Brain region-specific disruption of mitochondrial bioenergetics in cynomolgus macaques fed a Western versus a Mediterranean diet.

Mitochondrial dysfunction is evident in diseases affecting cognition and metabolism such as Alzheimer's disease and type 2 diabetes. Human studies of brain mitochondrial function are limited to postmortem tissue, preventing the assessment of bioenergetics by respirometry. Here, we investigated the effect of two diets on mitochondrial bioenergetics in three brain regions: the prefrontal cortex (PFC), the entorhinal cortex (ERC), and the cerebellum (CB), using middle-aged nonhuman primates. Eighteen female cynomolgus macaques aged 12.3 ± 0.7 yr were fed either a Mediterranean diet that is associated with healthy outcomes or a Western diet that is associated with poor cognitive and metabolic outcomes. Average bioenergetic capacity within each brain region did not differ between diets. Distinct brain regions have different metabolic requirements related to their function and disease susceptibility. Therefore, we also examined differences in bioenergetic capacity between brain regions. Mitochondria isolated from animals fed a Mediterranean diet maintained distinct differences in mitochondrial bioenergetics between brain regions, whereas animals fed the Western diet had diminished distinction in bioenergetics between brain regions. Notably, fatty acid ß-oxidation was not affected between regions in animals fed a Western diet. In addition, bioenergetics in animals fed a Western diet had positive associations with fasting blood glucose and insulin levels in PFC and ERC mitochondria but not in CB mitochondria. Altogether, these data indicate that a Western diet disrupts bioenergetic patterns across brain regions and that circulating blood glucose and insulin levels in Western-diet fed animals influence bioenergetics in brain regions susceptible to Alzheimer's disease and type 2 diabetes.NEW & NOTEWORTHY We show that compared with cynomolgus macaques fed a Mediterranean diet, a Western diet resulted in diminished bioenergetic pattern between brain regions related to blood glucose and insulin levels, specifically in brain regions susceptible to neurodegeneration and diabetes. In addition, fatty acid metabolism not directly linked to the TCA cycle and glucose metabolism did not show differences in bioenergetics due to diet.

Spatial Embryonic Origin Delineates GABAergic Hub Neurons Driving Network Dynamics in the Developing Entorhinal Cortex.

Coordinated neuronal activity is essential for the development of cortical circuits. GABAergic hub neurons that function in orchestrating early neuronal activity through a widespread net of postsynaptic partners are therefore critical players in the establishment of functional networks. Evidence for hub neurons was previously found in the hippocampus, but their presence in other cortical regions remains unknown. We examined this issue in the entorhinal cortex, an initiation site for coordinated activity in the neocortex and for the activity-dependent maturation of the entire entorhinal-hippocampal network. Using an unbiased approach that identifies "driver hub neurons" displaying a high number of functional links in living slices, we show that while almost half of the GABAergic cells single-handedly influence network dynamics, only a subpopulation of cells born in the MGE and composed of somatostatin-expressing neurons located in infragranular layers, spontaneously operate as "driver" hubs. This indicates that despite differences in the origin of interneuron diversity, the hippocampus and entorhinal cortex share similar developmental mechanisms for the establishment of functional circuits.

Cytoarchitectural, behavioural and neurophysiological dysfunctions in the BCNU-treated rat model of cortical dysplasia.

Cortical dysplasias (CDs) include a spectrum of cerebral lesions resulting from cortical development abnormalities during embryogenesis that lead to cognitive disabilities and epilepsy. The experimental model of CD obtained by means of in utero administration of BCNU (1-3-bis-chloroethyl-nitrosurea) to pregnant rats on embryonic day 15 mimics the histopathological abnormalities observed in many patients. The aim of this study was to investigate the behavioural, electrophysiological and anatomical profile of BCNU-treated rats in order to determine whether cortical and hippocampal lesions can directly lead to cognitive dysfunction. The BCNU-treated rats showed impaired short-term working memory but intact long-term aversive memory, whereas their spontaneous motor activity and anxiety-like response were normal. The histopathological and immunohistochemical analyses, made after behavioural tests, revealed the disrupted integrity of neuronal populations and connecting fibres in hippocampus and prefrontal and entorhinal cortices, which are involved in memory processes. An electrophysiological evaluation of the CA1 region of in vitro hippocampal slices indicated a decrease in the efficiency of excitatory synaptic transmission and impaired paired pulse facilitation, but enhanced long-term potentiation (LTP) associated with hyperexcitability in BCNU-treated rats compared with controls. The enhanced LTP, associated with hyperexcitability, may indicate a pathological distortion of long-term plasticity. These findings suggest that prenatal developmental insults at the time of peak cortical neurogenesis can induce anatomical abnormalities associated with severe impairment of spatial working memory in adult BCNU-treated rats and may help to clarify the pathophysiological mechanisms of cognitive dysfunction that is often associated with epilepsy in patients with CD.

A population of prenatally generated cells in the rat paleocortex maintains an immature neuronal phenotype into adulthood.

New neurons in the adult brain transiently express molecules related to neuronal development, such as the polysialylated form of neural cell adhesion molecule, or doublecortin (DCX). These molecules are also expressed by a cell population in the rat paleocortex layer II, whose origin, phenotype, and function are not clearly understood. We have classified most of these cells as a new cell type termed tangled cell. Some cells with the morphology of semilunar-pyramidal transitional neurons were also found among this population, as well as some scarce cells resembling semilunar, pyramidal. and fusiform neurons. We have found that none of these cells in layer II express markers of glial cells, mature, inhibitory, or principal neurons. They appear to be in a prolonged immature state, confirmed by the coexpression of DCX, TOAD/Ulip/CRMP-4, A3 subunit of the cyclic nucleotide-gated channel, or phosphorylated cyclic adenosine monophosphate response element-binding protein. Moreover, most of them lack synaptic contacts, are covered by astroglial lamellae, and fail to express cellular activity markers, such as c-Fos or Arc, and N-methyl-d-aspartate or glucocorticoid receptors. We have found that none of these cells appear to be generated during adulthood or early youth and that most of them have been generated during embryonic development, mainly in E15.5.

The tracing study of developing entorhino-hippocampal pathway.

The entorhino-hippocampal pathway is the major excitatory input from neurons of the entorhinal cortex on both ipsilateral and contralateral hippocampus/dentate gyrus. This fiber tract consists of the alvear path, the perforant path and a crossed commissural projection. In this study, the histogenesis and development of the various subsets of the entorhino-hippocampal projection have been investigated. DiI, DiO, Fast Blue tracing and calretinin immunocytochemistry as well as were carried out with pre and postnatal rats at different developmental stages. The alvear path and the commissural pathway start to develop as early as embryonic day E16, while the first perforant afferents reach the stratum lacunosum-moleculare of the hippocampus at E17 and at outer molecular layer of the denate gyrus at postnatal day 2. Retrograde tracing with DiI identifies entorhinal neurons in layer II-IV as the developmental origin of the entorhino-hippocampal pathway. Furthermore, calretinin immunocytochemistry revealed transitory Cajal-Retzius cells in the stratum lacunosum-moleculare of the hippocampus from E16. DiI labeling of entorhinal cortex fibers and combined calretinin-immunocytochemistry reveal a close relationship between Cajal-Retzius cells and entorhinal afferents. This temporal and spatial relationship suggests that Cajal-Retzius cell serves as a guiding cue for entorhinal afferents at early cortical development.

Structural development and dorsoventral maturation of the medial entorhinal cortex.

We investigated the structural development of superficial-layers of medial entorhinal cortex and parasubiculum in rats. The grid-layout and cholinergic-innervation of calbindin-positive pyramidal-cells in layer-2 emerged around birth while reelin-positive stellate-cells were scattered throughout development. Layer-3 and parasubiculum neurons had a transient calbindin-expression, which declined with age. Early postnatally, layer-2 pyramidal but not stellate-cells co-localized with doublecortin - a marker of immature neurons - suggesting delayed functional-maturation of pyramidal-cells. Three observations indicated a dorsal-to-ventral maturation of entorhinal cortex and parasubiculum: (i) calbindin-expression in layer-3 neurons decreased progressively from dorsal-to-ventral, (ii) doublecortin in layer-2 calbindin-positive-patches disappeared dorsally before ventrally, and (iii) wolframin-expression emerged earlier in dorsal than ventral parasubiculum. The early appearance of calbindin-pyramidal-grid-organization in layer-2 suggests that this pattern is instructed by genetic information rather than experience. Superficial-layer-microcircuits mature earlier in dorsal entorhinal cortex, where small spatial-scales are represented. Maturation of ventral-entorhinal-microcircuits - representing larger spatial-scales - follows later around the onset of exploratory behavior.

The repulsive guidance molecule RGMa is involved in the formation of afferent connections in the dentate gyrus.

In the developing dentate gyrus, afferent fiber projections terminate in distinct laminas. This relies on an accurately regulated spatiotemporal network of guidance molecules. Here, we have analyzed the functional role of the glycosylphosphatidylinositol (GPI)-anchored repulsive guidance molecule RGMa. In situ hybridization in embryonic and postnatal brain showed expression of RGMa in the cornu ammonis and hilus of the hippocampus. In the dentate gyrus, RGM immunostaining was confined to the inner molecular layer, whereas the outer molecular layers targeted by entorhinal fibers remained free. To test the repulsive capacity of RGMa, different setups were used: the stripe and explant outgrowth assays with recombinant RGMa, and entorhino-hippocampal cocultures incubated either with a neutralizing RGMa antibody (Ab) or with the GPI anchor-digesting drug phosphatidylinositol-specific phospholipase C. Entorhinal axons were clearly repelled by RGMa in the stripe and outgrowth assays. After disrupting the RGMa function, the specific laminar termination pattern in entorhino-hippocampal cocultures was lost, and entorhinal axons entered inappropriate hippocampal areas. Our data indicate an important role of RGMa for the layer-specific termination of the perforant pathway as a repulsive signal that compels entorhinal fibers to stay in their correct target zone.

Entorhinal cortex pre-alpha cell clusters in schizophrenia: quantitative evidence of a developmental abnormality.

BACKGROUND: Previous studies using semiquantitative or qualitative techniques demonstrated abnormalities of positioning of clusters of neurons (pre-alpha cells) in the entorhinal cortex in schizophrenia, suggesting a developmental mechanism could contribute to the illness. Recent quantitative studies of laminar thickness and laminar cell counts have been less consistent, and several failed to replicate the finding. However, none of the quantitative studies focused on the position of the pre-alpha cell clusters. METHODS: To study pre-alpha cell position in detail, we examined the entorhinal cortex in serial sections from 21 control and 19 schizophrenic brains. Cluster position relative to the gray-white matter junction and cluster size were measured. RESULTS: Quantitative assessment of 1991 clusters indicated clusters were positioned relatively closer to the gray-white matter junction in the anterior half of schizophrenic entorhinal cortices. In addition, the size of clusters in males with schizophrenia was reduced. CONCLUSIONS: These results support the model of schizophrenia as an illness in which brain development is impaired. The findings in males with schizophrenia may indicate the presence of more severe pathology, or an additional pathogenic mechanism.

Rapid expression and transport of embryonic N-CAM in dentate gyrus following entorhinal cortex lesion: ultrastructural analysis.

Neural cell adhesion molecules are known to be important in axon guidance and synapse formation in the developing brain. The embryonic form of neural cell adhesion molecule (eN-CAM) is reexpressed in the outer molecular layer (OML) of the dentate gyrus following entorhinal cortex (ERC) lesion. Ultrastructural analysis revealed localization of eN-CAM to the membrane of granule-cell dendritic membranes and occasionally axons within the denervated zone. Because eN-CAM is expressed rapidly (within 2 days) after ERC lesion, we were interested in the temporal sequence of expression. Denervated hippocampi (12, 15, 24, and 48 hours post-ERC lesion) were stained with anti-eN-CAM and processed for immunoelectron microscopy. At 12 hours, there was no evidence of staining for eN-CAM. By 15 hours after lesion, membranes of both dendrites and axons throughout the molecular layer exhibited moderate eN-CAM staining, and dendritic cytoplasm was heavily labeled. Twenty-four hours following lesion, plasma membrane staining of eN-CAM on both axons and dendrites had increased in intensity within the OML, whereas membrane eN-CAM staining was diminished in the inner molecular layer (IML), and the intradendritic cytoplasmic staining disappeared. By 48 hours after lesion, eN-CAM staining had disappeared from the IML but remained intense and widely distributed in the OML. These findings suggest a rapid transport of de novo synthesized protein. A generalized reaction appears to occur immediately following denervation, and eN-CAM is up-regulated in the complete expanse of the dendritic membrane, despite the fact that only the OML is denervated.(ABSTRACT TRUNCATED AT 250 WORDS)

Precocious development of parvalbumin-like immunoreactive interneurons in the hippocampal formation and entorhinal cortex of the fetal cynomolgus monkey.

The calcium-binding protein parvalbumin (PV), a reliable marker of the hippocampal basket and chandelier cells, is first expressed on embryonic day 83 (E83), corresponding to midgestation of the macaque monkey, in restricted hippocampal groups of immature neurons (Berger and Alvarez [1996] J. Comp. Neurol. 366:674-699). In the present study, PV-like immunoreactivity (LIR) was used to follow the further development of this subclass of interneurons. Asynchronous area-specific developmental sequences were observed, predominating initially in the caudal half of the hippocampal formation and the laterocaudal division of the entorhinal cortex and occurring relatively simultaneously in the interconnected hippocampal and entorhinal subfields. Dendritic elongation of PV-like immunoreactive interneurons and perisomatic distribution of PV-like immunoreactive terminal boutons on their cellular targets were first observed in the subiculum around E127; then from E127 to E142 in CA3/CA2 and layers III-V of the entorhinal cortex and, to a lesser extent in CA1, the dentate hilus and deep granule cell layer; and finally from E156 to postnatal day 12 in the rest of the dentate gyrus, the presubiculum and parasubiculum, and layers III-II-I of the entorhinal cortex. These data provide the first indication that a population of basket cells, a major gamma-aminobutyric acid (GABA)ergic component of the hippocampal intrinsic inhibitory circuitry, reaches its cellular targets several weeks before birth in primates in contrast to rodents. The role of the prenatal PV expression in the hippocampal formation of nonhuman primates and whether it coincides with the onset of postsynaptic inhibitory potentials or is accompanied or preceded by a period of gamma-aminobutyric acid-mediated excitatory effects as in rat pups, are crucial questions. They underline the need to pursue direct investigations on primates to be able to legitimately extrapolate the data obtained in rodents.

Ontogeny of the dopamine D2 receptor mRNA expressing cells in the human hippocampal formation and temporal neocortex.

The study details the cellular expression of the dopamine D2 receptor mRNA in the human temporal lobe during prenatal development. At 13 embryonic weeks (E13) D2 mRNA was widely expressed in the temporal lobe. At this time point in the dentate gyrus D2 mRNA positive cells first appeared at the outer border of the granular layer and their number increased with development. The CA1 exhibited the highest level of D2 mRNA expression. By E19-25 the hippocampal formation underwent rapid morphological maturation. D2 mRNA expression became more uniform and dense in the ammonic subfield. At all ages the subiculum appeared more mature morphologically but less intensely stained for D2 mRNA than the ammonic fields. In the entorhinal cortex D2 mRNA expression was most conspicuous in the future layer II at all ages. In the temporal neocortex D2 mRNA-positive cells were detected in the subplate and cortical plate. Differentiation of the cortical plate was accompanied by concentration of D2 mRNA-positive cells in layer V. The most conspicuous cells expressing D2 mRNA were found in the marginal zone of all regions and resembled Cajal-Retzius cells in morphology and location. Density of putative Cajal-Retzius cells expressing D2 mRNA decreased with development. They all but disappeared from the hippocampal areas by mid gestation, but in the temporal neocortex occasional cells were seen even at term. Early and widespread but region and cell type specific expression of D2 receptor mRNA suggests an important role of this DA receptor subtype in prenatal development of the human temporal lobe.

Endogenous synaptogenesis in the deafferented dentate gyrus does not exclude synapse formation by embryonic entorhinal transplants.

After partial deafferentation postsynaptic sites are reinnervated by local sprouting of remaining axons. We have investigated whether this process is sufficient to prevent new synapses being formed by transplanted embryonic tissue. We find that after unilateral entorhinal ablation endogenous sprouting by local axons is unable to reinnervate all the postsynaptic sites in the denervated outer dentate molecular layer. Axons from embryonic entorhinal tissue transplanted adjacent to the denervated area are able to reclaim a further proportion of the denervated postsynaptic sites. Thus, after a large lesion, endogenous sprouting is insufficient to preclude reinnervation by axons from embryonic transplants.

Transplanted embryonic entorhinal neurons make functional synapses in adult host hippocampus.

Grafts of embryonic entorhinal cortex (EC) or non-entorhinal cortex (NEC) were placed into the hippocampus of adult rats with transection of the perforant paths. Graft-host connectivity was investigated at 4-6 months post-transplantation by recording extracellular evoked responses in hippocampal slice preparations. Electrical stimulation of the grafts evoked excitatory postsynaptic potentials (EPSPs) in the outer molecular layer of the dentate gyrus, and the stratum lacunosum moleculare of CA1, CA3, and elicited population spikes in the granule cell layer and the pyramidal cell layer of CA1, but not CA3. While the latencies and the forms of these evoked response were similar to those in matched control slices from the normal animals, the amplitudes were smaller than normal controls. However, in the slices with NEC grafts, no such responses were recorded when stimulus was applied in similar position in the grafts. The findings suggest that grafted entorhinal neurons make viable synaptic connections with the host hippocampus.

The ganglionic eminence--a putative intermediate target of amygdaloid connections.

The superior part of the ganglionic eminence has been shown to act as an intermediate target for outgrowing axons of projections between the thalamus and the cerebral cortex. This study aims at investigating whether amygdaloid projections transiently contact the inferior portion of the human ganglionic eminence which directly borders upon the amygdala. Between 16 and 20 weeks of gestation a high number of small fiber bundles which were immunolabelled with anti-MAP1b and anti-SNAP-25 could be traced from the amygdala towards the mantle zone of the ganglionic eminence. These fiber bundles left a fiber system which coursed from the amygdala towards the entorhinal cortex. Within the mantle zone of the ganglionic eminence immunoreactive puncta indicative of fiber termination were observed. After 22 weeks of gestation the number of fibers entering the ganglionic eminence gradually decreased. These results provide the first evidence that the marginal zone of the inferior ganglionic eminence is likely to constitute an intermediate target for growing axons which belong the amygdaloid projection to the entorhinal cortex.

Reelin and mDab1 regulate the development of hippocampal connections.

We analyze in this study the participation of Reelin and mDab1 in the development of hippocampal connections. We show that mDab1 is present in growth cones and axonal tracts of developing hippocampal afferents. mdab1-deficiency produces severe alterations in the entorhino-hippocampal and commissural connections identical to those described in reeler mice, including innervation of ectopic areas, formation of abnormal patches of fiber termination and a delay in the refinement of projections. Organotypic slice cultures combining tissue from mdab1-mutant and control mice demonstrate that the abnormalities observed in the mutant entorhino-hippocampal projection are caused by mdab1-deficiency in both the projecting neurons and target hippocampal cells. Axonal afferents that innervate the hippocampus react to Reelin by reducing axonal growth, and increasing growth cone collapse and axonal branching. Altogether these results indicate that Reelin and mDab1 participate in the development and refinement of hippocampal connections by regulating axonal extension, targeting and branching.

A role for Cajal-Retzius cells and reelin in the development of hippocampal connections.

During development of the nervous system, specific recognition molecules provide the cues necessary for the formation of neural connections. In some regions, guiding cues for axonal pathfinding and target selection are provided by specific cells that exist only transiently during development, such as the floorplate or the cortical subplate. In the hippocampus, distinct groups of fibres innervate different layers. We have tested the hypothesis that transient neurons in the hippocampus provide positional information for the targeting of these fibres. Here we report that ablation of Cajal-Retzius cells in organotypic slice cultures of hippocampus prevented the ingrowth of entorhinal but not of commissural afferents. Experiments inhibiting Reelin (an extracellular matrix protein expressed by Cajal-Retzius cells) and analysis of reeler mutant mice showed dramatic abnormalities in the development of entorhinal afferents. Thus Cajal-Retzius cells and reelin are essential for the formation of layer-specific hippocampal connections.

Hippocampal Cajal-Retzius cells project to the entorhinal cortex: retrograde tracing and intracellular labelling studies.

Cajal-Retzius (CR) cells are characteristic horizontally orientated, early-generated transient neurons in the marginal zones of the neocortex and hippocampus that synthesize the extracellular matrix protein reelin. They have been implicated in the pathfinding of entorhino-hippocampal axons, but their role in this process remained unclear. Here we have studied the axonal projection of hippocampal CR cells. Following injection of the carbocyanine dye DiI into the entorhinal cortex of aldehyde-fixed rat embryos and young postnatal rats, neurons in the outer molecular layer of the dentate gyrus and stratum lacunosum-moleculare of the hippocampus proper with morphological characteristics of CR cells were retrogradely labelled. In a time course analysis, the first retrogradely labelled CR cells were observed on embryonic day 17. This projection of hippocampal CR cells to the entorhinal cortex was confirmed by retrograde tracing with Fast Blue in new-born rats and by intracellular biocytin filling of CR cells in acute slices from young postnatal rat hippocampus/entorhinal cortex and in entorhino-hippocampal slice cocultures using infrared videomicroscopy in combination with the patch-clamp technique. In double-labelling experiments CR cells were identified by their immunocytochemical staining for reelin or calretinin, and their interaction with entorhino-hippocampal axons labelled by anterograde tracers was analysed. Future studies need to investigate whether this early transient projection of hippocampal CR cells to the entorhinal cortex is used as a template by the entorhinal axons growing to their target layers in the hippocampus.

TrkB and TrkC signaling are required for maturation and synaptogenesis of hippocampal connections.

Recent studies have suggested a role for neurotrophins in the growth and refinement of neural connections, in dendritic growth, and in activity-dependent adult plasticity. To unravel the role of endogenous neurotrophins in the development of neural connections in the CNS, we studied the ontogeny of hippocampal afferents in trkB (-/-) and trkC (-/-) mice. Injections of lipophilic tracers in the entorhinal cortex and hippocampus of newborn mutant mice showed that the ingrowth of entorhinal and commissural/associational afferents to the hippocampus was not affected by these mutations. Similarly, injections of biocytin in postnatal mutant mice (P10-P16) did not reveal major differences in the topographic patterns of hippocampal connections. In contrast, quantification of biocytin-filled axons showed that commissural and entorhinal afferents have a reduced number of axon collaterals (21-49%) and decreased densities of axonal varicosities (8-17%) in both trkB (-/-) and trkC (-/-) mice. In addition, electron microscopic analyses showed that trkB (-/-) and trkC (-/-) mice have lower densities of synaptic contacts and important structural alterations of presynaptic boutons, such as decreased density of synaptic vesicles. Finally, immunocytochemical studies revealed a reduced expression of the synaptic-associated proteins responsible for synaptic vesicle exocytosis and neurotransmitter release (v-SNAREs and t-SNAREs), especially in trkB (-/-) mice. We conclude that neither trkB nor trkC genes are essential for the ingrowth or layer-specific targeting of hippocampal connections, although the lack of these receptors results in reduced axonal arborization and synaptic density, which indicates a role for TrkB and TrkC receptors in the developmental regulation of synaptic inputs in the CNS in vivo. The data also suggest that the genes encoding for synaptic proteins may be targets of TrkB and TrkC signaling pathways.

Repair of the entorhino-hippocampal projection in vitro.

The repair of axonal projections and the reconstruction of neuronal circuits after CNS lesions or during neurodegenerative disease are major challenges in restorative neuroscience. We have explored the potential of transplanted immature neurons to repair a specific axonal projection in an entorhino-hippocampal slice culture model system. When slices of immature entorhinal cortex (EC) from tau-GFP transgenic mice were cultured next to slices from postnatal hippocampus, an axonal projection from the E18 embryonic entorhinal cortex to the dentate gyrus of the postnatal hippocampus developed, which was similar to that observed in control cultures. Even more immature neuronal precursors in slices from E15 developing cerebral cortex differentiated and established an axonal projection to the hippocampal slice. This projection terminated specifically in the outer molecular layer of the dentate gyrus, the normal target area of the entorhino-hippocampal projection. When embryonic tissue from the presumptive brainstem area was used, there was still a subpopulation of fibers with a specific termination in the outer molecular layer, but few specific fibers were found in cocultures with embryonic midbrain. Our results show that very immature cortical neurons are potentially able to form an entorhino-hippocampal projection that terminates in a correct lamina-specific fashion in the dentate gyrus. These findings support the idea that immature neuronal precursor cells could be used for the reconstruction of specific neuronal circuits.

Regulation of Nogo and Nogo receptor during the development of the entorhino-hippocampal pathway and after adult hippocampal lesions.

Axonal regeneration in the adult CNS is limited by the presence of several inhibitory proteins associated with myelin. Nogo-A, a myelin-associated inhibitor, is responsible for axonal outgrowth inhibition in vivo and in vitro. Here we study the onset and maturation of Nogo-A and Nogo receptor in the entorhino-hippocampal formation of developing and adult mice. We also provide evidence that Nogo-A does not inhibit embryonic hippocampal neurons, in contrast to other cell types such as cerebellar granule cells. Our results also show that Nogo and Nogo receptor mRNA are expressed in the adult by both principal and local-circuit hippocampal neurons, and that after lesion, Nogo-A is also transiently expressed by a subset of reactive astrocytes. Furthermore, we analyzed their regulation after kainic acid (KA) treatment and in response to the transection of the entorhino-hippocampal connection. We found that Nogo-A and Nogo receptor are differentially regulated after kainic acid or perforant pathway lesions. Lastly, we show that the regenerative potential of lesioned entorhino-hippocampal organotypic slice co-cultures is increased after blockage of Nogo-A with two IN-1 blocking antibodies. In conclusion, our results show that Nogo and its receptor might play key roles during development of hippocampal connections and that they are implicated in neuronal plasticity in the adult.