Animals must ingest water via drinking to maintain fluid homeostasis, yet the neurons that specifically promote drinking behavior are incompletely characterized. The lateral hypothalamic area (LHA) ...as a whole is essential for drinking behavior but most LHA neurons indiscriminately promote drinking and feeding. By contrast, activating neurotensin (Nts)-expressing LHA neurons (termed LHA Nts neurons) causes mice to immediately drink water with a delayed suppression of feeding. We therefore hypothesized that LHA Nts neurons are sufficient to induce drinking behavior and that these neurons specifically bias for fluid intake over food intake. To test this hypothesis we used designer receptors exclusively activated by designer drugs (DREADDs) to selectively activate LHA Nts neurons and studied the impact on fluid intake, fluid preference and feeding. Activation of LHA Nts neurons stimulated drinking in water-replete and dehydrated mice, indicating that these neurons are sufficient to promote water intake regardless of homeostatic need. Interestingly, mice with activated LHA Nts neurons drank any fluid that was provided regardless of its palatability, but if given a choice they preferred water or palatable solutions over unpalatable (quinine) or dehydrating (hypertonic saline) solutions. Notably, acute activation of LHA Nts neurons robustly promoted fluid but not food intake. Overall, our study confirms that activation of LHA Nts neurons is sufficient to induce drinking behavior and biases for fluid intake. Hence, LHA Nts neurons may be important targets for orchestrating the appropriate ingestive behavior necessary to maintain fluid homeostasis.
This article is part of the Special Issue entitled ‘Hypothalamic Control of Homeostasis’.
•Activation of LHA Nts neurons is sufficient to promote voracious drinking.•Activation of the LHA Nts neurons biases for fluid consumption over food intake.•LHA Nts neuronal activation induces drinking of any provided liquid.•LHA Nts neuron-activated mice prefer water over dehydrating or unpalatable liquids.•LHA Nts neuron-activated mice prefer palatable liquids over water.
Abstract
The hormones ghrelin and leptin act via the lateral hypothalamic area (LHA) to modify energy balance, but the underlying neural mechanisms remain unclear. We investigated how leptin and ...ghrelin engage LHA neurons to modify energy balance behaviors and whether there is any crosstalk between leptin and ghrelin-responsive circuits. We demonstrate that ghrelin activates LHA neurons expressing hypocretin/orexin (OX) to increase food intake. Leptin mediates anorectic actions via separate neurons expressing the long form of the leptin receptor (LepRb), many of which coexpress the neuropeptide neurotensin (Nts); we refer to these as NtsLepRb neurons. Because NtsLepRb neurons inhibit OX neurons, we hypothesized that disruption of the NtsLepRb neuronal circuit would impair both NtsLepRb and OX neurons from responding to their respective hormonal cues, thus compromising adaptive energy balance. Indeed, mice with developmental deletion of LepRb specifically from NtsLepRb neurons exhibit blunted adaptive responses to leptin and ghrelin that discoordinate the mesolimbic dopamine system and ingestive and locomotor behaviors, leading to weight gain. Collectively, these data reveal a crucial role for LepRb in the proper formation of LHA circuits, and that NtsLepRb neurons are important neuronal hubs within the LHA for hormone-mediated control of ingestive and locomotor behaviors.
We investigated how energy cues engage the lateral hypothalamus, and reveal that leptin-sensing neurotensin neurons are hubs for hormone-mediated control of ingestive and locomotor behaviors.
The central mechanism by which neurotensin (Nts) potentiates weight loss has remained elusive. We leveraged chemogenetics to reveal that Nts-expressing neurons of the lateral hypothalamic area (LHA) ...promote weight loss in mice by increasing volitional activity and restraining food intake. Intriguingly, these dual weight loss behaviors are mediated by distinct signaling pathways: Nts action via NtsR1 is essential for the anorectic effect of the LHA Nts circuit, but not for regulation of locomotor or drinking behavior. Furthermore, although LHA Nts neurons cannot reduce intake of freely available obesogenic foods, they effectively restrain motivated feeding in hungry, weight-restricted animals. LHA Nts neurons are thus vital mediators of central Nts action, particularly in the face of negative energy balance. Enhanced action via LHA Nts neurons may, therefore, be useful to suppress the increased appetitive drive that occurs after lifestyle-mediated weight loss and, hence, to prevent weight regain.
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•LHA Nts neurons suppress feeding and promote weight loss via NtsR1•Enhanced LHA Nts action does not restrain palatable food intake in obesity•LHA Nts neurons suppress feeding and weight gain in food-deprived mice
Woodworth et al. demonstrate that neurotensin (Nts) neurons in the lateral hypothalamic area (LHA) suppress food intake while increasing energy expenditure, resulting in weight loss. Enhanced LHA Nts action does not restrain free intake of palatable food in sated mice, but it suppresses feeding and weight gain in food-deprived animals.
Survival depends on an organism's ability to sense nutrient status and accordingly regulate intake and energy expenditure behaviors. Uncoupling of energy sensing and behavior, however, underlies ...energy balance disorders such as anorexia or obesity. The hypothalamus regulates energy balance, and in particular the lateral hypothalamic area (LHA) is poised to coordinate peripheral cues of energy status and behaviors that impact weight, such as drinking, locomotor behavior, arousal/sleep and autonomic output. There are several populations of LHA neurons that are defined by their neuropeptide content and contribute to energy balance. LHA neurons that express the neuropeptides melanin-concentrating hormone (MCH) or orexins/hypocretins (OX) are best characterized and these neurons play important roles in regulating ingestion, arousal, locomotor behavior and autonomic function via distinct neuronal circuits. Recently, another population of LHA neurons containing the neuropeptide Neurotensin (Nts) has been implicated in coordinating anorectic stimuli and behavior to regulate hydration and energy balance. Understanding the specific roles of MCH, OX and Nts neurons in harmonizing energy sensing and behavior thus has the potential to inform pharmacological strategies to modify behaviors and treat energy balance disorders.
Pharmacologic treatment with the neuropeptide neurotensin (Nts) modifies motivated behaviors such as feeding, locomotor activity, and reproduction. Dopamine (DA) neurons of the ventral tegmental area ...(VTA) control these behaviors, and Nts directly modulates the activity of DA neurons via Nts receptor-1. While Nts sources to the VTA have been described in starlings and rats, the endogenous sources of Nts to the VTA of mice remain incompletely understood, impeding determination of which Nts circuits orchestrate specific behaviors in this model. To overcome this obstacle we injected the retrograde tracer Fluoro-Gold into the VTA of mice that express GFP in Nts neurons. Identification of GFP-Nts cells that accumulate Fluoro-Gold revealed the Nts afferents to the VTA in mice. Similar to rats, most Nts afferents to the VTA of mice arise from the medial and lateral preoptic areas (POA) and the lateral hypothalamic area (LHA), brain regions that are critical for coordination of feeding and reproduction. Additionally, the VTA receives dense input from Nts neurons in the nucleus accumbens shell (NAsh) of mice, and minor Nts projections from the amygdala and periaqueductal gray area. Collectively, our data reveal multiple populations of Nts neurons that provide direct afferents to the VTA and which may regulate specific aspects of motivated behavior. This work lays the foundation for understanding endogenous Nts actions in the VTA, and how circuit-specific Nts modulation may be useful to correct motivational and affective deficits in neuropsychiatric disease.
•Unlike rats, mice have few Ventral Tegemtnal Area (VTA) Neurotensin (Nts) neurons.•In mice, endogenous Nts is provided to the VTA via external (non-VTA) sources.•Most mouse Nts inputs to VTA come from the lateral hypothalamus and preoptic area.
Dopamine (DA) neurons in the ventral tegmental area (VTA) are heterogeneous and differentially regulate ingestive and locomotor behaviors that affect energy balance. Identification of which VTA DA ...neurons mediate behaviors that limit weight gain has been hindered, however, by the lack of molecular markers to distinguish VTA DA populations. Here, we identified a specific subset of VTA DA neurons that express neurotensin receptor-1 (NtsR1) and preferentially comprise mesolimbic, but not mesocortical, DA neurons. Genetically targeted ablation of VTA NtsR1 neurons uncouples motivated feeding and physical activity, biasing behavior toward energy expenditure and protecting mice from age-related and diet-induced weight gain. VTA NtsR1 neurons thus represent a molecularly defined subset of DA neurons that are essential for the coordination of energy balance. Modulation of VTA NtsR1 neurons may therefore be useful to promote behaviors that prevent the development of obesity.
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•NtsR1 is expressed on a subset of VTA DA neurons that projects to the NA•Loss of VTA NtsR1 neurons promotes energy use and prevents diet-induced obesity•VTA NtsR1 neurons are necessary to coordinate energy cues with ingestive behavior•Ablation of VTA NtsR1 neurons alters expression of mesolimbic DA markers
Woodworth et al. identify a subset of VTA dopamine neurons that express neurotensin receptor-1. Ablation of these neurons leads to enhanced physical activity and energy expenditure that protect mice from diet-induced obesity, revealing an important role for VTA NtR1 neurons in the regulation of body weight.
Inflammatory bowel diseases (IBD) increase the risk of developing colorectal cancer. Dietary components that reduce inflammation are associated with lower cancer risk. The long-chain omega-3 fatty ...acid docosahexaenoic acid (DHA) is present in fish oil and has potent anti-inflammatory properties. The objective of this study is to determine whether dietary fish oil enriched with DHA (DFO) could reduce experimentally induced colitis and colon cancer risk in a mouse model. When SMAD3-/- mice are exposed to Helicobacter hepaticus, mild colitis is observed 4 weeks postinfection. Mice were fed isocaloric diets modified to include corn oil, safflower oil, or DFO (doses ranging from 0.75% to 6.00%) as the fatty acid source for 8 weeks. Mice were gavaged with H. hepaticus; DFO feeding was continued; and mice were sacrificed 4 weeks after infection. The colon and cecum were collected for histopathology. Spleens and mesenteric lymph nodes were collected and analyzed for T-cell populations using flow cytometry. Contrary to expectations, DFO induced severe colitis and adenocarcinoma formation. DFO consumption was associated with decreased CD8(+) cell frequency and diminished CD69 expression on CD4(+) and CD8(+) T-cell populations. Mice consuming DFO also exhibited higher FoxP3(+) CD25(+) CD4(+) T regulatory cell frequency, FoxP3 expression, and altered L-selectin expression during infection. We concluded that DFO-fed mice may be less equipped to mount a successful response to H. hepaticus infection, increasing colon cancer risk. These results support the need to establish a tolerable upper limit for DHA intake particularly in the context of chronic inflammatory conditions such as IBD.
Neurotensin (Nts) promotes activation of dopamine (DA) neurons in the ventral tegmental area (VTA) via incompletely understood mechanisms. Nts can signal via the G protein-coupled Nts receptors 1 and ...2 (NtsR1 and NtsR2), but the lack of methods to detect NtsR1- and NtsR2-expressing cells has limited mechanistic understanding of Nts action. To overcome this challenge, we generated dual recombinase mice that express FlpO-dependent Cre recombinase in NtsR1 or NtsR2 cells. This strategy permitted temporal control over recombination, such that we could identify NtsR1- or NtsR2-expressing cells and determine whether their distributions differed between the developing and adult brain. Using this system, we found that NtsR1 is transiently expressed in nearly all DA neurons and in many non-DA neurons in the VTA during development. However, NtsR1 expression is more restricted within the adult brain, where only two thirds of VTA DA neurons expressed NtsR1. By contrast, NtsR2 expression remains constant throughout lifespan, but it is predominantly expressed within glia. Anterograde tract tracing revealed that NtsR1 is expressed by mesolimbic, not mesocortical DA neurons, suggesting that VTA NtsR1 neurons may represent a functionally unique subset of VTA DA neurons. Collectively, this work reveals a cellular mechanism by which Nts can directly engage NtsR1-expressing DA neurons to modify DA signaling. Going forward, the dual recombinase strategy developed here will be useful to selectively modulate NtsR1- and NtsR2-expressing cells and to parse their contributions to Nts-mediated behaviors.
Abstract only
In the lateral hypothalamic area (LHA), some neurons, express the neuropeptide neurotensin (Nts) and regulate feeding, drinking and physical activity. Many LHA Nts neurons also contain ...the inhibitory neurotransmitter GABA, but some modulate glutamate (glut) signaling. This suggests that there are different subtypes of LHA Nts neurons. LHA Nts neuronal terminals have been seen within both the Ventra Tegmental Area (VTA) and Substantia Nigra Compacta (SNc) implying that subpopulations of LHA Nts neurons have distinct midbrain projection targets and mechanisms of action. Furthermore, some LHA Nts neurons co‐express the long form of the leptin receptor (LepRb) and are activated by the anorectic hormone leptin (Nts
LepRb
neurons) while others are activated by dehydration (Nts
Dehy
neurons).
I examined the hypothesis that Nts
LepRb
and Nts
Dehy
neurons are distinguishable from each other based on their expression of GABA or glut and whether they project preferentially to the VTA or SNc.
Until now, the lack of reagents to simultaneously identify Nts, GABA and glutamate prevented this analysis. To overcome this, we designed a dual genetic recombinase approach in order to simultaneously label Nts and GABA or glutamate‐containing neurons. We first generated mice that express FlpO recombinase specifically in Nts neurons (
Nts
FlpO
mice) which we crossed with mice that express Cre recombinase in GABA or glutamate neurons. The resulting offspring expressed FlpO recombinase in Nts neurons and Cre in GABA/Glutamate Neurons; Nts
FlpO
/vGat
Cre
or Nts
FlpO
/vGlut
Cre
mice respectively. I injected vectors for FlpO‐inducible green fluorescent protein (GFP) and Cre‐inducible red fluorescent protein (RFP) in the LHA these mice with causes GFP expression only within LHA Nts neurons and RFP expression only in GABA/Glut neurons enabling the simultaneous detection of Nts and GABA and/or glutamate containing neurons via fluorescent microscopy. To examine the midbrain projections of each subtype of LHA Nts neurons, Fluorogold (FG) retrograde tract tracer was injected into the VTA or SNc of mice that express GFP only in Nts neurons (Nts
GFP
mice) and followed with leptin, or dehydration treatment. Brains were analyzed via immunostaining to label Nts
LepRb
, or Nts
Dehy
neurons and FG. Our data shows that many LHA Nts neurons contain GABA and some express glutamate. Additionally, both LHA Nts
LepRb
neurons project to the VTA to the SNc but LHA Nts
Dehy
neurons do not project to either midbrain region. The neurotransmitter content of these cue‐distinct subpopulations will be determined using Leptin and Dehydration treatment too.
Support or Funding Information
This work is supported by NIH awards to JAB (1F31 DK107081‐01A1, 5 T32 ES007255‐27) and GML (RC105025)
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