Reduction in phencyclidine induced sensorimotor gating deficits in the rat following increased system xc − activity in the medial prefrontal cortex

Rationale

Aspects of schizophrenia, including deficits in sensorimotor gating, have been linked to glutamate dysfunction and/or oxidative stress in the prefrontal cortex. System x_c ^?, a cystine–glutamate antiporter, is a poorly understood mechanism that contributes to both cellular antioxidant capacity and glutamate homeostasis.

Objectives

Our goal was to determine whether increased system x_c ^? activity within the prefrontal cortex would normalize a rodent measure of sensorimotor gating.

Methods

In situ hybridization was used to map messenger RNA (mRNA) expression of xCT, the active subunit of system x_c ^?, in the prefrontal cortex. Prepulse inhibition was used to measure sensorimotor gating; deficits in prepulse inhibition were produced using phencyclidine (0.3–3 mg/kg, sc). N-Acetylcysteine (10–100 μM) and the system x_c ^? inhibitor (S)-4-carboxyphenylglycine (CPG, 0.5 μM) were used to increase and decrease system x_c ^? activity, respectively. The uptake of ¹⁴C-cystine into tissue punches obtained from the prefrontal cortex was used to assay system x_c ^? activity.

Results

The expression of xCT mRNA in the prefrontal cortex was most prominent in a lateral band spanning primarily the prelimbic cortex. Although phencyclidine did not alter the uptake of ¹⁴C-cystine in prefrontal cortical tissue punches, intraprefrontal cortical infusion of N-acetylcysteine (10–100 μM) significantly reduced phencyclidine- (1.5 mg/kg, sc) induced deficits in prepulse inhibition. N-Acetylcysteine was without effect when coinfused with CPG (0.5 μM), indicating an involvement of system x_c ^?.

Conclusions

These results indicate that phencyclidine disrupts sensorimotor gating through system x_c ^? independent mechanisms, but that increasing cystine–glutamate exchange in the prefrontal cortex is sufficient to reduce behavioral deficits produced by phencyclidine.     

Social instigation and aggression in postpartum female rats: role of 5-Ht1A and 5-Ht1B receptors in the dorsal raph�� nucleus and prefrontal cortex

Rationale

5-HT_1A and 5-HT_1B receptor agonists effectively reduce aggressive behavior in males that has been escalated by social instigation. Important sites of action for these drugs are the receptors in dorsal raphé nuclei (DRN) and the ventral?Corbital prefrontal cortex (VO PFC). DRN and VO PFC areas are particularly relevant in the inhibitory control of escalated aggressive and impulsive behavior.

Objectives

The objectives of this study are to assess the anti-aggressive effects of 5-HT_1A (8-OH-DPAT) and 5-HT_1B (CP-93,129) receptor agonists microinjected into DRN and VO PFC, respectively, and to study the aggressive behavior in postpartum female Wistar rats using the social instigation protocol to increase aggression.

Methods and Results

8-OH-DPAT (0.56???g) in the DRN increased aggressive behavior in postpartum female rats. By contrast, CP-93,129 (1.0???g) microinjected into VO PFC decreased the number of attack bites and lateral threats. 5-HT_1A and 5-HT_1B receptor agonists differed in their effects on non-aggressive activities, the former decreasing rearing and grooming and the latter increasing these acts. When 8-OH-DPAT was microinjected into DRN and CP-93,129 was microinjected into VO PFC in female rats at the same time, maternal aggression decreased. Specific participation of 5-HT_1B receptors was verified by reversal of the anti-aggressive effects using the selective antagonist SB-224,289 (1.0???g).

Conclusions

The decrease in maternal aggressive behavior after microinjections of 5-HT_1B receptor agonists into the VO PFC and DRN of female postpartum rats that were instigated socially supports the hypothesis that activation of these receptors modulates high levels of aggression in a behaviorally specific manner, due to activation of 5-HT_1B receptors at the soma and terminals.     

Kaempferol regulates the lipid-profile in high-fat diet-fed rats through an increase in hepatic PPARα levels

The aim of this study was to investigate the antiobesity and antihyperlipidemic effects of the flavonoid kaempferol (3,5,7,4'-tetrahydroxyflavone). After being fed a high-fat diet (HFD) for two weeks, rats were dosed orally with kaempferol (75, 150, or 300 mg/kg) or fenofibrate (100?mg/kg) once daily for eight weeks. Fenofibrate is an antilipemic agent that exerts its therapeutic effects through activation of peroxisome proliferator-activated receptor α (PPAR α). Kaempferol (300?mg/kg/day) produced effects similar to fenofibrate in reducing body weight gain, visceral fat-pad weights, plasma lipid levels, as well as the coronary artery risk and atherogenic indices of HFD-fed rats. Kaempferol also caused dose-related reductions in hepatic triglyceride and cholesterol content and lowered hepatic lipid droplet accumulation and the size of epididymal adipocytes in HFD-fed rats. Kaempferol and fenofibrate reversed the HFD-induced downregulation of hepatic PPAR α. HFD-induced reductions in the hepatic levels of acyl-CoA oxidase (ACO), and cytochrome P450 isoform 4A1 (CYP4A1) proteins were reversed by kaempferol and fenofibrate. The elevated expression of hepatic sterol regulatory element binding proteins (SREBPs) in HFD-fed rats were lowered by kaempferol and fenofibrate. These results suggest that kaempferol reduced the accumulation of visceral fat and improved hyperlipidemia in HFD-fed obese rats by increasing lipid metabolism through the downregulation of SREBPs and promoting the hepatic expression of ACO and CYP4A1, secondary to a direct upregulation hepatic PPAR α expression.     

A role for metabolomics in the antidoping toolbox?

Evidence of the continuous rise of novel doping agents and novel doping strategies calls for the development of more accurate multi‐target screening methods. Direct multi‐target screening approaches are restricted to the targeted substances and their turnover. The development of effective “indirect” screening methods requires a priori a deep understanding of the metabolism of the substance. The biological passport has been demonstrated to be very effective, but it is limited to about 20 indirect parameters. The standard antidoping analytical methods are hence targeted and do not aim directly to identify unknown substances. Also, the detection of doping agents is limited by the excretion of the substance. This study considers metabolomics for the screening of performance enhancing hormone abuse by athletes, based on the following pieces of evidence: (1) hormones have a strong influence on human metabolism, changing several parameters in many tissues, organs, and bio‐fluids; (2) metabolomics has been demonstrated to be a very accurate tool to depict the metabolic status of several organisms, tissues, and for several human diseases, including hormone deficiencies; (3) metabolomics has been demonstrated to be able to distinguish hormone‐treated animals from controls in many species, without the need for a priori knowledge of the metabolism for the specific substance. The literature shows that metabolomics could be an appropriate tool to detect hormone abuse, keeping in mind the strength and the limitation of such an approach.     

Medial prefrontal cortex infusion of α-flupenthixol attenuates systemic d-amphetamine-induced disruption of conditional discrimination performance in rats

RATIONALE: It has been argued that tasks that necessitate the use of context in the service of goal-directed behaviour are disrupted in both schizophrenic patients and in animal analogues by dopamine (DA) manipulation with the prefrontal cortex being implicated. OBJECTIVES: To determine the effects on conditional discrimination performance of direct infusion of the DA D(1)/D(2) receptor antagonist alpha-flupenthixol into the medial prefrontal cortex (mPFC) and of its reversal potential on d-amphetamine-induced task disruption. MATERIALS AND METHODS: Conditional discrimination performance in which rats learn to respond on an appropriate lever, conditional upon specific auditory stimuli, was acquired and later tested under the above drug treatment protocol in extinction. RESULTS: Conditional discrimination performance was unaffected by bilateral intra-mPFC alpha-flupenthixol at doses of 12, 24 or 36 microg/microl. A dose of D-amphetamine (1.5 mg/kg) shown previously to disrupt conditional discrimination performance was attenuated by direct PFC infusion of alpha-flupenthixol at doses of 24 and 36 but not 12 microg/microl per site. CONCLUSIONS: These results show that conditional discrimination performance is at least in part mediated by prefrontal DA as local PFC DA antagonism attenuates task performance disruption by the indirect DA agonist d-amphetamine further implicating the role of dysfunctional forebrain DA in cognitive deficits evident in schizophrenia.     

Δ<Superscript>9</Superscript>-THC administered into the medial prefrontal cortex disrupts the spatial working memory

Rationale Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) disrupts working memory. The prefrontal cortex (PFC) is involved in the processing of working memory, and its medial portion (mPFC) is part of a brain reward circuit as constituted by the mesocorticolimbic dopaminergic system.Objective This study examined the involvement of the mPFC in the effects of Δ⁹-THC on spatial working memory.Methods Ten male Wistar rats well-trained in a radial arm maze and with bilateral cannula implanted in the mPFC received Δ⁹-THC intracortically (Δ⁹-THC IC) at doses of 0 (VEH), 32, 100 or 180 μg, 5 min before a 5-s or a 1-h delayed task in order to measure a short- or long-term spatial working memory, respectively. By contrast, 11 other animals received Δ⁹-THC intraperitoneally (Δ⁹-THC IP) at doses of 0 (VEH), 0.32, 1 or 1.8 mg/kg, 30 min before a 5-s or a 1-h delayed task. Additionally, after a 15-day washout, the effect of an IP or IC pre-exposure of Δ⁹-THC was examined by repeating both dose–effect curves in a crossover order for the routes of administration.Results Δ⁹-THC IP produced significantly larger number of errors at doses of 0.32 or 1 mg/kg as compared to VEH in the 1-h post-delay performance. Δ⁹-THC 100 μg IC also produced significantly larger number of errors as compared to VEH and also to the other doses (32 or 180 μg) IC in the 1-h post-delay performance. Previous exposure to Δ⁹-THC IP or IC did not significantly affect the disruptive effect of this cannabinoid.Conclusions Δ⁹-THC administered directly in the mPFC impaired 1-h delayed task in the radial arm maze in a manner similar to that observed for its systemic administration, suggesting that the mPFC is involved in the disruptive effects of Δ⁹-THC on spatial working memory.     

A role for retinoids in the treatment of COVID-19?

The 2020 global outbreak of the novel coronavirus (SARS-CoV-2 or COVID-19) is a serious threat to international health, and thus, there is an urgent need for discovery of novel therapies or use of repurposed drugs that can make a significant impact on slowing the spread of the virus. Type 1 interferons (IFN-I) are a family cytokines of the early innate immune response to viruses that are being tested against SARS-CoV-2. However, coronaviruses similar to SARS-CoV-2 can suppress host IFN-I antiviral responses. Retinoids are a family molecules related to vitamin A that possess robust immune-modulating properties, including the ability to increase and potentiate the actions of IFN-I. Therefore, adjuvants such as retinoids, capable of increasing IFN-I-mediated antiviral responses, should be tested in combinations of IFN-I and antiviral drugs in pre-clinical studies of SARS-CoV-2.     

Is there a role for reactive oxygen species in arterial medial elastocalcinosis?

Isolated systolic hypertension results from a gradual stiffening of large arteries, to which medial elastocalcinosis (calcification of elastic lamellae) contributes. There is compelling evidence that reactive oxygen species (ROS) are associated with several disease processes affecting the cardiovascular system, including hypertension. The present study was designed to investigate whether the inhibition of ROS production by alpha-lipoic acid can prevent vascular calcification. Sprague-Dawley rats were treated with warfarin (20 mg/kg/day) and vitamin K (15 mg/kg/day) (WVK) for 4 weeks to induce large artery calcification. Subgroups received either a normal diet or a diet supplemented with lipoic acid (1000 mg/kg/day). The WVK treatment produced a small elevation of aortic superoxide levels that did not reach statistical significance. Alpha-lipoic acid reduced the elevation below baseline levels. In rats treated with alpha-lipoic acid, the WVK-induced elevation of pulse wave velocity (an index of arterial stiffness), left ventricular hypertrophy, and aortic, femoral and carotid elastocalcinosis were not prevented. Although a contribution of oxidative stress has been suggested in the aging cardiovascular system, this alteration does not appear to contribute to the calcification process and the subsequent stiffening of large arteries in the animal model tested.     

Human interferon-α increases immobility in the forced swimming test in rats

Objectives: We examined the immobility of the forced swimming test induced in an animal model by human interferon (IFN), which has often been reported to induce depression in clinical use. Methods: In the present study, we examined the effects of human IFNs on results of the forced swimming test in rats. Results: Single intravenous (IV) administration of human IFN-α (6×10⁴ IU/kg), but not of human IFN-β or -γ, significantly increased immobility time in the forced swimming test in rats. Repeated administration of human IFN-α (6×10³ IU/kg) also significantly increased the immobility time. On the other hand, none of the rat IFNs (rat IFN-α, -β and -γ, 6×10⁴ IU/kg, IV) changed the immobility time. Neither human IFNs nor rat IFNs changed the locomotor activity of rats. Conclusions: These findings suggest that human IFN-α has a greater potential for inducing increase of the immobility in the rat forced swimming test than human IFN-β and -γ, and that the effect of human IFN-α might not be mediated through IFN-α/β receptors. Received: 2 June 1999 / Final version: 16 July 1999     

Is treatment-resistance in unipolar melancholic depression characterized by decreased serotonin2A receptors in the dorsal prefrontal – Anterior cingulate cortex?

ObjectivesQuite a number of patients diagnosed with major depression are resistant to several well carried-out psychopharmacological interventions. It remains unclear as to how the serotonergic system is implicated in the phenomenon of treatment-resistance.MethodsWe examined the involvement of post-synaptic 5-HT_2A receptors in the pathophysiology of treatment-resistance in unipolar melancholic major depression with ¹²³I-5-I-R91150 SPECT. 15 antidepressant-naïve (ADN) first-episode depressed patients, 15 antidepressant-free treatment-resistant depressed (TRD) patients and 15 never-depressed individuals, matched for age and gender were studied.ResultsCompared to ADN patients and healthy controls, TRD patients displayed significantly lower 5-HT_2A receptor binding index (BI) in the dorsal regions of the prefrontal and the anterior cingulate cortex. No significant 5-HT_2A receptor BI differences between ADN patients and controls were observed.ConclusionsAt the cortical level, 5-HT_2A receptor BI does not significantly differ in first-episode melancholic depressed patients compared to healthy controls. This observation might imply a limited short-term impact on the serotonergic system in first episode depression. Our results also suggest that when encountered with treatment-resistance, the 5-HT_2A receptors in the DPFC-ACC axis are significantly down-regulated. However, whether this assumed underlying pathophysiological mechanism is due solely to abnormalities in the serotonergic system remains to be answered.This article is part of a Special Issue entitled ‘Anxiety and Depression’.     

A neurochemical yin and yang: does serotonin activate and norepinephrine deactivate the prefrontal cortex?

Introduction

The prefrontal cortex (PFC) receives serotonergic input from the dorsal raphe nucleus of the brainstem, as well as noradrenergic input from another brainstem nucleus, the locus coeruleus. A large number of studies have shown that these two neurotransmitter systems, and drugs that affect them, modulate the functional properties of the PFC in both humans and animal models.

Results

Here I examine the hypothesis that serotonin (5-HT) plays a general role in activating the PFC, whereas norepinephrine (NE) plays a general role in deactivating this brain region. In this manner, the two neurotransmitter systems may have opposing effects on PFC-influenced behavior. To assess this hypothesis, three primary lines of evidence are examined comprising the effects of 5-HT and NE on impulsivity, cognitive flexibility, and working memory.

Discussion

While all of the existing data do not unequivocally support the activation/deactivation hypothesis, there is a large body of support for it.     

Is benzodiazepine-induced amnesia due to deactivation of the left prefrontal cortex?

The amnesic properties of benzodiazepines result from an impairment in explicit (conscious) acquisition of new material. RATIONALE: Explicit encoding of new material has consistently resulted in an increase in regional cerebral blood flow (rCBF) in the left prefrontal cortex, as measured by positron emission tomography (PET). OBJECTIVE: PET was used to determine whether an amnesic dose of midazolam (0.075 mg/kg) attenuated activation in this area during explicit memory encoding. METHODS: A second condition (condition A) used a task to control for the automatic processing that occurs during explicit learning (condition E). RESULTS: The subjects who received midazolam (n=7) recognised significantly fewer words than those who received placebo (n=8), but were not impaired with regard to automatic processing. rCBF was significantly increased in the left prefrontal cortex during explicit encoding of word lists in all subjects and in the temporal lobe and parieto-occipital regions during automatic processing. rCBF was significantly decreased in the prefrontal, superior temporal and parieto-occipital regions following midazolam. The midazolam-induced deactivation in the prefrontal cortex did not affect rCBF activations induced by the explicit memory condition (E-A). CONCLUSIONS: These results suggest that a specific interaction with prefrontal cortex activation does not underlie the amnesic effect of midazolam. However, it remains possible that a threshold level of prefrontal rCBF is necessary for encoding and that, after midazolam, this was not reached.     

Presynaptic long -term potentiation of neurotransmission in the pathway from auditory cortex to medial geniculate body

Objective To study the long- term potentiation （LTP） of synaptic transmission in the corticothalamic pathway to medial geniculate body （MGB） and mechanism underlying this synaptic potentiation. Methods After stimulating auditory thalamic radiation, excitatory postsynaptic currents （EPSCs） were recording at MGB neurons using whole- cell patch clamp technique in AC - MGB slices of postnatal day 14 - 20 rats. A brief 10Hz conditioning stimulation was used to study whether long - term potentiation （LTP） of synaptic transmission could be induced in MGB neurons.     

Bilobetin ameliorates insulin resistance by PKA-mediated phosphorylation of PPARα in rats fed a high-fat diet

BACKGROUND AND PURPOSE

The amelioration of insulin resistance by bilobetin is closely related to its hypolipidaemic effect. The aim of the present study was to determine the insulin-sensitizing mechanism of bilobetin by elucidating its effect on lipid metabolism.

EXPERIMENTAL APPROACH

Rats fed a high-fat diet were treated with bilobetin for either 4 or 14 days before applying a hyperinsulinaemic–euglycaemic clamp. Triglyceride and fatty acids labelled with radioactive isotopes were used to track the transportation and the fate of lipids in tissues. The activity of lipid metabolism-related enzymes and β-oxidation rate were measured. Western blot was used to investigate the phosphorylation, translocation and expression of PPARα in several tissues and cultured cells. The location of amino acid residues subjected to phosphorylation in PPARα was also studied.

KEY RESULTS

Bilobetin ameliorated insulin resistance, increased the hepatic uptake and oxidation of lipids, reduced very-low-density lipoprotein triglyceride secretion and blood triglyceride levels, enhanced the expression and activity of enzymes involved in β-oxidation and attenuated the accumulation of triglycerides and their metabolites in tissues. Bilobetin also increased the phosphorylation, nuclear translocation and activity of PPARα accompanied by elevated cAMP level and PKA activity. Threonine-129–alanine and/or serine-163–alanine mutations on the PPARα genes and PKA inhibitors prevented the effects of bilobetin on PPARα. However, cells overexpressing PKA appeared to stimulate the phosphorylation, nuclear translocation and activity of PPARα.

CONCLUSIONS AND IMPLICATIONS

Bilobetin treatment ameliorates hyperlipidaemia, lipotoxicity and insulin resistance in rats by stimulating PPARα-mediated lipid catabolism. PKA activation is crucial for this process.     

A role for membrane potential in regulating GPCRs?

G-protein-coupled receptors (GPCRs) have ubiquitous roles in transducing extracellular signals into cellular responses. Therefore, the concept that members of this superfamily of surface proteins are directly modulated by changes in membrane voltage could have widespread consequences for cell signalling. Although several studies have indicated that GPCRs can be voltage dependent, particularly P2Y(1) receptors in the non-excitable megakaryocyte, the evidence has been mostly indirect. Recent work on muscarinic receptors has stimulated substantial interest in this field by reporting the first voltage-dependent charge movements for a GPCR. An underlying mechanism is proposed whereby a voltage-induced conformational change in the receptor alters its ability to couple to the G protein and thereby influences its affinity for an agonist. We discuss the strength of the evidence behind this hypothesis and include suggestions for future work. We also describe other examples in which direct voltage control of GPCRs can account for effects of membrane potential on downstream signals and highlight the possible physiological consequences of this phenomenon.     

α1 and α2-adrenoceptors in the medial amygdaloid nucleus modulate differently the cardiovascular responses to restraint stress in rats

Medial amygdaloid nucleus (MeA) neurotransmission has an inhibitory influence on cardiovascular responses in rats submitted to restraint, which are characterized by both elevated blood pressure (BP) and intense heart rate (HR) increase. In the present study, we investigated the involvement of MeA adrenoceptors in the modulation of cardiovascular responses that are observed during an acute restraint. Male Wistar rats received bilateral microinjections of the selective α1-adrenoceptor antagonist WB4101 (10, 15, and 20 nmol/100 nL) or the selective α2-adrenoceptor antagonist RX821002 (10, 15, and 20 nmol/nL) into the MeA, before the exposure to acute restraint. The injection of WB4101 reduced the restraint-evoked tachycardia. In contrast, the injection of RX821002 increased the tachycardia. Both drugs had no influence on BP increases observed during the acute restraint. Our findings indicate that α1 and α2-adrenoceptors in the MeA play different roles in the modulation of the HR increase evoked by restraint stress in rats. Results suggest that α1-adrenoceptors and α2-adrenoceptors mediate the MeA-related facilitatory and inhibitory influences on restraint-related HR responses, respectively.