Characteristics of GABA receptors on the ocellar L-neurons of American cockroach Periplaneta americana.
The ocellar L-neurons of cockroach Periplaneta americana were used in the present study as model systems to investigate the pharmacological properties of the GABA receptors. To do so, a glass microelectrode was impaled into the axon of the L-neurons to record the membrane potential intracellularly and to monitor membrane response to GABA treatment and cercal stimulation by air puff. The traditional GABA and their receptor agonists were introduced through perfusion and/or iontophoresis to monitor their effects on the L-neurons. The GABA receptor antagonists were administered by perfusion to examine if the response of the L-neurons to GABA and/or cercal stimulation was changed. The results revealed that administration of GABA, muscimol and imidazole acetic acid, two GABAA agonists, produced depolarization on the L-neurons. However, treatment of 3-APS and guanidine acetic acid, another two GABAA agonists, evoked hyperpolarization on the L-neurons. Among those tested antagonists, only picrotoxin, GABAA antagonist, antagonize the depolarization induced by GABA and/or cercal stimulation. More interestingly, administration of strychnine, glycine receptor antagonist, largely attenuated the depolarization response of the L-neurons to cercal stimulation. This attenuation caused by strychnine was even stronger than that initiated by varied GABA antagonists. In addition, phaclofen, a GABAB receptor antagonist, showed no antagonistic effect. These results strongly suggest that the characteristics of GABA receptors of the ocellar L-neurons may differ from those in vertebrates. It may be more likely to be a novel GABA receptor.
Lee
Ming-Chung
MC
Department of Life Science, National Taiwan Normal University, Taipei 11617, Taiwan, ROC.
Hwang
Ji-Chuu
JC
Lin
Jin-Tun
JT
Tung
Li-Chu
LC
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D018755:GABA Agonists / Q000494:pharmacology*; D018756:GABA Antagonists / Q000494:pharmacology*; D005998:Glycine / Q000037:antagonists & inhibitors; D007478:Iontophoresis; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D010526:Periplaneta / Q000502:physiology*; D010852:Picrotoxin / Q000494:pharmacology; D018079:Receptors, GABA / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D001640:Bicuculline; D002712:Chlorides; D018755:GABA Agonists; D018756:GABA Antagonists; D005998:Glycine; D009118:Muscimol; D010852:Picrotoxin; D018079:Receptors, GABA; D012965:Sodium Chloride; D005680:gamma-Aminobutyric Acid