Possible neuroprotective property of nicotinic acetylcholine receptors in association with predominant upregulation of glial cell line-derived neurotrophic factor in astrocytes

Expression and function of nicotinic acetylcholine receptors in specific neuronal populations: Focus on striatal and prefrontal circuits

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in the central nervous system and play an important role in the control of neural functions including neuronal activity, transmitter release and synaptic plasticity. Although the common subtypes of nAChRs are abundantly expressed throughout the brain, their expression in different brain regions and by individual neuronal types is not homogeneous or incidental. In recent years, several studies have emerged showing that particular subtypes of nAChRs are expressed by specific neuronal populations in which they have major influence on the activity of local circuits and behavior. It has been demonstrated that even nAChRs expressed by relatively rare neuronal types can induce significant changes in behavior and contribute to pathological processes. Depending on the identity and connectivity of the particular nAChRs-expressing neuronal populations, the activation of nAChRs can have distinct or even opposing effects on local neuronal signaling. In this review, we will summarize the available literature describing the expression of individual nicotinic subunits by different neuronal types in two crucial brain regions, the striatum and the prefrontal cortex. The review will also briefly discuss nicotinic expression in non-neuronal, glial cells, as they cannot be ignored as potential targets of nAChRs-modulating drugs. The final section will discuss options that could allow us to target nAChRs in a neuronal-type-specific manner, not only in the experimental field, but also eventually in clinical practice.

A blood-based, metabolite and demographic characteristic markers panel for the diagnosis of Alzheimer's disease

Aims: This work was designed to provide early diagnosis strategies for Alzheimer's disease (AD) based on the identification of blood metabolic biomarkers. Patients & methods: A total of 90 subjects aged 60 years or older were included in this study; 45 patients were assigned to the case group and control group, respectively. A total of 31 target metabolites were quantitatively analyzed by parallel reaction monitoring between the two groups. Results & conclusion: Three metabolites were screened out, including cystine, serine and alanine/sarcosine. Logistic regression and random forest analysis were used to establish AD diagnosis models, and the model combining metabolic biomarkers and demographic variables had higher detection efficiency (area under the curve = 0.869). A combination diagnostic model to provide a scientific reference for early screening and diagnosis of AD was constructed.

Cholinergic and Neuroimmune Signaling Interact to Impact Adult Hippocampal Neurogenesis and Alcohol Pathology Across Development

Alcohol (ethanol) use and misuse is a costly societal issue that can affect an individual across the lifespan. Alcohol use and misuse typically initiates during adolescence and generally continues into adulthood. Not only is alcohol the most widely abused drug by adolescents, but it is also one of the most widely abused drugs in the world. In fact, high rates of maternal drinking make developmental ethanol exposure the most preventable cause of neurological deficits in the Western world. Preclinical studies have determined that one of the most consistent effects of ethanol is its disruption of hippocampal neurogenesis. However, the severity, persistence, and reversibility of ethanol’s effects on hippocampal neurogenesis are dependent on developmental stage of exposure and age at assessment. Complicating the neurodevelopmental effects of ethanol is the concurrent development and maturation of neuromodulatory systems which regulate neurogenesis, particularly the cholinergic system. Cholinergic signaling in the hippocampus directly regulates hippocampal neurogenesis through muscarinic and nicotinic receptor actions and indirectly regulates neurogenesis by providing anti-inflammatory regulatory control over the hippocampal environmental milieu. Therefore, this review aims to evaluate how shifting maturational patterns of the cholinergic system and its regulation of neuroimmune signaling impact ethanol’s effects on adult neurogenesis. For example, perinatal ethanol exposure decreases basal forebrain cholinergic neuron populations, resulting in long-term developmental disruptions to the hippocampus that persist into adulthood. Exaggerated neuroimmune responses and disruptions in adult hippocampal neurogenesis are evident after environmental, developmental, and pharmacological challenges, suggesting that perinatal ethanol exposure induces neurogenic deficits in adulthood that can be unmasked under conditions that strain neural and immune function. Similarly, adolescent ethanol exposure persistently decreases basal forebrain cholinergic neuron populations, increases hippocampal neuroimmune gene expression, and decreases hippocampal neurogenesis in adulthood. The effects of neither perinatal nor adolescent ethanol are mitigated by abstinence whereas adult ethanol exposure-induced reductions in hippocampal neurogenesis are restored following abstinence, suggesting that ethanol-induced alterations in neurogenesis and reversibility are dependent upon the developmental period. Thus, the focus of this review is an examination of how ethanol exposure across critical developmental periods disrupts maturation of cholinergic and neuroinflammatory systems to differentially affect hippocampal neurogenesis in adulthood.

Ameliorating Effect of Combined Cinnamon and Ginger Oils against the Neurotoxicity of Nicotine Administration on the Prefrontal Cortex of Adult Albino Rats: Immunohistochemical and Ultrastructural Study

Background: Nicotine is the active alkaloid in cigarettes. It was reported that tobacco smoking has many hazards; one of these hazards is the effect on the cognitive function of the prefrontal cortex. The aim of our study is to investigate the antioxidant effects of ginger, cinnamon oils, and their combination on morphological changes in the prefrontal cortex that were induced by nicotine. Materials and methods: Fifty adult male albino rats were divided into five groups: group I (control group), group II (nicotine), group III (nicotine + cinnamon), group IV (nicotine + ginger), and group V (nicotine + cinnamon + ginger). The coronal sections from the anterior part of the rat brain at the site of prefrontal cortex were examined by light microscope for (H&E and immunohistochemical staining with TNF-α and GFAP), while the ultrastructure morphology was examined by transmission electron microscopy. Levels of the oxidative stress markers (MDA, GSH) in the rats’ brain tissue homogenate were biochemically assessed. Results: Compared to the control group, the rats that were treated with nicotine (group II) showed a significant oxidative stress in the form of marked elevation of MDA and decrease in GSH, apoptotic changes especially in the pyramidal cells in the form of neuronal cell degeneration and pyknosis, and an elevation in the inflammatory marker TNF-α and GFAP expressions. These changes were observed to a lesser degree in rat group (III) and group (IV), while there was a marked improvement achieved by the combined usage of cinnamon and ginger oils, together compared to the nicotine group. Conclusions: Ginger and cinnamon are powerful antioxidants which ameliorate the degenerative and oxidative effects produced by nicotine on a rat’s prefrontal cortex.

Systematic Review of Nicotine Exposure's Effects on Neural Stem and Progenitor Cells

While various modalities of chronic nicotine use have been associated with numerous negative consequences to human health, one possible benefit of nicotine exposure has been uncovered. The discovery of an inverse correlation between smoking and Parkinson's disease, and later Alzheimer's disease as well, motivated investigation of nicotine as a neuroprotective agent. Some studies have demonstrated that nicotine elicits improvements in cognitive function. The hippocampus, along with the subventricular zone (SVZ), is a distinct brain region that allow for ongoing postnatal neurogenesis throughout adulthood and plays a major role in certain cognitive behaviors like learning and memory. Therefore, one hypothesis underlying nicotine-induced neuroprotection is possible effects on neural stem cells and neural precursor cells. On the other hand, nicotine withdrawal frequently leads to cognitive impairments, particularly in hippocampal-dependent behaviors, possibly suggesting an impairment of hippocampal neurogenesis with nicotine exposure. This review discusses the current body of evidence on nicotine's effects on neural stem cells and neural progenitors. Changes in neural stem cell proliferation, survival, intracellular dynamics, and differentiation following acute and chronic nicotine exposure are examined.

Independent and Combined Effects of Nicotine or Chronic Tobacco Smoking and HIV on the Brain: A Review of Preclinical and Clinical Studies

Tobacco smoking is highly prevalent among HIV-infected individuals. Chronic smokers with HIV showed greater cognitive deficits and impulsivity, and had more psychopathological symptoms and greater neuroinflammation than HIV non-smokers or smokers without HIV infection. However, preclinical studies that evaluated the combined effects of HIV-infection and tobacco smoking are scare. The preclinical models typically used cell cultures or animal models that involved specific HIV viral proteins or the administration of nicotine to rodents. These preclinical models consistently demonstrated that nicotine had neuroprotective and anti-inflammatory effects, leading to cognitive enhancement. Although the major addictive ingredient in tobacco smoking is nicotine, chronic smoking does not lead to improved cognitive function in humans. Therefore, preclinical studies designed to unravel the interactive effects of chronic tobacco smoking and HIV infection are needed. In this review, we summarized the preclinical studies that demonstrated the neuroprotective effects of nicotine, the neurotoxic effects of the HIV viral proteins, and the scant literature on nicotine or tobacco smoke in HIV transgenic rat models. We also reviewed the clinical studies that evaluated the neurotoxic effects of tobacco smoking, HIV infection and their combined effects on the brain, including studies that evaluated the cognitive and behavioral assessments, as well as neuroimaging measures. Lastly, we compared the different approaches between preclinical and clinical studies, identified some gaps and proposed some future directions. Graphical abstract Independent and combined effects of HIV and tobacco/nicotine. Left top and bottom panels: Both clinical studies of HIV infected persons and preclinical studies using viral proteins in vitro or in vivo in animal models showed that HIV infection could lead to neurotoxicity and neuroinflammation. Right top and bottom panels: While clinical studies of tobacco smoking consistently showed deleterious effects of smoking, clinical and preclinical studies that used nicotine show mild cognitive enhancement, neuroprotective and possibly anti-inflammatory effects. In the developing brain, however, nicotine is neurotoxic. Middle overlapping panels: Clinical studies of persons with HIV who were smokers typically showed additive deleterious effects of HIV and tobacco smoking. However, in the preclinical studies, when nicotine was administered to the HIV-1 Tg rats, the neurotoxic effects of HIV were attenuated, but tobacco smoke worsened the inflammatory cascade.

Neuromodulation of Glial Function During Neurodegeneration

Glia, a non-excitable cell type once considered merely as the connective tissue between neurons, is nowadays acknowledged for its essential contribution to multiple physiological processes including learning, memory formation, excitability, synaptic plasticity, ion homeostasis, and energy metabolism. Moreover, as glia are key players in the brain immune system and provide structural and nutritional support for neurons, they are intimately involved in multiple neurological disorders. Recent advances have demonstrated that glial cells, specifically microglia and astroglia, are involved in several neurodegenerative diseases including Amyotrophic lateral sclerosis (ALS), Epilepsy, Parkinson's disease (PD), Alzheimer's disease (AD), and frontotemporal dementia (FTD). While there is compelling evidence for glial modulation of synaptic formation and regulation that affect neuronal signal processing and activity, in this manuscript we will review recent findings on neuronal activity that affect glial function, specifically during neurodegenerative disorders. We will discuss the nature of each glial malfunction, its specificity to each disorder, overall contribution to the disease progression and assess its potential as a future therapeutic target.

Astrocytes in Parkinson's disease: from preclinical assays to in vivo imaging and therapeutic probes

Parkinson's disease (PD) is increasingly thought to be associated with glial pathology. Recently, research in neurodegenerative disorders has applied a greater focus to better understanding the role of astrocytes in the disease pathophysiology. In this article, we review results from the latest preclinical and clinical work, including functional imaging studies on astrocytes in PD and highlight key molecules that may prove valuable as biomarkers. We discuss how astrocytes may contribute to the initiation and progression of PD. We additionally present trials of investigational medicinal products and the current background for the design of future clinical trials.

Molecular and cellular mechanisms underlying the pathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder seen in age-dependent dementia. There is currently no effective treatment for AD, which may be attributed in part to lack of a clear underlying mechanism. Studies within the last few decades provide growing evidence for a central role of amyloid β (Aβ) and tau, as well as glial contributions to various molecular and cellular pathways in AD pathogenesis. Herein, we review recent progress with respect to Aβ- and tau-associated mechanisms, and discuss glial dysfunction in AD with emphasis on neuronal and glial receptors that mediate Aβ-induced toxicity. We also discuss other critical factors that may affect AD pathogenesis, including genetics, aging, variables related to environment, lifestyle habits, and describe the potential role of apolipoprotein E (APOE), viral and bacterial infection, sleep, and microbiota. Although we have gained much towards understanding various aspects underlying this devastating neurodegenerative disorder, greater commitment towards research in molecular mechanism, diagnostics and treatment will be needed in future AD research.

Effects of an adenosine A2A agonist on the rewarding associative properties of nicotine and neural plasticity in a rodent model of schizophrenia

BACKGROUND

Adenosine A_2a receptors form a mutually inhibitory heteromeric complex with dopamine D₂ receptors such that each receptor exhibits lower sensitivity to its agonist after the opposing receptor agonist is bound. This study analyzed the effects of CGS 21680, an adenosine A_2A agonist, on nicotine conditioned place preference (CPP) in adolescence using a rodent model of schizophrenia (SZ).

METHODS

Rats were treated from postnatal day (P) 1 to P21 with saline or the dopamine D₂/D₃ agonist quinpirole (NQ treatment) and raised to P41. After an initial preference test, rats were conditioned with saline or nicotine (0.6 mg/kg base) from P43 to P51. CGS 21680 (0.03 or 0.09 mg/kg) was given 15 minutes before nicotine was administered. The post-conditioning test was administered on P52. On P53, the nucleus accumbens (NAcc) was analyzed for brain-derived neurotrophic factor (BDNF) and glial cell-lined neurotrophic factor (GDNF).

RESULTS

Results revealed that NQ treatment enhanced nicotine CPP, and both doses of CGS 21680 alleviated this enhancement. Nicotine also resulted in a CPP in controls, which was alleviated by both doses of CGS 21680. BDNF closely followed the behavioral results: CGS 21680 alleviated the enhancement in NAcc BDNF in NQ-treated animals, and eliminated the increase in NAcc BDNF produced by nicotine in controls. NQ-treated animals conditioned to nicotine resulted in an increase of NAcc GDNF, but this was eliminated by CGS 21680. Both BDNF and GDNF correlated with CPP performance.

CONCLUSIONS

Results revealed that an adenosine A_2A agonist decreased the rewarding aspects of nicotine and its accompanying neural plasticity changes in a model of SZ.

Nicotine is neuroprotective to neonatal neurons of sympathetic ganglion in rat

Sympathetic neurons of SCG are dependent on availability of nerve growth factor (NGF) for their survival. SCG neurons express nicotinic receptors (nAChR) whose expression levels are modulated by nicotine. Nicotine exerts multiple effects on neurons, including neuroprotection, through nAChR binding. Although sympathetic neurons express robust levels of nAChR, a possible neuroprotective role for nicotine in these neurons is not well-understood. Therefore we determined the effect of nicotine exposure on survival of SCG neurons during NGF withdrawal in a well-established cell culture system. NGF was withdrawn in rat neonatal SCG neuron cultures which were then treated with either 10 μM nicotine alone or with nAChR antagonists 0.1 μM α-bungarotoxin (antagonist for α7 subunit bearing nAChR) and 10 μM mecamylamine (non-specific antagonist for ganglionic nAChR) for 48 h. Apoptotic death was determined by TUNEL staining. Cell survival was also determined by MTS assay. Western blot analysis of ERK1/2 was also performed. Our results showed that exposure to 10 μM nicotine significantly reduced apoptotic cell death in SCG neurons resulting from NGF withdrawal as shown by fewer TUNEL positive cells. The MTS assay results also revealed that 10 μM nicotine concentration significantly increased cell survival thus indicating neuroprotective effect of nicotine against cell death resulting from NGF withdrawal. Nicotinic receptor antagonists (bungarotoxin & mecamylamine) attenuated the effect of nicotine's action of neuroprotection. Western blot analysis showed an increased expression of ERK1/2 in nicotine treated cultures suggesting nicotine provided neuroprotection in SCG neurons by increasing the expression of ERK1/2 through nicotinic receptor dependent mechanisms.

Physiology of Astroglia

Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.

Physiology of Astroglia

Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.

Striatal hypodopamine phenotypes found in transgenic mice that overexpress glial cell line-derived neurotrophic factor

Glial cell line-derived neurotrophic factor (GDNF) positively regulates the development and maintenance of in vitro dopaminergic neurons. However, the in vivo influences of GDNF signals on the brain dopamine system are controversial and not fully defined. To address this question, we analyzed dopaminergic phenotypes of the transgenic mice that overexpress GDNF under the control of the glial Gfap promoter. Compared with wild-type, the GDNF transgenic mice contained higher levels of GDNF protein and phosphorylated RET receptors in the brain. However, there were reductions in the levels of tyrosine hydroxylase (TH), dopamine, and its metabolite homovanillic acid in the striatum of transgenic mice. The TH reduction appeared to occur during postnatal development. Immunohistochemistry revealed that striatal TH density was reduced in transgenic mice with no apparent signs of neurodegeneration. In agreement with these neurochemical traits, basal levels of extracellular dopamine and high K+-induced dopamine efflux were decreased in the striatum of transgenic mice. We also explored the influences of GDNF overexpression on lomomotor behavior. GDNF transgenic mice exhibited lower stereotypy and rearing in a novel environment compared with wild-type mice. These results suggest that chronic overexpression of GDNF in brain astrocytes exerts an opposing influence on nigrostriatal dopamine metabolism and neurotransmission.

Anti-neuropathic effects of Rosmarinus officinalis L. terpenoid fraction: relevance of nicotinic receptors

Traditional uses and current results highlight the neuroprotective properties of Rosmarinus officinalis L. The compelling need for novel strategies able to relieve neuropathic pain encouraged us to analyze different rosemary leaf extracts in rats following chronic constriction injury (CCI) of sciatic nerve. Ethanol, acetone, and the innovative ultrasound-hexane extractive methods were used to obtain: EE, AE, and for hexane extracts UREprel and URE. Extracts were characterized in terms of typical constituents and repeatedly administered to CCI-rats (13-days treatment, from the day of surgery). URE showed the best efficacy and potency in reducing hypersensitivity to noxious- and non-noxious stimuli and spontaneous pain. URE contained the higher quantity of the terpenoid carnosic acid (CA) and its efficacy was compared to pure CA. Histological analysis of the sciatic nerve revealed that URE prevented axon and myelin derangement, edema and inflammatory infiltrate. In the dorsal horn of the spinal cord, URE did not reduce astrocyte activation. Both the pain reliever and the neuroconservative effects of URE were significantly prevented by the nicotinic receptor (nAChR) antagonist mecamylamine. In conclusion, the hexane-ultrasound rosemary extract is able to reduce neuropathic hypersensitivity and protect nervous tissues. Effectiveness is mainly related to the terpenoid fraction by mechanisms involving nAChRs.

Astrocytic and microglial nicotinic acetylcholine receptors: an overlooked issue in Alzheimer's disease

It is increasingly recognized that astrocytes and microglia-associated dysfunction contribute to AD pathology. In addition, glial nicotinic acetylcholine receptors (nAChRs) play a role in AD-related phenomena, such as neuron survival, synaptic plasticity, and memory. From mechanistic point of view, the glial regulation of pro-inflammatory cytokines, as common contributors in AD, is modulated by nAChRs. Astrocytic and microglial nAChRs contribute to Aβ metabolism, including Aβ phagocytosis and degradation as well as Aβ-related oxidative stress and neurotoxicity. These receptors are also involved in neurotransmission and gliotransmission through indirect interaction with N-Methyl-D-aspartate (NMDA) and a-amino-3-hydroxy-5-methyl-4 isoxazolepropionic acid (AMPA) receptors as well as gamma-aminobutyric acid (GABA) and intracellular calcium regulation. In addition, glial nAChRs participate in trophic factors-induced neuroprotection. This review gathers the most recent advances along with the previous data on astrocytic and microglial nAChRs role in AD pathogenesis.

Anti-hypersensitive effect of intramuscular administration of αO-conotoxin GeXIVA[1,2] and GeXIVA[1,4] in rats of neuropathic pain

αO-conotoxin GeXIVA (GeXIVA) is a potent antagonist of α9α10 nicotinic acetylcholine receptors (nAChRs), which has four Cys residues and three disulfide isomers. Among the 3 isomers, both GeXIVA[1,2] (bead isomer) and GeXIVA[1,4] (ribbon isomer) showed potent block on α9α10 nAChRs with close low nanomolar IC50s. Here we report that anti-hypersensitive effects of the bead and ribbon isomers in the chronic constriction injury (CCI) model of neuropathic pain and acute pain model of tail flick test. Treatment was started and continued for 7 or 14days after the development of hyperalgesia which was induced by CCI surgery. GeXIVA[1,2] and GeXIVA[1,4] significantly reduced mechanical allodynia in CCI rats without tolerance, in which GeXIVA[1,2] remained up to two weeks after intramuscular administration of the toxins was ceased. The pain reliever effect of GeXIVA[1,2] on neuropathic rats was slightly better than GeXIVA[1,4]. The two isomers did not suppress the acute thermal pain behaviors significantly when they were tested in the tail flick model by intramuscular bolus injection. Both GeXIVA[1,2] and GeXIVA[1,4] had no significant effect on performance of rats in the accelerating rotarod test after intramuscular injections. This suggests that αO-conotoxin GeXIVA[1,2] and GeXIVA[1,4] may offer new strategies to the treatment of neuropathic pain.

Stimulation of α7 nicotinic acetylcholine receptor regulates glutamate transporter GLAST via basic fibroblast growth factor production in cultured cortical microglia

The α7 nicotinic acetylcholine (nACh) receptor expressed in microglia has a crucial role in neuroprotection. Simulation of α7 nACh receptor leads to increased expression of glutamate/aspartate transporter (GLAST), which in turn decreases synaptic glutamate levels. However, the upregulation of GLAST in cultured rat cortical microglia appears long after (over 18 h) stimulation of the α7 nACh receptor with nicotine. Thus, the current study elucidated the pathway responsible for the induction of GLAST expression in cultured cortical microglia. Nicotine-induced GLAST mRNA expression was significantly inhibited by cycloheximide pretreatment, indicating that a protein intermediary, such as a growth factor, is required for GLAST expression. The expression of fibroblast growth factor-2 (FGF-2) mRNA in cortical microglia was significantly increased 6 and 12h after treatment with nicotine, and this increase was potently inhibited by pretreatment with methyllycaconitine, a selective α7 nACh receptor antagonist. The treatment with nicotine also significantly increased FGF-2 protein expression. Furthermore, treatment with recombinant FGF-2 increased GLAST mRNA, protein expression and (14)C-glutamate uptake, a functional measurement of GLAST activity. Conversely, pretreatment with PD173074, an inhibitor of FGF receptor (FGFR) tyrosine kinase, significantly prevented the nicotine-induced expression of GLAST mRNA, its protein and (14)C-glutamate uptake. Reverse transcription polymerase chain reaction confirmed FGFR1 mRNA expression was confined to cultured cortical microglia. Together, the current findings demonstrate that the neuroprotective effect of activation of microglial α7 nACh receptors could be due to the expression of FGF-2, which in turn increases GLAST expression, thereby clearing glutamate from synapse and decreasing glutamate neurotransmission.

Smoking and the developing brain: altered white matter microstructure in attention-deficit/hyperactivity disorder and healthy controls

Brain white matter (WM) tracts, playing a vital role in the communication between brain regions, undergo important maturational changes during adolescence and young adulthood, a critical period for the development of nicotine dependence. Attention-deficit/hyperactivity disorder (ADHD) is associated with increased smoking and widespread WM abnormalities, suggesting that the developing ADHD brain might be especially vulnerable to effects of smoking. This study aims to investigate the effect of smoking on (WM) microstructure in adolescents and young adults with and without ADHD. Diffusion tensor imaging was performed in an extensively phenotyped sample of nonsmokers (n = 95, 50.5% ADHD), irregular smokers (n = 41, 58.5% ADHD), and regular smokers (n = 50, 82.5% ADHD), aged 14-24 years. A whole-brain voxelwise approach investigated associations of smoking, ADHD and their interaction, with WM microstructure as measured by fractional anisotropy (FA) and mean diffusivity (MD). Widespread alterations in FA and MD were found for regular smokers compared to irregular and nonsmokers, mainly located in the corpus callosum and WM tracts surrounding the basal ganglia. Several regions overlapped with regions of altered FA for ADHD versus controls, albeit in different directions. Irregular and nonsmokers did not differ, and ADHD and smoking did not interact. Results implicate that smoking and ADHD have independent effects on WM microstructure, and possibly do not share underlying mechanisms. Two mechanisms may play a role in the current results. First, smoking may cause alterations in WM microstructure in the maturing brain. Second, pre-existing WM microstructure differences possibly reflect a risk factor for development of a smoking addiction.

α-conotoxin RgIA protects against the development of nerve injury-induced chronic pain and prevents both neuronal and glial derangement

Neuropathic pain affects millions of people worldwide, causing substantial disability and greatly impairing quality of life. Commonly used analgesics or antihyperalgesic compounds are generally characterized by limited therapeutic outcomes. Thus, there is a compelling need for novel therapeutic strategies able to prevent nervous tissue alterations responsible for chronic pain. The α9α10 nicotinic acetylcholine receptor antagonist α-conotoxin RgIA (RgIA), a peptide isolated from the venom of a carnivorous cone snail, induces relief in both acute and chronic pain models. To evaluate potential disease-modifying effects of RgIA, the compound was given to rats following chronic constriction injury (CCI) of the sciatic nerve. Two or 10 nmol RgIA injected intramuscularly once a day for 14 days reduced the painful response to suprathreshold stimulation, increased pain threshold to nonnoxious stimuli, and normalized alterations in hind limb weight bearing. Histological analysis of the sciatic nerve revealed that RgIA prevented CCI-induced decreases of axonal compactness and diameter, loss of myelin sheath, and decreases in the fiber number. Moreover, RgIA significantly reduced edema and inflammatory infiltrate, including a decrease of CD86(+) macrophages. In L4-L5 dorsal root ganglia, RgIA prevented morphometric changes and reduced the inflammatory infiltrate consistent with a disease-modifying effect. In the dorsal horn of the spinal cord, RgIA prevented CCI-induced activation of microglia and astrocytes. These data suggest that RgIA-like compounds may represent a novel class of therapeutics for neuropathic pain that protects peripheral nervous tissues as well as prevents central maladaptive plasticity by inhibiting glial cell activation.

Long-term nicotine treatment suppresses IL-1β release and attenuates substance P- and 5-HT-evoked Ca²⁺ responses in astrocytes

The aim of this study was to investigate whether short- or long-term nicotine treatment, had an influence on Ca(2+)-induced intracellular Ca(2+) release in astrocytes co-cultured with microvascular endothelial cells, and if the release of interleukin-1β (IL-1β) changed during this treatment. We found that nicotine-evoked Ca(2+) transients were not attenuated up to 10d of incubation with nicotine, neither was the α7-nicotine acetylcholine receptor (α7-nAChR) protein. After 10d the IL-1β release was decreased. Furthermore, substance P- and 5-hydroxytryptamine (5-HT)-evoked Ca(2+) transients were attenuated after 10d of nicotine treatment, but glial cell line-derived neurotrophic factor (GDNF) had no effect on these transients. The results show that long-term nicotine treatment had no influence on nicotine-evoked Ca(2+) transients or protein expression of the α7-nAChR, but had with a decreased IL-1β release. The Gq protein and inositoltrisphosphate system seems to be influenced by the attenuation of Ca(2+)-evoked intracellular Ca(2+) release after stimulation with substance P and 5-HT.

Nicotine-induced neuroprotection against ischemic injury involves activation of endocannabinoid system in rats

Nicotine has been reported to exert certain protective effect in the Parkinson's and Alzheimer's diseases. Whether it has a similar action in focal cerebral ischemia was unclear. In the present study, rats received either an injection of (-)-nicotine hydrogen tartrate salt (1.2 mg/kg, i.p.) or the vehicle 2 h before the 120 min middle cerebral artery occlusion. Neurological deficits and histological injury were assessed at 24 h after reperfusion. The content of endocannabinoids and the expression of cannabinoid receptor CB1 in brain tissues were determined at different time points after nicotine administration. Results showed that nicotine administration ameliorated neurological deficits and reduced infarct volume induced by cerebral ischemia in the rats. The neuroprotective effect was partially reversed by CB1 blockage. The content of the endocannabinoids N-arachidonylethanolamine and 2-arachidonoylglycerol, as well as the expression of cannabinoid receptor CB1 were up-regulated in brain tissues after nicotine delivery. These results suggest that endogenous cannabinoid system is involved in the nicotine-induced neuroprotection against transient focal cerebral ischemia.