Nicotine-induced phosphorylation of ERK in mouse primary cortical neurons: evidence for involvement of glutamatergic signaling and CaMKII.

Extracellular signal-regulated kinase (ERK) is activated in vivo in a number of brain areas by nicotine and other drugs of abuse. Here we show that nicotine stimulation of cultured mouse cortical neurons leads to a robust induction of ERK phosphorylation that is dependent on nicotine concentration and duration of exposure. Calcium/calmodulin-dependent protein kinase II activity is necessary for nicotine-induced ERK phosphorylation and neither cAMP-dependent protein kinase or protein kinase C appear to be involved. Activity of glutamate receptors, L-type voltage-gated calcium channels, and voltage-gated sodium channels are also required for nicotine-induced ERK phosphorylation. Nicotine-induced ERK phosphorylation was inhibited by high concentrations of mecamylamine, however it was not blocked by other broad nicotinic acetylcholine receptor (nAChR) inhibitors (including hexamethonium and chlorisondamine) or nAChR subtype selective inhibitors (such as methyllycaconitine, alpha-bungarotoxin, dihydro-beta-erythroidine, and α-conotoxin Au1B). In accord with these pharmacological results, nicotine-induced ERK phosphorylation was normal in primary cultures made from β2 or α7 nAChR subunit knockout mice. The α3/beta4 nAChR agonist cytisine did not induce ERK phosphorylation suggesting that α3/β4 nAChRs were not involved in this process. Taken together, these data define a necessary role for glutamatergic signaling and calcium/calmodulin-dependent protein kinase II in nicotine-induced ERK phosphorylation in cortical neurons and do not provide evidence for the involvement of classical nAChRs

Autism as a disorder of neural information processing: directions for research and targets for therapy

The broad variation in phenotypes and severities within autism spectrum disorders suggests the involvement of multiple predisposing factors, interacting in complex ways with normal developmental courses and gradients. Identification of these factors, and the common developmental path into which theyfeed, is hampered bythe large degrees of convergence from causal factors to altered brain development, and divergence from abnormal brain development into altered cognition and behaviour. Genetic, neurochemical, neuroimaging and behavioural findings on autism, as well as studies of normal development and of genetic syndromes that share symptoms with autism, offer hypotheses as to the nature of causal factors and their possible effects on the structure and dynamics of neural systems. Such alterations in neural properties may in turn perturb activity-dependent development, giving rise to a complex behavioural syndrome many steps removed from the root causes. Animal models based on genetic, neurochemical, neurophysiological, and behavioural manipulations offer the possibility of exploring these developmental processes in detail, as do human studies addressing endophenotypes beyond the diagnosis itself

The Nicotinic Acetylcholine Receptor Dα7 Is Required for an Escape Behavior inDrosophila

Acetylcholine is the major excitatory neurotransmitter in the central nervous system of insects. Mutant analysis of the Dα7 nicotinic acetylcholine receptor (nAChR) ofDrosophila shows that it is required for the giant fiber-mediated escape behavior. The Dα7 protein is enriched in the dendrites of the giant fiber, and electrophysiological analysis of the giant fiber circuit showed that sensory input to the giant fiber is disrupted, as is transmission at an identified cholinergic synapse between the peripherally synapsing interneuron and the dorsal lateral muscle motor neuron. Moreover, we found thatgfA(1), a mutation identified in a screen for giant fiber defects more than twenty years ago, is an allele ofDα7. Therefore, a combination of behavioral, electrophysiological, anatomical, and genetic data indicate an essential role for the Dα7 nAChR in giant fiber-mediated escape inDrosophila

Wheel running during chronic nicotine exposure is protective against mecamylamine‐precipitated withdrawal and up‐regulates hippocampal α7 nACh receptors in mice

Background and purpose Evidence suggests that exercise decreases nicotine withdrawal symptoms in humans; however, the mechanisms mediating this effect are unclear. We investigate, in a mouse model, the effect of exercise intensity during chronic nicotine exposure on nicotine withdrawal severity, binding of α4β2*, α7 nicotinic acetylcholine (nAChR), μ-opioid (μ receptors) and D2 dopamine receptors, and on brain-derived neurotrophic factor (BDNF) and plasma corticosterone levels. Experimental approach Male C57Bl/6J mice treated with nicotine (minipump, 24 mg kg-1 day-1) or saline for 14 days underwent one of three concurrent exercise regimes: 24, 2 or 0 hrs day-1 voluntary wheel running. Mecamylamine-precipitated withdrawal symptoms were assessed on day 14. Quantitative autoradiography of α4β2*, α7 nAChRs, μ receptors and D2 receptor binding was performed in brain sections of these mice. Plasma corticosterone and brain BDNF levels were also measured. Key results Nicotine-treated mice undertaking 2 or 24 hrs day-1 wheel running displayed a significant reduction of withdrawal symptom severity compared with the sedentary group. Wheel-running induced a significant upregulation of α7 nAChR binding in the CA2/3 area of the hippocampus of nicotine-treated mice. Neither exercise nor nicotine treatment affected μ or D2 receptor binding or BDNF levels. Nicotine withdrawal increased plasma corticosterone levels and α4β2* nAChR binding, irrespective of exercise regimen. Conclusions and implications We demonstrate for the first time a profound effect of exercise on α7 nAChRs of nicotine-dependent animals, irrespective of exercise intensity. These findings shed light onto the mechanism underlining the protective effect of exercise in the development of nicotine dependence

Integrative Approach to Pain Genetics Identifies Pain Sensitivity Loci across Diseases

Identifying human genes relevant for the processing of pain requires difficult-to-conduct and expensive large-scale clinical trials. Here, we examine a novel integrative paradigm for data-driven discovery of pain gene candidates, taking advantage of the vast amount of existing disease-related clinical literature and gene expression microarray data stored in large international repositories. First, thousands of diseases were ranked according to a disease-specific pain index (DSPI), derived from Medical Subject Heading (MESH) annotations in MEDLINE. Second, gene expression profiles of 121 of these human diseases were obtained from public sources. Third, genes with expression variation significantly correlated with DSPI across diseases were selected as candidate pain genes. Finally, selected candidate pain genes were genotyped in an independent human cohort and prospectively evaluated for significant association between variants and measures of pain sensitivity. The strongest signal was with rs4512126 (5q32, ABLIM3, P = 1.3×10−10) for the sensitivity to cold pressor pain in males, but not in females. Significant associations were also observed with rs12548828, rs7826700 and rs1075791 on 8q22.2 within NCALD (P = 1.7×10−4, 1.8×10−4, and 2.2×10−4 respectively). Our results demonstrate the utility of a novel paradigm that integrates publicly available disease-specific gene expression data with clinical data curated from MEDLINE to facilitate the discovery of pain-relevant genes. This data-derived list of pain gene candidates enables additional focused and efficient biological studies validating additional candidates

Effects of 6-cyano-7-nitroquinoxaline-2,3-dione on nicotinic receptor subunit transcript expression in the rat brain

The nicotinic cholinergic system exerts potent modulatory effects on glutamatergic neurotransmission, an effect mediated in part by increased glutamate release following activation of presynaptic nicotinic cholinergic receptors. Ionotropic glutamate receptor agonists also stimulate release of acetylcholine, suggesting that these neurotransmitter systems reciprocally regulate one another. We investigated an interface between the nicotinic cholinergic and glutamatergic systems by measuring nicotinic receptor subunit transcript expression following administration of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an antagonist of the AMPA and kainate subtypes of glutamate receptors. Using [ 35 S] in situ hybridization, we measured expression of Α2, Α3, Α4, Α5, Α7, Β2, Β3, and Β4 nicotinic receptor subunit transcripts in the rat forebrain. Following 7 days of treatment with vehicle or CNQX (1 mg/kg/day or 10 mg/kg/day), changes in nicotinic receptor subunit transcript expression were restricted to subunits that form heteromeric receptors. We found increased levels of transcripts for Α2 and Β2 nicotinic receptor subunits in the hippocampus, decreased Α4 subunit transcripts in the medial habenula and amygdala, and increased Β2 subunit transcripts in the septum and piriform cortex. We did not detect changes in expression of transcripts for the Α7 subunit, which forms homomeric nicotinic receptors. Our findings indicate that expression of nicotinic cholinergic receptor subunit transcripts are regulated in a subunit- and region-specific fashion by CNQX, an antagonist of non-NMDA ionotropic glutamate receptors. Synapse 52:62–72, 2004. © 2004 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34997/1/20003_ftp.pd

Effects of Nicotine in the Dopaminergic System of Mice Lacking the Alpha4 Subunit of Neuronal Nicotinic Acetylcholine

The mesostriatal dopaminergic system influences locomotor activity and the reinforcing properties of many drugs of abuse including nicotine. Here we investigate the role of the a4 nicotinic acetylcholine receptor (nAChR) subunit in mediating the effects of nicotine in the mesolimbic dopamine system in mice lacking the a4 subunit. We show that there are two distinct populations of receptors in the substantia nigra and striatum by using autoradiographic labelling with I a-conotoxin MII. These receptors are comprised of the a4, b2 and a6 nAChR subunits and non-a4, b2, and a6 nAChR subunits. Non-a4 subunit-containing nAChRs are located on dopaminergic neurons, are functional and respond to nicotine as demonstrated by patch clamp recordings. In vivo microdialysis performed in awake, freely moving mice reveal that mutant mice have basal striatal dopamine levels which are twice as high as those observed in wild-type mice. Despite the fact that both wild-type and a4 null mutant mice show a similar increase in dopamine release in response to intrastriatal KCl perfusion, a nicotine-elicited increase in dopamine levels is not observed in mutant mice. Locomotor activity experiments show that there is no difference between wild-type and mutant mice in basal activity in both habituated and nonhabituated environments. Interestingly, mutant mice sustain an increase in cocaine-elicited locomotor activity longer than wild-type mice. In addition, mutant mice recover from depressant locomotor activity in response to nicotine at a faster rate. Our results indicate that a4-containing nAChRs exert a tonic control on striatal basal dopamine release, which is mediated by a heterogeneous population of nAChRs