Pharmacological properties of nicotinic acetylcholine receptors in isolated Locusta migratoria neurones

Abstract

Mechanically dissociated neuronal cell bodies from the thoracic ganglia of Locusta migratoria were viable in culture conditions for up to 2 days and were voltage-clamped to record the effects of GABAergic drugs and physostigmine on the membrane conductance and ACh responses of the dissociated cells. Bicuculline, hydrastine, and gabazine inhibited the EC50 ACh responses of the cells. Both bicuculline and hydrastine were full inhibitors of the ACh responses but gabazine behaved as a partial inhibitor. Bicuculline, hydrastine, and gabazine inhibited the ACh responses in a non-competitive and voltage-independent fashion, suggesting that they are allosteric inhibitors of locust nicotinic ACh receptors. Physostigmine activated currents when applied onto isolated locust neurones. The responses activated by physostigmine were inhibited competitively by tubocurarine, which indicates that physostigmine interacts with the ACh site of locust nicotinic ACh receptors. However, maximal concentrations of physostigmine elicited currents of smaller amplitudes to those evoked by maximal ACh concentrations. Single-channel recordings suggest that the partial efficacy of physostigmine may reflect the low frequency of opening of physostigmine-induced single currents relative to that of ACh-single currents.

Study of nicotinic acetylcholine receptors on cultured antennal lobe neurones from adult honeybee brains

“…This finding is in agreement with previous observations on a large number of insect preparations (Benson 1992;Cayre et al 1999;Jackson et al 2002). The sodium to potassium permeability ratio (P Na /P K ) was estimated to 1.61 by varying extracellular ionic sodium concentrations; to our knowledge, such a high P Na /P K was not reported before and the physiological role of such high P Na /P K value remains to be elucidated.…”

“…Native neuronal nAChRs have been described in several insect species such as cockroaches (Harrow and Sattelle 1983;Van Eyseren et al 1998;Courjaret et al 2003;Salgado and Saar 2004), locusts (Albert and Lingle 1993;Hermsen et al 1998;Jackson et al 2002), crickets (Cayre et al 1999), houseflies (Albert and Lingle 1993;Schmidt et al 2000;Jepson et al 2006), moths (Vermehren and Trimmer 2005) and honeybees (Goldberg et al 1999;Déglise et al 2002;Wustenberg and Grünewald 2004; Barbara et al 2005). These insect nAChRs are targets for neonicotinoids, a major class of pesticides and especially imidacloprid (IMI), the main insecticide of this class (Matsuda et al 2000;Tomizawa and Casida 2003).…”

Activation and Block of the Adult Muscle-Type Nicotinic Receptor by Physostigmine: Single-Channel Studies

“…Finally, we demonstrate that the blocking actions of physostigmine can be accounted for by two equivalent binding sites per receptor. Physostigmine elicits only a low level of activity, but previous studies have generally been noncommittal regarding the underlying cause for the weak activating properties of physostigmine (Pereira et al, 1993;Storch et al, 1995;Jackson et al, 2002). Our single-channel data from the wild-type receptor activated by physostigmine showed low open probability activity that did not condense into recognizable clusters.…”

“…Cooper et al (1996) found that in Xenopus oocytes expressing rat embryonic receptors, physostigmine-elicited singlechannel currents were not observed after an incubation with ␣-bungarotoxin, whereas the presence of mecamylamine or methyllycaconitine strongly reduced the frequency of single-channel events. Methyllycaconitine, ␣-bungarotoxin, and d-tubocurarine were also shown to inhibit receptors activated by physostigmine in L. migratoria neurons (van den Beukel et al, 1998;Jackson et al, 2002), whereas in oocytes expressing rat neuronal ␣4␤4 nicotinic receptors physostigmine competitively displaced 125 I-epibatidine, a high-affinity ligand to the ACh site (Zwart et al, 2000). In contrast to these studies, methyllycaconitine inhibited channel activation by ACh but not by physostigmine in clonal rat pheochromocytoma cells (Storch et al, 1995), and saturating concentrations of d-tubocurarine and ␣-bungarotoxin were found to be ineffective at blocking the ability of physostigmine to activate the T. californica receptor (Okonjo et al, 1991).…”

Expression of muscarinic acetylcholine receptors and choline acetyltransferase enzyme in cultured antennal sensory neurons and non-neural cells of the developing mothManduca sexta

“…Therefore, our discovery of ChAT immunoreactivity in cultured antennal sensory neurons is not surprising, but supports previous findings. Ionic currents induced by ACh have been recorded from several types of cultured or freshly dissociated insect cells, such as honeybee Kenyon cells and locust ganglion neurons, but these currents seem to occur via nicotinic receptors (Goldberg et al, 1999;Jackson et al, 2002). There is no previous evidence for the presence of mAChRs in antennal sensory neurons of pupal or adult Manduca, but muscarinic activity in larval mechanosensory afferents has been demonstrated (Trimmer and Weeks, 1989).…”