title: Development of GPCR modulation of GABAergic transmission in chicken nucleus laminaris neurons.
abstract: Neurons in the nucleus laminaris (NL) of birds act as coincidence detectors and encode interaural time difference to localize the sound source in the azimuth plane. GABAergic transmission in a number of CNS nuclei including the NL is subject to a dual modulation by presynaptic GABA(B) receptors (GABA(B)Rs) and metabotropic glutamate receptors (mGluRs). Here, using in vitro whole-cell patch clamp recordings from acute brain slices of the chick, we characterized the following important but unknown properties pertaining to such a dual modulation: (1) emergence of functional GABA synapses in NL neurons; (2) the temporal onset of neuromodulation mediated by GABA(B)Rs and mGluRs; and (3) the physiological conditions under which GABA(B)Rs and mGluRs are activated by endogenous transmitters. We found that (1) GABA(A)R-mediated synaptic responses were observed in about half of the neurons at embryonic day 11 (E11); (2) GABA(B)R-mediated modulation of the GABAergic transmission was detectable at E11, whereas the modulation by mGluRs did not emerge until E15; and (3) endogenous activity of GABA(B)Rs was induced by both low- (5 or 10 Hz) and high-frequency (200 Hz) stimulation of the GABAergic pathway, whereas endogenous activity of mGluRs was induced by high- (200 Hz) but not low-frequency (5 or 10 Hz) stimulation of the glutamatergic pathway. Furthermore, the endogenous activity of mGluRs was mediated by group II but not group III members. Therefore, autoreceptor-mediated modulation of GABAergic transmission emerges at the same time when the GABA synapses become functional. Heteroreceptor-mediated modulation appears at a later time and is receptor type dependent in vitro.
authors.affiliation: Department of Anatomy and Neurobiology, Northeast Ohio Medical University, College of Medicine, Rootstown, Ohio, United States of America.
authors.forename: Zheng-Quan
authors.initials: ZQ
authors.lastname: Tang
authors.forename: Yong
authors.initials: Y
authors.lastname: Lu
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology*; D002645:Chickens / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism; D018080:Receptors, GABA-B / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism; D013569:Synapses / Q000378:metabolism; D009435:Synaptic Transmission; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D043562:Receptors, G-Protein-Coupled; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D018094:Receptors, Metabotropic Glutamate; D005680:gamma-Aminobutyric Acid