Binding Of 3H-quinuclidinyl Benzilate Research Articles

Increase in muscarinic receptors in rat intestine by Thyrotropin Releasing Hormone (TRH)

The effect of Thyrotropin Releasing Hormone (TRH) on the contractile activity elicited by acetylcholine and electric stimulation in the rat ileum terminalis was investigated. TRH did not show any intrinsic contractile activity but, after a 30 minutes latency period, the peptide caused a shift to the left of the dose-response curve for both acetylcholine and electric stimulation. The binding of 3H-quinuclidinylbenzilate ( 3H-QNB) assayed on ileum slices disclosed that the addition of TRH increased the number of muscarinic cholinergic receptors without changes in affinity when incubation was performed at pH 7.8, but no effect of TRH was demonstrated at pH 7.4. Therefore, in spite of its neural and direct actions on intestine motor activity, TRH may affect the acetylcholine induced contraction by increasing the number of muscarinic receptors at a specific pH.

Increased muscarinic cholinergic receptors in prefrontal cortices of medicated schizophrenics

Alterations in 3H-quinuclidinyl benzilate binding sites associated with muscarinic cholinergic receptors were investigated in orbito-frontal and medial frontal cortices from 12 schizophrenics, 6 on-drug and 6 off-drug cases, and from 10 controls. Significantly lower affinities of the sites were found in both areas of schizophrenics than controls. An increase in receptor number was shown only in the orbito-frontal cortex from schizophrenics. On-drug group of schizophrenics did, however, show a significant increase in receptor number and a significant decrease in affinity in both areas, while there were no significant differences in any binding parameters of off-drug schizophrenics from controls. Also in the caudate the similar results were obtained. It is, thus, concluded that alterations in muscarinic cholinergic receptors of schizophrenic patients result from long-term medication with antimuscarinic actions.

Effect of urea-treatment on agonist binding affinity of the muscarinic acetylcholine receptor

Urea-treatment of the microsome fraction of the heart of guinea-pigs caused selective reduction in the apparent affinity of an agonist (carbachol), but not an antagonist (atropine), to muscarinic acetylcholine receptors (mAChR), measured as inhibition of binding of 3H-quinuclidinyl benzilate ( 3H-QNB). This effect was similar to that of Gpp(NH)p. The effects of urea-treatment and Gpp(NH)p were not additive. On the other hand, treatment of the microsome fraction with 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB) increased the apparent affinity of agonist, but not antagonist. The effect of DTNB predominated over those of urea-treatment and Gpp(NH)p, when these treatments were combined with DTNB.

Increase in muscarinic acetylcholine receptors in mouse intestine by hexamethonium treatment

The effects of hexamethonium (C6) administration on muscarinic acetylcholine receptors (mACh-R) in the intestine and brain of mice were investigated. Mice were treated with C6 with an osmotic mini-pump (330 mg/kg/day) for one week and then the binding of 3H-quinuclidinylbenzilate (3H-QNB) in the intestine and brain were assayed. This treatment increased the maximum specific binding (Bmax) of 3H-QNB from 160 to 320 fmoles/mg protein in the ileum and from 190 to 340 fmoles/mg protein in the rectum, without affecting the KD values in these regions. On the contrary, C6 treatment did not change the Bmax or KD value in brain tissues. This C6 treatment increased the sensitivity of the contractile response of the intestine to muscarinic agonists, possibly by increasing mACh-R.

Effects of trypsin-treatment on agonist binding affinity to the muscarinic acetylcholine receptor

Trypsin-treatment of the microsome fraction of the ileum and the synaptic membrane fraction of the cerebral cortex of guinea-pig caused selective reduction in the apparent affinity of an agonist (carbachol), but not an antagonist (atropine), to muscarinic acetylcholine receptors (mAChR), measured as inhibition of binding of 3H-quinuclidinyl benzilate ( 3H-QNB). This effect was similar to that of Gpp(NH)p. The effects of trypsin and Gpp(NH)p were not additive. On the other hand, treatment of these fractions with 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) increased the apparent affinity of agonist, but not antagonist. The effect of DTNB predominated over those of trypsin and Gpp(NH)p, when the fractions were treated with two reagents simultaneously.

Neural regulation of muscarinic receptors in chick expansor secundariorum muscle.

We have recently observed the loss of muscarinic receptors from a smooth muscle of the chicken wing, the expansor secundariorum, during post-hatch development1. The nerve supplying the muscle has been shown to consist mainly of sympathetic fibres that, when stimulated, cause muscle contraction by the release of noradrenaline and subsequent activation of α-adrenoreceptors. Although no acetylcholine release has been detected in isolated nerve–muscle preparations2, the presence of a cholinergic input has not been clearly excluded. Kuromi and Hagihara2 observed that atropine was ineffective in blocking the nerve stimulation-induced contraction of the muscle, whereas phentolamine partly and guanethedine totally abolished the contraction. We have now examined the effect of denervation of the muscle 1 day after hatch on the binding of 3H-quinuclidinyl benzilate (3H-QNB), a radioligand for muscarinic receptors3,4. Our results indicate that the normal loss of muscarinic receptors from the expansor secundariorum is prevented by denervation. This observation is important as it demonstrates the regulation of a receptor population by a nerve supply that apparently does not release the corresponding transmitter.

The effects of long-term ethanol on brain receptors for dopamine, acetylcholine, serotonin and noradrenaline

Rats were treated with ethanol for 11–15 days, after which the brain neurotransmitter receptors for dopamine, acetylcholine, serotonin and noradrenaline were measured. The rats were intubated at 12 h intervals with 4 g/kg ethanol, and sacrificed 10 h after the last intubation. After ethanol treatment, the specific binding of 3H-haloperidol to dopamine receptors was significantly decreased in the mesolimbic areas by 20 ± 6%, but was unchanged in the striatum. Specific binding of 3H-serotonin was increased by 63 ± 29% in the striatum and by 32 ± 9% in the brainstem, but decreased by 20 ± 7% in the hippocampus. The specific binding of 3H-quinuclidinyl benzilate to muscarinic acetylcholine receptors increased by 7 ± 2% in the striatum, but decreased by 5 ± 2% in the cerebral cortex. The specific binding of 3H-WB-4101 to α-adrenergic receptors was unchanged in all brain areas assayed, namely the striatum, mesolimbic areas, hippocampus, hypothalamus, brainstem and cerebral cortex. These changes may be related to some aspects of tolerance to, and dependence on, ethanol.

Pituitary cell cultures contain muscarinic receptors

The presence of muscarinic receptors in 5-day dissociated cell cultures of rat anterior pituitary glands was detected by atropine-sensitive binding of 3H-quinuclidinyl benzilate ( 3H-QNB). Muscarinic receptor levels in cultures were comparable to levels of receptors for dopamine and thyrotropin releasing hormone.

Brain neurotransmitter receptor systems in mice genetically selected for differences in sensitivity to ethanol

The density of receptors for neurotransmitters and receptor-mediated cellular responsiveness were determined in tissues from two lines of mice selectively bred for differences in sleep time after ethanol administration. The studies were undertaken to ascertain in differences in neurotransmitter receptors between the lines might explain any of the differences seen in initial sensitivity to ethanol. The results were compared with those obtained in studies using the parent heterogeneous stock (HS). The animals used in the current experiments did not receive ethanol. β-Adrenergic receptor density, as measured by the binding of ( 125I)-iodohydroxybenzylpindolol, was lower in cortices of alcohol-sensitive long-sleep mice (LS) as compared to the short-sleep (SS) animals or to HS controls. The densities of β 1 and β 2-adrenergic receptors were lower by approximately the same amount. The results were tissue specific in that there was no difference in the density of β-adrenergic receptors in the cerebellum. Cyclic AMP accumulation in response to isoproterenol was not significantly different in the cortex of LS mice despite the decrease in β-adrenergic receptors. No differences were found in 3H-spiroperidol binding to dopamine receptors in the striatum or in 3H-quinuclidinylbenzilate binding to muscarinic cholinergic receptors in the cortex, striatum or hippocampus. Dopamine-stimulated adenylate cyclase activity was, how- ever, lower in striata of SS mice. The affinities of the receptors for the various ligands studied were the same in the three lines of mice.

Changes in brain muscarinic acetylcholine receptors and behavioral responses to atropine and apomorphine in chronic atropine-treated rats

Chronic blockade of cholinergic transmission with atropine resulted in a decrease in atropine-induced activity in the rats, whereas apomorphine - induced locomotion was enhanced. Maximal binding of 3H-quinuclidinyl benzilate (QNB), a muscarinic antagonist, to homogenate of cerebral cortex, striatum and hippocampus was significantly higher in chronic atropine-treated rats than in control animals. No difference was observed in K D value of the specific 3H-QNB binding or in ID 50 value of oxotremorine in inhibiting 3H-QNB binding. No change in the specific binding of 3H-spiroperidol, a dopaminergic antagonist, was observed in those three regions of brains of chronic atropine-treated rats when it was compared with that of control animals. The role of brain muscarinic acetylcholine receptors in behavioral responses is discussed relating an effect of dopaminergic neurons on cholinergic activities.

Muscarinic cholinergic receptor binding: Influence of pimozide and chlorpromazine metabolites

The relative muscarinic anticholinergic actions of phenothiazines and related drugs are thought to regulate the propensity of these agents to elicit extrapyramidal side effects, especially those resembling the symptoms of Parkinson's disease. Pimozide, which closely resembles the butyrophenones in its chemical structure and its potent and selective dopamine receptor blockade, differs from the butyrophenones in its relatively low incidence of extrapyramidal side effects. In assays of the binding of 3H-quinuclidinyl benzilate (QNB) to muscarinic sites, pimozide displays a high affinity for these cholinergic receptors, similar to drugs, such as thioridizine and clozapine, which also have a low incidence of extrapyramidal side effects. This observation supports the notion that muscarinic anticholinergic actions can ameliorate the propensity of a drug to elicit extrapyramidal effects. The structure-activity relationships of chlorpromazine metabolites in binding to muscarinic sites in the brain parallels some of their structure-activity relationships as neuroleptic agents. 7-Hydroxychlorpromazine, which has been proposed as an antischizophrenic drug, binds to the muscarinic receptor with a potency similar to that of chlorpromazine itself, suggesting that the incidence of extrapyramidal side effects of 7-hydroxychlorpromazine might be similar to those of chlorpromazine.