title: Potentiating effect of eszopiclone on GABA(A) receptor-mediated responses in pedunculopontine neurons.
abstract: The pedunculopontine nucleus (PPN) is part of the cholinergic arm of the reticular activating system, which is mostly active during waking and REM sleep. GABAergic modulation of this area appears to regulate sleep-wake cycles. Eszopiclone (ESZ), a nonbenzodiazepine hypnotic agent, appears to modulate GABAergic receptors. However, the action site of ESZ in the brain is still unresolved. We tested the hypothesis that ESZ acts by potentiating GABA(A) receptors on PPN neurons. Wholecell voltage clamp recordings were performed on PPN neurons in 7-15 day rat brainstem slices, and the potentiating effects of ESZ on the responses to the GABA(A) receptor agonist isoguvacine (IGV), and on GABA(A) receptor-mediated inhibitory post-synaptic currents (IPSCs), were determined. In the presence of tetrodotoxin, ESZ (1) increased the amplitude of the outward current induced by IGV, (2) increased its duration, and (3) enhanced the IGV-induced decrease in input resistance (Rin). The GABA(A) receptor antagonist gabazine (GBZ) blocked these effects. ESZ alone did not induce detectable currents or change Rin at a holding potential of -60 mV, but when held at 0 mV, ESZ induced an outward current in 13/21 PPN cells, an effect blocked by GBZ. ESZ also increased the amplitude (n = 18/21), duration (n = 17/21), and frequency (n = 13/15) of IPSCs. ESZ may potentiate GABA(A) inhibition in the PPN via pre- and post-synaptic modulation, which may underlie the hypnotic effects of ESZ. The differential effects of ESZ on both pre- and post-synaptic sites may partially explain why it has less significant side effects compared to other hypnotic agents.
authors.affiliation: Center for Translational Neuroscience, Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
authors.forename: Meijun
authors.initials: M
authors.lastname: Ye
authors.forename: Edgar
authors.initials: E
authors.lastname: Garcia-Rill
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage; D000818:Animals; D000831:Animals, Newborn; D053961:Azabicyclo Compounds / Q000494:pharmacology*; D004357:Drug Synergism; D004558:Electric Stimulation; D000069582:Eszopiclone; D018755:GABA Agonists / Q000008:administration & dosage; D018756:GABA Antagonists / Q000008:administration & dosage; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D007539:Isonicotinic Acids / Q000008:administration & dosage; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques / Q000379:methods; D045042:Pedunculopontine Tegmental Nucleus / Q000187:drug effects*; D010879:Piperazines / Q000494:pharmacology*; D011724:Pyridazines / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects*; D013779:Tetrodotoxin / Q000008:administration & dosage; D013997:Time Factors
chemical_list: D000779:Anesthetics, Local; D053961:Azabicyclo Compounds; D018755:GABA Agonists; D018756:GABA Antagonists; D006993:Hypnotics and Sedatives; D007539:Isonicotinic Acids; D010879:Piperazines; D011724:Pyridazines; D011963:Receptors, GABA-A; D013779:Tetrodotoxin; C049853:gabazine; D000069582:Eszopiclone; C015300:isoguvacine