Rat strain differences in seizure frequency and hilar neuron loss after systemic treatment with pilocarpine.

At least 3 months after systemic treatment with pilocarpine to induce status epilepticus, Long-Evans and Sprague-Dawley rats were video-EEG monitored for seizures continuously for 1 month. Rats were then perfused, hippocampi were processed for Nissl staining, and hilar neurons were quantified. Seizure frequency in Long-Evans rats was 1/10th of that in Sprague-Dawley rats, and more variable. Hilar neuron loss was also less severe in Long-Evans rats. However, there was no correlation between hilar neuron loss and seizure frequency in either strain. The low and variable seizure frequency suggests limited usefulness of pilocarpine-treated Long-Evans rats for some epilepsy experiments.

Adaptive spike threshold dynamics associated with sparse spiking of hilar mossy cells are captured by a simple model.

Hilar mossy cells (hMCs) in the dentate gyrus (DG) receive inputs from DG granule cells (GCs), CA3 pyramidal cells and inhibitory interneurons, and provide feedback input to GCs. Behavioural and in vivo recording experiments implicate hMCs in pattern separation, navigation and spatial learning. Our experiments link hMC intrinsic excitability to their synaptically evoked in vivo spiking outputs. We performed electrophysiological recordings from DG neurons and found that hMCs displayed an adaptative spike threshold that increased both in proportion to the intensity of injected currents, and in response to spiking itself, returning to baseline over a long time scale, thereby instantaneously limiting their firing rate responses. The hMC activity is additionally limited by a prominent medium after-hyperpolarizing potential (AHP) generated by small conductance K+ channels. We hypothesize that these intrinsic hMC properties are responsible for their low in vivo firing rates. Our findings extend previous studies that compare hMCs, CA3 pyramidal cells and hilar inhibitory cells and provide novel quantitative data that contrast the intrinsic properties of these cell types. We developed a phenomenological exponential integrate-and-fire model that closely reproduces the hMC adaptive threshold nonlinearities with respect to their threshold dependence on input current intensity, evoked spike latency and long-lasting spike-induced increase in spike threshold. Our robust and computationally efficient model is amenable to incorporation into large network models of the DG that will deepen our understanding of the neural bases of pattern separation, spatial navigation and learning. KEY POINTS: Previous studies have shown that hilar mossy cells (hMCs) are implicated in pattern separation and the formation of spatial memory, but how their intrinsic properties relate to their in vivo spiking patterns is still unknown. Here we show that the hMCs display electrophysiological properties that distinguish them from the other hilar cell types including a highly adaptive spike threshold that decays slowly. The spike-dependent increase in threshold combined with an after-hyperpolarizing potential mediated by a slow K+ conductance is hypothesized to be responsible for the low-firing rate of the hMC observed in vivo. The hMC's features are well captured by a modified stochastic exponential integrate-and-fire model that has the unique feature of a threshold intrinsically dependant on both the stimulus intensity and the spiking history. This computational model will allow future work to study how the hMCs can contribute to spatial memory formation and navigation.

Leydig cell hyperplasia as a cause of virilization in a postmenopausal woman: A case report.

Virilization is a rare condition in postmenopausal women, usually attributed to androgen excess of ovarian or adrenal origin. A 62-year-old woman presented with excessive hair loss of 3 months' duration and was investigated for an endocrine cause of alopecia. The hormonal evaluation revealed increased testosterone but normal levels of androstenedione and dehydroepiandrosterone sulfate, while the results of transvaginal ultrasonography and abdominal computed tomography were unremarkable. Based on these findings, the possibility of an adrenal androgen-secreting tumor was ruled out and suspicion of Leydig cell hyperplasia was raised. A bilateral laparoscopic salpingo-oophorectomy was performed due to the age of the patient and the diagnosis of Leydig cell hyperplasia was confirmed by histopathological examination. The postoperative course of the patient was uneventful and a repeat hormonal evaluation after the operation showed a normalization of androgen levels. In conclusion, Leydig cell hyperplasia should be considered as a likely cause of hyperandrogenism of ovarian origin in women who develop virilization. In postmenopausal women, bilateral oophorectomy will treat the disorder and provide a conclusive diagnosis via histopathological examination.

Disrupted in Schizophrenia 1 Reverse Ectopic Migration of Neural Precursors in Mouse Hilus After Pilocarpine-Induced Status Epilepticus.

Neural precursors in the subgranular zone (SGZ) can be stimulated by status epilepticus (SE) and ectopically migrate to the hilus. These mislocated cells serve as "potential pacemakers" of spontaneous recurrent seizures, and targeting them could potentially reverse the seizure process. Disrupted-in-Schizophrenia 1 (DISC1) regulates hippocampal neurogenesis after seizures both in vitro and in vivo. Our previous study found that DISC1 was colocalized with neural precursors in the hilus after SE. However, its molecular mechanism and pathways contribute to the ectopic migration of neural precursors to the hilus induced by SE awaits exploration. Here, we showed that both Reelin-ApoER2/EphB2 and Reelin-Integrin ß1/Integrin α5 axes may participate in the modulation of neurogenesis after SE. Especially, DISC1, as a protective role, might partly reversed the ectopic progenitor migration via EphB2 pathway. Our findings demonstrated that DISC1 played a protective role in the ectopic migration of neural precursors induced by SE insults and DISC1 could be an attractive new target for the treatment of epilepsy.

Similar Presynaptic Action Potential-Calcium Influx Coupling in Two Types of Large Mossy Fiber Terminals Innervating CA3 Pyramidal Cells and Hilar Mossy Cells.

Morphologically similar axon boutons form synaptic contacts with diverse types of postsynaptic cells. However, it is less known to what extent the local axonal excitability, presynaptic action potentials (APs), and AP-evoked calcium influx contribute to the functional diversity of synapses and neuronal activity. This is particularly interesting in synapses that contact cell types that show only subtle cellular differences but fulfill completely different physiological functions. Here, we tested these questions in two synapses that are formed by rat hippocampal granule cells (GCs) onto hilar mossy cells (MCs) and CA3 pyramidal cells, which albeit share several morphologic and synaptic properties but contribute to distinct physiological functions. We were interested in the deterministic steps of the action potential-calcium ion influx coupling as these complex modules may underlie the functional segregation between and within the two cell types. Our systematic comparison using direct axonal recordings showed that AP shapes, Ca2+ currents and their plasticity are indistinguishable in synapses onto these two cell types. These suggest that the complete module that couples granule cell activity to synaptic release is shared by hilar mossy cells and CA3 pyramidal cells. Thus, our findings present an outstanding example for the modular composition of distinct cell types, by which cells employ different components only for those functions that are deterministic for their specialized functions, while many of their main properties are shared.

Propranolol Administration Modulates Neural Activity in the Hippocampal Hilus During Fear Retrieval.

Altered fear learning is a strong behavioral component of anxiety disorders such as post-traumatic stress disorder (PTSD). Recent efforts have attempted to combine exposure therapies with drugs that target fear memory retrieval and memory reconsolidation, in order to improve treatment efficacy. The noradrenergic (NA) signaling system is of particular interest, due to its role in regulating the stress response and its involvement in fear and learning processes. Importantly, propranolol (P), a non-selective ß-adrenergic antagonist, has shown the potential in decreasing exaggerated fear in both humans and animal models. In a previous study, we utilized an activity-dependent tagging murine model to determine the neural mechanisms by which propranolol attenuates learned fear. We found that propranolol acutely decreased memory trace reactivation specifically in the dorsal dentate gyrus (dDG), but not in CA3 or CA1. Here, we extended our previous study by investigating whether propranolol additionally altered activity in the hilus, a polymorphic layer that consists of neurons, mossy cells, and GABAergic interneurons. We found that propranolol acutely reduced overall hilar activity in both the dorsal and ventral hilus. Moreover, we report that propranolol significantly altered the activity of parvalbumin (PV)+ cells in the ventral (vDG), but not dorsal DG (dDG). Together, these results suggest that a ß-adrenergic blockade may affect the activity of excitatory and inhibitory cell types in the hilar layer of the DG, and that these alterations may contribute to manipulating fear memory traces.

Disrupted in Schizophrenia 1 Regulates Ectopic Neurogenesis in the Mouse Hilus After Pilocarpine-induced Status Epilepticus.

Augmentation of neurogenesis and migration of newly born neurons into ectopic regions like the hilus play critical roles during the pathophysiology of acute kindled seizures. Evidence shows that disrupted in schizophrenia 1 (DISC1) has an influence on adult neurogenesis in the dentate gyrus (DG); however, its role of regulating neurogenesis and mispositioned newborn neurons in the hilus after status epilepticus (SE) remains unknown. Using double immunofluorescence staining, the present study clarifies that DISC1 is co-expressed with nearly all of the neuronal markers, which are characterized by different stages of neuronal development, after pilocarpine-induced SE in mice. This reveals that DISC1 takes part in the modulation of neurogenesis in the hilus post-SE. Unexpectedly, an interesting phenomenon was observed as well. Some glial fibrillary acidic protein (GFAP)-positive cells in the hilus appeared to encircle the DISC1-positive cells, which possibly indicated that DISC1 may participate in the process of neuronal or neural development associated with astrocytes such as phagocytosis, dendritic spine development, synaptic transmission, and developmental and synaptic plasticity.

A rare case of postmenopausal hyperandrogenism due to ovarian hyperthecosis and hilus cell hyperplasia.

Postmenopausal hyperandrogenism is rare, and without consensus on specific investigative indices, diagnosis is challenging. A 77-year-old woman had a three-year history of hirsutism, male-pattern baldness and increased libido alongside elevated androstenedione, total testosterone and free androgen index levels. A magnetic resonance imaging (MRI) scan showed bilateral ovarian lesions, suggesting ovarian hyperthecosis. Histopathology obtained after a laparoscopic bilateral salpingo-oophorectomy confirmed ovarian hyperthecosis and hilus cell hyperplasia. We believe it's the first time they have been reported to occur in combination. The symptoms resolved within a month of surgery. This case highlights the difficulties of diagnosis alongside demonstrating the importance of management by a multidisciplinary team.

Radiofrequency ablation combined with transarterial chemoembolization in treatment of hepatocellular carcinoma adjacent to the second hepatic hilus.

PURPOSE: To explore the efficacy and safety of using radiofrequency ablation (RFA) combined with transarterial chemoembolization (TACE) for treating hepatocellular carcinoma (HCC) adjacent to the second hepatic hilus. METHODS: Between February 2011 and June 2013, 17 patients with HCC underwent combination therapy of TACE and RFA under DSA and CT guidance at our institution. The 17 patients had a total of 23 hepatic tumors, 17 of which were adjacent to the second hepatic hilus. RESULTS: TACE combined with RFA was performed successfully in all 17 patients with no mortalities or major morbidities. During the 1-month follow-up, tumors of 15 patients (88.2%) were completely ablated after one therapy session and 2 patients had detectable tumor residue. During the follow-up time period (range 6-52 months), local tumor progression developed in 1 patient (1/17, 5.9%) and both local tumor progression and new tumors appeared in 1 patient (1/17, 5.9%). Also, new tumors developed in the untreated portions of the liver in 8 patients (8/17, 47.1%). No distant metastasis was found. Of the 17 patients, 6 (35.3%) died due to tumor progression (3/17, 17.6%), liver failure (2/17, 11.8%), or massive hemorrhage of the gastrointestinal tract (1/17, 5.9%). The overall survival rates were 94.1% (16/17), 82.4% (14/17), and 61.8% (11/17) at 12, 18, and 24 months, respectively, and the median survival time was 25 months (95% CI 18-27). CONCLUSION: Treatment using combination of TACE and RFA is an effective and safe therapeutic strategy for treating HCC with tumor(s) adjacent to the second hepatic hilus.

Dietary Choline Protects Against Cognitive Decline After Surgery in Mice.

Perioperative neurocognitive disorders (PNDs) are a common complication following procedures such as orthopedic surgery. Using a mouse model of tibial fracture and repair surgery, we have previously shown an increase in neuroinflammation and hippocampal-dependent cognitive deficits. These changes were ameliorated with the addition of a cholinergic agonist. Here, we sought to examine the effects of a high-choline diet for 3 weeks prior to tibial fracture surgery. We evaluated memory using novel object recognition (NOR) as well as young neurons and glial cell morphology at 1 day and 2 weeks post-surgery. At both time points, tibial fracture impaired NOR performance, and dietary choline rescued these impairments. Astrocytic density and hilar granule cells increased 1 day after tibial fracture, and these increases were partially blunted by dietary choline. An increase in young neurons in the subgranular zone of the dentate gyrus was found 2 weeks after tibial fracture. This increase was partially blunted by choline supplementation. This suggests that shortly after tibial fracture, hippocampal reorganization is a possible mechanism for acute impaired memory. These findings together suggest that non-pharmaceutical approaches, such as pre-surgical dietary intervention with choline, may be able to prevent PNDs.

Direct synaptic excitation between hilar mossy cells revealed with a targeted voltage sensor.

The dentate gyrus not only gates the flow of information into the hippocampus, it also integrates and processes this information. Mossy cells (MCs) are a major type of excitatory neuron strategically located in the hilus of the dentate gyrus where they can contribute to this processing through networks of synapses with inhibitory neurons and dentate granule cells. Some prior work has suggested that MCs can form excitatory synapses with other MCs, but the role of these synapses in the network activity of the dentate gyrus has received little attention. Here, we investigated synaptic inputs to MCs in mouse hippocampal slices using a genetically encoded hybrid voltage sensor (hVOS) targeted to MCs by Cre-lox technology. This enabled optical recording of voltage changes from multiple MCs simultaneously. Stimulating granule cells and CA3 pyramidal cells activated well-established inputs to MCs and elicited synaptic responses as expected. However, the weak blockade of MC responses to granule cell layer stimulation by DCG-IV raised the possibility of another source of excitation. To evaluate synapses between MCs as this source, single MCs were stimulated focally. Stimulation of one MC above its action potential threshold evoked depolarizing responses in neighboring MCs that depended on glutamate receptors. Short latency responses of MCs to other MCs did not depend on release from granule cell axons. However, granule cells did contribute to the longer latency responses of MCs to stimulation of other MCs. Thus, MCs transmit their activity to other MCs both through direct synaptic coupling and through polysynaptic coupling with dentate granule cells. MC-MC synapses can redistribute information entering the dentate gyrus and thus shape and modulate the electrical activity underlying hippocampal functions such as navigation and memory, as well as excessive excitation during seizures.

A rare ovarian hilus cell tumour accompanying bilateral serous cystadenomas: report of a case.

BACKGROUND: Hilus cell tumours is considered an uncommon branch of androgen producing neoplasms that accounts for < 5% of all ovarian tumours. They are mostly benign and have characteristic gross and microscopic features. Here we present the first case of a hilus cell tumour in association with bilateral serous cystadenomas. CASE PRESENTATION: A 65-year-old lady with no symptoms of virilization, presented with postmenopausal dysfunctional uterine bleeding and radiological investigations revealing bilateral ovarian cysts that required a total abdominal hysterectomy with bilateral salpingo-oophorectomy. Gross and microscopic evaluation confirmed the diagnosis of hilus cell tumour associated with bilateral serous cystadenomas. CONCLUSIONS: This was the first case of hilus cell tumour in association with bilateral serous cystadenomas of the ovaries. Although, majority of hilus cell tumours that have been reported in the literature were benign, further studies are required to determine the behavior of the disease.

Subfield-specific effects of chronic mild unpredictable stress on hippocampal astrocytes.

Major depressive disorder (MDD) is a debilitating neuropsychiatric illness affecting over 20% of the population worldwide. Despite its prevalence, our understanding of its pathophysiology is severely limited, thus hampering the development of novel therapeutic strategies. Recent advances have clearly established astrocytes as major players in the pathophysiology, and plausibly pathogenesis, of major depression. In particular, astrocyte density in the hippocampus is severely diminished in MDD patients and correlates strongly with the disease outcome. Moreover, astrocyte densities from different subfields of the hippocampus show varying trends in terms of their correlation to the disease outcome. Given the central role that hippocampus plays in the pathophysiology of depression and in the action of antidepressant drugs, changes in hippocampal astrocyte density and physiology may have a significant effect on behavioral symptoms of MDD. In this study, we used chronic mild unpredictable stress (CMUS) in mice, which induces a depressive-like state, and examined its effects on astrocytes from different subfields of the hippocampus. We used SOX9 and S100ß immunostaining to estimate the number of astrocytes per square millimeter from various hippocampal subfields. Furthermore, using confocal images of fluorescently labeled glial fibrillary acidic protein (GFAP)-immunopositive hippocampal astrocytes, we quantified various morphology-related parameters and performed Sholl analysis. We found that CMUS exerts differential effects on astrocyte cell numbers, ramification, cell radius, surface area, and process width of hippocampal astrocytes from different hippocampal subfields. Taken together, our study reveals that chronic stress does not uniformly affect all hippocampal astrocytes; but exerts its effects differentially on different astrocytic subpopulations within the hippocampus.

Dorsal and ventral mossy cells differ in their axonal projections throughout the dentate gyrus of the mouse hippocampus.

Glutamatergic hilar mossy cells (MCs) have axons that terminate both near and far from their cell body but stay within the DG, making synapses primarily in the molecular layer. The long-range axons are considered the primary projection, and extend throughout the DG ipsilateral to the soma, and project to the contralateral DG. The specificity of MC axons for the inner molecular layer (IML) has been considered to be a key characteristic of the DG. In the present study, we made the surprising finding that dorsal MC axons are an exception to this rule. We used two mouse lines that allow for Cre-dependent viral labeling of MCs and their axons: dopamine receptor D2 (Drd2-Cre) and calcitonin receptor-like receptor (Crlr-Cre). A single viral injection into the dorsal DG to label dorsal MCs resulted in labeling of MC axons in both the IML and middle molecular layer (MML). Interestingly, this broad termination of dorsal MC axons occurred throughout the septotemporal DG. In contrast, long-range axons of ventral MCs terminated in the IML, consistent with the literature. Taken together, these results suggest that dorsal and ventral MCs differ significantly in their axonal projections. Since MC projections in the ML are thought to terminate primarily on GCs, the results suggest a dorsal-ventral difference in MC activation of GCs. The surprising difference in dorsal and ventral MC projections should therefore be considered when evaluating dorsal-ventral differences in DG function.

Bidirectional Regulation of Cognitive and Anxiety-like Behaviors by Dentate Gyrus Mossy Cells in Male and Female Mice.

The dentate gyrus (DG) of the hippocampus is important for cognition and behavior. However, the circuits underlying these functions are unclear. DG mossy cells (MCs) are potentially important because of their excitatory synapses on the primary cell type, granule cells (GCs). However, MCs also activate GABAergic neurons, which inhibit GCs. We used viral delivery of designer receptors exclusively activated by designer drugs (DREADDs) in mice to implement a gain- and loss-of-function study of MCs in diverse behaviors. Using this approach, manipulations of MCs could bidirectionally regulate behavior. The results suggest that inhibiting MCs can reduce anxiety-like behavior and improve cognitive performance. However, not all cognitive or anxiety-related behaviors were influenced, suggesting specific roles of MCs in some, but not all, types of cognition and anxiety. Notably, several behaviors showed sex-specific effects, with females often showing more pronounced effects than the males. We also used the immediate early gene c-Fos to address whether DREADDs bidirectionally regulated MC or GC activity. We confirmed excitatory DREADDs increased MC c-Fos. However, there was no change in GC c-Fos, consistent with MC activation leading to GABAergic inhibition of GCs. In contrast, inhibitory DREADDs led to a large increase in GC c-Fos, consistent with a reduction in MC excitation of GABAergic neurons, and reduced inhibition of GCs. Together, these results suggest that MCs regulate anxiety and cognition in specific ways. We also raise the possibility that cognitive performance may be improved by reducing anxiety.SIGNIFICANCE STATEMENT The dentate gyrus (DG) has many important cognitive roles as well as being associated with affective behavior. This study addressed how a glutamatergic DG cell type called mossy cells (MCs) contributes to diverse behaviors, which is timely because it is known that MCs regulate the activity of the primary DG cell type, granule cells (GCs), but how MC activity influences behavior is unclear. We show, surprisingly, that activating MCs can lead to adverse behavioral outcomes, and inhibiting MCs have an opposite effect. Importantly, the results appeared to be task-dependent and showed that testing both sexes was important. Additional experiments indicated what MC and GC circuitry was involved. Together, the results suggest how MCs influence behaviors that involve the DG.

Mossy Cells in the Dorsal and Ventral Dentate Gyrus Differ in Their Patterns of Axonal Projections.

Mossy cells (MCs) of the dentate gyrus (DG) are a major group of excitatory hilar neurons that are important for regulating activity of dentate granule cells. MCs are particularly intriguing because of their extensive longitudinal connections within the DG. It has generally been assumed that MCs in the dorsal and ventral DG have similar patterns of termination in the inner one-third of the dentate molecular layer. Here, we demonstrate that axonal projections of MCs in these two regions are considerably different. MCs in dorsal and ventral regions were labeled selectively with Cre-dependent eYFP or mCherry, using two transgenic mouse lines (including both sexes) that express Cre-recombinase in MCs. At four to six weeks following unilateral labeling of MCs in the ventral DG, a dense band of fibers was present in the inner one-fourth of the molecular layer and extended bilaterally throughout the rostral-caudal extent of the DG, replicating the expected distribution of MC axons. In contrast, following labeling of MCs in the dorsal DG, the projections were more diffusely distributed. At the level of transfection, fibers were present in the inner molecular layer, but they progressively expanded into the middle molecular layer and, most ventrally, formed a distinct band in this region. Optical stimulation of these caudal fibers expressing ChR2 demonstrated robust EPSCs in ipsilateral granule cells and enhanced the effects of perforant path stimulation in the ventral DG. These findings suggest that MCs in the dorsal and ventral DG differ in the distribution of their axonal projections and possibly their function.SIGNIFICANCE STATEMENT Mossy cells (MCs), a major cell type in the hilus of the dentate gyrus (DG), are unique in providing extensive longitudinal and commissural projections throughout the DG. Although it has been assumed that all MCs have similar patterns of termination in the inner molecular layer of the DG, we discovered that the axonal projections of dorsal and ventral MCs differ. While ventral MC projections exhibit the classical pattern, with dense innervation in the inner molecular layer, dorsal MCs have a more diffuse distribution and expand into the middle molecular layer where they overlap and interact with innervation from the perforant path. These distinct locations and patterns of axonal projections suggest that dorsal and ventral MCs may have different functional roles.

Melatonin Rescues the Dendrite Collapse Induced by the Pro-Oxidant Toxin Okadaic Acid in Organotypic Cultures of Rat Hilar Hippocampus.

The pro-oxidant compound okadaic acid (OKA) mimics alterations found in Alzheimer's disease (AD) as oxidative stress and tau hyperphosphorylation, leading to neurodegeneration and cognitive decline. Although loss of dendrite complexity occurs in AD, the study of this post-synaptic domain in chemical-induced models remains unexplored. Moreover, there is a growing expectation for therapeutic adjuvants to counteract these brain dysfunctions. Melatonin, a free-radical scavenger, inhibits tau hyperphosphorylation, modulates phosphatases, and strengthens dendritic arbors. Thus, we determined if OKA alters the dendritic arbors of hilar hippocampal neurons and whether melatonin prevents, counteracts, or reverses these damages. Rat organotypic cultures were incubated with vehicle, OKA, melatonin, and combined treatments with melatonin either before, simultaneously, or after OKA. DNA breaks were assessed by TUNEL assay and nuclei were counterstained with DAPI. Additionally, MAP2 was immunostained to assess the dendritic arbor properties by the Sholl method. In hippocampal hilus, OKA increased DNA fragmentation and reduced the number of MAP2(+) cells, whereas melatonin protected against oxidation and apoptosis. Additionally, OKA decreased the dendritic arbor complexity and melatonin not only counteracted, but also prevented and reversed the dendritic arbor retraction, highlighting its role in post-synaptic domain integrity preservation against neurodegenerative events in hippocampal neurons.

Constitutive accessibility of circulating proteins to hippocampal neurons in physiologically normal rats.

INTRODUCTION: Although the hippocampus (HIP) is thought impermeable to blood-borne proteins because of the integrity of the blood-brain barrier (BBB), it was recently suggested to be susceptible to hydrophilic hormones. The present study determined the accessibility of blood-borne signal molecules such as hormones to hippocampal neurons in physiologically normal rats. METHODS: As a probe for accessibility, Evans blue dye (EB) that rapidly binds to albumin (Alb), which is impermeable to the BBB, was injected intravenously. To increase the vascular permeability of the BBB, a daily single administration of angiotensin II (Ang II) was applied intravenously for seven consecutive days. RESULTS: Fifteen minutes after the injection of EB, histological observation revealed that a number of neurons had entrapped and accumulated EB into their cell bodies in the hippocampal dentate gyrus in all rats. Of these, relatively large oval neurons (>15 µm) in the hilus and molecular layer showed parvalbumin immunopositivity, indicating they are GABAergic interneurons. The population of EB-accumulating neurons (approximately 10 µm) were localized in the inner margin of the granule cell layer, suggesting they were granule cells. However, the number of EB-positive neurons did not change in rats treated with Ang II compared with vehicle injection. CONCLUSIONS: These findings suggest an intriguing possibility that blood-derived proteins such as hormones have access to hippocampal neurons constitutively in the absence of stimuli that increase the vascular permeability of the BBB in a physiologically normal state.

An Excitatory and Epileptogenic Effect of Dentate Gyrus Mossy Cells in a Mouse Model of Epilepsy.

The sparse activity of hippocampal dentate gyrus (DG) granule cells (GCs) is thought to be critical for cognition and behavior, whereas excessive DG activity may contribute to disorders such as temporal lobe epilepsy (TLE). Glutamatergic mossy cells (MCs) of the DG are potentially critical to normal and pathological functions of the DG because they can regulate GC activity through innervation of GCs or indirectly through GABAergic neurons. Here, we test the hypothesis that MC excitation of GCs is normally weak, but under pathological conditions, MC excitation of GCs is dramatically strengthened. We show that selectively inhibiting MCs during severe seizures reduced manifestations of those seizures, hippocampal injury, and chronic epilepsy. In contrast, selectively activating MCs was pro-convulsant. Mechanistic in vitro studies using optogenetics further demonstrated the unanticipated ability of MC axons to excite GCs under pathological conditions. These results demonstrate an excitatory and epileptogenic effect of MCs in the DG.