title: Synaptically released GABA activates both pre- and postsynaptic GABA(B) receptors in the rat globus pallidus.
abstract: The globus pallidus (GP) contains abundant GABAergic synapses and GABA(B) receptors. To investigate whether synaptically released GABA can activate pre- and postsynaptic GABA(B) receptors in the GP, physiological recordings were performed using rat brain slice preparations. Cell-attached recordings from GABA(A) antagonist-treated preparations revealed that repetitive local stimulation induced a GABA(B) antagonist-sensitive pause in spontaneous firings of GP neurons. Whole cell recordings revealed that the repetitive stimulation evoked fast excitatory postsynaptic potentials followed by a slow inhibitory postsynaptic potential (IPSP) in GP neurons. The slow IPSP was insensitive to a GABA(A) receptor antagonist, increased in amplitude with the application of ionotropic glutamate receptor antagonists, and was suppressed by the GABA(B) antagonist CGP55845. The reversal potential of the slow IPSP was close to the potassium equilibrium potential. These results suggest that synaptically released GABA activated postsynaptic GABA(B) receptors and induced the pause and the slow IPSP. On the other hand, in the neurons that were treated to block postsynaptic GABA(B) responses, CGP55845 increased the amplitudes of repetitive local stimulation-induced GABA(A)-mediated inhibitory postsynaptic currents (IPSCs) but not the ionotropic glutamate-mediated excitatory postsynaptic currents. Moreover, the GABA(B) receptor specific agonist baclofen reduced the frequency of miniature IPSCs without altering their amplitude distributions. These results suggest that synaptically released GABA also activated presynaptic GABA(B) autoreceptors, resulting in decreased GABA release in the GP. Together, we infer that both pre- and postsynaptic GABA(B) receptors may play crucial roles in the control of GP neuronal activity.
authors.affiliation: Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee, Memphis, TN 38163, USA.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Kaneda
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Kita
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001418:Baclofen / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005917:Globus Pallidus / Q000166:cytology* / Q000502:physiology; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D011724:Pyridazines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000502:physiology*; D018080:Receptors, GABA-B / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018755:GABA Agonists; D018756:GABA Antagonists; D011724:Pyridazines; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D005680:gamma-Aminobutyric Acid; C049853:gabazine; D001418:Baclofen