Mónica Méndez-Díaz

Anandamide-induced sleep is blocked by SR141716A, a CB1 receptor antagonist and by U73122, a phospholipase C inhibitor.

Anandamide (ANA) alters sleep by increasing the amount of time spent in slow wave sleep 2 (SWS2) and rapid eye movement sleep (REMS) at the expense of wakefulness (W) in rats. In this report, we describe a similar effect of ANA when injected itracerebroventricularly (i.c.v.) or into the peduriculopontine tegmental nucleus (PPTg) and the lack of an effect when ANA is administered into the medial preoptic area (MPOA). Furthermore, the i.c.v. or PPTg administration of SR141716A, a CB1 antagonist, or U73122, a PLC inhibitor, 15 min prior to ANA, readily prevents the ANA induced changes in sleep. The present results suggest that a cannabinoid system in the PPTg may be involved in sleep regulation and that the cannabinoid effect is mediated by the CB1 receptor coupled to a PLC second messenger system.

Potential role of the cannabinoid receptor cb1 in rapid eye movement sleep rebound

Sleep is an unavoidable activity of the brain. The delay of the time to sleep (sleep deprivation), induces an increase of slow-wave sleep and rapid-eye-movement (REM) sleep (rebound) once the subject is allowed to sleep. This drive to sleep has been hypothesized to be dependent on the accumulation of sleep-inducing molecules and on the high expression of these molecule receptors. In this study we selectively deprived rats of REM sleep for 24 h by using the flowerpot technique. One group deprived of REM sleep was treated with SR141716A, a cannabinoid receptor 1 (CB1) receptor antagonist and then allowed to sleep for the next 4 h. Two other groups were killed, one immediately after the REM sleep deprivation period and the other after 2 h of REM sleep rebound (REM sleep deprivation plus 2 h of rebound). In both groups we determined the expression of the CB1 receptor and its mRNA. Results indicated that SR141716A prevents REM sleep rebound and REM sleep deprivation does not modify the expression of the CB1 protein or mRNA. However, REM sleep deprivation plus 2 h of sleep rebound increased the CB1 receptor protein and, slightly but significantly, decreased mRNA expression. These results suggest that endocannabinoids may be participating in the expression of REM sleep rebound.

Inhibition of the ERK pathway prevents HIVgp120-induced REM sleep increase

Approximately 35% of HIV-infected subjects, both children and adults, exhibit alterations in the sleep-waking cycle. HIV surface glycoprotein gp120 has been postulated to contribute to this abnormality. For example, it has been reported that HIVgp120 modifies sleep in freely-moving rats and that it also activates the ERK pathway in brain slices. The goal of this work was to determine if sleep changes induced by HIVgp120 in normal rats are mediated by the MAPK pathway. Our results show that a single intraventricular administration of HIVgp120 selectively increases REMS and that such an increase can be prevented by U0126, an inhibitor of ERK activating enzyme, MEK. In contrast, SB202190, a MAPK-p38 inhibitor, had no effect on HIVgp120-induced increase in REMS. These results suggest that HIVgp120 increases REMS in the rat by specifically affecting the ERK signal transduction pathway.

The Bidirectional Relationship between Sleep and Immunity against Infections

Sleep is considered an important modulator of the immune response. Thus, a lack of sleep can weaken immunity, increasing organism susceptibility to infection. For instance, shorter sleep durations are associated with a rise in suffering from the common cold. The function of sleep in altering immune responses must be determined to understand how sleep deprivation increases the susceptibility to viral, bacterial, and parasitic infections. There are several explanations for greater susceptibility to infections after reduced sleep, such as impaired mitogenic proliferation of lymphocytes, decreased HLA-DR expression, the upregulation of CD14+, and variations in CD4+ and CD8+ T lymphocytes, which have been observed during partial sleep deprivation. Also, steroid hormones, in addition to regulating sexual behavior, influence sleep. Thus, we hypothesize that sleep and the immune-endocrine system have a bidirectional relationship in governing various physiological processes, including immunity to infections. This review discusses the evidence on the bidirectional effects of the immune response against viral, bacterial, and parasitic infections on sleep patterns and how the lack of sleep affects the immune response against such agents. Because sleep is essential in the maintenance of homeostasis, these situations must be adapted to elicit changes in sleep patterns and other physiological parameters during the immune response to infections to which the organism is continuously exposed.

2-AG into the lateral hypothalamus increases REM sleep and cFos expression in melanin concentrating hormone neurons in rats.

Orexins/hypocretins (OX) and melanin-concentrating hormone (MCH) neurons located in the lateral hypothalamus seem to modulate different stages of the sleep-wake cycle. OX are necessary for wakefulness and MCH appears to regulate rapid eye movement sleep (REMS). Likewise, endocannabinoids, the endogenous ligands for cannabinoid receptors 1 and 2 (CB1R, CB2R), also modulate REMS in rats. Moreover, it has been shown that the activation of the CB1R in the lateral hypothalamus of rats excites MCH neurons while inhibiting OX neurons in in vitro preparations. Hence, we assessed the effects of 2-arachidonoylglicerol (2-AG, an endocannabinoid) in the lateral hypothalamus on the sleep-wake cycle of rats. We also utilized the CB1R inverse agonist AM251 to further support the involvement of this receptor, and we performed double immunofluorescence experiments to detect c-Fos, as a marker of neural activation, in OX and in MCH neurons to determine which neurons were activated. Our results indicate that 2-AG increases REMS through CB1R activation, and increases c-Fos expression in MCH neurons. These results suggest that endocannabinoid activation of the CB1R in the lateral hypothalamus, which activates MCH neurons, is one mechanism by which REMS is triggered.

Working memory performance in young adults is associated to the AATn polymorphism of the CNR1 gene

Working memory (WM) depends on several neural networks and neurochemical systems. One of them is the endocannabinoid (eCB) system, which CB1 receptor (CB1R) is widely distributed all over the brain. The stimulation of CB1R by agonists reduces WM efficiency. The CNR1 human gene (6q14-15) encodes the CB1R. AATn polymorphism of the CNR1 gene has been related to psychiatric disorders, and to procedural learning and attention in healthy subjects. The aim of this exploratory research was to test whether AATn polymorphism of the CNR1 is related to the WM performance, by measuring n-back task. Mexican healthy young adults (n = 94) performed the WM n-back task. One of the most frequent AATn allele in our sample was the AAT12. We formed three groups, as a function of the AATn genotype: AAT ≤ 12/AAT≤12, AAT ≤ 12/AAT > 12 and AAT > 12/AAT > 12, and their accuracy on the n-back task was compared. WM accuracy differed among genotypes (P=0.03): AAT ≤ 12/AAT≤12 group had a higher performance than the AAT > 12/AAT > 12 group (statistical power: 0.65, f(2) = 0.20, P<0.05). These results suggest that the fewer AATn repeats of the CNR1 gene, the better WM performance, and sustain the idea that eCB system participates in the modulation of the human brain network involved in WM.

Cortistatin, a modulatory peptide of sleep and memory, induces analgesia in rats.

Cortistatin is a neuropeptide structurally related to somatostatin that induces sleep and interferes with the memory process. Very likely affecting other neurotransmission systems, such as: acetylcholine, gamma-aminobutyric acid, and noradrenaline. For example, cortistatin inhibits acetylcholine excitatory actions in the hippocampus. It is known that acetylcholine is involved in the regulation of several processes, such as pain, temperature, sleep, and memory. Since cortistatin seems to interact with acetylcholine, we decided to explore whether cortistatin participates in the system that modulates the noxious stimulus-evoked behavior. The intracerebroventricular administration of cortistatin increased the threshold to evoke a defensive behavior by a nociceptive stimulus. These observations suggest that cortistatin is part of the system that regulates pain perception.

Endocannabinoids and sleep.

Sleep is regulated by several brain structures, neurotransmitters and neuromodulators. Endocannabinoids (eCBs) are a group of lipids with modulatory activity in the brain and bind mainly to cannabinoid receptors CB1R and CB2R, thereby modulating several brain functions, (memory, mood, food intake, pain perception). Oleoylethanolamide and palmitoylethanolamide belong to the N-acylethanolamides (NAEs) family, another type of active endogenous lipids. They bind to the peroxisome proliferator-activated receptor α but not to CB1R, thereby modulating food satiety, inflammation and pain. Both eCBs and NAEs seem to be regulating the sleep-wake cycle. Our objective is to analyze the experimental evidence published in the literature and to discuss if eCBs and NAEs are actually sleep modulators. Studies suggested 1. eCBs and NAEs are under circadian control. 2. NAEs promote wake. 3. eCBs promote non-rapid-eye movement. 4. eCBs also promote rapid-eye-movement sleep by interacting with melanin-concentrating hormone neurons in the lateral hypothalamus. 5. The pharmacological blockade of the CB1R reduces sleep while increasing wake. 6. eCBs restore sleep in a model of insomnia in rats.

Performance in working memory and attentional control is associated with the rs2180619 SNP in the CNR1 gene

Individual differences in cognitive performance are partly dependent, on genetic polymporhisms. One of the single‐nucleotide polymorphisms (SNP) of the CNR1 gene, which codes for cannabinoid receptor 1 (CB1R), is the rs2180619, located in a regulatory region of this gene (6q14–q15). The alleles of the rs2180619 are A > G; the G allele has been associated with addiction and high levels of anxiety (when the G allele interacts with the SS genotype of the 5‐HTTLPR gene). However, GG genotype is observed also in healthy subjects. Considering G allele as risk for ‘psychopathological conditions’, it is possible that GG healthy subjects do not be addicted or anxious, but would have reduced performance, compared to AA subjects, in attentional control and working memory processing. One hundred and sixty‐four healthy young Mexican‐Mestizo subjects (100 women and 64, men; mean age: 22.86 years, SD=2.72) participated in this study, solving a task where attentional control and working memory were required. GG subjects, compared to AA subjects showed: (1) a general lower performance in the task (P = 0.02); (2) lower performance only when a high load of information was held in working memory (P = 0.02); and (3) a higher vulnerability to distractors (P = 0.03). Our results suggest that, although the performance of GG subjects was at normal levels, a lower efficiency of the endocannabinoid system, probably due to a lowered expression of CB1R, produced a reduction in the performance of these subjects when attentional control and working memory processing is challenged.

Activation of PAR1 in the lateral hypothalamus of rats enhances food intake and REMS through CB1R.

The activation of protease-activated receptor 1 (PAR1) in cultured rat hippocampal neurons triggers synaptic retrograde signaling through the endocannabinoid 2-arachidonoylglycerol, thereby activating the cannabinoid receptor 1 (CB1R). CB1R is a metabotropic receptor activated by marihuana and endocannabinoids that suppresses neurotransmitter release. Also, activation of the CB1R increases rapid eye movement sleep (REMS) and food intake. The lateral hypothalamus is a crucial structure to modulate both feeding and waking. To evaluate the effect of PAR1 stimulation in the lateral hypothalamus on food intake and on the sleep–waking cycle, we implanted rats with electrodes, for recording sleep, and cannulae, to administer S1820, a selective PAR1 agonist peptide, bilaterally into the lateral hypothalamus. To determine whether the effects induced by PAR1 stimulation were mediated by CB1R activation, we administered AM251, a CB1R inverse agonist, to block S1820 effects. Our results show that the stimulation of PAR1 into the lateral hypothalamus increases both food intake and REMS and such effects were prevented by AM251, indicating that PAR1 modulates both food intake and the sleep–waking cycle, in the lateral hypothalamus, through CB1R activation. This study shows novel behavioral changes induced by PAR1 activation and further supports the notion that endocannabinoids are food intake and REMS promoters.