Neural mechanisms of mood-induced modulation of reality monitoring in schizophrenia

Reality monitoring is the ability to accurately distinguish the source of self-generated information from externally-presented information. Although people with schizophrenia (SZ) show impaired reality monitoring, nothing is known about how mood state influences this higher-order cognitive process. Accordingly, we induced positive, neutral and negative mood states to test how different mood states modulate subsequent reality monitoring performance. Our findings indicate that mood affected reality monitoring performance in HC and SZ participants in both similar and dissociable ways. Only a positive mood facilitated task performance in Healthy Control (HC) subjects, whereas a negative mood facilitated task performance in SZ subjects. Yet, when both HC and SZ participants were in a positive mood, they recruited medial prefrontal cortex (mPFC) to bias better subsequent self-generated item identification, despite the fact that mPFC signal was reduced in SZ participants. Additionally, in SZ subjects, negative mood states also modulated left and right dorsal mPFC signal to bias better externally-presented item identification. Together our findings reveal that although the mPFC is hypoactive in SZ participants, mPFC signal plays a functional role in mood-cognition interactions during both positive and negative mood states to facilitate subsequent reality monitoring decision-making.

The emotive nature of conflict monitoring in the medial prefrontal cortex

The detection of conflict between incompatible impulses, thoughts, and actions is a ubiquitous source of motivation across theories of goal-directed action. In this overview, we explore the hypothesis that conflict is emotive, integrating perspectives from affective science and cognitive neuroscience. Initially, we review evidence suggesting that the mental and biological processes that monitor for information processing conflict-particularly those generated by the anterior midcingulate cortex-track the affective significance of conflict and use this signal to motivate increased control. In this sense, variation in control resembles a form of affect regulation in which control implementation counteracts the aversive experience of conflict. We also highlight emerging evidence proposing that states and dispositions associated with acceptance facilitate control by tuning individuals to the emotive nature of conflict, before proposing avenues for future research, including investigating the role of affect in reinforcement learning and decision making.

Acute stress enhances the glutamatergic transmission onto basoamygdala neurons embedded in distinct microcircuits

Amygdala activation is known to be critical for the processing of stressful events in brain. Recent studies have shown that the projection neurons (PNs) in amygdala, although architecturally intermingled, are integrated into distinct microcircuits and thus play divergent roles in amygdala-related behaviors. It remains unknown how stress regulates the individual amygdala PNs embedded in distinct microcircuits. Here, by using retrograde tracing and electrophysiological recording in in vitro slices, we explored the modulation of acute immobilization stress (AIS) on the basoamygdala (BA) PNs projecting either to medial prefrontal cortex (mPFC) or elsewhere, which we designated as BA-mPFC and non-BA-mPFC PNs respectively. The results showed that in the control mice, both the excitatory and inhibitory postsynaptic currents (sEPSCs/sIPSCs) were comparable between these two subsets of BA PNs. The influences of AIS on sEPSCs and sIPSCs were overall similar between the two neuronal populations. It markedly increased the sEPSCs amplitude but left unaltered their frequency as well as the sIPSCs amplitude and frequency. Despite this, several differences emerged between the effects of AIS on the distribution of sEPSCs/sIPSCs frequency in these two groups of BA PNs. Similar changes were also observed in the sEPSCs/sIPSCs of the two PN populations from mice experiencing forced swimming stress. Their intrinsic excitability, on the other hand, was nearly unaltered following AIS. Our results thus suggest that acute stress recruit both BA-mPFC and non-BA-mPFC PNs mainly through enhancing the glutamatergic transmission they receive.

The exercise-glucocorticoid paradox: How exercise is beneficial to cognition, mood, and the brain while increasing glucocorticoid levels

Exercise is known to have beneficial effects on cognition, mood, and the brain. However, exercise also activates the hypothalamic-pituitary-adrenal axis and increases levels of the glucocorticoid cortisol (CORT). CORT, also known as the "stress hormone," is considered a mediator between chronic stress and depression and to link various cognitive deficits. Here, we review the evidence that shows that while both chronic stress and exercise elevate basal CORT levels leading to increased secretion of CORT, the former is detrimental to cognition/memory, mood/stress coping, and brain plasticity, while the latter is beneficial. We propose three preliminary answers to the exercise-CORT paradox. Importantly, the elevated CORT, through glucocorticoid receptors, functions to elevate dopamine in the medial prefrontal cortex under chronic exercise but not chronic stress, and the medial prefrontal dopamine is essential for active coping. Future inquiries may provide further insights to promote our understanding of this paradox.

Histone deacetylase and acetyltransferase inhibitors modulate behavioral responses to social stress

Histone acetylation has emerged as a critical factor regulating learning and memory both during and after exposure to stressful stimuli. There are drugs that we now know affect histone acetylation that are already in use in clinical populations. The current study uses these drugs to examine the consequences of acutely increasing or decreasing histone acetylation during exposure to social stress. Using an acute model of social defeat in Syrian hamsters, we systemically and site-specifically administered drugs that alter histone acetylation and measured subsequent behavior and immediate-early gene activity. We found that systemic administration of a histone deacetylase inhibitor enhances social stress-induced behavioral responses in males and females. We also found that systemic administration completely blocks defeat-induced neuronal activation, as measured by Fos-immunoreactivity, in the infralimbic cortex, but not in the amygdala, after a mild social defeat stressor. Lastly, we demonstrated that site-specific administration of histone deacetylase inhibitors in the infralimbic region of the prefrontal cortex, but not in the basolateral amygdala, mimics the systemic effect. Conversely, decreasing acetylation by inhibiting histone acetyltransferases in the infralimbic cortex reduces behavioral responses to defeat. This is the first demonstration that acute pharmacological manipulation of histone acetylation during social defeat alters subsequent behavioral responses in both males and females. These results reveal that even systemic administration of drugs that alter histone acetylation can significantly alter behavioral responses to social stress and highlight the importance of the infralimbic cortex in mediating this effect.

Ketamine accelerates fear extinction via mTORC1 signaling

Impaired fear extinction contributes to the persistence of post-traumatic stress disorder (PTSD), and can be utilized for the study of novel therapeutic agents. Glutamate plays an important role in the formation of traumatic memories, and in the pathophysiology and treatment of PTSD, highlighting several possible drug targets. Recent clinical studies demonstrate that infusion of ketamine, a glutamate NMDA receptor antagonist, rapidly and significantly reduces symptom severity in PTSD patients. In the present study, we examine the mechanisms underlying the actions of ketamine in a rodent model of fear conditioning, extinction, and renewal. Rats received ketamine or saline 24h after fear conditioning and were then subjected to extinction-training on each of the following three days. Ketamine administration enhanced extinction on the second day of training (i.e., reduced freezing behavior to cue) and produced a long-lasting reduction in freezing on exposure to cue plus context 8days later. Additionally, ketamine and extinction exposure increased levels of mTORC1 in the medial prefrontal cortex (mPFC), a region involved in the acquisition and retrieval of extinction, and infusion of the selective mTORC1 inhibitor rapamycin into the mPFC blocked the effects of ketamine on extinction. Ketamine plus extinction also increased cFos in the mPFC and administration of a glutamate-AMPA receptor antagonist blocked the effects of ketamine. These results support the hypothesis that ketamine produces long-lasting mTORC1/protein synthesis and activity dependent effects on neuronal circuits that enhance the expression of extinction and could represent a novel approach for the treatment of PTSD.

Similarity to the self influences cortical recruitment during impression formation

Prior work has shown that whether or not someone is similar to the self influences person memory--a type of self-reference effect for others. In this study, we were interested in understanding the neural regions supporting the generation of impressions and subsequent memory for targets who vary in similarity to the self. Participants underwent fMRI scanning while forming positive or negative impressions of face-behavior pairs. We tested participants' memory for their generated impressions and then back-sorted the impression trials (encoding) into different levels of self-similarity (high, medium, low) using a self-similarity posttest that came after recognition. Extending prior behavioral work, our data confirmed our hypothesis that memory would be highest for self-similar others and lowest for self-dissimilar others. Dorsal anterior cingulate cortex (dACC) activity increased with self-similarity (high > medium > low) to targets, regardless of later memory for them. An analysis of regions supporting impression memory revealed a double dissociation within medial temporal lobe regions: for similar others, amygdala recruitment supported memory, whereas for dissimilar others, hippocampal activation supported memory. These results suggest that self-similarity influences evaluation and memory for targets but also affects the underlying neural resources engaged when thinking about others who vary in self-similarity.

Effects of active music therapy on the normal brain: fMRI based evidence

The aim of this study was to investigate the neurophysiological bases of Active Music Therapy (AMT) and its effects on the normal brain. Twelve right-handed, healthy, non-musician volunteers were recruited. The subjects underwent 2 AMT sessions based on the free sonorous-music improvisation using rhythmic and melodic instruments. After these sessions, each subject underwent 2 fMRI scan acquisitions while listening to a Syntonic (SP) and an A-Syntonic (AP) Production from the AMT sessions. A 3 T Discovery MR750 scanner with a 16-channel phased array head coil was used, and the image analysis was performed with Brain Voyager QX 2.8. The listening to SP vs AP excerpts mainly activated: (1) the right middle temporal gyrus and right superior temporal sulcus, (2) the right middle frontal gyrus and in particular the right precentral gyrus, (3) the bilateral precuneus, (4) the left superior temporal sulcus and (5) the left middle temporal gyrus. These results are consistent with the psychological bases of the AMT approach and with the activation of brain areas involved in memory and autobiographical processes, and also in personal or interpersonal significant experiences. Further studies are required to confirm these findings and to explain possible effects of AMT in clinical settings.

Neural connection supporting endogenous 5-hydroxytryptamine influence on autonomic activity in medial prefrontal cortex

5-hydroxytryptamine (5-HT) transmission in the medial prefrontal cortex (mPFC) enhances or suppresses signal outflow to influence emotion-/cognition-based function performances and, putatively, the autonomic responses. The top-down cortical modulation of autonomic activities may be mediated in part through projections from mPFC to brain stem dorsal vagal complex (DVC). The abundant and heterogeneous densities of 5-HT fibers across laminae in mPFC suggest serotonergic innervation of mPFC-DVC projection neurons whereby endogenous 5-HT acts to regulate autonomic activities. The present study investigated the physical relationship between 5-HT fibers and the autonomic-related mPFC neurons by examining and quantitatively characterizing the 5-HT contacts upon retrogradely labeled mPFC-DVC projection neurons in pre- and infra-limbic cortices (PrL/IL) with light and electron microscopies combined with immunocytochemistry for 5-HT and presynaptic vesicle marker synaptophysin (Syn). 5-HT varicosities were observed, under confocal microscope, to form close appositions to or, at ultrastructural level, to form asymmetric axodendritic synapses and direct contacts upon the target neurons. About 16% of the entire 5-HTergic varicosities in lamina V of PrL/IL coexpressed Syn and about 24% of the peri-somatic 5-HTergic swellings demonstrated Syn-immunoreactivity (ir), suggesting a low frequency of putative synapses estimated at optical level. Ultrastructurally, examination of thirty-seven serially cut thin 5-HT boutons closely apposed to the labeled dendritic profiles demonstrated that only three contacts presented with identifiable asymmetric, synaptic membrane specializations. These data provide the first and direct morphological evidence supporting that endogenous 5-HT may be released mainly via direct contacts bearing no identifiable synaptic specializations as well as synapses, targeting autonomic-related mPFC neurons for autonomic regulation.

Sex specific recruitment of a medial prefrontal cortex-hippocampal-thalamic system during context-dependent renewal of responding to food cues in rats

Renewal, or reinstatement, of responding to food cues after extinction may explain the inability to resist palatable foods and change maladaptive eating habits. Previously, we found sex differences in context-dependent renewal of extinguished Pavlovian conditioned responding to food cues. Context-induced renewal involves cue-food conditioning and extinction in different contexts and the renewal of conditioned behavior is induced by return to the conditioning context (ABA renewal). Male rats showed renewal of responding while females did not. In the current study we sought to identify recruitment of key neural systems underlying context-mediated renewal and sex differences. We examined Fos induction within the ventromedial prefrontal cortex (vmPFC), hippocampal formation, thalamus and amygdala in male and female rats during the test for renewal. We found sex differences in vmPFC recruitment during renewal. Male rats in the experimental condition showed renewal of responding and had more Fos induction within the infralimbic and prelimbic vmPFC areas compared to controls that remained in the same context throughout training and testing. Females in the experimental condition did not show renewal or an increase in Fos induction. Additionally, Fos expression differed between experimental and control groups and between the sexes in the hippocampal formation, thalamus and amygdala. Within the ventral subiculum, the experimental groups of both sexes had more Fos compared to control groups. Within the dorsal CA1 and the anterior region of the paraventricular nucleus of the thalamus, in males, the experimental group had higher Fos induction, while both females groups had similar number of Fos-positive neurons. Within the capsular part of the central amygdalar nucleus, females in the experimental group had higher Fos induction, while males groups had similar amounts. The differential recruitment corresponded to the behavioral differences between males and females and suggests the medial prefrontal cortex-hippocampal-thalamic system is a critical site of sex differences during renewal of appetitive Pavlovian responding to food cues. These findings provide evidence for novel neural mechanisms underlying sex differences in food motivation and contextual processing in associative learning and memory. The results should also inform future molecular and translational work investigating sex differences and maladaptive eating habits.

Wheel running reduces ethanol seeking by increasing neuronal activation and reducing oligodendroglial/neuroinflammatory factors in the medial prefrontal cortex

The therapeutic effects of wheel running (WR) during abstinence on reinstatement of ethanol seeking behaviors in rats that self-administered ethanol only (ethanol drinking, ED) or ED with concurrent chronic intermittent ethanol vapor experience (CIE-ED) were investigated. Neuronal activation as well as oligodendroglial and neuroinflammatory factors were measured in the medial prefrontal cortex (mPFC) tissue to determine cellular correlates associated with enhanced ethanol seeking. CIE-ED rats demonstrated escalated and unregulated intake of ethanol and maintained higher drinking than ED rats during abstinence. CIE-ED rats were more resistant to extinction from ethanol self-administration, however, demonstrated similar ethanol seeking triggered by ethanol contextual cues compared to ED rats. Enhanced seeking was associated with reduced neuronal activation, and increased number of myelinating oligodendrocyte progenitors and PECAM-1 expression in the mPFC, indicating enhanced oligodendroglial and neuroinflammatory response during abstinence. WR during abstinence enhanced self-administration in ED rats, indicating a deprivation effect. WR reduced reinstatement of ethanol seeking in CIE-ED and ED rats, indicating protection against relapse. The reduced ethanol seeking was associated with enhanced neuronal activation, reduced number of myelinating oligodendrocyte progenitors, and reduced PECAM-1 expression. The current findings demonstrate a protective role of WR during abstinence in reducing ethanol seeking triggered by ethanol contextual cues and establish a role for oligodendroglia-neuroinflammatory response in ethanol seeking. Taken together, enhanced oligodendroglia-neuroinflammatory response during abstinence may contribute to brain trauma in chronic alcohol drinking subjects and be a risk factor for enhanced propensity for alcohol relapse.

Prelimbic cortex GABAA receptors are involved in the mediation of restraint stress-evoked cardiovascular responses

Stress is a response of the organism to homeostasis-threatening stimuli and is coordinated by two main neural systems: the hypothalamic-pituitary-adrenal and the autonomic nervous system. Acute restraint stress (RS) is a model of unavoidable stress, which is characterized by autonomic responses including an increase in mean arterial pressure (MAP) and heart rate (HR), as well as a drop in tail temperature. The prelimbic cortex (PL) has been implicated in the modulation of functional responses caused by RS. The present study aimed to evaluate the role of PL GABAergic neurotransmission in the modulation of autonomic changes induced by RS. Bilateral microinjection of the GABA_A receptor antagonist bicuculline methiodide into the PL reduced pressor and tachycardic responses evoked by RS, in a dose-dependent manner, without affecting the tail temperature drop evoked by RS. In order to investigate which peripheral autonomic effector modulated the reduction in RS-cardiovascular responses caused by the blockade of PL GABA_A receptors, rats were intravenously pretreated with either atenolol or homatropine methylbromide. The blockade of the cardiac sympathetic nervous system with atenolol blunted the reducing effect of PL treatment with bicuculline methiodide on RS-evoked pressor and tachycardic responses. The blockade of the parasympathetic nervous system with homatropine methylbromide, regardless of affecting the beginning of the tachycardic response, did not impact on the reduction of RS-evoked tachycardic and pressor responses caused by the PL treatment with bicuculline methiodide. The present results indicate that both cardiac sympathetic and parasympathetic activities are involved in the reduction of RS-evoked cardiovascular responses evidenced after the blockade of PL GABA_A receptors by bicuculline methiodide.

Combined chronic blockade of hyper-active L-type calcium channels and NMDA receptors ameliorates HIV-1 associated hyper-excitability of mPFC pyramidal neurons

Human Immunodeficiency Virus type 1 (HIV-1) infection induces neurological and neuropsychological deficits, which are associated with dysregulation of the medial prefrontal cortex (mPFC) and other vulnerable brain regions. We evaluated the impact of HIV infection in the mPFC and the therapeutic potential of targeting over-active voltage-gated L-type Ca(2+) channels (L-channel) and NMDA receptors (NMDAR), as modeled in HIV-1 transgenic (Tg) rats. Whole-cell patch-clamp recording was used to assess the membrane properties and voltage-sensitive Ca(2+) potentials (Ca(2+) influx) in mPFC pyramidal neurons. Neurons from HIV-1 Tg rats displayed reduced rheobase, spike amplitude and inwardly-rectifying K(+) influx, increased numbers of action potentials, and a trend of aberrant firing compared to those from non-Tg control rats. Neuronal hyper-excitation was associated with abnormally-enhanced Ca(2+) influx (independent of NMDAR), which was eliminated by acute L-channel blockade. Combined chronic blockade of over-active L-channels and NMDARs with open-channel blockers abolished HIV effects on spiking, aberrant firing and Ca(2+) potential half-amplitude duration, though not the reduced inward rectification. In contrast, individual chronic blockade of over-active L-channels or NMDARs did not alleviate HIV-induced mPFC hyper-excitability. These studies demonstrate that HIV alters mPFC neuronal activity by dysregulating membrane excitability and Ca(2+) influx through the L-channels. This renders these neurons more susceptible and vulnerable to excitatory stimuli, and could contribute to HIV-associated neuropathogenesis. Combined targeting of over-active L-channels/NMDARs alleviates HIV-induced dysfunction of mPFC pyramidal neurons, emphasizing a potential novel therapeutic strategy that may effectively decrease HIV-induced Ca(2+) dysregulation in the mPFC.

Understand after like, viewer's delight? A fNIRS study of order-effect in combined hedonic and cognitive appraisal of art

We investigate neural and behavioral aspects of the interrelation between 'liking' and 'understanding' when both appraisals are made within one judgment task. Our goal was to explore questions regarding how these appraisals combine, and specifically whether there is an order-effect when both are employed in sequence. To this end, we tested a hypothesis derived from new models in neuroaesthetics, and concerning processing of art, which suggest that perception may involve a natural sequence from first processing for hedonic quality (i.e., liking) followed by processing for understanding. Thus, due to the initial liking assessment's capacity to prime deepened cognitive involvement, a Liking-Understanding order may show key differences in final assessments or brain activation when compared to an Understanding-Liking sequence. Thirty-two participants evaluated a range of paintings, balanced for visual appeal and understandability, in a two-part task in which half evaluated for understanding followed by liking and the other half had question order reversed. Brain activity was recorded via functional Near Infrared Spectroscopy (fNIRS). Results showed no assessment interrelation or order effect in artwork evaluations. However, participants who began with evaluation for liking, and who came to incongruent combinations (i.e., "I like, but I don't understand" or "I don't like, but I understand"), showed significantly higher activation in left medial prefrontal cortex. This area is functionally associated with attention and integration of hedonic/informational elements. Findings provide tentative support for a liking-driven order-effect, as well as for physiological connection between appraisals, which may not appear in behavioral evidence, and suggest need for further consideration of this topic in appraisal research.

The role of working memory and declarative memory in trace conditioning

Translational assays of cognition that are similarly implemented in both lower and higher-order species, such as rodents and primates, provide a means to reconcile preclinical modeling of psychiatric neuropathology and clinical research. To this end, Pavlovian conditioning has provided a useful tool for investigating cognitive processes in both lab animal models and humans. This review focuses on trace conditioning, a form of Pavlovian conditioning typified by the insertion of a temporal gap (i.e., trace interval) between presentations of a conditioned stimulus (CS) and an unconditioned stimulus (US). This review aims to discuss pre-clinical and clinical work investigating the mnemonic processes recruited for trace conditioning. Much work suggests that trace conditioning involves unique neurocognitive mechanisms to facilitate formation of trace memories in contrast to standard Pavlovian conditioning. For example, the hippocampus and prefrontal cortex (PFC) appear to play critical roles in trace conditioning. Moreover, cognitive mechanistic accounts in human studies suggest that working memory and declarative memory processes are engaged to facilitate formation of trace memories. The aim of this review is to integrate cognitive and neurobiological accounts of trace conditioning from preclinical and clinical studies to examine involvement of working and declarative memory.

Atypical Neural Activity in Males But Not Females with Autism Spectrum Disorder

The medial prefrontal cortex (mPFC) and the right temporo-parietal junction (rTPj) are highly involved in social understanding, a core area of impairment in autism spectrum disorder (ASD). We used fMRI to investigate sex differences in the neural correlates of social understanding in 27 high-functioning adults with ASD and 23 matched controls. There were no differences in neural activity in the mPFC or rTPj between groups during social processing. Whole brain analysis revealed decreased activity in the posterior superior temporal sulcus in males with ASD compared to control males while processing social information. This pattern was not observed in the female sub-sample. The current study indicates that sex mediates the neurobiology of ASD, particularly with respect to processing social information.

Differential effects of social isolation in adolescent and adult mice on behavior and cortical gene expression

Intact function of the medial prefrontal cortex (mPFC) function relies on proper development of excitatory and inhibitory neuronal populations and on integral myelination processes. Social isolation (SI) affects behavior and brain circuitry in adulthood, but previous rodent studies typically induced prolonged (post-weaning) exposure and failed to directly compare between the effects of SI in adolescent and adulthood. Here, we assessed the impact of a 3-week SI period, starting in mid-adolescence (around the onset of puberty) or adulthood, on a wide range of behaviors in adult male mice. Additionally, we asked whether adolescent SI would differentially affect the expression of excitatory and inhibitory neuronal markers and myelin-related genes in mPFC. Our findings indicate that mid-adolescent or adult SI increase anxiogenic behavior and locomotor activity. However, SI in adolescence uniquely affects the response to the psychotomimetic drug amphetamine, social and novelty exploration and performance in reversal and attentional set shifting tasks. Furthermore, adolescent but not adult SI increased the expression of glutamate markers in the adult mPFC. Our results imply that adolescent social deprivation is detrimental for normal development and may be particularly relevant to the investigation of developmental psychopathology.

Altered function in medial prefrontal cortex and nucleus accumbens links to stress-induced behavioral inflexibility

The medial prefrontal cortex (mPFC) and its output area, the nucleus accumbens (NAc), are implicated in mediating attentional set-shifting. Patients with posttraumatic stress disorder (PTSD) exhibit difficulties in the disengagement of attention from traumatic cues, which is associated with impairments in set-shifting ability. However, unknown is whether alterations in corticostriatal function underlie deficits in this behavioral flexibility in individuals with PTSD. An animal model of single prolonged stress (SPS) has been partially validated as a model for PTSD, in which SPS rats recapitulate the pathophysiological abnormalities and behavioral characteristics of PTSD. In the present study, we firstly found that exposure to SPS impaired the ability in the shift from visual-cue learning to place response discrimination in rats. Conversely, SPS induced no effect on a place-to-cue set-shifting performance. Based on SPS-impaired set-shifting model, we used Western blot and immunofluorescent approaches to clarify SPS-induced alternations in synaptic plasticity and neuronal activation in the mPFC and NAc. Rats that were subjected to SPS exhibited a large increase in pSer845-GluA1 and total GluA1 levels in the mPFC, while no significant change in the NAc. We further found that exposure to SPS significantly decreased c-Fos expression in the NAc core but not the shell after set-shifting behavior. Whereas, enhanced c-Fos expression was observed in prelimbic and infralimbic cortices. Collectively, these findings suggest that abnormal hyperactivity in the mPFC and dysfunction in the NAc core underlie long-term deficits in executive function after traumatic experience, which might play an important role in the development of PTSD symptoms.

Reduced local field potential power in the medial prefrontal cortex by noxious stimuli

Nociceptive signals produced by noxious stimuli at the periphery reach the brain through ascending pathways. These signals are processed by various brain areas and lead to activity changes in those areas. The medial prefrontal cortex (mPFC) is involved in higher cognitive functions and emotional processing. It receives projections from brain areas involved in nociception. In this study, we investigated how nociceptive input from the periphery changes the local field potential (LFP) activity in the mPFC. Three different types of noxious stimuli were applied to the hind paw contralateral to the LFP recording site. They were transcutaneous electrical stimulations, mechanical stimuli and a chemical stimulus (formalin injection). High intensity transcutaneous stimulations (10V to 50V) and noxious mechanical stimulus (pinch) significantly reduced the LFP power during the stimulating period (p<0.05), but not the low intensity subcutaneous stimulations (0.1V to 5V) and other innocuous mechanical stimuli (brush and pressure). More frequency bands were inhibited with increased intensity of transcutaneous electrical stimulation, and almost all frequency bands were inhibited by stimulations at or higher than 30v. Pinch significantly reduced the power for beta band and formalin injection significantly reduced the power of alpha and beta band. Our data demonstrated the noxious stimuli-induced reduction of LFP power in the mPFC, which indicates the active processing of nociceptive information by the mPFC.

Contingent and non-contingent recreational-like exposure to ethanol alters BDNF expression and signaling in the cortico-accumbal network differently

RATIONALE

Although brain-derived neurotrophic factor (BDNF) is part of a homeostatic pathway involved in the development of alcohol dependence, it is not clear whether this is also true after recreational ethanol consumption.

OBJECTIVES

We examined BDNF expression and signaling in the cortico-striatal network immediately and 24 h after either a single intravenous (i.v.) ethanol operant self-administration session or the last of 14 sessions.

METHODS

To compare contingent and non-contingent ethanol exposure, we incorporated the "yoked control-operant paradigm" in which rats actively taking ethanol (S-Et) were paired with two yoked controls receiving passive infusions of ethanol (Y-Et) or saline.

RESULTS

A single ethanol exposure transiently reduced BDNF mRNA levels in the medial prefrontal cortex (mPFC) of Y-Et. Immediately after the last of 14 sessions, mRNA and mature BDNF protein levels (mBDNF) were reduced in the mPFC in both S-Et and Y-Et while mBDNF expression was raised in the nucleus accumbens (NAc), suggesting enhanced anterograde transport from the mPFC. Conversely, 24 h later mBDNF expression and signaling were raised in the mPFC and NAc of S-Et rats but reduced in the NAc of Y-Et rats, with concomitant reduction of downstream signaling pathways.

CONCLUSIONS

Our findings indicate that recreational-like i.v. doses of ethanol promote early changes in neurotrophin expression, depending on the length and modality of administration, the brain region investigated, and the presence of the drug. A rapid intervention targeting the BDNF system might be useful to prevent escalation to alcohol abuse.

Altered neuronal spontaneous activity correlates with glutamate concentration in medial prefrontal cortex of major depressed females: An fMRI-MRS study

BACKGROUND

Major depressive disorder (MDD) is twice more prevalent in females than in males. Yet, there have only been a few studies on the functional brain activity in female MDD patients and the detailed mechanisms underlying their neurobiology merit further investigations. In the present work, we used combined fMRI-MRS methods to investigate the altered intrinsic neuronal activity and its association with neurotransmitter concentration in female MDD patients.

METHODS

The whole brain amplitude of low frequency fluctuation (ALFF) analysis using resting state functional magnetic resonance imaging (fMRI) was performed to explore the alteration of intrinsic neuronal signals in MDD females (n=11) compared with female healthy controls (n=11). With a specific interest in the medial prefrontal cortex (mPFC) area, we quantified the concentration of amino acid neurotransmitters including GABA ((r-aminobutyric acid)), Glu (Glutamate), and Glx (Glutamate + Glutamine) using (1)H-MRS technology. Moreover, we conducted Pearson correlation analysis between the ALFF value and neurotransmitter concentration to find out the functional-biochemical relation in mPFC area. The relationship between the metabolites concentration and MDD symptomatology was also examined through Spearman correlation analysis.

RESULTS

We found that the female MDD patients showed increased neuronal spontaneous activity in left medial prefrontal cortex (mPFC) and left middle frontal cortex, with decreased ALFF level in right putamen and right middle temporal cortex (p<0.01, Alphasim corrected). The ALFF in mPFC was shown positively correlated with Glu concentration in female MDD patients (r=0.67, p=0.023). The Glu concentration in mPFC was positively correlated with patients HAMA scores (r=0.641, p=0.033).

LIMITATIONS

The relatively small sample size, metabolite information acquired only in mPFC and not all patients were unmedicated are the major limitations of our study.

CONCLUSIONS

Using combined fMRI-MRS methods, we found increased spontaneous neuronal activity was correlated with Glu concentration in mPFC of female MDD patients. Other regions including left middle frontal gyrus, right putamen and middle temporal gyrus also showed altered spontaneous neuronal activities. The abnormal intrinsic neuronal activities in fronto-cortical regions shed light on the pathogenesis underlying MDD females. The multimodal resting-state neuroimaging technique served as a useful tool for functional-biochemical investigation of MDD pathophysiology.

Ceftriaxone pretreatment reduces the propensity of postpartum depression following stroke during pregnancy in rats

OBJECTIVE

Ischemic stroke increases the propensity to develop depression in humans and laboratory animals, and we hypothesized that such an incidence during pregnancy may increase the risk for the development of postpartum depression (PPD).

MATERIALS AND METHODS

To test this hypothesis, we used bilateral common carotid arteries occlusion (BCCAO) to induce transient cerebral ischemia in pregnant rats, and evaluated its effects on subsequent development of PPD in dams. Additionally, we investigated whether ceftriaxone pretreatments before the induction of brain ischemia could alter the propensity of PPD.

RESULTS

We found that 15min BCCAO during pregnancy enhanced immobility time and reduced the frequency of swimming or climbing behaviors in the forced swim test, and decreased the sucrose preference in dams at postpartum day 21. Such behavioral alterations were associated with lower level of GLT-1 expression in the medial prefrontal cortical regions (mPFC) of PPD dams. Specifically, mPFC GLT-1 expression levels in dams with ischemia history were correlated with sucrose preference levels at postpartum day 21. Finally, ceftriaxone pretreatment (200mg/kg/day, 5days) before the 15min BCCAO prevented the development of PPD, and prevented the reduction of GLT-1 expression in the mPFC.

CONCLUSIONS

Taken together, our results suggested that ceftriaxone pretreatment before brain ischemia during pregnancy may reduce the propensity for the development of PPD by preventing the loss of GLT-1 expression in the mPFC.

Theta oscillations integrate functionally segregated sub-regions of the medial prefrontal cortex

Reinforcement learning requires the dynamic interplay of several specialized networks distributed across the brain. A potential mechanism to establish accurate temporal coordination among these paths is through the synchronization of neuronal activity to a common rhythm of neuronal firing. Previous EEG studies have suggested that theta oscillatory activity might be crucial in the integration of information from motivational and attentional paths that converge into the medial Prefrontal Cortex (mPFC) during reward-guided learning. However, due to the low spatial resolution of EEG, this hypothesis has not been directly tested. Here, by combining EEG and fMRI, we show that theta oscillations serve as common substrate for the engagement of separated sub-regions within the mPFC (the pre-Supplementary Motor Area and the dorsomedial Prefrontal Cortex), underlying different cognitive operations (encoding of outcome valence and unsigned prediction errors) through separate functional paths (the Salience and the Central Executive Networks).

Are the emergence of affective disturbances in neuropathic pain states contingent on supraspinal neuroinflammation?

Neuro-immune interactions contribute to the pathogenesis of neuropathic pain due to peripheral nerve injury. A large body of preclinical evidence supports the idea that the immune system acts to modulate the sensory symptoms of neuropathy at both peripheral and central nervous system sites. The potential involvement of neuro-immune interactions in the highly debilitating affective disturbances of neuropathic pain, such as depression, anhedonia, impaired cognition and reduced motivation has received little attention. This is surprising given the widely accepted view that sickness behaviour, depression, cognitive impairment and other neuropsychiatric conditions can arise from inflammatory mechanisms. Moreover, there is a set of well-described immune-to-brain transmission mechanisms that explain how peripheral inflammation can lead to supraspinal neuroinflammation. In the last 5years increasing evidence has emerged that peripheral nerve injury induces supraspinal changes in cytokine or chemokine expression and alters glial cell activity. In this systematic review, based on strong preclinical evidence, we advance the argument that the emergence of affective disturbances in neuropathic pain states are contingent on pro-inflammatory mediators in the interconnected hippocampal-medial prefrontal circuitry that subserve affective behaviours. We explore how dysregulation of inflammatory mediators in these networks may result in affective disturbances through a wide variety of neuromodulatory mechanisms. There are also promising results from clinical trials showing that anti-inflammatory agents have efficacy in the treatment of a variety of neuropsychiatric conditions including depression and appear suited to sub-groups of patients with elevated pro-inflammatory profiles. Thus, although further research is required, aggressively targeting supraspinal pro-inflammatory mediators at critical time-points in appropriate clinical populations is likely to be a novel avenue to treat debilitating affective disturbances in neuropathic conditions.

The role of medial prefrontal corticosterone and dopamine in the antidepressant-like effect of exercise

Despite the well-documented beneficial effect of exercise on stress coping and depression treatment, its underlying neurobiological mechanism remains unclear. This is further complicated by a 'side effect' of exercise: it increases basal glucocorticoid (CORT), the stress hormone, which has been shown to be a mediator linking stress to depressive disorders. Here we show that three weeks of voluntary wheel running reduced rats' immobility in the forced swim test (FST), an antidepressant-like effect. Monitoring extracellular fluids in the medial prefrontal cortex PFC (mPFC) using microdialysis we found that, wheel running was associated with higher baseline CORT, but lower FST-responsive CORT. Further, wheel running resulted in a higher dopamine (DA) both at baseline and following FST. Interestingly, the antidepressant-like effect of wheel running was completely abolished by intra-mPFC pre-microinjection of a D2R (haloperidol) but not D1R (SCH23390) antagonist, at a dose that does not affect normal rats' performance in the FST. It suggests that exercise exerts antidepressant-like effect through upregulated DA and in a D2R dependent way in the mPFC. Importantly, the antidepressant-like effect of wheel running was also abolished by intra-mPFC pre-microinjection of a GR antagonist (RU486). Finally, intra-mPFC pre-microinjection of RU486 also downregulated the originally elevated basal and FST-responsive DA in the mPFC of exercise rats. These results suggest a causal pathway linking CORT, GR, DA, and D2R, to the antidepressant-like effect of exercise. In conclusion, exercise achieves antidepressant-like effect through the CORT-GR-DA-D2R pathway and that the increased basal CORT by exercise itself may be beneficial rather than detrimental.