Nicotinic acetylcholine receptors (nAChRs) on dopaminergic (DA) and GABAergic (Gaba) projection neurons of the substantia nigra (SN) and ventral tegmental area (VTA) are characterized by single-cell RT-PCR and patch-clamp recordings in slices of rat and wild-type, ␤2Ϫ/Ϫ, ␣4Ϫ/Ϫ, and ␣7Ϫ/Ϫ mice. The eight nAChR subunits expressed in these nuclei, ␣3-7 and ␤2-4, contribute to four different types of nAChR-mediated currents. Most DA neurons in the SN and VTA express two nAChR subtypes. One is inhibited by dihydro-␤-erythroidine (2 M), ␣-conotoxin MII (10 nM), and methyllycaconitine (1 nM) but does not contain the ␣7 subunit; it possesses a putative ␣4␣6␣5(␤2) 2 composition. The other subtype is inhibited by dihydro-␤-erythroidine (2 M) and has a putative ␣4␣5(␤2) 2 composition. Gaba neurons in the VTA exhibit a third subtype with a putative (␣4) 2 (␤2) 3 composition, whereas Gaba neurons in the SN have either the putative (␣4) 2 (␤2) 3 oligomer or the putative ␣4␣6␣5(␤2) 2 oligomer. The fourth subtype, a putative (␣7) 5 homomer, is encountered in less than half of DA and Gaba neurons, in the SN as well as in the VTA. Neurons in the DA nuclei thus exhibit a diversity of nAChRs that might differentially modulate reinforcement and motor behavior.

Nicotine exerts antinociceptive effects by interacting with one or more of the subtypes of nicotinic acetylcholine receptors (nAChRs) that are present throughout the neuronal pathways that respond to pain. To identify the particular subunits involved in this process, we generated mice lacking the alpha4 subunit of the neuronal nAChR by homologous recombination techniques and studied these together with previously generated mutant mice lacking the beta2 nAChR subunit. Here we show that the homozygous alpha4-/- mice no longer express high-affinity [3H]nicotine and [3H]epibatidine binding sites throughout the brain. In addition, both types of mutant mice display a reduced antinociceptive effect of nicotine on the hot-plate test and diminished sensitivity to nicotine in the tail-flick test. Patch-clamp recordings further reveal that raphe magnus and thalamic neurons no longer respond to nicotine. The alpha4 nAChR subunit, possibly associated with the beta2 nAChR subunit, is therefore crucial for nicotine-elicited antinociception.

Ciliary transport is required for ciliogenesis, signal transduction, and trafficking of receptors to the primary cilium. Mutations in inositol polyphosphate 5-phosphatase E (INPP5E) have been associated with ciliary dysfunction; however, its role in regulating ciliary phosphoinositides is unknown. Here we report that in neural stem cells, phosphatidylinositol 4-phosphate (PI4P) is found in high levels in cilia whereas phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2) is not detectable. Upon INPP5E inactivation, PI(4,5)P2 accumulates at the ciliary tip whereas PI4P is depleted. This is accompanied by recruitment of the PI(4,5)P2-interacting protein TULP3 to the ciliary membrane, along with Gpr161. This results in an increased production of cAMP and a repression of the Shh transcription gene Gli1. Our results reveal the link between ciliary regulation of phosphoinositides by INPP5E and Shh regulation via ciliary trafficking of TULP3/Gpr161 and also provide mechanistic insight into ciliary alterations found in Joubert and MORM syndromes resulting from INPP5E mutations.

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 ...

The dorsal striatum is critically involved in a variety of motor behaviours, including regulation of motor activity, motor skill learning and motor response to psychostimulant and neuroleptic drugs, but contribution of D 2 Rstriatopallidal and D 1 R-striatonigral neurons in the dorsomedial (DMS, associative) and dorsolateral (DLS, sensorimotor) striatum to distinct functions remains elusive. To delineate cell type-specific motor functions of the DMS or the DLS, we selectively ablated D 2 R-and D 1 Rexpressing striatal neurons with spatial resolution. We found that associative striatum exerts a population-selective control over locomotion and reactivity to novelty, striatopallidal and striatonigral neurons inhibiting and stimulating exploration, respectively. Further, DMS-striatopallidal neurons are involved only in early motor learning whereas gradual motor skill acquisition depends on striatonigral neurons in the sensorimotor striatum. Finally, associative striatum D 2 R neurons are required for the cataleptic effect of the typical neuroleptic drug haloperidol and for amphetamine motor response sensitization. Altogether, these data provide direct experimental evidence for cell-specific topographic functional organization of the dorsal striatum.

Sleep control is ascribed to a two-process model, a widely accepted concept that posits homoeostatic drive and a circadian process as the major sleep-regulating factors. Cognitive and emotional factors also influence sleep–wake behaviour; however, the precise circuit mechanisms underlying their effects on sleep control are unknown. Previous studies suggest that adenosine has a role affecting behavioural arousal in the nucleus accumbens (NAc), a brain area critical for reinforcement and reward. Here, we show that chemogenetic or optogenetic activation of excitatory adenosine A2A receptor-expressing indirect pathway neurons in the core region of the NAc strongly induces slow-wave sleep. Chemogenetic inhibition of the NAc indirect pathway neurons prevents the sleep induction, but does not affect the homoeostatic sleep rebound. In addition, motivational stimuli inhibit the activity of ventral pallidum-projecting NAc indirect pathway neurons and suppress sleep. Our findings reveal a prominent contribution of this indirect pathway to sleep control associated with motivation.

Concomitant with innervation, genes coding for components of the neuromuscular junction become exclusively expressed in subsynaptic nuclei. A six-base pair element, the N box, can confer synapse-specific transcription to the acetylcholine nicotinic receptor delta and epsilon subunit, utrophin, and acetylcholine esterase genes. N box-dependent synaptic expression is stimulated by the nerve-derived signal agrin and the trophic factor neuregulin, which triggers the MAPK and JNK signaling pathways, to ultimately allow activation by the N box binding Ets transcription factor GABP.

The contribution of neuronal dysfunction to neurodegeneration is studied in a mouse model of spinocerebellar ataxia type 1 (SCA1) displaying impaired motor performance ahead of loss or atrophy of cerebellar Purkinje cells. Presymptomatic SCA1 mice show a reduction in the firing rate of Purkinje cells (both in vivo and in slices) associated with a reduction in the efficiency of the main glutamatergic synapse onto Purkinje cells and with increased A-type potassium current. The A-type potassium channel Kv4.3 appears to be internalized in response to glutamatergic stimulation in Purkinje cells and accumulates in presymptomatic SCA1 mice. SCA1 mice are treated with aminopyridines, acting as potassium channel blockers to test whether the treatment could improve neuronal dysfunction, motor behavior, and neurodegeneration. In acutely treated young SCA1 mice, aminopyridines normalize the firing rate of Purkinje cells and the motor behavior of the animals. In chronically treated old SCA1 mice, 3,4-diaminopyridine improves the firing rate of Purkinje cells, the motor behavior of the animals, and partially protects against cell atrophy. Chronic treatment with 3,4-diaminopyridine is associated with increased cerebellar levels of BDNF, suggesting that partial protection against atrophy of Purkinje cells is possibly provided by an increased production of growth factors secondary to the reincrease in electrical activity. Our data suggest that aminopyridines might have symptomatic and/or neuroprotective beneficial effects in SCA1, that reduction in the firing rate of Purkinje cells can cause cerebellar ataxia, and that treatment of early neuronal dysfunction is relevant in neurodegenerative disorders such as SCA1.