Showing papers by "Richard D. Palmiter published in 2023"

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

Abstract: Abstract 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.

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

Abstract: 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.

Novel genetically encoded tools for imaging or silencing neuropeptide release from presynaptic terminals in vivo

Abstract: Neurons produce and release neuropeptides to communicate with one another. Despite their profound impact on critical brain functions, circuit-based mechanisms of peptidergic transmission are poorly understood, primarily due to the lack of tools for monitoring and manipulating neuropeptide release in vivo. Here, we report the development of two genetically encoded tools for investigating peptidergic transmission in behaving mice: a genetically encoded large dense core vesicle (LDCV) sensor that detects the neuropeptides release presynaptically, and a genetically encoded silencer that specifically degrades neuropeptides inside the LDCV. Monitoring and silencing peptidergic and glutamatergic transmissions from presynaptic terminals using our newly developed tools and existing genetic tools, respectively, reveal that neuropeptides, not glutamate, are the primary transmitter in encoding unconditioned stimulus during Pavlovian threat learning. These results show that our sensor and silencer for peptidergic transmission are reliable tools to investigate neuropeptidergic systems in awake behaving animals.

Prolonged activation of EP3 receptor-expressing preoptic neurons underlies torpor responses

Abstract: Many species use a temporary drop in body temperature and metabolic rate (torpor) as a strategy to survive food scarcity. A similar profound hypothermia is observed with activation of preoptic neurons that express the neuropeptides Pituitary Adenylate-Cyclase-Activating Polypeptide (PACAP)1, Brain Derived Neurotrophic Factor (BDNF)2, or Pyroglutamylated RFamide Peptide (QRFP)3, the vesicular glutamate transporter, Vglut24,5 or the leptin receptor6 (LepR), estrogen 1 receptor (Esr1)7 or prostaglandin E receptor 3 (EP3R) in mice8. However, most of these genetic markers are found on multiple populations of preoptic neurons and only partially overlap with one another. We report here that expression of the EP3R marks a unique population of median preoptic (MnPO) neurons that are required both for lipopolysaccharide (LPS)-induced fever9 and for torpor. These MnPOEP3R neurons produce persistent fever responses when inhibited and prolonged hypothermic responses when activated either chemo- or opto-genetically even for brief periods of time. The mechanism for these prolonged responses appears to involve increases in intracellular calcium in individual EP3R-expressing preoptic neurons that persist for many minutes up to hours beyond the termination of a brief stimulus. These properties endow MnPOEP3R neurons with the ability to act as a two-way master switch for thermoregulation.

CPT1A in AgRP neurons is required for sex-dependent regulation of feeding and thirst

Abstract: Abstract Background Fatty acid metabolism in the hypothalamus has an important role in food intake, but its specific role in AgRP neurons is poorly understood. Here, we examined whether carnitinea palmitoyltransferase 1A (CPT1A), a key enzyme in mitochondrial fatty acid oxidation, affects energy balance. Methods To obtain Cpt1a KO mice and their control littermates, Cpt1a (flox/flox) mice were crossed with tamoxifen-inducible AgRP CreERT2 mice. Food intake and body weight were analyzed weekly in both males and females. At 12 weeks of age, metabolic flexibility was determined by ghrelin-induced food intake and fasting–refeeding satiety tests. Energy expenditure was analyzed by calorimetric system and thermogenic activity of brown adipose tissue. To study fluid balance the analysis of urine and water intake volumes; osmolality of urine and plasma; as well as serum levels of angiotensin and components of RAAS (renin–angiotensin–aldosterone system) were measured. At the central level, changes in AgRP neurons were determined by: (1) analyzing specific AgRP gene expression in RiboTag– Cpt1a KO mice obtained by crossing Cpt1a KO mice with RiboTag mice; (2) measuring presynaptic terminal formation in the AgRP neurons with the injection of the AAV1 -EF1a-DIO-synaptophysin-GFP in the arcuate nucleus of the hypothalamus; (3) analyzing AgRP neuronal viability and spine formations by the injection AAV9 -EF1a-DIO-mCherry in the arcuate nucleus of the hypothalamus; (4) analyzing in situ the specific AgRP mitochondria in the ZsGreen- Cpt1a KO obtained by breeding ZsGreen mice with Cpt1a KO mice. Two-way ANOVA analyses were performed to determine the contributions of the effect of lack of CPT1A in AgRP neurons in the sex. Results Changes in food intake were just seen in male Cpt1a KO mice while only female Cpt1a KO mice increased energy expenditure. The lack of Cpt1a in the AgRP neurons enhanced brown adipose tissue activity, mainly in females, and induced a substantial reduction in fat deposits and body weight. Strikingly, both male and female Cpt1a KO mice showed polydipsia and polyuria, with more reduced serum vasopressin levels in females and without osmolality alterations, indicating a direct involvement of Cpt1a in AgRP neurons in fluid balance. AgRP neurons from Cpt1a KO mice showed a sex-dependent gene expression pattern, reduced mitochondria and decreased presynaptic innervation to the paraventricular nucleus, without neuronal viability alterations. Conclusions Our results highlight that fatty acid metabolism and CPT1A in AgRP neurons show marked sex differences and play a relevant role in the neuronal processes necessary for the maintenance of whole-body fluid and energy balance.