Additive neuroprotective effect of Ketanserin and Ipsapirone on the hippocampal damage after transient forebrain ischemia in the Mongolian gerbil

Activation of 5-HT1A postsynaptic receptors by NLX-101 results in functional recovery and an increase in neuroplasticity in mice with brain ischemia

Pharmacological interventions that selectively activate serotonin 5-hydroxytryptramine-1A (5-HT_1A) heteroreceptors may prevent or attenuate the consequences of brain ischemic episodes. The present study investigated whether the preferential 5-HT_1A postsynaptic receptor agonist NLX-101 (a.k.a. F15599) mitigates cognitive and emotional impairments and affects neuroplasticity in mice that are subjected to the bilateral common carotid artery occlusion (BCCAO) model of brain ischemia. The selective serotonin reuptake inhibitor escitalopram (Esc) was used for comparative purposes because it is able to decrease morbidity and improve recovery in stroke patients and ischemic rodents. Sham and BCCAO mice received daily doses of NLX-101 (0.32 mg/kg, i.p) or Esc (20 mg/kg, i.p) for 28 days. During this period, they were evaluated for locomotor activity, anxiety- and despair-related behaviors and hippocampus-dependent cognitive function, using the open field, elevated zero maze, forced swim test and object location test, respectivelly. The mice's brains were processed for biochemical and histological analyses. BCCAO mice exhibited high anxiety and despair-like behaviors and performed worse than controls in the cognitive assessment. BCCAO induced neuronal and dendritic spine loss and decreases in the protein levels of neuronal plasticity markers, including brain-derived neurotrophic factor (BDNF), synaptophysin (SYN), and postsynaptic density protein-95 (PSD-95), in prefrontal cortex (PFC) and hippocampus. NLX-101 and Esc attenuated cognitive impairments and despair-like behaviors in BCCAO mice. Only Esc decreased anxiety-like behaviors due to brain ischemia. Both NLX-101 and Esc blocked the increase in plasma corticosterone levels and, restored BDNF, SYN and PSD-95 protein levels in the hippocampus. Moreover, both compounds impacted positively dentritic remodeling in the hippocampus and PFC of ischemic mice. In the PFC, NLX-101 increased the BDNF protein levels, while Esc in turn, attenuated the decrease in the PSD-95 protein levels induced by BCCAO. The present results suggest that activation of post-synaptic 5-HT_1A receptors is the molecular mechanism for serotonergic protective effects in BCCAO. Moreover, post-synaptic biased agonists such as NLX-101 might constitute promising therapeutics for treatment of functional and neurodegenerative outcomes of brain ischemia.

Drug-induced hypothermia by 5HT1A agonists provide neuroprotection in experimental stroke: new perspectives for acute patient treatment

BACKGROUND

Drug-induced hypothermia reduces brain damage in animal stroke models and is an undiscovered potential in human stroke treatment. We studied hypothermia induced by the serotonergic agonists S14671 (1-[2-(2-thenoylamino)ethyl]-4[1-(7- methoxynaphtyl)]piperazine) and ipsapirone in a rat stroke model and in man by literature meta-analysis.

METHODS

Rats had 60 minutes of middle cerebral artery occlusion (MCAO) and then 7 days of survival. Body temperatures were monitored for 22 hours. Thirty minutes after MCAO, 1 group (n = 9) received bolus of S14671 (.75 mg/kg) and continuous infusion of .06 mg/kg hour(-1) S14671 for 20 hours. Other MCAO rats (n = 7) had bolus of ipsapirone (.75 mg/kg) and continuous infusion of .25 mg/kg hour(-1) ipsapirone for 3 hours. Controls (n = 9; n = 5) received similar amounts of vehicle as bolus and continuous infusion for 20 hours/3 hours. Additional controls of the S14761 effect in MCAO were performed as previously mentioned (n = 10) but with rats kept normothermic by a heating lamp for 22 hours. Finally, a meta-analysis of ipsapirone-induced hypothermia in man was included.

RESULTS

Infarct volumes were reduced by 50% in hypothermic rats versus controls (P < .05). S14671 rats kept normothermic did not show infarct reduction (P > .05). The body temperature after stroke was reduced 1.0-3.0°C compared with controls for 20 hours with S14671 treatment and for 6 hours with ipsapirone treatment. In humans, ipsapirone reduced temperature in average with .55 °C ranging between .1-1.4 °C.

CONCLUSIONS

5-hydroxytryptamine receptor 1A (5HT(1A)) agonists significantly reduce infarct volumes in MCAO rats primarily because of the hypothermic drug effect. 5HT(1A) agonists may be introduced to reduce body temperatures rapidly and prepare patients for further therapeutic hypothermia.

Ziprasidone attenuates brain injury after focal cerebral ischemia induced by middle cerebral artery occlusion in rats

Ziprasidone is an atypical antipsychotic drug used for the treatment of schizophrenia. Recent studies have reported that atypical antipsychotics have neuroprotective effects against brain injury. In the present study, the effect of ziprasidone on ischemic brain injury was investigated. Focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) in rats. All the animals experienced ischemia for 1h and then underwent reperfusion. The infarct size induced by MCAO was significantly reduced in the animals that received acute treatment with 5mg/kg ziprasidone and subchronic treatment with 2.5mg/kg ziprasidone for 7 days compared with that in the vehicle-treated animals. The acute treatment with ziprasidone significantly improved neurological functions, as measured by the modified neurological severity score, in a dose-dependent manner. The subchronic treatment produced more rapid recovery from functional deficits than the vehicle treatment. The immunohistochemical investigation revealed that the subchronic treatment prevented severe loss of neuronal marker intensity and attenuated the increased in microglial marker intensity in the infarcted cortical area. These results suggest that ziprasidone has neuroprotective effects in a rat model of ischemic stroke and provide new insight for its clinical applications.

MDMA produces a delayed and sustained increase in the extracellular concentration of glutamate in the rat hippocampus

The neurochemical effects of MDMA (3,4-methylenedioxymethamphetamine) on monoaminergic and cholinergic systems in the rat brain have been well documented. However, little is known regarding the effects of MDMA on glutamatergic systems in the brain. In the present study the effects of multiple injections of MDMA on extracellular concentrations of glutamate in the striatum, prefrontal cortex, and dorsal hippocampus were examined. Two or four, but not one, injections of MDMA (10 mg/kg, i.p. at 2 h intervals) resulted in a 2-3 fold increase in the extracellular concentration of glutamate in the hippocampus; no increase was evident in the striatum or prefrontal cortex. Reverse dialysis of MDMA (100 μM) into the hippocampus also elicited an increase in extracellular glutamate. Treatment with the 5-HT reuptake inhibitor fluoxetine prevented the increase in extracellular glutamate in the hippocampus following the systemic administration of MDMA, as did treatment with the serotonin 5-HT2A/C receptor antagonist ketanserin. Moreover, reverse dialysis of the sodium channel blocker tetrodotoxin did not prevent the increase in extracellular glutamate in the hippocampus. These data support the view that stimulation of 5-HT2A/2C receptors on non-neuronal cells by 5-HT released by MDMA promotes glutamate efflux in the hippocampus.

Low dose methamphetamine mediates neuroprotection through a PI3K-AKT pathway

High doses of methamphetamine induce the excessive release of dopamine resulting in neurotoxicity. However, moderate activation of dopamine receptors can promote neuroprotection. Therefore, we used in vitro and in vivo models of stroke to test the hypothesis that low doses of methamphetamine could induce neuroprotection. We demonstrate that methamphetamine does induce a robust, dose-dependent, neuroprotective response in rat organotypic hippocampal slice cultures exposed to oxygen-glucose deprivation (OGD). A similar dose dependant neuroprotective effect was observed in rats that received an embolic middle cerebral artery occlusion (MCAO). Significant improvements in behavioral outcomes were observed in rats when methamphetamine administration delayed for up to 12 h after MCAO. Methamphetamine-mediated neuroprotection was significantly reduced in slice cultures by the addition of D1 and D2 dopamine receptor antagonist. Treatment of slice cultures with methamphetamine resulted in the dopamine-mediated activation of AKT in a PI3K dependant manner. A similar increase in phosphorylated AKT was observed in the striatum, cortex and hippocampus of methamphetamine treated rats following MCAO. Methamphetamine-mediated neuroprotection was lost in rats when PI3K activity was blocked by wortmannin. Finally, methamphetamine treatment decreased both cleaved caspase 3 levels in slice cultures following OGD and TUNEL staining within the striatum and cortex in rats following transient MCAO. These data indicate that methamphetamine can mediate neuroprotection through activation of a dopamine/PI3K/AKT-signaling pathway.

Thermodynamics of peptide and non-peptide interactions with the human 5HT1a receptor

The human serotonin 1a receptor (H5HT1aR) is a highly studied member of the 7 transmembrane G protein-coupled receptors. This model receptor, negatively coupled to adenylyl cyclase via Gi, is linked to physiological processes such as cognition and mood regulation and to associated disorders like anxiety and depression. Gibb's free energies, enthalpies, and entropies were calculated for the agonist [(3)H]8-OH-DPAT in the presence of synthetic peptides derived from sequences of intracellular loops 2 and 3 of the H5HT1aR. For comparative purposes, the thermodynamic parameters were also determined in the presence of a limited number of ligand-binding site substances (the partial agonist dipropyltryptamine [DPT], and the full agonist [(3)H]8-OH-DPAT alone). All of these thermodynamic measurements were based on binding data accumulated over a range of temperatures (0-35 degrees C). Representative examples of binding constant experiments and van't Hoff plots are shown to establish the thermodynamic variables. Although differences exist between the peptides themselves and the non-peptide agonists, in all situations the binding events are highly entropy driven. Differences between this information and published data for rat 5HT1aR are discussed, as are relationships to other receptor systems. Overall, the conclusions should be useful in further defining a comprehensive model of 5HT1aR, and for future development of binding-site and non-binding-site directed agents for the receptor.

Serotonin 5HT1A receptor availability and pathological crying after stroke

OBJECTIVES

Post-stroke depression and pathological crying (PC) implicate an imbalance of serotonergic neurotransmission. We claim that PC follows serotonin depletion that raises the binding potential (p(B)) of the 5-HT(1A) receptor antagonist [carbonyl-(11)C]WAY-100635, which is reversible by selective serotonin re-uptake inhibitor (SSRI) treatment.

MATERIALS AND METHODS

We PET scanned patients with acute stroke and PC and age-matched control subjects. Maps of receptor availability were generated from the images of eight cortical regions and raphe nuclei.

RESULTS

The maps showed highest binding in limbic areas and raphe nuclei, while binding in basal ganglia and cerebellum was negligible. Baseline binding potentials of patients were lower than that of control subjects (3.7 +/- 0.6 vs 4.2 +/- 0.2). Treatment with SSRI markedly reduced free receptor sites, whereas placebo administration led to a global increase.

DISCUSSION

The study is the first suggestion of changes of serotonergic neurotransmission in the early phase of stroke and the modulation of these changes with SSRI treatment.

Regulation of G proteins by human 5-HT1a receptor TM3/i2 and TM5/i3 loop peptides

A bioactive synthetic 11 amino acid peptide probe (P11) was constructed according to the published sequence of the human 5HT1a receptor. The probe was used to enhance understanding of cytoplasmic loop 2/G protein coupling and activation. Additionally, two peptides (P8, P9) from the cytoplasmic loop 3 region were synthesized and studied. These probes were tested in a model system of human 5HT1a receptor stably expressed in Chinese Hamster Ovary cells. In agonist inhibition studies, P11 was active in all three receptor preparations tested: whole cells, membrane bound, and solubilized. In analyses of the membrane bound receptor system, P11 demonstrated uncompetitive inhibition characteristics. When forskolin-stimulated cAMP levels were measured, P11 was inactive in this negatively coupled system. Utilizing a [35S]gamma-S-GTP incorporation assay, P11 was unable to stimulate G protein incorporation of GTP. While P8 and P9 were also broadly active as non-competitive agonist inhibitors, their characteristics differed in the signal transduction system. P8 and P9 did not significantly change forskolin-stimulated cAMP levels. However, P8 increased [35S]gamma-S-GTP incorporation, while P9 decreased incorporation. Thus, P11, a synthetic peptide from the TM3/i2 region of the receptor, provides suggestive evidence that this receptor region is involved in G protein coupling but not activation. On the other hand, P8 and P9 activities suggest that the TM5/i3 region is involved in both coupling to and regulation of G protein activity. The current evidence from these cytoplasmic loop regions is discussed in the overall context of an emerging model for human 5HT1a receptor-G protein interactions.

Electroacupuncture prevents cognitive deficits in pilocarpine-epileptic rats

Here we investigated the effects of electroacupuncture over the cognitive deficits in the pilocarpine model of epilepsy in rats. Acupuncture stimulation was provided at acupoints located in either the midline of the back and of the head [HD]: Gv-20 (Baihui), Gv-14 (Dazhui), Gv-2 (Yaoshu) and M-HN-3 (Yin Tang); or acupoints located in the limbs [LB]: St-36 (Zusanli) and Sp-6 (Sanyinjiao). In the elevated T-maze test, electroacupuncture at HD and LB acupoints produced an improvement in the acquisition and retention parameters. Retention in the inhibitory avoidance test was seen only in short-term retention and only for animals stimulated at HD. At histology it was found that electroacupuncture at HD acupoints abolished tissue shrinkage in dorsal hippocampus, basolateral nucleus of the amygdala, substantia nigra and perirhinal cortex, whereas stimulation of LB acupoints prevented tissue shrinkage in all of the above structures except dorsal hippocampus. Administration of p-chlorophenylalanine, a serotonergic releaser, abolished both behavioral and part of the histological changes in these animals. We conclude that electroacupuncture at HD and LB acupoints prevents atrophy of some limbic structures and improves cognitive deficits in pilocarpine-epileptic rats and that this effect is dependent on the serotonergic system.

Clozapine, ziprasidone and aripiprazole but not haloperidol protect against kainic acid-induced lesion of the striatum in mice, in vivo: Role of 5-HT1A receptor activation

Excessive activation of non-NMDA receptors, AMPA and kainate, contributes to neuronal degeneration in acute and progressive pathologies, possibly including schizophrenia. Because 5-HT(1A) receptor agonists have neuroprotective properties (e.g., against NMDA-induced neurotoxicity), we compared the effects of the antipsychotics, clozapine, ziprasidone and aripiprazole, that are partial agonists at 5-HT(1A) receptor, with those of haloperidol, which is devoid of 5-HT(1A) agonist properties, on kainic acid (KA)-induced striatal lesion volumes, in C57Bl/6N mice. The involvement of 5-HT(1A) receptors was determined by antagonist studies with WAY100635, and data were compared with those obtained using the potent and high efficacy 5-HT(1A) receptor agonist, F13714. Intra-striatal KA lesioning and measurement of lesion volumes using cresyl violet staining were carried out at 48 h after surgery. F13714, antipsychotics or vehicle were administered ip twice, 30 min before and 3 1/2 h after KA injection. WAY100635 (0.63 mg/kg) or vehicle were given sc 30 min before each drug injection. Clozapine (2 x 10 mg/kg), ziprasidone (2 x 20 mg/kg) and aripiprazole (2 x 10 mg/kg) decreased lesion volume by 61%, 59% and 73%, respectively. WAY100635 antagonized the effect of ziprasidone and of aripiprazole but only slightly attenuated that of clozapine. In contrast, haloperidol (2 x 0.16 mg/kg) did not affect KA-induced lesion volume. F13714 dose-dependently decreased lesion volume. The 61% decrease of lesion volume obtained with F13714 (2 x 0.63 mg/kg) was antagonized by WAY100635. WAY100635 alone did not affect lesion volume. These results show that 5-HT(1A) receptor activation protects against KA-induced striatal lesions and indicate that some atypical antipsychotic agents with 5-HT(1A) agonist properties may protect against excitotoxic injury, in vivo.

Strategies of neuroprotection for intracranial aneurysms

Neuroprotection for patients with intracranial aneurysms encompasses the preservation of brain cells endangered by a limited blood and oxygen supply due to aneurysm rupture, clipping or coiling, as well as vasospasm. A large variety of prophylactic and therapeutic neuroprotective strategies have been proposed, but success in human disease is quite limited. Topics of this chapter are the pathophysiology and treatment options of aneurysms, as well as promising neuroprotective strategies in further developmental stages: both physiologically based (hyperoxygenation, hypothermia, avoidance of hyperthermia and hyperglycaemia, hypertension, haemodilution and hypervolaemia) and pharmacologically based (antifibrinolytic drugs, calcium antagonists, anaesthetics, magnesium, erythropoietin and others). New concepts are ischaemic preconditioning, growth factors, and gene therapy. Each strategy is rated on underlying evidence, and research agendas are mentioned.

The 5HT1A receptor agonist, 8-OH-DPAT, protects neurons and reduces astroglial reaction after ischemic damage caused by cortical devascularization

Serotonin 1A (5HT1A) receptor agonists have shown neuroprotective properties in different models of central nervous system injury. Activation of neuronal 5HT1A receptors appears to be involved in the neuroprotective effects. It remains to be elucidated if astroglial cells are responsive to the 5HT1A neuroprotective effects. The participation of astroglial S100B trophic factor has been proposed since 5HT1A activation leads to S100B release and nanomolar concentration level of this molecule showed pro-survival activity in neuronal cultures. Using the cortical devascularization model (CD; unilateral pial disruption), a procedure that results in localized ischemia without producing direct physical damage to brain tissue, we tested the effects of a full 5HT1A agonist, 8-OH-DPAT, or the antagonist WAY-100635 on cortical neuronal survival, astroglial cell response and S100B expression. Wistar rats were subjected to CD lesion which consisted of a craniotomy followed by physical damage to the underlying pial blood vessels. Two and twenty-four hours after the CD lesion, animals received intraperitoneally 8-OH-DPAT (1 mg/kg), WAY-100635 (1 mg/kg) or vehicle (sterile saline). At 3, 7 or 14 days post-lesion, animals were sacrificed and their brains processed for immunohistochemistry to detect GFAP, vimentin, MAP-2, S100B and nuclear Hoechst staining. S100B level in the brain cortex and serum was quantified by an ELISA assay. Serum S100B was considered an index of S100B release. 8-OH-DPAT treatment reduced neuronal death, dendrite loss, astroglial hypertrophy and hyperplasia. In contrast, WAY-100635 treatment increased these parameters of damage. S100B intracellular immunoreactivity in astrocytes and total S100B level showed long-lasting changes after the CD lesion and subsequent treatments depending on the 5HT1A activity. The level of serum S100B was increased in 8-OH-DPAT-treated animals. Increased damage observed in WAY-100635-treated animals supports the hypothesis that the protective 8-OH-DPAT action may be mediated by specific 5HT1A receptors. The reduction in astroglial hypertrophy and hyperplasia as well as long-term changes in S100B immunoreactivity and increased S100B release that we observed allows us to hypothesize that astroglial cells may play an important role in 5HT1A-mediated neuroprotection.