Joanna Sowa

Prenatal Stress Enhances Excitatory Synaptic Transmission and Impairs Long-Term Potentiation in the Frontal Cortex of Adult Offspring Rats

The effects of prenatal stress procedure were investigated in 3 months old male rats. Prenatally stressed rats showed depressive-like behavior in the forced swim test, including increased immobility, decreased mobility and decreased climbing. In ex vivo frontal cortex slices originating from prenatally stressed animals, the amplitude of extracellular field potentials (FPs) recorded in cortical layer II/III was larger, and the mean amplitude ratio of pharmacologically-isolated NMDA to the AMPA/kainate component of the field potential—smaller than in control preparations. Prenatal stress also resulted in a reduced magnitude of long-term potentiation (LTP). These effects were accompanied by an increase in the mean frequency, but not the mean amplitude, of spontaneous excitatory postsynaptic currents (sEPSCs) in layer II/III pyramidal neurons. These data demonstrate that stress during pregnancy may lead not only to behavioral disturbances, but also impairs the glutamatergic transmission and long-term synaptic plasticity in the frontal cortex of the adult offspring.

5-HT7 receptor modulates GABAergic transmission in the rat dorsal raphe nucleus and controls cortical release of serotonin.

The 5-HT7 receptor is one of the several serotonin (5-HT) receptor subtypes that are expressed in the dorsal raphe nucleus (DRN). Some earlier findings suggested that 5-HT7 receptors in the DRN were localized on GABAergic interneurons modulating the activity of 5-HT projection neurons. The aim of the present study was to find out how the 5-HT7 receptor modulates the GABAergic synaptic input to putative 5-HT DRN neurons, and whether blockade of the 5-HT7 receptor would affect the release of 5-HT in the target structure. Male Wistar rats with microdialysis probes implanted in the prefrontal cortex (PFC) received injections of the 5-HT7 receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride (SB 269970), which induced an increase in the levels of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the PFC. In another set of experiments whole-cell recordings from presumed projection neurons were carried out using DRN slices. SB 269970 application resulted in depolarization and in an increase in the firing frequency of the cells. In order to activate 5-HT7 receptors, 5-carboxamidotryptamine (5-CT) was applied in the presence of N-[2-[4-(2-methoxyphenyl)-1piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY100635). Hyperpolarization of cells and a decrease in the firing frequency were observed after activation of the 5-HT7 receptor. Blockade of 5-HT7 receptors caused a decrease in the mean frequency of spontaneous inhibitory postsynaptic currents (sIPSCs), while its activation induced an increase. The mechanism of these effects appears to involve tonically-active 5-HT7 receptors modulating firing and/or GABA release from inhibitory interneurons which regulate the activity of DRN serotonergic projection neurons.

Anti-interleukin-1β antibody prevents the occurrence of repeated restraint stress-induced alterations in synaptic transmission and long-term potentiation in the rat frontal cortex.

BACKGROUND The mechanisms of the influence of prolonged stress on glutamatergic transmission and synaptic plasticity in the cerebral cortex remain poorly understood. The purpose of this study was to determine an involvement of interleukin-1β (IL-1β) in the effects of repeated restraint stress on excitatory synaptic transmission and long-term potentiation (LTP) in the rat frontal cortex. METHODS The effects of restraint stress lasting for 10 min, repeated twice daily for 3 consecutive days were studied ex vivo in the rat frontal cortex slices prepared 24h after the last stress session. Rats received intraperitoneal injections of interleukin-1β antibody. In a separate experimental group, rats received injections of IL-1β. Field potentials were recorded in the cortical layer II/III. RESULTS In slices originating from stressed animals, the amplitude of field potentials was increased. Consistent with the previous studies, restraint stress resulted in a reduced magnitude of LTP. Similar effects were evident after administration of IL-1β. Stress-induced modifications of the glutamatergic transmission and synaptic plasticity were prevented by interleukin-1β antibody, which was administered 15 min before each restraint session. CONCLUSIONS These data point to an involvement of peripherally produced IL-1β in mediating the influence of repeated restraint stress on the functions of the frontal cortex.

NMDA Receptors on Dopaminoceptive Neurons Are Essential for Drug-Induced Conditioned Place Preference

Abstract Plasticity of the brain’s dopamine system plays a crucial role in adaptive behavior by regulating appetitive motivation and the control of reinforcement learning. In this study, we investigated drug- and natural-reward conditioned behaviors in a mouse model in which the NMDA receptor-dependent plasticity of dopaminoceptive neurons was disrupted. We generated a transgenic mouse line with inducible selective inactivation of the NR1 subunit in neurons expressing dopamine D1 receptors (the NR1D1CreERT2 mice). Whole-cell recordings of spontaneous EPSCs on neurons in the nucleus accumbens confirmed that a population of neurons lacked the NMDA receptor-dependent component of the current. This effect was accompanied by impaired long-term potentiation in the nucleus accumbens and in the CA1 area of the ventral, but not the dorsal, hippocampus. Mutant mice did not differ from control animals when tested for pavlovian or instrumental conditioning. However, NR1D1CreERT2 mice acquired no preference for a context associated with administration of drugs of abuse. In the conditioned place preference paradigm, mutant mice did not spend more time in the context paired with cocaine, morphine, or ethanol, although these mice acquired a preference for sucrose jelly and an aversion to naloxone injections, as normal. Thus, we observed that the selective inducible ablation of the NMDA receptors specifically blocks drug-associated context memory with no effect on positive reinforcement in general.

[Possible involvement of 5-HT₇ receptor in pathophysiology of affective disorders and action of antidepressant drugs].

The 5-HT7 receptor has recently received considerable attention since its involvement has been implicated in cognitive disturbances, sleep and circadian rhythmicity disorders, anxiety and depression. At the cellular level, 5-HT7 receptors increase the excitability of excitatory cells and appear to modulate both glutamatergic and GABAergic transmission in the hippocampus. It has been proposed that 5-HT7 receptors also modulate glutamatergic and GABAergic transmission in the raphe nuclei and these effects may play a role in the regulation of circadian rhythms. Repeated administration of the selective 5-HT7 receptor antagonist induced functional desensitization of the 5-HT7 receptor system at the level of its reactivity and effector proteins. These effects resemble the outcome of treatment of rats with antidepressant drugs. Chronic stress and elevated level of corticosterone increase the reactivity of 5-HT7 receptors in the hippocampus. Treatment of rats with a selective 5-HT7 receptor antagonist also results in attenuation of glutamatergic transmission in the frontal cortex and it prevents the occurrence of stress-induced modifications of glutamatergic transmission and long-term synaptic plasticity. These results are consistent with the hypothesis that 5-HT7 receptor antagonism might, potentially, be used for the treatment of cognitive deficits and mood disorders.

Cortical Synaptic Transmission and Plasticity in Acute Liver Failure Are Decreased by Presynaptic Events

Neurological symptoms of acute liver failure (ALF) reflect decreased excitatory transmission, but the status of ALF-affected excitatory synapse has not been characterized in detail. We studied the effects of ALF in mouse on synaptic transmission and plasticity ex vivo and its relation to distribution of (i) synaptic vesicles (sv) and (ii) functional synaptic proteins within the synapse. ALF-competent neurological and biochemical changes were induced in mice with azoxymethane (AOM). Electrophysiological characteristics (long-term potentiation, whole-cell recording) as well as synapse ultrastructure were evaluated in the cerebral cortex. Also, sv were quantified in the presynaptic zone by electron microscopy. Finally, presynaptic proteins in the membrane-enriched (P2) and cytosolic (S2) fractions of cortical homogenates were quantitated by Western blot. Slices derived from symptomatic AOM mice presented a set of electrophysiological correlates of impaired transmitter release including decreased field potentials (FPs), increased paired-pulse facilitation (PPF), and decreased frequency of spontaneous and miniature excitatory postsynaptic currents (sEPSCs/mEPSCs) accompanied by reduction of the spontaneous transmitter release-driving protein, vti1A. Additionally, an increased number of sv per synapse and a decrease of P2 content and/or P2/S2 ratio for sv-associated proteins, i.e. synaptophysin, synaptotagmin, and Munc18–1, were found, in spite of decreased content of the sv-docking protein, syntaxin-1. Slices from AOM-treated asymptomatic mice showed impaired long-term potentiation (LTP) and increased PPF but no changes in transmitter release or presynaptic protein composition. Our findings demonstrate that a decrease of synaptic transmission in symptomatic ALF is associated with inefficient recruitment of sv proteins and/or impaired sv trafficking to transmitter release sites.

Prenatal stress affects viability, activation, and chemokine signaling in astroglial cultures

CXCL12/SDF-1α and CX3CL1/fractalkine are constitutively expressed in the brain, which indicates their significant functions. Emerging evidence highlights the role of astrocytes and the immune system in the pathophysiology of stress-related disorders. The aim of this study was to assess whether prenatal stress affects chemokine signaling, cell viability/activation, and the iNOS pathway in astroglial cultures. Our results showed that prenatal stress lowered astrocyte viability and simultaneously increased GFAP expression. Furthermore, CX3CL1 production and the CXCL12/CXCR4-7 axis were also altered by prenatal stress. Taken together, malfunctions caused by prenatal stress may adversely influence brain development, leading to long-term effects on adult brain function and behavior.

How does fractalkine modulate synaptic transmission in the rat basolateral amygdala? Insights from electrophysiology

Background Convincing evidence has implicated chemokines in many neurobiological processes potentially relevant to psychiatric disorders, beyond their traditional chemotactic functions. These may include neuromodulator and neurotransmitter-like effects [1]. Yet, recognition and characterization of chemokine effects on neurophysiology are still lacking. The chemokine fractalkine (CX3CL1) is mostly expressed in neurons, whereas its cognate receptor, CX3CR1, is mainly expressed in microglia; however, some reports also demonstrate its neuronal localization [2]. They are constitutively and diffusively expressed in the brain, mostly in structures such as the hippocampus and amygdala [3]. The amygdala plays critical roles in a variety of behavioral responses, including fear and anxiety. The main input structure of the amygdala, the basolateral nuclei (BLA), receives sensory information from thalamus and cortex. Dysregulation in this region contributes to the pathophysiology of anxiety disorders. Therefore, this study aimed to elucidate the neurophysiological effects of fractalkine in the rat BLA. Method Whole-cell patch clamp recordings were performed from principal neurons in acute brain slices (300 μm) containing the BLA. After recording a baseline, fractalkine (2 nM) was bath-applied. Both inhibitory and excitatory synaptic transmission were measured by recording spontaneous synaptic currents (sIPSC/sEPSC). Additionally, synaptic responses were electrically evoked using concentric bipolar stimulating electrodes placed in either the external capsule or the BLA, inducing AMPA receptor-mediated excitatory synaptic currents (eEPSC), NMDA receptor-mediated currents or GABAA receptor-mediated inhibitory synaptic currents (eIPSC). Results Our data indicate that application of fractalkine results in the decreased amplitude of AMPA-mediated eEPSC (paired t-test; p=0.0081, t=3.379, df=9, n=10). On the contrary, the amplitude of NMDA currents was elevated (paired t-test; p=0.0056, t=5.425, df=4, n=5). Regarding inhibitory transmission, fractalkine increased the frequency (paired t-test; p=0.0434, t=2.917, df=4, n=5) and reduced the amplitude of recorded spontaneous currents (paired t-test; p=0.0346, t=3.149, df=4, n=5). These results were consistent with eIPSC data, as both amplitude (paired t-test; p=0.04, t=2.9, df=4, n=5) and paired-pulse ratio were altered (paired t-test; p=0.0275, t=3.4, df=4, n=5). Conclusions Our results suggest multifaceted effects of fractalkine application. The decreased amplitude of AMPA currents and the increased amplitude of NMDA currents result in a reduced AMPA/NMDA ratio and indicate a change in either expression or function of postsynaptic channels. Similar effects after fractalkine application were observed in the hippocampus, and they might be dependent on microglia [4,5]. Interestingly, changes in the inhibitory transmission involve both pre- and postsynaptic mechanisms and possibly homeostatic plasticity mechanisms affecting neural output. The actions of fractalkine in the BLA may be due to their ability to activate its only receptor CX3CR1 localized on neurons and microglia leading to changes in neuronal membrane properties and synaptic transmission. In conclusion, our data show that fractalkine has a profound effect on BLA synaptic transmission, indicating that this protein can be an active modulator of neuronal activity in the fear-related response circuitry, which may have significant scientific and therapeutic implications.