The antidepressant-like and glioprotective effects of the Y2 receptor antagonist SF-11 in the astroglial degeneration model of depression in rats: Involvement of glutamatergic inhibition

In this study, we explored the potential antidepressant-like properties of the brain-penetrant Y2 receptor (Y2R) antagonist SF-11 [N-(4-ethoxyphenyl)- 4-(hydroxydiphenylmethyl)- 1-piperidinecarbothioamide] in the astroglial degeneration model of depression with an emphasis on checking the possible mechanisms implicated in this antidepressant-like effect. The model of depression relies on the loss of astrocytes in the medial prefrontal cortex (mPFC) in Sprague-Dawley rats after administering the gliotoxin L-alpha-aminoadipic acid (L-AAA). SF-11 was administered intraperitoneally (i.p.) once (10 mg/kg) or for three consecutive days (10 mg/kg/day), and the effects of L-AAA and SF-11 injected alone or in combination were investigated using the forced swim test (FST), sucrose intake test (SIT), Western blotting, immunohistochemical staining, and microdialysis. SF-11 produced an antidepressant-like effect after single or three-day administration in rats subjected to astrocyte impairment, as demonstrated by the FST and SIT, respectively. Immunoblotting and immunohistochemical analyses showed that SF-11 reversed the L-AAA-induced astrocyte cell death in the mPFC, suggesting it is glioprotective. Microdialysis studies showed that SF-11 decreased extracellular glutamate (Glu) levels compared to basal value when administered alone and compared to the basal value and control group in LAAA-treated rats. The results from immunoblotting analysis indicated the involvement of Y2Rs in the astrocyte ablation model of depression and the antidepressant-like effect of SF-11. In addition, we observed the participation of the caspase-3 apoptotic pathway in the mechanism of gliotoxin action induced by L-AAA. These findings demonstrate that SF-11, a Y2R antagonist, elicited a rapid antidepressant-like response, possibly linked to its ability to inhibit glutamatergic neurotransmission.

Sequential host-bacteria and bacteria-bacteria interactions determine the microbiome establishment of Nematostella vectensis

BACKGROUND

The microbiota of multicellular organisms undergoes considerable changes during host ontogeny but the general mechanisms that control community assembly and succession are poorly understood. Here, we use bacterial recolonization experiments in Nematostella vectensis as a model to understand general mechanisms determining bacterial establishment and succession. We compared the dynamic establishment of the microbiome on the germfree host and on inert silicone tubes.

RESULTS

Following the dynamic reconstruction of microbial communities on both substrates, we show that the initial colonization events are strongly influenced by the host but not by the silicone tube, while the subsequent bacteria-bacteria interactions are the main driver of bacterial succession. Interestingly, the recolonization pattern on adult hosts resembles the ontogenetic colonization succession. This process occurs independently of the bacterial composition of the inoculum and can be followed at the level of individual bacteria. To identify potential metabolic traits associated with initial colonization success and potential metabolic interactions among bacteria associated with bacterial succession, we reconstructed the metabolic networks of bacterial colonizers based on their genomes. These analyses revealed that bacterial metabolic capabilities reflect the recolonization pattern, and the degradation of chitin might be a selection factor during early recolonization of the animal. Concurrently, transcriptomic analyses revealed that Nematostella possesses two chitin synthase genes, one of which is upregulated during early recolonization.

CONCLUSIONS

Our results show that early recolonization events are strongly controlled by the host while subsequent colonization depends on metabolic bacteria-bacteria interactions largely independent of host ontogeny. Video Abstract.

Group III metabotropic glutamate receptors as promising targets for neuroprotective therapy: Particular emphasis on the role of mGlu4 and mGlu7 receptors

There is still no effective treatment for central nervous system (CNS) pathologies, including cerebral ischemia, neurotrauma, and neurodegenerative diseases in which the Glu/GABA balance is disturbed with associated excitotoxicity. It is thus important to search for new efficacious therapeutic strategies. Preclinical studies on the role of metabotropic glutamate receptors (mGluRs) in neuroprotection conducted over the years show that these receptors may have therapeutic potential in these CNS disorders. However, clinical trials, especially for treating Parkinson's disease, have been unsatisfactory. This review focuses on the specific role of group III mGluRs in neuroprotection in experimental in vitro and in vivo models of excitotoxicity/neurotoxicity using neurotoxins as well as ischemia, traumatic brain injury, and neurodegenerative diseases such as Parkinson's disease, Alzheimer's diseases, and multiple sclerosis. The review highlights recent preclinical studies in which group III mGluR ligands (especially those acting at mGluR4 or mGluR7) were administered after damage, thus emphasizing the importance of the therapeutic time window in the treatment of ischemic stroke and traumatic brain injury. From a clinical standpoint, the review also highlights studies using group III mGluR agonists with favorable neuroprotective efficacy (histological and functional) in experimental ischemic stroke, including healthy normotensive and-hypertensive rats. This review also summarizes possible mechanisms underlying the neuroprotective activity of the group III mGluR ligands, which may be helpful in developing more effective and safe therapeutic strategies. Therefore, to fully assess the role of these receptors in neuroprotection, it is necessary to uncover new selective ligands, primarily those stimulating mGlu4 and mGlu7 receptors.

Neuropeptide Y Y2 and Y5 receptors as potential targets for neuroprotective and antidepressant therapies: Evidence from preclinical studies

There is currently no effective treatment either for neurological illnesses (ischemia and neurodegenerative diseases) or psychiatric disorders (depression), in which the Glu/GABA balance is disturbed and accompanied by significant excitotoxicity. Therefore, the search for new and effective therapeutic strategies is imperative for these disorders. Studies conducted over the last several years indicate that the neuropeptide Y (NPY)-ergic system may be a potential therapeutic target for neuroprotective or antidepressant compounds. This review focuses on the neuroprotective roles of Y2 and Y5 receptors (YRs) in neurological disorders such as ischemia, Alzheimer's disease, Parkinson's disease, Huntington's disease, and in psychiatric disorders such as depression. It summarizes current knowledge on the possible mechanisms underlying the neuroprotective or antidepressant-like actions of Y2R and Y5R ligands. The review also discusses ligands acting at Y2R and Y5R and their limitations as in vivo pharmacological tools. The results from the preclinical studies discussed here may be useful in developing effective therapeutic strategies to treat neurological diseases on the one hand and psychiatric disorders on the other, and may pave the way for the development of novel Y2R and Y5R ligands as candidate drugs for the treatment of these diseases.

A role of noradrenergic receptors in anxiolytic-like effect of high CRF in the rat frontal cortex

Corticotropin releasing factor (CRF) is a neuropeptide widely distributed in the brain as a hormonal modulator and neurotransmitter. The best known behavioral function of CRF is activation of stress and anxiety via the hypothalamus and limbic structures but the role of CRF in the cortex is still poorly understood. Our previous studies have shown anxiolytic-like effects of high doses of CRF injected into the Fr2 frontal cortex and involvement of CRF1 receptors (R) in that effect. These results seemed to be controversial as most other studies suggested anxiogenic and not anxiolytic effects of CRF1R stimulation. Since stress is associated with adrenergic system, in the present study, we focused on participation of alpha1 and alpha2 or beta adrenergic receptors in the anxiolytic-like effect of CRF. Moreover, we verified whether these effects of CRF in the Fr2 were really connected with CRF1R. Male Wistar rats were bilaterally microinjected with CRF in a dose of 0.2 μg/1 μl/site or with the specific agonist of CRF1R, stressin 1 (0.2-0.0125 μg/1 μl/site) into the Fr2 area. The elevated plus maze (EPM) test was performed 30 min later to assess the anxiolysis. An involvement of noradrenergic receptors in the CRF induced anxiolytic-like effect in the Fr2 was studied by pretreatment with the alpha1 antagonist prazosin, alpha2 agonist clonidine, alpha2 antagonist RS 79948 or beta antagonist propranolol, 20-30 min before CRF. The influence on anxiety was assessed in the EPM test. The results show that anxiolytic behavior after CRF microinjection into the Fr2 area seems to be mainly connected with the CRF1R activation because a similar effect was observed after stressin 1 administration and it was blocked by CRF1R antagonist. The results observed after administration of noradrenergic ligands indicated that anxiolytic effects of CRF in the Fr2 engaged the alpha1 and alpha2 adrenergic receptors but not beta receptors.

Application of Alanine Scanning to Determination of Amino Acids Essential for Peptide Adsorption at the Solid/Solution Interface and Binding to the Receptor: Surface-Enhanced Raman/Infrared Spectroscopy versus Bioactivity Assays

The article describes the application of the alanine-scanning technique used in combination with Raman, surface-enhanced Raman, attenuated total reflection Fourier transform infrared, and surface-enhanced infrared absorption (SEIRA) spectroscopies, which allowed defining the role of individual amino acid residues in the C-terminal 6-14 fragment of the bombesin chain (BN6-14) on the path of its adsorption on the surface of Ag (AgNPs) and Au nanoparticles (AuNPs). A reliable analysis of the SEIRA spectra of these peptides was possible, thanks to a curve fitting of these spectra. By combining alanine-scanning with biological activity studies using cell lines overexpressing bombesin receptors and the intracellular inositol monophosphate assay, it was possible to determine which peptide side chains play a significant role in binding a peptide to membrane-bound G protein-coupled receptors (GPCRs). Based on the analysis of spectral profiles and bioactivity results, conclusions for the specific peptide-metal and peptide-GPCR interactions were drawn and compared.

Ketamine and Ro 25-6981 Reverse Behavioral Abnormalities in Rats Subjected to Dietary Zinc Restriction

Clinical and preclinical studies indicate that zinc (Zn) is an essential factor in the development and treatment of major depressive disorder (MDD). Conventional monoamine-based antidepressants mobilize zinc in the blood and brain of depressed patients as well as rodents. N-methyl-D-aspartate acid receptor (NMDAR) antagonists exhibit antidepressant-like activity. However, not much is known about the antidepressant efficacy of NMDAR antagonists in zinc-deficient (ZnD) animals. We evaluated the antidepressant-like activity of two NMDAR antagonists (ketamine; global NMDAR antagonist and Ro 25-6981 (Ro); selective antagonist of the GluN2B NMDAR subunit) in ZnD rats using the forced swim test (FST) and sucrose intake test (SIT). A single dose of either Ro 25-6981 or ketamine normalized depressive-like behaviors in ZnD rats; however, Ro was effective in both tests, while ketamine was only effective in the FST. Additionally, we investigated the mechanism of antidepressant action of Ro at the molecular (analysis of protein expression by Western blotting) and anatomical (density of dendritic spines by Golgi Cox-staining) levels. ZnD rats exhibited decreased phosphorylation of the p70S6K protein, and enhanced density of dendritic spines in the prefrontal cortex (PFC) compared to control rats. The antidepressant-like activity of Ro was associated with the increased phosphorylation of p70S6K and ERK in the PFC. In summary, single doses of the NMDAR antagonists ketamine and Ro exhibited antidepressant-like activity in the ZnD animal model of depression. Animals were only deprived of Zn for 4 weeks and the biochemical effects of Zn deprivation and Ro were investigated in the PFC and hippocampus. The shorter duration of dietary Zn restriction may be a limitation of the study. However, future studies with longer durations of dietary Zn restriction, as well as the investigation of multiple brain structures, are encouraged as a supplement to this study.

Simultaneous activation of mGlu2 and muscarinic receptors reverses MK-801-induced cognitive decline in rodents

The activity of an allosteric agonist of muscarinic M₁ receptor, VU0357017, and a positive allosteric modulator (PAM) of M₅ receptor, VU0238429, were investigated alone or in combination with the mGlu₂ receptor PAM, LY487379 using the following behavioural tests: prepulse inhibition (PPI), novel object recognition (NOR), and spatial delayed alternation (SDA). VU0357017 (10 and 20 mg/kg) and VU0238429 (5 and 10 mg/kg) reversed deficits in PPI while VU0238429 (2.5 and 5 mg/kg) was effective in SDA. The simultaneous administration of subeffective doses of M₁ or M₅ activators (5, 1, or 0.25 mg/kg) with LY487379 (0.5 mg/kg) induced the same effect as that observed for the active dose of each compound. Selective M₁ or M₅ receptor blockers antagonized the effect exerted by these combinations, and pharmacokinetic studies confirmed independent transport through the blood-brain barrier. The expression of both receptors (M₁ and M₅) was established in brain structures involved in cognition (neocortex, hippocampus, and entorhinal cortex) in both the rat and the mouse brains by immunofluorescence staining. Specifically, double neuronal staining of mGlu₂-M₁ and mGlu₂-M₅ receptors was observed in many areas of the rat brain, while the number of double-stained mGlu₂-M₁ receptors was moderate in the mouse brain with no mGlu₂-M₅ colocalization. Finally, the combined administration of subeffective doses of the compounds did not alter prolactin levels or motor coordination, in contrast to the compounds given alone at the highest dose or in combination with standard neuroleptics.

Characterization of the Brain Penetrant Neuropeptide Y Y2 Receptor Antagonist SF-11

This paper discusses the biological and three-dimensional molecular structure of the novel, nonpeptide Y2R antagonist, SF-11 [N-(4-ethoxyphenyl)-4-(hydroxydiphenylmethyl)-1-piperidinecarbothioamide]. Pharmacokinetic studies in a rat model indicated that, following intraperitoneal dosing, SF-11 crossed the blood-brain barrier and was able to penetrate the brain, making it a suitable tool for behavioral studies. We showed for the first time that SF-11 decreased the immobility time in the forced swim test (FST) after acute peripheral administration (10 and 20 mg/kg), indicating that it has antidepressant potential. Inhibitors of the mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) and phosphatidylinositol 3-kinase (PI3K) signaling pathways blocked the anti-immobility effect of SF-11, suggesting that these pathways are involved in the antidepressant-like activity of SF-11 in the FST. The results of locomotor activity of rats indicate that the effects observed in the FST are specific and due to the antidepressant-like activity of SF-11. These findings provide further evidence for the antidepressant potential of Y2R antagonists. Also, the application of Fourier transform infrared absorption (FT-IR) and Raman spectroscopy (RS) methods combined with theoretical density functional theory (DFT) calculations allowed us to present the optimized spatial orientation of the investigated drug. Structural characterization of SF-11 based on vibrational spectroscopic data is of great importance and will aid in understanding its biological activity and pave the way for its development as a new antidepressant agent.

Neuroprotective effect of the group III mGlu receptor agonist ACPT-I after ischemic stroke in rats with essential hypertension

Our previous studies have shown that ACPT-I [(1S, 3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid], a blood-brain barrier permeable agonist of group III metabotropic glutamate (mGlu) receptors, was neuroprotective against middle cerebral artery occlusion/reperfusion (MCAO/R) in normotensive rats. Preclinical studies are typically performed on healthy animals, whereas stroke patients predominately exhibit comorbidities, such as hypertension; therefore, in the present study, we investigated the effect of ACPT-I in spontaneously hypertensive rats (SHR) after MCAO/R. We examined the potential neuroprotective action of ACPT-I (30 mg/kg) when administered during occlusion or reperfusion via the assessment of not only the brain infarction volume but also motor (CatWalk gait analysis and open field test) and sensorimotor (vibrissae-evoked forelimb-placing test) functions following MCAO/R. We determined that ACPT-I not only reduced the cortico-striatal infarction but also improved several gait parameters (run speed, run and stand durations, swing speed and stride length) and mobility when administered 30 min after the start of the occlusion or 30 min after the start of reperfusion. Moreover, the sensorimotor function was improved in hypertensive rats treated with ACPT-I during occlusion. In conclusion, the current findings provide further evidence for the neuroprotective effects of ACPT-I against ischemic damage. These findings may have clinical implications because hypertension is an important risk factor for ischemic stroke.

Involvement of extracellular signal-regulated kinase (ERK) in the short and long-lasting antidepressant-like activity of NMDA receptor antagonists (zinc and Ro 25-6981) in the forced swim test in rats

Short and long acting NMDA receptor (NMDAR) antagonists exert their antidepressant-like effects by activating signaling pathways involved in the synthesis of synaptic proteins and formation of new synaptic connections in the prefrontal cortex (PFC) of rats. The blockade of the ERK pathway abolishes ketamine and Ro 25-6981 antidepressant potency. However, the role of ERK in the antidepressant-like activity of short acting NMDAR antagonists is still unclear. More puzzling is the fact that the precise role of ERK in the short and long lasting effects of long-acting NMDAR antagonists is unknown. In this study, we show that zinc, (Zn) a short-acting NMDAR antagonist evokes only transient ERK activation, which is observed 7 min after its administration in the PFC of rats. In contrast to Zn, the long acting NMDAR antagonist Ro 25-6981 produces persistent ERK activation lasting up to 24 h. Pretreatment with the MAPK/ERK inhibitor (U0126) totally abolished Zn and Ro 25-6981 antidepressant-like activities in the forced swim test in rats. However, when U0126 is administered 15 min after Zn or Ro 25-6981 both compounds maintain their short-lasting antidepressant-like activity. On the other hand, posttreatment with U0126 significantly attenuated the long lasting antidepressant-like activity of Ro 25-6981. These results indicate that the activation of ERK is crucial for the short- and long lasting antidepressant-like activity observed in the FST in rats.

Antidepressant-like activity of the neuropeptide Y Y5 receptor antagonist Lu AA33810: behavioral, molecular, and immunohistochemical evidence

RATIONALE

It has recently been found that chronic treatment with the highly selective, brain-penetrating Y5 receptor antagonist, Lu AA33810 [N-[[trans-4-[(4,5-dihydro [1] benzothiepino[5,4-d] thiazol-2-yl) amino] cyclohexyl]methyl]-methanesulfonamide], produces antidepressant-like effects in the rat chronic mild stress model.

OBJECTIVE

In the present study, we investigated the possible antidepressant-like activity of Lu AA33810 in rats subjected to glial ablation in the prefrontal cortex (PFC) by the gliotoxin L-AAA, which is an astroglial degeneration model of depression.

RESULTS

We observed that Lu AA33810 administered intraperitoneally at a single dose of 10 mg/kg both reversed depressive-like behavioral changes in the forced swim test (FST) and prevented degeneration of astrocytes in the mPFC. The mechanism of antidepressant and glioprotective effects of Lu AA33810 has not been studied, so far. We demonstrated the contribution of the noradrenergic rather than the serotonergic pathway to the antidepressant-like action of Lu AA33810 in the FST. Moreover, we found that antidepressant-like effect of Lu AA33810 was connected with the influence on brain-derived neurotrophic factor (BDNF) protein expression. We also demonstrated the antidepressant-like effect of Lu AA33810 in the FST in rats which did not receive the gliotoxin. We found that intracerebroventricular injection of the selective MAPK/ERK inhibitor U0126 (5 μg/2 μl) and the selective PI3K inhibitor LY294002 (10 nmol/2 μl) significantly inhibited the anti-immobility effect of Lu AA33810 in the FST in rats, suggesting that MAPK/ERK and PI3K signaling pathways could be involved in the antidepressant-like effect of Lu AA33810.

CONCLUSION

Our results indicate that Lu AA33810 exerts an antidepressant-like effect and suggest the Y5 receptors as a promising target for antidepressant therapy.

Neuropeptide Y Y2 and Y5 receptors as promising targets for neuroprotection in primary neurons exposed to oxygen-glucose deprivation and in transient focal cerebral ischemia in rats

It was postulated that neuropeptide Y (NPY)-ergic system could be involved in the ischemic pathophysiology, however, the role of particular subtypes of NPY receptors (YRs) in neuroprotection against ischemia is still not well known. Therefore, we investigated the effect of NPY and YR ligands using in vitro and in vivo experimental ischemic stroke models. Our in vitro findings showed that NPY (0.5-1μM) and specific agonists of Y2R (0.1-1μM) and Y5R (0.5-1μM) but not that of Y1R produced neuroprotective effects against oxygen-glucose deprivation (OGD)-induced neuronal cell death, being also effective when given 30min after the end of OGD. The neuroprotective effects of Y2R and Y5R agonists were reversed by appropriate antagonists. Neuroprotection mediated by NPY, Y2R and Y5R agonists was accompanied by the inhibition of both OGD-induced calpain activation and glutamate release. Data from in vivo studies demonstrated that Y2R agonist (10μg/6μl; i.c.v.) not only diminished the infarct volume in rats subjected to transient middle cerebral artery occlusion (MCAO) but also improved selected gait parameters in CatWalk behavioral test, being also effective after delayed treatment. Moreover, we found that a Y5R agonist (10μg/6μl; i.c.v.) did not reduce MCAO-evoked brain damage but improved stride length, when it was given 30min after starting the occlusion. In conclusion, our studies indicate that Y5 and especially Y2 receptors may be promising targets for neuroprotection against ischemic damage.

Activation of mTOR dependent signaling pathway is a necessary mechanism of antidepressant-like activity of zinc

The rapid antidepressant response to the N-methyl-D-aspartate (NMDA) receptor antagonists is mediated by activation of the mammalian target of the rapamycin (mTOR) signaling pathway, an increase in the synthesis of synaptic proteins and formation of new synapses in the prefrontal cortex (PFC) of rats. Zinc (Zn), which is a potent NMDA receptor antagonist, exerts antidepressant-like effects in screening tests and models of depression. We focused these studies in investigating whether activation of the mTOR signaling pathway is also a necessary mechanism of the antidepressant-like activity of Zn. We observed that a single injection of Zn (5 mg/kg) induced an increase in the phosphorylation of mTOR and p70S6K 30 min and 3 h after Zn treatment at time points when Zn produced also an antidepressant-like effect in the forced swim test (FST). Furthermore, Zn administered 3 h before the decapitation increased the level of brain derived neurotrophic factor (BDNF), GluA1 and synapsin I. An elevated level of GluA1 and synapsin I was still observed 24 h after the Zn treatment, although Zn did not produce any effects in the FST at that time point. We also observed that pretreatment with rapamycin (mTORC1 inhibitor), LY294002 (PI3K inhibitor), H-89 (PKA inhibitor) and GF109203X (PKC inhibitor) blocked the antidepressant-like effect of Zn in FST in rats and blocks Zn-induced activation of mTOR signaling proteins (analyzed 30 min after Zn administration). These studies indicated that the antidepressant-like activity of Zn depends on the activation of mTOR signaling and other signaling pathways related to neuroplasticity, which can indirectly modulate mTOR function.

Neuroprotective effects of the allosteric agonist of metabotropic glutamate receptor 7 AMN082 on oxygen-glucose deprivation- and kainate-induced neuronal cell death

Although numerous studies demonstrated a neuroprotective potency of unspecific group III mGluR agonists in in vitro and in vivo models of excitotoxicity, little is known about the protective role of group III mGlu receptor activation against neuronal cell injury evoked by ischemic conditions. The aim of the present study was to assess neuroprotective potential of the allosteric agonist of mGlu7 receptor, N,N'-Bis(diphenylmethyl)-1,2-ethanediamine dihydrochloride (AMN082) against oxygen-glucose deprivation (OGD)- and kainate (KA)-evoked neuronal cell damage in primary neuronal cultures, with special focus on its efficacy after delayed application. We demonstrated that in cortical neuronal cultures exposed to a 180 min OGD, AMN082 (0.01-1 µM) in a concentration- and time-dependent way attenuated the OGD-induced changes in the LDH release and MTT reduction assays. AMN082 (0.5 and 1 µM) produced also neuroprotective effects against KA-evoked neurotoxicity both in cortical and hippocampal cultures. Of particular importance was the finding that AMN082 attenuated excitotoxic neuronal injury after delayed application (30 min after OGD, or 30 min-1 h after KA). In both models of neurotoxicity, namely OGD- and KA-induced injury, the neuroprotective effects of AMN082 (1 µM) were reversed by the selective mGlu7 antagonist, 6-(4-Methoxyphenyl)-5-methyl-3-(4-pyridinyl)-isoxazolo[4,5-c]pyridin-4(5H)-one hydrochloride (MMPIP, 1 µM), suggesting the mGlu7-dependent mechanism of neuroprotective effects of AMN082. Next, we showed that AMN082 (0.5 and 1 µM) attenuated the OGD-induced increase in the number of necrotic nuclei as well inhibited the OGD-evoked calpain activation, suggesting the participation of these processes in the mechanism of AMN082-mediated protection. Additionally, we showed that protection evoked by AMN082 (1 µM) in KA model was connected with the inhibition of toxin-induced caspase-3 activity, and this effect was abolished by the mGlu7 receptor antagonist. The obtained results indicated that the activation of mGlu7 receptors may be a promising target for neuroprotection against ischemic and excitotoxic insults.

Lack of neuroprotective effect of celastrol under conditions of proteasome inhibition by lactacystin in in vitro and in vivo studies: implications for Parkinson's disease

A number of studies suggest that the ubiquitin-proteasome system (UPS) impairment may underlie neuronal death in Parkinson's disease. Celastrol is a neuroprotective agent with anti-inflammatory and antioxidant properties. The aim of this study was to determine whether celastrol may exert neuroprotective effects both in vitro and in vivo under conditions of the lactacystin-induced UPS inhibition. In the in vitro study, mouse primary cortical neurons and neuroblastoma SH-SY5Y cells were incubated with lactacystin for 48 h (2.5 and 10 μg/ml, respectively). The animal study was performed on male Wistar rats injected unilaterally with lactacystin (5 μg/2 μl) into the substantia nigra (SN) pars compacta. In the in vitro study, we did not found any protective effects of celastrol, given either in the pre- or co-treatment mode. Moreover, in the higher concentrations, celastrol itself reduced cell viability, and enhanced the lactacystin-induced cell death in both types of cells. In the in vivo study, none of the celastrol doses (0.3-3 mg/kg) attenuated the lactacystin-induced decrease in the level of dopamine (DA) and its metabolites or protected nigral dopaminergic neurons against the lactacystin-induced degeneration. The highest celastrol dose potentiated the lactacystin-induced decrease in the level of DA and its metabolites in the lesioned striatum, and accelerated the lactacystin-induced increase in the oxidative and total metabolism of DA. Moreover, when given alone, this dose of celastrol bilaterally decreased the number and/or density of dopaminergic neurons in the SN. Our results demonstrate that celastrol does not induce neuroprotective effects under conditions of UPS inhibition.

Neuropeptide Y and its C-terminal fragments acting on Y2 receptor: Raman and SERS spectroscopy studies

In this paper, we present spectroscopic studies of neuropeptide Y (NPY) and its native NPY(3-36), NPY(13-36), and NPY(22-36) and mutated acetyl-(Leu(28,31))-NPY(24-36)C-terminal fragments acting on Y2 receptor. Since there is some evidence for the correlation between the SERS patterns and the receptor binding ability, we performed a detailed analysis for these compounds at the metal/water interface using Raman spectroscopy (RS) and surface-enhanced Raman spectroscopy (SERS) methods. Many studies have suggested that interactions of this kind are crucial for a variety of biomedical and biochemical phenomena. The identification of amino acids in these peptide sequences by SERS allowed us to determine which molecular fragments were responsible for the interaction with the silver nanoparticle surface. Our findings demonstrated that in all of the investigated compounds, the NPY(32-36)C-terminal fragment (Thr(32)-Arg(33)-Gln(34)-Arg(35)-Tyr(36)NH2) was involved in the adsorption process onto metal substrate. The results of the present study suggest that the same molecular fragment interacts with the Y2 receptor, what proved the usefulness of the SERS method in the study of these biologically active compounds. The search for analogs acting on Y2 receptor may be important from the viewpoint of possible future clinical applications.

Antidepressant-like effect of the mGluR5 antagonist MTEP in an astroglial degeneration model of depression

The glutamatergic predominance in the excitatory-inhibitory balance is postulated to be involved in the pathogenesis of depression. Such imbalance may be induced by astrocyte ablation which reduces glutamate uptake and increases glutamate level in the synaptic cleft. In the present study, we tried to ascertain whether astroglial degeneration in the prefrontal cortex could serve as an animal model of depression and whether inhibition of glutamatergic transmission by the mGluR5 antagonist MTEP could have antidepressant potential. Astrocytic toxins l-or dl-alpha-aminoadipic acid (AAA), 100μg/2μl, were microinjected, bilaterally into the rat medial prefrontal cortex (PFC) on the first and second day of experiment. MTEP (10mg/kg) or imipramine (30mg/kg) were administered on the fifth day. Following administration of MTEP or imipramine the forced swim test (FST) was performed for assessment of depressive-like behavior. The brains were taken out for analysis on day eight. The astrocytic marker, glial fibrillary acidic protein (GFAP) was quantified in PFC by Western blot method and by stereological counting of immunohistochemically stained sections. Both l-AAA and dl-AAA induced a significant increase in immobility time in the FST. This effect was reversed by imipramine, which indicates depressive-like effects of these toxins. A significant decrease in GFAP (about 50%) was found after l-AAA. Both the behavioral and GFAP level changes were prevented by MTEP injection. The obtained results indicate that the degeneration of astrocytes in the PFC by l-AAA may be a useful animal model of depression and suggest antidepressant potential of MTEP.

Group III mGlu receptor agonist, ACPT-I, exerts potential neuroprotective effects in vitro and in vivo

Many evidence suggest that metabotropic glutamate receptors (mGluRs) may modulate glutamatergic transmission, hence, these receptors are regarded as potential targets for neuroprotective drugs. Since group III mGlu receptor agonists are known to reduce glutamatergic transmission by inhibiting glutamate release, we decided to investigate the neuroprotective potential of the group III mGlu receptor agonist, (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid (ACPT-I) against kainate (KA)-induced excitotoxicity in vitro and in vivo. In primary neuronal cell cultures ACPT-I (1-200 μM), applied 30 min-3 h after starting the exposure to KA (150 μM), significantly attenuated the KA-induced LDH release, increased cell viability, and inhibited caspase-3 activity both in cortical and hippocampal cell cultures. The effects were dose-, time- and structure-dependent. The neuroprotective effects of ACPT-I were reversed by (RS)-alpha-cyclopropyl-4-phosphonophenyl glycine, a group III mGluR antagonist. In the in vivo studies, KA (2.5 nmol/1 μl) was unilaterally injected into the rat dorsal CA1 hippocampal region and the size of degeneration was examined by stereological counting of surviving neurons in the CA pyramidal layer. It was found that ACPT-I (7.5 or 15 nmol/1 μl), injected into the dorsal hippocampus 30 min, 1 or 3 h after KA in dose-dependent manner prevented the KA-induced neuronal damage. Moreover, in vivo microdialysis studies in the rat hippocampus showed that ACPT-I (200 μM) given simultaneously with KA (50 μM) significantly diminished the KA-induced glutamate release in the hippocampus. This mechanism seems to play a role in mediating the neuroprotective effect of ACPT-I.

Selective mGluR1 antagonist EMQMCM inhibits the kainate-induced excitotoxicity in primary neuronal cultures and in the rat hippocampus

Abundant evidence suggests that indirect inhibitory modulation of glutamatergic transmission, via metabotropic glutamatergic receptors (mGluR), may induce neuroprotection. The present study was designed to determine whether the selective antagonist of mGluR1 (3-ethyl-2-methyl-quinolin-6-yl)-(4-methoxy-cyclohexyl)-methanone methanesulfonate (EMQMCM), showed neuroprotection against the kainate (KA)-induced excitotoxicity in vitro and in vivo. In in vitro studies on mouse primary cortical and hippocampal neuronal cultures, incubation with KA (150 μM) induced strong degeneration [measured as lactate dehydrogenase (LDH) efflux] and apoptosis (measured as caspase-3 activity). EMQMCM (0.1-100 μM) added 30 min to 6 h after KA, significantly attenuated the KA-induced LDH release and prevented the increase in caspase-3 activity in the cultures. Those effects were dose- and time-dependent. In in vivo studies KA (2.5 nmol/1 μl) was unilaterally injected into the rat dorsal CA1 hippocampal region. Degeneration was calculated by counting surviving neurons in the CA pyramidal layer using stereological methods. It was found that EMQMCM (5-10 nmol/1 μl) injected into the dorsal hippocampus 30 min, 1 h, or 3 h (the higher dose only) after KA significantly prevented the KA-induced neuronal degeneration. In vivo microdialysis studies in rat hippocampus showed that EMQMCM (100 μM) significantly increased γ-aminobutyric acid (GABA) and decreased glutamate release. When perfused simultaneously with KA, EMQMCM substantially increased GABA release and prevented the KA-induced glutamate release. The obtained results indicate that the mGluR1 antagonist, EMQMCM, may exert neuroprotection against excitotoxicity after delayed treatment (30 min to 6 h). The role of enhanced GABAergic transmission in the neuroprotection is postulated.

Different effects of intranigral and intrastriatal administration of the proteasome inhibitor lactacystin on typical neurochemical and histological markers of Parkinson's disease in rats

Impairment of the ubiquitin-proteasome system, responsible for clearing of misfolded and unwanted proteins, has been implicated in the loss of nigrostriatal dopaminergic neurons characteristic of Parkinson's disease (PD). Recently, proteasome inhibitors have been used to model parkinsonian-like changes in animals. In the present study, the effects of intrastriatal and intranigral injections of the selective proteasome inhibitor lactacystin on key markers of PD were examined in Wistar rats. Comparisons of these two different routes of lactacystin administration revealed that only a unilateral, intranigral injection of lactacystin at a dose of 0.5, 1, 2.5 and 5 μg/2 μl produced after 7 days distinct decreases in the concentrations of dopamine (DA) and its metabolites (DOPAC, 3-MT, HVA) in the ipsilateral striatum. The used doses of lactacystin (except for 0.5 μg/2 μl) significantly accelerated DA catabolism, i.e. the total, oxidative MAO-dependent and COMT-catalyzed pathways, as assessed by HVA/DA, DOPAC/DA and 3-MT/DA ratios, respectively, in the ipsilateral striatum. Such alterations were not observed in the striatal DA content and catabolism either 7, 14 or 21 days after a unilateral, intrastriatal high-dose lactacystin injection (5 and 10 μg/2 μl). Intranigrally administered lactacystin (1 μg/2 μl) caused a marked decline of tyrosine hydroxylase (TH) and α-synuclein protein levels in that structure. Neither TH nor α-synuclein protein levels in the substantia nigra (SN) were affected by high lactacystin doses injected intrastriatally. Moreover, stereological counting of TH-immunoreactive neurons and autoradiographic analysis of [(3)H]GBR 12,935 binding to dopamine transporter confirmed a loss of nigrostriatal dopaminergic neurons after an intranigral lactacystin (1 and 2.5 μg/2 μl) injection. An appearance of cardinal neurochemical and histological changes of parkinsonian type only after intranigral lactacystin injection indicates that DA cell bodies in the SN, but not DA terminals in the striatum are susceptible to proteasome inhibition.

Neuroprotective effects of neuropeptide Y-Y2 and Y5 receptor agonists in vitro and in vivo

It is generally assumed that neurodegeneration is connected with glutamatergic hyperactivity, and that neuropeptide Y (NPY) inhibits glutamate release. Some earlier studies indicated that NPY may have neuroprotective effect; however, the results obtained so far are still divergent, and the role of different Y receptors remains unclear. Therefore in the presented study we investigated the neuroprotective potential of NPY and its Y2, Y5 or Y1 receptor (R) ligands against the kainate (KA)-induced excitotoxicity in neuronal cultures in vitro, as well as in vivo after intrahippocampal KA injection and also in an ischemic middle cerebral artery occlusion model after intraventricular injection of Y2R agonist. NPY compounds were applicated 30 min, 1, 3 or 6 h after the start of the exposure to KA, or 30 min after the onset of ischemia. Our results indicate the neuroprotective activity of NPY and its Y2R and Y5R ligands against the kainate-induced excitotoxicity in primary cortical and hippocampal cultures. Importantly, NPY was effective when given as late as 6 h, while Y2R or Y5R agonists 3 h, after starting the exposure to KA. In in vitro studies those protective effects were inhibited by the respective receptor antagonists. Neuroprotection was also observed in vivo after intrahippocampal injection of Y2R and Y5R agonists 30 min or 1 h after KA. No protection was found either in vitro or in vivo after the Y1R agonist. The Y2R agonist also showed neuroprotective activity in the ischemic model. The obtained results indicate that neuropeptide Y produces neuroprotective effect via Y2 and Y5 receptors, and that the compounds may be effective after delayed application.

The behavioural and electrophysiological effects of CRF in rat frontal cortex

Corticotropin releasing factor (CRF) is a neuropeptide widely distributed in the brain. The role of CRF in the behavioural activity and modulation of anxiety states in several brain structures has been well documented, but its function in the cerebral cortex still remains unknown. The aim of our study was to investigate the effect of CRF injected bilaterally into rat frontal cortex on the locomotor and exploratory activity and anxiety of rats. We also examined the effect of CRF on extracellularly recorded field potentials in rat frontal cortical slices in vitro. Behavioural experiments showed that CRF in doses of 0.05, 0.1, 0.2 microg/1 microl/site decreased locomotor and exploratory activity during a 40-min session in the open field test. In the elevated plus-maze test, CRF in a dose of 0.2 microg/1 microl/site produced a significant anxiolytic-like effect, which was prevented by CRF receptor antagonists (alpha-helicalCRF(9-41) and NBI 27914). Electrophysiological experiments showed that CRF-induced a transient depression of field potentials in slices partly disinhibited by GABA(A) and GABA(B) receptors antagonists. The blockade of NMDA receptors prevented the occurrence of that effect. The obtained results suggest that CRF may have anxiolytic-like effects in the frontal cortex. Moreover, the peptide inhibits locomotor and exploratory activity and depresses excitatory synaptic transmission in a NMDA receptor-dependent manner.

The effect of intrahippocampal injection of group II and III metobotropic glutamate receptor agonists on anxiety; the role of neuropeptide Y

Earlier studies conducted by our group and by other authors indicated that metabotropic glutamatergic receptor (mGluR) ligands might have anxiolytic activity and that amygdalar neuropeptide Y (NPY) neurons were engaged in that effect. Apart from the amygdala, the hippocampus, another limbic structure, also seems to be engaged in regulation of anxiety. It is rich in mGluRs and contains numerous NPY interneurons. In the present study, we investigated the anxiolytic activity of group II and III mGluR agonists after injection into the hippocampus, and attempted to establish whether hippocampal NPY neurons and receptors were engaged in the observed effects. Male Wistar rats were bilaterally microinjected with the group II mGluR agonist (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I), group III mGluR agonist O-Phospho-L-serine (L-SOP), NPY, the Y1 receptor antagonist BIBO 3304, and the Y2 receptor antagonist BIIE 0246 into the CA1 or dentate area (DG). The effect of those compounds on anxiety was tested in the elevated plus-maze. Moreover, the effects of L-CCG-I and L-SOP on the expression of NPYmRNA in the hippocampus were studied using in situ hybridization method. It was found that a significant anxiolytic effect was induced by L-SOP injection into the CA1 region or by L-CCG-I injection into the DG. The former effect was inhibited by BIBO 3304, the latter by BIIE 0246. NPY itself showed antianxiety action after injection into both structures. In the CA1 area, the effect of NPY was prevented by BIBO 3304, whereas in the DG by BIIE 0246. Both the mGluR agonists L-CCG-I and L-SOP induced a potent increase in NPYmRNA expression in the DG region of the hippocampal formation. The obtained results indicate that group II and III mGluR agonists, L-CCG-I and L-SOP, as well as NPY display anxiolytic activity in the hippocampus, but act differently in the CA1 and DG. It was observed that group III mGluRs and Y1 receptors were engaged in the response in the CA1 area, whereas group II mGluRs and Y2 receptors played a pivotal role in the DG region.

Genistein inhibits glutamate-induced apoptotic processes in primary neuronal cell cultures: an involvement of aryl hydrocarbon receptor and estrogen receptor/glycogen synthase kinase-3beta intracellular signaling pathway

Phytoestrogens prevent neuronal damage, however, mechanism of their neuroprotective action has not been fully elucidated. This study aimed to evaluate the effects of genistein on glutamate-induced apoptosis in mouse primary neuronal cell cultures. Glutamate (1 mM) enhanced caspase-3 activity and lactate dehydrogenase (LDH) release in the hippocampal, neocortical and cerebellar neurons in time-dependent manner, and these data were confirmed at the cellular level with Hoechst 33342 and calcein AM staining. Genistein (10-10,000 nM) significantly inhibited glutamate-induced apoptosis, and the effect of this isoflavone was most prominent in the hippocampal cells. Next, we studied an involvement of estrogen and aryl hydrocarbon receptors in anti-apoptotic effects of genistein. A high-affinity estrogen receptor antagonist, ICI 182, 780 (1 microM), reversed, whereas less specific antagonist/partial agonist, tamoxifen (1 microM), either intensified or partially inhibited genistein effects. Aryl hydrocarbon receptor antagonist, alpha-naphthoflavone (1 microM), exhibited a biphasic action: it enhanced genistein action toward a short-term exposure (3 h) to glutamate, but antagonized genistein action toward prolonged exposure (24 h) to that insult. SB 216763 (1 microM), which preferentially inhibits glycogen synthase kinase-3beta (GSK-3beta), potentiated genistein effects. These data point to strong effects of genistein at low micromolar concentrations in various brain tissues against glutamate-evoked apoptosis. Moreover, this study provided evidence for involvement of aryl hydrocarbon receptor and estrogen receptor/GSK-3beta intracellular signaling pathway in anti-apoptotic action of genistein.

Neuroprotective effects of MTEP, a selective mGluR5 antagonists and neuropeptide Y on the kainate-induced toxicity in primary neuronal cultures

The majority of studies on neuroprotection tested potentially protective compounds given before, simultaneously or shortly after damage. Such procedures are greatly different from the situation faced in clinical practice. In the present study, we tried to find out whether two compounds, a selective mGluR5 antagonist 3-[(2-methyl-1, 3-thiazol-4-yl) ethynyl]-pyridine (MTEP) and neuro-peptide Y (NPY) elicit neuroprotective action against excitotoxic damage in the mouse neocortical and hippocampal neuronal cultures after delayed treatment. In order to evoke toxic effects, primary cultures were exposed to 150 munic acid (KA) for 24 h (hippocampus) or for 48 h (neocortex). MTEP (1, 10 and 100 microM), or NPY (0.5 microM and 1 microM) were applied 30 min before, or 30 min, 1 h, 3 h or 6 h after KA. Kainate neurotoxicity was measured by lactate dehydrogenase (LDH) efflux from the damaged cells into the culture media. The results of our studies showed that MTEPor NPY treatment attenuated the kainate-induced LDH release in mouse neocortical and hippocampal cultures. The effect was observed when the compounds were added not only before, but also 30 min to 6 h after KA. Moreover, both MTEP and NPY displayed antiapoptotic activity as they prevented the KA-induced increase in the expression of caspase-3 activity in the cultures under study. Summing up, our data showed that MTEP and NPY were neuroprotective in wide time schedule. The effectiveness of late treatment with these compounds opens a new perspective for their potential therapeutic use.