Septal cholinergic input to CA2 hippocampal region controls social novelty discrimination via nicotinic receptor-mediated disinhibition.

Acetylcholine (ACh), released in the hippocampus from fibers originating in the medial septum/diagonal band of Broca (MSDB) complex, is crucial for learning and memory. The CA2 region of the hippocampus has received increasing attention in the context of social memory. However, the contribution of ACh to this process remains unclear. Here, we show that in mice, ACh controls social memory. Specifically, MSDB cholinergic neurons inhibition impairs social novelty discrimination, meaning the propensity of a mouse to interact with a novel rather than a familiar conspecific. This effect is mimicked by a selective antagonist of nicotinic AChRs delivered in CA2. Ex vivo recordings from hippocampal slices provide insight into the underlying mechanism, as activation of nAChRs by nicotine increases the excitatory drive to CA2 principal cells via disinhibition. In line with this observation, optogenetic activation of cholinergic neurons in MSDB increases the firing of CA2 principal cells in vivo. These results point to nAChRs as essential players in social novelty discrimination by controlling inhibition in the CA2 region.

Frequency-Dependent Synaptic Dynamics Differentially Tune CA1 and CA2 Pyramidal Neuron Responses to Cortical Input.

Entorhinal cortex neurons make monosynaptic connections onto distal apical dendrites of CA1 and CA2 pyramidal neurons through the perforant path (PP) projection. Previous studies show that differences in dendritic properties and synaptic input density enable the PP inputs to produce a much stronger excitation of CA2 compared with CA1 pyramidal neurons. Here, using mice of both sexes, we report that the difference in PP efficacy varies substantially as a function of presynaptic firing rate. Although a single PP stimulus evokes a 5- to 6-fold greater EPSP in CA2 compared with CA1, a brief high-frequency train of PP stimuli evokes a strongly facilitating postsynaptic response in CA1, with relatively little change in CA2. Furthermore, we demonstrate that blockade of NMDARs significantly reduces strong temporal summation in CA1 but has little impact on that in CA2. As a result of the differences in the frequency- and NMDAR-dependent temporal summation, naturalistic patterns of presynaptic activity evoke CA1 and CA2 responses with distinct dynamics, differentially tuning CA1 and CA2 responses to bursts of presynaptic firing versus single presynaptic spikes, respectively.SIGNIFICANCE STATEMENT Recent studies have demonstrated that abundant entorhinal cortical innervation and efficient dendritic propagation enable hippocampal CA2 pyramidal neurons to produce robust excitation evoked by single cortical stimuli, compared with CA1. Here we uncovered, unexpectedly, that the difference in efficacy of cortical excitation varies substantially as a function of presynaptic firing rate. A burst of stimuli evokes a strongly facilitating response in CA1, but not in CA2. As a result, the postsynaptic response of CA1 and CA2 to presynaptic naturalistic firing displays contrasting temporal dynamics, which depends on the activation of NMDARs. Thus, whereas CA2 responds to single stimuli, CA1 is selectively recruited by bursts of cortical input.

Kainate receptor modulation of glutamatergic synaptic transmission in the CA2 region of the hippocampus.

Kainate (KA) receptors (KARs) are important modulators of synaptic transmission. We studied here the role of KARs on glutamatergic synaptic transmission in the CA2 region of the hippocampus where the actions of these receptors are unknown. We observed that KA depresses glutamatergic synaptic transmission at Schaffer collateral-CA2 synapses; an effect that was antagonized by NBQX (a KA/AMPA receptors antagonist) under condition where AMPA receptors were previously blocked. The study of paired-pulse facilitation ratio, miniature responses, and fluctuation analysis indicated a presynaptic locus of action for KAR. Additionally, we determined the action mechanism for this depression of glutamate release mediated by the activation of KARs. We found that inhibition of protein kinase A suppressed the effect of KAR activation on evoked excitatory post-synaptic current, an effect that was not suppressed by protein kinase C inhibitors. Furthermore, in the presence of Pertussis toxin, the depression of glutamate release mediated by KAR activation was not present, invoking the participation of a Gi/o protein in this modulation. Finally, the KAR-mediated depression of glutamate release was not suppressed by treatments that affect calcium entry trough voltage-dependent calcium channels or calcium release from intracellular stores. We conclude that KARs present at these synapses mediate a depression of glutamate release through a mechanism that involves the activation of G protein and protein kinase A.

Cyclic changes and actions of progesterone and allopregnanolone on cognition and hippocampal basal (stratum oriens) dendritic spines of female rats.

Ovarian steroids modulate the neuronal structure and function during the estrous cycle, contrasting peak effects during the proestrus cycle and low effects during the metestrus cycle. An ovariectomy (OVX) decreases gonadal hormones and tests the effects of substitutive therapies. We studied female rats with a normal estrous cycle and we also studied the effects of systemic progesterone (P4, 4.0 mg/kg) or its reduced metabolite allopregnanolone (ALLO, 4.0 mg/kg, both for 10 days) in females who had had an OVX 16.5 weeks prior to the study (long-term OVX) with the novel object recognition test (NORT) for associative memory. The dendritic shape and spine density in Golgi-impregnated basal dendrites (stratum oriens) of hippocampal pyramidal neurons was also studied. Proestrus females had a better performance than metestrus or OVX females in short-term memory (tested 1 h after the acquisition phase). Proestrus and metestrus females showed better results than OVX females for long-term memory (24 h after the initial phase). Both P4 and ALLO recovered the cognitive impairment induced by long-term OVX. Also, proestrus females had a higher density of dendritic spines than metestrus females, OVX reduced the density of spines when compared to intact females, whereas both P4 and ALLO treatments increased the dendritic spine density, number of dendritic branches along the dendritic length, and branching order compared to vehicle. These data add the dendrites of the stratum oriens as an additional site for naturally occurring changes in spine density during the estrous cycle and evidence the actions of progestins in both behavioral recovery and the structural dendritic rearrangement of hippocampal pyramidal neurons in long-term OVX female rats.

Characterisation of the mechanisms underlying the special sensitivity of the CA2 hippocampal area to adenosine receptor antagonists.

Recent studies have underscored the importance of the CA2 area in social memory formation. This area, a narrow transition zone between hippocampal CA3 and CA1 areas, is endowed with special connectivity and a distinctive molecular composition. In particular, adenosine A1 receptors (A1R) are enriched in CA2, and based on the prominent synaptic potentiation induced by A1R antagonists (e.g., caffeine) in this area, it has been proposed that CA2 is under the strong tonic control of A1R activation. It is unclear whether this special sensitivity of CA2 to A1R antagonists is due to an elevated extracellular concentration of adenosine or to a different A1R function. Here, using the recording of field potentials evoked simultaneously in CA2 and CA1 by Schaffer collateral stimulation, we confirm that the application of A1R antagonists, caffeine and DPCPX has a stronger effect on synaptic responses in CA2 than in those evoked in CA1. This difference was, at least partially, explained by the action of A1R antagonists on presynaptic A1Rs. We found that caffeine-induced potentiation in CA2 was restricted to Schaffer collateral synapses, but not to those formed by temporoammonic inputs. We also observed that the apparent affinity of an A1R agonist is similar for A1R in both CA2 and CA1 areas, which indicates that the tonic activation of A1R in both areas is comparable. Furthermore, we show that the direct activation of adenylyl cyclase with forskolin in the presence of rolipram, a phosphodiesterase inhibitor, greatly enhances the synaptic potentials in CA2 compared to CA1. The forskolin-induced potentiation was exacerbated in the presence of caffeine or DPCPX, accentuating the differences between the two areas. These results indicate that the tonic activation of A1Rs in area CA2 is not different to that of other hippocampal areas, but it is more efficiently coupled to the downstream effectors.

Substance P induces plasticity and synaptic tagging/capture in rat hippocampal area CA2.

The hippocampal area Cornu Ammonis (CA) CA2 is important for social interaction and is innervated by Substance P (SP)-expressing supramammillary (SuM) nucleus neurons. SP exerts neuromodulatory effects on pain processing and central synaptic transmission. Here we provide evidence that SP can induce a slowly developing NMDA receptor- and protein synthesis-dependent potentiation of synaptic transmission that can be induced not only at entorhinal cortical (EC)-CA2 synapses but also at long-term potentiation (LTP)-resistant Schaffer collateral (SC)-CA2 synapses. In addition, SP-induced potentiation of SC-CA2 synapses transforms a short-term potentiation of EC-CA2 synaptic transmission into LTP, consistent with the synaptic tagging and capture hypothesis. Interestingly, this SP-induced potentiation and associative interaction between the EC and SC inputs of CA2 neurons is independent of the GABAergic system. In addition, CaMKIV and PKMζ play a critical role in the SP-induced effects on SC-CA2 and EC-CA2 synapses. Thus, afferents from SuM neurons are ideally situated to prime CA2 synapses for the formation of long-lasting plasticity and associativity.

Heterogeneity in Kv2 Channel Expression Shapes Action Potential Characteristics and Firing Patterns in CA1 versus CA2 Hippocampal Pyramidal Neurons.

The CA1 region of the hippocampus plays a critical role in spatial and contextual memory, and has well-established circuitry, function and plasticity. In contrast, the properties of the flanking CA2 pyramidal neurons (PNs), important for social memory, and lacking CA1-like plasticity, remain relatively understudied. In particular, little is known regarding the expression of voltage-gated K+ (Kv) channels and the contribution of these channels to the distinct properties of intrinsic excitability, action potential (AP) waveform, firing patterns and neurotransmission between CA1 and CA2 PNs. In the present study, we used multiplex fluorescence immunolabeling of mouse brain sections, and whole-cell recordings in acute mouse brain slices, to define the role of heterogeneous expression of Kv2 family Kv channels in CA1 versus CA2 pyramidal cell excitability. Our results show that the somatodendritic delayed rectifier Kv channel subunits Kv2.1, Kv2.2, and their auxiliary subunit AMIGO-1 have region-specific differences in expression in PNs, with the highest expression levels in CA1, a sharp decrease at the CA1-CA2 boundary, and significantly reduced levels in CA2 neurons. PNs in CA1 exhibit a robust contribution of Guangxitoxin-1E-sensitive Kv2-based delayed rectifier current to AP shape and after-hyperpolarization potential (AHP) relative to that seen in CA2 PNs. Our results indicate that robust Kv2 channel expression confers a distinct pattern of intrinsic excitability to CA1 PNs, potentially contributing to their different roles in hippocampal network function.

The role of neuropeptide-Y in nandrolone decanoate-induced attenuation of antidepressant effect of exercise.

Since the increased prevalence of anabolic androgenic steroids abuse in last few decades is usually accompanied by various exercise protocols, the scope of our study was to evaluate the effects of chronic nandrolone decanoate administration in supraphysiological dose and a prolonged swimming protocol (alone and simultaneously with nandrolone decanoate) on depressive state in male rats. Simultaneously, we investigated the possible alterations in neuropeptide Y (NPY) content in blood and the hippocampus, in order to determine the role of NPY in the modulation of depressive-like behavior.Exercise induced antidepressant effects in tail suspension test (decrease of the total duration of immobility), as well as significant increase in the number of hippocampal NPY-interneurons in CA1 region. Chronic nandrolone decanoate treatment attenuated the beneficial antidepressant effects of exercise as measured by the tail suspension test parameters. Simultaneously, nandrolone decanoate treatment resulted in diminution of NPY content both in blood (decreased serum levels) and in hippocampus (the significant decrease in NPY expression in all three investigated hippocampal regions-CA1, CA2/3 and DG). Our findings indicate that alterations in serum and hippocampal NPY contents may underlie the changes in depressive state in rats. The exercise was beneficial as it exerted antidepressant effect, while chronic nandrolone decanoate treatment resulted in depressive-like behavior. Furthermore, the behavioral indicators of depression showed strong correlations with the serum levels and the hippocampal content of NPY.

Bi-directional interplay between proximal and distal inputs to CA2 pyramidal neurons.

Hippocampal area CA2 is emerging as a critical region for memory formation. Excitatory Scaffer collateral (SC) inputs from CA3 do not express activity-dependent plasticity at SC-CA2 synapses, and are governed by a large feed-forward inhibition that prevents them from engaging CA2 pyramidal neurons. However, long-term depression at inhibitory synapses evoked by stimulation of SC inputs highly increases the excitatory/inhibitory balance coming from CA3 and allows the recruitment of CA2 pyramidal neurons. In contrast, distal excitatory inputs in stratum lacunosum moleculare (SLM) can drive action potential firing in CA2 pyramidal neurons and also express a long-term potentiation. However, it is unknown whether stimulation of distal inputs can also evoke plasticity at inhibitory synapses and if so, whether this plasticity can control the strength of excitatory inputs. Here we show that stimulation in SLM evokes a long-term depression at inhibitory synapses. This plasticity strongly increases the excitatory drive of both proximal and distal inputs and allows CA3 to recruit CA2 pyramidal neurons. These data reveal a bi-directional interplay between proximal and distal inputs to CA2 pyramidal neurons that is likely to play an important role in information transfer through the hippocampus.

Galectin-3 expression in hippocampal CA2 following transient forebrain ischemia and its inhibition by hypothermia or antiapoptotic agents.

Recent evidence has suggested that the hippocampal CA2 region plays an important role in the recognition process. We have reported that ischemic damage in the hippocampal CA2 region following transient ischemia is caused by apoptosis, but the underlying mechanisms are still not clear. Galectin-3 is a ß-galactosidase-binding lectin that is important in cell proliferation and apoptotic regulation. We have also reported that galectin-3 was expressed in activated microglia in the CA1 region 96 h after transient ischemia. The aim of this study is to determine the localization and time course of galectin-3 expression in the CA2 region following transient forebrain ischemia. Galectin-3 immunostaining was observed in both interior side of CA1 region and CA2 region in hippocampus 60 h after ischemic insult. At 66 h, galectin-3 was observed in the whole CA1 region adjacent to the CA2 region in the hippocampus. Both galectin-3 expression and neuronal cell death in the CA2 region were significantly inhibited by hypothermia and by apoptosis-inhibiting reagents. These results suggest that galectin-3 in the CA2 region is expressed independent of that in the CA1 region. Protection of the expression of galectin-3 in the CA2 region might contribute toward the survival of CA2 pyramidal neurons.

Effects of long-term treatment with the neuroleptics haloperidol, clozapine and olanzapine on immunoexpression of NMDA receptor subunits NR1, NR2A and NR2B in the rat hippocampus.

BACKGROUND: Antagonists of the N-methyl-d-aspartate receptor (NMDA-R) are associated with symptoms of schizophrenia, leading to the hypothesis that NMDA-R hypofunction leads to the pathogenesis of disease. We evaluated the long-term effect of neuroleptic administration on the NMDA subunits via immunohistochemical analysis. METHODS: Rats received olanzapine, clozapine and haloperidol before evaluation of the expression of the NR1, NR2A and NR2B subunit proteins in the hippocampal areas of the brain, via a densytometric analysis of immunoexpression in the rat hippocampus. RESULTS: All of the neuroleptics examined caused a decrease in the expression of the NR1 subunit, and thus, one can assume that both olanzapine, clozapine and haloperidol decreased the number of NMDA receptors in the CA1 and CA2 areas of the brain. CONCLUSIONS: A decrease in hippocampal glutamatergic signalling after long-term neuroleptic administration may cautiously explain the incomplete effectiveness of these drugs in the therapy of schizophrenia-related cognitive disturbances.

AM841, a covalent cannabinoid ligand, powerfully slows gastrointestinal motility in normal and stressed mice in a peripherally restricted manner.

BACKGROUND AND PURPOSE: Cannabinoid (CB) ligands have been demonstrated to have utility as novel therapeutic agents for the treatment of pain, metabolic conditions and gastrointestinal (GI) disorders. However, many of these ligands are centrally active, which limits their usefulness. Here, we examine a unique novel covalent CB receptor ligand, AM841, to assess its potential for use in physiological and pathophysiological in vivo studies. EXPERIMENTAL APPROACH: The covalent nature of AM841 was determined in vitro using electrophysiological and receptor internalization studies on isolated cultured hippocampal neurons. Mouse models were used for behavioural analysis of analgesia, hypothermia and hypolocomotion. The motility of the small and large intestine was assessed in vivo under normal conditions and after acute stress. The brain penetration of AM841 was also determined. KEY RESULTS: AM841 behaved as an irreversible CB1 receptor agonist in vitro. AM841 potently reduced GI motility through an action on CB1 receptors in the small and large intestine under physiological conditions. AM841 was even more potent under conditions of acute stress and was shown to normalize accelerated GI motility under these conditions. This compound behaved as a peripherally restricted ligand, showing very little brain penetration and no characteristic centrally mediated CB1 receptor-mediated effects (analgesia, hypothermia or hypolocomotion). CONCLUSIONS AND IMPLICATIONS: AM841, a novel peripherally restricted covalent CB1 receptor ligand that was shown to be remarkably potent, represents a new class of potential therapeutic agents for the treatment of functional GI disorders.

Regional upregulation of hippocampal melatonin MT2 receptors by valproic acid: therapeutic implications for Alzheimer's disease.

We have reported that clinically relevant concentrations of valproic acid (VPA) upregulate the G protein-coupled melatonin MT1 receptor in rat C6 glioma cells, and both MT1 and MT2 receptors in the rat hippocampus. The melatonin MT2 receptor is relatively enriched in the hippocampus, where it is thought to be involved in modulating synaptic plasticity and cognitive function. Importantly, a significant decrease in MT2 expression has been observed in the hippocampus of Alzheimer's patients. Therefore, we examined whether the global upregulation of this receptor (and also the MT1) by VPA, observed in earlier RT-PCR and real time PCR studies, could be localized to more discrete hippocampal regions, which are involved in cognitive function. In situ hybridization of rat brain slices, following chronic VPA treatment (3mg/mL or 4mg/mL in drinking water), revealed a significant upregulation of the MT2 receptor mRNA in the CA1, CA2, CA3 and dentate gyrus (DG) regions of the rat hippocampus. In contrast, the MT1 receptor was not detected in the hippocampus by in situ hybridization. The significant induction of melatonin MT2 receptor expression by VPA in hippocampal regions involved in learning, memory and/or neural stem cell proliferation, suggests that a combinatorial therapeutic strategy involving VPA together with melatonin or other MT2 agonists, would be beneficial in neurodegenerative disorders such as Alzheimer's disease.

Tualang honey supplement improves memory performance and hippocampal morphology in stressed ovariectomized rats.

Recently, our research team has reported that Tualang honey was able to improve immediate memory in postmenopausal women comparable with that of estrogen progestin therapy. Therefore the aim of the present study was to examine the effects of Tualang honey supplement on hippocampal morphology and memory performance in ovariectomized (OVX) rats exposed to social instability stress. Female Sprague-Dawley rats were divided into six groups: (i) sham-operated controls, (ii) stressed sham-operated controls, (iii) OVX rats, (iv) stressed OVX rats, (v) stressed OVX rats treated with 17ß-estradiol (E2), and (vi) stressed OVX rats treated with Tualang honey. These rats were subjected to social instability stress procedure followed by novel object recognition (NOR) test. Right brain hemispheres were subjected to Nissl staining. The number and arrangement of pyramidal neurons in regions of CA1, CA2, CA3 and the dentate gyrus (DG) were recorded. Two-way ANOVA analyses showed significant interactions between stress and OVX in both STM and LTM test as well as number of Nissl-positive cells in all hippocampal regions. Both E2 and Tualang honey treatments improved both short-term and long-term memory and enhanced the neuronal proliferation of hippocampal CA2, CA3 and DG regions compared to that of untreated stressed OVX rats.

Platinum drugs and neurotoxicity: effects on intracellular calcium homeostasis.

[Pt(O,O'-acac)(γ-acac)(DMS)] (PtAcacDMS) is a new platinum compound showing low reactivity with nucleobases and specific reactivity with sulfur ligands intracellularly. It induces apoptosis in breast cancer cells, but appears to be less neurotoxic to the developing cerebellum than cisplatin (cisPt). The aim of this study was to assess the neurotoxicity of platinum compounds on calcium homeostasis in the dentate gyrus and Cornu Ammonis regions of the hippocampal formation during rat postnatal development. Two intracellular calcium homeostasis systems were taken for measurement, calbindin, a calcium buffer protein, and a plasma membrane calcium ATPase (PMCA1). The platinum compounds showed different effects on these markers in the two areas. One day after injection (PD11), cisPt decreased calbindin immunoreactivity and PMCA1 labeling in both regions; at PD17, the downregulation of PMCA1 persisted. Instead, PtAcacDMS produced varying effects on calbindin immunoreactivity in the two regions at PD11 and PD17; but in all cases, the changes incurred in calbindin immunoreactivity were counterbalanced by changes produced in PMCA1 expression. In conclusion, PtAcacDMS seems to affect calcium homeostasis in the central nervous system differently than cisPt. Both the platinum compounds act early to alter the calbindin buffering system. However, the most important difference between cisPt and PtAcacDMS is that, in vivo, the latter acts early to stimulate calcium efflux from nerve cells as reflected by its effect on PMCA1. The rapid onset of an activated calcium pump appears to be essential to cope with the excessive intracellular calcium concentration stemming from the downregulation of calbindin which could damage neuron function and morphology.

Vasopressin inhibits LTP in the CA2 mouse hippocampal area.

Growing evidence points to vasopressin (AVP) as a social behavior regulator modulating various memory processes and involved in pathologies such as mood disorders, anxiety and depression. Accordingly, AVP antagonists are actually envisaged as putative treatments. However, the underlying mechanisms are poorly characterized, in particular the influence of AVP on cellular or synaptic activities in limbic brain areas involved in social behavior. In the present study, we investigated AVP action on the synapse between the entorhinal cortex and CA2 hippocampal pyramidal neurons, by using both field potential and whole-cell recordings in mice brain acute slices. Short application (1 min) of AVP transiently reduced the synaptic response, only following induction of long-term potentiation (LTP) by high frequency stimulation (HFS) of afferent fibers. The basal synaptic response, measured in the absence of HFS, was not affected. The Schaffer collateral-CA1 synapse was not affected by AVP, even after LTP, while the Schaffer collateral-CA2 synapse was inhibited. Although investigated only recently, this CA2 hippocampal area appears to have a distinctive circuitry and a peculiar role in controlling episodic memory. Accordingly, AVP action on LTP-increased synaptic responses in this limbic structure may contribute to the role of this neuropeptide in controlling memory and social behavior.

Human intravenous immunoglobulins suppress seizure activities and inhibit the activation of GFAP-positive astrocytes in the hippocampus of picrotoxin-kindled rats.

We previously showed that human intravenous immunoglobulin (IVIG) can lower seizure severity and prolong seizure latency in picrotoxin-kindled rats. The aim of this study was to further characterize the effects of IVIG on seizure activity and investigate its influence on astrocytes in the hippocampus of picrotoxin-kindled rats. A rat kindling model was established by peritoneal injections of picrotoxin for 21 days in Wistar rats. Seventy-five rats were equally divided into five groups: picrotoxin, IVIG pretreatment, IVIG post-treatment, normal saline control, and IVIG control. Seizure severity was evaluated according to a six-stage classification. The number and morphology of glial fibrillary acidic protein (GFAP)-positive astrocytes were studied by immunohistochemistry using the anti-GFAP antibody. The cross-sectional area and grayscale of GFAP-positive astrocytes were also determined. In picrotoxin-kindled rats, pretreatment with IVIG appeared to inhibit full kindling rates, and it significantly reduced the number of GFAP-positive cells in the hippocampus (p < .001). IVIG also significantly (p < .001) attenuated the increase in the cross-sectional area and grayscale of GFAP-positive astrocytes in the hippocampus. Our results suggest that by suppressing the expression of GFAP, IVIGs may reduce seizure activity and inhibit the activation of GFAP-positive astrocytes in picrotoxin-kindled rats.

Reduction of vesicle-associated membrane protein 2 expression leads to a kindling-resistant phenotype in a murine model of epilepsy.

Our previous work has correlated permanent alterations in the rat neurosecretory machinery with epileptogenesis. Such findings highlighted the need for a greater understanding of the molecular mechanisms underlying epilepsy so that novel therapeutic regimens can be designed. To this end, we examined kindling in transgenic mice with a defined reduction of a key element of the neurosecretory machinery: the v-SNARE (vesicle-bound SNAP [soluble NSF attachment protein] receptor), synaptobrevin/vesicle-associated membrane protein 2 (VAMP2). Initial analysis of biochemical markers, which previously displayed kindling-dependent alterations in rat hippocampal synaptosomes, showed similar trends in both wild-type and VAMP2(+/-) mice, demonstrating that kindled rat and mouse models are comparable. This report focuses on the effects that a ~50% reduction of synaptosomal VAMP2 has on the progression of electrical kindling and on glutamate release in hippocampal subregions. Our studies show that epileptogenesis is dramatically attenuated in VAMP2(+/-) mice, requiring both higher current and more stimulations to reach a fully kindled state (two successive Racine stage 5 seizures). Progression through the five identifiable Racine stages was slower and more variable in the VAMP2(+/-) animals compared with the almost linear progression seen in wild-type littermates. Consistent with the expected effects of reducing a major neuronal v-SNARE, glutamate-selective, microelectrode array (MEA) measurements in specific hippocampal subregions of VAMP2(+/-) mice showed significant reductions in potassium-evoked glutamate release. Taken together these studies demonstrate that manipulating the levels of the neurosecretory machinery not only affects neurotransmitter release but also mitigates kindling-induced epileptogenesis.

Caffeine-induced synaptic potentiation in hippocampal CA2 neurons.

Caffeine enhances cognition, but even high non-physiological doses have modest effects on synapses. A(1) adenosine receptors (A(1)Rs) are antagonized by caffeine and are most highly enriched in hippocampal CA2, which has not been studied in this context. We found that physiological doses of caffeine in vivo or A(1)R antagonists in vitro induced robust, long-lasting potentiation of synaptic transmission in rat CA2 without affecting other regions of the hippocampus.