| Biological rhythm is one of the characteristics of life. In the occurrence and biological evolution, the organism formed the endogenous rhythm which sychronous with seasonal changes of the natural environment in order to adapt to the changes of the environment. But it is different from the rhythm of the natural environment in the time features. As the result of organisms living in the light-dark cycle of day and night environment, many activities of lives have shown 24h cycle of biological rhythm—the circadian rhythm. Cirdadian rhythm is the strongest biological rhythm of the body. Many physiological and biochemical parameters of body are changed following the circadian rhythm.In mammals, the circadian rhythm exists widespreadly on the level of cells, tissues and organs. There is a complex control system to regulate it. The suprachiasmatic nucleus (SCN) of hypothalamus is the circadian pacemaker of mammalian. The oscillation of variety of circadian clock gene of the SCN is the basis of circadian rhythm. Pineal gland (PG) is an important target of SCN integration. The melatonin (MT) is produced by PG. As the most important zeitgeber of the body, MT could act on SCN to induce the changes of circadian rhythm and this effect has phase-dependence. The SCN-PG as the most important control system of circadian rhythm controls the input, oscillation and output process of circadian rhythm.The habenular nucleus (Hb) which located behind the hypothalamus is the major relay station between forebrain and midbrain. The vasopressin nerve fibers relationship between the Hb and the SCN had been proved. And the Hb also could get indirect relationship with the SCN via preoptic area and rapheal nuclei. The Hb has a close relationship with the PG both morphologically and functionally. The stimulation of the Hb can influence the firing rate of PG neurons. The Hb, especially the medial part of lateral Hb contains abundant of MT receptors. It suggests that the Hb is an important target of PG. The Hb could project to PG. And the Hb also can get relationship with the SCN via PG to regulate the circadian rhythm.In this study, we observed the changes of spontaneous firing rate of LHb and MHb neurons after elctric stimulating or microinjection of Glu/Lid into the SCN by extracellular recording. We observed the mRNA expression of Per2, Clock and Bmal1 in SCN and PG by RT-polymerase chain reaction (RT-PCR) after chemical destroied LHb by kainic acid (KA). And the expression level changes of melatonin synthesis limited enzyme—NAT, and its receptors MT1, MT2 at 8:00, 12:00, 16:00, 20:00, 24:00 and 4:00. The results are as followed:1. The firing rate of 46 neurons were recorded when electric stimulate SCN. Among them 8 neurons were excited in LHb, 7 neurons were inhibited in LHb, 3 neurons were excited in MHb and 4 neurons were inhibited in MHb. There are no significant difference between LHb and MHb (P>0.05). 2. The firing rate of 105 neurons were recorded after microinjection of Glu into SCN. 13 of these neurons were excited and 15 of them were inhibited in LHb after micrinjection. 7 of these neurons were excited and 26 of these neurons were inhibited in MHb after microinjection. Excited SCN could inhibit the activities of MHb (P<0.05).3. The firing rate of 49 neurons were recorded after microinjection of Lid into SCN. In LHb, 3 of them were exctied and 7 of them were inhibited. In MHb, 11 of neurons were excited and 4 of them were inhibited. Inhibition of SCN could excite the MHb and inhibit the LHb (P<0.05).4. The day and night oscillate rhythm of clock gene Per2, Bmall and Clock in SCN were not changed . But the mRNA of Per2 were decreased at all of six points. The mRNA of Bmall were decreased at 8:00, 16:00, 20:00 and 4:00. The mRNA of Clock were decreased at 8:00, 12:00, 16:00, 20:00 and 4:00.(P<0.05)5. The circadian rhythm of clock gene Per2, Bmall and Clock in PG were not changed. But the mRNA of Per2 were decreased at 8:00, 12:00, 24:00. The mRNA of Bmall were decreased at 12:00, 16:00, 20:00 and 4:00. The mRNA of Clock were decreased at all of six points (8:00, 12:00, 16:00, 20:00, 24:00 and 4:00).(P<0.05)6. The expression of MT related gene NAT, MT1 and MT2 in SCN were decreased in lesion groups at all of six points, but the day and night oscillate rhythm was not changed. The decrease of NAT was occurred at all of six points. The decrease of MT1 occurred at 8:00, 12:00, 20:00, 24:00 and 4:00. The decrease of MT2 was occurred at 12:00, 16:00, 20:00, 24:00 and 4:00. (P<0.05) 7. In PG, the expression of MT related gene NAT, MT1 and MT2 were decreased in lesion groups. But the circadian rhythm of them were not changed. The points of change of NAT are 8:00, 16:00, 20:00, 24:00. The changed points of MT1 are 8:00, 12:00 and 4:00. The changed point of MT2 is 24:00. (P<0.05)We have confirmed that there is a functional relationship between the Hb and SCN by elctrophysiological methods. Coupled with the results of RT-PCR, we further prove that chemical lesions of the LHb can decrease the expression of clock genes in SCN and PG, but can not change their circadian rhythm. The mechanism is implicated in the effect of the LHb on the synthesis of melatonin in the PG which may further induceof the change of clock genes expression in the SCN. Thus, the LHb can affect the function of the SCN through the effect of the LHb on the activities of the PG; in turn, the Hb is also controlled by the SCN and PG. These studies suggest that the LHb is an important component of the central circadian rhythm control system and the Hb participates in the circadian rhythm regulation through the functional interaction with the SCN and PG. |
PDF Full Text Request