Hypothalamic Circuits for Predation and Evasion

Hierarchical Representations of Aggression in a Hypothalamic-Midbrain Circuit

Although the ventromedial hypothalamus ventrolateral area (VMHvl) is now well established as a critical locus for the generation of conspecific aggression, its role is complex, with neurons responding during multiple phases of social interactions with both males and females. It has been previously unclear how the brain uses this complex multidimensional signal and coordinates a discrete action: the attack. Here, we find a hypothalamic-midbrain circuit that represents hierarchically organized social signals during aggression. Optogenetic-assisted circuit mapping reveals a preferential projection from VMHvlvGlut2 to lPAGvGlut2 cells, and inactivation of downstream lPAGvGlut2 populations results in aggression-specific deficits. lPAG neurons are selective for attack action and exhibit short-latency, time-locked spiking relative to the activity of jaw muscles during biting. Last, we find that this projection conveys male-biased signals from the VMHvl to downstream lPAGvGlut2 neurons that are sensitive to features of ongoing activity, suggesting that action selectivity is generated by a combination of pre- and postsynaptic mechanisms.

Regulation of aggressive behaviors by nicotinic acetylcholine receptors: Animal models, human genetics, and clinical studies

Neuropsychiatric disorders are frequently complicated by aggressive behaviors. For some individuals, existing behavioral and psychopharmacological treatments are ineffective or confer significant side effects, necessitating development of new ways to treat patients with severe aggression. Nicotinic acetylcholine receptors (nAChRs) are a large and diverse family of ligand-gated ion channels expressed throughout the brain that influence behaviors highly relevant for neuropsychiatric disorders, including attention, mood, and impulsivity. Nicotine and other drugs targeting nAChRs can reduce aggression in animal models of offensive, defensive, and predatory aggression, as well as in human laboratory studies. Human genetic studies have suggested a relationship between the CHRNA7 gene encoding the alpha-7 nAChR and aggressive behavior, although these effects are heterogeneous and strongly influenced by genetic background and environment. Here we review animal, human genetic, and clinical studies supporting a consistent role of nicotine and nAChR signaling in modulation of aggressive behaviors. We integrate findings from recent studies of aggression neuroscience, discuss the circuitry that may be involved in these effects of nAChRs, and identify multiple key questions that must be answered prior to safe and effective translation for human patients. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Role of spontaneous and sensory orexin network dynamics in rapid locomotion initiation

Appropriate motor control is critical for normal life, and requires hypothalamic hypocretin/orexin neurons (HONs). HONs are slowly regulated by nutrients, but also display rapid (subsecond) activity fluctuations in vivo. The necessity of these activity bursts for sensorimotor control and their roles in specific phases of movement are unknown. Here we show that temporally-restricted optosilencing of spontaneous or sensory-evoked HON bursts disrupts locomotion initiation, but does not affect ongoing locomotion. Conversely, HON optostimulation initiates locomotion with subsecond delays in a frequency-dependent manner. Using 2-photon volumetric imaging of activity of >300 HONs during sensory stimulation and self-initiated locomotion, we identify several locomotion-related HON subtypes, which distinctly predict the probability of imminent locomotion initiation, display distinct sensory responses, and are differentially modulated by food deprivation. By causally linking HON bursts to locomotion initiation, these findings reveal the sensorimotor importance of rapid spontaneous and evoked fluctuations in HON ensemble activity.

The Raphe Dopamine System Controls the Expression of Incentive Memory

The brain dopamine (DA) system participates in forming and expressing memory. Despite a well-established role of DA neurons in the ventral tegmental area in memory formation, the exact DA circuits that control memory expression remain unclear. Here, we show that DA neurons in the dorsal raphe nucleus (DRN) and their medulla input control the expression of incentive memory. DRN DA neurons are activated by both rewarding and aversive stimuli in a learning-dependent manner and exhibit elevated activity during memory recall. Disrupting their physiological activity or DA synthesis blocks the expression of natural appetitive and aversive memories as well as drug memories associated with opioids. Moreover, a glutamatergic pathway from the lateral parabrachial nucleus to the DRN selectively regulates the expression of reward memories associated with opioids or foods. Our study reveals a specialized DA subsystem important for memory expression and suggests new targets for interventions against opioid addiction.

The neurobiology of innate and learned vocalizations in rodents and songbirds

Vocalizations are an important medium for sexual and social signaling in mammals and birds. In most mammals other than humans, vocalizations are specified by innate mechanisms and develop normally in the absence of auditory experience. By contrast, juvenile songbirds memorize and copy the songs of adult tutors, a process with many parallels to human speech learning. Despite the centrality of vocal learning to human speech, vocal production in humans as well as in songbirds exploits ancestral circuitry for innate vocalizations, and effective vocal communication depends on the fluent blending of innate and learned elements. This review covers recent advances in our understanding of central mechanisms for learned and innate vocalizations in birds and mice, including brainstem mechanisms that help to 'gate' vocalizations on or off, cortical involvement in learned and innate vocalizations, and the delineation of circuits that evaluate and reinforce song performance to facilitate vocal learning.

Choosing to urinate. Circuits and mechanisms underlying voluntary urination

The decision to urinate is a social behavior that is calculated multiple times a day. Many animals perform urine scent-marking which broadcasts their pheromones to regulate the behavior of others and humans are trained at an early age to urinate only at a socially acceptable time and place. The inability to control when and where to void, that is incontinence, causes extreme social discomfort yet targeted therapeutics are lacking because little is known about the underlying circuits and mechanisms. The use of animal models, neurocircuit analysis, and functional manipulation is beginning to reveal basic logic of the circuit that modulates the decision of when and where to void.

Neural Regulation of Feeding Behavior

Food intake and energy homeostasis determine survival of the organism and species. Information on total energy levels and metabolic state are sensed in the periphery and transmitted to the brain, where it is integrated and triggers the animal to forage, prey, and consume food. Investigating circuitry and cellular mechanisms coordinating energy balance and feeding behaviors has drawn on many state-of-the-art techniques, including gene manipulation, optogenetics, virus tracing, and single-cell sequencing. These new findings provide novel insights into how the central nervous system regulates food intake, and shed the light on potential therapeutic interventions for eating-related disorders such as obesity and anorexia.

The role of the periaqueductal gray in escape behavior

Escape behavior is a defensive action deployed by animals in response to imminent threats. In mammalian species, a variety of different brain circuits are known to participate in this crucial survival behavior. One of these circuits is the periaqueductal gray, a midbrain structure that can command a variety of instinctive behaviors. Recent experiments using modern systems neuroscience techniques have begun to elucidate the specific role of the periaqueductal gray in controlling escape. These have shown that periaqueductal gray neurons are crucial units for gating and commanding the initiation of escape, specifically activated in situations of imminent, escapable threat. In addition, it is becoming clear that the periaqueductal gray integrates brain-wide information that can modulate escape initiation to generate flexible defensive behaviors.

Sources of off-target expression from recombinase-dependent AAV vectors and mitigation with cross-over insensitive ATG-out vectors

In combination with transgenic mouse lines expressing Cre or Flp recombinases in defined cell types, recombinase-dependent adeno-associated viruses (AAVs) have become the tool of choice for localized cell-type-targeted gene expression. Unfortunately, applications of this technique when expressing highly sensitive transgenes are impeded by off-target, or "leak" expression, from recombinase-dependent AAVs. We investigated this phenomenon and find that leak expression is mediated by both infrequent transcription from the inverted transgene in recombinant-dependent AAV designs and recombination events during bacterial AAV plasmid production. Recombination in bacteria is mediated by homology across the antiparallel recombinase-specific recognition sites present in recombinase-dependent designs. To address both of these issues we designed an AAV vector that uses mutant "cross-over insensitive" recognition sites combined with an "ATG-out" design. We show that these CIAO (cross-over insensitive ATG-out) vectors virtually eliminate leak expression. CIAO vectors provide reliable and targeted transgene expression and are extremely useful for recombinase-dependent expression of highly sensitive transgenes.

Stress experience and hormone feedback tune distinct components of hypothalamic CRH neuron activity

Stress leaves a lasting impression on an organism and reshapes future responses. However, the influence of past experience and stress hormones on the activity of neural stress circuits remains unclear. Hypothalamic corticotropin-releasing hormone (CRH) neurons orchestrate behavioral and endocrine responses to stress and are themselves highly sensitive to corticosteroid (CORT) stress hormones. Here, using in vivo optical recordings, we find that CRH neurons are rapidly activated in response to stress. CRH neuron activity robustly habituates to repeated presentations of the same, but not novel stressors. CORT feedback has little effect on CRH neuron responses to acute stress, or on habituation to repeated stressors. Rather, CORT preferentially inhibits tonic CRH neuron activity in the absence of stress stimuli. These findings reveal how stress experience and stress hormones modulate distinct components of CRH neuronal activity to mediate stress-induced adaptations.

Stress activates corticotropin-releasing hormone (CRH) neurons in the hypothalamus, but how their activity is regulated during and after stress is unclear. Here, the authors show that stress habituation and corticosteroid feedback tune different components of CRH neuron activity.

Defined Cell Types in Superior Colliculus Make Distinct Contributions to Prey Capture Behavior in the Mouse

The superior colliculus (SC) plays a highly conserved role in visual processing and mediates visual orienting behaviors across species, including both overt motor orienting [1, 2] and orienting of attention [3, 4]. To determine the specific circuits within the superficial superior colliculus (sSC) that drive orienting and approach behavior toward appetitive stimuli, we explored the role of three genetically defined cell types in mediating prey capture in mice. Chemogenetic inactivation of two classically defined cell types, the wide-field (WF) and narrow-field (NF) vertical neurons, revealed that they are involved in distinct aspects of prey capture. WF neurons were required for rapid prey detection and distant approach initiation, whereas NF neurons were required for accurate orienting during pursuit as well as approach initiation and continuity. In contrast, prey capture did not require parvalbumin-expressing (PV) neurons that have previously been implicated in fear responses. The visual coding and projection targets of WF and NF cells were consistent with their roles in prey detection versus pursuit, respectively. Thus, our studies link specific neural circuit connectivity and function with stimulus detection and orienting behavior, providing insight into visuomotor and attentional mechanisms mediated by superior colliculus.

Pretectal neurons control hunting behaviour

For many species, hunting is an innate behaviour that is crucial for survival, yet the circuits that control predatory action sequences are poorly understood. We used larval zebrafish to identify a population of pretectal neurons that control hunting. By combining calcium imaging with a virtual hunting assay, we identified a discrete pretectal region that is selectively active when animals initiate hunting. Targeted genetic labelling allowed us to examine the function and morphology of individual cells and identify two classes of pretectal neuron that project to ipsilateral optic tectum or the contralateral tegmentum. Optogenetic stimulation of single neurons of either class was able to induce sustained hunting sequences, in the absence of prey. Furthermore, laser ablation of these neurons impaired prey-catching and prevented induction of hunting by optogenetic stimulation of the anterior-ventral tectum. We propose that this specific population of pretectal neurons functions as a command system to induce predatory behaviour.

The amygdala differentially regulates defensive behaviors evoked by CO2

CO₂ inhalation can provoke panic attacks in humans, and the likelihood is increased in patients with panic disorder. Identifying brain sites involved could provide important mechanistic insight into the illness. In mice, the amygdala has been suggested to promote CO₂ responses; however, recent studies in humans with amygdala damage indicate the amygdala is not required for CO₂-induced fear and panic and might actually oppose these responses. To clarify the role of the amygdala, we produced lesions in mice paralleling the human lesions, and characterized behavioral responses to CO₂. Compared to sham controls, we found that amygdala-lesioned mice froze less to 10% CO₂, and unlike shams they also began to jump frenetically. At 20% CO₂, controls also exhibited jumping, suggesting it is a normal response to more extreme CO₂ concentrations. The effect of amygdala lesions was specific to CO₂ as amygdala-lesioned mice did not jump in response to a predator odor or to an auditory conditioned stimulus. In amygdala-lesioned mice, jumping evoked by 10% CO₂ was eliminated by co-lesioning the dorsal periaqueductal gray, a structure implicated in panic and escape-related behaviors. Together, these observations suggest a dual role for the amygdala in the CO₂ response: promoting CO₂-induced freezing, and opposing CO₂-induced jumping, which may help explain the exaggerated CO₂ responses in humans with amygdala lesions.

Food Craving, Seeking, and Consumption Behaviors: Conceptual Phases and Assessment Methods Used in Animal and Human Studies

What drives us to eat? It is one of the most fundamental questions in the obesity research field which have been investigated for centuries. Numerous novel in vivo technologies in the neuroscience field allows us to reevaluate the multiple components and phases of food-related behaviors. Focused on the cognitive, executive, behavioral and temporal aspects, food-related behaviors can be distinguished into appetitive phase (food craving→food seeking) and consummatory phase (food consumption). Food craving phase is an internal state or stage in which the animal has the motivation to eat the food but there is no actual food specific behaviors or actions. Food seeking phase entails repeated behaviors with a food searching purpose until the animal discovers the food (or food-related cue) and the approach behavior stage after the discovery of food. Food consumption phase is the step that the animal grabs, chews and intake the food. This review will specifically focus on characteristics and evaluation methods for each phase of food-related behavior in rodent, non-human primates and human.

A Specialized Neural Circuit Gates Social Vocalizations in the Mouse

Vocalizations are fundamental to mammalian communication, but the underlying neural circuits await detailed characterization. Here, we used an intersectional genetic method to label and manipulate neurons in the midbrain periaqueductal gray (PAG) that are transiently active in male mice when they produce ultrasonic courtship vocalizations (USVs). Genetic silencing of PAG-USV neurons rendered males unable to produce USVs and impaired their ability to attract females. Conversely, activating PAG-USV neurons selectively triggered USV production, even in the absence of any female cues. Optogenetic stimulation combined with axonal tracing indicates that PAG-USV neurons gate downstream vocal-patterning circuits. Indeed, activating PAG neurons that innervate the nucleus retroambiguus, but not those innervating the parabrachial nucleus, elicited USVs in both male and female mice. These experiments establish that a dedicated population of PAG neurons gives rise to a descending circuit necessary and sufficient for USV production while also demonstrating the communicative salience of male USVs. VIDEO ABSTRACT.

Direct auditory cortical input to the lateral periaqueductal gray controls sound-driven defensive behavior

Threatening sounds can elicit a series of defensive behavioral reactions in animals for survival, but the underlying neural substrates are not fully understood. Here, we demonstrate a previously unexplored neural pathway in mice that projects directly from the auditory cortex (ACx) to the lateral periaqueductal gray (lPAG) and controls noise-evoked defensive behaviors. Electrophysiological recordings showed that the lPAG could be excited by a loud noise that induced an escape-like behavior. Trans-synaptic viral tracing showed that a great number of glutamatergic neurons, rather than GABAergic neurons, in the lPAG were directly innervated by those in layer V of the ACx. Activation of this pathway by optogenetic manipulations produced a behavior in mice that mimicked the noise-evoked escape, whereas inhibition of the pathway reduced this behavior. Therefore, our newly identified descending pathway is a novel neural substrate for noise-evoked escape and is involved in controlling the threat-related behavior.

A striatal interneuron circuit for continuous target pursuit

Most adaptive behaviors require precise tracking of targets in space. In pursuit behavior with a moving target, mice use distance to target to guide their own movement continuously. Here, we show that in the sensorimotor striatum, parvalbumin-positive fast-spiking interneurons (FSIs) can represent the distance between self and target during pursuit behavior, while striatal projection neurons (SPNs), which receive FSI projections, can represent self-velocity. FSIs are shown to regulate velocity-related SPN activity during pursuit, so that movement velocity is continuously modulated by distance to target. Moreover, bidirectional manipulation of FSI activity can selectively disrupt performance by increasing or decreasing the self-target distance. Our results reveal a key role of the FSI-SPN interneuron circuit in pursuit behavior and elucidate how this circuit implements distance to velocity transformation required for the critical underlying computation.

Many natural behaviours involve tracking of a target in space. Here, the authors describe a task to assess this behaviour in mice and use in vivo electrophysiology, calcium imaging, optogenetics, and chemogenetics to investigate the role of the striatum in target pursuit.

Nucleus Isthmi Is Required to Sustain Target Pursuit during Visually Guided Prey-Catching

Animals must frequently perform a sequence of behaviors to achieve a specific goal. However, the neural mechanisms that promote the continuation and completion of such action sequences are not well understood. Here, we characterize the anatomy, physiology, and function of the nucleus isthmi (NI), a cholinergic nucleus thought to modulate tectal-dependent, goal-directed behaviors. We find that the larval zebrafish NI establishes reciprocal connectivity with the optic tectum and identify two distinct types of isthmic projection neuron that either connect ipsilaterally to retinorecipient laminae of the tectum and pretectum or bilaterally to both tectal hemispheres. Laser ablation of NI caused highly specific deficits in tectally mediated loom-avoidance and prey-catching behavior. In the context of hunting, NI ablation did not affect prey detection or hunting initiation but resulted in larvae failing to sustain prey-tracking sequences and aborting their hunting routines. Moreover, calcium imaging revealed elevated neural activity in NI following onset of hunting behavior. We propose a model in which NI provides state-dependent feedback facilitation to the optic tectum and pretectum to potentiate neural activity and increase the probability of consecutive prey-tracking maneuvers during hunting sequences.

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Nucleus isthmi contains two types of neuron with distinct (pre)-tectal connectivity

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Neural activity in nucleus isthmi is recruited at onset of hunting behavior

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Nucleus isthmi is required for maintenance, but not initiation, of hunting routines

Recent Advancements Surrounding the Role of the Periaqueductal Gray in Predators and Prey

Recent advances in neural circuitry techniques, like optogenetics and chemogenetics, have allowed for a greater understanding of the periaqueductal gray (PAG) and its importance in predator and prey behaviors. These studies in rodents have highlighted the role of the rostrolateral PAG in hunting behaviors, and have demonstrated functional differences across the dorsal-ventral/rostral-caudal axes of the PAG associated with defensive behaviors. Human imaging studies have further demonstrated that the PAG is active during situations involving imminent threat suggesting that the function of the PAG is likely largely conserved across species. This mini-review article highlights some of the recent advancements towards our understanding of the functional neuroanatomy of the PAG and its importance in the predator and prey behaviors that are critical for survival.

Long-term Fiber Photometry for Neuroscience Studies

Fiber photometry is a sensitive and easy way to detect changes in fluorescent signals. The combination of fiber photometry with various fluorescent biomarkers has substantially advanced neuroscience research over the last decade. Despite the wide use of fiber photometry in biomedical fields, the lack of a detailed and comprehensive protocol has limited progress and sometimes complicated the interpretation of data. Here, we describe detailed procedures of fiber photometry for the long-term monitoring of neuronal activity in freely-behaving animals, including surgery, apparatus setup, data collection, and analysis.

What, If, and When to Move: Basal Ganglia Circuits and Self-Paced Action Initiation

Deciding what to do and when to move is vital to our survival. Clinical and fundamental studies have identified basal ganglia circuits as critical for this process. The main input nucleus of the basal ganglia, the striatum, receives inputs from frontal, sensory, and motor cortices and interconnected thalamic areas that provide information about potential goals, context, and actions and directly or indirectly modulates basal ganglia outputs. The striatum also receives dopaminergic inputs that can signal reward prediction errors and also behavioral transitions and movement initiation. Here we review studies and models of how direct and indirect pathways can modulate basal ganglia outputs to facilitate movement initiation, and we discuss the role of cortical and dopaminergic inputs to the striatum in determining what to do and if and when to do it. Complex but exciting scenarios emerge that shed new light on how basal ganglia circuits modulate self-paced movement initiation.

Central Processing of Itch in the Midbrain Reward Center

Itch is an aversive sensation that evokes a desire to scratch. Paradoxically, scratching the itch also produces a hedonic experience. The specific brain circuits processing these different aspects of itch, however, remain elusive. Here, we report that GABAergic (GABA) and dopaminergic (DA) neurons in the ventral tegmental area (VTA) are activated with different temporal patterns during acute and chronic itch. DA neuron activation lags behind GABA neurons and is dependent on scratching of the itchy site. Optogenetic manipulations of VTA GABA neurons rapidly modulated scratching behaviors through encoding itch-associated aversion. In contrast, optogenetic manipulations of VTA DA neurons revealed their roles in sustaining recurrent scratching episodes through signaling scratching-induced reward. A similar dichotomy exists for the role of VTA in chronic itch. These findings advance understanding of circuit mechanisms of the unstoppable itch-scratch cycles and shed important insights into chronic itch therapy.

Cognitive Control of Escape Behaviour

When faced with potential predators, animals instinctively decide whether there is a threat they should escape from, and also when, how, and where to take evasive action. While escape is often viewed in classical ethology as an action that is released upon presentation of specific stimuli, successful and adaptive escape behaviour relies on integrating information from sensory systems, stored knowledge, and internal states. From a neuroscience perspective, escape is an incredibly rich model that provides opportunities for investigating processes such as perceptual and value-based decision-making, or action selection, in an ethological setting. We review recent research from laboratory and field studies that explore, at the behavioural and mechanistic levels, how elements from multiple information streams are integrated to generate flexible escape behaviour.

Single-cell transcriptomic analysis of the lateral hypothalamic area reveals molecularly distinct populations of inhibitory and excitatory neurons

The lateral hypothalamic area (LHA) coordinates an array of fundamental behaviors, including sleeping, waking, feeding, stress and motivated behavior. The wide spectrum of functions ascribed to the LHA may be explained by a heterogeneous population of neurons, the full diversity of which is poorly understood. We employed a droplet-based single-cell RNA-sequencing approach to develop a comprehensive census of molecularly distinct cell types in the mouse LHA. Neuronal populations were classified based on fast neurotransmitter phenotype and expression of neuropeptides, transcription factors and synaptic proteins, among other gene categories. We define 15 distinct populations of glutamatergic neurons and 15 of GABAergic neurons, including known and novel cell types. We further characterize a novel population of somatostatin-expressing neurons through anatomical and behavioral approaches, identifying a role for these neurons in specific forms of innate locomotor behavior. This study lays the groundwork for better understanding the circuit-level underpinnings of LHA function.

A lateral hypothalamus to basal forebrain neurocircuit promotes feeding by suppressing responses to anxiogenic environmental cues

Animals must consider competing information before deciding to eat: internal signals indicating the desirability of food and external signals indicating the risk involved in eating within a particular environment. The behaviors driven by the former are manifestations of hunger, and the latter, anxiety. The connection between pathologic anxiety and reduced eating in conditions like typical depression and anorexia is well known. Conversely, anti-anxiety drugs such as benzodiazepines increase appetite. Here, we show that GABAergic neurons in the diagonal band of Broca (DBB^GABA) are responsive to indications of risk and receive monosynaptic inhibitory input from lateral hypothalamus GABAergic neurons (LH^GABA). Activation of this circuit reduces anxiety and causes indiscriminate feeding. We also found that diazepam rapidly reduces DBB^GABA activity while inducing indiscriminate feeding. Our study reveals that the LH^GABA→DBB^GABA neurocircuit overrides anxiogenic environmental cues to allow feeding and that this pathway may underlie the link between eating and anxiety-related disorders.

A hypothalamus-habenula circuit controls aversion

Encoding and predicting aversive events are critical functions of circuits that support survival and emotional well-being. Maladaptive circuit changes in emotional valence processing can underlie the pathophysiology of affective disorders. The lateral habenula (LHb) has been linked to aversion and mood regulation through modulation of the dopamine and serotonin systems. We have defined the identity and function of glutamatergic (Vglut2) control of the LHb, comparing the role of inputs originating in the globus pallidus internal segment (GPi), and lateral hypothalamic area (LHA), respectively. We found that LHb-projecting LHA neurons, and not the proposed GABA/glutamate co-releasing GPi neurons, are responsible for encoding negative value. Monosynaptic rabies tracing of the presynaptic organization revealed a predominantly limbic input onto LHA Vglut2 neurons, while sensorimotor inputs were more prominent onto GABA/glutamate co-releasing GPi neurons. We further recorded the activity of LHA Vglut2 neurons, by imaging calcium dynamics in response to appetitive versus aversive events in conditioning paradigms. LHA Vglut2 neurons formed activity clusters representing distinct reward or aversion signals, including a population that responded to mild foot shocks and predicted aversive events. We found that the LHb-projecting LHA Vglut2 neurons encode negative valence and rapidly develop a prediction signal for negative events. These findings establish the glutamatergic LHA-LHb circuit as a critical node in value processing.

A Neural Circuit Mechanism for Encoding Aversive Stimuli in the Mesolimbic Dopamine System

Ventral tegmental area (VTA) dopamine (DA) neurons play a central role in mediating motivated behaviors, but the circuitry through which they signal positive and negative motivational stimuli is incompletely understood. Using in vivo fiber photometry, we simultaneously recorded activity in DA terminals in different nucleus accumbens (NAc) subnuclei during an aversive and reward conditioning task. We find that DA terminals in the ventral NAc medial shell (vNAcMed) are excited by unexpected aversive outcomes and to cues that predict them, whereas DA terminals in other NAc subregions are persistently depressed. Excitation to reward-predictive cues dominated in the NAc lateral shell and was largely absent in the vNAcMed. Moreover, we demonstrate that glutamatergic (VGLUT2-expressing) neurons in the lateral hypothalamus represent a key afferent input for providing information about aversive outcomes to vNAcMed-projecting DA neurons. Collectively, we reveal the distinct functional contributions of separate mesolimbic DA subsystems and their afferent pathways underlying motivated behaviors. VIDEO ABSTRACT.

AGRP Neurons Project to the Medial Preoptic Area and Modulate Maternal Nest-Building

AGRP (agouti-related neuropeptide) expressing inhibitory neurons sense caloric needs of an animal to coordinate homeostatic feeding. Recent evidence suggests that AGRP neurons also suppress competing actions and motivations to mediate adaptive behavioral selection during starvation. Here, in adult mice of both sexes we show that AGRP neurons form inhibitory synapses onto ∼30% neurons in the medial preoptic area (mPOA), a region critical for maternal care. Remarkably, optogenetically stimulating AGRP neurons decreases maternal nest-building while minimally affecting pup retrieval, partly recapitulating suppression of maternal behaviors during food restriction. In parallel, optogenetically stimulating AGRP projections to the mPOA or to the paraventricular nucleus of hypothalamus but not to the LHA (lateral hypothalamus area) similarly decreases maternal nest-building. Chemogenetic inhibition of mPOA neurons that express Vgat (vesicular GABA transporter), the population targeted by AGRP terminals, also decreases maternal nest-building. In comparison, chemogenetic inhibition of neurons in the LHA that express vesicular glutamate transporter 2, another hypothalamic neuronal population critical for feeding and innate drives, is ineffective. Importantly, nest-building during low temperature thermal challenge is not affected by optogenetic stimulation of AGRP→mPOA projections. Finally, via optogenetic activation and inhibition we show that distinctive subsets of mPOA Vgat+ neurons likely underlie pup retrieval and maternal nest-building. Together, these results show that AGRP neurons can modulate maternal nest-building, in part through direct projections to the mPOA. This study corroborates other recent discoveries and underscores the broad functions that AGRP neurons play in antagonizing rivalry motivations to modulate behavioral outputs during hunger.SIGNIFICANCE STATEMENT In order for animals to initiate ethologically appropriate behaviors, they must typically decide between behavioral repertoires driven by multiple and often conflicting internal states. How neural pathways underlying individual behaviors interact to coherently modulate behavioral outputs, in particular to achieve a proper balance between behaviors that serve immediate individual needs versus those that benefit the propagation of the species, remains poorly understood. Here, by investigating projections from a neuronal population known to drive hunger behaviors to a brain region critical for maternal care, we show that activation of AGRP→mPOA projections in females dramatically inhibits maternal nest-building while leaving mostly intact pup retrieval behavior. Our findings shed new light on neural organization of behaviors and neural mechanisms that coordinate behavioral selection.

Neural Circuit Motifs in Valence Processing

How do our brains determine whether something is good or bad? How is this computational goal implemented in biological systems? Given the critical importance of valence processing for survival, the brain has evolved multiple strategies to solve this problem at different levels. The psychological concept of "emotional valence" is now beginning to find grounding in neuroscience. This review aims to bridge the gap between psychology and neuroscience on the topic of emotional valence processing. Here, I highlight a subset of studies that exemplify circuit motifs that repeatedly appear as implementational systems in valence processing. The motifs I identify as being important in valence processing include (1) Labeled Lines, (2) Divergent Paths, (3) Opposing Components, and (4) Neuromodulatory Gain. Importantly, the functionality of neural substrates in valence processing is dynamic, context-dependent, and changing across short and long timescales due to synaptic plasticity, competing mechanisms, and homeostatic need.

Cholinergic modulation of spatial learning, memory and navigation

Spatial learning, including encoding and retrieval of spatial memories as well as holding spatial information in working memory generally serving navigation under a broad range of circumstances, relies on a network of structures. While central to this network are medial temporal lobe structures with a widely appreciated crucial function of the hippocampus, neocortical areas such as the posterior parietal cortex and the retrosplenial cortex also play essential roles. Since the hippocampus receives its main subcortical input from the medial septum of the basal forebrain (BF) cholinergic system, it is not surprising that the potential role of the septo-hippocampal pathway in spatial navigation has been investigated in many studies. Much less is known of the involvement in spatial cognition of the parallel projection system linking the posterior BF with neocortical areas. Here we review the current state of the art of the division of labour within this complex 'navigation system', with special focus on how subcortical cholinergic inputs may regulate various aspects of spatial learning, memory and navigation.

Emotion and the Cardiovascular System: Postulated Role of Inputs From the Medial Prefrontal Cortex to the Dorsolateral Periaqueductal Gray

The midbrain periaqueductal gray (PAG) plays a major role in generating different types of behavioral responses to emotional stressors. This review focuses on the role of the dorsolateral (dl) portion of the PAG, which on the basis of anatomical and functional studies, appears to have a unique and distinctive role in generating behavioral, cardiovascular and respiratory responses to real and perceived emotional stressors. In particular, the dlPAG, but not other parts of the PAG, receives direct inputs from the primary auditory cortex and from the secondary visual cortex. In addition, there are strong direct inputs to the dlPAG, but not other parts of the PAG, from regions within the medial prefrontal cortex that in primates correspond to cortical areas 10 m, 25 and 32. I first summarise the evidence that the inputs to the dlPAG arising from visual, auditory and olfactory signals trigger defensive behavioral responses supported by appropriate cardiovascular and respiratory effects, when such signals indicate the presence of a real external threat, such as the presence of a predator. I then consider the functional roles of the direct inputs from the medial prefrontal cortex, and propose the hypothesis that these inputs are activated by perceived threats, that are generated as a consequence of complex cognitive processes. I further propose that the inputs from areas 10 m, 25 and 32 are activated under different circumstances. The input from cortical area 10 m is of special interest, because this cortical area exists only in primates and is much larger in the brain of humans than in all other primates.

Extending the Time Domain of Neuronal Silencing with Cryptophyte Anion Channelrhodopsins

Optogenetic inhibition of specific neuronal types in the brain enables analysis of neural circuitry and is promising for the treatment of a number of neurological disorders. Anion channelrhodopsins (ACRs) from the cryptophyte alga Guillardia theta generate larger photocurrents than other available inhibitory optogenetic tools, but more rapid channels are needed for temporally precise inhibition, such as single-spike suppression, of high-frequency firing neurons. Faster ACRs have been reported, but their potential advantages for time-resolved inhibitory optogenetics have not so far been verified in neurons. We report RapACR, nicknamed so for "rapid," an ACR from Rhodomonas salina, that exhibits channel half-closing times below 10 ms and achieves equivalent inhibition at 50-fold lower light intensity in lentivirally transduced cultured mouse hippocampal neurons as the second-generation engineered Cl--conducting channelrhodopsin iC++. The upper limit of the time resolution of neuronal silencing with RapACR determined by measuring the dependence of spiking recovery after photoinhibition on the light intensity was calculated to be 100 Hz, whereas that with the faster of the two G. theta ACRs was 13 Hz. Further acceleration of RapACR channel kinetics was achieved by site-directed mutagenesis of a single residue in transmembrane helix 3 (Thr111 to Cys). We also show that mutation of another ACR (Cys to Ala at the same position) with a greatly extended lifetime of the channel open state acts as a bistable photochromic tool in mammalian neurons. These molecules extend the time domain of optogenetic neuronal silencing while retaining the high light sensitivity of Guillardia ACRs.