title: Tonic and phasic receptor neurons in the vertebrate olfactory epithelium.
abstract: Olfactory receptor neurons (ORNs) respond to odorants with characteristic patterns of action potentials that are relevant for odor coding. Prolonged odorant exposures revealed three populations of dissociated toad ORNs, which were mimicked by depolarizing currents: tonic (TN, displaying sustained firing, 49% of 102 cells), phasic (PN, exhibiting brief action potential trains, 36%) and intermediate neurons (IN, generating trains longer than PN, 15%). We studied the biophysical properties underlying the differences between TNs and PNs, the most extreme cases among ORNs. TNs and PNs possessed similar membrane capacitances (approximately 4 pF), but they differed in resting potential (-82 versus -64 mV), input resistance (4.2 versus 2.9 G(Omega)) and unspecific current, I(u) (TNs: 0 < I(u) <or= 1 pA/pF; and PNs: I(u) > 1 pA/pF). Firing behavior did not correlate with differences in voltage-gated conductances. We developed a mathematical model that accurately simulates tonic and phasic patterns. Whole cell recordings from rat ORNs in fragments (approximately 4 mm(2)) of olfactory epithelium showed that such a tissue normally contains tonic and phasic receptor neurons, suggesting that this feature is common across a wide range of vertebrates. Our findings show that the individual passive electrical properties can govern the firing patterns of ORNs.
authors.affiliation: Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile.
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Madrid
authors.forename: Magdalena
authors.initials: M
authors.lastname: Sanhueza
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Alvarez
authors.forename: Juan
authors.initials: J
authors.lastname: Bacigalupo
mesh_terms: D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology*; D000080462:Acyclic Monoterpenes; D000222:Adaptation, Physiological / Q000187:drug effects* / Q000502:physiology*; D000818:Animals; D001001:Anura; D020013:Calcium Signaling / Q000502:physiology; D004558:Electric Stimulation; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009812:Odorants; D009831:Olfactory Mucosa / Q000187:drug effects / Q000502:physiology; D018034:Olfactory Receptor Neurons / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity; D013729:Terpenes / Q000494:pharmacology
chemical_list: D000080462:Acyclic Monoterpenes; D013729:Terpenes; C007836:geraniol