Changes In Spine Density Research Articles

Dendritic Spine Density of Rat Hippocampal Neurons is Increased Following Consumption of Diet Containing a Prebiotic Blend and Bioactive Whey Protein Fractions

Modulation of neuronal dendritic spine density in animal models has been reported to result in cognitive benefits. However the extent to which early life dietary factors can impact neuronal structure is largely unknown. The aim of this study was to determine if a diet containing a prebiotic blend of polydextrose and galactooligosaccharides with bioactive whey protein fractions (TEST) alters dendritic spine morphology compared to a control (CONT) diet. Weanling Long Evans rats received CONT or TEST diets for 40 days. Brains were perfused, sectioned, and target neurons labeled using ballistic dye labeling. Individual spines were measured on medial prefrontal cortex (mPFC) and hippocampal dentate gyrus (DG) neurons manually for head diameter, length, and neck diameter using the Afraxis ESP platform. While total spine density did not differ between diets on mPFC neurons, TEST diet produced a significant increase in total dendritic spines in DG neurons in the hippocampus. Similar changes in spine density have been reported in association with cognitive benefits from early life enrichment and exercise in rodents. In-depth analysis further revealed that the increase in spine density was largely driven by increases in the immature-type spine phenotypes, including filopodia-like spines. Further research is warranted to determine if functional effects produced by TEST diet are associated with DG-related functions of the hippocampus. Supported by Mead Johnson Nutrition.

Serum 25 hydroxyvitamin D, bone mineral density and fracture risk across the menopause.

Low levels of serum 25 Hydroxyvitamin D [25(OH)D] have been linked to greater fracture risk in older women. This study aimed to determine whether higher 25(OH)D is associated with slower loss of bone mineral density (BMD) and lower fracture risk during the menopausal transition. This was a prospective cohort study at five clinical centers in the United States. Mean age was 48.5 ± 2.7 years. The fracture analysis included 124 women with an incident traumatic fracture, 88 with incident nontraumatic fracture, and 1532 women without incident fractures; average followup was 9.5 years. BMD analysis included 922 women with a documented final menstrual period. Serum 25(OH)D was measured by liquid chromatography tandem mass spectrometry at the third annual clinic visit. BMD was measured and incident fractures ascertained at each annual visit. The mean 25(OH)D was 21.8 ng/mL; seven-hundred two (43%) of the women had 25(OH)D values <20 ng/mL. There was no significant association between 25(OH)D and traumatic fractures. In multivariate adjusted hazards models, the hazard ratio (HR) for nontraumatic fractures (95% confidence interval [CI]) was 0.72 (0.54-0.96) for each 10-ng/mL increase in 25(OH)D. Comparing women whose 25(OH)D was ≥20 vs <20 ng/mL, the HR (95% CI) for fracture was 0.54 (0.32-0.89). Changes in lumbar spine and femoral neck bone mineral density across menopause were not significantly associated with serum 25(OH)D level. Serum 25(OH)D levels are inversely associated with nontraumatic fracture in mid-life women. Vitamin D supplementation is warranted in midlife women with 25(OH)D levels <20 ng/mL.

Deletion of KIBRA, protein expressed in kidney and brain, increases filopodial-like long dendritic spines in neocortical and hippocampal neurons in vivo and in vitro

Spines are small protrusions arising from dendrites that receive most excitatory synaptic input in the brain. Dendritic spines represent dynamic structures that undergo activity-dependent adaptations, for example, during synaptic plasticity. Alterations of spine morphology, changes of spine type ratios or density have consequently been found in paradigms of learning and memory, and accompany many neuropsychiatric disorders. Polymorphisms in the gene encoding KIBRA, a protein present in kidney and brain, are linked to memory performance and cognition in humans and mouse models. Deletion of KIBRA impairs long-term synaptic plasticity and postsynaptic receptor recycling but no information is available on the morphology of dendritic spines in null-mutant mice. Here, we directly examine the role of KIBRA in spinous synapses using knockout mice. Since KIBRA is normally highly expressed in neocortex and hippocampus at juvenile age, we analyze synapse morphology in intact tissue and in neuronal cultures from these brain regions. Quantification of different dendritic spine types in Golgi-impregnated sections and in transfected neurons coherently reveal a robust increase of filopodial-like long protrusions in the absence of KIBRA. While distribution of pre- and postsynaptic marker proteins, overall synapse ultrastructure and density of asymmetric contacts were remarkably normal, electron microscopy additionally uncovered less perforated synapses and spinules in knockout neurons. Thus, our results indicate that KIBRA is involved in the maintenance of normal ratios of spinous synapses, and may thus provide a structural correlate of altered cognitive functions when this memory-associated molecule is mutated.

Impact of immersion oils and mounting media on the confocal imaging of dendritic spines

BackgroundStructural plasticity, such as changes in dendritic spine morphology and density, reflect changes in synaptic connectivity and circuitry. Procedural variables used in different methods for labeling dendritic spines have been quantitatively evaluated for their impact on the ability to resolve individual spines in confocal microscopic analyses. In contrast, there have been discussions, though no quantitative analyses, of the potential effects of choosing specific mounting media and immersion oils on dendritic spine resolution. New methodHere we provide quantitative data measuring the impact of these variables on resolving dendritic spines in 3D confocal analyses. Medium spiny neurons from the rat striatum and nucleus accumbens are used as examples. ResultsBoth choice of mounting media and immersion oil affected the visualization of dendritic spines, with choosing the appropriate immersion oil as being more imperative. These biologic data are supported by quantitative measures of the 3D diffraction pattern (i.e. point spread function) of a point source of light under the same mounting medium and immersion oil combinations. Comparison with existing methodAlthough not a new method, this manuscript provides quantitative data demonstrating that different mounting media and immersion oils can impact the ability to resolve dendritic spines. These findings highlight the importance of reporting which mounting medium and immersion oil are used in preparations for confocal analyses, especially when comparing published results from different laboratories. ConclusionCollectively, these data suggest that choosing the appropriate immersion oil and mounting media is critical for obtaining the best resolution, and consequently more accurate measures of dendritic spine densities.

BA11 FKBP5 expression levels correlate with dendritic spine density in postmortem PTSD and controls

Genetic variants of the immunophilin FKBP5 have been implicated in susceptibility to post-traumatic stress disorder (PTSD) and other stress-related disorders. We examined the relationship between mushroom, stubby, thin and filopodial spine densities measured with Golgi staining and FKBP5 gene expression in the medial orbitofrontal cortex (BA11) in individuals diagnosed with PTSD and normal controls (n = 8/8). ANCOVA revealed PTSD cases had a significantly elevated density of stubby spines (29%, P < 0.037) and a trend for a reduction in mushroom spine density (25%, p < 0.082). Levels of FKBP5 mRNA were marginally elevated in the PTSD cases (z = 1.94, p = 0.053) and levels correlated inversely with mushroom (Spearman's rho = −0.83, p < 0.001) and overall spine density (rho = −0.75, p < 0.002) and directly with stubby spine density (rho = 0.55, p < 0.027). These data suggest that FKBP5 may participate in a cellular pathway modulating neuronal spine density changes in the brain, and that this pathway may be dysregulated in PTSD.

Inhibiting geranylgeranyltransferase I activity decreases spine density in central nervous system.

Geranylgeranyltransferase I (GGT), a protein prenyltransferase, is responsible for the posttranslational lipidation of Rho GTPases, such as Rac, Rho and Cdc42, all of which play an important role in neuronal synaptogenesis. We previously demonstrated that GGT promotes dendritic morphogenesis in cultured hippocampal neurons and cerebellar slices. We report here that inhibiting GGT activity decreases basal- and activity-dependent changes in spine density as well as in learning and memory ability of mice in vivo. We found that KCl- or bicuculline-induced dendritic spine density increases was abolished by specific GGT inhibitor GGTi-2147 treatment in cultured hippocampal neurons. GGTi-2147 lateral ventricular injection reduced GGT activity and membrane association of Rac and decreased the density of dendritic spines in the mouse hippocampus, frontal cortex and cerebellum. GGTi-2147 administration also impaired learning and memory ability of mice. More importantly, mice exposed to environmental enrichment (EE) showed increased spine density and learning and memory ability, which were significantly reversed by GGTi-2147 administration. These data demonstrate that inhibiting GGT activity prevents both basal- and activity-dependent changes in spine density in central nervous system both in vitro and in vivo. Manipulating GGT activity may be a promising strategy for the therapies of neurodevelopmental disorders, such as autism, depression, and schizophrenia.

Bisphosphonates May Protect against Bone Loss in Postmenopausal Women with Early Breast Cancer Receiving Adjuvant Aromatase Inhibitor Therapy: Results from a Meta-analysis

The efficacy of bisphosphonates (BPs) in treating bone loss associated with cancer therapies has been demonstrated in completed studies and ongoing clinical trials. The aim of this study was to investigate the evidence for BP use in treatment of bone loss in postmenopausal, early breast cancer (EBC) patients scheduled to receive aromatase inhibitors (AI). A comprehensive search for relative articles published until December 2013 was performed. The outcomes included the percentage and absolute change in lumbar spine (LS) and total hip (TH) bone mineral density (BMD). Before pooled meta-analysis, the studies were evaluated for publication bias and heterogeneity. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated. We also performed subgroup and sensitivity analyses. A total of 11 trials contributed to the analysis. BP was shown to be efficacious in increasing BMD at the LS and TH. WMD in BMD absolute change was 0.21 g/cm(2) (95% CI, 0.13-0.28) at the LS and 0.27 g/cm(2) (95% CI, 0.02-0.12) at the TH. WMD in BMD percentage change was 5.42 (95% CI, 4.37-6.48) at the LS and 3.03 (95% CI, 2.01-4.01) at the TH. Subgroup analysis revealed that age difference, interventional duration, types of interventions and BP types were associated with variable effects on BMD at the LS and TH. BPs may protect against bone loss in postmenopausal women with EBC receiving adjuvant AI treatment.

Developmental alterations in anxiety and cognitive behavior in serotonin transporter mutant mice.

A promoter variant of the serotonin transporter (SERT) gene is known to affect emotional and cognitive regulation. In particular, the "short" allelic variant is implicated in the etiology of multiple neuropsychiatric disorders. Heterozygous (SERT(+/-)) and homozygous (SERT(-/-)) SERT mutant mice are valuable tools for understanding the mechanisms of altered SERT levels. Although these genetic effects are well investigated in adulthood, the developmental trajectory of altered SERT levels for behavior has not been investigated. We assessed anxiety-like and cognitive behaviors in SERT mutant mice in early adolescence and adulthood to examine the developmental consequences of reduced SERT levels. Spine density of pyramidal neurons was also measured in corticolimbic brain regions. Adult SERT(-/-) mice exhibited increased anxiety-like behavior, but these differences were not observed in early adolescent SERT(-/-) mice. Conversely, SERT(+/-) and SERT(-/-) mice did display higher spontaneous alternation during early adolescence and adulthood. SERT(+/-) and SERT(-/-) also exhibited greater neuronal spine densities in the orbitofrontal but not the medial prefrontal cortices. Adult SERT(-/-) mice also showed an increased spine density in the basolateral amygdala. Developmental alterations of the serotonergic system caused by genetic inactivation of SERT can have different influences on anxiety-like and cognitive behaviors through early adolescence into adulthood, which may be associated with changes of spine density in the prefrontal cortex and amygdala. The altered maturation of serotonergic systems may lead to specific age-related vulnerabilities to psychopathologies that develop during adolescence.

P.1.017 Isoflurane anesthesia rapidly activates TrkB receptor signaling and produces antidepressant-like behavioral effects

Purpose of the study: Emerging evidence suggests that induction of TrkB signaling and the subsequent changes in synaptic plasticity are involved in the therapeutic effects of antidepressant drugs, including rapid-acting antidepressant ketamine [1]. Intriguingly, isoflurane, a commonly used volatile anesthetic, has been shown to produce rapid antidepressant effects in treatment resistant depressive patients [2]. The mechanism of isoflurane’s antidepressant action, however, is completely unknown. We have here investigated the effects of isoflurane anesthesia on TrkB activation and on its downstream signaling pathways related to synaptogenesis and neuronal plasticity. Furthermore, we have studied the effects of single isoflurane treatment on cortical spine formation and morphology, hippocampal long-term potentiation and antidepressant-like behavior in mice. Methods: Adult mice were anesthetized with isoflurane (maximum 30min). For biochemical experiments the animals were killed during the anesthesia or after described recovery period. Hippocampus and prefrontal cortex were dissected out and protein and mRNA levels were analysed using western blotting/ELISA and qPCR, respectively. For electrophysiological recordings mice were decapitated by guillotine 24 h after isoflurane treatment. Parasagittal 400mm hippocampal slices were cut using vibroslicer. Field excitatory potentials (fEPSP) were evoked in Schaffer collateral pathway of the hippocampal slices and LTP was induced by 100 Hz tetanic stimulation. For spine density analysis animals expressing YFP in a subset of cortical layer V pyramidal neurons were perfused with PFA 24 hours after isoflurane treatment. Brains were extracted and 70mm sections were cut using a vibratome. Immunohistochemistry was performed to enhance the fluorescence and sections were analyzed using confocal microscope. Isoflurane-induced antidepressantlike behavior in the forced swim test was monitored 15 minutes and 2 weeks after anesthesia. Results: Isoflurane anesthesia (30min) increased TrkB phosphorylation and its downstream signaling related to neuronal plasticity (pCREB, pAkt) and to synaptogenesis (pmTOR, pP70S6k) in the mouse hippocampus and prefrontal cortex but BDNF protein and mRNA levels remained unaltered. Increased pTrkB, pCREB and pmTOR levels were detected already within 2 minutes from isoflurane treatment onset. Isoflurane’s effects on TrkB signaling could not be blocked with pre-treatment of AMPA receptor blocker NBQX (10mg/kg, ip). LTP was facilitated in hippocampal slices obtained from mice treated with isoflurane 24 h before but any change in cortical spine density and morphological types could not be observed. A single isoflurane anesthesia led to rapid antidepressant-like behavioral effect in the forced swim test that persisted for at least 2 weeks. Conclusions: We show that isoflurane anesthesia rapidly activates TrkB neurotrophin signaling in the mouse brain. This phenomenon is followed by antidepressantlike behavioral responses and facilitation of LTP but not by changes in spine formation or morphology. The biochemical, functional and behavioral effects of isoflurane partially resemble those of rapid-acting antidepressant ketamine. Our findings may provide the neurobiological basis for the previously observed rapid antidepressant effect of isoflurane narcotherapy and encourage investigating further the therapeutic potential of isoflurane.

Persistent changes in neuronal structure and synaptic plasticity caused by proton irradiation

Cranial radiotherapy is used routinely to control the growth of primary and secondary brain tumors, but often results in serious and debilitating cognitive dysfunction. In part due to the beneficial dose depth distributions that may spare normal tissue damage, the use of protons to treat CNS and other tumor types is rapidly gaining popularity. Astronauts exposed to lower doses of protons in the space radiation environment are also at risk for developing adverse CNS complications. To explore the consequences of whole body proton irradiation, mice were subjected to 0.1 and 1Gy and analyzed for morphometric changes in hippocampal neurons 10 and 30days following exposure. Significant dose-dependent reductions (~33%) in dendritic complexity were found, when dendritic length, branching and area were analyzed 30days after exposure. At equivalent doses and times, significant reductions in the number (~30%) and density (50-75%) of dendritic spines along hippocampal neurons of the dentate gyrus were also observed. Immature spines (filopodia, long) exhibited the greatest sensitivity (1.5- to 3-fold) to irradiation, while more mature spines (mushroom) were more resistant to changes over a 1-month post-irradiation timeframe. Irradiated granule cell neurons spanning the subfields of the dentate gyrus showed significant and dose-responsive reductions in synaptophysin expression, while the expression of postsynaptic density protein (PSD-95) was increased significantly. These findings corroborate our past work using photon irradiation, and demonstrate for the first time, dose-responsive changes in dendritic complexity, spine density and morphology and synaptic protein levels following exposure to low-dose whole body proton irradiation.

One-year changes in bone mineral density and bone turnover markers in premenopausal amateur runners: a prospective study.

A prospective study was conducted to clarify the 1-year changes in lumbar spine and hip bone mineral density (BMD) and bone turnover markers in premenopausal amateur runners and to determine whether jumping and muscle-strengthening exercises have additive effects on the bone parameters in these runners. Thirty-six premenopausal amateur runners were recruited and were divided into the following two groups: a jumping plus muscle-strengthening exercise group (n =21) and a control group (n =15). All participants continued their running practice for 1 year, and the lumbar spine and total hip BMD and bone turnover markers were monitored. For all participants, the lumbar spine and total hip BMD increased modestly after 1 year (1.31% and 1.54%, respectively) in addition to increases in the bone-specific alkaline phosphatase, osteocalcin, and tartrate-resistant acid phosphatase 5b levels (13.2%-27.8%), indicating mild effects of running activity on bone turnover and BMD at clinically relevant skeletal sites. Jumping plus muscle-strengthening exercises did not significantly influence any bone parameters; however, it was difficult to draw definite conclusions because compliance was poor. These results suggest that long-distance running at the recreational level may be useful in maintaining bone health in premenopausal women.

Changes of Dendritic Spine Density and Morphology in the Superficial Layers of the Medial Entorhinal Cortex Induced by Extremely Low-Frequency Magnetic Field Exposure

In the present study, we investigated the effects of chronic exposure (14 and 28 days) to a 0.5 mT 50 Hz extremely low-frequency magnetic field (ELM) on the dendritic spine density and shape in the superficial layers of the medial entorhinal cortex (MEC). We performed Golgi staining to reveal the dendritic spines of the principal neurons in rats. The results showed that ELM exposure induced a decrease in the spine density in the dendrites of stellate neurons and the basal dendrites of pyramidal neurons at both 14 days and 28 days, which was largely due to the loss of the thin and branched spines. The alteration in the density of mushroom and stubby spines post ELM exposure was cell-type specific. For the stellate neurons, ELM exposure slightly increased the density of stubby spines at 28 days, while it did not affect the density of mushroom spines at the same time. In the basal dendrites of pyramidal neurons, we observed a significant decrease in the mushroom spine density only at the later time point post ELM exposure, while the stubby spine density was reduced at 14 days and partially restored at 28 days post ELM exposure. ELM exposure-induced reduction in the spine density in the apical dendrites of pyramidal neurons was only observed at 28 days, reflecting the distinct vulnerability of spines in the apical and basal dendrites. Considering the changes in spine number and shape are involved in synaptic plasticity and the MEC is a part of neural network that is closely related to learning and memory, these findings may be helpful for explaining the ELM exposure-induced impairment in cognitive functions.

A tetra(ethylene glycol) derivative of benzothiazole aniline ameliorates dendritic spine density and cognitive function in a mouse model of Alzheimer's disease

We recently reported that the tetra(ethylene glycol) derivative of benzothiazole aniline, BTA-EG4, acts as an amyloid-binding small molecule that promotes dendritic spine density and cognitive function in wild-type mice. This raised the possibility that BTA-EG4 may benefit the functional decline seen in Alzheimer's disease (AD). In the present study, we directly tested whether BTA-EG4 improves dendritic spine density and cognitive function in a well-established mouse model of AD carrying mutations in APP, PS1 and tau (APPswe;PS1M146V;tauP301L, 3xTg AD mice). We found that daily injections of BTA-EG4 for 2weeks improved dendritic spine density and cognitive function of 3xTg AD mice in an age-dependent manner. Specifically, BTA-EG4 promoted both dendritic spine density and morphology alterations in cortical layers II/III and in the hippocampus at 6–10months of age compared to vehicle-injected mice. However, at 13–16months of age, only cortical spine density was improved without changes in spine morphology. The changes in dendritic spine density correlated with Ras activity, such that 6–10month old BTA-EG4 injected 3xTg AD mice had increased Ras activity in the cortex and hippocampus, while 13–16month old mice only trended toward an increase in Ras activity in the cortex. Finally, BTA-EG4 injected 3xTg AD mice at 6–10months of age showed improved learning and memory; however, only minimal improvement was observed at 13–16months of age. This behavioral improvement corresponds to a decrease in soluble Aβ 40 levels. Taken together, these findings suggest that BTA-EG4 may be beneficial in ameliorating the synaptic loss seen in early AD.

Changes in bone mineral density are correlated with bone markers and reductions in hot flush severity in postmenopausal women treated with bazedoxifene/conjugated estrogens

A post hoc exploratory analysis was conducted to examine correlations between changes in bone density, bone markers, and hot flushes after the treatment of postmenopausal women with bazedoxifene (BZA)/conjugated estrogens (CE). In a 2-year phase 3 study, 3,397 postmenopausal women were randomized to BZA 10 mg/CE 0.45 mg, BZA 20 mg/CE 0.45 mg, BZA 40 mg/CE 0.45 mg, BZA 10 mg/CE 0.625 mg, BZA 20 mg/CE 0.625 mg, BZA 40 mg/CE 0.625 mg, raloxifene 60 mg, or placebo. In this analysis, bone density changes at 2 years were compared with baseline levels of the bone markers serum C-telopeptide and osteocalcin. Correlations between changes in bone density and changes in 12-week hot flush composite scores in symptomatic women were also analyzed. Treatment with BZA 20 mg/CE 0.45 mg or BZA 20 mg/CE 0.625 mg increased lumbar spine bone density more in women with higher bone resorption and formation, categorized by baseline levels of C-telopeptide and osteocalcin (P < 0.001, both BZA/CE doses). With placebo, larger decreases in lumbar spine bone density were seen in the highest tertile of serum C-telopeptide. There was no correlation between changes in total hip bone density and baseline bone markers. There were significant correlations between percent change in hot flush score at week 12 and percent changes in lumbar spine (r = -0.31, P = 0.006) and total hip (r = -0.23, P = 0.044) bone densities at month 24. With 2-year BZA/CE treatment, women with larger increases in lumbar spine and total hip densities also have higher baseline bone markers. Early reductions in hot flush score (12 wk) are predictive of long-term increases in bone density (24 mo).

Dab1 Is Required for Synaptic Plasticity and Associative Learning

Disabled-1 (Dab1) is an adaptor protein that is an obligate effector of the Reelin signaling pathway, and is critical for neuronal migration and dendrite outgrowth during development. Components of the Reelin pathway are highly expressed during development, but also continue to be expressed in the adult brain. Here we investigated in detail the expression pattern of Dab1 in the postnatal and adult forebrain, and determined that it is expressed in excitatory as well as inhibitory neurons. Dab1 was found to be localized in different cellular compartments, including the soma, dendrites, presynaptic and postsynaptic structures. Mice that are deficient in Dab1, Reelin, or the Reelin receptors ApoER2 and VLDLR exhibit severely perturbed brain cytoarchitecture, limiting the utility of these mice for investigating the role of this signaling pathway in the adult brain. In this study, we developed an adult forebrain-specific and excitatory neuron-specific conditional knock-out mouse line, and demonstrated that Dab1 is a critical regulator of synaptic function and hippocampal-dependent associative and spatial learning. These dramatic abnormalities were accompanied by a reduction in dendritic spine size, and defects in basal and plasticity-induced Akt and ERK1/2 signaling. Deletion of Dab1 led to no obvious changes in neuronal positioning, dendrite morphology, spine density, or synaptic composition. Collectively, these data conclusively demonstrate an important role for Reelin-Dab1 signaling in the adult forebrain, and underscore the importance of this pathway in learning and memory.

Effects of cholecystokinin-8 on morphine-induced spatial reference memory impairment in mice

Acute and chronic exposure to opiate drugs impaired various types of memory processes. To date, there is no preventive treatment for opiate-induced memory impairment and the related mechanism is still unclear. CCK-8 is the most potent endogenous anti-opioid peptide and has been shown to exert memory-enhancing effect, but the effect of CCK-8 on morphine-induced memory impairment has not been reported. By using Morris water maze, we found that escape latency to the hidden platform in navigation test was not influenced, but performance in the probe test was seriously poor in morphine dependency mice. Amnesia induced by chronic morphine treatment was significantly alleviated by pre-treatment with CCK-8 (0.01, 0.1 and 1μg, i.c.v.), and CCK-8 (0.1 and 1μg, i.c.v.) treatment alone could improve performance in either navigation or probe test. Furthermore, Golgi-Cox staining analysis revealed that pre-treatment with CCK-8 (1μg, i.c.v.) reversed spine density decreased in CA1 region of hippocampus in morphine dependency mice, and CCK-8 (1μg, i.c.v.) alone obviously increased spine density in CA1. Our findings conclude spine density change in CA1 region of hippocampus may be the structural plasticity mechanism which is responsible for enhancing effect of CCK-8 on spatial reference memory. Therefore, CCK-8 could effectively improve memory impairment in morphine dependency mice.

Systematic correlation between spine plasticity and the anxiety/depression-like phenotype induced by corticosterone in mice

Unraveling the pathophysiological basis for the development of and recovery from depression is a unique challenge. Dendritic plasticity has been reported to be involved in the development of depression. We modeled an anxiety/depression-like phenotype by chronic corticosterone exposure in mice and reversed this anxiety/depression-like phenotype by long-term treatment with fluoxetine (FLX). Spine density in the hippocampus was detected by Golgi-Cox staining at five time points. The data showed that 35 days of corticosterone exposure led to a decrease in spine density in CA1, concomitant with the onset of depression. Following 25 days of treatment with FLX, the decrease in both the dendritic spine density in the hippocampus and the anxiety/depression-like phenotype induced by chronic corticosterone recovered to normal levels concomitantly. Interestingly, the total spine density changes are all mainly driven by changes in thin and stubby spines, not mushroom spines, following chronic corticosterone or FLX treatment. Our results suggest that the changes in dendritic spine density in the hippocampus may be one of the pathophysiological mechanisms underlying the development of and recovery from depression, and the neuronal plasticity of CA1 is first impaired during the development of depression.

Delayed dendritic development in newly generated dentate granule cells by cell-autonomous expression of the amyloid precursor protein

Neuronal connectivity and synaptic remodeling are fundamental substrates for higher brain functions. Understanding their dynamics in the mammalian allocortex emerges as a critical step to tackle the cellular basis of cognitive decline that occurs during normal aging and in neurodegenerative disorders. In this work we have designed a novel approach to assess alterations in the dynamics of functional and structural connectivity elicited by chronic cell-autonomous overexpression of the human amyloid precursor protein (hAPP). We have taken advantage of the fact that the hippocampus continuously generates new dentate granule cells (GCs) to probe morphofunctional development of GCs expressing different variants of hAPP in a healthy background. hAPP was expressed together with a fluorescent reporter in neural progenitor cells of the dentate gyrus of juvenile mice by retroviral delivery. Neuronal progeny was analyzed several days post infection (dpi). Amyloidogenic cleavage products of hAPP such as the β-C terminal fragment (β-CTF) induced a substantial reduction in glutamatergic connectivity at 21 dpi, at which time new GCs undergo active growth and synaptogenesis. Interestingly, this effect was transient, since the strength of glutamatergic inputs was normal by 35 dpi. This delay in glutamatergic synaptogenesis was paralleled by a decrease in dendritic length with no changes in spine density, consistent with a protracted dendritic development without alterations in synapse formation. Finally, similar defects in newborn GC development were observed by overexpression of α-CTF, a non-amyloidogenic cleavage product of hAPP. These results indicate that hAPP can elicit protracted dendritic development independently of the amyloidogenic processing pathway.

Long-term effects of cocaine experience on neuroplasticity in the nucleus accumbens core of addiction-prone rats

Repeated exposure to drugs of abuse is associated with structural plasticity in brain reward pathways. Rats selectively bred for locomotor response to novelty differ on a number of neurobehavioral dimensions relevant to addiction. This unique genetic animal model was used here to examine both pre-existing differences and long-term consequences of repeated cocaine treatment on structural plasticity. Selectively bred high-responder (bHR) and low-responder (bLR) rats received repeated saline or cocaine injections for 9 consecutive days. Escalating doses of cocaine (7.5, 15 and 30mg/kg) were administered on the first (day 1) and last (day 9) days of treatment and a single injection of the intermediate dose (15mg/kg) was given on days 2–8. Motor activity in response to escalating doses of cocaine was compared on the first and last days of treatment to assess the acute and sensitized response to the drug. Following prolonged cocaine abstinence (28days), spine density was examined on terminal dendrites of medium spiny neurons in the nucleus accumbens core. Relative to bLRs, bHRs exhibited increased psychomotor activation in response to both the acute and repeated effects of cocaine. There were no differences in spine density between bHR and bLR rats under basal conditions or following repeated saline treatment. However, spine density differed markedly between these two lines following prolonged cocaine abstinence. All spine types were decreased in cocaine-treated bHRs, while only mushroom spines were decreased in bLRs that received cocaine. Changes in spine density occurred specifically near the branch point of terminal dendrites. These findings indicate that structural plasticity associated with prolonged cocaine abstinence varies markedly in two selected strains of rats that vary on numerous traits relevant to addiction. Thus, genetic factors that contribute to individual variation in the behavioral response to cocaine also influence cocaine-induced structural plasticity.

L-DOPA Treatment Selectively Restores Spine Density in Dopamine Receptor D2–Expressing Projection Neurons in Dyskinetic Mice

L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia is an incapacitating complication of L-DOPA therapy that affects most patients with Parkinson's disease. Previous work indicating that molecular sensitization to dopamine receptor D1 (D1R) stimulation is involved in dyskinesias prompted us to perform electrophysiological recordings of striatal projection "medium spiny neurons" (MSN). Moreover, because enhanced D1R signaling in drug abuse induces changes in spine density in striatum, we investigated whether the dyskinesia is related to morphological changes in MSNs. Wild-type and bacterial artificial chromosome transgenic mice (D1R-tomato and D2R-green fluorescent protein) mice were lesioned with 6-hydroxydopamine and subsequently treated with L-DOPA to induce dyskinesia. Functional, molecular, and structural changes were assessed in corticostriatal slices. Individual MSNs injected with Lucifer-Yellow were detected by immunohistochemistry for three-dimensional reconstructions with Neurolucida software. Intracellular current-clamp recordings with high-resistance micropipettes were used to characterize electrophysiological parameters. Both D1R-MSNs and D2R-MSNs showed diminished spine density in totally denervated striatal regions in parkinsonian mice. Chronic L-DOPA treatment, which induced dyskinesia and aberrant FosB expression, restored spine density in D2R-MSNs but not in D1R-MSNs. In basal conditions, MSNs are more excitable in parkinsonian than in sham mice, and excitability decreases toward normal values after L-DOPA treatment. Despite this normalization of basal excitability, in dyskinetic mice, the selective D1R agonist SKF38393 increased the number of evoked action potentials in MSNs, compared with sham animals. Chronic L-DOPA induces abnormal spine re-growth exclusively in D2R-MSNs and robust supersensitization to D1R-activated excitability in denervated striatal MSNs. These changes might constitute the anatomical and electrophysiological substrates of dyskinesia.