Optogenetic induction of hibernation-like state with modified human Opsin4 in mice.

We recently determined that the excitatory manipulation of Qrfp-expressing neurons in the preoptic area of the hypothalamus (quiescence-inducing neurons [Q neurons]) induced a hibernation-like hypothermic/hypometabolic state (QIH) in mice. To control the QIH with a higher time resolution, we develop an optogenetic method using modified human opsin4 (OPN4; also known as melanopsin), a G protein-coupled-receptor-type blue-light photoreceptor. C-terminally truncated OPN4 (OPN4dC) stably and reproducibly induces QIH for at least 24 h by illumination with low-power light (3 µW, 473 nm laser) with high temporal resolution. The high sensitivity of OPN4dC allows us to transcranially stimulate Q neurons with blue-light-emitting diodes and non-invasively induce the QIH. OPN4dC-mediated QIH recapitulates the kinetics of the physiological changes observed in natural hibernation, revealing that Q neurons concurrently contribute to thermoregulation and cardiovascular function. This optogenetic method may facilitate identification of the neural mechanisms underlying long-term dormancy states such as sleep, daily torpor, and hibernation.

The light switch-off response as a putative rodent test of innate fear.

Recent discussions on the ethics in animal experimentation instigate the refinement of methods used in Behavioral Neuroscience, particularly regarding fear/anxiety paradigms. We propose the Light Switch-Off Test (LSOT), based on the innate motivation to cease an aversive stimulus (bright light), displayed naturally by rodents in their habitat. Forty-six male adult Wistar rats were allocated into independent groups: control, diazepam at 1 or 2mg/kg, and meta-Chlorophenylpiperazine (mCPP) at 0.5 or 1mg/kg. The experimental box has two square compartments, separated by an acrylic portal. In each side of the box, there is a 40-W incandescent light bulb. After a habituation period in the box, 40 light stimuli (trials lasting up to 20s each) are emitted at random intervals. By crossing compartments during the lighted period, the rat could switch-off the stimulus. Parameters observed are the number of switch-off responses (SORs), latency of SOR and intertrial locomotion. The SOR frequency was higher in rats treated with mCPP at 1mg/kg, an anxiogenic drug, while diazepam at the doses used in this study did not produce effects. Animals exposed solely to the box for the length of the test did not respond in a false positive way. Therefore, the SOR represents a good index to measure the innate rodent fear of bright-lighten areas, once they react quickly in order to turn off the stimulus. Among its many advantages, the LSOT is a simple, replicable, non-invasive and minimally stressful procedure, since it does not expose animals to excessively aversive stimulus.

The benzodiazepine midazolam acts on the expression of the defensive behavior, but not on the processing of aversive information, produced by exposure to the elevated plus maze and electrical stimulations applied to the inferior colliculus of rats.

Electrical stimulation of midbrain tectum structures, particularly the dorsal periaqueductal gray (dPAG) and inferior colliculus (IC), produces defensive responses such as freezing and escape behavior. Freezing also results after termination of this stimulation (post-stimulation freezing; PSF). Whereas these responses are critically mediated by GABA in the dPAG, it is unclear how GABA-benzodiazepine mechanisms mediate the expression of fear (freezing and escape behaviors) and the processing of aversive information (PSF) produced by electrical stimulation of the IC. Since dorsal (ICd) and ventral regions (ICv) of the IC react differentially to aversive stimulation, we hypothesized that these regions might be sensitive to the action of benzodiazepine drugs when rats are submitted to animal models of anxiety: the elevated plus maze (EPM) and the IC electrical stimulation procedure. Midazolam (5, 10 or 20 nmol) was injected into the ICd or ICv of rats subjected to one of these tests. Intra-ICv, but not intra-ICd injections, of midazolam reduced the aversiveness of the IC electrical stimulation and decreased fear in the EPM, as assessed by its traditional and complementary measures. In contrast, the IC post-stimulation freezing remained unaltered with midazolam treatments. Thus, there is a clear pharmacological dissociation in the reactivity of dorsal and ventral regions of the IC to fear-provoking stimuli of the two animal models of anxiety used in this study. The present results support the proposal that benzodiazepine-mediated mechanisms are only involved in the output mechanisms of defensive behavior and not involved in the processing of ascending aversive information from the IC.

Further evidence for the role of interferon-gamma on anxiety- and depressive-like behaviors: involvement of hippocampal neurogenesis and NGF production.

A series of evidence suggests that interferon-gamma (IFN-γ) plays an important role in central nervous system (CNS) functions. However, previous studies have obtained inconsistent results regarding the role of IFN-γ in modulating emotion-related behaviors. The present study aimed to evaluate the behavioral profile of IFN-γ knockout (K.O.) mice in models of anxiety and depression. Male C57Bl6 wild type (WT) or IFN-γ K.O. mice were submitted to the following tests: contextual fear conditioning (CFC), elevated plus maze (EPM), open field (OF) and forced swimming test (FST). To explore the possible neurobiological mechanisms involved, we also assessed hippocampal neurogenesis by means of hippocampal doublecortin expression, and the levels of brain-derived neurothophic factor (BDNF) and nerve growth factor (NGF) in the hippocampus and prefrontal cortex. Our results suggested that IFN-γ K.O. mice exhibited an anxiogenic profile in CFC, EPM and OF tests. In FST, the K.O. group spent more time immobile than the WT group. The number of doublecortin positive cells was reduced in the dentate gyrus, and the expression of NGF was down regulated in the prefrontal cortex of IFN-γ K.O. mice. Our results suggest that IFN-γ is involved in CNS plasticity, contributing to the modulation of anxiety and depressive states.

Cannabinoid modulation of neuroinflammatory disorders.

In recent years, a growing interest has been dedicated to the study of the endocannabinoid system. The isolation of Cannabis sativa main psychotropic compound, Δ(9)-tetrahydrocannabinol (THC), has led to the discovery of an atypical neurotransmission system that modulates the release of other neurotransmitters and participates in many biological processes, including the cascade of inflammatory responses. In this context, cannabinoids have been studied for their possible therapeutic properties in neuroinflammatory diseases. In this review, historic and biochemical aspects of cannabinoids are discussed, as well as their function as modulators of inflammatory processes and therapeutic perspectives for neurodegenerative disorders, particularly, multiple sclerosis.

[Pharmacological exploitation of the endocannabinoid system: new perspectives for the treatment of depression and anxiety disorders?]. / Exploração farmacológica do sistema endocanabinoide: novas perspectivas para o tratamento de transtornos de ansiedade e depressão?

OBJECTIVE: The present review provides a brief introduction into the endocannabinoid system and discusses main strategies of pharmacological interventions. METHOD: We have reviewed the literature relating to the endocannabinoid system and its pharmacology; both original and review articles written in English were considered. DISCUSSION: Cannabinoids are a group of compounds present in Cannabis Sativa (hemp), such as Delta(9)-tetrahydrocannabinol, and their synthetic analogues. Research on their pharmacological profile led to the discovery of the endocannabinoid system in the mammalian brain. This system comprises at least two G-protein coupled receptors, CB(1) and CB(2), their endogenous ligands (endocannabinoids; e.g. the fatty acid derivatives anandamide and 2-arachydonoyl glycerol), and the enzymes responsible for endocannabinoid synthesis and catabolism. Endocannabinoids represent a class of neuromessengers, which are synthesized on demand and released from post-synaptic neurons to restrain the release of classical neurotransmitters from pre-synaptic terminals. This retrograde signalling modulates a variety of brain functions, including anxiety, fear and mood, whereby activation of CB(1) receptors was shown to exert anxiolytic-and antidepressant-like effects in preclinical studies. CONCLUSION: Animal experiments suggest that drugs promoting endocannabinoid action may represent a novel strategy for the treatment of depression and anxiety disorders.

Cannabinoids, anxiety, and the periaqueductal gray

The use of Cannabis sativa by humans dates back several thousand years, for both its psychotomimetic and potential medicinal properties. As scientific research methods developed, the cannabinoids present in this herb were characterized, as well as their complex interface with the human central nervous system, provided by the activation of specific receptors. The subsequent description of an endogenous cannabinoid system in the mammalian brain shifted the notion of cannabis as a recreational drug to a therapeutic alternative for psychiatric disorders. However, the neuroanatomical sites mediating its effects have remained uncertain. In the present paper, we review recent data suggesting that the midbrain periaqueductal gray may be a structure involved in the anxiolytic-like effects of cannabinoids.

Exploração farmacológica do sistema endocanabinoide: novas perspectivas para o tratamento de transtornos de ansiedade e depressão? / Pharmacological exploitation of the endocannabinoid system: new perspectives for the treatment of depression and anxiety disorders?

OBJETIVO: Este artigo revisa o sistema endocanabinoide e as respectivas estratégias de intervenções farmacológicas. MÉTODO: Realizou-se uma revisão da literatura sobre o sistema endocanabinoide e a sua farmacologia, considerando-se artigos originais ou de revisão escritos em inglês. DISCUSSÃO: Canabinoides são um grupo de compostos presentes na Cannabis Sativa (maconha), a exemplo do Δ9-tetraidrocanabinol e seus análogos sintéticos. Estudos sobre o seu perfil farmacológico levaram à descoberta do sistema endocanabinoide do cérebro de mamíferos. Este sistema é composto por pelo menos dois receptores acoplados a uma proteína G, CB1 e CB2, pelos seus ligantes endógenos (endocanabinoides; a exemplo da anandamida e do 2-araquidonoil glicerol) e pelas enzimas responsáveis por sintetizá-los e metabolizá-los. Os endocanabinoides representam uma classe de mensageiros neurais que são sintetizados sob demanda e liberados de neurônios pós-sinápticos para restringir a liberação de neurotransmissores clássicos de terminais pré-sinápticos. Esta sinalização retrógrada modula uma diversidade de funções cerebrais, incluindo ansiedade, medo e humor, em que a ativação de receptores CB1 pode exercer efeitos dos tipos ansiolítico e antidepressivo em estudos préclínicos. CONCLUSÃO: Experimentos com modelos animais sugerem que drogas que facilitam a ação dos endocanabinoides podem representar uma nova estratégia para o tratamento de transtornos de ansiedade e depressão.

OBJECTIVE: The present review provides a brief introduction into the endocannabinoid system and discusses main strategies of pharmacological interventions. METHOD: We have reviewed the literature relating to the endocannabinoid system and its pharmacology; both original and review articles written in English were considered. DISCUSSION: Cannabinoids are a group of compounds present in Cannabis Sativa (hemp), such as Δ9-tetrahydrocannabinol, and their synthetic analogues. Research on their pharmacological profile led to the discovery of the endocannabinoid system in the mammalian brain. This system comprises at least two G-protein coupled receptors, CB1 and CB2, their endogenous ligands (endocannabinoids; e.g. the fatty acid derivatives anandamide and 2-arachydonoyl glycerol), and the enzymes responsible for endocannabinoid synthesis and catabolism. Endocannabinoids represent a class of neuromessengers, which are synthesized on demand and released from post-synaptic neurons to restrain the release of classical neurotransmitters from pre-synaptic terminals.This retrograde signalling modulates a variety of brain functions, including anxiety, fear and mood, whereby activation of CB1 receptors was shown to exert anxiolytic-and antidepressant-like effects in preclinical studies. CONCLUSION: Animal experiments suggest that drugs promoting endocannabinoid action may represent a novel strategy for the treatment of depression and anxiety disorders.