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A7 Receptors

The nAChR subtypes vary in response to pharmacological manipulation. The a7 receptors have a low affinity for nicotine and are sensitive to a-bungarotoxin (a-BTX) antagonism, whereas the heteromeric nAChRs are not.14 The p2 containing (p2 asterisk denotes the presence of additional subunits) nAChRs have the highest affinity for nicotine binding and some selectivity for antagonism... [Pg.24]

Nicotine is an agonist at the nicotinic acetylcholine receptor (nAChR). Activation of this receptor depolarizes target cells (see Ch. 11). nAChRs are composed of five subunits surrounding a central ion-channel pore. Twelve different nicotinic receptor subunits are expressed in the nervous system (a2-oclO and (32—134). Of these, a subset is expressed in the VTA (a3-a7 and P2—134). It is thought that a7 receptors form homomeric receptors a3, a4 and a6 form heteromeric channels with 02 or 04 and a5 and 03 can associate with other a/0 pairs. Studies in knockout mice implicate several subunits in the ability of nicotine to modulate dopamine neurons (a4, a6, a7, 02, 03) but... [Pg.921]

Striatum, Flippocampus, Thalamus Relatively few studies have investigated the expression of AChRs outside the cortex in schizophrenia ( Table 4.2-7). However, studies done in the striatum, the hippocampus, and the thalamus have identified changes similar to those in the cortex including increased (striatum), unaltered (thalamus), or decreased (striatum, hippocampus) binding of [3H] nicotine to 4P2 type nAChRs in schizophrenia (Leonard et al., 1998 Court et al., 1999 Breese et al., 2000 Court et al., 2000). Supporting decreased expression of nicotinic type receptor in the striatum and the hippocampus, [3H]cytosine and [3H]epibatidine were similarly reported decreased in schizophrenia (Freedman et al., 1995 Breese et al., 2000 Durany et al., 2000). Additionally, a7 receptor binding in the hippocampus and the thalamus, as well as a.7 protein expression in the striatum, was reported to be decreased in this illness (Freedman et al., 1995 Leonard et al., 1998 Court et al., 1999). [Pg.469]

Structural Requirements for nAChR Ligands. Schmitt (211) summarized the general structural requirements for binding at the of4/32 and a7 receptors (the most abundant nAChRs subtypes in the CNS) as follows. [Pg.456]

The first broad functional distinction is between homomeric-type and heteromeric-type receptors (the edges are blurred when we take into account the existence of a7 receptors, although the distinction is clear for recombinant receptors). The most distinctive properties for homomeric receptors in this context are their sensitivity to the antagonist effects of a-bungarotoxin and methyllycaconitine (the latter selective at concentrations up to approximately 1 nM) and their faster desensitization and higher calcium permeability than those of heteromeric a/]3 receptors. [Pg.385]

Nicotinic receptors formed by a 7 or a 9 are hy far the most calcium permeant. Thus for recombinant or native aT-like receptors reported values for relative calcium permeability range from 6 to 20 (147-150), with fractional current carried by calcium as high as 20%( 151 ) for work on the M2 determ inants of this high calcium permeability, see Bertrand et al. (147). This would mean that a7 receptors are almost as calcium permeable as the NMDA-type of glutamate receptor. Equally high calcium permeability was reported for a9-type receptors (152,153), expressed alone or withalO (121). [Pg.387]

Finally, changes in extracellular calcium (in the low millimolar range) can modulate nicotinic responses. Increases in calcium concentration strongly enhance macroscopic responses of either native or recombinant heteromeric nicotinic receptors to low ACh concentrations, decreasing the BC value of ACh and increasing the Hill slope of the curve (133, 140, 160, 161). This effect is not seen with muscle embryonic channels (133). In native a7 receptors the modulation has been reported to be biphasic, with potentiation at submillimolar calcium concentrations and depression at higher concentrations (162). The sequence determinants for this effect have... [Pg.387]

The M2 determinants for inward rectification have been investigated in recombinant chick a7 receptors by Forster and Bertrand (172). [Pg.388]

It is interesting to note that an endogenous molecule related to snake neurotoxins, lynxl, is present in the rodent CNS, where it is surface anchored and expressed by neurons positive for nicotinic a4)32 and a7 receptors. In recombinant systems, the effects of coexpressing this molecule with a4jS2 receptors are complex increases in EC50 and in the relative fre-... [Pg.394]

Conversely, a-conotoxin 1ml (GlyCysCysSerAspProArgCysAlaTryArg-CysNH2 [134]) from the cone snaU Conus imperials preferentially inhibits the homomeric ay- and Og-receptors, but not, like a-bungarotoxin, receptor combinations composed of aj-subunits. Selectivities across species have been documented as well Whereas the poison from the many-banded krait acts primarily on mammalian nerve cells, a-conotoxin Iml blocks for example also the nicotinic a7-receptors of locusts (Locusta migratoria). [Pg.732]


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See also in sourсe #XX -- [ Pg.311 , Pg.312 , Pg.314 , Pg.317 , Pg.322 , Pg.419 ]




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