Multiple Roles of Cannabinoids in the Olfactory System.

Infertility is a worldwide reproductive health problem whose consequences have deep psychological and social impact in health, demographic change, and wellbeing. Thus, the knowledge of basic, conserved modulators of reproduction might contribute to the discovery of new potential target for the exploitation of drugs to treat infertility in humans. Besides the well known effects of endocannabinoids in the control of pain and visceral functions, in the last decade the deep involvement of endocannabinoid system in the control of reproductive functions in both males and females emerged. In fact, endocannabinoids, endogenous lipids that bind to cannabinoid receptors, modulate reproductive axis at both central and local level. Endocannabinoid signalling is critical for gonadotropin release and sex steroid biosynthesis, for the formation of functional male and female gametes, for fertilization, preimplantation embryo development, implantation, and postimplantation embryonic growth, and for labouring delivery as well. Endocannabinoids are also involved in the neuroendocrine control of reproduction functions through the modulation of stress, food intake, appetite, and sexual behaviour. Recently, new roles in sperm “startup” and gamete quality emerged and impairment of the physiological endocannabinoid tone and signalling has been reported in clinical cases of human infertility. Our hope is that this special issue may be important and timely since a deep knowledge of endocannabinoid system in reproduction might open new perspectives in clinical applications, pointing to endocannabinoid signalling as a novel target for correcting infertility, and for improving reproductive health in humans. The papers submitted to this special issue in the International Journal of Endocrinology take into account the multifaceted aspects of reproduction. Basic and evolutionarily conserved mechanisms of endocannabinoid activity in reproduction have also been included. E. Cottone et al. submitted an extensive review on the role of the endocannabinoids in the central regulation of reproduction in nonmammalian vertebrates, especially fish and amphibian; they correlate the morphofunctional distribution of cannabinoid receptors to key molecules involved in the control of reproductive functions, such as Gonadotropin Releasing Hormone (GnRH), dopamine, aromatase, and pituitary gonadotropins. The role of the endocannabinoid system as an ancient signalling system, that has been evolved over 500 million years, is highlighted in the paper of R. Chianese et al. that reports the presence of endocannabinoids in a nonmammalian model, the anuran amphibian Rana esculenta, and the functional crosstalk between these bioactive lipids and the GnRH system, shedding light on their different regulation in the brain and in the testis. In particular, a new role for vanilloid receptor emerged in the modulation of testicular GnRH system (both ligands and receptors) providing evidence that an opposite regulation occurs via type-1 cannabinoid receptor and vanilloid receptor signalling. The paper of G. Cacciola et al. is a very interesting and comprehensive review on the pivotal role played by type-1 cannabinoid receptor in spermiogenesis and on its involvement in the chromatin remodelling process that might affect negatively the sperm quality. The emerging evidences on estrogen activity in sperm quality are deeply detailed in a knock-out animal model, opening new intriguing perspectives in the clinical practice for the treatment of male infertility. The deep involvement of endocannabinoid signalling in driving the neurophysiological outcomes of mating behaviours has been reported in the research article submitted by J. M. Stuart et al. By means of lipidomic techniques, this group demonstrates that the levels of endocannabinoids, prostaglandins, and N-acylethanolamines rapidly change in specific brain areas in relationship to different mating strategies providing evidence that the endogenous cannabinoid systems is rapidly modified in response to changes in environment. In the context of the signalling events of pregnancy, B. M. Fonseca et al. presented the most recent progress on the endocannabinoid regulatory functions during decidualization and placentation. They summarized that while the endocannabinoid machinery was found to be expressed in decidual and placental tissues, aberrant endocannabinoid signalling was associated with pregnancy disorders, highlighting the content that the endocannabinoid signalling is a potential player coordinating successful decidualization and placentation. All of these papers have illustrated the potential regulatory interactions of sex steroid hormones with the endogenous cannabinoid system and how they allow reproduction to optimally function. The outstanding review by T. Ayakannu et al. that details the latest understandings of how sex steroids and the endogenous cannabinoid system work synergistically in a variety of cancers truly illustrates how the malfunctions of these signalling mechanisms can have dire effects. Using data from prostate, breast, and endometrial cancers, the review from Konje's group provides compelling evidence that to understand how to fix pathophysiology we must work towards understanding basic functioning physiology in the first place. Rosaria Meccariello Natalia Battista Heather B. Bradshaw Haibin Wang

Potentiation of Electrical and Chemical Synaptic Transmission Mediated by Endocannabinoids

IntroductionThe olfactory system acts as an interface between the environment and the brain. Its direct neural connection makes it a target for xenobiotics and a suitable model for studying olfactory dysfunction and related neurotoxic effects. This study aimed to characterize an animal model of olfactory dysfunction induced by nose-to-brain (NTB) delivery of vanadium pentoxide (V2O5).MethodsRats received 182 or 273 μg intranasally, thrice weekly over 4 weeks, followed by behavioral, histological, and biochemical analysis of the olfactory epithelium (OE), olfactory bulbs (OBs), and hippocampus.ResultsBehavioral tests showed significant olfactory deficits, longer latencies, and reduced investigation times in exposed groups. Histological analysis revealed coagulative necrosis in the OE, disrupted cellular organization, reduced number and size of OB glomeruli, and hippocampal neuronal loss with gliosis. Immunohistochemistry revealed increased proliferating cell nuclear antigen (PCNA) expression in the OE, dopaminergic neuron loss and astroglial proliferation in the OB, and hippocampal astroglial proliferation at the highest dose. Myelin basic protein (MBP) expression remained unchanged. Oxidative stress markers were largely unaltered, except for increased superoxide dismutase (SOD) in OBs and glutathione S-transferase (GST) in the hippocampus, especially at the high dose.DiscussionThe results reveal dose-dependent vanadium-induced neurotoxicity in the olfactory system. The higher dose induced pronounced structural damage, neuroinflammation, and oxidative stress, resulting in olfactory and cognitive impairments relevant to advanced olfactory dysfunction and neurodegeneration. The lower dose induced milder yet significant effects, supporting its use in early-stage dysfunction studies. This NTB-based model offers a valuable tool for investigating olfactory dysfunction mechanisms in toxicological and neurodegenerative contexts.

The ECS (endocannabinoid system) plays an important role in the onset of obesity and metabolic disorders, implicating central and peripheral mechanisms predominantly via CB1 (cannabinoid type 1) receptors. CB1 receptor antagonist/inverse agonist treatment improves cardiometabolic risk factors and insulin resistance. However, the relative contribution of peripheral organs to the net beneficial metabolic effects remains unclear. In the present study, we have identified the presence of the endocannabinoid signalling machinery in skeletal muscle and also investigated the impact of an HFD (high-fat diet) on lipid-metabolism-related genes and endocannabinoid-related proteins. Finally, we tested whether administration of the CB1 inverse agonist AM251 restored the alterations induced by the HFD. Rats were fed on either an STD (standard/low-fat diet) or an HFD for 10 weeks and then treated with AM251 (3 mg/kg of body weight per day) for 14 days. The accumulated caloric intake was progressively higher in rats fed on the HFD than the STD, resulting in a divergence in body weight gain. AM251 treatment reduced accumulated food/caloric intake and body weight gain, being more marked in rats fed on the HFD. CB2 (cannabinoid type 2) receptor and PPARα (peroxisome-proliferator-activated receptor α) gene expression was decreased in HFD-fed rats, whereas MAGL (monoglyceride lipase) gene expression was up-regulated. These data suggest an altered endocannabinoid signalling as a result of the HFD. AM251 treatment reduced CB2 receptor, PPARγ and AdipoR1 (adiponectin receptor 1) gene expression in STD-fed rats, but only partially normalized the CB2 receptor in HFD-fed rats. Protein levels corroborated gene expression results, but also showed a decrease in DAGL (diacylglycerol) β and DAGLα after AM251 treatment in STD- and HFD-fed rats respectively. In conclusion, the results of the present study indicate a diet-sensitive ECS in skeletal muscle, suggesting that blockade of CB1 receptors could work towards restoration of the metabolic adaption imposed by diet.

The endocannabinoid system and the cannabinoid type 1 receptor (CB1R) are required for the extinction of conditioned fear. CB1 antagonists have been shown to prevent extinction when delivered both systemically and within the amygdala. Anatomical studies suggest that CB1Rs in the basolateral amygdala (BLA) are expressed on GABAergic interneurons expressing the anxiogenic peptide cholecystokinin (CCK). Pre-synaptic CB1Rs inhibit neurotransmitter release, suggesting that CB1R activation during extinction may decrease CCK peptide release as well as GABA release. Thus, we examined whether extinction involves the CB1R modulation of CCK2 receptor activation. We found that intracerebroventricular administration of the CCK2 agonist pentagastrin dose-dependently impaired extinction of conditioned fear. Systemic administration of a CB1 antagonist, rimonabant (SR141716), also potently inhibited extinction learning. This effect was ameliorated with systemic administration of a CCK2 antagonist, CR2945. Furthermore, the extinction blockade by systemic SR141716 was reversed with intra-BLA, but not intrastriatal, infusion of CR2945. Lastly, as extinction usually leads to an increase in Akt phosphorylation, a biochemical effect antagonized by systemic CB1 antagonist treatment, we examined whether CR2945 co-administration would increase extinction-induced p-Akt levels. We observed that extinction-trained animals showed increased Akt phosphorylation following extinction, CB1 antagonist-treated animals showed p-Akt levels similar to those of non-extinction trained animals, and co-administration of CR2945 with SR141716 led to levels of p-Akt similar to those of vehicle-treated, extinction-trained controls. Together, these data suggest that interactions between the endocannabinoid and CCKergic transmitter systems may underlie the process of extinction of conditioned fear.

Olfactory dysfunction has been reported in 47.85% of COVID patients. It can be broadly categorized into conductive or sensorineural olfactory loss. Conductive loss occurs due to impaired nasal air flow, while sensorineural loss implies dysfunction of the olfactory epithelium or central olfactory pathways. The aim of this study was to analyze the clinical and imaging findings in patients with COVID-related olfactory dysfunction. Additionally, the study aimed to investigate the possible mechanisms of COVID-related olfactory dysfunction. The study included 110 patients with post-COVID-19 olfactory dysfunction, and a control group of 50 COVID-negative subjects with normal olfactory function. Endoscopic nasal examination was performed for all participants with special focus on the olfactory cleft. Smell testing was performed for all participants by using a smell diskettes test. Olfactory pathway magnetic resonance imaging (MRI) was done to assess the condition of the olfactory cleft and the dimensions and volume of the olfactory bulb. Olfactory dysfunction was not associated with nasal symptoms in 51.8% of patients. MRI showed significantly increased olfactory bulb dimensions and volume competed to controls. Additionally, it revealed olfactory cleft edema in 57.3% of patients. On the other hand, radiological evidence of sinusitis was detected in only 15.5% of patients. The average olfactory bulb volumes were significantly higher in the patients' group compared to the control group, indicating significant edema and swelling in the olfactory bulb in patients with COVID-related olfactory dysfunction. Furthermore, in most patients, no sinonasal symptoms such as nasal congestion or rhinorrhea were reported, and similarly, no radiological evidence of sinusitis was detected. Consequently, the most probable mechanism of COVID-related olfactory dysfunction is sensorineural loss through virus spread and damage to the olfactory epithelium and pathways.

Olfactory dysfunction and altered neurogenesis are observed in several neurodegenerative disorders including Huntington disease (HD). These deficits occur early and correlate with a decline in global cognitive performance, depression and structural abnormalities of the olfactory system including the olfactory epithelium, bulb and cortices. However, the role of olfactory system dysfunction in the pathogenesis of HD remains poorly understood and the mechanisms underlying this dysfunction are unknown. We show that deficits in odour identification, discrimination and memory occur in HD individuals. Assessment of the olfactory system in an HD murine model demonstrates structural abnormalities in the olfactory bulb (OB) and piriform cortex, the primary cortical recipient of OB projections. Furthermore, a decrease in piriform neuronal counts and altered expression levels of neuronal nuclei and tyrosine hydroxylase in the OB are observed in the YAC128 HD model. Similar to the human HD condition, olfactory dysfunction is an early phenotype in the YAC128 mice and concurrent with caspase activation in the murine HD OB. These data provide a link between the structural olfactory brain region atrophy and olfactory dysfunction in HD and suggest that cell proliferation and cell death pathways are compromised and may contribute to the olfactory deficits in HD.

IntroductionOlfaction is important for the quality of life; however, in Kallmann syndrome (KS), defective development results in olfactory dysfunction. Notably, the mechanism underlying olfactory development, especially in the olfactory epithelium (OE), which detects olfactory signals, remains unclear. Mutations in PROK2, which encodes prokineticin-2, have been identified in approximately 9% of the KS patients with olfactory defects.MethodsWe examined olfactory function and analyzed the causes of olfactory dysfunction based on spatiotemporal development and gene expression changes in Prok2 knockout (KO) model mice with KS.ResultsThe ability of the OE to detect olfactory signals was diminished in adult Prok2 KO mice. Maturation of olfactory sensory neurons (OSNs) in the OE and formation of glomeruli in the olfactory bulb (OB) in adult Prok2 KO mice were disrupted, thus causing olfactory dysfunction. Furthermore, molecular analysis of Prok2 KO mice during embryonic development revealed abnormal development of OB layers and diminished differentiation to mature OSNs in the OE at the later stage, which caused defects in the entire olfactory system. Remarkably, downstream signaling genes of Prok2, including intermediate filament genes and genes expressed in the putative OB, were found to mediate olfactory system organization.DiscussionOverall, these findings reveal the role of Prok2 in olfactory system organization and elucidate how olfactory development defects translate to olfactory function.

Glutamate is an excitatory neurotransmitter in the olfactory system and its N-methyl-D-aspartate-(NMDA) receptor subunits [GluN1 (NR1), GluN2A (NR2A), and GluN2B (NR2B)] are expressed at synapses in the olfactory bulb and olfactory epithelium. Thus, glutamatergic neurons and NMDA receptors play key roles in olfaction. GluN3A (NR3A) is a unique inhibitory subunit in the NMDA receptor complex; however, the expression and functional role of GluN3A in the olfactory bulb and epithelium remain unclear. The present study examined the expression patterns of GluN3A in the olfactory bulb and epithelium and explored its functional role in the olfactory system. Immunohistochemical and Western blot analyses revealed that GluN3A is abundantly expressed in different cellular layers of the olfactory bulb and epithelium of the adult wild type (WT) mice. In littermate GluN3A knockout (GluN3A(-/-); KO) mice, the expression of olfactory marker protein normally found in mature olfactory sensory neurons was significantly reduced in the olfactory bulb and epithelium. A butyl alcohol stimulus increased immediate-early gene c-Fos expression in the olfactory system of WT mice, while this response was absent in GluN3A KO mice. The level of phosphorylated Ca(2+)/calmodulin-dependent kinase II was significantly lower in GluN3A KO mice compared to WT mice. In buried food finding test, GluN3A mice took significantly longer time to find food compared to WT mice. Consistently, impaired odor distinguishing ability was seen in GluN3A KO mice. These findings suggest that GluN3A, expressed in the adult olfactory system, plays a significant regulatory role in olfactory development and functional activity.

Evidence for the involvement of the endocannabinoid system (ECS) in anxiety and fear has been accumulated, providing leads for novel therapeutic approaches. In anxiety, a bidirectional influence of the ECS has been reported, whereby anxiolytic and anxiogenic responses have been obtained after both increases and decreases of the endocannabinoid tone. The recently developed genetic tools have revealed different but complementary roles for the cannabinoid type 1 (CB1) receptor on GABAergic and glutamatergic neuronal populations. This dual functionality, together with the plasticity of CB1 receptor expression, particularly on GABAergic neurons, as induced by stressful and rewarding experiences, gives the ECS a unique regulatory capacity for maintaining emotional homeostasis. However, the promiscuity of the endogenous ligands of the CB1 receptor complicates the interpretation of experimental data concerning ECS and anxiety. In fear memory paradigms, the ECS is mostly involved in the two opposing processes of reconsolidation and extinction of the fear memory. Whereas ECS activation deteriorates reconsolidation, proper extinction depends on intact CB1 receptor signalling. Thus, both for anxiety and fear memory processing, endocannabinoid signalling may ensure an appropriate reaction to stressful events. Therefore, the ECS can be considered as a regulatory buffer system for emotional responses.

The Incredible Elastic Brain: How Neural Stem Cells Expand Our Minds

Adolescent binge drinking has detrimental effects on brain function, leading to long-lasting impairments in synaptic plasticity, cognition, and behavior. These effects are mediated, in part, by disruption of the endocannabinoid system (ECS) and its cannabinoid type-1 (CB1) receptor. Alcohol consumption also depletes omega-3 fatty acids, which are essential for maintaining cell membrane integrity and supporting brain function. This depletion impairs synaptic plasticity by disrupting endocannabinoid signaling and reducing CB1 receptor expression and function. Conversely, enhancement of the ECS can restore brain function and reverse the loss of endocannabinoid-dependent synaptic plasticity associated with omega-3 deficiency. Notably, omega-3 supplementation has been shown to restore CB1 receptor expression in specific brain regions in adult mice following adolescent alcohol exposure. However, despite the established interplay between alcohol, omega-3, and the ECS, the direct impact of omega-3 supplementation on the subcellular localization of CB1 receptors after alcohol exposure remains poorly understood. In this study, we used immunoelectron microscopy to investigate whether omega-3 supplementation influences CB1 receptor distribution in the hippocampal CA1 region following alcohol withdrawal in adolescent male mice. Our results demonstrate that omega-3 partially restore the excitatory/inhibitory balance disrupted by alcohol, as evidenced by an increased number of excitatory terminals and a significant reduction in inhibitory terminals. However, the distribution and density of CB1 receptors within neuronal and glial compartments remain unchanged following alcohol exposure and omega-3 supplementation. These findings highlight novel structural effects of omega-3 in mitigating alcohol-induced brain damage.

The Age of Olfactory Bulb Neurons in Humans

Olfactory neurons are unique in the mammalian nervous system because of their capacity to regenerate in adult animals. It has been shown that olfactory receptor cells located in the olfactory epithelium are replaced on a continuous basis and in response to injury throughout the life span of most species. NGF, which is one of the neurotrophic factors, is present in many areas of the central and peripheral nervous system. It has been shown that NGF in the olfactory bulb plays a role in the survival of cholinergic neurons in the horizontal limb of the diagonal band (HDB). Recent studies of NGF in the olfactory bulb suggest that it is involved in the development, maintenance, and regeneration of olfactory receptor cells. In this study, we review reports examining the relationship between NGF in the olfactory bulb and neuronal regeneration and development in the mammalian olfactory systems. Low- and high-affinity NGF receptor immunoreactivity is markedly expressed during regeneration and at different stages of development in the mouse olfactory system. This level of immunoreactivity is no longer present after completion of regeneration and at maturation. Other findings indicate that NGF injected into the olfactory bulb is transported retrogradely to the olfactory epithelium. It has also been shown that continuous anti-NGF antibody injection into the olfactory bulb causes degeneration and olfactory dysfunction. Administration of NGF directory into nasal cavity results in an increase in the expression of olfactory marker protein within the olfactory epithelium in axotomized rats. These findings suggested that the presence of NGF in the olfactory bulb plays an essential role in regeneration, maintenance, and development in the olfactory system of mammals.

British Journal of Pharmacology (2003) 140, 781–789. doi:10.1038/sj.bjp.0705466