Neuronal Nicotinic Cholinergic Receptors Research Articles

Antagonism of nicotine's action by cocaine analogs

Structure-activity relationships of a number of synthetic cocaine analogs are described comparing their effectiveness in antagonizing the behavioral effects of nicotine in mice with their ability to compete for [3H]mecamylamine, [3H]nicotine, and [3H]3-quinuclidinylbenzilate ([3H]QNB) binding to calf brain membranes. Within a series of phenyltropane carboxylic acid methyl esters the most potent analogues were the 4-I and 4-F-phenyl analogs, while replacement of F by Cl or alkyl groups diminished potency. The isopropyl and phenylcarboxylic acid esters were comparable in potency to the methyl esters. There appeared to be a relationship between the potency of the analogs in inhibiting the dopamine transporter and nicotine antagonism. A good correlation was observed between pharmacologic potency and [3H]mecamylamine binding to brain membranes. It was concluded that the antagonistic action of the cocaine analogs involved an ion channel site on the neuronal nicotinic cholinergic receptors.

Antagonism of nicotine's action by cocaine analogs

Structure-activity relationships of a number of synthetic cocaine analogs are described comparing their effectiveness antagonizing the behavioral effects of nicotine in mice with their ability to compete for [ 3H]mecamylamine, [ 3H]nicotine, and [ 3H]3-quinuclidinylbenzilate ([ 3H]QNB) binding to calf brain membranes. Within a series of phenyltropane carboxylic acid methyl esters the most potent anlogues were the 4-I and 4-F -phenyl analogs, while replacement of F by Cl or alkyl groups diminishhed potency. The isopropyl and phenylcarboxylic acid esters were comparable in potencty to the methyl esters. There appeared to be a relationship between the potency of the analogs in inhibiting the dopamine transporter and nictoine antagonism. A good correlation was observed between pharmacologic potency and [ 3H]mecamylaine binding to brain membranes. It was concluded that the antagonistic action of the cocaine analogs involved an ion channel site on the neuronal nicotinic cholinergic receptors.

Effects of chlorisondamine on nicotinic receptor binding in whole brain and nicotine‐induced changes in locomotor activity in rats

AbstractChlorisondamine, a nicotinic cholinergic receptor antagonist, can block many of the in vivo effects of nicotine for weeks after a single icv injection. The time course of this effect was examined in a single group of rats by assessing the effects of nicotine on locomotor activity at 1, 3, and 6 weeks after the icv administration of 23 nmol of chlorisondamine. The effects of nicotine on locomotor activity were biphasic as has been previously reported, with decreases in activity early in the session and increases in activity later in the session. These effects of nicotine were blocked in chlorisondamine‐treated rats at 1 or 3 weeks but not 6 weeks after administration of chlorisondamine. Nicotinic receptor binding in the brains of chlorisondamine‐treated rats revealed no change in Bmax but a significant increase in affinity (47–59% decrease in Kd) 1, 3, 6, or 7 weeks after treatment. In contrast to its effects on affinity when administered icv, chlorisondamine did not alter binding affinity when added directly to the incubation buffer in vitro. Thus, although chlorisondamine significantly alters neuronal nicotinic cholinergic receptor binding affinity, this effect of chlorisondamine on binding affinity does not appear to be a direct effect of chlorisondamine on the receptor or to match the time course of chlorisondamine blockade of nicotine‐induced changes in locomotor activity. © 1994 Wiley‐Liss, Inc.

Differential effects of pretreatment with nicotine and lobeline on nicotine‐induced changes in body temperature and locomotor activity in mice

AbstractAlthough lobeline and nicotine are both potent ligands at neuronal nicotinic cholinergic receptors, chronic lobeline does not produce the upregulation of nicotinic receptors found with chronic nicotine or the less potent agonist anabasine. Since agonist‐induced receptor upregulation is believed to result from receptor desensitization during chronic treatment, this suggests that lobeline may not desensitize neuronal nicotinic receptors. We addressed this question by comparing lobeline‐ and nicotine‐induced desensitization of the actions of nicotine, using body temperature and locomotor activity as dependent variables. Nicotine pretreatment reduced the hypothermia and locomotor suppression produced by a subsequent nicotine challenge, whereas lobeline pretreatment did not. When tested alone, both nicotine and lobeline reduced locomotor activity and body temperature to a similar degree, but lobeline was significantly less potent. The reductions in activity and temperature produced by nicotine were significantly attenuated in chlorisondamine‐treated mice, whereas treatment with this long‐lasting nicotinic cholinergic antagonist did not alter the effects of lobeline. Thus, nicotine and lobeline appear to differ in their ability to produce desensitization. Furthermore, the effects of these two compounds on locomotor activity and body temperature may be mediated via different mechanisma. © 1994 Wiley‐Liss, Inc.

Protein kinase A regulates nicotinic cholinergic receptors and subunit messenger ribonucleic acids in PC 12 cells.

To delineate mechanisms regulating the expression of neuronal nicotinic cholinergic receptors (nAcChRs), we studied the cAMP-dependent second messenger system. PC 12 cells were grown in (Bu)2cAMP (0.001-1.0 mM) or vehicle for 7 days, and specific [3H] nicotine binding was measured. (Bu)2cAMP (0.1 mM) increased specific binding 2- and 4-fold at 3 and 7 days, respectively, whereas 1.0 mM enhanced binding 4-fold at both time intervals. Cells grown in 8-bromo-cAMP (1.0 mM) showed a 2-fold increase in [3H]nicotine binding at 3 days. Forskolin (10-100 microM), in combination with isobutyl-methylxanthine (1.0 mM), enhanced [3H]nicotine binding 2- to 3-fold at 7 days; forskolin or isobutyl-methylxanthine alone had no effect. Specific [3H] nicotine binding to PC 12 cell mutants (A126.1B2 and A123.7), deficient in cAMP-responsive protein kinase A types I and II, were unaffected by (Bu)2cAMP. Northern gel analysis of nAcChR subunit messenger RNAs showed that the alpha-3, alpha-5, and beta-4 subunits were significantly decreased by (Bu)2cAMP at 4 h. However, (Bu)2cAMP caused an increase in the beta-2 messenger RNA transcript at 4 h, which returned to baseline by 24 h. These studies indicate that the cAMP-protein kinase A system regulates expression of nAcChR by PC 12 cells. These studies also suggest that enhancement of [3H]nicotine binding by activated protein kinase A may not involve synthesis of new receptor subunit proteins.

Nerve growth factor enhances [3H]nicotine binding to a nicotinic cholinergic receptor on PC 12 cells.

Although nicotinic cholinergic agonists have functional effects on PC 12 cells, radioligand-binding sites have not been detected. We, therefore, studied PC 12 cells incubated in the presence of nerve growth factor (NGF) and determined that specific [3H]nicotine-binding sites were induced approximately 2.5-fold in the presence of NGF (50 or 100 ng/ml). Specific binding was maximal between the first (100 ng/ml NGF) and seventh (50 ng/ml NGF) days of treatment and was stable for 2 weeks with addition of NGF every 3 days. Using intact cells, average association and dissociation rates for [3H]nicotine were 0.00021 min-1 nM-1 (n = 2) and 0.048 min-1 (n = 2), respectively, at 4 C, yielding an average apparent Kd of 229 nM. At 22 C, stable equilibrium was not attained during association studies. A similar Kd value for broken cell preparations was obtained by kinetic analysis (i.e. an average association rate of 0.00042 min-1 nM-1 and dissociation rate of 0.087 min-1), yielding an average Kd value of 207 nM (n = 2) at 4 C. By saturation binding analysis of intact cells, an average Kd of 292 nM (n = 2) and a binding capacity (Bmax) of 15,118 molecules/cell were obtained. [3H]Nicotine binding was inhibited on an equimolar basis by L-(-)nicotine and N-methylcarbamylcholine. D-(+) Nicotine was 7-fold less potent, whereas alpha-bungarotoxin, mecamylamine, and atropine showed no significant inhibition. [3H]Nicotine binding was also inhibited quantitatively by mono-specific polyclonal antibodies raised against the predicted alpha 3-subunit sequence (amino acids 130-139) of the rat neuronal nicotinic cholinergic receptor. This study represents the first biochemical characterization of NGF-stimulated nicotine-binding sites on PC 12 cells and confirms previous evidence of the presence of functional nicotinic cholinergic receptors on these cells.