The dynamic expression of AMPA-type glutamate receptors (AMPA-R) at synapses is a key determinant of synaptic plasticity, including neuroadaptations to drugs of abuse. Recently, microRNAs (miRNAs) have emerged as important posttranscriptional regulators of synaptic plasticity, but whether they target glutamate receptors to mediate this effect is not known. Here we used microarray screening to identify miRNAs that regulate synaptic plasticity within the nucleus accumbens, a brain region critical to forming drug-seeking habits. One of the miRNAs that showed a robust enrichment at medium spiny neuron synapses was miR-181a. Using bioinformatics tools, we detected a highly conserved miR-181a binding site within the mRNA encoding the GluA2 subunit of AMPA-Rs. Overexpression and knockdown of miR-181a in primary neurons demonstrated that this miRNA is a negative posttranscriptional regulator of GluA2 expression. Additionally, miR-181a overexpression reduced GluA2 surface expression, spine formation, and miniature excitatory postsynaptic current (mEPSC) frequency in hippocampal neurons, suggesting that miR-181a could regulate synaptic function. Moreover, miR-181a expression was induced by dopamine signaling in primary neurons, as well as by cocaine and amphetamines, in a mouse model of chronic drug treatment. Taken together, our results identify miR-181a as a key regulator of mammalian AMPA-type glutamate receptors, with potential implications for the regulation of drug-induced synaptic plasticity.

By acting through retinal nicotinic acetylcholine receptors (nAChRs), acetylcholine plays an important role in the development of both the retina and central visual pathways. Ligand binding and immunoprecipitation studies with subunit-specific antibodies showed that the expression of ␣Bungarotoxin (␣Bgtx) and high-affinity epibatidine (Epi) receptors is regulated developmentally and increases until postnatal day 21 (P21). The increase in Epi receptors is caused by a selective increase in the subtypes containing the ␣2, ␣4, ␣6, ␤2, and ␤3 subunits. Immunopurification studies revealed three major populations of Epi receptors on P21: ␣6* receptors (26%), which contain the ␣6␤3␤2, ␣6␣4␤3␤2, and ␣6␣3/␣2␤3␤2 subtypes; ␣4(non-␣6)* receptors (60%), which contain the ␣2␣4␤2 and ␣4␤2 subtypes; and (non-␣4/non-␣6)* receptors (14%), which contain the ␣2␤2/␤4 and ␣3␤2/␤4 subtypes. These three populations can be pharmacologically discriminated using ␣conotoxin MII, which binds the ␣6* population with high affinity. In situ hybridization showed that the transcripts for all of the subunits are heterogeneously distributed throughout retinal neurons at P21, with ␣3, ␣6, and ␤3 transcripts preferentially concentrated in the ganglion cell layer, ␣5 in the inner nuclear layer, and ␣4 and ␤2 distributed rather homogeneously. To investigate whether nAChR expression is affected by visual experience, we also studied dark-reared P21 rats. Visual deprivation had no effect on the expression of ␣Bgtx receptors or the developmentally regulated Epi receptors containing the ␣2, ␣6, and/or ␤3 subunits but significantly increased the expression of the Epi receptors containing the ␣4 and ␤2 subunits. Overall, this study demonstrates that the retina is the rat neural region that expresses the widest array of nAChR subtypes. These receptors have a specific distribution, and their expression is finely regulated during development and by visual experience.The nicotinic acetylcholine receptors (nAChRs) in vertebrate retina play a role in signaling at the earliest stages of development (long before there is any evidence of synaptic transmission) and also later during neuronal growth and synaptogenesis (Zhou, 2001;Feller, 2002). Neuronal nAChRs are cationic channels whose opening is physiologically controlled by acetylcholine (ACh) neurotransmitter. They form a heterogeneous family of pentameric oligomers made up of combinations of subunits encoded by at least 12 different genes. Although there are many subtypes consisting of different subunits, depending on their phylogenetic, functional, and pharmacological properties (Gotti et al., 1997a;Corringer et al., 2000;Hogg et al., 2003), two main classes have been identified: the ␣Bungarotoxin (␣Bgtx)-sensitive receptors made up of the ␣7, ␣8, ␣9, and/or ␣10 subunits, which can form homomeric or heteromeric receptors; and the ␣Bgtx-insensitive receptors consisting of the ␣2 to ␣6 and ␤2 to ␤4 subunits, which only form heteromeric receptors that bind epibatidine (Epi) with a high affinity. The number ...

Regulation of Arpc3 by miRNA alters dendritic spine morphology.

SUMMARY A critical feature of neural networks is that they balance excitation and inhibition to prevent pathological dysfunction. How this is achieved is largely unknown, though deficits in the balance contribute to many neurological disorders. We show here that a microRNA (miR-101) is a key orchestrator of this essential feature, shaping the developing network to constrain excitation in the adult. Transient early blockade of miR-101 induces long-lasting hyper-excitability and persistent memory deficits. Using target-site blockers in vivo, we identify multiple developmental programs regulated in parallel by miR-101 to achieve balanced networks. Repression of one target, NKCC1, initiates the switch in GABA signaling, limits early spontaneous activity, and constrains dendritic growth. Kif1a and Ank2 are targeted to prevent excessive synapse formation. Simultaneous de-repression of these three targets completely phenocopies major dysfunctions produced by miR-101 blockade. Our results provide new mechanistic insight into brain development and suggest novel candidates for therapeutic intervention.

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.

SUMMARY Changes in social preference of amphibian larvae result from sustained exposure to kinship odorants. To understand the molecular and cellular mechanisms of this neuroplasticity, we investigated the effects of olfactory system activation on neurotransmitter (NT) expression in accessory olfactory bulb (AOB) interneurons during development. We show that protracted exposure to kin or non-kin odorants changes the number of dopamine (DA)- or gamma aminobutyric acid (GABA)-expressing neurons, with corresponding changes in attraction/aversion behavior. Changing the relative number of dopaminergic and GABAergic AOB interneurons or locally introducing DA or GABA receptor antagonists alters kinship preference. We then isolate AOB microRNAs (miRs) differentially regulated across these conditions. Inhibition of miR-375 and miR-200b reveals that they target Pax6 and Bcl11b to regulate the dopaminergic and GABAergic phenotypes. The results illuminate the role of NT switching governing experience-dependent social preference.

Astrocytes, an abundant form of glia, are known to promote and modulate synaptic signaling between neurons. They also express α7-containing nicotinic acetylcholine receptors (α7-nAChRs), but the functional relevance of these receptors is unknown. We show here that stimulation of α7-nAChRs on astrocytes releases components that induce hippocampal neurons to acquire more a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors post-synaptically at glutamatergic synapses. The increase is specific in that no change is seen in synaptic NMDA receptor clusters or other markers for glutamatergic synapses, or in markers for GABAergic synapses. Moreover, the increases in AMPA receptors on the neuron surface are accompanied by increases in the frequency of spontaneous miniature synaptic currents mediated by the receptors and increases in the ratio of evoked synaptic currents mediated by AMPA versus NMDA receptors. This suggests that stimulating α7-nAChRs on astrocytes can convert ‘silent’ glutamatergic synapses to functional status. Astrocyte-derived thrombospondin is necessary but not sufficient for the effect, while tumor necrosis factor-α is sufficient but not necessary. The results identify astrocyte α7-nAChRs as a novel pathway through which nicotinic cholinergic signaling can promote the development of glutamatergic networks, recruiting AMPA receptors to post-synaptic sites and rendering the synapses more functional.

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