Abstract
Juvenile hormone (JH) synthesized and released from endocrine gland corpus allatum (CA) plays important roles in insect metamorphosis, vitellogenesis and reproduction. Glutamate is the main neurotransmitter to mediate a complex of physiological function and its activated receptors have been shown to possess excitatory and inhibitory responses in muscle fibers and nervous system of invertebrates. Previously, excitatory D-type glutamate receptors (NMDA and non-NMDA subtypes) elicit an increase of the cytosolic free calcium concentration ([Ca2+]i) to cause stimulation of JH synthesis in the cockroach, Diploptera puntata. Here, the occurrence of inhibitory H-type glutamate receptor, which increases chloride channel conductance, has been demonstrated on CA cell membranes while application of channel activators, ibotenic acid and ivermectin, but not GABA and activation of GluCl channels could induce hyperpolarization of membrane potential and cause a dramatic decline in JH synthesis at either highly active or inactive glands during the gonadotrophic cycle. Since the regulation of JH is involved in both excitatory D- and inhibitory H-type glutamate receptors, we hypothesize that two typed glutamate receptors act as synergistic effects to contribute the rates of JH synthesis during the gonadotrophic cycle and peak JH synthesis at highly active glands. These results illustrate a novel function of glutamate gated-chloride channels in the endocrine system and suggest that glutamate may act as a new releasing factor to regulate JH synthesis and could be a potential pathway for developing a new generation of insecticide.