Embryonic ethanol exposure induces ectopic Hcrt and MCH neurons outside hypothalamus in rats and zebrafish: Role in ethanol-induced behavioural disturbances

Sleep Loss and Substance Use Disorders: An Issue from Adolescents to Adults

Unsatisfactory sleep is a worldwide concern, as evidenced by the high prevalence of insomnia symptoms and diagnosis in the general population, and an issue that has also risen among adolescents. These circumstances are a cause of worry due to, among other factors, the observed bidirectional association of sleep disturbances and the risk of substance use disorder development. In this regard, across the globe, several reports indicate that substance consumption is at an all-time high, with alcohol, nicotine, and cannabis leading the charts. Additionally, the age of onset has dropped, with reports suggesting that first contact is usually during adolescence. Although the nature of the link between poor sleep and substance use disorder development is still not fully understood, it is possible that an overactive orexinergic system could play a role, as it has been observed that treatment with orexinergic antagonists improves insomnia symptoms and that postmortem studies show an increase in orexin immunoreactive neurons in sections obtained from habitual opioid consumers. We further argue that it is during adolescence that this maladaptive loop can be established, priming for the development of substance use disorders.

Contribution of hypothalamic orexin (hypocretin) circuits to pathologies of motivation

The orexin (also known as hypocretin) system, consisting of neuropeptides orexin-A and orexin-B, was discovered over 25 years ago and was immediately identified as a central regulator of sleep and wakefulness. These peptides interact with two G-protein coupled receptors, orexin 1 (OX1) and orexin 2 (OX2) receptors which are capable of coupling to all heterotrimeric G-protein subfamilies, but primarily transduce increases in calcium signalling. Orexin neurons are regulated by a variety of transmitter systems and environmental stimuli that signal reward availability, including food and drug related cues. Orexin neurons are also activated by anticipation, stress, cues predicting motivationally relevant information, including those predicting drugs of abuse, and engage neuromodulatory systems, including dopamine neurons of the ventral tegmental area (VTA) to respond to these signals. As such, orexin neurons have been characterized as motivational activators that coordinate a range of functions, including feeding and arousal, that allow the individual to respond to motivationally relevant information, critical for survival. This review focuses on the role of orexins in appetitive motivation and highlights a role for these neuropeptides in pathologies characterized by inappropriately high levels of motivated arousal (overeating, anxiety and substance use disorders) versus those in which motivation is impaired (depression).

Neurological Disorders Induced by Drug Use: Effects of Adolescent and Embryonic Drug Exposure on Behavioral Neurodevelopment

Clinical studies demonstrate that the risk of developing neurological disorders is increased by overconsumption of the commonly used drugs, alcohol, nicotine and cannabis. These drug-induced neurological disorders, which include substance use disorder (SUD) and its co-occurring emotional conditions such as anxiety and depression, are observed not only in adults but also with drug use during adolescence and after prenatal exposure to these drugs, and they are accompanied by long-lasting disturbances in brain development. This report provides overviews of clinical and preclinical studies, which confirm these adverse effects in adolescents and the offspring prenatally exposed to the drugs and include a more in-depth description of specific neuronal systems, their neurocircuitry and molecular mechanisms, affected by drug exposure and of specific techniques used to determine if these effects in the brain are causally related to the behavioral disturbances. With analysis of further studies, this review then addresses four specific questions that are important for fully understanding the impact that drug use in young individuals can have on future pregnancies and their offspring. Evidence demonstrates that the adverse effects on their brain and behavior can occur: (1) at low doses with short periods of drug exposure during pregnancy; (2) after pre-conception drug use by both females and males; (3) in subsequent generations following the initial drug exposure; and (4) in a sex-dependent manner, with drug use producing a greater risk in females than males of developing SUDs with emotional conditions and female offspring after prenatal drug exposure responding more adversely than male offspring. With the recent rise in drug use by adolescents and pregnant women that has occurred in association with the legalization of cannabis and increased availability of vaping tools, these conclusions from the clinical and preclinical literature are particularly alarming and underscore the urgent need to educate young women and men about the possible harmful effects of early drug use and to seek novel therapeutic strategies that might help to limit drug use in young individuals.

An overview of current advances in perinatal alcohol exposure and pathogenesis of fetal alcohol spectrum disorders

The adverse use of alcohol is a serious global public health problem. Maternal alcohol consumption during pregnancy usually causes prenatal alcohol exposure (PAE) in the developing fetus, leading to a spectrum of disorders known as fetal alcohol spectrum disorders (FASD) and even fetal alcohol syndrome (FAS) throughout the lifelong sufferers. The prevalence of FASD is approximately 7.7 per 1,000 worldwide, and is even higher in developed regions. Generally, Ethanol in alcoholic beverages can impair embryonic neurological development through multiple pathways leading to FASD. Among them, the leading mechanism of FASDs is attributed to ethanol-induced neuroinflammatory damage to the central nervous system (CNS). Although the underlying molecular mechanisms remain unclear, the remaining multiple pathological mechanisms is likely due to the neurotoxic damage of ethanol and the resultant neuronal loss. Regardless of the molecular pathway, the ultimate outcome of the developing CNS exposed to ethanol is almost always the destruction and apoptosis of neurons, which leads to the reduction of neurons and further the development of FASD. In this review, we systematically summarize the current research progress on the pathogenesis of FASD, which hopefully provides new insights into differential early diagnosis, treatment and prevention for patents with FASD.

The Impact of Prenatal Alcohol Exposure on the Autonomic Nervous System and Cardiovascular System in Rats in a Sex-Specific Manner

BACKGROUND

Fetal Alcohol Spectrum Disorder (FASD) is a consequence of prenatal alcohol exposure (PAE) associated with a range of effects, including dysmorphic features, prenatal and/or postnatal growth problems, and neurodevelopmental difficulties. Despite advances in treatment methods, there are still gaps in knowledge that highlight the need for further research. The study investigates the effect of PAE on the autonomic system, including sex differences that may aid in early FASD diagnosis, which is essential for effective interventions.

METHODS

During gestational days 5 to 20, five pregnant female Wistar rats were orally administered either glucose or ethanol. After 22 days, 26 offspring were born and kept with their mothers for 21 days before being isolated. Electrocardiographic recordings were taken on the 29th and 64th day. Heart rate variability (HRV) parameters were collected, including heart rate (HR), standard deviation (SD), standard deviation of normal-to-normal intervals (SDNN), and the root mean square of successive differences between normal heartbeats (RMSSD). Additionally, a biochemical analysis of basic serum parameters was performed on day 68 of the study.

RESULTS

The study found that PAE had a significant impact on HRV. While electrolyte homeostasis remained mostly unaffected, sex differences were observed across various parameters in both control and PAE groups, highlighting the sex-specific effects of PAE. Specifically, the PAE group had lower mean heart rates, particularly among females, and higher SDNN and RMSSD values. Additionally, there was a shift towards parasympathetic activity and a reduction in heart rate entropy in the PAE group. Biochemical changes induced by PAE were also observed, including elevated levels of alanine transaminase (ALT) and aspartate aminotransferase (AST), especially in males, increased creatinine concentration in females, and alterations in lipid metabolism.

CONCLUSIONS

PAE negatively affects the development of the autonomic nervous system, resulting in decreased heart rate and altered sympathetic activity. PAE also induces cardiovascular abnormalities with sex-specific effects, highlighting a relationship between PAE consequences and sex. Elevated liver enzymes in the PAE group may indicate direct toxic effects, while increased creatinine levels, particularly in females, may suggest an influence on nephrogenesis and vascular function. The reduced potassium content may be linked to hypothalamus-pituitary-adrenal axis overactivity.

Understanding zebrafish sleep and wakefulness physiology as an experimental model for biomedical research

Sleep is a globally observable fact, or period of reversible distracted rest, that can be distinguished from arousal by various behavioral criteria. Although the function of sleep is an evolutionarily conserved behavior, its mechanism is not yet clear. The zebrafish (Danio rerio) has become a valuable model for neurobehavioral studies such as studying learning, memory, anxiety, and depression. It is characterized by a sleep-like state and circadian rhythm, making it comparable to mammals. Zebrafish are a good model for behavioral studies because they share genetic similarities with humans. A number of neurotransmitters are involved in sleep and wakefulness. There is a binding between melatonin and the hypocretin system present in zebrafish. The full understanding of sleep and wakefulness physiology in zebrafish is still unclear among researchers. Therefore, to make a clear understanding of the sleep/wake cycle in zebrafish, this article covers the mechanism involved behind it, and the role of the neuromodulator system followed by the mechanism of the HPA axis.

Embryonic ethanol exposure and optogenetic activation of hypocretin neurons stimulate similar behaviors early in life associated with later alcohol consumption

The initiation of alcohol use early in life is one of the strongest predictors of developing a future alcohol use disorder. Clinical studies have identified specific behaviors during early childhood that predict an increased risk for excess alcohol consumption later in life. These behaviors, including increased hyperactivity, anxiety, novelty-seeking, exploratory behavior, impulsivity, and alcohol-seeking, are similarly stimulated in children and adolescent offspring of mothers who drink alcohol during pregnancy. Here we tested larval zebrafish in addition to young pre-weanling rats and found this repertoire of early behaviors along with the overconsumption of alcohol during adolescence to be increased by embryonic ethanol exposure. With hypocretin/orexin (Hcrt) neurons known to be stimulated by ethanol and involved in mediating these alcohol-related behaviors, we tested their function in larval zebrafish and found optogenetic activation of Hcrt neurons to stimulate these same early alcohol-related behaviors and later alcohol intake, suggesting that these neurons have an important role in producing these behaviors. Together, these results show zebrafish to be an especially useful animal model for investigating the diverse neuronal systems mediating behavioral changes at young ages that are produced by embryonic ethanol exposure and predict an increased risk for developing alcohol use disorder.

Utility of the Zebrafish Model for Studying Neuronal and Behavioral Disturbances Induced by Embryonic Exposure to Alcohol, Nicotine, and Cannabis

It is estimated that 5% of pregnant women consume drugs of abuse during pregnancy. Clinical research suggests that intake of drugs during pregnancy, such as alcohol, nicotine and cannabis, disturbs the development of neuronal systems in the offspring, in association with behavioral disturbances early in life and an increased risk of developing drug use disorders. After briefly summarizing evidence in rodents, this review focuses on the zebrafish model and its inherent advantages for studying the effects of embryonic exposure to drugs of abuse on behavioral and neuronal development, with an emphasis on neuropeptides known to promote drug-related behaviors. In addition to stimulating the expression and density of peptide neurons, as in rodents, zebrafish studies demonstrate that embryonic drug exposure has marked effects on the migration, morphology, projections, anatomical location, and peptide co-expression of these neurons. We also describe studies using advanced methodologies that can be applied in vivo in zebrafish: first, to demonstrate a causal relationship between the drug-induced neuronal and behavioral disturbances and second, to discover underlying molecular mechanisms that mediate these effects. The zebrafish model has great potential for providing important information regarding the development of novel and efficacious therapies for ameliorating the effects of early drug exposure.

Subpopulations of hypocretin/orexin neurons differ in measures of their cell proliferation, dynorphin co-expression, projections, and response to embryonic ethanol exposure

Numerous studies in animals demonstrate that embryonic exposure to ethanol (EtOH) at low-moderate doses stimulates neurogenesis and increases the number of hypothalamic neurons expressing the peptide, hypocretin/orexin (Hcrt). A recent study in zebrafish showed that this effect on the Hcrt neurons in the anterior hypothalamus (AH) is area specific, evident in the anterior (aAH) but not posterior (pAH) part of this region. To understand specific factors that may determine the differential sensitivity to EtOH of these Hcrt subpopulations, we performed additional measures in zebrafish of their cell proliferation, co-expression of the opioid dynorphin (Dyn), and neuronal projections. In association with the increase in Hcrt neurons in the aAH but not pAH, EtOH significantly increased only in the aAH the proliferation of Hcrt neurons and their number lacking Dyn co-expression. The projections of these subpopulations differed markedly in their directionality, with those from the pAH primarily descending to the locus coeruleus and those from the aAH ascending to the subpallium, and they were both stimulated by EtOH, which induced specifically the most anterior subpallium-projecting Hcrt neurons to become ectopically expressed beyond the aAH. These differences between the Hcrt subpopulations suggest they are functionally distinct in their regulation of behavior.

Role of Chemokine Cxcl12a in Mediating the Stimulatory Effects of Ethanol on Embryonic Development of Subpopulations of Hypocretin/Orexin Neurons and Their Projections

Studies in zebrafish and rats show that embryonic ethanol exposure at low-moderate concentrations stimulates hypothalamic neurons expressing hypocretin/orexin (Hcrt) that promote alcohol consumption, effects possibly involving the chemokine Cxcl12 and its receptor Cxcr4. Our recent studies in zebrafish of Hcrt neurons in the anterior hypothalamus (AH) demonstrate that ethanol exposure has anatomically specific effects on Hcrt subpopulations, increasing their number in the anterior AH (aAH) but not posterior AH (pAH), and causes the most anterior aAH neurons to become ectopically expressed further anterior in the preoptic area (POA). Using tools of genetic overexpression and knockdown, our goal here was to determine whether Cxcl12a has an important function in mediating the specific effects of ethanol on these Hcrt subpopulations and their projections. The results demonstrate that the overexpression of Cxcl12a has stimulatory effects similar to ethanol on the number of aAH and ectopic POA Hcrt neurons and the long anterior projections from ectopic POA neurons and posterior projections from pAH neurons. They also demonstrate that knockdown of Cxcl12a blocks these effects of ethanol on the Hcrt subpopulations and projections, providing evidence supporting a direct role of this specific chemokine in mediating ethanol's stimulatory effects on embryonic development of the Hcrt system.