Abstract
The habenular nucleus (Hb) located in the epithalamus is an important connection between the limbic forebrain and midbrain pathway and it regulates physiological activities including reproduction, sleep-wake, body temperature. Hb is anatomically close to the suprachiasmatic nucleus (SCN), the pacemaker of circadian rhythms in mammals. In vivo data showed circadian oscillation of Period2 (Per2) expression in Hb. However, it remains unknown whether the circadian oscillation of Per2 expression is regulated by SCN. We used semi-quantity RT-PCR methods to examine the relative expression of Per2 and c-fos mRNA in the Hb at 13:00 and 1:00 in the LD (light-dark) cycle either SCN was intact or destroyed. The expression of Per2 and c-fos mRNA in the Hb was higher at 13:00 than at 1:00. However, damaging the SCN abolished the difference of Per2 and c-fos mRNA expression at the two time ponits in the Hb, suggesting circadian oscillation of Per2 and c-fos gene in the Hb may be regulated by SCN under in vivo condition.
Highlights
Habenular nucleus(Hb) is located on the dorsomedial surface of the epithalamus and served as a key position from the limbic forebrain inputs to mid-brain structures(Aghajanian, 1977;Andres,1999)
Damaging the suprachiasmatic nucleus (SCN) abolished the difference of Per2 and c-fos mRNA expression at the two time ponits in the habenular nucleus (Hb), suggesting circadian oscillation of Per2 and c-fos gene in the Hb may be regulated by SCN under in vivo condition
Our previous study found that Per2 gene and protein expression in the lateral habenular nucleus (LHb) at six zeitgeber time points in a 12h light and 12h dark(LD) condition had rhythmic oscillation with higher expression at the daytime and lower expression at the nighttime (Zhao, 2015)
Summary
Habenular nucleus(Hb) is located on the dorsomedial surface of the epithalamus and served as a key position from the limbic forebrain inputs to mid-brain structures(Aghajanian, 1977;Andres,1999). The Hb was reported to play an important role in regulating many biological functions, including reproduction function, cardiovascular activity, pain, stress, themoregulation, sleep-wake and ingestive behavior (Wagner, 1998; Lv, 2012; Aizawa, 2013; Heldt, 2006; Ootsuka, 2015; Christensen, 2013), which all show daily rhythmicity. Our previous experiments have manifested that there are activated and suppressed cells by the retinal illumination in the Hb and the Hb neurons show obvious daily rhythmicity with higher baseline firing rates during the day than the night (Zhao, 2005). Recent research found that Per 2 circadian gene expression is present in the Hb both in vitro and in vivo (Guilding, 2010; Zhao, 2015). It is still unclear that whether Per circadian expression in the Hb may be modulated by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus as the major pacemaker of circadian rhythm system (Moore, 1972)
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