Induction of Dendritic Spines by 2-Containing Nicotinic Receptors

Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, California 92093-0357, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 06/2012; 32(24):8391-400. DOI: 10.1523/JNEUROSCI.6247-11.2012
Source: PubMed


Glutamatergic synapses are located mostly on dendritic spines in the adult nervous system. The spines serve as postsynaptic compartments, containing components that mediate and control the synaptic signal. Early in development, when glutamatergic synapses are initially forming, waves of excitatory activity pass through many parts of the nervous system and are driven in part by a class of heteropentameric β2-containing nicotinic acetylcholine receptors (β2*-nAChRs). These β2*-nAChRs are widely distributed and, when activated, can depolarize the membrane and elevate intracellular calcium levels in neurons. We show here that β2*-nAChRs are essential for acquisition of normal numbers of dendritic spines during development. Mice constitutively lacking the β2-nAChR gene have fewer dendritic spines than do age-matched wild-type mice at all times examined. Activation of β2*-nAChRs by nicotine either in vivo or in organotypic slice culture quickly elevates the number of spines. RNA interference studies both in vivo and in organotypic culture demonstrate that the β2*-nAChRs act in a cell-autonomous manner to increase the number of spines. The increase depends on intracellular calcium and activation of calcium, calmodulin-dependent protein kinase II. Absence of β2*-nAChRs in vivo causes a disproportionate number of glutamatergic synapses to be localized on dendritic shafts, rather than on spines as occurs in wild type. This shift in synapse location is found both in the hippocampus and cortex, indicating the breadth of the effect. Because spine synapses differ from shaft synapses in their signaling capabilities, the shift observed is likely to have significant consequences for network function.

Download full-text


Available from: Darwin K Berg, Oct 07, 2015
26 Reads
  • Source
    • "Regardless of the specific effect(s), nAChRs could regulate GABAergic transmission in at least two ways (not mutually exclusive ). First, nAChRs are known to regulate the development of the excitatory/inhibitory balance by regulating the maturation of both GABAergic transmission (Liu et al., 2006a) and dendritic spines (Lozada et al., 2012), during brain development . Second, because ADNFLE-linked mutations often potentiate the nAChR function, they may cause direct nAChRdependent hyperexcitability of the mature neocortex. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is a partial sleep-related epilepsy which can be caused by mutant neuronal nicotinic acetylcholine receptors (nAChR). We applied multi-electrode array (MEA) recording methods to study the spontaneous firing activity of neocortical cultures obtained from mice expressing or not (WT) an ADNFLE-linked nAChR subunit (β2-V287L). More than 100,000 up-states were recorded during experiments sampling from several thousand neurons. Data were analyzed by using a fast sliding-window procedure which computes histograms of the up-state durations. Differently from the WT, cultures expressing β2-V287L displayed long (10-32 s) synaptic-induced up-state firing events. The occurrence of such long up-states was prevented by both negative (gabazine, penicillin G) and positive (benzodiazepines) modulators of GABAA receptors. Carbamazepine (CBZ), a drug of choice in ADNFLE patients, also inhibited the long up-states at micromolar concentrations. In cultures expressing β2-V287L, no significant effect was observed on the action potential waveform either in the absence or in the presence of pharmacological treatment. Our results show that some aspects of the spontaneous hyperexcitability displayed by a murine model of a human channelopathy can be reproduced in neuronal cultures. In particular, our cultures represent an in vitro chronic model of spontaneous epileptiform activity, i.e., not requiring pre-treatment with convulsants. This opens the way to the study in vitro of the role of β2-V287L on synaptic formation. Moreover, our neocortical cultures on MEA platforms allow to determine the effects of prolonged pharmacological treatment on spontaneous network hyperexcitability (which is impossible in the short-living brain slices). Methods such as the one we illustrate in the present paper should also considerably facilitate the preliminary screening of antiepileptic drugs (AEDs), thereby reducing the number of in vivo experiments.
    Frontiers in Neural Circuits 07/2014; 8:87. DOI:10.3389/fncir.2014.00087 · 3.60 Impact Factor
  • Source
    • "At the synaptic level, recent studies have identified nicotinic receptor-dependent alterations in development of glutamatergic synapses (Lozada et al., 2012a; Morley and Mervis, 2013). Activation of postsynaptic α 7 -nicotinic receptors in cultured neurons or slice preparations promotes glutamatergic synapse formation, whereas knockout of the α 7 subunit in mice decreases the number of dendritic spines (Lozada et al., 2012b) and glutamatergic synapses, suggesting that cholinergic signaling through this nicotinic receptor subtype is normally important in modulating the number of excitatory synapses. Inhibitory effects of CBs would be expected to affect formation of glutamatergic synaptic transmission and plasticity of neuronal networks. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cannabinoids are among the earliest known drugs to humanity. Cannabis plant contains various phytochemicals that bind to cannabinoid receptors. In addition, synthetic and endogenously produced cannabinoids (endocannabinoids) constitute other classes of cannabinoid receptor ligands. Although many of the pharmacological effects of these cannabinoids are mediated by the activation of cannabinoid receptors, recent studies indicate that cannabinoids also modulate the functions of various integral membrane proteins including ion channels, receptors, neurotransmitter transporters, and enzymes by mechanism(s) not involving the activation of known cannabinoid receptors. Currently, the mechanisms of these effects were not fully understood. However, it is likely that direct actions of cannabinoids are closely linked to their lipophilic structures. This report will focus on the actions of cannabinoids on nicotinic acetylcholine receptors and will examine the results of recent studies in this field. In addition some mechanistic approaches will be provided. The results discussed in this review indicate that, besides cannabinoid receptors, further molecular targets for cannabinoids exist and that these targets may represent important novel sites to alter neuronal excitability.
    European journal of pharmacology 03/2014; 731(1). DOI:10.1016/j.ejphar.2014.03.010 · 2.53 Impact Factor
  • Source
    • "Establishing molecular function classifications with PAN- THER pathway analysis [29] reveals that the primary interactions of mature b2 * nAChRs occur with structural proteins that are part of, and regulate the growth and assembly of, the cytoskeleton. These data are consistent with studies showing that b2 * nAChRs are involved in production and maintenance of dendritic spines during development [37]. Of particular interest are the cytoskeletal proteins that appear to Figure 3 Frequency distribution of correlations for proteins associated with b2 subunit Frequency distribution of calculated correlations between relative abundances of putative interacting proteins and b2 nAChR log 2 MRIPA was shown. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Nicotine, the primary psychoactive component in tobacco smoke, produces its behavioral effects through interactions with neuronal nicotinic acetylcholine receptors (nAChRs). α4β2 nAChRs are the most abundant in mammalian brain, and converging evidence shows that this subtype mediates the rewarding and reinforcing effects of nicotine. A number of rare variants in the CHRNA4 gene that encodes the α4 nAChR subunit have been identified in human subjects and appear to be underrepresented in a cohort of smokers. We compared three of these variants (α4R336C, α4P451L and α4R487Q) to the common variant to determine their effects on α4β2 nAChR pharmacology. We examined [3H]-epibatidine binding, interacting proteins and phosphorylation of the α4 nAChR subunit with LC-MS/MS in HEK 293 cells, and voltage-clamp electrophysiology in Xenopus oocytes. We observed significant effects of the α4 variants on nAChR expression, subcellular distribution, and sensitivity to nicotine-induced receptor upregulation. Proteomic analysis of immunopurified α4β2 nAChRs incorporating the rare variants identified considerable differences in the intracellular interactomes due to these single amino acid substitutions. Electrophysiological characterization in Xenopus oocytes revealed alterations in the functional parameters of activation by nAChR agonists conferred by these α4 rare variants, as well as shifts in receptor function following incubation with nicotine. Taken together, these experiments suggest that genetic variation at CHRNA4 alters the assembly and expression of α4β2 nAChRs resulting in receptors that are more sensitive to nicotine exposure than those assembled with the common α4 variant. The changes in nAChR pharmacology could contribute to differences in responses to smoked nicotine in individuals harboring these rare variants.
    Journal of Pharmacology and Experimental Therapeutics 01/2014; 348(3). DOI:10.1124/jpet.113.209767 · 3.97 Impact Factor
Show more