Distinct neuronal excitability alterations of medial prefrontal cortex in early-life neglect model of rats

Object:Early-life neglect has irreversible emotional effects on the central nervous system.In this work,we aimed to elucidate distinct functional neural changes in me-dial prefrontal cortex(mPFC)of model rats.Methods:Maternal separation with early weaning was used as a rat model of early-life neglect.The excitation of glutamatergic and GABAergic neurons in rat mPFC was recorded and analyzed by whole-cell patch clamp.Results:Glutamatergic and GABAergic neurons of mPFC were distinguished by typi-cal electrophysiological properties.The excitation of mPFC glutamatergic neurons was significantly increased in male groups,while the excitation of mPFC GABAergic neurons was significant in both female and male groups,but mainly in terms of rest membrane potential and amplitude,respectively.Conclusions:Glutamatergic and GABAergic neurons in medial prefrontal cortex showed different excitability changes in a rat model of early-life neglect,which can contribute to distinct mechanisms for emotional and cognitive manifestations.

High frequency heart rate variability evoked by repetitive transcranial magnetic stimulation over the medial prefrontal cortex: A preliminary investigation on brain processing of acute stressor-evoked cardiovascular reactivity

Introduction: Transcranial Magnetic Stimulation (TMS) is a non-invasive technique for brain stimulation. Repetitive TMS (rTMS) over the medial Prefrontal Cortex (mPFC), Broadman Area 10 (BA10) may stimulate transynaptically perigenual Anterior Cingulate Cortex (pACC, BA 33), insula, amigdala, hypothalamus and connected branches of the Autonomic Nervous System (ANS) involved in stressorevoked cardiovascular reactivity. Stressors are associated with an increase in sympathetic cardiac control, a decrease in parasympathetic control, or both, and, consequently, an increase in systolic/stroke volume, total vascular impedance/resistance and heart rate, a decrease of baroreflex sensitivity, i.e., an increase in blood pressure/arterial tension. Objectives and Aims: The present work aims, using TMS and accordingly to Gianaros modeling, based on functional neuroimaging studies and previous neuroanatomical data from animal models, to probe the connectivity of brain systems involved in stressor-evoked cardiovascular reactivity and to explore TMS potential as a tool for detection and stratification of individual differences concerning this reactivity and hemorreological risk factors correlated with the development of Coronary Heart Disease (CHD). Methods: Both subjects, a 52 years old male and a 40 years old female with previous increased Low Frequency (LF)/High Frequency (HF) Heart Rate Variability (HRV) ratios (respectively, 4.209/3.028) without decompensated cardiorespiratory symptoms, gave informed consent, and ethico-legal issues have been observed. Electroencephalographic (EEG) monitoring has been performed for safety purposes. Immediately after administration, over the mPFC, of 15 pulses of rTMS, during 60 second, with an inductive electrical current, at the stimulating coil, of 85.9 Ampère per μsecond and 66 Ampère per μsecond, respectively, for male and female subjects (a “figure-of-eight” coil and magnetic stimulator MagLite, Dantec/Medtronic, have been used), HRV spectrum analysis (cStress software) has been performed (during 5 minutes, in supine position). Results: In both subjects, LF power, HF power and LF/HF ratio results, before and after rTMS administration, pointed towards sympathetic attenuation and parasympathetic augmentation (respectively, in male/female subject: decreased LF power—65.1 nu/69.3 nu, before rTMS;56.1 nu/41.6 nu, after rTMS;increased HF power—15.5 nu/22.9 nu, before rTMS;30.9 nu/45.5 nu, after rTMS). Conclusions: In this preliminary investigation, the existence of a link between “mind” and heart’s function has been put in evidence, through a reversible “virtual” lesion, of brain systems involved in cardiovascular control, caused by TMS. Repetitive TMS over mPFC decreased brain function involved in stressorevoked cardiovascular reactivity, suggesting the importance of TMS in the management of stress-related cardiovascular disorders.

Dopamine D2 receptors in the dorsomedial prefrontal cortex modulate social hierarchy in male mice

Social hierarchy greatly influences behavior and health.Both human and animal studies have signaled the medial prefrontal cortex(mPFC)as specifically related to social hierarchy.Dopamine D1 receptors(D1Rs)and D2 receptors(D2Rs)are abundantly expressed in the mPFC,modulat-ing its functions.However,it is unclear how DR-expressing neurons in the mPFC regulate social hierarchy.Here,using a confrontation tube test,we found that most adult C57BL/6J male mice could establish a linear social rank after 1 week of cohabitation.Lower rank individuals showed social anxiety together with decreased serum testosterone levels.D2R expression was significantly downregulated in the dorsal part of mPFC(dmPFC)in lower rank individuals,whereas D1R expression showed no significant difference among the rank groups in the whole mPFC.Virus knockdown of D2Rs in the dmPFC led to mice being particularly prone to lose the contests in the confrontation tube test.Finally,simultaneous D2R activation in the subordinates and D2R inhibition in the dominants in a pair switched their dominant-subordinate relationship.The above results indicate that D2Rs in the dmPFC play an important role in social dominance.Our findings provide novel insights into the divergent func-tions of prefrontal D1Rs and D2Rs in social dominance,which may contribute to ameliorating social dysfunctions along with abnormal social hierarchy.

Reversal of Social Recognition Deficit in Adult Mice with MECP2 Duplication via Normalization of MeCP2 in the Medial Prefrontal Cortex

Methyl-CpG binding protein 2(MeCP2) is a basic nuclear protein involved in the regulation of gene expression and microRNA processing.Duplication of MECP2-containing genomic segments causes MECP2 duplication syndrome,a severe neurodevelopmental disorder characterized by intellectual disability,motor dysfunction,heightened anxiety,epilepsy,autistic phenotypes,and early death.Reversal of the abnormal phenotypes in adult mice with MECP2 duplication(MECP2-TG) by normalizing the MeCP2 levels across the whole brain has been demonstrated.However,whether different brain areas or neural circuits contribute to different aspects of the behavioral deficits is still unknown.Here,we found that MECP2-TG mice showed a significant social recognition deficit,and were prone to display aversive-like behaviors,including heightened anxiety-like behaviors and a fear generalization phenotype.In addition,reduced locomotor activity was observed in MECP2-TG mice.However,appetitive behaviors and learning and memory were comparable in MECP2-TG and wild-type mice.Functional magnetic resonance imaging illustrated that the differences between MECP2-TG and wild-type mice were mainly concentrated in brain areas regulating emotion and social behaviors.We used the CRISPR-Cas9 method to restore normal MeCP2 levels in the medial prefrontal cortex(mPFC) and bed nuclei of the stria terminalis(BST) of adult MECP2-TG mice,and found that normalization of MeCP2 levels in the mPFC but not in the BST reversed the social recognition deficit.These data indicate that the mPFC is responsible for the social recognition deficit in the transgenic mice,and provide new insight into potential therapies for MECP2 duplication syndrome.

Chronic lithium treatment ameliorates ketamine-induced mania-like behavior via the PI3K-AKT signaling pathway

Ketamine, a rapid-acting antidepressant drug, has been used to treat major depressive disorder and bipolar disorder(BD). Recent studies have shown that ketamine may increase the potential risk of treatment-induced mania in patients. Ketamine has also been applied to establish animal models of mania. At present, however, the underlying mechanism is still unclear. In the current study, we found that chronic lithium exposure attenuated ketamine-induced mania-like behavior and c-Fos expression in the medial prefrontal cortex(mPFC) of adult male mice. Transcriptome sequencing was performed to determine the effect of lithium administration on the transcriptome of the PFC in ketamine-treated mice, showing inactivation of the phosphoinositide 3-kinase(PI3K)-protein kinase B(AKT) signaling pathway. Pharmacological inhibition of AKT signaling by MK2206(40 mg/kg), a selective AKT inhibitor, reversed ketamine-induced mania.Furthermore, selective knockdown of AKT via AAVAKT-sh RNA-EGFP in the mPFC also reversed ketamine-induced mania-like behavior. Importantly,pharmacological activation of AKT signaling by SC79(40 mg/kg), an AKT activator, contributed to mania in low-dose ketamine-treated mice. Inhibition of PI3K signaling by LY294002(25 mg/kg), a specific PI3K inhibitor, reversed the mania-like behavior in ketamine-treated mice. However, pharmacological inhibition of mammalian target of rapamycin(mTOR)signaling with rapamycin(10 mg/kg), a specific mTOR inhibitor, had no effect on ketamine-induced mania-like behavior. These results suggest that chronic lithium treatment ameliorates ketamine-induced mania-like behavior via the PI3K-AKT signaling pathway, which may be a novel target for the development of BD treatment.

Role of 5-hydroxytryptamine type 3 receptors in the regulation of anxiety reactions

5-Hydroxytryptamine(5-HT)type 3 receptor(5-HT_(3)R)is the only type of ligand-gated ion channel in the 5-HT receptor family.Through the high permeability of Na+,K+,and Ca2+and activation of subsequent voltage-gated calcium channels(VGCCs),5-HT_(3)R induces a rapid increase of neuronal excitability or the release of neurotransmitters from axon terminals in the central nervous system(CNS).5-HT_(3)Rs are widely expressed in the medial prefrontal cortex(mPFC),amygdala(AMYG),hippocampus(HIP),periaqueductal gray(PAG),and other brain regions closely associated with anxiety reactions.They have a bidirectional regulatory effect on anxiety reactions by acting on different types of cells in different brain regions.5-HT_(3)Rs mediate the activation of the cholecystokinin(CCK)system in the AMYG,and theγ-aminobutyric acid(GABA)“disinhibition”mechanism in the prelimbic area of the mPFC promotes anxiety by the activation of GABAergic intermediate inhibitory neurons(IINs).In contrast,a 5-HT_(3)R-induced GABA“disinhibition”mechanism in the infralimbic area of the mPFC and the ventral HIP produces anxiolytic effects.5-HT_(2)R-mediated regulation of anxiety reactions are also activated by 5-HT_(3)R-activated 5-HT release in the HIP and PAG.This provides a theoretical basis for the treatment of anxiety disorders or the production of anxiolytic drugs by targeting 5-HT_(3)Rs.However,given the circuit specific modulation of 5-HT_(3)Rs on emotion,systemic use of 5-HT_(3)R agonism or antagonism alone seems unlikely to remedy anxiety,which deeply hinders the current clinical application of 5-HT_(3)R drugs.Therefore,the exploitation of circuit targeting methods or a combined drug strategy might be a useful developmental approach in the future.

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response.Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region–specific,particularly involving the corticolimbic system,including the ventral tegmental area,nucleus accumbens,prefrontal cortex,amygdala,and hippocampus.Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology.In this review,we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression.We focused on associated molecular pathways and neural circuits,with special attention to the brain-derived neurotrophic factor–tropomyosin receptor kinase B signaling pathway and the ventral tegmental area–nucleus accumbens dopamine circuit.We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature,severity,and duration of stress,especially in the above-mentioned brain regions of the corticolimbic system.Therefore,BDNF might be a biological indicator regulating stress-related processes in various brain regions.

In vivo imaging reveals a synchronized correlation among neurotransmitter dynamics during propofol and sevoflurane anesthesia

General anesthesia is widely applied in clinical practice.However,the precise mechanism of loss of consciousness induced by general anesthetics remains unknown.Here,we measured the dynamics of five neurotransmitters,includingγ-aminobutyric acid,glutamate,norepinephrine,acetylcholine,and dopamine,in the medial prefrontal cortex and primary visual cortex of C57BL/6 mice through in vivo fiber photometry and genetically encoded neurotransmitter sensors under anesthesia to reveal the mechanism of general anesthesia from a neurotransmitter perspective.Results revealed that the concentrations of γ-aminobutyric acid,glutamate,norepinephrine,and acetylcholine increased in the cortex during propofol-induced loss of consciousness.Dopamine levels did not change following the hypnotic dose of propofol but increased significantly following surgical doses of propofol anesthesia.Notably,the concentrations of the five neurotransmitters generally decreased during sevoflurane-induced loss of consciousness.Furthermore,the neurotransmitter dynamic networks were not synchronized in the non-anesthesia groups but were highly synchronized in the anesthetic groups.These findings suggest that neurotransmitter dynamic network synchronization may cause anesthetic-induced loss of consciousness.

Projections from Infralimbic Cortex to Paraventricular Thalamus Mediate Fear Extinction Retrieval

The paraventricular nucleus of the thalamus(PVT),which serves as a hub,receives dense projections from the medial prefrontal cortex(mPFC)and projects to the lateral division of central amygdala(CeL).The infralimbic(IL)cortex plays a crucial role in encoding and recalling fear extinction memory.Here,we found that neurons in the PVT and IL were strongly activated during fear extinction retrieval.Silencing PVT neurons inhibited extinction retrieval at recent time point(24 h after extinction),while activating them promoted extinction retrieval at remote time point(7 d after extinction),suggesting a critical role of the PVT in extinction retrieval.In the mPFC-PVT circuit,projections from IL rather than prelimbic cortex to the PVT were dominant,and disrupting the IL-PVT projection suppressed extinction retrieval.Moreover,the axons of PVT neurons preferentially projected to the CeL.Silencing the PVT-CeL circuit also suppressed extinction retrieval.Together,our findings reveal a new neural circuit for fear extinction retrieval outside the classical IL-amygdala circuit.

Chronic Oral Administration of Magnesium-L-Threonate Prevents Oxaliplatin-Induced Memory and Emotional Deficits by Normalization of TNF-a/NF-j B Signaling in Rats

Antineoplastic drugs such as oxaliplatin(OXA)often induce memory and emotional deficits.At present,the mechanisms underlying these side-effects are not fully understood,and no effective treatment is available.Here,we show that the short-term memory deficits and anxietylike and depression-like behaviors induced by intraperitoneal injections of OXA(4 mg/kg per day for 5 consecutive days) were accompanied by synaptic dysfunction and downregulation of the NR2 B subunit of N-methyl-Daspartate receptors in the hippocampus,which is critically involved in memory and emotion.The OXA-induced behavioral and synaptic changes were prevented by chronic oral administration of magnesium-L-threonate(L-TAMS,604 mg/kg per day,from 2 days before until the end of experiments).We found that OXA injections significantly reduced the free Mg~(2+) in serum and cerebrospinal fluid(from ~0.8 mmol/L to ~ 0.6 mmol/L).The Mg~(2+) deficiency(0.6 mmol/L) upregulated tumor necrosis factor(TNF-α) and phospho-p65(p-p65),an active form of nuclear factor-kappaB(NF-κB),and downregulated the NR2 B subunit in cultured hippocampal slices.Oral L-TAMS prevented the OXA-induced upregulation of TNF-α and p-p65,as well as microglial activation in the hippocampus and the medial prefrontal cortex.Finally,similar to oral L-TAMS,intracerebroventricular injection of PDTC,an NF-κB inhibitor,also prevented the OXAinduced memory/emotional deficits and the changes in TNF-α,p-p65,and microglia.Taken together,the activation of TNF-α/NF-κB signaling resulting from reduced brain Mg~(2+) is responsible for the memory/emotional deficits induced by OXA.Chronic oral L-TAMS may be a novel approach to treating chemotherapy-induced memory/emotional deficits.