The Effect of Cannabinoids on the Brain's Circadian Clock.

The circadian rhythm is without a doubt the main element influencing the way human lead their lives. Emerging evidence indicate that cannabinoids affect these routines by regulating neuronal firing within the suprachiasmatic nucleus, the master circadian pacemaker in the brain. These actions of cannabinoids on the brain's clock may also underlie time-wraps commonly experienced by marijuana users.

Cannabinoids excite circadian clock neurons.

Cannabinoids, the primary active agent in drugs of abuse such as marijuana and hashish, tend to generate a distorted sense of time. Here we study the effect of cannabinoids on the brain's circadian clock, the suprachiasmatic nucleus (SCN), using patch clamp and cell-attached electrophysiological recordings, RT-PCR, immunocytochemistry, and behavioral analysis. The SCN showed strong expression of the cannabinoid receptor CB1R, as detected with RT-PCR.

Cholinergic activation of M2 receptors leads to context-dependent modulation of feedforward inhibition in the visual thalamus.

In many brain regions, inhibition is mediated by numerous classes of specialized interneurons, but within the rodent dorsal lateral geniculate nucleus (dLGN), a single class of interneuron is present. dLGN interneurons inhibit thalamocortical (TC) neurons and regulate the activity of TC neurons evoked by retinal ganglion cells (RGCs), thereby controlling the visually evoked signals reaching the cortex. It is not known whether neuromodulation can regulate interneuron firing mode and the resulting inhibition.

Neuroendocrine proopiomelanocortin neurons are excited by hypocretin/orexin.

Hypocretin/orexin, produced by a group of neurons in the lateral hypothalamus/perifornical area, enhances cognitive arousal and also may play a crucial role in modulating the neuroendocrine system. How hypocretin modulates the endocrine system remains an open question. Hypocretin cells innervate the mediobasal hypothalamus where they can potentially influence the activity of specific cell populations within the arcuate nucleus.

Active dendritic conductances dynamically regulate GABA release from thalamic interneurons.

Inhibitory interneurons in the dorsal lateral geniculate nucleus (dLGN) process visual information by precisely controlling spike timing and by refining the receptive fields of thalamocortical (TC) neurons. Previous studies indicate that dLGN interneurons inhibit TC neurons by releasing GABA from both axons and dendrites. However, the mechanisms controlling GABA release are poorly understood.

Cannabinoids excite hypothalamic melanin-concentrating hormone but inhibit hypocretin/orexin neurons: implications for cannabinoid actions on food intake and cognitive arousal.

Cannabinoids modulate energy homeostasis and decrease cognitive arousal, possibly by acting on hypothalamic neurons including those that synthesize melanin-concentrating hormone (MCH) or hypocretin/orexin. Using patch-clamp recordings, we compared the actions of cannabinoid agonists and antagonists on identified MCH or hypocretin neurons in green fluorescent protein-expressing transgenic mice. The cannabinoid type-1 receptor (CB1R) agonist R-(+)-[2,3-dihydro-5-methyl-3-(4-morpho linylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN55,212,2) depolarized MCH cells and increased spike frequency; in contrast, WIN55,212,2 hyperpolarized and reduced spontaneous firing of the neighboring hypocretin cells, both results consistent with reduced activity seen with intracerebral cannabinoid infusions.

Peptide YY(3-36) inhibits both anorexigenic proopiomelanocortin and orexigenic neuropeptide Y neurons: implications for hypothalamic regulation of energy homeostasis.

Peptide YY(3-36) (PYY(3-36)) is released by endocrine cells of the gut and may serve as an important long-distance neuropeptide signal relating energy balance information to the brain to depress food intake. The postulated mechanism is the activation of anorexigenic proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus. In striking contrast, using voltage and current-clamp recording, we found that PYY(3-36) consistently, dose dependently, and reversibly inhibited POMC cells by reducing action potentials, hyperpolarizing the membrane potential, decreasing input resistance and inward calcium currents, increasing G-protein-gated inwardly rectifying K+ channel currents, and presynaptically inhibiting release of excitatory glutamate.

Mechanisms of neuropeptide Y, peptide YY, and pancreatic polypeptide inhibition of identified green fluorescent protein-expressing GABA neurons in the hypothalamic neuroendocrine arcuate nucleus.

The fast inhibitory transmitter GABA is robustly expressed in the arcuate nucleus (ARC) and appears to play a major role in hypothalamic regulation of endocrine function and energy homeostasis. Previously, it has not been possible to record selectively from GABA cells, because they have no defining morphological or physiological characteristics. Using transgenic mice that selectively express GFP (green fluorescent protein) in GAD67 (glutamic acid decarboxylase 67)-synthesizing cells, we identified ARC GABA neurons (n > 300) and used whole-cell recording to study their physiological response to neuropeptide Y (NPY), the related peptide YY(3-36) (PYY(3-36)), and pancreatic polypeptide (PP), important modulators of ARC function.

Direct excitation of hypocretin/orexin cells by extracellular ATP at P2X receptors.

Hypocretin/orexin (hcrt) neurons play an important role in hypothalamic arousal and energy homeostasis. ATP may be released by neurons or glia or by pathological conditions. Here we studied the effect of extracellular ATP on hypocretin cells using whole cell patch-clamp recording in hypothalamic slices of transgenic mice expressing green fluorescent protein (GFP) exclusively in hcrt-producing cells.

Neuropeptide Y inhibits hypocretin/orexin neurons by multiple presynaptic and postsynaptic mechanisms: tonic depression of the hypothalamic arousal system.

Neurons that release neuropeptide Y (NPY) have important effects on hypothalamic homeostatic regulation, including energy homeostasis, and innervate hypocretin neurons. Using whole-cell patch-clamp recording, we explored NPY actions on hypocretin cells identified by selective green fluorescent protein expression in mouse hypothalamic slices. NPY reduced spike frequency and hyperpolarized the membrane potential of hypocretin neurons.

Glucagon-like peptide 1 excites hypocretin/orexin neurons by direct and indirect mechanisms: implications for viscera-mediated arousal.

Glucagon-like peptide 1 (GLP-1) is produced by neurons in the caudal brainstem that receive sensory information from the gut and project to several hypothalamic regions involved in arousal, interoceptive stress, and energy homeostasis. GLP-1 axons and receptors have been detected in the lateral hypothalamus, where hypocretin neurons are found. The electrophysiological actions of GLP-1 in the CNS have not been studied.

Physiological properties of hypothalamic MCH neurons identified with selective expression of reporter gene after recombinant virus infection.

Neurons that synthesize melanin-concentrating hormone (MCH) may modulate arousal and energy homeostasis. The scattered MCH neurons have been difficult to study, as they have no defining morphological characteristics. We have developed a viral approach with AAV for selective long-term reporter gene (GFP) expression in MCH neurons, allowing the study of their cellular physiology in hypothalamic slices.

Group III metabotropic glutamate receptors maintain tonic inhibition of excitatory synaptic input to hypocretin/orexin neurons.

Hypocretin/orexin neurons play an important role in hypothalamic arousal. Synaptic glutamate input to hypocretin neurons regulates cell firing. We studied the actions of group III metabotropic glutamate receptors (mGluRs) in modulating the activity of hypocretin neurons using whole-cell voltage- and current-clamp recording in mouse whole hypothalamic slices or minislices consisting only of the lateral hypothalamus.