A COMPARATIVE STUDY OF TRYPTOPHAN HYDROXYLASE'S CIRCADIAN RHYTHM IN THE FUNCTIONAL PARTS OF DORSAL RAPHE NUCLEI IN THE MESENCEPHALON

Zeina Malek and Louay Labban*

ABSTRACT

Dorsal Raphe (DR), the most developed part of the Raphe complex, is divided into three cellular well defined subnuclei: the ventromedian (VM), the dorsomedian (DM), and the lateral (L). Also, the raphe complex is known to exhibit circadian variations within numerous processes concerning synthesis and release of Serotonin, its main neurotransmitter. On the other hand, it has been established that the biological clock of the Suprachiasmatic Nuclei (SCN), controls the circadian behavior of the Serotonin neurons. In this study, the rate limiting enzyme in serotonin synthesis, Tryptophan Hydroxylase, was measured within all the DR subdivisions among which only the lateral parts showed circadian variations. Our findings suggest a differential regulation in Serotonin synthesis at the cellular levels of DR, taking in consideration that the lateral parts were thought to be the most involved subdivision in the circadian system, both upon anatomical and functional levels.

Keywords: Tryptophan hydroxylase, Biological Clock, Circadian rhythm, Dorsal raphe.