Selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat depression, but their chronic use is associated with side effects and residual symptoms of depression. Both effects induced by SSRIs are mediated by serotonin receptor-dependent signaling pathways, yet the molecular mechanisms underlying these effects remain unclear. Here, we investigated the impact of chronic and acute activation of the 5-HT7 receptor (5-HT7R) using the selective agonist AGH-194 in male mice. Behavioral assessment revealed that chronic AGH-194 administration induced depressive-like effects in the novelty suppressed feeding test (NSFT), female urine sniffing test (FUST), and novel object location test (NOLT). After acute injection, depressive-like effects were observed only in NSFT. At the molecular level, AGH-194 administration activated matrix metalloproteinase 9 (MMP-9) through a 5-HT7R-Gαs signaling-dependent mechanism. Acute treatment induced transient activation, while chronic treatment led to prolonged enzymatic activity, accompanied by a reduction in the expression of the GluA1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) in the hippocampus. At the cellular level, acute but not chronic AGH-194 treatment induced a shift toward more juvenile dendritic spine morphology in the CA1 and dentate gyrus (DG) regions of the hippocampus, along with an increase in dendritic spine density in DG. Electrophysiological recordings demonstrated that acute AGH-194 administration enhanced hippocampal excitability by increasing population spike amplitude in CA1. Chronic AGH-194 treatment further modulated short-term plasticity, increasing both population spike and extracellular field potential paired-pulse ratios (PS-PPR and EPSP-PPR) in CA1, while also enhancing the maximum EPSP slope amplitude. These findings provide novel evidence that chronic 5-HT7R activation can induce depressive-like behaviors in male mice, potentially through sustained MMP-9 activation and alterations in synaptic plasticity. Understanding the molecular and electrophysiological consequences of selective 5-HT7R stimulation may provide insights into receptor-specific mechanisms that could contribute to SSRI-induced side effects, thereby contributing to the development of improved antidepressant strategies.

INTRODUCTION:Dysfunction of the pathway between the ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC) may be responsible for the weaker or lack of efficacy of antidepressant drugs in patients suffering from treatment-resistant depression. This study aims to evaluate the behavioural effects of vHPC lesion with ibotenic acid (IBO) in animals subjected to the chronic mild stress (CMS) procedure and treated with either chronic venlafaxine or acute deep brain stimulation (DBS) in the mPFC. In addition, electrophysiological studies are expected to reveal neuromodulatory effects on the function and plasticity of mPFC neurons in response to stress, lesion, and deep brain stimulation (DBS). METHODS:Wistar Han rats were exposed to the chronic mild stress model of depression and IBO lesion in vHPC. The effects of both procedures were evaluated in a series of behavioural tests (sucrose test, elevated plus maze, novel object recognition, and social interaction) and in electrophysiological recordings (field potential recording and LTP induction). RESULTS:The CMS procedure caused a decrease in sucrose consumption, deficits in cognitive function and social interaction, and increased anxiety. The lesion in vHPC with IBO resulted in similar behavioral changes. Repeated (5 weeks) administration of venlafaxine (10 mg/kg, IP) reversed these deficits in stressed animals but was only partially effective in reversing the effects of IBO lesion in HPC. In contrast, the neuromodulation strategy with DBS of the mPFC produced a robust reversal of all behavioural changes observed in both stressed and lesioned rats. The CMS did not affect the amplitude of Field potentials in mPFC slices, but the induction of Long-Term Potentiation was impaired in these animals. The IBO lesion significantly reduced the amplitude of Field potentials as compared to unstressed rats. Both repeated venlafaxine and acute DBS normalized these effects of the IBO lesion. DISCUSSION:Observed effects were fully normalized by DBS in mPFC but not by venlafaxine, which only partially reversed the IBO lesion-induced effects. The weaker sensitivity of vHPC-lesioned animals to the therapeutic action of venlafaxine provides further evidence that insufficient transmission from the vHPC to the mPFC could be responsible for antidepressant non-response. CONCLUSION:These data support the hypothesis that resistance to antidepressant treatment may result from the inability of antidepressants to fully activate the impaired vHPC-PFC pathway, which could be overcome by the neuromodulatory properties of deep brain stimulation.

Vanadium (V) is a trace element in the environment; it is detected in soil, water, air, dust, and food products. V-containing compounds have shown therapeutic potential in the treatment of diabetes. However, studies on the effects of V on animal behavior remain limited and sporadic. This study investigates the impact of acute (0.2, 2, 5 mg/kg, and 20 mg/kg) or repeated V administration (2 mg/kg/day; 7 days) in mice, employing stress-induced hyperthermia (SIH) as the primary behavioral assay. Additionally, its influence was assessed through single-dose administration in the tail suspension test (TST) and the Rota-rod test. The findings indicate no significant effects of V on the studied parameters, although motor coordination was notably impaired. Electrophysiological experiments were conducted to further elucidate vanadium's influence on neuronal function to assess its effects on long-term potentiation (LTP), a key process in synaptic plasticity, revealing no discernible impact. Moreover, the expression levels of gamma-aminobutyric acid (GABA) receptors, specifically GABAA1, GABAB1, and GABAB2, as well as glutamic acid decarboxylase (GAD67), were analyzed in the frontal cortex (FCx) using western blotting. Collectively, the results indicate a negligible influence of V on glutamatergic transmission and GABAergic receptor activity, after a single administration to healthy mice.

Scopolamine, whose rapid and sustained antidepressant effects were first described nearly two decades ago, is associated with significant adverse effects that limit its clinical use. A safer alternative may involve coadministration of scopolamine at lower doses with other compounds that exhibit antidepressant properties. Growing evidence highlights the potential of group II metabotropic glutamate (mGlu) receptors as targets for depression treatment. This study aimed to evaluate whether the mGlu2 receptor NAM, VU6001966, can enhance the antidepressant-like effects of a subeffective dose of scopolamine in a mouse model of depression and to explore the underlying mechanism. Unpredictable chronic mild stress (UCMS) was employed as an animal model of depression. Behavioral tests assessing anhedonia-, apathy-, and helplessness-like states were used to evaluate the effects of a four-day coadministration of scopolamine and VU6001966. The impact of the drug combination on spatial and non-spatial learning was assessed in both naïve and stressed mice. Protein expression levels in the prefrontal cortex (PFC) and hippocampus were measured via Western blotting. Electrophysiological recordings in the medial PFC (mPFC) were conducted to assess excitatory synaptic transmission and long-term potentiation (LTP). Subchronic VU6001966 treatment dose-dependently alleviated stress-induced depressive-like behaviors in mice. Moreover, a subeffective dose of VU6001966 potentiated the effects of a subeffective dose of scopolamine, significantly reducing UCMS-induced apathy- and anhedonia-like behaviors. Behavioral effects of the AMPA receptor antagonist NBQX and the TrkB receptor antagonist ANA-12 suggest that both AMPA and TrkB receptors contribute to the antidepressant-like actions of scopolamine combined with VU6001966. Consistent with these findings, Western blot analysis revealed accompanying changes in the pTrkB/TrkB ratio in the PFC. The combination of scopolamine and VU6001966 did not impair cognitive function or locomotor activity. However, electrophysiological recordings did not reveal any improvement in UCMS-induced impairments in excitatory synaptic transmission or LTP in the mPFC. Coadministration of scopolamine with the mGlu2 NAM VU6001966 may offer a promising therapeutic strategy for the treatment of depression. Further studies are needed to clarify the underlying mechanisms and confirm its efficacy.

Anxiety is a severe social problem. It is a disease entity that occurs alone or accompanies other diseases such as depression, phobia, or post-traumatic stress disorder. Our earlier studies demonstrated that blockage of arachidonic acid (AA) pathway via inhibition of cyclooxygenase-2 (COX-2) enzyme can modulate mGluRs-induced anxiety-like behavior. Here, we hypothesized that modulation of 2-arachidoglycerol (2-AG), a component of the AA pathway, concomitantly with modulation of mGluR7 signaling, should be adequate to trigger a similar response from the test organism. Since 2-AG is an endogenous agonist for CB1 receptors, we used a CB1/GPR55/μ-opioid receptor antagonist (AM251) alone and in combination with mGluR7 allosteric agonist (AMN082). Stress-induced hyperthermia (SIH) test was performed as a behavioral readout. AM251 has a dual mode on AMN082-mediated effects in SIH in CD-1 mice. Furthermore, the CB1 receptor ligand influenced adaptation to stress in repeated SIH procedures and learning possibilities of mice in the Barnes maze. We also found changes in mGluR7 protein expression levels in the prefrontal cortex (PFC) after mice were exposed to AM251, which showed the potential to attenuate the AMN082-induced decline in mGluR7 levels. The changes induced by AM251 on AMN082-mediated behavioral and biochemical effects were confirmed in electrophysiological experiments in which AM251 abolished AMN082-mediated LTP escalation in PFC. The mGluR7 overexpressed cell line was used to exclude the direct involvement of mGluR7 in AM251 activity. All the above results and the co-localization of CB1 and mGlu7 receptors detected in specific brain regions strongly suggest the specific interaction between CB1 and mGlu7 receptors and their signaling.

Neuronal excitation/inhibition (E/I) imbalance, epileptiform activity, and synaptic dysfunction are present in individuals diagnosed with dementia, including sporadic Alzheimer's disease (sAD), even at early stages. These abnormalities are associated with altered neuronal oscillatory activity, as seen in EEG recordings of sAD patients and transgenic rodents. Hippocampal theta oscillations are crucial for sensorimotor integration, memory consolidation, and network coordination, and depend on synaptic and ionic mechanisms, including the Ih current, mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Lamotrigine (LTG), an HCN channel modulator, influences neuronal excitability and oscillations. Amyloid beta (Aβ) peptide, specifically Aβ1-42 form plays a key role in AD pathology, promoting hyperexcitability, synaptic dysfunction, and neurodegeneration, particularly in the hippocampus (HPC) and associative cortices. However, only a few electrophysiological studies have examined HPC theta in relation to early cognitive deficits in sAD animal models. Our first goal was to study the temporal progression of theta oscillations impairment following repeated unilateral intracerebroventricular (ICV) Aβ1-42 infusions in rats at 7, 14, and 21 days, in vivo and in vitro. Second, we assessed whether local LTG administration could restore theta oscillations and long-term potentiation (LTP) in this model. We found that: i) Aβ1-42 ICV infusions led to significant reductions in theta amplitude and power on days 7 and 14, with a complete loss by day 21; ii) LTG restored LTP and theta rhythms in terms of power and amplitude in HPC obtained from Aβ1-42-treated animals 14 days post-ICV infusion; iii) histological analysis confirmed neurodegeneration, Tau hyperphosphorylation, astrogliosis, increased number of parvalbimun positive (PV+) interneurons, and GluN2B receptor upregulation in HPC of Aβ1-42-treated animals 14 days post-ICV infusion. These findings suggest that hippocampal theta disruption may serve as an early biomarker of network dysfunction in sAD, and that LTG-mediated partial restoration of theta and LTP offers a potential early therapeutic strategy.

Rationale Due to the numerous limitations of ketamine as a rapid-acting antidepressant drug (RAAD), research is still being conducted to find an effective and safe alternative to this drug. Recent studies indicate that the partial mGlu5 receptor negative allosteric modulator (NAM), 2-(2-(3-methoxyphenyl)ethynyl)-5-methylpyridine (M-5MPEP), has therapeutic potential as an antidepressant. Objectives The study aimed to investigate the potential rapid antidepressant-like effect of M-5MPEP in a mouse model of depression and to determine the mechanism of this action. Methods Chronic unpredictable mild stress (CUMS) was used as an animal model of depression. The effects of single and four-day administration of M-5MPEP on CUMS-induced animal behaviors reflecting anhedonia, apathy, and helplessness were studied. Western blot was applied to measure the levels of proteins potentially involved in a rapid antidepressant effect, including mammalian target of rapamycin (mTOR), eukaryotic elongation factor 2 (eEF2), tropomyosin receptor kinase B (TrkB), and serotonin transporter (SERT), both in the hippocampus and the prefrontal cortex (PFC). Furthermore, excitatory synaptic transmission and long-term potentiation (LTP) were measured in the medial PFC (mPFC). Results We showed that M-5MPEP administration for four consecutive days abolished CUMS-induced apathy- and anhedonia-like symptoms in a mouse model of depression. We also found that these effects were accompanied by changes in hippocampal TrkB levels and mTOR and eEF2 levels in the PFC. Using electrophysiological techniques, we showed that the four-day M-5MPEP treatment reversed chronic stress-induced increases in excitatory synaptic potential and CUMS-impaired LTP in the mPFC. Conclusions Partial mGlu5 receptor NAM, M-5MPEP, appears to be a potentially effective new RAAD and deserves further study.

Background The study examined the effects of 5-HT7 receptor activation on GABAergic transmission within the dentate gyrus and plasticity at the glutamatergic perforant path input. Methods Immunofluorescence imaging was performed using transverse hippocampal slices from transgenic mice expressing green fluorescent protein (GFP) under the Htr7 promoter. This was followed by whole-cell patch clamp electrophysiological recordings assessing the effects of pharmacologically activating 5-HT7 receptors on spontaneous inhibitory postsynaptic currents recorded from dentate granule cells and hilar mossy cells-two glutamatergic neuron types present in the dentate gyrus. Extracellular recordings of field excitatory postsynaptic potentials were then performed to assess whether 5-HT7 receptor activation influenced theta-burst stimulation-evoked plasticity of the perforant path synaptic input. Results It was found that parvalbumin and somatostatin interneurons in the dentate gyrus expressed GFP, which suggests they express 5-HT7 receptors. However, activation of 5-HT(7 )receptors had no effect on GABAergic transmission targeting mossy cells or granule cells. There was also no effect of 5-HT7 receptor activation on perforant path plasticity either with intact or blocked GABAA receptor signaling. Conclusion The presence of 5-HT(7 )receptors in a subset of parvalbumin and somatostatin interneurons in the mouse dentate gyrus could mean that they are involved in the inhibitory control of dentate gyrus activity. However, this potential effect was not evident in slice recordings of inhibitory transmission targeting principal cells and did not affect perforant path plasticity. Further experiments are needed to fully elucidate the functional role of these receptors in the dentate gyrus.

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are commonly prescribed to women during pregnancy and breastfeeding despite posing a risk of adverse cognitive outcomes and affective disorders for the child. The consequences of SSRI-induced excess of 5-HT during development for the brain neuromodulatory 5-HT system remain largely unexplored. In this study, an SSRI- fluoxetine (FLX)- was administered to C57BL/6 J mouse dams during pregnancy and lactation to assess its effects on the offspring. We found that maternal FLX decreased field potentials, impaired long-term potentiation, facilitated long-term depression and tended to increase the density of 5-HTergic fibers in the medial prefrontal cortex (mPFC) of female but not male adolescent offspring. These effects were accompanied by deteriorated performance in the temporal order memory task and reduced sucrose preference with no change in marble burying behavior in FLX-exposed female offspring. We also found that maternal FLX reduced the axodendritic tree complexity of 5-HT dorsal raphe nucleus (DRN) neurons in female but not male offspring, with no changes in the excitability of DRN neurons of either sex. While no effects of maternal FLX on inhibitory postsynaptic currents (sIPSCs) in DRN neurons were found, we observed a significant influence of FLX exposure on kinetics of spontaneous excitatory postsynaptic currents (sEPSCs) in DRN neurons. Finally, we report that no changes in field potentials and synaptic plasticity were evident in the mPFC of the offspring after maternal exposure during pregnancy and lactation to a new antidepressant, vortioxetine. These findings show that in contrast to the mPFC, long-term consequences of maternal FLX exposure on the structure and function of DRN 5-HT neurons are mild and suggest a sex-dependent, distinct sensitivity of cortical and brainstem neurons to FLX exposure in early life. Vortioxetine appears to exert fewer side effects with regards to the mPFC when compared with FLX.

The use of a selective serotonin reuptake inhibitor fluoxetine in depression during pregnancy and the postpartum period might increase the risk of affective disorders and cognitive symptoms in progeny. In animal models, maternal exposure to fluoxetine throughout gestation and lactation negatively affects the behavior of the offspring. Little is known about the effects of maternal fluoxetine on synaptic transmission and plasticity in the offspring cerebral cortex. During pregnancy and lactation C57BL/6J mouse dams received fluoxetine (7.5 mg/ kg/day) with drinking water. Female offspring mice received intraperitoneal injections of the selective 5-HT 7 receptor antagonist SB 269970 (2.5 mg/kg) for 7 days. Whole-cell and field potential electrophysiological recordings were performed in the medial prefrontal cortex (mPFC) ex vivo brain slices. Perinatal exposure to fluoxetine resulted in decreased field potentials and impaired long-term potentiation (LTP) in layer II/III of the mPFC of female young adult offspring. Neither the intrinsic excitability nor spontaneous excitatory postsynaptic currents were altered in layer II/III mPFC pyramidal neurons. In mPFC slices obtained from fluoxetine-treated mice that were administered SB 269970 both field potentials and LTP magnitude were restored and did not differ from controls. Treatment of fluoxetine-exposed mice with a selective 5-HT 7 receptor antagonist, SB 269970, normalizes synaptic transmission and restores the potential for plasticity in the mPFC of mice exposed in utero and postnatally to fluoxetine.

In the search for new options for the pharmacological treatment of major depressive disorder, compounds with a rapid onset of action and high efficacy but lacking a psychotomimetic effect are of particular interest. In the present study, we evaluated the antidepressant potential of NitroSynapsin (NS) at behavioural, structural, and functional levels. NS is a memantine derivative and a dual allosteric N-methyl-d-aspartate receptors (NMDAR) antagonist using targeted delivery by the aminoadamantane of a warhead nitro group to inhibitory redox sites on the NMDAR. In a chronic restraint stress (CRS) mouse model of depression, five doses of NS administered on three consecutive days evoked antidepressant-like activity in the chronically stressed male C57BL/6J mice, reversing CRS-induced behavioural disturbances in sucrose preference and tail suspension tests. CRS-induced changes in morphology and density of dendritic spines in cerebrocortical neurons in the medial prefrontal cortex (mPFC) were also reversed by NS. Moreover, CRS-induced reduction in long-term potentiation (LTP) in the mPFC was found to be prevented by NS based on the electrophysiological recordings. Our study showed that NS restores structural and functional synaptic plasticity and reduces depressive behaviour to the level found in naïve animals. These results preliminarily revealed an antidepressant-like potency of NS.

(S)-Ketamine is the first rapid-acting antidepressant drug (RAAD) introduced for the treatment of depression. However, research is still being carried out on the search for further RAADs that will be not only effective but also safe to use. Recent data have indicated that the combined administration of (R)-ketamine and the mGlu2/3 receptor antagonist LY341495 (mixRL) induces rapid and sustained effects in the chronic unpredictable mild stress (CUMS) model of depression in mice, and the use of this drug combination is associated with a low risk of undesirable effects. Considering the possible influence of stress on cortical plasticity and, on the other hand, the role of this plasticity in the mechanism of action of ketamine, we decided to investigate whether mixed RL affects synaptic plasticity in the prefrontal cortex (PFC) in the CUMS model of depression using electrophysiological techniques and explore whether these effects are related to memory impairments. Using behavioral methods, we found that a single administration of mixRL reversed CUMS-induced PFC-dependent memory deficits and alleviated depression-like effects induced by CUMS. In turn, electrophysiological experiments indicated that the amplitude of field potentials as well as paired-pulse responses in CUMS mice were increased, and mixRL was found to reverse these effects. Additionally, the magnitude of long-term potentiation (LTP) was reduced in CUMS mice, and mixRL was shown to restore this parameter. In summary, mixRL appeared to exert its antidepressant effects and cognitive enhancing effects in a mouse model of depression, at least in part, by mechanisms involving modulation of glutamatergic transmission and LTP in the PFC.

Exogenous corticosterone administration reduces GABAergic transmission and impairs its 5-HT7 receptor-dependent modulation in the rat dorsal raphe nucleus (DRN), but it is largely unknown how neuronal functions of the DRN are affected by repeated physical and psychological stress. This study compared the effects of repeated restraint stress and corticosterone injections on DRN neuronal excitability, spontaneous synaptic transmission, and its 5-HT7 receptor-dependent modulation. Male Wistar rats received corticosterone injections for 7 or 14 days or were restrained for 10 min twice daily for 3 days. Repeated restraint stress and repeated corticosterone administration evoked similar changes in performance in the forced swim test. They increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from DRN neurons. In contrast to the treatment with corticosterone, restraint stress-induced changes in sEPSC kinetics and decreased intrinsic excitability of DRN neurons did not modify inhibitory transmission. Repeated injections of the 5-HT7 receptor antagonist SB 269970 ameliorated the effects of restraint on excitability and sEPSC frequency but did not restore the altered kinetics of sEPSCs. Thus, repeated restraint stress and repeated corticosterone administration differ in consequences for the intrinsic excitability of DRN projection neurons and their excitatory and inhibitory synaptic inputs. Effects of repeated restraint stress on DRN neurons can be partially abrogated by blocking the 5-HT7 receptor.

Decreased platelet count represents a feature of acute liver failure (ALF) pathogenesis. Platelets are the reservoir of transforming growth factor 1 (TGF-β1), a multipotent cytokine involved in the maintenance of, i.a., central nervous system homeostasis. Here, we analyzed the effect of a decrease in TGF-β1 active form on synaptic proteins levels, and brain electrophysiology, in mice after intraperitoneal (ip) administration of TGF-β1 antibody (anti-TGF-β1; 1 mg/mL). Next, we correlated it with a thrombocytopenia-induced TGF-β1 decrease, documented in an azoxymethane-induced (AOM; 100 mM ip) model of ALF, and clarified the impact of TGF-β1 decrease on blood–brain barrier functionality. The increase of both synaptophysin and synaptotagmin in the cytosolic fraction, and its reduction in a membrane fraction, were confirmed in the AOM mice brains. Both proteins’ decrease in analyzed fractions occurred in anti-TGF-β1 mice. In turn, an increase in postsynaptic (NR1 subunit of N-methyl-D-aspartate receptor, postsynaptic density protein 95, gephyrin) proteins in the AOM brain cortex, but a selective compensatory increase of NR1 subunit in anti-TGF-β mice, was observed. The alterations of synaptic proteins levels were not translated on electrophysiological parameters in the anti-TGF-β1 model. The results suggest the impairment of synaptic vesicles docking to the postsynaptic membrane in the AOM model. Nevertheless, changes in synaptic protein level in the anti-TGF-β1 mice do not affect neurotransmission and may not contribute to neurologic deficits in AOM mice.

The role that thyroid hormone deficiency plays in depression and synaptic plasticity in adults has only begun to be elucidated. This paper analyzes the possible link between depression and hypothyroidism in cognitive function alterations, using Wistar–Kyoto (WKY—an animal model of depression) rats and control Wistar rats under standard and thyroid hormone deficiency conditions (propylthiouracil administration—PTU). A weakening of memory processes in the WKY rats is shown behaviorally, and in the reduction of long-term potentiation (LTP) in the dentate gyrus (DG) and CA1 hippocampal regions. PTU administration decreased LTP and increased basal excitatory transmission in the DG in Wistar rats. A decrease in short-term synaptic plasticity is shown by the paired-pulse ratio measurement, occurring during hypothyroidism in DG and CA1 in WKY rats. Differences between the strains may result from decreases in the p-CaMKII, p-AKT, and the level of acetylcholine, while in the case of the co-occurrence of depression and hypothyroidism, an increase in the p-ERK1-MAP seemed to be important. Obtained results show that thyroid hormones are less involved in the inhibition of glutamate release and/or excitability of the postsynaptic neurons in WKY rats, which may indicate a lower sensitivity of the hippocampus to the action of thyroid hormones in depression.

The basal amygdala (BA) has been implicated in encoding fear and its extinction. The level of serotonin (5-HT) in the BA increases due to arousal and stress related to aversive stimuli. The effects of 5-HT7 receptor (5-HT7R) activation and blockade on the activity of BA neurons have not yet been investigated. In the present study, a transgenic mouse line carrying green fluorescent protein (GFP) reporter gene was used to identify neurons that express the 5-HT7R. GFP immunoreactivity was present mainly in cells that also expressed GAD67 or parvalbumin (PV), the phenotypic markers for GABAergic interneurons. Most cells showing GFP fluorescence demonstrated firing patterns characteristic of BA inhibitory interneurons. Activation of 5-HT7Rs resulted in a depolarization and/or occurrence of spontaneous spiking activity of BA interneurons that was accompanied by an increase in the mean frequency and mean amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) recorded from BA principal neurons. These effects were blocked by a specific 5-HT7R antagonist, SB269970 and were absent in slices from 5-HT7R knockout mice. Activation of 5-HT7Rs also decreased the mean frequency of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from BA principal neurons, which was blocked by the GABAA receptor antagonist picrotoxin. Neither inhibitory nor excitatory miniature postsynaptic currents (mIPSCs/mEPSCs) were affected by 5-HT7R activation. These results show that in the BA 5-HT7Rs stimulate an activity-dependent enhancement of inhibitory input from local interneurons to BA principal neurons and provide insights about the possible involvement of BA serotonergic receptors in neuronal mechanisms underlying fear memory.

This study demonstrates how exposure to psychosocial crowding stress (CS) for 3, 7, and 14 days affects glutamate synapse functioning and signal transduction in the frontal cortex (FC) of rats. CS effects on synaptic activity were evaluated in FC slices of the primary motor cortex (M1) by measuring field potential (FP) amplitude, paired-pulse ratio (PPR), and long-term potentiation (LTP). Protein expression of GluA1, GluN2B mGluR1a/5, VGLUT1, and VGLUT2 was assessed in FC by western blot. The body's response to CS was evaluated by measuring body weight and the plasma level of plasma corticosterone (CORT), adrenocorticotropic hormone (ACTH), and interleukin 1 beta (IL1B). CS 3 14d increased FP and attenuated LTP in M1, while PPR was augmented in CS 14d. The expression of GluA1, GluN2B, and mGluR1a/5 was up-regulated in CS 3d and downregulated in CS 14d. VGLUTs expression tended to increase in CS 7d. The failure to blunt the effects of chronic CS on FP and LTP in M1 suggests the impairment of habituation mechanisms by psychosocial stressors. PPR augmented by chronic CS with increased VGLUTs level in the CS 7d indicates that prolonged CS exposure changed presynaptic signaling within the FC. The CS bidirectional profile of changes in glutamate receptors' expression seems to be a common mechanism evoked by stress in the FC.

Since we found that inhibition of cyclooxygenase-2 (COX-2) with concomitant application of a metabotropic glutamate receptor subtype 5 (mGluR5) antagonist (MTEP) down-regulates mGluR7 in the hippocampus (HC) and changes behavior of mice, our team decided to investigate the mechanism responsible for the observed changes. The amino acid glutamate (Glu) is a major excitatory neurotransmitter in the brain. Glu uptake is regulated by excitatory amino acid transporters (EAAT). There are five transporters with documented expression in neurons and glia in the central nervous system (CNS). EAATs, maintain the correct transmission of the Glu signal and prevent its toxic accumulation by removing Glu from the synapse. It has been documented that the toxic level of Glu is one of the main causes of mental and cognitive abnormalities. Given the above mechanisms involved in the functioning of the Glu synapse, we hypothesized modification of Glu uptake, involving EAATs as the cause of the observed changes. This study investigated the level of selected EAATs in the HC after chronic treatment with mGluR5 antagonist MTEP, NS398, and their combination using Western blot. Concomitant MTEP treatment with NS398 or a single administration of the above causes changes in LTP and modulation of EAAT levels in mouse HC. As EAATs are cellular markers of oxidative stress mechanisms, the E. coli lipopolysaccharide (LPS) challenge was performed. The modified Barnes maze test (MBM) revealed alterations in the mouse spatial learning abilities. This study reports an interaction between the mGluR5 and COX-2 in the HC, with EAAT1 and EAAT3 involvement.

Our earlier study demonstrated, that antidepressant-like and also cognitive action of MTEP, a metabotropic glutamate receptor subtype 5 (mGluR5) antagonist, was influenced by cyclooxygenase-2 (COX-2) inhibition in mice. We detected a decrease in the mGluR7 protein level in the hippocampus (HC) of mice co-treated chronically with MTEP and NS398 (a COX-2 inhibitor). We found both antidepressant-like effects and cognitive to be associated with mGlu7 receptor-mediated mechanisms.