Differential timing of amino acid and 5-HIAA rhythms in suprachiasmatic hypothalamus.
In vivo brain microdialysis was used to characterize the daily pattern of extracellular excitatory amino acids (EAA; glutamate and aspartate), glutamine and 5-hydroxyindoleacetic acid (5-HIAA) in the region of the suprachiasmatic nucleus (SCN) in freely behaving male Syrian hamsters. Diurnal variations in the extracellular concentrations of EAA and 5-HIAA observed under 14:10-h light-dark (LD) photoperiod were confirmed by cosinor analysis. Peak levels occurred during the night, with the mean acrophasis for 5-HI-AA concentration preceding that for EAA by 1-2 h. Release of EAA was stimulated by K(+)-induced depolarization in a Ca(2+)-dependent manner and was not affected by tetrodotoxin. In the absence of light cues (constant dim red light, < 0.4 lx; DD) there was a significant time-of-day effect in peak glutamate concentration (occurring during subjective night), but the rhythmic pattern of 5-HIAA output was lost. There was no apparent direct temporal linkage between peaks in extracellular EAA or 5-HIAA and bouts of wheel-running activity under LD or DD. These results are evidence that 1) the daily release pattern of extracellular glutamate, but not 5-HIAA, is circadian in nature; and 2) this rhythm in glutamate is not based on Na+ channel-dependent action potentials. Finally, a discordance in the timing of peak nocturnal extracellular 5-HIAA and EAA concentrations was evident, possibly reflecting an interplay between serotonergic and EAA pathways in the SCN.
Glass
J D
JD
Department of Biological Sciences, Kent State University, Ohio 44242.
Hauser
U E
UE
Blank
J L
JL
Selim
M
M
Rea
M A
MA
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D006224:Cricetinae; D003956:Dialysis; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism*; D008297:Male; D008647:Mesocricetus; D010507:Periodicity; D017440:Photoperiod; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*; D013997:Time Factors
D000596:Amino Acids; D006897:Hydroxyindoleacetic Acid