Biologic effects of nerve growth factor on lesioned basal forebrain neurons.
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Alzheimer Disease↗
Biomedical subjects
D L Price
Publications and source records attributed to D L Price.
Studies on the proteolytic degradation of the beta-protein precursor by proteases purified from Alzheimer's disease brain.
In Alzheimer's disease, Down's syndrome, hereditary cerebral hemorrhage with amyloidosis of Dutch origin, and normal aging, amyloid accumulates in the brain parenchyma and blood vessels. The major protein in the deposits is the beta-protein, a 4-kD peptide possibly generated by an abnormal degradation of its precursor, the beta-protein precursor (beta PP). We found, as a second component of the brain amyloid, the serine protease inhibitor alpha 1-antichymotrypsin (ACT). Inasmuch as ACT is tightly associated with the beta-protein and is never found in other amyloidoses, we hypothesized a role for ACT in the degradation of the beta PP. We used synthetic peptides made according to the sequence flanking the N-terminus of the beta-protein to screen brain fractions for protease activity. After several purification steps, two protease fractions were found that can cleave the peptide between methionine and aspartic acid, aspartic acid being the N-terminus of the beta-protein. One protease is activated by calcium and inhibited by ACT, beta PP containing the Kunitz-type inhibitory domain, diisofluorophosphate, and 1,10-phenanthroline. This protease fraction is also able to degrade the beta PP in vitro. The second protease is a metal-dependent cysteine protease.
Alzheimer Disease↗
Aged non-human primates: an animal model of age-associated neurodegenerative disease.
Aged non-human primates develop age-associated behavioral and brain abnormalities similar to those that occur in aged humans and, to a greater extent, in individuals with Alzheimer's disease. Declines in performance on cognitive and memory tasks begin at the monkey equivalent of late-middle life. As occurs in elderly humans, significant differences have been demonstrated in levels of performance between animals within older age groups. The brains of old monkeys show degenerative changes in neurons, abnormal axons and neurites (particularly in telencephalic areas), and deposits of amyloid in senile plaques and around blood vessels. Moreover, in some older animals, decrements occur in markers of specific neurotransmitter circuits, including the basal forebrain cholinergic system. It has been suggested that alterations in these cholinergic neurons contribute to the memory deficits that occur in older individuals. Because axotomy-induced retrograde degeneration of these neurons can be prevented by the administration of nerve growth factor, we have begun studies to determine whether administration of nerve growth factor improves performance of aged animals on memory tasks. This review describes the complementary nature of studies of non-human primates and human subjects, illustrating how these investigations can clarify factors that influence behavior and brain biology in age-associated diseases.
Aging↗
Identification and localization of muscarinic acetylcholine receptor proteins in brain with subtype-specific antibodies.
mRNAs encoding five genetically distinct muscarinic ACh receptors are present in the CNS. Because of their pharmacological similarities, it has not been possible to detect the individual encoded proteins; thus, their physiological functions are not well defined. To characterize the family of proteins, a panel of subtype-selective antibodies was generated against recombinant muscarinic receptor proteins and shown to bind specifically to each of the cloned receptors. Using immunoprecipitation, three receptor proteins (m1, m2, and m4) accounted for the vast majority of the total solubilized muscarinic binding sites in rat brain. These receptor subtypes had marked differences in regional and cellular localization as shown by immunocytochemistry. The m1-protein was present in cortex and striatum and was localized to cell bodies and neurites, consistent with its role as a major postsynaptic muscarinic receptor. The m2-receptor protein was abundant in basal forebrain, scattered striatal neurons, mesopontine tegmentum, and cranial motor nuclei; this distribution is similar to that of cholinergic neurons and suggests that m2 is an autoreceptor. However, m2 was also present in noncholinergic cortical and subcortical structures, providing evidence that this subtype may presynaptically modulate release of other neurotransmitters and/or function postsynaptically. The m4-receptor was enriched in neostriatum, olfactory tubercle, and islands of Calleja, indicating an important role in extrapyramidal function. These results clarify the roles of these genetically defined receptor proteins in cholinergic transmission in brain.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Regulation of peripherin and neurofilament expression in regenerating rat motor neurons.
Northern blotting, in situ hybridization and immunocytochemistry were used to study the changes in levels of mRNA coding for peripherin and in immunoreactivity of peripherin, a type III neuronal intermediate filament, in rat spinal motor neurons following axotomy of the sciatic nerve. For comparison, parallel studies examined the biology of neurofilament (NF) proteins in this model. The sciatic nerve was crushed at the junction of the L4-L5 spinal nerves. Levels of messenger RNA (mRNA) coding for peripherin in the motor neurons doubled by 4 days postaxotomy and remained elevated for a period of 6 weeks. Within 4-7 days of injury peripherin immunoreactivity increased significantly in cell bodies of motor neurons and remained elevated through 6 weeks. In contrast, no changes were detected in NF-M immunoreactivity over the same time period. By 8 weeks postaxotomy, levels of peripherin mRNA and protein returned to control values. The increases in the expression of peripherin parallel those of beta-tubulin and actin, and these changes are quite different from the alterations in neurofilament mRNA that decrease after axotomy. The contrasting responses of peripherin and NF to nerve injury indicates that each of these intermediate filaments may play distinct roles in nerve growth and regeneration.
Animals↗
Noradrenergic innervation of human inferior olivary complex.
Antisera to human dopamine beta-hydroxylase (DBH) was used to stain noradrenergic axons in the inferior olivary complex (IOC) of human controls. A modest plexus of thin, beaded, immunoreactive fibers was present in all subdivisions of the IOC, and many fibers coursed in the rostrocaudal axis. This noradrenergic plexus is similar to that of monkey, provides complementary evidence to reports of beta-adrenergic receptors in human IOC, and supports the concept of noradrenergic projections to IOC.
Adult↗
Evidence that beta-amyloid protein in Alzheimer's disease is not derived by normal processing.
The beta-amyloid protein (beta/A4), derived from a larger amyloid precursor protein (APP), is the principal component of senile plaques in Alzheimer's disease. APP is an integral membrane glycoprotein and is secreted as a carboxyl-terminal truncated molecule. APP cleavage, which is a membrane-associated event, occurred at a site located within the beta/A4 region. This suggests that an intact amyloidogenic beta/A4 fragment is not generated during normal APP catabolism. Therefore, an early event in amyloid formation may involve altered APP processing that results in the release and subsequent deposition of intact beta/A4.
Aged↗
The human pineal gland in aging and Alzheimer's disease: patterns of cytoskeletal antigen immunoreactivity.
Patients with Alzheimer's disease (AD) and some aged controls may have diminished functions of the pineal gland. In this immunocytochemical study, we stained pineal glands from cases of AD and young and aged controls for cytoskeletal elements and amyloid. We found no evidence of neurofibrillary tangles (NFT) or the accumulation of neurofilaments, tau, A68, or beta/A4 amyloid deposition in pinealocytes or associated structures in cases of AD or controls. In both AD and controls, we observed dense immunoreactivity for phosphorylated neurofilaments in marginal plexuses associated with processes of pinealocytes, boutons, and knob-like endings. The accumulation of phosphorylated neurofilaments in the processes of pinealocytes appears to be a normal morphological characteristic of the pineal gland and may not represent a pathological change.
Adolescent↗
Amyloid in the brains of aged squirrel monkeys.
In this immunocytochemical study, the brains of nine squirrel monkeys (Saimiri sciureus), ranging from 8 to 27 years of age, were examined for the presence and distribution of beta/A4 amyloid, a 4-kilodalton peptide. In aged squirrel monkeys, amyloid is associated primarily with intracerebral and meningeal capillaries and arterioles and occurs to a lesser degree as small and/or diffuse deposits in the neural parenchyma and in the dense cores of senile plaques. Cerebrovascular amyloid is found primarily in neocortex, amygdala, and septum verum and is rare or nonexistent in other subcortical gray structures, white matter, cerebellum, and spinal cord; this pattern of localization is comparable to that in humans with cerebral amyloid angiopathy. There is a significant correlation between cerebrovascular and parenchymal deposits of amyloid. However, cerebrovascular amyloid is always the most abundant form in squirrel monkeys, even in cases of severe cerebral amyloidosis. In contrast to squirrel monkeys, aged rhesus monkeys (Macaca mulatta) develop mostly parenchymal deposits of amyloid and have relatively less vascular amyloid. This species difference in the histological distribution of amyloid suggests that separate mechanisms may influence the accumulation of amyloid in cerebral blood vessels and in the neural parenchyma. These data also indicate that the squirrel monkey can serve as a model for investigations of cerebrovascular amyloidosis.
Aging↗
Nigral dopamine type-1 receptors are reduced in Huntington's disease: a postmortem autoradiographic study using [3H]SCH 23390 and correlation with [3H]forskolin binding.
Intrastriatal injection of excitatory amino acids, particularly quinolinic acid, has been proposed as an animal model of Huntington's disease. Such neurotoxic lesions of caudate-putamen result in marked dopamine type-1 (D1) receptor losses in the injected nuclei as well as in the ipsilateral substantia nigra pars reticulata. Postmortem human substantia nigra from Huntington's disease brains and from control brains were examined using in vitro autoradiography. A marked reduction in [3H]SCH 23390 binding (labeling D1 receptors) in the substantia nigra of postmortem brains of Huntington's patients was identified, thus paralleling the alterations seen in the animal models. A positive, statistically significant correlation was also encountered between D1 receptor binding (labeled by [3H]SCH 23390) and [3H]forskolin binding (which identifies adenylate cyclase, a second messenger system linked to D1 receptor activation). The results suggest that in the human--as in lower vertebrates--D1 receptors are located on striatonigral terminals and that D1 receptor loss tends to be paralleled by a reduction in adenylate cyclase. Radioactive agents selective for the D1 receptor may prove useful in future studies of Huntington's disease using positron emission tomography scanning.
Adolescent↗
Trophic actions of recombinant human nerve growth factor on cultured rat embryonic CNS cells.
NGF is a neurotrophic factor for basal forebrain cholinergic neurons and may serve to counteract the cholinergic deficits that are observed in Alzheimer's disease. Prior to the introduction of clinical trials, it is essential that recombinant human NGF (rhNGF) be produced and that its actions on target cells in the CNS be demonstrated. We prepared rhNGF and examined its actions on fetal rat brain neurons in culture including, in particular, the cholinergic neurons of the basal forebrain. rhNGF was more potent in increasing choline acetyltransferase (ChAT) activity in septal cultures than NGF purified from mouse salivary glands (mNGF). ED50s of the beta-NGF dimers were 4.9 pM for rhNGF and 12.4 pM for mNGF. The maximal ChAT activity response was achieved at approximately 35 pM with both NGFs and their efficacies were not significantly different. The two NGFs were not additive in effect. Identical to the results with mNGF, rhNGF strongly enhanced the intensity of ChAT immunostaining in septal cultures. Neither rhNGF nor mNGF affected the appearance of the cultures under phase-contrast illumination. Survival of cells at very low plating density on polyornithine/laminin-coated culture dishes was not affected by rhNGF or mNGF. Protein content and the uptake of GABA were also unaffected. At concentrations of up to 10 micrograms/ml, rhNGF did not significantly increase uptake of dopamine into cultures of ventral mesencephalon. We conclude that rhNGF produces potent and selective actions on cholinergic neurons of the basal forebrain as previously shown for mNGF.
Animals↗
Alterations in levels of mRNAs coding for neurofilament protein subunits during regeneration.
Animal models of neuronal injury can be used to explore mechanisms that regulate the expression of genes coding for cytoskeletal proteins and transmitter-related markers. In the present study, in situ hybridization was used to measure levels of messenger ribonucleic acid (mRNA) encoding each of the neurofilament subunits and beta-tubulin in spinal motor neurons at intervals (4 to 56 days) following a unilateral crush of the sciatic nerve. Levels of beta-tubulin mRNA increased (approximately twofold), peaked at 28 days postaxotomy, and returned to control values by 56 days postaxotomy. In contrast, levels of mRNA encoding neurofilament subunits were reduced and returned to control values at 56 days following the lesion. There were significant differences among relative levels of mRNAs coding for each subunit. Other studies have demonstrated that the ratio of pulse-labeled neurofilament subunits in motor axons remained unaltered during regeneration. Therefore, the ratios of neurofilament subunits in axons must be regulated at one of the steps that intervenes between the control of levels of mRNA and the anterograde axonal transport of assembled neurofilaments.
Animals↗
Differential expression of amyloid precursor protein mRNAs in cases of Alzheimer's disease and in aged nonhuman primates.
Senile plaques are a characteristic feature in brains of individuals with Alzheimer's disease (AD) and aged monkeys. The principal component of amyloid in senile plaques is beta/A4, a peptide derived from a larger amyloid precursor protein (APP). To date, several alternatively spliced APP transcripts have been described. The relationship between levels of these APP mRNAs and amyloid deposition is unclear. In this study, we directly measured the relative levels of APP transcripts that lack the protease inhibitor domain (APP-695) and transcripts that encode the inhibitor sequences (APP-751/770). Our results indicate that the expression of APP mRNAs is not selectively altered in AD cortex. Moreover, the differential expression of APP transcripts is not correlated with the deposition of amyloid in cases of AD and aged monkeys. These findings suggest that other factors, not directly related to the relative expression of APP mRNAs, may contribute to amyloidogenesis in the brain.
Aging↗
Neuronal responses to injury and aging: lessons from animal models.
Alzheimer's disease (AD), the most common type of adult-onset dementia, is characterized by a variety of brain abnormalities, including degeneration of certain populations of nerve cells, alterations in the neuronal cytoskeleton, and the abnormal deposition of amyloid within brain parenchyma. Pathogenetic processes that lead to these brain abnormalities are difficult to study in humans. Recently, investigators have begun to utilize animal models to examine some of the mechanisms that cause cellular/molecular alterations in transmitter systems, cytoskeletal elements, and APP. These investigations have helped to clarify issues related to the lesions that occur in aged humans and individuals with AD.
Aging↗
Precursor of amyloid protein in Alzheimer disease undergoes fast anterograde axonal transport.
In the brains of aged humans and cases of Alzheimer disease, deposits of amyloid in senile plaques are located in proximity to nerve processes. The principal component of this extracellular amyloid is beta/A4, a peptide derived from a larger amyloid precursor protein (APP), which is actively expressed in brain and systemic organs. Mechanisms that result in the proteolysis of APP to form beta/A4, previously termed beta-amyloid protein, and the subsequent deposition of the peptide in brain are unknown. If beta/A4 in senile plaques is derived from neuronally synthesized APP and deposited at locations remote from sites of synthesis, then APP must be transported from neuronal cell bodies to distal nerve processes in proximity to deposits of amyloid. In this study, using several immunodetection methods, we demonstrate that APP is transported axonally in neurons of the rat peripheral nervous system. Moreover, our investigations show that APP is transported by means of the fast anterograde component. These findings are consistent with the hypothesis of a neuronal origin of beta/A4, in which amyloid is deposited in the brain parenchyma of aged individuals and cases of Alzheimer disease. In this setting, we suggest that APP is synthesized in neurons and delivered to dystrophic nerve endings, where subsequent alterations of local processing of APP result in deposits of brain amyloid.
Acetylcholinesterase↗
Neuronal disorders: studies of animal models and human diseases.
The peripheral nervous system and the central nervous system (CNS) are comprised of assemblies of neurons that communicate via electrical and chemical signals. Different disease processes selectively affect specific populations of neurons and/or specific cell functions (i.e., "selective vulnerability" of neurons is a principal determinant of phenotypes of disease). New cellular and molecular biological approaches have begun to clarify some of the mechanisms of selective cell injury in human diseases and their animal models. Following a brief review of the normal biology of nerve cells, we use illustrations drawn from studies of experimental and human diseases to discuss the mechanisms of structural/chemical abnormalities that occur in a variety of neuronal disorders.
Animals↗
Postmenopausal hypertrophy of neurons expressing the estrogen receptor gene in the human hypothalamus.
Computer microscopy and in situ hybridization were used to investigate neuronal hypertrophy in the infundibular nucleus of postmenopausal women. In the first experiment, hypothalami from premenopausal (n = 3) and postmenopausal (n = 3) women were formalin fixed, paraffin embedded, serially sectioned, and stained with cresyl violet. Soma areas of more than 3500 neurons were digitized using an image-combining computer microscope. The mean cross-sectional area of infundibular neurons in the postmenopausal women was 30% greater than that in premenopausal women, with no change in cell density. The mean cross-sectional area of mammillary neurons was unchanged, indicating that the infundibular neuronal hypertrophy was not an artifact of tissue processing. In the second experiment, hypothalami from premenopausal (n = 3) and postmenopausal (n = 2) women were frozen, serially sectioned, and incubated with a 48-base synthetic cDNA probe complementary to estrogen receptor (ER) mRNA. Adjacent sections were incubated with a cDNA probe complementary to GnRH mRNA. Morphometric analysis revealed that the mean cross-sectional area of infundibular neurons expressing the ER gene in the postmenopausal women was twice as large as the mean area in premenopausal hypothalami. The hypertrophied neurons did not contain GnRH mRNA. Finally, analysis of the infundibular nucleus from an oophorectomized 38-yr-old woman also revealed hypertrophied neurons containing ER mRNA. These data support the hypothesis that hypertrophy of infundibular neurons in postmenopausal women is secondary to loss of the inhibitory feedback of ovarian steroids.
Adult↗
Development of senile plaques. Relationships of neuronal abnormalities and amyloid deposits.
The evolution of senile plaques and the relationships among neuritic elements, extracellular deposits of the beta-amyloid protein (beta/A4), and vascular beta/A4 are poorly understood. Immunocytochemical methods were used to examine fixed-frozen prefrontal cortices of 14 rhesus monkeys (Macaca mulatta) (14 to 37 years of age) for the presence of abnormal fibers/neurites, alpha 1-antichymotrypsin (alpha-ACT), and beta/A4. Age-associated alterations included abnormal fibers/neurites, presence of beta/A4, and association of alpha-ACT with beta/A4 in plaques and blood vessels. Vascular amyloid was present only in the oldest monkeys. The topographic distribution of abnormal fibers/neurites was mapped with acetylcholinesterase (AChE) histochemistry, and deposits of amyloid were visualized with immunocytochemistry for beta/A4. beta/A4 often was associated with neurites, but many neurites lacked demonstrable beta/A4. Thus in aged monkeys, abnormal neurites may provide one type of focus for the accumulation of the amyloid precursor, which is subsequently abnormally processed to form beta/A4. Our data in rhesus monkeys suggest that fiber and neuritic abnormalities increase with age and that they may precede the majority of beta/A4 deposits; the initial stages of neurite formation and parenchymal amyloid deposits may be independent of the appearance of vascular amyloid; and these processes may be synergistic with advanced age.
Acetylcholinesterase↗