Potentiation of excitatory serotonergic responses by MK-801 in the medial prefrontal cortex

Neuroprotective effects of MK-801 against cerebral ischemia reperfusion

Introduction

& Objective: Cerebral ischemia/reperfusion (I/R) injury, the second cause of death globally, involves increased NMDA receptor activity leading to neuronal damage due to excessive sodium and calcium ion entry. Therefore, targeting NMDA receptor may potentially reduce cell death induced by brain injury. Our study aimed to investigate the role of NMDA receptors in hippocampal neuronal activity induced by I/R.

Methods

In this study, Wistar rats were divided into four groups: sham, I/R, I/R + MK801, and I/R + NMDA. Cerebral I/R injury was induced by temporarily occluding the common and vertebral carotid arteries, followed by reperfusion. MK801 or NMDA was administered to the rats after a specific reperfusion time. Neuronal density and cell morphology in the hippocampal CA1 region were assessed using Nissl and H&E staining. The expression of BDNF, p-CREB, and c-fos was evaluated through Western blot analysis. Additionally, neuronal activity in CA1 pyramidal neurons were examined using single unit recording technique.

Results

Our results showed that cerebral I/R injury caused significant damage to CA1 pyramidal neurons compared to the sham group. However, treatment with MK-801 improved hippocampal cell survival compared to the I/R group. Furthermore, MK-801 administration in I/R rats increased BDNF, c-fos, and p-CREB levels while decreasing cleaved caspase-3 activity compared to the I/R group. Additionally, electrophysiological data showed that MK-801 increased firing rates of CA1 pyramidal neurons during the reperfusion phase.

Conclusion

MK-801 shows promise as a therapeutic agent for cerebral I/R injury by enhancing cell survival, upregulating neuroplasticity factors, and increasing firing rates of CA1 pyramidal neurons. It exerts a specific protective effect against cerebral I/R injury.

The Role of Glutamate Neurotransmission in Mismatch Negativity (MMN), A Measure of Auditory Synaptic Plasticity and Change-detection

Mismatch negativity (MMN) is an electrophysiological signature that occurs in response to unexpected stimuli. It is often referred to as a measure of memory-based change detection, because the elicitation of a prediction error response relies on the formation of a prediction, which in turn, is dependent upon intact memory of previous auditory stimulation. As such, the MMN is altered in conditions in which memory is affected, such as Alzheimer's disease, schizophrenia and healthy aging. The most prominent pharmacological finding for MMN strengthens the link between MMN and synaptic plasticity, as glutamate N-methyl-d-aspartate receptor (NMDA-R) antagonists reduce the MMN response. However, recent data has begun to demonstrate that the link between NMDA-R function and MMN is not as clear as once thought, with low dose and low affinity NMDA-R antagonists observed to facilitate MMN.

In vivo electrophysiological recordings of the effects of antidepressant drugs

Antidepressant drugs are a standard biological treatment for various neuropsychiatric disorders, yet relatively little is known about their electrophysiologic and synaptic effects on mood systems that set moment-to-moment emotional tone. In vivo electrical recording of local field potentials (LFPs) and single neuron spiking has been crucial for elucidating important details of neural processing and control in many other systems, and yet electrical approaches have not been broadly applied to the actions of antidepressants on mood-related circuits. Here we review the literature encompassing electrophysiologic effects of antidepressants in animals, including studies that examine older drugs, and extending to more recently synthesized novel compounds, as well as rapidly acting antidepressants. The existing studies on neuromodulator-based drugs have focused on recording in the brainstem nuclei, with much less known about their effects on prefrontal or sensory cortex. Studies on neuromodulatory drugs have moreover focused on single unit firing patterns with less emphasis on LFPs, whereas the rapidly acting antidepressant literature shows the opposite trend. In a synthesis of this information, we hypothesize that all classes of antidepressants could have common final effects on limbic circuitry. Whereas NMDA receptor blockade may induce a high powered gamma oscillatory state via direct and fast alteration of glutamatergic systems in mood-related circuits, neuromodulatory antidepressants may induce similar effects over slower timescales, corresponding with the timecourse of response in patients, while resetting synaptic excitatory versus inhibitory signaling to a normal level. Thus, gamma signaling may provide a biomarker (or “neural readout”) of the therapeutic effects of all classes of antidepressants.

The fatty acid amide hydrolase inhibitor URB597 modulates serotonin-dependent emotional behaviour, and serotonin1A and serotonin2A/C activity in the hippocampus

The fatty acid amide hydrolase (FAAH) inhibitor URB597 increases anandamide, resulting in antidepressant/anxiolytic-like activity, likely via CB1 receptor-mediated modulation of serotonin (5-HT) and norepinephrine (NE) neurotransmission. However, the relative importance of the 5-HT and NE systems in these effects and on effects of URB597 on postsynaptic 5-HT receptors remain to be determined. Using behavioural and electrophysiological approaches, we assessed the effects of acute-single and repeated URB597 treatment on responses predicting antidepressant/anxiolytic activity, and on hippocampal 5-HT1A and 5-HT2A/C receptor sensitivity. Acute-single or serial URB597 treatment, compared to vehicle, reduced immobility in the forced swim test (FST), increased open arm visits in the elevated plus maze and shortened feeding latency in the novelty-suppressed feeding test (NSFT). Repeated URB597 treatment yielded more profound behavioural effects, which were associated with an increase in hippocampal brain-derived neurotrophic factor (BDNF). The 5-HT synthesis inhibitor para-chlorophenylalanine (pCPA), but not the NE neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) prevented URB597-mediated antidepressant/anxiolytic-like response in the FST and NSFT, while DSP4 did not further affect URB597-mediated increase in raphe 5-HT neuron firing. Repeated URB597 administration decreased hippocampal pyramidal firing in response to 5-HT2A/C and 5-HT1A stimulation with 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI) and 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT), respectively, suggesting plastic adaptation of these receptors. The effects of acute-single and repeated URB597 administration on hippocampal cell firing in response to DOI or 8-OH-DPAT were similar in magnitude and intensity to the positive control citalopram. These data indicate that URB597 acts, either directly or indirectly, on the 5-HT system, increases hippocampal BDNF expression, and modifies 5-HT1A and 5-HT2A/C function.

Decreased serotonin2C receptor responses in male patients with schizophrenia

Serotonin (5-HT)2C receptors in brain affect psychosis, reward, substance abuse, anxiety, other behaviors, appetite, body temperature, and other physiological measures. They also have been implicated in antipsychotic drug efficacy and side effects. We previously reported that the hyperthermia following administration of MK-212, a predominantly 5-HT(2C) receptor agonist, was diminished in a small sample of patients with schizophrenia (SCH), suggesting decreased 5-HT(2C) receptor responsiveness. We have now studied the responses to oral MK-212 and placebo in a larger sample of unmedicated male SCH (n = 69) and normal controls (CON) (n = 33), and assessed the influence of comorbid substance abuse (SA) on oral body temperature, behavioral responses, etc. The placebo-adjusted oral body temperature response to MK-212 was significantly lower in SCH compared to CON and not significantly different between the SCH with or without SA. Some behavioral responses to MK-212, e.g. self-rated feelings of increased anxiety, depression and decreased calmness, or good overall feeling, were significantly lower in the SCH patients compared to CON. These results add to the evidence for diminished 5-HT(2C) receptor responsiveness in SCH patients compared to CON and are consistent with reported association of HTR(2C) polymorphisms, leading to decreased expression or function of the HTR(2C) in patients with SCH.

Father absence in the monogamous california mouse impairs social behavior and modifies dopamine and glutamate synapses in the medial prefrontal cortex

The role of the father in psycho-affective development is indispensable. Yet, the neurobehavioral effects of paternal deprivation (PD) are poorly understood. Here, we examined the behavioral consequences of PD in the California mouse, a species displaying monogamous bonding and biparental care, and assessed its impact on dopamine (DA), serotonin (5-HT), and glutamate (GLU) transmission in the medial prefrontal cortex (mPFC). In adult males, deficits in social interaction were observed, when a father-deprived (PD) mouse was matched with a PD partner. In adult females, deficits were observed when matching a PD animal with a non-PD control, and when matching 2 PD animals. PD also increased aggression in females. Behavioral abnormalities in PD females were associated with a sensitized response to the locomotor-activating effect of amphetamine. Following immunocytochemical demonstration of DA, 5-HT, and GLU innervations in the mPFC, we employed in vivo electrophysiology and microiontophoresis, and found that PD attenuated the basal activity of low-spiking pyramidal neurons in females. PD decreased pyramidal responses to DA in females, while enhancing responses to NMDA in both sexes. We thus demonstrate that, during critical neurodevelopmental periods, PD leads to sex-dependent abnormalities in social and reward-related behaviors that are associated with disturbances in cortical DA and GLU neurotransmission.

Periadolescent exposure to the NMDA receptor antagonist MK-801 impairs the functional maturation of local GABAergic circuits in the adult prefrontal cortex

A developmental disruption of prefrontal cortical inhibitory circuits is thought to contribute to the adolescent onset of cognitive deficits observed in schizophrenia. However, the developmental mechanisms underlying such a disruption remain elusive. The goal of this study is to examine how repeated exposure to the NMDA receptor antagonist dizocilpine maleate (MK-801) during periadolescence [from postnatal day 35 (P35) to P40] impacts the normative development of local prefrontal network response in rats. In vivo electrophysiological analyses revealed that MK-801 administration during periadolescence elicits an enduring disinhibited prefrontal local field potential (LFP) response to ventral hippocampal stimulation at 20 Hz (beta) and 40 Hz (gamma) in adulthood (P65-P85). Such a disinhibition was not observed when MK-801 was given during adulthood, indicating that the periadolescent transition is indeed a sensitive period for the functional maturation of prefrontal inhibitory control. Accordingly, the pattern of prefrontal LFP disinhibition induced by periadolescent MK-801 treatment resembles that observed in the normal P30-P40 prefrontal cortex (PFC). Additional pharmacological manipulations revealed that these developmentally immature prefrontal responses can be mimicked by single microinfusion of the GABA(A) receptor antagonist picrotoxin into the normal adult PFC. Importantly, acute administration of the GABA(A)-positive allosteric modulator Indiplon into the PFC reversed the prefrontal disinhibitory state induced by periadolescent MK-801 to normal levels. Together, these results indicate a critical role of NMDA receptors in regulating the periadolescent maturation of GABAergic networks in the PFC and that pharmacologically induced augmentation of local GABA(A)-receptor-mediated transmission is sufficient to overcome the disinhibitory prefrontal state associated with the periadolescent MK-801 exposure.

The psychopharmacology of aggressive behavior: a translational approach: part 1: neurobiology

Patients with mental disorders are at an elevated risk for developing aggressive behavior. In the last 19 years, the psychopharmacological treatment of aggression has changed dramatically because of the introduction of atypical antipsychotics into the market and the increased use of anticonvulsants and lithium in the treatment of aggressive patients.Using a translational medicine approach, this review (part 1 of 2) examines the neurobiology of aggression, discussing the major neurotransmitter systems implicated in its pathogenesis, namely, serotonin, glutamate, norepinephrine, dopamine, and γ-aminobutyric acid, and also their respective receptors. The preclinical and clinical pharmacological studies concerning the role of these neurotransmitters have been reviewed, as well as research using transgenic animal models. The complex interaction among these neurotransmitters occurs at the level of brain areas and neural circuits such as the orbitoprefrontal cortex, anterior cortex, amygdala, hippocampus, periaqueductal gray, and septal nuclei, where the receptors of these neurotransmitters are expressed. The neurobiological mechanism of aggression is important to understand the rationale for using atypical antipsychotics, anticonvulsants, and lithium in treating aggressive behavior. Further research is necessary to establish how these neurotransmitter systems interact with brain circuits to control aggressive behavior at the intracellular level.

5-HT2A/C receptors mediate the antipsychotic-like effects of alstonine

The purpose of this study was to determine the effects of alstonine, an indole alkaloid with putative antipsychotic effects, on working memory by using the step-down inhibitory avoidance paradigm and MK801-induced working memory deficits in mice. Additionally, the role of serotonin 5-HT2A/C receptors in the effects of alstonine on mouse models associated with positive (MK801-induced hyperlocomotion), negative (MK801-induced social interaction deficit), and cognitive (MK801-induced working memory deficit) schizophrenia symptoms was examined. Treatment with alstonine was able to prevent MK801-induced working memory deficit, indicating its potential benefit for cognitive deficits now seen as a core symptom in the disease. Corroborating previously reported data, alstonine was also effective in counteracting MK801-induced hyperlocomotion and social interaction deficit. Ritanserin, a 5-HT2A/C receptor antagonist, prevented alstonine's effects on these three behavioral parameters. This study presents additional evidence that 5-HT2A/C receptors are central to the antipsychotic-like effects of alstonine, consistently seen in mouse models relevant to the three dimensions of schizophrenia symptoms.

In vivo electrophysiological effects of methylphenidate in the prefrontal cortex: involvement of dopamine D1 and alpha 2 adrenergic receptors

Attention deficit hyperactivity disorder (ADHD) is the most commonly diagnosed psychiatric disorder in children. Psychostimulants such as methylphenidate (MPH) are used as first line treatment. The prefrontal cortex (PFC) has a proven role in the expression of ADHD. Previous studies from our laboratory have demonstrated that MPH activates the firing activity of medial PFC neurones in anaesthetised rats. The aim of the present study was to determine the respective contribution and location of the different types of catecholamine receptors in mediating these excitatory effects and to compare these effects with those induced by other selective dopamine or noradrenaline uptake blockers. Single unit activity of presumed pyramidal PFC neurones was recorded in rats anaesthetised with urethane. The activation of firing elicited by an iv administration of MPH (1 or 3mg/kg) was partially reduced or prevented by the selective D1 receptor antagonist SCH 23390 administered systemically (0.5mg/kg, iv), or locally by passive diffusion through the recording electrode. On the other hand, administration of the alpha 2 receptor antagonist yohimbine (1mg/kg, iv) significantly potentiated the excitatory effect of MPH and activated PFC neurones previously treated with a low inactive dose of MPH (0.3mg/kg, iv). Local administration of MPH (1mM through the recording electrode) significantly increased the firing of PFC neurones in a D1 receptor-dependent manner. In addition, the response of PFC neurones to MPH, administered at a low dose (0.3mg/kg, iv), is greatly potentiated by dopamine (1mM), but not by noradrenaline (1mM), diffusing passively through the recording electrode, and this effect is reversed by D1 receptor blockade. Finally, the selective dopamine uptake inhibitor GBR 12909 (6 mg/kg, iv) and desipramine (6 mg/kg, iv) only activate a subset of PFC neurones. These results demonstrate the involvement of cortical dopamine D1 and noradrenergic alpha 2 receptors in the in vivo electrophysiological effects of MPH on PFC neurones.

Age-dependent effects of methylphenidate in the prefrontal cortex: evidence from electrophysiological and Arc gene expression measurements

Methylphenidate, a drug widely used for attention deficit hyperactivity disorder in children, may affect neuronal function differently in young and adult subjects, particularly in the prefrontal cortex, a brain structure that does not fully develop until adulthood. We compared the impact of development on the effects of methylphenidate on single unit electrical activity and mRNA expression of the effector immediate early gene activity-regulated cytoskeletal-associated protein (Arc) following methylphenidate in the prefrontal cortex in adult (more than 60 days old) and juvenile (25-35 days old) rats. Methylphenidate, administered under urethane anaesthesia to adult rats, at doses ranging from 1 mg/kg to 3 mg/kg intravenously, exerts a progressive activation of firing of prefrontal cortex neurones (30% to 84% from baseline). This activation was significantly lower in the juvenile rats, reaching only 37% of baseline levels at the highest dose (3 mg/kg, intravenous). In adults, methylphenidate (4 mg/kg intraperitoneal) produced marked increases in Arc mRNA levels compared with saline controls by 123% and 164% in cingulated and orbital cortex, respectively. Corresponding values for the juvenile rats were significantly lower (42% and 79%). In summary, this multi-approach investigation showed that the reactivity of prefrontal cortex neurones to methylphenidate differs markedly in juvenile and adult rats.

Genetic deletion of fatty acid amide hydrolase alters emotional behavior and serotonergic transmission in the dorsal raphe, prefrontal cortex, and hippocampus

Pharmacological blockade of the anandamide-degrading enzyme, fatty acid amide hydrolase (FAAH), produces CB(1) receptor (CB(1)R)-mediated analgesic, anxiolytic-like and antidepressant-like effects in murids. Using behavioral and electrophysiological approaches, we have characterized the emotional phenotype and serotonergic (5-HT) activity of mice lacking the FAAH gene in comparison to their wild type counterparts, and their response to a challenge of the CB(1)R antagonist, rimonabant. FAAH null-mutant (FAAH(-/-)) mice exhibited reduced immobility in the forced swim and tail suspension tests, predictive of antidepressant activity, which was attenuated by rimonabant. FAAH(-/-) mice showed an increase in the duration of open arm visits in the elevated plus maze, and a decrease in thigmotaxis and an increase in exploratory rearing displayed in the open field, indicating anxiolytic-like effects that were reversed by rimonabant. Rimonabant also prolonged the initiation of feeding in the novelty-suppressed feeding test. Electrophysiological recordings revealed a marked 34.68% increase in dorsal raphe 5-HT neural firing that was reversed by rimonabant in a subset of neurons exhibiting high firing rates (33.15% mean decrease). The response of the prefrontocortical pyramidal cells to the 5-HT(2A/2C) agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane ((+/-)-DOI) revealed desensitized 5-HT(2A/2C) receptors, likely linked to the observed anxiolytic-like behaviors. The hippocampal pyramidal response to the 5-HT(1A) antagonist, WAY-100635, indicates enhanced tonus on the hippocampal 5-HT(1A) heteroreceptors, a hallmark of antidepressant-like action. Together, these results suggest that FAAH genetic deletion enhances anxiolytic-like and antidepressant-like effects, paralleled by altered 5-HT transmission and postsynaptic 5-HT(1A) and 5-HT(2A/2C) receptor function.