Associations of Telehealth Care Delivery with Pediatric Health Care Provider Well-Being.

BACKGROUND: The rapid, large-scale deployment of new health technologies can introduce challenges to clinicians who are already under stress. The novel coronavirus disease 19 (COVID-19) pandemic transformed health care in the United States to include a telehealth model of care delivery. Clarifying paths through which telehealth technology use is associated with change in provider well-being and interest in sustaining virtual care delivery can inform planning and optimization efforts. OBJECTIVE: This study aimed to characterize provider-reported changes in well-being and daily work associated with the pandemic-accelerated expansion of telehealth and assess the relationship of provider perceptions of telehealth effectiveness, efficiency, and work-life balance with desire for future telehealth. METHODS: A cross-sectional survey study was conducted October through November 2020, 6 months after the outbreak of COVID-19 at three children's hospitals. Factor analysis and structural equation modeling (SEM) were used to examine telehealth factors associated with reported change in well-being and desire for future telehealth. RESULTS: A total of 947 nontrainee physicians, advanced practice providers, and psychologists were surveyed. Of them, 502 (53.0%) providers responded and 467 (49.3%) met inclusion criteria of telehealth use during the study period. Of these, 325 (69.6%) were female, 301 (65.6%) were physicians, and 220 (47.1%) were medical subspecialists. Providers were 4.77 times as likely (95% confidence interval [CI]: 3.29-7.06) to report improved versus worsened well-being associated with telehealth. Also, 95.5% of providers (95% CI: 93.2-97.2%) wish to continue performing telehealth postpandemic. Our model explains 66% of the variance in telehealth-attributed provider well-being and 59% of the variance for future telehealth preference and suggests telehealth resources significantly influence provider-perceived telehealth care effectiveness which in turn significantly influences provider well-being and desire to perform telehealth. CONCLUSION: Telehealth has potential to promote provider well-being; telehealth-related changes in provider well-being are associated with both provider-perceived effectiveness of telemedicine for patients and adequacy of telehealth resources.

Rapid Development of a Telehealth Patient Satisfaction Survey Using a Multi-Stakeholder Approach.

Introduction: The COVID-19 pandemic has hastened the adoption of telehealth and the drastic shift to an unfamiliar process may impose significant impact to the quality-of-care delivery. Many providers are interested in understanding the quality of their telehealth services from the patients' experience. Materials and Methods: A telehealth patient satisfaction survey (TPSS) was developed by using an iterative stakeholder-centered design approach, incorporating elements from validated telemedicine and customer service survey instruments, and meeting the operational needs and constraints. A cross-sectional study design was employed to collect survey responses from patients and families of a large pediatric hospital. Finally, we performed exploratory factor analysis (EFA) to extract latent constructs and factor loadings of the survey items to further explain relationships. Results: A 22-item TPSS closely matched the existing in-person patient satisfaction survey and mapped to a revised SERVPERF conceptual model that was proposed by the interdisciplinary committee. Survey was implemented in the HIPAA-compliant online platform REDCap® with survey link embedded in an automated Epic MyChart (Verona, WI) visit follow-up message. In total, 2,394 survey responses were collected between July 7, 2020, and September 2, 2020. EFA revealed three constructs (with factor loadings >0.30): admission process, perceived quality of services, and telehealth satisfaction. Conclusions: We reported the development of TPSS that met the operational needs of compatibility with existing data and possible comparison to in-person survey. The survey is short and yet covers both the clinical experience and telehealth usability, with acceptable survey validity.

Identifying the Factors Influencing Patients' Telehealth Visit Satisfaction: Survey Validation Through a Structural Equation Modeling Approach.

Introduction: The COVID-19 pandemic accelerated the adoption of telehealth as an alternative to in-person hospital visits. To understand the factors impacting the quality of telehealth services, there is a need for validated survey instruments and conceptual frameworks. The objective of this study is to validate a telehealth patient satisfaction survey by structural equation modeling (SEM) and determine the relationship between the factors in the proposed telehealth patient satisfaction model (TPSM). Methods: We conducted a cross-sectional survey of pediatric patients and families receiving care from a comprehensive pediatric hospital in the Midwest between September 2020 and January 2021. In total, 2,039 usable responses were collected. We used an SEM approach by performing confirmatory factor analysis with Diagonally Weighted Least Squares modeling and Partial Least Squares-Path Modeling to establish the structural validity and examined the relationships among the constructs of "Admission Process" (AP), "Perceived Quality of Service" (PQS), and "Telehealth Satisfaction" (TS). Results: Participants were predominantly White (75%) and English-speaking (95%) parents (85%) of patients (mean age of patients was 10.2 years old). The survey responses were collected from patients visiting 43 department specialties, whereas 50% were behavioral and occupational therapy patients. The structural model showed that the admission process (AP) had a strong positive impact on perceived quality of service (PQS) (p = 0.67, t = 36.1, p < 0.001). The PQS had a strong positive impact on telehealth satisfaction (TS) (p = 0.66, t = 31.8, p < 0.001). The AP had a low positive direct impact on TS (p = 0.16, t = 7.46, p < 0.05). Overall, AP and PQS explained 61% variances (R2) of TS. Conclusions: We validated a newly proposed TS assessment model by using SEM. The TPSM will inform researchers to better understand the influencing factors in TS and help health care systems to improve telehealth patient satisfaction through a validated model.

Feasibility and usability study of a pilot immersive virtual reality-based empathy training for dental providers.

PURPOSE: Social determinants of health (SDOH) significantly impact individuals' engagement with the healthcare system. To address SDOH-related oral health disparities, providers must be equipped with knowledge, skills, and attitudes (KSAs) to understand how SDOH affect patients and how to mitigate these effects. Traditional dental school curricula provide limited training on recognizing SDOH or developing empathy for those with SDOH-related access barriers. This study describes the design and evaluation of such a virtual reality (VR)-based simulation in dental training. We hypothesize the simulation will increase post-training KSAs. METHODS: We developed "MPATHI" (Making Professionals Able THrough Immersion), a scripted VR simulation where participants take the role of an English-speaking caregiver with limited socioeconomic resources seeking dental care for a child in a Spanish-speaking country. The simulation is a combination of 360° video recording and virtual scenes delivered via VR headsets. A pilot was conducted with 29 dental residents/faculty, utilizing a pre-post design to evaluate effectiveness in improving immediate and retention of KSAs toward care delivery for families facing barriers. RESULTS: MPATHI led to increased mean scores for cognitive (pre = 3.48 ± 0.80, post = 4.56 ± 0.51, p < 0.001), affective (pre = 4.20 ± 0.4, post = 4.47 ± 0.44, p < 0.001), and skill-based learning (pre = 4.00 ± 0.47, post = 4.52 ± 0.37, p < 0.001) immediately post-training. There was not a significant difference between skills measured immediately post-training and in the 1-month post-training survey (p = 0.41). Participants reported high satisfaction with the content and methods used in this training. CONCLUSIONS: This pilot study supports using VR SDOH training in dental education. VR technology provides new opportunities for innovative content design.

A deep learning model for pediatric patient risk stratification.

OBJECTIVES: Current models for patient risk prediction rely on practitioner expertise and domain knowledge. This study presents a deep learning model-a type of machine learning that does not require human inputs-to analyze complex clinical and financial data for population risk stratification. STUDY DESIGN: A comparative predictive analysis of deep learning versus other popular risk prediction modeling strategies using medical claims data from a cohort of 112,641 pediatric accountable care organization members. METHODS: "Skip-Gram," an unsupervised deep learning approach that uses neural networks for prediction modeling, used data from 2014 and 2015 to predict the risk of hospitalization in 2016. The area under the curve (AUC) of the deep learning model was compared with that of both the Clinical Classifications Software and the commercial DxCG Intelligence predictive risk models, each with and without demographic and utilization features. We then calculated costs for patients in the top 1% and 5% of hospitalization risk identified by each model. RESULTS: The deep learning model performed the best across 6 predictive models, with an AUC of 75.1%. The top 1% of members selected by the deep learning model had a combined healthcare cost $5 million higher than that of the group identified by the DxCG Intelligence model. CONCLUSIONS: The deep learning model outperforms the traditional risk models in prospective hospitalization prediction. Thus, deep learning may improve the ability of managed care organizations to perform predictive modeling of financial risk, in addition to improving the accuracy of risk stratification for population health management activities.

Environmental and Genetic Activation of Hypothalamic BDNF Modulates T-cell Immunity to Exert an Anticancer Phenotype.

Macroenvironmental factors, including a patient's physical and social environment, play a role in cancer risk and progression. Our previous studies show that living in an enriched environment (EE) providing complex stimuli confers an anticancer phenotype in mice mediated, in part by a specific neuroendocrine axis, with brain-derived neurotrophic factor (BDNF) as the key brain mediator. Here, we investigated how an EE modulated T-cell immunity and its role in the EE-induced anticancer effects. Our data demonstrated that CD8 T cells were required to mediate the anticancer effects of an EE in an orthotropic model of melanoma. In secondary lymphoid tissue (SLT), an EE induced early changes in the phenotype of T-cell populations, characterized by a decrease in the ratio of CD4 T helper to CD8 cytotoxic T lymphocytes (CTL). Overexpression of hypothalamic BDNF reproduced EE-induced T-cell phenotypes in SLT, whereas knockdown of hypothalamic BDNF inhibited EE-induced immune modulation in SLT. Both propranolol and mifepristone blocked the EE-associated modulation of CTLs in SLT, suggesting that both the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis were involved. Our results demonstrated that enhanced anticancer effect of an EE was mediated at least in part through modulation of T-cell immunity and provided support to the emerging concept of manipulating a single gene in the brain to improve cancer immunotherapy. Cancer Immunol Res; 4(6); 488-97. ©2016 AACR.

Social overcrowding as a chronic stress model that increases adiposity in mice.

Stress is a widely recognized risk factor for psychiatric and metabolic disorders. A number of animal models utilizing various stressors have been developed to facilitate our understanding in the pathophysiology of stress-related dysfunctions. The most commonly used chronic stress paradigms include the unpredictable chronic mild stress paradigm, the social defeat paradigm and the social deprivation paradigm. Here we assess the potential of social crowding as an alternative chronic stress model to study the effects on affective behaviors and metabolic disturbances. Ten-week-old male C57BL/6 mice were housed in groups of four (control) or eight (social crowding; SC) in standard cage for 9 weeks. Exploration, anxiety- and depressive-like behaviors were assessed in the open field test, the elevated T-maze, the novelty-suppressed feeding test and the forced swim test. SC mice exhibited a modest anxiety-like phenotype without change in depressive-like behaviors. Nine weeks of social crowding did not affect the body weight, but robustly increased adiposity as determined by increased mass of fat depots. Consistent with the increased fat content, serum leptin was markedly elevated in the SC mice. Specific changes in gene expression were also observed in the hypothalamus and the white adipose tissue following SC housing. Our study demonstrates the potential of social crowding as an alternative model for the study of stress-related metabolic and behavioral dysfunctions.

An Immunological Approach to Increase the Brain's Resilience to Insults.

We have previously demonstrated the therapeutic potential of inducing a humoral response with autoantibodies to the N-methyl D-aspartate (NMDA) receptor using a genetic approach. In this study, we generated three recombinant proteins to different functional domains of the NMDA receptor, which is implicated in mediating brain tolerance, specifically NR1[21-375], NR1[313-619], NR1[654-800], and an intracellular scaffolding protein, Homer1a, with a similar anatomical expression pattern. All peptides showed similar antigenicity and antibody titers following systemic vaccination, and all animals thrived. Two months following vaccination, rats were administered the potent neurotoxin, kainic acid. NR1[21-375] animals showed an antiepileptic phenotype but no neuroprotection. Remarkably, despite ineffective antiepileptic activity, 6 of 7 seizing NR1[654-800] rats showed absolutely no injury with only minimal changes in the remaining animal, whereas the majority of persistently seizing rats in the other groups showed moderate to severe hippocampal injury. CREB, BDNF, and HSP70, proteins associated with preconditioning, were selectively upregulated in the hippocampus of NR1[654-800] animals, consistent with the observed neuroprotective phenotype. These results identify NR1 epitopes important in conferring anticonvulsive and neuroprotective effects and support the concept of an immunological strategy to induce a chronic state of tolerance in the brain.

Metabolic Effects of Social Isolation in Adult C57BL/6 Mice.

Obesity and metabolic dysfunction are risk factors for a number of chronic diseases, such as type 2 diabetes, hypertension, heart disease, stroke, and certain forms of cancers. Both animal studies and human population-based and clinical studies have suggested that chronic stress is a risk factor for metabolic disorders. A good social support system is known to exert positive effects on the mental and physical well-being of an individual. On the other hand, long-term deprivation of social contacts may represent a stressful condition that has negative effects on health. In the present study, we investigated the effects of chronic social isolation on metabolic parameters in adult C57BL/6 mice. We found that individually housed mice had increased adipose mass compared to group-housed mice, despite comparable body weight. The mechanism for the expansion of white adipose tissue mass was depot-specific. Notably, food intake was reduced in the social isolated animals, which occurred around the light-dark phase transition periods. Similarly, reductions in heat generated and the respiratory exchange ratio were observed during the light-dark transitions. These phase-specific changes due to long-term social isolation have not been reported previously. Our study shows social isolation contributes to increased adiposity and altered metabolic functions.

Neuropeptides as therapeutic targets in anxiety disorders.

In addition to the classical neurotransmitters, neuropeptides represent an important class of modulators for affective behaviors and associated disorders, such as anxiety disorders. Many neuropeptides are abundantly expressed in brain regions involved in emotional processing and anxiety behaviors. Moreover, risk factors for anxiety disorders such as stress modulate the expression of various neuropeptides in the brain. Due to the high prevalence of anxiety disorders and yet limited treatment options, there is a clear need for more effective therapeutics. In this regard, the various neuropeptides represent exciting candidates for new therapeutic designs. In this review, I will provide an up-to-date summary on the evidences for the involvement of seven neuropeptides in anxiety: corticotropin-releasing factor, urocortins, vasopressin, oxytocin, substance P, neuropeptide Y and galanin. This review will cover the behavioral effects of these neuropeptides in animal models of anxiety by both genetic and pharmacological manipulations. Human studies indicating a role for these neuropeptides in anxiety disorders will also be discussed.

Environmental enrichment exerts sex-specific effects on emotionality in C57BL/6J mice.

Environmental enrichment (EE) has been shown to exert various behavioral and mood effects in rodents including emotionality, which has a high propensity to be influenced by sex. However, there are only a few comparative studies evaluating the effect of EE and their results are both inconsistent and inconclusive. In the present study, male and female C57BL/6J adolescent mice were housed in either physical enrichment or standard conditions for four weeks with analysis of affective behaviors in the open field, elevated T-maze and forced swim tests. Hippocampal gene expression was characterized in an additional group of mice. In the open field test, exploration was similarly inhibited by EE in male and female mice. Both sex and housing condition influenced the time mice spent in the center of the arena. In the elevated T-maze, anxiety-like behavior was increased in female and decreased in male mice following EE. We observed a trend for EE-induced inhibition of glucocorticoid receptor (GR) mRNA expression in male but not in female mice. In contrast, mineralocorticoid receptor (MR) expression was unaffected by 10 days of physical enrichment but was lower in female mice compared to male mice. Our data suggest that the balance between hippocampal GR and MR may contribute to the observed sex-specific effect of physical enrichment on emotionality-related behavior.

Environmental and genetic activation of a brain-adipocyte BDNF/leptin axis causes cancer remission and inhibition.

Cancer is influenced by its microenvironment, yet broader, environmental effects also play a role but remain poorly defined. We report here that mice living in an enriched housing environment show reduced tumor growth and increased remission. We found this effect in melanoma and colon cancer models, and that it was not caused by physical activity alone. Serum from animals held in an enriched environment (EE) inhibited cancer proliferation in vitro and was markedly lower in leptin. Hypothalamic brain-derived neurotrophic factor (BDNF) was selectively upregulated by EE, and its genetic overexpression reduced tumor burden, whereas BDNF knockdown blocked the effect of EE. Mechanistically, we show that hypothalamic BDNF downregulated leptin production in adipocytes via sympathoneural beta-adrenergic signaling. These results suggest that genetic or environmental activation of this BDNF/leptin axis may have therapeutic significance for cancer.

Neuropeptide Y knockout mice reveal a central role of NPY in the coordination of bone mass to body weight.

Changes in whole body energy levels are closely linked to alterations in body weight and bone mass. Here, we show that hypothalamic signals contribute to the regulation of bone mass in a manner consistent with the central perception of energy status. Mice lacking neuropeptide Y (NPY), a well-known orexigenic factor whose hypothalamic expression is increased in fasting, have significantly increased bone mass in association with enhanced osteoblast activity and elevated expression of bone osteogenic transcription factors, Runx2 and Osterix. In contrast, wild type and NPY knockout (NPY (-/-)) mice in which NPY is specifically over expressed in the hypothalamus (AAV-NPY+) show a significant reduction in bone mass despite developing an obese phenotype. The AAV-NPY+ induced loss of bone mass is consistent with models known to mimic the central effects of fasting, which also show increased hypothalamic NPY levels. Thus these data indicate that, in addition to well characterized responses to body mass, skeletal tissue also responds to the perception of nutritional status by the hypothalamus independently of body weight. In addition, the reduction in bone mass by AAV NPY+ administration does not completely correct the high bone mass phenotype of NPY (-/-) mice, indicating the possibility that peripheral NPY may also be an important regulator of bone mass. Indeed, we demonstrate the expression of NPY specifically in osteoblasts. In conclusion, these data identifies NPY as a critical integrator of bone homeostatic signals; increasing bone mass during times of obesity when hypothalamic NPY expression levels are low and reducing bone formation to conserve energy under 'starving' conditions, when hypothalamic NPY expression levels are high.

Molecular therapy of obesity and diabetes by a physiological autoregulatory approach.

Hypothalamic brain-derived neurotrophic factor (BDNF) is a key element in the regulation of energy balance. Here we investigated the therapeutic efficacy of BDNF by gene transfer in mouse models of obesity and diabetes. Gene transfer of BDNF led to marked weight loss and alleviation of obesity-associated insulin resistance. To facilitate clinical translation and ensure that BDNF protein expression was appropriately decreased as weight loss progressed, thus preventing cachexia, we developed a molecular autoregulatory system involving a single recombinant adeno-associated virus vector harboring two expression cassettes, one constitutively driving BDNF and the other driving a specific microRNA targeting BDNF. The microRNA element was controlled by a promoter (that controlling the Agrp gene encoding agouti-related peptide) responsive to BDNF-induced physiological changes. Hence, as body weight decreased and agouti-related protein is induced, microRNA expression was activated, inhibiting transgene expression. In contrast to the progressive weight loss associated with a nonregulated approach, this microRNA-approach led to a sustainable plateau of body weight after notable weight loss was achieved. This strategy mimics the body's endogenous physiological feedback mechanisms, thereby resetting the hypothalamic set point to reverse obesity and metabolic syndrome.

Hippocampal NPY gene transfer attenuates seizures without affecting epilepsy-induced impairment of LTP.

Recently, hippocampal neuropeptide Y (NPY) gene therapy has been shown to effectively suppress both acute and chronic seizures in animal model of epilepsy, thus representing a promising novel antiepileptic treatment strategy, particularly for patients with intractable mesial temporal lobe epilepsy (TLE). However, our previous studies show that recombinant adeno-associated viral (rAAV)-NPY treatment in naive rats attenuates long-term potentiation (LTP) and transiently impairs hippocampal learning process, indicating that negative effect on memory function could be a potential side effect of NPY gene therapy. Here we report how rAAV vector-mediated overexpression of NPY in the hippocampus affects rapid kindling, and subsequently explore how synaptic plasticity and transmission is affected by kindling and NPY overexpression by field recordings in CA1 stratum radiatum of brain slices. In animals injected with rAAV-NPY, we show that rapid kindling-induced hippocampal seizures in vivo are effectively suppressed as compared to rAAV-empty injected (control) rats. Six to nine weeks later, basal synaptic transmission and short-term synaptic plasticity are unchanged after rapid kindling, while LTP is significantly attenuated in vitro. Importantly, transgene NPY overexpression has no effect on short-term synaptic plasticity, and does not further compromise LTP in kindled animals. These data suggest that epileptic seizure-induced impairment of memory function in the hippocampus may not be further affected by rAAV-NPY treatment, and may be considered less critical for clinical application in epilepsy patients already experiencing memory disturbances.

Activity-dependent volume transmission by transgene NPY attenuates glutamate release and LTP in the subiculum.

Neuropeptide Y (NPY) gene transduction of the brain using viral vectors in epileptogenic regions can effectively suppress seizures in animals, and is being considered as a promising alternative treatment strategy for epilepsy. Therefore, it is fundamental to understand the detailed mechanisms governing the release and action of transgene NPY in neuronal circuitries. Using whole-cell recordings from subicular neurons, we show that in animals transduced by recombinant adeno-associated viral (rAAV) vector carrying the NPY gene, transgene NPY is released during high-frequency activation of CA1-subicular synapses. Released transgene NPY attenuates excitatory synaptic transmission not only in activated, but also in neighboring, non-activated synapses. Such broad action of transgene NPY may prevent recruitment of excitatory synapses in epileptic activity and could play a key role in limiting the spread and generalization of seizures.

Viral mediated neuropeptide Y expression in the rat paraventricular nucleus results in obesity.

OBJECTIVE: Chronic central administration of neuropeptide Y (NPY) has dramatic effects on energy balance; however, the exact role of the hypothalamic paraventricular nucleus (PVN) in this is unknown. The aim of this study was to further unravel the contribution of NPY signaling in the PVN to energy balance. RESEARCH METHODS AND PROCEDURES: Recombinant adeno-associated viral particles containing NPY (rAAV-NPY) were injected in the rat brain with coordinates targeted at the PVN. For three weeks, body weight, food intake, endocrine parameters, body temperature, and locomotor activity were measured. Furthermore, effects on insulin sensitivity and expression of NPY, agouti-related protein (AgRP), and pro-opiomelanocortin in the arcuate nucleus were studied. RESULTS: Food intake was increased specifically in the light period, and dark phase body temperature and locomotor activity were reduced. This resulted in obesity characterized by increased fat mass; elevated plasma insulin, leptin, and adiponectin; decreased AgRP expression in the arcuate nucleus; and decreased insulin sensitivity; whereas plasma corticosterone was unaffected. DISCUSSION: These data suggest that increased NPY expression targeted at the PVN is sufficient to induce obesity. Interestingly, plasma concentrations of leptin and insulin were elevated before a rise in food intake, which suggests that NPY in the PVN influences leptin and insulin secretion independently from food intake. This strengthens the role of the PVN in regulation of energy balance by NPY.

Novel role of Y1 receptors in the coordinated regulation of bone and energy homeostasis.

The importance of neuropeptide Y (NPY) and Y2 receptors in the regulation of bone and energy homeostasis has recently been demonstrated. However, the contributions of the other Y receptors are less clear. Here we show that Y1 receptors are expressed on osteoblastic cells. Moreover, bone and adipose tissue mass are elevated in Y1(-/-) mice with a generalized increase in bone formation on cortical and cancellous surfaces. Importantly, the inhibitory effects of NPY on bone marrow stromal cells in vitro are absent in cells derived from Y1(-/-) mice, indicating a direct action of NPY on bone cells via this Y receptor. Interestingly, in contrast to Y2 receptor or germ line Y1 receptor deletion, conditional deletion of hypothalamic Y1 receptors in adult mice did not alter bone homeostasis, food intake, or adiposity. Furthermore, deletion of both Y1 and Y2 receptors did not produce additive effects in bone or adiposity. Thus Y1 receptor pathways act powerfully to inhibit bone production and adiposity by nonhypothalamic pathways, with potentially direct effects on bone tissue through a single pathway with Y2 receptors.

Dynorphin knockout reduces fat mass and increases weight loss during fasting in mice.

Endogenous opioids, particularly dynorphins, have been implicated in regulation of energy balance, but it is not known how they mediate this in vivo. We investigated energy homeostasis in dynorphin knockout mice (Dyn(-/-) mice) and probed the interactions between dynorphins and the neuropeptide Y (NPY) system. Dyn(-/-) mice were no different from wild types with regards to body weight and basal and fasting-induced food intake, but fecal output was increased, suggesting decreased nutrient absorption, and they had significantly less white fat and lost more weight during a 24-h fast. The neuroendocrine and thermal responses to fasting were at least as pronounced in Dyn(-/-) as in wild types, and there was no stimulatory effect of dynorphin knockout on 24-h energy expenditure (kilocalories of heat produced) or physical activity. However, Dyn(-/-) mice showed increased circulating concentrations of 3,4-dihydroxyphenlacetic acid and 3,4-dihydroxyphenylglycol, suggesting increased activity of the sympathetic nervous system. The respiratory exchange ratio of male but not female Dyn(-/-) mice was reduced, demonstrating increased fat oxidation. Interestingly, expression of the orexigenic acting NPY in the hypothalamic arcuate nucleus was reduced in Dyn(-/-) mice. However, fasting-induced increases in pre-prodynorphin expression in the arcuate nucleus, the paraventricular nucleus, and the ventromedial hypothalamus but not the lateral hypothalamus were abolished by deletion of Y(1) but not Y(2) receptors. Therefore, ablation of dynorphins results in increases in fatty acid oxidation in male mice, reductions in adiposity, and increased weight loss during fasting, possibly via increases in sympathetic activity, decreases in intestinal nutrient absorption, and interactions with the NPYergic system.

Fasting inhibits the growth and reproductive axes via distinct Y2 and Y4 receptor-mediated pathways.

Neuropeptide Y, a neuropeptide abundantly expressed in the brain, has been implicated in the regulation of the hypothalamo-pituitary-somatotropic axis and the hypothalamo-pituitary-gonadotropic axis. Elevated hypothalamic neuropeptide Y expression, such as that occurs during fasting, is known to inhibit both of these axes. However, it is not known which Y receptor(s) mediate these effects. Here we demonstrate, using Y receptor knockout mice, that Y2 and Y4 receptors are separately involved in the regulation of these axes. Fasting-induced inhibition of hypothalamic GHRH mRNA expression and reduction of circulating IGF-I levels were observed in wild-type and Y4(-/-) mice but not Y2(-/-) or Y2(-/-)Y4(-/-) mice. In contrast, fasting-induced reduction of GnRH expression in the medial preoptic area and testis testosterone content were abolished in the absence of Y4 receptors. Colocalization of Y2 receptors and GHRH in the arcuate nucleus (Arc) suggests that GHRH mRNA expression in this region might be directly regulated by Y2 receptors. Indeed, hypothalamic-specific deletion of Y2 receptors in conditional knockout mice prevented the fasting-induced reduction in Arc GHRH mRNA expression. On the other hand, fasting-induced decrease in GnRH mRNA expression in the medial preoptic area is more likely indirectly influenced by Y4 receptors because no Y4 receptors could be detected on GnRH neurons in this region. Together these data show that fasting inhibits the somatotropic axis via direct action on Y2 receptors in the Arc and indirectly inhibits the gonadotropic axis via Y4 receptors.