Reproductive experience differentially affects spatial reference and working memory performance in the mother

The transition to motherhood results in a number of hormonal, neurological, and behavioral changes necessary to ensure offspring survival. Once motherhood is established, further neurological and behavioral changes may result with additional parity and mothering. Recent research has shown that motherhood enhances both hippocampal-dependent learning and memory and oxytocin-induced long-term potentiation, suggesting that the hippocampus is affected by mothering. In turn, degree of maternal behavior, either high or low, has been shown to affect spatial learning and memory performance in adult offspring. The present experiment aimed to investigate the effect of reproductive experience (nulli-, primi-, and multiparity and mothering) and degree of maternal behavior on hippocampus-dependent learning and memory in the mother. Results show that regardless of error type, primiparous rats make fewer errors compared to nulliparous rats, while multiparous rats show a trend towards making fewer errors compared to nulliparous rats. In addition, mothers who spend less time licking and nursing offspring had fewer reference memory errors. Perhaps the enhanced learning and memory in the inexperienced, new mother allows her to effectively acquire the suite of maternal behaviors necessary to ensure offspring survival and achieve reproductive success with subsequent reproductive experience.     

Cranial irradiation alters dendritic spine density and morphology in the hippocampus

Therapeutic irradiation of the brain is a common treatment modality for brain tumors, but can lead to impairment of cognitive function. Dendritic spines are sites of excitatory synaptic transmission and changes in spine structure and number are thought to represent a morphological correlate of altered brain functions associated with hippocampal dependent learning and memory. To gain some insight into the temporal and sub region specific cellular changes in the hippocampus following brain irradiation, we investigated the effects of 10 Gy cranial irradiation on dendritic spines in young adult mice. One week or 1 month post irradiation, changes in spine density and morphology in dentate gyrus (DG) granule and CA1 pyramidal neurons were quantified using Golgi staining. Our results showed that in the DG, there were significant reductions in spine density at both 1 week (11.9%) and 1 month (26.9%) after irradiation. In contrast, in the basal dendrites of CA1 pyramidal neurons, irradiation resulted in a significant reduction (18.7%) in spine density only at 1 week post irradiation. Analysis of spine morphology showed that irradiation led to significant decreases in the proportion of mushroom spines at both time points in the DG as well as CA1 basal dendrites. The proportions of stubby spines were significantly increased in both the areas at 1 month post irradiation. Irradiation did not alter spine density in the CA1 apical dendrites, but there were significant changes in the proportion of thin and mushroom spines at both time points post irradiation. Although the mechanisms involved are not clear, these findings are the first to show that brain irradiation of young adult animals leads to alterations in dendritic spine density and morphology in the hippocampus in a time dependent and region specific manner.     

Spatial and Working Memory Is Linked to Spine Density and Mushroom Spines

Background

Changes in synaptic structure and efficacy including dendritic spine number and morphology have been shown to underlie neuronal activity and size. Moreover, the shapes of individual dendritic spines were proposed to correlate with their capacity for structural change. Spine numbers and morphology were reported to parallel memory formation in the rat using a water maze but, so far, there is no information on spine counts or shape in the radial arm maze (RAM), a frequently used paradigm for the evaluation of complex memory formation in the rodent.

Methods

24 male Sprague-Dawley rats were divided into three groups, 8 were trained, 8 remained untrained in the RAM and 8 rats served as cage controls. Dendritic spine numbers and individual spine forms were counted in CA1, CA3 areas and dentate gyrus of hippocampus using a DIL dye method with subsequent quantification by the Neuronstudio software and the image J program.

Results

Working memory errors (WME) and latency in the RAM were decreased along the training period indicating that animals performed the task. Total spine density was significantly increased following training in the RAM as compared to untrained rats and cage controls. The number of mushroom spines was significantly increased in the trained as compared to untrained and cage controls. Negative significant correlations between spine density and WME were observed in CA1 basal dendrites and in CA3 apical and basal dendrites. In addition, there was a significant negative correlation between spine density and latency in CA3 basal dendrites.

Conclusion

The study shows that spine numbers are significantly increased in the trained group, an observation that may suggest the use of this method representing a morphological parameter for memory formation studies in the RAM. Herein, correlations between WME and latency in the RAM and spine density revealed a link between spine numbers and performance in the RAM.     

Assessment of estradiol influence on spatial tasks and hippocampal CA1 spines: evidence that the duration of hormone deprivation after ovariectomy compromises 17beta-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.     

Effects of multiparity on recognition memory, monoaminergic neurotransmitters, and brain-derived neurotrophic factor (BDNF)

Recognition memory and anxiety were examined in nulliparous (NP: 0 litters) and multiparous (MP: 5-6 litters) middle-aged female rats (12 months old) to assess possible enduring effects of multiparity at least 3 months after the last litter was weaned. MP females performed significantly better than NP females on the non-spatial memory task, object recognition, and the spatial memory task, object placement. Anxiety as measured on the elevated plus maze did not differ between groups. Monoaminergic activity and levels were measured in prefrontal cortex, CA1 hippocampus, CA3 hippocampus, and olfactory bulb (OB). NP and MP females differed in monoamine concentrations in the OB only, with MP females having significantly greater concentrations of dopamine and metabolite DOPAC, norepinephrine and metabolite MHPG, and the serotonin metabolite 5-HIAA, as compared to NP females. These results indicate a long-term change in OB neurochemistry as a result of multiparity. Brain-derived neurotrophic factor (BDNF) was also measured in hippocampus (CA1, CA3, dentate gyrus) and septum. MP females had higher BDNF levels in both CA1 and septum; as these regions are implicated in memory performance, elevated BDNF may underlie the observed memory task differences. Thus, MP females (experiencing multiple bouts of pregnancy, birth, and pup rearing during the first year of life) displayed enhanced memory task performance but equal anxiety responses, as compared to NP females. These results are consistent with previous studies showing long-term changes in behavioral function in MP, as compared to NP, rats and suggest that alterations in monoamines and a neurotrophin, BDNF, may contribute to the observed behavioral changes.     

Dendritic morphology of hippocampal and amygdalar neurons in adolescent mice is resilient to genetic differences in stress reactivity

Many studies have shown that chronic stress or corticosterone over-exposure in rodents leads to extensive dendritic remodeling, particularly of principal neurons in the CA3 hippocampal area and the basolateral amygdala. We here investigated to what extent genetic predisposition of mice to high versus low stress reactivity, achieved through selective breeding of CD-1 mice, is also associated with structural plasticity in Golgi-stained neurons. Earlier, it was shown that the highly stress reactive (HR) compared to the intermediate (IR) and low (LR) stress reactive mice line presents a phenotype, with respect to neuroendocrine parameters, sleep architecture, emotional behavior and cognition, that recapitulates some of the features observed in patients suffering from major depression. In late adolescent males of the HR, IR, and LR mouse lines, we observed no significant differences in total dendritic length, number of branch points and branch tips, summated tip order, number of primary dendrites or dendritic complexity of either CA3 pyramidal neurons (apical as well as basal dendrites) or principal neurons in the basolateral amygdala. Apical dendrites of CA1 pyramidal neurons were also unaffected by the differences in stress reactivity of the animals; marginally higher length and complexity of the basal dendrites were found in LR compared to IR but not HR mice. In the same CA1 pyramidal neurons, spine density of distal apical tertiary dendrites was significantly higher in LR compared to IR or HR animals. We tentatively conclude that the dendritic complexity of principal hippocampal and amygdala neurons is remarkably stable in the light of a genetic predisposition to high versus low stress reactivity, while spine density seems more plastic. The latter possibly contributes to the behavioral phenotype of LR versus HR animals.     

Motherhood and the hormones of pregnancy modify concentrations of hippocampal neuronal dendritic spines

Short-term fluctuations in steroid hormones such as estradiol (E2) and progesterone (P) can affect the concentration of hippocampal dendritic spines in adult, cycling nulliparous female rats. Pregnancy is characterized by a significantly longer duration of substantially elevated E2 and P compared to the estrous cycle. Thus, even greater changes than those reported during estrus may be evident. In two experiments, we examined the extent to which reproductive and hormonal state altered the concentration of apical neuronal dendritic spines of the CA1 region of the hippocampus in the following age-matched groups (N's = 7-10/group) of rats: in Exp. 1., CA1 dendritic spine density was examined in nulliparous diestrus (DES), proestrus (PRO), and estrus (ES) females, and late-pregnant (LP) (day 21) and lactating (day 5-6; LACT) females. In Exp. 2, the effects on spine density of a regimen mimicking pregnancy (and that stimulates maternal behavior) were examined, using ovariectomized, no hormone-exposed (OVX-minus) vs. sequential P&E(2)-treated (OVX + P&E2) groups. For both experiments, brains were removed, Golgi-Cox-stained and the most lateral tertiary branches of the apical dendrite of completely-stained hippocampal CA1 pyramidal neurons were traced with oil-immersion at x 1600 and dendritic spine density (# spines/10 micro dendritic segment) recorded. In Exp. 1, spine density was increased in LP and LACT females (which were not different) compared to the other virgin groups, including PRO females, who had more spines than DES and ES. In Exp. 2, OVX + P&E2 displayed significantly more dendritic spines per 10 micro than OVX-minus females (and had numbers that were similar to those of LP and LACT from Exp. 1). Pregnancy and its attendant hormonal fluctuations, therefore, may alter hippocampal neurons that regulate some non-pup-directed components of maternal behavior (e.g., nest building) or behaviors that support maternal behavior (e.g., foraging, associative memory).     

Postnatal neuronal plasticity of the pyramidal cells of CA1 area of the hippocampus as a reaction to neurotoxic damage.

Kainic acid (KA) was injected into both lateral ventricles of the brain of adult laboratory rats with the aim of verifying whether damage to afferent fibres in the hippocampal CA1 area would also be reflected in changes in the dendritic arborization of the neurones after maturation of these structures was completed. A significant proportion of the afferent fibres ending in area CA1 comes from CA3-4. The neurodegenerative effect of KA on the neurones in CA3-4 thus leads to marked reconstruction of the dendritic network of the pyramidal cells in the CA1 area. In the CA1 area of the experimental animals, there are fewer segments in the proximal part of the basal dendrites and in the lateral branches of the apical dendrites. The total number of segments in the apical dendrites is smaller and the higher order segments are likewise reduced. In the experimental group, the segments of both the basal and the apical dendrites are shorter. In the experimental animals, dendritic spine density in the lateral preterminal branches, the distal part of the apical shaft, the terminal segments of the lateral branches and the apical preterminal branches are smaller than in the controls, whereas in the segments proximal to the soma of the pyramidal cells it is greater. It can be seen from the results that area CA1 of the hippocampus is endowed, even in adulthood, not only with high functional plasticity, but also with surprisingly high morphological plasticity.     

Bisphenol-A exposure during adolescence leads to enduring alterations in cognition and dendritic spine density in adult male and female rats

We have previously demonstrated that adolescent exposure of rats to bisphenol-A (BPA), an environmental endocrine disrupter, increases anxiety, impairs spatial memory, and decreases dendritic spine density in the CA1 region of the hippocampus (CA1) and medial prefrontal cortex (mPFC) when measured in adolescents in both sexes. The present study examined whether the behavioral and morphological alterations following BPA exposure during adolescent development are maintained into adulthood. Male and female, adolescent rats received BPA, 40 μg/kg/bodyweight, or control treatments for one week. In adulthood, subjects were tested for anxiety and locomotor activity, spatial memory, non-spatial visual memory, and sucrose preference. Additionally, stress-induced serum corticosterone levels and dendritic spine density in the mPFC and CA1 were measured. BPA-treated males, but not females, had decreased arm visits on the elevated plus maze, but there was no effect on anxiety. Non-spatial memory, object recognition, was also decreased in BPA treated males, but not in females. BPA exposure did not alter spatial memory, object placement, but decreased exploration during the tasks in both sexes. No significant group differences in sucrose preference or serum corticosterone levels in response to a stress challenge were found. However, BPA exposure, regardless of sex, significantly decreased spine density of both apical and basal dendrites on pyramidal cells in CA1 but had no effect in the mPFC. Current data are discussed in relation to BPA dependent changes, which were present during adolescence and did, or did not, endure into adulthood. Overall, adolescent BPA exposure, below the current reference safe daily limit set by the U.S.E.P.A., leads to alterations in some behaviors and neuronal morphology that endure into adulthood.     

Reduced Hippocampal Dendritic Spine Density and BDNF Expression following Acute Postnatal Exposure to Di(2-Ethylhexyl) Phthalate in Male Long Evans Rats

Early developmental exposure to di(2-ethylhexyl) phthalate (DEHP) has been linked to a variety of neurodevelopmental changes, particularly in rodents. The primary goal of this work was to establish whether acute postnatal exposure to a low dose of DEHP would alter hippocampal dendritic morphology and BDNF and caspase-3 mRNA expression in male and female Long Evans rats. Treatment with DEHP in male rats led to a reduction in spine density on basal and apical dendrites of neurons in the CA3 dorsal hippocampal region compared to vehicle-treated male controls. Dorsal hippocampal BDNF mRNA expression was also down-regulated in male rats exposed to DEHP. No differences in hippocampal spine density or BDNF mRNA expression were observed in female rats treated with DEHP compared to controls. DEHP treatment did not affect hippocampal caspase-3 mRNA expression in male or female rats. These results suggest a gender-specific vulnerability to early developmental DEHP exposure in male rats whereby postnatal DEHP exposure may interfere with normal synaptogenesis and connectivity in the hippocampus. Decreased expression of BDNF mRNA may represent a molecular mechanism underlying the reduction in dendritic spine density observed in hippocampal CA3 neurons. These findings provide initial evidence for a link between developmental exposure to DEHP, reduced levels of BDNF and hippocampal atrophy in male rats.     

Systematic regulation of spine sizes and densities in pyramidal neurons

Dendritic spines receive most excitatory inputs in the CNS. Recent evidence has demonstrated that the spine head volume is linearly correlated with the readily releasable pool of neurotransmitter and the PSD size. These correlations can be used to functionally interpret spine morphology. Using Golgi impregnations and light microscopy, we reconstructed 23000 spines from pyramidal neurons in layers 2/3, 4, 5 and 6 of mouse primary visual cortex and CA1 hippocampal region and measured their spine head diameters and densities. Spine head diameters and densities are variable within and across cells, although they are similar between apical and basal dendrites. When compared to other regions, layer 5 neurons have larger spine heads and CA1 neurons higher spine densities. Interestingly, we detect a correlation between spine head diameter and interspine distance within and across cells, whereby larger spines are spaced further away from each other than smaller spines. Finally, in CA1 neurons, spine head diameters are larger, and spine density lower, in distal apical dendrites (>200 microm from soma) compared to proximal regions. These results reveal that spine morphologies and densities, and therefore synaptic properties, are jointly modulated with respect to cortical region, laminar position, and, in some cases, even the position of the spine along the dendritic tree. Individual neurons also appear to regulate their apical and basal spine densities and morphologies in concert. Our data provide evidence for a homeostatic control of excitatory synaptic strength.     

Gonadal hormone modulation of dendrites in the mammalian CNS

This review focuses on the effect of gonadal steroid hormones, androgen and estrogen, on dendrites in the adult rat central nervous system (CNS). Four hormone-responsive nuclei are considered: The spinal nucleus of the bulbocavernosus (SNB), the medial nucleus of the amygdala (MeA), the ventromedial nucleus of the hypothalamus (VMN), and the CA1 region of the dorsal hippocampus. Particular emphasis is placed on the mode of hormone action in each nucleus. In the SNB, VMN, and hippocampus, hormones appear to mediate their effects indirectly, via cells other than those that display morphological plasticity. In the MeA, estrogen and/or androgen appears to act primarily on those cells whose dendrites are modulated by the hormone. Importantly, increasing levels of gonadal hormones do not simply result in increases in dendritic parameters. In the VMN, high levels of estrogen associated with proestrus increase dendritic spine density in one subset of cells and reduce spine density in another subset. The pyramidal cells of dorsal CA1 also undergo phasic changes in dendritic spine and synapse density across the estrous cycle. The estrogen-induced excitatory synapses connect with preexisting axonal boutons that also form synapses with other CA1 cells, thereby increasing the divergence of excitatory afferents to dorsal CA1. These findings indicate that gonadal steroids have a profound impact on the morphology of dendrites and patterns of synaptic connectivity. Consequently, the experimental manipulation of hormone levels is a powerful tool to study structure-function relationships in the mammalian brain.     

Dendritic morphology is altered in hippocampal neurons following prenatal compromise

Chronic placental insufficiency (CPI), a known cause of intrauterine growth restriction, can lead to structural alterations in the developing brain that might underlie postnatal neurological deficits. We have previously demonstrated significant reductions in the volumes of hippocampal neuropil layers in fetal guinea pig brains following experimentally induced growth restriction. To determine the components of the neuropil affected in the brains of growth restricted (GR) fetuses, the dendritic morphology of CA1 pyramidal neurons and dentate granule cells was examined. CPI was induced by unilateral uterine artery ligation in pregnant guinea pigs at midgestation (term approximately 67 days). Hippocampi from control and GR fetuses were stained using the Rapid Golgi technique and the growth and branching of the dendritic arbors were quantified using the Sholl method. In addition, the density of dendritic spines was determined on the apical arbors of each population. In GR brains (n = 7) compared to controls (n = 7), there was a reduction in dendritic elongation (p < 0.005) and an alteration in the branch point distribution in CA1 basal arbors, and a reduction both in the outgrowth (p < 0.05) and branch point number (p < 0.05) of CA1 apical arbors. Dentate granule cells from GR brains also demonstrated reduced dendritic outgrowth (p < 0.05). There was an increase in dendritic spine density in both neuronal populations; this might be due either to altered synaptic pruning or as a compensatory mechanism for reduced dendritic length. These findings demonstrate that a chronic prenatal insult causes selective changes in the morphology of hippocampal cell dendrites and may lead to alterations in hippocampal function in the postnatal period.     

Reelin in the extracellular matrix and dendritic spines of the cortex and hippocampus: a comparison between wild type and heterozygous reeler mice by immunoelectron microscopy

Reelin is a glycoprotein (～400 kDa) secreted by GABAergic neurons into the extracellular matrix of the neocortex and hippocampus as well as other areas of adult rodent and nonhuman primate brains. Recent findings indicate that the heterozygote reeler mouse (haploinsufficient for the reeler gene) shares several neurochemical and behavioral abnormalities with schizophrenia and bipolar disorder with mania. These include (1) a downregulation of both reelin mRNA and the translated proteins, (2) a decrease in the number of dendritic spines in cortical and hippocampal neurons, (3) a concomitant increase in the packing density of cortical pyramidal neurons, and (4) an age-dependent decrease in prepulse inhibition of startle. Interestingly, the heterozygous reeler mouse does not exhibit the unstable gait or the neuroanatomy characteristic of the null mutant reeler mouse. Immunocytochemical studies of the expression of reelin in mice have been primarily limited to light microscopy. In this study we present new immunoelectron microscopy data that delineates the subcellular localization of reelin in the cortex and hippocampus of the wild-type mouse, and compares these results to reelin expression in the heterozygous reeler mouse. In discontinuous areas of cortical layers I and II and the inner blade area of the dentate gyrus of the wild type mouse, extracellular reelin is associated with dendrites and dendritic spine postsynaptic specializations. Similar associations have been detected in the CA1 stratum oriens and other areas of the hippocampus. In the hippocampus, reelin expression is more expansive and more widespread than in cortical layers I and II. In contrast, extracellular reelin immunoreactivity is greatly diminished in all areas examined in the heterozygous reeler mouse. However, some cell bodies of GABAergic neurons in the cortex and hippocampus demonstrate an increased accumulation of reelin in the Golgi and endoplasmic reticulum. We suggest that in the heterozygous reeler mouse a downregulation of reelin biosynthesis results in a decreased rate of secretion into the extracellular space. This inhibits dendritic spine maturation and plasticity and leads to dissociation of dendritic postsynaptic density integrity and atrophy of spines. We speculate that the haploinsufficient reeler mouse may provide a model for future studies of the role of reelin, as it may be related to psychosis vulnerability.     

Self-Stimulation Rewarding Experience Restores Stress-Induced CA3 Dendritic Atrophy,Spatial Memory Deficits and Alterations in the Levels of Neurotransmitters in the Hippocampus

Chronic restraint stress causes spatial learning and memory deficits, dendritic atrophy of the hippocampal pyramidal neurons and alterations in the levels of neurotransmitters in the hippocampus. In contrast, intracranial self-stimulation (ICSS) rewarding behavioral experience is known to increase dendritic arborization, spine and synaptic density, and increase neurotransmitter levels in the hippocampus. In addition, ICSS facilitates operant and spatial learning, and ameliorates fornix-lesion induced behavioral deficits. Although the effects of stress and ICSS are documented, it is not known whether ICSS following stress would ameliorate the stress-induced deficits. Accordingly, the present study was aimed to evaluate the role of ICSS on stress-induced changes in hippocampal morphology, neurochemistry, and behavioral performance in the T-maze. Experiments were conducted on adult male Wistar rats, which were randomly divided into four groups; normal control, stress (ST), self-stimulation (SS), and stress + self-stimulation (ST + SS). Stress group of rats were subjected to restraint stress for 6 h daily over 21 days, SS group animals were subjected to SS from ventral tegmental area for 10 days and ST + SS rats were subjected to restraint stress for 21 days followed by 10 days of SS. Interestingly, our results show that stress-induced behavioral deficits, dendritic atrophy, and decreased levels of neurotransmitters were completely reversed following 10 days of SS experience. We propose that SS rewarding behavioral experience ameliorates the stress-induced cognitive deficits by inducing structural and biochemical changes in the hippocampus.     

Wip1 phosphatase positively modulates dendritic spine morphology and memory processes through the p38MAPK signaling pathway

Dendritic spine morphology is modulated by protein kinase p38, a mitogen-activated protein (MAPK), in the hippocampus. Protein p38MAPK is a substrate of wip1, a protein phosphatase. The role of wip1 in the central nervous system (CNS) has never been explored. Here, we report a novel function of wip1 in dendritic spine morphology and memory processes. Wip1 deficiency decreases dendritic spine size and density in pyramidal neurons of the hippocampal CA1 region. Simultaneously, impairments in object recognition tasks and contextual memory occur in wip1 deficient mice, but are reversed in wip1/p38 double mutant mice. Thus, our findings demonstrate that wip1 modulates dendritic morphology and memory processes through the p38MAPK signaling pathway. In addition to the well-characterized role of the wip1/p38MAPK in cell death and differentiation, we revealed the novel contribution of wip1 to cognition and dendritic spine morphology, which may suggest new approaches to treating neurodegenerative disorders.     

Wip1 phosphatase positively modulates dendritic spine morphology and memory processes through the p38MAPK signaling pathway

Dendritic spine morphology is modulated by protein kinase p38, a mitogen-activated protein (MAPK), in the hippocampus. Protein p38MAPK is a substrate of wip1, a protein phosphatase. The role of wip1 in the central nervous system (CNS) has never been explored. Here, we report a novel function of wip1 in dendritic spine morphology and memory processes. Wip1 deficiency decreases dendritic spine size and density in pyramidal neurons of the hippocampal CA1 region. Simultaneously, impairments in object recognition tasks and contextual memory occur in wip1 deficient mice, but are reversed in wip1/p38 double mutant mice. Thus, our findings demonstrate that wip1 modulates dendritic morphology and memory processes through the p38MAPK signaling pathway. In addition to the well-characterized role of the wip1/p38MAPK in cell death and differentiation, we revealed the novel contribution of wip1 to cognition and dendritic spine morphology, which may suggest new approaches to treating neurodegenerative disorders.     

Post-synaptic Density-95 (PSD-95) Binding Capacity of G-protein-coupled Receptor 30 (GPR30), an Estrogen Receptor That Can Be Identified in Hippocampal Dendritic Spines

The estrogen 17β-estradiol (E2) modulates dendritic spine plasticity in the cornu ammonis 1 (CA1) region of the hippocampus, and GPR30 (G-protein coupled estrogen receptor 1 (GPER1)) is an estrogen-sensitive G-protein-coupled receptor (GPCR) that is expressed in the mammalian brain and in specific subregions that are responsive to E2, including the hippocampus. The subcellular localization of hippocampal GPR30, however, remains unclear. Here, we demonstrate that GPR30 immunoreactivity is detected in dendritic spines of rat CA1 hippocampal neurons in vivo and that GPR30 protein can be found in rat brain synaptosomes. GPR30 immunoreactivity is identified at the post-synaptic density (PSD) and in the adjacent peri-synaptic zone, and GPR30 can associate with the spine scaffolding protein PSD-95 both in vitro and in vivo. This PSD-95 binding capacity of GPR30 is specific and determined by the receptor C-terminal tail that is both necessary and sufficient for PSD-95 interaction. The interaction with PSD-95 functions to increase GPR30 protein levels residing at the plasma membrane surface. GPR30 associates with the N-terminal tandem pair of PDZ domains in PSD-95, suggesting that PSD-95 may be involved in clustering GPR30 with other receptors in the hippocampus. We demonstrate that GPR30 has the potential to associate with additional post-synaptic GPCRs, including the membrane progestin receptor, the corticotropin releasing hormone receptor, and the 5HT1a serotonin receptor. These data demonstrate that GPR30 is well positioned in the dendritic spine compartment to integrate E2 sensitivity directly onto multiple inputs on synaptic activity and might begin to provide a molecular explanation as to how E2 modulates dendritic spine plasticity.     

Effects of estrogen and progesterone treatment on rat hippocampal NMDA receptors: relationship to Morris water maze performance

Estrogen modulates NMDA receptors function in the brain. It increases both dendritic spine density and synapse number in the hippocampus, an effect that can be blocked by NMDA antagonist. In this study, we investigated the effect of 17beta-estradiol and progesterone treatment on NMDA receptors in ovariectomized rats. Two different doses were used for 10 weeks. Receptor autoradiography was done on brain sections using [(3)H] MK-801 as a ligand. Our results showed a significant increase in [(3)H] MK-801 binding in the dentate gyrus, CA3 and CA4 areas of the hippocampus of ovariectomized compared to sham operated rats. In addition, we observed similar changes in CA1. 17beta-estradiol treatment in both doses reduced the binding back to the normal level while progesterone treatment did not show any effect. Spatial reference memory was tested on Morris water maze task. Ovariectomy severely impaired spatial reference memory. Estradiol but not progesterone treatment significantly improved the memory performance of the ovariectomized rats. Low dose treatment showed better learning than high dose estrogen treatment. The decrease in the antagonist sites by estradiol treatment could result in an increase in the sensitivity of the hippocampus to the excitatory stimulation by glutamate system and hence the effect of estradiol on learning and memory. The changes of NMDA receptors in the hippocampus support the concept that estrogen-enhancing effect on spatial reference memory could be through the enhancing of NMDA function.     

Perinatal Exposure to Bisphenol-A Impairs Spatial Memory through Upregulation of Neurexin1 and Neuroligin3 Expression in Male Mouse Brain

Bisphenol-A (BPA), a well known endocrine disruptor, impairs learning and memory in rodents. However, the underlying molecular mechanism of BPA induced impairment in learning and memory is not well known. As synaptic plasticity is the cellular basis of memory, the present study investigated the effect of perinatal exposure to BPA on the expression of synaptic proteins neurexin1 (Nrxn1) and neuroligin3 (Nlgn3), dendritic spine density and spatial memory in postnatal male mice. The pregnant mice were orally administered BPA (50 µg/kgbw/d) from gestation day (GD) 7 to postnatal day (PND) 21 and sesame oil was used as a vehicle control. In Morris water maze (MWM) test, BPA extended the escape latency time to locate the hidden platform in 8 weeks male mice. RT-PCR and Immunoblotting results showed significant upregulation of Nrxn1 and Nlgn3 expression in both cerebral cortex and hippocampus of 3 and 8 weeks male mice. This was further substantiated by in-situ hybridization and immunofluorescence techniques. BPA also significantly increased the density of dendritic spines in both regions, as analyzed by rapid Golgi staining. Thus our data suggest that perinatal exposure to BPA impairs spatial memory through upregulation of expression of synaptic proteins Nrxn1 and Nlgn3 and increased dendritic spine density in cerebral cortex and hippocampus of postnatal male mice.