A variety of stressors activate the hypothalamic-pituitary-adrenal axis, with secretion and compensatory enhanced synthesis of hypothalamic corticotropin-releasing hormone (CRH). Whether CRH is a major effector in the stress response of the neonatal rat and whether the peptide's gene expression is subsequently up-regulated are not fully understood. We studied the effect of cold-separation stress on plasma corticosterone (CORT) levels and CRH messenger RNA (CRH-mRNA) abundance in the paraventricular nucleus. Rats (4-16 days old) were subjected to maximal tolerated cold-separation. CORT and CRH-mRNA abundance were measured before and at several time points after stress. Cold-separation stress resulted in a significant plasma CORT increase in all age groups studied. This was abolished by the administration of an antiserum to CRH on both postnatal days 6 and 9. CRH-mRNA increased in rats aged 9 days or older, but not in 6-day-old rats, by 4 h after stress. These results suggest the presence of robust CRH-mediated adrenal responses to cold-separation stress in neonatal rats. Before postnatal day 9, however, the compensatory increase in CRH-mRNA abundance is minimal.

Band 3 is the most abundant integral protein of the red blood cell membrane. It performs two critical biological functions: maintaining ionic homeostasis, by transporting Cl- and HCO3-ions, and providing mechanical stability to the erythroid membrane. Erythroid band 3 (AE1) is one of three anion exchangers that are encoded by separate genes. The AE1 gene is transcribed by two promoters: the upstream promoter produces erythroid band 3, whereas the downstream promoter initiates transcription of the band 3 isoform in kidney. To assess the biological consequences of band 3 deficiency, we have selectively inactivated erythroid but not kidney band 3 by gene targeting in mice. Although no death in utero occurred, the majority of homozygous mice die within two weeks after birth. The erythroid band 3 null mice show retarded growth, spherocytic red blood cell morphology and severe haemolytic anaemia. Remarkably, the band 3-/- red blood cells assembled normal membrane skeleton thus challenging the notion that the presence of band 3 is required for the stable biogenesis of membrane skeleton. The availability of band 3-/- mice offers a unique opportunity to investigate the role of erythroid band 3 in the regulation of membrane-skeletal interactions, anion transport and the invasion and growth of malaria parasite into red blood cells.

The ontogeny of corticotropin-releasing hormone (CRH) receptor messenger ribonucleic acid (mRNA) in rat brain, using in situ hybridization, is the focus of this study. The developmental profile of CRH receptor using binding assays and receptor autoradiography has been reported, but may be confounded by the presence of a binding protein. The recent cloning of the rat CRH receptor gene has permitted the use of in situ hybridization histochemistry to map the distribution of cells expressing CRH receptor mRNA in the developing brain. We used antisense 35 S-labeled oligodeoxynucleotide probes for the two reported splice-variants of the CRH receptor mRNA, which yielded essentially identical localization patterns. CRH receptor mRNA was clearly detectable in infant brain starting on the second postnatal day. Signal in hippocampal CA1, CA2 and CA3a increased to 300-600% of adult levels by postnatal day 6 with a subsequent gradual decline. In the amygdala, in contrast, CRH receptor mRNA abundance increased steadily between the second and the ninth postnatal days, to levels twice higher than those in the adult. In the cortex, CRH receptor mRNA levels were high on postnatal day 2 and decreased to adult levels by day 12. Transient signal over the hypothalamic paraventricular nucleus, observed on the second postnatal day, was not evident at older ages. These results demonstrate robust synthesis of CRH receptor as early as on the second postnatal day and unique region-specific developmental profiles for CRH receptor gene expression.