(-)-nicotine protects against systemic kainic acid-induced excitotoxic effects

Polyamine regulation of ion channel assembly and implications for nicotinic acetylcholine receptor pharmacology

Small molecule polyamines are abundant in all life forms and participate in diverse aspects of cell growth and differentiation. Spermidine/spermine acetyltransferase (SAT1) is the rate-limiting enzyme in polyamine catabolism and a primary genetic risk factor for suicidality. Here, using genome-wide screening, we find that SAT1 selectively controls nicotinic acetylcholine receptor (nAChR) biogenesis. SAT1 specifically augments assembly of nAChRs containing α7 or α4β2, but not α6 subunits. Polyamines are classically studied as regulators of ion channel gating that engage the nAChR channel pore. In contrast, we find polyamine effects on assembly involve the nAChR cytosolic loop. Neurological studies link brain polyamines with neurodegenerative conditions. Our pharmacological and transgenic animal studies find that reducing polyamines enhances cortical neuron nAChR expression and augments nicotine-mediated neuroprotection. Taken together, we describe a most unexpected role for polyamines in regulating ion channel assembly, which provides a new avenue for nAChR neuropharmacology.

Small molecule polyamines participate in diverse aspects of cell growth and differentiation and are known to regulate ion channel gating. Here authors reveal that cellular polyamines control nicotinic acetylcholine receptor (nAChR) biogenesis, and either catabolic degradation or inhibition of polyamine production augments nAChR assembly.

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.

Nicotine and Kainic Acid Effects on Cortical Epileptic Afterdischarges in Immature Rats

Aim of the study was to test the effect of nicotine (NIC) and kainic acid (KA) co-treatment in immature rats. Male Wistar albino rats (two different age groups) were chosen for the study. Experiments started on postnatal day (PD) 8 or 21 and animals were treated twice a day for three days with nicotine, fourth day KA was administered. Animals at PD12 (PD25 respectively) were examined electrophysiologically for cortical epileptic afterdischarges (ADs). First cortical ADs in PD12 animals were longer, when compared to PD25 rats (group treated with both substances). Nor NIC or KA treatment affected the length of discharges in PD12 rats. Older experimental group exhibited the shortening of the first ADs (group treated with NIC and KA, compared with groups exposed to single treatment). Few changes were found in KA treated group – 2nd and 4th ADs were shorter when compared with first ADs. These results demonstrate that NIC treatment played minor role in seizure susceptibility of PD12 rats, sensitivity to NIC differs during ontogenesis and subconvulsive dose of KA influenced the length of discharges only in PD25 animals.

Translating laboratory discovery to the clinic: from nicotine and mecamylamine to Tourette's, depression, and beyond

The early development of novel nicotinic drugs for Tourette's and depression was a very long journey in discovery, which began with basic behavioral neuroscience studies aimed at understanding how cholinergic and dopaminergic systems interact in the basal ganglia to control goal directed movement. These early rodent studies with nicotine and dopamine antagonists formed the basis for investigating a potentially improved treatment for children suffering from Tourette's syndrome (TS). Clinically, the research trajectory first focused on studies employing the use of nicotine gum to potentiate the therapeutic effect of the dopamine receptor antagonist, haloperidol, in patients with TS. These projects led to the discovery of a new use for a decades-old blood pressure medication, mecamylamine, a nicotine antagonist, which also appeared to provide symptomatic relief in some TS patients when used clinically and was found to reduce symptoms of mood instability and depression. This unexpected discovery led to a new hypothesis regarding the mechanism of action of antidepressants as well as a series of successful independent trials employing mecamylamine, and its active enantiomer, TC5214, as an augmenting agent in the treatment of major depression. This article is a chronological mini review of these basic and clinical translational studies on nicotinic therapeutics for Tourette's syndrome and depression over the past 25 years.

Revisiting the cholinergic hypothesis in the development of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia affecting the elderly population today; however, there is currently no accurate description of the etiology of this devastating disorder. No single factor has been demonstrated as being causative; however, an alternative co-factors theory suggests that the interaction of multiple risk factors is responsible for AD. We have used this model, in combination with the original cholinergic hypothesis of AD to propose a "new" cholinergic hypothesis that we present in this review. This new version takes into account recent findings from the literature and our reports of removal of medial septum cholinergic projections to the hippocampus reduces both behavioural and anatomical plasticity, resulting in greater cognitive impairment in response to secondary insults (stress, injury, disease, etc.). We will first summarize the experimental results and discuss some potential mechanisms that could explain our results. We will then present our 'new' version of the cholinergic hypothesis and how it relates to the field of AD research today. Finally we will discuss some of the implications for treatment that arise from this model and present directions for future study.

TOLERANCE TO PENTYLENTETRAZOL-INDUCED CONVULSIONS AND PROTECTION OF CEREBROVASCULAR INTEGRITY BY CHRONIC NICOTINE

The authors' previous studies have shown that in nicotine-induced seizures sensitivity was decreased and blood-brain barrier (BBB) disruption was prevented as a consequence of nicotine pretreatment. This study aimed to investigate the possible protective actions of nicotine on cerebrovascular permeability and seizures induced by pentylentetrazol (PTZ) injection. Cerebrovascular effects of nicotine were evaluated by measuring the permeability changes of BBB using Evans-Blue (EB) dye and specific gravity (SG), which indicates brain water and protein content. The experiments were carried out on Wistar rats. Animals were randomly divided into two groups. Convulsions were induced by injection of PTZ (80 mg/kg i.v.) in rats either pretreated with nicotine daily with a low dose of 0.8 mg/kg day for 21 days or injected with a single dose of 6 mg/kg mecamylamine. The same procedures were followed in control rats with the exception that they were injected only with saline. PTZ injection caused tonic-clonic convulsions and increased the EB dye leakage and specific gravity values in saline-injected control rat brains. Daily injection of nicotine lessened the intensity of seizures. These were accompanied by marked decreases in both the leakage of EB and brain water content. Acute administration of a nAChR antagonist mecamylamine significantly increased seizure latency and decreased the duration of seizures. Thereby, mecamylamine reduced the EB leakage and water content in most brain regions. These results indicate that development of tolerance to PTZ convulsions can be produced by chronic nicotine administration in rats. The mechanism for this effect currently needs clarification. Moreover, the data also suggest that cholinergic activity may account for occurrence of PTZ-induced convulsions.

Repeated intracerebroventricular infusion of nicotine prevents kainate-induced neurotoxicity by activating the α7 nicotinic acetylcholine receptor

We examined whether (-)-nicotine infusion can affect kainic acid (KA)-induced neurotoxicity in rats. Although treatment with a single nicotine infusion (0.5 or 1.0 microg/side, i.c.v.) failed to attenuate KA-induced neurotoxicity, repeated nicotine infusions (1.0 microg/side/day for 10 days) attenuated the seizures, the severe loss of cells in hippocampal regions CA1 and CA3, the increase in activator protein (AP)-1 DNA binding activity, and mortality after KA administration. alpha-Bungarotoxin and mecamylamine blocked the neuroprotective effects of nicotine. These results suggest that repeated nicotine treatment provides alpha7 nicotinic acetylcholine receptor-mediated neuroprotection against KA toxicity.

Nicotine, but neither the α4β2 ligand RJR2403 nor an α7 nAChR subtype selective agonist, protects against a partial 6-hydroxydopamine lesion of the rat median forebrain bundle

Although previous studies suggest nicotine protects against a 6-hydroxydopamine (6-OHDA)-induced lesion of the nigrostriatal tract in rats, it is not known whether functional motor recovery occurs or which nicotinic acetylcholine receptor (nAChR) subtypes mediate this effect. These issues were investigated by comparing the effects of the subtype-specific nAChR agonists, RJR2403 (alpha4beta2 preferring) and (R)-N-(1-azabicyclo[2.2.2.]oct-3-yl)(5-(2-pyridyl)thiopene-2-carboxamide (Compound A; alpha7-selective) and nicotine given 30 min prior to and daily for 14 days after a partial 6-OHDA lesion. In vehicle treated animals, 6-OHDA (6 microg) produced a 65 +/- 1.8% loss of striatal tyrosine hydroxylase (TH) immunoreactivity in the lesion versus intact hemisphere. This loss was reduced in animals treated with nicotine (0.6 and 0.8 mg kg(-1)), reaching significance at the higher dose (36.6 +/- 3.7% loss; P < 0.01 versus vehicle). Treatment with nicotine (0.6 and 0.8 mg kg(-1)) also significantly reduced the number of amphetamine-induced rotations compared to vehicle treatment. In contrast, treatment with RJR2403 (0.2 and 0.4 mg kg(-1)) or Compound A (10 and 20 mg kg(-1)) reduced neither the degree of amphetamine-induced rotations nor the loss of striatal TH immunoreactivity. These data suggest that whilst nicotine is neuroprotective in this partial lesion model, activation of neither the alpha4beta2 nor alpha7 subtypes alone is sufficient to provide protection.

Pro-inflammatory cytokines modify neuronal nicotinic acetylcholine receptor assembly

We have examined the impact of the inflammatory cytokines interleukin-1 beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) on assembly of nAChRs from subunit mixtures of nAChRalpha4, beta2 and beta4 transiently transfected into 293 cells. In control transfections approximately 55% of alpha4 associated preferentially with beta4, but less than 15% complexed with beta2 and the remainder was associated with both beta subunits. These relative ratios were modified by pro-inflammatory cytokines. IL-1beta strongly enhanced alpha4/beta2 association and decreased alpha4/beta4, whereas TNFalpha promoted mixed alpha4/beta2/beta4 interactions. These results show that the emerging rules governing assembly of nAChRs are subject to modification by the pro-inflammatory cytokine environment.

TC-1734: an orally active neuronal nicotinic acetylcholine receptor modulator with antidepressant, neuroprotective and long-lasting cognitive effects

The development of selective ligands targeting neuronal nicotinic acetylcholine receptors to alleviate symptoms associated with neurodegenerative diseases presents the advantage of affecting multiple deficits that are the hallmarks of these pathologies. TC-1734 is an orally active novel neuronal nicotinic agonist with high selectivity for neuronal nicotinic receptors. Microdialysis studies indicate that TC-1734 enhances the release of acetylcholine from the cortex. TC-1734, by either acute or repeated administration, exhibits memory enhancing properties in rats and mice and is neuroprotective following excitotoxic insult in fetal rat brain in cultures and against alterations of synaptic transmission induced by deprivation of glucose and oxygen in hippocampal slices. At submaximal doses, TC-1734 produced additive cognitive effects when used in combination with tacrine or donepezil. Unlike (-)-nicotine, behavioral sensitization does not develop following repeated administration of TC-1734. Its pharmacokinetic (PK) profile (half-life of 2 h) contrasts with the long lasting improvement in working memory (18 h) demonstrating that cognitive improvement extends beyond the lifetime of the compound. The very low acute toxicity of TC-1734 and its receptor activity profile provides additional mechanistic basis for its suggested potential as a clinical candidate. TC-1734 was very well tolerated in acute and chronic oral toxicity studies in mice, rats and dogs. Phase I clinical trials demonstrated TC-1734's favorable pharmacokinetic and safety profile by acute oral administration at doses ranging from 2 to 320 mg. The bioavailability, pharmacological, pharmacokinetic, and safety profile of TC-1734 provides an example of a safe, potent and efficacious neuronal nicotinic modulator that holds promise for the management of the hallmark symptomatologies observed in dementia.

Neuroprotection by nicotine in mouse primary cortical cultures involves activation of calcineurin and L-type calcium channel inactivation

Regulation of intracellular calcium influences neuronal excitability, synaptic plasticity, gene expression, and neurotoxicity. In this study, we investigated the role of calcium in mechanisms underlying nicotine-mediated neuroprotection from glutamate excitotoxicity. Neuroprotection by nicotine in primary cortical cultures was not seen in knock-out mice lacking the beta2 subunit of the nicotinic acetylcholine receptor (nAChR). Neuroprotection was partially blocked in wild-type cultures by alpha-bungarotoxin, an antagonist of the alpha7 nAChR subtype, suggesting a potential cooperative role for these subtypes. Pretreatment with nicotine decreased glutamate-mediated calcium influx in primary cortical cultures by 41%, an effect that was absent in cultures from knock-out mice lacking the beta2 subunit of the nAChR. This effect was dependent on calcium entry through L-type channels during nicotine pretreatment in wild-type cultures. The ability of nicotine to decrease glutamate-mediated calcium influx was occluded by cotreatment with nifedipine during glutamate application, suggesting that nicotine pretreatment decreased subsequent activity of L-type calcium channels. Treatment with the calcineurin antagonists FK506 and cyclosporine during pretreatment eliminated both nicotine-mediated neuroprotection and the effects of nicotine on L-type channels. We conclude that neuroprotective effects of nicotine in cortical neurons involve both beta2- and alpha7-containing nAChRs, activation of calcineurin, and decreased intracellular calcium via L-type channels.

Chronic exposure of nicotine modulates the expressions of the cerebellar glial glutamate transporters in rats

Rats were given nicotine (25 ppm) in their drinking water at the start of their mating period in order to study the expressions of glutamate transporter subtypes in cerebellar astrocytes following the chronic exposure of nicotine after mating. After the offspring were delivered, each group was divided into two subgroups. One group, the control group, was given distilled water only and the other group, the experimental group, was given distilled water containing nicotine. The cerebellar astrocytes were prepared from 7 day-old pups at each group. Ten days after the cells were cultured, the expression of the glutamate transporter subtypes (GLAST and GLT-1) was determined using immunochemistry and immunoblotting. During the continuous treatments, the developmental expression patterns of the GLAST and GLT-1 in the cerebellum were also determined from 2, 4 and 8 week-old rats. The expression levels of GLAST in cultured astrocytes of both the pre- or post-natally exposed groups were higher than those of the control group. However, these expression levels of the continuously exposed group were lower than those of the control group. Compared to those of the control group, the GLT-1 expression levels of all the nicotine-treated groups were higher, particularly in the continuously treated group. According to the results from the immochemistry procedure, the cerebellar GLAST and GLT-1 expression levels of all nicotine-treated groups were lower than those of the control group at each age. However, the immunoblotting procedure showed that the cerebellar GLT-1 expression levels of all the nicotine-treated groups were higher than those of the control group, except for the rats that were continuously exposed for 8 weeks using immunoblotting. These results suggest that the expression of the glial GLAST and GLT-1 are altered differently depending on the initial exposure time and the particular period of nicotine exposure. In addition, nicotine exposure during gestation has persistent effects on glial cells.

Nicotinic receptors in aging and dementia

Activation of neuronal nicotinic acetylcholine receptors (nAChRs) has been shown to maintain cognitive function following aging or the development of dementia. Nicotine and nicotinic agonists have been shown to improve cognitive function in aged or impaired subjects. Smoking has also been shown in some epidemiological studies to be protective against the development of neurodegenerative diseases. This is supported by animal studies that have shown nicotine to be neuroprotective both in vivo and in vitro. Treatment with nicotinic agonists may therefore be useful in both slowing the progression of neurodegenerative illnesses, and improving function in patients with the disease. While increased nicotinic function has been shown to be beneficial, loss of cholinergic markers is often seen in patients with dementia, suggesting that decreased cholinergic function could contribute to both the cognitive deficits, and perhaps the neuronal degeneration, associated with dementia. In this article we will review the literature on each of these areas. We will also present hypotheses that might address the mechanisms underlying the ability of nAChR function to protect against neurodegeneration or improve cognition, two potentially distinct actions of nicotine.

Selective activation of central subtypes of the nicotinic acetylcholine receptor has opposite effects on neonatal excitotoxic brain injuries

The incidence of neurological disabilities ascribable to perinatal injury is rising in Western countries, raising ethical and financial problems. No curative treatments are available. The pathophysiology of brain lesions of hypoxic-ischemic or inflammatory origin involves various neurotransmitters or neuromodulators. Among these, glutamate plays a key role. By overactivating N-methyl-D-aspartate receptors, it triggers the excitotoxic cascade. Although addictive, nicotine prevents excitotoxic neuronal death in adult animals. Its potential neuroprotective effects have not been evaluated in neonates. We found that nicotine is neuroprotective in vivo, in a murine model of neonatal excitotoxic brain injury, and in vitro, in primary cultures of cortical neurons. We investigated the respective roles in nicotine-related neuroprotection of the two dominant nicotinic acetylcholine receptor (nAChR) isoforms, namely, alpha4beta2 (heteropentameric) and alpha7 (homopentameric). Inhibition of alpha4beta2, either pharmacological (i.e., an alpha4beta2 nAChR antagonist) or molecular (beta2-/- knockout mice), abolished the protective effect of nicotine in vivo and in vitro, suggesting the involvement of alpha4beta2 nAChR in neonatal nicotine-related neuroprotection. In contrast, activation of alpha7 nAChR, which is protective in adult animals, was deleterious in our neonatal model, whereas its blockade, either pharmacological or molecular (alpha7-/- knockout mice) provided neuroprotection. Neuroprotective strategies must consider these opposite properties of distinct nAChR isoforms in neonates.

Changes in the glutamate release and uptake of cerebellar cells in perinatally nicotine-exposed rat pups

Cerebellar granule and glial cells were cultured from 7 day-old rat pups after pre- and post-natal nicotine treatment. Ten days later, the basal release of glutamate in the granule cells prepared from the pre- and post-natally nicotine-exposed pups was higher and lower than the controls, respectively. The N-methyl-D-aspartate-induced release of glutamate was higher in the granule cells of post-natal nicotine exposed rats. However, the nicotine-induced glutamate release was either unchanged or was lower in the granule cells of all nicotine-treated pups. The basal glutamate uptake was higher in the glial cells from those exposed pre-natally and lower in the continuously nicotine-exposed pups. The sensitivities of L-trans-pyrrolidine-2,4-dicarboxylic acid on glutamate uptake were higher in all nicotine treated groups. There was a higher number of specific [3H]dizocilpine binding sites in the pre- or continuously nicotine-exposed group. These results suggest that the cerebellar cell properties are altered after perinatal nicotine exposure and that the development of an excitatory amino acid system might be affected differently depending on the nicotine exposure time.

Effects of nicotine on ethanol dependence and brain damage

Almost all alcoholics (80%-95%) smoke tobacco. When alcoholics binge, they achieve high, sustained blood alcohol levels, become physically dependent, and often suffer loss of cognition and other higher cortical functions. Nicotine could have a modulatory effect on ethanol drinking behavior and ethanol-induced brain damage through its cholinergic actions. To determine whether nicotine altered alcohol dependence, alcohol-induced brain damage, or both, a rat model of binge drinking was used to study the effects of nicotine on the alcohol withdrawal syndrome and its associated brain damage. After administration of the last dose of ethanol in a 4-day binge model, rats remained intoxicated for approximately 5 h, slowly returned to a neutral state, and entered a hyperexcited period, which peaked around 24 h and lasted a total of 60 h. Behavioral signs of withdrawal included splayed limbs, tremors, and seizures. Continuous transdermal nicotine did not alter the duration or severity of ethanol withdrawal. The 4-day binge ethanol treatment caused considerable brain damage in the perirhinal cortex, entorhinal cortex, ventral dentate gyrus, and olfactory bulb as visualized with amino cupric silver stain. Nicotine alone caused little or no brain damage and did not markedly alter binge ethanol-induced damage in cortical or hippocampal regions. In the olfactory bulb, nicotine reduced ethanol-induced brain damage. Although results of other studies seem to indicate that nicotine increases alcohol consumption, our findings indicate that nicotine does not markedly change the development of alcohol dependence or alcohol-induced cortical damage.

TC-2559: a novel orally active ligand selective at neuronal acetylcholine receptors

TC-2559 [(E)-N-Methyl-4-[3-(5-ethoxypyridin)yl]-3-buten-1-amine] is a novel nicotinic agonist markedly more selective than recently reported novel nicotinic receptor ligands (selectivity ratio for central nervous system (CNS) to peripheral nervous system (PNS)>4000). TC-2559 competes effectively with [3H]-nicotine binding (K(i)=5 nM) but not with [125I]-bungarotoxin (>50,000 nM). Dopamine release from striatal synaptosomes and ion flux from thalamic synaptosomes indicate that TC-2559 is potent and efficacious in the activation of CNS receptors and significantly reduced glutamate-induced neurotoxicity in vitro. TC-2559 has no detectable effects on muscle and ganglion-type nicotinic acetylcholine receptors at concentrations up to 1 mM. TC-2559 significantly attenuates scopolamine-induced cognitive deficits in a step-through passive avoidance task. Acute and repeated oral dosing of TC-2559 enhances performance in a radial arm maze task. In contrast to the effects of equimolar concentrations of (-) nicotine, TC-2559 does not induce hypothermia and locomotor activity is not enhanced following repeated daily administration of 14 days. TC-2559 has a markedly enhanced CNS-PNS selectivity ratio and an intra-CNS selectivity as evidenced by the improved cognition without increased locomotor activity. The in vitro and in vivo studies in the present study suggest that TC-2559 has the desired profile to be further evaluated as a potential therapeutic agent for neurodegenerative diseases.

The alpha7 nicotinic acetylcholine receptor subtype mediates nicotine protection against NMDA excitotoxicity in primary hippocampal cultures through a Ca(2+) dependent mechanism

Neuronal nicotinic acetylcholine receptors (nAChR) have been suggested to play a role in a variety of modulatory and regulatory processes, including neuroprotection. Here we have characterized the neuroprotective effects of nicotine against an excitotoxic insult in primary hippocampal cultures. Exposure of hippocampal neurons to 200 microM NMDA for 1 h decreased cell viability by 25+/-5%, an effect blocked by NMDA receptor antagonists. Nicotine (10 microM) counteracted the NMDA-induced cell death when co-incubated with NMDA or when present subsequent to the NMDA treatment. Nicotine protection was prevented by 1 microM MLA, confirming that it was mediated by nAChR, and by 1 microM alpha-bungarotoxin, demonstrating that the alpha7 nAChR subtype was responsible. Both the NMDA evoked neurotoxicity and nicotine neuroprotection were Ca(2+)-dependent. In Fura-2-loaded hippocampal neurons, nicotine (10 microM) and NMDA (200 microM) acutely increased intracellular resting Ca(2+) from 70 nM to 200 and 500 nM, respectively. Responses to NMDA were unaffected by the presence of nicotine. (45)Ca(2+) uptake after a 1 h exposure to nicotine or NMDA also demonstrated quantitative differences between the two drugs. This study demonstrates that the alpha7 subtype of nAChR can support neuronal survival after an excitotoxic stimulus, through a Ca(2+) dependent mechanism that operates downstream of NMDA receptor activation.

Subacute nicotine exposure in cultured cerebellar cells increased the release and uptake of glutamate

Cerebellar granule and glial cells prepared from 7 day-old rat pups were used to investigate the effects of sub-acute nicotine exposure on the glutamatergic nervous system. These cells were exposed to nicotine in various concentrations for 2 to 10 days in situ. Nicotine-exposure did not result in any changes in cerebellar granule and glial cell viability at concentrations of up to 500 microM. In cerebellar granule cells, the basal extracellular levels of glutamate, aspartate and glycine were enhanced in the nicotine-exposed granule cells. In addition, the responses of N-methyl-D-aspartate (NMDA)-induced glutamate release were enhanced at low NMDA concentrations in the nicotine-exposed granule cells. However, this decreased at higher NMDA concentrations. The glutaminase activity was increased after nicotine exposure. In cerebellar glial cells, glutamate uptake in the nicotine-exposed glial cells were either increased at low nicotine exposure levels or decreased at higher levels. The inhibition of glutamate uptake by L-trans-pyrollidine-2,4-dicarboxylic acid (PDC) was lower in glial cells exposed to 50 microM nicotine. Glutamine synthetase activity was lower in glial cells exposed to 100 or 500 microM of nicotine. These results indicate that the properties of cerebellar granule and glial cells may alter after subacute nicotine exposure. Furthermore, they suggest that nicotine exposure during development may modulate glutamatergic nervous activity.

Inhibition by neuroprotective drug NS-7 of nicotine-induced 22Na(+) influx, 45Ca(2+) influx and catecholamine secretion in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride], a newly-synthesized neuroprotective drug, inhibited nicotine-induced 22Na(+) influx via nicotinic receptors (IC(50)=15.5 microM); the suppression by NS-7 was observed in the presence of ouabain, an inhibitor of Na(+),K(+)-ATPase, and was not attenuated upon the washout of NS-7. NS-7 decreased nicotine-induced maximum influx of 22Na(+) without altering the EC(50) value of nicotine. Also, NS-7 diminished nicotine-induced 45Ca(2+) influx via nicotinic receptors and voltage-dependent Ca(2+) channels (IC(50)=14.1 microM) and catecholamine secretion (IC(50)=19.5 microM). These results suggest that NS-7 produces noncompetitive and long-lasting inhibitory effects on neuronal nicotinic receptors in adrenal chromaffin cells, and interferes with the stimulus-secretion coupling.

Central nicotinic receptors, neurotrophic factors and neuroprotection

The multiple combinations of nAChR subunits identified in central nervous structures possess distinct pharmacological and physiological properties. A growing number of data have shown that compounds interacting with neuronal nAChRs have, both in vivo and in vitro, the potential to be neuroprotective and that treatment with nAChR agonists elicit long-lasting improving of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Epidemiological and clinical studies suggested also a potential neuroprotective/trophic role of (-)-nicotine in neurodegenerative disease, such as Alzheimer's and Parkinson's disease. Taken together experimental and clinical data largely indicate a neuroprotective/trophic role of nAChR activation involving mainly alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR antagonists, and by potent nAChR agonists recently found displaying efficacy and/or larger selective affinities than (-)-nicotine for neuronal nAChR subtypes. A neurotrophic factor gene regulation by nAChR signalling has been taken into consideration as possible mechanism involved in neuroprotective/trophic effects by nAChR activation and has evidenced an involvement of the fibroblast growth factor (FGF-2) gene as a target of nAChR signalling. These findings suggested that FGF-2 could be involved, according to the FGF-2 neurotrophic functions, in nAChR mechanisms mediating the neuronal survival, trophism and plasticity.

Nicotine attenuates arachidonic acid-induced neurotoxicity in cultured spinal cord neurons

Arachidonic acid release from cellular membranes due to spinal cord trauma may be one of the principal destructive events that can lead to progressive injury to spinal cord tissue. Exposure to arachidonic acid can compromise neuronal survival and viability. Because nicotine is known to be a neuroprotective agent, we propose that it can prevent arachidonic acid-induced neurotoxicity. To study this hypothesis, effects of nicotine on mitochondrial function, cellular energy content and apoptotic cell death were measured in cultured spinal cord neurons treated with arachidonic acid. Nicotine attenuated arachidonic acid-induced compromised cell viability and cellular ATP levels in spinal cord neurons. Nicotine exerted these protective effects when used at the concentration of 10 microM and only after a 2-h pre-treatment before a co-exposure to arachidonic acid. Antagonists of nicotinic receptors, such as alpha-bungarotoxin or mecamylamine, only partially reversed these neuroprotective effects of nicotine. In addition, nicotine prevented arachidonic acid-induced activation of caspase-3 activity and apoptotic cell death. These results indicate that nicotine pre-treatment can exert a protective effect against arachidonic acid-induced injury to spinal cord neurons.

Nicotinic systems in central nervous systems disease: degenerative disorders and beyond

Advances in the understanding of the structure, function, and distribution of central nervous system (CNS) nicotinic receptors has provided the impetus for new studies examining the role(s) that these receptors and associated processes may play in CNS functions. Further motivation has come from the realization that such receptors are changed in degenerative neurologic diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Ongoing investigations of the molecular substructure of CNS nicotinic receptors and their pharmacology have begun to open up new possibilities for novel CNS therapeutics with nicotinic agents. Exploiting these possibilities will require understanding of the role(s) that these receptor systems play in human cognitive, behavioral, motor, and sensory functioning. Clues from careful studies of human cognition and behavior are beginning to emerge and will provide direction for studies of potentially therapeutic novel nicotinic agents. Modulation of these receptors with the ultimate goal of producing therapeutic benefits is the goal of these investigations and drug development. This paper will review studies from our laboratory and others that point to the importance of CNS nicotinic mechanisms in normal human cognitive and behavioral functioning as well as their role in disease states. In addition, this paper will examine potential clinical applications of nicotine and/or nicotinic agonists in a variety of CNS disorders with particular emphasis on structural brain disease including: movement disorders such as Parkinson's disease and Tourette's syndrome, cognitive/behavioral disorders such as Alzheimer's disease, attention deficit/hyperactivity disorder, and schizophrenia, and other more speculative applications. Important results from early therapeutic studies of nicotine and/or nicotinic agonists in these disease states are presented. For example, recent studies with nicotine and novel nicotinic agonists such as ABT-418 by our group in AD patients suggest that nicotinic stimulation can improve the acquisition and retention of verbal information and decrease errors. Preliminary results from a series of studies examining the acute and subchronic quantitative effects of nicotine on cognitive and motor functioning in Parkinson's disease suggest that acute nicotine administration and stimulation improves some aspects of cognitive and motor performance and may improve the processing speed of more complex tasks. The most likely near-term applications of novel nicotinic agonists in CNS disorders are likely to be in those disorders that are degenerative in nature, e.g. Parkinson's disease and Alzheimer's disease, or other movement disorders such as Tourette's syndrome. The most likely direct therapeutic role for nicotinic agonists is as augmentation therapy in combination with other agents rather than as monotherapy, except early in disease states or as a prophylactic or preventative treatment.

Neurotrophic effects of central nicotinic receptor activation

A growing number of data have shown that compounds interacting with neuronal nicotinic acetylcholine receptors (nAChRs) have, both in vivo and in vitro, the potential to be neuroprotective and that treatment with nAChR agonists elicit long-lasting improvement of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Epidemiological and clinical studies suggested also a potential neuroprotective/trophic role of (-)-nicotine in neurodegenerative disease, such as Alzheimer's disease and Parkinson's disease. This neuroprotective/trophic role of nAChR activation has been mainly mediated by alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR antagonists, and by potent nAChR agonists recently found displaying efficacy and/or larger selective affinities than (-)-nicotine for neuronal nAChR subtypes. A neurotrophic factor gene regulation by nAChR signalling has been taken into consideration as a possible mechanism involved in neuroprotective/trophic effects of nAChR activation and has given evidence that the fibroblast growth factor (FGF-2) gene is a target for nAChR signalling. These findings suggested that FGF-2 could be involved, in view of its neurotrophic functions, in nAChR mechanisms mediating neuronal survival, trophism and plasticity.

Prolonged exposure to cigarette smoke blocks the neurotoxicity induced by kainic acid in rats

We examined the effects of cigarette smoke (CS) on three parameters associated with kainic acid (KA)-induced neurotoxicity: seizure activity, cell loss in the hippocampus, and increased Fos-related antigen (FRA) expression. Animals were exposed to the main stream of CS from 15 Kentucky 2R1F research cigarettes containing 28.6 mg tar and 1.74 mg nicotine per cigarette, for 10 min a day, 6 days per week, for 4 weeks, using an automatic smoking machine. KA administration (10 mg/kg, i.p.) produced robust behavioral convulsions lasting 4-5 h. Pre-exposure to CS significantly reduced the seizures, mortality, and severe loss of cells in regions CA1 and CA3 of the hippocampus after KA administration. Consistently, pre-exposure to CS significantly attenuated the KA-induced increased FRA immunoreactivity in the hippocampus. In contrast, pretreatment with central nicotinic antagonist, mecamylamine (2 or 10 mg/kg, i.p.) blocked the neuroprotective effects mediated by CS in a dose-dependent manner. These results indicate that CS exposure provides neuroprotection against the KA insult via nicotinic receptor activation.

Chronic nicotine pretreatment protects the blood-brain barrier against nicotine-induced seizures in the rat

This study was designed to investigate the possible protective actions of nicotine on cerebrovascular permeability in convulsions during nicotine-induced seizures. We have measured the permeability changes in the blood-brain barrier (BBB) macroscopically and spectrophotometrically by using Evans blue dye. Specific gravity measurements were also performed to assess brain edema which develops after blood-brain barrier opening. The experiments were carried out on Wistar rats. Rats were divided into two groups. They received acutely a convulsive dose of nicotine 3, 5, 8 and 9 mg kg(-1)i.p. or pretreated with a low dose of nicotine (0.8 mg kg(-1)i. p.) for 21 days followed by the procedure mentioned in the first group. Acute nicotine injection induced a significant increase in blood pressure and Evans-blue passage, despite a decline in specific gravity values. Low doses of chronic nicotine administration markedly reduced both the leakage of dye, and brain water content. Chronic treatment with low doses of nicotine (0.8 mg kg(-1)day(-1)s. c.) lessened the intensity of tonic-clonic seizures observed with a single dose of 3, 5, 8 or 9 mg kg(-1)nicotine. The data presented here demonstrate that nicotine pretreatment results in decreased sensitivity to nicotine-induced seizures in rats.

Increased neurodegeneration during ageing in mice lacking high-affinity nicotine receptors

We have examined neuroanatomical, biochemical and endocrine parameters and spatial learning in mice lacking the beta2 subunit of the nicotinic acetylcholine receptor (nAChR) during ageing. Aged beta2(-/-) mutant mice showed region-specific alterations in cortical regions, including neocortical hypotrophy, loss of hippocampal pyramidal neurons, astro- and microgliosis and elevation of serum corticosterone levels. Whereas adult mutant and control animals performed well in the Morris maze, 22- to 24-month-old beta2(-/-) mice were significantly impaired in spatial learning. These data show that beta2 subunit-containing nAChRs can contribute to both neuronal survival and maintenance of cognitive performance during ageing. beta2(-/-) mice may thus serve as one possible animal model for some of the cognitive deficits and degenerative processes which take place during physiological ageing and in Alzheimer's disease, particularly those associated with dysfunction of the cholinergic system.

Nicotine prevents glutamate-induced proteolysis of the microtubule-associated protein MAP-2 and glutamate neurotoxicity in primary cultures of cerebellar neurons

The aim of this work was to assess whether nicotine prevents glutamate neurotoxicity in primary cultures of cerebellar neurons, to try to identify the receptor mediating the protective effect and to shed light on the step of the neurotoxic process which is prevented by nicotine. It is shown that nicotine prevents glutamate and NMDA neurotoxicity in primary cultures of cerebellar neurons. The protective effect of nicotine is not prevented by atropine, mecamylamine or dihydro-beta-erythroidine, but is slightly prevented by hexamethonium and completely prevented by tubocurarine and alpha-bungarotoxin, indicating that the protective effect is mediated by activation of alpha7 neuronal nicotinic receptors. Moreover, alpha-bungarotoxin potentiates glutamate neurotoxicity, suggesting a tonic prevention of glutamate neurotoxicity by basal activation of nicotinic receptors. Nicotine did not prevent glutamate-induced rise of free intracellular calcium nor depletion of ATP. Nicotine prevents glutamate-induced proteolysis of the microtubule-associated protein MAP-2 and disaggregation of the neuronal microtubular network. The possible mechanism responsible for this prevention is discussed.