Apical Dendritic Spine Density Research Articles

Serine racemase deletion disrupts memory for order and alters cortical dendritic morphology

There is substantial evidence implicating N-methyl-D-aspartate receptors (NMDARs) in memory and cognition. It has also been suggested that NMDAR hypofunction might underlie the cognitive deficits observed in schizophrenia as morphological changes, including alterations in the dendritic architecture of pyramidal neurons in the prefrontal cortex (PFC), have been reported in the schizophrenic brain post mortem. Here, we used a genetic model of NMDAR hypofunction, a serine racemase knockout (SR-/-) mouse in which the first coding exon of the mouse SR gene has been deleted, to explore the role of D-serine in regulating cognitive functions as well as dendritic architecture. SR-/- mice exhibited a significantly disrupted representation of the order of events in distinct experiences as showed by object recognition and odor sequence tests; however, SR-/- animals were unimpaired in the detection of novel objects and in spatial displacement, and showed intact relational memory in a test of transitive inference. In addition, SR-/- mice exhibited normal sociability and preference for social novelty. Neurons in the medial PFC of SR-/- mice displayed reductions in the complexity, total length and spine density of apical dendrites. These findings show that D-serine is important for specific aspects of cognition, as well as in regulating dendritic morphology of pyramidal neurons in the medial PFC (mPFC). Moreover, they suggest that NMDAR hypofunction might, in part, be responsible for the cognitive deficits and synaptic changes associated with schizophrenia, and highlight this signaling pathway as a potential target for therapeutic intervention.

Neurobehavioral consequences of cortical adaptation disruption during ontogeny

Filtering of redundant or stable inputs is a critical function of all sensory pathways. Normal sensory gating can allow processing resources to be differentially devoted to changing or otherwise biologically significant stimuli. In olfaction, short-term odor habituation is mediated by a metabotropic glutamate receptor (mGluR)-mediated depression of afferent synapses in the piriform cortex. Given the role of early experience in shaping cortical function and anatomy, the present experiments examined the effects of chronic habituation disruption during development on behavior and local circuit anatomy. Rats were chronically intra-cerebrally infused with the mGluR group III antagonist ( RS)-a-cyclopropyl-4-phosphonophenylglycine (CPPG) during early development. The results demonstrated that early onset mGluRIII blockade resulted in a long-lasting decrement in odor habituation compared to controls, evident for at least 2 weeks post-infusion offset. Odor investigation time in the youngest animals was correlated with cortical laminar thickness, though the long-lasting behavioral effect showed no such correlation. No changes in apical dendritic spine density in the piriform cortex were detected. Combined with previous work, these results suggest that sensory gating disruption during development can have both immediate and long-lasting effects on sensory-guided behavior.

Assessment of estradiol influence on spatial tasks and hippocampal CA1 spines: Evidence that the duration of hormone deprivation after ovariectomy compromises 17β-estradiol effectiveness in altering CA1 spines

Two pulses of 17β-estradiol (10 µg) are commonly used to increase hippocampal CA1 apical dendritic spine density and alter spatial performance in ovariectomized (OVX) female rats, but rarely are the measures combined. The goal of this study was to use this two-pulse injection protocol repeatedly with intervening wash-out periods in the same rats to: 1) measure spatial ability using different tasks that require hippocampal function and 2) determine whether ovarian hormone depletion for an extended 10-week period reduces 17β-estradiol's effectiveness in elevating CA1 apical dendritic spine density. Results showed that two injections of 10 µg 17β-estradiol (72 and 48 h prior to testing and timed to maximize CA1 apical spine density at behavioral assessment) corresponded to improved spatial memory performance on object placement. In contrast, two injections of 5 µg 17β-estradiol facilitated spatial learning on the water maze compared to rats given two injections of 10 µg 17β-estradiol or the sesame oil vehicle. Neither 17β-estradiol dose altered Y-maze performance. As expected, the intermittent two-pulse injection protocol increased CA1 apical spine density, but 10 weeks of OVX without estradiol treatment decreased the effectiveness of 10 µg 17β-estradiol to increase CA1 apical spine density. Moreover, two pulses of 5 µg 17β-estradiol injected intermittently failed to alter CA1 apical spine density and decreased basal spine density. These results demonstrate that extended time without ovarian hormones reduces 17β-estradiol's effectiveness to increase CA1 apical spine density. Collectively, these findings highlight the complex interactions among estradiol, CA1 spine density/morphology, and task requirements, all of which contribute to behavioral outcomes.

Dendritic spine changes in medial prefrontal cortex of male diabetic rats using Golgi-impregnation method.

Neuropathy is one of the major complications contributing to morbidity in patients with diabetes mellitus. The effect of diabetes on brain has not been studied so much and no gross abnormality has been found in the central nervous system of patients with diabetic neuropathy. This study was conducted to evaluate the time-dependent structural changes in medial prefrontal cortex of male diabetic rats using Golgi-impregnation method. Male Wistar rats were randomly divided into the control and diabetic groups. For induction of diabetes, a single dose of streptozotocin (60 mg/kg) was injected intraperitoneally. At the end of the first and second months, the rats were transcardially perfused with a solution of phosphate buffer containing paraformaldehyde and Golgi-impregnated method was used to evaluate the changes of dendritic spines in medial prefrontal cortex. There was a significant reduction in the mean density of pyramidal neuron dendritic spines in the layers II and III of medial prefrontal cortex only after 2 months in the diabetic group compared to age-matched controls (P < 0.05). Diabetes induces a reduction in the spine density of apical dendrites of medial prefrontal cortex only in two-month diabetic rats.

Reduced Spinophilin in Schizophrenia

Back to table of contents Previous article Next article Letter to the EditorFull AccessReduced Spinophilin in SchizophreniaANDREW J. DWORK, M.D., GORAZD ROSOKLIJA, M.D., Ph.D., and LIESL B. JONES, Ph.D., ANDREW J. DWORKSearch for more papers by this author, M.D., GORAZD ROSOKLIJASearch for more papers by this author, M.D., Ph.D., and LIESL B. JONESSearch for more papers by this author, Ph.D., New York, N.Y.Published Online:1 Jul 2005https://doi.org/10.1176/appi.ajp.162.7.1389AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: Amanda J. Law, Ph.D., et al. (1) reported decreased mRNA for spinophilin in the hippocampal formation in patients with schizophrenia and mood disorders. The potential implications of this abnormality are curious since spinophilin is involved in limiting or decreasing the length of dendritic spines. Spinophilin immunoreactivity is predominantly (although not exclusively) localized to dendritic spines (2), for which it is a meaningful marker, with hippocampal spine density and spinophilin immunoreactivity both increasing in response to estrogen (3). However, spinophilin is not necessary for the formation of spines, which are increased in density in young spinophilin knockout mice or for their removal, since spine density returns to normal when such animals mature (4).Spinophilin links protein phosphatase-1 to actin. Dephosphorylation of actin by protein phosphatase-1 leads to its disassembly (5), so the targeting of protein phosphatase-1 to actin is likely to result in fewer or shorter dendritic spines. Linking protein phosphatase-1 to actin also promotes dephosphorylation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (4). The subsequent decrease in the activity of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors should decrease calcium influx into the spine, reducing the phosphorylation of spinophilin by calcium-calmodulin kinase II and thereby enhancing its affinity for actin (6).The reported subicular decrease in spinophilin mRNA in schizophrenia is approximately 30% (1). We observed a decrease of 75%–80% in the density of apical dendritic spines (plus a more modest decrease in apical dendritic arborization) (7), but the density of spines on basilar dendrites has not been measured. If the diminished pool of mRNA is supporting the synthesis of spinophilin for an even more diminished set of dendritic spines, increased synthesis of spinophilin, on a per-spine basis, might function to keep spine density reduced. Posttranscriptional mechanisms are also likely, as evidenced by estrogen-induced increases in spine density and spinophilin immunoreactivity, without altered levels of spinophilin mRNA (3).

Repeated Stress Induces Dendritic Spine Loss in the Rat Medial Prefrontal Cortex

The prefrontal cortex (PFC) plays an important role in higher cognitive processes, and in the regulation of stress-induced hypothalamic-pituitary-adrenal (HPA) activity. Here we examined the effect of repeated restraint stress on dendritic spine number in the medial PFC. Rats were perfused after receiving 21 days of daily restraint stress, and intracellular iontophoretic injections of Lucifer Yellow were carried out in layer II/III pyramidal neurons in the anterior cingulate and prelimbic cortices. We found that stress results in a significant (16%) decrease in apical dendritic spine density in medial PFC pyramidal neurons, and confirmed a previous observation that total apical dendritic length is reduced by 20% in the same neurons. We estimate that nearly one-third of all axospinous synapses on apical dendrites of pyramidal neurons in medial PFC are lost following repeated stress. A decrease in medial PFC dendritic spines may not only be indicative of a decrease in the total population of axospinous synapses, but may impair these neurons' capacity for biochemical compartmentalization and plasticity in which dendritic spines play a major role. Dendritic atrophy and spine loss may be important cellular features of stress-related psychiatric disorders where the PFC is functionally impaired.

Neural Cell Adhesion Molecule-Secreting Transgenic Mice Display Abnormalities in GABAergic Interneurons and Alterations in Behavior

The extracellular region of the transmembrane neural cell adhesion molecule (NCAM-EC) is shed as a soluble fragment at elevated levels in the schizophrenic brain. A novel transgenic mouse line was generated to identify consequences on cortical development and function of expressing soluble NCAM-EC from the neuron-specific enolase promoter in the developing and mature neocortex and hippocampus. NCAM-EC transgenic mice exhibited a striking reduction in synaptic puncta of GABAergic interneurons in the cingulate, frontal association cortex, and amygdala but not hippocampus, as shown by decreased immunolabeling of glutamic acid decarboxylase-65 (GAD65), GAD67, and GABA transporter 1. Interneuron cell density was unaltered in the transgenic mice. Affected subpopulations of interneurons included basket interneurons evident in NCAM-EC transgenic mice intercrossed with a reporter line expressing green fluorescent protein and by parvalbumin staining. In addition, there appeared to be a reduction in excitatory synapses, as revealed by synaptophysin staining and apical dendritic spine density of cortical pyramidal cells. Behavioral analyses demonstrated higher basal locomotor activity of NCAM-EC mice and enhanced responses to amphetamine and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate compared with wild-type controls. Transgenic mice were deficient in prepulse inhibition, which was restored by clozapine but not by haloperidol. Additionally, NCAM-EC mice were impaired in contextual and cued fear conditioning. These results suggested that elevated shedding of NCAM perturbs synaptic connectivity of GABAergic interneurons and produces abnormal behaviors that may be relevant to schizophrenia and other neuropsychiatric disorders.

ERK1/2 activation is necessary for BDNF to increase dendritic spine density in hippocampal CA1 pyramidal neurons.

Brain-derived neurotrophic factor (BDNF) is a potent modulator of synaptic transmission and plasticity in the CNS, acting both pre- and postsynaptically. We demonstrated recently that BDNF/TrkB signaling increases dendritic spine density in hippocampal CA1 pyramidal neurons. Here, we tested whether activation of the prominent ERK (MAPK) signaling pathway was responsible for BDNF's effects on spine growth. Slice cultures were transfected with enhanced yellow fluorescent protein (eYFP) by particle-mediated gene transfer, and CA1 pyramidal neurons were imaged by laser-scanning confocal microscopy. We confirmed that BDNF (24 h) increases spine density in apical dendrites of CA1 neurons. The MEK (ERK kinase) inhibitors PD98059 and U0126 completely prevented the increase in spine density induced by BDNF, without having an effect on spine density by themselves. In contrast to its actions on cortical pyramidal neurons, BDNF had minor and rather localized effects on dendritic complexity in hippocampal pyramidal neurons, increasing the total length, but not the branching of apical dendrites within CA1 stratum radiatum, without affecting basal dendrites in stratum oriens. Our results support the hypothesis that the ERK-signaling pathway not only mediates long-term synaptic plasticity and hippocampal-dependent learning, but it is also involved in the structural remodeling of excitatory spine synapses triggered by neurotrophins.

Miniature synaptic transmission and BDNF modulate dendritic spine growth and form in rat CA1 neurones.

The refinement and plasticity of neuronal connections require synaptic activity and neurotrophin signalling; their specific contributions and interplay are, however, poorly understood. We show here that brain-derived neurotrophic factor (BDNF) increased spine density in apical dendrites of CA1 pyramidal neurones in organotypic slice cultures prepared from postnatal rat hippocampal slices. This effect was observed also in the absence of action potentials, and even when miniature synaptic transmission was inhibited with botulinum neurotoxin C (BoNT/C). There were, however, marked differences in the morphology of individual spines induced by BDNF across these different levels of spontaneous ongoing synaptic activity. During both normal synaptic transmission, and when action potentials were blocked with TTX, BDNF increased the proportion of stubby, type-I spines. However, when SNARE-dependent vesicular release was inhibited with BoNT/C, BDNF increased the proportion of thin, type-III spines. Our results indicate that BDNF increases spine density irrespective of the levels of synaptic transmission. In addition, miniature synaptic transmission provides sufficient activity for the functional translation of BDNF-triggered spinogenesis into clearly defined morphological spine types, favouring those spines potentially responsible for coordinated Ca2+ transients thought to mediate synaptic plasticity. We propose that BDNF/TrkB signalling represents a mechanism of expression of both morphological and physiological homeostatic plasticity in the hippocampus, leading to a more efficient synaptic information transfer across widespread levels of synaptic activity.

Sex Differences and Opposite Effects of Stress on Dendritic Spine Density in the Male Versus Female Hippocampus

Dendritic spines are postsynaptic sites of excitatory input in the mammalian nervous system. Despite much information about their structure, their functional significance remains unknown. It has been reported that females in proestrus, when estrogen levels are elevated, have a greater density of apical dendritic spines on pyramidal neurons in area CA1 of the hippocampus than females in other stages of estrous (Woolley et al., 1990). Here we replicate these findings and in addition, show that females in proestrus have a greater density of spines in area CA1 of the hippocampus than males. Moreover, this sex difference in spine density is affected in opposite directions by stressful experience. In response to one acute stressful event of intermittent tailshocks, spine density was enhanced in the male hippocampus but reduced in the female hippocampus. The decrease in the female was observed for those that were stressed during diestrus 2 and perfused 24 hr later during proestrus. The opposing effects of stress were not evident immediately after the stressor but rather occurred within 24 hr and were evident on apical and to a lesser extent on basal dendrites of pyramidal cells in area CA1. Neither sex nor stress affected spine density on pyramidal neurons in somatosensory cortex. Sex differences in hippocampal spine density correlated with sex hormones, estradiol and testosterone, whereas stress effects on spine density were not directly associated with differences in the stress hormones, glucocorticoids. In summary, males and females have different levels of dendritic spine density in the hippocampus under unstressed conditions, and their neuronal anatomy can respond in opposite directions to the same stressful event.

Chronic Psychosocial Stress Causes Apical Dendritic Atrophy of Hippocampal CA3 Pyramidal Neurons in Subordinate Tree Shrews

We have shown previously that repeated laboratory restraint stress or daily corticosterone administration affects the structure of CA3 hippocampal neurons in rats. In the present study, we investigated the effect of repeated daily psychosocial stress on the structure of hippocampal CA3 pyramidal neurons in male tree shrews (Tupaia belangeri). Male tree shrews develop social hierarchies in which subordinates show characteristic changes in physiological and behavioral parameters when confronted with a dominant. In the present experiments, subordinate animals lost body weight soon after starting the daily social conflict, and urinary excretion of cortisol was elevated throughout the experiment as compared with the control period. Golgi-impregnated brain tissue from subordinates exposed to 28 d (1 hr/d) of social confrontations was compared with that from control nonstressed animals. The apical dendrites of the CA3 pyramidal cells from subordinates had a decreased number of branch points and total dendritic length as compared with controls. No differences were observed in apical dendritic spine density or in the basal dendritic tree morphology. The stress-induced CA3 apical dendritic atrophy in subordinates was prevented by administering daily oral doses of the antiepileptic drug phenytoin (Dilantin, Sigma, St. Louis, MO) (200 mg/kg), which interferes with excitatory amino acid (EAA) action. These results suggest that the naturalistic stressor psychosocial stress induces specific structural changes in hippocampal neurons of subordinate male tree shrews. These changes, like those in the rat after glucocorticoid treatment or restraint stress, probably are mediated by activation of the hypothalamo-pituitary-adrenal-axis acting in concert with endogenous EAAs from mossy fiber input.

Dendritic branching in cortical pyramidal cells in response to ovariectomy in adult female rats: Suppression by neonatal exposure to testosterone

Female Long-Evans rats were treated with oil or testosterone propionate (TP) at birth (postnatal day zero, PN0) and PN1. As adults, animals from each group were ovariectomized or sham operated. Four months later the brains were prepared using a modified Golgi-Cox staining procedure. In neonatally oil-treated females, ovariectomized in adulthood increased the dendritic arbor of layer II/III pyramidal neurons of the parietal cortex; in addition, there were modest increases in apical dendritic spine density. The dendritic arbor of the pyramidal neurons of intact neonatally TP-treated females was greater than that of intact oil-treated females, but in these animals there was no increase in dendritic arbor in response to ovariectomy.

Naturally occurring fluctuation in dendritic spine density on adult hippocampal pyramidal neurons

We have used Golgi-impregnated tissue to demonstrate that apical dendritic spine density in CA1 hippocampal pyramidal cells undergoes a cyclic fluctuation as estradiol and progesterone levels vary across the estrous cycle in the adult female rat. We observed a 30% decrease in apical dendritic spine density over the 24-hr period between the late proestrus and the late estrus phases of the cycle. Spine density then appears to cycle back to proestrus values over a period of several days. In contrast, no significant changes in dendritic spine density across the estrous cycle occur in CA3 pyramidal cells or dentate gyrus granule cells. These results demonstrate rapid and ongoing dendritic plasticity in a specific population of hippocampal neurons in experimentally unmanipulated animals.

Dendritic spine density of adult hippocampal pyramidal cells is sensitive to thyroid hormone

In order to determine whether pyramidal cells of the adult hippocampus are morphologically sensitive to thyroid hormone, we performed single-section Golgi impregnation analyses on brains from hyperthyroid and control rats. Quantitative analyses of Golgi-impregnated pyramidal cells from the CA1 region showed a significant decrease in the density of apical dendritic spines with hyperthyroidism. In contrast, no changes were observed in spine density of basal dendrites or in cross-sectional cell body area of CA1 pyramidal cells. No changes in any of these morphological variables were detected in pyramidal cells of the CA3 region with hyperthyroidism. These results suggest that spine density of the apical dendrites of CA1 pyramidal cells is specifically affected by thyroid hormone in adulthood. Since dendritic spines are thought to represent postsynaptic sites it is likely that this morphological change results in altered hippocampal function.

Deprived somatosensory‐motor experience in stumptailed monkey neocortex: Dendritic spine density and dendritic branching of layer IIIB pyramidal cells

Infant macaque monkeys (Macaca arctoides) were individually raised to age 6 months in large clear cubes built into one wall of a control colony that allowed them visual access to it but not tactile contact. The two deprivation conditions (Cond 2 and Cond 3) were equal both in physical size and with respect to partial social isolation. They differed in the degree of somatosensory-motor opportunity available during development in that the Cond 2 chamber was empty, whereas Cond 3 contained ladders, a trapeze, and play objects. Four monkeys from each of these conditions were compared with four colony-reared (Cond CR) monkeys. Neuroanatomical changes were evaluated by using light microscopy in Golgi-Cox-stained neocortex. Dendritic spines on the apical shafts of layer IIIB pyramidal cells were counted in primary motor (MI), somatosensory (SI), and visual (area 17, V1) cortical regions. Layer IIIB pyramidal neurons with somas of medium size were selected from each cortical region and the density of apical dendritic spines determined. The basilar dendritic branches of these same neurons were traced, and the dendritic branching complexity was assessed in order to compare the sensitivity of the dendritic spine and branching measures consequent to deprived rearing. The number of apical dendritic spines was significantly reduced in Cond 2 when compared with either Cond 3 or Cond CR (which did not differ from each other). This occurred in both MI and SI cortex, but not in the visual cortex, the region used as a control for a global brain effect. Branching complexity measured on the same pyramidal neurons was reduced only in MI cortex of Cond 2. These results show spine density, a more direct measure of neuronal connectivity, to be the more sensitive measure of early environmental deprivation. Also, the enriched environment provided by Cond 3 relative to Cond 2 offset the effect of partial social isolation such that both morphometric measures had values comparable to Cond CR monkeys.