大麻素受体在海马CA1区锥体神经元的功能表达

目的观察大麻素受体在孤立的海马CA1区锥体神经元的功能表达。方法将出生15~20d的Wistar大鼠取脑,急性分离出单个CA1区锥体神经元,用膜片钳技术记录神经元电活动,观察非选择性大麻素受体激动剂Win55212-2(5μmol/L)对神经元静息电位、动作电位、自发发放频率的影响。根据Win55212-2对膜电位的影响分为超极化组(n=7)和去极化组(n=6)。组织切片活性用MTT染色法检测。结果与给药前比较,超极化组神经元给药中动作电位频率和膜电压显著降低[0Hz vs(4.3±3.2)Hz,P0.05;(-57.0±4.6)mVvs(-54.1±3.8)mV,P0.01];与给药中比较,给药后动作电位频率及膜电压显著升高,差异有统计学意义(P0.01)。与给药前比较,去极化组神经元给药中动作电位频率显著降低,膜电压显著升高(P0.01);与给药中比较,给药后动作电位频率显著升高,膜电压显著降低,差异有统计学意义(P0.05)。结论 CA1区锥体神经元可能存在大麻素受体功能表达且不限于大麻素受体1;激活大麻素受体可能通过不同的机制起到抑制CA1区锥体神经元的作用。     

Two populations of kainate receptors with separate signaling mechanisms in hippocampal interneurons

Consistent with the epileptogenic and deleterious effects of the potent neurotoxin kainate, the activation of kainate receptors reduces the synaptic inhibition induced by the amino acid gamma-aminobutyric acid (GABA). Extrapolating from these data led to the conclusion that kainate receptors are located presynaptically. However, kainate directly depolarizes the inhibitory interneurons, causing them to fire repeatedly. This effect might indirectly decrease the size of inhibitory postsynaptic currents recorded from pyramidal cells and places in doubt the presynaptic location for kainate receptors. Here we show that both effects, membrane depolarization and the reduction of inhibitory potentials, can be dissociated by several means, particularly by the natural agonist of kainate receptors, glutamate. Indeed, when applied at low concentrations, glutamate inhibited GABA release without affecting the firing rate of GABA interneurons. These results indicate that CA1 interneurons contain two populations of kainate receptors, each with different agonist sensitivity and coupled to distinct signaling pathways.     

Readily releasable vesicles recycle at the active zone of hippocampal synapses

During the synaptic vesicle cycle, synaptic vesicles fuse with the plasma membrane and recycle for repeated exo/endocytic events. By using activity-dependent N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino) styryl) pyridinium dibromide dye uptake combined with fast (<1 s) microwave-assisted fixation followed by photoconversion and ultrastructural 3D analysis, we tracked endocytic vesicles over time, “frame by frame.” The first retrieved synaptic vesicles appeared 4 s after stimulation, and these endocytic vesicles were located just above the active zone. Second, the retrieved vesicles did not show any sign of a protein coat, and coated pits were not detected. Between 10 and 30 s, large labeled vesicles appeared that had up to 5 times the size of an individual synaptic vesicle. Starting at around 20 s, these large labeled vesicles decreased in number in favor of labeled synaptic vesicles, and after 30 s, labeled vesicles redocked at the active zone. The data suggest that readily releasable vesicles are retrieved as noncoated vesicles at the active zone.The mechanisms that govern synaptic vesicle (SV) retrieval have been debated since the discovery of the SV cycle (1, 2). Currently the two original mechanisms via coated vesicles and via “kiss and run” are proposed for mammalian excitatory central synapses (3–6). The proposed clathrin-mediated mechanism that retrieves the membrane via coated vesicles has comparable slow kinetics (7) (15–40 s until the endocytic vesicle separates from the plasma membrane) and a retrieval site outside the active zone (8, 9). First, the SV fully collapses into the release site and diffuses outside the active zone either as an entity or by its parts. At regions outside the active zone, coated pits form that sort SV proteins, and eventually a coated endocytic vesicle pinches off the plasma membrane. It is generally believed that coated vesicles shed their coat and fuse with early endosomes from which SVs bud off that join the SV cluster (8). This endosomal budding step is also believed to be mediated via coated vesicles. In contrast, SV retrieval via kiss and run has faster kinetics (10, 11) (<1 s), and SVs are retrieved at the active zone. During kiss and run, the SV is thought to maintain its identity and SVs are available for redocking and rapid reuse (12–14). Because SVs maintain their identity, fusion steps with potential endosomal compartments after endocytosis are not believed to occur after kiss and run.There is overwhelming evidence that SV retrieval at mammalian central synapses depends on the major coat protein clathrin, but the visualization of coated vesicles shortly after physiological stimulation has only been shown for lower vertebrate synapses (8, 15, 16). Kiss and run, on the other hand, is not generally accepted as a retrieval mechanism at mammalian central synapses. Several fluorescent imaging techniques (e.g., pHluorin-based SV protein chimeras and nanoparticles) recently provided unique insights into kiss and run (6), but many open questions remain. The visualization of a labeled endocytic vesicle at or near the active zone right after a physiological stimulus would provide elegant additional proof for kiss and run. More so, if one could follow such a labeled vesicle until “redocking,” it would greatly facilitate the investigation of the various steps SVs pass through on their way through the SV cycle.Here, we introduce a technique that is based on activity-dependent labeling of SV retrieval with N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino) styryl) pyridinium dibromide (FM1-43) followed by photoconversion and electron microscopic 3D analysis. This technique is combined with fast microwave-assisted fixation, ensuring a high time resolution that allows tracking of endocytic vesicles “frame by frame”—that is, at distinct time points (0, 4, 10, 20, 30, and 40 s) after stimulation.     

Left-right asymmetry of the hippocampal synapses with differential subunit allocation of glutamate receptors

Left-right asymmetry of the brain has been studied mostly through psychological examination and functional imaging in primates, leaving its molecular and synaptic aspects largely unaddressed. Here, we show that hippocampal CA1 pyramidal cell synapses differ in size, shape, and glutamate receptor expression depending on the laterality of presynaptic origin. CA1 synapses receiving neuronal input from the right CA3 pyramidal cells are larger and have more perforated PSD and a GluR1 expression level twice as high as those receiving input from the left CA3. The synaptic density of GluR1 increases as the size of a synapse increases, whereas that of NR2B decreases because of the relatively constant NR2B expression in CA1 regardless of synapse size. Densities of other major glutamate receptor subunits show no correlation with synapse size, thus resulting in higher net expression in synapses having right input. Our study demonstrates universal left-right asymmetry of hippocampal synapses with a fundamental relationship between synaptic area and the expression of glutamate receptor subunits.     

Recruitment of oriens-lacunosum-moleculare interneurons during hippocampal ripples

Sharp wave-associated ∼200-Hz ripple oscillations in the hippocampus have been implicated in the consolidation of memories. However, knowledge on mechanisms underlying ripples is still scarce, in particular with respect to synaptic involvement of specific cell types. Here, we used cell-attached and whole-cell recordings in vitro to study activity of pyramidal cells and oriens-lacunosum-moleculare (O-LM) interneurons during ripples. O-LM cells received ripple-associated synaptic input that arrived delayed (3.3 ± 0.3 ms) with respect to the maximum amplitude of field ripples and was locked to the ascending phase of field oscillations (mean phase: 209 ± 6°). In line, O-LM cells episodically discharged late during ripples (∼6.5 ms after the ripple maximum), and firing was phase-locked to field oscillations (mean phase: 219 ± 9°). Our data unveil recruitment of O-LM neurons during ripples, suggesting a previously uncharacterized role of this cell type during sharp wave-associated activity.     

Bidirectional alterations of hippocampal cannabinoid 1 receptors and their endogenous ligands in a rat model of alcohol withdrawal and dependence

BACKGROUND: The hippocampus is strongly implicated in memory processes and contains high concentrations of both cannabinoid receptors and their endogenous ligands. Chronic alcohol consumption impairs a variety of cognitive and performance tasks, including memory and learning. As the activation of cannabinoid receptors by their endogenous ligands modulates hippocampal neurotransmission, we hypothesized that the impaired memory and learning in alcoholism may be due to alterations in the hippocampal endocannabinoid system. METHODS: We used the rat chronic intermittent ethanol (CIE) model for alcohol withdrawal and dependence which involves intermittent episodes of ethanol intoxication (60 doses) and withdrawal (approximating binge drinking episodes in humans). We measured the levels of cannabinoid 1 receptor (CB1R) protein (Western blot using a C-terminal-directed antibody), CB1R mRNA (real-time RT-PCR), CB1R localization (immunocytochemistry), tissue levels of the endocannabinoids N-arachidonoylethanolamine/anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and function (patch-clamp recordings of depolarization-induced suppression of inhibition (DSI), as well as effects of CB1R agonist WIN 55,212-2 on inhibitory currents) in the hippocampus of CIE rats and their saline-treated controls. RESULTS: Results were obtained in saline and CIE-treated rats after 2 and 40 days of withdrawal (DW) from their respective treatments. In 2 DW CIE rats, CB1R mRNA and protein levels were decreased by 27% (p<0.05) compared with saline controls. Surprisingly, in 40 DW CIE rats, CB1R mRNA increased by 100% and protein increased by 21%, confirmed by immunohistochemistry. Hippocampal [2-AG] increased in both 2 and 40 DW CIE rats; [AEA] increased only at 40 DW. Hippocampal DSI of CIE rats was significantly reduced at 2 DW but not at 40 DW. The CB1R agonist WIN 55,212-2 (0.5 microM) produced a significantly greater decrease in the frequency of spontaneous inhibitory currents from saline-treated rats compared with CIE rats at 2 DW, but not at 40 DW. CONCLUSIONS: These data demonstrate that CIE treatment and withdrawal transiently down-regulates hippocampal CB1 Rs followed by a long-term up-regulation, including increased levels of endogenous cannabinoids. These findings are consistent with our hypothesis and suggest that long-term up-regulation of hippocampal CB1Rs may contribute to the long-term cognitive impairments in alcoholism. The data further suggest that the effectiveness of CB1R blockade in decreasing alcohol consumption may be greater after protracted abstinence from alcohol.     

Use-dependent amplification of presynaptic Ca2+ signaling by axonal ryanodine receptors at the hippocampal mossy fiber synapse

Presynaptic Ca²⁺ stores have been suggested to regulate Ca²⁺ dynamics within the nerve terminals at certain types of the synapse. However, little is known about their mode of activation, molecular identity, and detailed subcellular localization. Here, we show that the ryanodine-sensitive stores exist in axons and amplify presynaptic Ca²⁺ accumulation at the hippocampal mossy fiber synapses, which display robust presynaptic forms of plasticity. Caffeine, a potent drug inducing Ca²⁺ release from ryanodine-sensitive stores, causes elevation of presynaptic Ca²⁺ levels and enhancement of transmitter release from the mossy fiber terminals. The blockers of ryanodine receptors, TMB-8 or ryanodine, reduce presynaptic Ca²⁺ transients elicited by repetitive stimuli of mossy fibers but do not affect those evoked by single shocks, suggesting that ryanodine receptors amplify presynaptic Ca²⁺ dynamics in an activity dependent manner. Furthermore, we generated the specific antibody against the type 2 ryanodine receptor (RyR2; originally referred to as the cardiac type) and examined the cellular and subcellular localization using immunohistochemistry. RyR2 is highly expressed in the stratum lucidum of the CA3 region and mostly colocalizes with axonal marker NF160 but not with terminal marker VGLUT1. Immunoelectron microscopy revealed that RyR2 is distributed around smooth ER within the mossy fibers but is almost excluded from their terminal portions. These results suggest that axonal localization of RyR2 at sites distant from the active zones enables use dependent Ca²⁺ release from intracellular stores within the mossy fibers and thereby facilitates robust presynaptic forms of plasticity at the mossy fiber-CA3 synapse.     

INAUGURAL ARTICLE by a Recently Elected Academy Member:The hippocampal formation and action at a distance

The question of why our conceptions of space and time are intertwined with memory in the hippocampal formation is at the forefront of much current theorizing about this brain system. In this article I argue that animals bridge spatial and temporal gaps through the creation of internal models that allow them to act on the basis of things that exist in a distant place and/or existed at a different time. The hippocampal formation plays a critical role in these processes by stitching together spatiotemporally disparate entities and events. It does this by 1) constructing cognitive maps that represent extended spatial contexts, incorporating and linking aspects of an environment that may never have been experienced together; 2) creating neural trajectories that link the parts of an event, whether they occur in close temporal proximity or not, enabling the construction of event representations even when elements of that event were experienced at quite different times; and 3) using these maps and trajectories to simulate possible futures. As a function of these hippocampally driven processes, our subjective sense of both space and time are interwoven constructions of the mind, much as the philosopher Immanuel Kant postulated.

Action at a distance in physics involves the nonlocal interaction of objects separated in space and/or time. It has a long and checkered history and is frequently discussed in terms of quantum entanglement, which Einstein famously called “spooky.” Philosophers talk about action at a distance whenever there is a spatial or temporal gap (or both) between a cause and its effect. Controversy arises with regard to the notion of unmediated action at a distance, involving a gap between cause and effect with no obvious intermediaries filling the gap. There is little argument with examples of mediated action at a distance, where spatially and temporally continuous events stretch across time and space to fill an apparent gap.Mediated action at a distance is central to much of what psychologists care about, given that behavior is frequently motivated by things that are at a spatial and/or temporal remove from the here and now. I will argue that mediating action at a distance is so important that a brain system, centered on the hippocampal formation, is largely devoted to carrying it out. Staresina and Davachi (1) pointed to a role for this brain region in “minding” the small spatial and temporal gaps they manipulated in their stimulus displays. Expanding on this idea, I will assert that animals, including humans, bridge large spatial and temporal gaps through the creation of internal models that allow them to act on the basis of things that exist in a distant place, and/or existed at a different time. But not only to act: Humans often think about, and plan for, the future. The hippocampal formation also plays a role in imagining places and times in the future (2). Memory, in this view, serves to bridge these extensive spatiotemporal gaps, providing the mechanistic basis for action at an apparent distance. In brief, the hippocampal formation accomplishes the goal of stitching together spatiotemporally disparate entities and events by 1) constructing cognitive maps that represent extended spatial contexts, incorporating and linking aspects of an environment that may never have been experienced together; 2) creating neural trajectories that link the parts of an event, whether they occur in close temporal proximity or not, enabling the construction of event representations even when elements of that event were experienced at quite different times; and 3) using these maps and trajectories to simulate possible futures. As a function of these hippocampally driven processes, our subjective sense of both space and time are interwoven constructions of the mind, much as the philosopher Kant postulated.The question of why our conceptions of space and time are intertwined with memory in the hippocampal formation is at the forefront of much current theorizing about this brain system (e.g., refs. 3 –7). I will suggest that what distinguishes its involvement from that of most other brain systems engaged with space, time and memory is its role in mediating action at a distance. Without a hippocampal formation, I will argue, organisms are largely incapable of escaping the here and now—a state of being captured quite well in the title of Suzanne Corkin’s book (8) about the famous amnesic patient H.M.: “Permanent Present Tense.” This assertion leads to a number of implications, which I consider, albeit briefly, in the conclusion.     

Prioritized experience replays on a hippocampal predictive map for learning

Hippocampal cells are central to spatial and predictive representations, and experience replays by place cells are crucial for learning and memory. Nonetheless, how hippocampal replay patterns dynamically change during the learning process remains to be elucidated. Here, we designed a spatial task in which rats learned a new behavioral trajectory for reward. We found that as rats updated their behavioral strategies for a novel salient location, hippocampal cell ensembles increased theta-sequences and sharp wave ripple-associated synchronous spikes that preferentially replayed salient locations and reward-related contexts in reverse order. The directionality and contents of the replays progressively varied with learning, including an optimized path that had never been exploited by the animals, suggesting prioritized replays of significant experiences on a predictive map. Online feedback blockade of sharp wave ripples during a learning process inhibited stabilizing optimized behavior. These results implicate learning-associated experience replays that act to learn and reinforce specific behavioral strategies.

To adapt to continuous changes in the external environment, animals need to encode new salient episodes and update their behavioral policy. To achieve flexible spatial navigation in particular, hippocampal place cells are thought to provide fundamental neural spatial coding and constitute a cognitive map (1). Recently, the view of the cognitive map has been proposed to extend to a predictive map theory in which place cells potentially encode expectations about an animal’s future states (2). In addition to these map representations, hippocampal place cells that encode animals’ past or future trajectories are sequentially activated during sharp wave ripples (SWRs) within a short time window (∼100 ms) in a phenomenon known as “place cell replays” (3–5). The time window of such SWR-associated sequential firing is potentially appropriate to induce plastic changes in the hippocampal circuit. Consistent with this idea, a growing amount of evidence demonstrates that the frequency of SWR-associated place cell replays (or reactivation) is prominently increased during learning of new experiences (online replays) (6) and during rest/sleep states after learning of new experiences (offline replays) (7). In addition, selective disruption of waking SWRs during spatial learning has been demonstrated to reduce subsequent task performance (8) and impair the stabilization and refinement of place cell maps (9). Taken together, these results suggest an essential role of SWR-associated replays of an animal’s experiences in novel spatial learning.Experience replays by place cells are also suggested to be a key neuronal basis for a reinforcement learning framework (10, 11). When agents encounter a prediction error, such as a change in reward, experience replays may be an efficient mechanism for the evaluation of their experienced action–outcome associations by providing a solution to the temporal credit assignment problem, which is helpful to update their behavioral policy to maximize future reward (12, 13). In line with this idea, empirical observations have demonstrated that the receipt of reward or novel experiences leads to increased rates of SWRs and coordinated reactivation of place cells (6, 14), and increased reward leads to increased reverse replays (4, 15).Despite accumulating evidence and theory, the field still lacks key insights into how the contents of place cell replays change to (re)assign the values of salient locations as animals develop new navigation strategies in response to environmental changes. Theoretical works demonstrate that incorporating replay algorithms with prioritized memory access for learned salient locations (16), rather than random access from all stored memory, into a reinforcement learning architecture—a strategy termed “prioritized experience replays” (17)—improves integrative learning in artificial agents. Whether living neuronal networks adopt the same computations to enhance learning capability remains an open question. To address this issue, we designed a spatial learning task requiring rats to learn new spatial navigation within a recording period within an hour, and analyzed how hippocampal replays of salient locations associated with learning progressively varied with the animal’s learning processes.     

Distinct nonuniform cable properties optimize rapid and efficient activation of fast-spiking GABAergic interneurons

Fast-spiking, parvalbumin-expressing basket cells (BCs) play a key role in feedforward and feedback inhibition in the hippocampus. However, the dendritic mechanisms underlying rapid interneuron recruitment have remained unclear. To quantitatively address this question, we developed detailed passive cable models of BCs in the dentate gyrus based on dual somatic or somatodendritic recordings and complete morphologic reconstructions. Both specific membrane capacitance and axial resistivity were comparable to those of pyramidal neurons, but the average somatodendritic specific membrane resistance (R_m) was substantially lower in BCs. Furthermore, R_m was markedly nonuniform, being lowest in soma and proximal dendrites, intermediate in distal dendrites, and highest in the axon. Thus, the somatodendritic gradient of R_m was the reverse of that in pyramidal neurons. Further computational analysis revealed that these unique cable properties accelerate the time course of synaptic potentials at the soma in response to fast inputs, while boosting the efficacy of slow distal inputs. These properties will facilitate both rapid phasic and efficient tonic activation of BCs in hippocampal microcircuits.     

Robust but delayed thalamocortical activation of dendritic-targeting inhibitory interneurons

GABA-releasing cortical interneurons are crucial for the neural transformations underlying sensory perception, providing “feedforward” inhibition that constrains the temporal window for synaptic integration. To mediate feedforward inhibition, inhibitory interneurons need to fire in response to ascending thalamocortical inputs, and most previous studies concluded that ascending inputs activate mainly or solely proximally targeting, parvalbumin-containing “fast-spiking” interneurons. However, when thalamocortical axons fire at frequencies that are likely to occur during natural exploratory behavior, activation of fast-spiking interneurons is rapidly and strongly depressed, implying the paradoxical conclusion that feedforward inhibition is absent when it is most needed. To address this issue, we took advantage of lines of transgenic mice in which either parvalbumin- or somatostatin-containing interneurons express GFP and recorded the responses of interneurons from both subtypes to thalamocortical stimulation in vitro. We report that during thalamocortical activation at behaviorally expected frequencies, fast-spiking interneurons were indeed activated only transiently because of rapid depression of their thalamocortical inputs, but a subset of layer 5 somatostatin-containing interneurons were robustly and persistently activated after a delay, due to the facilitation and temporal summation of their thalamocortical excitatory postsynaptic potentials. Somatostatin-containing interneurons are considered distally targeting. Thus, they are likely to provide delayed dendritic inhibition during exploratory behavior, contributing to the maintenance of a balance between cortical excitation and inhibition while leaving a wide temporal window open for synaptic integration and plasticity in distal dendrites.     

Presence of functional cannabinoid receptors in human endocrine pancreas

Aims/hypothesis We examined the presence of functional cannabinoid receptors 1 and 2 (CB1, CB2) in isolated human islets, phenotyped the cells producing cannabinoid receptors and analysed the actions of selective cannabinoid receptor agonists on insulin, glucagon and somatostatin secretion in vitro. We also described the localisation on islet cells of: (1) the endocannabinoid-producing enzymes N-acyl-phosphatidyl ethanolamine-hydrolysing phospholipase D and diacylglycerol lipase; and (2) the endocannabinoid-degrading enzymes fatty acid amidohydrolase and monoacyl glycerol lipase. Methods Real-time PCR, western blotting and immunocytochemistry were used to analyse the presence of endocannabinoid-related proteins and genes. Static secretion experiments were used to examine the effects of activating CB1 or CB2 on insulin, glucagon and somatostatin secretion and to measure changes in 2-arachidonoylglycerol (2-AG) levels within islets. Analyses were performed in isolated human islets and in paraffin-embedded sections of human pancreas. Results Human islets of Langerhans expressed CB1 and CB2 (also known as CNR1 and CNR2) mRNA and CB1 and CB2 proteins, and also the machinery involved in synthesis and degradation of 2-AG (the most abundant endocannabinoid, levels of which were modulated by glucose). Immunofluorescence revealed that CB1 was densely located in glucagon-secreting alpha cells and less so in insulin-secreting beta cells. CB2 was densely present in somatostatin-secreting delta cells, but absent in alpha and beta cells. In vitro experiments revealed that CB1 stimulation enhanced insulin and glucagon secretion, while CB2 agonism lowered glucose-dependent insulin secretion, showing these cannabinoid receptors to be functional. Conclusions/interpretation Together, these results suggest a role for endogenous endocannabinoid signalling in regulation of endocrine secretion in the human pancreas. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Melatonin increases dendritogenesis in the hilus of hippocampal organotypic cultures

Neuropsychiatric disorders are characterized by hippocampus decreased volume and loss of dendrite arborizations in the subiculum and prefrontal cortex. These structural changes are associated with diminished memory performance. Hilar neurons of the hippocampus integrate spatial memory and are lost in dementia. They receive information from dentate gyrus neurons through dendrites, while they send axonal tracts to the CA3 region. Dendrites are complex structures of neurons that receive chemical information from presynaptic and postsynaptic terminals. Melatonin, the main product of the pineal gland, has neuroprotective actions through its free radical-scavenging properties and decreases neuronal apoptosis. Recently, we found that melatonin increases dendrite maturation and complexity in new neurons formed in the dentate gyrus of mice. In addition, in N1E-115 cultured cells, the indole stimulates early stages of neurite formation, a process that is known to antecede dendrite formation and maturation. Thus, in this study, we explored whether melatonin stimulates dendrite formation and complexity in the adult rat hippocampus in organotypic slice cultures, which is a model that preserves the hippocampal circuitry and their tridimensional organizations of connectivity. The effects of melatonin were studied in nonpathological conditions and in the absence of harmful agents. The results showed that the indole at nocturnal concentrations reached in the cerebrospinal fluid stimulates dendritogenesis at formation, growth, and maturation stages. Also, data showed that dendrites formed became competent to form presynaptic specializations. Evidence strongly suggests that melatonin may be useful in the treatment of neuropsychiatric diseases to repair the loss of dendrites and re-establish lost synaptic connections.     

A hebbian form of long-term potentiation dependent on mGluR1a in hippocampal inhibitory interneurons.

Hippocampal inhibitory interneurons play important roles in controlling the excitability and synchronization of pyramidal cells, but whether they express long-term synaptic plasticity that contributes to hippocampal network function remains uncertain. We found that pairing postsynaptic depolarization with theta-burst stimulation induced long-term potentiation (LTP) of putative single-fiber excitatory postsynaptic currents in interneurons. Either postsynaptic depolarization or theta-burst stimulation alone failed to induce LTP. LTP was expressed as a decrease in failure rates and an increase in excitatory postsynaptic current amplitude, independent of N-methyl-d-aspartate receptors, and dependent on metabotropic glutamate receptors subtype 1a. LTP was induced specifically in interneurons in stratum oriens and not in interneurons of stratum radiatum/lacunosum-moleculare. Thus, excitatory synapses onto specific subtypes of inhibitory interneurons express a new form of hebbian LTP that will contribute to hippocampal network plasticity.     

Constitutively active receptors as a disease-causing mechanism

Membrane receptors have appeared early in evolution as the means for the unicellular organism to sense its environment. With the emergence of social cellular life in multicellular organisms, membrane receptors have acquired the additional functions of sensing the presence of similar cells (as in the aggregation phenomenon of Dictyostelium discoideum) (Klein et al., 1988) or the presence of the mate (in Saccharomyces cerevisiae) (Cross et al., 1988), and to detect endocrine signals emmitted by cells in distant tissues. As the latter function is central to homeostasis and regulation of cell growth, the downstream regulatory cascades under receptor control are the subject of intense research with implications in virtually all fields of biomédical science. The impact of the analysis of tyrosine kinase-activated cascades on our understanding of carcinogenesis is but one example of such an advance     

Extent of hippocampal atrophy predicts degree of deficit in recall

Which specific memory functions are dependent on the hippocampus is still debated. The availability of a large cohort of patients who had sustained relatively selective hippocampal damage early in life enabled us to determine which type of mnemonic deficit showed a correlation with extent of hippocampal injury. We assessed our patient cohort on a test that provides measures of recognition and recall that are equated for difficulty and found that the patients'' performance on the recall tests correlated significantly with their hippocampal volumes, whereas their performance on the equally difficult recognition tests did not and, indeed, was largely unaffected regardless of extent of hippocampal atrophy. The results provide new evidence in favor of the view that the hippocampus is essential for recall but not for recognition.A long-standing issue in memory research is the identity of the mnemonic process served by each of the components of the medial temporal lobe (MTL). Recall, which is the ability to retrieve from memory a stimulus or its context that is no longer present, is a more complex function than recognition, which is the ability to identify a current stimulus as old or new, or to choose a previously encountered stimulus among competing distractors. Over the years, a large number of studies have been conducted, aiming to tease apart the relative contribution of different MTL structures to recall and recognition. Many investigators have proposed that these two distinct memory processes rely on different MTL structures, with recall being dependent on the hippocampus and recognition being supported by parahippocampal structures, such as the perirhinal and entorhinal cortices (1–5, but see ref. 6). Also, studies examining the effects of damage to the mammillary bodies and fornices, structures within the hippocampal circuit, have shown that volume loss is correlated with deficits in recall but not in recognition (7, 8).However, there is also evidence suggesting that both processes rely on the hippocampus (for a review, see ref. 6). Most of the literature on either side of this controversy is composed of studies with single cases or small sample sizes. Indeed, to date, none of the studies involving humans has been able to demonstrate a clear relationship between memory process and hippocampal volume (HV), possibly due to lack of variability in HV loss. Additionally, many of the contradictory findings could result from measures used to test recognition and recall not being equated for level of difficulty.Previous work from our group demonstrated that patients with developmental amnesia due to severe hippocampal pathology sustained early in life are seriously impaired in their ability to recall visual or verbal stimuli but are relatively unimpaired in recognizing them (9). By identifying a group of patients with varying extents of HV reduction, and applying a standardized measure of memory [the Doors and People test (D&P test) (10)] in which the recognition and recall subtests are matched for difficulty, we were able to test whether or not these mnemonic processes depend equally on the magnitude of hippocampal damage. The outcome could help determine the specific mnemonic role of the hippocampus.     

Roller Coaster Scanning reveals spontaneous triggering of dendritic spikes in CA1 interneurons

Inhibitory interneurons are considered to be the controlling units of neural networks, despite their sparse number and unique morphological characteristics compared with excitatory pyramidal cells. Although pyramidal cell dendrites have been shown to display local regenerative events--dendritic spikes (dSpikes)--evoked by artificially patterned stimulation of synaptic inputs, no such studies exist for interneurons or for spontaneous events. In addition, imaging techniques have yet to attain the required spatial and temporal resolution for the detection of spontaneously occurring events that trigger dSpikes. Here we describe a high-resolution 3D two-photon laser scanning method (Roller Coaster Scanning) capable of imaging long dendritic segments resolving individual spines and inputs with a temporal resolution of a few milliseconds. By using this technique, we found that local, NMDA receptor-dependent dSpikes can be observed in hippocampal CA1 stratum radiatum interneurons during spontaneous network activities in vitro. These NMDA spikes appear when approximately 10 spatially clustered inputs arrive synchronously and trigger supralinear integration in dynamic interaction zones. In contrast to the one-to-one relationship between computational subunits and dendritic branches described in pyramidal cells, here we show that interneurons have relatively small (～14 μm) sliding interaction zones. Our data suggest a unique principle as to how interneurons integrate synaptic information by local dSpikes.     

短暂脑缺血对大鼠海马脑区锥体神经元外向整流氯通道功能的影响

目的 研究短暂前脑缺血对大鼠海马CA1和CA3脑区锥体神经元外向整流氯通道功能的影响.方法 采用膜片钳全细胞技术,在成年大鼠海马脑区锥体神经元上记录到可以被氯通道阻断剂DIDS阻断,具有外向整流特性的氯通道.结果 15 min前脑缺血再灌注6h和24 h后,海马CA1区锥体神经元氯通道电流持续性增强,而CA3区锥体神经元活动无明显改变.结论 氯通道功能增强可能参与海马CA1区锥体神经元在脑缺血后的迟发性死亡过程,并且为治疗缺血性脑损伤提供了新的手段.     

Preschool is a sensitive period for the influence of maternal support on the trajectory of hippocampal development

Building on well-established animal data demonstrating the effects of early maternal support on hippocampal development and adaptive coping, a few longitudinal studies suggest that early caregiver support also impacts human hippocampal development. How caregiving contributes to human hippocampal developmental trajectories, whether there are sensitive periods for these effects, as well as whether related variation in hippocampal development predicts later childhood emotion functioning are of major public health importance. The current study investigated these questions in a longitudinal study of preschoolers assessed annually for behavioral and emotional development, including observed caregiver support. One hundred and twenty-seven children participated in three waves of magnetic resonance brain imaging through school age and early adolescence. Multilevel modeling of the effects of preschool and school-age maternal support on hippocampal volumes across the three waves was conducted. Hippocampal volume increased faster for those with higher levels of preschool maternal support. Subjects with support 1 SD above the mean had a 2.06 times greater increase in total hippocampus volume across the three scans than those with 1 SD below the mean (2.70% vs. 1.31%). No effect of school-age support was found. Individual slopes of hippocampus volume were significantly associated with emotion regulation at scan 3. The findings demonstrate a significant effect of early childhood maternal support on hippocampal volume growth across school age and early adolescence and suggest an early childhood sensitive period for these effects. They also show that this growth trajectory is associated with later emotion functioning.A large body of developmental data from studies of rodents has clearly established that the early experience of a highly nurturing caregiver has a powerful effect on hippocampal development in the rat pup, through an epigenetic mechanism (1–4). Building on these findings in animals, an increasing body of data in humans has emerged suggesting that early experiences of support, or conversely of abuse, neglect, or adversity, similarly impact human hippocampal development (5–7). The hippocampus, a region dense with glucocorticoid receptors, plays an integral role in the hypothalamic pituitary axis stress response (8, 9). Related to this role, reductions in hippocampal volume have been implicated in maladaptive stress reactivity and coping, as well as in affective psychopathology (10, 11). Therefore, a greater understanding of the environmental factors, particularly early caregiving experiences, that contribute to healthy hippocampal development in humans is of significant public health importance. Further, it is critical to examine whether variation in hippocampal development related to early caregiving predicts later childhood emotion functioning, as would be expected based on the animal data but not yet established in humans (12).Although retrospective studies establish a link between childhood trauma and abuse and decreases in hippocampal volume in adults, these findings are limited by the known bias and possible inaccuracy of retrospective accounts of early childhood experiences by adult reporters (13, 14). More recently, some prospective data have become available to inform this issue. Using one wave of scan data from the study sample presented here, we have previously reported a link between higher early childhood maternal support and larger hippocampal volumes measured at school age in nondepressed subjects (15). Another prospective study that followed a small sample of cocaine-exposed infants from birth through adolescence reported decreased hippocampal volumes in adolescents who experienced higher maternal nurturance at age 4 (16). Although this effect was opposite what would be expected from the animal literature, the use of a relatively small sample exposed to drugs in utero may represent a unique developmental trajectory. Alterations in patterns of connectivity between the medial prefrontal cortex and amygdala have been reported in children who experienced early maternal deprivation (17, 18). Notably, another unique prospective study of a small group of children exposed to chronically depressed and less nurturing mothers displayed increases in amygdala volumes but no changes in hippocampus when scanned at age 10 (19). These conflicting findings underscore the need for further investigation of these relationships in larger samples with broader early risk exposures. In addition, there is a need to examine brain outcomes across the trajectory of brain development using multiple scan waves longitudinally. It is possible that disparate findings may reflect the unique risk trajectories of the various study samples, small sample sizes, as well as the limitations of cross-sectional imaging outcomes. As such, the question of whether the effect of early caregiver support impacts hippocampal development across its growth trajectory is of key interest. The current study aimed to address this question using a longitudinal neuroimaging design across childhood to investigate whether there are effects of support on brain development from school age through early adolescence.Another key question that has been of interest in the study of the effects of caregiving quality on emotional, cognitive, and related brain development has been whether there are sensitive periods during which these environmental factors may have a particularly powerful effect on developmental outcomes. Such sensitive periods in development, when environmental exposures have a uniquely large and formative effect on neural structure and function, are well-established in visual and sensory-motor systems (20, 21). There has been some emerging evidence for sensitive periods in emotional development as well. This includes data from the Bucharest Early Intervention Project, where institutionalized children randomized to foster care before the age of 2 had superior cognitive and socioemotional outcomes to those randomized at later ages (22). Similarly, Rao et al. (16) report evidence for a sensitive period for the effects of maternal support (although in the opposite direction of that expected from animal studies), with childhood support at age 4 predicting adolescent brain outcomes whereas later childhood support at age 8 did not. If sensitive periods for the effects of supportive caregiving on brain development could be identified, it would have very important early intervention and prevention implications.To address these questions, we sought to investigate whether experiences of maternal support predicted the trajectory of hippocampal development through school age and early adolescence using a longitudinal neuroimaging study with three waves of structural imaging data. We also tested whether caregiver support during the preschool versus school-age periods had unique effects on hippocampal outcomes. Last, to better interpret the functional significance of any effects found on hippocampal growth trajectories, we examined whether these trajectories predicted emotion reactivity and/or regulation at late school age.