Gonadectomy differentially regulates steroid receptor coactivator-1 and synaptic proteins in the hippocampus of adult female and male C57BL/6 mice

Hippocampus is one of the most important structures that mediates learning and memory, cognition, and mental behaviors and profoundly regulated by sex hormones in a sex‐specific manner, but the mechanism of underlying sex differences regulation is still unclear. We have previously reported that in the male and female mice, steroid receptor coactivator‐1 (SRC‐1) and some key synaptic proteins share similar developmental profile in the hippocampus, but how circulating sex hormones affect hippocampal SRC‐1 as well as these synaptic proteins remain unclear. In this study, we examined how gonad sex hormones regulate hippocampal SRC‐1, synaptophysin, PSD‐95, and AMPA receptor subtype GluR1 by using immunohistochemistry and Western blot. The results showed that in the female mice, ovariectomy affected hippocampal SRC‐1 and GluR1 were only detected at 2 weeks post operation, then it recovered to sham level; synaptophysin was unaffected at any timepoint examined; significant decrease of PSD‐95 was only detected at 4 weeks post operation. However, in the male hippocampus, SRC‐1 and PSD‐95 were decreased from one week and lasted to 4 weeks after orchidectomy, GluR1 decreased from 2 weeks after orchidectomy, but synaptophysin remained unchanged as in the females. Correlation analysis showed the profiles of SRC‐1 were positively correlated with GluR1 of the females, PSD‐95 and GluR1 of the males, respectively. The above results suggested a distinct regulatory mode between female and male gonad hormones in the regulation of hippocampal SRC‐1 and synaptic proteins, which may be one of the mechanisms contributing to the dimorphism of hippocampus during development and ageing. Synapse, 2012. © 2012 Wiley Periodicals, Inc.     

Kainate‐induced toxicity in the hippocampus: potential role of lithium

Crespo‐Biel N, Camins A, Canudas AM, Pallàs M. Kainate‐induced toxicity in the hippocampus: potential role of lithium.
Bipolar Disord 2010: 12: 425–436. © 2010 The Authors. Journal compilation © 2010 John Wiley & Sons A/S. Objectives: We investigated the neuroprotective effects of lithium in an experimental neurodegeneration model gated to kainate (KA) receptor activation. Methods: The hippocampus from KA‐treated mice and hippocampal cell cultures were used to evaluate the pathways regulated by chronic lithium pretreatment in both in vivo and in vitro models. Results: Treatment with KA, as measured by fragmentation of α‐spectrin and biochemically, induced the activation of calpain resulting in p35 cleavage to p25, indicating activation of cyclin‐dependent kinase 5 (cdk5) and glycogen synthase kinase‐3ß (GSK‐3ß) and an increase in tau protein phosphorylation. Treatment with lithium reduced calpain activation and reduced the effects of cdk5 and GSK‐3ß on tau. KA treatment of cultures resulted in neuronal demise. According to nuclear condensed cell counts, the addition of lithium to neuronal cell cultures (0.5–1 mM) a few days before KA treatment had neuroprotective and also antiapoptotic effects. The action of lithium on calpain/cdk5 and GSK‐3ß pathways produced similar results in vivo. As calpain is activated by an increase in intracellular calcium, we showed that lithium reduced calcium concentrations in basal and KA‐treated hippocampal cells, which was accompanied by an increase in NCX3, a Na⁺/Ca²⁺ exchanger pump. Conclusion: A robust neuroprotective effect of lithium in the excitotoxic process induced by KA in mouse hippocampus was demonstrated via modulation of calcium entry and the subsequent inhibition of the calpain pathway. These mechanisms may act in an additive way with other mechanisms previously described for lithium, suggesting that it may be useful as a possible therapeutic strategy for Alzheimer’s disease.     

Coactivation of GABA receptors inhibits the JNK3 apoptotic pathway via disassembly of GluR6‐PSD‐95‐MLK3 signaling module in KA‐induced seizure

Purpose: Past work has demonstrated that kainic acid (KA)–induced seizures could cause the enhancement of excitation and lead to neuronal death in rat hippocampus. To counteract such an imbalance between excitation and inhibition, we designed experiments by activating the inhibitory γ‐aminobutyric acid (GABA) receptor to investigate whether such activation suppresses the excitatory glutamate signaling induced by KA and to elucidate the underlying molecular mechanisms. Methods: Muscimol coapplied with baclofen was intraperitoneally administrated to the rats 40 min before KA injection by intracerebroventricular infusion. Subsequently we used a series of methods including immunoprecipitation, immunoblotting, histologic analysis, and immunohistochemistry to analyze the interaction, expression, and phosphorylation of relevant proteins as well as the survival of the CA1/CA3 pyramidal neurons. Results: Coadministration of muscimol and baclofen exerted neuroprotection against neuron death induced by KA; inhibited the increased assembly of the GluR6‐PSD‐95‐MLK3 module induced by KA; and suppressed the activation of MLK3, MKK7, and JNK3. Discussion: Taken together, we demonstrate that coactivation of the inhibitory GABA receptors can attenuate the excitatory JNK3 apoptotic signaling pathway via inhibiting the increased assembly of the GluR6‐PSD‐95‐MLK3 signaling module induced by KA. This provides a new insight into the therapeutic approach to epileptic seizure.     

Overexpression of the PDZ1 domain of PSD‐95 diminishes ischemic brain injury via inhibition of the GluR6·PSD‐95·MLK3 pathway

Recent studies have shown that kainate (KA) receptors are involved in neuronal cell death induced by seizure, which is mediated by the GluR6·PSD‐95·MLK3 signaling module and subsequent JNK activation. In our previous studies, we demonstrated the neuroprotective role of a GluR6 c‐terminus containing peptide against KA or cerebral ischemia‐induced excitotoxicity in vitro and in vivo. Here, we first report that overexpression of the PDZ1 domain of PSD‐95 protein exerts a protective role against neuronal death induced by cerebral ischemia‐reperfusion in vivo and can prevent neuronal cell death induced by oxygen‐glucose deprivation. Further studies show that overexpression of PDZ1 can perturb the interaction of GluR6 with PSD‐95 and suppress the assembly of the GluR6·PSD‐95·MLK3 signaling module and therefore inhibit JNK activation. Thus, it not only inhibits phosphorylation of c‐Jun and down‐regulates Fas ligand expression but also inhibits phosphorylation of 14‐3‐3 and decreases Bax translocation to mitochondria, decreases the release of cytochrome c, and decreases caspase‐3 activation. Overall, the essential role of the PDZ1 domain of PSD‐95 in apoptotic cell death in neurons provides an experimental foundation for gene therapy of neurodegenerative diseases with overexpression of the PDZ1 domain. © 2009 Wiley‐Liss, Inc.     

Spatiotemporal expression of PSD‐95 in Fmr1 knockout mice brain

To investigate and compare the spatial and temporal expression of post‐synaptic density‐95 (PSD‐95) in Fmr1 knockout mice (the animal model of fragile X syndrome, FXS) and wild‐type mice brain, on postnatal day 7 (P7), P14, P21, P28 and P90, mice from each group were decapitated, and three principal brain regions (cerebral cortex, hippocampus and cerebellum) were obtained and stored for later experiments. PSD‐95 mRNA in the three brain areas was analyzed with quantitative RT‐PCR. PSD‐95 protein was measured by immunohistochemical staining and Western blot. In the three principal brain areas of Fmr1 knockout mice and wild‐type mice, the expression of PSD‐95 mRNA and protein were detected at the lowest levels on P7, and then significantly increased on P14, reaching the peak levels in adolescents or adults. Moreover, it was found that PSD‐95 mRNA and protein in the hippocampus were significantly decreased in Fmr1 knockout mice during the developmental period (P7, P14, P21 and P28) as well as at adulthood (P90) (P < 0.05, and P < 0.01, respectively). However, there was no significant difference of expression of PSD‐95 in the cortex and cerebellum between Fmr1 knockout and wild mice. The expression of PSD‐95 in the hippocampus might be regulated by fragile X mental retardation protein (FMRP) during mice early developmental and adult periods. It is suggested that impairment of PSD‐95 is possibly involved in hippocampal‐dependent learning defects, which are common in people with FXS.     

Characterization of physiological phenotypes of dentate gyrus synapses of PDZ1/2 domain‐deficient PSD‐95‐knockin mice

The hippocampal formation is involved in several important brain functions of animals, such as memory formation and pattern separation, and the synapses in the dentate gyrus (DG) play critical roles as the first step in the hippocampal circuit. Previous studies have reported that mice with genetic modifications of the PDZ1/2 domains of postsynaptic density (PSD)‐95 exhibit altered synaptic properties in the DG and impaired hippocampus‐dependent behaviors. Based on the involvement of the DG in the regulation of behaviors, these data suggest that the abnormal behavior of these knockin (KI) mice is due partly to altered DG function. Precise understanding of the phenotypes of these mutant mice requires characterization of the synaptic properties of the DG, and here we provide detailed studies of DG synapses. We have demonstrated global changes in the PSD membrane‐associated guanylate kinase expression pattern in the DG of mutant mice, and DG synapses in these mice exhibited increased long‐term potentiation under a wide range of stimulus intensities, although the N‐methyl‐d ‐aspartic acid receptor dependence of the long‐term potentiation was unchanged. Furthermore, our data also indicate increased silent synapses in the DG of the KI mice. These findings suggest that abnormal protein expression and physiological properties disrupt the function of DG neurons in these KI mice.     

Genome‐wide gene expression profiling in GluR1 knockout mice: key role of the calcium signaling pathway in glutamatergically mediated hippocampal transmission

α‐Amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid receptors (AMPARs) convey fast synaptic transmission in the CNS and mediate various forms of hippocampal plasticity. Disruption of glutamate receptor type 1 (GluR1), a member of the AMPAR family, causes synaptic alterations and learning/memory deficits in mice. To gain mechanistic insight into the synaptic and behavioral changes associated with GluR1 deletion, hippocampal genome‐wide expression profiling was conducted using groups of GluR1 knockout (KO) mice and their wild‐type littermates. Regulation of 38 genes was found to be altered more than 30% (P < 0.01, n = 8), and seven of these genes were studied with additional quantitative experiments. A large portion of the altered genes encoded molecules involved in calcium signaling, including calcium channel components, calcium‐binding proteins and calcium‐calmodulin‐dependent protein kinase II subunits. At the protein level, we further evaluated some genes in the calcium pathway that were altered in GluR1 KO mice. Protein levels of two key molecules in the calcium pathway – GluR, ionotropic, N‐methyl‐d ‐aspartate‐1 and calcium/calmodulin‐dependent protein kinase II alpha – showed similar changes to those observed in mRNA levels. These findings raise the possibility that calcium signaling and other plasticity molecules may contribute to the hippocampal plasticity and behavioral deficits observed in GluR1 KO mice.     

Gender differences in response of hippocampus to chronic glucocorticoid stress: role of glutamate receptors

Glucocorticoids (GC) play critical roles in the pathophysiological reactions to environmental stress. In brain, morphological changes were examined in hippocampal CA3 neurons with 2 weeks of chronic elevation of GC in male and female mice. Molecular correlates and underlying mechanisms paralleling these morphologic changes in hippocampus were investigated. Although the hippocampal neurons in the CA3 area in male mice atrophy with chronically elevated GC, female mice show minimal morphological changes with comparable GC regimens. These sexual morphological differences correlate with differences in the postsynaptic dense protein (PSD95) as well as the spectrum of glutamate receptors induced by GC treatment in male and female mice, including NMDA, AMPA, and KA receptors. These findings suggest that synaptic receptor composition is adapted to the unique physiological requirements of males and females and illuminate underlying mechanisms of GC/stress responses in the brain.     

Blockade of corticotropin‐releasing hormone receptor 1 attenuates early‐life stress‐induced synaptic abnormalities in the neonatal hippocampus

Adult individuals with early stressful experience exhibit impaired hippocampal neuronal morphology, synaptic plasticity and cognitive performance. While our knowledge on the persistent effects of early‐life stress on hippocampal structure and function and the underlying mechanisms has advanced over the recent years, the molecular basis of the immediate postnatal stress effects on hippocampal development remains to be investigated. Here, we reported that repeated blockade of corticotropin‐releasing hormone receptor 1 (CRHR1) ameliorated postnatal stress‐induced hippocampal synaptic abnormalities in neonatal mice. Following the stress exposure, pups with fragmented maternal care showed retarded dendritic outgrowth and spine formation in CA3 pyramidal neurons and reduced hippocampal levels of synapse‐related proteins. During the stress exposure, repeated blockade of glucocorticoid receptors (GRs) by daily administration of RU486 (100 µg g^?1) failed to attenuate postnatal stress‐evoked synaptic impairments. Conversely, daily administration of the CRHR1 antagonist antalarmin hydrochloride (20 µg g^?1) in stressed pups normalized hippocampal protein levels of synaptophysin, postsynaptic density‐95, nectin‐1, and nectin‐3, but not the N‐methyl‐d ‐aspartate receptor subunits NR1 and NR2A. Additionally, GR or CRHR1 antagonism attenuated postnatal stress‐induced endocrine alterations but not body growth retardation. Our data indicate that the CRH‐CRHR1 system modulates the deleterious effects of early‐life stress on dendritic development, spinogenesis, and synapse formation, and that early interventions of this system may prevent stress‐induced hippocampal maldevelopment. © 2014 Wiley Periodicals, Inc.     

GluR6-containing KA receptor mediates the activation of p38 MAP kinase in rat hippocampal CA1 region during brain ischemia injury

Our previous study showed that kainate (KA) receptor subunit GluR6 played an important role in ischemia-induced MLK3 and JNK activation and neuronal degeneration through the GluR6-PSD95-MLK3 signaling module. However, whether the KA receptors subunit GluR6 is involved in the activation of p38 MAP kinase during the transient brain ischemia/reperfusion (I/R) in the rat hippocampal CA1 subfield is still unknown. In this present study, we first evaluated the time-course of phospho-p38 MAP kinase at various time-points after 15 min of ischemia and then observed the effects of antagonist of KA receptor subunit GluR6, GluR6 antisence oligodeoxynucleotides on the phosphorylation of p38 MAP kinase induced by I/R. Results showed that inhibiting KA receptor GluR6 or suppressing the expression of KA receptor GluR6 could down-regulate the elevation of phospho-p38 MAP kinase induced by I/R. These drugs also reduced the phosphorylation of MLK3, MKK3/MKK6, MKK4, and MAPKAPK2. Additionally, our results indicated administration of three drugs, including p38 MAP kinase inhibitor before brain ischemia significantly decreased the number of TUNEL-positive cells detected at 3 days of reperfusion and increased the number of the surviving CA1 pyramidal cells at 5 days of reperfusion after 15 min of ischemia. Taken together, we suggest that GluR6-contained KA receptors can mediate p38 MAP kinase activation through a kinase cascade, including MLK3, MKK3/MKK6, and MKK4 and then induce increased phosphorylation of MAPKAPK-2 during ischemia injury and ultimately result in neuronal cell death in the rat hippocampal CA1 region.     

Amyloid fibrils induce dysfunction of hippocampal glutamatergic silent synapses

Silent glutamatergic synapses lacking functional AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionate) receptors exist in several brain regions including the hippocampus. Their involvement in the dysfunction of hippocampal glutamatergic transmission in the setting of Alzheimer's disease (AD) is unknown. This study demonstrated a decrease in the percentage of silent synapses in rats microinjected with amyloid fibrils (Aβ_1–40) into the hippocampal CA1. Also, pairing low‐frequency electric stimuli failed to induce activation of the hippocampal silent synapses in the modeled rats. Immunoblotting studies revealed a decreased expression of GluR1 subunits in the hippocampal CA1 synaptosomal preparation, indicating a potential reduction in the GluR1 subunits anchoring in postsynaptic density in the modeled rats. We also noted a decreased expression of phosphorylated cofilin, which regulates the function of actin cytoskeleton and receptor trafficking, and reduced expression of the scaffolding protein PSD95 in the hippocampal CA1 synaptosome in rats injected with Aβ_1–40. Taken together, this study illustrates dysfunction of hippocampal silent synapse in the rodent model of AD, which might result from the impairments of actin cytoskeleton and postsynaptic scaffolding proteins induced by amyloid fibrils.     

Postnatal and ovariectomic regulation of postsynaptic density protein‐95 in the hippocampus of female Sprague‐Dawley rats

Postsynaptic density protein‐95 (PSD‐95) is hypothesized to control the excitatory‐to‐inhibitory ratio and plays an important role in the regulation of hippocampal synaptic plasticity, synaptogenesis, and learning and memory. In this report, we used immunoblotting to study the effects of aging and ovariectomy (OVX) on the expression of PSD‐95 in the hippocampus of female rats. The results indicated that postnatal expression of hippocampal PSD‐95 correlated with the fluctuation of circulating female sex hormones such as estrogen. Neonatal PSD‐95 level was very low, but dramatically increased within the first month. The highest expression of PSD‐95 was detected at postnatal day 30 (P30) and significantly decreased by 18 months. In the adult hippocampus, OVX significantly decreased PSD‐95 expression within the first week, but it had recovered to adult levels 2 weeks later. Taken together, we conclude that circulating ovarian hormones may play a crucial role in the regulation of excitatory synapses within the hippocampus. Depletion of ovarian hormones can transiently and dramatically decrease the level of excitatory synapses for a limited time. Synapse 64:875–878, 2010. © 2010 Wiley‐Liss, Inc.     

Distribution and properties of kainate receptors distinct in the CA3 region of the hippocampus of the guinea pig

To characterize the nature of kainate (KA) receptors distinct in the CA3 region of the hippocampus, properties of depolarizations induced by pulses of KA or AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionate) applied to dendrites of CA3 neurons with micropipettes were studied in thin transverse slices of the guinea pig hippocampus. KA induced depolarizations at negligible latencies only when administered to the most proximal dendritic areas. The depolarization was unaffected by tetrodotoxin or by a decrease in Ca²⁺ and an increase in Mg²⁺ concentrations. The declining slope of the KA-induced depolarization was significantly slower than that of the AMPA-induced depolarization. In comparison with the AMPA-induced depolarization, the KA-induced depolarization was much less susceptible to antagonists such as 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI52466). 6,7,8,9-Tetrahydro-5-nitro-1H-benz[g]indole-2,3-dione-3-oxime (NS-102) and (2S,4R)-4-methylglutamate (SYM 2081) were without effects. The threshold concentration of pressure-ejected KA to induce depolarizations was about 200 nM. Excitatory postsynaptic potentials elicited by mossy fiber stimulation were more potently suppressed by CNQX than by GYKI52466. These results indicate that receptors responsible for the slow KA depolarization in the CA3 region of the hippocampus are not AMPA receptors but KA receptors. They are localized in the most proximal part of the apical dendrite and distinct from those observed in primary cultures of hippocampal neurons.     

Expression of the metabotropic glutamate receptor mGluR1α and the ionotropic glutamate receptor GluR1 in the brain during the postnatal development of normal mouse and in the cerebellum from mutant mice

Expression of the metabotropic glutamate receptor type 1α (mGluR1α) and the non-N-methyl-D-aspartate (NMDA) ionotropic glutamate receptor type 1 (GluR1) in mouse brain was investigated using the antibodies raised against the synthetic peptides corresponding to their C-terminal amino acid sequences. Both receptor proteins are glycosylated predominantly in an asparagine-linked manner, and are abundant in post-synaptic membranes. We showed that mGluR1α and GluR1 expression within the first 3 postnatal weeks undergoes dramatic changes in time and space, i.e., in the hippocampus and cerebellum. These spatio-temporal expression patterns appear to be correlated with the postnatal ontogenesis and establishment of the glutamatergic neurotransmission system in the hippocampus and cerebellum, cell migration, dendritic and axonal growth, spine formation, and synaptogenesis. In the adult cerebellum, mGluR1α is intensely expressed in Purkinje neurons and GluR1 in Bergmann glial cells. Both receptors are expressed to a fair degree in weaver mutant cerebellum despite granule cell degeneration. However, the intrinsic expression levels of both mGluR1α and GluR1 are markedly reduced in the cerebellum of the Purkinje cell-deficient and underdeveloped mutant mice, Purkinje-cell-degeneration, Lurcher, and staggerer, suggesting that GluR1 expression in Bergmann glia cells may be correlated with the sustained interaction with adjacent Purkinje neurons. © 1993 Wiley-Liss, Inc.     

Development of kainic acid and N-methyl-d-aspartic acid toxicity in organotypic hippocampal cultures

The excitotoxic effects of N-methyl-d-aspartic acid (NMDA) and kainic acid (KA) were studied in organotypic hippocampal slices maintained in vitro for various periods of time. Cultures aged to equivalent Postnatal Day (EPD) 10–12,15–17, and 23–26 were exposed to 50 μM KA or 50 μM NMDA and were analyzed at 0, 3, 6, 9, 12, 24, 48 h, or 5 days after the initiation of the excitotoxin exposure. Neuronal injury was determined by: (1) propidium iodide (PI) uptake; (2) lactate dehydrogenase (LDH) release; (3) morphological damage in hematoxylin and eosin (H/E) stained sections; (4) loss of Nissl stain. Changes in PI uptake and LDH release after KA or NMDA treatment indicated that there was a developmental shift towards increasing sensitivity to KA toxicity during in vitro development, whereas cultures of all ages were equally sensitive to NMDA toxicity. The profile of damage in H/E-stained sections after treatment with KA or NMDA indicated a transient phase of damaged morphology at 12 and 24 h that was not evident after 5 days. To determine whether the disappearance of morphological manifestations of neuronal damage 5 days after treatment was due to recovery of morphology or to neuronal death, neuronal loss in Nissl-stained sections was also quantified. KA treatment did not cause significant neuronal loss in any hippocampal region in EPD 10–12 cultures, indicating that the neurons were able to successfully recover from the damage demonstrated in H/E sections at 12 and 24 h in these cultures. KA treatment in mature cultures (EPD 23–26) and NMDA treatment in all cultures produced a marked loss of identifiable Nissl-stained neurons at 5 days, indicating neuronal death and disintegration. The results provide further support for the similarities between the organotypic hippocampal culture model and in vivo excitotoxic models and also confirm that excitotoxic neuronal injury can be reversible under some conditions.     

Overexpression of C-terminal fragment of glutamate receptor 6 prevents neuronal injury in kainate-induced seizure via disassembly of GluR6-PSD95-MLK3 signaling module

Our previous study showed that when glutamate receptor （GluR）6 C terminus-containing peptide conjugated with the human immunodeficiency virus Tat protein （GluR6）-9c is delivered into hippocampal neurons in a brain ischemic model, the activation of mixed lineage kinase 3 （MLK3） and c-Jun NH2-terminal kinase （JNK） is inhibited via GluR6-postsynaptic density protein 95 （PSD95）. In the present study, we investigated whether the recombinant adenovirus （Ad） carrying GluR6c could suppress the assembly of the GluR6-PSD95-MLK3 signaling module and decrease neuronal cell death induced by kainate in hippocampal CA1 subregion. A seizure model in Sprague-Dawley rats was induced by intraperitoneal injections of kainate. The effect of Ad- Glur6-9c on the phosphorylation of INK, MLK3 and mitogen-activated ldnase kinase 7 （MKK7） was observed with western immunoblots and immunohistochemistry. Our findings revealed that overexpression of GluR6c inhibited the interaction of GluR6 with PSD95 and prevented the kainate-induced activation of INK, MLK3 and MKK7. Furthermore, kainate-mediated neuronal cell death was significantly suppressed by GluR6c. Taken together, GluR6 may play a pivotal role in neuronal cell death.     

Effects of antipsychotic drugs on the expression of synaptic proteins and dendritic outgrowth in hippocampal neuronal cultures

Recent evidence has suggested that atypical antipsychotic drugs regulate synaptic plasticity. We investigated whether some atypical antipsychotic drugs (olanzapine, aripiprazole, quetiapine, and ziprasidone) altered the expression of synapse‐associated proteins in rat hippocampal neuronal cultures under toxic conditions induced by B27 deprivation. A typical antipsychotic, haloperidol, was used for comparison. We measured changes in the expression of various synaptic proteins including postsynaptic density protein‐95 (PSD‐95), brain‐derived neurotrophic factor (BDNF), and synaptophysin (SYP). Then we examined whether these drugs affected the dendritic morphology of hippocampal neurons. We found that olanzapine, aripiprazole, and quetiapine, but not haloperidol, significantly hindered the B27 deprivation‐induced decrease in the levels of these synaptic proteins. Ziprasidone did not affect PSD‐95 or BDNF levels, but significantly increased the levels of SYP under B27 deprivation conditions. Moreover, olanzapine and aripiprazole individually significantly increased the levels of PSD‐95 and BDNF, respectively, even under normal conditions, whereas haloperidol decreased the levels of PSD‐95. These drugs increased the total outgrowth of hippocampal dendrites via PI3K signaling, whereas haloperidol had no effect in this regard. Together, these results suggest that the up‐regulation of synaptic proteins and dendritic outgrowth may represent key effects of some atypical antipsychotic drugs but that haloperidol may be associated with distinct actions. Synapse 67:224–234, 2013. © 2013 Wiley Periodicals, Inc.