Chronic Fluoxetine Induces the Enlargement of Perforant Path-Granule Cell Synapses in the Mouse Dentate Gyrus.

A selective serotonin reuptake inhibitor is the most commonly prescribed antidepressant for the treatment of major depression. However, the mechanisms underlying the actions of selective serotonin reuptake inhibitors are not fully understood. In the dentate gyrus, chronic fluoxetine treatment induces increased excitability of mature granule cells (GCs) as well as neurogenesis. The major input to the dentate gyrus is the perforant path axons (boutons) from the entorhinal cortex (layer II). Through voltage-sensitive dye imaging, we found that the excitatory neurotransmission of the perforant path synapse onto the GCs in the middle molecular layer of the mouse dentate gyrus (perforant path-GC synapse) is enhanced after chronic fluoxetine treatment (15 mg/kg/day, 14 days). Therefore, we further examined whether chronic fluoxetine treatment affects the morphology of the perforant path-GC synapse, using FIB/SEM (focused ion beam/scanning electron microscopy). A three-dimensional reconstruction of dendritic spines revealed the appearance of extremely large-sized spines after chronic fluoxetine treatment. The large-sized spines had a postsynaptic density with a large volume. However, chronic fluoxetine treatment did not affect spine density. The presynaptic boutons that were in contact with the large-sized spines were large in volume, and the volumes of the mitochondria and synaptic vesicles inside the boutons were correlated with the size of the boutons. Thus, the large-sized perforant path-GC synapse induced by chronic fluoxetine treatment contains synaptic components that correlate with the synapse size and that may be involved in enhanced glutamatergic neurotransmission.

Edaravone attenuates impairment of synaptic plasticity in granule cell layer of the dentate gyrus following traumatic brain injury.

Effects of edaravone, a free radical scavenger, on post-traumatic impairment of long-term potentiation (LTP) were examined in granule cell layers of the dentate gyrus (DG) in vitro. Field EPSPs (fEPSPs) evoked by stimulation of the perforant path (PP) were recorded extracellularly in the DG one week after a moderate impact applied by a fluid percussion injury (FPI) device. High frequency stimulation (HFS) of the PP caused LTP of the fEPSP-slope in slices from naïve and sham-operated rats, however, the LTP was strongly depressed in slices from FPI rats. Intraperitoneal administration of edaravone 15 min after FPI prevented the hyperactivities of DG neurons and attenuated impairment of the LTP in FPI rat dentate granular cells. In vitro application of spermine NONOate (sp-NO), a nitric oxide (NO) donor, for 30 min produced a gradual increase in the fEPSP-slope, lasting for more than 2 h. Edaravone attenuated the enhancement of the fEPSP-slope induced by sp-NO. After sp-NO treatment HFS could not produce an obvious LTP in the DG granule cell layer. Pretreatment of DG slices with edaravone prevented the sp-NO-induced impairment of LTP. These results suggest that administration of edaravone after FPI protects against post-traumatic impairment of LTP in granule cell layers of the DG, possibly by scavenging NO-related radicals.

Mild hypothermia prevents post-traumatic hyperactivity of excitatory synapses in rat hippocampal CA1 pyramidal neurons.

The present experiment examined the effect of mild hypothermia (35 degrees C) on the post-traumatic hyperactivity of rat hippocampal CA1 neurons in horizontal brain slices. One week after fluid percussion injury (FPI), the optical response evoked by stimulation of the Schaffer collaterals increased in amplitude and propagation area in hippocampal CA1 slices. FPI did not alter the fast optical response that reflected the action potential of the Schaffer collaterals but enhanced the slow component that reflected the excitatory postsynaptic response. FPI increased the slope of the input-output relation (I/O function), suggesting that FPI increases the efficacy of excitatory synaptic transmission in the hippocampal CA1 pyramidal neurons. To examine the effect of low temperature on post-traumatic hyperactivity of hippocampal CA1 neurons, mild hypothermia (35 degrees C) was administered to rats 15 min after FPI and maintained for 1-3 h. One week after FPI, the activity of hippocampal CA1 neurons in rats with mild hypothermia appeared to be reduced as compared with those receiving FPI alone. The post-traumatic enhancement of the I/O function of the slow optical response was prevented by mild hypothermia. These results suggest that mild hypothermia applied 15 min after FPI attenuates the post-traumatic hyperactivity of excitatory synapses in rat hippocampal CA1 neurons.

Facilitation of glutamatergic synaptic transmission in hippocampal CA1 area of rats with traumatic brain injury.

We investigated the effects of traumatic brain injury (TBI) on the glutamatergic synaptic transmission in the hippocampal CA1 area. A moderate impact (3.8-4.8atm) was applied onto the left parietal cerebral cortex by a fluid percussion injury (FPI) device. Conventional intracellular recordings were made from hippocampal CA1 pyramidal neurons in vitro. Electrophysiological properties of these neurons were compared between three groups (control, FPI-ipsilateral, and FPI-contralateral). The excitability of postsynaptic membrane of CA1 pyramidal neurons was not altered by the moderate FPI; however, the evoked glutamatergic excitatory synaptic transmission in the pyramidal neurons of post-FPI-CA1 was enhanced. Paired-pulse facilitation (PPF) was significantly suppressed in both the FPI-ipsilateral and FPI-contralateral groups and the frequencies of mEPSPs in neurons from the bilateral FPI groups were greater than the frequency in the control group. These results suggest that the glutamatergic synaptic transmission in the hipppocampal CA1 area is facilitated through presynaptic mechanisms after TBI.

Dopamine presynaptically depresses fast inhibitory synaptic transmission via D4 receptor-protein kinase A pathway in the rat dorsolateral septal nucleus.

The lateral septal nucleus receives a diffuse dopaminergic input originating from the ventral tegmental area of the brain stem. We examined whether dopamine (DA) modulates synaptic transmission in the slice preparation of the rat dorsolateral septal nucleus (DLSN). Bath application (10-15 min) of DA (30 muM) markedly depressed the amplitude of fast and slow inhibitory postsynaptic potentials (IPSPs) in DLSN neurons, while it produced only a minor depression of the amplitude of excitatory postsynaptic potentials (EPSPs) obtained in the presence of bicuculline. DA (30 muM) depressed the monosynaptic fast IPSP to approximately 50% of control, but did not depress the inward current (I(GABA)) induced by exogenous gamma-aminobutyric acid (GABA). DA decreased the frequency of miniature fast IPSPs (m-fIPSPs) without significantly changing their amplitude. PD 168077, a selective D4 receptor agonist, depressed the fast and slow IPSPs but not the EPSP and decreased the frequency of m-fIPSPs. Both DA and PD 168077 increased the paired-pulse ratio of the monosynaptic fast IPSP. The inhibitory effect of DA on the fast IPSP was significantly attenuated by L-741,742, an antagonist at D4 receptors, but not by SCH 23390 and sulpiride, a D1-like and a D2-like receptor antagonist, respectively. N-ethylmaleimide, a blocker of pertussis toxin (PTX)-sensitive G protein (G(i/o)), attenuated the DA-induced depression of the fast IPSP. N-[2-((p-bromocinnamyl) amino)ethyl]-5-isoquinoline sulfonamide, a protein kinase A (PKA) inhibitor, attenuated the DA-induced depression of the fast IPSP. These results suggest that DA inhibits spontaneous and evoked release of GABA via the D4 receptor-G(i)-protein-PKA system in DLSN neurons.

Effects and wavelet spectral entropy analysis of rhubarb extracts rhein on synaptic transmission in rat hippocampal ca1 area in vitro.

BACKGROUND: 5-dihydroxyanthraquinone-2-carboxylic acid (rhein) inhibits oxidoreduction induced by reducing nicotingamide adenine dinucleotide in the mitochondria and reducing reactive oxygen species, it also suppresses lipid peroxidation in rat brain homogenates. This study was to assess the effects of anthraquinone derivatives, rhein on synaptic transmission in the rat hippocampal CA1 pyramidal cell layer by intracellular recording. METHODS: The excitatory postsynaptic potential (EPSP) evoked by stimulation of the Schaffer collaterals in the presence of bicuculline (15 micromol/L) was depressed by application of rhein (0.3 - 30 micromol/L). The amplitude of the EPSP was restored within 20 minutes after removal of rhein from the supernatant. At a concentration of 30 micromol/L, rhein reduced the amplitude of the EPSP to 42% +/- 3.7% (n = 24) of the control. Subsequently, wavelet spectral entropy was used to analyze the EPSP. RESULTS: A strong positive correlation was observed between the wavelet spectral entropy and other parameters such as amplitude, slope of rising phase and slope of descending phase of the EPSP. The paired-pulse facilitation (PPF) of the EPSP was significantly increased by rhein (30 micromol/L). The inhibitory postsynaptic potential (IPSP) recorded in the presence of CNQX (20 micromol/L) and APV (40 micromol/L) is not altered by rhein (30 micromol/L). CONCLUSIONS: Rhein (30 micromol/L) can decrease the frequency but not the amplitude of the miniature EPSP (mEPSP). It is suggested that rhein inhibits excitatory synaptic transmission by decreasing the release of glutamate in rat hippocampal CA1 pyramidal neurons.

Effects of emodin on synaptic transmission in rat hippocampal CA1 pyramidal neurons in vitro.

Rhubarb extracts provide neuroprotection after brain injury, but the mechanism of this protective effect is not known. The present study tests the hypothesis that rhubarb extracts interfere with the release of glutamate by brain neurons and, therefore, reduce glutamate excitotoxicity. To this end, the effects of emodin, an anthraquinone derivative extracted from Rheum tanguticum Maxim. Ex. Balf, on the synaptic transmission of CA1 pyramidal neurons in rat hippocampus were studied in vitro. The excitatory postsynaptic potential (EPSP) was depressed by bath-application of emodin (0.3-30 microM). Paired-pulse facilitation (PPF) of the EPSP was significantly increased by emodin. The monosynaptic inhibitory postsynaptic potential (IPSP) recorded in the presence of glutamate receptor antagonists (DNQX and AP5) was not altered by emodin. Emodin decreased the frequency, but not the amplitude, of the miniature EPSP (mEPSP). The inhibition of the EPSP induced by emodin was blocked by either 8-CPT, an adenosine A1 receptor antagonist, or by adenosine deaminase. These results suggest that emodin inhibits the EPSP by decreasing the release of glutamate from Schaffer collateral/commissural terminals via the activation of adenosine A1 receptors in rat hippocampal CA1 area and that the neuroprotective effects of rhubarb extracts may result from decreased glutamate excitotoxicity.

5-Hydroxytryptamine 1B receptors mediate presynaptic inhibition of monosynaptic IPSC in the rat dorsolateral septal nucleus.

Effects of 5-hydroxytryptamine (5-HT) on inhibitory synaptic transmission in the rat dorsolateral septal nucleus (DLSN) were examined by conventional intracellular and voltage-clamp recording methods. 5-HT (1-30 microM) depressed the monosynaptic fast IPSC evoked by local stimulation of the DLSN in the presence of DNQX, AP5 and CGP 55845A. CP 93129, a selective 5-HT1B receptor agonist, depressed the fast IPSC. The 5-HT-induced depression of the fast IPSC was attenuated by SB 216641, a selective antagonist for 5-HT1B receptors. 5-HT did not change the inward currents mediated by GABAA receptors, suggesting that 5-HT presynaptically inhibited the fast IPSC. 5-HT and CP 93129 depressed the frequency of miniature fast IPSPs (mIPSPs) without changing their amplitudes. Neither a selective protein kinase A inhibitor, H-89, nor a selective protein kinase C inhibitor, calphostin C, blocked the 5-HT-induced depression of the fast IPSC. N-Ethylmaleimide (NEM) blocked the 5-HT-induced depression of the evoked IPSC. These results suggest that activation of presynaptic 5-HT1B receptors depresses the release of GABA via a pertussis toxin (PTX)-sensitive G-protein in the rat DLSN.

L-arginine enhances heat-induced depression of neuronal activity in the rat hippocampal CA1 area.

Effects of L-arginine on the heat-induced depression of the neuronal activity in the hippocampal CA1 area were investigated using optical recording techniques. An increase in the temperature of hippocampal neurons from 32 degrees C to 38 degrees C reversibly depressed the fast and slow components of the optical response to stimulation of the Schaffer collaterals that correspond to the presynaptic action potential and excitatory postsynaptic response, respectively. The neuronal activity recovered almost completely after cooling the hippocampal neurons back to 32 degrees C. A temperature increase to 40 degrees C produced irreversible depression of the neuronal activity. Pyruvate, but not lactate, in the artificial cerebrospinal fluid (ACSF) attenuated the depression of the neuronal activity induced by a temperature increase to 38 degrees C. Bath-application of L-arginine (1 mM), a nitric oxide (NO) donor, enhanced the depression of the neuronal activity at 38 degrees C. In the presence of L-arginine, the recovery of neuronal activity, upon return to 32 degrees C, was incomplete. The contribution of NO to the heat-induced impairment of the neuronal activity was discussed.

Contribution of nitric oxide to the depression of neuronal activity induced by temperature increase in the rat hippocampal CA1 area.

Using optical recording techniques, we examined whether nitric oxide (NO) is implicated in the impairment of the activity of hippocampal CA1 neurons induced by mild heat stress. A temperature increase from 32 to 38 degrees C reversibly depressed the neuronal activity in hippocampal slices. L-Arginine (1 mM), an NO donor, enhanced the heat-induced depression of the activity of hippocampal CA1 neurons. N(omega)-Nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase, attenuated the inhibition of the neuronal activity induced by a temperature increase. Methylcobalamin (10 microM), a vitamin B(12) analogue that reduces NO production, reduced the heat-induced depression of the neuronal activity. These results suggest that NO contributes, at least in part, to the heat-induced depression of the neuronal activity in the hippocampal CA1 region.

Monocarboxylate transporters contribute to the adaptation of neuronal activity to repeated glucose deprivation in the rat lateral septal nucleus.

Using optical recording methods in the rat lateral septal nucleus (LSN) slice, we examined the question of whether antecedent hypoglycemia protects neurons from the adverse effects of subsequent hypoglycemic stimuli. The first exposure of LSN neurons to glucose deprivation for 15 min produced a marked depression of neuronal activity. The neuronal activity recovered by reapplication of glucose to the neurons. In neurons previously exposed to glucose deprivation, subsequent applications of glucose-free artificial cerebrospinal fluid (ACSF) produced only weak depression of the neuronal activity. The contribution of monocarboxylate transporters to this adaptation of neuronal activity to repeated glucose deprivation was examined in LSN neurons. alpha-Cyano-4-hydroxycinnamate (4-CIN, 100 microM), an inhibitor of the monocarboxylate transporters, did not significantly affect the depression of the neuronal activity induced by the first glucose deprivation. However, in the presence of 4-CIN (100 microM), a second glucose deprivation produced a typical depression of the neuronal activity, indicating that 4-CIN had nullified the adaptation of neuronal activity to a second glucose deprivation. Cytochalasin B (CCB, 20 microM), an inhibitor of glucose transporters, depressed the neuronal activity in the presence of 11 mM glucose. Pyruvate (11 mM) partially restored the neuronal activity depressed by pretreatment with CCB (20 microM) for 30-40 min. These results suggest that antecedent glucose deprivation stimulates monocarboxylate-transporters to supply energy substrates to LSN neurons, thus protecting the neurons against subsequent glucose deprivation. .

Activation of presynaptic 5-hydroxytryptamine 2A receptors facilitates excitatory synaptic transmission via protein kinase C in the dorsolateral septal nucleus.

Effects of 5-hydroxytryptamine (5-HT) on EPSPs and EPSCs in the rat dorsolateral septal nucleus (DLSN) were examined in the presence of GABA(A) and GABA(B) receptor antagonists. Bath application of 5-HT (10 microm) for 5-10 min increased the amplitude of the EPSP and EPSC. (+/-)-8-hydroxy-2-(di-N-propylamino)tetralin hydrobromide (10 microm), an agonist for 5-HT1A and 5-HT7 receptors, did not facilitate the EPSP. alpha-Methyl-5-HT (10 microm), a 5-HT2 receptor agonist, increased the amplitude of the EPSC. Alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine (10 microm) and 6-chloro-2-(1-piperazinyl)pyrazine (10 microm), selective 5-HT2B and 5-HT2C receptor agonists, respectively, had no effect on the EPSP. The 5-HT-induced facilitation of the EPSP was blocked by ketanserin (10 microm), a 5-HT2A/2C receptor antagonist. However, N-desmethylclozapine (10 microm), a selective 5-HT2C receptor antagonist, did not block the facilitation of the EPSP induced by alpha-methyl-5-HT. The inward current evoked by exogenous glutamate was unaffected by 5-HT. 5-HT (10 microm) and alpha-methyl-5-HT (10 microm) increased the frequency of miniature EPSPs (mEPSPs) without changing the mEPSP amplitude. The ratio of the paired pulse facilitation was significantly decreased by 5-HT and alpha-methyl-5-HT. The 5-HT-induced facilitation of the EPSP was blocked by calphostin C (100 nm), a specific protein kinase C (PKC) inhibitor, but not by N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (10 microm), a protein kinase A inhibitor. Phorbol 12,13-dibutyrate (3 microm) mimicked the facilitatory effects of 5-HT. These results suggest that 5-HT enhances the EPSP by increasing the release of glutamate via presynaptic 5-HT2A receptors that link with PKC in rat DLSN neurons.

Hyperexcitability of hippocampal CA1 neurons after fluid percussion injury of the rat cerebral cortex.

Effects of fluid percussion injury (FPI) of the parietal cerebral cortex on the neuronal activity in the temporal region of the rat hippocampal CA1 area were investigated by using optical and extracellular recording techniques. Application of moderate impact (1.5-2.0 atm) to the parietal cerebral cortex enhanced the optical signal of the neuronal activity in the ipsilateral hippocampal CA1 area. The field potential evoked by the Schaffer collaterals had multiple population spikes in the ipsilateral hippocampal CA1 pyramidal cell layer. Bicuculline (15 microM) increased the amplitude and the number of population spikes of the field potential even after the brain injury. These results suggest that FPI produces hyperexcitability of hippocampal CA1 neurons, probably by increasing the activity of the Schaffer collaterals of hippocampal CA3 neurons.

Effects of temperature increase on the propagation of presynaptic action potentials in the pathway between the Schaffer collaterals and hippocampal CA1 neurons.

Effects of temperature increase on the neuronal activity of hippocampal CA2-CA1 regions were examined by using optical and electrophysiological recording techniques. Stimulation of the Schaffer collaterals at the CA2 region evoked depolarizing optical signals that spread toward the CA1 region at 32 degrees C. The optical signal recorded by 49 pixels was characterized by fast and slow components that were closely related to presynaptic action potentials and excitatory postsynaptic responses, respectively. The optical signal was depressed by temperature increase to 38-40 degrees C. The temperature increase to 38 degrees C produced a hyperpolarization and a depression of the excitatory postsynaptic potential (EPSP) in single hippocampal CA1 pyramidal neurons. The depression of the neuronal activity induced by temperature increase was attenuated by application of glucose (22 mM) or pyruvate (22 mM). Adenosine (200 microM) did not block the presynaptic action potential but strongly depressed the excitatory postsynaptic response. 8-Cyclopentyl-1,3-dimethylxanthine (8-CPT) (10 microM), an antagonist for adenosine A(1) receptors, attenuated the depression of the excitatory postsynaptic response but not the inhibition of the presynaptic action potential at 38 degrees C. These results suggest that adenosine mediates the high-temperature-induced depression of the excitatory synaptic transmission but not that of action potential propagation in rat CA1 neurons.

Effect of ONO-1101, a novel short-acting ß-blocker on hemodynamic responses to isoflurane inhalation and tracheal intubation.

PURPOSE: We investigated the effect of a new ultrashort-acting ß-blocker, ONO-1101, on hemodynamic responses to isoflurane inhalation and tracheal intubation. METHODS: Fifty-four ASA PS 1 or 2 patients were randomly allocated to receive either ONO-1101, 0.04 mg·kg-1·min-1, or saline prior to tracheal intubation. Anesthesia was induced with thiamylal, 4 mg·kg-1, and vecuronium, 0.15 mg·kg-1. Tracheal intubation was carried out after 3 min controlled mask ventilation with 66% N2O and 3% inspired isoflurane in oxygen. Heart rate and blood pressure were continuously recorded from the start of induction until 5 min after intubation. Plasma concentrations of catecholamines were measured before induction, 3 min after initiating inhalation of isoflurane, and 1 min after tracheal intubation. RESULTS: Significant increases in heart rate occurred in both groups in response to isoflurane inhalation and tracheal intubation, but the magnitude of the increase was significantly less in the ONO-1101 group. Blood pressure increased after tracheal intubation in the saline group but remained unchanged in the ONO-1101 group. Plasma concentrations of norepinephrine increased after induction and intubation in both groups, with no significant difference between the groups. CONCLUSION: ONO-1101 infusion is effective for the attenuation of hemodynamic responses to isoflurane inhalation and tracheal intubation.