This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 Although some of the neural circuits involved in the acute and chronic effects of nicotine have been identified, much less is known about which native nAChR subtypes are involved in specific physiological functions and pathophysiological conditions.We briefly review some recent findings concerning the structure and function of native nAChRs, focusing on the subtypes identified in the meso-striatal and habenulo-interpeduncular pathways, two systems involved in nicotine reinforcement and withdrawal. We also discuss recent findings concerning the effect of chronic nicotine on the expression of native subtypes.

The specific functions of dopamine D 2 receptor-positive (D 2 R) striatopallidal neurons remain poorly understood. Using a genetic mouse model, we found that ablation of D 2 R neurons in the entire striatum induced hyperlocomotion, whereas ablation in the ventral striatum increased amphetamine conditioned place preference. Thus D 2 R striatopallidal neurons limit both locomotion and, unexpectedly, drug reinforcement.The striatum is critically involved in motor and motivational functions 1,2 . The dorsal striatum, caudate-putamen, is primarily implicated in motor control and the learning of habits and skills, whereas the ventral striatum, the nucleus accumbens (NAc), is essential for motivation and drug reinforcement 1,3 . Striatal dysfunction has been demonstrated in movement disorders, including Parkinson's and Huntington's disease, and in psychiatric disorders, such as schizophrenia and drug addiction 4 .The GABA medium-sized spiny neurons (MSNs, about 95% of striatal neurons), which are targets of the cerebral cortex and the midbrain dopaminergic neurons, form two pathways 5 . The dopamine D 1 receptor-positive (D 1 R) striatonigral MSNs project to the medial globus pallidus and substantia nigra pars reticulata (direct pathway) and coexpress dopamine D 1 receptors and substance P, whereas D 2 R striatopallidal MSNs project to the lateral globus pallidus (indirect pathway) and coexpress dopamine D 2 receptor, adenosine A 2A receptor (A 2A R) and enkephalin (Enk). The specific role of the two efferent pathways in motor and motivational control remains poorly understood. D 1 R striatonigral and D 2 R striatopallidal neurons, which are intermingled and morphologically indistinguishable, cannot be functionally dissociated with techniques such as chemical lesions or surgery and the currently available tools for selective targeting of these populations are unsatisfactory. The Drd1a-and Drd2-egfp transgenic mice obtained by BAC transgenesis 6 have recently shed some light on the role of MSN subpopulations or genes in striatal pathophysiology [7][8][9][10] . In regards to their role in motivation and drug addiction, current studies are focused mostly on the D 1 R striatonigral neurons 2 .To assess the role of D 2 R striatopallidal neurons, we selectively ablated these cells in adult mice by Cre-mediated expression of a diphtheria toxin receptor (DTR) and diphtheria toxin injection 11 (Supplementary Methods online). All animal procedures were approved by the Université Libre de Bruxelles School of Medicine Ethical Committee. We generated mice expressing Cre recombinase under the control of the Adora2a (A 2A R) promoter (Adora2a-cre mice, Supplementary Fig. 1 online) by BAC transgenesis. A 2A R was chosen because it is expressed more in D 2 R neurons than in any other brain area 12 and, in contrast to D 2 R, A 2A R is supposed to not be expressed in striatal cholinergic interneurons and mesostriatal dopaminergic cells. In Adora2a-cre mice mated with a Rosa26-LacZ reporter strain, b-galactosidase staining was only found ...

␣6* nicotinic acetylcholine receptors (nAChRs) are highly and selectively expressed by mesostriatal dopamine (DA) neurons. These neurons are thought to mediate several behavioral effects of nicotine, including locomotion, habit learning, and reinforcement. Yet the functional role of ␣6* nAChRs in midbrain DA neurons is mostly unknown. The aim of this study was to determine the composition and in vivo functional role of ␣6* nAChR in mesolimbic DA neurons of male rats. Immunoprecipitation and immunopurification techniques coupled with cell-specific lesions showed that the composition of ␣6* nAChR in the mesostriatal system is heterogeneous, with (non-␣4)␣6␤2* being predominant in the mesolimbic pathway and ␣4␣6␤2* in the nigrostriatal pathway. We verified whether ␣6* receptors mediate the systemic effects of nicotine on the mesolimbic DA pathway by perfusing the selective antagonists ␣-conotoxin MII (CntxMII) (␣3/␣6␤2* selective) or ␣-conotoxin PIA (CntxPIA) (␣6␤2* selective) into ventral tegmental area (VTA). The intra-VTA perfusion of CntxMII or CntxPIA markedly decreased systemic nicotine-elicited DA release in the nucleus accumbens and habituated locomotion; the intra-VTA perfusion of CntxMII also decreased the rate of nicotine infusion in the maintenance phase of nicotine, but not of food, self-administration. Overall, the results of these experiments show that the ␣6␤2* nAChRs expressed in the VTA are necessary for the effects of systemic nicotine on DA neuron activity and DA-dependent behaviors such as locomotion and reinforcement, and suggest that ␣6␤2*-selective compounds capable of crossing the blood-brain barrier may affect the addictive properties of nicotine and therefore be useful in the treatment of tobacco dependence.

Nicotine, the major psychoactive component of cigarette smoke, modulates neuronal activity to produce Ca 2 þ -dependent changes in gene transcription. However, the downstream targets that underlie the long-term effects of nicotine on neuronal function, and hence behaviour, remain to be elucidated. Here, we demonstrate that nicotine administration to mice upregulates levels of the type 2 ryanodine receptor (RyR2), a Ca 2 þ -release channel present on the endoplasmic reticulum, in a number of brain areas associated with cognition and addiction, notably the cortex and ventral midbrain. Nicotine-mediated RyR2 upregulation was driven by CREB, and caused a long-lasting reinforcement of Ca 2 þ signalling via the process of Ca 2 þ -induced Ca 2 þ release. RyR2 upregulation was itself required for long-term phosphorylation of CREB in a positive-feedback signalling loop. We further demonstrate that inhibition of RyR-activation in vivo abolishes sensitization to nicotine-induced habituated locomotion, a well-characterised model for onset of drug dependence. Our findings, therefore, indicate that gene-dependent reprogramming of Ca 2 þ signalling is involved in nicotine-induced behavioural changes.

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