Nicotinic effects on cognitive function: behavioral characterization, pharmacological specification, and anatomic localization

Role of medial prefrontal cortex voltage-dependent potassium 4.3 channels in nicotine-induced enhancement of object recognition memory in male mice

Nicotine has been shown to enhance object recognition memory in the novel object recognition (NOR) test by activating excitatory neurons in the medial prefrontal cortex (mPFC). However, the exact neuronal mechanisms underlying the nicotine-induced activation of mPFC neurons and the resultant memory enhancement remain poorly understood. To address this issue, we performed brain-slice electrophysiology and the NOR test in male C57BL/6J mice. Whole-cell patch-clamp recordings from layer V pyramidal neurons in the mPFC revealed that nicotine augments the summation of evoked excitatory postsynaptic potentials (eEPSPs) and that this effect was suppressed by N-[3,5-Bis(trifluoromethyl)phenyl]-N'-[2,4-dibromo-6-(2H-tetrazol-5-yl)phenyl]urea (NS5806), a voltage-dependent potassium (Kv) 4.3 channel activator. In line with these findings, intra-mPFC infusion of NS5806 suppressed systemically administered nicotine-induced memory enhancement in the NOR test. Additionally, miRNA-mediated knockdown of Kv4.3 channels in mPFC pyramidal neurons enhanced object recognition memory. Furthermore, inhibition of A-type Kv channels by intra-mPFC infusion of 4-aminopyridine was found to enhance object recognition memory, while this effect was abrogated by prior intra-mPFC NS5806 infusion. These results suggest that nicotine augments the summation of eEPSPs via the inhibition of Kv4.3 channels in mPFC layer V pyramidal neurons, resulting in the enhancement of object recognition memory.

Adrenalectomy exacerbates stress-induced impairment in fear discrimination: A causal role for kynurenic acid?

Impaired activity of the hypothalamic-pituitary axis and reduced blood levels of glucocorticoids (GCs) are signature features of stress-related maladies. Recent evidence suggests a possible role of the tryptophan metabolite kynurenic acid (KYNA) in this context. Here we investigated possible causal relationships in adult male rats, using stress-induced fear discrimination as a translationally relevant behavioral outcome measure. One week following adrenalectomy (ADX) or sham surgery, animals were for 2 h either physically restrained or exposed to a predator odor, which caused a much milder stress response. Extracellular KYNA levels were determined before, during and after stress by in vivo microdialysis in the prefrontal cortex. Separate cohorts underwent a fear discrimination procedure starting immediately after stress termination. Different auditory conditioned stimuli (CS) were either paired with a foot shock (CS+) or non-reinforced (CS-). One week later, fear was assessed by re-exposing the animals to each CS. Separate groups of rats were treated with the KYNA synthesis inhibitor BFF-816 prior to stress initiation to test a causal role of KYNA in fear discrimination. Restraint stress raised extracellular KYNA levels by ∼85 % in ADX rats for several hours, and these animals were unable to discriminate between CS+ and CS-. Both effects were prevented by BFF-816 and were not observed after exposure to predator odor or in sham-operated rats. These findings suggest that a causal connection exists between adrenal function, stress-induced KYNA increases, and behavioral deficits. Pharmacological inhibition of KYNA synthesis may therefore be an attractive, novel option for the treatment of stress-related disorders.

Western diet consumption impairs memory function via dysregulated hippocampus acetylcholine signaling

Western diet (WD) consumption during early life developmental periods is associated with impaired memory function, particularly for hippocampus (HPC)-dependent processes. We developed an early life WD rodent model associated with long-lasting HPC dysfunction to investigate the neurobiological mechanisms mediating these effects. Rats received either a cafeteria-style WD (ad libitum access to various high-fat/high-sugar foods; CAF) or standard healthy chow (CTL) during the juvenile and adolescent stages (postnatal days 26-56). Behavioral and metabolic assessments were performed both before and after a healthy diet intervention period beginning at early adulthood. Results revealed HPC-dependent contextual episodic memory impairments in CAF rats that persisted despite the healthy diet intervention. Given that dysregulated HPC acetylcholine (ACh) signaling is associated with memory impairments in humans and animal models, we examined protein markers of ACh tone in the dorsal HPC (HPCd) in CAF and CTL rats. Results revealed significantly lower protein levels of vesicular ACh transporter in the HPCd of CAF vs. CTL rats, indicating chronically reduced ACh tone. Using intensity-based ACh sensing fluorescent reporter (iAChSnFr) in vivo fiber photometry targeting the HPCd, we next revealed that ACh release during object-contextual novelty recognition was highly predictive of memory performance and was disrupted in CAF vs. CTL rats. Neuropharmacological results showed that alpha 7 nicotinic ACh receptor agonist infusion in the HPCd during training rescued memory deficits in CAF rats. Overall, these findings reveal a functional connection linking early life WD intake with long-lasting dysregulation of HPC ACh signaling, thereby identifying an underlying mechanism for WD-associated memory impairments.

Structural mechanisms of α7 nicotinic receptor allosteric modulation and activation

The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that plays an important role in cholinergic signaling throughout the nervous system. Its unique physiological characteristics and implications in neurological disorders and inflammation make it a promising but challenging therapeutic target. Positive allosteric modulators overcome limitations of traditional α7 agonists, but their potentiation mechanisms remain unclear. Here, we present high-resolution structures of α7-modulator complexes, revealing partially overlapping binding sites but varying conformational states. Structure-guided functional and computational tests suggest that differences in modulator activity arise from the stable rotation of a channel gating residue out of the pore. We extend the study using a time-resolved cryoelectron microscopy (cryo-EM) approach to reveal asymmetric state transitions for this homomeric channel and also find that a modulator with allosteric agonist activity exploits a distinct channel-gating mechanism. These results define mechanisms of α7 allosteric modulation and activation with implications across the pentameric receptor superfamily.

Critical roles of nicotinic acetylcholine receptors in olfactory memory formation and retrieval in crickets

Acetylcholine (ACh) is a major excitatory neurotransmitter in the insect central nervous system, and insect neurons express several types of ACh receptors (AChRs). AChRs are classified into two subgroups, muscarinic AChRs and nicotinic AChRs (nAChRs). nAChRs are also divided into two subgroups by sensitivity to α-bungarotoxin (α-BGT). The cricket Gryllus bimaculatus is one of the useful insects for studying the molecular mechanisms in olfactory learning and memory. However, the roles of nAChRs in olfactory learning and memory of the cricket are still unknown. In the present study, to investigate whether nAChRs are involved in cricket olfactory learning and memory, we tested the effects of two different AChR antagonists on long-term memory (LTM) formation and retrieval in a behavioral assay. The two AChR antagonists that we used are mecamylamine (MEC), an α-BGT-insensitive nAChR antagonist, and methyllycaconitine (MLA), an α-BGT-sensitive nAChR antagonist. In crickets, multiple-trial olfactory conditioning induced 1-day memory (LTM), whereas single-trial olfactory conditioning induced 1-h memory (mid-term memory, MTM) but not 1-day memory. Crickets injected with MEC 20 min before the retention test at 1 day after the multiple-trial conditioning exhibited no memory retrieval. This indicates that α-BGT-insensitive nAChRs participate in memory retrieval. In addition, crickets injected with MLA before the multiple-trial conditioning exhibited MTM but not LTM, indicating that α-BGT-sensitive nAChRs participate in the formation of LTM. Moreover, injection of nicotine (an nAChR agonist) before the single-trial conditioning induced LTM. Finally, the nitric oxide (NO)-cGMP signaling pathway is known to participate in the formation of LTM in crickets, and we conducted co-injection experiments with an agonist or inhibitor of the nAChR and an activator or inhibitor of the NO-cGMP signaling pathway. The results suggest that nAChR works upstream of the NO-cGMP signaling system in the LTM formation process.

Distinct resting-state functional connectivity patterns of Anterior Insula affected by smoking in mild cognitive impairment

Smoking is a modifiable risk factor for Alzheimer's disease (AD). The insula plays a vital role in both smoking and cognition. However, the smoking effects on insula-related networks in cognitively normal controls (CN) and mild cognitive impairment (MCI) patients remain unknown. We identified 129 CN (85 non-smokers and 44 smokers) and 83 MCI (54 non-smokers and 29 smokers). Each underwent neuropsychological assessment and MRI (structural and resting-state functional). Seed-based functional analyses in the anterior and posterior insula were performed to calculate the functional connectivity (FC) with voxels in the whole brain. Mixed-effect analyses were performed to explore the interactive effects on smoking and cognitive status. Associations between FC and neuropsychological scales were assessed. Mixed-effect analyses revealed the FC differences between the right anterior insula (RAI) with the left middle temporal gyrus (LMTG) and that with the right inferior parietal lobule (RIPL) (p < 0.01, cluster level < 0.05, two-tailed, gaussian random field correction). The FC of RAI in both LMTG and RIPL sees a significant decrease in MCI smokers (p < 0.01). Smoking affects insula FC differently between MCI and CN, and could decrease the insula FC in MCI patients. Our study provides evidence of neural mechanisms between smoking and AD.

Western diet consumption impairs memory function via dysregulated hippocampus acetylcholine signaling

Western diet (WD) consumption during development yields long-lasting memory impairments, yet the underlying neurobiological mechanisms remain elusive. Here we developed an early life WD rodent model to evaluate whether dysregulated hippocampus (HPC) acetylcholine (ACh) signaling, a pathology associated with memory impairment in human dementia, is causally-related to WD-induced cognitive impairment. Rats received a cafeteria-style WD (access to various high-fat/high-sugar foods; CAF) or healthy chow (CTL) during the juvenile and adolescent periods (postnatal days 26-56). Behavioral, metabolic, and microbiome assessments were performed both before and after a 30-day healthy diet intervention beginning at early adulthood. Results revealed CAF-induced HPC-dependent contextual episodic memory impairments that persisted despite healthy diet intervention, whereas CAF was not associated with long-term changes in body weight, body composition, glucose tolerance, anxiety-like behavior, or gut microbiome. HPC immunoblot analyses after the healthy diet intervention identified reduced levels of vesicular ACh transporter in CAF vs. CTL rats, indicative of chronically reduced HPC ACh tone. To determine whether these changes were functionally related to memory impairments, we evaluated temporal HPC ACh binding via ACh-sensing fluorescent reporter in vivo fiber photometry during memory testing, as well as whether the memory impairments could be rescued pharmacologically. Results revealed dynamic HPC ACh binding during object-contextual novelty recognition was highly predictive of memory performance and was disrupted in CAF vs. CTL rats. Further, HPC alpha-7 nicotinic receptor agonist infusion during consolidation rescued memory deficits in CAF rats. Overall, these findings identify dysregulated HPC ACh signaling as a mechanism underlying early life WD-associated memory impairments.

Sex differences in cognitive function among Chinese older adults using data from the Chinese longitudinal healthy longevity survey: a cross-sectional study

Objective

To compare the sex differences in cognitive function and its influencing factors among Chinese older adults.

Method

We conducted a cross-sectional study by using data from the China Longitudinal Healthy Longevity Survey (CLHLS). According to the 32 provinces and 4 municipalities directly under the Central Government of China, 3-5 counties or districts were randomly selected in each province or city (except Tibet), and then 1-3 villages or streets were randomly selected in each county or district, from which the target population was sampled. Mini Mental State Examination (MMSE) was used to assess the cognitive function of 9,262 older adults aged 65 and above in China. Descriptive analysis was applied to demonstrate the participants' demographic characteristics, health-related behaviors, social and non-social activity, disease status, mental and sleep condition. And then, univariate and multifactor analyses were performed to validate different risk factors for cognitive function, respectively in the general population, male older adults and female older adults.

Result

The older adults with cognitive impairment accounted for 10.4% of the total population. There are significant differences in cognitive function between male and female older adults. The odds of cognitive impairment in older adult women was 1.291 times that of older adult men (OR = 1.291, 95%CI: 1.084-1.538). Among the male older adults, those who were older, highly educated, spouseless, had depressive symptoms, and lacked social activities were more likely to have cognitive impairment, whereas among the female older adults, those who were older, highly educated, and lacked social activities were more likely to have cognitive impairment.

Conclusion

Overall, there are subtle differences in potential influencing factors for cognitive function between the male older adults and female older adults. Attention should be paid to the different cognitive protection measures for the older adults with different sexes.

Nicotine's effect on cognition, a friend or foe?

Tobacco smoking is a preventable cause of morbidity and mortality throughout the world. Smoking comes in form of absorption of many compounds, among which nicotine is the main psychoactive component of tobacco and its positive and negative reinforcement effects are proposed to be the key mechanism for the initiation and maintenance of smoking. Growing evidence suggests that the cognitive enhancement effects of nicotine may also contribute to the difficulty of quitting smoking, especially in individuals with psychiatric disorders. In this review, we first introduce the beneficial effect of nicotine on cognition including attention, short-term memory and long-term memory. We next summarize the beneficial effect of nicotine on cognition under pathological conditions, including Alzheimer's disease, Parkinson's disease, Schizophrenia, Stress-induced Anxiety, Depression, and drug-induced memory impairment. The possible mechanism underlying nicotine's effect is also explored. Finally, nicotine's detrimental effect on cognition is discussed, including in the prenatal and adolescent periods, and high-dose nicotine- and withdrawal-induced memory impairment is emphasized. Therefore, nicotine serves as both a friend and foe. Nicotine-derived compounds could be a promising strategy to alleviate neurological disease-associated cognitive deficit, however, due to nicotine's detrimental effect, continued educational programs and public awareness campaigns are needed to reduce tobacco use among pregnant women and smoking should be quitted even if it is e-cigarette, especially for the adolescents.

Nicotine pretreatment alleviates MK-801-induced behavioral and cognitive deficits in mice by regulating Pdlim5/CRTC1 in the PFC

Increasing evidence shows that smoking-obtained nicotine is indicated to improve cognition and mitigate certain symptoms of schizophrenia. In this study, we investigated whether chronic nicotine treatment alleviated MK-801-induced schizophrenia-like symptoms and cognitive impairment in mice. Mice were injected with MK-801 (0.2 mg/kg, i.p.), and the behavioral deficits were assessed using prepulse inhibition (PPI) and T-maze tests. We showed that MK-801 caused cognitive impairment accompanied by increased expression of PDZ and LIM domain 5 (Pdlim5), an adaptor protein that is critically associated with schizophrenia, in the prefrontal cortex (PFC). Pretreatment with nicotine (0.2 mg · kg-1 · d-1, s.c., for 2 weeks) significantly ameliorated MK-801-induced schizophrenia-like symptoms and cognitive impairment by reversing the increased Pdlim5 expression levels in the PFC. In addition, pretreatment with nicotine prevented the MK-801-induced decrease in CREB-regulated transcription coactivator 1 (CRTC1), a coactivator of CREB that plays an important role in cognition. Furthermore, MK-801 neither induced schizophrenia-like behaviors nor decreased CRTC1 levels in the PFC of Pdlim5-/- mice. Overexpression of Pdlim5 in the PFC through intra-PFC infusion of an adreno-associated virus AAV-Pdlim5 induced significant schizophrenia-like symptoms and cognitive impairment. In conclusion, chronic nicotine treatment alleviates schizophrenia-induced memory deficits in mice by regulating Pdlim5 and CRTC1 expression in the PFC.

Brain Structure and Function Show Distinct Relations With Genetic Predispositions to Mental Health and Cognition

BACKGROUND

Mental health and cognitive achievement are partly heritable, highly polygenic, and associated with brain variations in structure and function. However, the underlying neural mechanisms remain unclear.

METHODS

We investigated the association between genetic predispositions to various mental health and cognitive traits and a large set of structural and functional brain measures from the UK Biobank (N = 36,799). We also applied linkage disequilibrium score regression to estimate the genetic correlations between various traits and brain measures based on genome-wide data. To decompose the complex association patterns, we performed a multivariate partial least squares model of the genetic and imaging modalities.

RESULTS

The univariate analyses showed that certain traits were related to brain structure (significant genetic correlations with total cortical surface area from r_g = -0.101 for smoking initiation to r_g = 0.230 for cognitive ability), while other traits were related to brain function (significant genetic correlations with functional connectivity from r_g = -0.161 for educational attainment to r_g = 0.318 for schizophrenia). The multivariate analysis showed that genetic predispositions to attention-deficit/hyperactivity disorder, smoking initiation, and cognitive traits had stronger associations with brain structure than with brain function, whereas genetic predispositions to most other psychiatric disorders had stronger associations with brain function than with brain structure.

CONCLUSIONS

These results reveal that genetic predispositions to mental health and cognitive traits have distinct brain profiles.

The Effect of High Nicotine Dose on Maximum Anaerobic Performance and Perceived Pain in Healthy Non-Smoking Athletes: Crossover Pilot Study

Background: In recent years, there has been intensive discussion about the positive effect of nicotine usage on enhancing sports performance. It is frequently applied through a non-burned tobacco form before physical activity. Nicotine is under the World Anti-Doping Agency (WADA) 2021 monitoring program. Therefore, study results that reveal either positive or negative effects are expected. This is the pilot study that reports the effect of 8 mg dose of nicotine on performance and perceived pain. Material and Methods: This research aimed to explore the oral intake effect of a high-nicotine dose (8 mg) on the maximum anaerobic performance and other selected physical performance parameters in healthy, well-trained adult athletes (n = 15, age 30.7 ± 3.6, BMI 25.3 ± 1.7). The cross-sectional study protocol included the oral administration of either sublingual nicotine or placebo tablets before the anaerobic load assessed by a standardized 30 s Wingate test of the lower limbs. Afterward, the Borg subjective perception of pain (CR 10) and Borg rating of perceived exertion (RPE) were evaluated. Wilcoxon signed-rank test was used for the analysis of data with a 0.05 level of significance. Results: The results revealed that oral administration of an 8 mg nicotine dose does not significantly improve any of the physical performance parameters monitored. We only reported the statistically significant positive effect in RPE (p = 0.03). Conclusion: Lower perception of pain intensity that we reported after nicotine application might be an important factor that affects performance. However, we did not report any improvement in physical performance parameters.

An application of the stress-diathesis model: A review about the association between smoking tobacco, smoking cessation, and mental health

Background

Worldwide, approximately 24% of all adults smoke, but smoking is up to twice as prevalent in people with mental ill-health. There is growing evidence that smoking may be a causal risk factor in the development of mental illness, and that smoking cessation leads to improved mental health.

Methods

In this scholarly review we have: (1) used a modern adaptation of the Bradford-Hill criteria to bolster the argument that smoking could cause mental ill-health and that smoking cessation could reverse these effects, and (2) by considering psychological, biological, and environmental factors, we have structured the evidence to-date into a stress-diathesis model.

Results

Our model suggests that smoking is a psychobiological stressor, but that the magnitude of this effect is mediated and modulated by the individual's diathesis to develop mental ill-health and other vulnerability and protective factors. We explore biological mechanisms that underpin the model, such as tobacco induced damage to neurological systems and oxidative stress pathways. Furthermore, we discuss evidence indicating that it is likely that these systems repair after smoking cessation, leading to better mental health.

Conclusion

Based on a large body of literature including experimental, observational, and novel causal inference studies, there is consistent evidence showing that smoking can negatively affect the brain and mental health, and that smoking cessation could reverse the mental ill-health caused by smoking. Our model suggests that smoking prevention and treatment strategies have a role in preventing and treating mental illness as well as physical illness.

Cholinergic regulation of object recognition memory

Object recognition memory refers to a basic memory mechanism to identify and recall various features of objects. This memory has been investigated by numerous studies in human, primates and rodents to elucidate the neuropsychological underpinnings in mammalian memory, as well as provide the diagnosis of dementia in some neurological diseases, such as Alzheimer's disease and Parkinson's disease. Since Alzheimer's disease at the early stage is reported to be accompanied with cholinergic cell loss and impairment in recognition memory, the central cholinergic system has been studied to investigate the neural mechanism underlying recognition memory. Previous studies have suggested an important role of cholinergic neurons in the acquisition of some variants of object recognition memory in rodents. Cholinergic neurons in the medial septum and ventral diagonal band of Broca that project mainly to the hippocampus and parahippocampal area are related to recognition memory for object location. Cholinergic projections from the nucleus basalis magnocellularis innervating the entire cortex are associated with recognition memory for object identification. Especially, the brain regions that receive cholinergic projections, such as the perirhinal cortex and prefrontal cortex, are involved in recognition memory for object-in-place memory and object recency. In addition, experimental studies using rodent models for Alzheimer's disease have reported that neurodegeneration within the central cholinergic system causes a deficit in object recognition memory. Elucidating how various types of object recognition memory are regulated by distinct cholinergic cell groups is necessary to clarify the neuronal mechanism for recognition memory and the development of therapeutic treatments for dementia.

Impact of the use of illicit and licit substances and anxiety disorders on the academic performance of medical students: a pilot study

BACKGROUND

Medical students have a considerable prevalence of anxiety and substance use disorders. Our aim was to assess the presence of anxiety disorders and the use of alcohol and licit and illicit substances, and their influence on the academic performance of medical students.

METHODS

This is a cross-sectional, non-experimental pilot study, with quantitative analyses, in which 67 medical students at the Federal University of Rondonópolis, Mato Grosso, Brazil (UFR), were evaluated through the application of non-invasive anxiety assessment instruments, screening for involvement with tobacco, alcohol and other substances, related to school performance coefficient, between June 2019 and March 2020.

RESULTS

Worse academic performance was associated with frequent use of tobacco and its derivatives (p = 0.0022), marijuana (p = 0.0020), hypnotics and sedatives (p = 0.0138). Also, the performance was negatively correlated with the use of tobacco (p = 0.0004), alcoholic beverages (p = 0.0261), cannabis (p = 0.0075), sedatives (p = 0.0116) and trait anxiety (p = 0.0036). Greater trait anxiety intensity was associated with previous use of tobacco (p = 0.0276), marijuana (p = 0.0466), amphetamines/ecstasy (p = 0.0151), and hypnotics/sedatives (p = 0.0103). State anxiety was positively correlated with heavy alcohol use (p = 0.0434). Higher state anxiety intensity was related to needing intervention due to the use of amphetamines/ecstasy (p = 0.00379). Students from the intermediate classes of the course (3rd and 4th years) had a higher frequency and intensity of use of tobacco and its derivatives (p = 0.0133), amphetamines or ecstasy (p = 0.0006), and inhalants (p = 0.0256).

CONCLUSIONS

Worse academic performance in medical students was correlated with licit and illicit substances use and anxiety disorders. Mid-course students had a higher frequency and intensity of substance use.

Time-dependent effects of nicotine on reversal of dizocilpine-induced attentional impairment in female rats

Nicotine and nicotinic compounds have been found to attenuate the attentional impairments caused by the glutamate NMDA antagonist dizocilpine (MK-801). The timing of the nicotine effect on attention in rodents has not yet been determined. In the current study, we tested the interaction of dizocilpine with nicotine. Nicotine was given at a range of times (30 to 240 min) prior to dizocilpine administration and before testing on an operant signal detection task. Each rat was assessed with each dose timing. This protocol was repeated twice with one week between phases of testing. In the first phase, correct rejection performance was significantly impaired by 0.05 mg/kg of dizocilpine and this impairment was significantly attenuated by nicotine given sc 30-150 min prior to dizocilpine administration. The greater dizocilpine-induced percent correct rejection impairment seen during the first phase of drug challenge, was significantly attenuated by nicotine given 30 or 90 min before the start of the 1-h test session. During the second phase, the dizocilpine-induced repeated acquisition impairment was more modest. During this phase of testing nicotine administered 60, 90 or 150 min before testing significantly attenuated the dizocilpine-induced impairment. In both phases of testing, nicotine administration 240 min prior to testing was not seen to attenuate the dizocilpine-induced impairment. During the first phase but not the second phase, dizocilpine administration caused a significant impairment in percent hit. Nicotine was not found to have a significant effect in the second phase. Response omissions were significantly increased by dizocilpine during the first, but not the second phase. Nicotine was not found to have any significant effects on response omission. Overall, our data show that nicotine administration prior to dizocilpine administration was able to significantly improve dizocilpine-induced attentional impairment in a time-dependent manner.

Affect and subjective cognitive functioning by depression symptom levels during naturalistic cigarette smoking in premenopausal females who smoke daily

Objective: High negative affect, low positive affect, and low cognitive functioning are depression-related states that may be particularly relevant to females who smoke cigarettes and may be more prominent following overnight tobacco abstinence. This study aimed to assess relations between depression symptom levels and negative affect, positive affect, and subjective cognitive functioning in premenopausal females who smoke. Methods: Premenopausal females who smoke daily with low (n = 66) or elevated (n = 33) baseline depression symptoms completed subjective ratings of negative affect, positive affect, and cognitive functioning pre-first cigarette (i.e., after overnight tobacco abstinence) and at random prompts throughout the day via ecological momentary assessment (EMA) for 35 days. Results: Participants with elevated depression symptoms reported overall higher negative affect (p = .01). Positive affect was significantly lower prior to the first cigarette of the day (p < .001), but did not significantly differ between depression symptom groups. Subjective cognitive functioning was significantly lower pre-first cigarette of the day (p < .001). There was a significant Depression Symptom × Prompt Type interaction for subjective cognitive functioning (p = .01). Subjective cognitive functioning did not significantly differ by depression symptom group pre-first cigarette of the day but was significantly different at random prompts throughout the day. Conclusions: As participants smoked as usual, findings identify naturalistic factors which may influence smoking behavior among premenopausal females who smoke with elevated depression symptoms. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Age-Dependent and Pathway-Specific Bimodal Action of Nicotine on Synaptic Plasticity in the Hippocampus of Mice Lacking the miR-132/212 Genes

Nicotine addiction develops predominantly during human adolescence through smoking. Self-administration experiments in rodents verify this biological preponderance to adolescence, suggesting evolutionary-conserved and age-defined mechanisms which influence the susceptibility to nicotine addiction. The hippocampus, a brain region linked to drug-related memory storage, undergoes major morpho-functional restructuring during adolescence and is strongly affected by nicotine stimulation. However, the signaling mechanisms shaping the effects of nicotine in young vs. adult brains remain unclear. MicroRNAs (miRNAs) emerged recently as modulators of brain neuroplasticity, learning and memory, and addiction. Nevertheless, the age-dependent interplay between miRNAs regulation and hippocampal nicotinergic signaling remains poorly explored. We here combined biophysical and pharmacological methods to examine the impact of miRNA-132/212 gene-deletion (miRNA-132/212-/-) and nicotine stimulation on synaptic functions in adolescent and mature adult mice at two hippocampal synaptic circuits: the medial perforant pathway (MPP) to dentate yrus (DG) synapses (MPP-DG) and CA3 Schaffer collaterals to CA1 synapses (CA3-CA1). Basal synaptic transmission and short-term (paired-pulse-induced) synaptic plasticity was unaltered in adolescent and adult miRNA-132/212-/- mice hippocampi, compared with wild-type controls. However, nicotine stimulation promoted CA3-CA1 synaptic potentiation in mature adult (not adolescent) wild-type and suppressed MPP-DG synaptic potentiation in miRNA-132/212-/- mice. Altered levels of CREB, Phospho-CREB, and acetylcholinesterase (AChE) expression were further detected in adult miRNA-132/212-/- mice hippocampi. These observations propose miRNAs as age-sensitive bimodal regulators of hippocampal nicotinergic signaling and, given the relevance of the hippocampus for drug-related memory storage, encourage further research on the influence of miRNAs 132 and 212 in nicotine addiction in the young and the adult brain.

The Effects of Erythrina subumbrans (Hassk.) Merr. Leaves Extract on Nicotine Withdrawal Syndrome and β2 nAChRs Expression in The Ventral Tegmental Area of Rats

Erythrina subumbrans (Hassk.) Merr. is an alkaloid plant with dihydro-β-erythroidine (DhβE) content which is considered to block α4β2 nAChRs subtype and, therefore, may suppress the desire to use nicotine. This study aimed to investigate these possible effects of E.subumbrans (Hassk.) Merr. extract on nicotine withdrawal syndrome and β2 nAChRs expression in rats' ventral tegmental area (VTA). The rats were divided into six groups, i.e., control (OO), nicotine treated (NO), nicotine, and E. subumbrans (Hassk.) Merr.-treated (NE 100, NE 200, NE 400), and E. subumbrans (Hassk.) Merr.-treated (OE 200) groups. Nicotine was given ad libitum via drinking water with a step-wise increase of dosage every four days for 30 days. Somatic and affective signs were observed during the dark cycle of 24 hours abstinent period (days 31and 46). The expression of β2 nAChRs in the VTA was examined semi-quantitatively. It has been found that the rearing behavior of the NE 100 group was fewer on day 46 than on day 31. The body scratching behavior of the NE 100 group was fewer than that of the OO group on day 46. The front paws and penile licking behaviors of the NE 100 group were fewer than those of the NO group on day 46. The open arm entries of the NO group were fewer than that of the NE 200 group on day 46. The β2nAChRs expression of the NO group was lower than that of the OO group. E. Subumbrans (Hassk.) Merr. at a dosage of 100mg/kg BW may decrease some somatic signs of nicotine withdrawal syndrome.

Varenicline as a treatment for cannabis use disorder: A placebo-controlled pilot trial

BACKGROUND

An efficacious pharmacotherapy for cannabis use disorder (CUD) has yet to be established. This study preliminarily evaluated the safety and efficacy of varenicline for CUD in a proof-of-concept clinical trial.

METHODS

Participants in this 6-week randomized, placebo-controlled pilot trial received either varenicline (n = 35) or placebo (n = 37), added to a brief motivational enhancement therapy intervention. Outcomes included cannabis withdrawal, cannabis abstinence, urine cannabinoid levels, percent cannabis use days, and cannabis sessions per day.

RESULTS

Both treatment groups noted significant decreases in self-reported cannabis withdrawal, percentage of days used, and use sessions per day during treatment compared to baseline. While this pilot trial was not powered to detect statistically significant between-group differences, participants randomized to varenicline evidenced numerically greater rates of self-reported abstinence at the final study visit [Week 6 intent-to-treat (ITT): Varenicline: 17.1% vs. Placebo: 5.4%; RR = 3.2 (95% CI: 0.7,14.7)]. End-of-treatment urine creatinine corrected cannabinoid levels were numerically lower in the varenicline group and higher in the placebo group compared to baseline [Change from baseline: Varenicline -1.7 ng/mg (95% CI: -4.1,0.8) vs. Placebo: 1.9 ng/mg (95% CI: -0.4,4.3); Δ = 3.5 (95% CI: 0.1,6.9)]. Adverse events related to study treatment did not reveal new safety signals.

CONCLUSIONS

Findings support the feasibility of conducting clinical trials of varenicline as a candidate pharmacotherapy for CUD, and indicate that a full-scale efficacy trial, powered based on effect sizes and variability yielded in this study, is warranted.

Acute effects of the imidacloprid metabolite desnitro-imidacloprid on human nACh receptors relevant for neuronal signaling

Several neonicotinoids have recently been shown to activate the nicotinic acetylcholine receptor (nAChR) on human neurons. Moreover, imidacloprid (IMI) and other members of this pesticide family form a set of diverse metabolites within crops. Among these, desnitro-imidacloprid (DN-IMI) is of special toxicological interest, as there is evidence (i) for human dietary exposure to this metabolite, (ii) and that DN-IMI is a strong trigger of mammalian nicotinic responses. We set out here to quantify responses of human nAChRs to DN-IMI and an alternative metabolite, IMI-olefin. To evaluate toxicological hazards, these data were then compared to those of IMI and nicotine. Ca²⁺-imaging experiments on human neurons showed that DN-IMI exhibits an agonistic effect on nAChRs at sub-micromolar concentrations (equipotent with nicotine) while IMI-olefin activated the receptors less potently (in a similar range as IMI). Direct experimental data on the interaction with defined receptor subtypes were obtained by heterologous expression of various human nAChR subtypes in Xenopus laevis oocytes and measurement of the transmembrane currents evoked by exposure to putative ligands. DN-IMI acted on the physiologically important human nAChR subtypes α7, α3β4, and α4β2 (high-sensitivity variant) with similar potency as nicotine. IMI and IMI-olefin were confirmed as nAChR agonists, although with 2–3 orders of magnitude lower potency. Molecular docking studies, using receptor models for the α7 and α4β2 nAChR subtypes supported an activity of DN-IMI similar to that of nicotine. In summary, these data suggest that DN-IMI functionally affects human neurons similar to the well-established neurotoxicant nicotine by triggering α7 and several non-α7 nAChRs.

Differential signalling induced by α7 nicotinic acetylcholine receptors in hippocampal dentate gyrus in vitro and in vivo

The activation of α7 nicotinic acetylcholine receptors (nAChRs) has been shown to improve hippocampus-dependent learning and memory. α7 nAChRs are densely expressed among several different cell types in the hippocampus, with high Ca²⁺  permeability, although it is unclear if α7 nAChRs mobilize differential signalling mechanisms among distinct neuronal populations. To address this question, we compared α7 nAChR agonist-induced responses (i.e. calcium and cAMP changes) between granule cells and GABAergic neurons in the hippocampal dentate gyrus both in vitro and in vivo. In cultured organotypic hippocampal slices, we observed robust intracellular calcium and cAMP increases in dentate granule cells upon activation of α7 nAChRs. In contrast, GABAergic interneurons displayed little change in either calcium or cAMP concentration after α7 nAChR activation, even though they displayed much larger α7 nAChR current responses than those of dentate granule cells. We found that this was due to smaller α7 nAChR-induced Ca²⁺ rises in GABAergic interneurons. Thus, the regulation of the Ca²⁺ transients in different cell types resulted in differential subsequent intracellular signalling cascades and likely the ultimate outcome of α7 nAChR activation. Furthermore, we monitored neuronal activities of dentate granule cells and GABAergic interneurons in vivo via optic fibre photometry. We observed enhancement of neuronal activities after nicotine administration in dentate granule cells, but not in GABAergic neurons, which was absent in α7 nAChR-deficient granule cells. In summary, we reveal a mechanism for α7 nAChR-mediated increase of neuronal activity via cell type-specific intracellular signalling pathways. KEY POINTS: α7 nicotinic acetylcholine receptors (nAChRs) are widely distributed throughout the central nervous system and regulate a variety of brain functions including learning and memory. Understanding the cellular signalling mechanisms of their activations among different neuronal populations is important for delineating their actions in cognitive function, and developing effective treatment strategies for cognitive deficits. We report that α7 nAChR activation leads to Ca²⁺ and cAMP increases in granule cells (but not in GABAergic interneurons) in hippocampal dentate gyrus in vitro, a key region for pattern separation during learning. We also found that nicotine enhanced granule cell (but not in GABAergic interneurons) activity in an α7 nAChR-dependent manner via in vivo fibre photometry recording. Based on our findings, we propose that differential responses to α7 nAChR activation between granule cells and GABAergic interneurons is responsible for the increase of excitation by α7 nAChR agonists in hippocampal circuits synergistically.

Task-dependent effects of nicotine treatment on auditory performance in young-adult and elderly human nonsmokers

Electrophysiological studies show that nicotine enhances neural responses to characteristic frequency stimuli. Previous behavioral studies partially corroborate these findings in young adults, showing that nicotine selectively enhances auditory processing in difficult listening conditions. The present work extended previous work to include both young and older adults and assessed the nicotine effect on sound frequency and intensity discrimination. Hypotheses were that nicotine improves auditory performance and that the degree of improvement is inversely proportional to baseline performance. Young (19-23 years old) normal-hearing nonsmokers and elderly (61-80) nonsmokers with normal hearing between 500 and 2000 Hz received nicotine gum (6 mg) or placebo gum in a single-blind, randomized crossover design. Participants performed three experiments (frequency discrimination, frequency modulation identification, and intensity discrimination) before and after treatment. The perceptual differences were analyzed between pre- and post-treatment, as well as between post-treatment nicotine and placebo conditions as a function of pre-treatment baseline performance. Compared to pre-treatment performance, nicotine significantly improved frequency discrimination. Compared to placebo, nicotine significantly improved performance for intensity discrimination, and the improvement was more pronounced in the elderly with lower baseline performance. Nicotine had no effect on frequency modulation identification. Nicotine effects are task-dependent, reflecting possible interplays of subjects, tasks and neural mechanisms.

Translational Research in Nicotine Addiction

While commendable strides have been made in reducing smoking initiation and improving smoking cessation rates, current available smoking cessation treatment options are still only mildly efficacious and show substantial interindividual variability in their therapeutic responses. Therefore, the primary goal of preclinical research has been to further the understanding of the neural substrates and genetic influences involved in nicotine's effects and reassess potential drug targets. Pronounced advances have been made by investing in new translational approaches and placing more emphasis on bridging the gap between human and rodent models of dependence. Functional neuroimaging studies have identified key brain structures involved with nicotine-dependence phenotypes such as craving, impulsivity, withdrawal symptoms, and smoking cessation outcomes. Following up with these findings, rodent-modeling techniques have made it possible to dissect the neural circuits involved in these motivated behaviors and ascertain mechanisms underlying nicotine's interactive effects on brain structure and function. Likewise, translational studies investigating single-nucleotide polymorphisms (SNPs) within the cholinergic, dopaminergic, and opioid systems have found high levels of involvement of these neurotransmitter systems in regulating the reinforcing aspects of nicotine in both humans and mouse models. These findings and coordinated efforts between human and rodent studies pave the way for future work determining gene by drug interactions and tailoring treatment options to each individual smoker.

Hippocampal asymmetry and regional dispersal of nAChRs alpha4 and alpha7 subtypes in the adult rat

To better comprehend the relationship between left/right (L/R) differences and hippocampus functions is necessary knowledge of lateral asymmetry and regional distribution. This research was design to examine hippocampal L/R asymmetry and regional distribution profile of the alpha7 and alpha4 subtypes of nicotinic acetylcholine receptors (nAChRs) in the adult rat. 10-12-week-old twenty-four male wistar rats were randomly selected. After removing the brains, immunohistochemistry, real-time PCR, and western blot methods were applied to distinguish the presence of the receptors in the hippocampus. Outcomes stated that the mentioned receptors expression profile was spatial-dependent. As, the hippocampal dispersal of alpha7 and alpha4 subtypes in the left hippocampus (LH) was remarkably maximum compare with the right hippocampus (RH) (p = 0.001, p = 0.005 respectively). Furthermore, the alpha7 optical density (OD) was not significantly different in the diverse regions in hippocampus of adult rat (p = 0.057), while the maximum OD of the alpha4 was detected in the hippocampal dentate gyrus and CA3 regions of LH (p = 0.007, p = 0.009 respectively) and the minimum OD was in the CA1 of the RH (p = 0.019). In real time PCR evaluation, there is a significantly higher expression of alpha7 and alpha4 in LH compared to RH (p = 0.043, p = 0.049 respectively), also, for western blot (p = 0.042, p = 0.030 respectively). According to present data, the alpha7 and alpha4 nAChR subtypes expression profile demonstrated lateral asymmetry, the uniform regional dispersal for alpha7 and different regional dispersal for alpha4 in the adult rat hippocampus.

Differential effects of alkaloids on memory in rodents

Nicotinic acetylcholine receptors (nAChRs) play a critical role in the neuropharmacology of learning and memory. As such, naturally occurring alkaloids that regulate nAChR activity have gained interest for understanding and potentially improving memory function. In this study, we tested the acute effects of three known nicotinic alkaloids, nicotine, cotinine, and anatabine, in suppressing scopolamine-induced memory deficit in rodents by using two classic memory paradigms, Y-maze and novel object recognition (NOR) in mice and rats, respectively. We found that all compounds were able to suppress scopolamine-induced spatial memory deficit in the Y-maze spontaneous alternation paradigm. However, only nicotine was able to suppress the short-term object memory deficit in NOR, despite the higher doses of cotinine and anatabine used to account for their potential differences in nAChR activity. These results indicate that cotinine and anatabine can uniquely regulate short-term spatial memory, while nicotine seems to have more robust and general role in memory regulation in rodents. Thus, nAChR-activating alkaloids may possess distinct procognitive properties in rodents, depending on the memory types examined.

APOE genotype influences P3b amplitude and response to smoking abstinence in young adults

RATIONALE

There is strong evidence that nicotine can enhance cognitive functions and growing evidence that this effect may be larger in young healthy APOE ε4 carriers. However, the moderating effects of the APOE ε4 allele on cognitive impairments caused by nicotine deprivation in chronic smokers have not yet been studied with brain indices.

OBJECTIVE

We sought to determine whether young female carriers of the APOE ε4 allele, relative to noncarriers, would exhibit larger abstinence-induced decreases in P3b amplitude during a two-stimulus auditory oddball task.

METHODS

We compared parietal P3bs in female chronic smokers with either APOE ε3/ε3 (n = 54) or ε3/ε4 (n = 20) genotype under nicotine-sated conditions and after 12-17-h nicotine deprivation.

RESULTS

Nicotine deprivation significantly reduced P3b amplitudes in APOE ε4 carriers, but not in APOE-ε3/ε3 individuals, such that the difference seen prior to nicotine deprivation was eliminated.

CONCLUSIONS

The results suggest that subjects with the APOE ε4 allele are more sensitive to nicotine, which could influence smoking patterns, the risk for nicotine dependence, and the cognitive effects of nicotine use in these individuals.

Functional alterations by a subgroup of neonicotinoid pesticides in human dopaminergic neurons

Neonicotinoid pesticides, originally developed to target the insect nervous system, have been reported to interact with human receptors and to activate rodent neurons. Therefore, we evaluated in how far these compounds may trigger signaling in human neurons, and thus, affect the human adult or developing nervous system. We used SH-SY5Y neuroblastoma cells as established model of nicotinic acetylcholine receptor (nAChR) signaling. In parallel, we profiled dopaminergic neurons, generated from LUHMES neuronal precursor cells, as novel system to study nAChR activation in human post-mitotic neurons. Changes of the free intracellular Ca²⁺ concentration ([Ca²⁺]_i) were used as readout, and key findings were confirmed by patch clamp recordings. Nicotine triggered typical neuronal signaling responses that were blocked by antagonists, such as tubocurarine and mecamylamine. Pharmacological approaches suggested a functional expression of α7 and non-α7 nAChRs on LUHMES cells. In this novel test system, the neonicotinoids acetamiprid, imidacloprid, clothianidin and thiacloprid, but not thiamethoxam and dinotefuran, triggered [Ca²⁺]_i signaling at 10-100 µM. Strong synergy of the active neonicotinoids (at low micromolar concentrations) with the α7 nAChR-positive allosteric modulator PNU-120596 was observed in LUHMES and SH-SY5Y cells, and specific antagonists fully inhibited such signaling. To provide a third line of evidence for neonicotinoid signaling via nAChR, we studied cross-desensitization: pretreatment of LUHMES and SH-SY5Y cells with active neonicotinoids (at 1-10 µM) blunted the signaling response of nicotine. The pesticides (at 3-30 µM) also blunted the response to the non-α7 agonist ABT 594 in LUHMES cells. These data show that human neuronal cells are functionally affected by low micromolar concentrations of several neonicotinoids. An effect of such signals on nervous system development is a toxicological concern.

The cognitive and behavioral effects of D-amphetamine and nicotine sensitization in adult zebrafish

BACKGROUND

Zebrafish are growing in use as a model for understanding drug dependence and addiction. Sensitization paradigms have been a useful tool in identifying mechanisms involved in drug-induced behavioral and neurological changes, but in zebrafish have tended to focus on locomotor, rather than cognitive, endpoints.

METHODS

Here, we used a novel method, the FMP Y-maze, which measures continuous performance through a series of repeated binary choices (L vs R), to establish a model for assessing parameters associated with psychostimulant-induced behavioral and cognitive sensitization in adult zebrafish.

RESULTS

Repeat, intermittent exposure to d-amphetamine (AMPH) for 14 days increased alternations (LRLR) in the maze, suggesting improved working memory, which was enhanced further following drug challenge after a short withdrawal period, suggesting behavioral sensitization. However, this cognitive enhancement coincided with a reduction in the use of other exploration strategies, hypolocomotion, and inhibition of cognitive flexibility. Like AMPH, exposure to nicotine (NIC) increased alternations following drug challenge after chronic treatment. Repeat NIC exposure appeared to induce both cognitive and psychomotor sensitization, as evidenced by increased working memory performance (alternations) and locomotor activity, without negatively impacting other search strategies or cognitive flexibility.

CONCLUSION

Chronic treatment with AMPH or NIC boosts cognitive performance in adult zebrafish. Cognitive sensitization occurred with both drugs, resulting in enhanced working memory; however, repeat AMPH exposure, following a withdrawal period, resulted in inhibited cognitive flexibility, an effect not evident with repeat NIC exposure. Cognitive and behavioral sensitization paradigms in zebrafish could serve as a useful tool for assessing cognitive states which result in cognitive enhancing or impairing effects of drugs.

Associations Between Smoking Abstinence, Inhibitory Control, and Smoking Behavior: An fMRI Study

Nicotine addiction is associated with dysregulated inhibitory control (IC), mediated by corticothalamic circuitry including the right inferior frontal gyrus (rIFG). Among sated smokers, worse IC task performance and greater IC-related rIFG activity have been shown to be associated with greater relapse vulnerability. The present study investigated the effects of smoking abstinence on associations between IC task performance, rIFG activation, and smoking behavior. Smokers (N = 26, 15 female) completed an IC task (Go/Go/No-go) during fMRI scanning followed by a laboratory-based smoking relapse analog task (SRT) on two visits: once when sated and once following 24 h of smoking abstinence. During the SRT, smokers were provided with monetary rewards for incrementally delaying smoking. A significant main effect of No-go accuracy on latency to smoke during the SRT was observed when collapsing across smoking states (abstinent vs. sated). Similarly, a significant main effect of IC-related activation in rIFG on SRT performance was observed across states. The main effect of state, however, was non-significant in both of these models. Furthermore, the interaction between smoking state and No-go accuracy on SRT performance was non-significant, indicating a similar relationship between IC and lapse vulnerability under both sated and abstinent conditions. The state X rIFG activation interaction on SRT performance was likewise non-significant. Post-hoc whole brain analyses indicated that abstinence resulted in greater IC-related activity in the right middle frontal gyrus (MFG) and insula. Activation during IC in these regions was significantly associated with decreased No-go accuracy. Moreover, greater abstinence induced activity in right MFG during IC was associated with smoking sooner on the SRT. These findings are bolstered by the extant literature on the effects of nicotine on executive function and also contribute novel insights on how individual differences in behavioral and neuroimaging measures of IC may influence relapse propensity independent of smoking state.

The role of acetylcholine in negative encoding bias: Too much of a good thing?

Optimal acetylcholine (ACh) signaling is important for sustained attention and facilitates learning and memory. At the same time, human and animal studies have demonstrated increased levels of ACh in the brain during depressive episodes and increased symptoms of anxiety, depression, and reactivity to stress when ACh breakdown is impaired. While it is possible that the neuromodulatory roles of ACh in cognitive and affective processes are distinct, one possibility is that homeostatic levels of ACh signaling are necessary for appropriate learning, but overly high levels of cholinergic signaling promote encoding of stressful events, leading to the negative encoding bias that is a core symptom of depression. In this review, we outline this hypothesis and suggest potential neural pathways and underlying mechanisms that may support a role for ACh signaling in negative encoding bias.

Effects of Smoking on Regional Homogeneity in Mild Cognitive Impairment: A Resting-State Functional MRI Study

Background

Smoking is a modifiable risk factor for Alzheimer’s disease (AD). However, smoking-related effects on intrinsic brain activity in high-risk AD population are still unclear.

Objective

We aimed to explore differences in smoking effects on brain function between healthy elderly and amnestic mild cognitive impairment (aMCI) patients using ReHo mapping.

Methods

We identified 64 healthy elderly controls and 116 aMCI patients, including 98 non-smoking and 18 smoking aMCI. Each subject underwent structural and resting-state functional MRI scanning and neuropsychological evaluations. Regional homogeneity (ReHo) mapping was used to assess regional brain synchronization. After correction for age, gender, education, and gray matter volume, we explored the difference of ReHo among groups in a voxel-wise way based on analysis of covariance (ANCOVA), followed by post hoc two-sample analyses (p < 0.05, corrected). Further, we correlated the mean ReHo with neuropsychological scales.

Results

Three groups were well-matched in age, gender, and education. Significant ReHo differences were found among three groups, located in the left supramarginal gyrus (SMG) and left angular gyrus (AG). Specifically, non-smoking aMCI had lower ReHo in SMG and AG than smoking aMCI and controls. By contrast, smoking aMCI had greater AG ReHo than healthy controls (p < 0.05). Across groups, correlation analyses showed that left AG ReHo correlated with MMSE (r = 0.18, p = 0.015), clock drawing test (r = 0.20, p = 0.007), immediate recall (r = 0.36, p < 0.001), delayed recall (r = 0.34, p < 0.001), and auditory verbal learning test (r = 0.20, p = 0.007).

Conclusion

Smoking might pose compensatory or protective effects on intrinsic brain activity in aMCI patients.

Endogenous Cholinergic Signaling Modulates Sound-Evoked Responses of the Medial Nucleus of the Trapezoid Body

The medial nucleus of trapezoid body (MNTB) is a major source of inhibition in auditory brainstem circuitry. The MNTB projects well-timed inhibitory output to principal sound-localization nuclei in the superior olive (SOC) as well as other computationally important centers. Acoustic information is conveyed to MNTB neurons through a single calyx of Held excitatory synapse arising from the cochlear nucleus. The encoding efficacy of this large synapse depends on its activity rate, which is primarily determined by sound intensity and stimulus frequency. However, MNTB activity rate is additionally influenced by inhibition and possibly neuromodulatory inputs, albeit their functional role is unclear. Happe and Morley (2004) discovered prominent expression of α7 nAChRs in rat SOC, suggesting possible engagement of ACh-mediated modulation of neural activity in the MNTB. However, the existence and nature of this putative modulation have never been physiologically demonstrated. We probed nicotinic cholinergic influences on acoustic responses of MNTB neurons from adult gerbils (Meriones unguiculatus) of either sex. We recorded tone-evoked MNTB single-neuron activity in vivo using extracellular single-unit recording. Piggyback multibarrel electrodes enabled pharmacological manipulation of nAChRs by reversibly applying antagonists to two receptor types, α7 and α4β2. We observed that tone-evoked responses are dependent on ACh modulation by both nAChR subtypes. Spontaneous activity was not affected by antagonist application. Functionally, we demonstrate that ACh contributes to sustaining high discharge rates and enhances signal encoding efficacy. Additionally, we report anatomic evidence revealing novel cholinergic projections to MNTB arising from pontine and superior olivary nuclei.SIGNIFICANCE STATEMENT This study is the first to physiologically probe how acetylcholine, a pervasive neuromodulator in the brain, influences the encoding of acoustic information by the medial nucleus of trapezoid body, the most prominent source of inhibition in brainstem sound-localization circuitry. We demonstrate that this cholinergic input enhances neural discrimination of tones from noise stimuli, which may contribute to processing important acoustic signals, such as speech. Additionally, we describe novel anatomic projections providing cholinergic input to the MNTB. Together, these findings shed new light on the contribution of neuromodulation to fundamental computational processes in auditory brainstem circuitry and to a more holistic understanding of modulatory influences in sensory processing.

Effect of 4-Fluoro-N-(4-sulfamoylbenzyl) Benzene Sulfonamide on cognitive deficits and hippocampal plasticity during nicotine withdrawal in rats

Withdrawal from chronic nicotine has damaging effects on a variety of learning and memory tasks. Various Sulfonamides that act as carbonic anhydrase inhibitors have documented role in modulation of various cognitive, learning, and memory processing. We investigated the effects of 4-Fluoro-N-(4-sulfamoylbenzyl) Benzene Sulfonamide (4-FBS) on nicotine withdrawal impairments in rats using Morris water maze (MWM), Novel object recognition, Passive avoidance, and open field tasks. Also, Brain-derived neurotrophic factor (BDNF) profiling and in vivo field potential recording were assessed. Rats were exposed to saline or chronic nicotine 3.8 mg/kg subcutaneously for 14 days in four divided doses, spontaneous nicotine withdrawal was induced by quitting nicotine for 72 h (hrs). Animals received 4-FBS at 20, 40, and 60 mg/kg after 72 h of withdrawal in various behavioral and electrophysiological paradigms. Nicotine withdrawal causes a deficit in learning and long-term memory in the MWM task. No significant difference was found in novel object recognition tasks among all groups while in passive avoidance task nicotine withdrawal resulted in a deficit of hippocampus-dependent fear learning. Anxiety like behavior was observed during nicotine withdrawal. Plasma BDNF level was reduced during nicotine withdrawal as compared to the saline group reflecting mild cognitive impairment, stress, and depression. Withdrawal from chronic nicotine altered hippocampal plasticity, caused suppression of long-term potentiation (LTP) in the CA1 area of the hippocampus. Our results showed that 4-FBS at 40 and 60 mg/kg significantly prevented nicotine withdrawal-induced cognitive deficits in behavioral as well as electrophysiological studies. 4-FBS at 60 mg/kg upsurge nicotine withdrawal-induced decrease in plasma BDNF. We conclude that 4-FBS at 40 and 60 mg /kg effectively prevented chronic nicotine withdrawal-induced impairment in long term potentiation and cognitive performance.

Exposure to elevated embryonic kynurenine in rats: Sex-dependent learning and memory impairments in adult offspring

Distinct abnormalities in kynurenine pathway (KP) metabolism have been reported in various psychiatric disorders, including schizophrenia (SZ). Kynurenic acid (KYNA), a neuroactive metabolite of the KP, is elevated in individuals diagnosed with SZ and has been linked to cognitive impairments seen in the disorder. To further understand the role of KYNA in SZ etiology, we developed a prenatal insult model where kynurenine (100 mg/day) is fed to pregnant Wistar rats from embryonic day (ED) 15 to ED 22. As sex differences in the prevalence and severity of SZ have been observed, we presently investigated the impact of prenatal kynurenine exposure on KP metabolism and spatial learning and memory in male and female offspring. Specifically, brain tissue and plasma from offspring (control: ECon; kynurenine-treated: EKyn) in prepuberty (postnatal day (PD) 21), adolescence (PD 32-35), and adulthood (PD 56-85) were collected. Separate cohorts of adult offspring were tested in the Barnes maze to assess hippocampus- and prefrontal cortex-mediated learning and memory. Plasma tryptophan, kynurenine, and KYNA were unchanged between ECon and EKyn offspring across all three ages. Hippocampal and frontal cortex KYNA were elevated in male EKyn offspring only in adulthood, compared to ECon, while brain KYNA levels were unchanged in adult females. Male EKyn offspring were significantly impaired during acquisition of the Barnes maze and during reversal learning in the task. In female EKyn offspring, learning and memory remained relatively intact. Taken together, our data demonstrate that exposure to elevated kynurenine during the last week of gestation results in intriguing sex differences and further support the EKyn model as an attractive tool to study the pathophysiology of schizophrenia.

Stress-induced impairment in fear discrimination is causally related to increased kynurenic acid formation in the prefrontal cortex

RATIONALE

Stress is related to cognitive impairments which are observed in most major brain diseases. Prior studies showed that the brain concentration of the tryptophan metabolite kynurenic acid (KYNA) is modulated by stress, and that changes in cerebral KYNA levels impact cognition. However, the link between these phenomena has not been tested directly so far.

OBJECTIVES

To investigate a possible causal relationship between acute stress, KYNA, and fear discrimination.

METHODS

Adult rats were exposed to one of three acute stressors-predator odor, restraint, or inescapable foot shocks (ISS)-and KYNA in the prefrontal cortex was measured using microdialysis. Corticosterone was analyzed in a subset of rats. Another cohort underwent a fear discrimination procedure immediately after experiencing stress. Different auditory conditioned stimuli (CSs) were either paired with foot shock (CS+) or were non-reinforced (CS-). One week later, fear was assessed by re-exposing rats to each CS. Finally, to test whether stress-induced changes in KYNA causally impacted fear discrimination, a group of rats that received ISS were pre-treated with the selective KYNA synthesis inhibitor PF-04859989.

RESULTS

ISS caused the greatest increase in circulating corticosterone levels and raised extracellular KYNA levels by ~ 85%. The two other stressors affected KYNA much less (< 25% increase). Moreover, only rats that received ISS were unable to discriminate between CS+ and CS-. PF-04859989 abolished the stress-induced KYNA increase and also prevented the impairment in fear discrimination in animals that experienced ISS.

CONCLUSIONS

These findings demonstrate a causal connection between stress-induced KYNA increases and cognitive deficits. Pharmacological manipulation of KYNA synthesis therefore offers a novel approach to modulate cognitive processes in stress-related disorders.

Association of retinal layer measurements and adult cognitive function: A population-based study

OBJECTIVE

To quantify the associations of peripapillary retinal nerve fiber layer (pRNFL) thickness and macular ganglion cell layer (mGCL) volume with cognitive functioning and to investigate how demographic and vascular health factors affect these associations in a population-based sample of adults.

METHODS

The sample included the first 3,000 participants (age range 30-95 years) of the Rhineland Study (recruited from March 2016 to December 2018) who underwent spectral-domain optical coherence tomography and cognitive assessment at 1 of 2 identical study centers in Bonn, Germany. We used multiple linear regression models to examine the relationships between retinal layer measurements and cognitive functioning after adjustment for confounders, and we examined the moderating effects of demographic and vascular health factors.

RESULTS

The analytical sample included 2,483 participants who were 54.3 years old (SD 13.8 years) on average. After full adjustment, each 1-SD decrease in mGCL volume was associated with a greater decrease in global function than that of pRNFL thickness (β = -0.048 [95% confidence interval (CI) -0.077 to -0.018] vs β = -0.021 [95% CI -0.049 to 0.007]). These relationships increased in strength with advancing age, were stronger in participants with hypertension, and were reversed in current smokers relative to nonsmokers.

CONCLUSIONS

mGCL volume is more strongly related to adult cognitive functioning than pRNFL thickness, making it a better potential biomarker of neurodegeneration. Age and vascular health factors play important roles in determining the strength and direction of this association.

Nicotinic Receptor Subunit Distribution in Auditory Cortex: Impact of Aging on Receptor Number and Function

The presence of novel or degraded communication sounds likely results in activation of basal forebrain cholinergic neurons increasing release of ACh onto presynaptic and postsynaptic nAChRs in primary auditory cortex (A1). nAChR subtypes include high-affinity heteromeric nAChRs commonly composed of α4 and β2 subunits and low-affinity homomeric nAChRs composed of α7 subunits. In young male FBN rats, we detail the following: (1) the distribution/expression of nAChR subunit transcripts in excitatory (VGluT1) and inhibitory (VGAT) neurons across A1 layers; (2) heteromeric nAChR binding across A1 layers; and (3) nAChR excitability in A1 layer (L) 5 cells. In aged rats, we detailed the impact of aging on A1 nAChR subunit expression across layers, heteromeric nAChR receptor binding, and nAChR excitability of A1 L5 cells. A majority of A1 cells coexpressed transcripts for β2 and α4 with or without α7, while dispersed subpopulations expressed β2 and α7 or α7 alone. nAChR subunit transcripts were expressed in young excitatory and inhibitory neurons across L2-L6. Transcript abundance varied across layers, and was highest for β2 and α4. Significant age-related decreases in nAChR subunit transcript expression (message) and receptor binding (protein) were observed in L2-6, most pronounced in infragranular layers. In vitro patch-clamp recordings from L5B pyramidal output neurons showed age-related nAChR subunit-selective reductions in postsynaptic responses to ACh. Age-related losses of nAChR subunits likely impact ways in which A1 neurons respond to ACh release. While the elderly require additional resources to disambiguate degraded speech codes, resources mediated by nAChRs may be compromised with aging.SIGNIFICANCE STATEMENT When attention is required, cholinergic basal forebrain neurons may trigger increased release of ACh onto auditory neurons in primary auditory cortex (A1). Laminar and phenotypic differences in neuronal nAChR expression determine ways in which A1 neurons respond to release of ACh in challenging acoustic environments. This study detailed the distribution and expression of nAChR subunit transcript and protein across A1 layers in young and aged rats. Results showed a differential distribution of nAChR subunits across A1 layers. Age-related decreases in transcript/protein expression were reflected in age-related subunit specific functional loss of nAChR signaling to ACh application in A1 layer 5. Together, these findings could reflect the age-related decline in selective attention observed in the elderly.

Cognitive performance effects of nicotine and industry affiliation: a systematic review

BACKGROUND AND AIMS

Studies assessing the cognitive performance effects of nicotine show inconsistent results and tobacco industry funding has been correlated with study outcomes. We conducted a systematic review of the primary literature assessing the cognitive performance effects of nicotine and assessed potential associations between tobacco and pharmaceutical industry affiliation and reported study conclusions.

METHODS

We searched PubMed, EMBASE, PsycINFO, BIOSIS, and Web of Science for peer-reviewed journal articles published between 2009 and 2016 that: (1) were randomized controlled trials; (2) investigated the effects of nicotine on cognitive performance in a laboratory setting; (3) administered nicotine to healthy adults (18-60 years); and (4) included participants were nonsmokers or minimally deprived smokers (⩽2 hours of abstaining from smoking). Study disclosures and tobacco industry documents were reviewed to determine industry funding.

RESULTS

Searches yielded 3,771 abstracts; 32 studies were included in the review. The majority of studies investigated the effects of nicotine on attention (n = 22). Nicotine had a non-uniform effect on attention: studies reported positive (41%; n = 9), mixed (41%; n = 9), and no effect (18%; n = 4). The majority of study authors had received prior tobacco industry funding (59%; n = 19), however over half of tobacco-industry funded authors did not report this (53%; n = 10).

CONCLUSIONS

Nicotine does not appear to be associated with consistent cognitive performance effects. Although no association was found between reported outcomes and tobacco or pharmaceutical industry funding, findings likely underestimate the influence of industry funding due to strict inclusion criteria and incomplete data on pharmaceutical industry funding.

CLINICAL TRIAL REGISTRATION

Not applicable.

Effects of basal forebrain stimulation on the vibrotactile responses of neurons from the hindpaw representation in the rat SI cortex

Basal forebrain (BF) cholinergic system is important for attention and modulates sensory processing. We focused on the hindpaw representation in rat primary somatosensory cortex (S1), which receives inputs related to mechanoreceptors identical to those in human glabrous skin. Spike data were recorded from S1 tactile neurons (n = 87) with (ON condition: 0.5-ms bipolar current pulses at 100 Hz; amplitude 50 μA, duration 0.5 s at each trial) and without (OFF condition) electrical stimulation of BF in anesthetized rats. We expected that prior activation of BF would induce changes in the vibrotactile responses of neurons during sinusoidal (5, 40, and 250 Hz) mechanical stimulation of the glabrous skin. The experiment consisted of sequential OFF-ON conditions in two-time blocks separated by 30 min to test possible remaining effects. Average firing rates (AFRs) and vector strengths of spike phases (VS) were analyzed for different neuron types [regular spiking (RS) and fast spiking (FS)] in different cortical layers (III-VI). Immediate effect of BF activation was only significant by increasing synchronization to 5-Hz vibrotactile stimulus within the second block. Regardless of frequency, ON-OFF paired VS differences were significantly higher in the second block compared to the first, more prominent for RS neurons, and in general for neurons in layers III and VI. No such effects could be found on AFRs. The results suggest that cholinergic activation induces some changes in the hindpaw area, enabling relatively higher increases in synchronization to vibrotactile inputs with subsequent BF modulation. In addition, this modulation depends on neuron type and layer, which may be related to detailed projection pattern from BF.

Persistent cognitive and affective alterations at late withdrawal stages after long-term intermittent exposure to tobacco smoke or electronic cigarette vapour: Behavioural changes and their neurochemical correlates

Smoking cessation induces a withdrawal syndrome associated with anxiety, depression, and impaired neurocognitive functions, but much less is known about the withdrawal of e-cigarettes (e-CIG). We investigated in Balb/c mice the behavioural and neurochemical effects of withdrawal for up to 90 days after seven weeks' intermittent exposure to e-CIG vapour or cigarette smoke (CIG). The withdrawal of e-CIG and CIG induced early behavioural alterations such as spatial memory deficits (spatial object recognition task), increased anxiety (elevated plus maze test) and compulsive-like behaviour (marble burying test) that persisted for 60-90 days. Notably, attention-related (virtual object recognition task) and depression-like behaviours (tail suspension and sucrose preference tests) appeared only 15-30 days after withdrawal and persisted for as long as up to 90 days. At hippocampal level, the withdrawal-induced changes in the levels of AMPA receptor GluA1 and GluA2/3 subunits, PSD 95 protein, corticotropin-releasing factor (Crf) and Crf receptor 1 (CrfR1) mRNA were biphasic: AMPA receptor subunit and PSD95 protein levels initially remained unchanged and decreased after 60-90 days, whereas Crf/CrfR1 mRNA levels initially increased and then markedly decreased after 60 days. These late reductions correlated with the behavioural impairments, particularly the appearance of depression-like behaviours. Our findings show that major behavioural and neurochemical alterations persist or even first appear late after the withdrawal of chronic CIG smoke or e-CIG vapour exposure, and underline importance of conducting similar studies of humans, including e-CIG vapers.

Nicotinic acetylcholine receptors: Conventional and unconventional ligands and signaling

Postsynaptic nAChRs in the peripheral nervous system are critical for neuromuscular and autonomic neurotransmission. Pre- and peri-synaptic nAChRs in the brain modulate neurotransmission and are responsible for the addictive effects of nicotine. Subtypes of nAChRs in lymphocytes and non-synaptic locations may modulate inflammation and other cellular functions. All AChRs that function as ligand-gated ion channels are formed from five homologous subunits organized to form a central cation channel whose opening is regulated by ACh bound at extracellular subunit interfaces. nAChR subtype subunit composition can range from α7 homomers to α4β2α6β2β3 heteromers. Subtypes differ in affinities for ACh and other agonists like nicotine and in efficiencies with which their channels are opened and desensitized. Subtypes also differ in affinities for antagonists and for positive and negative allosteric modulators. Some agonists are "silent" with respect to channel opening, and AChRs may be able to signal metabotropic pathways by releasing G-proteins independent of channel opening. Electrophysiological studies that can resolve single-channel openings and molecular genetic approaches have allowed characterization of the structures of ligand binding sites, the cation channel, and the linkages between them, as well as the organization of AChR subunits and their contributions to function. Crystallography and cryo-electron-microscopy are providing increasing insights into the structures and functions of AChRs. However, much remains to be learned about both AChR structure and function, the in vivo functional roles of some AChR subtypes, and the development of better pharmacological tools directed at AChRs to treat addiction, pain, inflammation, and other medically important issues. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Water-soluble variant of human Lynx1 positively modulates synaptic plasticity and ameliorates cognitive impairment associated with α7-nAChR dysfunction

Lynx1 is a GPI-tethered protein colocalized with nicotinic acetylcholine receptors (nAChRs) in the brain areas important for learning and memory. Previously, we demonstrated that at low micromolar concentrations the water-soluble Lynx1 variant lacking GPI-anchor (ws-Lynx1) acts on α7-nAChRs as a positive allosteric modulator. We hypothesized that ws-Lynx1 could be used for improvement of cognitive processes dependent on nAChRs. Here we showed that 2 µM ws-Lynx1 increased the acetylcholine-evoked current at α7-nAChRs in the rat primary visual cortex L1 interneurons. At higher concentrations ws-Lynx1 inhibits α7-nAChRs expressed in Xenopus laevis oocytes with IC₅₀  ~ 50 µM. In mice, ws-Lynx1 penetrated the blood-brain barrier upon intranasal administration and accumulated in the cortex, hippocampus, and cerebellum. Chronic ws-Lynx1 treatment prevented the olfactory memory and motor learning impairment induced by the α7-nAChRs inhibitor methyllycaconitine (MLA). Enhanced long-term potentiation and increased paired-pulse facilitation ratio were observed in the hippocampal slices incubated with ws-Lynx1 and in the slices from ws-Lynx1-treated mice. Long-term potentiation blockade observed in MLA-treated mice was abolished by ws-Lynx1 co-administration. To understand the mechanism of ws-Lynx1 action, we studied the interaction of ws-Lynx1 and MLA at α7-nAChRs, measured the basal concentrations of endogenous Lynx1 and the α7 nAChR subunit and their association in the mouse brain. Our findings suggest that endogenous Lynx1 limits α7-nAChRs activation in the adult brain. Ws-Lynx1 partially displaces Lynx1 causing positive modulation of α7-nAChRs and enhancement of synaptic plasticity. Ws-Lynx1 and similar compounds may constitute useful hits for treatment of cognitive deficits associated with the cholinergic system dysfunction.

Predictors of Working Memory Maintenance and Decline in Older Adults

The aging process is associated with the gradual decline of several cognitive functions, and working memory is particularly affected. Although the majority of older adults experience a deterioration of their working memory, some individuals maintain their working memory in older age, and some suffer an extreme deterioration of their working memory. The purpose of the present study was to identify, among a total of 120 potential predictors, those that significantly contributed to these two extreme outcomes in working memory. A sample of 588 healthy adults was examined with the n-back task in the spatial and verbal domains using a 2-back level of difficulty. Individuals were classified as working memory maintainers or decliners if their discrimination level in the two domains was superior to the 80th percentile or inferior to the 20th percentile, respectively. Logistic regression identified eight and six significant predictors of working memory maintenance and decline, respectively. High vocabulary scores and smoking more were significant predictors of working memory maintenance; however, in the opposite direction, these same variables predicted working memory decline. Several consumption habits that influenced cerebrovascular function were found in both models. Psychological traits and everyday activities were present in both models. We identified specific predictors that contribute to extremely high or low working memory performance in older age.

Increased subjective and reinforcing effects of initial nicotine exposure in young adults with attention deficit hyperactivity disorder (ADHD) compared to matched peers: results from an experimental model of first-time tobacco use

Individuals with attention deficit hyperactivity disorder (ADHD) are at increased risk for adverse cigarette smoking outcomes, and little is known about factors underlying this risk. This study sought to evaluate the effects of initial nicotine exposure in young adults with and without ADHD using a novel paradigm of exposure to model initial smoking experiences. Participants were young adult nonsmokers (n = 61 ADHD, n = 75 Control) between the ages of 18-25 years (inclusive) who reported never having smoked a full cigarette, and no tobacco use in the prior 3 years. Participants were exposed to three different blinded doses of intranasally administered nicotine (0, 0.5, 1.0 mg) across three separate fixed dose experimental sessions. In subsequent sessions, participants were given the opportunity to self-administer nicotine under two different conditions-high and low cognitive demand. Physiological, subjective, and reinforcing effects of nicotine were the main outcomes. Nicotine plasma levels, and no group differences in effects of nicotine on heart rate or blood pressure, confirmed comparable dosing exposure across groups. ADHD participants reported significantly greater dizziness following nicotine, and greater pleasant subjective effects across all conditions, compared to non-ADHD non-smokers. There were no group differences on subjective reports of bad or unpleasant effects. Subsequent nicotine self-administration was significantly higher among non-smokers with ADHD, and their choices of nicotine were not influenced by cognitive condition. There are meaningful differences between young adults with and without ADHD with respect to the initial subjective and reinforcing effects of nicotine; and interventions to prevent use should start prior to typical age of experimentation among ADHD patients.

Activation of Alpha-7 Nicotinic Acetylcholine Receptors (α7nAchR) Promotes the Protective Autophagy in LPS-Induced Acute Lung Injury (ALI) In Vitro and In Vivo

The release of inflammatory cytokines and chemokines and autophagy has been reported to be involved in the pathogenic mechanism of acute lung injury (ALI). Reportedly, alpha-7 nicotinic acetylcholine receptors (α7nAchR) might play a protective role in LPS-induced ALI. In the current research, we established LPS-induced ALI model in mice and α7nAchR agonist PNU-282987 improved LPS-induced injury. In MH-S cells, LPS stimulation inhibited, whereas α7nAchR agonist PNU-282987 enhanced the autophagy. α7nAchR agonist PNU-282987 protected MH-S cells from LPS-induced inflammation by reducing the concentrations of IL-6, TNF-α, and IL-1β. Finally, LPS stimulation dramatically inhibited MH-S cell viability but enhanced cell apoptosis, whereas PNU-282987 treatment exerted opposite effects; α7nAchR might regulate the cellular homeostasis via affecting the crosstalk between the autophagy and apoptosis in MH-S cells; in other words, α7nAChR agonist enhances MH-S cell autophagy and inhibits MH-S cell apoptosis. In conclusion, α7nAchR promote the protective autophagy in LPS-induced ALI model in mice and MH-S cells. The application of α7nAchR agonist is considered a potent target for LPS-induced ALI, which needs further clinical investigation.