Effects of fluoxetine on ischemic cells and expressions in BDNF and some antioxidants in the gerbil hippocampal CA1 region induced by transient ischemia

Fluoxetine, a selective serotonin reuptake inhibitor, alters several physiological processes, for example, elevating intracellular cAMP level, in the hippocampus. We examined the effect of fluoxetine on ischemia-induced neuronal death, the expression of brain-derived neurotrophic factor (BDNF) and changes in some antioxidative enzymes in the hippocampal CA1 region induced by transient ischemia. In addition, we also studied the effect of fluoxetine on locomotor activity in gerbils after ischemia/reperfusion. Animals were administered with various doses of fluoxetine (10, 20, and 40 mg/kg, i.p.) once daily for 3 days before the ischemic surgery. The treatment of 10 mg/kg and 20 mg/kg fluoxetine did not show significant neuroprotective effects on CA1 pyramidal cells 4 days after ischemia/reperfusion, while the treatment with 40 mg/kg fluoxetine in ischemic animals showed about 77% neuronal survival rate compared to the control group. The treatment of 40 mg/kg fluoxetine in ischemic animals enhanced significantly BDNF, catalase (CAT), glutathione peroxidase (GPX), and superoxide dismutase-1 (SOD1) immunoreactivity in the CA1 region compared to those in the saline-treated group 4 days after ischemia/reperfusion. In addition, the treatment of fluoxetine (10, 20, 40 mg/kg) significantly inhibited post-ischemic hyperactivity. In brief, treatment with fluoxetine protects neuronal damage after transient ischemia, and the neuroprotective effect of fluoxetine in an ischemic animal model may be related with the up-regulation of BDNF, CAT, GPX, and SOD1 expression.     

Acute and repeated administration of fluoxetine, citalopram, and paroxetine significantly alters the activity of midbrain dopamine neurons in rats: an in vivo electrophysiological study

We examined the effect of the administration of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine, citalopram, and paroxetine on the activity of spontaneously active dopamine (DA) neurons in the substantia nigra pars compacta (SNC) and ventral tegmental area (VTA) in anesthetized adult male Sprague-Dawley rats. This was accomplished using the technique of in vivo extracellular recording. A single injection of 2.5 mg/kg (i.p.) of fluoxetine significantly increased the number of spontaneously active SNC and VTA DA neurons. In contrast, a single injection of either 1 mg/kg (i.p.) of paroxetine or 5 mg/kg of fluoxetine significantly increased the number of spontaneously active VTA DA neurons. The repeated administration (one injection per day for 21 days) of all of the SSRIs produced a significant increase in the number of spontaneously active VTA DA neurons. Overall, our results indicate that the systemic administration of SSRI alters the activity of midbrain DA neurons with differential effects on VTA compared with SNC DA neurons.     

A serotonin S2 antagonist, naftidrofuryl, exhibited a protective effect on ischemic neuronal damage in the gerbil

The effect of a serotonin S₂ antagonist, naftidrofuryl, on ischemic neuronal damage was examined in the gerbil. Naftidrofuryl was injected i.p. 5 min prior to a single 5-min forebrain ischemia or immediately after each of three 2-min forebrain ischemic insults at 60-min intervals. In both groups the number of intact hippocampal CA1 neurons were significantly higher than in the saline-treated group. These results indicate that serotonin S₂ antagonists have a protective effect against ischemic neuronal damage.     

The selective A2A receptor antagonist SCH 58261 reduces striatal transmitter outflow,turning behavior and ischemic brain damage induced by permanent focal ischemia in the rat

Adenosine A(2A) receptor antagonists have been proved protective in different ischemia models. In this study we verified if the protective effect of the selective A(2A) antagonist, SCH 58261, could be attributed to the reduction of the excitatory amino acid outflow induced by cerebral focal ischemia. A vertical microdialysis probe was inserted into the striatum of male Wistar rats and, after 24 h, permanent right intraluminal middle cerebral artery occlusion (MCAo) was induced. Soon after waking, rats showed a definite contralateral turning behavior, which persisted up to 7 h after MCAo. During 4 h after MCAo, glutamate, aspartate, GABA, adenosine and taurine outflow increased. SCH 58261 (0.01 mg/kg, i.p.), administered 5 min after MCAo, suppressed turning behavior and significantly reduced the outflow of glutamate, aspartate, GABA and adenosine. At 24 h after MCAo, the rats showed severe sensorimotor deficit and damage in both the striatum and cortex. SCH 58261 significantly reduced cortical damage but did not protect against the sensorimotor deficit. The protective effect of SCH 58261 against turning behavior and increased outflow of excitatory amino acids in the first hours after MCAo suggests the potential utility of selective adenosine A(2A) antagonists when administered in the first hours after ischemia. Furthermore, this study, for the first time, proposes that turning behavior after permanent intraluminal MCAo, be used as a precocious index of neurological deficit and neuronal damage.     

Effects of S‐citalopram,citalopram, and R‐citalopram on the firing patterns of dopamine neurons in the ventral tegmental area,N‐methyl‐D‐aspartate receptor‐mediated transmission in the medial prefrontal cortex and cognitive function in the rat

Escitalopram, the S‐enantiomer of citalopram, possesses superior efficacy compared to other selective serotonin reuptake inhibitors (SSRIs) in the treatment of major depression. Escitalopram binds to an allosteric site on the serotonin transporter, which further enhances the blockade of serotonin reuptake, whereas R‐citalopram antagonizes this positive allosteric modulation. Escitalopram's effects on neurotransmitters other than serotonin, for example, dopamine and glutamate, are not well studied. Therefore, we here studied the effects of escitalopram, citalopram, and R‐citalopram on dopamine cell firing in the ventral tegmental area, using single‐cell recording in vivo and on NMDA receptor‐mediated currents in pyramidal neurons in the medial prefrontal cortex using in vitro electrophysiology in rats. The cognitive effects of escitalopram and citalopram were also compared using the novel object recognition test. Escitalopram (40–640 μg/kg i.v.) increased both firing rate and burst firing of dopaminergic neurons, whereas citalopram (80–1280 μg/kg) had no effect on firing rate and only increased burst firing at high dosage. R‐citalopram (40–640 μg/kg) had no significant effects. R‐citalopram (320 μg/kg) antagonized the effects of escitalopram (320 μg/kg). A very low concentration of escitalopram (5 nM), but not citalopram (10 nM) or R‐citalopram (5 nM), potentiated NMDA‐induced currents in pyramidal neurons. Escitalopram's effect was antagonized by R‐citalopram and blocked by the dopamine D₁ receptor antagonist SCH23390. Escitalopram, but not citalopram, improved recognition memory. Our data suggest that the excitatory effect of escitalopram on dopaminergic and NMDA receptor‐mediated neurotransmission may have bearing on its cognitive‐enhancing effect and superior efficacy compared to other SSRIs in major depression. Synapse, 2010. © 2010 Wiley‐Liss, Inc.     

alpha2-Adrenergic agonists antagonise the anxiolytic-like effect of antidepressants in the four-plate test in mice

Selective serotonin reuptake inhibitors (SSRIs) and serotonin/noradrenaline reuptake inhibitors (SNRIs) has been reported to be efficient in anxiety disorders. Some animal models have demonstrated an anxiolytic-like effect following acute administration, however, it is not yet known how noradrenergic receptors are implicated in the therapeutic effects of antidepressants (ADs) in anxiety. The effects of two alpha(2)-adrenoceptor agonists (clonidine, guanabenz) on anxiolytic-like effect of two SSRIs (paroxetine and citalopram) and two SNRIs (venlafaxine and milnacipran) were evaluated in the four-plate test (FPT) in mice. Paroxetine (4 mg/kg), citalopram (8 mg/kg), venlafaxine (8 mg/kg), and milnacipran (8 mg/kg) administered intraperitoneally (i.p.) increased the number of punishments accepted by mice in the FPT. Clonidine (0.0039-0.5 mg/kg) and guanabenz (0.03-0.5mg/kg) had no effect on the number of punishments accepted by mice. Clonidine (0.03 and 0.06 mg/kg) and guanabenz (0.125 and 0.5 mg/kg) (i.p. -45 min) reversed the anti-punishment effect of paroxetine, citalopram, venlafaxine and milnacipran (i.p. -30 min). But if the antidepressants are administered 45 min before the test and alpha(2)-adrenoceptor agonists 30 min before the test, alpha(2)-adrenoceptor agonists failed to alter the anti-punishment effect of antidepressants. The results of this present study indicate that alpha(2)-adrenoceptor agonists antagonise the anxiolytic-like effect of antidepressants in mice when they are administered 15 min before the administration of antidepressant suggesting a close inter-regulation between noradrenergic and serotoninergic system in the mechanism of SSRIs and SNRIs in anxiety-like behaviour.     

Nicotine, but not mecamylamine, enhances antidepressant-like effects of citalopram and reboxetine in the mouse forced swim and tail suspension tests

Current literature suggests that nicotinic acetylcholine receptors (nAChRs) are involved in major depression. In rodents, antidepressant-like effects of both nicotine and the non-selective nAChR antagonist mecamylamine have been reported. Nicotine increases serotonergic and noradrenergic neuronal activity and facilitates serotonin and noradrenaline release. Thus, we hypothesise that nicotine may enhance the behavioural effects of serotonin (e.g., citalopram) and/or noradrenaline (e.g., reboxetine) reuptake inhibitors. Here, we tested if nicotine enhanced the activity of citalopram or reboxetine in the mouse forced swim test (mFST) and the mouse tail suspension test (mTST). The potential for mecamylamine to augment antidepressant drug action was also investigated. Sub-threshold and threshold doses of citalopram (3 and 10mg/kg) or reboxetine (3, 10 and 20mg/kg) were tested alone and in combination with nicotine (0.3 and 1.0mg/kg) and mecamylamine (1 and 3mg/kg). Locomotor activity experiments were performed to rule out non-specific stimulant effects. Nicotine (1.0mg/kg) enhanced the effect of 10mg/kg citalopram and 20mg/kg reboxetine in the mFST. Similarly, nicotine (1.0mg/kg) enhanced the effect of 3 and 10mg/kg citalopram and 3 and 10mg/kg reboxetine in the mTST. No concomitant locomotor stimulation was observed at the tested dose combinations. Mecamylamine was effective on its own in some tests, but did not augment the effects of citalopram or reboxetine at the doses tested. The data show that nicotine enhances the effects of both serotonin and noradrenaline reuptake inhibitors, possibly reflecting nicotine's facilitating effects on the release of these two neurotransmitters, and indicating that nicotine may enhance antidepressant action.     

Pre- and post-treatments with escitalopram protect against experimental ischemic neuronal damage via regulation of BDNF expression and oxidative stress

Selective serotonin re-uptake inhibitors (SSRI) have been widely used in treatment of major depression because of their efficacy, safety, and tolerability. Escitalopram, an SSRI, is known to decrease oxidative stress in chronic stress animal models. In the present study, we examined the neuroprotective effects of pre- and post-treatments with 20 mg/kg and 30 mg/kg escitalopram in the gerbil hippocampal CA1 region (CA1) after transient cerebral ischemia. Pre-treatment with escitalopram protected against ischemia-induced neuronal death in the CA1 after ischemia/reperfusion (I/R). Post-treatment with 30 mg/kg, not 20 mg/kg, escitalopram had a neuroprotective effect against ischemic damage. In addition, 20 mg/kg pre- and 30 mg/kg post-treatments with escitalopram increased brain-derived neurotrophic factor (BDNF) protein levels in the ischemic CA1 compared to vehicle-treated ischemia animals. In addition, 20 mg/kg pre- and 30 mg/kg post-treatments with escitalopram reduced microglia activation and decreased 4-hydroxy-2-nonenal and Cu,Zn-superoxide dismutase immunoreactivity and their levels in the ischemic CA1 compared to vehicle-treated ischemia animals after transient cerebral ischemia. In conclusion, these results indicated that pre- and post-treatments with escitalopram can protect against ischemia-induced neuronal death in the CA1 induced by transient cerebral ischemic damage by increase of BDNF as well as decrease of microglia activation and oxidative stress.     

Baclofen does not protect against cerebral ischemia in rats

Presynaptic release of glutamate into the extracellular compartment and activation of receptor-operated calcium channels may contribute to ischemic neuronal damage. We evaluated the effect of baclofen, a selective inhibitor of presynaptic glutamate release, on mortality, working memory, and light microscopic hippocampal and cortical damage in the four-vessel occlusion model of cerebral ischemia using 64 male Wistar rats. Baclofen (10 mg/kg i.p.) given 1 hour before and 30-60 minutes after 20 minutes of global ischemia did not lessen mortality, prevent ischemic cellular damage, or significantly improve working memory compared with no treatment. We conclude that preischemic and postischemic administration of baclofen does not protect neurons from ischemic injury.     

Inhibition of hippocampal 5-HT synthesis by fluoxetine and paroxetine: evidence for the involvement of both 5-HT1A and 5-HT1B/D autoreceptors

Hippocampal serotonin (5-hydroxytryptamine, 5-HT) synthesis, as determined by the accumulation of 5-hydroxytryptophan (5-HTP) following inhibition of L-aromatic amino acid decarboxylase with NSD 1015, was inhibited by systemic administration of the selective serotonin reuptake inhibitors fluoxetine (10 mg/kg i.p.) and paroxetine (3 mg/kg i.p.). Pretreatment of rats with the selective 5-HT1A receptor antagonist WAY 100635 for a period of 7 days using subcutaneously implanted osmotic minipumps (1 mg/kg/day) was sufficient to block the inhibition of 5-HT synthesis following the 5-HT 1A receptor agonist 8-OH-DPAT (0.3 mg/kg s.c.), but failed to inhibit the decrease of hippocampal 5-HT synthesis by fluoxetine (10 mg/kg i.p.) or paroxetine (3 mg/kg i.p.). Similarly, pretreatment of rats with GR 127935 (5 mg/kg i.p.), an antagonist with high affinity for 5-HT1B/D receptors, blocked the reduction of hippocampal 5-HT synthesis following the 5-HT receptor agonist TFMPP (3 mg/kg s.c.) without affecting the reduction of hippocampal 5-HT synthesis by either fluoxetine or paroxetine. In contrast, pretreatment with WAY 100635 (1 mg/kg/day, for 7 days s.c. in osmotic minipumps) in combination with GR 127935 (5 mg/kg i.p.) significantly attenuated the decrease of hippocampal 5-HT synthesis by both fluoxetine and paroxetine. These results indicate that both 5-HT1A and 5-HT1B/1D receptors, which function in the rat as inhibitory somatodendritic and nerve terminal autoreceptors, independently regulate hippocampal 5-HT synthesis and must be simultaneously blocked to prevent the inhibition of 5-HT synthesis by selective serotonin reuptake inhibitors which increase 5-HT availability at both nerve terminals in hippocampus and 5-HT cell bodies in the raphe nuclei.     

Citalopram''s ability to increase the extracellular concentrations of serotonin in the dorsal raphe prevents the drug''s effect in the frontal cortex

Administered intraperitoneally to rats at 1 mg/kg, citalopram, a potent and selective inhibitor of serotonin uptake, significantly increased dialysate serotonin in the dorsal raphe, but not in the frontal cortex. At 10 mg/kg citalopram had a greater effect on raphe serotonin and a moderate and short-lasting increase in the dialysate serotonin in the frontal cortex. Citalopram 1 mg/kg i.p. significantly increased the extracellular concentration of serotonin in the frontal cortex of rats which had received a continuous infusion of 1 microM methiothepine in the dorsal raphe, a condition which by itself did not change cortical serotonin concentrations. The results suggest that the ability of serotonin uptake inhibitors to enhance the extracellular concentrations of serotonin in the dorsal raphe attenuates the drug's effect in the frontal cortex.     

Differential effects of coadministration of fluoxetine and WAY-100635 on serotonergic neurotransmission in vivo: sensitivity to sequence of injections

Serotonin 5-HT(1A) receptor antagonists potentiate the effects of serotonin reuptake inhibitors on extracellular serotonin levels in a variety of brain regions. These effects are quite variable, however, with reports indicating potentiations of anywhere from 100-1900%. One factor that might impact the magnitude of such potentiations is the timing of administration of the two agents; reports in which the reuptake inhibitor is given prior to the serotonin receptor antagonist consistently report larger potentiations than reports in which the antagonist is given first. To test this relationship directly, microdialysis and electrophysiology studies were performed to assess the magnitude of increase in extracellular serotonin and changes in cellular activity produced by the serotonin reuptake inhibitor fluoxetine and the 5-HT(1A) receptor antagonist WAY-100635 under various dosing regimens. In microdialysis studies, when WAY-100635 (0.5 mg/kg s.c.) was administered 80 min after fluoxetine (10 mg/kg i.p.) the increase in serotonin was more than twice that observed when the compounds were coadministered. In electrophysiology studies in vivo, WAY-100635 reversed the depression of cell firing produced by fluoxetine when administered 30 min after fluoxetine, but when the two compounds were coadministered, a depression in firing rate was observed comparable to that produced by fluoxetine alone. In contrast, slice recording studies showed that WAY-100635 blocked the effects of fluoxetine regardless of the order of administration. These results indicate that fluoxetine and WAY-100635 can interact in a fashion not predicted by the currently accepted model. It is likely that neuronal circuitry outside of the raphe nuclei underlies this relationship.     

The highly selective cyclooxygenase-2 inhibitor DFU is neuroprotective when given several hours after transient cerebral ischemia in gerbils

Several studies suggest that cyclooxygenase-2 contributes to the delayed progression of ischemic brain damage. In this study we examined whether the highly selective cyclooxygenase-2 inhibitor DFU reduces neuronal damage when administered several hours after 5 min of transient forebrain ischemia in gerbils. The extent of ischemic injury was assessed behaviorally by measuring the increases in locomotor activity and by histopathological evaluation of the extent of CA1 hippocampal pyramidal cell injury 7 days after ischemia. DFU treatment (10 mg/kg, p.o.) significantly reduced hippocampal neuronal damage even if the treatment is delayed until 12 h after ischemia. These results suggest that selective cyclooxygenase-2 inhibitors may be a valuable therapeutic strategy for ischemic brain injury.     

The protective effect of adenosine A2A receptor antagonism in cerebral ischemia

OBJECTIVES: We reviewed our most recent work on the protective effect of adenosine A(2A)antagonism in cerebral ischemia. METHODS: Focal ischemia was produced in rats by introducing a nylon monofilament pre-coated with silicone through the external carotid artery to occlude the right MCA at its origin. RESULTS: A(2A) antagonism was found protective in the model of permanent focal ischemia induced by the monofilament technique. This methodology provides the possibility of evaluating the protection against the outflow of excitatory amino acids and against an acute motor disturbance, i.e.contralateral turning to the ischemic side in the first hours after ischemia in awake rats. Hours later, a definite neurological deficit and necrotic neuronal damage can be evaluated. DISCUSSION: Our results suggest that A(2A) antagonism may be protective from the earliest up to several hours after the ischemic event.     

Selective noradrenaline reuptake inhibition enhances serotonergic neuronal activity and transmitter release in the rat forebrain

Summary. Present pharmacotherapy of major depression is, in principle, based on enhancement of central monoaminergic neurotransmission. Clinical studies utilizing depletion experiments indicate that antidepressants which primarily enhance serotonergic or noradrenergic central activity, i.e. serotonin or nor-adrenaline reuptake inhibitors, largely work by two separate neuronal pathways. However, experimental studies have shown that noradrenaline may regulate serotonergic neurotransmission both at the serotonin cell body and nerve-terminal level. We therefore investigated the effects of the selective NRI reboxetine on serotonergic neuronal activity and extracellular levels of transmitter in the nerve-terminal area. In vivo electrophysiological experiments showed that low doses of reboxetine significantly enhance the firing rate of serotonergic neurons in the dorsal raphe nucleus of anaesthetized rats. Also, in the medial prefrontal cortex reboxetine (3mg/kg s.c.) enhanced, whereas citalopram (3mg/kg s.c.) reduced, extracellular concentrations of serotonin measured by means of microdialysis in awake rats, using a low dose of citalopram (0,5µM) in the perfusion solution. Local administration of reboxetine only induced an increase in cortical serotonin levels at very high concentrations (1000µM). Hence, NRIs may cause a secondary enhancement of central serotonergic activity by a mechanism separate from 5-HT reuptake inhibition; an effect that may contribute to their clinical antidepressant efficacy.     

Platelet-activating factor antagonists reduce excitotoxic damage in cultured neurons from embryonic chick telencephalon and protect the rat hippocampus and neocortex from ischemic injury in vivo

The neuroprotective effects of the platelet-activating factor (PAF) antagonists BN 52020 and BN 52021 were determined in a temperature-controlled model of transient forebrain ischemia in the rat (occlusion of both common carotid arteries combined with lowering of the mean arterial blood pressure to 40 mm Hg for 10 min). After 7 days of recirculation, the ischemic neuronal damage was evaluated histologically within the hippocampus and neocortex. Combined pre- and post-treatment with the PAF antagonists (2 × 25 mg/kg, s.c.) significantly reduced the resulting neuronal damage of the CA1 and CA3 hippocampal subfields and of the occipital and parietal cerebral cortex. The two PAF antagonists were also tested for their neuroprotective activity in primary neuronal cultures isoalted from embryonic chick telencephalon. Since an excessive activation of excitatory amino acid receptors is discussed to be of importance for the ischemic brain damage, the cultured neurons were exposed to the excitatory amino acid L-glutamate (1 mM) for a period of 60 min. Twenty hours after the excitotoxic insult, BN 52020- and BN 52021- treated cultured (1–100 μM) showed both a better preserved morphology, as well as a dose-dependent increase in cell viability and protein content compared to the control cultures. Our results demonstrate that the PAF antagonists BN 52020 and BN-52021 have the capacity to protect brain tissue against ischemic neuronal damge independent of hypothermic effects and are also capable of reducing excitotoxic damage of telencephalic neurons from chick embryos cultured in the absence of glial or endothelial cells. We thus propose that PAF plays an important role in the pathophysiology of ischemic/excitotoxic neuronal injury via a direct action on neurons. © 1993 Wiley-Liss, Inc.     

Wide therapeutic time window for fasudil neuroprotection against ischemia-induced delayed neuronal death in gerbils

The neuroprotective potential and therapeutic time window for fasudil, a Rho-kinase inhibitor (RKI), were evaluated for delayed neuronal death in gerbils. A preliminary screening was done on fasudil, ozagrel, and edaravone using a single administration in a delayed neuronal death study. Intraperitoneal (i.p.) administration of edaravone, a free radical scavenger (3, 10 mg/kg) immediately after re-circulation did not reduce neuronal degeneration. We previously reported that ozagrel, a thromboxane A(2) synthetase inhibitor (30 mg/kg) also did not reduce neuronal degeneration, while fasudil (3, 30 mg/kg) significantly protected against the ischemia-induced neuronal loss. To clarify the therapeutic time window of fasudil, which showed a positive effect in a preliminary screening, animals received their first i.p. administration of fasudil (10 mg/kg) 24 or 48 h after ischemia. Administration of fasudil twice daily was continued until day 6. Fasudil significantly protected against the ischemia-induced delayed neuronal death when the treatment was started 24 h after ischemia. In gerbils, hydroxyfasudil, an active metabolite of fasudil, was found following an i.p. administration of fasudil (10 mg/kg), and the value of the area under the plasma level curve of hydroxyfasudil was 7 times higher than that of fasudil. Hydroxyfasudil may contribute to the potency of fasudil. The present findings indicate that the RKI fasudil reduces ischemic neuronal damage with a wide therapeutic time window in gerbil, and may be useful in the treatment of acute ischemic stroke in humans.     

The neuroactive steroid 3-alpha-ol-5-beta-pregnan-20-one hemisuccinate, a selective NMDA receptor antagonist improves behavioral performance following spinal cord ischemia

The initial response to an ischemic event is the rapid release of excitatory amino acid's followed by the activation of the "ischemic cascade". It has been suggested that neurosteroids, which act as negative modulators of excitatory amino acid receptors, may improve behavioral functions and promote neuronal survival following ischemia. The present study evaluated the pharmacological effects of 3-alpha-ol-5-beta-pregnan-20-one hemisuccinate (ABHS), a neurosteroid that inhibits excitatory amino acid receptor function, in a rabbit reversible spinal cord ischemia model (RSCIM). ABHS was administered (25 mg/kg) intravenously (i.v.) 5 or 30 min following the start of occlusion to groups of rabbits exposed to ischemia induced by temporary occlusion of the infrarenal aorta. The group P50 represents the duration of ischemia (min) associated with a 50% probability of resultant permanent paraplegia. Quantal analysis indicated that the P50 of the control group was 23.44 +/- 4.32 min. Using the RSCIM, neuroprotection is observed if a drug significantly prolongs the P50 compared to the control group. Treatment with ABHS (25 mg/kg) 5 min post-occlusion significantly (p < 0.05) prolonged the P50 of the group to 49.18 +/- 10.44 min, an increase of 110%. The effect of ABHS was not durable following a single injection since a significant difference between the control and ABHS-treated groups was not measurable at 48 h. However, if ABHS was injected 5 min following the start of ischemia and again 24 h after ischemia, there was a persistent effect of the drug at 48 h. Moreover, ABHS also increased the tolerance to ischemia if administered 30 min following the start of occlusion. Our results suggest that neuroactive steroids such as ABHS, which are selective NMDA receptor antagonists, may have substantial therapeutic benefit for the treatment of ischemic injuries including spinal cord neurodegeneration and stroke.     

Evidence for the involvement of 5-HT1A receptor in the acute antidepressant-like effect of creatine in mice

Creatine was previously shown to produce an antidepressant-like effect in the tail suspension test through a modulation of the dopaminergic system. In this study, the mechanisms underlying its antidepressant-like effect were further evaluated by investigating the involvement of the serotonergic system in its effect. The anti-immobility effect of creatine (1 mg/kg) was prevented by the pretreatment of mice with p-chlorophenylalanine methyl ester (PCPA; 100 mg/kg, i.p., for 4 consecutive days, an inhibitor of serotonin (5-HT) synthesis). Creatine (0.01 mg/kg, sub-effective dose) in combination with sub-effective doses of WAY100635 (0.1 mg/kg, s.c., a 5-HT_1A receptor antagonist), 8-OH-DPAT (0.1 mg/kg, i.p., a 5-HT_1A receptor agonist) or selective serotonin reuptake inhibitors fluoxetine (5 mg/kg, p.o.), paroxetine (0.1 mg/kg, p.o.), citalopram (0.1 mg/kg, p.o.) and sertraline (3 mg/kg, p.o.) reduced the immobility time in the tail suspension test as compared with either drug alone. These results indicate that the antidepressant-like effect of creatine is likely mediated by an interaction with 5-HT_1A receptors. Of note, the present results also indicate that creatine improves the effectiveness of the selective serotonin reuptake inhibitors, a finding that may have therapeutic implications for the treatment of depressive disorders.     

Regional neuroprotective effects of pentobarbital on ischemia-induced brain damage

We investigated the neuroprotective effect of pentobarbital, a GABAA receptor-effector, on ischemic neuronal damage in the gerbils. The animals were allowed to survive for 7 days after 10-min ischemia induced by bilateral occlusion of the common carotid arteries. Morphological changes and abnormal calcium accumulation were evaluated in selectively vulnerable areas after ischemia. Pentobarbital (40 mg/kg, IP), administered 30 min prior to ischemia, significantly reduced neuronal cell loss in the neocortex, the striatum, and the hippocampal CA3 sector. However, pentobarbital failed to prevent the damage to the hippocampal CA1 sector and the thalamus. 45Ca autoradiographic study also revealed that a marked calcium accumulation was found in the selectively vulnerable regions after ischemia, which was consistent with the extent of histological neuronal damage. The abnormal calcium accumulation was reduced in the sites corresponding to most of the regions in which the protective effect of pentobarbital was found. The results suggest that ischemia-induced neuronal damage may be partly caused by an imbalance between excitatory and inhibitory input.