Developmental Brain Research最新文献

Mice with a targeted disruption of the gene encoding the stilbene-insensitive electroneutral sodium bicarbonate cotransporter (NBC3; slc4a7) exhibit cochlear and retinal degeneration. To establish the progressive nature of sensory cells loss in slc4a7^−/− deficient mice, we studied the morphology of cochleas of slc4a7^−/− and slc4a7^+/+ mice from postnatal day two (P2) to ninety (P90). Cell death was evaluated in slc4a7^−/− cochleas using the TUNEL technique and caspase-3 immunoreactivity. The time course of NBC3 expression in the cochlea was assessed by immunohistochemistry using an antibody against NBC3. Between P2 and P8, slc4a7^−/− mice cochlea exhibit normal morphology. There was a normal complement of inner and outer hair cells from the hook to the apical region. At P15, slc4a7^−/− mice cochlea inner and outer hair cells were still present at the hook region, and vacuoles were seen underneath Hensen's cells. At P21, inner and outer hair cells were degenerated in this region. Between P30 and P90, there was a pronounced loss of hair cells and spiral ganglia neurons. Morphological analysis of the spiral ligament showed a progressive loss of type II and IV fibrocytes beginning at day 21. Transmission electron microscopy observations at P30 and P90 revealed that type II and IV fibrocytes showed shrinkage and vacuolization. In addition, hair cells were deteriorated with evidence of shrinkage and picnotic nuclei. TUNEL staining showed apoptotic cells at P8 in the organ of Corti at the basal region of the cochlea. At P15, caspase-3 immunoreactivity was present in supporting cells of the organ of Corti. NBC3 mild immunoreactivity was detected in the organ of Corti at P11. There was an increase in the expression of NBC3 in the spiral ligament between P17 and P19. From P21 to P90, NBC3 expression was confined to the spiral ligament and inner and outer sulcus cells. The vestibular sensory epithelia from slc4a7^−/− mice were normal from P2 to P90. Damage of the sensory epithelia at the high frequency zone of the cochlea suggests that NBC3 may play an important physiological role in this region.

γ-Aminobutyric acid (GABA), which is inhibitory in the adult central nervous system, can be excitatory in the developing brain. The change from excitatory to inhibitory action of GABA during development is caused by a negative shift in its reversal potential. Here, we report a presynaptic activity-mediated negative shift in the reversal potential of the GABA-mediated synaptic currents in immature deep cerebellar nuclei neurons. This shift appears to be due to an increased expression and activation of the K⁺–Cl⁻ co-transporter type 2 (KCC-2) through the activation of protein kinase A, protein synthesis and activation of protein phosphatases. Thus, maturation of the GABA response may rely on an activity-dependent up-regulation of KCC-2.

The mammalian GATA family of transcription factors comprises of 6 members that are involved in diverse roles. The expression profile of GATA6 has been poorly defined in the central nervous system (CNS). In this report, we identify GATA6 expression in the normal mouse and human CNS, using Northern blot analyses, immunohistochemistry (IHC), and immunofluorescence (IF). GATA6 is expressed as a 2.2 kb transcript in the adult mouse brain and several regions of the adult human brain. Furthermore, cellular characterization demonstrates GATA6 nuclear expression in neurons, astrocytes, choroids plexus epithelium, and endothelial cells.

Hyperhomocysteinemia is a risk factor for a range of neurodegenerative conditions, yet its effects in the developing nervous system have been poorly elucidated. We studied the in vitro response of cerebellar granule neurons (CGCs) to homocysteine. We have shown that embryonic CGCs are resistant to homocysteine-induced neurotoxicity, whilst postnatal CGCs are not. This is the first demonstration of a neuronal population undergoing a developmental switch in their response to homocysteine. Greater understanding of this change may have important implications for both neurodegenerative conditions and neurodevelopmental disorders.

Previously, we reported a line of mice (Hoxa5SV2) that ectopically expresses HOXA5 in the developing cervical and brachial dorsal spinal cord. Animals from this line exhibited a clear loss of cells in the outer lamina of the mature dorsal horn that coincided with an adult phenotype of sensory and motor defects of the forelimb. In this report, we examined the etiology of lost dorsal horn cells. Cells normally fated to populate the outer laminae I–III of the dorsal horn migrated inappropriately, as the percentage of laterally positioned cells in the dorsal horn was significantly reduced in Hoxa5SV2 transgenics. Apoptosis was a major cause of cell loss while proliferation of neurons was not affected in Hoxa5SV2 animals. Although Hoxa5 has been shown in vitro to regulate p53 expression and cause p53-dependent apoptosis, p53 was not required in vivo for the inappropriate apoptosis seen in Hoxa5SV2 mice, or for the normal death of motor neurons. Normal apoptosis is not dependent on Hoxa5, as the level of ventral horn motor neuron apoptosis was not changed in Hoxa5 null animals. As a possible cause of aberrant migration and/or apoptosis of dorsal neurons, misexpression of cell type markers was demonstrated. Further, the expression pattern of laminar markers was altered and sensory fibers aberrantly penetrated the outer lamina of mutants. Our evidence suggests that the loss of dorsal horn neurons in Hoxa5SV2 mutants was due to misexpression of dorsal horn neuronal markers, aberrant migration, and inappropriate apoptosis.

Perinatal brain injury is associated with the release of amino acids, principally glutamate and GABA, resulting in massive increases in intracellular calcium and eventual cell death. We have previously demonstrated that independent administration of kainic acid (KA), an AMPA/kainate receptor agonist, or muscimol, a GABA_A receptor agonist, to newborn rats results in hippocampal damage [Hilton, G.D., Ndubuizu, A., and McCarthy, M.M., 2004. Neuroprotective effects of estradiol in newborn female rat hippocampus. Dev. Brain Res. 150, 191–198; Hilton, G. D., Nunez, J.L. and McCarthy, M.M., 2003. Sex differences in response to kainic acid and estradiol in the hippocampus of newborn rats. Neuroscience. 116, 383–391; Nunez, J.L. and McCarthy, M.M., 2003. Estradiol exacerbates hippocampal damage in a model of preterm infant brain injury. Endocrinology. 144, 2350–2359; Nunez, J.L., Alt, J.J. and McCarthy, M.M., 2003. A new model for prenatal brain damage. I. GABA(A) receptor activation induces cell death in developing rat hippocampus. Exp. Neurol. 181, 258–269]. We now report that KA or muscimol alone administered to immature hippocampal neurons in culture induces significant cell death as evidenced by TUNEL assay. Surprisingly, simultaneous administration of equimolar quantities of these two agonists blocks the effect of either one alone. Moreover, treatment of newborn pups results in less damage compared to either muscimol or KA alone. We further observed that immunoreactivity for the calcium-binding protein, calbindin D_28K, is increased in the brains of pups simultaneously administered KA and muscimol as compared to either alone.

Alterations in maternal dietary choline availability during days 12–17 of pregnancy led to an increase in the level of immunoreactive netrin-1 and a decrease in the level of DCC protein in the developing fetal mouse brain hippocampus compared with controls. Changes in the expression of cell migration cues during development could account for some of the lifelong consequences of maternal dietary choline availability for cognitive and memory processes.

The effects of a single course of antenatal betamethasone on S100B protein concentration were investigated in Fisher 344 rats. On day 20 of gestation, pregnant rats were injected twice 8 h apart with either (1) 170 μg kg⁻¹ body weight betamethasone (“clinically-equivalent dose”, equivalent to 12 mg twice, 24 h apart in humans), (2) half of this dose (equivalent to 6 mg) or (3) vehicle. We report reference values for S100B protein in the serum and different brain regions in both genders at 1, 2, and 21 days after birth. Interestingly, S100B concentration showed a time-dependent and brain region-specific pattern of expression. At P1, S100B was higher in the serum of males compared to females. In addition, we show that both doses of betamethasone decreased S100B concentration in the serum of males at P1, whereas in the hippocampus, it was reduced by the clinically-equivalent dose only. This suggests that lowering the dose of antenatal betamethasone may be less detrimental for brain maturation and therefore we reiterate the need for clinical trials with a low dose regimen.

The cytoarchitecture of dorsal cochlear nucleus (DCN), characterized by a distinct laminar structure similar to the cerebellar cortex of the normal mouse, is known to be disrupted in the Reelin-deficient mouse, reeler. Here, we have reexamined both the cytoarchitecture and myeloarchitecture of this nucleus and described expression pattern of Reelin protein during perinatal periods. Reelin-immunopositive granule cells were firstly recognized in the external granular layer of the DCN at embryological day 16 (E16). Next, we examined the cytoarchitecture of the DCN of the normal and reeler mice with Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα) immunostaining. CaMKIIα-immunoreactive cartwheel cells were laminarly distributed in the layer II of the normal DCN, but scattered throughout the reeler DCN. Injection of retrograde tracer, Fluoro-Gold (FG) into the inferior colliculus of the reeler mouse resulted in that retrogradely labeled neurons in the DCN were radially scattered instead of being confined to a single layer as seen in the normal mouse. To examine whether CaMKIIα-immunopositive cartwheel cells are neurons projecting to the inferior colliculus or not, double labeling with CaMKIIα immunohistochemistry and retrograde labeling with an injection of FG into the inferior colliculus were made, which revealed that CaMKIIα-immunoreactive cartwheel cells do not send axons to the inferior colliculus. The present findings imply that Reelin may have some roles in the formation of laminar structures of the DCN.