RESUMEN
Synthesis of triiodothyronine (T3) in the hypothalamus induces marked seasonal neuromorphology changes across taxa. How species-specific responses to T3 signaling in the CNS drive annual changes in body weight and energy balance remains uncharacterized. These experiments sequenced and annotated the Siberian hamster (Phodopus sungorus) genome, a model organism for seasonal physiology research, to facilitate the dissection of T3-dependent molecular mechanisms that govern predictable, robust, and long-term changes in body weight. Examination of the Phodopus genome, in combination with transcriptome sequencing of the hamster diencephalon under winter and summer conditions, and in vivo-targeted expression analyses confirmed that proopiomelanocortin (pomc) is a primary genomic target for the long-term T3-dependent regulation of body weight. Further in silico analyses of pomc promoter sequences revealed that thyroid hormone receptor 1ß-binding motif insertions have evolved in several genera of the Cricetidae family of rodents. Finally, experimental manipulation of food availability confirmed that hypothalamic pomc mRNA expression is dependent on longer-term photoperiod cues and is unresponsive to acute, short-term food availability. These observations suggest that species-specific responses to hypothalamic T3, driven in part by the receptor-binding motif insertions in some cricetid genomes, contribute critically to the long-term regulation of energy balance and the underlying physiological and behavioral adaptations associated with the seasonal organization of behavior.
Asunto(s)
Metabolismo Energético/fisiología , Hipotálamo/metabolismo , Phodopus/fisiología , Fotoperiodo , Proopiomelanocortina/metabolismo , Aclimatación/fisiología , Animales , Peso Corporal/fisiología , Frío/efectos adversos , Biología Computacional , Regulación hacia Abajo , Ingestión de Alimentos/fisiología , Evolución Molecular , Femenino , Privación de Alimentos/fisiología , Perfilación de la Expresión Génica , Masculino , Anotación de Secuencia Molecular , Neuropéptidos/metabolismo , Proopiomelanocortina/genética , Regiones Promotoras Genéticas/genética , Dominios y Motivos de Interacción de Proteínas/genética , Receptores de Hormona Tiroidea/metabolismo , Estaciones del Año , Especificidad de la Especie , Triyodotironina/administración & dosificación , Triyodotironina/metabolismo , Aumento de Peso/efectos de los fármacos , Aumento de Peso/fisiología , Secuenciación Completa del GenomaRESUMEN
Seasonal changes in day length enhance and suppress immune function in a trait-specific manner. In Siberian hamsters (Phodopus sungorus) winter-like short days (SDs) increase blood leukocyte concentrations and adaptive T cell dependent immune responses, but attenuate innate inflammatory responses to simulated infections. Thyroid hormone (TH) signaling also changes seasonally and has been implicated in modulation of the reproductive axis by day length. Immunologically, TH administration in long days (LD) enhances adaptive immune responses in male Siberian hamsters, mimicking effects of SDs. This experiment tested the hypothesis that T3 is also sufficient to mimic the effects of SD on innate immune responses. Adult male hamsters housed in LDs were pretreated with triiodothyronine (T3; 1⯵g, s.c.) or saline (VEH) daily for 6â¯weeks; additional positive controls were housed in SD and received VEH, after which cytokine, behavioral, and physiological responses to simulated bacterial infection (lipopolysaccharide; LPS) were evaluated. SD pretreatment inhibited proinflammatory cytokine mRNA expression (i.e. interleukin 1ß, nuclear factor kappa-light-chain-enhancer of activated B cells). In addition, the magnitude and persistence of anorexic and cachectic responses to LPS were also lower in SD hamsters, and LPS-induced inhibition of nest building behavior was absent in SD. T3 treatments failed to affect behavioral (food intake, nest building) or somatic (body mass) responses to LPS in LD hamsters, but one CNS cytokine response to LPS (e.g., hypothalamic TNFα) was augmented by T3. Together these data implicate thyroid hormone signaling in select aspects of innate immune responses to seasonal changes in day length.
Asunto(s)
Conducta Animal/efectos de los fármacos , Citocinas/metabolismo , Phodopus , Síndrome de Respuesta Inflamatoria Sistémica/patología , Triyodotironina/farmacología , Animales , Anorexia/inducido químicamente , Anorexia/metabolismo , Anorexia/patología , Peso Corporal/fisiología , Cricetinae , Modelos Animales de Enfermedad , Hipotálamo/efectos de los fármacos , Hipotálamo/metabolismo , Conducta de Enfermedad/efectos de los fármacos , Inmunidad Innata/efectos de los fármacos , Infecciones/inducido químicamente , Infecciones/metabolismo , Infecciones/patología , Lipopolisacáridos , Masculino , Phodopus/metabolismo , Fotoperiodo , Reproducción/efectos de los fármacos , Estaciones del Año , Síndrome de Respuesta Inflamatoria Sistémica/inducido químicamente , Síndrome de Respuesta Inflamatoria Sistémica/metabolismo , Síndrome de Respuesta Inflamatoria Sistémica/fisiopatologíaRESUMEN
Diverse mammalian ultradian rhythms (URs) with periods in the 1-6h range, are omnipresent at multiple levels of biological organization and of functional and adaptive significance. Specification of neuroendocrine substrates that generate URs remains elusive. The suprachiasmatic (SCN) and arcuate (ARC) nuclei of the rodent hypothalamus subserve several behavioral URs. Recently, in a major advance, dopaminergic signaling in striatal circuitry, likely at D2 receptors, has been implicated in behavioral and thermoregulatory URs of mice. We propose a neural network in which reciprocal communication among the SCN, the ARC and striatal dopaminergic circuitry modulates the period and waveform of behavioral and physiological URs.
Asunto(s)
Conducta Animal/fisiología , Red Nerviosa/fisiología , Ritmo Ultradiano/fisiología , Animales , Núcleo Arqueado del Hipotálamo/fisiología , Neuronas Dopaminérgicas/fisiología , Hipotálamo/fisiología , Transducción de Señal/fisiologíaRESUMEN
Cancer is associated with an increased prevalence of depression. Peripheral tumors induce inflammatory cytokine production in the brain and depressive-like behaviors. Mounting evidence indicates that cytokines are part of a pathway by which peripheral inflammation causes depression. Neuroinflammatory responses to immune challenges can be exacerbated (primed) by prior immunological activation associated with aging, early-life infection, and drug exposure. This experiment tested the hypothesis that peripheral tumors likewise induce neuroinflammatory sensitization or priming. Female rats with chemically-induced mammary carcinomas were injected with either saline or lipopolysaccharide (LPS, 250µg/kg; i.p.), and expression of mRNAs involved in the pathway linking inflammation and depression (interleukin-1beta [Il-1ß], CD11b, IκBα, indolamine 2,3-deoxygenase [Ido]) was quantified by qPCR in the hippocampus, hypothalamus, and frontal cortex, 4 or 24h post-treatment. In the absence of LPS, hippocampal Il-1ß and CD11b mRNA expression were elevated in tumor-bearing rats, whereas Ido expression was reduced. Moreover, in saline-treated rats basal hypothalamic Il-1ß and CD11b expression were positively correlated with tumor weight; heavier tumors, in turn, were characterized by more inflammatory, necrotic, and granulation tissue. Tumors exacerbated CNS proinflammatory gene expression in response to LPS: CD11b was greater in hippocampus and frontal cortex of tumor-bearing relative to tumor-free rats, IκBα was greater in hippocampus, and Ido was greater in hypothalamus. Greater neuroinflammatory responses in tumor-bearing rats were accompanied by attenuated body weight gain post-LPS. The data indicate that neuroinflammatory pathways are potentiated, or primed, in tumor-bearing rats, which may exacerbate future negative behavioral consequences.
Asunto(s)
Depresión/inmunología , Endotoxemia/inmunología , Endotoxinas/toxicidad , Lóbulo Frontal/metabolismo , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Hipocampo/metabolismo , Hipotálamo/metabolismo , Inflamación/inmunología , Neoplasias Mamarias Experimentales/inmunología , Animales , Antígeno CD11b/biosíntesis , Antígeno CD11b/genética , Depresión/etiología , Depresión/genética , Regulación hacia Abajo/efectos de los fármacos , Endotoxemia/genética , Endotoxemia/psicología , Inducción Enzimática/efectos de los fármacos , Femenino , Lóbulo Frontal/efectos de los fármacos , Hipocampo/efectos de los fármacos , Hipotálamo/efectos de los fármacos , Indolamina-Pirrol 2,3,-Dioxigenasa/biosíntesis , Indolamina-Pirrol 2,3,-Dioxigenasa/genética , Inflamación/inducido químicamente , Inflamación/genética , Inflamación/psicología , Interleucina-1beta/biosíntesis , Interleucina-1beta/genética , Neoplasias Mamarias Experimentales/inducido químicamente , Neoplasias Mamarias Experimentales/psicología , ARN Mensajero/biosíntesis , ARN Neoplásico , Ratas , Ratas Wistar , Carga Tumoral/efectos de los fármacos , Aumento de PesoRESUMEN
In seasonally breeding vertebrates, changes in day length induce categorically distinct behavioral and reproductive phenotypes via thyroid hormone-dependent mechanisms. Winter photoperiods inhibit reproductive neuroendocrine function but cannot sustain this inhibition beyond 6 mo, ensuring vernal reproductive recrudescence. This genomic plasticity suggests a role for epigenetics in the establishment of seasonal reproductive phenotypes. Here, we report that DNA methylation of the proximal promoter for the type III deiodinase (dio3) gene in the hamster hypothalamus is reversible and critical for photoperiodic time measurement. Short photoperiods and winter-like melatonin inhibited hypothalamic DNA methyltransferase expression and reduced dio3 promoter DNA methylation, which up-regulated dio3 expression and induced gonadal regression. Hypermethylation attenuated reproductive responses to short photoperiods. Vernal refractoriness to short photoperiods reestablished summer-like methylation of the dio3 promoter, dio3 expression, and reproductive competence, revealing a dynamic and reversible mechanism of DNA methylation in the mammalian brain that plays a central role in physiological orientation in time.
Asunto(s)
Metilación de ADN/fisiología , Epigénesis Genética/fisiología , Regulación de la Expresión Génica/fisiología , Fotoperiodo , Estaciones del Año , Percepción del Tiempo/fisiología , Análisis de Varianza , Animales , Cricetinae , Enzimas de Restricción del ADN , Ensayo de Inmunoadsorción Enzimática , Femenino , Hipotálamo/metabolismo , Inmunohistoquímica , Yoduro Peroxidasa/metabolismo , Masculino , Phodopus , Análisis de Secuencia de ADNRESUMEN
The immune system is under strong circadian control, and circadian desynchrony is a risk factor for metabolic disorders, inflammatory responses and cancer. Signaling pathways that maintain circadian rhythms (CRs) in immune function in vivo, and the mechanisms by which circadian desynchrony impairs immune function, remain to be fully identified. These experiments tested the hypothesis that the hypothalamic circadian pacemaker in the suprachiasmatic nucleus (SCN) drives CRs in the immune system, using a non-invasive model of SCN circadian arrhythmia. Robust CRs in blood leukocyte trafficking, with a peak during the early light phase (ZT4) and nadir in the early dark phase (ZT18), were absent in arrhythmic hamsters, as were CRs in spleen clock gene (per1, bmal1) expression, indicating that a functional pacemaker in the SCN is required for the generation of CRs in leukocyte trafficking and for driving peripheral clocks in secondary lymphoid organs. Pinealectomy was without effect on CRs in leukocyte trafficking, but abolished CRs in spleen clock gene expression, indicating that nocturnal melatonin secretion is necessary for communicating circadian time information to the spleen. CRs in trafficking of antigen presenting cells (CD11c(+) dendritic cells) in the skin were abolished, and antigen-specific delayed-type hypersensitivity skin inflammatory responses were markedly impaired in arrhythmic hamsters. The SCN drives robust CRs in leukocyte trafficking and lymphoid clock gene expression; the latter of which is not expressed in the absence of melatonin. Robust entrainment of the circadian pacemaker provides a signal critical to diurnal rhythms in immunosurveilliance and optimal memory T-cell dependent immune responses.
Asunto(s)
Relojes Circadianos/inmunología , Dermatitis/inmunología , Leucocitos/inmunología , Ciclos de Actividad/inmunología , Animales , Relojes Circadianos/genética , Ritmo Circadiano/genética , Cricetinae , ADN Complementario/biosíntesis , ADN Complementario/genética , Oscuridad , Células Dendríticas/efectos de los fármacos , Células Dendríticas/fisiología , Femenino , Citometría de Flujo , Expresión Génica , Hidrocortisona/sangre , Hipersensibilidad Tardía/inmunología , Iluminación , Tejido Linfoide/inmunología , Tejido Linfoide/fisiología , Masculino , Melatonina/farmacología , Actividad Motora/fisiología , Proteínas Circadianas Period , Phodopus , Glándula Pineal/fisiología , Reacción en Cadena de la Polimerasa , ARN/biosíntesis , ARN/aislamiento & purificación , Bazo/fisiología , Estrés Psicológico/inmunología , Estrés Psicológico/psicologíaRESUMEN
Perihypothalamic thyroid hormone signaling features prominently in the seasonal control of reproductive physiology. Triiodothyronine (T(3)) signaling stimulates gonadal development, and decrements in T(3) signaling are associated with gonadal regression. Type 3 iodothyronine deiodinase (DIO3) converts the prohormone thyroxine (T(4)) into biologically inactive 3,3',5'-triiodothyronine, and in long-day breeding Siberian hamsters exposure to long (LD) and short (SD) photoperiods, respectively, inhibit and stimulate hypothalamic dio3 mRNA expression. Reproductive responses to intermediate-duration photoperiods (IntD) occur in a history-dependent manner; IntDs are interpreted as inhibitory only when preceded by longer photoperiods. Because dio3 expression has only been evaluated under LD or SD photoperiods, it is not known whether hypothalamic dio3 encodes absolute photoperiod duration or the reproductive interpretation of photoperiod. Male Siberian hamsters with and without a prior history of LD were exposed to IntD photoperiods, and hypothalamic dio3 mRNA expression was measured 6 wk later. Hamsters with a LD photoperiod history exhibited gonadal regression in IntD and a marked upregulation of hypothalamic dio3 expression, whereas in hamsters without prior exposure to LD, gonadal responses to IntD were absent, and dio3 expression remained low. Patterns of deiodinase expression in hamsters maintained in chronic IntD photoperiods did not appear to reflect feedback effects of gonadal status. Hypothalamic expression of dio3 does not exclusively reflect ambient photoperiod, but rather the context-dependent reproductive interpretation of photoperiod. Neuroendocrine mechanisms that compare current and prior photoperiods, which permit detection of directional changes in day length, occur either upstream, or at the level, of hypothalamic dio3 expression.
Asunto(s)
Hipotálamo/enzimología , Hipotálamo/fisiología , Yoduro Peroxidasa/biosíntesis , Fotoperiodo , ARN Mensajero/biosíntesis , Animales , Cricetinae , Femenino , Regulación Enzimológica de la Expresión Génica/genética , Regulación Enzimológica de la Expresión Génica/fisiología , Yoduro Peroxidasa/genética , Yoduro Peroxidasa/fisiología , Masculino , Melatonina/fisiología , Actividad Motora/fisiología , Tamaño de los Órganos/fisiología , Phodopus , Reacción en Cadena en Tiempo Real de la Polimerasa , Reproducción/fisiología , Estaciones del Año , Vesículas Seminales/crecimiento & desarrollo , Vesículas Seminales/fisiología , Testículo/crecimiento & desarrollo , Testículo/fisiologíaRESUMEN
Production of T(3) in the mediobasal hypothalamus is critical for regulation of seasonal reproductive physiology. Type 2 iodothyronine deiodinase (DIO2) and DIO3 enzymes catalyze the prohormone T(4) into biologically-active T(3) and biologically-inactive rT(3), respectively. In several seasonally-breeding vertebrates, DIO2 and DIO3 expression is implicated in photoperiod signal transduction in adulthood. These experiments tested the hypothesis that juvenile Siberian hamsters, which are highly responsive to photoperiod at weaning (postnatal day [PND]18), exhibit rapid and sustained changes in hypothalamic dio3 mRNA expression during photoperiod-induced and photoperiod-inhibited puberty. Hypothalamic dio2 and dio3 expression was measured via quantitative PCR in hamsters born and reared in a long-day photoperiod (15L:9D) and weaned on PND18 into short-day photoperiods (9L:15D). In SD males, hypothalamic dio3 mRNA was elevated 2.5-fold within 3 days (PND21) and continued to increase (>20-fold) through PND32; changes in dio3 mRNA preceded inhibition of gonadotropin (FSH) secretion and gonadal regression in SD. Females exhibited comparable dio3 responses to SD. In LD males, dio3 remained low and invariant from PND18-PND32. In contrast, dio2 mRNA rose conspicuously on PND21, independent of photoperiod, returning to basal levels thereafter. In LD, a single afternoon melatonin (MEL) injection on PND18 or PND20 was sufficient to increase hypothalamic dio3 mRNA, and dio3 increased in proportion to the number of successive days of MEL treatment. SD photoperiods and MEL exert rapid, sustained, and additive effects on hypothalamic dio3 mRNA, which may play a central role in inhibiting maturation of the peripubertal hypothalamo-pituitary-gonadal axis.
Asunto(s)
Hipotálamo/enzimología , Yoduro Peroxidasa/biosíntesis , Melatonina/farmacología , Fotoperiodo , Animales , Cricetinae , Inducción Enzimática , Femenino , Yoduro Peroxidasa/genética , Masculino , Phodopus , ARN Mensajero/metabolismo , DesteteRESUMEN
Experience-dependent functional plasticity is a hallmark of the primary visual system, but it is not known if analogous mechanisms govern development of the circadian visual system. Here we investigated molecular, anatomical, and behavioral consequences of complete monocular light deprivation during extended intervals of postnatal development in Syrian hamsters. Hamsters were raised in constant darkness and opaque contact lenses were applied shortly after eye opening and prior to the introduction of a light-dark cycle. In adulthood, previously-occluded eyes were challenged with visual stimuli. Whereas image-formation and motion-detection were markedly impaired by monocular occlusion, neither entrainment to a light-dark cycle, nor phase-resetting responses to shifts in the light-dark cycle were affected by prior monocular deprivation. Cholera toxin-b subunit fluorescent tract-tracing revealed that in monocularly-deprived hamsters the density of fibers projecting from the retina to the suprachiasmatic nucleus (SCN) was comparable regardless of whether such fibers originated from occluded or exposed eyes. In addition, long-term monocular deprivation did not attenuate light-induced c-Fos expression in the SCN. Thus, in contrast to the thalamocortical projections of the primary visual system, retinohypothalamic projections terminating in the SCN develop into normal adult patterns and mediate circadian responses to light largely independent of light experience during development. The data identify a categorical difference in the requirement for light input during postnatal development between circadian and non-circadian visual systems.
Asunto(s)
Ritmo Circadiano , Mesocricetus/fisiología , Visión Binocular , Visión Monocular , Animales , Toxina del Cólera/metabolismo , Cricetinae , Femenino , Hipotálamo/fisiología , Inmunohistoquímica , Masculino , Retina/fisiología , Núcleo Supraquiasmático/fisiología , Agudeza VisualRESUMEN
In common with reproduction, immune function exhibits strong seasonal patterns, which are driven by annual changes in day length (photoperiod) and melatonin secretion. Whereas changes in melatonin communicate seasonal time into the reproductive axis via subcortical receptors, the relevant melatonin targets for communicating seasonal time into the immune system remain unspecified. The authors report that melatonin implants targeting the hypothalamic suprachiasmatic nuclei (SCN) induced a winter phenotype in the immune system. SCN melatonin implants attenuated infection-induced anorexia and cachexia, indicating that the SCN mediate the effects of melatonin on these behavioral and metabolic symptoms of infection. However, SCN melatonin implants failed to induce winter-like peripheral leukocyte concentrations or behavioral thermoregulatory responses to infection. In contrast, subcutaneous melatonin implants induced winter-like changes in all behavioral and immunological parameters. Melatonin acts directly at the SCN to induce seasonal changes in neural-immune systems that regulate behavior. The data identify anatomical overlap between neural substrates mediating the effects of melatonin on the reproductive and immune systems but also suggest that the SCN are not the sole mediator of photoperiodic effects of melatonin on immunity.
Asunto(s)
Antioxidantes/uso terapéutico , Síntomas Conductuales/tratamiento farmacológico , Síntomas Conductuales/patología , Melatonina/uso terapéutico , Núcleo Supraquiasmático/efectos de los fármacos , Análisis de Varianza , Animales , Síntomas Conductuales/etiología , Cricetinae , Ingestión de Alimentos/efectos de la radiación , Infecciones/complicaciones , Leucocitos , Masculino , Phodopus , Fototerapia/métodos , Glándula Pineal/fisiología , Glándula Pineal/cirugía , Conducta Sexual Animal/efectos de los fármacos , Conducta Sexual Animal/fisiología , Testículo/patologíaRESUMEN
An interval timing mechanism in the brain governs reproduction in seasonally breeding mammals by triggering refractoriness to inhibitory short photoperiods during midwinter. The neural mechanisms responsible for the timing and induction of photorefractoriness by this seasonal clock are unknown. Using cDNA microarrays and RT-PCR, we identified a class of genes encoding thyroxine (T4)-binding proteins (transthyretin, T4-binding globulin, albumin) whose expression is associated with reproductive refractoriness to short day lengths. Down-regulation of these genes was associated with reduced hypothalamic T4 uptake, which was reversed by long-day photoperiod treatments that restored responsiveness to short days. Circulating T4 concentrations did not vary with states of photoresponsiveness in euthyroid hamsters, but blockade of thyroid function accelerated the onset of photorefractoriness to short days. These data link changes in gene expression in the hypothalamus to the functional output of a seasonal clock. Reproductive inhibition in short days depends on T4 only late in the nonbreeding season. Down-regulation of genes encoding T4-binding proteins in the hypothalamus during this interval may restrict access of a static T4 signal to hypothalamic target tissues that regulate reproduction, thereby timing annual transitions in reproductive function. Hypothalamic autoregulation of T4 influx may constitute a critical cellular process involved in the generation and expression of seasonal reproductive rhythms and suggests a previously undescribed mechanism by which neural targets gain access to peripheral hormones.
Asunto(s)
Regulación de la Expresión Génica/efectos de la radiación , Hipotálamo/metabolismo , Hipotiroidismo/genética , Proteínas del Tejido Nervioso/biosíntesis , Phodopus/genética , Fotoperiodo , Prealbúmina/biosíntesis , Proteínas de Unión a Tiroxina/biosíntesis , Albúminas/biosíntesis , Albúminas/genética , Animales , Relojes Biológicos/genética , Cricetinae , Perfilación de la Expresión Génica , Sistema Hipotálamo-Hipofisario/fisiología , Hipotiroidismo/inducido químicamente , Masculino , Proteínas del Tejido Nervioso/genética , Análisis de Secuencia por Matrices de Oligonucleótidos , Tamaño de los Órganos , Phodopus/metabolismo , Prealbúmina/genética , Reproducción/fisiología , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Estaciones del Año , Testículo/anatomía & histología , Tiourea/toxicidad , Glándula Tiroides/fisiología , Tiroxina/metabolismo , Proteínas de Unión a Tiroxina/genéticaRESUMEN
Golden-mantled ground squirrels (Spermophilus lateralis) undergo seasonal hibernation during which core body temperature (T(b)) values are maintained 1-2 degrees C above ambient temperature. Hibernation is not continuous. Squirrels arouse at approximately 7-day intervals, during which T(b) increases to 37 degrees C for approximately 16 h; thereafter, they return to hibernation and sustain low T(b)s until the next arousal. Over the course of the hibernation season, arousals consume 60-80% of a squirrel's winter energy budget, but their functional significance is unknown and disputed. Host-defense mechanisms appear to be downregulated during the hibernation season and preclude normal immune responses. These experiments assessed immune function during hibernation and subsequent periodic arousals. The acute-phase response to bacterial lipopolysaccharide (LPS) was arrested during hibernation and fully restored on arousal to normothermia. LPS injection (ip) resulted in a 1-1.5 degrees C fever in normothermic animals that was sustained for > 8 h. LPS was without effect in hibernating squirrels, neither inducing fever nor provoking arousal, but a fever did develop several days later, when squirrels next aroused from hibernation; the duration of this arousal was increased sixfold above baseline values. Intracerebroventricular infusions of prostaglandin E(2) provoked arousal from hibernation and induced fever, suggesting that neural signaling pathways that mediate febrile responses are functional during hibernation. Periodic arousals may activate a dormant immune system, which can then combat pathogens that may have been introduced immediately before or during hibernation.