Prefrontal cortical mechanisms underlying delayed alternation in mice

Role of medial prefrontal cortex voltage-dependent potassium 4.3 channels in nicotine-induced enhancement of object recognition memory in male mice

Nicotine has been shown to enhance object recognition memory in the novel object recognition (NOR) test by activating excitatory neurons in the medial prefrontal cortex (mPFC). However, the exact neuronal mechanisms underlying the nicotine-induced activation of mPFC neurons and the resultant memory enhancement remain poorly understood. To address this issue, we performed brain-slice electrophysiology and the NOR test in male C57BL/6J mice. Whole-cell patch-clamp recordings from layer V pyramidal neurons in the mPFC revealed that nicotine augments the summation of evoked excitatory postsynaptic potentials (eEPSPs) and that this effect was suppressed by N-[3,5-Bis(trifluoromethyl)phenyl]-N'-[2,4-dibromo-6-(2H-tetrazol-5-yl)phenyl]urea (NS5806), a voltage-dependent potassium (Kv) 4.3 channel activator. In line with these findings, intra-mPFC infusion of NS5806 suppressed systemically administered nicotine-induced memory enhancement in the NOR test. Additionally, miRNA-mediated knockdown of Kv4.3 channels in mPFC pyramidal neurons enhanced object recognition memory. Furthermore, inhibition of A-type Kv channels by intra-mPFC infusion of 4-aminopyridine was found to enhance object recognition memory, while this effect was abrogated by prior intra-mPFC NS5806 infusion. These results suggest that nicotine augments the summation of eEPSPs via the inhibition of Kv4.3 channels in mPFC layer V pyramidal neurons, resulting in the enhancement of object recognition memory.

TAF15 downregulation contributes to the benefits of physical training on dendritic spines and working memory in aged mice

Moderate physical training has been shown to hinder age-related memory decline. While the benefits of physical training on hippocampal memory function are well-documented, little is known about its impact on working memory, which is linked to the prelimbic cortex (PrL), one major subdivision of the prefrontal cortex. Here, we examined the effects of physical training on spatial working memory in a well-established animal model of physical training, starting at 16 months of age and continuing for 5 months (running wheel 1 h/day and 5 days/week). This training strategy improved spatial working memory in aged mice (22-month-old), which was accompanied by an increased spine density and a lower TAF15 expression in the PrL. Specifically, physical training affected both thin and mushroom-type spines on PrL pyramidal cells, and prevented age-related loss of spines on selective segments of apical dendritic branches. Correlation analysis revealed that increased TAF15-expression was detrimental to the dendritic spines. However, physical training downregulated TAF15 expression in the PrL, preserving the dendritic spines on PrL pyramidal cells and improving working memory in trained aged mice. When TAF15 was overexpressed in the PrL via a viral approach, the benefits of physical training on the dendritic spines and working memory were abolished. These data suggest that physical training at a moderate pace might downregulate TAF15 expression in the PrL, which favors the dendritic spines on PrL pyramidal cells, thereby improving spatial working memory.

Striatum-projecting prefrontal cortex neurons support working memory maintenance

Neurons in the medial prefrontal cortex (mPFC) are functionally linked to working memory (WM) but how distinct projection pathways contribute to WM remains unclear. Based on optical recordings, optogenetic perturbations, and pharmacological interventions in male mice, we report here that dorsomedial striatum (dmStr)-projecting mPFC neurons are essential for WM maintenance, but not encoding or retrieval, in a T-maze spatial memory task. Fiber photometry of GCaMP6m-labeled mPFC→dmStr neurons revealed strongest activity during the maintenance period, and optogenetic inhibition of these neurons impaired performance only when applied during this period. Conversely, enhancing mPFC→dmStr pathway activity-via pharmacological suppression of HCN1 or by optogenetic activation during the maintenance period-alleviated WM impairment induced by NMDA receptor blockade. Moreover, cellular-resolution miniscope imaging revealed that >50% of mPFC→dmStr neurons are active during WM maintenance and that this subpopulation is distinct from neurons active during encoding and retrieval. In all task periods, neuronal sequences were evident. Striatum-projecting mPFC neurons thus critically contribute to spatial WM maintenance.

Sharp-wave-ripple-associated activity in the medial prefrontal cortex supports spatial rule switching

Previous studies have highlighted an important role for hippocampal sharp-wave ripples in spatial alternation learning, as well as in modulating activity in the medial prefrontal cortex (mPFC). However, the direct influence of hippocampal sharp-wave ripples on mPFC activity during spatial alternation learning has not been investigated. Here, we train Long Evans rats on a three-arm radial maze to perform a sequence of alternations. Three alternation sequences needed to be learned, and while learning a sequence, the activity in the mPFC was inhibited either directly following sharp-wave ripples in the hippocampus (on-time condition) or with a randomized delay (delayed condition). In the on-time condition, the behavioral performance is significantly worse compared to the same animals in the delayed inhibition condition, as measured by a lower correct alternation performance and more perseverative behavior. This indicates that the activity in the mPFC directly following hippocampal sharp-wave ripples is necessary for spatial rule switching.

Loss of spines in the prelimbic cortex is detrimental to working memory in mice with early-life adversity

Adverse experiences in early life can shape neuronal structures and synaptic function in multiple brain regions, leading to deficits of distinct cognitive functions later in life. Focusing on the pyramidal cells of the prelimbic cortex (PrL), a main subregion of the medial prefrontal cortex, the impact of early-life adversity (ELA) was investigated in a well-established animal model generated by changing the rearing environment during postnatal days 2 to 9 (P2-P9), a sensitive developmental period. ELA has enduring detrimental impacts on the dendritic spines of PrL pyramidal cells, which is most apparent in a spatially circumscribed region. Specifically, ELA affects both thin and mushroom-type spines, and ELA-provoked loss of spines is observed on selective dendritic segments of PrL pyramidal cells in layers II-III and V-VI. Reduced postsynaptic puncta represented by postsynaptic density protein-95 (PSD-95), but not synaptophysin-labelled presynaptic puncta, in ELA mice supports the selective loss of spines in the PrL. Correlation analysis indicates that loss of spines and postsynaptic puncta in the PrL contributes to the poor spatial working memory of ELA mice, and thin spines may play a major role in working memory performance. To further understand whether loss of spines affects glutamatergic transmission, AMPA- and NMDA-receptor-mediated synaptic currents (EPSCs) were recorded in a group of Thy1-expressing PrL pyramidal cells. ELA mice exhibited a depressed glutamatergic transmission, which is accompanied with a decreased expression of GluR1 and NR1 subunits in the PrL. Finally, upregulating the activation of Thy1-expressing PrL pyramidal cells via excitatory DREADDs can efficiently improve the working memory performance of ELA mice in a T-maze-based task, indicating the potential of a chemogenetic approach in restoring ELA-provoked memory deficits.

UBE3A expression during early postnatal brain development is required for proper dorsomedial striatal maturation

Angelman syndrome (AS) is a severe neurodevelopmental disorder (NDD) caused by loss of functional ubiquitin protein ligase E3A (UBE3A). Previous studies showed that UBE3A plays an important role in the first postnatal weeks of mouse brain development, but its precise role is unknown. Since impaired striatal maturation has been implicated in several mouse models for NDDs, we studied the importance of UBE3A in striatal maturation. We used inducible Ube3a mouse models to investigate the maturation of medium spiny neurons (MSNs) from dorsomedial striatum. MSNs of mutant mice matured properly till postnatal day 15 (P15) but remained hyperexcitable with fewer excitatory synaptic events at later ages, indicative of stalled striatal maturation in Ube3a mice. Reinstatement of UBE3A expression at P21 fully restored MSN excitability but only partially restored synaptic transmission and the operant conditioning behavioral phenotype. Gene reinstatement at P70 failed to rescue both electrophysiological and behavioral phenotypes. In contrast, deletion of Ube3a after normal brain development did not result in these electrophysiological and behavioral phenotypes. This study emphasizes the role of UBE3A in striatal maturation and the importance of early postnatal reinstatement of UBE3A expression to obtain a full rescue of behavioral phenotypes associated with striatal function in AS.

Role of the locus coeruleus and basal forebrain in arousal and attention

Experimental evidence has implicated multiple neurotransmitter systems in either the direct or indirect modulation of cortical arousal and attention circuitry. In this review, we selectively focus on three such systems: 1) norepinephrine (NE)-containing neurons of the locus coeruleus (LC), 2) acetylcholine (ACh)-containing neurons of the basal forebrain (BF), and 3) parvalbumin (PV)-containing gamma-aminobutyric acid neurons of the BF. Whereas BF-PV neurons serve as a rapid and transient arousal system, LC-NE and BF-ACh neuromodulation are typically activated on slower but longer-lasting timescales. Recent findings suggest that the BF-PV system serves to rapidly respond to even subtle sensory stimuli with a microarousal. We posit that salient sensory stimuli, such as those that are threatening or predict the need for a response, will quickly activate the BF-PV system and subsequently activate both the BF-ACh and LC-NE systems if the circumstances require longer periods of arousal and vigilance. We suggest that NE and ACh have overlapping psychological functions with the main difference being the precise internal/environmental sensory situations/contexts that recruit each neurotransmitter system - a goal for future research to determine. Implications of dysfunction of each of these three attentional systems for our understanding of neuropsychiatric conditions are considered. Finally, the contemporary availability of research tools to selectively manipulate and measure the activity of these distinctive neuronal populations promises to answer longstanding questions, such as how various arousal systems influence downstream decision-making and motor responding.

Striatal mechanisms of turning behaviour following unilateral dopamine depletion in mice

Unilateral dopamine (DA) depletion produces ipsiversive turning behaviour, and the injection of DA receptor agonists can produce contraversive turning, but the underlying mechanisms remain unclear. We conducted in vivo recording and pharmacological and optogenetic manipulations to study the role of DA and striatal output in turning behaviour. We used a video-based tracking programme while recording single unit activity in both putative medium spiny projection neurons (MSNs) and fast-spiking interneurons (FSIs) in the dorsal striatum bilaterally. Our results suggest that unilateral DA depletion reduced striatal output from the depleted side, resulting in asymmetric striatal output. Depletion systematically altered activity in both MSNs and FSIs, especially in neurons that increased firing during turning movements. Like D1 agonist SKF 38393, optogenetic stimulation in the depleted striatum increased striatal output and reversed biassed turning. These results suggest that relative striatal outputs from the two cerebral hemispheres determine the direction of turning: Mice turn away from the side of higher striatal output and towards the side of the lower striatal output.

Release of endogenous dynorphin opioids in the prefrontal cortex disrupts cognition

Following repeated opioid use, some dependent individuals experience persistent cognitive deficits that contribute to relapse of drug-taking behaviors, and one component of this response may be mediated by the endogenous dynorphin/kappa opioid system in neocortex. In C57BL/6 male mice, we find that acute morphine withdrawal evokes dynorphin release in the medial prefrontal cortex (PFC) and disrupts cognitive function by activation of local kappa opioid receptors (KORs). Immunohistochemical analyses using a phospho-KOR antibody confirmed that both withdrawal-induced and optically evoked dynorphin release activated KOR in PFC. Using a genetically encoded sensor based on inert KOR (kLight1.2a), we revealed the in vivo dynamics of endogenous dynorphin release in the PFC. Local activation of KOR in PFC produced multi-phasic disruptions of memory processing in an operant-delayed alternation behavioral task, which manifest as reductions in response number and accuracy during early and late phases of an operant session. Local pretreatment in PFC with the selective KOR antagonist norbinaltorphimine (norBNI) blocked the disruptive effect of systemic KOR activation during both early and late phases of the session. The early, but not late phase disruption was blocked by viral excision of PFC KORs, suggesting an anatomically dissociable contribution of pre- and postsynaptic KORs. Naloxone-precipitated withdrawal in morphine-dependent mice or optical stimulation of pdyn^Cre neurons using Channelrhodopsin-2 disrupted delayed alternation performance, and the dynorphin-induced effect was blocked by local norBNI. Our findings describe a mechanism for control of cortical function during opioid dependence and suggest that KOR antagonism could promote abstinence.

Elevated expression of complement C4 in the mouse prefrontal cortex causes schizophrenia-associated phenotypes

Accumulating evidence supports immune involvement in the pathogenesis of schizophrenia, a severe psychiatric disorder. In particular, high expression variants of C4, a gene of the innate immune complement system, were shown to confer susceptibility to schizophrenia. However, how elevated C4 expression may impact brain circuits remains largely unknown. We used in utero electroporation to overexpress C4 in the mouse prefrontal cortex. We found reduced glutamatergic input to pyramidal cells of juvenile and adult, but not of newborn C4-overexpressing (C4-OE) mice, together with decreased spine density, which mirrors spine loss observed in the schizophrenic cortex. Using time-lapse two-photon imaging in vivo, we observed that these deficits were associated with decreased dendritic spine gain and elimination in juvenile C4-OE mice, which may reflect poor formation and/or stabilization of immature spines. In juvenile and adult C4-OE mice, we found evidence for NMDA receptor hypofunction, another schizophrenia-associated phenotype, and synaptic accumulation of calcium-permeable AMPA receptors. Alterations in cortical GABAergic networks have been repeatedly associated with schizophrenia. We found that functional GABAergic transmission was reduced in C4-OE mice, in line with diminished GABA release probability from parvalbumin interneurons, lower GAD67 expression, and decreased intrinsic excitability in parvalbumin interneurons. These cellular abnormalities were associated with working memory impairment. Our results substantiate the causal relationship between an immunogenetic risk factor and several distinct cortical endophenotypes of schizophrenia and shed light on the underlying cellular mechanisms.

Catecholaminergic Innervation of the Lateral Nucleus of the Cerebellum Modulates Cognitive Behaviors

The cerebellum processes neural signals related to rewarding and aversive stimuli, suggesting that the cerebellum supports nonmotor functions in cognitive and emotional domains. Catecholamines are a class of neuromodulatory neurotransmitters well known for encoding such salient stimuli. Catecholaminergic modulation of classical cerebellar functions have been demonstrated. However, a role for cerebellar catecholamines in modulating cerebellar nonmotor functions is unknown. Using biochemical methods in male mice, we comprehensively mapped TH+ fibers throughout the entire cerebellum and known precerebellar nuclei. Using electrochemical (fast scan cyclic voltammetry), and viral/genetic methods to selectively delete Th in fibers innervating the lateral cerebellar nucleus (LCN), we interrogated sources and functional roles of catecholamines innervating the LCN, which is known for its role in supporting cognition. The LCN has the most TH+ fibers in cerebellum, as well as the most change in rostrocaudal expression among the cerebellar nuclei. Norepinephrine is the major catecholamine measured in LCN. Distinct catecholaminergic projections to LCN arise only from locus coeruleus, and a subset of Purkinje cells that are positive for staining of TH. LC stimulation was sufficient to produce catecholamine release in LCN. Deletion of Th in fibers innervating LCN (LCN-Th-cKO) resulted in impaired sensorimotor integration, associative fear learning, response inhibition, and working memory in LCN-Th-cKO mice. Strikingly, selective inhibition of excitatory LCN output neurons with inhibitory designer receptor exclusively activated by designer drugs led to facilitation of learning on the same working memory task impaired in LCN-Th-cKO mice. Collectively, these data demonstrate a role for LCN catecholamines in cognitive behaviors.SIGNIFICANCE STATEMENT Here, we report on interrogating sources and functional roles of catecholamines innervating the lateral nucleus of the cerebellum (LCN). We map and quantify expression of TH, the rate-limiting enzyme in catecholamine synthesis, in the entire cerebellar system, including several precerebellar nuclei. We used cyclic voltammetry and pharmacology to demonstrate sufficiency of LC stimulation to produce catecholamine release in LCN. We used advanced viral techniques to map and selectively KO catecholaminergic neurotransmission to the LCN, and characterized significant cognitive deficits related to this manipulation. Finally, we show that inhibition of excitatory LCN neurons with designer receptor exclusively activated by designer drugs, designed to mimic Gi-coupled catecholamine GPCR signaling, results in facilitation of a working memory task impaired in LCN-specific TH KO mice.

The Role of Parvalbumin Interneuron GIRK Signaling in the Regulation of Affect and Cognition in Male and Female Mice

Pathological impairments in the regulation of affect (i.e., emotion) and flexible decision-making are commonly observed across numerous neuropsychiatric disorders and are thought to reflect dysfunction of cortical and subcortical circuits that arise in part from imbalances in excitation and inhibition within these structures. Disruptions in GABA transmission, in particular, that from parvalbumin-expressing interneurons (PVI), has been highlighted as a likely mechanism by which this imbalance arises, as they regulate excitation and synchronization of principle output neurons. G protein-gated inwardly rectifying potassium ion (GIRK/Kir3) channels are known to modulate excitability and output of pyramidal neurons in areas like the medial prefrontal cortex and hippocampus; however, the role GIRK plays in PVI excitability and behavior is unknown. Male and female mice lacking GIRK1 in PVI (Girk1flox/flox:PVcre) and expressing td-tomato in PVI (Girk1flox/flox:PVCre:PVtdtom) exhibited increased open arm time in the elevated plus-maze, while males showed an increase in immobile episodes during the forced swim test (FST). Loss of GIRK1 did not alter motivated behavior for an appetitive reward or impair overall performance in an operant-based attention set-shifting model of cognitive flexibility; however it did alter types of errors committed during the visual cue test. Unexpectedly, baseline sex differences were also identified in these tasks, with females exhibiting overall poorer performance compared to males and distinct types of errors, highlighting potential differences in task-related problem-solving. Interestingly, reductions in PVI GIRK signaling did not correspond to changes in membrane excitability but did increase action potential (AP) firing at higher current injections in PVI of males, but not females. This is the first investigation on the role that PVI GIRK-signaling has on membrane excitability, AP firing, and their role on affect and cognition together increasing the understanding of PVI cellular mechanisms and function.

Enhanced synaptic properties of the prefrontal cortex and hippocampus after learning a spatial working memory task in adult male mice

Working memory (WM) is the ability to hold on-line and manipulate information. The prefrontal cortex (PFC) is a key brain region involved in WM, while the hippocampus is also involved, particularly, in spatial WM. Although several studies have investigated the neuronal substrates of WM in trained animals, the effects and the mechanisms underlying learning WM tasks have not been explored. In our study, we investigated the effects of learning WM tasks in mice on the function of PFC and hippocampus, by training mice in the delayed alternation task for 9 days (adaptive group). This group was compared to naïve mice (which stayed in their homecage) and mice trained in the alternation procedure only (non-adaptive). Following training, a cohort of mice (Experiment A) was tested in the left-right discrimination task and the reversal learning task, while another cohort (Experiment B) was tested in the attention set-shifting task (AST). The adaptive group performed significantly better in the reversal learning task (Experiment A) and AST (Experiment B), compared to non-adaptive and naïve groups. At the end of the behavioral experiments in Experiment A, field excitatory post-synaptic potential (fEPSP) recordings were performed in PFC and hippocampal brain slices. The adaptive group had enhanced the long-term potentiation (LTP) in the PFC, compared to the other groups. In the hippocampus, both the adaptive and the non-adaptive groups exhibited increased fEPSP compared to the naïve group, but no differences in LTP. In Experiment B, the dendritic spine density was measured, which, in the PFC, was found increased in the adaptive group, compared to the non-adaptive and naïve groups. In the hippocampus, there was an increase in mature dendritic spine density in the adaptive group, compared to the other two groups. Our results indicate a role for LTP and dendritic spine density in learning WM tasks.

Hypothalamic-Extended Amygdala Circuit Regulates Temporal Discounting

Choice behavior is characterized by temporal discounting, i.e., preference for immediate rewards given a choice between immediate and delayed rewards. Agouti-related peptide (AgRP)-expressing neurons located in the arcuate nucleus of the hypothalamus (ARC) regulate food intake and energy homeostasis, yet whether AgRP neurons influence choice behavior and temporal discounting is unknown. Here, we demonstrate that motivational state potently modulates temporal discounting. Hungry mice (both male and female) strongly preferred immediate food rewards, yet sated mice were largely indifferent to reward delay. More importantly, selective optogenetic activation of AgRP-expressing neurons or their axon terminals within the posterior bed nucleus of stria terminalis (BNST) produced temporal discounting in sated mice. Furthermore, activation of neuropeptide Y (NPY) type 1 receptors (Y1Rs) within the BNST is sufficient to produce temporal discounting. These results demonstrate a profound influence of hypothalamic signaling on temporal discounting for food rewards and reveal a novel circuit that determine choice behavior.SIGNIFICANCE STATEMENT Temporal discounting is a universal phenomenon found in many species, yet the underlying neurocircuit mechanisms are still poorly understood. Our results revealed a novel neural pathway from agouti-related peptide (AgRP) neurons in the hypothalamus to the bed nucleus of stria terminalis (BNST) that regulates temporal discounting in decision-making.

Nicotine Enhances Object Recognition Memory via Stimulating α4β2 and α7 Nicotinic Acetylcholine Receptors in the Medial Prefrontal Cortex of Mice

Nicotine has been known to enhance recognition memory in various species. However, the brain region where nicotine acts and exerts its effect remains unclear. Since the medial prefrontal cortex (mPFC) is associated with memory, we examined the role of the mPFC in nicotine-induced enhancement of recognition memory using the novel object recognition test in male C57BL/6J mice. Systemic nicotine administration 10 min before training session significantly enhanced object recognition memory in test session that was performed 24 h after the training. Intra-mPFC infusion of mecamylamine, a non-selective nicotinic acetylcholine receptor (nAChR) antagonist, 5 min before nicotine administration blocked the effect of nicotine. Additionally, intra-mPFC infusion of dihydro-β-erythroidine, a selective α4β2 nAChR antagonist, or methyllycaconitine, a selective α7 nAChR antagonist, significantly suppressed the nicotine-induced object recognition memory enhancement. Finally, intra-mPFC infusion of nicotine 1 min before the training session augmented object recognition memory in a dose-dependent manner. These findings suggest that mPFC α4β2 and α7 nAChRs mediate the nicotine-induced object recognition memory enhancement.

Prefrontal contributions to action control in rodents

The rodent medial prefrontal cortex (mPFC) is typically considered to be involved in cognitive aspects of action control, e.g., decision making, rule learning and application, working memory and generally guiding adaptive behavior (Euston, Gruber, & McNaughton, 2012). These cognitive aspects often occur on relatively slow time scales, i.e., in the order of several trials within a block structure (Murakami, Shteingart, Loewenstein, & Mainen, 2017). In this way, the mPFC is able to set up a representational memory (Goldman-Rakic, 1987). On the other hand, the mPFC can also impact action control more directly (i.e., more on the motoric and less cognitive side). This impact on motor control manifests on faster time scales, i.e., on a single trial level (Hardung et al., 2017). While the more cognitive aspects have been reviewed previously as well as in other subchapters of this book, we explicitly focus on the latter aspect in this chapter, particularly on movement inhibition. We discuss models of prefrontal motor interactions, the impact of the behavioral paradigm, evidences for mPFC involvement in action control, and the anatomical connections between mPFC and motor cortex.

Purkinje Cell-Specific Knockout of Tyrosine Hydroxylase Impairs Cognitive Behaviors

Tyrosine hydroxylase (Th) expression has previously been reported in Purkinje cells (PCs) of rodents and humans, but its role in the regulation of behavior is not understood. Catecholamines are well known for facilitating cognitive behaviors and are expressed in many regions of the brain. Here, we investigated a possible role in cognitive behaviors of PC catecholamines, by mapping and testing functional roles of Th positive PCs in mice. Comprehensive mapping analyses revealed a distinct population of Th expressing PCs primarily in the posterior and lateral regions of the cerebellum (comprising about 18% of all PCs). To identify the role of PC catecholamines, we selectively knocked out Th in PCs using a conditional knockout approach, by crossing a Purkinje cell-selective Cre recombinase line, Pcp2-Cre, with a floxed tyrosine hydroxylase mouse line (Thlox/lox) to produce Pcp2-Cre;Thlox/lox mice. This manipulation resulted in approximately 50% reduction of Th protein expression in the cerebellar cortex and lateral cerebellar nucleus, but no reduction of Th in the locus coeruleus, which is known to innervate the cerebellum in mice. Pcp2-Cre;Thlox/lox mice showed impairments in behavioral flexibility, response inhibition, social recognition memory, and associative fear learning relative to littermate controls, but no deficits in gross motor, sensory, instrumental learning, or sensorimotor gating functions. Catecholamines derived from specific populations of PCs appear to support cognitive functions, and their spatial distribution in the cerebellum suggests that they may underlie patterns of activation seen in human studies on the cerebellar role in cognitive function.

Prefrontal - subthalamic pathway supports action selection in a spatial working memory task

Subthalamic nucleus (STN) is the main source of feed-forward excitation in the basal ganglia and a main target of therapeutic deep brain stimulation in movement disorders. Alleviation of motor symptoms during STN stimulation can be accompanied by deterioration of abilities to quickly choose between conflicting alternatives. Cortical afferents to the subthalamic region (ST), comprising STN and zona incerta (ZI), include projections from the medial prefrontal cortex (mPFC), yet little is known about prefrontal-subthalamic coordination and its relevance for decision-making. Here we combined electrophysiological recordings with optogenetic manipulations of projections from mPFC to ST in mice as they performed a spatial working memory task (T-maze) or explored an elevated plus maze (anxiety test). We found that gamma oscillations (30–70 Hz) are coordinated between mPFC and ST at theta (5–10 Hz) and, less efficiently, at sub-theta (2–5 Hz) frequencies. An optogenetic detuning of the theta/gamma cross-frequency coupling between the regions into sub-theta range impaired performance in the T-maze, yet did not affect anxiety-related behaviors in the elevated plus maze. Both detuning and inhibition of the mPFC-ST pathway led to repeated incorrect choices in the T-maze. These effects were not associated with changes of anxiety and motor activity measures. Our findings suggest that action selection in a cognitively demanding task crucially involves theta rhythmic coordination of gamma oscillatory signaling in the prefrontal-subthalamic pathway.

Mediodorsal Thalamus Contributes to the Timing of Instrumental Actions

The perception of time is critical to adaptive behavior. While prefrontal cortex and basal ganglia have been implicated in interval timing in the seconds to minutes range, little is known about the role of the mediodorsal thalamus (MD), which is a key component of the limbic cortico-basal ganglia-thalamocortical loop. In this study, we tested the role of the MD in timing, using an operant temporal production task in male mice. In this task, that the expected timing of available rewards is indicated by lever pressing. Inactivation of the MD with muscimol produced rightward shifts in peak pressing on probe trials as well as increases in peak spread, thus significantly altering both temporal accuracy and precision. Optogenetic inhibition of glutamatergic projection neurons in the MD also resulted in similar changes in timing. The observed effects were found to be independent of significant changes in movement. Our findings suggest that the MD is a critical component of the neural circuit for interval timing, without playing a direct role in regulating ongoing performance.SIGNIFICANCE STATEMENT The mediodorsal nucleus (MD) of the thalamus is strongly connected with the prefrontal cortex and basal ganglia, areas which have been implicated in interval timing. Previous work has shown that the MD contributes to working memory and learning of action-outcome contingencies, but its role in behavioral timing is poorly understood. Using an operant temporal production task, we showed that inactivation of the MD significantly impaired timing behavior.

Medial prefrontal lesions impair performance in an operant delayed nonmatch to sample working memory task

Cognitive functions, such as working memory, are disrupted in most psychiatric disorders. Many of these processes are believed to depend on the medial prefrontal cortex (mPFC). Traditionally, maze-based behavioral tasks, which have a strong exploratory component, have been used to study the role of the mPFC in working memory in mice. In maze tasks, mice navigate through the environment and require a significant amount of time to complete each trial, thereby limiting the number of trials that can be run per day. Here, we show that an operant-based delayed nonmatch to sample (DNMS) working memory task, with shorter trial lengths and a smaller exploratory component, is also mPFC-dependent. We created excitotoxic lesions in the mPFC of mice and found impairments in both the acquisition of the task, with no delay, and in the performance with delays introduced. Importantly, we saw no differences in trial length, reward collection, or lever-press latencies, indicating that the difference in performance was not due to a change in motivation or mobility. Using this operant DNMS task will facilitate the analysis of working memory and improve our understanding of the physiology and circuit mechanisms underlying this cognitive process. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Selective optogenetic inhibition of medial prefrontal glutamatergic neurons reverses working memory deficits induced by neuropathic pain

Stability of local medial prefrontal cortex (mPFC) network activity is believed to be critical for sustaining cognitive processes such as working memory (WM) and decision making. Dysfunction of the mPFC has been identified as a leading cause to WM deficits in several chronic pain conditions; however, the underlying mechanisms remain largely undetermined. Here, to address this issue, we implanted multichannel arrays of electrodes in the prelimbic region of the mPFC and recorded the neuronal activity during a food-reinforced delayed nonmatch to sample (DNMS) task of spatial WM. In addition, we used an optogenetic technique to selectively suppress the activity of excitatory pyramidal neurons that are considered the neuronal substrate for memory retention during the delay period of the behavioral task. Within-subject behavioral performance and pattern of neuronal activity were assessed after the onset of persistent pain using the spared nerve injury model of peripheral neuropathy. Our results show that the nerve lesion caused a disruption in WM and prelimbic spike activity and that this disruption was reversed by the selective inhibition of prelimbic glutamatergic pyramidal neurons during the delay period of the WM task. In spared nerve injury animals, photoinhibition of excitatory neurons improved the performance level and restored neural activity to a similar profile observed in the control animals. In addition, we found that selective inhibition of excitatory neurons does not produce antinociceptive effects. Together, our findings suggest that disruption of balance in local prelimbic networks may be crucial for the neurological and cognitive deficits observed during painful syndromes.

N-Acetyl Cysteine Supplement Minimize Tau Expression and Neuronal Loss in Animal Model of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the accumulation of neurofibrillary tangles (NFT), deposition of beta amyloid plaques, and consequent neuronal loss in the brain tissue. Oxidative stress to the neurons is often attributed to AD, but its link to NFT and β-amyloid protein (BAP) still remains unclear. In an animal model of AD, we boosted the oxidative defense by N-Acetyl cysteine (NAC), a precursor of glutathione, a powerful antioxidant and free radical scavenger, to understand the link between oxidative stress and NFT. In mimicking AD, intracerebroventricular (ICV) colchicine, a microtubule disrupting agent also known to cause oxidative stress was administered to the rats. The animal groups consisted of an age-matched control, sham operated, AD, and NAC treated in AD models of rats. Cognitive function was evaluated in a passive avoidance test; neuronal degeneration was quantified using Nissl staining. NFT in the form of abnormal tau expression in different regions of the brain were evaluated through immunohistochemistry using rabbit anti-tau antibody. ICV has resulted in significant cognitive and neuronal loss in medial prefrontal cortex (MFC) and all the regions of the hippocampus. It has also resulted in increased accumulation of intraneuronal tau in the hippocampus and MFC. NAC treatment in AD model rats has reversed the cognitive loss and neuronal degeneration. The intraneuronal tau expression also minimized with NAC treatment in AD model rats. Thus, our findings suggest that an antioxidant supplement during the progression of AD is likely to prevent neuronal degeneration by minimizing the neurofibrillary degeneration in the form of tau accumulation.

Postnatal TrkB ablation in corticolimbic interneurons induces social dominance in male mice

The tight balance between synaptic excitation and inhibition (E/I) within neocortical circuits in the mammalian brain is important for complex behavior. Many loss-of-function studies have demonstrated that brain-derived neurotrophic factor (BDNF) and its cognate receptor tropomyosin receptor kinase B (TrkB) are essential for the development of inhibitory GABAergic neurons. However, behavioral consequences of impaired BDNF/TrkB signaling in GABAergic neurons remain unclear, largely due to confounding motor function deficits observed in previous animal models. In this study, we generated conditional knockout mice (TrkB cKO) in which TrkB was ablated from a majority of corticolimbic GABAergic interneurons postnatally. These mice showed intact motor coordination and movement, but exhibited enhanced dominance over other mice in a group-housed setting. In addition, immature fast-spiking GABAergic neurons of TrkB cKO mice resulted in an E/I imbalance in layer 5 microcircuits within the medial prefrontal cortex (mPFC), a key region regulating social dominance. Restoring the E/I imbalance via optogenetic modulation in the mPFC of TrkB cKO mice normalized their social dominance behavior. Taken together, our results provide strong evidence for a role of BDNF/TrkB signaling in inhibitory synaptic modulation and social dominance behavior in mice.

Dopamine D1 Receptor-Positive Neurons in the Lateral Nucleus of the Cerebellum Contribute to Cognitive Behavior

BACKGROUND

Studies in humans and nonhuman primates have identified a region of the dentate nucleus of the cerebellum, or the lateral cerebellar nucleus (LCN) in rodents, activated during performance of cognitive tasks involving complex spatial and sequential planning. Whether such a subdivision exists in rodents is not known. Dopamine and its receptors, which are implicated in cognitive function, are present in the cerebellar nuclei, but their function is unknown.

METHODS

Using viral and genetic strategies in mice, we examined cellular phenotypes of dopamine D₁ receptor-positive (D1R+) cells in the LCN with whole-cell patch clamp recordings, messenger RNA profiling, and immunohistochemistry to examine D1R expression in mouse LCN and human dentate nucleus of the cerebellum. We used chemogenetics to inhibit D1R+ neurons and examined behaviors including spatial navigation, social recognition memory, prepulse inhibition of the acoustic startle reflex, response inhibition, and working memory to test the necessity of these neurons in these behaviors.

RESULTS

We identified a population of D1R+ neurons that are localized to an anatomically distinct region of the LCN. We also observed D1R+ neurons in human dentate nucleus of the cerebellum, which suggests an evolutionarily conserved population of dopamine-receptive neurons in this region. The genetic, electrophysiological, and anatomical profile of mouse D1R neurons is consistent with a heterogeneous population of gamma-aminobutyric acidergic, and to a lesser extent glutamatergic, cell types. Selective inhibition of D1R+ LCN neurons impairs spatial navigation memory, response inhibition, working memory, and prepulse inhibition of the acoustic startle reflex.

CONCLUSIONS

Collectively, these data demonstrate a functional link between genetically distinct neurons in the LCN and cognitive behaviors.

PV Interneurons: Critical Regulators of E/I Balance for Prefrontal Cortex-Dependent Behavior and Psychiatric Disorders

Elucidating the prefrontal cortical microcircuit has been challenging, given its role in multiple complex behaviors, including working memory, cognitive flexibility, attention, social interaction and emotional regulation. Additionally, previous methodological limitations made it difficult to parse out the contribution of certain neuronal subpopulations in refining cortical representations. However, growing evidence supports a fundamental role of fast-spiking parvalbumin (PV) GABAergic interneurons in regulating pyramidal neuron activity to drive appropriate behavioral responses. Further, their function is heavily diminished in the prefrontal cortex (PFC) in numerous psychiatric diseases, including schizophrenia and autism. Previous research has demonstrated the importance of the optimal balance of excitation and inhibition (E/I) in cortical circuits in maintaining the efficiency of cortical information processing. Although we are still unraveling the mechanisms of information representation in the PFC, the E/I balance seems to be crucial, as pharmacological, chemogenetic and optogenetic approaches for disrupting E/I balance induce impairments in a range of PFC-dependent behaviors. In this review, we will explore two key hypotheses. First, PV interneurons are powerful regulators of E/I balance in the PFC, and help optimize the representation and processing of supramodal information in PFC. Second, diminishing the function of PV interneurons is sufficient to generate an elaborate symptom sequelae corresponding to those observed in a range of psychiatric diseases. Then, using this framework, we will speculate on whether this circuitry could represent a platform for the development of therapeutic interventions in disorders of PFC function.

Prefrontal cortex NG2 glia undergo a developmental switch in their responsiveness to exercise

Aerobic exercise is known to influence brain function, e.g., enhancing executive function in both children and adults, with many of these influences being attributed to alterations in neurogenesis and neuronal function. Yet oligodendroglia in adult brains have also been reported to be highly responsive to exercise, including in the prefrontal cortex (PFC), a late myelinating region implicated in working memory. However, whether exercise affects oligodendroglia or myelination in juveniles, either in the PFC or in other brain regions, remains unknown. To address this, both juvenile and young adult mice were provided free access to running wheels for four weeks followed by an analysis of oligodendrocyte development and myelination in the PFC and the corpus callosum, a major white matter tract. Working memory and PFC NG2+ cell development were both affected by exercise in juvenile mice, yet surprisingly these exercise-mediated effects were distinct in juveniles and young adults. In the PFC, NG2+ cell proliferation was increased in exercising juveniles, but not young adults, whereas newly-born oligodendrocyte production was increased in exercising young adults, but not juveniles. Although no overall changes in myelin genes were found, elevated levels of Monocarboxylate Transporter 1, a glial lactate transporter important during active myelination, were found in the PFC of exercising young adults. Overall our findings reveal that long-term exercise modulates PFC glial development and does so differentially in juvenile and young adult mice, providing insight into the cellular responses that may underlie cognitive benefits to teenagers and young adults in response to exercise. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 78: 687-700, 2018.

Environmental Enrichment Expedites Acquisition and Improves Flexibility on a Temporal Sequencing Task in Mice

Environmental enrichment (EE) via increased opportunities for voluntary exercise, sensory stimulation and social interaction, can enhance the function of and behaviours regulated by cognitive circuits. Little is known, however, as to how this intervention affects performance on complex tasks that engage multiple, definable learning and memory systems. Accordingly, we utilised the Olfactory Temporal Order Discrimination (OTOD) task which requires animals to recall and report sequence information about a series of recently encountered olfactory stimuli. This approach allowed us to compare animals raised in either enriched or standard laboratory housing conditions on a number of measures, including the acquisition of a complex discrimination task, temporal sequence recall accuracy (i.e., the ability to accurately recall a sequences of events) and acuity (i.e., the ability to resolve past events that occurred in close temporal proximity), as well as cognitive flexibility tested in the style of a rule reversal and an Intra-Dimensional Shift (IDS). We found that enrichment accelerated the acquisition of the temporal order discrimination task, although neither accuracy nor acuity was affected at asymptotic performance levels. Further, while a subtle enhancement of overall performance was detected for both rule reversal and IDS versions of the task, accelerated performance recovery could only be attributed to the shift-like contingency change. These findings suggest that EE can affect specific elements of complex, multi-faceted cognitive processes.

Do TRPC channels support working memory? Comparing modulations of TRPC channels and working memory through G-protein coupled receptors and neuromodulators

Working memory is a crucial ability we use in daily life. However, the cellular mechanisms supporting working memory still remain largely unclear. A key component of working memory is persistent neural firing which is believed to serve short-term (hundreds of milliseconds up to tens of seconds) maintenance of necessary information. In this review, we will focus on the role of transient receptor potential canonical (TRPC) channels as a mechanism underlying persistent firing. Many years of in vitro work have been suggesting a crucial role of TRPC channels in working memory and temporal association tasks. If TRPC channels are indeed a central mechanism for working memory, manipulations which impair or facilitate working memory should have a similar effect on TRPC channel modulation. However, modulations of working memory and TRPC channels were never systematically compared, and it remains unanswered whether TRPC channels indeed contribute to working memory in vivo or not. In this article, we review the effects of G-protein coupled receptors (GPCR) and neuromodulators, including acetylcholine, noradrenalin, serotonin and dopamine, on working memory and TRPC channels. Based on comparisons, we argue that GPCR and downstream signaling pathways that activate TRPC, generally support working memory, while those that suppress TRPC channels impair it. However, depending on the channel types, areas, and systems tested, this is not the case in all studies. Further work to clarify involvement of specific TRPC channels in working memory tasks and how they are affected by neuromodulators is still necessary in the future.

Inactivation of nucleus reuniens impairs spatial working memory and behavioral flexibility in the rat

The hippocampal formation (HF) and medial prefrontal cortex (mPFC) play critical roles in spatial working memory (SWM). The nucleus reuniens (RE) of the ventral midline thalamus is an important anatomical link between the HF and mPFC, and as such is crucially involved in SWM functions that recruit both structures. Little is known, however, regarding the role of RE in other behaviors mediated by this circuit. In the present study, we examined the role of RE in spatial working memory and executive functioning following reversible inactivation of RE with either muscimol or procaine. Rats were implanted with an indwelling cannula targeting RE and trained in a delayed nonmatch to sample spatial alternation T-maze task. For the task, sample and choice runs were separated by moderate or long delays (30, 60, and 120 s). Following asymptotic performance, rats were tested following infusions of drug or vehicle. Muscimol infused into RE impaired SWM at all delays, whereby procaine only impaired performance at the longest delays. Furthermore, RE inactivation with muscimol produced a failure in win-shift strategy as well as severe spatial perseveration, whereby rats persistently made re-entries into incorrect arms during correction trials, despite the absence of reward. This demonstrated marked changes in behavioral flexibility and response strategy. These results strengthen the role of nucleus reuniens as a pivotal link between hippocampus and prefrontal cortex in cognitive and executive functions and suggest that nucleus reuniens may be a potential target in the treatment of CNS disorders such as schizophrenia, attention deficit hyperactivity disorder, addiction, and obsessive-compulsive disorder, whose symptoms are defined by hippocampal-prefrontal dysfunctions.

Assessment of the acquisition of executive function during the transition from adolescence to adulthood in male and female mice

Executive functions (EF) reached full maturity during the transition from adolescence to adulthood. Human studies provide important information about adolescent developmental trajectories; however, little remains known about the neural circuits underlying the acquisition of mature EF. Ethical and technical considerations with human subjects limit opportunities to design experimental studies that allows for an in-depth understanding of developmental changes in neural circuits that regulate cognitive maturation. Preclinical models can offer solutions to this problem. Unfortunately, current rodent models of adolescent development have inherent flaws that limit their translational value. For instance, females are often omitted from studies, preventing the assessment of potential sex-specific developmental trajectories. Furthermore, it remains unclear whether cognitive developmental changes in rodents are similar to those observed in humans. Here, we tested adolescent and adult male and female mice in a neurocognitive battery of assays. Based on this approach, we assessed mice performances within distinct subdomains of EF, and observed similarities with human developmental trajectories. Furthermore, the sex-specific cognitive changes we observed were paralleled by molecular and neural activity changes demonstrating that our approach can be used in future research to assess the contribution of precise neural circuits to adolescent cognitive maturation.

Functional perturbation of forebrain principal neurons reveals differential effects in novel and well-learned tasks

Neural circuits in mammalian brains consist of large numbers of different cell types having different functional properties. To better understand the separate roles of individual neuron types in specific aspects of spatial learning and memory, we perturbed the function of principal neurons in vivo during maze performance or in hippocampal slices during recording of evoked excitatory synaptic potentials. Transgenic mice expressing the Drosophila allatostatin receptor (AlstR) in cortical and hippocampal pyramidal cells were tested on an elevated plus maze, in a Y-maze, and in the Morris water maze. Relative to a control cohort, AlstR-positive mice treated with allatostatin exhibited no difference in open arm dwell time on the elevated plus maze or total number of arm entries in a Y-maze, but displayed reduced spontaneous alternation. When animals received massed or spaced training trials in the Morris water maze, and the peptide was delivered prior to an immediate probe, no effects on performance were observed. When the peptide was delivered during a probe trial performed 24h after seven days of spaced training, allatostatin delivery to AlstR positive mice enhanced direct navigation to the escape platform. Combined, these results suggest that cortical and hippocampal pyramidal neurons are required during spatial decision-making in a novel environment and compete with other neural systems after extended training in a long-term reference memory task. In hippocampal slices collected from AlstR positive animals, allatostatin delivery produced frequency dependent alterations in the Schaffer collateral fiber volley (attenuated accommodation at 100Hz) and excitatory postsynaptic potential (attenuated facilitation at 5Hz). Combined, the neural and behavioral discoveries support the involvement of short-term plasticity of Schaffer collateral axons and synapses during exploration of a novel environment and during initial orientation to a goal in a well-learned setting.

Mice heterozygous for an inactivated allele of the schizophrenia associated Brd1 gene display selective cognitive deficits with translational relevance to schizophrenia

Schizophrenia is a debilitating brain disorder characterized by disturbances of emotion, perception and cognition. Cognitive impairments predict functional outcome in schizophrenia and are detectable even in the prodromal stage of the disorder. However, our understanding of the underlying neurobiology is limited and procognitive treatments remain elusive. We recently demonstrated that mice heterozygous for an inactivated allele of the schizophrenia-associated Brd1 gene (Brd1^+/- mice) display behaviors reminiscent of schizophrenia, including impaired social cognition and long-term memory. Here, we further characterize performance of these mice by following the preclinical guidelines recommended by the 'Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS)' and 'Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS)' initiatives to maximize translational value. Brd1^+/- mice exhibit relational encoding deficits, compromised working and long term memory, as well as impaired executive cognitive functioning with cognitive behaviors relying on medial prefrontal cortex being particularly affected. Akin to patients with schizophrenia, the cognitive deficits displayed by Brd1^+/- mice are not global, but selective. Our results underline the value of Brd1^+/- mice as a promising tool for studying the neurobiology of cognitive deficits in schizophrenia.

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.

Quinolinic acid injection in mouse medial prefrontal cortex affects reversal learning abilities, cortical connectivity and hippocampal synaptic plasticity

Intracerebral injection of the excitotoxic, endogenous tryptophan metabolite, quinolinic acid (QA), constitutes a chemical model of neurodegenerative brain disease. Complementary techniques were combined to examine the consequences of QA injection into medial prefrontal cortex (mPFC) of C57BL6 mice. In accordance with the NMDAR-mediated synapto- and neurotoxic action of QA, we found an initial increase in excitability and an augmentation of hippocampal long-term potentiation, converting within two weeks into a reduction and impairment, respectively, of these processes. QA-induced mPFC excitotoxicity impaired behavioral flexibility in a reversal variant of the hidden-platform Morris water maze (MWM), whereas regular, extended MWM training was unaffected. QA-induced mPFC damage specifically affected the spatial-cognitive strategies that mice use to locate the platform during reversal learning. These behavioral and cognitive defects coincided with changes in cortical functional connectivity (FC) and hippocampal neuroplasticity. FC between various cortical regions was assessed by resting-state fMRI (rsfMRI) methodology, and mice that had received QA injection into mPFC showed increased FC between various cortical regions. mPFC and hippocampus (HC) are anatomically as well as functionally linked as part of a cortical network that controls higher-order cognitive functions. Together, these observations demonstrate the central functional importance of rodent mPFC as well as the validity of QA-induced mPFC damage as a preclinical rodent model of the early stages of neurodegeneration.

Distinct Roles of Parvalbumin- and Somatostatin-Expressing Interneurons in Working Memory

Inhibitory interneurons are thought to play crucial roles in diverse brain functions. However, roles of different inhibitory interneuron subtypes in working memory remain unclear. We found distinct activity patterns and stimulation effects of two major interneuron subtypes, parvalbumin (PV)- and somatostatin (SOM)-expressing interneurons, in the medial prefrontal cortex of mice performing a spatial working memory task. PV interneurons showed weak target-dependent delay-period activity and were strongly inhibited by reward. By contrast, SOM interneurons showed strong target-dependent delay-period activity, and only a subtype of them was inhibited by reward. Furthermore, optogenetic stimulation of PV and SOM interneurons preferentially suppressed discharges of putative pyramidal cells and interneurons, respectively. These results indicate different contributions of PV and SOM interneurons to prefrontal cortical circuit dynamics underlying working memory.

Maternal immune activation leads to selective functional deficits in offspring parvalbumin interneurons

Abnormalities in prefrontal gamma aminobutyric acid (GABA)ergic transmission, particularly in fast-spiking interneurons that express parvalbumin (PV), are hypothesized to contribute to the pathophysiology of multiple psychiatric disorders, including schizophrenia, bipolar disorder, anxiety disorders and depression. While primarily histological abnormalities have been observed in patients and in animal models of psychiatric disease, evidence for abnormalities in functional neurotransmission at the level of specific interneuron populations has been lacking in animal models and is difficult to establish in human patients. Using an animal model of a psychiatric disease risk factor, prenatal maternal immune activation (MIA), we found reduced functional GABAergic transmission in the medial prefrontal cortex (mPFC) of adult MIA offspring. Decreased transmission was selective for interneurons expressing PV, resulted from a decrease in release probability and was not observed in calretinin-expressing neurons. This deficit in PV function in MIA offspring was associated with increased anxiety-like behavior and impairments in attentional set shifting, but did not affect working memory. Furthermore, cell-type specific optogenetic inhibition of mPFC PV interneurons was sufficient to impair attentional set shifting and enhance anxiety levels. Finally, we found that in vivo mPFC gamma oscillations, which are supported by PV interneuron function, were linearly correlated with the degree of anxiety displayed in adult mice, and that this correlation was disrupted in MIA offspring. These results demonstrate a selective functional vulnerability of PV interneurons to MIA, leading to affective and cognitive symptoms that have high relevance for schizophrenia and other psychiatric disorders.

A GABAergic nigrotectal pathway for coordination of drinking behavior

The contribution of basal ganglia outputs to consummatory behavior remains poorly understood. We recorded from the substantia nigra pars reticulata (SNR), the major basal ganglia output nucleus, during self-initiated drinking. The firing rates of many lateral SNR neurons were time-locked to individual licks. These neurons send GABAergic projections to the deep layers of the orofacial region of the lateral tectum (superior colliculus, SC). Many tectal neurons are also time-locked to licking, but their activity is usually antiphase to that of SNR neurons, suggesting inhibitory nigrotectal projections. We used optogenetics to selectively activate the GABAergic nigrotectal afferents in the deep layers of the SC. Photo-stimulation of the nigrotectal projections transiently inhibited the activity of the lick-related tectal neurons, disrupted their licking-related oscillatory pattern, and suppressed self-initiated drinking. These results demonstrate that GABAergic nigrotectal projections play a crucial role in coordinating drinking behavior.

Striatonigral control of movement velocity in mice

The basal ganglia have long been implicated in action initiation. Using three-dimensional motion capture, we quantified the effects of optogenetic stimulation of the striatonigral (direct) pathway on movement kinematics. We generated transgenic mice with channelrhodopsin-2 expression in striatal neurons that express the D1-like dopamine receptor. With optic fibres placed in the sensorimotor striatum, an area known to contain movement velocity-related single units, photo-stimulation reliably produced movements that could be precisely quantified with our motion capture programme. A single light pulse was sufficient to elicit movements with short latencies (< 30 ms). Increasing stimulation frequency increased movement speed, with a highly linear relationship. These findings support the hypothesis that the sensorimotor striatum is part of a velocity controller that controls rate of change in body configurations.

Spine pruning drives antipsychotic-sensitive locomotion via circuit control of striatal dopamine

Psychiatric and neurodevelopmental disorders may arise from anomalies in long-range neuronal connectivity downstream of pathologies in dendritic spines. However, the mechanisms that may link spine pathology to circuit abnormalities relevant to atypical behavior remain unknown. Using a mouse model to conditionally disrupt a critical regulator of the dendritic spine cytoskeleton, the actin-related protein 2/3 complex (Arp2/3), we report here a molecular mechanism that unexpectedly reveals the inter-relationship of progressive spine pruning, elevated frontal cortical excitation of pyramidal neurons and striatal hyperdopaminergia in a cortical-to-midbrain circuit abnormality. The main symptomatic manifestations of this circuit abnormality are psychomotor agitation and stereotypical behaviors, which are relieved by antipsychotics. Moreover, this antipsychotic-responsive locomotion can be mimicked in wild-type mice by optogenetic activation of this circuit. Collectively these results reveal molecular and neural-circuit mechanisms, illustrating how diverse pathologies may converge to drive behaviors relevant to psychiatric disorders.

Spotlight on movement disorders: What optogenetics has to offer

Elucidating the neuronal mechanisms underlying movement disorders is a major challenge because of the intricacy of the relevant neural circuits, which are characterized by diverse cell types and complex connectivity. A major limitation of traditional techniques, such as electrical stimulation or lesions, is that individual elements of a neural circuit cannot be selectively manipulated. Moreover, available treatments are largely based on trial and error rather than a detailed understanding of the circuit mechanisms. Gaps in our knowledge of the circuit mechanisms for movement disorders, as well as mechanisms underlying known treatments such as deep brain stimulation, make it difficult to design new and improved treatment options. In this perspective, we discuss how optogenetics, which allows researchers to use light to manipulate neuronal activity, can contribute to the understanding and treatment of movement disorders. We outline the advantages and limitations of optogenetics and discuss examples of studies that have used this tool to clarify the role of the basal ganglia circuitry in movement.

A wirelessly controlled implantable LED system for deep brain optogenetic stimulation

In recent years optogenetics has rapidly become an essential technique in neuroscience. Its temporal and spatial specificity, combined with efficacy in manipulating neuronal activity, are especially useful in studying the behavior of awake behaving animals. Conventional optogenetics, however, requires the use of lasers and optic fibers, which can place considerable restrictions on behavior. Here we combined a wirelessly controlled interface and small implantable light-emitting diode (LED) that allows flexible and precise placement of light source to illuminate any brain area. We tested this wireless LED system in vivo, in transgenic mice expressing channelrhodopsin-2 in striatonigral neurons expressing D₁-like dopamine receptors. In all mice tested, we were able to elicit movements reliably. The frequency of twitches induced by high power stimulation is proportional to the frequency of stimulation. At lower power, contraversive turning was observed. Moreover, the implanted LED remains effective over 50 days after surgery, demonstrating the long-term stability of the light source. Our results show that the wireless LED system can be used to manipulate neural activity chronically in behaving mice without impeding natural movements.

Optogenetic dissection of medial prefrontal cortex circuitry

The medial prefrontal cortex (mPFC) is critically involved in numerous cognitive functions, including attention, inhibitory control, habit formation, working memory and long-term memory. Moreover, through its dense interconnectivity with subcortical regions (e.g., thalamus, striatum, amygdala and hippocampus), the mPFC is thought to exert top-down executive control over the processing of aversive and appetitive stimuli. Because the mPFC has been implicated in the processing of a wide range of cognitive and emotional stimuli, it is thought to function as a central hub in the brain circuitry mediating symptoms of psychiatric disorders. New optogenetics technology enables anatomical and functional dissection of mPFC circuitry with unprecedented spatial and temporal resolution. This provides important novel insights in the contribution of specific neuronal subpopulations and their connectivity to mPFC function in health and disease states. In this review, we present the current knowledge obtained with optogenetic methods concerning mPFC function and dysfunction and integrate this with findings from traditional intervention approaches used to investigate the mPFC circuitry in animal models of cognitive processing and psychiatric disorders.

Activation of prefrontal cortical parvalbumin interneurons facilitates extinction of reward-seeking behavior

Forming and breaking associations between emotionally salient environmental stimuli and rewarding or aversive outcomes is an essential component of learned adaptive behavior. Importantly, when cue-reward contingencies degrade, animals must exhibit behavioral flexibility to extinguish prior learned associations. Understanding the specific neural circuit mechanisms that operate during the formation and extinction of conditioned behaviors is critical because dysregulation of these neural processes is hypothesized to underlie many of the maladaptive and pathological behaviors observed in various neuropsychiatric disorders in humans. The medial prefrontal cortex (mPFC) participates in the behavioral adaptations seen in both appetitive and aversive-cue-mediated responding, but the precise cell types and circuit mechanisms sufficient for driving these complex behavioral states remain largely unspecified. Here, we recorded and manipulated the activity of parvalbumin-positive fast spiking interneurons (PV+ FSIs) in the prelimbic area (PrL) of the mPFC in mice. In vivo photostimulation of PV+ FSIs resulted in a net inhibition of PrL neurons, providing a circuit blueprint for behavioral manipulations. Photostimulation of mPFC PV+ cells did not alter anticipatory or consummatory licking behavior during reinforced training sessions. However, optical activation of these inhibitory interneurons to cues associated with reward significantly accelerated the extinction of behavior during non-reinforced test sessions. These data suggest that suppression of excitatory mPFC networks via increased activity of PV+ FSIs may enhance reward-related behavioral flexibility.

Cholinergic modulation of the medial prefrontal cortex: the role of nicotinic receptors in attention and regulation of neuronal activity

Acetylcholine (ACh) release in the medial prefrontal cortex (mPFC) is crucial for normal cognitive performance. Despite the fact that many have studied how ACh affects neuronal processing in the mPFC and thereby influences attention behavior, there is still a lot unknown about how this occurs. Here we will review the evidence that cholinergic modulation of the mPFC plays a role in attention and we will summarize the current knowledge about the role between ACh receptors (AChRs) and behavior and how ACh receptor activation changes processing in the cortical microcircuitry. Recent evidence implicates fast phasic release of ACh in cue detection and attention. This review will focus mainly on the fast ionotropic nicotinic receptors and less on the metabotropic muscarinic receptors. Finally, we will review limitations of the existing studies and address how innovative technologies might push the field forward in order to gain understanding into the relation between ACh, neuronal activity and behavior.