title: Ionic basis of the differential neuronal activity of guinea-pig septal nucleus studied in vitro.
abstract: 1. The electrical properties and ionic conductances of septal neurones were studied by intracellular recording in an in vitro slice preparation. Within the total number of cells recorded (n = 150) we identified three electrophysiological cell types, each one of them located in a separate septal region. Dorsolateral septal neurones comprised 60% of the cells, intermediate septal neurons 10%, and medical septal neurones 30%. 2. Passive electrical constants of dorsolateral, intermediate and medial septal neurones were, respectively:resting potential (-60.2 +/- 4.8, -59.8 +/- 3.3 and -56 +/- 4.3 mV); input resistance (82.5 +/- 17, 63 +/- 16 and 83 +/- 18 M omega) and membrane time constant (18.5 +/- 7.3, 14.2 +/- 6.8 and 10.7 +/- 3.4 ms). 3. Direct activation of dorsolateral septal neurones by current injection below 0.2 nA triggered repetitive firing of fast action potentials. Larger current pulses elicited a characteristic response consisting of an initial fast action potential followed by a train of slow spikes. An after-hyperpolarization followed termination of the pulse and the characteristic response. 4. In dorsolateral septal neurons tetrodotoxin (TTX) abolished the fast action potentials. The slow spikes and the after-hyperpolarization disappeared in presence of Co2+ or after brief removal of external Ca2+. This suggests that the characteristic response is mediated by Ca2+ and the after-hyperpolarization by a Ca2+-dependent K+ conductance. 5. The firing pattern of intermediate septal neurones activated from the resting potential spontaneously measured in the cells was similar to that of dorsolateral septal neurones; but direct activation from a hyperpolarized membrane potential evoked in intermediate septal cells a bursting response due to the generation of a low-threshold spike. The low-threshold spike was TTX-resistant but abolished by Co2+ and reached a maximal amplitude after hyperpolarization to -75 mV lasting for 100-150 ms. These results suggest the existence in intermediate septal neurons of a low-threshold Ca2+ conductance inactivated at the resting potential and deinactivated by hyperpolarization. 6. Depolarization of medial septal neurons by current pulses of amplitude greater than 0.2-0.3 nA elicited a typical burst of two to six action potentials. The bursts lasted for 20-50 ms and were followed by a marked after-hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
authors: Departamento de Fisiología, Facultad de Medicina, Universidad de Sevilla, Spain.
authors: G
authors: G
authors: Alvarez de Toledo
authors: J
authors: J
authors: López-Barneo
mesh_terms: D015761:4-Aminopyridine; D000200:Action Potentials / Q000187:drug effects; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D009474:Neurons / Q000502:physiology*; D012686:Septal Nuclei / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000631:Aminopyridines; D007473:Ion Channels; D001464:Barium; D003035:Cobalt; D013779:Tetrodotoxin; D015761:4-Aminopyridine; D002118:Calcium