Do rats have a prefrontal cortex?

Adolescent THC Exposure Causes Enduring Prefrontal Cortical Disruption of GABAergic Inhibition and Dysregulation of Sub-Cortical Dopamine Function

Chronic adolescent marijuana use has been linked to the later development of psychiatric diseases such as schizophrenia. GABAergic hypofunction in the prefrontal cortex (PFC) is a cardinal pathological feature of schizophrenia and may be a mechanism by which the PFC loses its ability to regulate sub-cortical dopamine (DA) resulting in schizophrenia-like neuropsychopathology. In the present study, we exposed adolescent rats to Δ-9-tetra-hydrocannabinol (THC), the psychoactive component in marijuana. At adulthood, we characterized the functionality of PFC GABAergic neurotransmission and its regulation of sub-cortical DA function using molecular, behavioral and in-vivo electrophysiological analyses. Our findings revealed a persistent attenuation of PFC GABAergic function combined with a hyperactive neuronal state in PFC neurons and associated disruptions in cortical gamma oscillatory activity. These PFC abnormalities were accompanied by hyperactive DAergic neuronal activity in the ventral tegmental area (VTA) and behavioral and cognitive abnormalities similar to those observed in psychiatric disorders. Remarkably, these neuronal and behavioral effects were reversed by pharmacological activation of GABA_A receptors in the PFC. Together, these results identify a mechanistic link between dysregulated frontal cortical GABAergic inhibition and sub-cortical DAergic dysregulation, characteristic of well-established neuropsychiatric endophenotypes.

Reduced Slc1a1 expression is associated with neuroinflammation and impaired sensorimotor gating and cognitive performance in mice: Implications for schizophrenia

We previously reported a 84-Kb hemi-deletion copy number variant at the SLC1A1 gene locus that reduces its expression and appeared causally linked to schizophrenia. In this report, we characterize the in vivo and in vitro consequences of reduced expression of Slc1a1 in mice. Heterozygous (HET) Slc1a1^+/- mice, which more closely model the hemi-deletion we found in human subjects, were examined in a series of behavioral, anatomical and biochemical assays. Knockout (KO) mice were also included in the behavioral studies for comparative purposes. Both HET and KO mice exhibited evidence of increased anxiety-like behavior, impaired working memory, decreased exploratory activity and impaired sensorimotor gating, but no changes in overall locomotor activity. The magnitude of changes was approximately equivalent in the HET and KO mice suggesting a dominant effect of the haploinsufficiency. Behavioral changes in the HET mice were accompanied by reduced thickness of the dorsomedial prefrontal cortex. Whole transcriptome RNA-Seq analysis detected expression changes of genes and pathways involved in cytokine signaling and synaptic functions in both brain and blood. Moreover, the brains of Slc1a1^+/- mice displayed elevated levels of oxidized glutathione, a trend for increased oxidative DNA damage, and significantly increased levels of cytokines. This latter finding was further supported by SLC1A1 knockdown and overexpression studies in differentiated human neuroblastoma cells, which led to decreased or increased cytokine expression, respectively. Taken together, our results suggest that partial loss of the Slc1a1 gene in mice causes haploinsufficiency associated with behavioral, histological and biochemical changes that reflect an altered redox state and may promote the expression of behavioral features and inflammatory states consistent with those observed in schizophrenia.

Effect of psychotropic drug treatment on sterol metabolism

Cholesterol metabolism is vital for brain function. Previous work in cultured cells has shown that a number of psychotropic drugs inhibit the activity of 7-dehydrocholesterol reductase (DHCR7), an enzyme that catalyzes the final steps in cholesterol biosynthesis. This leads to the accumulation of 7-dehydrocholesterol (7DHC), a molecule that gives rise to oxysterols, vitamin D, and atypical neurosteroids. We examined levels of cholesterol and the cholesterol precursors desmosterol, lanosterol, 7DHC and its isomer 8-dehydrocholesterol (8DHC), in blood samples of 123 psychiatric patients on various antipsychotic and antidepressant drugs, and 85 healthy controls, to see if the observations in cell lines hold true for patients as well. Three drugs, aripiprazole, haloperidol and trazodone increased circulating 7DHC and 8DHC levels, while five other drugs, clozapine, escitalopram/citalopram, lamotrigine, olanzapine, and risperidone, did not. Studies in rat brain verified that haloperidol dose-dependently increased 7DHC and 8DHC levels, while clozapine had no effect. We conclude that further studies should investigate the role of 7DHC and 8DHC metabolites, such as oxysterols, vitamin D, and atypical neurosteroids, in the deleterious and therapeutic effects of psychotropic drugs. Finally, we recommend that drugs that increase 7DHC levels should not be prescribed during pregnancy, as children born with DHCR7 deficiency have multiple congenital malformations.

Deciphering Decision Making: Variation in Animal Models of Effort- and Uncertainty-Based Choice Reveals Distinct Neural Circuitries Underlying Core Cognitive Processes

Maladaptive decision-making is increasingly recognized to play a significant role in numerous psychiatric disorders, such that therapeutics capable of ameliorating core impairments in judgment may be beneficial in a range of patient populations. The field of "decision neuroscience" is therefore in its ascendancy, with researchers from diverse fields bringing their expertise to bear on this complex and fascinating problem. In addition to the advances in neuroimaging and computational neuroscience that contribute enormously to this area, an increase in the complexity and sophistication of behavioral paradigms designed for nonhuman laboratory animals has also had a significant impact on researchers' ability to test the causal nature of hypotheses pertaining to the neural circuitry underlying the choice process. Multiple such decision-making assays have been developed to investigate the neural and neurochemical bases of different types of cost/benefit decisions. However, what may seem like relatively trivial variation in behavioral methodologies can actually result in recruitment of distinct cognitive mechanisms, and alter the neurobiological processes that regulate choice. Here we focus on two areas of particular interest, namely, decisions that involve an assessment of uncertainty or effort, and compare some of the most prominent behavioral paradigms that have been used to investigate these processes in laboratory rodents. We illustrate how an appreciation of the diversity in the nature of these tasks can lead to important insights into the circumstances under which different neural regions make critical contributions to decision making.

The ventromedial prefrontal cortex in a model of traumatic stress: fear inhibition or contextual processing?

The ventromedial prefrontal cortex (vmPFC) has consistently appeared altered in post-traumatic stress disorder (PTSD). Although the vmPFC is thought to support the extinction of learned fear responses, several findings support a broader role for this structure in the regulation of fear. To further characterize the relationship between vmPFC dysfunction and responses to traumatic stress, we examined the effects of pretraining vmPFC lesions on trauma reactivity and enhanced fear learning in a rodent model of PTSD. In Experiment 1, lesions did not produce differences in shock reactivity during an acute traumatic episode, nor did they alter the strength of the traumatic memory. However, when lesioned animals were subsequently given a single mild aversive stimulus in a novel context, they showed a blunting of the enhanced fear response to this context seen in traumatized animals. In order to address this counterintuitive finding, Experiment 2 assessed whether lesions also attenuated fear responses to discrete tone cues. Enhanced fear for discrete cues following trauma was preserved in lesioned animals, indicating that the deficit observed in Experiment 1 is limited to contextual stimuli. These findings further support the notion that the vmPFC contributes to the regulation of fear through its influence on context learning and contrasts the prevailing view that the vmPFC directly inhibits fear.

Differential dendritic remodeling in prelimbic cortex of male and female rats during recovery from chronic stress

Chronic stress produces differential dendritic remodeling of pyramidal neurons in medial prefrontal cortex of male and female rats. In males, this dendritic remodeling is reversible. However, the timeline of recovery, as well as the potential for reversibility in females, is unknown. Here, we examined dendritic recovery of pyramidal neurons in layer II-II of prelimbic cortex in male and female rats following chronic restraint stress (3h/day for 10days). Dendritic morphology and spine density were analyzed immediately following the cessation of stress, or following a 7- or 10-day recovery period. Chronic stress produced apical dendritic retraction in males, which was coupled with a decrease in the density of stubby spine on apical dendrites. Further, following a 10-day recovery period, the morphology of neurons from stressed rats resembled that of unstressed rats. Male rats given a 7-day recovery period had apical dendritic outgrowth compared to unstressed rats. Immediately after cessation of stress, females showed only minimal dendritic remodeling. The morphology of neurons in stressed females resembled those of unstressed rats following only 7days of recovery, at which time there was also a significant increase in stubby spine density. Males and females also showed different changes in baseline corticosterone concentrations during recovery. These findings not only indicate that dendritic remodeling in prelimbic cortex following chronic stress is different between males and females, but also suggest chronic stress induces differential hypothalamic-pituitary-adrenal axis dysregulation in males and females. These differences may have important implications for responses to subsequent stressors.

Different Brain Circuitries Mediating Controllable and Uncontrollable Pain

Uncontrollable, compared with controllable, painful stimulation can lead to increased pain perception and activation in pain-processing brain regions, but it is currently unknown which brain areas mediate this effect. When pain is controllable, the lateral prefrontal cortex (PFC) seems to inhibit pain processing, although it is unclear how this is achieved. Using fMRI in healthy volunteers, we examined brain activation during controllable and uncontrollable stimulation to answer these questions. In the controllable task, participants self-adjusted temperatures applied to their hand of pain or warm intensities to provoke a constant sensation. In the uncontrollable task, the temperature time courses of the controllable task were replayed (yoked control) and participants rated their sensation continuously. During controllable pain trials, participants significantly downregulated the temperature to keep their sensation constant. Despite receiving the identical nociceptive input, intensity ratings increased during the uncontrollable pain trials. This additional sensitization was mirrored in increased activation of pain-processing regions such as insula, anterior cingulate cortex, and thalamus. Further, increased connectivity between the anterior insula and medial PFC (mPFC) in the uncontrollable and increased negative connectivity between dorsolateral PFC (dlPFC) and insula in the controllable task were observed. This suggests a pain-facilitating role of the mPFC during uncontrollable pain and a pain-inhibiting role of the dlPFC during controllable pain, both exerting their respective effects via the anterior insula. These results elucidate neural mechanisms of context-dependent pain modulation and their relation to subjective perception.

SIGNIFICANCE STATEMENT

Pain control is of uttermost importance and stimulus controllability is an important way to achieve endogenous pain modulation. Here, we show differential effects of controllability and uncontrollability on pain perception and cerebral pain processing. When pain was controllable, the dorsolateral prefrontal cortex downregulated pain-evoked activation in important pain-processing regions. In contrast, sensitization during uncontrollable pain was mediated by increased connectivity of the medial prefrontal cortex with the anterior insula and other pain-processing regions. These novel insights into cerebral pain modulation by stimulus controllability have the potential to improve treatment approaches in pain patients.

Prefrontal connections of the perirhinal and postrhinal cortices in the rat

Knowing how prefrontal regions interact with medial temporal lobe structures is important for understanding memory and cognition. Using anterograde and retrograde tract tracing methods in the rat, we report a detailed study of the perirhinal (PER) and postrhinal (POR) connections with the lateral, ventrolateral, and medial orbitofrontal cortices (ORBl, ORBvl, ORBm), infralimbic and prelimbic cortices (IL, PL), ventral and dorsal anterior cingulate cortices (ACAv, ACAd), and secondary motor cortex (MOs). Our analyses included the topography and laminar patterns of these connections. The PER and POR showed reciprocal connectivity with all prefrontal regions examined, but the patterns of connections differed. In general, PER areas 36 and 35 showed patterns of connectivity that were more similar to each other than to those of the POR. Analysis of anterograde tracers showed that PER areas 36 and 35 provide the strongest projections to prefrontal regions. The heaviest fiber labeling was in IL and PL, closely followed by orbital regions. Fiber labeling arising from injections in POR was weaker overall. The strongest POR efferents targeted MOs, ACAv, and ORBvl. For return projections, analysis of retrograde tracers showed that PER areas 36 and 35 receive strong inputs from orbitofrontal and medial prefrontal regions. Interestingly, PER also received substantial inputs from MOs and ACAd. The POR receives a very strong input from MOs, followed by ACAd, and ORBvl. Based on comparison of our findings with those obtained in monkeys, we argue that the rodent ACAd and MOs may be a functional homolog of the primate dorsolateral prefrontal cortex.

A Novel Multisensory Integration Task Reveals Robust Deficits in Rodent Models of Schizophrenia: Converging Evidence for Remediation via Nicotinic Receptor Stimulation of Inhibitory Transmission in the Prefrontal Cortex

Atypical multisensory integration is an understudied cognitive symptom in schizophrenia. Procedures to evaluate multisensory integration in rodent models are lacking. We developed a novel multisensory object oddity (MSO) task to assess multisensory integration in ketamine-treated rats, a well established model of schizophrenia. Ketamine-treated rats displayed a selective MSO task impairment with tactile-visual and olfactory-visual sensory combinations, whereas basic unisensory perception was unaffected. Orbitofrontal cortex (OFC) administration of nicotine or ABT-418, an α₄β₂ nicotinic acetylcholine receptor (nAChR) agonist, normalized MSO task performance in ketamine-treated rats and this effect was blocked by GABA_A receptor antagonism. GABAergic currents were also decreased in OFC of ketamine-treated rats and were normalized by activation of α₄β₂ nAChRs. Furthermore, parvalbumin (PV) immunoreactivity was decreased in the OFC of ketamine-treated rats. Accordingly, silencing of PV interneurons in OFC of PV-Cre mice using DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) selectively impaired MSO task performance and this was reversed by ABT-418. Likewise, clozapine-N-oxide-induced inhibition of PV interneurons in brain slices was reversed by activation of α₄β₂ nAChRs. These findings strongly imply a role for prefrontal GABAergic transmission in the integration of multisensory object features, a cognitive process with relevance to schizophrenia. Accordingly, nAChR agonism, which improves various facets of cognition in schizophrenia, reversed the severe MSO task impairment in this study and appears to do so via a GABAergic mechanism. Interactions between GABAergic and nAChR receptor systems warrant further investigation for potential therapeutic applications. The novel behavioral procedure introduced in the current study is acutely sensitive to schizophrenia-relevant cognitive impairment and should prove highly valuable for such research.

SIGNIFICANCE STATEMENT

Adaptive behaviors are driven by integration of information from different sensory modalities. Multisensory integration is disrupted in patients with schizophrenia, but little is known about the neural basis of this cognitive symptom. Development and validation of multisensory integration tasks for animal models is essential given the strong link between functional outcome and cognitive impairment in schizophrenia. We present a novel multisensory object oddity procedure that detects selective multisensory integration deficits in a rat model of schizophrenia using various combinations of sensory modalities. Moreover, converging data are consistent with a nicotinic-GABAergic mechanism of multisensory integration in the prefrontal cortex, results with strong clinical relevance to the study of cognitive impairment and treatment in schizophrenia.

The phosphodiesterase 10A selective inhibitor, TAK-063, induces c-Fos expression in both direct and indirect pathway medium spiny neurons and sub-regions of the medial prefrontal cortex in rats

TAK-063, a selective phosphodiesterase 10A (PDE10A) inhibitor, produces potent antipsychotic-like and pro-cognitive effects in rodents via balanced activation of striatal direct and indirect pathway medium spiny neurons (MSNs). Brain activity modulation by TAK-063 has been characterized using pharmacological magnetic resonance imaging and electroencephalography in animals, revealing modulation of activity in the prefrontal cortex (PFC) where there is little or no PDE10A expression. To understand the specific brain regions and cells affected by TAK-063 in rats, we assessed neural activation in the striatal complex and PFC using immunofluorescence staining to measure c-Fos expression. TAK-063 at 0.3 and 3mg/kg induced a dose-dependent increase in the number of c-Fos immunoreactive cells in the striatal complex. Furthermore, TAK-063 increased the number of MSNs expressing c-fos mRNA in both the D₁ receptor-expressing direct pathway and D₂ receptor-expressing indirect pathway of the striatal complex. TAK-063 (0.3 and 3mg/kg) induced c-Fos expression in the anterior cingulate cortex (ACC) and prelimbic cortex (PrL), but not the infralimbic, dorsal peduncular, primary motor or anterior insular cortices. These findings suggest that administration of TAK-063 activates similar numbers of direct and indirect pathway MSNs, resulting in activation predominantly in medial PFC sub-regions, such as the ACC and PrL.

Similarity in Neuronal Firing Regimes across Mammalian Species

The architectonic subdivisions of the brain are believed to be functional modules, each processing parts of global functions. Previously, we showed that neurons in different regions operate in different firing regimes in monkeys. It is possible that firing regimes reflect differences in underlying information processing, and consequently the firing regimes in homologous regions across animal species might be similar. We analyzed neuronal spike trains recorded from behaving mice, rats, cats, and monkeys. The firing regularity differed systematically, with differences across regions in one species being greater than the differences in similar areas across species. Neuronal firing was consistently most regular in motor areas, nearly random in visual and prefrontal/medial prefrontal cortical areas, and bursting in the hippocampus in all animals examined. This suggests that firing regularity (or irregularity) plays a key role in neural computation in each functional subdivision, depending on the types of information being carried.

SIGNIFICANCE STATEMENT

By analyzing neuronal spike trains recorded from mice, rats, cats, and monkeys, we found that different brain regions have intrinsically different firing regimes that are more similar in homologous areas across species than across areas in one species. Because different regions in the brain are specialized for different functions, the present finding suggests that the different activity regimes of neurons are important for supporting different functions, so that appropriate neuronal codes can be used for different modalities.

Topographical projections from the nucleus basalis magnocellularis (Meynert) to the frontal cortex: A voltage-sensitive dye imaging study in rats

BACKGROUND

The nucleus basalis magnocellularis/Meynert (NBM) has been explored as a new target for deep brain stimulation for neurological disorders. Although anatomical studies suggest the existence of cholinergic topographical projections of the NBM, it is still unknown whether NBM subregions differentially activate the frontal cortex.

OBJECTIVE

To investigate the topography between the NBM and frontal cortex.

METHODS

Electrical stimulation was applied to the anterior and posterior sites of the NBM in rats, and the evoked frontal activity was investigated using voltage-sensitive dye (VSD) imaging.

RESULTS

VSD imaging revealed the functional topography of the NBM and frontal cortex: the anteroposterior axis of the NBM corresponded to the mediolateral axis of the dorsal frontal cortex.

CONCLUSION

The present results suggest site-specific control of frontal neuronal activity by the NBM. These findings have practical implications, as the anterior and posterior parts of the NBM could be targeted to improve cognitive and motor function, respectively.

Nicotine disrupts safety learning by enhancing fear associated with a safety cue via the dorsal hippocampus

Learned safety, a learning process in which a cue becomes associated with the absence of threat, is disrupted in individuals with post-traumatic stress disorder (PTSD). A bi-directional relationship exists between smoking and PTSD and one potential explanation is that nicotine-associated changes in cognition facilitate PTSD emotional dysregulation by disrupting safety associations. Therefore, we investigated whether nicotine would disrupt learned safety by enhancing fear associated with a safety cue. In the present study, C57BL/6 mice were administered acute or chronic nicotine and trained over three days in a differential backward trace conditioning paradigm consisting of five trials of a forward conditioned stimulus (CS)+ (Light) co-terminating with a footshock unconditioned stimulus followed by a backward CS- (Tone) presented 20 s after cessation of the unconditioned stimulus. Summation testing found that acute nicotine disrupted learned safety, but chronic nicotine had no effect. Another group of animals administered acute nicotine showed fear when presented with the backward CS (Light) alone, indicating the formation of a maladaptive fear association with the backward CS. Finally, we investigated the brain regions involved by administering nicotine directly into the dorsal hippocampus, ventral hippocampus, and prelimbic cortex. Infusion of nicotine into the dorsal hippocampus disrupted safety learning.

Viral strategies for targeting cortical circuits that control cocaine-taking and cocaine-seeking in rodents

Addiction to cocaine is a chronic disease characterized by persistent drug-taking and drug-seeking behaviors, and a high likelihood of relapse. The prefrontal cortex (PFC) has long been implicated in the development of cocaine addiction, and relapse. However, the PFC is a heterogeneous structure, and understanding the role of PFC subdivisions, cell types and afferent/efferent connections is critical for gaining a comprehensive picture of the contribution of the PFC in addiction-related behaviors. Here we provide an update on the role of the PFC in cocaine addiction from recent work that used viral-mediated optogenetic and chemogenetic tools to study the role of the PFC in drug-taking and drug-seeking behavior in rodents. Following overviews of rodent PFC neuroanatomy and of viral-mediated optogenetic and chemogenetic techniques, we review studies of manipulations within the PFC, followed by a review of work that utilized targeted manipulations to PFC inputs and outputs.

Area-Specific Features of Pyramidal Neurons-a Comparative Study in Mouse and Rhesus Monkey

A principal challenge of systems neuroscience is to understand the unique characteristics of cortical neurons and circuits that enable area- and species-specific sensory encoding, motor function, cognition, and behavior. To address this issue, we compared properties of layer 3 pyramidal neurons in 2 cortical areas that span a broad range of cortical function-primary sensory (V1), to cognitive (frontal)-in the mouse and the rhesus monkey. Hierarchical clustering and discriminant analyses of 15 physiological and 25 morphological variables revealed 2 fundamental principles. First, V1 and frontal neurons are remarkably similar with regard to nearly every property in the mouse, while the opposite is true in the monkey, with V1 and frontal neurons exhibiting significant differences in nearly every property assessed. Second, neurons within visual and frontal areas differ significantly between the mouse and the monkey. Neurons in mouse and monkey V1 are the same size, but differ in nearly every other way; mouse frontal cortical neurons are smaller than those in the monkey and also differ substantially with regard to most other properties. These findings have broad implications for understanding the differential contributions of heterogeneous neuronal types in construction of cortical microcircuitry in diverse brain areas and species.

Pyramidal Neurons Are Not Generalizable Building Blocks of Cortical Networks

A key challenge in cortical neuroscience is to gain a comprehensive understanding of how pyramidal neuron heterogeneity across different areas and species underlies the functional specialization of individual neurons, networks, and areas. Comparative studies have been important in this endeavor, providing data relevant to the question of which of the many inherent properties of individual pyramidal neurons are necessary and sufficient for species-specific network and areal function. In this mini review, the importance of pyramidal neuron structural properties for signaling are outlined, followed by a summary of our recent work comparing the structural features of mouse (C57/BL6 strain) and rhesus monkey layer 3 (L3) pyramidal neurons in primary visual and frontal association cortices and their implications for neuronal and areal function. Based on these and other published data, L3 pyramidal neurons plausibly might be considered broadly “generalizable” from one area to another in the mouse neocortex due to their many similarities, but major differences in the properties of these neurons in diverse areas in the rhesus monkey neocortex rules this out in the primate. Further, fundamental differences in the dendritic topology of mouse and rhesus monkey pyramidal neurons highlight the implausibility of straightforward scaling and/or extrapolation from mouse to primate neurons and cortical networks.

Secondary Motor Cortex: Where 'Sensory' Meets 'Motor' in the Rodent Frontal Cortex

In rodents, the medial aspect of the secondary motor cortex (M2) is known by other names, including medial agranular cortex (AGm), medial precentral cortex (PrCm), and frontal orienting field (FOF). As a subdivision of the medial prefrontal cortex (mPFC), M2 can be defined by a distinct set of afferent and efferent connections, microstimulation responses, and lesion outcomes. However, the behavioral role of M2 remains mysterious. Here, we focus on evidence from rodent studies, highlighting recent findings of early and context-dependent choice-related activity in M2 during voluntary behavior. Based on the current understanding, we suggest that a major function for M2 is to flexibly map antecedent signals such as sensory cues to motor actions, thereby enabling adaptive choice behavior.

A Functional Gradient in the Rodent Prefrontal Cortex Supports Behavioral Inhibition

The ability to plan and execute appropriately timed responses to external stimuli is based on a well-orchestrated balance between movement initiation and inhibition. In impulse control disorders involving the prefrontal cortex (PFC) [1], this balance is disturbed, emphasizing the critical role that PFC plays in appropriately timing actions [2-4]. Here, we employed optogenetic and electrophysiological techniques to systematically analyze the functional role of five key subareas of the rat medial PFC (mPFC) and orbitofrontal cortex (OFC) in action control [5-9]. Inactivation of mPFC subareas induced drastic changes in performance, namely an increase (prelimbic cortex, PL) or decrease (infralimbic cortex, IL) of premature responses. Additionally, electrophysiology revealed a significant decrease in neuronal activity of a PL subpopulation prior to premature responses. In contrast, inhibition of OFC subareas (mainly the ventral OFC, i.e., VO) significantly impaired the ability to respond rapidly after external cues. Consistent with these findings, mPFC activity during response preparation predicted trial outcomes and reaction times significantly better than OFC activity. These data support the concept of opposing roles of IL and PL in directing proactive behavior and argue for an involvement of OFC in predominantly reactive movement control. By attributing defined roles to rodent PFC sections, this study contributes to a deeper understanding of the functional heterogeneity of this brain area and thus may guide medically relevant studies of PFC-associated impulse control disorders in this animal model for neural disorders [10-12].

Modulation of azimuth tuning plasticity in rat primary auditory cortex by medial prefrontal cortex

Neurons in the primary auditory cortex (A1) of adult animals exhibit short-term plasticity of frequency selectivity and tonotopic organization in behavioral contexts ranging from classical conditioning to attention tasks. However, it is still largely unknown whether short-term plasticity of spatial tuning takes place in A1 of adult animals and whether this spatial turning plasticity in A1 of adults is mediated by medial prefrontal cortex (mPFC) as there are reciprocal connection between mPFC and auditory cortex (AC). In the present study, we used extracellular recordings to test whether azimuth tuning in A1 of anesthetized rats can be reshaped by repeated sound stimuli at neurons' non-preferred azimuth. We also identified whether and how such A1 azimuth tuning plasticity was modulated by the neural activities of mPFC. Our results showed that A1 neurons in adult rats have azimuth tuning plasticity when repeated acoustic stimuli were delivered at the azimuth with a deviation by less than 15° from the best azimuth (BA). The BA shifted toward the exposure azimuth when repeated acoustic stimuli were played for 20-60min and plasticity decayed within one hour. The less the angle deviated from the BA, the shorter exposure time and longer decay time were required to induce azimuth tuning plasticity. Neural activity in mPFC modulated azimuth tuning plasticity of A1 neurons as reflected by the shorter induction time when mPFC was activated by focal electrical stimulation and the longer induction time when mPFC was inactivated by drug application. Our results suggest that spatial location selectivity in A1 neurons remains plastic in mature animals and that short-term plasticity of spatial tuning can be modulated by the neural activities of mPFC.

Modulation of Synaptic Plasticity in the Cortex Needs to Understand All the Players

The prefrontal cortex (PFC) is involved in cognitive tasks such as working memory, decision making, risk assessment and regulation of attention. These functions performed by the PFC are supposed to rely on rhythmic electrical activity generated by neuronal network oscillations determined by a precise balance between excitation and inhibition balance (E/I balance) resulting from the coordinated activities of recurrent excitation and feedback and feedforward inhibition. Functional alterations in PFC functions have been associated with cognitive deficits in several pathologies such as major depression, anxiety and schizophrenia. These pathological situations are correlated with alterations of different neurotransmitter systems (i.e., serotonin (5-HT), dopamine (DA), acetylcholine…) that result in alterations of the E/I balance. The aim of this review article is to cover the basic aspects of the regulation of the E/I balance as well as to highlight the importance of the complementarity role of several neurotransmitters in the modulation of the plasticity of excitatory and inhibitory synapses. We illustrate our purpose by recent findings that demonstrate that 5-HT and DA cooperate to regulate the plasticity of excitatory and inhibitory synapses targeting layer 5 pyramidal neurons (L5PyNs) of the PFC and to fine tune the E/I balance. Using a method based on the decomposition of the synaptic conductance into its excitatory and inhibitory components, we show that concomitant activation of D1-like receptors (D1Rs) and 5-HT_1ARs, through a modulation of NMDA receptors, favors long term potentiation (LTP) of both excitation and inhibition and consequently does not modify the E/I balance. We also demonstrate that activation of D2-receptors requires functional 5-HT_1ARs to shift the E-I balance towards more inhibition and to favor long term depression (LTD) of excitatory synapses through the activation of glycogen synthase kinase 3β (GSK3β). This cooperation between different neurotransmitters is particularly relevant in view of pathological situations in which alterations of one neurotransmitter system will also have consequences on the regulation of synaptic efficacy by other neurotransmitters. This opens up new perspectives in the development of therapeutic strategies for the pharmacological treatment of neuronal disorders.

Hippocampal-prefrontal connectivity as a translational phenotype for schizophrenia

Finding novel biological targets in psychiatry has been difficult, partly because current diagnostic categories are not defined by pathophysiology and difficult to model in animals. The study of species-conserved systems-level mechanisms implicated in psychiatric disease could be a promising strategy to address some of these difficulties. Altered hippocampal-prefrontal (HC-PFC) connectivity during working memory (WM) processing is a candidate for such a translational phenotype as it has been repeatedly associated with impaired cognition in schizophrenia patients and animal models for psychiatric risk factors. Specifically, persistent hippocampus-dorsolateral prefrontal cortex (HC-DLPFC) coupling during WM is an intermediate phenotype for schizophrenia that has been observed in patients, healthy relatives and carriers of two different risk polymorphisms identified in genome-wide association studies. Rodent studies report reduced coherence between HC and PFC during anesthesia, sleep and task performance in both genetic, environmental and neurodevelopmental models for schizophrenia. We discuss several challenges for translation including differences in anatomy, recording modalities and WM paradigms and suggest that a better understanding of HC-PFC coupling across species can be achieved if translational neuroimaging is used to control for task differences. The evidence for potential neurobiological substrates underlying HC-PFC dysconnectivity is evaluated and research strategies are proposed that aim to bridge the gap between findings from large-scale association studies and disease mechanisms.

Individual mediodorsal thalamic neurons project to multiple areas of the rat prefrontal cortex: A single neuron-tracing study using virus vectors

The prefrontal cortex has an important role in a variety of cognitive and executive processes, and is generally defined by its reciprocal connections with the mediodorsal thalamic nucleus (MD). The rat MD is mainly subdivided into three segments, the medial (MDm), central (MDc), and lateral (MDl) divisions, on the basis of the cytoarchitecture and chemoarchitecture. The MD segments are known to topographically project to multiple prefrontal areas at the population level: the MDm mainly to the prelimbic, infralimbic, and agranular insular areas; the MDc to the orbital and agranular insular areas; and the MDl to the prelimbic and anterior cingulate areas. However, it is unknown whether individual MD neurons project to single or multiple prefrontal cortical areas. In the present study, we visualized individual MD neurons with Sindbis virus vectors, and reconstructed whole structures of MD neurons. While the main cortical projection targets of MDm, MDc, and MDl neurons were generally consistent with those of previous results, it was found that individual MD neurons sent their axon fibers to multiple prefrontal areas, and displayed various projection patterns in the target areas. Furthermore, the axons of single MD neurons were not homogeneously spread, but were rather distributed to form patchy axon arbors approximately 1 mm in diameter. The multiple-area projections and patchy axon arbors of single MD neurons might be able to coactivate cortical neuron groups in distant prefrontal areas simultaneously. Furthermore, considerable heterogeneity of the projection patterns is likely, to recruit the different sets of cortical neurons, and thus contributes to a variety of prefrontal functions. J. Comp. Neurol. 525:166-185, 2017. © 2016 Wiley Periodicals, Inc.

Reprogramming of mPFC transcriptome and function in alcohol dependence

Despite its limited immediate reinforcement value, alcohol has a potent ability to induce neuroadaptations that promote its incentive salience, escalation of voluntary alcohol intake and aversion-resistant alcohol seeking. A constellation of these traits, collectively called 'post-dependent', emerges following brain exposure to repeated cycles of intoxication and withdrawal. The medial prefrontal cortex (mPFC) and its subdivisions exert top-down regulation of approach and avoidance behaviors, including those that lead to alcohol intake. Here, we review an emerging literature which indicates that a reprogramming of mPFC function occurs with prolonged exposure of the brain to cycles of alcohol intoxication and withdrawal. This reprogramming results in molecular dysregulations that contribute to the post-dependent syndrome. Convergent evidence has identified neuroadaptations resulting in altered glutamatergic and BDNF-mediated signaling, and for these pathways, direct evidence for a mechanistic role has been obtained. Additional evidence points to a dysregulation of pathways involving calcium homeostasis and neurotransmitter release. Recent findings indicate that global DNA hypermethylation is a key factor in reprogramming the mPFC genome after a history of dependence. As one of the results of this epigenetic remodeling, several histone modifying epigenetic enzymes are repressed. Among these, PR-domain zinc-finger protein 2, a methyltransferase that selectively mono-methylates histone H3 at lysine 9 has been functionally validated to drive several of the molecular and behavioral long-term consequences of alcohol dependence. Information processing within the mPFC involves formation of dynamic neuronal networks, or functional ensembles that are shaped by transcriptional responses. The epigenetic dysregulations identified by our molecular studies are likely to alter this dynamic processing in multiple ways. In summary, epigenetic molecular switches in the mPFC appear to be turned on as alcoholism develops. Strategies to reverse these processes may offer targets for disease-modifying treatments.

Posttraumatic Stress Disorder: Perspectives for the Use of Deep Brain Stimulation

OBJECTIVES

Deep Brain Stimulation (DBS) has been either approved or is currently under investigation for a number of psychiatric disorders.

MATERIALS AND METHODS

We review clinical and preclinical concepts as well as the neurocircuitry that may be of relevance for the implementation of DBS in posttraumatic stress disorder (PTSD).

RESULTS

PTSD is a chronic and debilitating illness associated with dysfunction in well-established neural circuits, including the amygdala and prefrontal cortex. Although most patients often improve with medications and/or psychotherapy, approximately 20-30% are considered to be refractory to conventional treatments. In other psychiatric disorders, DBS has been investigated in treatment-refractory patients. To date, preclinical work suggests that stimulation at high frequency delivered at particular timeframes to different targets, including the amygdala, ventral striatum, hippocampus, and prefrontal cortex may improve fear extinction and anxiety-like behavior in rodents. In the only clinical report published so far, a patient implanted with electrodes in the amygdala has shown striking improvements in PTSD symptoms.

CONCLUSIONS

Neuroimaging, preclinical, and preliminary clinical data suggest that the use of DBS for the treatment of PTSD may be practical but the field requires further investigation.

Sodium fluoride does not affect the working memory and number of pyramidal cells in rat medial prefrontal cortex

Fluoride is a chemical compound known to bring about fluorosis. It is thought to disrupt the central nervous system because of its ability to induce excitotoxicity and oxidative stress. Any damage of pyramidal cells in the prefrontal cortex would result in cognitive function and working memory regulation disorders. The present study aimed at investigating the effects of sodium fluoride (NaF) on the working memory and estimated total number of medial prefrontal cortex pyramidal cells of adult male rats. Thirty-two male Wistar rats were assigned into four groups, namely control and three treated groups receiving 5, 10 and 20 mg/kg BW, respectively, of oral NaF solution for 30 days. The working memory test was carried out using a Y-maze. The number of pyramidal cells in the medial prefrontal cortex was estimated using an unbiased stereological method. There was no significant difference among groups in the working memory and number of pyramidal neurons in the medial prefrontal cortex cells.

Comparative Overview of Visuospatial Working Memory in Monkeys and Rats

Neural mechanisms of working memory, particularly its visuospatial aspect, have long been studied in non-human primates. On the other hand, rodents are becoming more important in systems neuroscience, as many of the innovative research methods have become available for them. There has been a question on whether primates and rodents have similar neural backgrounds for working memory. In this article, we carried out a comparative overview of the neural mechanisms of visuospatial working memory in monkeys and rats. In monkeys, a number of lesion studies indicate that the brain region most responsible for visuospatial working memory is the ventral dorsolateral prefrontal cortex (vDLPFC), as the performance in the standard tests for visuospatial working memory, such as delayed response and delayed alternation tasks, are impaired by lesions in this region. Single-unit studies revealed a characteristic firing pattern in neurons in this area, a sustained delay activity. Further studies indicated that the information maintained in the working memory, such as cue location and response direction in a delayed response, is coded in the sustained delay activity. In rats, an area comparable to the monkey vDLPFC was found to be the dorsal part of the medial prefrontal cortex (mPFC), as the delayed alternation in a T-maze is impaired by its lesion. Recently, the sustained delay activity similar to that found in monkeys has been found in the dorsal mPFC of rats performing the delayed response task. Furthermore, anatomical studies indicate that the vDLPFC in monkeys and the dorsal mPFC in rats have much in common, such as that they are both the major targets of parieto-frontal projections. Thus lines of evidence indicate that in both monkeys and rodents, the PFC plays a critical role in working memory.

The Web-Surf Task: A translational model of human decision-making

Animal models of decision-making are some of the most highly regarded psychological process models; however, there remains a disconnection between how these models are used for pre-clinical applications and the resulting treatment outcomes. This may be due to untested assumptions that different species recruit the same neural or psychological mechanisms. We propose a novel human foraging paradigm (Web-Surf Task) that we translated from a rat foraging paradigm (Restaurant Row) to evaluate cross-species decision-making similarities. We examined behavioral parallels in human and non-human animals using the respective tasks. We also compared two variants of the human task, one using videos and the other using photos as rewards, by correlating revealed and stated preferences. We demonstrate similarities in choice behaviors and decision reaction times in human and rat subjects. Findings also indicate that videos yielded more reliable and valid results. The joint use of the Web-Surf Task and Restaurant Row is therefore a promising approach for functional translational research, aiming to bridge pre-clinical and clinical lines of research using analogous tasks.

Parvalbumin neurons and perineuronal nets in the mouse prefrontal cortex

The prefrontal cortex (PFC) plays a key role in cognitive functions, memory, and attention. Alterations in parvalbumin interneurons (PV neurons) and perineuronal nets (PNNs) within the PFC have been implicated in schizophrenia and autism spectrum disorder pathology. However, it remains unclear why PV neurons and PNNs in the PFC are selectively impaired. Here we aimed to clarify if PV neurons and PNNs in the PFC have region-specific features. We found that PV neurons and PNNs were increased in a region-specific manner in the PFC during postnatal development. In the mature PFC, the expression of PV protein is lower than in other parts of the cortex. Furthermore, PNNs in the mature PFC are not typical lattice-like structures and do not have the major components of PNNs and tenascin-R. The present study indicates that PV neurons and PNNs have region-specific features, and our results suggest that PV neurons and PNNs have structural vulnerability within the PFC.

DNA Methylation Signatures of Early Childhood Malnutrition Associated With Impairments in Attention and Cognition

BACKGROUND

Early childhood malnutrition affects 113 million children worldwide, impacting health and increasing vulnerability for cognitive and behavioral disorders later in life. Molecular signatures after childhood malnutrition, including the potential for intergenerational transmission, remain unexplored.

METHODS

We surveyed blood DNA methylomes (~483,000 individual CpG sites) in 168 subjects across two generations, including 50 generation 1 individuals hospitalized during the first year of life for moderate to severe protein-energy malnutrition, then followed up to 48 years in the Barbados Nutrition Study. Attention deficits and cognitive performance were evaluated with the Connors Adult Attention Rating Scale and Wechsler Abbreviated Scale of Intelligence. Expression of nutrition-sensitive genes was explored by quantitative reverse transcriptase polymerase chain reaction in rat prefrontal cortex.

RESULTS

We identified 134 nutrition-sensitive, differentially methylated genomic regions, with most (87%) specific for generation 1. Multiple neuropsychiatric risk genes, including COMT, IFNG, MIR200B, SYNGAP1, and VIPR2 showed associations of specific methyl-CpGs with attention and IQ. IFNG expression was decreased in prefrontal cortex of rats showing attention deficits after developmental malnutrition.

CONCLUSIONS

Early childhood malnutrition entails long-lasting epigenetic signatures associated with liability for attention and cognition, and limited potential for intergenerational transmission.

Large-scale analysis reveals populational contributions of cortical spike rate and synchrony to behavioural functions

KEY POINTS

There have been few systematic population-wide analyses of relationships between spike synchrony within a period of several milliseconds and behavioural functions. In this study, we obtained a large amount of spike data from > 23,000 neuron pairs by multiple single-unit recording from deep layer neurons in motor cortical areas in rats performing a forelimb movement task. The temporal changes of spike synchrony in the whole neuron pairs were statistically independent of behavioural changes during the task performance, although some neuron pairs exhibited correlated changes in spike synchrony. Mutual information analyses revealed that spike synchrony made a smaller contribution than spike rate to behavioural functions. The strength of spike synchrony between two neurons was statistically independent of the spike rate-based preferences of the pair for behavioural functions.

ABSTRACT

Spike synchrony within a period of several milliseconds in presynaptic neurons enables effective integration of functional information in the postsynaptic neuron. However, few studies have systematically analysed the population-wide relationships between spike synchrony and behavioural functions. Here we obtained a sufficiently large amount of spike data among regular-spiking (putatively excitatory) and fast-spiking (putatively inhibitory) neuron subtypes (> 23,000 pairs) by multiple single-unit recording from deep layers in motor cortical areas (caudal forelimb area, rostral forelimb area) in rats performing a forelimb movement task. After holding a lever, rats pulled the lever either in response to a cue tone (external-trigger trials) or spontaneously without any cue (internal-trigger trials). Many neurons exhibited functional spike activity in association with forelimb movements, and the preference of regular-spiking neurons in the rostral forelimb area was more biased toward externally triggered movement than that in the caudal forelimb area. We found that a population of neuron pairs with spike synchrony does exist, and that some neuron pairs exhibit a dependence on movement phase during task performance. However, the population-wide analysis revealed that spike synchrony was statistically independent of the movement phase and the spike rate-based preferences of the pair for behavioural functions, whereas spike rates were clearly dependent on the movement phase. In fact, mutual information analyses revealed that the contribution of spike synchrony to the behavioural functions was small relative to the contribution of spike rate. Our large-scale analysis revealed that cortical spike rate, rather than spike synchrony, contributes to population coding for movement.

Sex-dependent changes in neuronal morphology and psychosocial behaviors after pediatric brain injury

Chronic social behavior problems after pediatric traumatic brain injury (TBI) significantly contribute to poor quality of life for survivors. Using a well-characterized mouse model of early childhood TBI, we have previously demonstrated that young brain-injured mice develop social deficits by adulthood. As biological sex may influence both normal and aberrant social development, we here evaluated potential sex differences in post-TBI psychosocial deficits by comparing the behavior of male and female mice at adulthood (8 weeks post-injury). Secondly, we hypothesized that pediatric TBI would influence neuronal morphology identified by Golgi-Cox staining in the hippocampus and prefrontal cortex, regions involved in social cognition and behavior, before the onset of social problems (3 weeks post-injury). Morphological analysis of pyramidal neurons in the ipsilateral prefrontal cortex and granule cells of the hippocampal dentate gyrus revealed a reduction in dendritic complexity after pediatric TBI. This was most apparent in TBI males, whereas neurons from females were less affected. At adulthood, consistent with previous studies, TBI males showed deficits in sociability and social recognition. TBI females also showed a reduction in sociability, but intact social recognition and increased sociosexual avoidance. Together, these findings indicate that sex is a determinant of regional neuroplasticity and social outcomes after pediatric TBI. Reduced neuronal complexity in the prefrontal cortex and hippocampus, several weeks after injury in male mice, appears to precede the subsequent emergence of social deficits. Sex-specific alterations in the social brain network are thus implicated as an underlying mechanism of social dysfunction after pediatric TBI.

Medial prefrontal-perirhinal cortical communication is necessary for flexible response selection

The ability to use information from the physical world to update behavioral strategies is critical for survival across species. The prefrontal cortex (PFC) supports behavioral flexibility; however, exactly how this brain structure interacts with sensory association cortical areas to facilitate the adaptation of response selection remains unknown. Given the role of the perirhinal cortex (PER) in higher-order perception and associative memory, the current study evaluated whether PFC-PER circuits are critical for the ability to perform biconditional object discriminations when the rule for selecting the rewarded object shifted depending on the animal's spatial location in a 2-arm maze. Following acquisition to criterion performance on an object-place paired association task, pharmacological blockade of communication between the PFC and PER significantly disrupted performance. Specifically, the PFC-PER disconnection caused rats to regress to a response bias of selecting an object on a particular side regardless of its identity. Importantly, the PFC-PER disconnection did not interfere with the capacity to perform object-only or location-only discriminations, which do not require the animal to update a response rule across trials. These findings are consistent with a critical role for PFC-PER circuits in rule shifting and the effective updating of a response rule across spatial locations.

α4β2∗ nicotinic receptors stimulate GABA release onto fast-spiking cells in layer V of mouse prefrontal (Fr2) cortex

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α4β2^∗ nAChRs stimulate IPSCs in FS interneurons, in layer V of the mouse PFC (Fr2).

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In P16–P63 mice, nicotine increased both IPSC and mIPSC frequencies.

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GABAergic terminals adjacent to PV+ cells expressed α4 nAChR.

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The percentage of FS cells with somatic α4β2^∗ currents decreased with age.

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Hence, nAChRs may be able to induce local circuit disinhibition in Fr2 PFC.

Nicotinic acetylcholine receptors (nAChRs) produce widespread and complex effects on neocortex excitability. We studied how heteromeric nAChRs regulate inhibitory post-synaptic currents (IPSCs), in fast-spiking (FS) layer V neurons of the mouse frontal area 2 (Fr2). In the presence of blockers of ionotropic glutamate receptors, tonic application of 10 μM nicotine augmented the spontaneous IPSC frequency, with minor alterations of amplitudes and kinetics. These effects were studied since the 3rd postnatal week, and persisted throughout the first two months of postnatal life. The action of nicotine was blocked by 1 μM dihydro-β-erythroidine (DHβE; specific for α4^∗ nAChRs), but not 10 nM methyllycaconitine (MLA; specific for α7^∗ nAChRs). It was mimicked by 10 nM 5-iodo-3-[2(S)-azetidinylmethoxy]pyridine (5-IA; which activates β2^∗ nAChRs). Similar results were obtained on miniature IPSCs (mIPSCs). Moreover, during the first five postnatal weeks, approximately 50% of FS cells displayed DHβE-sensitive whole-cell nicotinic currents. This percentage decreased to ∼5% in mice older than P45. By confocal microscopy, the α4 nAChR subunit was immunocytochemically identified on interneurons expressing either parvalbumin (PV), which mainly labels FS cells, or somatostatin (SOM), which labels the other major interneuron population in layer V. GABAergic terminals expressing α4 were observed to be juxtaposed to PV-positive (PV+) cells. A fraction of these terminals displayed PV immunoreactivity. We conclude that α4β2^∗ nAChRs can produce sustained regulation of FS cells in Fr2 layer V. The effect presents a presynaptic component, whereas the somatic regulation decreases with age. These mechanisms may contribute to the nAChR-dependent stimulation of excitability during cognitive tasks as well as to the hyperexcitability caused by hyperfunctional heteromeric nAChRs in sleep-related epilepsy.

The importance of mammillary body efferents for recency memory: towards a better understanding of diencephalic amnesia

Despite being historically one of the first brain regions linked to memory loss, there remains controversy over the core features of diencephalic amnesia as well as the critical site for amnesia to occur. The mammillary bodies and thalamus appear to be the primary locus of pathology in the cases of diencephalic amnesia, but the picture is complicated by the lack of patients with circumscribed damage. Impaired temporal memory is a consistent neuropsychological finding in Korsakoff syndrome patients, but again, it is unclear whether this deficit is attributable to pathology within the diencephalon or concomitant frontal lobe dysfunction. To address these issues, we used an animal model of diencephalic amnesia and examined the effect of mammillothalamic tract lesions on tests of recency memory. The mammillothalamic tract lesions severely disrupted recency judgements involving multiple items but left intact both recency and familiarity judgements for single items. Subsequently, we used disconnection procedures to assess whether this deficit reflects the indirect involvement of the prefrontal cortex. Crossed-lesion rats, with unilateral lesions of the mammillothalamic tract and medial prefrontal cortex in contralateral hemispheres, were unimpaired on the same recency tests. These results provide the first evidence for the selective importance of mammillary body efferents for recency memory. Moreover, this contribution to recency memory is independent of the prefrontal cortex. More broadly, these findings identify how specific diencephalic structures are vital for key elements of event memory.

Corticolimbic regulation of cardiovascular responses to stress

Cardiovascular disease, a leading cause of death worldwide, is frequently initiated or exacerbated by stress. In fact, chronic stress exposure and heightened reactions to acute psychological stress are both associated with increased cardiovascular morbidity. This brief review focuses on the mechanisms by which corticolimbic nuclei, critical for stress appraisal and emotional reactivity, regulate heart rate and blood pressure responses to psychological stress. Both human and rodent data are examined with a major emphasis on basic studies investigating prefrontal cortex, amygdala, and hippocampus. A detailed literature review reveals substantial limitations in our understanding of this circuitry, as well as significant opportunities for future investigation that may ultimately reduce the burden of cardiovascular illness.

The Structural and Functional Organization of Cognition

This article proposes that what have been historically and contemporarily defined as different domains of human cognition are served by one of four functionally- and structurally-distinct areas of the prefrontal cortex (PFC). Their contributions to human intelligence are as follows: (a) BA9, enables our emotional intelligence, engaging the psychosocial domain; (b) BA47, enables our practical intelligence, engaging the material domain; (c) BA46 (or BA46-9/46), enables our abstract intelligence, engaging the hypothetical domain; and (d) BA10, enables our temporal intelligence, engaging in planning within any of the other three domains. Given their unique contribution to human cognition, it is proposed that these areas be called the, social (BA9), material (BA47), abstract (BA46-9/46) and temporal (BA10) mind. The evidence that BA47 participates strongly in verbal and gestural communication suggests that language evolved primarily as a consequence of the extreme selective pressure for practicality; an observation supported by the functional connectivity between BA47 and orbital areas that negatively reinforce lying. It is further proposed that the abstract mind (BA46-9/46) is the primary seat of metacognition charged with creating adaptive behavioral strategies by generating higher-order concepts (hypotheses) from lower-order concepts originating from the other three domains of cognition.

Effect of Ovarian Hormone Therapy on Cognition in the Aged Female Rhesus Macaque

Studies of the effect of hormone therapy on cognitive function in menopausal women have been equivocal, in part due to differences in the type and timing of hormone treatment. Here we cognitively tested aged female rhesus macaques on (1) the delayed response task of spatial working memory, (2) a visuospatial attention task that measured spatially and temporally cued reaction times, and (3) a simple reaction time task as a control for motor speed. After task acquisition, animals were ovariectomized (OVX). Their performance was compared with intact controls for 2 months, at which time no group differences were found. The OVX animals were then assigned to treatment with either a subcutaneous sham implant (OVX), 17-β estradiol (E) implant (OVX+E) or E implant plus cyclic oral progesterone (OVX+EP). All groups were then tested repeatedly over 12 months. The OVX+E animals performed significantly better on the delayed response task than all of the other groups for much of the 12 month testing period. The OVX+EP animals also showed improved performance in the delayed response task, but only at 30 s delays and with performance levels below that of OVX+E animals. The OVX+E animals also performed significantly better in the visuospatial attention task, particularly in the most challenging invalid cue condition; this difference also was maintained across the 12 month testing period. Simple reaction time was not affected by hormonal manipulation. These data demonstrate that chronic, continuous administration of E can exert multiple beneficial cognitive effects in aged, OVX rhesus macaque females.

SIGNIFICANCE STATEMENT

Hormone therapy after menopause is controversial. We tested the effects of hormone replacement in aged rhesus macaques, soon after surgically-induced menopause [ovariectomy (OVX)], on tests of memory and attention. Untreated ovarian-intact and OVX animals were compared with OVX animals receiving estradiol (E) alone or E with progesterone (P). E was administered in a continuous fashion via subcutaneous implant, whereas P was administered orally in a cyclic fashion. On both tests, E-treated animals performed better than the other 3 experimental groups across 1 year of treatment. Thus, in this monkey model, chronic E administered soon after the loss of ovarian hormones had long-term benefits for cognitive function.

Prefrontal-hippocampal pathways underlying inhibitory control over memory

A key function of the prefrontal cortex is to support inhibitory control over behavior. It is widely believed that this function extends to stopping cognitive processes as well. Consistent with this, mounting evidence establishes the role of the right lateral prefrontal cortex in a clear case of cognitive control: retrieval suppression. Retrieval suppression refers to the ability to intentionally stop the retrieval process that arises when a reminder to a memory appears. Functional imaging data indicate that retrieval suppression involves top-down modulation of hippocampal activity by the dorsolateral prefrontal cortex, but the anatomical pathways supporting this inhibitory modulation remain unclear. Here we bridge this gap by integrating key findings about retrieval suppression observed through functional imaging with a detailed consideration of relevant anatomical pathways observed in non-human primates. Focusing selectively on the potential role of the anterior cingulate cortex, we develop two hypotheses about the pathways mediating interactions between lateral prefrontal cortex and the medial temporal lobes during suppression, and their cellular targets: the entorhinal gating hypothesis, and thalamo-hippocampal modulation via the nucleus reuniens. We hypothesize that whereas entorhinal gating is well situated to stop retrieval proactively, thalamo-hippocampal modulation may interrupt an ongoing act of retrieval reactively. Isolating the pathways that underlie retrieval suppression holds the potential to advance our understanding of a range of psychiatric disorders characterized by persistent intrusive thoughts. More broadly, an anatomical account of retrieval suppression would provide a key model system for understanding inhibitory control over cognition.

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.

Representational changes of latent strategies in rat medial prefrontal cortex precede changes in behaviour

The ability to change behavioural strategies in the face of a changing world has been linked to the integrity of medial prefrontal cortex (mPFC) function in several species. While recording studies have found that mPFC representations reflect the strategy being used, lesion studies suggest that mPFC is necessary for changing strategy. Here we examine the relationship between representational changes in mPFC and behavioural strategy changes in the rat. We found that on tasks with a forced change in reward criterion, strategy-related representational transitions in mPFC occurred after animals learned that the reward contingency had changed, but before their behaviour changed. On tasks in which animals made their own strategic decisions, representational transitions in mPFC preceded changes in behaviour. These results suggest that mPFC does not merely reflect the action–selection policy of the animal, but rather that mPFC processes information related to a need for a change in strategy.

The medial prefrontal cortex (mPFC) is involved in changing behavioural strategies. Recording neural ensembles in rats, Powell and Redish find that the requirement for those changes is represented in mPFC before they manifest behaviourally, both in tasks that externally force a change and in tasks with self-determined change.

Characterization of oscillatory changes in hippocampus and amygdala after deep brain stimulation of the infralimbic prefrontal cortex

Deep brain stimulation (DBS) is a new investigational therapy that has generated positive results in refractory depression. Although the neurochemical and behavioral effects of DBS have been examined, less attention has been paid to the influence of DBS on the network dynamics between different brain areas, which could contribute to its therapeutic effects. Herein, we set out to identify the effects of 1 h DBS in the infralimbic cortex (IL) on the oscillatory network dynamics between hippocampus and basolateral amygdala (BLA), two regions implicated in depression and its treatment. Urethane-anesthetized rats with bilaterally implanted electrodes in the IL were exposed to 1 h constant stimulation of 130 Hz of frequency, 60 μA of constant current intensity and biphasic pulse width of 80 μsec. After a period of baseline recording, local field potentials (LFP) were recorded with formvar-insulated stainless steel electrodes. DBS of the IL increased the power of slow wave (SW, <1.5 Hz) and theta (3-12 Hz) frequencies in the hippocampus and BLA Furthermore, IL DBS caused a precise coupling in different frequency bands between both brain structures. The increases in SW band synchronization in hippocampus and BLA after DBS suggest that these changes may be important for the improvement of depressive behavior. In addition, the augmentation in theta synchrony might contribute to improvement in emotional and cognitive processes.

Advantages of nonhuman primates as preclinical models for evaluating stem cell-based therapies for Parkinson's disease

The derivation of dopaminergic neurons from induced pluripotent stem cells brings new hope for a patient-specific, stem cell-based replacement therapy to treat Parkinson's disease (PD) and related neurodegenerative diseases; and this novel cell-based approach has already proven effective in animal models. However, there are several aspects of this procedure that have yet to be optimized to the extent required for translation to an optimal cell-based transplantation protocol in humans. These challenges include pinpointing the optimal graft location, appropriately scaling up the graft volume, and minimizing the risk of chronic immune rejection, among others. To advance this procedure to the clinic, it is imperative that a model that accurately and fully recapitulates characteristics most pertinent to a cell-based transplantation to the human brain is used to optimize key technical aspects of the procedure. Nonhuman primates mimic humans in multiple ways including similarities in genomics, neuroanatomy, neurophysiology, immunogenetics, and age-related changes in immune function. These characteristics are critical to the establishment of a relevant model in which to conduct preclinical studies to optimize the efficacy and safety of cell-based therapeutic approaches to the treatment of PD. Here we review previous studies in rodent models, and emphasize additional advantages afforded by nonhuman primate models in general, and the baboon model in particular, for preclinical optimization of cell-based therapeutic approaches to the treatment of PD and other neurodegenerative diseases. We outline current unresolved challenges to the successful application of stem cell therapies in humans and propose that the baboon model in particular affords a number of traits that render it most useful for preclinical studies designed to overcome these challenges.

Chronic stress affects the number of GABAergic neurons in the orbitofrontal cortex of rats

Cortical GABAergic dysfunctions have been documented by clinical studies in major depression. We used here an animal model for depression and investigated whether long-term stress exposure can affect the number of GABAergic neurons in the orbitofrontal cortex (OFC). Adult male rats were subjected to 7-weeks of daily stress exposure and behaviorally phenotyped as anhedonic or stress-resilient animals. GABAergic interneurons were identified by immunohistochemistry and systematically quantified. We analyzed calbindin-(CB), calretinin-(CR), cholecystokinin-(CCK), parvalbumin-(PV), neuropeptide Y-(NPY) and somatostatin-positive (SST+) neurons in the following specific subareas of the OFC: medial orbital (MO), ventral orbital (VO), lateral orbital (LO) and dorsolateral orbital (DLO) cortex. For comparison, we also analyzed the primary motor cortex (M1) as a non-limbic cortical area. Stress had a pronounced effect on CB+ neurons and reduced their densities by 40-50% in the MO, VO and DLO. Stress had no effect on CCK+, CR+, PV+, NPY+ and SST+ neurons in any cortical areas. None of the investigated GABAergic neurons were affected by stress in the primary motor cortex. Interestingly, in the stress-resilient animals, we observed a significantly increased density of CCK+ neurons in the VO. NPY+ neuron densities were also significantly different between the anhedonic and stress-resilient rats, but only in the LO. Our present data demonstrate that chronic stress can specifically reduce the density of calbindin-positive GABAergic neurons in the orbitofrontal cortex and suggest that NPY and CCK expression in the OFC may relate to the stress resilience of the animals.