic complexity in stretch-injured neurons in vitro, and reduced GAP43+ NEUN cell percentage and apical dendritic spine density in the pericontusion region in vivo. Motor coordination was also impaired in mice treated with stretch-injured microglia-derived exosomes after FPI. A microRNA microarray showed that the level of miR-5121 was decreased most greatly in exosomes derived from stretch-injured microglia. Overexpression of miR-5121 in stretch-injured microglia-derived exosomes partly reversed the suppression of neurite outgrowth and synapse recovery of neurons both in vitro and in vivo. Moreover, motor coordination in miR-5121 overexpressed exosomes treated mice was significantly improved after FPI. Following mechanistic study demonstrated that miR-5121 might promote neurite outgrowth and synapse recovery by directly targeting RGMa. In conclusion, our finding revealed a novel exosome-mediated mechanism of microglia-neuron interaction that suppressed neurite outgrowth and synapse recovery of neurons following TBI.

Compromised Hippocampal Neuroplasticity in the Interferon-\u03b1 and Toll-like Receptor-3 Activation-Induced Mouse Depression Model

Disrupted neuronal plasticity due to subtle inflammation is considered to play a fundamental role in the pathogenesis of major depressive disorder. Interferon-α (IFN-α) potentiates immune responses against viral pathogens that induce toll-like receptor-3 (TLR3) activation but evokes severe major depressive disorder in humans by mechanisms that remain insufficiently described. By using a previously established mouse model of depression induced by combined delivery of IFN-α and polyinosinic:polycytidylic acid (poly(I:C)), a TLR3 agonist, we provide evidence that IFN-α and poly(I:C) reduce apical dendritic spine density in the hippocampal CA1 area ex vivo via mechanisms involving decreased TrkB signaling. In vitro, IFN-α and poly(I:C) treatments required neuronal activity to reduce dendritic spine density and TrkB signaling. The levels of presynaptic protein vesicular glutamate transporter (VGLUT)-1 and postsynaptic protein postsynaptic density-95 (PSD95) were specifically decreased, whereas the expression of both synaptic and extrasynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor 1 (AMPAR1) was increased by IFN-α and poly(I:C) delivery. Patch clamp recordings in primary hippocampal neurons revealed that morphological changes at the synapse induced by IFN-α and poly(I:C) costimulation were accompanied by an increased action potential threshold and action potential frequency, indicative of impaired neuronal excitability. Taken together, IFN-α and poly(I:C) delivery leads to structural and functional alterations at the synapse indicating that compromised neuroplasticity may play an integral role in the pathogenesis of immune response-induced depression.

Estrogen-Dependent Functional Spine Dynamics in Neocortical Pyramidal Neurons of the Mouse.

Surgical ovariectomy has been shown to reduce spine density in hippocampal CA1 pyramidal cells of rodents, and this reduction is reversed by 17β-estradiol (E2) treatment in a model of human estrogen replacement therapy. Here, we report reduction of spine density in apical dendrites of layer 5 pyramidal neurons of several neocortical regions that is reversed by subsequent E2 treatment in ovariectomized (OVX) female Thy1M-EGFP mice. We also found that OVX-associated reduction of spine density in somatosensory cortex was accompanied by a reduction in miniature EPSC (mEPSC) frequency (but not mIPSC frequency), indicating a change in functional synapses. OVX-associated spine loss in somatosensory cortex was also rescued by an agonist of the G-protein-linked estrogen receptor (GPER) but not by agonists of the classic estrogen receptors ERα/ERβ, whereas the opposite selectivity was found in area CA1. Acute treatment of neocortical slices with E2 also rescued the OVX-associated reduction in mEPSC frequency, which could be mimicked by a GPER agonist and abolished by a GPER antagonist. Time-lapse in vivo two-photon imaging showed that OVX-associated reduction in spine density is achieved by both an increase in spine loss rate and a decrease in spine gain rate and that subsequent rescue by E2 reversed both of these processes. Crucially, the spines added after E2 rescue were no more likely to reappear at or nearby the sites of pre-OVX spines than those in control mice treated with vehicle. Thus, a model of estrogen replacement therapy, although restoring spine density and dynamics, does not entirely restore functional connectivity.SIGNIFICANCE STATEMENT Estrogen replacement therapy following menopause or surgical removal of the ovaries is a widespread medical practice, yet little is known about the consequences of such treatment for cells in the brain. Here, we show that estrogen replacement reverses some of the effects of surgical removal of the ovaries on the structure and function of brain cells in the mouse. Yet, importantly, the fine wiring of the brain is not returned to the presurgery state by estrogen treatment, suggesting lasting functional consequences.

Daytime Light Intensity Modulates Spatial Learning and Hippocampal Plasticity in Female Nile Grass Rats (Arvicanthis niloticus)

Light has pervasive effects on the physiology and behavior of mammals. Several human studies have shown that light modulates cognitive functions; however, the mechanisms responsible for the effects of light remain unclear. Our previous work using diurnal male Nile grass rats (Arvicanthis niloticus) revealed that reduced illuminance during the day leads to impairments in hippocampal-dependent spatial learning/memory, reduced CA1 dendritic spine density, and attenuated hippocampal brain-derived neurotrophic factor (BDNF) expression in males. The present study examined the impact of ambient light intensity on hippocampal functions in female grass rats and explored sex differences in behavioral and hippocampal responses. Female grass rats were housed in either a 12:12-hr bright light–dark (brLD, 1000 lx) or dim light–dark (dimLD, 50 lx) cycle for four weeks. The dimLD group showed impaired spatial memory in the Morris water maze task and reduced CA1 apical dendritic spine density, similar to prior observations in males. However, the behavioral deficits seen in females were more severe than those seen in males, with dimLD females showing no evidence of long-term retention over the 24-hour periods between training sessions. In contrast to the attenuated hippocampal BDNF expression found in dimLD males, there was no significant difference in the expression of BDNF and of its receptor TrkB between females in brLD and dimLD. The results suggest that, as seen in male grass rats, reduced illuminance during the day impairs hippocampal-dependent spatial memory and hippocampal plasticity in female diurnal grass rats, but the underlying signaling pathways responsible for the effects of light restriction may differ between the sexes.

Conditional Deletion of Hippocampal CA2/CA3a Oxytocin Receptors Impairs the Persistence of Long-Term Social Recognition Memory in Mice.

Oxytocin (OXT) receptors (OXTRs) are prominently expressed in hippocampal CA2 and CA3 pyramidal neurons, but little is known about its physiological function. As the functional necessity of hippocampal CA2 for social memory processing, we tested whether CA2 OXTRs may contribute to long-term social recognition memory (SRM) formation. Here, we found that conditional deletion of Oxtr from forebrain (Oxtr-/-) or CA2/CA3a-restricted excitatory neurons in adult male mice impaired the persistence of long-term SRM but had no effect on sociability and preference for social novelty. Conditional deletion of CA2/CA3a Oxtr showed no changes in anxiety-like behavior assessed using the open-field, elevated plus maze and novelty-suppressed feeding tests. Application of a highly selective OXTR agonist [Thr4,Gly7]-OXT to hippocampal slices resulted in an acute and lasting potentiation of excitatory synaptic responses in CA2 pyramidal neurons that relied on N-methyl-d-aspartate receptor activation and calcium/calmodulin-dependent protein kinase II activity. In addition, Oxtr-/- mice displayed a defect in the induction of long-term potentiation, but not long-term depression, at the synapses between the entorhinal cortex and CA2 pyramidal neurons. Furthermore, Oxtr deletion led to a reduced complexity of basal dendritic arbors of CA2 pyramidal neurons, but caused no alteration in the density of apical dendritic spines. Considering that the methodologies we have used to delete Oxtr do not rule out targeting the neighboring CA3a region, these findings suggest that OXTR signaling in the CA2/CA3a is crucial for the persistence of long-term SRM.SIGNIFICANCE STATEMENT Oxytocin receptors (OXTRs) are abundantly expressed in hippocampal CA2 and CA3 regions, but there are little known about their physiological function. Taking advantage of the conditional Oxtr knock-out mice, the present study highlights the importance of OXTR signaling in the induction of long-term potentiation at the synapses between the entorhinal cortex and CA2 pyramidal neurons and the persistence of long-term social recognition memory. Thus, OXTRs in the CA2/CA3a may provide a new target for therapeutic approaches to the treatment of social cognition deficits, which are often observed in patients with neuropsychiatric disorders.

Separation increases passive stress-coping behaviors during forced swim and alters hippocampal dendritic morphology in California mice

Individuals within monogamous species form bonds that may buffer against the negative effects of stress on physiology and behavior. In some species, involuntary termination of the mother-offspring bond results in increased symptoms of negative affect in the mother, suggesting that the parent-offspring bond may be equally as important as the pair bond. To our knowledge, the extent to which affect in paternal rodents is altered by involuntary termination of the father-offspring bond is currently unknown. Here, we investigated to what extent separation and paternal experience alters passive stress-coping behaviors and dendritic morphology in hippocampal subfields of California mice (Peromyscus californicus). Irrespective of paternal experience, separated mice displayed shorter latencies to the first bout of immobility, longer durations of immobility, and more bouts of immobility than control (non-separated) mice. This effect of separation was exacerbated by paternal experience in some measures of behavioral despair—separation from offspring further decreased the latency to immobility and increased bouts of immobility. In the dentate gyrus, separation reduced dendritic spine density regardless of paternal experience. Increased spine density was observed on CA1 basal, but not apical, dendrites following paternal experience. Regardless of offspring presence, fatherhood was associated with reduced apical dendritic spine density in area CA3 of the hippocampus. Separation enhanced complexity of both basal and apical dendrites in CA1, while fatherhood reduced dendritic complexity in this region. Our data suggest that forced dissolution of the pair bond induces passive stress-coping behaviors and contributes to region-specific alterations in hippocampal structure in California mouse males.

Alzheimer-related decrease in CYFIP2 links amyloid production to tau hyperphosphorylation and memory loss.

Characteristic features of Alzheimer's disease are memory loss, plaques resulting from abnormal processing of amyloid precursor protein (APP), and presence of neurofibrillary tangles and dystrophic neurites containing hyperphosphorylated tau. Currently, it is not known what links these abnormalities together. Cytoplasmic FMR1 interacting protein 2 (CYFIP2) has been suggested to regulate mRNA translation at synapses and this may include local synthesis of APP and alpha-calcium/calmodulin-dependent kinase II, a kinase that can phosphorylate tau. Further, CYFIP2 is part of the Wiskott-Aldrich syndrome protein-family verprolin-homologous protein complex, which has been implicated in actin polymerization at synapses, a process thought to be required for memory formation. Our previous studies on p25 dysregulation put forward the hypothesis that CYFIP2 expression is reduced in Alzheimer's disease and that this contributes to memory impairment, abnormal APP processing and tau hyperphosphorylation. Here, we tested this hypothesis. First, in post-mortem tissue CYFIP2 expression was reduced by ∼50% in severe Alzheimer's hippocampus and superior temporal gyrus when normalized to expression of a neuronal or synaptic marker protein. Interestingly, there was also a trend for decreased expression in mild Alzheimer's disease hippocampus. Second, CYFIP2 expression was reduced in old but not in young Tg2576 mice, a model of familial Alzheimer's disease. Finally, we tested the direct impact of reduced CYFIP2 expression in heterozygous null mutant mice. We found that in hippocampus this reduced expression causes an increase in APP and β-site amyloid precursor protein cleaving enzyme 1 (BACE1) protein, but not mRNA expression, and elevates production of amyloid-β42 Reduced CYFIP2 expression also increases alpha-calcium/calmodulin-dependent kinase II protein expression, and this is associated with hyperphosphorylation of tau at serine-214. The reduced expression also impairs spine maturity without affecting spine density in apical dendrites of CA1 pyramidal neurons. Furthermore, the reduced expression prevents retention of spatial memory in the water maze. Taken together, our findings indicate that reduced CYFIP2 expression triggers a cascade of change towards Alzheimer's disease, including amyloid production, tau hyperphosphorylation and memory loss. We therefore suggest that CYFIP2 could be a potential hub for targeting treatment of the disease.

Effects of Chronic Dopamine D2R Agonist Treatment and Polysialic Acid Depletion on Dendritic Spine Density and Excitatory Neurotransmission in the mPFC of Adult Rats.

Dopamine D2 receptors (D2R) in the medial prefrontal cortex (mPFC) are key players in the etiology and therapeutics of schizophrenia. The overactivation of these receptors contributes to mPFC dysfunction. Chronic treatment with D2R agonists modifies the expression of molecules implicated in neuronal structural plasticity, synaptic function, and inhibitory neurotransmission, which are also altered in schizophrenia. These changes are dependent on the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a plasticity-related molecule, but nothing is known about the effects of D2R and PSA-NCAM on excitatory neurotransmission and the structure of mPFC pyramidal neurons, two additional features affected in schizophrenia. To evaluate these parameters, we have chronically treated adult rats with PPHT (a D2R agonist) after enzymatic removal of PSA with Endo-N. Both treatments decreased spine density in apical dendrites of pyramidal neurons without affecting their inhibitory innervation. Endo-N also reduced the expression of vesicular glutamate transporter-1. These results indicate that D2R and PSA-NCAM are important players in the regulation of the structural plasticity of mPFC excitatory neurons. This is relevant to our understanding of the neurobiological basis of schizophrenia, in which structural alterations of pyramidal neurons and altered expression of D2R and PSA-NCAM have been found.

Learning, memory and synaptic plasticity in hippocampus in rats exposed to sevoflurane

PurposeDevelopmental exposure to volatile anesthetics has been associated with cognitive deficits at adulthood. Rodent studies have revealed impairments in performance in learning tasks involving the hippocampus. However, how the duration of anesthesia exposure impact on hippocampal synaptic plasticity, learning, and memory is as yet not fully elucidated. MethodsOn postnatal day 7(P7), rat pups were divided into 3 groups: control group (n=30), 3% sevoflurane treatment for 1h (Sev 1h group, n=30) and 3% sevoflurane treatment for 6h (Sev 6h group, n=28). Following anesthesia, synaptic vesicle-associated proteins and dendrite spine density and synapse ultrastructure were measured using western blotting, Golgi staining, and transmission electron microscopy (TEM) on P21. In addition, the effects of sevoflurane treatment on long-term potentiation (LTP) and long-term depression (LTD), two molecular correlates of memory, were studied in CA1 subfields of the hippocampus, using electrophysiological recordings of field potentials in hippocampal slices on P35-42. Rats’ neurocognitive performance was assessed at 2 months of age, using the Morris water maze and novel-object recognition tasks. ResultsOur results showed that neonatal exposure to 3% sevoflurane for 6h results in reduced spine density of apical dendrites along with elevated expression of synaptic vesicle-associated proteins (SNAP-25 and syntaxin), and synaptic ultrastructure damage in the hippocampus. The electrophysiological evidence indicated that hippocampal LTP, but not LTD, was inhibited and that learning and memory performance were impaired in two behavioral tasks in the Sev 6h group. In contrast, lesser structural and functional damage in the hippocampus was observed in the Sev 1h group. ConclusionOur data showed that 6-h exposure of the developing brain to 3% sevoflurane could result in synaptic plasticity impairment in the hippocampus and spatial and nonspatial hippocampal-dependent learning and memory deficits. In contrast, shorter-duration exposure (1h) results in less damage. These results provide further evidences that duration of anesthesia exposure could have differential effects on neuronal plasticity and neurocognitive performance.

Effects of Tetramethylpyrazine on Functional Recovery and Neuronal Dendritic Plasticity after Experimental Stroke.

The 2,3,5,6-tetramethylpyrazine (TMP) has been widely used in the treatment of ischemic stroke by Chinese doctors. Here, we report the effects of TMP on functional recovery and dendritic plasticity after ischemic stroke. A classical model of middle cerebral artery occlusion (MCAO) was established in this study. The rats were assigned into 3 groups: sham group (sham operated rats treated with saline), model group (MCAO rats treated with saline) and TMP group (MCAO rats treated with 20 mg/kg/d TMP). The neurological function test of animals was evaluated using the modified neurological severity score (mNSS) at 3 d, 7 d, and 14 d after MCAO. Animals were euthanized for immunohistochemical labeling to measure MAP-2 levels in the peri-infarct area. Golgi-Cox staining was performed to test effect of TMP on dendritic plasticity at 14 d after MCAO. TMP significantly improved neurological function at 7 d and 14 d after ischemia, increased MAP-2 level at 14 d after ischemia, and enhanced spine density of basilar dendrites. TMP failed to affect the spine density of apical dendrites and the total dendritic length. Data analyses indicate that there was significant negative correlation between mNSS and plasticity measured at 14 d after MCAO. Thus, enhanced dendritic plasticity contributes to TMP-elicited functional recovery after ischemic stroke.

Regional-specific effects of ovarian hormone loss on synaptic plasticity in adult human APOE targeted replacement mice.

The human apolipoprotein ε4 allele (APOE4) has been implicated as one of the strongest genetic risk factors associated with Alzheimer’s disease (AD) and in influencing normal cognitive functioning. Previous studies have demonstrated that mice expressing human apoE4 display deficits in behavioral and neurophysiological outcomes compared to those with apoE3. Ovarian hormones have also been shown to be important in modulating synaptic processes underlying cognitive function, yet little is known about how their effects are influenced by apoE. In the current study, female adult human APOE targeted replacement (TR) mice were utilized to examine the effects of human APOE genotype and long-term ovarian hormone loss on synaptic plasticity in limbic regions by measuring dendritic spine density and electrophysiological function. No significant genotype differences were observed on any outcomes within intact mice. However, there was a significant main effect of genotype on total spine density in apical dendrites in the hippocampus, with post-hoc t-tests revealing a significant reduction in spine density in apoE3 ovariectomized (OVX) mice compared to sham operated mice. There was also a significant main effect of OVX on the magnitude of LTP, with post-hoc t-tests revealing a decrease in apoE3 OVX mice relative to sham. In contrast, apoE4 OVX mice showed increased synaptic activity relative to sham. In the lateral amygdala, there was a significant increase in total spine density in apoE4 OVX mice relative to sham. This increase in spine density was consistent with a significant increase in spontaneous excitatory activity in apoE4 OVX mice. These findings suggest that ovarian hormones differentially modulate synaptic integrity in an apoE-dependent manner within brain regions that are susceptible to neurophysiological dysfunction associated with AD.

Developmental patterns of sleep slow wave activity and synaptic density in adolescent mice.

In humans sleep slow wave activity (SWA) declines during adolescence. It has been suggested that this decline reflects the elimination of cortical synapses, but this hypothesis has never been tested directly. We focused on mouse frontal cortex and collected data from early adolescence (∼postnatal day 20, P20) to adulthood (P60) of (1) SWA; (2) expression of synapsin I, a presynaptic marker; and (3) number of dendritic spines in layers I-II. Basic sleep research laboratory. YFP-line H mice (n = 70; P15-87, all males) and GFP-line S mice (n = 14; P17-60, 8 females) were used for EEG recording. Forty-five YFP mice (P19-119, 12 females) and 42 GFP-S mice (P20-60, 14 females) were used for in vivo 2-photon imaging and ex vivo confocal microscopy, respectively. Other YGP mice (n = 57, P10-77) were used for western blot analysis of synapsin I. N/A. As in humans, SWA in mice declined from early adolescence to adulthood. Synapsin I levels increased from P10 to P24, with little change afterwards. Mean spine density in apical dendrites of layer V pyramidal neurons (YFP-H) showed no change from P20 to P60. Spine number in layers I-II apical dendrites, belonging to layer III and V pyramidal neurons (GFP-S), increased slightly from P20 to P30 and decreased from P30 to P60; smaller spines decreased in number from P20 to P60, while bigger spines increased. In mice, it is unlikely that the developmental decrease in SWA can be accounted for by a net pruning of cortical synapses.

Estradiol increases dendritic length and spine density in CA1 neurons of the hippocampus of spontaneously hypertensive rats: A Golgi impregnation study

Increased neuronal vulnerability has been described in the brain of spontaneously hypertensive rats (SHR), models of primary hypertension. Previous data indicate that estradiol treatment corrects several dysfunctions of the hippocampus and hypothalamus of SHR. Considering this evidence we analyzed the dendritic arborization and spine density of the CA1 subfield in SHR and Wistar–Kyoto (WKY) normotensive rats with and without estradiol treatment. Five month old male SHR and WKY rats received single estradiol or cholesterol pellets (sham treatment) for 2weeks. A substantial rise of circulating estradiol (>25 fold) and testicular atrophy was present in all estradiol-receiving rats. In both SHR and WKY rats, estradiol decreased blood pressure by ~20mmHg; however, a moderate hypertension persisted in SHR (164mmHg). Using a modified Golgi impregnation technique, apical and basal dendrites of the CA1 subfield were subjected to Sholl analysis. Spine density was also statistically analyzed. Apical dendritic length was significantly lower in SHR compared to WKY rats (p<0.01), whereas estradiol treatment increased dendritic length in the SHR group only (SHR vs SHR+estradiol; p<0.01). Apical dendritic length plotted against the shell distances 20–100, 120–200 and 220–300μm, revealed that changes were more pronounced in the range 120–200μm between SHR vs. WKY rats (p<0.05) and SHR vs. SHR+estradiol (p<0.05). Instead, basal dendrites were not significantly modified by hypertension or steroid treatment. Spine density of apical dendrites was lower in SHR than WKY (p<0.05) and was up-regulated in the SHR+estradiol group compared to the SHR group (p<0.001). Similar changes were obtained for basal dendritic spines. These data suggest that changes of neuronal processes in SHR are plastic events restorable by estradiol treatment. In conjunction with previous results, the present data reveal new targets of estradiol neuroprotection in the brain of hypertensive rats.

Variant Brain-Derived Neurotrophic Factor Val66Met Polymorphism Alters Vulnerability to Stress and Response to Antidepressants

Brain-derived neurotrophic factor (BDNF) plays important roles in cell survival, neural plasticity, learning, and stress regulation. However, whether the recently found human BDNF Val66Met (BDNF(Met)) polymorphism could alter stress vulnerability remains controversial. More importantly, the molecular and structural mechanisms underlying the interaction between the BDNF(Met) polymorphism and stress are unclear. We found that heterozygous BDNF(+/Met) mice displayed hypothalamic-pituitary-adrenal axis hyperreactivity, increased depressive-like and anxiety-like behaviors, and impaired working memory compared with WT mice after 7 d restraint stress. Moreover, BDNF(+/Met) mice exhibited more prominent changes in BDNF levels and apical dendritic spine density in the prefrontal cortex and amygdala after stress, which correlated with the impaired working memory and elevated anxiety-like behaviors. Finally, the depressive-like behaviors in BDNF(+/Met) mice could be selectively rescued by acute administration of desipramine but not fluoxetine. These data indicate selective behavioral, molecular, and structural deficits resulting from the interaction between stress and the human genetic BDNF(Met) polymorphism. Importantly, desipramine but not fluoxetine has antidepressant effects on BDNF(+/Met) mice, suggesting that specific classes of antidepressant may be a more effective treatment option for depressive symptoms in humans with this genetic variant BDNF.

Air pollution impairs cognition, provokes depressive-like behaviors and alters hippocampal cytokine expression and morphology

Particulate matter air pollution is a pervasive global risk factor implicated in the genesis of pulmonary and cardiovascular disease. Although the effects of prolonged exposure to air pollution are well characterized with respect to pulmonary and cardiovascular function, comparatively little is known about the impact of particulate matter on affective and cognitive processes. The central nervous system may be adversely affected by activation of reactive oxygen species and pro-inflammatory pathways that accompany particulate matter pollution. Thus, we investigated whether long-term exposure to ambient fine airborne particulate matter (<2.5 μm (PM(2.5))) affects cognition, affective responses, hippocampal inflammatory cytokines and neuronal morphology. Male mice were exposed to either PM(2.5) or filtered air (FA) for 10 months. PM(2.5) mice displayed more depressive-like responses and impairments in spatial learning and memory as compared with mice exposed to FA. Hippocampal pro-inflammatory cytokine expression was elevated among PM(2.5) mice. Apical dendritic spine density and dendritic branching were decreased in the hippocampal CA1 and CA3 regions, respectively, of PM(2.5) mice. Taken together, these data suggest that long-term exposure to particulate air pollution levels typical of exposure in major cities around the globe can alter affective responses and impair cognition.

A Kinase Anchor Protein 150 (AKAP150)-associated Protein Kinase A Limits Dendritic Spine Density

The A kinase anchor protein AKAP150 recruits the cAMP-dependent protein kinase (PKA) to dendritic spines. Here we show that in AKAP150 (AKAP5) knock-out (KO) mice frequency of miniature excitatory post-synaptic currents (mEPSC) and inhibitory post-synaptic currents (mIPSC) are elevated at 2 weeks and, more modestly, 4 weeks of age in the hippocampal CA1 area versus litter mate WT mice. Linear spine density and ratio of AMPAR to NMDAR EPSC amplitudes were also increased. Amplitude and decay time of mEPSCs, decay time of mIPSCs, and spine size were unaltered. Mice in which the PKA anchoring C-terminal 36 residues of AKAP150 are deleted (D36) showed similar changes. Furthermore, whereas acute stimulation of PKA (2-4 h) increases spine density, prolonged PKA stimulation (48 h) reduces spine density in apical dendrites of CA1 pyramidal neurons in organotypic slice cultures. The data from the AKAP150 mutant mice show that AKAP150-anchored PKA chronically limits the number of spines with functional AMPARs at 2-4 weeks of age. However, synaptic transmission and spine density was normal at 8 weeks in KO and D36 mice. Thus AKAP150-independent mechanisms correct the aberrantly high number of active spines in juvenile AKAP150 KO and D36 mice during development.