GABAergic and glutamatergic inhibition of nonspiking local interneurons in the terminal abdominal ganglion of the crayfish.
Nonspiking local interneurons in the terminal abdominal ganglion of the crayfish Procambarus clarkii receive inhibitory inputs from mainly glutamatergic spiking local interneurons and GABAergic nonspiking interneurons. In this study, the inhibitory responses of nonspiking interneurons to local application of glutamate and GABA into the neuropil were compared. Glutamate and GABA injection mediated the hyperpolarization of the nonspiking interneurons with an increase in membrane conductance. The glutamate-mediated membrane hyperpolarization was reversed by injection of 1 or 2 nA hyperpolarizing current. By contrast, more than 3 nA hyperpolarizing current was frequently necessary to reverse the GABA-mediated hyperpolarization. Bath application of a chloride channel blocker, 50 microM picrotoxin (PTX), reduced the glutamate-mediated hyperpolarization, but had no effect on the GABA-mediated hyperpolarization. The GABA-mediated hyperpolarization was not consistently affected by bath application of low chloride solution. These results suggest that the glutamate-mediated inhibition was related to the gating of a Cl(-) conductance, while the GABA-mediated inhibition was not. Electrical stimulation of sensory afferents innervating the exopodite elicited ipsps in uropod opener motor neurons. These sensory-evoked ipsps were also PTX-insensitive, suggesting GABAergic nonspiking interneurons could be the predominant premotor elements in organizing the uropod motor control system.
Nagayama
Toshiki
T
Division of Biological Sciences, Graduate School of Science, Hokkaido University, 060 Sapporo, Japan. Nagayama@sci.hokudai.ac.jp
D000818:Animals; D003400:Astacoidea / Q000378:metabolism*; D017952:Ganglia, Invertebrate / Q000378:metabolism*; D018698:Glutamic Acid / Q000494:pharmacology*; D007395:Interneurons / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects; D010852:Picrotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018698:Glutamic Acid; D010852:Picrotoxin; D005680:gamma-Aminobutyric Acid