A stable, distributed code for cue value in mouse cortex during reward learning.

The ability to associate reward-predicting stimuli with adaptive behavior is frequently attributed to the prefrontal cortex, but the stimulus-specificity, spatial distribution, and stability of prefrontal cue-reward associations are unresolved. We trained head-fixed mice on an olfactory Pavlovian conditioning task and measured the coding properties of individual neurons across space (prefrontal, olfactory, and motor cortices) and time (multiple days). Neurons encoding cues or licks were most common in the olfactory and motor cortex, respectively. By quantifying the responses of cue-encoding neurons to six cues with varying probabilities of reward, we unexpectedly found value coding in all regions we sampled, with some enrichment in the prefrontal cortex. We further found that prefrontal cue and lick codes were preserved across days. Our results demonstrate that individual prefrontal neurons stably encode components of cue-reward learning within a larger spatial gradient of coding properties.

Parabrachial tachykinin1-expressing neurons involved in state-dependent breathing control.

Breathing is regulated automatically by neural circuits in the medulla to maintain homeostasis, but breathing is also modified by behavior and emotion. Mice have rapid breathing patterns that are unique to the awake state and distinct from those driven by automatic reflexes. Activation of medullary neurons that control automatic breathing does not reproduce these rapid breathing patterns. By manipulating transcriptionally defined neurons in the parabrachial nucleus, we identify a subset of neurons that express the Tac1, but not Calca, gene that exerts potent and precise conditional control of breathing in the awake, but not anesthetized, state via projections to the ventral intermediate reticular zone of the medulla. Activating these neurons drives breathing to frequencies that match the physiological maximum through mechanisms that differ from those that underlie the automatic control of breathing. We postulate that this circuit is important for the integration of breathing with state-dependent behaviors and emotions.

Topographic representation of current and future threats in the mouse nociceptive amygdala.

Adaptive behaviors arise from an integration of current sensory context and internal representations of past experiences. The central amygdala (CeA) is positioned as a key integrator of cognitive and affective signals, yet it remains unknown whether individual populations simultaneously carry current- and future-state representations. We find that a primary nociceptive population within the CeA of mice, defined by CGRP-receptor (Calcrl) expression, receives topographic sensory information, with spatially defined representations of internal and external stimuli. While Calcrl+ neurons in both the rostral and caudal CeA respond to noxious stimuli, rostral neurons promote locomotor responses to externally sourced threats, while caudal CeA Calcrl+ neurons are activated by internal threats and promote passive coping behaviors and associative valence coding. During associative fear learning, rostral CeA Calcrl+ neurons stably encode noxious stimulus occurrence, while caudal CeA Calcrl+ neurons acquire predictive responses. This arrangement supports valence-aligned representations of current and future threats for the generation of adaptive behaviors.

Chronic Gq signaling in AgRP neurons does not cause obesity.

Maintaining energy homeostasis requires coordinating physiology and behavior both on an acute timescale to adapt to rapid fluctuations in caloric intake and on a chronic timescale to regulate body composition. Hypothalamic agouti-related peptide (AgRP)-expressing neurons are acutely activated by caloric need, and this acute activation promotes increased food intake and decreased energy expenditure. On a longer timescale, AgRP neurons exhibit chronic hyperactivity under conditions of obesity and high dietary fat consumption, likely due to leptin resistance; however, the behavioral and metabolic effects of chronic AgRP neuronal hyperactivity remain unexplored. Here, we use chemogenetics to manipulate Gq signaling in AgRP neurons in mice to explore the hypothesis that chronic activation of AgRP neurons promotes obesity. Inducing chronic Gq signaling in AgRP neurons initially increased food intake and caused dramatic weight gain, in agreement with published data; however, food intake returned to baseline levels within 1 wk, and body weight returned to baseline levels within 60 d. Additionally, we found that, when mice had elevated body weight due to chronic Gq signaling in AgRP neurons, energy expenditure was not altered but adiposity and lipid metabolism were both increased, even under caloric restriction. These findings reveal that the metabolic and behavioral effects of chronic Gq signaling in AgRP neurons are distinct from the previously reported effects of acute Gq signaling and also of leptin insensitivity.

Dissociable control of unconditioned responses and associative fear learning by parabrachial CGRP neurons.

Parabrachial CGRP neurons receive diverse threat-related signals and contribute to multiple phases of adaptive threat responses in mice, with their inactivation attenuating both unconditioned behavioral responses to somatic pain and fear-memory formation. Because CGRPPBN neurons respond broadly to multi-modal threats, it remains unknown how these distinct adaptive processes are individually engaged. We show that while three partially separable subsets of CGRPPBN neurons broadly collateralize to their respective downstream partners, individual projections accomplish distinct functions: hypothalamic and extended amygdalar projections elicit assorted unconditioned threat responses including autonomic arousal, anxiety, and freezing behavior, while thalamic and basal forebrain projections generate freezing behavior and, unexpectedly, contribute to associative fear learning. Moreover, the unconditioned responses generated by individual projections are complementary, with simultaneous activation of multiple sites driving profound freezing behavior and bradycardia that are not elicited by any individual projection. This semi-parallel, scalable connectivity schema likely contributes to flexible control of threat responses in unpredictable environments.

Encoding of danger by parabrachial CGRP neurons.

Animals must respond to various threats to survive. Neurons that express calcitonin gene-related peptide in the parabrachial nucleus (CGRPPBN neurons) relay sensory signals that contribute to satiation and pain-induced fear behaviour, but it is unclear how they encode these distinct processes. Here, by recording calcium transients in vivo from individual neurons in mice, we show that most CGRPPBN neurons are activated by noxious cutaneous (shock, heat, itch) and visceral stimuli (lipopolysaccharide). The same neurons are inhibited during feeding, but become activated during satiation, consistent with evidence that CGRPPBN neurons prevent overeating. CGRPPBN neurons are also activated during consumption of novel foods or by an auditory cue that has previously been paired with electrical footshocks. Correspondingly, silencing of CGRPPBN neurons attenuates the expression of food neophobia and conditioned fear responses. Therefore, in addition to transducing primary sensory danger signals, CGRPPBN neurons promote affective-behavioural states that limit harm in response to potential threats.

Cancer-induced anorexia and malaise are mediated by CGRP neurons in the parabrachial nucleus.

Anorexia is a common manifestation of chronic diseases, including cancer. Here we investigate the contribution to cancer anorexia made by calcitonin gene-related peptide (CGRP) neurons in the parabrachial nucleus (PBN) that transmit anorexic signals. We show that CGRPPBN neurons are activated in mice implanted with Lewis lung carcinoma cells. Inactivation of CGRPPBN neurons before tumor implantation prevents anorexia and loss of lean mass, and their inhibition after symptom onset reverses anorexia. CGRPPBN neurons are also activated in Apcmin/+ mice, which develop intestinal cancer and lose weight despite the absence of reduced food intake. Inactivation of CGRPPBN neurons in Apcmin/+ mice permits hyperphagia that counteracts weight loss, revealing a role for these neurons in a 'nonanorexic' cancer model. We also demonstrate that inactivation of CGRPPBN neurons prevents lethargy, anxiety and malaise associated with cancer. These findings establish CGRPPBN neurons as key mediators of cancer-induced appetite suppression and associated behavioral changes.

Parabrachial CGRP Neurons Control Meal Termination.

The lateral parabrachial nucleus is a conduit for visceral signals that cause anorexia. We previously identified a subset of neurons located in the external lateral parabrachial nucleus (PBel) that express calcitonin gene-related peptide (CGRP) and inhibit feeding when activated by illness mimetics. We report here that in otherwise normal mice, functional inactivation of CGRP neurons markedly increases meal size, with meal frequency being reduced in a compensatory manner, and renders mice insensitive to the anorexic effects of meal-related satiety peptides. Furthermore, CGRP neurons are directly innervated by orexigenic hypothalamic AgRP neurons, and photostimulation of AgRP fibers supplying the PBel delays satiation by inhibiting CGRP neurons, thereby contributing to AgRP-driven hyperphagia. By establishing a role for CGRP neurons in the control of meal termination and as a downstream mediator of feeding elicited by AgRP neurons, these findings identify a node in which hunger and satiety circuits interact to control feeding behavior.