Oleate induces KATP channel-dependent hyperpolarization in mouse hypothalamic glucose-excited neurons without altering cellular energy charge

Decreases in metabolic ATP open KATP channels and reduce firing in an auditory brainstem neuron: A dynamic mechanism of firing control during intense activity

Cartwheel (CW) neurons are glycinergic interneurons in the dorsal cochlear nucleus (DCN) that exhibit spontaneous firing, resulting in potent tonic inhibition of fusiform neurons. CW neurons expressing open ATP-sensitive potassium (KATP) channels do not fire spontaneously, and activation of KATP channels halts spontaneous firing in these neurons. However, the conditions that regulate KATP channel opening in CW neurons remain unknown. Here, we tested the hypothesis that fluctuations in metabolic ATP levels modulate KATP channels in CW neurons. Using whole-cell patch-clamp recordings in CW neurons from young rat brain slices (p17-22) with an ATP-free internal solution, we observed that the mitochondrial uncoupler CCCP hyperpolarized the membrane potential, reduced spontaneous firing, and generated an outward current, which was inhibited by the KATP channel antagonist tolbutamide. Additionally, a glucose-free external solution quickly activated KATP channels and ceased spontaneous firing. We hypothesized that intense membrane ion ATPase activity during strong depolarization would deplete intracellular ATP, leading to KATP channel opening. Consistent with this, depolarizing CW neurons with a 250 pA DC did not increase spontaneous firing because the depolarization activated KATP channels; however, the same depolarization after tolbutamide administration increased firing, suggesting that ATP depletion triggered KATP channel opening to limit action potential firing. These results indicate that KATP channels in the DCN provide dynamic control over action potential firing, preventing excessive excitation during high-firing activity.

Long Chain Fatty Acids Differentially Regulate Sub-populations of Arcuate POMC and NPY Neurons

Long chain fatty acids (LCFAs) have been suggested to influence the activity of hypothalamic neurons, however, limited studies have attempted to identify the neurochemical phenotype of these neurons. We aimed to determine if physiological levels of LCFAs alter the electrical excitability of pro-opiomelanocortin (POMC) and neuropeptide Y (NPY) neurons in the arcuate nucleus of the hypothalamus. We utilised whole-cell patch-clamp electrophysiology on brain slice preparations from genetic mouse models where green fluorescent protein was expressed in either POMC or NPY expressing cells. All animals had undergone an overnight fast to replicate conditions in which fatty acids would usually increase. Bath application of LCFAs were found to predominantly inhibit POMC neurons and predominantly excite NPY neurons. Differences between oleic and palmitic acid were not observed. These results suggest that LCFAs in the cerebrospinal fluid exert an underlying orexigenic tone to key hypothalamic neurons known to regulate energy homeostasis.

A Neural basis for Octanoic acid regulation of energy balance

Objectives

Nutrient sensing by hypothalamic neurons is critical for the regulation of food intake and energy expenditure. We aimed to identify long- and medium-chain fatty acid species transported into the brain, their effects on energy balance, and the mechanisms by which they regulate activity of hypothalamic neurons.

Methods

Simultaneous blood and cerebrospinal fluid (CSF) sampling was undertaken in rats and metabolic analyses using radiolabeled fatty acid tracers were performed on mice. Electrophysiological recording techniques were used to investigate signaling mechanisms underlying fatty acid-induced changes in activity of pro-opiomelanocortin (POMC) neurons.

Results

Medium-chain fatty acid (MCFA) octanoic acid (C8:0), unlike long-chain fatty acids, was rapidly transported into the hypothalamus of mice and almost exclusively oxidized, causing rapid, transient reductions in food intake and increased energy expenditure. Octanoic acid differentially regulates the excitability of POMC neurons, activating these neurons directly via GPR40 and inducing inhibition via an indirect non-synaptic, purine, and adenosine receptor-dependent mechanism.

Conclusions

MCFA octanoic acid is a central signaling nutrient that targets POMC neurons via distinct direct and indirect signal transduction pathways to instigate changes in energy status. These results could explain the beneficial health effects that accompany MCFA consumption.

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Octanoic acid (C8:0) is rapidly transported from blood to the cerebrospinal fluid.

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Octanoic acid rapidly reduces food intake and increases energy expenditure.

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Octanoic acid targets POMC neurons through direct and indirect signaling pathways.

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Activation of POMC neurons occurs directly through GPR40.

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Inhibition occurs through a nonsynaptic, purine and adenosine receptor-dependent mechanism.

Role of the saturated fatty acid palmitate in the interconnected hypothalamic control of energy homeostasis and biological rhythms

The brain, specifically the hypothalamus, controls whole body energy and glucose homeostasis through neurons that synthesize specific neuropeptides, whereas hypothalamic dysfunction is linked directly to insulin resistance, obesity, and type 2 diabetes mellitus. Nutrient excess, through overconsumption of a Western or high-fat diet, exposes the hypothalamus to high levels of free fatty acids, which induces neuroinflammation, endoplasmic reticulum stress, and dysregulation of neuropeptide synthesis. Furthermore, exposure to a high-fat diet also disrupts normal circadian rhythms, and conversely, clock gene knockout models have symptoms of metabolic disorders. While whole brain/animal studies have provided phenotypic end points and important clues to the genes involved, there are still major gaps in our understanding of the intracellular pathways and neuron-specific components that ultimately control circadian rhythms and energy homeostasis. Because of its complexity and heterogeneous nature, containing a diverse mix cell types, it is difficult to dissect the critical hypothalamic components involved in these processes. Of significance, we have the capacity to study these individual components using an extensive collection of both embryonic- and adult-derived, immortalized hypothalamic neuronal cell lines from rodents. These defined neuronal cell lines have been used to examine the impact of nutrient excess, such as palmitate, on circadian rhythms and neuroendocrine signaling pathways, as well as changes in vital neuropeptides, leading to the development of neuronal inflammation; the role of proinflammatory molecules in this process; and ultimately, restoration of normal signaling, clock gene expression, and neuropeptide synthesis in disrupted states by beneficial anti-inflammatory compounds in defined hypothalamic neurons.

Plant-Derived Anticancer Agents: Lessons from the Pharmacology of Geniposide and Its Aglycone, Genipin

For centuries, plants have been exploited by mankind as sources of numerous cancer chemotherapeutic agents. Good examples of anticancer compounds of clinical significance today include the taxanes (e.g., taxol), vincristine, vinblastine, and the podophyllotoxin analogues that all trace their origin to higher plants. While all these drugs, along with the various other available therapeutic options, brought some relief in cancer management, a real breakthrough or cure has not yet been achieved. This critical review is a reflection on the lessons learnt from decades of research on the iridoid glycoside geniposide and its aglycone, genipin, which are currently used as gold standard reference compounds in cancer studies. Their effects on tumour development (carcinogenesis), cancer cell survival, and death, with particular emphasis on their mechanisms of actions, are discussed. Particular attention is also given to mechanisms related to the dual pro-oxidant and antioxidant effects of these compounds, the mitochondrial mechanism of cancer cell killing through reactive oxygen species (ROS), including that generated through the uncoupling protein-2 (UCP-2), the inflammatory mechanism, and cell cycle regulation. The implications of various studies for the evaluation of glycosidic and aglycone forms of natural products in vitro and in vivo through pharmacokinetic scrutiny are also addressed.

CD36 Deficiency Suppresses Epileptic Seizures

Cluster of differentiation 36 (CD36) belongs to the class B scavenger receptor family. CD36 is a glycoprotein found on the surface of various cell types and has been implicated in the mechanism of numerous central nervous system (CNS) diseases. However, the relationship between CD36 and epilepsy remains unknown. In this study, we aimed to detect the expression of CD36 in two different chronic epileptic mouse models and determine whether CD36 deficiency leads to suppressive neuronal hyperexcitability and decreased susceptibility of epileptic seizures. Here, we found that CD36 was expressed in the neurons and that CD36 expression was significantly elevated in epileptic mice induced by pentylenetetrazol (PTZ) and kainic acid (KA). Behavioral studies revealed that CD36 deletion in mice (CD36-/- mice) resulted in an attenuated progression of chronic epilepsy compared with wild-type (WT) mice. Whole-cell patch-clamp technique exhibited a decreased frequency of action potentials (APs) in the hippocampal slices of CD36-/- mice. In addition, local field potential (LFP) analysis further indicated that CD36 deletion reduced the frequency and duration of epileptiform-like discharges. These results revealed that CD36 deficiency could produce an antiepileptic effect and could provide new insight into antiepileptic treatment.