title: Calcium-dependent prepotentials contribute to spontaneous activity in rat tuberomammillary neurons.
abstract: 1. Intracellular recordings from histaminergic neurons of the tuberomammillary (TM) nucleus reveal subthreshold depolarizing potentials (DPs) which persist in the presence of tetrodotoxin. 2. Block of hyperpolarization-activated current by 1-4 mM Cs+ failed to reduce spontaneous activity or DPs. 3. In the presence of tetrodotoxin DPs are voltage dependent and are depressed by Cd2+ and Co2+. 4. Ba2+ (100 microM) treatment enhances DP amplitude and converts low-amplitude potentials to tetrodotoxin-insensitive action potentials. 5. In the presence of TTX, DPs are reduced by Ni2+. Spontaneous action potentials are also reduced by Ni2+ (100-300 microM). A low-threshold Ca2+ current is present which is sensitive to Ni2+. These results indicate the presence of calcium currents, perhaps of the low-threshold type, which contribute to activation of action potentials in TM neurons.
authors.affiliation: Physiologie Institüt II, Heinrich-Heine-Universität, Düsseldorf, Germany. Stevensd@uni-duesseldorf.de
authors.forename: D R
authors.initials: DR
authors.lastname: Stevens
authors.forename: H L
authors.initials: HL
authors.lastname: Haas
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002586:Cesium / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D006632:Histamine / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D008326:Mammillary Bodies / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D002104:Cadmium; D002586:Cesium; D001464:Barium; D013779:Tetrodotoxin; D009532:Nickel; D006632:Histamine; D002118:Calcium