The nicotinic modulation of [(3)H]D-aspartate outflow in primary cultures of rat neocortical neurons: effect of acute and long term nicotine treatment

The effects on steroidogenesis and histopathology of adult male Japanese quails (Coturnix coturnix japonica) testis following pre-pubertal exposure to di(n-butyl) phthalate (DBP)

In the present study, we have investigated the effects of 30-day dietary (pre-pubertal) exposure to different doses (0 (control), 1, 10, 50, 200 and 400 mg/kg bodyweight/day) of di(n-butyl) phthalate (DBP) on Leydig cells of adult male Japanese quails by quantifying the transcript levels for P450 side-chain cleavage (p450scc), P450c17 (CYP17), and 3β- and 17β-hydroxysteroid dehydrogenase (hsd) using quantitative (real-time) polymerase chain reaction (qRT-PCR). In addition, the plasma testosterone levels were analysed using radioimmunoassay (RIA) and testis was examined for evidence of gross pathology and histopathology. Our data showed that pre-pubertal exposure to DBP produced alterations in testicular architecture as evident by poorly developed or mis-shaped testis, and altered spermatogenesis due to tubular degeneration and atrophy of seminiferous tubules especially in the high DBP dose (200 and 400 mg/kg) treated groups. In addition, DBP altered several key enzymes involved in testicular steroidogenesis pathways in an apparent dose-dependent manner. For example, biphasic effects of DBP were observed for P450scc and 3β-hsd mRNA, that were generally increasing at low dose 10 mg/kg, and thereafter, an apparent dose-dependent decrease between 50 and 400mg/kg. The steroidogenic acute regulatory (StAR) protein was at the lowest detectable limits and therefore not quantifiable. These effects did not parallel the non-significant changes observed for plasma testosterone levels. The present data is consistent with previous reports showing that DBP modulates Leydig cell steroidogenesis in several species, with a potential negative effect on reproduction in those avian species that are vulnerable to endocrine disrupting chemicals.

Effects of mecamylamine on alcohol consumption and preference in male C57BL/6J mice

Alcohol and nicotine (in the form of tobacco) are 2 commonly used recreational drugs and studies show a high correlation between tobacco use and alcohol consumption. In the present study, using C57BL/6J mice, we investigated the ability of mecamylamine (a nicotinic antagonist) to reduce alcohol consumption and alcohol preference with free 24-hour access using a 2-bottle choice test drinking procedure. Male C57BL/6J mice were individually housed and acclimatized to 10% alcohol. Immediately following the last day of alcohol acclimatization, the mice (n = 5/group) received subcutaneous injections of mecamylamine (0.5, 1 and 2 mg/kg) or saline consisting of either intermittent (3 injections given every other day) or daily (injections on all 5 days) exposures. Fluid consumption (alcohol and water) was recorded daily. The results showed that mecamylamine significantly reduced alcohol consumption and alcohol preference in both phases of intermittent and daily drug exposures, while the total fluid consumption was unchanged. These results provide further support that mecamylamine is effective in reducing alcohol consumption and preference, and nicotinic-receptor-based drugs could further be explored as potential treatments for alcoholism.

Presynaptic α7 and non-α7 nicotinic acetylcholine receptors modulate [3H]d-aspartate release from rat frontal cortex in vitro

The presynaptic nicotinic modulation of glutamatergic transmission in the CNS has been associated with activation of the alpha7 subtype of nicotinic acetylcholine receptor (nAChR) in sub-cortical regions, whereas in the frontal cortex, non-alpha7 nAChRs have been implicated. The aim of this investigation was to directly characterise nAChR-evoked release of excitatory amino acids from rat frontal cortex, by monitoring the release of [3H]D-aspartate from superfused synaptosomes or minces. Co-administration of a nAChR agonist with a depolarising stimulus enhanced [3H]D-aspartate release above the effect of depolarising agent alone. This enhancement was blocked by the nicotinic antagonist mecamylamine. Other experiments revealed that in the absence of a depolarising stimulus, the nAChR agonists nicotine, epibatidine and anatoxin-a could evoke the release of [3H]D-aspartate in a Ca2+- and concentration-dependant manner. Differential sensitivity to the alpha7- and beta2*-selective nAChR antagonists alpha-bungarotoxin (alpha-Bgt) and dihydro-beta-erythroidine (DHbetaE) implicated two nAChR subtypes (alpha7 and beta2*), and this was supported by using the subtype-selective agonists choline (10 mM; alpha7 selective, blocked by alpha-Bgt but not by DHbetaE) and 5-Iodo-A-85380 (10 nM; beta2*-selective, blocked by DHbetaE but not by alpha-Bgt). Immunocytochemistry showed that alpha-Bgt labelling was associated with structures immunopositive for vesicular glutamate transporters, in both frontal cortex sections and synaptosome preparations, supporting the presence of alpha7 nAChR on glutamatergic terminals in rat frontal cortex.

Effects of nociceptin/orphanin FQ and endomorphin-1 on glutamate and GABA release, intracellular [Ca2+] and cell excitability in primary cultures of rat cortical neurons

The effects of nociceptin/orphanin FQ (N/OFQ) and endomorphin-1 (EM-1) on glutamate and GABA release, intracellular calcium, neuronal excitability and glutamate current were investigated in rat primary cortical neuronal cultures. Through their specific receptors N/OFQ and EM-1 (0.02-1 microM) inhibited the electrically evoked outflow of [3H]D-aspartate at most to -50% and that of [3H]GABA to -30%. In addition, at 1 microM, both peptides induced a decrease of the firing rate caused by electrical depolarization. N/OFQ 1-10 microM did not influence either the electrically evoked calcium influx or the glutamate-evoked currents, whereas EM-1 1 microM significantly inhibited them. Thus, in cortical neurons in culture, both N/OFQ and EM-1 inhibited the secretory process and neuronal excitability but EM-1 also affected calcium influx and cell body responsiveness to glutamate. Consequently, EM-1 appeared to dampen this excitatory signal more then N/OFQ did.

ABT-089: pharmacological properties of a neuronal nicotinic acetylcholine receptor agonist for the potential treatment of cognitive disorders

ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine dihydrochloride salt] is a selective neuronal nicotinic receptor (NNR) modulator with cognitive enhancing properties in animal models of cognitive functioning. Amongst NNR subtypes, ABT-089 shows selectivity for the cytisine binding site on the alpha4beta2 receptor subtype as compared to the alpha-bungarotoxin (alpha-BgT) binding sites on the alpha7 and alpha1beta1deltagamma receptor subtypes. In functional in vitro electrophysiological and cation flux assays, ABT-089 displays differential activity including agonism, partial agonism and antagonism depending upon the NNR subtype and assay. ABT-089 is as potent and efficacious as (-)-nicotine at evoking acetylcholine (ACh) release from hippocampal synaptosomes. Furthermore, ABT-089 is neuroprotective against excitotoxic glutamate insults, with even greater potency seen after chronic treatment. Similarly, ABT-089 is effective in models of cognitive functioning, including enhancement of baseline functioning as well as improvement of impaired cognitive functioning seen following septal lesioning and natural aging. In neuroprotective assays the compound is most potent by chronic administration. In stark contrast to the positive effects in the cognitive models, ABT-089 shows little propensity to induce adverse effects such as ataxia, hypothermia, seizures, cardiovascular or gastrointestinal side effects. Together these data suggest that ABT-089 is a NNR modulator with the potential for treating cognitive disorders with markedly limited adverse cardiovascular and gastrointestinal side effects.

Proconvulsant-induced seizures in alpha(4) nicotinic acetylcholine receptor subunit knockout mice

The genetic basis of a number of epilepsy syndromes has been identified but the precise mechanism whereby these mutations produce seizures is unknown. Three mutations of the alpha(4) subunit of the neuronal nicotinic acetylcholine receptor (nAChR) have been identified in autosomal dominant nocturnal frontal lobe epilepsy. In vitro studies of two mutations suggest an alteration of receptor function resulting in decreased ion channel current flow. We investigated the response of alpha(4) nAChR subunit knockout mice to the gamma-aminobutyric acid (GABA) receptor antagonists; pentylenetetrazole (PTZ) and bicuculline (BIC), the glutamate receptor agonist kainic acid (KA), the glycine receptor antagonist strychnine and the K(+) channel blocker 4-aminopyridine (4-AP). Mutant (Mt) mice had a greater sensitivity to PTZ and BIC, with an increase in major motor seizures and seizure-related deaths. Furthermore, Mt mice were more sensitive to KA and strychnine, but the effects were much smaller compared to those seen with the GABA receptor antagonists. Paradoxically, Mt mice appeared to be relatively protected from 4-AP-induced major motor seizures and death. The results show that a functional deletion of the alpha(4) nAChR subunit in vivo is associated with a major increase in sensitivity to GABA receptor blockers.

Involvement of nicotinic acetylcholine receptors in suppression of antimicrobial activity and cytokine responses of alveolar macrophages to Legionella pneumophila infection by nicotine

Although nicotine is thought to be one of the major immunomodulatory components of cigarette smoking, how nicotine alters the host defense of the lung and, in particular, immune responses of alveolar macrophages, which are critical effector cells in the lung defense to infection, is poorly understood. Nicotinic acetylcholine receptors (nAChRs) are the receptor for nicotine and may be involved in the modulation of macrophage function by nicotine. In this study, therefore, nicotine-induced suppression of antimicrobial activity and cytokine responses of alveolar macrophages mediated by nAChRs to Legionella pneumophila, a causative agent for pneumonia, were examined. The murine MH-S alveolar macrophage cell line cells expressed the messages for alpha4 and beta2 subunits of nAChRs, but not alpha7 subunits, determined by RT-PCR. The nicotine treatment of MH-S alveolar macrophages after infection with L. pneumophila significantly enhanced the replication of bacteria in the macrophages and selectively down-regulated the production of IL-6, IL-12, and TNF-alpha, but not IL-10, induced by infection. These effects were completely blocked by a nonselective antagonist, d-tubocurarine, for nAChRs, but not by a selective antagonist, alpha-bungarotoxin, for alpha7-nAChRs. Furthermore, the stimulation of nAChRs with another agonist, 1,1-dimethyl-4-phenylpiperazinium iodide, showed the same effects, which were blocked by the antagonist d-tubocurarine, on the bacterial replication and cytokine regulation with that of nicotine. Thus, the results revealed that nAChRs, the major exogenous ligands of which are nicotine, are involved in the regulation of macrophage immune function by nicotine and may contribute to the cigarette-induced risk factors for respiratory infections in smokers.