Prefrontal cortex in the rat: projections to subcortical autonomic, motor, and limbic centers

Serotonergic neuromodulation of synaptic plasticity

Synaptic plasticity constitutes a fundamental process in the reorganization of neural networks that underlie memory, cognition, emotional responses, and behavioral planning. At the core of this phenomenon lie Hebbian mechanisms, wherein frequent synaptic stimulation induces long-term potentiation (LTP), while less activation leads to long-term depression (LTD). The synaptic reorganization of neuronal networks is regulated by serotonin (5-HT), a neuromodulator capable of modify synaptic plasticity to appropriately respond to mental and behavioral states, such as alertness, attention, concentration, motivation, and mood. Lately, understanding the serotonergic Neuromodulation of synaptic plasticity has become imperative for unraveling its impact on cognitive, emotional, and behavioral functions. Through a comparative analysis across three main forebrain structures-the hippocampus, amygdala, and prefrontal cortex, this review discusses the actions of 5-HT on synaptic plasticity, offering insights into its role as a neuromodulator involved in emotional and cognitive functions. By distinguishing between plastic and metaplastic effects, we provide a comprehensive overview about the mechanisms of 5-HT neuromodulation of synaptic plasticity and associated functions across different brain regions.

Sensing, feeling and regulating: investigating the association of focal brain damage with voluntary respiratory and motor control

Breathing is a complex, vital function that can be modulated to influence physical and mental well-being. However, the role of cortical and subcortical brain regions in voluntary control of human respiration is underexplored. Here we investigated the influence of damage to human frontal, temporal or limbic regions on the sensation and regulation of breathing patterns. Participants performed a respiratory regulation task across regular and irregular frequencies ranging from 6 to 60 breaths per minute (bpm), with a counterbalanced hand motor control task. Interoceptive and affective states induced by each condition were assessed via questionnaire, and autonomic signals were indexed via skin conductance. Participants with focal lesions to the bilateral frontal lobe, right insula/basal ganglia and left medial temporal lobe showed reduced performance relative to individually matched healthy comparisons during the breathing and motor tasks. They also reported significantly higher anxiety during the 60 bpm regular and irregular breathing trials, with anxiety correlating with difficulty in rapid breathing specifically within this group. This study demonstrates that damage to frontal, temporal or limbic regions is associated with abnormal voluntary respiratory and motor regulation and tachypnoea-related anxiety, highlighting the role of the forebrain in affective and motor responses during breathing. This article is part of the theme issue 'Sensing and feeling: an integrative approach to sensory processing and emotional experience'.

Recording of single-unit activities with flexible micro-electrocorticographic array in rats for decoding of whole-body navigation

Objective.Micro-electrocorticographic (μECoG) arrays are able to record neural activities from the cortical surface, without the need to penetrate the brain parenchyma. Owing in part to small electrode sizes, previous studies have demonstrated that single-unit spikes could be detected from the cortical surface, and likely from Layer I neurons of the neocortex. Here we tested the ability to useμECoG arrays to decode, in rats, body position during open field navigation, through isolated single-unit activities.Approach. μECoG arrays were chronically implanted onto primary motor cortex (M1) of Wistar rats, and neural recording was performed in awake, behaving rats in an open-field enclosure. The signals were band-pass filtered between 300-3000 Hz. Threshold-crossing spikes were identified and sorted into distinct units based on defined criteria including waveform morphology and refractory period. Body positions were derived from video recordings. We used gradient-boosting machine to predict body position based on previous 100 ms of spike data, and correlation analyses to elucidate the relationship between position and spike patterns.Main results.Single-unit spikes could be extracted during chronic recording fromμECoG, and spatial position could be decoded from these spikes with a mean absolute error of prediction of 0.135 and 0.090 in the x- and y- dimensions (of a normalized range from 0 to 1), and Pearson's r of 0.607 and 0.571, respectively.Significance. μECoG can detect single-unit activities that likely arise from superficial neurons in the cortex and is a promising alternative to intracortical arrays, with the added benefit of scalability to cover large cortical surface with minimal incremental risks. More studies should be performed in human related to its use as brain-machine interface.

Using synchronized brain rhythms to bias memory-guided decisions

Functional interactions between the prefrontal cortex and hippocampus, as revealed by strong oscillatory synchronization in the theta (6-11 Hz) frequency range, correlate with memory-guided decision-making. However, the degree to which this form of long-range synchronization influences memory-guided choice remains unclear. We developed a brain-machine interface that initiated task trials based on the magnitude of prefrontal-hippocampal theta synchronization, then measured choice outcomes. Trials initiated based on strong prefrontal-hippocampal theta synchrony were more likely to be correct compared to control trials on both working memory-dependent and -independent tasks. Prefrontal-thalamic neural interactions increased with prefrontal-hippocampal synchrony and optogenetic activation of the ventral midline thalamus primarily entrained prefrontal theta rhythms, but dynamically modulated synchrony. Together, our results show that prefrontal-hippocampal theta synchronization leads to a higher probability of a correct choice and strengthens prefrontal-thalamic dialogue. Our findings reveal new insights into the neural circuit dynamics underlying memory-guided choices and highlight a promising technique to potentiate cognitive processes or behavior via brain-machine interfacing.

Dopamine Release Dynamics in the Nucleus Accumbens Are Modulated by the Timing of Electrical Stimulation Pulses When Applied to the Medial Forebrain Bundle and Medial Prefrontal Cortex

Electrical brain stimulation has been used in vivo and in vitro to investigate neural circuitry. Historically, stimulation parameters such as amplitude, frequency, and pulse width were varied to investigate their effects on neurotransmitter release and behavior. These experiments have traditionally employed fixed-frequency stimulation patterns, but it has previously been found that neurons are more precisely tuned to variable input. Introducing variability into the interpulse interval of stimulation pulses will inform on how dopaminergic release can be modulated by variability in pulse timing. Here, dopaminergic release in rats is monitored in the nucleus accumbens (NAc), a key dopaminergic center which plays a role in learning and motivation, by fast-scan cyclic voltammetry. Dopaminergic release in the NAc could also be modulated by stimulation region due to differences in connectivity. We targeted two regions for stimulation─the medial forebrain bundle (MFB) and the medial prefrontal cortex (mPFC)─due to their involvement in reward processing and projections to the NAc. Our goal is to investigate how variable interpulse interval stimulation patterns delivered to these regions affect the time course of dopamine release in the NAc. We found that stimulating the MFB with these variable stimulation patterns saw a highly responsive, frequency-driven dopaminergic response. In contrast, variable stimulation patterns applied to the mPFC were not as sensitive to the variable frequency changes. This work will help inform on how stimulation patterns can be tuned specifically to the stimulation region to improve the efficiency of electrical stimulation and control dopamine release.

Functionally linked amygdala and prefrontal cortical regions are innervated by both single and double projecting cholinergic neurons

Cholinergic cells have been proposed to innervate simultaneously those cortical areas that are mutually interconnected with each other. To test this hypothesis, we investigated the cholinergic innervation of functionally linked amygdala and prefrontal cortical regions. First, using tracing experiments, we determined that cholinergic cells located in distinct basal forebrain (BF) areas projected to the different nuclei of the basolateral amygdala (BLA). Specifically, cholinergic cells in the ventral pallidum/substantia innominata (VP/SI) innervated the basal nucleus (BA), while the horizontal limb of the diagonal band of Broca (HDB) projected to its basomedial nucleus (BMA). In addition, cholinergic neurons in these two BF areas gave rise to overlapping innervation in the medial prefrontal cortex (mPFC), yet their axons segregated in the dorsal and ventral regions of the PFC. Using retrograde-anterograde viral tracing, we demonstrated that a portion of mPFC-projecting cholinergic neurons also innervated the BLA, especially the BA. By injecting retrograde tracers into the mPFC and BA, we found that 28% of retrogradely labeled cholinergic cells were double labeled, which typically located in the VP/SI. In addition, we found that vesicular glutamate transporter type 3 (VGLUT3)-expressing neurons within the VP/SI were also cholinergic and projected to the mPFC and BA, implicating that a part of the cholinergic afferents may release glutamate. In contrast, we uncovered that GABA is unlikely to be a co-transmitter molecule in HDB and VP/SI cholinergic neurons in adult mice. The dual innervation strategy, i.e., the existence of cholinergic cell populations with single as well as simultaneous projections to the BLA and mPFC, provides the possibility for both synchronous and independent control of the operation in these cortical areas, a structural arrangement that may maximize computational support for functionally linked regions. The presence of VGLUT3 in a portion of cholinergic afferents suggests more complex functional effects of cholinergic system in cortical structures.

Dynamic Changes of the Infralimbic Cortex and Its Regulation of the Prelimbic Cortex in Rats with Chronic Inflammatory Pain

The prelimbic cortex (PL) is actively engaged in pain modulation. The infralimbic cortex (IL) has been reported to regulate the PL. However, how this regulation affects pain remains unclear. In the present study, we recorded temporary hyper-activity of PL pyramidal neurons responding to nociceptive stimuli, but a temporary hypo-function of the IL by in vivo electrophysiological recording in rats with peripheral inflammation. Manipulation of the PL or IL had opposite effects on thermal hyperalgesia. Furthermore, the functional connectivity and chemogenetic regulation between the subregions indicated an inhibitory influence of the IL on the PL. Activation of the pathway from the IL to the PL alleviated thermal hyperalgesia, whereas its inhibition exacerbated chronic pain. Overall, our results suggest a new mechanism underlying the role of the medial prefrontal cortex in chronic pain: hypo-function of the IL leads to hyperactivity of the PL, which regulates thermal hyperalgesia, and thus contributes to the chronicity of pain.

Ketamine and fluoxetine exert similar actions on prelimbic and infralimbic responsivity to lateral septal nucleus stimulation in Wistar rats

Ketamine is a dissociative anesthetic that has been proposed to be a useful alternative in cases of a poor response to other treatments in patients with depression. Remarkably, beneficial clinical actions of ketamine are detected once its psychotropic actions disappear. Therefore, clinical actions may occur independently of dose. Most current studies focus on actions of ketamine on neurotrophic factors, but few studies have investigated actions of ketamine on neural structures for which actions of antidepressants have been previously explored. Lateral septal nucleus (LSN) stimulation reduces neural activity in the prelimbic cortex (PL) and infralimbic cortex (IL) subregions of the medial prefrontal cortex (mPFC). Fluoxetine increases inhibitory responsivity of the LSN-IL connection. In the present study, actions of an anesthetic dose of ketamine were compared with a high dose of fluoxetine on behavior and neural responsivity 24 h after drug administration. Fluoxetine reduced immobility in the forced swim test without changing locomotor activity in the open field test. Ketamine strongly decreased locomotor activity and did not produce changes in immobility. In another set of Wistar rats that received similar drug treatment regimens, the results indicated that LSN stimulation in saline-treated animals produced a long-lasting inhibitory afterdischarge in these mPFC subregions. Actions of ketamine on the LSN-mPFC connection reproduced actions of fluoxetine, consisting of accentuated inhibition of the LSN action on the mPFC. These findings suggest that independent of different actions on neurotransmission, the common final pathway of antidepressants lies in their actions on forebrain structures that are related to emotional regulation.

Border cells without theta rhythmicity in the medial prefrontal cortex

The medial prefrontal cortex (mPFC) is a key brain structure for higher cognitive functions such as decision-making and goal-directed behavior, many of which require awareness of spatial variables including one's current position within the surrounding environment. Although previous studies have reported spatially tuned activities in mPFC during memory-related trajectory, the spatial tuning of mPFC network during freely foraging behavior remains elusive. Here, we reveal geometric border or border-proximal representations from the neural activity of mPFC ensembles during naturally exploring behavior, with both allocentric and egocentric boundary responses. Unlike most of classical border cells in the medial entorhinal cortex (MEC) discharging along a single wall, a large majority of border cells in mPFC fire particularly along four walls. mPFC border cells generate new firing fields to external insert, and remain stable under darkness, across distinct shapes, and in novel environments. In contrast to hippocampal theta entrainment during spatial working memory tasks, mPFC border cells rarely exhibited theta rhythmicity during spontaneous locomotion behavior. These findings reveal spatially modulated activity in mPFC, supporting local computation for cognitive functions involving spatial context and contributing to a broad spatial tuning property of cortical circuits.

Active avoidance recruits the anterior cingulate cortex regardless of social context in male and female rats

Actively avoiding danger is necessary for survival. Most research has focused on the behavioral and neurobiological processes when individuals avoid danger alone, under solitary conditions. Therefore, little is known about how social context affects active avoidance. Using a modified version of the platform-mediated avoidance task in rats, we investigated whether the presence of a social partner attenuates conditioned freezing and enhances avoidance learning compared to avoidance learned under solitary conditions. Rats spent a similar percentage of time avoiding during the tone under both conditions; however, rats trained under social conditions exhibited greater freezing during the tone as well as lower rates of darting and food seeking compared to solitary rats. Under solitary conditions, we observed higher levels of avoidance in females compared to males, which was not present in rats trained under social conditions. To gain greater mechanistic insight, we optogenetically inactivated glutamatergic projection neurons in the anterior cingulate cortex (ACC) following avoidance training. Photoinactivation of ACC neurons reduced expression of avoidance under social conditions both in the presence and absence of the partner. Under solitary conditions, photoinactivation of ACC delayed avoidance in males but blocked avoidance in females. Our findings suggest that avoidance is mediated by the ACC, regardless of social context, and may be dysfunctional in those suffering from trauma-related disorders. Furthermore, sex differences in prefrontal circuits mediating active avoidance warrant further investigation, given that females experience a higher risk of developing anxiety disorders.

NARP-related alterations in the excitatory and inhibitory circuitry of socially isolated mice: developmental insights and implications for autism spectrum disorder

Background

Social isolation during critical periods of development is associated with alterations in behavior and neuronal circuitry. This study aimed to investigate the immediate and developmental effects of social isolation on firing properties, neuronal activity-regulated pentraxin (NARP) and parvalbumin (PV) expression in the prefrontal cortex (PFC), social behavior in juvenile socially isolated mice, and the biological relevance of NARP expression in autism spectrum disorder (ASD).

Methods

Mice were subjected to social isolation during postnatal days 21-35 (P21-P35) and were compared with group-housed control mice. Firing properties in the PFC pyramidal neurons were altered in P35 socially isolated mice, which might be associated with alterations in NARP and PV expression.

Results

In adulthood, mice that underwent juvenile social isolation exhibited difficulty distinguishing between novel and familiar mice during a social memory task, while maintaining similar levels of social interaction as the control mice. Furthermore, a marked decrease in NARP expression in lymphoblastoid cell lines derived from adolescent humans with ASD as compared to typically developing (TD) humans was found.

Conclusion

Our study highlights the role of electrophysiological properties, as well as NARP and PV expression in the PFC in mediating the developmental consequences of social isolation on behavior.

Adenosine receptors are the on-and-off switch of astrocytic cannabinoid type 1 (CB1) receptor effect upon synaptic plasticity in the medial prefrontal cortex

The medial prefrontal cortex (mPFC) is involved in cognitive functions such as working memory. Astrocytic cannabinoid type 1 receptor (CB1R) induces cytosolic calcium (Ca2+) concentration changes with an impact on neuronal function. mPFC astrocytes also express adenosine A1 and A2A receptors (A1R, A2AR), being unknown the crosstalk between CB1R and adenosine receptors in these cells. We show here that a further level of regulation of astrocyte Ca2+ signaling occurs through CB1R-A2AR or CB1R-A1R heteromers that ultimately impact mPFC synaptic plasticity. CB1R-mediated Ca2+ transients increased and decreased when A1R and A2AR were activated, respectively, unveiling adenosine receptors as modulators of astrocytic CB1R. CB1R activation leads to an enhancement of long-term potentiation (LTP) in the mPFC, under the control of A1R but not of A2AR. Notably, in IP3R2KO mice, that do not show astrocytic Ca2+ level elevations, CB1R activation decreases LTP, which is not modified by A1R or A2AR. The present work suggests that CB1R has a homeostatic role on mPFC LTP, under the control of A1R, probably due to physical crosstalk between these receptors in astrocytes that ultimately alters CB1R Ca2+ signaling.

Parvalbumin interneuron mGlu5 receptors govern sex differences in prefrontal cortex physiology and binge drinking

Despite established sex differences in the prevalence and presentation of psychiatric disorders, little is known about the cellular and synaptic mechanisms that guide these differences under basal conditions. The proper function of the prefrontal cortex (PFC) is essential for the top-down regulation of motivated behaviors. The activity of the PFC is tightly controlled by parvalbumin-expressing interneurons (PV-INs), a key subpopulation of fast-spiking GABAergic cells that regulate cortical excitability through direct innervations onto the perisomatic regions of nearby pyramidal cells. Recent rodent studies have identified notable sex differences in PV-IN activity and adaptations to experiences such as binge drinking. Here, we investigated the cellular and molecular mechanisms that underlie sex-specific regulation of PFC PV-IN function. Using whole-cell patch-clamp electrophysiology and selective pharmacology, we report that PV-INs from female mice are more excitable than those from males. Moreover, we find that mGlu1 and mGlu5 metabotropic glutamate receptors regulate cell excitability, excitatory drive, and endocannabinoid signaling at PFC PV-INs in a sex-dependent manner. Genetic deletion of mGlu5 receptors from PV-expressing cells abrogates all sex differences observed in PV-IN membrane and synaptic physiology. Lastly, we report that female, but not male, PV-mGlu5-/- mice exhibit decreased voluntary drinking on an intermittent access schedule, which could be related to changes in ethanol's stimulant properties. Importantly, these studies identify mGlu1 and mGlu5 receptors as candidate signaling molecules involved in sex differences in PV-IN activity and behaviors relevant to alcohol use.

An unbiased method to partition diverse neuronal responses into functional ensembles reveals interpretable population dynamics during innate social behavior

In neuroscience, understanding how single-neuron firing contributes to distributed neural ensembles is crucial. Traditional methods of analysis have been limited to descriptions of whole population activity, or, when analyzing individual neurons, criteria for response categorization varied significantly across experiments. Current methods lack scalability for large datasets, fail to capture temporal changes and rely on parametric assumptions. There's a need for a robust, scalable, and non-parametric functional clustering approach to capture interpretable dynamics. To address this challenge, we developed a model-based, statistical framework for unsupervised clustering of multiple time series datasets that exhibit nonlinear dynamics into an a-priori-unknown number of parameterized ensembles called Functional Encoding Units (FEUs). FEU outperforms existing techniques in accuracy and benchmark scores. Here, we apply this FEU formalism to single-unit recordings collected during social behaviors in rodents and primates and demonstrate its hypothesis-generating and testing capacities. This novel pipeline serves as an analytic bridge, translating neural ensemble codes across model systems.

Opioid modulation of prefrontal cortex cells and circuits

Several neurochemical systems converge in the prefrontal cortex (PFC) to regulate cognitive and motivated behaviors. A rich network of endogenous opioid peptides and receptors spans multiple PFC cell types and circuits, and this extensive opioid system has emerged as a key substrate underlying reward, motivation, affective behaviors, and adaptations to stress. Here, we review the current evidence for dysregulated cortical opioid signaling in the pathogenesis of psychiatric disorders. We begin by providing an introduction to the basic anatomy and function of the cortical opioid system, followed by a discussion of endogenous and exogenous opioid modulation of PFC function at the behavioral, cellular, and synaptic level. Finally, we highlight the therapeutic potential of endogenous opioid targets in the treatment of psychiatric disorders, synthesizing clinical reports of altered opioid peptide and receptor expression and activity in human patients and summarizing new developments in opioid-based medications. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Sex differences in the rodent medial prefrontal cortex - What Do and Don't we know?

The prefrontal cortex, particularly its medial subregions (mPFC), mediates critical functions such as executive control, behavioral inhibition, and memory formation, with relevance for everyday functioning and psychopathology. Despite broad characterization of the mPFC in multiple model organisms, the extent to which mPFC structure and function vary according to an individual's sex is unclear - a knowledge gap that can be attributed to a historical bias for male subjects in neuroscience research. Recent efforts to consider sex as a biological variable in basic science highlight the great need to close this gap. Here we review the knowns and unknowns about how rodents categorized as male or female compare in mPFC neuroanatomy, pharmacology, as well as in aversive, appetitive, and goal- or habit-directed behaviors that recruit the mPFC. We propose that long-standing dogmatic concepts of mPFC structure and function may not remain supported when we move beyond male-only studies, and that empirical challenges to these dogmas are warranted. Additionally, we note some common pitfalls in this work. Most preclinical studies operationalize sex as a binary categorization, and while this approach has furthered the inclusion of non-male rodents it is not as such generalizable to what we know of sex as a multidimensional, dynamic variable. Exploration of sex variability may uncover both sex differences and sex similarities, but care must be taken in their interpretation. Including females in preclinical research needs to go beyond the investigation of sex differences, improving our knowledge of how this brain region and its subregions mediate behavior and health. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Dorsal peduncular cortex activity modulates affective behavior and fear extinction in mice

The medial prefrontal cortex (mPFC) is critical to cognitive and emotional function and underlies many neuropsychiatric disorders, including mood, fear and anxiety disorders. In rodents, disruption of mPFC activity affects anxiety- and depression-like behavior, with specialized contributions from its subdivisions. The rodent mPFC is divided into the dorsomedial prefrontal cortex (dmPFC), spanning the anterior cingulate cortex (ACC) and dorsal prelimbic cortex (PL), and the ventromedial prefrontal cortex (vmPFC), which includes the ventral PL, infralimbic cortex (IL), and in some studies the dorsal peduncular cortex (DP) and dorsal tenia tecta (DTT). The DP/DTT have recently been implicated in the regulation of stress-induced sympathetic responses via projections to the hypothalamus. While many studies implicate the PL and IL in anxiety-, depression-like and fear behavior, the contribution of the DP/DTT to affective and emotional behavior remains unknown. Here, we used chemogenetics and optogenetics to bidirectionally modulate DP/DTT activity and examine its effects on affective behaviors, fear and stress responses in C57BL/6J mice. Acute chemogenetic activation of DP/DTT significantly increased anxiety-like behavior in the open field and elevated plus maze tests, as well as passive coping in the tail suspension test. DP/DTT activation also led to an increase in serum corticosterone levels and facilitated auditory fear extinction learning and retrieval. Activation of DP/DTT projections to the dorsomedial hypothalamus (DMH) acutely decreased freezing at baseline and during extinction learning, but did not alter affective behavior. These findings point to the DP/DTT as a new regulator of affective behavior and fear extinction in mice.

Pathophysiology in cortico-amygdala circuits and excessive aversion processing: the role of oligodendrocytes and myelination

Stress-related psychiatric illnesses, such as major depressive disorder, anxiety and post-traumatic stress disorder, present with alterations in emotional processing, including excessive processing of negative/aversive stimuli and events. The bidirectional human/primate brain circuit comprising anterior cingulate cortex and amygdala is of fundamental importance in processing emotional stimuli, and in rodents the medial prefrontal cortex-amygdala circuit is to some extent analogous in structure and function. Here, we assess the comparative evidence for: (i) Anterior cingulate/medial prefrontal cortex<->amygdala bidirectional neural circuits as major contributors to aversive stimulus processing; (ii) Structural and functional changes in anterior cingulate cortex<->amygdala circuit associated with excessive aversion processing in stress-related neuropsychiatric disorders, and in medial prefrontal cortex<->amygdala circuit in rodent models of chronic stress-induced increased aversion reactivity; and (iii) Altered status of oligodendrocytes and their oligodendrocyte lineage cells and myelination in anterior cingulate/medial prefrontal cortex<->amygdala circuits in stress-related neuropsychiatric disorders and stress models. The comparative evidence from humans and rodents is that their respective anterior cingulate/medial prefrontal cortex<->amygdala circuits are integral to adaptive aversion processing. However, at the sub-regional level, the anterior cingulate/medial prefrontal cortex structure-function analogy is incomplete, and differences as well as similarities need to be taken into account. Structure-function imaging studies demonstrate that these neural circuits are altered in both human stress-related neuropsychiatric disorders and rodent models of stress-induced increased aversion processing. In both cases, the changes include altered white matter integrity, albeit the current evidence indicates that this is decreased in humans and increased in rodent models. At the cellular-molecular level, in both humans and rodents, the current evidence is that stress disorders do present with changes in oligodendrocyte lineage, oligodendrocytes and/or myelin in these neural circuits, but these changes are often discordant between and even within species. Nonetheless, by integrating the current comparative evidence, this review provides a timely insight into this field and should function to inform future studies-human, monkey and rodent-to ascertain whether or not the oligodendrocyte lineage and myelination are causally involved in the pathophysiology of stress-related neuropsychiatric disorders.

Potentiation of the M 1 muscarinic acetylcholine receptor normalizes neuronal activation patterns and improves apnea severity in Mecp2+/- mice

Rett syndrome (RTT) is a neurodevelopmental disorder that is caused by loss-of-function mutations in the methyl-CpG binding protein 2 ( MeCP2 ) gene. RTT patients experience a myriad of debilitating symptoms, which include respiratory phenotypes that are often associated with lethality. Our previous work established that expression of the M 1 muscarinic acetylcholine receptor (mAchR) is decreased in RTT autopsy samples, and that potentiation of the M 1 receptor improves apneas in a mouse model of RTT; however, the population of neurons driving this rescue is unclear. Loss of Mecp2 correlates with excessive neuronal activity in cardiorespiratory nuclei. Since M 1 is found on cholinergic interneurons, we hypothesized that M 1 -potentiating compounds decrease apnea frequency by tempering brainstem hyperactivity. To test this, Mecp2 +/- and Mecp2 +/+ mice were screened for apneas before and after administration of the M 1 positive allosteric modulator (PAM) VU0453595 (VU595). Brains from the same mice were then imaged for c-Fos, ChAT, and Syto16 using whole-brain light-sheet microscopy to establish genotype and drug-dependent activation patterns that could be correlated with VU595's efficacy on apneas. The vehicle-treated Mecp2 +/- brain exhibited broad hyperactivity when coupled with the phenotypic prescreen, which was significantly decreased by administration of VU595, particularly in regions known to modulate the activity of respiratory nuclei (i.e. hippocampus and striatum). Further, the extent of apnea rescue in each mouse showed a significant positive correlation with c-Fos expression in non-cholinergic neurons in the striatum, thalamus, dentate gyrus, and within the cholinergic neurons of the brainstem. These results indicate that Mecp2 +/- mice are prone to hyperactivity in brain regions that regulate respiration, which can be normalized through M 1 potentiation.

Adenosinergic Modulation of Layer 6 Microcircuitry in the Medial Prefrontal Cortex Is Specific to Presynaptic Cell Type

Adenosinergic modulation in the PFC is recognized for its involvement in various behavioral aspects including sleep homoeostasis, decision-making, spatial working memory and anxiety. While the principal cells of layer 6 (L6) exhibit a significant morphological diversity, the detailed cell-specific regulatory mechanisms of adenosine in L6 remain unexplored. Here, we quantitatively analyzed the morphological and electrophysiological parameters of L6 neurons in the rat medial prefrontal cortex (mPFC) using whole-cell recordings combined with morphological reconstructions. We were able to identify two different morphological categories of excitatory neurons in the mPFC of both juvenile and young adult rats with both sexes. These categories were characterized by a leading dendrite that was oriented either upright (toward the pial surface) or inverted (toward the white matter). These two excitatory neuron subtypes exhibited different electrophysiological and synaptic properties. Adenosine at a concentration of 30 µM indiscriminately suppressed connections with either an upright or an inverted presynaptic excitatory neuron. However, using lower concentrations of adenosine (10 µM) revealed that synapses originating from L6 upright neurons have a higher sensitivity to adenosine-induced inhibition of synaptic release. Adenosine receptor activation causes a reduction in the probability of presynaptic neurotransmitter release that could be abolished by specifically blocking A1 adenosine receptors (A1ARs) using 8-cyclopentyltheophylline (CPT). Our results demonstrate a differential expression level of A1ARs at presynaptic sites of two functionally and morphologically distinct subpopulations of L6 principal neurons, suggesting the intricate functional role of adenosine in neuronal signaling in the brain.

Large-scale coupling of prefrontal activity patterns as a mechanism for cognitive control in health and disease: evidence from rodent models

Cognitive control of behavior is crucial for well-being, as allows subject to adapt to changing environments in a goal-directed way. Changes in cognitive control of behavior is observed during cognitive decline in elderly and in pathological mental conditions. Therefore, the recovery of cognitive control may provide a reliable preventive and therapeutic strategy. However, its neural basis is not completely understood. Cognitive control is supported by the prefrontal cortex, structure that integrates relevant information for the appropriate organization of behavior. At neurophysiological level, it is suggested that cognitive control is supported by local and large-scale synchronization of oscillatory activity patterns and neural spiking activity between the prefrontal cortex and distributed neural networks. In this review, we focus mainly on rodent models approaching the neuronal origin of these prefrontal patterns, and the cognitive and behavioral relevance of its coordination with distributed brain systems. We also examine the relationship between cognitive control and neural activity patterns in the prefrontal cortex, and its role in normal cognitive decline and pathological mental conditions. Finally, based on these body of evidence, we propose a common mechanism that may underlie the impaired cognitive control of behavior.

Cognition-enhancing and cognition-impairing doses of psychostimulants exert opposing actions on frontostriatal neural coding of delay in working memory

The prefrontal cortex (PFC) and extended frontostriatal circuitry play a critical role in executive cognitive processes that guide goal-directed behavior. Dysregulation of frontostriatal-dependent cognition is implicated in a variety of cognitive/behavioral disorders, including addiction and attention deficit hyperactivity disorder (ADHD). Psychostimulants exert dose-dependent and opposing actions on frontostriatal cognitive function. Specifically, low and clinically-relevant doses improve, while higher doses associated with abuse and addiction impair, frontostriatal-dependent cognitive function. Frontostriatal cognition is supported by the coordinated activity of neurons across this circuit. To date, the neural coding mechanisms that support the diverse cognitive actions of psychostimulants are unclear. This represents a significant deficit in our understanding of the neurobiology of frontostriatal cognition and limits the development of novel treatments for frontostriatal cognitive impairment. The current studies examined the effects of cognition-enhancing and cognition-impairing doses of methylphenidate (MPH) on the spiking activity of dorsomedial PFC (dmPFC) and dorsomedial striatal (dmSTR) neurons in 17 male rats engaged in a working memory task. Across this frontostriatal circuit, we observed opposing actions of low- and high-dose MPH on the population-based representation of delay: low-dose strengthened, while high-dose weakened, representation of this event. MPH elicited a more complex pattern of actions on reward-related signaling, that were highly dose-, region- and neuron-dependent. These observations provide novel insight into the neurophysiological mechanisms that support the cognitive actions of psychostimulants.

Mystery of the memory engram: History, current knowledge, and unanswered questions

The quest to understand the memory engram has intrigued humans for centuries. Recent technological advances, including genetic labelling, imaging, optogenetic and chemogenetic techniques, have propelled the field of memory research forward. These tools have enabled researchers to create and erase memory components. While these innovative techniques have yielded invaluable insights, they often focus on specific elements of the memory trace. Genetic labelling may rely on a particular immediate early gene as a marker of activity, optogenetics may activate or inhibit one specific type of neuron, and imaging may capture activity snapshots in a given brain region at specific times. Yet, memories are multifaceted, involving diverse arrays of neuronal subpopulations, circuits, and regions that work in concert to create, store, and retrieve information. Consideration of contributions of both excitatory and inhibitory neurons, micro and macro circuits across brain regions, the dynamic nature of active ensembles, and representational drift is crucial for a comprehensive understanding of the complex nature of memory.

The mediodorsal thalamus in executive control

Executive control, the ability to organize thoughts and action plans in real time, is a defining feature of higher cognition. Classical theories have emphasized cortical contributions to this process, but recent studies have reinvigorated interest in the role of the thalamus. Although it is well established that local thalamic damage diminishes cognitive capacity, such observations have been difficult to inform functional models. Recent progress in experimental techniques is beginning to enrich our understanding of the anatomical, physiological, and computational substrates underlying thalamic engagement in executive control. In this review, we discuss this progress and particularly focus on the mediodorsal thalamus, which regulates the activity within and across frontal cortical areas. We end with a synthesis that highlights frontal thalamocortical interactions in cognitive computations and discusses its functional implications in normal and pathological conditions.

Parvalbumin interneuron mGlu5 receptors govern sex differences in prefrontal cortex physiology and binge drinking

Despite established sex differences in the prevalence and presentation of psychiatric disorders, little is known about the cellular and synaptic mechanisms that guide these differences under basal conditions. Proper function of the prefrontal cortex (PFC) is essential for the top-down regulation of motivated behaviors. Activity of the PFC is tightly controlled by parvalbumin-expressing interneurons (PV-INs), a key subpopulation of fast-spiking GABAergic cells that regulate cortical excitability through direct innervations onto the perisomatic regions of nearby pyramidal cells. Recent rodent studies have identified notable sex differences in PV-IN activity and adaptations to experiences such as binge drinking. Here, we investigated the cellular and molecular mechanisms that underlie sex-specific regulation of PFC PV-IN function. Using whole-cell patch clamp electrophysiology and selective pharmacology, we report that PV-INs from female mice are more excitable than those from males. Moreover, we find that mGlu1 and mGlu5 metabotropic glutamate receptors regulate cell excitability, excitatory drive, and endocannabinoid signaling at PFC PV-INs in a sex-dependent manner. Genetic deletion of mGlu5 receptors from PV-expressing cells abrogates all sex differences observed in PV-IN membrane and synaptic physiology. Lastly, we report that female, but not male, PV-mGlu5-/- mice exhibit decreased voluntary drinking on an intermittent access schedule, which could be related to changes in ethanol's stimulant properties. Importantly, these studies identify mGlu1 and mGlu5 receptors as candidate signaling molecules involved in sex differences in PV-IN activity and behaviors relevant for alcohol use.

The role of serotonin in depression-A historical roundup and future directions

Depression is one of the most common psychiatric disorders worldwide, affecting approximately 280 million people, with probably much higher unrecorded cases. Depression is associated with symptoms such as anhedonia, feelings of hopelessness, sleep disturbances, and even suicidal thoughts. Tragically, more than 700 000 people commit suicide each year. Although depression has been studied for many decades, the exact mechanisms that lead to depression are still unknown, and available treatments only help a fraction of patients. In the late 1960s, the serotonin hypothesis was published, suggesting that serotonin is the key player in depressive disorders. However, this hypothesis is being increasingly doubted as there is evidence for the influence of other neurotransmitters, such as noradrenaline, glutamate, and dopamine, as well as larger systemic causes such as altered activity in the limbic network or inflammatory processes. In this narrative review, we aim to contribute to the ongoing debate on the involvement of serotonin in depression. We will review the evolution of antidepressant treatments, systemic research on depression over the years, and future research applications that will help to bridge the gap between systemic research and neurotransmitter dynamics using biosensors. These new tools in combination with systemic applications, will in the future provide a deeper understanding of the serotonergic dynamics in depression.

Top-down and bottom-up alterations of connectivity patterns of the suprachiasmatic nucleus in chronic insomnia disorder

The importance of the suprachiasmatic nucleus (SCN, also called the master circadian clock) in regulating sleep and wakefulness has been confirmed by multiple animal research. However, human studies of SCN in vivo are still nascent. Recently, the development of resting-state functional magnetic resonance imaging (fMRI) has made it possible to study SCN-related connectivity changes in patients with chronic insomnia disorder (CID). Hence, this study aimed to explore whether sleep-wake circuitry (i.e., communication between the SCN and other brain regions) is disrupted in human insomnia. Forty-two patients with CID and 37 healthy controls (HCs) underwent fMRI scanning. Resting-state functional connectivity (rsFC) and Granger causality analysis (GCA) were performed to find abnormal functional and causal connectivity of the SCN in CID patients. In addition, correlation analyses were conducted to detect associations between features of disrupted connectivity and clinical symptoms. Compared to HCs, CID patients showed enhanced rsFC of the SCN-left dorsolateral prefrontal cortex (DLPFC), as well as reduced rsFC of the SCN-bilateral medial prefrontal cortex (MPFC); these altered cortical regions belong to the "top-down" circuit. Moreover, CID patients exhibited disrupted functional and causal connectivity between the SCN and the locus coeruleus (LC) and the raphe nucleus (RN); these altered subcortical regions constitute the "bottom-up" pathway. Importantly, the decreased causal connectivity from the LC-to-SCN was associated with the duration of disease in CID patients. These findings suggest that the disruption of the SCN-centered "top-down" cognitive process and "bottom-up" wake-promoting pathway may be intimately tied to the neuropathology of CID.

Cortical-brainstem circuitry attenuates physiological stress reactivity

Exposure to stressful stimuli promotes multi-system biological responses to restore homeostasis. Catecholaminergic neurons in the rostral ventrolateral medulla (RVLM) facilitate sympathetic activity and promote physiological adaptations, including glycaemic mobilization and corticosterone release. While it is unclear how brain regions involved in the cognitive appraisal of stress regulate RVLM neural activity, recent studies found that the rodent ventromedial prefrontal cortex (vmPFC) mediates stress appraisal and physiological stress responses. Thus, a vmPFC-RVLM connection could represent a circuit mechanism linking stress appraisal and physiological reactivity. The current study investigated a direct vmPFC-RVLM circuit utilizing genetically encoded anterograde and retrograde tract tracers. Together, these studies found that stress-activated vmPFC neurons project to catecholaminergic neurons throughout the ventrolateral medulla in male and female rats. Next, we utilized optogenetic terminal stimulation to evoke vmPFC synaptic glutamate release in the RVLM. Photostimulating the vmPFC-RVLM circuit during restraint stress suppressed glycaemic stress responses in males, without altering the female response. However, circuit stimulation decreased corticosterone responses to stress in both sexes. Circuit stimulation did not modulate affective behaviour in either sex. Further analysis indicated that circuit stimulation preferentially activated non-catecholaminergic medullary neurons in both sexes. Additionally, vmPFC terminals targeted medullary inhibitory neurons. Thus, both male and female rats have a direct vmPFC projection to the RVLM that reduces endocrine stress responses, likely by recruiting local RVLM inhibitory neurons. Ultimately, the excitatory/inhibitory balance of vmPFC synapses in the RVLM may regulate stress reactivity and stress-related health outcomes. KEY POINTS: Glutamatergic efferents from the ventromedial prefrontal cortex target catecholaminergic neurons throughout the ventrolateral medulla. Partially segregated, stress-activated ventromedial prefrontal cortex populations innervate the rostral and caudal ventrolateral medulla. Stimulating ventromedial prefrontal cortex synapses in the rostral ventrolateral medulla decreases stress-induced glucocorticoid release in males and females. Stimulating ventromedial prefrontal cortex terminals in the rostral ventrolateral medulla preferentially activates non-catecholaminergic neurons. Ventromedial prefrontal cortex terminals target medullary inhibitory neurons.

High-throughput mapping of single-neuron projection and molecular features by retrograde barcoded labeling

Deciphering patterns of connectivity between neurons in the brain is a critical step toward understanding brain function. Imaging-based neuroanatomical tracing identifies area-to-area or sparse neuron-to-neuron connectivity patterns, but with limited throughput. Barcode-based connectomics maps large numbers of single-neuron projections, but remains a challenge for jointly analyzing single-cell transcriptomics. Here, we established a rAAV2-retro barcode-based multiplexed tracing method that simultaneously characterizes the projectome and transcriptome at the single neuron level. We uncovered dedicated and collateral projection patterns of ventromedial prefrontal cortex (vmPFC) neurons to five downstream targets and found that projection-defined vmPFC neurons are molecularly heterogeneous. We identified transcriptional signatures of projection-specific vmPFC neurons, and verified Pou3f1 as a marker gene enriched in neurons projecting to the lateral hypothalamus, denoting a distinct subset with collateral projections to both dorsomedial striatum and lateral hypothalamus. In summary, we have developed a new multiplexed technique whose paired connectome and gene expression data can help reveal organizational principles that form neural circuits and process information.

Sensing, Feeling, and Regulating: Investigating the Association of Focal Brain Damage with Voluntary Respiratory and Motor Control

Breathing is a complex, vital function that can be modulated to influence physical and mental well-being. However, the role of cortical and subcortical brain regions in voluntary control of human respiration is underexplored. Here we investigated the influence of damage to human frontal, temporal, or limbic regions on the sensation and regulation of breathing patterns. Participants performed a respiratory regulation task across regular and irregular frequencies ranging from 6 to 60 breaths per minute (bpm), with a counterbalanced hand motor control task. Interoceptive and affective states induced by each condition were assessed via questionnaire and autonomic signals were indexed via skin conductance. Participants with focal lesions to the bilateral frontal lobe, right insula/basal ganglia, and left medial temporal lobe showed reduced performance than individually matched healthy comparisons during the breathing and motor tasks. They also reported significantly higher anxiety during the 60-bpm regular and irregular breathing trials, with anxiety correlating with difficulty in rapid breathing specifically within this group. This study demonstrates that damage to frontal, temporal, or limbic regions is associated with abnormal voluntary respiratory and motor regulation and tachypnea-related anxiety, highlighting the role of the forebrain in affective and motor responses during breathing.

Highlights

Impaired human respiratory regulation is associated with cortical/subcortical brain lesionsFrontolimbic/temporal regions contribute to rhythmic breathing and hand motor controlFrontolimbic/temporal damage is associated with anxiety during tachypnea/irregular breathingThe human forebrain is vital for affective and interoceptive experiences during breathing.

A stress-sensitive frontostriatal circuit supporting effortful reward-seeking behavior

Effort valuation-a process for selecting actions based on the anticipated value of rewarding outcomes and expectations about the work required to obtain them-plays a fundamental role in decision-making. Effort valuation is disrupted in chronic stress states and is supported by the anterior cingulate cortex (ACC), but the circuit-level mechanisms by which the ACC regulates effort-based decision-making are unclear. Here, we show that ACC neurons projecting to the nucleus accumbens (ACC-NAc) play a critical role in effort valuation behavior in mice. Activity in ACC-NAc cells integrates both reward- and effort-related information, encoding a reward-related signal that scales with effort requirements and is necessary for supporting future effortful decisions. Chronic corticosterone exposure reduces motivation, suppresses effortful reward-seeking, and disrupts ACC-NAc signals. Together, our results delineate a stress-sensitive ACC-NAc circuit that supports effortful reward-seeking behavior by integrating reward and effort signals and reinforcing effort allocation in the service of maximizing reward.

Using synchronized brain rhythms to bias memory-guided decisions

Functional interactions between the prefrontal cortex and hippocampus, as revealed by strong oscillatory synchronization in the theta (6-11 Hz) frequency range, correlate with memory-guided decision-making. However, the degree to which this form of long-range synchronization influences memory-guided choice remains unclear. We developed a brain machine interface that initiated task trials based on the magnitude of prefrontal hippocampal theta synchronization, then measured choice outcomes. Trials initiated based on strong prefrontal-hippocampal theta synchrony were more likely to be correct compared to control trials on both working memory-dependent and -independent tasks. Prefrontal-thalamic neural interactions increased with prefrontal-hippocampal synchrony and optogenetic activation of the ventral midline thalamus primarily entrained prefrontal theta rhythms, but dynamically modulated synchrony. Together, our results show that prefrontal-hippocampal theta synchronization leads to a higher probability of a correct choice and strengthens prefrontal-thalamic dialogue. Our findings reveal new insights into the neural circuit dynamics underlying memory-guided choices and highlight a promising technique to potentiate cognitive processes or behavior via brain machine interfacing.

Alpha-Synuclein Pre-Formed Fibrils Injected into Prefrontal Cortex Primarily Spread to Cortical and Subcortical Structures

BACKGROUND

Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) are characterized by diffuse spread of alpha-synuclein (α-syn) throughout the brain. Patients with PDD and DLB have a neuropsychological pattern of deficits that include executive dysfunction, such as abnormalities in planning, timing, working memory, and behavioral flexibility. The prefrontal cortex (PFC) plays a major role in normal executive function and often develops α-syn aggregates in DLB and PDD.

OBJECTIVE

To investigate the long-term behavioral and cognitive consequences of α-syn pathology in the cortex and characterize pathological spread of α-syn.

METHODS

We injected human α-syn pre-formed fibrils into the PFC of wild-type male mice. We then assessed the behavioral and cognitive effects between 12- and 21-months post-injection and characterized the spread of pathological α-syn in cortical, subcortical, and brainstem regions.

RESULTS

We report that PFC PFFs: 1) induced α-syn aggregation in multiple cortical and subcortical regions with sparse aggregation in midbrain and brainstem nuclei; 2) did not affect interval timing or spatial learning acquisition but did mildly alter behavioral flexibility as measured by intraday reversal learning; and 3) increased open field exploration.

CONCLUSIONS

This model of cortical-dominant pathology aids in our understanding of how local α-syn aggregation might impact some symptoms in PDD and DLB.

Anatomical analyses of collateral prefrontal cortex projections to the basolateral amygdala and the nucleus accumbens core in rats

The basolateral amygdala (BLA) and the nucleus accumbens core (NAcc) share some similar behavioral functions, such as associative learning, Pavlovian to instrumental transfer, and choice behavior. However, their prefrontal anatomical inputs have not been well characterized before, especially the collateral projections. In this study, we analyzed the distribution and collateralization of projections to the BLA and the NAcc from the prefrontal cortices (PFC), including the prelimbic (PL) and the infralimbic (IL) divisions of the medial prefrontal cortex (mPFC) and the subregions of the orbitofrontal cortex (OFC), such as the medial OFC (MO), the lateral OFC (LO), and the ventral OFC (VO). Double retrograde tracing approach was used, in which Cholera toxin subunit B conjugated with the Alexa Fluor 488 (CTB-AF488) or Alexa Fluor 594 (CTB-AF594) were unilaterally injected into the BLA and the NAcc, respectively, in male Long-Evans rats (n = 6). Among the sampled neurons, prefrontal projection to the BLA or the NAcc is more robust on the ipsilateral side, and more robust from the PL, the IL, and the MO compared to from the LO and the VO. The majority of the projections from the PFC to the BLA and/or the NAcc are confined in deep layer. In addition, for each of the prefrontal areas, about 15-25% BLA-projecting neurons send collateral projections to the NAcc, and vice versa. In conclusion, our data suggested that prefrontal control over the BLA and the NAcc is not entirely independent. The functional importance of the collateral projections awaits further examination.

Photic sensitization is mediated by cortico-accumbens pathway in rats with trigeminal neuropathic pain

Exposure to light stimuli may trigger or exacerbate perception of pain, also known as a common yet debilitating symptom of photophobia in patient with chronic orofacial pain. Mechanism underlying this phenomenon of photic sensitization in neuropathic condition remains elusive. Here, we found that rats developed hypersensitivity to normal light illumination after establishment of chronic constriction injury of infraorbital nerve (ION-CCI) model, which can be attenuated by blocking the exposure of photic stimulation. Additionally, this behavioral phenotype of light-sensitivity impairment was associated with overexpression of anterior cingulate cortex (ACC) c-fos positive neurons, enhancement of neural excitability in the ACC neurons and its excitatory synaptic transmission between nucleus accumbens (NAc). Optogenetic and chemogenic silencing of ACC-NAc pathway improved trigeminal sensitization in responses to light stimuli by decreasing spontaneous pain-like episodes in ION-CCI animals. In contrast, selective activation of ACC-to-NAc circuits enhanced photic hypersensitivity in dark environment. Thus, our data provided novel role of ACC and its projection to NAc in bidirectional modulation of photic sensation, which may contribute to the understanding of photic allodynia in trigeminal neuropathic pain status.

Harnessing axonal transport to map reward circuitry: Differing brain-wide projections from medial prefrontal cortical domains

Neurons project long axons that contact other distant neurons. Neurons in the medial prefrontal cortex project into the limbic system to regulate responses to reward or threat. Diminished neural activity in prefrontal cortex is associated with loss of executive function leading to drug use, yet the specific circuitry that mediate these effects is unknown. Different regions within the medial prefrontal cortex may project to differing limbic system nuclei. Here, we exploited the cell biology of intracellular membrane trafficking, fast axonal transport, to map projections from two adjacent medial prefrontal cortical regions. We used Mn(II), a calcium analog, to trace medial prefrontal cortical projections in the living animal by magnetic resonance imaging (MRI). Mn(II), a contrast agent for MRI, enters neurons through voltage-activated calcium channels and relies on kinesin-1 and amyloid-precursor protein to transport out axons to distal destinations. Aqueous MnCl2 together with fluorescent dextran (3--5 nL) was stereotactically injected precisely into two adjacent regions of the medial prefrontal cortex: anterior cingulate area (ACA) or infralimbic/prelimbic (IL/PL) region. Projections were traced, first live by manganese-enhanced MRI (MEMRI) at four time points in 3D, and then after fixation by microscopy. Data-driven unbiased voxel-wise statistical maps of aligned normalized MR images after either ACA or IL/PL injections revealed statistically significant progression of Mn(II) over time into deeper brain regions: dorsal striatum, globus pallidus, amygdala, hypothalamus, substantia nigra, dorsal raphe and locus coeruleus. Quantitative comparisons of these distal accumulations at 24 h revealed dramatic differences between ACA and IL/PL injection groups throughout the limbic system, and most particularly in subdomains of the hypothalamus. ACA projections targeted dorsomedial nucleus of the hypothalamus, posterior part of the periventricular region and mammillary body nuclei as well as periaqueductal gray, while IL/PL projections accumulated in anterior hypothalamic areas and lateral hypothalamic nuclei as well as amygdala. As hypothalamic subsegments relay CNS activity to the body, our results suggest new concepts about mind-body relationships and specific roles of distinct yet adjacent medial prefrontal cortical segments. Our MR imaging strategy, when applied to follow other cell biological processes in the living organism, will undoubtedly lead to an expanded perspective on how minute details of cellular processes influence whole body health and wellbeing.

Involvement of orexin type-2 receptors in genetic absence epilepsy rats

Introduction

Orexin is a neuropeptide neurotransmitter that regulates the sleep/wake cycle produced by the lateral hypothalamus neurons. Recent studies have shown the involvement of orexin system in epilepsy. Limited data is available about the possible role of orexins in the pathophysiology of absence seizures. This study aims to understand the role of orexinergic signaling through the orexin-type 2 receptor (OX2R) in the pathophysiology of absence epilepsy. The pharmacological effect of a selective OX2R agonist, YNT-185 on spike-and-wave-discharges (SWDs) and the OX2R receptor protein levels in the cortex and thalamus in adult GAERS were investigated.

Methods

The effect of intracerebroventricular (ICV) (100, 300, and 600 nmol/10 μL), intrathalamic (30 and 40 nmol/500 nL), and intracortical (40 nmol/500 nL) microinjections of YNT-185 on the duration and number of spontaneous SWDs were evaluated in adult GAERS. The percentage of slow-wave sleep (SWS) and spectral characteristics of background EEG were analyzed after the ICV application of 600 nmol YNT-185. The level of OX2R expression in the somatosensory cortex and projecting thalamic nuclei of adult GAERS were examined by Western blot and compared with the non-epileptic Wistar rats.

Results

We showed that ICV administration of YNT-185 suppressed the cumulative duration of SWDs in GAERS compared to the saline-administered control group (p < 0.05). However, intrathalamic and intracortical microinjections of YNT-185 did not show a significant effect on SWDs. ICV microinjections of YNT-185 affect sleep states by increasing the percentage of SWS and showed a significant treatment effect on the 1-4 Hz delta frequency band power during the 1-2 h post-injection period where YNT-185 significantly decreased the SWDs. OXR2 protein levels were significantly reduced in the cortex and thalamus of GAERS when compared to Wistar rats.

Conclusion

This study investigated the efficacy of YNT-185 for the first time on absence epilepsy in GAERS and revealed a suppressive effect of OX2R agonist on SWDs as evidenced by the significantly reduced expression of OX2R in the cortex and thalamus. YNT-185 effect on SWDs could be attributed to its regulation of wake/sleep states. The results constitute a step toward understanding the effectiveness of orexin neuropeptides on absence seizures in GAERS and might be targeted by therapeutic intervention for absence epilepsy.

Dynamic Regulation of brsk2 in the Social and Motor Development of Zebrafish: A Developmental Behavior Analysis

Both social and motor development play an essential role in an individual's physical, psychological, and social well-being. It is essential to conduct a dynamic analysis at multiple time points during the developmental process as it helps us better understand and evaluate the trajectory and changes in individual development. Recently, some studies found that mutations in the BRSK2 gene may contribute to motor impairments, delays in achieving motor milestones, and deficits in social behavior and communication skills in patients. However, little is known about the dynamic analysis of social and motor development at multiple time points during the development of the brsk2 gene. We generated a novel brsk2-deficient (brsk2ab-/-) zebrafish model through CRISPR/Cas9 editing and conducted comprehensive morphological and neurobehavioral evaluations, including that of locomotor behaviors, social behaviors, and anxiety behaviors from the larval to adult stages of development. Compared to wild-type zebrafish, brsk2ab-/- zebrafish exhibited a catch-up growth pattern of body length and gradually improved locomotor activities during the developmental process. In contrast, multimodal behavior tests showed that the brsk2ab-/- zebrafish displayed escalating social deficiency and anxiety-like behaviors over time. We reported for the first time that the brsk2 gene had dynamic regulatory effects on motor and social development. It helps us understand developmental trends, capture changes, facilitate early interventions, and provide personalized support and development opportunities for individuals.

Maternal separation modifies spontaneous synaptic activity in the infralimbic cortex of stress-resilient male rats

Glutamate and GABA signaling systems are necessary to maintain proper function of the central nervous system through excitation/inhibition (E/I) balance. Alteration of this balance in the medial prefrontal cortex (mPFC), as an effect of early-life stress, may lead to the development of anxiety and depressive disorders. Few studies exist in the infralimbic division of the mPFC to understand the effect of early-life stress at different ages, which is the purpose of the present work. Newborn Sprague Dawley male rats were subjected to maternal separation (MS) for two weeks. First, tests measuring anxiety- and depression-like behaviors were performed on adolescent and adult rats subjected to MS (MS-rats). Then, to establish a relationship with behavioral results, electrophysiological recordings were performed in neurons of the infralimbic cortex in acute brain slices of infant, adolescent, and adult rats. In the behavioral tests, there were no significant differences in MS-rats compared to control rats at any age. Moreover, MS had no effect on the passive membrane properties nor neuronal excitability in the infralimbic cortex, whereas spontaneous synaptic activity in infralimbic neurons was altered. The frequency of spontaneous glutamatergic synaptic events increased in infant MS-rats, whereas in adolescent MS-rats both the frequency and the amplitude of spontaneous GABAergic events increased without any effect on glutamatergic synaptic responses. In adult MS-rats, these two parameters decreased in spontaneous GABAergic synaptic events, whereas only the frequency of glutamatergic events decreased. These data suggest that rats subjected to MS did not exhibit behavioral changes and presented an age-dependent E/I imbalance in the infralimbic cortex, possibly due to differential changes in neurotransmitter release and/or receptor expression.

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.

Chronic stress promotes basal ganglia disinhibition by increasing the excitatory drive of direct-pathway neurons

Chronic stress (CS) is a well-recognized triggering factor in obsessive-compulsive disorder (OCD) and Tourette's syndrome (TS), two neuropsychiatric disorders characterized by the presence of stereotypic motor symptoms. Planning and execution of motor actions are controlled by the dorsal striatum, a brain region that promotes or suppresses motor movement by activating striatal neurons from the direct- or indirect-pathway, respectively. Despite the dorsal striatum being affected in motor disorders and by CS exposure, how CS affects the two opposing pathways is not fully understood. Here, we report that CS in mice selectively potentiates the direct-pathway, while sparing the indirect-pathway. Specifically, we show that CS both increases excitation and reduces inhibition over direct-pathway neurons in the dorsomedial striatum (DMS). Furthermore, inhibitory interneurons located in the DMS also display reduced excitatory drive after chronic stress, thus amplifying striatal disinhibition. Altogether, we propose a model where both increased excitatory drive and decreased inhibitory drive in the striatum causes disinhibition of basal ganglia's motor direct pathway - a mechanism that might explain the emergence of motor stereotypies and tic disorders under stress.

Spatial transcriptomics reveals the distinct organization of mouse prefrontal cortex and neuronal subtypes regulating chronic pain

The prefrontal cortex (PFC) is a complex brain region that regulates diverse functions ranging from cognition, emotion and executive action to even pain processing. To decode the cellular and circuit organization of such diverse functions, we employed spatially resolved single-cell transcriptome profiling of the adult mouse PFC. Results revealed that PFC has distinct cell-type composition and gene-expression patterns relative to neighboring cortical areas-with neuronal excitability-regulating genes differently expressed. These cellular and molecular features are further segregated within PFC subregions, alluding to the subregion-specificity of several PFC functions. PFC projects to major subcortical targets through combinations of neuronal subtypes, which emerge in a target-intrinsic fashion. Finally, based on these features, we identified distinct cell types and circuits in PFC underlying chronic pain, an escalating healthcare challenge with limited molecular understanding. Collectively, this comprehensive map will facilitate decoding of discrete molecular, cellular and circuit mechanisms underlying specific PFC functions in health and disease.

Prelimbic area to lateral hypothalamus circuit drives social aggression

Controlling aggression is a vital skill in social species such as rodents and humans and has been associated with the medial prefrontal cortex (mPFC). In this study, we showed that during aggressive behavior, the activity of GABAergic neurons in the prelimbic area (PL) of the mPFC was significantly suppressed. Specific activation of GABAergic PL neurons significantly curbed male-to-male aggression and inhibited conditioned place preference (CPP) for aggression-paired contexts, whereas specific inhibition of GABAergic PL neurons brought about the opposite effect. Moreover, GABAergic projections from PL neurons to the lateral hypothalamus (LH) orexinergic neurons mediated aggressive behavior. Finally, directly modulated LH-orexinergic neurons influence aggressive behavior. These results suggest that GABAergic PL-orexinergic LH projection is an important control circuit for intermale aggressive behavior, both of which could be targets for curbing aggression.

Structural Organization of Perisomatic Inhibition in the Mouse Medial Prefrontal Cortex

Perisomatic inhibition profoundly controls neural function. However, the structural organization of inhibitory circuits giving rise to the perisomatic inhibition in the higher-order cortices is not completely known. Here, we performed a comprehensive analysis of those GABAergic cells in the medial prefrontal cortex (mPFC) that provide inputs onto the somata and proximal dendrites of pyramidal neurons. Our results show that most GABAergic axonal varicosities contacting the perisomatic region of superficial (layer 2/3) and deep (layer 5) pyramidal cells express parvalbumin (PV) or cannabinoid receptor type 1 (CB1). Further, we found that the ratio of PV/CB1 GABAergic inputs is larger on the somatic membrane surface of pyramidal tract neurons in comparison with those projecting to the contralateral hemisphere. Our morphologic analysis of in vitro labeled PV+ basket cells (PVBC) and CCK/CB1+ basket cells (CCKBC) revealed differences in many features. PVBC dendrites and axons arborized preferentially within the layer where their soma was located. In contrast, the axons of CCKBCs expanded throughout layers, although their dendrites were found preferentially either in superficial or deep layers. Finally, using anterograde trans-synaptic tracing we observed that PVBCs are preferentially innervated by thalamic and basal amygdala afferents in layers 5a and 5b, respectively. Thus, our results suggest that PVBCs can control the local circuit operation in a layer-specific manner via their characteristic arborization, whereas CCKBCs rather provide cross-layer inhibition in the mPFC.SIGNIFICANCE STATEMENT Inhibitory cells in cortical circuits are crucial for the precise control of local network activity. Nevertheless, in higher-order cortical areas that are involved in cognitive functions like decision-making, working memory, and cognitive flexibility, the structural organization of inhibitory cell circuits is not completely understood. In this study we show that perisomatic inhibitory control of excitatory cells in the medial prefrontal cortex is performed by two types of basket cells endowed with different morphologic properties that provide inhibitory inputs with distinct layer specificity on cells projecting to disparate areas. Revealing this difference in innervation strategy of the two basket cell types is a key step toward understanding how they fulfill their distinct roles in cortical network operations.

The Role of Ryanodine Receptor 2 in Drug-Associated Learning

Type-2 ryanodine receptor (RyR2) ion channels facilitate the release of Ca 2+ from stores and serve an important function in neuroplasticity. The role for RyR2 in hippocampal-dependent learning and memory is well established and chronic hyperphosphorylation of RyR2 (RyR2P) is associated with pathological calcium leakage and cognitive disorders, including Alzheimer's disease. By comparison, little is known about the role of RyR2 in the ventral medial prefrontal cortex (vmPFC) circuitry important for working memory, decision making, and reward seeking. Here, we evaluated the basal expression and localization of RyR2 and RyR2P in the vmPFC. Next, we employed an operant model of sucrose, cocaine, or morphine self-administration (SA) followed by a (reward-free) recall test, to reengage vmPFC neurons and reactivate reward-seeking and re-evaluated the expression and localization of RyR2 and RyR2P in vmPFC. Under basal conditions, RyR2 was expressed in pyramidal cells but not regularly detected in PV/SST interneurons. On the contrary, RyR2P was rarely observed in PFC somata and was restricted to a different subcompartment of the same neuron - the apical dendrites of layer-5 pyramidal cells. Chronic SA of drug (cocaine or morphine) and nondrug (sucrose) rewards produced comparable increases in RyR2 protein expression. However, recalling either drug reward impaired the usual localization of RyR2P in dendrites and markedly increased its expression in somata immunoreactive for Fos, a marker of highly activated neurons. These effects could not be explained by chronic stress or drug withdrawal and instead appeared to require a recall experience associated with prior drug SA. In addition to showing the differential distribution of RyR2/RyR2P and affirming the general role of vmPFC in reward learning, this study provides information on the propensity of addictive drugs to redistribute RyR2P ion channels in a neuronal population engaged in drug-seeking. Hence, focusing on the early impact of addictive drugs on RyR2 function may serve as a promising approach to finding a treatment for substance use disorders.

Prefrontal cortical regulation of REM sleep

Rapid eye movement (REM) sleep is accompanied by intense cortical activity, underlying its wake-like electroencephalogram. The neural activity inducing REM sleep is thought to originate from subcortical circuits in brainstem and hypothalamus. However, whether cortical neurons can also trigger REM sleep has remained unknown. Here we show in mice that the medial prefrontal cortex (mPFC) strongly promotes REM sleep. Bidirectional optogenetic manipulations demonstrate that excitatory mPFC neurons promote REM sleep through their projections to the lateral hypothalamus and regulate phasic events, reflected in accelerated electroencephalogram theta oscillations and increased eye movement density during REM sleep. Calcium imaging reveals that the majority of lateral hypothalamus-projecting mPFC neurons are maximally activated during REM sleep and a subpopulation is recruited during phasic theta accelerations. Our results delineate a cortico-hypothalamic circuit for the top-down control of REM sleep and identify a critical role of the mPFC in regulating phasic events during REM sleep.

Inactivation of medial or lateral orbitofrontal cortex during fear extinction did not interfere with fear renewal

Hyperactive orbitofrontal cortical activation is commonly seen in patients of obsessive-compulsive disorder (OCD). Previous studies from our laboratory showed that for rats with aberrant activation of the orbitofrontal cortex (OFC) during the extinction phase, they were unable to use contexts as the reference for proper retrieval of fear memory during renewal test. This result supported the phenomenon that many OCD patients show poor regulation of fear-related behavior. Since there are robust anatomical connections of the OFC with the fear-circuit, we aim to further examine whether the OFC is actively engaged in fear regulation under normal circumstances. In this study, the lateral or medial OFC was inactivated during the extinction phase using the ABA fear renewal procedure. We found that these animals showed intact fear renewal during retrieval test with their freezing levels equivalent to the control rats, revealing that the OFC did not have decisive roles in extinction acquisition. Together with our previous study, we suggest that the OFC only interferes with fear regulation when it becomes pathophysiologically hyperactive.

The Basolateral Amygdala: The Core of a Network for Threat Conditioning, Extinction, and Second-Order Threat Conditioning

Threat conditioning, extinction, and second-order threat conditioning studied in animal models provide insight into the brain-based mechanisms of fear- and anxiety-related disorders and their treatment. Much attention has been paid to the role of the basolateral amygdala (BLA) in such processes, an overview of which is presented in this review. More recent evidence suggests that the BLA serves as the core of a greater network of structures in these forms of learning, including associative and sensory cortices. The BLA is importantly regulated by hippocampal and prefrontal inputs, as well as by the catecholaminergic neuromodulators, norepinephrine and dopamine, that may provide important prediction-error or learning signals for these forms of learning. The sensory cortices may be required for the long-term storage of threat memories. As such, future research may further investigate the potential of the sensory cortices for the long-term storage of extinction and second-order conditioning memories.

Activation patterns in male and female forebrain circuitries during food consumption under novelty

The influence of novelty on feeding behavior is significant and can override both homeostatic and hedonic drives due to the uncertainty of potential danger. Previous work found that novel food hypophagia is enhanced in a novel environment and that males habituate faster than females. The current study's aim was to identify the neural substrates of separate effects of food and context novelty. Adult male and female rats were tested for consumption of a novel or family food in either a familiar or in a novel context. Test-induced Fos expression was measured in the amygdalar, thalamic, striatal, and prefrontal cortex regions that are important for appetitive responding, contextual processing, and reward motivation. Food and context novelty induced strikingly different activation patterns. Novel context induced Fos robustly in almost every region analyzed, including the central (CEA) and basolateral complex nuclei of the amygdala, the thalamic paraventricular (PVT) and reuniens nuclei, the nucleus accumbens (ACB), the medial prefrontal cortex prelimbic and infralimbic areas, and the dorsal agranular insular cortex (AI). Novel food induced Fos in a few select regions: the CEA, anterior basomedial nucleus of the amygdala, anterior PVT, and posterior AI. There were also sex differences in activation patterns. The capsular and lateral CEA had greater activation for male groups and the anterior PVT, ACB ventral core and shell had greater activation for female groups. These activation patterns and correlations between regions, suggest that distinct functional circuitries control feeding behavior when food is novel and when eating occurs in a novel environment.

Harnessing axonal transport to map reward circuitry: Differing brain-wide projections from medial forebrain domains

Neurons project long axons that contact other distant neurons. Projections can be mapped by hijacking endogenous membrane trafficking machinery by introducing tracers. To witness functional connections in living animals, we developed a tracer detectible by magnetic resonance imaging (MRI), Mn(II). Mn(II) relies on kinesin-1 and amyloid-precursor protein to travel out axons. Within 24h, projection fields of cortical neurons can be mapped brain-wide with this technology. MnCl2 was stereotactically injected either into anterior cingulate area (ACA) or into infralimbic/prelimbic (IL/PL) of medial forebrain (n=10-12). Projections were imaged, first by manganese-enhanced MRI (MEMRI) live, and then after fixation by microscopy. MR images were collected at 100μm isotropic resolution (~5 neurons) in 3D at four time points: before and at successive time points after injections. Images were preprocessed by masking non-brain tissue, followed by intensity scaling and spatial alignment. Actual injection locations, measured from post-injection MR images, were found to be 0.06, 0.49 and 0.84mm apart between cohorts, in R-L, A-P, and D-V directions respectively. Mn(II) enhancements arrived in hindbrains by 24h in both cohorts, while co-injected rhodamine dextran was not detectible beyond immediate subcortical projections. Data-driven unbiased voxel-wise statistical maps after ACA injections revealed significant progression of Mn(II) distally into deeper brain regions: globus pallidus, dorsal striatum, amygdala, hypothalamus, substantia nigra, dorsal raphe and locus coeruleus. Accumulation was quantified as a fraction of total volume of each segment containing significantly enhanced voxels (fractional accumulation volumes), and results visualized in column graphs. Unpaired t-tests between groups of brain-wide voxel-wise intensity profiling by either region of interest (ROI) measurements or statistical parametric mapping highlighted distinct differences in distal accumulation between injection sites, with ACA projecting to periaqueductal gray and IL/PL to basolateral amygdala (p<0.001 FDR). Mn(II) distal accumulations differed dramatically between injection groups in subdomains of the hypothalamus, with ACA targeting dorsal medial, periventricular region and mammillary body nuclei, while IL/PL went to anterior hypothalamic areas and lateral hypothalamic nuclei. Given that these hypothalamic subsegments communicate activity in the central nervous system to the body, these observations describing distinct forebrain projection fields will undoubtedly lead to newer insights in mind-body relationships.