Large-Scale Multi-Omic Approaches and Atlas-Based Profiling for Cellular, Molecular, and Functional Specificity, Heterogeneity, and Diversity in the Endocannabinoid System

The endocannabinoid system (ECS) is a widely-recognized lipid messenger system involved in many aspects of our our lives in health and diseases [...].

Space and Time Coherent Mapping for Subcellular Resolution of Imaging Mass Spectrometry

Space and time coherent mapping (STCM) is a technology developed in our laboratory for improved matrix-assisted laser desorption ionization (MALDI) time of flight (TOF) imaging mass spectrometry (IMS). STCM excels in high spatial resolutions, which probe-based scanning methods cannot attain in conventional MALDI IMS. By replacing a scanning probe with a large field laser beam, focusing ion optics, and position-sensitive detectors, STCM tracks the entire flight trajectories of individual ions throughout the ionization process and visualizes the ionization site on the sample surface with a subcellular scale of precision and a substantially short acquisition time. Results obtained in thinly sectioned leech segmental ganglia and epididymis demonstrate that STCM IMS is highly suited for (1) imaging bioactive lipid messengers such as endocannabinoids and the mediators of neuronal activities in situ with spatial resolution sufficient to detail subcellular localization, (2) integrating resultant images in mass spectrometry to optically defined cell anatomy, and (3) assembling a stack of ion maps derived from mass spectra for cluster analysis. We propose that STCM IMS is the choice over a probe-based scanning mass spectrometer for high-resolution single-cell molecular imaging.

Ghrelin-O-acyltransferase (GOAT) acylates ghrelin in the hippocampus

Ghrelin is an appetite-stimulating peptide hormone and produced in the stomach. Serine 3 on ghrelin must be acylated by the lipid transferase known as Ghrelin-O-acyltransferase (GOAT) in order for the peptide to become physiologically-active and bind to the cognate receptor, growth hormone secretagogue receptor type 1a (GHSR1a). GHSR1a has been known to be expressed in the feeding center of the hypothalamus. However, the interest in GHSR1a increased dramatically among researchers in various biomedical fields when GHSR1a mRNA was found wide-spread in the brain including the hippocampus. Current understanding is that GHSR1a has multifaceted functions beyond the regulation of metabolism. In the blood, a nonacylated form of ghrelin (des-acyl ghrelin) exists in far greater amounts. Des-acyl ghrelin can cross the blood-brain barrier (BBB), but it cannot bind to GHSR1a in the brain. Thus, the identification of the source for acyl ghrelin in the brain became the critical and urgent quest. Here, we discuss the presence of GOAT in the hippocampus and its ability to acylate ghrelin locally within the hippocampus. We will show that GOAT is localized specifically at the base of the dentate granule cell layer in the rat and wild-type mouse, but not in the GHSR1a knockout mouse. This evidence points the possibility that the expression of GHSR1a may be a prerequisite for the synthesis of GOAT in the hippocampus. We will also show that: (1) the activation of GHSR1a by acyl ghrelin upregulates the cAMP and CREB phosphorylation, (2) amplifies the NMDA receptor-mediated synaptic transmission by phosphorylating GluN1 subunit at Ser896/897, and (3) activates Fyn kinase and induces GluN2B phosphorylation at Tyr1336. In summary, GOAT is a critical molecule that acts as the master switch in the initiation of ghrelin-induced hippocampal synapse and neuron plasticity.

Endogenous ghrelin-O-acyltransferase (GOAT) acylates local ghrelin in the hippocampus

Ghrelin is an appetite-stimulating peptide. Serine 3 on ghrelin must be acylated by octanoate via the enzyme ghrelin-O-acyltransferase (GOAT) for the peptide to bind and activate the cognate receptor, growth hormone secretagogue receptor type 1a (GHSR1a). Interest in GHSR1a increased dramatically when GHSR1a mRNA was demonstrated to be widespread in the brain, including the cortex and hippocampus, indicating that it has multifaceted functions beyond the regulation of metabolism. However, the source of octanoylated ghrelin for GHSR1a in the brain, outside of the hypothalamus, is not well understood. Here, we report the presence of GOAT and its ability to acylate non-octanoylated ghrelin in the hippocampus. GOAT immunoreactivity is aggregated at the base of the dentate granule cell layer in the rat and wild-type mouse. This immunoreactivity was not affected by the pharmacological inhibition of GHSR1a or the metabolic state-dependent fluctuation of systemic ghrelin levels. However, it was absent in the GHSR1a knockout mouse hippocampus, pointing the possibility that the expression of GHSR1a may be a prerequisite for the production of GOAT. Application of fluorescein isothiocyanate (FITC)-conjugated non-octanoylated ghrelin in live hippocampal slice culture (but not in fixed culture or in the presence of GOAT inhibitors) mimicked the binding profile of FITC-conjugated octanoylated ghrelin, suggesting that extracellularly applied non-octanoylated ghrelin was acylated by endogenous GOAT in the live hippocampus while GOAT being mobilized out of neurons. Our results will advance the understanding for the role of endogenous GOAT in the hippocampus and facilitate the search for the source of ghrelin that is intrinsic to the brain.

Ghrelin upregulates the phosphorylation of the GluN2B subunit of the NMDA receptor by activating GHSR1a and Fyn in the rat hippocampus

Ghrelin and its receptor GHSR1a have been shown to exert numerous physiological functions in the brain, in addition to the well-established orexigenic role in the hypothalamus. Earlier work indicated that ghrelin stimulated the phosphorylation of the GluN1 subunit of the NMDA receptor (NMDAR) and enhanced synaptic transmission in the hippocampus. In the present study, we report that the exogenous application of ghrelin increased GluN2B phosphorylation. This increase was independent of GluN2B subunit activity or NMDAR channel activity. However, it depended on the activation of GHSR1a and Fyn as it was blocked by D-Lys3-GHRP-6 and PP2, respectively. Inhibitors for G-protein-regulated second messengers, such as Rp-cAMP, H89, TBB, ryanodine, and thapsigargin, unexpectedly enhanced GluN2B phosphorylation, suggesting that cAMP, PKA, casein kinase II, and cytosolic calcium signaling may oppose to the effect of ghrelin on the phosphorylation of GluN2B. Our findings suggest that 1) GluN2B is likely a molecular target of ghrelin and GHSR1a-driven signaling cascades, and 2) the ghrelin-mediated phosphorylation of GluN2B depends on Fyn activation under complex negative regulation by other second messengers.

Ghrelin receptor activity amplifies hippocampal N-methyl-d-aspartate receptor-mediated postsynaptic currents and increases phosphorylation of the GluN1 subunit at Ser896 and Ser897

Although ghrelin and its cognate receptor growth hormone secretagogue receptor (GHSR1a) are highly localized in the hypothalamic nuclei for the regulation of metabolic states and feeding, GHSR1a is also highly localized in the hippocampus, suggesting its involvement in extra-hypothalamic functions. Indeed, exogenous application of ghrelin has been reported to improve hippocampal learning and memory. However, the underlying mechanism of ghrelin regulation of hippocampal functions is poorly understood. Here, we report ghrelin-promoted phosphorylation of GluN1 and amplified N-methyl-d-aspartate receptor (NMDAR)-mediated excitatory postsynaptic currents in the CA1 pyramidal cells of the hippocampus in slice preparations. The ghrelin-induced responses were sensitive to a GHSR1a antagonist and inverse agonist, and were absent in GHSR1a homozygous knock-out mice. These results indicated that activation of GHSR1a was critical in the ghrelin-induced enhancement of the NMDAR function. Interestingly, heterozygous mouse hippocampi were also insensitive to ghrelin treatment, suggesting that a slight reduction in the availability of GHSR1a may be sufficient to negate the effect of ghrelin on GluN1 phosphorylation and NMDAR channel activities. In addition, NMDAR-mediated spike currents, which are of dendritic origin, were blocked by the GHSR1a antagonist, suggesting the presence of GHSR1a on the pyramidal cell dendrites in physical proximity to NMDAR. Together with our findings on the localization of GHSR1a in the CA1 region of the hippocampus, which was shown by fluorescent ghrelin binding, immunoreactivity, and enhanced green fluorescent protein reporter gene expression, we conclude that the activation of GHSR1a favours rapid modulation of the NMDAR-mediated glutamatergic synaptic transmission by phosphorylating GluN1 in the hippocampus.

Ghrelin promotes reorganization of dendritic spines in cultured rat hippocampal slices

Recent evidence suggests ghrelin may up-regulate the number of spine synapses. However, it is not completely understood whether an increased number of synapses are expressed on existing spines or accommodated in newly generated spines. We examined if ghrelin might have promoted the generation of new dendritic spines. Localization of polymerized actin (F-actin), highly expressed in dendritic spines, was assayed using phalloidin, a mushroom toxin that has a high affinity to F-actin. Alexa 488-conjugated phalloidin was visualized and relative changes in fluorescing puncta were quantified using a confocal microscope. Ghrelin was applied to cultured hippocampal slices for either 60 min or 23 h. Ghrelin increased the phalloidin fluorescent signals. The antagonist of the ghrelin receptor, D-Lys3-GHSR-6, blocked the ghrelin's effect of increasing the phalloidin signal, suggesting that the ghrelin's effect was mediated by the ghrelin receptor (GHSR1a). The ghrelin-mediated increase in phalloidin signals remained elevated while ghrelin was present in the culture media for 23 h. However, removal of ghrelin from culture media restored the phalloidin signal to control level. Our results suggest ghrelin may have a stimulating effect on the generation or remodeling of dendritic spines, and the spine change persists in the presence of ghrelin. The serum ghrelin level is high when the stomach is empty, and the ghrelin level remains high until metabolic demands are fulfilled. Thus, ghrelin may be involved in food-related and appetite-related learning in the hippocampus.

Ghrelin-induced activation of cAMP signal transduction and its negative regulation by endocannabinoids in the hippocampus

Increasing evidence indicates that the gut peptide ghrelin facilitates learning behavior and memory tasks. The present study demonstrates a cellular signaling mechanism of ghrelin in the hippocampus. Ghrelin stimulated CREB (cAMP response-element binding protein) through the activation of cAMP, protein kinase A (PKA), and PKA-dependent phosphorylation of NR1 subunit of the NMDA receptor. Ghrelin increased phalloidin-binding to F-actin suggesting CREB-induced gene expression might include reorganization of cytoskeletal proteins. The effect was blocked by the antagonist of the ghrelin receptor in spite of the receptor's primary coupling to Gq proteins. We also discovered inhibitory effect of endocannabinoids on ghrelin-induced NR1 phosphorylation and CREB activity. 2-arachidonoylglycerol (2-AG) exerted its inhibitory effect in the Type 1 cannabinoid receptor (CB1R)-dependent manner, while anandamide's inhibitory effect persisted in the presence of antagonists of CB1R and the vanilloid receptor, suggesting that anandamide might directly inhibit NMDA receptor/channels. Our findings may explain how ghrelin and endocannabinoids regulate hippocampal appetitive learning and plasticity.

Time-dependent induction of CREB phosphorylation in the hippocampus by the endogenous cannabinoid

The involvement of the endogenous cannabinoid system has been implicated in the rewarding actions of several drugs of abuse. Recent evidence indicates that the transcription factor CREB (cAMP response element-binding protein) may be an important biochemical substrate for behavioral plasticity that has been associated with the chronic administration of drugs of abuse and addiction. Increased CREB activity was reported as a chronic effect of drugs of abuse in the neurons of the nucleus accumbens, a brain reward region that expresses high-density levels in the CB1 cannabinoid receptors. However, little is known whether a similar change occurs in the hippocampus, a region of the brain that also expresses high-density levels of the CB1 cannabinoid receptors and has intimate synaptic connections with the brain's reward regions. The present study revealed that CREB activities were present in the hippocampal neurons of cultured slice preparations in response to acute and chronic applications of endogenous cannabinoid, anandamide and R(+)-methanandamide (a non-hydrolyzing form of anandamide). When administered acutely at a dose effective for inducing self-administration in vivo, anandamide and R(+)-methanandamide stimulated the expression of pCREB in our hippocampal slice culture. Interestingly, a sub-threshold dose of R(+)-methanandamide, which was not effective in producing acute changes in the CREB activity, was also found to effectively increase pCREB when administered chronically for 10 days. These increases were blocked by the antagonist of the CB1 cannabinoid receptor. Present findings demonstrate: (1) the hippocampus is vulnerable to the direct chemical effect of anandamide and R(+)-methanandamide in isolation of synaptic influences from the midbrain reward neurons, and (2) the effect of R(+)-methanandamide is cumulative as evidenced by the sustained elevation of CREB activities in response to a chronic dosage that is too low and thus fails to exert any acute effect. The ability of hippocampal neurons to integrate a time-dependent effect on the endogenous cannabinoid signaling may be a key function of plasticity as related to the induction and maintenance of maladaptive learning and memory that underlies both cue-induced cravings as well as relapses in drug-seeking.

Metabolic Demand Stimulates CREB Signaling in the Limbic Cortex: Implication for the Induction of Hippocampal Synaptic Plasticity by Intrinsic Stimulus for Survival

Caloric restriction by fasting has been implicated to facilitate synaptic plasticity and promote contextual learning. However, cellular and molecular mechanisms underlying the effect of fasting on memory consolidation are not completely understood. We hypothesized that fasting-induced enhancement of synaptic plasticity was mediated by the increased signaling mediated by CREB (cAMP response element binding protein), an important nuclear protein and the transcription factor that is involved in the consolidation of memories in the hippocampus. In the in vivo rat model of 18 h fasting, the expression of phosphorylated CREB (pCREB) was examined using anti-phospho-CREB (Ser133) in cardially-perfused and cryo-sectioned rat brain specimens. When compared with control animals, the hippocampus exhibited up to a twofold of increase in pCREB expression in fasted animals. The piriform cortex, the entorhinal cortex, and the cortico-amygdala transitional zone also significantly increased immunoreactivities to pCREB. In contrast, the amygdala did not show any change in the magnitude of pCREB expression in response to fasting. The arcuate nucleus in the medial hypothalamus, which was previously reported to up-regulate CREB phosphorylation during fasting of up to 48 h, was also strongly immunoreactive and provided a positive control in the present study. Our findings demonstrate a metabolic demand not only stimulates cAMP-dependent signaling cascades in the hypothalamus, but also signals to various limbic brain regions including the hippocampus by activating the CREB signaling mechanism. The hippocampus is a primary brain structure for learning and memory. It receives hypothalamic and arcuate projections directly from the fornix. The hippocampus is also situated centrally for functional interactions with other limbic cortexes by establishing reciprocal synaptic connections. We suggest that hippocampal neurons and those in the surrounding limbic cortexes are intimately involved in the metabolism-dependent plasticity, which may be essential and necessary for successful achievement of adaptive appetitive behavior.

Homeostatic and stimulus-induced coupling of the L-type Ca2+ channel to the ryanodine receptor in the hippocampal neuron in slices

Activity-dependent increase in cytosolic calcium ([Ca(2+)](i)) is a prerequisite for many neuronal functions. We previously reported a strong direct depolarization, independent of glutamate receptors, effectively caused a release of Ca(2+) from ryanodine-sensitive stores and induced the synthesis of endogenous cannabinoids (eCBs) and eCB-mediated responses. However, the cellular mechanism that initiated the depolarization-induced Ca(2+)-release is not completely understood. In the present study, we optically recorded [Ca(2+)](i) from CA1 pyramidal neurons in the hippocampal slice and directly monitored miniature Ca(2+) activities and depolarization-induced Ca(2+) signals in order to determine the source(s) and properties of [Ca(2+)](i)-dynamics that could lead to a release of Ca(2+) from the ryanodine receptor. In the absence of depolarizing stimuli, spontaneously occurring miniature Ca(2+) events were detected from a group of hippocampal neurons. This miniature Ca(2+) event persisted in the nominal Ca(2+)-containing artificial cerebrospinal fluid (ACSF), and increased in frequency in response to the bath-application of caffeine and KCl. In contrast, nimodipine, the antagonist of the L-type Ca(2+) channel (LTCC), a high concentration of ryanodine, the antagonist of the ryanodine receptor (RyR), and thapsigargin (TG) reduced the occurrence of the miniature Ca(2+) events. When a brief puff-application of KCl was given locally to the soma of individual neurons in the presence of glutamate receptor antagonists, these neurons generated a transient increase in the [Ca(2+)](i) in the dendrosomal region. This [Ca(2+)](i)-transient was sensitive to nimodipine, TG, and ryanodine suggesting that the [Ca(2+)](i)-transient was caused primarily by the LTCC-mediated Ca(2+)-influx and a release of Ca(2+) from RyR. We observed little contribution from N- or P/Q-type Ca(2+) channels. The coupling between LTCC and RyR was direct and independent of synaptic activities. Immunohistochemical study revealed a cellular localization of LTCC and RyR in a juxtaposed configuration in the proximal dendrites and soma. We conclude in the hippocampal CA1 neuron that: (1) homeostatic fluctuation of the resting membrane potential may be sufficient to initiate functional coupling between LTCC and RyR; (2) the juxtaposed localization of LTCC and RyR has anatomical advantage of synchronizing a Ca(2+)-release from RyR upon the opening of LTCC; and (3) the synchronized Ca(2+)-release from RyR occurs immediately after the activation of LTCC and determines the peak amplitude of depolarization-induced global increase in dendrosomal [Ca(2+)](i).

Ryanodine Receptor Regulates Endogenous Cannabinoid Mobilization in the Hippocampus

Endogenous cannabinoids (eCBs) are produced and mobilized in a cytosolic calcium ([Ca2+]i)–dependent manner, and they regulate excitatory and inhibitory neurotransmitter release by acting as retrograde messengers. An indirect but real-time bioassay for this process on GABAergic transmission is DSI (depolarization-induced suppression of inhibition). The magnitude of DSI correlates linearly with depolarization-induced increase of [Ca2+]ithat is thought to be initiated by Ca2+influx through voltage-gated Ca2+channels. However, the identity of Ca2+sources involved in eCB mobilization in DSI remains undetermined. Here we show that, in CA1 pyramidal cells, DSI-inducing depolarizing voltage steps caused Ca2+-induced Ca2+release (CICR) by activating the ryanodine receptor (RyR) Ca2+-release channel. CICR was reduced, and the remaining increase in [Ca2+]iwas less effective in generating DSI, when the RyR antagonists, ryanodine or ruthenium red, were applied intracellularly, or the Ca2+stores were depleted by the Ca2+-ATPase inhibitors, cyclopiazonic acid or thapsigargin. The CICR-dependent effects were most prominent in cultured or immature acute slices, but were also detectable in slices from adult tissue. Thus we suggest that voltage-gated Ca2+entry raises local [Ca2+]isufficiently to activate nearby RyRs and that the resulting CICR plays a critical role in initiating eCB mobilization. RyR may be a key molecule for the depolarization-induced production of eCBs that inhibit GABA release in the hippocampus.

Electrophysiological and morphological characterization of dentate astrocytes in the hippocampus

We studied electrophysiological and morphological properties of astrocytes in the dentate gyrus of the rat hippocampus in slices. Intracellular application of Lucifer yellow revealed two types of morphology: one with a long process extruding from the cell body, and the other with numerous short processes surrounding the cell body. Their electrophysiological properties were either passive, that is, no detectable voltage-dependent conductance, or complex, with Na+/K+ currents similar to those reported in the Ammon's horn astrocytes. We did not find any morphological correlate to the types of electrophysiological profile or dye coupling. Chelation of cytoplasmic calcium ([Ca2+]i) by BAPTA increased the incidence of detecting a low Na+) conductance and transient outward K+ currents. However, an inwardly rectifying K+ current (Kir), a hallmark of differentiated CA1/3 astrocytes, was not a representative K+-current in the complex dentate astrocytes, suggesting that these astrocytes could retain an immature form of K-currents. Dentate astrocytes may possess a distinct current profile that is different from those in CA1/3 Ammon's horn.

Retrograde endocannabinoid regulation of GABAergic inhibition in the rat dentate gyrus granule cell

The dentate gyrus is a key input gateway for the hippocampus, and dentate function is potently regulated by GABAergic inhibition. GABAergic inhibition is plastic and modulated by many factors. Cytoplasmic calcium ([Ca(+)](i)) is one of these factors, and its elevation inhibits GABA-mediated transmission in the hippocampus including the dentate gyrus granule cells (DGCs). We examined whether the [Ca(+)](i)-dependent decrease of GABA(A) receptor-mediated inhibitory postsynaptic current (IPSC) is explained by the retrograde suppression of GABA release caused by the depolarization-induced elevation of [Ca(+)](i) in DGCs (DSI: depolarization-induced suppression of inhibition). Repeated brief depolarizations or a single long depolarization inhibited spontaneous IPSCs with amplitudes over 25 pA for up to a minute, and reduced the amplitude of IPSCs evoked by direct stimulation in the molecular layer, suggesting that DGCs are susceptible to DSI. The magnitude of DSI correlated linearly with the duration of depolarization, and so did the increase of [Ca(+)](i). DSI was blocked by intrapipette application of BAPTA. In addition, bath application of thapsigargin and ryanodine, and intrapipette application of ryanodine and ruthenium red reduced the [Ca(+)](i) increase caused by the DSI-inducing depolarization, and substantially reduced the magnitude of DSI. Finally, the cannabinoid receptor agonists, CP55,942 and WIN55,212-2, mimicked DSI and prevented further IPSC reduction by DSI. DSI was blocked by the antagonist, SR141716A. We conclude that GABAergic inhibition in DGCs is subject to endogenous cannabinoid (eCB)-mediated retrograde regulation, and this process involves a depolarization-initiated release of Ca(+) from ryanodine-sensitive stores. Our findings suggest eCBs probably have physiological functions in the regulation of GABAergic plasticity in the dentate gyrus.

N-methyl-D-aspartic acid-induced and Ca-dependent neuronal swelling and its retardation by brain-derived neurotrophic factor in the epileptic hippocampus

Dentate granule cell (DGC) swelling was studied by imaging changes in light transmittance from hippocampal slices in the rat pilocarpine model of epilepsy and human epileptic specimens. Brief bath-application of N-methyl-D-aspartic acid (NMDA) induced swelling in the control rat DGC (physiological swelling). Physiological swelling was short-lasting, and rapidly recovered upon removal of NMDA. In contrast, the swelling induced in the pilocarpine-treated rat hippocampus and human epileptic hippocampus (epileptic swelling) was long-lasting, and often recovered slowly over an hour. Both types of swelling were blocked by the NMDA receptor (NMDAR) antagonist, D-APV, suggesting that they shared the same induction mechanism. However, the swellings differed in their sensitivity to a calcium chelator, 1.2-bis(2-aminophenoxy)ethane-N,N,N,N-tetra-acetate (BAPTA), and an endoplasmic reticulum (ER) Ca2+-ATPase inhibitor, thapsigargin (TG). BAPTA and TG affected only epileptic swelling, and physiological swelling was spared. This suggested that the NMDAR-induced epileptic swelling might involve an additional mechanism for its maintenance, likely recruiting ER Ca2+ stores. Brain-derived neurotrophic factor (BDNF) slightly attenuated physiological swelling, and blocked epileptic swelling. The present study suggests a functional link between the activation of NMDAR and a release of Ca2+ from internal stores during the induction of epileptic swelling, and a neuroprotective role of BDNF on the NMDAR-induced swelling in the epileptic hippocampus.

Activation of muscarinic acetylcholine receptors enhances the release of endogenous cannabinoids in the hippocampus

Endogenous cannabinoids (endocannabinoids) are endogenous compounds that resemble the active ingredient of marijuana and activate the cannabinoid receptor in the brain. They mediate retrograde signaling from principal cells to both inhibitory ["depolarization-induced suppression of inhibition" (DSI)] and excitatory ("depolarization-induced suppression of excitation") afferent fibers. Transient endocannabinoid release is triggered by voltage-dependent Ca(2+) influx and is upregulated by group I metabotropic glutamate receptor activation. Here we show that muscarinic acetylcholine receptor (mAChR) activation also enhances transient endocannabinoid release (DSI) and induces persistent release. Inhibitory synapses in the rat hippocampal CA1 region of acute slices were studied using whole-cell patch-clamp techniques. We found that low concentrations (0.2-0.5 microm) of carbachol (CCh) enhanced DSI without affecting basal evoked IPSCs (eIPSCs) by activating mAChRs on postsynaptic cells. Higher concentrations of CCh (> or =1 microm) enhanced DSI and also persistently depressed basal eIPSCs, mainly by releasing endocannabinoids. Persistent CCh-induced endocannabinoid release did not require an increase in [Ca2+]i but was dependent on G-proteins. Although they were independent at the receptor level, muscarinic and glutamatergic mechanisms of endocannabinoid release shared intracellular machinery. Replication of the effects of CCh by blocking acetylcholinesterase with eserine suggests that mAChR-mediated endocannabinoid release is physiologically relevant. This study reveals a new role of the muscarinic cholinergic system in mammalian brain.

Architectural characteristics of dominant leg muscles in junior soccer players

The preferential use of dominant over non-dominant limbs produces muscle hypertrophy in the dominant limb. The purpose of this study was to investigate the architectural characteristics of the muscle that are associated with dominant leg use in junior soccer players. Fascicle length, pennation angle and muscle thickness of the medial gastrocnemius (MG) were measured by B-mode ultrasound in 26 junior soccer players [mean (SD) age: 16.5 (0.6) years] and 20 control college students [age: 18.5 (0.5) years]. Lower leg circumference and MG muscle thickness were significantly (P < 0.05) greater in the soccer players than in the controls. The percent difference (dominant minus non-dominant legs) in muscle thickness and fascicle length were significantly (P < 0.01) larger in the soccer players than in the controls, but the percent difference in pennation angle was similar between groups. The difference (dominant leg minus non-dominant leg) in muscle thickness was significantly correlated (r = 0.55; P < 0.05) with the difference in muscle fascicle length in the soccer players, but not in the controls (r = 0.18). In conclusion, the preferential use of one limb over another, as seen in junior soccer players, results in a greater difference in muscle thickness between the dominant and non-dominant legs. This difference in muscle size was associated with longer fascicle lengths of the dominant leg. Thus, it appears possible that fascicle length may be further influenced by physical training in dominant legs.

Altered pattern of light transmittance and resistance to AMPA-induced swelling in the dentate gyrus of the epileptic hippocampus

Glutamate receptor-mediated changes in light transmittance were imaged in the dentate gyri of the epileptic hippocampi, taken from patients with temporal lobe epilepsy and the rat pilocarpine model, to investigate epilepsy-associated alterations in activity-induced cell swelling. A static pattern of light transmittance corresponded to the layered structure of dentate gyrus and reflected epilepsy-associated alterations. Hypoosmotic stress produced more than 35% of dynamic changes in the increase of light transmittance as a reflection of osmotic swelling in the epileptic dentate gyri. This degree of increase was not different from the increase observed in control dentate gyri, suggesting that the capability of osmotically regulating cell volume was preserved in the epileptic dentate gyri. In contrast, alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) induced activity-dependent swelling and an increase in light transmittance by 60.5% in the control dentate gyri, whereas the degree of increase in the epileptic dentate gyri remained 17.9% in response to AMPA. Selective attenuation of light transmittance in response to AMPA in the epileptic but not control dentate gyri suggested a possible alteration in the swelling properties of the epileptic dentate gyri that are linked to the AMPA receptor activation. Surviving cells in the epileptic hippocampus may have a mechanism of downregulating neuronal activity-dependent swelling to maintain optimal cell volume during repeated network hyperexcitation in epilepsy.

Remodeling dendritic spines of dentate granule cells in temporal lobe epilepsy patients and the rat pilocarpine model

PURPOSE

To study when dendritic alteration can occur in the epileptic hippocampus and how it is influenced by epileptic axonal reorganization.

METHODS

Human specimens and the rat pilocarpine model were used. Dentate granule cells (DGCs) were visualized by intracellular biocytin injection for spine count.

RESULTS

In the rat pilocarpine model, dendrites of DGCs revealed a generalized spine loss immediately after the acute status epilepticus induced by pilocarpine. However, this generalized damage was transient and was followed by recovery and plastic changes in spine shape and density, which occurred 15 to 35 days after the initial acute status, i.e., during the period of establishing a chronic phase of this model with the induction of spontaneous seizures. In human epileptic hippocampi, spine density was significantly higher when DGCs generated aberrant mossy fiber collaterals. This was particularly so in the proximal dendrite of DGCs, where the aberrant collaterals were densely localized. These findings suggest that initial acute seizures do not cause permanent damage in dendrites and spines of DGCs and that dendritic spines of epileptic neurons can respond to changes in the local cellular environment, including newly formed afferents, in a plastic manner.

CONCLUSION

Dendritic spines are dynamically maintained in chronic epilepsy during the course of establishment and maintenance of spontaneous seizures. Local dendritic spine alteration, detected later in the chronic phase of epilepsy, must have a separate cause from initial acute insults.

Developmental changes in NMDA-induced intrinsic optical signals in the hippocampal dentate gyrus of children with medically intractable seizures

The N-methyl-D-aspartate (NMDA) receptor is one of the ionotropic glutamate receptor subtypes and exhibits a voltage-dependent blockade of its channel function by extracellular magnesium. This magnesium block is known to be absent or weak early in development and is gradually acquired while the brain matures. Interestingly, in adult patients with temporal lobe epilepsy, the magnesium block appears to be altered allowing more current to flow at a negative membrane potential. We are interested whether a similar change might be observed in children's hippocampi that have frequently been involved in medically intractable seizures. In the present study, we grouped the patients into 2 categories based on the degree of brain maturity: (I) children under the age of 2 (immature, n = 2) and (II) children over the age of 2 (mature, n = 6). Dentate gyri were imaged in real time for intrinsic optical signals with the use of a transmitted light in hippocampal slice preparations. Light transmittance (LT), which reflects a neuronal synaptic depolarization and a concomitant change in cell volume, was calculated. In the immature hippocampus, LT increased significantly in response to NMDA in the presence of extracellular magnesium. However, the mature hippocampi showed little response to NMDA unless magnesium ions were removed from the extracellular artificial cerebrospinal fluid. LT increase was also induced in response to alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA); however, there were no age-dependent differences in the AMPA induced LT increase. Differential sensitivity of the NMDA receptor to extracellular magnesium between immature and mature hippocampi suggests the probable presence of developmental regulation of magnesium block for the NMDA receptor in the human hippocampus of children with medically intractable seizures.

Remodeling dendritic spines in the rat pilocarpine model of temporal lobe epilepsy

Dendritic degeneration is a common pathology in temporal lobe epilepsy and its animal models. However, little is known when and how the degeneration occurs. In the present study of the rat pilocarpine model, visualization of dendrites of the hippocampal dentate granule cells (DGCs) by biocytin revealed a generalized spine loss immediately after the acute seizure induced by pilocarpine. However, this generalized damage was followed by recovery and plastic changes in spine shape and density, which occurred 15-35 days after the initial acute seizure, i.e., during the period of establishing a chronic phase of this model with the induction of spontaneous seizures. The present finding suggests that initial acute seizures do not cause permanent damages in dendrites and spines of DGCs; instead, dendritic spines are dynamically maintained in the course of the establishment and maintenance of spontaneous seizures. Local dendritic spine degeneration, detected later in the chronic phase of epilepsy, is likely to have a separate cause from initial acute insults.

Modulation of GABAA receptor-mediated inhibition by postsynaptic calcium in epileptic hippocampal neurons

Visualization of neurons during patch clamp recordings from slices provides concurrent neuroanatomical information for physiological studies. Although, the technique becomes increasingly popular in immature brains, it has not been fully utilized in aged/adult and diseased brains including post-surgical human specimen. In the present study, glutamatergic modulation of GABAA receptor-mediated inhibition was investigated by whole-cell patch clamp recordings from visualized hippocampal dentate granule cells (DGCs) in slices that were prepared from surgically-removed human medial temporal lobe specimens and the rat pilocarpine model of temporal lobe epilepsy. GABAA receptor-mediated synaptic inhibition was recorded by isolating inhibitory postsynaptic currents (IPSCs) at a membrane potential of 0 mV where glutamatergic excitatory postsynaptic currents are near equilibrium. Peak amplitude of GABAA IPSC was not different between epileptic DGCs of both human and pilocarpine-treated rat hippocampi and those in the control rat DGCs. However, when high frequency stimulation (30 Hz for 10 s) preceded immediately before the generation of a GABAA IPSC, its peak amplitude was significantly reduced in epileptic DGCs. The application of an NMDA receptor antagonist prevented this decrease indicating that the high frequency stimulation activated the NMDA receptor and that this activation is involved in the induction of response-decrement of GABAA IPSCs in epileptic DGCs. In addition, intracellular application of a calcium chelator, BAPTA through a patch pipette was found effective in preventing the response-decrement of GABAA IPSCs suggesting that postsynaptic calcium-increase is also involved in this process. It is proposed that activation of the NMDA receptor in epileptic DGC may trigger an epileptogenic increase of intracellular free calcium, and this calcium-increase plays a crucial role for the induction of the response-decrement of GABAA IPSCs in epileptic hippocampus, which possibly leads to the initiation of epileptic seizures and ictal events.

Paired pulse suppression and facilitation in human epileptogenic hippocampal formation

Paired pulse stimulation has commonly been employed to investigate changes in excitability in epileptic hippocampal tissue employing the in vitro slice preparation. We used paired pulse stimulation in the intact temporal lobe of patients with temporal lobe seizures to compare the excitability of pathways in the epileptogenic hippocampus (located in the temporal lobe in which seizures arise) with those in the non-epileptogenic hippocampus of the contralateral temporal lobe (in the hemisphere to which seizures spread). A total of 20 patients with temporal lobe seizure onsets were studied during chronic depth electrode monitoring for seizure localization. Intracranial in vivo stimulation and recording sites included the hippocampus, entorhinal cortex, subicular cortex and parahippocampal gyrus. A comparison of all hippocampal pathways located in the temporal lobe where seizures typically started (n = 37) with those in temporal lobes contralateral to seizure onset (n = 53) showed significantly greater paired pulse suppression of population post-synaptic potentials on the epileptogenic side (F(1,87) = 6.1, P < 0.01). Similarly, mean paired pulse suppression was significantly greater for epileptogenic perforant path responses than for contralateral perforant path responses (F(1,13) = 7.5, P < 0.01). In contrast, local stimulation activating intrinsic associational pathways of the epileptogenic hippocampus showed decreased paired pulse suppression in comparison to the epileptogenic perforant path. These results may be a functional consequence of the formation of abnormal recurrent inhibitory and recurrent excitatory pathways in the sclerotic hippocampus. Enhanced inhibition may be adaptive in suppressing seizures during interictal periods, while abnormal recurrent excitatory circuits in the presence of enhanced inhibition may drive the hypersynchronization of principal neurons necessary for seizure genesis.

The effect of exposure to negative air ions on the recovery of physiological responses after moderate endurance exercise

This study examined the effects of negative air ion exposure on the human cardiovascular and endocrine systems during rest and during the recovery period following moderate endurance exercise. Ten healthy adult men were studied in the presence (8,000-10,000 cm-3) or absence (200-400 cm-3) of negative air ions (25 degrees C, 50% humidity) after 1 h of exercise. The level of exercise was adjusted to represent a 50-60% load compared with the subjects' maximal oxygen uptake, which was determined using a bicycle ergometer in an unmodified environment (22-23 degrees C, 30-35% humidity, 200-400 negative air ions.cm-3). The diastolic blood pressure (DBP) values during the recovery period were significantly lower in the presence of negative ions than in their absence. The plasma levels of serotonin (5-HT) and dopamine (DA) were significantly lower in the presence of negative ions than in their absence. These results demonstrated that exposure to negative air ions produced a slow recovery of DBP and decreases in the levels of 5-HT and DA in the recovery period after moderate endurance exercise. 5-HT is thought to have contributed to the slow recovery of DBP.

Common clonal origin of lymphocytes and plasma cells in splenic lymphoma with villous lymphocytes

In two-thirds of patients with splenic lymphoma with villous lymphocytes (SLVL) a small amount of M-protein can be detected in association with the presence of plasma cells in the peripheral blood (PB) and/or bone marrow (BM). However, it is not known whether lymphoma cells and plasma cells originate from the same clone. In this report we describe a case of SLVL which was characterized by the presence of marked monoclonal gammopathy (IgG-kappa 90 g/l) and increased plasma cells in the BM. In an attempt to elucidate the origin of lymphoma cells and plasma cells, we performed morphological, cytogenetic and molecular studies on PB mononuclear cells (PBMNC) without plasma cells and BMMNC containing 10% plasma cells from this patient. Immunofluorescence showed that lymphoma cells and plasma cells were positive for cytoplasmic gamma heavy and kappa light chains. Well-developed endoplasmic reticulum was observed in the cytoplasmic organelles of PBMNC using an electron microscope. The mean IgG concentration in the 3 d supernatant cultures of PBMNC was 374 +/- 24 microg/l. More than 50% PBMNC differentiated into plasmacytoid cells in 6 d of liquid culture with IL-3 and IL-6. Analysis by two-colour FISH revealed that karyotypic abnormalities of monosomy X and trisomy 17 existed simultaneously in both lymphoma cells and plasma cells. JH gene rearranged bands from PBMNC and BMMNC by Southern blot hybridization were identical, whereas DNAs from PBMNC failed to hybridize with the Cmu probe. These observations strongly suggest that lymphoma cells and plasma cells originate from the same clone, and that plasma cells, as well as lymphoma cells, which have undergone class switch recombination, could produce IgG type M-protein in this case.

Evaluation of bone marrow iron by magnetic resonance imaging

Bone marrow iron was estimated by magnetic resonance imaging (MRI) using spin-echo sequences with multiple echoes in 22 patients with varying degrees of tissue storage iron. Levels of bone marrow iron concentration (BMIC) were determined chemically in biopsied specimens concurrently. Concentrations of serum iron, serum ferritin, and transferrin saturation were also measured to evaluate body iron status. Significant correlation was observed between BMIC and T2 relaxation rate (1/T2) (r = 0.77; p < 0.001) in all patients with BMIC levels below 400 micrograms/ml, while BMIC was not correlated with T2 in patients with extremely high BMIC levels. MRI was considered to be inappropriate for quantitation of 1/T2 in patients with extremely high BMIC due to an extreme shortening of T2 relaxation time. These observations suggest that MRI may be a useful and noninvasive method for systemic quantitative determination of bone marrow iron.

Glutamate currents in morphologically identified human dentate granule cells in temporal lobe epilepsy

Glutamate-receptor-mediated synaptic transmission was studied in morphologically identified hippocampal dentate granule cells (DGCs; n = 31) with the use of whole cell patch-clamp recording and intracellular injection of biocytin or Lucifer yellow in slices prepared from surgically removed medial temporal lobe specimens of epileptic patients (14 specimens from 14 patients). In the current-clamp recording, low-frequency stimulation of the perforant path generated depolarizing postsynaptic potentials that consisted of excitatory postsynaptic potentials and phase-inverted inhibitory postsynaptic potentials mediated by the gamma-aminobutyric acid-A (GABA(A)) receptor at a resting membrane potential of -62.7 +/- 2.0 (SE) mV. In the voltage-clamp recording, two glutamate conductances, a fast alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor-mediated excitatory postsynaptic current (EPSC; AMPA EPSC) and a slowly developing N-methyl-D-aspartate (NMDA)-receptor-mediated EPSC (NMDA EPSC), were isolated in the presence of a GABA(A) receptor antagonist. NMDA EPSCs showed a voltage-dependent increase in conductance with depolarization by exhibiting an N-shaped current-voltage relationship. The slope conductance of the NMDA EPSC ranged from 1.1 to 9.4 nS in 31 DGCs, reaching up to twice the size of the AMPA conductance. This widely varying size of the NMDA conductance resulted in the generation of double-peaked EPSCs and a nonlinear increase of the slope conductance of up to 37.5 nS with positive membrane potentials, which resembled "paroxysmal currents," in a subpopulation of the neurons. In contrast, AMPA EPSCs, which were isolated in the presence of an NMDA receptor antagonist (2-amino-5-phosphonovaleric acid), showed voltage-independent linear changes in the current-voltage relationship and were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione. The AMPA conductance showed little variance, regardless of the size of the NMDA conductance of a given neuron. The average AMPA slope conductance was 5.28 +/- 0.65 (SE) nS in 31 human DGCs. This value was similar to AMPA EPSC conductances in normal rat DGCs (5.35 +/- 0.52 nS, mean +/- SE; n = 55). Dendritic morphology and spine density were quantified in the individual DGCs to assess epileptic pathology. Dendritic spine density showed an inverse correlation (r2 = 0.705) with a slower rise time and a longer half-width of the excitatory postsynaptic potentials mediated by the NMDA receptor. It is concluded that both AMPA and NMDA EPSCs contribute to human DGC synaptic transmission in epileptic hippocampus. However, a wide range of changes in the slope conductance of the NMDA EPSCs suggests that the NMDA-receptor-mediated conductance could be altered in human epileptic DGCs. These changes may influence the generation of chronic subthreshold epileptogenic synaptic activity and give rise to pathological excitation leading to epileptic seizures and dendritic pathology.

Membrane time constant as a tool to assess cell degeneration

Changes in neuronal surface area may be monitored by measuring the plasma membrane capacitance [8]. Membrane time constant (tao m) is given by the product of the membrane resistance (rm) and membrane capacitance (Cm), tao m = rm Cm. Thus, when membrane resistance is kept constant at a steady state (resting), membrane time constant can reflect the size of neuronal surface area. Membrane time constant is the time for the potential to fall from the resting to a fraction (1-l/e), or 63%, of its final value in the charging curve during the application of a small negative current pulse. Negative voltage shift from the resting potential hardly activates any voltage-dependent ion channel, resulting in nominal changes in cell membrane resistance. Although elaborated methods for mathematical models and simulations are available for the electrophysiological assessment of neuron geometry in order to estimate subthreshold potential attenuation during the propagation of synaptically mediated electrical signals, they involve a number of critical assumptions for the convenience to each model, and some of these assumptions are unlikely to be valid. With these restrictive assumptions, very little can be determined about the electronic structure of a neuron beyond the measurement of neuronal membrane resistance and membrane time constant. Alternatively, numerous tracers are available to visualize morphologies of neurons intracellularly and extracellularly. These anatomical methods provide direct and quantitative evidence for neuron geometry; however, they involve tissue processing and a series of chemical reactions, some of which are time- and effort-demanding. The purpose of the present paper is to show that membrane time constant can be effectively used as a tool to assess diminution in cell surface area without involving extensive mathematical theories and/or neuroanatomical techniques. This approach is particularly effective in electrotonically compact cells such as hippocampal neurons. Recent development in the technique of the whole-cell patch clamp recording in the slice preparation yielded longer time constant with better resolution due to the absence of the leak conductance associated with microelectrode impalement. Indeed, when membrane time constant was measured with the whole-cell patch clamp recording technique, it successfully detected the reduction in dendritic arbors (dendritic degeneration) in dentate granule cells in the pilocarpine model of chronic epilepsy, and this finding is supported by the neuroanatomical evidence that was obtained from the same specimen samples. Membrane time constant is an easy-to-measure "passive membrane property" and can be used as a reliable probe by itself for detecting dendritic degeneration or as a tool for decision-making in introducing neuroanatomical technique in combination with slice neurophysiology.

Preservation of dendrites with the presence of reorganized mossy fiber collaterals in hippocampal dentate granule cells in patients with temporal lobe epilepsy

Dendritic morphology was studied in human hippocampal dentate granule cells (DGCs) by intracellularly-injecting biocytin in slice preparations that were obtained from temporal lobe epilepsy patients who underwent a surgical treatment for medically-intractable seizures. These DGCs had a fan-shaped dendritic domain of 54.1 degrees +/- 4.1 S.E.M. with 13.8 +/- 1.1 branch points and an estimated total dendritic length of 11535.6 microns +/- 3045.4. Dendritic spines were counted, and spine density was calculated to be 0.25 spines/microns +/- 0.16 S.E.M.. However, when the cells were categorized into two groups based on the presence or absence of the aberrant mossy fiber collaterals, the number of dendritic branches was significantly lower and spine density was significantly higher in DGCs that had aberrant collaterals. In particular, in the proximal dendrite, the spine density was 5 times higher in DGCs whose own mossy fibers were reorganized sending aberrant collaterals to this dendritic region (0.750 spines/microns +/- 0.203 S.E.M.: P < 0.01) than the DGCs without such collaterals (0.082 spines/microns +/- p.021 S.E.M.). These results suggest that the axonal reorganization may have an effect on the morphology of DGC dendrites directly or indirectly in such a way that dendritic structure and spines could be protected from seizure-induced excitotoxic cell damage.

Extracellular slow negative transient in the dentate gyrus of human epileptic hippocampus in vitro

We investigated extracellular slow negative transient in dentate granule cells of human epileptic hippocampus. Hippocampal slices were prepared from brain specimens removed from 23 patients who underwent surgical treatment for medically intractable seizures. In 15 patients, hippocampi were sclerotic and the aberrant anatomical reorganization of dentate granule cell axons (mossy fibers) was detected. In eight patients, hippocampi were non-sclerotic and nominal reorganization was detected. Single perforant path stimulation evoked field responses in dentate granule cells in all 23 hippocampi. In sclerotic hippocampi, evoked field responses were followed by a slow onset extracellularly negative potential, which appeared gradually in the course of low frequency stimulation of the perforant path. Single action potentials could be recorded from negative potentials indicating that these potentials represented dentate granule cell depolarization. A low concentration of bicuculline methiodide (10 microM), a GABAA receptor antagonist, facilitated the appearance of negative potentials suggesting that a reduction in functional inhibition could unmask these potentials. The application of D-2 amino-5-phosphonovaleric acid blocked extracellular negative potentials, but initial perforant path responses were spared. This finding suggested that negative potentials were at least in part mediated by the N-methyl-D-aspartate receptor subtypes in their generation. In contrast, in non-sclerotic hippocampi with nominal "reorganization", no extracellular negative potentials were observed. The present study suggests that dentate granule cell excitability could be amplified when their reorganized axonal pathways were present in human sclerotic hippocampus as previously proposed in animal models of epilepsy.

Decrement of GABAA receptor-mediated inhibitory postsynaptic currents in dentate granule cells in epileptic hippocampus

1. Inhibitory postsynaptic currents (IPSCs) were studied in hippocampal dentate granule cells (DGCs) in the pilocarpine model and human temporal lobe epilepsy, with the use of the whole cell patch-clamp recording technique in slice preparations. 2. In the pilocarpine model, hippocampal slices were prepared from rats that were allowed to experience spontaneous seizures for 2 mo. Human hippocampal specimens were obtained from epileptic patients who underwent surgical treatment for medically intractable seizures. 3. IPSCs were generated by single perforant path stimulation and recorded at a membrane potential (Vm) of 0 mV near the reversal potential of glutamate excitatory postsynaptic currents in the voltage-clamp recording. IPSCs were pharmacologically identified as gamma-aminobutyric acid-A (GABAA) IPSCs by 10 microM bicuculline methiodide. 4. During low-frequency stimulation, IPSCs were not different in amplitude among non-seizure-experienced rat hippocampi, human nonsclerotic hippocampi, seizure-experienced rat hippocampi, and human sclerotic hippocampi. In the last two groups of DGCs, current-clamp recordings indicated the presence of prolonged excitatory postsynaptic potentials (EPSPs) mediated by the N-methyl-D-aspartate (NMDA) receptor. 5. High-frequency stimulation, administered at Vm = -30 mV to activate NMDA currents, reduced GABAA IPSC amplitude specifically in seizure-experienced rat hippocampi (t = 2.5, P < 0.03) and human sclerotic hippocampi (t = 7.7, P < 0.01). This reduction was blocked by an NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid (APV) (50 microM). The time for GABAA IPSCs to recover to their original amplitude was also shortened by the application of APV. 6. I conclude that, when intensively activated, NMDA receptor-mediated excitatory transmission may interact with GABAergic synaptic inhibition in DGCs in seizure-experienced hippocampus to transiently reduce GABA(A) receptor-channel function. Such interactions may contribute to give rise to epileptic excitation in chronically seizure-prone hippocampus.

Decreased time constant in hippocampal dentate granule cells in pilocarpine-treated rats with progressive seizure frequencies

Glutamate-mediated excitotoxic cell damage has been implicated in epilepsy. Although evidence accumulates for prolonged acute seizures resulting in unequivocal cell damage, whether excitotoxicity is involved in spontaneous seizures in chronic epilepsy is poorly understood. In the present study, a frequency of spontaneous seizures, independent of exogenously applied stimulus, was studied in relation to hippocampal hyperexcitability in the pilocarpine model. A long-term observation (12 h/day for 120 or 280 days) of spontaneous seizures identified an average basic seizure frequency of 0.11 seizures/day +/- 0.03 S.E.M. in 30 animals. However, in 1/3 of these animals (n = 9), a seizure frequency significantly increased to 2.57 seizures/day +/- 0.25 S.E.M. (ranging from 2-13 seizures/day) in 40-165 days, and this period of high frequency of seizures lasted for 20-95 days. Hippocampal slices were prepared at the end of the observation period for extracellular field responses and whole-cell patch clamp recordings. In slices that were prepared from rats that showed progressive frequencies of seizures, glutamate-mediated excitatory postsynaptic responses were prolonged in hippocampal dentate granule cells (DGCs) from which multiple spikes were generated in higher probability. Average time constant was shorter in these cells (14.2 ms +/- 2.1 S.E.M., P < 0.01) compared with normal DGCs in control animals (21.2 ms +/- 3.7 S.E.M.) suggesting that cell structural diminution possibly occurred during the recurrence of spontaneous seizures. It is suggested that on-going seizure activities could progress in frequency during the recurrence of spontaneous seizures and neuronal degeneration might be accompanied with increasing frequencies of spontaneous seizures that were mediated by the increased activation of glutamate receptors.

[Successful treatment of refractory anemia with excess of blasts in transformation with cytarabine ocfosfate]

A 58-year-old female was diagnosed as myelodysplastic syndrome (MDS) [refractory anemia with excess of blasts (RAEB)]. Although melphalan was administered, no response was obtained in the peripheral blood. Sixteen months after diagnosis, she developed RAEB in transformation (RAEB-t), and then overt leukemia. White blood cell (WBC) count elevated to 28,600/microliters with 34% of blasts. She was administered cytarabine ocfosfate (200 mg-->300 mg/day) orally, resulting in decrease of WBC count and blasts in peripheral blood. The drug has been given for 11 months, and her hematological data have now remained stable in RAEB. Cytarabine ocfosfate might be a useful drug for the treatment of high risk MDS such as RAEB and RAEB-t.

Single mossy fiber axonal systems of human dentate granule cells studied in hippocampal slices from patients with temporal lobe epilepsy

Previous histological and immunocytochemical studies suggest that reorganization of the dentate granule cell axons, the mossy fibers, can occur in epileptic human hippocampus (Sutula et al., 1989; Houser et al., 1990; Babb et al., 1991) and in animal models of epilepsy (Tauck and Nadler, 1985; Sutula et al., 1988; Cronin et al., 1992). However, neuroanatomical analyses of the trajectory and morphology of reorganized axons are not yet available. The present study was conducted to investigate single dentate granule cell axonal systems in human epileptic hippocampus. Individual mossy fibers were directly visualized by injecting a tracer (biocytin or Lucifer yellow) intracellularly in hippocampal slices prepared from temporal lobes that were surgically removed from patients for treatment of intractable epilepsy. Two major arborization patterns were identified: (1) the parent axons extended to and coursed through the hilus toward CA3, leaving collaterals along their paths in the hilus (N = 19 neurons); (2) in addition to the aforementioned axonal system, collateral(s) branched from the parent axon near the soma and projected to the granule cell layer and molecular layer, forming an aberrant axonal pathway (N = 9 neurons). These aberrant collaterals bore large boutons similar to those of the hilar axons and formed extensive plexuses in the granule cell layer and/or in the molecular layer. The summed length of collaterals in the granular/molecular layers was 1110.8 microns on average, which was one-fourth of the total summed length of the mossy fibers (3698.5 microns on average). The size of the somata in neurons that had aberrant collaterals was significantly larger than that of neurons without such collaterals (p < 0.025). In four cases, filopodium-like fine processes were present near the axon hillock and proximal parts of the parent axon, suggesting that the aberrant collateral formation might be an ongoing process in these tissues. The lack of control slices from normal living human hippocampus makes it difficult to assess to what extent the present findings are epilepsy associated. However, the presence of aberrant mossy fiber collaterals in the hippocampi used in the present study has been confirmed by Timm's staining and/or dynorphin immunohistochemistry in comparison with nonepileptic autopsy material, indicating its relation to epilepsy (Babb et al., 1991, 1992). At present, there seems to be a consensus that the projection of mossy fiber collaterals to the supragranular layer is a rare occurrence in normal rats (Lorento de Nó, 1934; Claiborne et al., 1986; Seress et al., 1991; present study), normal monkeys (Seress et al., 1991), and normal humans (Houser et al., 1990).(ABSTRACT TRUNCATED AT 400 WORDS)

Increased NMDA responses and dendritic degeneration in human epileptic hippocampal neurons in slices

To investigate physiological properties of epileptogenic neurons in relation to epileptic pathology, intracellular recording and intracellular dye injection after the recording were obtained in dentate granule cells in slices prepared from excised human epileptic hippocampus in which selective cell degeneration has been documented. Markedly prolonged excitatory postsynaptic potentials (EPSPs) were recorded in 67% of the total neurons sampled during perforant path stimulation. Such EPSPs were voltage dependent and sensitive to the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid. Neurons that generated the increased N-methyl-D-aspartate (NMDA) responses were accompanied by abnormal dendritic morphology, i.e. loss of dendritic spines and development of beaded shafts. These findings suggest that an NMDA receptor-mediated toxic process that impinges specifically on dendritic components might take place in intractable epilepsy.

Physiologic properties of human dentate granule cells in slices prepared from epileptic patients

The neurophysiological properties of human dentate granule cells were studied in hippocampal slices prepared from patients undergoing surgical treatment for medically intractable temporal lobe epilepsy. In 24 neurons which were morphologically identified as dentate granule cells by intracellular staining with biocytin, there were 2 types of synaptic responses to perforant path stimulation: one showed an EPSP-IPSP sequence (n = 10) and the other showed prolonged EPSPs without accompanying hyperpolarizing IPSPs (n = 14). The prolonged EPSPs were markedly retarded by the application of an NMDA receptor antagonist, APV. Membrane properties of neurons showing the different classes of synaptic responses were similar in resting membrane potential (pooled average: -56.2 mV +/- 0.94 SEM) and spike amplitude (pooled average: 65.2 mV +/- 1.69 SEM). However, membrane resistance tended to be lower in neurons with prolonged EPSPs (31.8 M omega +/- 2.63 SEM) than in neurons that showed EPSP-IPSP responses (40.2 +/- 4.33) (P less than 0.05, Fisher). No spontaneous and/or evoked burst firing was observed. These data provide fuller information on the neurophysiological properties of human dentate granule cells in surgically resected epileptogenic hippocampus, implicating a role of NMDA receptor activation in human temporal lobe epilepsy.

NMDA receptor-mediated excitability in dendritically deformed dentate granule cells in pilocarpine-treated rats

Membrane properties and synaptic responses were analyzed in dentate granule cells in hippocampal slices prepared from pilocarpine-treated, chronically epileptic rats. Perforant path stimulation evoked a long-lasting excitatory postsynaptic potential (EPSP) with multiple spikes in a stimulus intensity-dependent fashion. The response was strongly facilitated by paired-pulse stimulation. Application of N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonovalerate (APV), not only blocked the paired pulse facilitation but also reduced the amplitude of the EPSP, indicating the involvement of the NMDA-receptor in synaptic responses of pilocarpine-treated dentate granule cells. Dendrites of these neurons showed loss of spines and beaded branches. These findings suggest that a degenerating dendrite could be a morphological substrate of neuronal hyperexcitability mediated by NMDA receptors, implicating possible in vivo glutamate toxicity as an underlying mechanism of chronic epilepsy.

Commissural responses of rat retrohippocampal neurons

Synaptic responses of commissurally activated rat subicular and entorhinal neurons were studied intracellularly in vivo by stimulating the contralateral dentate gyrus. The most prominent synaptic responses in both subicular and entorhinal neurons were inhibitory postsynaptic potentials (IPSPs). IPSPs were generated in combination with antidromic spikes and/or excitatory postsynaptic potentials (EPSPs) and orthodromic spikes. No dependency between any two response types were found. Commissurally projecting subicular neurons (identified by the presence of antidromic spikes evoked by contralateral stimulation) were found, extending previous anatomical studies. Commissurally projecting entorhinal neurons were found in layer II, confirming previous anatomical studies. Positive correlations between antidromic spike latency and depth of recording sites supported the interpretation that axons projected along the fiber bundles of the hippocampal commissures and angular bundle to distribute to their targets. Possible circuits that could have mediated the excitatory and inhibitory responses of these retrohippocampal neurons are considered.

Functional connections in the human temporal lobe. II. Evidence for a loss of functional linkage between contralateral limbic structures

In a previous investigation of functional limbic pathways in the human mesial temporal lobe, we found evidence for strong connections between ipsilateral mesial temporal structures, but none for contralateral functional connections (Wilson et al. 1990). In the present study, we focused specifically upon the question of functional commissural linkages between these structures by systematic stimulation of a total of 390 electrode placements in 74 epileptic patients with temporal lobe depth electrodes implanted for surgical diagnosis. Eight standard electrode placement regions were targeted: amygdala, entorhinal cortex, anterior, middle and posterior hippocampus, subicular cortex, middle parahippocampal gyrus, and posterior parahippocampal gyrus. Three to six electrodes were implanted bilaterally in each patient, and each electrode was individually stimulated while recording from all the other sites. Out of the 390 electrodes stimulated, 78% were effective in evoking clear responses in adjacent ipsilateral structures, and 75% of 581 ipsilateral recording sites were responsive to stimulation. Only one of the stimulated electrode sites was effective in evoking responses in contralateral recording sites, and only two of 511 contralateral recording sites were responsive to that stimulation. The effective stimulation site was in presubicular cortex, and the responsive contralateral recording sites were in entorhinal and presubicular cortices. Response to this stimulation site was intermittent and variable in latency. The relative ease of obtaining functional verification of significant ipsilateral anatomical pathways in the human limbic system, and the sharply contrasting difficulty of functionally activating commissural pathways to contralateral limbic sites are discussed in the context of decreases in hippocampal contribution to commissural pathways in the primate brain compared to sub-primate mammals, and the significance of this change to normal limbic system function as well as to mechanisms of seizure spread in epilepsy.

Functional connections in the human temporal lobe. I. Analysis of limbic system pathways using neuronal responses evoked by electrical stimulation

Connections in the human mesial temporal lobe were investigated using brief, single pulses of electrical stimulation to evoke field potential responses in limbic structures of 74 epileptic patients. Eight specific areas within these structures were stereotactically targeted for study, including amygdala, entorhinal cortex, presubiculum, the anterior, middle and posterior levels of hippocampus and the middle and posterior levels of parahippocampal gyrus. These sites were studied systematically in order to quantitatively assess the response characteristics and reliability of responses evoked during stimulation of pathways connecting the areas. Specific measures included response probability, amplitude, latency and conduction velocities. The results are assumed to be representative of typical human limbic pathways since all recordings were made interictally and response probabilities across sites were not found to differ significantly between non-epileptogenic vs. identified epileptogenic regions. Field potentials ranging in amplitude from less than 0.1 to greater than 6.0 mV were evoked ipsilaterally, with mean onset latencies and conduction velocities ranging from 4.4 ms and 3.64 m/s in the perforant pathway connecting entorhinal cortex to anterior hippocampus to 24.8 ms and 0.88 m/s in the pathway connecting the amygdala and middle hippocampus. Stimulation of presubiculum and entorhinal cortex were most effective in evoking widespread responses in adjacent limbic recording sites, whereas posterior parahippocampal gyrus appeared functionally separated from other limbic sites since its probability of influencing ipsilateral sites was significantly lower than any other area. It was particularly noteworthy that stimulation did not evoke responses in any sites in contralateral hippocampal formation; even though a large number of sites were tested with bilateral implantation of homotopic electrodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Convergence of finger tremor and EEG rhythm at the alpha frequency induced by rhythmical photic stimulation

The frequencies of EEG alpha rhythm and physiological finger tremor overlap at 9-10 c/sec, suggesting a functional relationship between the two mechanisms. We measured the correlation between the two rhythms when they occurred spontaneously and when rhythmical photic stimulation was applied. Rhythmical physiological finger tremor (9.7 c/sec +/- 1.06 S.D.) was accompanied by an alpha rhythm (10.3 c/sec +/- 0.51 S.D.) spontaneously, showing a one-to-one relationship at times. When photic stimulation was provided at a frequency (11 Hz) close to the subject's spontaneous alpha rhythm, a frequency-convergence occurred between finger tremor (10.3 c/sec +/- 0.68 S.D.) and the EEG (10.6 c/sec +/- 0.35 S.D.). The correlation coefficient between the two rhythms under photic stimulation was significantly higher (0.49 +/- 0.14 S.D.) than under the spontaneous condition (0.13 +/- 0.16; P less than 0.05). Consistent with this, the mean difference between finger tremor and EEG frequencies was significantly lower during photic stimulation (0.83 c/sec +/- 0.46 S.D.) than during the spontaneous condition (1.23 c/sec +/- 0.82 S.D.) (t = 2.54; P less than 0.05, t-test for correlated means). These findings indicate that the EEG and physiological finger tremor tend toward synchrony with each other in an environment of photic stimulation, supporting our hypothesis of a functional relationship between the two mechanisms.

Temporal analysis of REM sleep after nest-building behavior in nulliparous albino rat

EEG recording was performed, during nest-building behavior (NBB), from the hippocampus and sensorimotor cortex of nulliparous albino rats with simultaneous recordings of EMGs of neck-muscle and eye movements. The duration of NBB varied with a period of 4-5 days. However, the relative durations of behavioral transitions in NBB, i.e., nest-building, grooming, and sleeping, were regular in both long lasting and early terminated NBB. REM sleep was identified, in every instance, immediately after NBB. The latency of REM sleep was significantly tied to the termination of NBB without regard to the duration of NBB. Differences in the duration of NBB, however, affected REM-propensity: the longer the NBB was, the shorter the latency of REM sleep tended to be. NBB might accelerate the induction of the physiological condition responsible for REM sleep generation.