Differential timing of amino acid and 5-HIAA rhythms in suprachiasmatic hypothalamus

Abstract

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.

Circadian Regulation of cAMP Response Element-mediated Gene Expression in the Suprachiasmatic Nuclei

“…Given that extracellular membrane receptor-mediated signaling events regulate CRE-mediated gene expression, one may expect to observe circadian changes in the level of extracellular transmitters capable of eliciting CRE-mediated gene expression. In support of this idea, circadian variations in the concentrations of excitatory amino acids have been observed within the region of the SCN under free-running conditions, and in slice preparations (62)(63)(64). Circadian oscillations in CRE-dependent transcription also may be a result of an inherent rhythmic transcriptional program of SCN pacemaker cells.…”

A Systematic Search and Mapping Review of Studies on Intracerebral Microdialysis of Amino Acids, and Systematized Review of Studies on Circadian Rhythms

“…According to the authors, aspartate levels started to decrease before light onset, and increase before dark onset. In hamsters kept on a 14:10 light-dark cycle (lights on at 08:00) and measured for 24 h, Glass et al standardised values to a percentage of the daily mean [31]. Time-of-day effects were tested by a multivariate time series analysis (MANOVA) followed by Student Newman Keuls tests.…”

“…To conclude, in the suprachiasmatic nucleus, aspartate is higher during the dark than during the light phase in both rats and hamsters, and the rhythm is also present under urethane anaesthesia [2431]. …”

Circadian variation in GFAP immunoreactivity in the mouse suprachiasmatic nucleus

“…All of these neurotransmitters show daily variations and thus could modulate the plasticity of the astrocytes. The rhythmic liberation of glutamate in terminals of the RHT in the SCN (Glass et al, 1993) could induce variations in the GFAP-Ir. Glutamate also seems to be involved in the signalization between the neuronal activation and uptake of glucose by the astrocytes (Pellerin & Magistretti, 1994).…”