Melanin-concentrating hormone in rat nucleus accumbens or lateral hypothalamus differentially impacts morphine and food seeking behaviors

Effects of glucose modulation in lateral hypothalamus on motivated behavior to obtain sucrose in an operant task

Orexin neurons in the Lateral Hypothalamus (LH) play an important role in food seeking behavior. Approximately 60 percent of LH orexin neurons are inhibited by elevated extracellular glucose. It has been shown that elevated LH glucose decreases conditioned place preference for a food associated chamber. However, it has never been shown how modulation of LH extracellular glucose effects a rat's motivation to work for food. In this experiment we used reverse microdialysis to modulate extracellular glucose levels in LH during an operant task. Results from a progressive ratio task demonstrated that 4 mM glucose perfusion significantly decreased the animal's motivation to work for sucrose pellets while not effecting the hedonic value of the pellets. In a second experiment we demonstrated that 4 mM but not 2.5 mM glucose perfusion was sufficient to significantly decrease the number of sucrose pellets earned. Finally, we showed that modulating LH extracellular glucose mid-session from 0.7 mM to 4 mM did not affect behavior. This indicates that once feeding behavior has begun the animal becomes unresponsive to changes in extracellular glucose levels in LH. Taken together these experiments indicate that LH glucose sensing neurons play an important role in motivation to initiate feeding. However, once consumption has begun it is likely that feeding is controlled by brain regions downstream of LH.

Exposure to Morphine and Cocaine Modify the Transcriptomic Landscape in Zebrafish Embryos

Morphine and other opioid analgesics are the drugs of election to treat moderate-to-severe pain, and they elicit their actions by binding to the opioid receptors. Cocaine is a potent inhibitor of dopamine, serotonin, and noradrenaline reuptake, as it blocks DAT, the dopamine transporter, causing an increase in the local concentration of these neurotransmitters in the synaptic cleft. The molecular effects of these drugs have been studied in specific brain areas or nuclei, but the systemic effects in the whole organism have not been comprehensively analyzed. This study aims to analyze the transcriptomic changes elicited by morphine (10 uM) and cocaine (15 uM) in zebrafish embryos. An RNAseq assay was performed with tissues extracts from zebrafish embryos treated from 5 hpf (hours post fertilization) to 72 hpf, and the most representative deregulated genes were experimentally validated by qPCR. We have found changes in the expression of genes related to lipid metabolism, chemokine receptor ligands, visual system, hemoglobins, and metabolic detoxification pathways. Besides, morphine and cocaine modified the global DNA methylation pattern in zebrafish embryos, which would explain the changes in gene expression elicited by these two drugs of abuse.

The zona incerta in control of novelty seeking and investigation across species

Many organisms rely on a capacity to rapidly replicate, disperse, and evolve when faced with uncertainty and novelty. But mammals do not evolve and replicate quickly. They rely on a sophisticated nervous system to generate predictions and select responses when confronted with these challenges. An important component of their behavioral repertoire is the adaptive context-dependent seeking or avoiding of perceptually novel objects, even when their values have not yet been learned. Here, we outline recent cross-species breakthroughs that shed light on how the zona incerta (ZI), a relatively evolutionarily conserved brain area, supports novelty-seeking and novelty-related investigations. We then conjecture how the architecture of the ZI's anatomical connectivity - the wide-ranging top-down cortical inputs to the ZI, and its specifically strong outputs to both the brainstem action controllers and to brain areas involved in action value learning - place the ZI in a unique role at the intersection of cognitive control and learning.

The melanin-concentrating hormone system as a target for the treatment of sleep disorders

Given the widespread prevalence of sleep disorders and their impacts on health, it is critical that researchers continue to identify and evaluate novel avenues of treatment. Recently the melanin-concentrating hormone (MCH) system has attracted commercial and scientific interest as a potential target of pharmacotherapy for sleep disorders. This interest emerges from basic scientific research demonstrating a role for MCH in regulating sleep, and particularly REM sleep. In addition to this role in sleep regulation, the MCH system and the MCH receptor 1 (MCHR1) have been implicated in a wide variety of other physiological functions and behaviors, including feeding/metabolism, reward, anxiety, depression, and learning. The basic research literature on sleep and the MCH system, and the history of MCH drug development, provide cause for both skepticism and cautious optimism about the prospects of MCH-targeting drugs in sleep disorders. Extensive efforts have focused on developing MCHR1 antagonists for use in obesity, however, few of these drugs have advanced to clinical trials, and none have gained regulatory approval. Additional basic research will be needed to fully characterize the MCH system’s role in sleep regulation, for example, to fully differentiate between MCH-neuron and peptide/receptor-mediated functions. Additionally, a number of issues relating to drug design will continue to pose a practical challenge for novel pharmacotherapies targeting the MCH system.

The role of the nucleus accumbens and ventral pallidum in feeding and obesity

Obesity is a growing global epidemic that stems from the increasing availability of highly-palatable foods and the consequent enhanced calorie consumption. Extensive research has shown that brain regions that are central to reward seeking modulate feeding and evidence linking obesity to pathology in such regions have recently started to accumulate. In this review we focus on the contribution of two major interconnected structures central to reward processing, the nucleus accumbens and the ventral pallidum, to obesity. We first review the known literature linking these structures to feeding behavior, then discuss recent advances connecting pathology in the nucleus accumbens and ventral pallidum to obesity, and finally examine the similarities and differences between drug addiction and obesity in the context of these two structures. The understanding of how pathology in brain regions involved in reward seeking and consumption may drive obesity and how mechanistically similar obesity and addiction are, is only now starting to be revealed. We hope that future research will advance knowledge in the field and open new avenues to studying and treating obesity.

Melanin-concentrating hormone and food intake control: Sites of action, peptide interactions, and appetition

Given the increased prevalence of obesity and its associated comorbidities, understanding the mechanisms through which the brain regulates energy balance is of critical importance. The neuropeptide melanin-concentrating hormone (MCH) is produced in the lateral hypothalamic area and the adjacent incerto-hypothalamic area and promotes both food intake and energy conservation, overall contributing to body weight gain. Decades of research into this system has provided insight into the neural pathways and mechanisms (behavioral and neurobiological) through which MCH stimulates food intake. Recent technological advancements that allow for selective manipulation of MCH neuron activity have elucidated novel mechanisms of action for the hyperphagic effects of MCH, implicating neural "volume" transmission in the cerebrospinal fluid and sex-specific effects of MCH on food intake control as understudied areas for future investigation. Highlighted here are historical and recent findings that illuminate the neurobiological mechanisms through which MCH promotes food intake, including the identification of various specific neural signaling pathways and interactions with other peptide systems. We conclude with a framework that the hyperphagic effects of MCH signaling are predominantly mediated through enhancement of an "appetition" process in which early postoral prandial signals promote further caloric consumption.