Dentate Gyrus Of Adult Rats Research Articles

Synergistic effects of dehydroepiandrosterone and fluoxetine on proliferation of progenitor cells in the dentate gyrus of the adult male rat

The 5-HT re-uptake inhibitor (SSRI) fluoxetine and the adrenal hormone dehydroepiandrosterone (DHEA) both increase the proliferation of progenitor cells in the adult hippocampus and also have antidepressant activity. This paper explores the combined ability of fluoxetine and DHEA to affect this process in the dentate gyrus of adult rats. We show that DHEA can render an otherwise ineffective dose of fluoxetine (2.5 mg/kg) able to increase progenitor cell proliferation to the same extent as doses four times higher (10 mg/kg). This synergistic action does not appear to be mediated by alterations in brain-derived neurotrophic factor (BDNF) gene expression; or by TrkB, mineralocorticoid, glucocorticoid, or 5-HT (5HT1A) receptor expression in the dentate gyrus; or by altered levels of plasma corticosterone. In a second experiment, the synergism between DHEA and fluoxetine was replicated. Furthermore, flattening the diurnal rhythm of plasma corticosterone by implanting additional corticosterone pellets s.c. prevented the effect of fluoxetine on progenitor cell division. This was not overcome by simultaneous treatment with DHEA, despite the latter's reported anti-glucocorticoid actions. The cellular mechanism for the potentiating action of DHEA on the pro- proliferative effects of fluoxetine in the adult hippocampus remains to be revealed. Since altered neurogenesis has been linked to the onset or recovery from depression, one consequence of these results is to suggest DHEA as a useful adjunct therapy for depression.

Effects of vagus nerve stimulation on rat hippocampal progenitor proliferation

Vagus nerve stimulation (VNS), used in the treatment of epilepsy, was approved recently for treatment-resistant depression. The mechanisms of action of the VNS anti-depressive effects are not yet fully elucidated. Modulation of hippocampal neurogenesis has been proposed as an important factor in depression pathogenesis. We evaluated the effects of VNS on hippocampal progenitor turnover in the adult rat brain. Rats receiving VNS at the output current of 0.75 mA VNS for 2 days showed a significant 50% increase in dentate gyrus BrdU-incorporation consistent with an increase in progenitor proliferation. Output currents of 0.5 or 1.5 mA yielded non-significant trends for increased BrdU-labeling indicating an inverted U-shaped proliferative dose response to VNS as previously reported for other VNS-induced effects. Specific analysis for progenitor survival revealed no effects by VNS on dentate gyrus BrdU-labeling. These results suggest that VNS induced an increase in the number of available progenitor cells in the adult rat dentate gyrus by a mechanism presumably involving increased progenitor proliferation.

Regional-specific global cytosine methylation and DNA methyltransferase expression in the adult rat hippocampus

Recent observations suggest that DNA methylation plays an important role in memory and long-term potentiation (LTP) in the hippocampus and is involved in programming the offspring epigenome in response to maternal care. Global DNA methylation is believed to be stable postnatally and to be similar across tissues in the adult mammal. It has also been a long held belief that DNA methyltransferases (DNMTs) play a very limited role in postmitotic tissues. Recent data suggests a more dynamic role for DNA methylation in the brain postnatally, therefore we examined the global state of methylation and the expression of the known DNMTs in the different regions of the hippocampus. We observed strikingly different levels of global methylation in the adult rat dentate gyrus (DG) and CA1 region in comparison with the CA2 and CA3 regions. mRNA levels of DNA methyltransferases exhibited similar regional specificity and were correlated with global DNA methylation levels. These regional differences in global methylation and expression of the DNA methylation machinery in the adult brain are consistent with the emerging hypothesis that DNA methylation may play a dynamic physiological role in the adult brain.

Endogenous secreted amyloid precursor protein-α regulates hippocampal NMDA receptor function, long-term potentiation and spatial memory

Secreted amyloid precursor protein-α (sAPPα) levels are reduced during the pathogenesis of Alzheimer's disease, but the significance of this for neural function is not well understood. Here, we show that intrahippocampal infusion of antibodies targeted to endogenous sAPPα reduced long-term potentiation (LTP) in the dentate gyrus of adult rats by approximately 50%. Conversely, infusion of recombinant sAPPα dose-dependently increased LTP and facilitated in vitro tetanically evoked NMDA receptor-mediated currents. Pharmacological inhibition of α-secretase and other a-disintegrin-and-metalloproteases by TAPI-1 reduced both LTP and tetanus-evoked NMDA receptor-mediated currents in dentate granule cells. Both effects were prevented by co-application of exogenous recombinant sAPPα. Similarly, spatial memory was inhibited by intrahippocampal TAPI-1, an effect that was prevented by co-application of recombinant sAPPα. Together these findings indicate that endogenous sAPPα is a key contributor to synaptic plasticity and spatial memory. Its reduced production in Alzheimer's disease may thus contribute to the clinical memory deficits.

Quercetin relieves chronic lead exposure-induced impairment of synaptic plasticity in rat dentate gyrus in vivo

Increasing evidence suggests that lead (Pb) produces impairments partly through oxidative stress. Though many researchers have investigated protective effect of some antioxidant nutrients against Pb toxicity, little information is available about the effect of antioxidants on Pb-induced impairment of synaptic plasticity. Quercetin, a strong antioxidant and radical scavenger, is the representative natural flavonoid molecule abundant in fruits and vegetables. Previous studies have found that quercetin was neuroprotective in many cases. This study was designed to evaluate the effect of quercetin on chronic Pb exposure-induced impairment of synaptic plasticity in adult rat dentate gyrus (DG) area in vivo. The input/output (I/O) functions, paired-pulse reactions (PPR), excitatory postsynaptic potential (EPSP), and population spike (PS) amplitude were measured in the DG area of different groups of rats in response to stimulation applied to the lateral perforant path. The results showed that the depressed I/O, PPR, and long-term potentiation (LTP) of Pb-exposed group were significantly increased by quercetin treatment. In addition, hippocampal Pb concentration was partially reduced after quercetin treatment. These findings suggest that quercetin treatment could relieve chronic Pb exposure-induced impairment of synaptic plasticity and might be a potential therapeutic intervention to cure cognitive deficits induced by Pb.

Brain‐derived neurotropic factor and neurogenesis in the adult rat dentate gyrus: interactions with corticosterone

Flattening the diurnal corticosterone rhythm prevented the stimulating action of L-NAME (a nitric oxide synthase, NOS, inhibitor) on progenitor cell proliferation in the dentate gyrus in Lister-Hooded adult male rats. The increased expression of brain-derived neurotrophic factor (BDNF) and trkB mRNA in the dentate gyrus which otherwise occurred after L-NAME was also prevented by clamping the corticoid rhythm in adrenalectomized rats, but was restored by daily additional injections of corticosterone (which replicates the diurnal rhythm). Unilateral infusions of BDNF into the lateral ventricle increased proliferation in the dentate gyrus on the side of the infusion, but this was not observed following implantation of subcutaneous corticosterone, which flattened the diurnal corticosterone rhythm. 5HT1A mRNA in the dentate gyrus was increased on both sides of the brain by unilateral BDNF infusions, but this was also prevented by subcutaneous corticosterone pellets. These results show that the diurnal rhythm of corticosterone regulates the stimulating action of NOS inhibitors on BDNF as well as on neurogenesis in the dentate gyrus, and that BDNF becomes ineffective on both proliferation rates and 5HT1A expression in the absence of a rhythm in corticosterone. This, together with our previous findings, suggests that corticoid rhythms permit both serotonin and NO access to BDNF, and the latter to regulate progenitor cell activity.

Rapid Eye Movement Sleep Deprivation Contributes to Reduction of Neurogenesis in the Hippocampal Dentate Gyrus of the Adult Rat

The dentate gyrus (DG) of the adult hippocampus contains progenitor cells, which have potential to differentiate into neurons. Previously we reported that 96 hours of total sleep deprivation reduces neurogenesis in the DG of adult rats. Loss of either non-rapid eye movement (NREM) or rapid eye movement (REM) sleep could have contributed to the effect of total sleep deprivation. The present study assessed the effect of 4 days of REM sleep deprivation (REMD) on neurogenesis. REMD was achieved by brief treadmill movement initiated by automatic online detection of REM sleep. A yoked-control (YC) rat was placed in the same treadmill and experienced the identical movement regardless the stage of the sleep-wake cycle. The thymidine analog 5- bromo- 2'- deoxy-uridine and the intrinsic proliferation marker, Ki-67, were both used to label proliferating cells. Basic neurophysiology laboratory. Male Sprague-Dawley male rats (300-320 g). REM sleep was reduced by 85% in REMD rats and by 43% in YC, compared with cage control animals and by 79% in REMD rats compared with YC. NREM sleep and slow wave activity within NREM did not differ in REMD and YC groups. Cell proliferation was reduced by 63 % in REMD compared with YC rats, and by 82% and 51%, respectively, in REMD and YC rats compared with cage controls. Across all animals, cell proliferation exhibited a positive correlation with the percentage of REM sleep (r = 0.84, P < 0.001). Reduced cell proliferation in REMD rats was confirmed with the intrinsic proliferation marker, Ki-67. REMD also reduced the percentage of proliferating cells that later expressed a mature neuronal marker. The present findings support a hypothesis that REM sleep-associated processes facilitate proliferation of granule cells in the adult hippocampal DG.

Different effects of mild and severe seizures on hippocampal neurogenesis in adult rats

Recent evidence shows that functional neurogenesis exists in the adult hippocampus and that epileptic seizures can increase neurogenesis in the dentate gyrus (DG). However, it is unknown whether different seizure severity has different effects on neurogenesis in the DG of adult rats. In this study, we examined hippocampal neurogenesis in the rat mild and severe seizure preparations characterized with frequent wet dog shakes and severe status epilepticus, respectively. Both mild and severe seizures promoted the mitotic activity in the DG, but severe seizures caused a stronger cell proliferative response than mild seizures. Less than 20% of newborn cells in the DG differentiated into neurons in rats suffering severe seizures, whereas more than 60% of newborn dentate cells differentiated into neurons in control and mild seizure groups. Most newborn neurons migrated into the granular cell layer in control and mild seizure groups, but severe seizures were associated with an aberrant migration of newborn neurons into the dentate hilus. Severe seizures induced astrocyte activation and the expression of nestin and the migration directional molecules netrin 1 and Sema-3A in the hilus, which were not present in the hilus of control and mild seizure-attacked rats, suggesting that these molecules are involved in the aberrant migration of newborn neurons.

Myocyte-specific enhancer binding factor 2C (MEF2C) expression in the dentate gyrus during development and after pilocarpine-induced status epilepticus: a preliminary report

As axon outgrowth and dentate granule cell neurogenesis are hallmarks of hippocampal development and are also the two morphologic changes in the structure of the dentate gyrus after status epilepticus (SE), we hypothesized that molecules involved in normal development may also play a role during epileptogenesis. Using in situ hybridization, we have characterized mRNA expression of myocyte-specific enhancer binding factor 2C (MEF2C) in the dentate gyrus during development (P0, P3, P7, P14 and P28) and at multiple time points following pilocarpine-induced SE (3, 7, 14, 28 days after SE). It was demonstrated that MEF2C is up-regulated during development (P0, P3, P7, P14 and P28) and in the adult rat dentate gyrus following SE (3, 7, 14, 28 days after SE). The molecules controlling cell-fate decisions in the developing dentate gyrus are also operative during epileptogenesis.

Differential Trafficking of AMPA and NMDA Receptors during Long-Term Potentiation in Awake Adult Animals

Despite a wealth of evidence in vitro that AMPA receptors are inserted into the postsynaptic membrane during long-term potentiation (LTP), it remains unclear whether this occurs in vivo at physiological concentrations of receptors. To address the issue of whether native AMPA or NMDA receptors undergo such trafficking during LTP in the adult brain, we examined the synaptic and surface expression of glutamate receptor subunits during the early induction phase of LTP in the dentate gyrus of awake adult rats. Induction of LTP was accompanied by a rapid NMDA receptor-dependent increase in surface expression of glutamate receptor 1-3 (GluR1-3) subunits. However, in the postsynaptic density fraction only GluR1 accumulated. GluR2/3-containing AMPA receptors, in contrast, were targeted exclusively to extrasynaptic sites in a protein synthesis-dependent manner. NMDA receptor subunits exhibited a delayed accumulation, both at the membrane surface and in postsynaptic densities, that was dependent on protein synthesis. These data suggest that trafficking of native GluR1-containing AMPA receptors to synapses is important for early-phase LTP in awake adult animals, and that this increase is followed homeostatically by a protein synthesis-dependent trafficking of NMDA receptors.

Corrigenda

CorrigendaCorrigendaPublished Online:01 Nov 2007https://doi.org/10.1152/jn.z9k-8470-corr.2007Original articlesPREGS Induces LTP in the Hippocampal Dentate Gyrus of Adult Rats Via the Tyrosine Phosphorylation International Cooperative Research CREB SignalingSimple Models Show the General Advantages of Dendrites in Coincidence DetectionMoreSectionsPDF (24 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmail Volume 97, May 2007Pages 3449–3459: Dasika VK, White JA, and Colburn HS. “Simple Models Show the General Advantages of Dendrites in Coincidence Detection” (doi:10.1152/jn.00669.2005; http://jn.physiology.org/cgi/content/full/97/5/3449). Regrettably, an error was inadvertently made in Eq. 15. Also, during production, Equation A2 was misrepresented. The correct forms for these equations are: (15)(A2)Pages 1538–1548: Chen L, Miyamoto Y, Furuya K, Mori N, and Sokabe M. “PREGS Induces LTP in the Hippocampal Dentate Gyrus of Adult Rats Via the Tyrosine Phosphorylation International Cooperative Research CREB Signaling” (doi: 10.1152/jn.01151.2006; http://jn.physiology.org/cgi/content/full/98/3/1538). The title of this article was incorrectly altered during production. The correct title is: “PREGS Induces LTP in the Hippocampal Dentate Gyrus of Adult Rats Via the Tyrosine Phosphorylation of NR2B Coupled to ERK/CREB Signaling.”This article has no references to display. Previous Back to Top FiguresReferencesRelatedInformationRelated articlesPREGS Induces LTP in the Hippocampal Dentate Gyrus of Adult Rats Via the Tyrosine Phosphorylation International Cooperative Research CREB Signaling 01 Sep 2007Journal of NeurophysiologySimple Models Show the General Advantages of Dendrites in Coincidence Detection 01 May 2007Journal of Neurophysiology More from this issue > Volume 98Issue 5November 2007Pages 3120-3120 Copyright & PermissionsCopyright © 2007 by the American Physiological Societyhttps://doi.org/10.1152/jn.z9k-8470-corr.2007History Published online 1 November 2007 Published in print 1 November 2007 PDF download Metrics Downloaded 86 times

2R, 4R-APDC decreases cell proliferation in the dentate gyrus of adult rats: the effect of 2R, 4R-APDC on cell proliferation

This study investigated the effects of group II metabotropic glutamate receptor agonist, 2R, 4R-4-aminopyrrolidine-2,4-dicarboxylate (2R, 4R-APDC), on cell proliferation in the dentate gyrus of adult rats. 2R, 4R-APDC at a dose of 1 and 10 nmol/day resulted in decreased bromodeoxyuridine immunoreactive cells in the dentate gyrus. In addition, we found that APDC treatment had no effect on the number of BrdU+ and GFAP(+)-labeled cells or BrdU+ and NeuN(+)-labeled cells compared with controls. These data suggest that group II metabotropic glutamate receptor is an important site for glutamate's regulation on cell proliferation in the dentate gyrus, but 2R, 4R-APDC had no effects on newborn cell's ability to differentiate into neurons or astrocytes.

Newly generated granule cells show rapid neuroplastic changes in the adult rat dentate gyrus during the first five days following pilocarpine‐induced seizures

Long-term neuroplastic changes to dentate granule cells have been reported after seizures and were shown to contribute to recurrent excitatory circuitry. These changes include increased numbers of newborn granule cells, sprouted mossy fibers, granule cell layer dispersion, increased hilar ectopic granule cells and formation of hilar basal dendrites on granule cells. The goal of the current study was to determine the acute progression of neuroplastic changes involving newly generated granule cells after pilocarpine-induced seizures. Doublecortin (DCX) immunocytochemical preparations were used to examine the newly generated granule cells 1-5 days after seizures were induced. The results showed that there are rapid neuroplastic changes to the DCX-labeled cells. At 1 day after seizures were induced, there were significant increases in the percentage of DCX-labeled cells with hilar basal dendrites and in the progenitor cell population. At 2 days after seizures were induced, an increase in the thickness of the layer of DCX-labeled cells occurred. At 3 days after seizures were induced, the number of DCX-labeled cells was significantly increased. At 4 days after seizures were induced, developing synapses were observed on DCX-labeled hilar basal dendrites. Thus, newly generated granule cells in the adult dentate gyrus display neuroplastic changes by 1 day after pilocarpine-induced seizures and further changes occur to this population of cells in the subsequent 4 days. The presence of synapses, albeit developing ones, on hilar basal dendrites during this period indicates that newly generated granule cells become rapidly incorporated into dentate gyrus circuitry following seizures.

Fluoxetine does not affect the ischemia-induced increase of neurogenesis in the adult rat dentate gyrus

Ischemic insult enhances the proliferation of precursor cells in the dentate subgranular zone. This study was performed to determine whether fluoxetine further promotes the neurogenesis induced by transient forebrain ischemia in the rat dentate gyrus. Transient forebrain ischemia was induced by four-vessel occlusion for 10 min. First, to investigate whether the short-term treatment of fluoxetine influences ischemia-induced cell proliferation, rats were administered fluoxetine (5 mg/kg, i.p.) or a vehicle on days three to nine post-ischemia, and 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdU, 75 mg/kg, i.p.) one hour after the last fluoxetine injection. On examination one day later, the number of BrdU-labeled cells was not significantly different between the fluoxetine- and vehicle-treated groups. Second, to identify whether the chronic treatment of fluoxetine has an effect on the survival of ischemia-induced newborn cells, rats were administered fluoxetine or a vehicle on days 3 to 23 post-ischemia, and BrdU (75 mg/kg, three times) nine days post-ischemia. On examination four weeks after the BrdU injection, the number of BrdU-labeled cells was not significantly different between the fluoxetine- and vehicle-treated groups. Also, the rate of neuronal maturation was not significantly different between the two groups. These results show that fluoxetine does not affect the ischemia-induced increase of neurogenesis in the dentate gyrus of the adult rat.

Reelin Regulates Neuronal Progenitor Migration in Intact and Epileptic Hippocampus

Dentate granule cell (DGC) neurogenesis persists throughout life in the mammalian hippocampal dentate gyrus and increases after epileptogenic insults. The DGC layer in human and experimental mesial temporal lobe epilepsy (mTLE) often shows abnormal dispersion and the appearance of hilar-ectopic DGCs. In the pilocarpine mTLE model, hilar-ectopic DGCs arise as a result of an aberrant chain migration of neural progenitors. Reelin is a secreted migration guidance cue that persists in the adult rodent and human hippocampus. We tested the hypothesis that loss of Reelin in the epileptic dentate gyrus leads to aberrant chain migration of DGC precursors. We found that interneuron subsets typically lost in human and experimental mTLE express Reelin, and DGC progenitors express the downstream Reelin signaling molecule Disabled 1 (Dab1). Prolonged seizures decreased Reelin immunoreactivity in the adult rat dentate gyrus and increased Dab1 expression in hilar-ectopic neuroblasts. Exogenous Reelin increased detachment of chain-migrating neuroblasts in dentate gyrus explants, and blockade of Reelin signaling increased chain migration. These findings suggest that Reelin modulates DGC progenitor migration to maintain normal DGC integration in the neonatal and adult mammalian dentate gyrus. Loss of Reelin expression in the epileptic adult hippocampus, moreover, likely contributes to ectopic chain migration and aberrant integration of newborn DGCs.

Extensive training in a maze task reduces neurogenesis in the adult rat dentate gyrus probably as a result of stress

It has recently been shown that hippocampal neurogenesis can be modulated either directly or indirectly by ascending cholinergic inputs from the basal forebrain. In the present work, we sought to address whether extended training in a spatial navigation task would affect hippocampal neurogenesis in the presence of a severe and selective cholinergic depletion. Young female rats received stereotaxic injections of the immunotoxin 192 IgG-saporin into the basal forebrain nuclei and/or the cerebellar cortex. Starting from 4 to 5 weeks post-lesion, and for the subsequent 2 weeks, the animals were trained on paradigms of reference and working memory in the water maze and received single daily i.p. injections of bromodeoxyuridine (BrdU) at the end of each testing session. In line with previous observations, a dramatic 80% decrease in neuron proliferation was seen in the dentate gyrus of lesioned animals, as compared to vehicle-injected or intact controls. Interestingly, however, rats subjected to maze training over 2 weeks, irrespective of their learning success, exhibited significantly fewer newborn neurons than matched controls with no maze exposure. Thus, at least for the type of task used here, which has previously been shown to impose a certain degree of stress, extended training and learning does not appear to affect proliferation in the dentate gyrus.

Differential neurogenesis in the adult rat dentate gyrus: an identifiable zone that consistently lacks neurogenesis

The dentate gyrus continues to produce new neurons in adult rodents. The possibility of differential regulation of neurogenesis within regions of the dentate gyrus is largely unexplored, despite several other aspects of this phenomenon being well characterized in a large number of studies. In this report, we describe an area located at the anterior pole of the dentate gyrus that consistently lacks neurogenesis. This neurogenically quiescent zone invariably lacks expression of the neuroblast marker doublecortin (DCX), bromodeoxyuridine and Ki-67, though DCX expression can be elicited in response to a combined paradigm of environmental enrichment and wheel running. We propose that this region may provide a valuable model system to discern the factors that regulate the process of neurogenesis.

Involvement of over-expressed BMP4 in pentylenetetrazol kindling-induced cell proliferation in the dentate gyrus of adult rats

The dentate gyrus (DG) of the hippocampus is one of a few regions in the adult mammalian brain characterized by ongoing neurogenesis. Proliferation of neural precursors in the granule cell layer of the DG has been identified in pentylenetetrazol (PTZ) kindling epilepsy model, however, little is known about the molecular mechanism. We previously reported that the expression pattern of bone morphogenetic proteins-4 (BMP4) mRNA in the hippocampus was developmentally regulated and mainly localized in the DG of the adult. To explore the role of BMP4 in epileptic activity, we detected BMP4 expression in the DG during PTZ kindling process and explore its correlation with cell proliferation combined with bromodeoxyuridine (BrdU) labeling technique. We found that dynamic changes in BMP4 level and BrdU labeled cells dependent on the kindling stage of PTZ induced seizure-prone state. The number of BMP4 mRNA-positive cells and BrdU labeled cells reached the top level 1 day after PTZ kindled, then declined to base level 2 months later. Furthermore, there was a significant correlation between increased BMP4 mRNA expression and increased number of BrdU labeled cells. After effectively blocked expression of BMP4 with antisense oligodeoxynucleotides(ASODN), the BrdU labeled cells in the dentate gyrus subgranular zone(DG-SGZ) and hilus were significantly decreased 16d after the first PTZ injection and 1, 3, 7, 14d after kindled respectively. These findings suggest that increased proliferation in the DG of the hippocampus resulted from kindling epilepsy elicited by PTZ maybe be modulated by BMP4 over-expression.

N-methyl- d-aspartate receptor expression during adult neurogenesis in the rat dentate gyrus

N-methyl- d-aspartate (NMDA) receptors play a crucial role in the regulation of neuronal development during embryogenesis and they also regulate the rate of neurogenesis and proliferation in the adult dentate gyrus. However, the mechanism by which they influence these processes is not fully understood. NMDA receptors seem to be functional in hippocampal precursor cells and recently generated granule neurons, although there is no anatomical correlate of these physiological observations. We have analyzed the expression of the NMDA receptor subunits NR1 and NR2B in precursor cells and recently generated granule neurons of the adult rat dentate gyrus, using 5′bromodeoxyuridine, green fluorescent protein–retrovirus and immunohistochemistry. Our results indicate that NR1 and NR2B are expressed in some proliferating cells of the adult subgranular zone. These receptors are absent from transiently amplifying progenitors (type 2–3 cells) but they are found in glial fibrillar acidic protein expressing cells in the subgranular zone, suggesting its presence in bipotential (type-1) precursor cells. NR1 and NR2B are rarely found in granule cells younger than 60 h. By contrast, many granule cells generated 14 days before killing express both NMDA receptor subunits. These results demonstrate that adult hippocampal neurogenesis may be regulated by NMDA receptors present in precursor cells and in differentiating granule neurons, although these receptors are probably not located on synapses. However, an indirect effect through NMDA receptors located in other cell types should not be excluded.

Extranuclear estrogen receptor beta immunoreactivity is on doublecortin-containing cells in the adult and neonatal rat dentate gyrus

In adult female rats, estrogen receptor (ER) activation, particularly of ERβ, promotes hippocampal neurogenesis. We previously reported that extranuclear ERβ immunoreactivity (ir) in adult rats is on cellular profiles in or near the granule cell layer, which is the location of newly generated cells. During development, cells in or near the granule cell layer transiently express high levels of estrogen binding and nuclear ERs. Thus, we sought to determine if extranuclear ERβ is in newly generated cells in adult and neonatal rat dentate gyrus. Sections from the dentate gyrus of adult proestrus or postnatal day 7 and 14 female rats were dual-labeled for ERβ and the new-cell marker doublecortin (DCX) and examined by electron microscopy. DCX-containing neurons were found in the subgranular hilus in adult rats and were more widespread throughout the granule cell layer and hilus of neonatal rats. In both adults and neonatal rats, ERβ immunoreactivity was found in a subset of DCX-labeled neurons. Electron microscopic examination of the adult dentate gyrus revealed that most perikarya with DCX-ir had the morphological characteristics of granule cells, although a few resembled interneurons. Dendrites with DCX-ir also were observed. In both adults and neonates, DCX-labeled neuronal perikarya and dendrites contained ERβ-ir; ERβ-ir usually was aggregated near the plasma membrane, mitochondria or endoplasmic reticula. ERβ-ir was in glial profiles that apposed DCX-labeled perikarya and dendrites. These findings are consistent with data showing that estrogens can exert non-genomic effects directly and indirectly on newly generated cells in neonatal and adult rat dentate gyrus.