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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 76 (2001), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Presenilin-1 (PS1) protein concentration is linked to neuronal development and to the pathogenesis of Alzheimer's disease, yet little is known about the biological factors and mechanisms that control cellular levels of PS1 protein. As PS1 levels are highest in the developing brain, we tested whether neurotrophin-induced differentiation influences PS1 expression using neuronotypic pheochromocytoma (PC12) cells. Treatment of PC12 cells with nerve growth factor (NGF) caused ∼ 60–75% increases in the steady-state levels of endogenous PS1 N- and C-terminal fragments. PS1 protein accumulation was dose-responsive to NGF and required the presence of the TrkA NGF receptor tyrosine kinase. NGF also induced PS1 fragment accumulation in cultured explants of rat dorsal root ganglia. Quantitative northern blot analysis using PC12 cultures indicated that NGF did not increase steady-state PS1 mRNA levels. However, pulse-chase experiments indicated that NGF slowed the degradation rate of endogenous PS1 fragments, increasing the half-life from t1/2 @22.5 to @25.0 h. This increase in half-life was insufficient to account for the ∼ 60–75% increase in PS1 fragment levels measured in NGF-treated cells. Thus, NGF may regulate PS1 protein concentration in NGF-responsive cells by a complex mechanism that increases PS1 fragment production independent of holoprotein synthesis.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The gene for the vesicular acetylcholine transporter (VAChT) was recently cloned and found to be located within a 5′ noncoding intron of the gene for choline acetyltransferase (ChAT). There appear to be several shared and unique promoters for each gene, suggesting that control of expression of these two genes can be either coordinated or independent. Two lesions, axotomy and immunotoxin, directed at the well defined septohippocampal cholinergic pathway were used to determine VAChT and ChAT protein expression in the degenerating terminal fields in the hippocampus and the cell bodies of the medial septum nucleus after injury. Two weeks after lesioning, decreases of up to 90% in VAChT were found in the affected hippocampus by immunoblotting and immunocytochemistry, similar to ChAT activity. The number of VAChT- and ChAT-immunopositive neurons in the medial septum decreased by up to 95%. Eight weeks following axotomy, the number of VAChT- and ChAT-immunopositive neurons had increased to almost 50% in fimbria-fornix-lesioned animals, indicating coordinate reexpression of both cholinergic markers in recovered neurons. There was no recovery of either VAChT or ChAT immunoreactivity after the irreversible immunotoxin lesions. Thus, with use of immunological techniques, there appears to be coordinate expression of VAChT and ChAT in the septohippocampal pathway following either unilateral fimbria-fornix or bilateral immunotoxin lesion.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Galanin (GAL) inhibits midbrain dopamine (DA) activity in several experimental paradigms, yet the mechanism underlying this inhibition is unclear. We examined the effects of GAL on the expression of tyrosine hydroxylase (TH) in primary cultures of rat embryonic (E14) ventral mesencephalon (VM). One micromolar GAL had no effect on the number of TH-immunoreactive (ir) neurons in VM cultures. However, 1 µm GAL reduced an approximately 100% increase in TH-ir neurons in 1 mm dibutyryl cAMP (dbcAMP)-treated cultures by ∼50%. TH-ir neuron number in dbcAMP-treated VM cultures was dose-responsive to GAL and the GAL receptor antagonist M40 blocked GAL effects. Semi-quantitative RT-PCR and quantitative immunoblotting experiments revealed that GAL had no effect on TH mRNA levels in VM cultures but reduced TH protein. VM cultures expressed GALR1, GALR2, and GALR3 receptor mRNA. However, dbcAMP treatment resulted in a specific ∼200% increase in GALR1 mRNA. GALR1 activity is linked to a pertussis toxin (PTX)-sensitive opening of G protein-gated K+ channels (GIRKs). GAL reduction of TH-ir neuron number in dbcAMP + GAL-treated cultures was sensitive to both PTX and tertiapin, a GIRK inhibitor. GAL inhibition of midbrain DA activity may involve a GALR1- mediated reduction of TH in midbrain dopaminergic neurons.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1527-3458
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The neuropeptide galanin (GAL) is widely distributed in the mammalian CNS. Several lines of evidence suggest that GAL may play a critical role in cognitive processes such as memory and attention through an inhibitory modulation of cholinergic basal forebrain activity. Furthermore, GAL fibers hyperinnervate remaining cholinergic basal forebrain neurons in Alzheimer's disease (AD). This suggests that GAL activity impacts cholinergic dysfunction in advanced AD. Pharmacological and in vitro autoradiographic studies indicate the presence of heterogeneous populations of GAL receptor (GALR) sites in the basal forebrain which bind GAL with both high and low affinity. Interestingly, we have recently observed that GALR binding sites increase in the anterior basal forebrain in late-stage AD. Three G protein-coupled GALRs have been identified to date that signal through a diverse array of effector pathways in vitro, including adenylyl cyclase inhibition and phospholipase C activation. The repertoire and distribution of GALR expression in the basal forebrain remains unknown, as does the nature of GAL and GALR plasticity in the AD basal forebrain. Recently, GAL knockout and overexpressing transgenic mice have been generated to facilitate our understanding of GAL activity in basal forebrain function. GAL knockout mice result in fewer cholinergic basal forebrain neurons and memory deficits. On the other hand, mice overexpressing GAL display hyperinnervation of basal forebrain and memory deficits. These data highlight the need to explore further the putative mechanisms by which GAL signaling might be beneficial or deleterious for cholinergic cell survival and activity within basal forebrain. This information will be critical to understanding whether pharmacological manipulation of GALRs would be effective for the amelioration of cognitive deficits in AD.
    Type of Medium: Electronic Resource
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