Ontogeny of gene expression of inositol 1,4,5-trisphosphate receptor in the rat brain: high mRNA levels in the cerebellar Purkinje cells

Early developmental changes in intracellular Ca2+ stores in rat brain

Developmental changes in intracellular Ca2+ stores in brain was studied by examining: (1) IP3- and cADPR-induced increase in [Ca2+]i in synaptosomes; (2) Ca(2+)-ATPase activity and ATP-dependent 45Ca2+ uptake into Ca2+ store in ER microsomes; (3) TG-induced inhibition of Ca(2+)-ATPase activity and ATP-dependent 45Ca2+ uptake into Ca2+ store in ER microsomes; and (4) gene expression of Ca(2+)-ATPase pump in neurons obtained from brains of the new-born and the 3-week-old rats. IP3 (EC50 310 +/- 8 nM, 200% maximum increase in [Ca2+]i) and cADPR (EC50 25 +/- 3 nM, greater than 170% maximum increase in [Ca2+]i) both were potent agonist of Ca2+ release from internal stores in synaptosomes obtained from the 3-week-old rats. However, IP3 (EC50 250 +/- 10 nM, 175 maximum increase in [Ca2+]i) was a potent, but cADPR (EC50 300 +/- 20 nM, 75% maximum increase) was a poor agonist of Ca2+ release from intracellular stores in synaptosomes obtained from the new-born rats. [3H]IP3, [32P]cADPR and [3H]Ry binding in the new-born samples were significantly less than that in the 3-week-old samples. [3H]Ry binding to its receptor was more sensitive to cADPR in microsomes from the 3-week-old rats than those from the new-born rats. Microsomes from the new-born rats exhibited TG-sensitive (IC50 30 +/- 4 nM) and TG-insensitive forms of Ca(2+)-ATPase, while microsomes from the 3-week-old rats exhibited only the TG-sensitive form of Ca(2+)-ATPase (5 +/- 1 nM IC50). Microsomes from the 3-week-old rats were more sensitive to TG but less sensitive to IP3, while microsomes from the new-born rats were more sensitive to IP3 but less sensitive to TG. The lower TG sensitivity of the new-born Ca2+ store may be because they poorly express a 45 amino acid C-terminal tail of Ca(2+)-ATPase that contains the TG regulatory sites. This site is adequately expressed in the older brain. This suggests that: (1) the new-born brain contains fully operational IP3 pathway but poorly developed cADPR pathway, while the older brain contains both IP3 and cADPR pathways; and (2) a developmental switch occurs in the new-born Ca(2+)-ATPase as a function of maturity.

Changes in mRNA levels for group I metabotropic glutamate receptors following in utero hypoxia-ischemia

The expression of group I metabotropic glutamate receptors (mGluR1 and mGluR5) and inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) mRNA was studied by in situ hybridization in the developing rat hippocampus after in utero hypoxia-ischemia. In utero hypoxia-ischemia was induced by clamping the uterine blood vessels of near-term fetuses for 10 min. Fetuses were delivered surgically, resuscitated and raised by foster mothers until postnatal day 7 and 14. Results indicated a temporal delay in the expression of mGluR1 mRNA in the dentate gyrus of the ischemic animals. The mGluR1 mRNA level was significantly lower in the ischemic animals at postnatal day 7, but reached a similar level as that of controls at postnatal day 14. In utero hypoxia-ischemia did not change the temporal-spatial expression pattern of either mGluR5 or IP3R1 mRNA in the hippocampus. Between postnatal day 7 and 14, mGluR5 mRNA showed a high and relatively constant expression, whereas IP3R1 mRNA levels were increased in all regions examined. The differences in the expressions of group I mGluRs indicate that these receptors may have different functions during hippocampal development and may play different roles in excitotoxicity.

Comparative effects of age and chronic low-level lead exposure on calcium mobilization from intracellular calcium stores in brain samples obtained from the neonatal and the adult rats

The effects of age and chronic low-level lead exposure were studied on (a) [3H]IP3 and [3H]Ry binding to their respective receptors in brain membranes and (b) Ca2+ release from internal Ca2+ stores in brain synaptosomes obtained from the neonatal and adult rats. [3H]IP3 and [3H]Ry binding sites in the control-adult membranes were greater than those in the control-neonatal membranes. [3H]IP3 bound to a single high-affinity site, IP3-R. Ca2+ decreased [3H]IP3 binding to its receptor. [3H]Ry bound to at least four subspecies of Ry-Rs. KCl and IP3 increased, but Ca2+ caused a biphasic affect on [3H]Ry binding in brain membranes. IP1 and caffeine both caused greater increase in [Ca2+]I in the adult synaptosomes than the neonatal synaptosomes. IP4 redistributed Ca2+ from the caffeine-sensitive pool to the IP3-sensitive pool. IP3 increased the caffeine-induced mobilization of Ca2+ in synaptosomes. Chronic low-level lead exposure decreased the binding of [3H]IP3 to its receptors in membranes, attenuated the IP3-induced Ca2+ mobilization in synaptosomes, abolished the IP4-induced redistribution of Ca2+ from Ry sensitive Ca2+ store to IP3-sensitive Ca2+ store, and attenuated the effects of IP1 on [Ca2+]I in caffeine stimulated synaptosomes. Lead exposure, however, did not affect [3H]Ry binding to Ry-R in membranes or the caffeine-induced increase in [Ca2+]I in synaptosomes. Chronic lead exposure protected IP3-R against Ca(2+)-induced inhibition in membranes. This protection was greater in the neonatal samples than the adult samples. This suggests that chronic low-level lead exposure down-regulated the IP3-induced Ca2+ mobilization in synaptosomes without effecting the caffeine-induced Ca2+ mobilization.

Regional variation in expression of calbindin and inositol 1,4,5-trisphosphate receptor type 1 mRNAs in the cerebellum of the staggerer mutant mouse

The Purkinje cells in the staggerer mutant mouse have various cellular abnormalities, including reduced cell number, ectopia, smaller size and absence of dendritic spines. It is also know that some of these abnormalities exhibit regional variations in the cerebellum. In this paper we have investigated expression in the staggerer Purkinje cells of the calbindin and inositol 1,4, 5-trisphosphate receptor type 1 mRNAs by in situ hybridization. Although the transcription levels of both mRNAs were significantly reduced compared with the wild-type cells, the reduction among the Purkinje cell populations was not even, varying greatly from region to region. Purkinje cells with different transcription levels were distributed in discrete regions and arranged alternately in the mediolateral direction. Moreover, the cell bodies with higher transcription levels were larger in size and aligned in a monolayer between the granular and molecular layers, whereas those with lower levels were smaller in size, fewer in number and dispersed throughout the granular layer. These findings suggest that there is a distinct mediolateral heterogeneity in the staggerer cerebellum with respect to transcription levels of these Purkinje cell-specific molecules, which might correlate with some cytological phenotypes.