cinanserin and bemesetron

In the central nervous system of the pond snail Lymnaea stagnalis, serotonergic transmission plays an important role in controlling feeding behavior. Recent electrophysiological studies have claimed that only metabotropic serotonin (5-HT(2)) receptors, and not ionotropic (5-HT(3)) receptors, are used in synapses between serotonergic neurons (the cerebral giant cells, CGCs) and the follower buccal motoneurons (the B1 cells). However, these data are inconsistent with previous results. In the present study, we therefore reexamined the serotonin receptors to identify the receptor subtypes functioning in the synapses between the CGCs and the B1 cells by recording the compound excitatory postsynaptic potential (EPSP) of the B1 cells evoked by a train of stimulation to the CGC in the presence of antagonists: cinanserin for 5-HT(2) and/or MDL72222 for 5-HT(3). The compound EPSP amplitude was partially suppressed by the application of these antagonists. The rise time of the compound EPSP was longer in the presence of MDL72222 than in that of cinanserin. These results suggest that these two subtypes of serotonin receptors are involved in the CGC-B1 synapses, and that these receptors contribute to compound EPSP. That is, the fast component of compound EPSP is mediated by 5-HT(3)-like receptors, and the slow component is generated via 5-HT(2)-like receptors.

Topics: Animals; Central Nervous System; Cinanserin; Feeding Behavior; Neurons; Pertussis Toxin; Receptors, Serotonin; Serotonin Antagonists; Snails; Tropanes

Synchronous oscillation of membrane potentials, generated by assemblies of neurons, is a prominent feature in the olfactory systems of many vertebrate and invertebrate species. However, its generation mechanism is still controversial. Biogenic amines play important roles for mammalian olfactory learning and are also implicated in molluscan olfactory learning. Here, we investigated the role of serotonin, a biogenic amine, in the oscillatory dynamics in the procerebrum (PC), the molluscan olfactory center. Serotonin receptor blockers inhibited the spontaneous synchronous oscillatory activity of low frequency (approximately 0.5 Hz) in the PC. This was due to diminishing the periodic slow oscillation of membrane potential in bursting (B) neurons, which are essential neuronal elements for the synchronous oscillation in the PC. On the other hand, serotonin enhanced the amplitude of the slow oscillation in B neurons and subsequently increased the number of spikes in each oscillatory cycle. These results show that the extracellular serotonin level regulates the oscillation amplitude in B neurons and thus serotonin may be called an oscillation generator in the PC. Although nitric oxide (NO) is known to also be a crucial factor for generating the PC oscillatory activity and setting the PC oscillation frequency, the present study showed that NO only regulates the oscillation frequency in B neurons but could not increase the spikes in each oscillatory cycle. These results suggest complementary regulation of the PC oscillatory activity: NO determines the probability of occurrence of slow potentials in B neurons, whereas serotonin regulates the amplitude in each cycle of the oscillatory activity in B neurons.

Topics: Action Potentials; Animals; Cinanserin; Electrophysiology; Ganglia, Invertebrate; Mollusca; Nitric Oxide; Olfactory Receptor Neurons; Periodicity; Serotonin; Serotonin Antagonists; Tropanes