title: Synaptic feedback excitation has hypothalamic neural networks generate quasirhythmic burst activity.
abstract: 1. Dissociated neurons from embryonic rat hypothalamus form synaptically coupled networks when cultured for several weeks. When synaptic inhibition is suppressed by the gamma-aminobutyric acid-A (GABAA) antagonist picrotoxin, neurons exhibit "rhythmic" burst activity that is blocked by the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 2. We have examined whether this type of activity is generated by pacemaker cells driving follower cells synaptically or whether it is generated by a neuronal network through feedback excitation by Ca2+ imaging of Fura-2/AM-loaded neurons and single-cell recording. 3. IN the presence of the GABAA antagonist picrotoxin (20 microM), a large majority of neurons (> 85%) displayed quasirhythmic increases in intracellular concentration of Ca2+ ([Ca2+]i). Single-cell recording revealed that these increases in [Ca2+]i correspond to burst discharges in individual neurons. When excitatory synaptic transmission was blocked by CNQX (20 microM), none of the imaged neurons exhibited significant oscillations in [Ca2+]i. 4. Investigation of the intervals between bursts from single-cell recording revealed a random distribution over a range of 400% from the minimum interval. Poincaré maps of burst intervals, i.e., graphs of all burst intervals versus their preceding burst interval, revealed that a burst interval is unpredictable from its predecessor. 5. When synaptic coupling was attenuated by low concentrations of CNQX (50-500 nM), the mean burst interval was considerably increased without a change in the random character of burst activity. 4-Aminopyridine (1 mM), known to increase synaptic efficiency, reduced the mean burst interval.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Max-Planck-Institut für Biophysikalische Chemie, Abt. Membranbiophysik, AG Zellphysiologie, Göttingen, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Müller
authors.forename: D
authors.initials: D
authors.lastname: Swandulla
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D005246:Feedback; D007031:Hypothalamus / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism; D009415:Nerve Net / Q000502:physiology*; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000187:drug effects / Q000502:physiology*
chemical_list: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D002118:Calcium