Neurogenic gastrointestinal movement caused by the peripheral neuronal network and its extrinsic regulation in Lymnaea stagnalis

Abstracts

409

WS5

WS6

Local interneurons comprising presynaptic pathways to NGIs in the crayfish brain

Neurogenic gastrointestinal movement caused by the peripheral neuronal network and its extrinsic regulation in Lymnaea stagnalis

Kenichi Fujisawa a, Noriyuki Hama b, Masakazu Takahata b, aDiv. Biol. Sci., Grad. Sch. Sci.; bDiv. Life Sci., Fac. Sci., Hokkaido Univ., Sapporo 060-0810 Japan

Takanobu Okamoto, Makoto Kurokawa, Dept. Life. Sci., Tokyo Metropolitan Univ., Hachioji-shi, Tokyo 192-0397, Japan

In the central compensation of crayfish following unilateral statolith removal, significant changes occur in the membrane properties of premotor NGIs (Nonspiking Giant Interneurons) and the synaptic inputs to them, suggesting that the site of physiological changes subserving the compensation is located, at least partly, presynaptic to NGIs. To clarify its cellular mechanisms, we adopted intracellular recording/staining techniques to identify 10 interneurons including one spiking and one nonspiking interneurons each making a monosynaptic connection with NGIs. Other interneurons, consisting of seven spiking and one nonspiking interneurons, were found to make polysynaptic connection with NGIs, the intercalated cell remaining unidentified. We identified another four interneurons that were presumed to be presynaptic to NGIs on the morphological basis: they projected dendrites to the protocerebrum where NGIs are located and to the parolfactory lobe where statocyst afferents terminate. Among them, a class of neurons named L-neurons, making monosynaptic and polysynaptic connections with NGIs, was found to show changes that were parallel to the behavioral changes during central compensation. The finding that these interneurons received leg proprioceptive input as well as statocyst input led us to the conclusion that they, together with NGIs, represent the site of physiological changes in the central compensation process. doi:10.1016/j.cbpb.2006.10.025

Neural mechanisms of feeding behavior in gastropods have been extensively examined using the central nervous system (CNS) as a model for the study of neuronal and neurohumoral bases of behaviors. In the periphery, the neural plexus containing many neuronal somata, whose function remains to be examined, is located in the digestive tract. We isolated the digestive tract from which the CNS had been removed. In that preparation, periodic bursting activities that appeared to cause the neurogenic movement of the digestive tract were recorded extracellularly from the neural plexus. In order to locate the origin of the bursting activities, we examined the direction of impulse propagation by means of simultaneous recordings of these bursts and found them to originate in neurons scattered on the crop. The interburst intervals of the bursts were decreased or increased by electrical stimuli applied to the oesophageal nerve. During superfusion of the preparation with high Mg 2+ saline, the effect of the stimulation was blocked while we observed the interburst intervals to increase. The peripheral neuronal network responsible for the burst formation may involve chemical synaptic transmission. It is suggested that there are extrinsic regulations of the gastrointestinal motility, mediated by chemical synapses through the neuronal network. doi:10.1016/j.cbpb.2006.10.026