Suprachiasmatic nucleus neurons are glucose sensitive.
The suprachiasmatic nucleus (SCN) in the hypothalamus serves as the pacemaker for mammalian circadian rhythms. In a hamster brain slice preparation, the authors were able to record spontaneous activity from SCN cells for up to 4 days in vitro and verify a self-sustained rhythm in firing. The phase of this rhythm was altered by the concentration of glucose in the bathing medium, with time of peak firing advanced for a 20 mM glucose condition and slightly delayed for a 5 mM glucose condition, relative to 10 mM. The advancing effect of 20 mM glucose and the delaying effect of 5 mM glucose were not maintained during a 2nd day in vitro after changing the bathing medium back to 10 mM glucose, thus indicating the effect was not a permanent phase shift of the underlying oscillation. In experiments recording from cell-attached membrane patches on acutely dissociated hamster SCN neurons, exchanging the bathing medium from high (20 mM) to zero glucose increased potassium (K+)-selective channel activity. With inside-out membrane patches, the authors revealed the presence of a glybenclamide-sensitive K+ channel (190 pS) and a larger conductance (260 pS) Ca(2+)-dependent K+ channel that were both reversibly inhibited by ATP at the cytoplasmic surface. Furthermore, 1 mM tetraethylammonium chloride was demonstrated to advance peak firing time in the brain slice in a similar manner to a high concentration of glucose (20 mM). The authors interpret the result to imply that SCNs are sensitive to glucose, most probably via ATP modulation of K+ channel activity in these neurons. Tonic modulation of K+ channel activity appears to alter output of the pacemaker but does not reset the phase.
Hall
A C
AC
Department of Psychology, Smith College, Northampton, MA 01063, USA.
Hoffmaster
R M
RM
Stern
E L
EL
Harrington
M E
ME
Bickar
D
D
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006224:Cricetinae; D005947:Glucose / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008647:Mesocricetus; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D015221:Potassium Channels; D000255:Adenosine Triphosphate; D005947:Glucose