Prenatal stress induces vulnerability to nicotine addiction and alters D2 receptors' expression in the nucleus accumbens in adult rats

Prenatal Hypoxia Predisposes to Impaired Expression of the chrna4 and chrna7 Genes in Adult Rats without Affecting Acetylcholine Metabolism during Embryonic Development

Previous studies have shown that the combined effect of fetal hypoxia and maternal stress hormones predetermines tendency to nicotine addiction in adulthood. This study in rats aimed to investigate the effect of prenatal severe hypoxia (PSH) on acetylcholine metabolism in the developing brain, as well as on expression of acetylcholine receptors chrna4 and chrna7 in both the developing brain and adult brain structures following nicotine consumption. In the developing brain of PSH rats, no changes were found in the activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) or disturbances in the acetylcholine levels. However, decreased chrna4 expression was detected on the day 15 of pregnancy, while elevation in the chrna7 expression was observed on the days 15 and 16 of embryogenesis. In adulthood, the consequences of PSH were manifested as decreased expression of chrna4 in the medial prefrontal cortex (PFC), nucleus accumbens (NAacc), and hypothalamus (HT), decreased expression of chrna7 in the PFC and hippocampus (HPC). Whereas, nicotine consumption did not decrease the expression levels of chrna4 and chrna7 compared to the control group in the adult PSH rats. Thus, prenatal hypoxia predisposes to impaired expression of the chrna4 and chrna7 genes in adult rats without affecting acetylcholine metabolism during embryonic development.

Prenatal Hypoxia Triggers a Glucocorticoid-Associated Depressive-like Phenotype in Adult Rats, Accompanied by Reduced Anxiety in Response to Stress

Fetal hypoxia and maternal stress frequently culminate in neuropsychiatric afflictions in life. To replicate this condition, we employed a model of prenatal severe hypoxia (PSH) during days 14-16 of rat gestation. Subsequently, both control and PSH rats at 3 months old were subjected to episodes of inescapable stress to induce learned helplessness (LH). The results of the open field test revealed an inclination towards depressive-like behavior in PSH rats. Following LH episodes, control (but not PSH) rats displayed significant anxiety. LH induced an increase in glucocorticoid receptor (GR) levels in extrahypothalamic brain structures, with enhanced nuclear translocation in the hippocampus (HPC) observed both in control and PSH rats. However, only control rats showed an increase in GR nuclear translocation in the amygdala (AMG). The decreased GR levels in the HPC of PSH rats correlated with elevated levels of hypothalamic corticotropin-releasing hormone (CRH) compared with the controls. However, LH resulted in a reduction of the CRH levels in PSH rats, aligning them with those of control rats, without affecting the latter. This study presents evidence that PSH leads to depressive-like behavior in rats, associated with alterations in the glucocorticoid system. Notably, these impairments also contribute to increased resistance to severe stressors.

The Prenatal Hypoxic Pathology Associated with Maternal Stress Predisposes to Dysregulated Expression of the chrna7 Gene and the Subsequent Development of Nicotine Addiction in Adult Offspring

INTRODUCTION

Previous studies have shown that fetal hypoxia predisposes individuals to develop addictive disorders in adulthood. However, the specific impact of maternal stress, mediated through glucocorticoids and often coexisting with fetal hypoxia, is not yet fully comprehended.

METHODS

To delineate the potential effects of these pathological factors, we designed models of prenatal severe hypoxia (PSH) in conjunction with maternal stress and prenatal intrauterine ischemia (PII). We assessed the suitability of these models for our research objectives by measuring HIF1α levels and evaluating the glucocorticoid neuroendocrine system. To ascertain nicotine dependence, we employed the conditioned place aversion test and the startle response test. To identify the key factor implicated in nicotine addiction associated with PSH, we employed techniques such as Western blot, immunohistochemistry, and correlational analysis between chrna7 and nr3c1 genes across different brain structures.

RESULTS

In adult rats exposed to PSH and PII, we observed increased levels of HIF1α in the hippocampus (HPC). However, the PSH group alone exhibited reduced glucocorticoid receptor levels and disturbed circadian glucocorticoid rhythms. Additionally, they displayed signs of nicotine addiction in the conditioned place aversion and startle response tests. We also observed elevated levels of phosphorylated DARPP-32 protein in the nucleus accumbens (NAc) indicated compromised glutamatergic efferent signaling. Furthermore, there was reduced expression of α7 nAChR, which modulates glutamate release, in the medial prefrontal cortex (PFC) and HPC. Correlation analysis revealed strong associations between chrna7 and nr3c1 expression in both brain structures.

CONCLUSION

Perturbations in the glucocorticoid neuroendocrine system and glucocorticoid-dependent gene expression of chrna7 associated with maternal stress response to hypoxia in prenatal period favor the development of nicotine addiction in adulthood.

Preventive putative effect of agmatine on cognitive and molecular outcomes in ventral tegmental area of male offspring following physical and psychological prenatal stress

Prenatal stress (PS) results from a maternal experience of stressful events during pregnancy, which has been associated with an increased risk of behavioral disorders including substance abuse and anxiety in the offspring. PS is known to result in heightened dopamine release in the ventral tegmental area (VTA), in part through the effects of corticotropin-releasing hormone, which directly excites dopaminergic cells. It has recently been suggested that agmatine plays a role in modulating anxiety-like behaviors. In this study, we investigated whether agmatine could reduce negative cognitive outcomes in male mice prenatally exposed to psychological/physical stress, and whether this could be associated with molecular changes in VTA. Agmatine (37.5 mg/kg) was administrated 30 min prior to PS induction in pregnant Swiss mice. Male offspring were evaluated in a series of behavioral and molecular assays. Findings demonstrated that agmatine reduced the impairment in locomotor activity induced by both psychological and physical PS. Agmatine also decreased heightened conditioned place preference to morphine seen in PS offspring. Moreover, agmatine ameliorated the anxiety-like behavior and drug-seeking behavior induced by PS in the male offspring. Molecular effects were seen in VTA as the enhanced brain-derived neurotrophic factor (BDNF) induced by PS in the VTA was reduced by agmatine. Behavioral tests indicate that agmatine exerts a protective effect on PS-induced impairments in male offspring, which could be due in part to agmatine-associated molecular alterations in the VTA. Taken together, our data suggest that prenatal treatment with agmatine exerts protective effect against negative consequences of PS on the development of affective circuits in the offspring.

The hyperexcitability of laterodorsal tegmentum cholinergic neurons accompanies adverse behavioral and cognitive outcomes of prenatal stress

Exposure to prenatal stress (PS) leads to the offspring's vulnerability towards the development of cognitive and behavioral disorders. Laterodorsal tegmentum (LDT) is a part of the brainstem cholinergic system that is believed to play a pivotal role in the stress-associated progression of anxiety, memory impairment, and addictive behaviors. In this study, we aimed to investigate the electrophysiological alterations of LDT cholinergic neurons and its accompanied behavioral and cognitive outcomes in the offspring of mice exposed to physical or psychological PS. Swiss Webster mice were exposed to physical or psychological stress on the tenth day of gestation. Ex vivo investigations in LDT brain slices of adolescent male offspring were performed to evaluate the effects of two stressor types on the activity of cholinergic neurons. Open field test, elevated plus maze, passive avoidance test, and conditioned place preference were conducted to assess behavioral and cognitive alterations in the offspring. The offspring of both physical and psychological PS-exposed mice exhibited increased locomotor activity, anxiety-like behavior, memory impairment, and preference to morphine. In both early- and late-firing cholinergic neurons of the LDT, stressed groups demonstrated higher firing frequency, lower adaptation ratio, decreased action potential threshold, and therefore increased excitability compared to the control group. The findings of the present study suggest that the hyperexcitability of the cholinergic neurons of LDT might be involved in the development of PS-associated anxiety-like behaviors, drug seeking, and memory impairment.

Cross-talk between the HPA axis and addiction-related regions in stressful situations

Addiction is a worldwide problem that has a negative impact on society by imposing significant costs on health care, public security, and the deactivation of the community economic cycle. Stress is an important risk factor in the development of addiction and relapse vulnerability. Here we review studies that have demonstrated the diverse roles of stress in addiction. Term searches were conducted manually in important reference journals as well as in the Google Scholar and PubMed databases, between 2010 and 2022. In each section of this narrative review, an effort has been made to use pertinent sources. First, we will provide an overview of changes in the Hypothalamus-Pituitary-Adrenal (HPA) axis component following stress, which impact reward-related regions including the ventral tegmental area (VTA) and nucleus accumbens (NAc). Then we will focus on internal factors altered by stress and their effects on drug addiction vulnerability. We conclude that alterations in neuro-inflammatory, neurotrophic, and neurotransmitter factors following stress pathways can impact related mechanisms on craving and relapse susceptibility.

Prenatal Effects of Nicotine on Obesity Risks: A Narrative Review

Nicotine usage by mothers throughout pregnancy has been observed to relate to numerous deleterious effects in children, especially relating to obesity. Children who have prenatally been exposed to nicotine tend to have lower birth weights, with an elevated risk of becoming overweight throughout development and into their adolescent and adult life. There are numerous theories as to how this occurs: catch-up growth theory, thrifty phenotype theory, neurotransmitter or endocrine imbalances theory, and a more recent examination on the genetic factors relating to obesity risk. In addition to the negative effect on bodyweight and BMI, individuals with obesity may also suffer from numerous comorbidities involving metabolic disease. These may include type 1 and 2 diabetes, high cholesterol levels, and liver disease. Predisposition for obesity with nicotine usage may also be associated with genetic risk alleles for obesity, such as the DRD2 A1 variant. This is important for prenatally nicotine-exposed individuals as an opportunity to provide early prevention and intervention of obesity-related risks.

Hyperexcitability of VTA dopaminergic neurons in male offspring exposed to physical or psychological prenatal stress

Prenatal stress (PS) exposure leads to cognitive and behavioral alterations in offspring including an increased risk of substance abuse and anxiety disorders. Signalling from dopamine (DA) neurons of the ventral tegmental area (VTA) in the mesoaccumbal and mesocortical pathways plays a vital role in drug dependency and anxiety behavior. To provide further knowledge about the changes in drug seeking behavior and anxiety behaviors in prenatally stressed mice, we conducted ex vivo investigations in VTA brain slices of adult male PS offspring to evaluate the effects of two types of PS (physical vs. psychological) on activity of DA neurons. Elevated plus maze (EPM) was used to assess anxiety-like behaviors and conditioned place preference (CPP) was used to evaluate drug reinforcing effects in mice. An increased anxiety-like behavior and preference to morphine was observed in prenatally stressed mice. PS VTA DA cells exhibited greater I_h current and a higher frequency and amplitude of sEPSCs, which were consistent with a greater degree of pre- or postsynaptic excitability of the VTA. This was confirmed by lower rheobase and lower firing thresholds in PS VTA neurons, as well as increases in spontaneous firing frequency. When taken together, these data suggest that alterations in VTA DA neurons in this mouse model of prenatal stress might be associated with later life alterations in drug seeking and anxiety-like behaviors through their role in mesocortical and mesoaccumbal pathways.

Mechanisms of Shared Vulnerability to Post-traumatic Stress Disorder and Substance Use Disorders

Psychoactive substance use is a nearly universal human behavior, but a significant minority of people who use addictive substances will go on to develop an addictive disorder. Similarly, though ~90% of people experience traumatic events in their lifetime, only ~10% ever develop post-traumatic stress disorder (PTSD). Substance use disorders (SUD) and PTSD are highly comorbid, occurring in the same individual far more often than would be predicted by chance given the respective prevalence of each disorder. Some possible reasons that have been proposed for the relationship between PTSD and SUD are self-medication of anxiety with drugs or alcohol, increased exposure to traumatic events due to activities involved in acquiring illegal substances, or addictive substances altering the brain's stress response systems to make users more vulnerable to PTSD. Yet another possibility is that some people have an intrinsic vulnerability that predisposes them to both PTSD and SUD. In this review, we integrate clinical and animal data to explore these possible etiological links between SUD and PTSD, with an emphasis on interactions between dopaminergic, adrenocorticotropic, GABAergic, and glutamatergic neurobehavioral mechanisms that underlie different emotional learning styles.

A pilot study showing that repeated exposure to stress produces alterations in subsequent responses to anesthetics in rats

The repeated use of a drug frequently leads to alterations in the response to that drug. We undertook this study to determine whether multiple exposures to the general anesthetic produced alterations in subsequent exposures to this anesthetic. For this study, adult male rats were anesthetized with 2.5% isoflurane for one hour. The rats were divided into 4 groups of 8 rats each. Groups 1-3 were transported between their homeroom and the anesthesia testing room and were handled in an identical manner weekly for a period of 12 weeks, but were anesthetized on different schedules. Group 1 was anesthetized weekly for 12 weeks, Group 2 on either a 3 or 4 week schedule and Group 3 was anesthetized a single time, at the end of the 12 week period. To receive anesthesia multiple times, animals were transported from their homeroom to the anesthesia location and handled repeatedly. We took into consideration of the frequency of anesthesia exposure and the stress involved. Rats in groups 2 and 3 were placed in the anesthesia chamber, with O2 but with no anesthetic, every week when they were not scheduled to receive anesthesia. In Group 4, rats were not transported or handled in any way and stayed in the home room for a period of 12 weeks. Rats in this group were anesthetized once, at the very end of the study. Recovery of the rat's righting reflex was used to assess the acceleration of recovery time from general anesthesia. Group 1 rats showed dramatically faster emergence from anesthesia after several rounds of anesthesia. Surprisingly, Groups 2 and 3 rats, treated in an identical manner as Group 1, but which were anesthetized on different schedules, also exhibited more rapid emergence from anesthesia, when compared to Group 4 rats, which were never handled or transported prior to a single anesthesia. These results suggest that the stress of transportation and handling altered responsiveness to anesthesia. Our results show that responsiveness to anesthetic agents can change over time outside of the normal developmental changes taking place in rats as they age.

Chronic stress increases susceptibility to food addiction by increasing the levels of DR2 and MOR in the nucleus accumbens

Background: Stress-related obesity might be related to the suppression of the hypothalamic-pituitary- adrenocortical axis and dysregulation of the metabolic system. Chronic stress also induces the dysregulation of the reward system and increases the risk of food addiction, according to recent clinical findings. However, few studies have tested the effect of chronic stress on food addiction in animal models. Purpose: The objective of this study was to identify whether chronic stress promotes food addiction or not and explore the possible mechanisms. Method: We applied adaily 2 hrsflashing LED irradiation stress to mice fed chow or palatable food to mimic the effect of chronic stress on feeding. After 1 month of chronic stress exposure, we tested their binge eating behaviors, cravings for palatable food, responses for palatable food, and compulsive eating behaviors to evaluate the effect of chronic stress on food addiction-like behaviors. We detected changes in the levels of various genes and proteins in the nucleus accumbens (NAc), ventral tegmental area (VTA) and lateral hypothalamus using qPCR and immunofluorescence staining, respectively. Results: Behaviors results indicated chronic stress obviously increased food addiction score (FAS) in the palatable food feeding mice. Moreover, the FAS had astrong relationship with the extent of the increase in body weight. Chronic stress increased the expression of corticotropin-releasing factor receptor 1(CRFR1) was increased in the NAc shell and core but decreased in the VTA of the mice fed with palatable food. Chronic stress also increased expression of both dopamine receptor 2 (DR2) and mu-opioid receptor (MOR) in the NAc. Conclusion: Chronic stress aggravates the FAS and contributed to the development of stress-related obesity. Chronic stress drives the dysregulation of the CRF signaling pathway in the reward system and increases the expression of DR2 and MOR in the nucleus accumbens.

Animal models of PTSD: a challenge to be met

Recent years have seen increased interest in psychopathologies related to trauma exposure. Specifically, there has been a growing awareness to posttraumatic stress disorder (PTSD) in part due to terrorism, climate change-associated natural disasters, the global refugee crisis, and increased violence in overpopulated urban areas. However, notwithstanding the increased awareness to the disorder, the increasing number of patients, and the devastating impact on the lives of patients and their families, the efficacy of available treatments remains limited and highly unsatisfactory. A major scientific effort is therefore devoted to unravel the neural mechanisms underlying PTSD with the aim of paving the way to developing novel or improved treatment approaches and drugs to treat PTSD. One of the major scientific tools used to gain insight into understanding physiological and neuronal mechanisms underlying diseases and for treatment development is the use of animal models of human diseases. While much progress has been made using these models in understanding mechanisms of conditioned fear and fear memory, the gained knowledge has not yet led to better treatment options for PTSD patients. This poor translational outcome has already led some scientists and pharmaceutical companies, who do not in general hold opinions against animal models, to propose that those models should be abandoned. Here, we critically examine aspects of animal models of PTSD that may have contributed to the relative lack of translatability, including the focus on the exposure to trauma, overlooking individual and sex differences, and the contribution of risk factors. Based on findings from recent years, we propose research-based modifications that we believe are required in order to overcome some of the shortcomings of previous practice. These modifications include the usage of animal models of PTSD which incorporate risk factors and of the behavioral profiling analysis of individuals in a sample. These modifications are aimed to address factors such as individual predisposition and resilience, thus taking into consideration the fact that only a fraction of individuals exposed to trauma develop PTSD. We suggest that with an appropriate shift of practice, animal models are not only a valuable tool to enhance our understanding of fear and memory processes, but could serve as effective platforms for understanding PTSD, for PTSD drug development and drug testing.

Palatable Food Dampens the Long-Term Behavioral and Endocrine Effects of Juvenile Stressor Exposure but May Also Provoke Metabolic Syndrome in Rats

The juvenile period is marked by a reorganization and growth of important brain regions including structures associating with reward seeking behaviors such as the nucleus accumbens (NA) and prefrontal cortex (PFC). These changes are impacted by stressors during the juvenile period and may lead to a predisposition to stress induced psychopathology and abnormal development of brain reward systems. Like in humans, adult rodents engage certain coping mechanisms such as increases in the consumption of calorie-rich palatable foods to reduce stress, but this behavior can lead to obesity and metabolic disorders. In this study, we examined whether stressors during the juvenile period led to increased caloric intake when a palatable diet was accessible, and whether this diet attenuated adult stress responses. In addition, we examined if the stress buffering effects produced by the palatable diet were also accompanied by an offset propensity towards obesity, and by alterations in mRNA expression of dopamine (DA) receptors in the NA and PFC in adulthood. To this end, juvenile male Wistar rats underwent episodic stressor exposure (forced swim, elevated platform stress and restraint) on postnatal days (PD) 27-29 and received access to regular chow or daily limited access to a palatable diet until adulthood. At the age of 2 months, rats were tested on a social interaction test that screens for anxiety-like behaviors and their endocrine responses to an acute stressor. Animals were sacrificed, and their brains processed to detect differences in DA receptor subtype expression in the PFC and NA using qPCR. Results showed that rats that were stressed during the juvenile period displayed higher social anxiety and a sensitized corticosterone response as adults and these effects were attenuated by access to the palatable diet. Nevertheless, rats that experienced juvenile stress and consumed a palatable diet showed greater adiposity in adulthood. Interestingly, the same group displayed greater mRNA expression of DA receptors at the NA. This suggests that access to a palatable diet mitigates the behavioral and endocrine effects of juvenile stressor exposure in adulthood, but at the cost of metabolic imbalances and a sensitized dopaminergic system.

Notes on the Recent History of Neuroscience in Africa

Neuroscience began with neuroanatomy and neurosurgery in Egypt more than 5000 years ago. Knowledge grew over time and specialized neurosurgery centers were established in north Africa in the eleventh century. However, it was not until the twentieth century that neuroscience research became established in sub-Saharan Africa. In most African countries, clinical research focused on understanding the rationale and improving treatment of epilepsy, infections, nutritional neuropathies, stroke and tumors. Significant advances were made. In the twenty-first century, African knowledge expanded to include all branches of neuroscience, contributing to genetic, biochemical and inflammatory determinants of brain disorders. A major focus of basic neuroscience research has been, and is, investigation of plant extracts, drugs and stress in animal models, providing insight and identifying potential novel therapies. A significant event in the history of African neuroscience was the founding of the Society of Neuroscientists of Africa (SONA) in 1993. The International Brain Research Organization (IBRO) supported SONA conferences, as well as workshops and neuroscience training schools in Africa. Thanks to their investment, as well as that of funding agencies, such as the National Institutes of Health (NIH), International Society for Neurochemistry (ISN), World Federation of Neurosurgical Societies (WFNS), World Federation of Neurology (WFN) and the International League Against Epilepsy (ILAE), neuroscience research is well-established in Africa today. However, in order to continue to develop, African neuroscience needs continued international support and African neuroscientists need to engage in policy and decision-making to persuade governments to fund studies that address the unique regional needs in Africa.

Cognitive Dysfunction, Affective States, and Vulnerability to Nicotine Addiction: A Multifactorial Perspective

Although smoking prevalence has declined in recent years, certain subpopulations continue to smoke at disproportionately high rates and show resistance to cessation treatments. Individuals showing cognitive and affective impairments, including emotional distress and deficits in attention, memory, and inhibitory control, particularly in the context of psychiatric conditions, such as attention-deficit hyperactivity disorder, schizophrenia, and mood disorders, are at higher risk for tobacco addiction. Nicotine has been shown to improve cognitive and emotional processing in some conditions, including during tobacco abstinence. Self-medication of cognitive deficits or negative affect has been proposed to underlie high rates of tobacco smoking among people with psychiatric disorders. However, pre-existing cognitive and mood disorders may also influence the development and maintenance of nicotine dependence, by biasing nicotine-induced alterations in information processing and associative learning, decision-making, and inhibitory control. Here, we discuss the potential forms of contribution of cognitive and affective deficits to nicotine addiction-related processes, by reviewing major clinical and preclinical studies investigating either the procognitive and therapeutic action of nicotine or the putative primary role of cognitive and emotional impairments in addiction-like features.