| Summary: | 碩士 === 國立陽明大學 === 神經科學研究所 === 95 === It is a well established fact that calbindin-D28K mRNA is increased by retinoic acid in cerebellum (Wang and Christakos,1995; Matsumoto et al.,1998). However, very little is known about the regulation of calbindin-D28K by retinoid signaling in the developing striatum. Therefore the present study is to investigate whether retinoid signaling through RARb and RXRg may regulate the expression of calbindin. Accordingly it is divided into three parts:
The first part is that RARb signaling may regulate the expression of calbindin. In the loss-of-function study, calbindin mRNA levels of newborn, postnatal day 7 and adult striatum were assayed by in situ hybridization in the RARb-/- and wild-type littermates. The results indicated that calbindin expression was increased in the nucleus accumbens but decreased in rostral caudate/putamen in postnatal and adult RARb-/- mice; In the gain-of-function study, we treated pregnant ICR mice with RA and then assayed calbindin expression. The results indicated that calbindin expression was decreased in the nucleus accumbens but increased in caudate/putamen.
The second part is to examine whether RXRg may regulate the expression of calbindin in the postnatal and adult striatum. In the loss-of-function study, calbindin mRNA levels of newborn, postnatal day 3, 7, 14 and adult caudate/putamen were assayed by in situ hybridization in the RXRg-/- and wild-type littermates. The results indicated calbindin mRNA levels were increased in the dorsolateral caudate/putamen at caudal levels from postnatal day 3 to adult RXRg-/- mice, as well as at the middle level from postnatal day 14 to adult RXRg-/- mice. On the other hand, we tested whether the heterodimeric partners of RXRg, thyroid hormone receptor-b1(TRb1) might be involved in RXRg mediated regulation of calbindin. The calbindin mRNA levels were assayed by in situ hybridization in the wild-type and TRbPV adult mice. The data indicated no changes. Hence, TRb1 might not be the partner of RXRg in the regulation of calbindin-D28K.
The third part is to investigate the physiological consequences of increased calbindin-D28K in the RARb-/- and RXRg-/- mutant striatum. We used acute brain slices of postnatal day 7 to 10 mice that were loaded with fura-2 to measure intracellular calcium concentration by optical imaging of calcium influx . The slices were stimulated by NMDA activation of NMDA receptors and KCl-induced depolarization. This set of experiments was preliminary and incompleted, due to the time consuming process of setting up the system. To determine if RARb and RXRg signaling regulates NMDA receptor expression, the mRNA levels of NMDA receptor subunits were assayed by in situ hybridization. The indicated NR1 and NR2B were increased in the nucleus accumbens of RARb-/- mice . NR2A was decreased but NR2B was increased in the dorsolateral caudate/putamen of caudal level of RXRg-/- mice.
In conclusion, our findings suggest that retinoid signaling can regulate the expression of calbindin-D28K in the postnatal and adult striatum.
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