Ionic and synaptic mechanisms underlying a brainstem oscillator: an in vitro study of the pacemaker nucleus of Apteronotus.
1. In an in vitro preparation of the medullary pacemaker nucleus of Apteronotus, the consequences of a variety of ionic and pharmacological manipulations upon both ongoing activity and synaptic modulation of the nucleus were assessed. 2. Spontaneous rhythmicity in the pacemaker nucleus was found to be Na+-, K+-, and Ca(2+)-dependent. The extreme sensitivity to 4-aminopyridine (4-AP) relative to other treatments suggested that the K+ A-current is a critical element in the oscillations. 3. Elevated K+ or 4-AP were titrated to concentrations that suppressed spontaneous oscillations, but allowed modulatory, 'chirp' epsps to persist. The transition to elevated K+ revealed oscillatory properties in some neurons in the form of epsp-induced ringing 4. Threshold concentrations of 4-AP sufficient to halt oscillations, caused epsps to become larger and complex, increased input resistance, and enhanced the effects of current injection on epsp amplitude. A greater degree of voltage-sensitivity was also seen in later components of the complex epsp. 5. Several treatments presumed to increase Ca2+ caused desynchronization of firing and revealed diverging intrinsic frequencies among cells.
Department of Neurosciences & Neurobiology Unit, Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093.
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D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D001933:Brain Stem / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology; D003080:Cold Temperature; D004555:Electric Fish / Q000502:physiology*; D005583:Fourier Analysis; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D006801:Humans; D066298:In Vitro Techniques; D015221:Potassium Channels / Q000187:drug effects; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D005971:Glutamates; D015221:Potassium Channels; D015222:Sodium Channels; D018698:Glutamic Acid; D013779:Tetrodotoxin; D015761:4-Aminopyridine; D002118:Calcium