A single neonatal dose of methamphetamine suppresses dentate granule cell proliferation in adult gerbils which is restored to control values by acute doses of haloperidol

Summary. A single non-invasive dose of methamphetamine (50 mg/kg; i.p.) was administered to neonatal male gerbils (Meriones unguiculatus) aged 14 days. The first objective of the present study was to examine whether this early drug challenge, which has been shown to induce suppressive postnatal maturation of prefrontal dopamine (DA) innervation (Dawirs et al., 1994), interferes with adult granule cell proliferation in the dentate gyrus. Proliferation of granule cells was identified by in-vivo labeling with 5-bromo-2′-desoxyuridine (BrdU). BrdU-labeled granule cell nuclei were identified in consecutive horizontal sections along the mid-septotemporal axis of the hippocampus and light-microscopically quantified 7 days after BrdU-labeling. It was found that a single neonatal dose of methamphetamine was a stimulus strong enough to significantly attenuate adult granule cell proliferation. This effect was clearly lateralized with significant suppression of mitotic activity becoming apparent solely in the left dentate gyrus (−34%). The second objective of the present study was to examine whether acute doses of haloperidol, which have been found to stimulate granule cell proliferation in healthy adult animals (Dawirs et al., 1988), might restore mitotic activity to control values. For that purpose, at the age of postnatal day 90 adult animals which had been challenged with methamphetamine as juveniles received 4 doses of haloperidol (5 mg/kg; i.p.). Proliferation of granule cells was identified by BrdU-labeling. It was found that this neuroleptic treatment acutely restored granule cell proliferation rates to control values. The present results are discussed with regard to (1) factors, regulating mitotic activity in the hippocampus and (2) probable clues they may provide for understanding the neurobiological basis of psychotic behavior. Received September 4, 1998; accepted November 11, 1998     

Septotemporal variation of the supragranular projection of the mossy fiber pathway in the dentate gyrus of normal and kindled rats.

Previous studies have demonstrated regional variation in the anatomical organization and physiological properties of the hippocampus along its septotemporal (dorsoventral) axis. In this study, regional variation of the supragranular projection of the mossy fiber pathway in the dentate gyrus of normal and kindled rats was characterized with a scoring method for assessment of the distribution of mossy fiber synaptic terminals detected by Timm histochemistry. In normal rats, there was a sparse projection of the mossy fiber pathway into the supragranular region near the tips and crest of the dentate gyrus along the entire septotemporal axis, and a prominent projection into the supragranular region at the temporal pole. Kindling of the perforant path, amygdala, and olfactory bulb induced synaptic reorganization of the mossy fiber pathway into the supragranular region along the entire septotemporal axis of the dentate gyrus. There was regional variation of the seizure-induced synaptic reorganization along this axis, and distinct septotemporal patterns were observed as a function of the site of kindling stimulation. Kindling of the perforant path induced mossy fiber synaptic reorganization that was relatively more prominent in the septal pole than in the temporal pole of the dentate gyrus. In contrast, rats that received kindling stimulation of the amygdala had a more uniform distribution of synaptic reorganization along the septotemporal axis. As there is regional variation of the anatomical and physiological properties of the human epileptic hippocampus, these observations could be pertinent to human epilepsy.     

Adult treatment with methamphetamine transiently decreases dentate granule cell proliferation in the gerbil hippocampus

Summary. The objective of the present study was to examine whether acute treatment with the recreational drug methamphetamine influences adult granule cell proliferation in the dentate gyrus of the hippocampus. For that purpose, at the age of postnatal day 90 adult male gerbils (Meriones unguiculatus) received a single dose of either methamphetamine (25 mg/kg; i.p.) or saline. Proliferation of granule cells was identified by in-vivo labeling with 5-bromo-2'-desoxyuridine (BrdU) which was applied either simultaneously with methamphetamine or 36 h after administration of the drug. BrdU-labeled granule cell nuclei were identified in consecutive horizontal slices along the mid-septotemporal axis of the hippocampus and light-microscopically quantified 7 days after the BrdU-labeling. It was found that in both saline- and methamphetamine-treated animals there was a highly significant spatial septotemporal gradient in granule cell proliferation with numbers of BrdU-labeled cells gradually declining from the septal towards the temporal pole. The acute treatment with methamphetamine suppressed granule cell proliferation by about 28% and the septotemporal gradient of mitotic activity became significantly attenuated. It was further found that 36 h after the drug challenge granule cell proliferation rates had been restored almost to the control values along the whole septotemporal axis of the hippocampus. The present results are discussed with regard to (1) pharmacological regulation of neurogenesis in the hippocampus and (2) probable clues they may provide for both understanding the biological correlates of psychotic disorders and evolution of future concepts in neuropharmacological intervention. Received January 8, 1999; accepted July 12, 1999     

Ipsilateral associational pathway in the dentate gyrus: An excitatory feedback system that supports N-methyl-D-aspartate—dependent long-term potentiation

Axons from granule cells in the dentate gyrus of the rat hippocampus project to cells in the hilar region, including mossy cells, which project along the longitudinal axis of the hippocampus and synapse in the inner (proximal) one-third of the molecular layer of the dentate gyrus. To study this feedback system, multiple recording electrodes were located along the longitudinal (septo-temporal) axis in the dorsal leaf of the dentate gyrus in urethane-anesthetized rats. Single pulse electrical stimuli delivered to the hilar region evoked negative-going, monosynaptic field potentials that were largest in the inner one-third of the molecular layer (commissural zone). These evoked field potentials (EFPs) were recorded simultaneously at three to five locations. The latency to onset and peak amplitude of the EFP varied linearly with distance from point of stimulation, and EFPs were elicited in both directions along the longitudinal axis. The transmission speed was estimated to be 1.4 m/s. Tetanic stimulation of the hilar region potentiated the EFP slopes (mean= 26%). Potentiation lasted at least 2 hours and was specific to responses from the tetanized stimulating electrode; the responses to other stimulating electrodes in the hilus and the angular bundle of the perforant path changed less than 4%. Combined stimulation of the hilus and the medial perforant path increased the magnitude of recorded field potentials and population spikes, demonstrating that both pathways are excitatory. NMDA antagonist NPC-17742 blocked potentiation of EFP slopes in both the medial perforant path and hilus pathways. The results suggest that the ipsilateral associational system of the dentate gyrus is excitatory and capable of supporting long-lasting, NMDA-dependent, synapse-specific plasticity. © 1994 Wiley-Liss, Inc.     

Functional dissociation of adult‐born neurons along the dorsoventral axis of the dentate gyrus

Adult‐born granule cells in the mammalian dentate gyrus have long been implicated in hippocampal dependent spatial learning and behavioral effects of chronic antidepressant treatment. Although recent anatomical and functional evidence indicates a dissociation of the dorsal and ventral regions of the hippocampus, it is not known if adult neurogenesis within each region specifically contributes to distinct functions or whether adult‐born cells along the entire dorsoventral axis are required for these behaviors. We examined the role of distinct subpopulations of adult‐born hippocampal granule cells in learning‐ and anxiety‐related behaviors using low‐dose focal x‐irradiation directed specifically to the dorsal or ventral dentate gyrus. Our findings indicate a functional dissociation between adult‐born neurons along the longitudinal axis of the dentate gyrus wherein new neurons in the dorsal dentate gyrus are required for timely acquisition of contextual discrimination while immature neurons in the ventral dentate gyrus are necessary for anxiolytic/antidepressant‐related effects of fluoxetine. Interestingly, when contexts are presented with altered temporal cues, or fluoxetine is administered alongside chronic glucocorticoid treatment, this dissociation is abrogated such that adult‐born neurons across the entire dorsoventral extent of the dentate gyrus appear to contribute to these behaviors. Our results suggest that individual subpopulations of adult‐born hippocampal neurons may be sufficient to mediate distinct behaviors in certain conditions, but are required to act in concert in more challenging situations. © 2014 Wiley Periodicals, Inc.     

Excitability changes within transverse lamellae of dentate granule cells and their longitudinal spread following orthodromic or antidromic activation

The functional organization of the perforant path input to the dentate gyrus of the exposed hippocampus was studied in adult rabbits anesthetized with urethane and chloralose. Electrical stimulation of perforant path fibers caused excitation of granule cells along narrow, nearly transverse strips (lamellae) of tissue. Stimulation of granule cell axons (mossy fibers) in CA3 caused antidromic activation of granule cells along similar strips. Paired‐pulse stimulation revealed marked changes in granule cell excitability both within a lamella (on‐line) and for several mm off‐line along the septo‐temporal axis of the dentate gyrus. After the first pulse, granule cells were inhibited for up to about 100 ms and then facilitated for up to hundreds of ms. Feedback activity along mossy fiber collaterals exciting local inhibitory and excitatory neurons appeared to dominate in producing on‐ and off‐line inhibition and facilitation. Neurons mediating these effects could be inhibitory basket cells and other inhibitory interneurons targeting granule cells on‐ and off‐line. In addition, excitatory mossy cells with far reaching, longitudinally running axons could affect off‐line granule cells by exciting them directly or inhibit them indirectly by exciting local inhibitory interneurons. A scheme for dentate gyrus function is proposed whereby information to the dentate gyrus becomes split into interacting transverse strips of neuronal assemblies along which temporal processing occurs. A matrix of neuronal assemblies thus arises within which fragments of events and experiences is stored through the plasticity of synapses within and between the assemblies. Similar fragments may then be recognized at later times allowing memories of the whole to be created by pattern completion at subsequent computational stages in the hippocampus. © 2008 Wiley‐Liss, Inc.     

Disambiguating the similar: the dentate gyrus and pattern separation

The human hippocampus supports the formation of episodic memory without confusing new memories with old ones. To accomplish this, the brain must disambiguate memories (i.e., accentuate the differences between experiences). There is convergent evidence linking pattern separation to the dentate gyrus. Damage to the dentate gyrus reduces an organism's ability to differentiate between similar objects. The dentate gyrus has tenfold more principle cells than its cortical input, allowing for a divergence in information flow. Dentate gyrus granule neurons also show a very different pattern of representing the environment than “classic” place cells in CA1 and CA3, or grid cells in the entorhinal cortex.More recently immediate early genes have been used to “timestamp” activity of individual cells throughout the dentate gyrus. These data indicate that the dentate gyrus robustly differentiates similar situations. The degree of differentiation is non-linear, with even small changes in input inducing a near maximal response in the dentate. Furthermore this differentiation occurs throughout the dentate gyrus longitudinal (dorsal-ventral) axis. Conversely, the data point to a divergence in information processing between the dentate gyrus suprapyramidal and infrapyramidal blades possibly related to differences in organization within these regions.The accumulated evidence from different approaches converges to support a role for the dentate gyrus in pattern separation. There are however inconsistencies that may require incorporation of neurogenesis and hippocampal microcircuits into the currents models. They also suggest different roles for the dentate gyrus suprapyramidal and infrapyramidal blades, and the responsiveness of CA3 to dentate input.     

The morphology of the hippocampus and dentate gyrus in normal and reeler mice.

The morphology of the hippocampus and dentate gyrus in normal and reeler mice has been studied in Nissl, myelin, Golgi, Timm's sulfide silver and gold chloride-sublimate preparations. It is evident from both cell-and fiber-stained sections that despite the obvious defect in the positioning of the hippocampal pyramidal and dentate granule cells in the reeler mouse within the radial dimension, the hippocampal formation as a whole shows a normal and consistent progression of cytoarchitectonic fields along its transverse axis, and a normal and consistent progression of changes in the structure of the hippocampus and dentate gyrus along their longitudinal axes. Thus, at least in these structures, the reeler gene seems to exert its effect only in the radial dimension. Cell counts in the area dentata indicate that the number of dentate granule cells in the reeler mouse is reduced compared to that found in normal or heterozygous animals. Although it has been known for some time that the number of granule cells in the reeler cerebellar cortex is markedly reduced, this appears to be the first evidence for a reduction in cell number in a forebrain structure. All the major cell types normally found in the hippocampus and the dentate gyrus are recognizable in Golgi-stained preparations from the brains of reeler mutants. However, in both regions there are a number of abnormalities in the appearance of the cells which seem to be related to the cellular ectopia. Thus, whereas most of the pyramidal and granule cells which attain a normal position in the mutant usually have normal, or near-normal dendritic arbors, the dendrites of nearly all ectopic cells are severely distorted, both in their orientation and general configuration. In preparations stained by the Timm's sulfide silver technique it is evident that the general lamination pattern seen in normal mice is retained in the reeler hippocampus and dentate gyrus despite the gross malpositioning of many of the relevant neurons. However, although the overall laminar arrangement is preserved, there are some fairly consistent abnormalities; for example, the normal trilaminar staining pattern seen in the stratum moleculare of the dentate gyrus is replaced in the reeler by a bilaminar pattern. In gold chloride-sublimate impregnated preparations there is no obvious alignment of the astrocytes in the stratum moleculare of the dentate gyrus in either normal or reeler mice. Moreover, the distribution of the astrocytes within this zone is fairly normal in the reeler mouse, although, in general, these cells appear to be more consistently stellate in form than in normal animals.     

Somatostatin-immunoreactivity in the hippocampus of mouse,rat, guinea pig,and rabbit

The hippocampi of species commonly used for in vitro physiologic studies were examined to determine if there were species-specific and regional differences in somatostatin immunoreactivity. The distributions of somatostatin-immunoreactive somata and fiber plexuses were determined, and the concentration of somatostatin along the septotemporal axis of the hippocampus was measured using a radioimmunoassay. There are many similarities in the patterns of somatostatin immunoreactivity in the hippocampi of mice, rats, guinea pigs, and rabbits. All species had a relatively even distribution of somatostatin-positive perikarya across three fields of the hippocampus (dentate gyrus, CA3, and CA1-2), a similar distribution of somatostatin-immunoreactive perikarya across the strata of the CA1-2 field and the dentate gyrus; and more somatostatin-positive cells in temporal than in septal hippocampus. However, there are species-specific differences in the distribution of somatostatin-immunoreactive perikarya across the strata of CA3. In addition, unlike the other species examined, mice appeared not to have a somatostatin-immunoreactive fiber plexus in the molecular layer of the dentate gyrus. The functional significance of these differences remains to be determined. © 1994 Wiley-Liss, Inc.     

Neuron loss,granule cell axon reorganization,and functional changes in the dentate gyrus of epileptic kainate-treated rats

We sought to describe quantitatively the morphological and functional changes that occur in the dentate gyrus of kainate-treated rats, an experimental model of temporal lobe epilepsy. Adult rats were treated systemically with kainic acid, and, months later, after displaying spontaneous recurrent motor seizures, their dentate gyri were examined. Histological, immunocytochemical, and quantitative stereological techniques were used to estimate numbers of neurons per dentate gyrus of various classes and to estimate the extent of granule cell axon reorganization along the septotemporal axis of the hippocampus in control rats and epileptic kainate-treated rats. Compared with control rats, epileptic kainate-treated rats had fewer Nissl-stained hilar neurons and fewer somatostatin-immunoreactive neurons. There was a correlation between the extent of hilar neuron loss and the extent of somatostatin-immunoreactive neuron loss. However, functional inhibition in the dentate gyrus, assessed with paired-pulse responses to perforant-pathway stimulation, revealed enhanced, and not the expected reduced, inhibition in epileptic kainate-treated rats. Numbers of parvalbumin- and cholecystokinin-immunoreactive neurons were similar in control rats and in most kainate-treated rats. A minority (36%) of the epileptic kainate-treated rats had fewer parvalbumin- and cholecystokinin-immunoreactive neurons than control rats, and those few (8%) with extreme loss in these interneuron classes showed markedly hyperexcitable dentate gyrus field-potential responses to orthodromic stimulation. Compared with control rats, epileptic kainate-treated rats had larger proportions of their granule cell and molecular layers infiltrated with Timm stain. There was a correlation between the extent of abnormal Timm staining and the extent of hilar neuron loss. Granule cell axon reorganization and dentate gyrus neuron loss were more severe in temporal vs. septal hippocampus. These findings from the dentate gyrus of epileptic kainate-treated rats are strikingly similar to those reported for human temporal lobe epilepsy, and they suggest that neuron loss and axon reorganization in the temporal hippocampus may be important in epileptogenesis. J. Comp. Neurol. 385:385–404, 1997. © 1997 Wiley-Liss, Inc.     

The effects of brain-irradiation-induced decreases in hippocampal mitotic activity on flurothyl-induced epileptogenesis in adult C57BL/6J mice

Previous studies have demonstrated that seizures are potent inducers of mitotic activity in the rodent hippocampus. The role of this mitotic activity in epileptogenesis currently remains unknown. In the present study, we investigated the effect of alterations in hippocampal mitotic activity on changes in seizure threshold and phenotype using flurothyl kindling. In flurothyl kindling, eight repeated flurothyl-induced generalized forebrain (clonic) seizures result in a rapid, progressive, and permanent lowering of the generalized seizure threshold in mice and in a slowly evolving increase in the percentage of animals expressing forebrain-brain stem (clonic-tonic) seizures when reexposed to flurothyl following a 2- to 4-week stimulation-free period. Therefore, flurothyl kindling serves as an excellent model for evaluating mechanisms of generalized seizure threshold and seizure propagation. To investigate this relationship between hippocampal mitotic activity and epileptogenesis, mice were given brain irradiation, focused mainly on the hippocampus, bilaterally, and were exposed to the flurothyl kindling model of epileptogenesis. Brain irradiation virtually eliminated all basal and seizure-induced mitotic activity in the hippocampal dentate gyrus of mice. In addition, animals that underwent irradiation and flurothyl kindling did not differ from control mice on measures of seizure threshold (threshold induction and maintenance) and seizure phenotype. Overall, these results suggest that seizure-induced increases in mitotic activity in the hippocampal dentate gyrus are not directly related to the processes that underlie the shift in behavioral seizure phenotype or in either the induction or the maintenance of lowered seizure threshold that is observed in this flurothyl model of epileptogenesis.     

Neurons co-localizing calretinin immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in the hippocampus and dentate gyrus of the rat

Co-localization of calretinin immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity was studied in the rat hippocampus and dentate gyrus. Neurons co-expressing both markers (CR/NADPH-d) were observed throughout the hippocampus and dentate gyrus. However, they were more abundant in the stratum pyramidale and radiatum of CA3, stratum pyramidale of CA1, and in the juxtagranular zone of the hilus. The NADPH-d activity appeared in 37% of the calretinin immunoreactive neurons in CA3, 42% in CA1, and 36% in the dentate gyrus, whereas calretinin immunoreactivity occurred in 41% of the NADPH-d positive neurons in the hippocampus, and 16% in the dentate gyrus. The morphology and location of the double marked cells could not be used as a characteristic of the co-localizing neurons. The heavily stained NADPH-d neurons occurring mainly in CA1 do not show calretinin immunoreactivity. NADPH-d fiber swellings could be observed in close apposition to calretinin immunoreactive neurons and dendrites, suggesting synaptic contacts. It has been reported that calretinin immunoreactivity and NADPH-d activity co-localize infrequently in other areas such as the neocortex, striatum, hypothalamus and tegmental nucleus. The relatively high proportion of double marked cells found in the hippocampus and dentate gyrus could be indicative of the importance of the CR/NADPH-d interneurons in the circuitries of these areas.     

Organization of radial glial cells during the development of the rat dentate gyrus

The temporal and spatial patterns of development of radial glial processes in the rat dentate gyrus have been studied in immunohistochemical preparations stained for the presence of either the glial fibrillary acidic protein (GFAP) or the vimentin-associated antigen R4. Additional electron microscopic (EM) observations were made from material prepared either immunohistochemically or by the Golgi method. R4 immunoreactive radial fibers were observed in the incipient dentate gyrus as early as E13 and by E14 the density of stained fibers was clearly higher in the anlage of the dentate gyrus than in the adjacent hippocampus. By E15 it was possible to identify in the EM the endfeet of radial glial cells that contained numerous glycogen particles. GFAP-positive radial processes were first observed on E17; these processes tended to be of larger diameter than those stained with the R4 antibody, suggesting that they were among the more mature processes. The orientation of both the R4- and GFAP-positive glial processes changed throughout the last week of embryonic life and by the end of the first postnatal week they formed a complex meshwork of intertwined processes. The distribution of their cell bodies also changed with time; initially their perikarya were located in the neuroepithelium at the lateral margin of the hippocampal primordium; later they were found mainly beneath the granule cell layer. Dividing cells that contained GFAP were observed along the trajectory of the migrating granule cell precursors and in the hilus of the dentate gyrus; at later stages some GFAP-positive mitotic figures were seen within and immediately below the granule cell layer. On the basis of these observations, we have attempted to reconstruct the role that radial glial processes play in the morphogenesis of the dentate gyrus. First, radial processes extend from the neuroepithelium to the pial surface prior to the migration of neurons that will form the dentate gyrus. These early generated glia appear to form the boundaries of the developing dentate gyrus and provide an internal lattice that may guide the initial wave of migrating progenitor cells. As the dentate gyrus enlarges, these early formed processes maintain their contacts along the hippocampal fissure and along the pial surface of the dentate anlage. Thus, with time they become increasingly distorted and are ultimately compressed into two bundles; one lies deep to the hippocampal fissure parallel to the granule cell layer and the other is located at the fimbriodentate juncture.(ABSTRACT TRUNCATED AT 400 WORDS)     

Mossy Cells of the Rat Dentate Gyrus are lmmunoreactive for Calcitonin Gene-related Peptide (CGRP)

The neuropeptide calcitonin gene-related peptide (CGRP) was localized in the hippocampus and dentate gyrus of the rat by immunocytochemistry at the light and electron microscopic levels. Without colchicine treatment only faint neuropil labelling was found in the inner molecular layer of the dentate gyrus. Following colchicine treatment, a large number of neurons with numerous complex spines along the proximal dendrites were visualized in the hilus of the dentate gyrus, particularly in the ventral areas, and, in addition, staining of the inner molecular layer became stronger. Several CA3c pyramidal cells located adjacent to the hilar region in the ventral hippocampus also appeared to be faintly positive, although in most cases only their axon initial segments were labelled. Outside this region, the subicular end of the CA1 subfield contained occasional CGRP-positive non-pyramidal cells. The hilar CGRP-positive neurons were negative for parvalbumin, calretinin, cholecystokinin and somatostatin, whereas most of them were immunoreactive for GluR2/3 (the AMPA-type glutamate receptor known to be expressed largely by principal cells). Correlated electron microscopy showed that the spines along the proximal dendritic shafts indeed correspond to thorny excrescences engulfed by large complex mossy terminals forming asymmetrical synapses. Pre-embedding immunogold staining demonstrated that CGRP immunoreactivity in the inner molecular layer was confined to axon terminals that form asymmetrical synapses, and the labelling was associated with large dense-core vesicles. The present data provide direct evidence that CGRP is present in mossy cells of the dentate gyrus and to a lesser degree in CA3c pyramidal cells of the ventral hippocampus. These CGRP-containing principal cells terminate largely in the inner molecular layer of the dentate gyrus, and may release the neuropeptide in conjunction with their 'classical' neurotransmitter, glutamate.     

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.     

Origin of microglia in the quail retina: Central-to-peripheral and vitreal-to-scleral migration of microglial precursors during development

Collateral sprouting of dentate granule cell axons, the mossy fibers, occurs in response to denervation, kindling, or excitotoxic damage to the hippocampus. Organotypic slice culture of rodent hippocampal tissue is a model system for the controlled study of collateral sprouting in vitro. Organotypic roller-tube cultures were prepared from hippocampal slices derived from postnatal day 7 mice. The Timm heavy metal stain and densitometry were used to assay the degree of mossy fiber collateral sprouting in the molecular layer of the hippocampal dentate gyrus. Factors influencing mossy fiber collateral sprouting were time in culture, positional origin of the slice culture along the septotemporal axis of the hippocampus, and presence of attached subicular-entorhinal cortical tissues. Collateral sprouting in the molecular layer was first detected after 6 days in culture and increased steadily thereafter. By 2 weeks considerable sprouting was apparent, and at 3 weeks intense sprouting was observed within the molecular layer. An intrinsic septal-to-temporal gradient of collateral sprouting was apparent at 14 days in culture. To determine whether differential damage to the mossy fibers was the basis for the differences in collateral sprouting along the septotemporal axis, we made complete transections of the mossy fiber projection as it exited the dentate hilus at various levels along the septotemporal axis; no differences were found on subsequent collateral sprouting in the dentate molecular layer. Timm-stained hippocampal cultures with an attached entorhinal cortex, a major source of afferent innervation to the dentate granule cells, displayed significantly less collateral sprouting at 10 days in culture compared to that in cultures from adjacent sections without attached subicular-entorhinal tissues present. Thus, time in culture, position along the septotemporal axis, and presence of afferent cortical tissues influence aberrant neurite collateral sprouting in organotypic slice cultures of neonatal mouse hippocampus. © Wiley-Liss, Inc.     

NDRG2通过Hes1参与癫痫发作后海马齿状回的神经发生

目的 探讨N-Myc下游调节基因2(N-Myc downstream regulated gene 2,NDRG2)与癫痫发作后海马齿状回神经发生的关系。方法 C57BL/6小鼠20只,随机分为癫痫组和对照组,每组又分为癫痫造模后1和7 d两个时间点,每个时间点5只,通过蛋白免疫印迹检测癫痫后海马齿状回NDRG2蛋白相对表达水平和mRNA相对表达水平变化; 使用双皮质素(DCX)染色标记未成熟神经元,神经巢蛋白(Nestin)标记神经干细胞,神经核蛋白(NeuN)标记成熟神经元,观察NDRG2对海马齿状回神经干细胞增殖影响; 采用RT-PCR检测发状分裂相关增强子1(hairy and enhancer of split 1,Hes 1)、NDRG2 mRNA相对表达表达水平,并分析两者之间的相关性; 观察NDRG2参与癫痫发作后神经发生的可能机制。结果 癫痫组与对照组比较,DCX、Nestin、NeuN、Hes1、NDRG2蛋白相对表达水平在1和7 d这2个时间点有显著性增高,并随时间逐渐递增。结论 癫痫发作后海马NDRG2蛋白相对表达水平增高,与癫痫发作后海马齿状回的神经细胞增值时间具有一致性和相关性,NDRG2可能参与癫痫发作后海马齿状回的神经发生过程; 同时发现海马NDRG2表达增加和Hes1分子表达增加具有相关性,故推测NDRG2可能通过Hes1参与癫痫发作后海马齿状回的神经发生。     

NADPH-Diaphorase in the central nervous system of the larval lamprey (Lampetra planeri)

The anatomy of the hippocampus, including the organization of its intrinsic neural circuits and afferents, is organized along a rostrocaudal axis. Dopamine D2 receptors are expressed in specific regions of the hippocampal complex (hippocampal subfields, entorhinal cortex, perirhinal cortex) and show differential expression along this axis. The dentate gyrus and CA3/CA4 subfields show higher numbers of D2 receptors in the rostral than in the caudal levels. In contrast, the subiculum shows the reverse gradient. We report here that Alzheimer's disease (AD) is associated with reduced expression of the dopamine D2 receptor, but the effects differ with respect to the rostrocaudal axis and area within the hippocampal complex. The number of D2 receptors is significantly reduced in the molecular layer of the dentate gyrus, CA3 subfield, and subiculum. For the dentate gyrus and subiculum, there were greater losses at more rostral levels. The CA3/CA4 subfields showed the greatest losses caudally. The entorhinal cortex, which shows only modest expression of D2 receptors in controls, does not exhibit reduced numbers in AD. The external laminae of the rostral perirhinal cortex showed more significant losses than more caudally in this cortical field. The regions showing loss of D2 receptors do not typically contain neuritic plaques, neurofibrillary tangles, or significant neuron loss. Thus other mechanisms must account for the unique gradient of D2 receptor loss in the hippocampus. The regions of reduced expression of dopamine D2 receptors do correlate well with the terminal zone of the dentate association pathway, the afferents from the anlygdala and perirhinal cortex, and the sources of those afferents within the amygdala and perirhinal cortex. The specific patterns of reduced D2 receptor expression in AD are likely to contribute significantly to the disrupted information flow into and out of the hippocampus and, thus, of functions subserved by this system. © 1994 Wiley-Liss, Inc.     

New insights into the role of hilar ectopic granule cells in the dentate gyrus based on quantitative anatomic analysis and three-dimensional reconstruction

The dentate gyrus is one of two main areas of the mammalian brain where neurons are born throughout adulthood, a phenomenon called postnatal neurogenesis. Most of the neurons that are generated are granule cells (GCs), the major principal cell type in the dentate gyrus. Some adult-born granule cells develop in ectopic locations, such as the dentate hilus. The generation of hilar ectopic granule cells (HEGCs) is greatly increased in several animal models of epilepsy and has also been demonstrated in surgical specimens from patients with intractable temporal lobe epilepsy (TLE). Herein we review the results of our quantitative neuroanatomic analysis of HEGCs that were filled with Neurobiotin following electrophysiologic characterization in hippocampal slices. The data suggest that two types of HEGCs exist, based on a proximal or distal location of the cell body relative to the granule cell layer, and based on the location of most of the dendrites, in the molecular layer or hilus. Three-dimensional reconstruction revealed that the dendrites of distal HEGCs can extend along the transverse and longitudinal axis of the hippocampus. Analysis of axons demonstrated that HEGCs have projections that contribute to the normal mossy fiber innervation of CA3 as well as the abnormal sprouted fibers in the inner molecular layer of epileptic rodents (mossy fiber sprouting). These data support the idea that HEGCs could function as a "hub" cell in the dentate gyrus and play a critical role in network excitability.     

慢性强迫游泳应激对大鼠海马神经元再生和p-CREB表达的影响

目的 研究慢性强迫游泳应激模型大鼠海马神经元再生和磷酸化环磷酸腺苷反应元件结合蛋白（p-CREB）的表达.方法 30只雄性SD大鼠随机分为3组：强迫游泳7 d组（S1组）、强迫游泳14 d组（S2组）和对照组.S1组和S2组分别连续强迫游泳7 d和14 d,每天5 min,水温（10±0.5）℃.采用免疫组化半定量测定大鼠海马5-溴脱氧尿苷（BrdU）和p-CREB阳性细胞表达情况.结果 免疫组化结果 显示,在整个海马结构中BrdU及p-CREB的阳性细胞主要集中于齿状回的颗粒细胞下层.与对照组比较,S1组、S2组大鼠海马齿状回BrdU和p-CREB阳性细胞数均明显减少（P＜0.01）;而与S1组比较,BrdU阳性细胞数无统计学差异（P＞0.05）,S2组p-CREB阳性细胞数进一步减少（P＜0.01）.结论 慢性强迫游泳应激可导致海马神经元再生功能障碍,其机制可能与p-CREB信号转导通路有关. 基金项目：