Biology subjects

Palmiter, R. D.

Publications and source records attributed to Palmiter, R. D..

15 recordsLinked to original sources

bioRxiv2026

Optogenetic activation of parabrachial tachykinin1 neurons drives nonphotic circadian entrainment

Mammalian circadian rhythms are primarily entrained by light, but nonphotic cues can also reorganize behavioral timing through mechanisms that remain poorly understood. Nocturnal foot shocks delivered to rodents while they forage away from the safety of their nesting area have been shown to entrain circadian behavioral rhythms and shift foraging and feeding to the daytime. To identify the neural circuits underlying this nonphotic fear entrainment, we optogenetically stimulated tachykinin 1-expressing neurons in the parabrachial nucleus (Tac1PBN) during the subjective night while the animals foraged outside of their nest, which recapitulated the total activity-rest phase switch in circadian behaviors induced by foot shocks. Furthermore, selective stimulation of Tac1PBN projections to the central amygdala (CeA) produced a significant but reduced phase shift compared to direct stimulation of Tac1PBN cell bodies. When Bmal1, a core clock gene, was conditionally deleted from the CeA, mice failed to fear-entrain, implicating the CeA molecular clock as a necessary component for fear entrainment. Together, these experiments demonstrate that activation of a defined neuronal population outside of the suprachiasmatic nucleus (SCN) can reorganize circadian behavior by engaging a non-SCN circadian oscillator network that requires an intact CeA molecular clock.

neuroscience↗

bioRxiv2026

Temporal single-cell profiling of the parabrachial Calca neurons reveals molecular dynamics driving nociplastic pain

Parabrachial Calca neurons are necessary for chronic pain and sufficient to drive nociplastic pain in mice, but how they sustain a pain state that outlasts its trigger is unknown. We performed temporal single-cell mRNA sequencing of the parabrachial nucleus (PBN) across the onset, chronic, and recovery phases of Calca neuron-driven tactile allodynia, using fixed-tissue profiling and reference-atlas registration to track molecularly defined populations over time. Activation broadly induced immediate-early genes, after which Calca neurons displayed changes in expression of genes that affect signaling and synaptic plasticity, with bidirectional changes that mirrored the onset and resolution of allodynia. The gene encoding brain-derived neurotrophic factor (Bdnf) remained persistently elevated in the chronic phase. BDNF infusion in the PBN prolonged allodynia, whereas blockade of its receptor (TrkB) attenuated it, and inactivating the Bdnf gene in Calca neurons abolished their hyperexcitability, attenuated allodynia, and relieved pain in a migraine model. These observations pinpoint BDNF as a driver of persistent nociplastic pain.

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bioRxiv2026

Parabrachial oxytocin receptor-expressing neurons link social observation of distress to defensive behavior

The ability to detect and respond to threat signals in the environment, including those conveyed by the distress of a familiar social partner, is fundamental to survival and disrupted in a range of neuropsychiatric conditions. This study identifies oxytocin receptor (Oxtr)-expressing neurons within the lateral parabrachial nucleus (lPBN) of mice as a key node in the neural circuitry underlying threat-related and social behaviors. These Oxtr neurons are activated by aversive stimuli and by observing demonstrator mice in stressful situations, including foot shock or inflammatory pain. Chemogenetic inhibition of these neurons alters social proximity and pain contagion in observers without affecting general anxiety-like behavior. Inhibition also transiently suppresses non-social central sensitization. Direct activation of lPBNOxtr neurons with a selective Oxtr agonist is anxiogenic and results in increased tactile sensitivity. Together, these findings suggest that lPBNOxtr neurons are poised to integrate information about environmental threat, whether experienced directly or witnessed in a conspecific to coordinate appropriate defensive behavioral responses.

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bioRxiv2026

A cholinergic eligibility trace facilitates amygdala plasticity in flavour avoidance learning

When an animal consumes a new food and consequently feels ill, it rapidly and robustly learns to avoid this food in the future, a form of learning termed conditioned flavour avoidance (CFA). Postingestive malaise often occurs long after novel food consumption, necessitating a neural mechanism that can facilitate plasticity between temporally distant events. Neuromodulators, acting through G-protein-coupled receptors (GPCRs) that can influence neuronal excitability on extended timescales, may facilitate this process. The projection of parabrachial (PB) Calca neurons to the central amygdala (CeA) is critical for formation of CFA. Here, we demonstrate that these neurons overlap with a PB population that releases acetylcholine (ACh) in the CeA. ACh is released in CeA during consumption of a novel solution and subsequent visceral malaise, consistent with a role in CFA acquisition. Two-photon calcium imaging in brain slices reveals that ACh widely activates CeA neurons and enhances glutamatergic responsivity on a timescale consistent with CFA learning. CRISPR-Cas9-mediated genetic knockdown and optogenetics demonstrate that ACh from PB facilitates CFA behavior. Large-scale neuronal recordings in the CeA along with our CRISPR approach reveal that loss of ACh signaling to CeA blocks key signatures of CFA-associated plasticity. Together, these data point to the cholinergic input from PB to central amygdala as a critical neuromodulatory signal that links activity over long timespans to facilitate associative learning in CFA.

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bioRxiv2025

Esr1-Dependent Signaling and Transcriptional Maturation in the Medial Preoptic Area of the Hypothalamus Shapes the Development of Mating Behavior during Adolescence

Mating and other behaviors emerge during adolescence through the coordinated actions of steroid hormone signaling throughout the nervous system and periphery. In this study, we investigated the transcriptional dynamics of the medial preoptic area (MPOA), a critical region for reproductive behavior, using single-cell RNA sequencing (scRNAseq) and in situ hybridization techniques in male and female mice throughout adolescence development. Our findings reveal that estrogen receptor 1 (Esr1) plays a pivotal role in the transcriptional maturation of GABAergic neurons within the MPOA during adolescence. Deletion of the estrogen receptor gene, Esr1, in GABAergic neurons (Vgat+) disrupted the developmental progression of mating behaviors in both sexes, while its deletion in glutamatergic neurons (Vglut2+) had no observable effect. In males and females, these neurons displayed distinct transcriptional trajectories, with hormone-dependent gene expression patterns emerging throughout adolescence and regulated by Esr1. Esr1 deletion in MPOA GABAergic neurons, prior to adolescence, arrested adolescent transcriptional progression of these cells and uncovered sex-specific gene-regulatory networks associated with Esr1 signaling. Our results underscore the critical role of Esr1 in orchestrating sex-specific transcriptional dynamics during adolescence, revealing gene regulatory networks implicated in the development of hypothalamic controlled reproductive behaviors. One Sentence SummarySingle cell RNA sequencing reveals how adolescent sex hormones sculpt hypothalamic cell types required for mating behavior.

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bioRxiv2024

Gustatory Thalamic Neurons Mediate Aversive Behaviors

The parvicellular part of the ventral posteromedial nucleus (VPMpc) of the thalamus, also known as the gustatory thalamus, receives input from the parabrachial nucleus and relays taste sensation to the gustatory (or insular) cortex. Prior research has focussed on the role of the VPMpc in relaying taste signals. Here we provide evidence showing that VPMpc also mediates aversive behaviors. By recording calcium transients in vivo from single neurons in mice, we show that neurons expressing cholecystokinin and the mu-opioid receptor in the VPMpc respond to various noxious stimuli and fear memory. Chemogenetic and optogenetic activation of these neurons enhances the response to aversive stimuli, whereas silencing them attenuates aversive behaviors. The VPMpc neurons directly innervate neurons in the insular cortex and rostral lateral amygdala. This study expands the role of the VPMpc to include mediating aversive and threating signals to the insular cortex and lateral amygdala.

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bioRxiv2023

Parabrachial Calca neurons drive nociplasticity

Pain that persists beyond the time required for tissue healing and pain that arises in the absence of tissue injury are poorly understood phenomena mediated by plasticity within the central nervous system. The parabrachial nucleus (PBN) is a hub that relays aversive sensory information and appears to play a role in nociplasticity. Here, by preventing PBN Calca neurons from releasing neurotransmitter or directly stimulating them we demonstrate that activation of Calca neurons is both necessary for the manifestation of chronic pain after nerve ligation and is sufficient to drive nociplasticity in wild-type mice. Aversive stimuli such as exposure to nitroglycerin, cisplatin, or LiCl can drive nociplasticity in a Calca-neuron-dependent manner. Calcium fluorescence imaging reveals that nitroglycerin activates PBN Calca neurons and potentiates their responses to mechanical stimulation. The activity and excitability of Calca neurons increased for several days after aversive events, but prolonged nociplasticity likely occurs in downstream circuitry.

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bioRxiv2023

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

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.

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bioRxiv2022

Molecular and Anatomical Characterization of Parabrachial Neurons and Their Axonal Projections

The parabrachial nucleus (PBN) is a major hub that receives sensory information from both internal and external environments. Specific populations of PBN neurons are involved in behaviors including food and water intake, pain sensation, breathing regulation, as well as learning and responding appropriately to threatening stimuli. However, it is unclear how many PBN neuron populations exist and how different behaviors may be encoded by unique signaling molecules or receptors. Here we provide a repository of data on the molecular identity, spatial location, and projection patterns on dozens of PBN neuron subclusters. Using single-cell RNA sequencing, we identified 21 subclusters of neurons in the PBN and neighboring regions. Multiplexed in situ hybridization showed many of these subclusters are localized to distinct PBN subregions. We also describe two major ascending pathways that innervate distinct brain regions by analyzing axonal projections in 21 Cre-driver lines of mice. These results are all publicly available for download and provide a foundation for further interrogation of PBN functions and connections.

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bioRxiv2020

Activation of Kiss1 neurons in the preoptic hypothalamus stimulates testosterone synthesis in adult male mice

Kisspeptin-expressing neurons in the rostral periventricular region of the third ventricle (RP3V) play an essential role in female reproduction. However, adult male mice were reported to have very few Kisspeptin-expressing neurons in the RP3V compared to females. This led to the hypothesis that Kiss1RP3V neurons are responsible for the ability of females, but not males, to generate a surge of LH, triggering ovulation and steroid synthesis in the female. Using mouse genetics and cell type-specific gene expression analysis, we show that male mice harbor almost as many Kiss1RP3V neurons as the female and that gene expression in these neurons is very similar. Specific activation of male Kiss1RP3V neurons expressing viral-encoded hM3Dq caused a surge in serum testosterone levels. These results demonstrate that Kiss1RP3V neurons are present in the adult male and fully capable of regulating the hypothalamic/pituitary/gonadal axis. We suggest that these neurons may continue to play a role in reproductive behavior in adult male mice.

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bioRxiv2020

Neural basis of opioid-induced respiratory depression and its rescue

Opioid-induced respiratory depression (OIRD) causes death following an opioid overdose, yet the neurobiological mechanisms of this process are not well understood. Here, we show that neurons within the lateral parabrachial nucleus that express the -opioid receptor (PBLOprm1 neurons) are involved in OIRD pathogenesis. PBLOprm1 neuronal activity is tightly correlated with respiratory rate, and this correlation is abolished following morphine injection. Chemogenetic inactivation of PBLOprm1 neurons mimics OIRD in mice, whereas their chemogenetic activation following morphine injection rescues respiratory rhythms to baseline levels. We identified several excitatory G-protein coupled receptors expressed by PBLOprm1 neurons and show that agonists for these receptors restore breathing rates in mice experiencing OIRD. Thus, PBLOprm1 neurons are critical for OIRD pathogenesis, providing a promising therapeutic target for treating OIRD in patients.

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bioRxiv2020

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, 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.

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bioRxiv2020

Gfral-expressing Neurons Suppress Food Intake via Aversive Pathways

To determine the function and mechanisms of action for hindbrain neurons that express GFRAL, the receptor for the anorexigenic peptide, GDF-15, we generated Gfralcre and conditional GfralCreERT mice. While signals of infection or pathophysiologic states (rather than meal ingestion) stimulate GFRAL neurons, the artificial activation of GfralCre- expressing neurons inhibited feeding, decreased gastric emptying, and promoted a conditioned taste aversion (CTA). Additionally, activation of the smaller population of GFRAL neurons captured by the GfralCreERT allele decreased gastric emptying and produced a CTA without suppressing food intake, suggesting that GFRAL neurons primarily modulate gastric physiology and stimulate aversive responses. GFRAL neurons most strongly innervated the parabrachial nucleus (PBN), where they targeted CGRP-expressing (CGRPPBN) neurons. Silencing CGRPPBN neurons abrogated the aversive and anorexic effects of GDF-15. These findings suggest that GFRAL neurons link non-meal-associated, pathophysiologic signals to the aversive suppression of nutrient uptake and absorption.

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bioRxiv2019

Kappa Opioid Receptor and Dynorphin Signaling in the Central Amygdala Regulates Alcohol Intake

Excessive alcohol drinking has been shown to modify brain circuitry to predispose individuals for future alcohol abuse. Previous studies have implicated the central nucleus of the amygdala (CeA) as an important site for mediating the somatic symptoms of withdrawal and for regulating alcohol intake. In addition, recent work has established a role for both the Kappa Opioid Receptor (KOR) and its endogenous ligand dynorphin in mediating these processes. However, it is unclear whether these effects are due to dynorphin or KOR arising from within the CeA itself or other input brain regions. To directly examine the role of preprodynorphin (PDYN) and KOR expression in CeA neurons, we performed region-specific conditional knockout of these genes and assessed the effects on the Drinking in the Dark (DID) and Intermittent Access (IA) paradigms. We then examined the effects of DID on PDYN and KOR modulation of CeA circuit physiology. Conditional gene knockout resulted in sex-specific responses wherein PDYN knockout decreased alcohol drinking in both male and female mice, whereas KOR knockout decreased drinking in males only. We also found that neither PDYN nor KOR knockout protected against anxiety caused by alcohol drinking. Lastly, a history of alcohol drinking did not alter synaptic transmission in PDYN neurons in the CeA of either sex, but excitability of PDYN neurons was increased in male mice only. Taken together, our findings indicate that PDYN and KOR signaling in the CeA plays an important role in regulating excessive alcohol consumption and highlight the need for future studies to examine how this is mediated through downstream effector regions.

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bioRxiv2018

NKB Signaling in the Medial Amygdala Stimulates Gonadotropin Release in a Kisspeptin-Independent Manner in Female Mice

Neurokinin B (NKB) signaling is critical for reproduction in all studied species. The existing consensus is that NKB induces GnRH release via kisspeptin (Kiss1) stimulation in the arcuate nucleus. However, the stimulatory action of NKB is dependent on circulating estrogen (E2) levels, without which, NKB inhibits LH release. Importantly, the evidence supporting the kisspeptin-dependent role of NKB, derives from models of persistent hypogonadal state [e.g. Kiss1r knockout (KO) mice], with reduced E2 levels. Here, we demonstrate that in the presence of E2, NKB signaling induces LH release in a kisspeptin-independent manner. Moreover, senktide (NKB receptor agonist) delivery to the medial amygdala (MeA) increases LH in E2-treated Kiss1 KO females (but not males or sham-treated females) similar to controls, and thus, this increase is independent of Kiss1 neurons. These results document a novel kisspeptin-independent regulatory pathway of reproductive function in females mediated by NKB-responsive neurons in the MeA.

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