Possible involvement of M5 muscarinic receptor in the enhancing actions of the novel gastroprokinetic agent Z-338 on nifedipine-sensitive voltage-dependent Ca2+ currents in guinea pig stomach

Acotiamide, a novel gastroprokinetic for the treatment of patients with functional dyspepsia: postprandial distress syndrome

Functional dyspepsia (FD) is a highly prevalent condition with major socioeconomic and healthcare impact. To date, no pharmacological treatment for FD has been approved. The Rome consensus proposed to subdivide FD into postprandial distress syndrome (PDS), characterized by meal-related symptoms and epigastric pain syndrome, characterized by pain and burning. Acotiamide (Z-338 or YM443) is a new drug, developed for the treatment of FD. Acotiamide enhances acetylcholine release from enteric neurons through muscarinic receptor antagonism and acetycholinesterase inhibition, thereby enhancing gastric emptying and gastric accommodation. Acotiamide was evaluated in FD in clinical studies in Europe, Japan and the USA, beneficial effects were observed for the PDS symptoms of postprandial fullness and early satiation, with a dose of 100 mg three-times a day. A 4-week placebo-controlled Phase III study in PDS patients in Japan confirmed efficacy of acotiamide in relieving postprandial fullness, early satiation and upper abdominal bloating.

Effects of Z-338, a novel gastroprokinetic agent, on the actions of excitatory and inhibitory neurotransmitters on neurons in area postrema

We investigated the effects of the novel gastroprokinetic agent Z-338 on the actions of excitatory and inhibitory neurotransmitters on neurons in area postrema (AP). Iontophoretic applications of acetylcholine (ACh), AMPA and NMDA increased, while GABA suppressed the firing rates of AP neurons recorded by extracellular electrodes. Z-338 (10 microM) suppressed the ACh-induced acceleratory and GABA-induced inhibitory actions without affecting the excitatory actions of AMPA and NMDA. Under voltage-clamp conditions, nicotine, NMDA, kainic acid (KA) and ATP evoked inward currents in dissociated single AP neurons recorded by whole-cell patch clamp technique, and GABA produced outward currents, at holding potentials (V(H)) of -60 or 0 mV. Z-338 (>3 microM) specifically suppressed the nicotine- and GABA-induced currents without affecting the currents induced by NMDA, KA and ATP. In addition, we found that Z-338 (30 microM) suppressed the spontaneous inhibitory postsynaptic currents (sIPSCs) recorded from AP neurons in slice preparations. Experiments with microelectrode and histochemical methods revealed the presence of direct excitatory and di-synaptic inhibitory neural connections from AP to dorsal motor nucleus of the vagus (DMV). In some AP neurons, Z-338 (10 microM) enhanced the spontaneous firing rates recorded by extracellular electrode. The excitatory or inhibitory effects of Z-338 on the firing rates or actions of nicotine and GABA on AP neurons observed in the present study may explain the postmeal relaxation induced by Z-338 in patients with functional dyspepsia.

Activation of muscarinic cholinergic receptors inhibits giant neurones in the caudal pontine reticular nucleus

Giant neurones in the caudal pontine reticular nucleus (PnC) play a crucial role in mediating the mammalian startle response. They receive input from cochlear, trigeminal and vestibular nuclei and project directly to motoneurones. Furthermore, they integrate modulatory input from different brain regions either enhancing or inhibiting startle responses. One prominent startle modulation is prepulse inhibition where a non-startling stimulus presented prior to the startle stimulus inhibits a subsequent startle response. Several behavioural studies have indicated that this inhibition is mediated by muscarinic receptors at the level of the PnC. Here, we performed whole-cell patch-clamp recordings from PnC giant neurones in acute rat brain slices in order to examine muscarinic inhibition. We stimulated afferent trigeminal and auditory fibres and applied muscarinic agonists and antagonists in order to investigate their effect on excitatory postsynaptic current amplitudes, paired-pulse ratio and passive membrane properties of PnC giant neurones. The cholinergic agonist carbachol and the muscarinic agonist oxotremorine significantly reduced excitatory postsynaptic current amplitudes and increased the paired-pulse ratio. Carbachol additionally reduced the membrane resistance of postsynaptic PnC giant neurones. The subtype-specific antagonists AF-DX116 (M2 preferring) and tropicamide (M4 preferring) antagonized the oxotremorine effect indicating that M4 and possibly M2 receptor subtypes are involved in this inhibition. The G-protein-activated inward rectifying potassium channel blocker tertiapin-Q had no effect on oxotremorine-induced inhibition of giant neurones. Our results show a mainly presynaptically mediated strong inhibition of PnC giant neurones by activation of M4 and possibly M2 receptors that presumably contribute to prepulse inhibition.