Serotonergic inhibition of light-induced fos protein expression and extracellular glutamate in the suprachiasmatic nuclei.
The present experiments were undertaken to explore a role for serotonin (5-HT) in modulating photic signal transduction and extracellular glutamate (Glu) concentration in the suprachiasmatic nuclei (SCN) of the Syrian hamster. Pretreatment with an i.p. injection of the serotonergic, quipazine, caused a marked decrease in the number of SCN cells expressing Fos protein-like immunoreactivity (Fos-LI) induced by a light pulse delivered during the latter part of the dark phase (7 h after lights-off; 55.6 +/- 7.5% of vehicle controls, P < 0.004). This effect of quipazine was dose-dependent and was limited principally to the ventrolateral region of the SCN. In a likewise manner, intra-SCN microinjection of quipazine inhibited light-induced Fos-LI in the ventrolateral SCN, indicating that the suppressive action of quipazine is centered in the SCN. In a separate experiment, localized perfusion of the SCN region with 5-HT using the microdialysis technique caused a significant reduction in the extracellular concentration of Glu. The effect was greater during the dark phase, compared to the light phase of the day-night cycle (60.7 +/- 6.8% vs. 39.3 +/- 6.8% maximal suppression, respectively; P < 0.05). Similar localized application of quipazine also decreased extracellular Glu (48.0 +/- 6.1% maximal suppression; P < 0.05). Collectively, these results are evidence for a serotonergic modulation of retinohypothalamic input in the SCN, which could involve a presynaptic inhibition of Glu release.
Selim
M
M
Department of Biological Sciences, Kent State University, OH 44242.
Glass
J D
JD
Hauser
U E
UE
Rea
M A
MA
D000818:Animals; D006224:Cricetinae; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D007150:Immunohistochemistry; D008297:Male; D008647:Mesocricetus; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D010775:Photic Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D011814:Quipazine / Q000494:pharmacology; D012701:Serotonin / Q000502:physiology*; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000378:metabolism*
D005971:Glutamates; D009419:Nerve Tissue Proteins; D016760:Proto-Oncogene Proteins c-fos; D012701:Serotonin; D018698:Glutamic Acid; D011814:Quipazine