Osmoresponsiveness of the rat supraoptic nucleus in vivo depends on glutamatergic inputs.
Intracellular recording from supraoptic nucleus (SON) neurones in hypothalamic slices revealed that a 40 mOsm change in osmolality had little effect on membrane conductance. However, intracellular recordings in vivo revealed a significant increase in EPSP frequency after the plasma osmolality had been raised by approximately 10 mOsM. We recorded extracellularly in vivo from 18 antidromically identified SON neurones in urethane-anaesthetised male Wistar rats, while hypertonic saline was infused intravenously (1.05M NaCl, 50 microliters/min for 35 minutes). In 9 experiments an intracerebroventricular (ICV) injection of 5 microliters 10mM kynurenic acid was given 5 minutes prior to start of the infusion. Kynurenate significantly reduced the osmotic response (P < 0.001, Student's t-test); the rat of increase in spike frequency was reduced from 0.089 +/- 0.004 Hz/min (n = 9) to 0.035 +/- 0.003 Hz/min (n = 9). Kynurenic acid did not reduce the basal firing rate of SON neurones, but in osmotically stimulated neurones, it reduced the firing rate to basal levels. Hence the osmoresponsiveness of SON neurones depends on a glutamatergic input that is independent of mechanisms that maintain basal electrical activity.
Dyball
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RE
Department of Anatomy, University of Cambridge.
McKenzie
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DN
Thomas
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GP
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D066298:In Vitro Techniques; D007276:Injections, Intraventricular; D007736:Kynurenic Acid / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000187:drug effects*; D009490:Neurosecretory Systems / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000187:drug effects / Q000502:physiology*; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D012462:Saline Solution, Hypertonic; D007736:Kynurenic Acid