title: Control of Phasic Firing by a Background Leak Current in Avian Forebrain Auditory Neurons.
abstract: Central neurons express a variety of neuronal types and ion channels that promote firing heterogeneity among their distinct neuronal populations. Action potential (AP) phasic firing, produced by low-threshold voltage-activated potassium currents (VAKCs), is commonly observed in mammalian brainstem neurons involved in the processing of temporal properties of the acoustic information. The avian caudomedial nidopallium (NCM) is an auditory area analogous to portions of the mammalian auditory cortex that is involved in the perceptual discrimination and memorization of birdsong and shows complex responses to auditory stimuli We performed in vitro whole-cell patch-clamp recordings in brain slices from adult zebra finches (Taeniopygia guttata) and observed that half of NCM neurons fire APs phasically in response to membrane depolarizations, while the rest fire transiently or tonically. Phasic neurons fired APs faster and with more temporal precision than tonic and transient neurons. These neurons had similar membrane resting potentials, but phasic neurons had lower membrane input resistance and time constant. Surprisingly phasic neurons did not express low-threshold VAKCs, which curtailed firing in phasic mammalian brainstem neurons, having similar VAKCs to other NCM neurons. The phasic firing was determined not by VAKCs, but by the potassium background leak conductances, which was more prominently expressed in phasic neurons, a result corroborated by pharmacological, dynamic-clamp, and modeling experiments. These results reveal a new role for leak currents in generating firing diversity in central neurons.
authors.affiliation: Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo Ribeirão Preto, Brazil.
authors.forename: André A
authors.initials: AA
authors.lastname: Dagostin
authors.affiliation: Department of Behavioral Neuroscience, Oregon Health and Science University, Portland OR, USA.
authors.forename: Peter V
authors.initials: PV
authors.lastname: Lovell
authors.affiliation: Brain Institute, Federal University of Rio Grande do Norte Natal, Brazil ; Institute for Analysis and Scientific Computing, Vienna University of Technology Vienna, Austria.
authors.forename: Markus M
authors.initials: MM
authors.lastname: Hilscher
authors.affiliation: Department of Behavioral Neuroscience, Oregon Health and Science University, Portland OR, USA.
authors.forename: Claudio V
authors.initials: CV
authors.lastname: Mello
authors.affiliation: Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo Ribeirão Preto, Brazil.
authors.forename: Ricardo M
authors.initials: RM
authors.lastname: Leão
keywords: action potentials; birdsong; leak current; potassium currents; zebra finch