Postnatal regulation of ZnT-1 expression in the mouse brain

We have characterized the postnatal development of ZnT-1, a putative zinc transporter, in the mouse brain with respect to chelatable zinc in four distinct brain areas: cerebral cortex, hippocampus, olfactory bulb and cerebellum. At birth, both zinc and ZnT-1 immunoreactivity were nearly undetectable. Beginning at the end of the first postnatal week, ZnT-1 expression increased significantly in all areas examined except the cerebellum, which contains virtually no synaptic zinc. Moreover, neurons immunoreactive for ZnT-1 were typically present in areas rich in synaptic zinc, which increased in parallel with ZnT-1. In the cerebellum, in contrast, Purkinje cells exhibited robust immunoreactivity for ZnT-1 only in the second postnatal week. While the parallel development of zinc and ZnT-1 in forebrain regions supports a direct role for synaptic zinc in regulating ZnT-1 expression, ZnT-1 in cerebellar Purkinje cells could indicate that expression of this zinc transporter may also be regulated by a non-synaptic pool of zinc or by other mechanism(s). The striking developmental regulation of ZnT-1 expression together with synaptic zinc indicates that ZnT-1 may play a key role in protecting developing neurons against potentially toxic zinc.     

Downhill training upregulates mice hippocampal and striatal brain-derived neurotrophic factor levels

This study examined the effects of downhill treadmill exercise on brain-derived neurotrophic factor (BDNF) protein on the hippocampus and striatum of mice. Twenty-four adult mice were assigned to three groups: non-runners control, level or downhill (16 degrees decline) running exercise. The exercise schedule consisted of progressive treadmill running for 5 days week(-1) over 8 weeks. Blood lactate levels classified exercise intensity as moderate to high. Both training types increased citrate synthase activity of the soleus muscle when compared to untrained controls. While level running increased BDNF levels selectively in the hippocampus (68.5%), the eccentric running resulted in a pronounced BDNF increase in both the hippocampus (137.0%) and the striatum (49.9%). Further studies will specify whether the observed alterations in BDNF are due to downhill-induced upregulation or complex learning-induced mechanisms that influence BDNF levels in these brain regions.     

Glucose administration enhances fMRI brain activation and connectivity related to episodic memory encoding for neutral and emotional stimuli

Glucose enhances memory in a variety of species. In humans, glucose administration enhances episodic memory encoding, although little is known regarding the neural mechanisms underlying these effects. Here we examined whether elevating blood glucose would enhance functional MRI (fMRI) activation and connectivity in brain regions associated with episodic memory encoding and whether these effects would differ depending on the emotional valence of the material. We used a double-blind, within-participants, crossover design in which either glucose (50 g) or a saccharin placebo were administered before scanning, on days approximately 1 week apart. We scanned healthy young male participants with fMRI as they viewed emotionally arousing negative pictures and emotionally neutral pictures, intermixed with baseline fixation. Free recall was tested at 5 min after scanning and again after 1 day. Glucose administration increased activation in brain regions associated with successful episodic memory encoding. Glucose also enhanced activation in regions whose activity was correlated with subsequent successful recall, including the hippocampus, prefrontal cortex, and other regions, and these effects differed for negative vs. neutral stimuli. Finally, glucose substantially increased functional connectivity between the hippocampus and amygdala and a network of regions previously implicated in successful episodic memory encoding. These findings fit with evidence from nonhuman animals indicating glucose modulates memory by selectively enhancing neural activity in brain regions engaged during memory tasks. Our results highlight the modulatory effects of glucose and the importance of examining both regional changes in activity and functional connectivity to fully characterize the effects of glucose on brain function and memory.     

Altered levels and distribution of amyloid precursor protein and its processing enzymes in Niemann‐Pick type C1‐deficient mouse brains

Niemann‐Pick type C (NPC) disease is an autosomal recessive neurodegenerative disorder characterized by intracellular accumulation of cholesterol and glycosphingolipids in many tissues including the brain. The disease is caused by mutations of either NPC1 or NPC2 gene and is accompanied by a severe loss of neurons in the cerebellum, but not in the hippocampus. NPC pathology exhibits some similarities with Alzheimer's disease, including increased levels of amyloid β (Aβ)‐related peptides in vulnerable brain regions, but very little is known about the expression of amyloid precursor protein (APP) or APP secretases in NPC disease. In this article, we evaluated age‐related alterations in the level/distribution of APP and its processing enzymes, β‐ and γ‐secretases, in the hippocampus and cerebellum of Npc1^−/− mice, a well‐established model of NPC pathology. Our results show that levels and expression of APP and β‐secretase are elevated in the cerebellum prior to changes in the hippocampus, whereas γ‐secretase components are enhanced in both brain regions at the same time in Npc1^−/− mice. Interestingly, a subset of reactive astrocytes in Npc1^−/− mouse brains expresses high levels of APP as well as β‐ and γ‐secretase components. Additionally, the activity of β‐secretase is enhanced in both the hippocampus and cerebellum of Npc1^−/− mice at all ages, while the level of C‐terminal APP fragments is increased in the cerebellum of 10‐week‐old Npc1^−/− mice. These results, taken together, suggest that increased level and processing of APP may be associated with the development of pathology and/or degenerative events observed in Npc1^−/− mouse brains. © 2010 Wiley‐Liss, Inc.     

Developmental expression of voltage-gated potassium channel beta subunits.

Expression of potassium channel beta subunits (Kvbeta) was determined in the developing mouse CNS using an antiserum against an amino acid sequence present in the C-terminus of Kvbeta1, Kvbeta2, and Kvbeta3. Using the anti-Kvbeta antiserum, we determined that Kvbeta expression is restricted to the spinal cord and dorsal root ganglia in the embryonic CNS. At birth, Kvbeta expression is detected in brainstem and midbrain nuclei, but was not detected in the hippocampus, cerebellum or cerebral cortex. During the first postnatal week, Kvbeta expression is present in hippocampal and cortical pyramidal cells and in cerebellar Purkinje cells. Expression of Kvbeta subunits reaches adult levels by the third postnatal week in all of the brain regions examined. A rabbit antiserum directed against a unique peptide sequence in the N-terminus of the Kvbeta1 protein demonstrates that this subunit displays a novel expression pattern in the developing mouse brain. Kvbeta1 expression is high at birth in all brain regions examined and decreases with age. In contrast, Kvbeta2 expression is low at birth and increases with age to reach adult levels by the third postnatal week. These findings support the notion that the differential regulation of distinct potassium channel beta subunits, in the developing mouse nervous system, may confer the functional diversity required to mediate both neuronal survival and maturation.     

Differential appearance of extensively phosphorylated forms of the high molecular weight neurofilament protein in regions of mouse brain during postnatal development

The appearance and accumulation of extensively phosphorylated forms of the high molecular weight neurofilament protein (H-phos) was studied in six regions of mouse brain during postnatal development by quantitative immunoblot analyses. H-phos (migrating at 200 kDa) was detected in brainstem, cerebellum, cortex and hippocampus as early as postnatal day 1. While NF-H levels increased dramatically during subsequent postnatal development in these regions, and reached levels similar to those observed in adult brain by postnatal day 14, quantitative differences were observed in both the rate and the extent of increase among individual regions. The most rapid accumulation of H-phos was observed in brainstem and cortex, where H-phos increased within the first postnatal week to levels comparable to those of adult brain. However, H-phos exhibited a slower developmental change in cerebellum, where the levels increased uniformly over the first two postnatal weeks. In hippocampus, the major increase in H-phos levels was delayed until the second postnatal week. In contrast to its early detection in the above regions, H-phos was not detected in immunoblot analyses of olfactory bulb or hypothalamus cytoskeletons at postnatal day 1, indicating that in these regions the accumulated levels of posttranslationally modified forms of this protein appeared relatively late. Furthermore, H-phos levels in hippocampus did not level off at postnatal day 14 and continued to increase until at least postnatal day 21. Immunoblot analyses of whole embryonic brain revealed the presence of H-phos as early as embryonic day 17, demonstrating that some mouse brain regions carry out extensive phosphorylation of NF-H during embryonic development.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise enhances hippocampal‐dependent learning in the rat: Evidence for a BDNF‐related mechanism

Short periods of forced exercise have been reported to selectively induce enhancements in hippocampal‐dependent cognitive function, possibly via brain‐derived neurotrophic factor (BDNF)‐mediated mechanisms. In this study, we report that 1 week of treadmill running significantly enhanced both object displacement (spatial) and object substitution (nonspatial) learning. These behavioral changes were accompanied by increased expression of BDNF protein in the dentate gyrus, hippocampus, and perirhinal cortex. The effects of exercise on object substitution were mimicked by intracerebroventricular injection of BDNF protein. These data are consistent with the hypothesis that exercise has the potential to enhance cognitive function in young healthy rats, possibly via a mechanism involving increased BDNF expression in specific brain regions. © 2009 Wiley‐Liss, Inc.     

Developmental lead neurotoxicity: alterations in brain cholinergic system

Developing brain has been shown to be susceptible to the neurotoxic effects of lead (Pb). Our earlier studies (Reddy GR, Riyaz Basha Md, Devi CB, Suresh A, Baker JL, Shafeek A, Heinz J, Chetty CS. Lead induced effects on acetylcholinesterase activity in cerebellum and hippocampus of developing rat. Int J Devl Neurosci 2003;21:347-52) have shown decrease in acetylcholinesterase (AChE) activity in the crude homogenates of cerebellum and hippocampus of rat brain exposed to Pb. In this study, we have further examined in detail, the alterations in AChE activity and acetylcholine (ACh) levels in different brain regions using histochemical and spectrophotometric methods. Rats were lactationally exposed to low level (0.2%) and high level (1%) Pb. The studies were conducted in young (1 month) and adult (3 months) rats. Pb exposure significantly decreased the specific activity of AChE and increased the levels of ACh in the synaptosomal fractions of cerebellum, hippocampus and cerebral cortex in a dose- and age-dependent manner. These alterations in AChE and ACh were more predominant in young rat brain as compared to adult brain. Maximum AChE activity and ACh level as well as maximum alterations following Pb exposure were observed in synaptosomes of hippocampus. Histochemical studies also showed higher AChE activity in the hippocampal region compared to other areas of brain as revealed by the intensity of AChE staining. Though high level Pb exposure remarkably decreased the intensity of AChE staining in the dentate gyrus, CA2 and CA3 areas of hippocampus, and different cell layers of cortex and cerebellum, highly significant loss of AChE activity was observed in the CA3 region of hippocampus, molecular layer of cerebellum and cortical cell layers. These data suggest that Pb exposure may selectively affect cholinergic system in brain areas controlling learning and cognitive behavior.     

Expression of Na(+)-K(+)-Cl(-) cotransporter in rat brain during development and its localization in mature astrocytes

Na(+)-K(+)-Cl(-) cotransporter has been proposed to play an important role in the regulation of intracellular Cl(-) concentration in neurons during development. In this study, the expression pattern of the cotransporter in different regions of rat brain was examined at birth (P0), postnatal days 7 (P7), P14, P21, and adult by Western blotting analysis. In cortex, thalamus, cerebellum and striatum, the cotransporter expression level was low at P0 and significantly increased at P14 (P<0.05). The expression peaked at P21 and was maintained at the same level in adulthood. However, in hippocampus, a peak level of the cotransporter expression was detected in adult brain. The immunocytochemistry study of adult rat brain revealed that an intense staining of the Na(+)-K(+)-Cl(-) cotransporter protein was observed in dendritic processes of CA1-CA3 hippocampal pyramidal neurons. In contrast, abundant immuno-reactive signals of the cotransporter were found in somata of thalamic nucleus. Immunofluorescence double staining demonstrates that the Na(+)-K(+)-Cl(-) cotransporter was expressed in astrocytes within cortex, corpus callosum, hippocampus and cerebellum. In addition, co-localization of the cotransporter and glial fibrillary acidic protein (GFAP), or with aquaporin 4, was found in perivascular astrocytes of cortical cortex and white matter. The results indicate that a time-dependent expression of the Na(+)-K(+)-Cl(-) cotransporter protein occurs not only in cortex but also in hippocampus, striatum, thalamus and cerebellum. In addition, the cotransporter is expressed in astrocytes and perivascular astrocytes of adult rat brain.     

Hippocampal NMDA receptor mRNA undergoes subunit specific changes during developmental lead exposure

The N-methyl- -aspartate (NMDA) receptor has shown to play an important role in the cognitive deficits associated with developmental lead (Pb) exposure. In this study, we examined the effects of low-level Pb exposure on NMDA receptor subunit gene expression in the developing rat brain. The pattern of NR1, NR2A, NR2B, and NR2C subunit mRNA in situ hybridization was consistent with previous studies. Brain levels of NR1 and NR2A mRNAs were lowest shortly after birth, increasing to reach peak levels by 14 or 21 days of age and subsequently decreasing at 28 days of age. NR2B mRNA levels were highest during early development and decreased as the animals aged. NR2C subunit mRNA was restricted to the cerebellum and a signal was not detectable until the second week of life. Lead exposure resulted in significant and opposite effects in NR1 and NR2A subunit mRNA expression with no changes in NR2B or NR2C subunit expression. The Pb-induced changes in NR1 and NR2A subunit mRNA were mainly present in the hippocampus. Hippocampal NR1 mRNA levels were significantly increased in the CA1 (15.3%) and CA4 (26.8%) pyramidal cells from 14-day-old Pb-exposed rats. At 21 days of age, only the NR1 mRNA at the CA4 subfield remained significantly elevated (10.3%). Lead exposure caused reductions of NR2A mRNA levels (11.9–19.3%) in the pyramidal and granule cell layers of the hippocampus at 14 and 21 days of age. NR1 mRNA levels were also significantly increased (14.0%) in the cerebellum of 28-day-old rats with no change in NR2A mRNA at any age. No significant changes in subunit mRNA levels were present in cortical or subcortical regions at any age. The Pb-induced changes in hippocampal NMDA receptor subunit mRNA expression measured in the present study may lead to modifications in receptor levels or subtypes and alter the development of defined neuronal connections which require NMDA receptor activation.