CA1 Region Of Hippocampal Slices Research Articles

Characterization of Inhibitory Circuits in the Malformed Hippocampus of Lis1 Mutant Mice

Heterozygous mutation or deletion of a lissencephaly gene (Lis1) in humans is associated with a severe disruption of cortical and hippocampal lamination, cognitive deficit, and severe seizures. Mice with one null allele of Lis1 (Lis1(+/-) mice) exhibit significant brain malformations and slowed migration of interneuron precursors. Although hyperexcitability was demonstrated in dysplastic hippocampal slices from Lis1(+/-) mice, little is known about synaptic function in these animals. Here we analyzed GABA-mediated synaptic inhibition. We recorded isolated whole cell inhibitory postsynaptic currents (IPSCs) on visually identified pyramidal neurons in disorganized CA1 regions of hippocampal slices prepared from Lis1(+/-) mice. We observed a 32% increase in spontaneous IPSC frequency in Lis1(+/-) mice compared with normotopic CA1 pyramidal neurons in age-matched controls. This increase was not associated with a change in spontaneous IPSC decay or miniature IPSC frequency. Mean IPSC amplitude was increased, and event histograms indicated a greater number of large (>125 pA) events. Tonic inhibition, response to paired-pulse stimulation and evoked IPSC decay kinetics were not altered. Consistent with increased synaptic inhibition, Lis1(+/-) interneurons also exhibited more spontaneous firing in cell-attached recordings and increased excitation as measured by voltage-clamp recording of spontaneous excitatory postsynaptic currents (EPSCs) onto interneurons. Our results reveal a significant alteration in the function of inhibitory circuits within the malformed Lis1(+/-) hippocampus. Given that precisely coordinated GABAergic activity is vital to generation of oscillatory activity and place field precision in hippocampus, these alterations in synaptic inhibition may contribute to seizures and altered cognitive function in type I Lissencephaly.

Neuroexcitatory actions of Tamiflu and its carboxylate metabolite

Oseltamivir (Tamiflu) is now being stockpiled by several governments as a first line treatment for an anticipated outbreak of avian influenza caused by H5N1. However, abnormal behaviors and death associated with the use of Tamiflu have developed into a major issue in Japan where Tamiflu is often prescribed for seasonal influenza. Thus, it is critical to determine neuropsychiatric effects of oseltamivir and to establish methods for safe administration. Using juvenile rats and rat hippocampal slices, we investigated whether oseltamivir has adverse effects on the central nervous system. Systemic injection of oseltamivir (50mg/kg i.p.) produced no change in behavior within 2h. However, prior injection of oseltamivir significantly altered the duration of loss of lightning reflex following ethanol injection (3.3g/kg, i.p.). Ethanol injection in the presence of oseltamivir also resulted in enhanced hypothermia. In the CA1 region of hippocampal slices, oseltamivir (100 microM) induced paired-pulse facilitation in population spikes without changes in excitatory postsynaptic potentials. Similarly, 3 microM oseltamivir carboxylate, the active metabolite of oseltamivir, facilitated neuronal firing, though the facilitation did not involve GABAergic disinhibition. Moreover, oseltamivir carboxylate produced further facilitation following administration of 60mM ethanol. These findings indicate that oseltamivir has effects on the central nervous system, especially when combined with other agents.

A brief, but repeated, swimming protocol is sufficient to overcome amyloid β‐protein inhibition of hippocampal long‐term potentiation

Alzheimer's disease starts as an almost imperceptible malady, first observed clinically as a mild memory problem. Accumulating genetic and biochemical data have suggested that amyloid beta-protein (Abeta) plays an important role in this memory loss, and Abeta has been shown to suppress long-term potentiation (LTP), a cellular model for memory and learning. Here we show that a very brief (3 min) swimming, twice daily for 2 weeks, rescues LTP inhibition in the CA1 region of hippocampal slices caused by Abeta(42) or Abeta(40) carrying the Arctic mutation using a theta burst stimulation (TBS) protocol. Whereas the input-output curve was not affected, the paired-pulse ratio was reduced in mice receiving our repeated swimming protocol, suggesting a possible involvement of presynaptic facilitation. Similar to swimming, Abeta's inhibition of LTP could be rescued with the adenylyl cyclase, forskolin. Interestingly, this swimming protocol produced conditions in which a weak-TBS could invoke LTP not observed in naïve mice, which again was mimicked by forskolin. In contrast, the protein kinase A (PKA) inhibitor, H89, blocked both the forskolin and swimming potentiation of LTP; these data implicate cAMP/PKA signaling in the protective effect of swimming and mediating Abeta' detrimental effects. Our data add a new simple behavior paradigm that shows the importance of an environmental factor in reversing the pathophysiological effects of Abeta, and suggest new therapeutic avenues.

Effects of repeated prenatal glucocorticoid exposure on long‐term potentiation in the juvenile guinea‐pig hippocampus

Synthetic glucocorticoids (sGCs) are routinely used to treat women at risk of preterm labour to promote fetal lung maturation. There is now strong evidence that exposure to excess glucocorticoid during periods of rapid brain development has permanent consequences for endocrine function and behaviour in the offspring. Prenatal exposure to sGC alters the expression of N-methyl-D-aspartate receptor (NMDA-R) subunits in the fetal and neonatal hippocampus. Given the integral role of the NMDA-R in synaptic plasticity, we hypothesized that prenatal sGC exposure will have effects on hippocampal long-term potentiation (LTP) after birth. Further, this may occur in either the presence or absence of elevated cortisol concentrations, in vitro. Pregnant guinea-pigs were injected with betamethasone (Beta, 1 mg kg(-1)) or vehicle on gestational days (gd) 40, 41, 50, 51, 60 and 61 (term approximately 70 days), a regimen comparable to that given to pregnant women. On postnatal day 21, LTP was examined at Schaffer collateral synapses in the CA1 region of hippocampal slices prepared from juvenile animals exposed to betamethasone or vehicle, in utero. Subsequently, the acute glucocorticoid receptor (GR)- and mineralocorticoid receptor (MR)-dependent effects of cortisol (0.1-10 microM; bath applied 30 min before LTP induction) were examined. There was no effect of prenatal sGC treatment on LTP under basal conditions. The application of 10 microM cortisol depressed excitatory synaptic transmission in all treatment groups regardless of sex. Similarly, LTP was depressed by 10 microM cortisol in all groups, with the exception of Beta-exposed females, in which LTP was unaltered. Hippocampal MR and GR protein levels were increased in Beta-exposed females, but not in any other prenatal treatment group. This study reveals sex-specific effects of prenatal exposure to sGC on LTP in the presence of elevated cortisol, a situation that would occur in vivo during stress.

Neuroprotective effects of interleukin-10 and tumor necrosis factor-α against hypoxia-induced hyperexcitability in hippocampal slice neurons

In our previous experiments we have demonstrated that repeated exposures of rat hippocampal slices to brief episodes of hypoxia induce a sustained decrease in the threshold of stimulus-evoked epileptiform discharges in CA1 pyramidal neurons. The aim of this study was to investigate the comparative effects of interleukin-10 (IL-10) and tumor necrosis factor-α (TNF-α) on the hyperexcitability of CA1 pyramidal neurons induced by brief episodes of hypoxia in the rat hippocampal slices. The method of field potentials measurement in CA1 region of hippocampal slices have been described in our previous work [O. Godukhin, A. Savin, S. Kalemenev, S. Levin, Neuronal hyperexcitability induced by repeated brief episodes of hypoxia in rat hippocampal slices: involvement of ionotropic glutamate receptors and L-type Ca 2+ channels, Neuropharmacology 42 (2002) 459–466]. The principal results of our work are summarized as follow. Pro-inflammatory cytokine TNF-α (0.8, 4 and 20 ng/ml) and anti-inflammatory cytokine IL-10 (1 and 10 ng/ml) significantly reduced the hyperexcitability in CA1 pyramidal neurons induced by brief episodes of hypoxia in the rat hippocampal slices. The neuroprotective effects of IL-10 and TNF-α against the hypoxia-induced hyperexcitability were mediated by anti-hypoxic actions of these cytokines through, possibly, mechanism of preconditioning.

In Vitro Anticonvulsant Action of 2-Arachidonyl Glycerol

Previous studies had shown that the exogenous cannabinoids can induce anticonvulsion, which was believed to be mediated through the activation of central cannabinoid Type 1 receptors. Moreover, the endogenous cannabinoid anandamide has shown anticonvulsant properties in the in vitro preparations. The current study used 27 adult Sprague-Dawley rats to investigate the effects of another endogenously occurring cannabinoid called 2-arachidonyl glycerol on epileptiform activity induced by picrotoxin. Extracellular recordings were made from the pyramidal cell layer of the CA1 region of hippocampal slices maintained in an interface type recording chamber. Stimulation was performed by using single pulses. It evoked population spikes of approximately equal amplitude. Using single pulse stimulation, perfusion of 500 nM picrotoxin caused an increase in the amplitude of the first population spike, and caused epilepsy by introducing a second or multiple population spikes. In the presence of picrotoxin, 2-AG reduced the amplitude of the population spikes, thus reducing the epilepsy. The CB1 receptor antagonist, AM281 (500 nM) had no effect on responses recorded in the presence of picrotoxin, but totally blocked the effect of subsequently perfused 2-AG. The current results showed that 2-AG caused anticonvulsion in the in vitro preparations. The results will open avenues for cannabinoid receptors as possible future therapeutic targets.

Identification and two-photon imaging of oligodendrocyte in CA1 region of hippocampal slices

Oligodendrocyte (OL) plays a critical role in myelination and axon maintenance in central nervous system. Recent studies show that OL can also express NMDA receptors in development and pathological situations in white matter. There is still lack of studies about OL properties and function in gray matter of brain. Here we reported that some glial cells in CA1 region of rat hippocampal slices (P15–23) had distinct electrophysiological characteristics from the other glia cells in this region, while they displayed uniform properties with OL from white matter in previous report; therefore, they were considered as OL in hippocampus. By loading dye in recording pipette and imaging with two-photon laser scanning microscopy, we acquired the high spatial resolution, three-dimension images of these special cells in live slices. The OL in hippocampus shows a complex process-bearing shape and the distribution of several processes is parallel to Schaffer fiber in CA1 region. When stimulating Schaffer fiber, OL displays a long duration depolarization mediated by inward rectifier potassium channel. This suggested that the OL in CA1 region could sense the neuronal activity and contribute to potassium clearance.

Depletion of ATP and release of presynaptic inhibition in the CA1 region of hippocampal slices during hypoglycemic hypoxia

Transient recovery (TR) of evoked synaptic potentials and ATP depletion during the late stage of hypoxic hypoglycemic insults were investigated in rat hippocampal slices. TR was observed not only in the late stage of insult, but also during recovery. The concentration of ATP corresponded to the appearance (27% of control) and disappearance (15% of control) of TR. Paired pulse studies showed the presynaptic nature of the release of inhibition of synaptic transmission during TR. Both N- and P/Q-type voltage-dependent calcium channels were involved in the appearance of TR. This evidence suggests that underlying mechanisms of TR appearance during hypoxic hypoglycemic insult might be related to ATP depletion and release of A1 adenosine receptor mediated inhibition of presynaptic voltage-dependent calcium channels.

Differential roles of NR2A and NR2B-containing NMDA receptors in LTP and LTD in the CA1 region of two-week old rat hippocampus

The role of NMDA receptors in the induction of long-term potentiation (LTP) and long-term depression (LTD) is well established but which particular NR2 subunits are involved in these plasticity processes is still a matter of controversy. We have studied the effects of subtype selective NMDA receptor antagonists on LTP induced by high frequency stimulation (100 Hz for 1 s) and LTD induced by low frequency stimulation (1 Hz for 15 min) in the CA1 region of hippocampal slices from 14 day old Wistar rats. Against recombinant receptors in HEK293 cells NVP-AAM077 (NVP) was approximately 14-fold selective for NR2A vs NR2B receptors, whilst Ro 25-6981 (Ro) was highly selective for NR2B receptors. On NMDA receptor-mediated EPSCs from Schaffer collaterals in CA1 neurones, NVP and Ro both reduced the amplitude but differentially affected the time constant of decay. The data are compatible with the selective effect of NVP (0.1 μM) and Ro (4 μM) on native NR2A and NBR2B receptors, respectively. NVP reduced both LTP and LTD whereas Ro reduced only LTP. Thus, LTP was reduced by 63% at 0.1 μM NVP and almost completely at 0.4 μM whereas 5 μM Ro reduced LTP by 45%. These data are consistent with a role for both NR2A and NR2B in the induction of LTP, under our experimental conditions. In comparison, LTD was unaffected by Ro (5 μM) even in the presence of a glutamate uptake inhibitor threo-β-benzylaspartic acid (TBOA) to increase the concentration of glutamate at NR2B containing receptors. NVP (0.2–0.4 μM), however, produced a concentration dependent inhibition of LTD which was complete at 0.4 μM. The lack of effect of 0.1 μM NVP on LTD contrasts with its marked effect on LTP and raises the possibility that different NVP-sensitive NR2 subunit-containing NMDA receptors are required for LTP and LTD in this preparation.

The role of NMDAR subtypes and charge transfer during hippocampal LTP induction

Activation of NMDA receptors (NMDARs) is a requirement for persistent synaptic alterations, such as long-term potentiation of synaptic transmission (LTP). NMDARs are composed of NR1 and NR2 subunits, and NR2 subunit-dependent gating properties of NMDAR subtypes cause dramatic differences in the timing of charge transfer. These postsynaptic temporal profiles are further influenced by the frequency of synaptic activation. Here, we investigated in the CA1 region of hippocampal slices from P28 mice, whether particular NMDAR subtypes are recruited based on NR2 subunit-specific gating following different induction protocols. For high frequency afferent stimulation (HFS), we found that genetic impairment of NR2A or pharmacological block of NR2A- or NR2B-type NMDARs can reduce field LTP. In contrast, when pairing low frequency synaptic stimulation with postsynaptic depolarization (LFS pairing) in single CA1 neurons, pharmacological antagonism of either subtype modestly reduced the charge transfer during LFS pairing without reducing the LTP magnitude. These results indicate that HFS-triggered LTP is induced by more than one NMDAR subtype, whereas a single subtype is sufficient during LFS pairing. Analysis of charge transfer during LFS pairing in 13 different conditions revealed a threshold for LTP induction, which was independent of the NR2 antagonist tested. Thus, at least for LFS pairing, the amount of charge transfer, and thus Ca 2+ influx, during LTP induction is a factor more critical than the participation of a particular NMDAR subtype.

DPCPX-resistant hypoxic synaptic depression in the CA1 region of hippocampal slices: Possible role of intracellular accumulation of monocarboxylates

Adenosine plays the principal role in synaptic depression during various energy-depleted conditions. However, additional inhibitory factors not associated with A1 adenosine receptors appear to be involved in hypoxic insults. Monocarboxylate accumulation and consequent acidic changes during hypoxia may be responsible for this remaining depression in synaptic activity. Field evoked potentials were recorded in the CA1 region of rat hippocampal slices. Preincubation with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) disclosed 43% of DPCPX-resistant synaptic depression (DRSD) during oxygen deprivation (OD). In contrast, no DRSD was detected in various conditions with limited glucose utilization, such as glucose deprivation and oxygen-glucose deprivation. Inhibition of anaerobic glycolysis (iodoacetate, sodium fluoride) abolished DRSD during OD, whereas blockade of monocarboxylate utilization with alpha-cyano-4-hydroxycinnamic acid (4-CIN) provoked DRSD in normoxic medium. These observations suggest that an intracellular accumulation of monocarboxylates is responsible for DRSD during hypoxia.

Semaphorin3A regulates synaptic function of differentiated hippocampal neurons

Semaphorins are major chemorepellents for developing neuronal projections. Their persistent expression at adult stages suggests that they may contribute to the functioning of neuronal circuits. We investigated the functional properties of semaphorin3A (Sema3A) in adult hippocampal neurons, and report that exogenous application of this cue decreases the efficacy of synaptic transmission evoked in the CA1 region of hippocampal slices. In situ hybridization, imaging and biochemical techniques showed that the Sema3A receptor component neuropilin-1 is present at hippocampal synapses and localizes in the presynaptic membrane. In differentiated cultured hippocampal neurons, Sema3A elicited Erk1/2 phosphorylation in somata and neuritic compartments. Furthermore, Sema3A application resulted in a striking reduction of synaptophysin and postsynaptic density 95 puncta without affecting the axon diameter. These observations reveal novel functional potentialities for secreted semaphorins, which suggest that these cues could modulate the morphology and function of synapses in the adult brain.

Hypoosmolar conditions reduce extracellular volume fraction and enhance epileptiform activity in the CA3 region of the immature rat hippocampus

The osmolarity of the extracellular space (ECS) compartment is an important factor determining the excitability of neuronal tissue. In the adult hippocampus an important role of osmolarity and ECS diffusion parameters on the susceptibility to epileptic events is well established, but the influence of hypo- and hyperosmolar conditions on the immature hippocampus remains elusive. To investigate the influence of osmolarity on epileptiform activity, extracellular field potentials were recorded in the CA3 region of hippocampal slices of immature (postnatal days 4-7) Wistar rats. The ECS diffusion parameters were determined by the real-time tetramethylammonium (TMA+) iontophoretic method with ion-selective microelectrodes in immature hippocampal slices and showed a lack of diffusion anisotropy; a tortuosity of about 1.39; and a volume fraction, alpha, of 0.41 +/- 0.01 (n = 10 slices). A reduction in osmolarity of -90 mOsm induced a decrease in alpha to 0.17 +/- 0.02 (n = 4 slices). The frequency of epileptiform activity elicited in 10-50 microM 4-AP-containing low-Mg2+ solution was increased under -90 mOsm and -40 mOsm hypoosmolar conditions by 39.9% +/- 8.1% (n = 16) and 24.1% +/- 4.8% (n = 10), respectively, whereas hyperosmolar solutions decreased the frequency. A -90-mOsm reduction in the osmolarity of low-Mg2+ solution induced epileptiform activity in nine of 19 slices. In summary, these results demonstrate that hypoosmolar conditions increased excitability and susceptibility to epileptiform activity in immature hippocampal slices, suggesting a functional role of the larger alpha in suppression of seizures.

Protein tyrosine phosphatase receptor type Z is involved in hippocampus-dependent memory formation through dephosphorylation at Y1105 on p190 RhoGAP

Ptprz is a receptor-type protein tyrosine phosphatase predominantly expressed in the brain as a chondroitin sulfate proteoglycan. Ptprz-deficient mice exhibit an age (maturation)-dependent impairment of spatial learning in the Morris water maze test and enhancement of long-term potentiation (LTP) in the CA1 region in hippocampal slices. The enhanced LTP is canceled out by pharmacological inhibition of Rho-associated kinase (ROCK), suggesting that the lack of Ptprz causes learning impairment due to aberrant activation of ROCK. Here, we report that Ptprz-deficient mice exhibit impairments in hippocampus-dependent contextual fear memory because of abnormal tyrosine phosphorylation of p190 RhoGAP, a GTPase-activating protein (GAP) for Rho GTPase. We found that phosphorylation at Y1105, a major tyrosine phosphorylation site on p190 RhoGAP, is decreased 1 h after the conditioning in the hippocampus of wild-type mice, but not of Ptprz-deficient mice. Pleiotrophin, a ligand for Ptprz, increased tyrosine phosphorylation of p190 RhoGAP in B103 neuroblastoma cells. Furthermore, Ptprz selectively dephosphorylated pY1105 of p190 RhoGAP in vitro, and the tyrosine phosphorylation at Y1105 controls p190 RhoGAP activity in vivo. These results suggest that Ptprz plays a critical role in memory formation by modulating Rho GTPase activity through dephosphorylation at Y1105 on p190 RhoGAP.

Persistent Tolerance to Oxygen and Nutrient Deprivation and N-methyl-D-Aspartate in Cultured Hippocampal Slices from Hibernating Arctic Ground Squirrel

Hibernating Arctic ground squirrel (hAGS), Spermophilus parryii, survive profound decreases in cerebral perfusion during torpor and return to normal blood flow during intermittent rewarming periods without neurologic damage. Hibernating AGS tolerate traumatic brain injury in vivo, and acute hippocampal slices from hibernating animals tolerate oxygen and glucose deprivation. It remains unclear, however, if neuroprotection results from intrinsic tissue properties or from differences in response to acute trauma associated with slice preparation. The goal of this work was therefore to determine whether an intrinsic tissue tolerance persists in chronic culture of AGS hippocampal slices at 37 degrees C. A second goal was to address N-methyl-D-aspartate (NMDA) receptor involvement and channel arrest as potential mechanisms of intrinsic tissue tolerance. Baseline neuronal survival and tolerance to oxygen and nutrient deprivation (OND), an in vitro model of ischemia-reperfusion, were assessed in the CA1 region of hippocampal slices from juvenile, hAGS and interbout euthermic AGS (ibeAGS). Early in culture (insult onset at 3 h), slices from both hAGS and ibeAGS tolerate OND (4 h deprivation followed by 20 h recovery) and 500 micromol/L NMDA plus 20 mmol/L KCl. Later in culture (insult onset at 24 h), tolerance persists in slices from hAGS but not in slices from ibeAGS. Ouabain (Na(+)K(+)ATPase inhibitor) administered 24 h in culture enhances survival of slices from hAGS (assessed 24 h later). Thus, tolerance to OND in slices from hAGS is due to intrinsic tissue properties likely involving NMDA receptors and ion channel arrest.

Extrasynaptic Membrane Trafficking Regulated by GluR1 Serine 845 Phosphorylation Primes AMPA Receptors for Long-term Potentiation

Enhancement of synaptic transmission, as occurs in long-term potentiation (LTP), can result from several mechanisms that are regulated by phosphorylation of the AMPA-type glutamate receptor (AMPAR). Using a quantitative assay of net serine 845 (Ser-845) phosphorylation in the GluR1 subunit of AMPARs, we investigated the relationship between phospho-Ser-845, GluR1 surface expression, and synaptic strength in hippocampal neurons. About 15% of surface AMPARs in cultured neurons were phosphorylated at Ser-845 basally, whereas chemical potentiation (forskolin/rolipram treatment) persistently increased this to 60% and chemical depression (N-methyl-D-aspartate treatment) decreased it to 10%. These changes in Ser-845 phosphorylation were paralleled by corresponding changes in the surface expression of AMPARs in both cultured neurons and hippocampal slices. For every 1% increase in net phospho-Ser-845, there was 0.75% increase in the surface fraction of GluR1. Phosphorylation of Ser-845 correlated with a selective delivery of AMPARs to extrasynaptic sites, and their synaptic localization required coincident synaptic activity. Furthermore, increasing the extrasynaptic pool of AMPA receptors resulted in stronger theta burst LTP. Our results support a two-step model for delivery of GluR1-containing AMPARs to synapses during activity-dependent LTP, where Ser-845 phosphorylation can traffic AMPARs to extrasynaptic sites for subsequent delivery to synapses during LTP.

A similar impairment in CA3 mossy fibre LTP in the R6/2 mouse model of Huntington's disease and in the complexin II knockout mouse

Complexin II is reduced in Huntington's disease (HD) patients and in the R6/2 mouse model of HD. Mice lacking complexin II (Cplx2-/- mice) show selective cognitive deficits that reflect those seen in R6/2 mice. To determine whether or not there is a common mechanism that might underlie the cognitive deficits, long-term potentiation (LTP) was examined in the CA3 region of hippocampal slices from R6/2 mice and Cplx2-/- mice. While associational/commissural (A/C) LTP was not significantly different, mossy fibre (MF) LTP was significantly reduced in slices from R6/2 mice and Cplx2-/- mice compared with wild-type (WT) and Cplx2+/+ control mice. MF field excitatory postsynaptic potentials (fEPSPs) in response to paired stimuli were not significantly different between control mice and R6/2 or Cplx2-/- mice, suggesting that MF basal glutamate release is unaffected. Forskolin (30 microm) caused an increase in glutamate release at MF synapses in slices from R6/2 mice and from Cplx2-/- mice that was not significantly different from that seen in control mice, indicating that the capacity for increased glutamate release is not diminished. Thus, R6/2 mice and Cplx2-/- mice have a common selective impairment of MF LTP in the CA3 region. Together, these data suggest that complexin II is required for MF LTP, and that depletion of complexin II causes a selective impairment in MF LTP in the CA3 region. This impairment in MF LTP could contribute to spatial learning deficits observed in R6/2 and Cplx2-/- mice.

Neurocognitive and Psychotiform Behavioral Alterations and Enhanced Hippocampal Long-Term Potentiation in Transgenic Mice Displaying Neuropathological Features of Human α-Mannosidosis

Mice with alpha-mannosidase gene inactivation provide an experimental model for alpha-mannosidosis, a lysosomal storage disease with severe neuropsychological and psychopathological complications. Neurohistological alterations in these mice were similar to those in patients and included vacuolations and axonal spheroids in the CNS and peripheral nervous system. Vacuolation was most prominent and evenly distributed in neuronal perikarya of the hippocampal CA2 and CA3 regions, whereas CA1 and dentate gyrus were weakly or not affected. Field potential recordings from CA1 region in hippocampal slices showed enhanced theta burst-induced long-term potentiation (LTP) in alpha-mannosidase-deficient mice. Longitudinal assessment in age-matched alpha-mannosidase-deficient and wild-type littermates, using an extended test battery, demonstrated a neurocognitive and psychotiform profile that may relate to the psychopathological alterations in clinical alpha-mannosidosis. Brainstem auditory-evoked potentials and basic neuromotor abilities were not impaired and did not deteriorate with age. Exploratory and conflict tests revealed consistent decreases in exploratory activity and emotional blunting in the knock-out group. alpha-Mannosidosis mice were also impaired in aversively motivated learning and acquisition of signal-shock associations. Acquisition and reversal learning in the water maze task, passive avoidance learning in the step-through procedure, as well as emotional response conditioning in an operant procedure were all impaired. Acquisition or shaping of an appetitive instrumental conditioning task was unchanged. Appetitive odor discrimination learning was only marginally impaired during shaping, whereas both the discrimination and reversal subtasks were normal. We propose that prominent storage and enhanced LTP in hippocampus have contributed to these specific behavioral alterations in alpha-mannosidase-deficient mice.

Chronic intermittent ethanol exposure enhances NMDA-receptor-mediated synaptic responses and NMDA receptor expression in hippocampal CA1 region

In previous studies, we found that chronic intermittent ethanol (CIE) treatment–a model of ethanol consumption in which animals are exposed to and withdrawn from intoxicating levels of ethanol on a daily basis–produces neuroadaptive changes in hippocampal area CA1 excitatory synaptic transmission and plasticity. Synaptic responses mediated by N-methyl- d-aspartate (NMDA) receptors are known to be sensitive to ethanol and could play an important role in the neuroadaptive changes induced by CIE treatment. To address this issue, we compared electrophysiological recordings of pharmacologically isolated NMDA-receptor-mediated field excitatory postsynaptic potentials (fEPSPs) in the CA1 region of hippocampal slices prepared from control rats and rats exposed to 2 weeks of CIE treatment administered by vapor inhalation. We found that fEPSPs induced by NMDA receptor activation were unaltered in slices prepared shortly after cessation of CIE treatment (i.e., ≤1 day of withdrawal from CIE). However, following 7 days of withdrawal from CIE treatment, NMDA-receptor-mediated fEPSPs were augmented relative to age-matched controls. Western blot analysis of NMDA receptor subunit expression showed that, at 7 days of withdrawal, the level of protein for NR2A and NR2B subunits was elevated in the CA1 region of hippocampal slices from CIE-treated animals compared with slices from age-matched controls. These results are consistent with an involvement of NMDA-receptor-mediated synaptic responses in the neuroadaptive effects of CIE on hippocampal physiology and suggest that such changes may contribute to ethanol-induced changes in processes dependent on NMDA-receptor-mediated synaptic responses such as learning and memory, neural development, hyperexcitability and seizures, and neurotoxicity.

Antisecretory factor modulates GABAergic transmission in the rat hippocampus

Antisecretory Factor (AF) is a protein that has been implicated in the suppression of intestinal hypersecretion and inflammation. Intestinal secretion and inflammation are partly under local and central neural control raising the possibility that AF might exert its action by modulating neural signaling. In the present study we have investigated whether AF can modulate central synaptic transmission. Evoked glutamatergic and GABAergic synaptic transmissions were investigated using extracellular recordings in the CA1 region of hippocampal slices from adult rats. AF (0.5 μg/ml) suppressed GABA A-mediated synaptic transmission by about 40% while having no effect on glutamatergic transmission. Per oral administration of cholera toxin as well as feeding of rats with a diet containing hydrothermally processed cereals, known to upregulate endogenous AF plasma activity, mimicked the effect of exogenously administered AF on hippocampal GABAergic transmission. Our results identify AF as a neuromodulator and further raise the possibility that the hippocampus and AF are involved in a gut–brain loop controlling intestinal secretion and inflammation.