Wake promoting effects of cocaine and amphetamine-regulated transcript (CART)

Neuroanatomical, electrophysiological, and morphological characterization of melanin-concentrating hormone cells coexpressing cocaine- and amphetamine-regulated transcript

Melanin-concentrating hormone (MCH) cells in the hypothalamus regulate fundamental physiological functions like energy balance, sleep, and reproduction. This diversity may be ascribed to the neurochemical heterogeneity among MCH cells. One prominent subpopulation of MCH cells coexpresses cocaine- and amphetamine-regulated transcript (CART), and as MCH and CART can have opposing actions, MCH/CART+ and MCH/CART- cells may differentially modulate behavioral outcomes. However, it is not known if there are differences in the cellular properties underlying their functional differences; thus, we compared the neuroanatomical, electrophysiological, and morphological properties of MCH cells in male and female Mch-cre;L10-Egfp reporter mice. Half of MCH cells expressed CART and were most prominent in the medial hypothalamus. Whole-cell patch-clamp recordings revealed differences in their passive and active membrane properties in a sex-dependent manner. Female MCH/CART+ cells had lower input resistances, but male cells largely differed in their firing properties. All MCH cells increased firing when stimulated, but their firing frequency decreases with sustained stimulation. MCH/CART+ cells showed stronger spike rate adaptation than MCH/CART- cells. The kinetics of excitatory events at MCH cells also differed by cell type, as the rising rate of excitatory events was slower at MCH/CART+ cells. By reconstructing the dendritic arborization of our recorded cells, we found no sex differences, but male MCH/CART+ cells had less dendritic length and fewer branch points. Overall, distinctions in topographical division and cellular properties between MCH cells add to their heterogeneity and help elucidate their response to stimuli or effect on modulating their respective neural networks.

Reproductive phase related variations in the expression of neuropeptide, cocaine- and amphetamine- regulated transcript (CART) in the brain and pituitary gland of adult male Microhyla ornata

Cocaine- and amphetamine-regulated transcript (CART) peptide is a multifaceted neuropeptide involved in several physiological functions including appetite and reproduction. While studies in mammals, aves and fishes suggest evolutionary conserved role of CART, the information in amphibian is scanty. We have investigated the reproductive phase related variations of CART in the brain of adult male Microhyla ornata. Seasonal changes in the expression of CART peptide were noticed in the brain and pituitary of M. ornata. Significant differences were observed in the nucleus infundibularis ventralis (NIV), epiphysis (E), anteroventral tegmental region (AV), raphe nucleus (Ra) of the brain and pars intermedia (PI), pars distalis (PD) of the pituitary. Compared to the pre-breeding and post-breeding seasons, increase in CART immunoreactivity was seen in E, NIV, AV, Ra of brain and PI, PD of pituitary gland of animals collected during breeding season. Similarly, highest mRNA levels of CART were also observed in the breeding season in the middle region of brain that includes hypothalamus and pituitary gland. Variation in the levels of CART peptide and mRNA in the brain of M. ornata suggests its conserved role in seasonal control of appetite and reproduction.

Loss of the metabolism and sleep regulating neuronal populations expressing orexin and oxytocin in the hypothalamus in amyotrophic lateral sclerosis

AIMS

To determine the underlying cellular changes and clinical correlates associated with pathology of the hypothalamus in amyotrophic lateral sclerosis (ALS), as hypothalamic atrophy occurs in the preclinical phase of the disease.

METHODS

The hypothalamus was pathologically examined in nine patients with amyotrophic lateral sclerosis in comparison to eight healthy control subjects. The severity of regional atrophy (paraventricular nucleus: PVN, fornix and total hypothalamus) and peptidergic neuronal loss (oxytocin, vasopressin, cocaine- and amphetamine-regulating transcript: CART, and orexin) was correlated with changes in eating behaviour, sleep function, cognition, behaviour and disease progression.

RESULTS

Tar DNA-binding protein 43 (TDP-43) inclusions were present in the hypothalamus of all patients with amyotrophic lateral sclerosis. When compared to controls, there was atrophy of the hypothalamus (average 21% atrophy, p = 0.004), PVN (average 30% atrophy p = 0.014) and a loss of paraventricular oxytocin-producing neurons (average 49% loss p = 0.02) and lateral hypothalamic orexin-producing neurons (average 37% loss, significance p = 0.02). Factor analysis identified strong relationships between abnormal eating behaviour, hypothalamic atrophy and loss of orexin-producing neurons. With increasing disease progression, abnormal sleep behaviour and cognition associated with atrophy of the fornix.

CONCLUSIONS

Substantial loss of hypothalamic oxytocin-producing neurons occurs in ALS, with regional atrophy and the loss of orexin neurons relating to abnormal eating behaviour in ALS. Oxytocin- and orexin neurons display TDP43 inclusions. Our study points to significant pathology in the hypothalamus that may play a key role in metabolic and pathogenic changes in ALS.

Sleep/Wake Behavior and EEG Signatures of the TgF344-AD Rat Model at the Prodromal Stage

Transgenic modification of the two most common genes (APPsw, PS1ΔE9) related to familial Alzheimer's disease (AD) in rats has produced a rodent model that develops pathognomonic signs of AD without genetic tau-protein modification. We used 17-month-old AD rats (n = 8) and age-matched controls (AC, n = 7) to evaluate differences in sleep behavior and EEG features during wakefulness (WAKE), non-rapid eye movement sleep (NREM), and rapid eye movement sleep (REM) over 24-h EEG recording (12:12h dark-light cycle). We discovered that AD rats had more sleep-wake transitions and an increased probability of shorter REM and NREM bouts. AD rats also expressed a more uniform distribution of the relative spectral power. Through analysis of information content in the EEG using entropy of difference, AD animals demonstrated less EEG information during WAKE, but more information during NREM. This seems to indicate a limited range of changes in EEG activity that could be caused by an AD-induced change in inhibitory network function as reflected by increased GABAAR-β2 expression but no increase in GAD-67 in AD animals. In conclusion, this transgenic rat model of Alzheimer's disease demonstrates less obvious EEG features of WAKE during wakefulness and less canonical features of sleep during sleep.

Gene expression analysis in the mouse brainstem identifies Cart and Nesfatin as neuropeptides coexpressed in the Calbindin-positive neurons of the Nucleus papilio

Study Objectives: The brainstem contains several neuronal populations, heterogeneous in terms of neurotransmitter/neuropeptide content, which are important for controlling various aspects of the rapid eye movement (REM) phase of sleep. Among these populations are the Calbindin (Calb)-immunoreactive NP^Calb neurons, located in the Nucleus papilio, within the dorsal paragigantocellular nucleus (DPGi), and recently shown to control eye movement during the REM phase of sleep. Methods: We performed in-depth data mining of the in situ hybridization data collected at the Allen Brain Atlas, in order to identify potentially interesting genes expressed in this brainstem nucleus. Our attention focused on genes encoding neuropeptides, including Cart (Cocaine and Amphetamine Regulated Transcripts) and Nesfatin 1. Results: While nesfatin 1 appeared ubiquitously expressed in this Calb-positive neuronal population, Cart was coexpressed in only a subset of these glutamatergic NP^Calb neurons. Furthermore, an REM sleep deprivation and rebound assay performed with mice revealed that the Cart-positive neuronal population within the DPGi was activated during REM sleep (as measured by c-fos immunoreactivity), suggesting a role of this neuropeptide in regulating some aspects of REM sleep. Conclusions: The assembled information could afford functional clues to investigators, conducive to further experimental pursuits.

Melanin-concentrating hormone neurons promote rapid eye movement sleep independent of glutamate release

Neurons containing melanin-concentrating hormone (MCH) in the posterior lateral hypothalamus play an integral role in rapid eye movement sleep (REMs) regulation. As MCH neurons also contain a variety of other neuropeptides [e.g., cocaine- and amphetamine-regulated transcript (CART) and nesfatin-1] and neurotransmitters (e.g., glutamate), the specific neurotransmitter responsible for REMs regulation is not known. We hypothesized that glutamate, the primary fast-acting neurotransmitter in MCH neurons, is necessary for REMs regulation. To test this hypothesis, we deleted vesicular glutamate transporter (Vglut2; necessary for synaptic release of glutamate) specifically from MCH neurons by crossing MCH-Cre mice (expressing Cre recombinase in MCH neurons) with Vglut2^flox/flox mice (expressing LoxP-modified alleles of Vglut2), and studied the amounts, architecture and diurnal variation of sleep-wake states during baseline conditions. We then activated the MCH neurons lacking glutamate neurotransmission using chemogenetic methods and tested whether these MCH neurons still promoted REMs. Our results indicate that glutamate in MCH neurons contributes to normal diurnal variability of REMs by regulating the levels of REMs during the dark period, but MCH neurons can promote REMs even in the absence of glutamate.

Dietary challenges differentially affect activity and sleep/wake behavior in mus musculus: Isolating independent associations with diet/energy balance and body weight

BACKGROUND AND AIMS

Associated with numerous metabolic and behavioral abnormalities, obesity is classified by metrics reliant on body weight (such as body mass index). However, overnutrition is the common cause of obesity, and may independently contribute to these obesity-related abnormalities. Here, we use dietary challenges to parse apart the relative influence of diet and/or energy balance from body weight on various metabolic and behavioral outcomes.

MATERIALS AND METHODS

Seventy male mice (mus musculus) were subjected to the diet switch feeding paradigm, generating groups with various body weights and energetic imbalances. Spontaneous activity patterns, blood metabolite levels, and unbiased gene expression of the nutrient-sensing ventral hypothalamus (using RNA-sequencing) were measured, and these metrics were compared using standardized multivariate linear regression models.

RESULTS

Spontaneous activity patterns were negatively related to body weight (p<0.0001) but not diet/energy balance (p = 0.63). Both body weight and diet/energy balance predicted circulating glucose and insulin levels, while body weight alone predicted plasma leptin levels. Regarding gene expression within the ventral hypothalamus, only two genes responded to diet/energy balance (neuropeptide y [npy] and agouti-related peptide [agrp]), while others were related only to body weight.

CONCLUSIONS

Collectively, these results demonstrate that individual components of obesity-specifically obesogenic diets/energy imbalance and elevated body mass-can have independent effects on metabolic and behavioral outcomes. This work highlights the shortcomings of using body mass-based indices to assess metabolic health, and identifies novel associations between blood biomarkers, neural gene expression, and animal behavior following dietary challenges.

Low cocaine- and amphetamine-regulated transcript (CART) peptide levels in human cerebrospinal fluid of major depressive disorder (MDD) patients

BACKGROUND

Cocaine- and amphetamine-regulated transcript (CART) peptide is a candidate neuropeptide as a biomarker for major depressive disorder (MDD) because of its effects on emotion and distribution covering brain areas involved in the pathophysiology of MDD symptoms. However, it is unknown whether CART peptide levels are altered in the cerebrospinal fluid (CSF) of patients with MDD patients and are correlated with MDD symptoms.

METHODS

Subjects were 24 patients with MDD and 25 healthy controls matched for age, gender and ethnicity (Japanese). We measured CSF CART levels by a commercially available immunoassay kit and analyzed the relationships of the levels with antidepressant dose and symptoms assessed with the 21 item Hamilton Depression Rating Scale (HAMD-21).

RESULTS

CSF CART levels were significantly decreased in the patients than in the controls (p < 0.05). In MDD patient group, the CART levels had a negative correlation with antidepressant dose (imipramine-equivalent dose) (ρ = -0.55, p < 0.01) and significantly decreased in antidepressant-treated group (AD-treated group) compared to controls (p < 0.05). CSF CART levels showed significant negative correlations with psychomotor retardation, somatic anxiety, and general somatic symptoms (all p < 0.05) and a positive correlation with obsessive and compulsive symptoms (p < 0.05).

LIMITATIONS

In our analysis, all classes of antidepressants were combined together and the effects of medication use in a longitudinal manner did not confirm.

CONCLUSIONS

We report for the first time that CSF CART peptide levels are reduced in patients with MDD compared with healthy controls. The CART levels showed negative correlations with antidepressant dose and some symptoms, supporting the possibility that CART peptide is involved in the development of depressive symptoms.

Effects of γ-Aminobutyric Acid Type A Receptor Modulation by Flumazenil on Emergence from General Anesthesia

BACKGROUND

Transitions into conscious states are partially mediated by inactivation of sleep networks and activation of arousal networks. Pharmacologic hastening of emergence from general anesthesia has largely focused on activating subcortical monoaminergic networks, with little attention on antagonizing the γ-aminobutyric acid type A receptor (GABAAR). As the GABAAR mediates the clinical effects of many common general anesthetics, the authors hypothesized that negative GABAAR modulators would hasten emergence, possibly via cortical networks involved in sleep.

METHODS

The authors investigated the capacity of the benzodiazepine rescue agent, flumazenil, which had been recently shown to promote wakefulness in hypersomnia patients, to alter emergence. Using an in vivo rodent model and an in vitro GABAAR heterologous expression system, they measured flumazenil's effects on behavioral, neurophysiologic, and electrophysiologic correlates of emergence from isoflurane anesthesia.

RESULTS

Animals administered intravenous flumazenil (0.4 mg/kg, n = 8) exhibited hastened emergence compared to saline-treated animals (n = 8) at cessation of isoflurane anesthesia. Wake-like electroencephalographic patterns occurred sooner and exhibited more high-frequency electroencephalography power after flumazenil administration (median latency ± median absolute deviation: 290 ± 34 s) compared to saline administration (473 ± 186 s; P = 0.042). Moreover, in flumazenil-treated animals, there was a decreased impact on postanesthesia sleep. In vitro experiments in human embryonic kidney-293T cells demonstrated that flumazenil inhibited isoflurane-mediated GABA current enhancement (n = 34 cells, 88.7 ± 2.42% potentiation at 3 μM). Moreover, flumazenil exhibited weak agonist activity on the GABAAR (n = 10 cells, 10.3 ± 3.96% peak GABA EC20 current at 1 μM).

CONCLUSIONS

Flumazenil can modulate emergence from isoflurane anesthesia. The authors highlight the complex role GABAARs play in mediating consciousness and provide mechanistic links between emergence from anesthesia and arousal.

The Blood-Brain Barrier: Regulatory Roles in Wakefulness and Sleep

Sleep and its disorders are known to affect the functions of essential organs and systems in the body. However, very little is known about how the blood-brain barrier (BBB) is regulated. A few years ago, we launched a project to determine the impact of sleep fragmentation and chronic sleep restriction on BBB functions, including permeability to fluorescent tracers, tight junction protein expression and distribution, glucose and other solute transporter activities, and mediation of cellular mechanisms. Recent publications and relevant literature allow us to summarize here the sleep-BBB interactions in five sections: (1) the structural basis enabling the BBB to serve as a huge regulatory interface; (2) BBB transport and permeation of substances participating in sleep-wake regulation; (3) the circadian rhythm of BBB function; (4) the effect of experimental sleep disruption maneuvers on BBB activities, including regional heterogeneity, possible threshold effect, and reversibility; and (5) implications of sleep disruption-induced BBB dysfunction in neurodegeneration and CNS autoimmune diseases. After reading the review, the general audience should be convinced that the BBB is an important mediating interface for sleep-wake regulation and a crucial relay station of mind-body crosstalk. The pharmaceutical industry should take into consideration that sleep disruption alters the pharmacokinetics of BBB permeation and CNS drug delivery, being attentive to the chrono timing and activation of co-transporters in subjects with sleep disorders.

Neuropeptidergic control of sleep and wakefulness

Sleep and wake are fundamental behavioral states whose molecular regulation remains mysterious. Brain states and body functions change dramatically between sleep and wake, are regulated by circadian and homeostatic processes, and depend on the nutritional and emotional condition of the animal. Sleep-wake transitions require the coordination of several brain regions and engage multiple neurochemical systems, including neuropeptides. Neuropeptides serve two main functions in sleep-wake regulation. First, they represent physiological states such as energy level or stress in response to environmental and internal stimuli. Second, neuropeptides excite or inhibit their target neurons to induce, stabilize, or switch between sleep-wake states. Thus, neuropeptides integrate physiological subsystems such as circadian time, previous neuron usage, energy homeostasis, and stress and growth status to generate appropriate sleep-wake behaviors. We review the roles of more than 20 neuropeptides in sleep and wake to lay the foundation for future studies uncovering the mechanisms that underlie the initiation, maintenance, and exit of sleep and wake states.

Microinjection of cocaine- and amphetamine-regulated transcript 55-102 peptide into the nucleus accumbens could modulate anxiety-related behavior in rats

Cocaine- and amphetamine-regulated transcript (CART) peptide is abundantly expressed in the nucleus accumbens (NAcc) and is involved in stress, anxiety and reward responses. To examine the role of CART peptide in anxiety-related behavior, naïve rats were bilaterally injected with CART 55-102 peptide (0.5, 1.0 or 2.5 µg/0.5 µl/side) or vehicle into the NAcc. Following this, their anxiety-related behavior was assessed using the elevated plus maze and the open field tests with a one-week interval between the tests. There was no difference in the time spent in open arms, or number of entries into open arms on the elevated plus maze in the CART-treated animals at any dose, when compared with the vehicle-treated group. However, there was a significant increase in the time spent in the center of the open field with administration of the low dose of CART peptide (0.5 µg/0.5 µl/side), although this effect disappeared at the high dose (2.5 µg/0.5 µl/side). None of the doses of CART peptide altered total locomotion in these tests. To further determine the possible anxiety-modulating effect of CART peptide at low dosages, the light and dark test was performed. Additional groups of rats given doses of 0.01 µg/0.5 µl/side or 0.5 µg/0.5 µl/side of CART peptide showed increased exploration time in the light side. These results suggest that accumbal-CART peptide reduces anxiety-like behavior in a dose-dependent manner.

CART in the brain of vertebrates: circuits, functions and evolution

Cocaine- and amphetamine-regulated transcript peptide (CART) with its wide distribution in the brain of mammals has been the focus of considerable research in recent years. Last two decades have witnessed a steady rise in the information on the genes that encode this neuropeptide and regulation of its transcription and translation. CART is highly enriched in the hypothalamic nuclei and its relevance to energy homeostasis and neuroendocrine control has been understood in great details. However, the occurrence of this peptide in a range of diverse circuitries for sensory, motor, vegetative, limbic and higher cortical areas has been confounding. Evidence that CART peptide may have role in addiction, pain, reward, learning and memory, cognition, sleep, reproduction and development, modulation of behavior and regulation of autonomic nervous system are accumulating, but an integration has been missing. A steady stream of papers has been pointing at the therapeutic potentials of CART. The current review is an attempt at piecing together the fragments of available information, and seeks meaning out of the CART elements in their anatomical niche. We try to put together the CART containing neuronal circuitries that have been conclusively demonstrated as well as those which have been proposed, but need confirmation. With a view to finding out the evolutionary antecedents, we visit the CART systems in sub-mammalian vertebrates and seek the answer why the system is shaped the way it is. We enquire into the conservation of the CART system and appreciate its functional diversity across the phyla.

Neuropeptidergic signaling partitions arousal behaviors in zebrafish

Animals modulate their arousal state to ensure that their sensory responsiveness and locomotor activity match environmental demands. Neuropeptides can regulate arousal, but studies of their roles in vertebrates have been constrained by the vast array of neuropeptides and their pleiotropic effects. To overcome these limitations, we systematically dissected the neuropeptidergic modulation of arousal in larval zebrafish. We quantified spontaneous locomotor activity and responsiveness to sensory stimuli after genetically induced expression of seven evolutionarily conserved neuropeptides, including adenylate cyclase activating polypeptide 1b (adcyap1b), cocaine-related and amphetamine-related transcript (cart), cholecystokinin (cck), calcitonin gene-related peptide (cgrp), galanin, hypocretin, and nociceptin. Our study reveals that arousal behaviors are dissociable: neuropeptide expression uncoupled spontaneous activity from sensory responsiveness, and uncovered modality-specific effects upon sensory responsiveness. Principal components analysis and phenotypic clustering revealed both shared and divergent features of neuropeptidergic functions: hypocretin and cgrp stimulated spontaneous locomotor activity, whereas galanin and nociceptin attenuated these behaviors. In contrast, cart and adcyap1b enhanced sensory responsiveness yet had minimal impacts on spontaneous activity, and cck expression induced the opposite effects. Furthermore, hypocretin and nociceptin induced modality-specific differences in responsiveness to changes in illumination. Our study provides the first systematic and high-throughput analysis of neuropeptidergic modulation of arousal, demonstrates that arousal can be partitioned into independent behavioral components, and reveals novel and conserved functions of neuropeptides in regulating arousal.

Comparing label-free quantitative peptidomics approaches to characterize diurnal variation of peptides in the rat suprachiasmatic nucleus

Mammalian circadian rhythm is maintained by the suprachiasmatic nucleus (SCN) via an intricate set of neuropeptides and other signaling molecules. In this work, peptidomic analyses from two times of day were examined to characterize variation in SCN peptides using three different label-free quantitation approaches: spectral count, spectra index and SIEVE. Of the 448 identified peptides, 207 peptides were analyzed by two label-free methods, spectral count and spectral index. There were 24 peptides with significant (adjusted p-value < 0.01) differential peptide abundances between daytime and nighttime, including multiple peptides derived from secretogranin II, cocaine and amphetamine regulated transcript, and proprotein convertase subtilisin/kexin type 1 inhibitor. Interestingly, more peptides were analyzable and had significantly different abundances between the two time points using the spectral count and spectral index methods than with a prior analysis using the SIEVE method with the same data. The results of this study reveal the importance of using the appropriate data analysis approaches for label-free relative quantitation of peptides. The detection of significant changes in so rich a set of neuropeptides reflects the dynamic nature of the SCN and the number of influences such as feeding behavior on circadian rhythm. Using spectral count and spectral index, peptide level changes are correlated to time of day, suggesting their key role in circadian function.

Leptin receptor neurons in the mouse hypothalamus are colocalized with the neuropeptide galanin and mediate anorexigenic leptin action

Leptin acts centrally via leptin receptor (LepRb)-expressing neurons to regulate food intake, energy expenditure, and other physiological functions. LepRb neurons are found throughout the brain, and several distinct populations contribute to energy homeostasis control. However, the function of most LepRb populations remains unknown, and their contribution to regulate energy homeostasis has not been studied. Galanin has been hypothesized to interact with the leptin signaling system, but literature investigating colocalization of LepRb and galanin has been inconsistent, which is likely due to technical difficulties to visualize both. We used reporter mice with green fluorescent protein expression from the galanin locus to recapitulate the colocalization of galanin and leptin-induced p-STAT3 as a marker for LepRb expression. Here, we report the existence of two populations of galanin-expressing LepRb neurons (Gal-LepRb neurons): in the hypothalamus overspanning the perifornical area and adjacent dorsomedial and lateral hypothalamus [collectively named extended perifornical area (exPFA)] and in the brainstem (nucleus of the solitary tract). Surprisingly, despite the known orexigenic galanin action, leptin induces galanin mRNA expression and stimulates LepRb neurons in the exPFA, thus conflicting with the expected anorexigenic leptin action. However, we confirmed that intra-exPFA leptin injections were indeed sufficient to mediate anorexic responses. Interestingly, LepRb and galanin-expressing neurons are distinct from orexin or melanin-concentrating hormone (MCH)-expressing neurons, but exPFA galanin neurons colocalized with the anorexigenic neuropeptides neurotensin and cocaine- and amphetamine-regulated transcript (CART). Based on galanin's known inhibitory function, we speculate that in exPFA Gal-LepRb neurons galanin acts inhibitory rather than orexigenic.

Daytime sleepiness in obesity: mechanisms beyond obstructive sleep apnea--a review

Increasing numbers of overweight children and adults are presenting to sleep medicine clinics for evaluation and treatment of sleepiness. Sleepiness negatively affects quality of life, mental health, productivity, and safety. Thus, it is essential to comprehensively address all potential causes of sleepiness. While many obese individuals presenting with hypersomnolence will be diagnosed with obstructive sleep apnea and their sleepiness will improve with effective therapy for sleep apnea, a significant proportion of patients will continue to have hypersomnolence. Clinical studies demonstrate that obesity without sleep apnea is also associated with a higher prevalence of hypersomnolence and that bariatric surgery can markedly improve hypersomnolence before resolution of obstructive sleep apnea. High fat diet in both humans and animals is associated with hypersomnolence. This review critically examines the relationships between sleepiness, feeding, obesity, and sleep apnea and then discusses the hormonal, metabolic, and inflammatory mechanisms potentially contributing to hypersomnolence in obesity, independent of sleep apnea and other established causes of excessive daytime sleepiness.

Thyrotropin Releasing Hormone (TRH) in goldfish (Carassius auratus): role in the regulation of feeding and locomotor behaviors and interactions with the orexin system and cocaine- and amphetamine regulated transcript (CART)

TRH is a peptide produced by the hypothalamus which major function in mammals is the regulation of TSH secretion by the pituitary. In fish, TRH does not appear to affect TSH secretion, suggesting that it might regulate other functions. In this study, we assessed the effects of central (intracerebroventricular, icv) injections of TRH on feeding and locomotor behavior in goldfish. TRH at 10 and 100 ng/g, but not 1 ng/g, significantly increased feeding and locomotor behaviors, as indicated by an increase in food intake and in the number of total feeding acts as compared to saline-injected fish. In order to assess possible interactions between TRH and other appetite regulators, we examined the effects of icv injections of TRH on the hypothalamic expression of orexin, orexin receptor and CART. The mRNA expression levels of all three peptides were significantly increased in fish injected with TRH at 100 ng/g as compared to saline-injected fish. Fasting increased TRH, orexin, and orexin receptor hypothalamic mRNA levels and decreased CART hypothalamic mRNA levels. Our results suggest that TRH is involved in the regulation of feeding/locomotor activity in goldfish and that this action is associated with a stimulation of both the orexin and CART systems.