Glial Fibrillary Acidic Protein In Hippocampus Research Articles

An aluminum-induced increase in GFAP is attenuated by some chelators.

Enhanced expression of glial fibrillary acidic protein (GFAP) has been shown to be associated with gliosis, a generic response of the CNS to neural injury. The effects of aluminum (Al) on regional GFAP concentrations were evaluated to determine potential sites of Al-induced neural injury. Rabbits received 20 Al (100 mumol/kg) or sodium lactate injections over 1 month. Frontal cortical GFAP increased (approximately twofold above control) in Al-loaded rabbits; whereas hippocampal and cerebellar GFAP concentrations were not affected. Frontal cortical synaptophysin, neurofilament 68, and myelin basic protein concentrations were then examined in an attempt to determine cell-specific targets of Al neurotoxicity. These proteins were not affected by Al. The ability of chelators to influence brain Al concentrations and the Al effect on GFAP were assessed. Desferrioxamine (DFO) and six 3-hydroxypyridin-4-ones (CPs) were given 12 times, over 1 month, to Al-loaded rabbits. CP24 significantly reduced brain Al. CP93, CP52, and CP24 significantly reduced frontal cortical GFAP. The data suggest an Al-induced gliosis consequent to subtle damage in the frontal cortex and a protective role of some chelators against this CNS injury.

Life-Long Dietary Restriction Attenuates Age-Related Increases in Hippocampal Glial Fibrillary Acidic Protein mRNA

The expression of astrocyte-specific glial fibrillary acidic protein increases after experimental lesions and is elevated throughout the brain in aged rodents and primates. Clusterin (ApoJ) expression increases in astrocytes and microglia after lesions, but changes during aging have not been reported. Dietary restriction (DR) delays the onset and progression of many age-related physiological deficits in rodents. This study showed that the age-related increase in glial fibrillary acidic protein mRNA in the hippocampus was attenuated in 24-month-old male Fischer 344 rats subjected to a 50% DR beginning at 6 weeks of age. ApoJ mRNA expression in astrocytes was unchanged by DR. These results demonstrate that DR can delay neurodegeneration in aged rats as assessed by a marker of reactive astrogliosis.

Acute and chronic administration of ibogaine to the rat results in astrogliosis that is not confined to the cerebellar vermis.

Acute administration of high doses of ibogaine (IBG) to the male rat results in degeneration of Purkinje cells and reactive gliosis in the cerebellar vermis. We examined whether acute and chronic administration of IBG to male and female rats results in gliosis as determined by quantification of the astroglial intermediate filament protein, glial fibrillary acidic protein (GFAP). After acute administration of IBG, rats of both sexes showed dose-related increases in GFAP that were not confined to the cerebellar vermis. After chronic administration of IBG, female, but not male rats, showed large (as much as 200% of control), dose-related increases in GFAP in hippocampus, olfactory bulbs, brain stem and striatum, but not cerebellum. In hippocampus, the cytoskeletal proteins, neurofilament 68 (NF-68) and beta-tubulin were increased in females treated chronically with IBG, findings consistent with a damage-induced sprouting response. Together, the data indicate that IBG damages areas of the brain outside the cerebellum and that the sites damaged are dependent on sex and dosage regimen.

Molecular Indices of Neuronal and Glial Plasticity in the Hippocampal Formation in a Rodent Model of Age-Induced Spatial Learning Impairment

Spatial learning ability was quantitated in young and aged Long-Evans rats, and molecular markers were assessed in the striatum and hippocampal formation using immunocytochemical, immunoblotting, and in situ hybridization histochemical procedures. The mRNA for beta-amyloid precursor protein (beta APP), most likely the transcript encoding the 695-amino acid form of this protein, was elevated in pyramidal and granule cells in the hippocampus of aged rats exhibiting poorer spatial learning. In immunoblots of hippocampal protein extracts, however, the level of beta APP-like immunoreactivity was depressed in the more impaired subjects. Similarly, the level in hippocampus of the mRNA for manganese-dependent superoxide dismutase (Mn-SOD), a marker of oxidative stress, was positively correlated with the degree of behavioral impairment, but immunoblotting revealed that Mn-SOD protein was depressed in the aged hippocampus compared with young. The mRNAs for the neuronal form of nitric oxide synthase and for the astrocyte marker glial fibrillary acidic protein (GFAP) were elevated in the hippocampus in correlation with the extent of learning impairment. In the striatum, the levels of mRNA and protein for several candidate genes, including GFAP, were elevated in parallel with the learning index, but these were age effects. Several hippocampal proteins were unchanged (GFAP) or depressed (beta APP and Mn-SOD) in level, despite elevations in corresponding mRNAs. In the aged cohort, hippocampal GFAP mRNA, Mn-SOD mRNA, and beta APP emerged as predictors of behavioral impairment, suggesting the involvement of these hippocampal systems in age-related cognitive impairment.

Chronic reduction of cerebral blood flow in the adult rat: late-emerging CA1 cell loss and memory dysfunction

Ten-month-old rats were subjected to permanent bilateral occlusion of both common carotid arteries (2-VO) to chronically but moderately reduce brain blood flow. 2-VO impaired Morris water maze acquisition as soon as 7 days post-surgery. 2-VO also caused a later-appearing impairment on the radial arm maze which did not reach significance until 63 days post-surgery. At 14 dats post-surgery there were no effects of 2-VO on hippocampal CAI pyramidal cell number or density of glial fibrillary acidic protein (GFAP). Hippocampal choline acetyltransferase activity at 70 days was also unaffected by 2-VO. At 190 days post-surgery, however, the 2-VO rats showed loss of cells and increased GFAP density in CAI. The increased density of hippocampal GFAP correlated with radial arm maze but not Morris water maze impairment. It is suggested that 2-VO causes neuronal dysfunction which can be exacerbated by stress and thereby manifested on aversively motivated tasks such as the water maze. As well, CAI neurons begin to degenerate after several weeks of the reduced energy availability caused by 2-VO and this impairs memory. Since reduced neuronal energy metabolism is associated with the progressive neurodegeneration that underlies disorders such as Alzheimer's, research should further explore the possibility that the effects of 2-VO may model age-related dementia.

The role of neuronal activity in upregulating GFAP mRNA levels after electrolytic lesions of the entorhinal cortex

This study evaluates whether the rapid transient increases in glial fibrillary acidic protein (GFAP) mRNA in the hippocampus after electrolytic lesions of the entorhinal cortex (EC) are triggered by lesion-induced changes in hippocampal neuronal activity (either the decreases that result from loss of afferent drive or transient increases that occur during lesion production). To evaluate the role of activity, we carried out four experiments: 1.(1) tetrodotoxin (TTX) was injected into the EC to mimic the decreases in afferent drive that occur after lesion;2.(2) TTX was injected into the EC or hippocampus before producing electrolytic lesions to block any abnormal activity induced during lesion production;3.(3) the EC was destroyed by aspiration, thus creating a lesion comparable in size to the electrolytic lesion, without passing direct current;4.(4) seizures were elicited by stimulating the EC of anesthetized rats, to examine whether electrographic seizures alone can induce the same type of increases in GFAP mRNA as lesions. Our results demonstrated that: 1.(1) TTX injections into the EC did not induce the same increases in GFAP mRNA levels that occurred after EC lesions;2.(2) animals that received TTX injections into the EC prior to lesions exhibited increases in hippocampal GFAP mRNA that were nearly as great as following EC lesions alone;3.(3) aspiration lesions of the EC resulted in increases in GFAP mRNA that were comparable to those observed after electrolytic lesions4.(4) seizure-inducing stimulation of the EC resulted in 2-fold increases in GFAP mRNA in the hippocampus 24 hr after stimulation rather than the 5–13-fold increases observed after lesions. These results suggest that lesion-induced changes in hippocampal neuronal activity are not solely responsible for inducing the rapid transient increases in GFAP mRNA levels in the hippocampus ipsilateral to EC lesions.

Glucocorticoids Regulate the Synthesis of Glial Fibrillary Acidic Protein in Intact and Adrenalectomized Rats but Do Not Affect Its Expression Following Brain Injury

Short (5 days)- to long-term (4 months) corticosterone (CORT) administration by injection, pellet implantation, or in the drinking water decreased glial fibrillary acidic protein (GFAP) by 20-40% in hippocampus and cortex of intact rats. In contrast to CORT, adrenalectomy (ADX) caused elevations (50-125%) in hippocampus and cortex GFAP within 12 days of surgery that persisted for at least 4 months. CORT replacement of ADX rats decreased GFAP amount in hippocampus and cortex. The effects of long-term CORT and ADX on GFAP in hippocampus and cortex were also seen in striatum, midbrain, and cerebellum, findings suggestive of brain-wide adrenal steroid regulation of this astrocyte protein. The changes in GFAP amount due to CORT and ADX were paralleled by changes in GFAP mRNA, indicating a possible transcriptional or at least genomic effect of adrenal steroids. Glucocorticoid regulation of GFAP was relatively specific; it could not be generalized to other astrocyte proteins or other major structural proteins of neurons. The negative regulation of GFAP and GFAP mRNA by adrenal steroids suggested that increases in GFAP that result from brain injury may be attenuated by glucocorticoids. However, chronic CORT treatment of intact rats did not reverse or reduce the large increases in GFAP caused by trauma- or toxicant-induced brain damage. Thus, glucocorticoids and injury appear to regulate the expression of GFAP through different mechanisms. In contrast to the lack of effects of CORT on brain damage-induced increases in GFAP, CORT treatment begun in 2-week ADX rats, after an increase in GFAP had time to occur, did reverse the ADX-induced increase in GFAP. These results suggest that the increase in GFAP resulting from ADX is not mediated through an injury-linked mechanism.

Astrocytic apolipoprotein E mRNA and GFAP mRNA in hippocampus after entorhinal cortex lesioning

Entorhinal cortex lesions (ECL) that damage the perforant path to the hippocampus induce rapid increases of apolipoprotein E (apo E) mRNA in the hippocampus. Apo E mRNA was localized in astrocytes by in situ hybridization in combination with immunocytochemistry for glial fibrillary acidic protein (GFAP). Unilateral ECL also increased hippocampal GFAP mRNA, with increases preceding those of apo E mRNA. The apo E mRNA and GFAP mRNA responses were transiently bilateral in non-denervated zones. The timing of response in apo E mRNA to deafferentation supports suggestions that apo E has roles in membrane remodelling during responses to neuron injury.

Messenger RNA for glial fibrillary acidic protein is decreased in rat brain following acute and chronic corticosterone treatment

RNA coding for a 50 kDa polypeptide decreased by 50% in 5 brain regions after corticosterone (CORT) treatment (40 mg/kg for 3 days). By hybrid selection and in vitro translation, the 50 kDa polypeptide is identified as glial fibrillary acidic protein (GFAP). Hippocampal GFAP mRNA (2.9 kb) decreases in a dose-dependent manner in response to CORT by RNA blot hybridization using a mouse GFAP cRNA probe; a similar decrease in response to the glucocorticoid agonist, RU 28362, is consistent with a type II glucocorticoid receptor-mediated effect. GFAP mRNA is decreased in both hippocampus and cortex following acute (1–3 days) and chronic (3 days to 3 months) CORT treatment. GFAP gene expression is disinhibited in the rat hippocampus by 7 days post adrenalectomy but not by 3 days. Finally, two clones (CR46 and CR59) that were isolated from a rat hippocampal cDNA library by differential hybridization, show decreased RNA abundance in CORT-treated rats compared to controls. A partial DNA sequence derived from the two clones exhibits 94% nucleotide identity and 96% derived amino acid identity with mouse GFAP mRNA. These results indicate that GFAP mRNA is under negative regulation by glucocorticoids and suggests that glucocorticoids may be used to inhibit GFAP gene expression in vivo in order to assess the role of GFAP in temporal aspects of central nervous system damage.

Effects of delay, intertrial interval, delay behavior and trimethyltin on spatial delayed response in rats

Working memory was modeled in rats using a delayed response task with spatial location as the discriminative cue. Rats received food for pressing 1 of 2 retractable levers in the choice phase of a trial if that lever had been presented in the prior sample phase of that trial. When delays of 0–20 sec were imposed between sample and choice, choice accuracy declined with increasing delay. With short intertrial intervals (ITIs), choice accuracy decreased more at long delays than at short delays, showing that interference from previous trials impaired memory but not discrimination. Rats emitted overt mediating responses during delay by pressing the levers in the retracted position. However, the frequency of delay presses was low (<2/trial in all rats) and neither their frequency nor accuracy was related to choice accuracy. Resetting the delay interval for each delay press did not significantly alter choice response accuracy. Trimethyltin (TMT), 7 mg/kg IV, reduced the choice accuracy of one rat to chance levels at all delays; two other rats were affected transiently. TMT reduced choice accuracy during weeks 1 and 4 postinjection, with significant effects on the linear slope and intercept of the mean retention gradient during week 4. TMT did not affect responses to the retracted levers during delays. TMT treatment also elevated levels of glial fibrillary acidic protein (GFAP) in the CNS, measured 4 weeks after treatment. Hippocampal GFAP correlated highly with the reduction in choice accuracy during week 1 ( r = −.903) and week 4 ( r = −.797) postTMT. GFAP levels also correlated significantly with TMT-induced changes in the slopes and intercepts of the retention gradients for individual animals at both times after treatment. The delay and ITI effects suggest that the task adequately assessed working memory. The lack of effect of delay presses on choice accuracy suggests that these overt mediating responses did not differentially affect choice responding. The preferential disruption of choice accuracy at long delays by TMT indicates that the compound impaired the retention of spatial information over time, supporting the view that time-dependent processes are particularly vulnerable to this lesion. This spatial delayed response task thus provides a practical analytical tool for the characterization of memory deficits following exposure to neurotoxicants.

Quantitative changes in the synaptic vesicle proteins synapsin I and p38 and the astrocyte-specific protein glial fibrillary acidic protein are associated with chemical-induced injury to the rat central nervous system

Measurements of neuron-specific and glia-specific proteins were used to characterize chemical-induced injury to the rat CNS. Trimethyltin (TMT), a neurotoxicant that preferentially damages neurons in limbic structures, was employed to produce consistent, time-dependent, dose-related, cell type-specific alterations in CNS morphology. Brain weights and histology were used to verify the cytopathological effects of TMT. Accompanying changes in 2 synaptic vesicle-associated proteins, synapsin I and p38, and the astrocyte-associated protein, glial fibrillary acidic protein (GFAP), were measured by radioimmunoassay (RIA). Immunohistochemistry of GFAP and incorporation of 3H-thymidine into GFAP-positive astrocytes also were used to characterize astrocytic responses to TMT-induced injury. Finally, quantitative 2-dimensional PAGE was employed to detect additional proteins affected by TMT. Acute administration of TMT caused large dose- and time-dependent decreases in synapsin I and p38 in hippocampus; the same proteins were largely unaffected in a nonlimbic structure, the frontal cortex. Twelve weeks after dosing, the concentrations of synapsin I and p38 and, to a lesser extent, the absolute amount of these proteins in hippocampus had returned to near control values, findings that are suggestive of reactive synaptogenesis. TMT caused large dose- and time-dependent increases in GFAP that were not confined to hippocampus. Twelve weeks after dosing, the amounts of GFAP in hippocampus and frontal cortex had returned to near control values, findings indicative of a transient astrocytic response to brain injury. Immunohistochemistry of GFAP revealed widespread astrocytic reactivity as a consequence of exposure to TMT, a response that resulted in part from the proliferation of astrocytes. Additional neurotypic proteins altered by TMT-induced injury included one of the neurofilament (NF) triplet proteins (p68) and a protein with the electrophoretic characteristics of neuron-specific enolase (NSE). The data indicate that measurements of neurotypic and gliotypic proteins may be used to characterize the temporal and regional patterns of neuronal and glial responses to injury.