Biomedical subjects

N J Laping

Publications and source records attributed to N J Laping.

At least 37 records · Page 2Linked to original sources

PubMed1995

Expression of vimentin increases in the hippocampus and cerebral cortex after entorhinal cortex lesioning and in response to transforming growth factor beta 1.

Entorhinal cortex lesions (ECL) that damage the perforant path to the dentate gyrus of the hippocampal formation were used to model the regulation of vimentin (VIM) mRNA. ECL increased VIM mRNA in the ipsilateral hippocampus and in the ipsilateral cortex including the wound cavity within 1 day. By in situ hybridization, at 4 days post-ECL, VIM mRNA increased two-fold in the molecular layer of the dentate gyrus. VIM protein was co-localized by immunocytochemistry to astrocytes and microglia/macrophages. Transforming growth factor-beta 1 (TGF-beta 1), which was previously shown to increase in microglia/macrophages of the molecular layer after hippocampal deafferentation by ECL, was investigated as a regulator of VIM expression. Infusions of TGF-beta 1 into the lateral ventricle induced VIM mRNA with dose-dependence, e.g. infusion of 100 ng TGF-beta 1 increased VIM mRNA three-fold. The increase in VIM mRNA was localized by in situ hybridization to astrocytes and microglia in the molecular layer of the dentate gyrus. These findings further implicate TGF-beta 1 as a regulator of cytoskeletal proteins during synaptic reorganization.

Animals↗

PubMed1995

Clusterin expression by astrocytes is influenced by transforming growth factor beta 1 and heterotypic cell interactions.

This study characterizes the effect of transforming growth factor (TGF) beta 1 on clusterin expression in rat brain cells. 24 h after an acute unilateral intracerebroventricular infusion of TGF-beta 1, clusterin mRNA prevalence was increased in astrocytes that contained immunoreactive (IR) glial fibrillary acidic protein (GFAP). TGF-beta 1 selectively induced clusterin mRNA in astrocytes, as no clusterin mRNA was detected in neurons, oligodendrocytes, or microglia. TGF-beta 1 induced a bilateral increase in clusterin mRNA per astrocyte. Astrocyte hypertrophy (GFAP-IR area) was only increased on the ipsilateral side. In pure astrocyte cultures, TGF-beta 1 (200 pM) decreased clusterin mRNA levels and the rate of clusterin RNA transcription. However, in cultures of astrocytes that contained microglia and oligodendrocytes (mixed glia cultures), TGF-beta 1 caused a dose-dependent increase in astrocytic clusterin mRNA levels. The astrocytes that responded to TGF-beta 1 included two GFAP-IR subtypes, type 1 and 2. TGF-beta 1 increased clusterin protein in the conditioned medium from cultured glia, in either monotypic or mixed glial cultures. Thus, TGF-beta 1 and heterotypic cell interactions influence clusterin expression by astrocytes and may be important to the role of clusterin in multiple sclerosis, AIDS, and Alzheimer's disease.

Animals↗

PubMed1995

Transcriptional regulation of glial fibrillary acidic protein by corticosterone in rat astrocytes in vitro is influenced by the duration of time in culture and by astrocyte-neuron interactions.

In the rat hippocampus and cortex, the transcription of glial fibrillary acidic protein (GFAP), an astrocyte intermediate filament protein, is inhibited by glucocorticoids. The present study examined the regulation of GFAP expression by glucocorticoids in astrocytes in vitro. Corticosterone (CORT) increased GFAP messenger RNA, protein, and transcription rates in cultured primary neonatal astrocytes, responses opposite the GFAP responses to CORT in vivo. The direction of GFAP regulation by corticosterone in vitro is reversed by coculture with neurons or by extended culture for 3 months. The switch in the direction of GFAP regulation by CORT during prolonged culture is associated with a 3-fold increased prevalence of type II glucocorticoid receptor (GR). These findings were corroborated with a promoter construct that contained 1.9 kilobases of 5'-up-stream rat GFAP DNA with a luciferase reporter. Thus, the direction of GFAP transcription to CORT is subject to the postreplicative time in culture and to interactions with neurons, in which 5'-up-stream sequences contain sufficient information to mediate the switch in the direction of the response to CORT. This in vitro model may be used to analyze how interactions of astrocytes with neurons or other cell types influence the hormonal regulation of GFAP.

Animals↗

PubMed1994

Age-related increases in glial fibrillary acidic protein do not show proportionate changes in transcription rates or DNA methylation in the cerebral cortex and hippocampus of male rats.

Age-related increases in the expression of glial fibrillary acidic protein (GFAP) in many brain regions are observed in short- and long-lived mammals. Possible genomic mechanisms for the increase of GFAP mRNA and protein were studied in the hippocampus and cortex of male F344 rats and a longer-lived hybrid F1 (F344 x Brown Norway). No age-related changes were found in the extent of cytosine methylation at 19 CpG sites in the 5'-upstream GFAP promoter and in exon 1. With the nuclear runon assay, no change was found in the transcription rate of GFAP in the cerebral cortex or hippocampus. Thus, age-related increases in GFAP are not associated with proportionate changes in transcription rates or DNA methylation. However, the transcription of glutamine synthetase was increased by about 60%. These findings contrast with age-related loss of bulk tissue DNA methylation and decreased transcription rates of other genes reported in non-neural tissues.

Aging↗

PubMed1994

Transforming growth factor-beta 1 induces neuronal and astrocyte genes: tubulin alpha 1, glial fibrillary acidic protein and clusterin.

Transforming growth factor-beta 1 was studied as a possible regulator of messenger RNAs in astrocytes and neurons that increase after hippocampal deafferentation by perforant path transection: tubulin alpha 1, clusterin and glial fibrillary acidic protein messenger RNA. Because transforming growth factor-beta 1 messenger RNA is increased after this lesion, we examined which messenger RNA lesion responses could be induced by transforming growth factor-beta 1 alone. Porcine transforming growth factor-beta 1 infused into the lateral ventricle elevated the messenger RNAs for tubulin alpha 1, clusterin and glial fibrillary acidic protein 24 h after infusion in the ipsilateral hippocampus. As assayed by nuclear run-on, the transcription of glial fibrillary acidic protein RNA was increased in the ipsilateral hippocampus after perforant path transection and in primary rat astrocyte cultures by transforming growth factor-beta 1. In contrast, transforming growth factor-beta 1 did not change apolipoprotein-E messenger RNA or transcription, or growth associated protein-43 messenger RNA levels. We conclude that transforming growth factor-beta 1 increases subsets of neuronal and astrocyte messenger RNAs coding for cytoskeletal proteins that are also elevated in response to experimental lesions and Alzheimer's disease. This suggests that transforming growth factor-beta 1 might be a local organizing factor of neuronal and astrocyte responses to brain injury.

Animals↗

PubMed1994

Glial fibrillary acidic protein: regulation by hormones, cytokines, and growth factors.

Levels of glial fibrillary acidic protein (GFAP), an astrocyte-specific intermediate filament protein, are altered during development and aging, GFAP also responds dynamically to neurodegenerative lesions. Changes in GFAP expression can occur at both transcriptional and translational levels. Modulators of GFAP expression include steroids, cytokines, and growth factors. GFAP expression also shows brain region-specific responses to sex steroids and of astrocyte-neuronal interactions. The 5'-upstream sequences of rat, mouse, and human are compared for the presence of response elements that are candidates for transcriptional regulation of GFAP. We propose that the regulation of the GFAP gene has evolved a system of controls that allow integrated responses to neuroendocrine and inflammatory modulators.

Aging↗

PubMed1994

Transcriptional control of glial fibrillary acidic protein and glutamine synthetase in vivo shows opposite responses to corticosterone in the hippocampus.

Transcriptional regulation of two astrocyte genes, glial fibrillary acidic protein (GFAP) and glutamine synthase (GS), by glucocorticoids was determined by nuclear run-on assay with hippocampal tissues from adult male F344 rats. Transcriptional responses of GFAP to corticosterone were slower than those observed for GS, but were more sensitive to changes in plasma corticosterone. The transcription of GFAP did not change 2 h after the injection of 10 mg corticosterone, but was reduced by 50% at 6 and 24 h. In contrast, corticosterone increased GS transcription at 2 and 6 h. Seven days after adrenalectomy, GFAP, but not GS, transcription was increased. Corticosterone replacement (200 micrograms/ml in the drinking water) suppressed GFAP, but did not increase GS transcription in adrenalectomized rats. Therefore, GFAP transcription is more sensitive to low physiological levels of corticosterone than transcription of GS. The slower response of GFAP than GS to corticosterone suggests that glucocorticoids may have indirect effects on GFAP expression that require additional transcriptional regulators besides the glucocorticoid receptor.

Adrenalectomy↗

PubMed1993

TGF-beta 1 is an organizer of responses to neurodegeneration.

TGF-beta 1 mRNA and protein were recently found to increase in animal brains after experimental lesions that cause local deafferentation or neuron death. Elevations of TGF-beta 1 mRNA after lesions are prominent in microglia but are also observed in neurons and astrocytes. Moreover, TGF-beta 1 mRNA autoinduces its own mRNA in the brain. These responses provide models for studying the increases of TGF-beta 1 protein observed in beta A/amyloid-containing extracellular plaques of Alzheimer's disease (AD) and Down's syndrome (DS) and in brain cells of AIDS victims. Involvement of TGF-beta 1 in these human brain disorders is discussed in relation to the potent effects of TGF-beta 1 on wound healing and inflammatory responses in peripheral tissues. We hypothesize that TGF-beta 1 and possibly other TGF-beta peptides have organizing roles in responses to neurodegeneration and brain injury that are similar to those observed in non-neural tissues. Work from many laboratories has shown that activities of TGF-beta peptides on brain cells include chemotaxis, modification of extracellular matrix, and regulation of cytoskeletal gene expression and of neurotrophins. Similar activities of the TGF-beta's are well established in other tissues.

Animals↗

PubMed1993

Gonadal steroids regulate the expression of glial fibrillary acidic protein in the adult male rat hippocampus.

This study demonstrates that gonadal steroids (estradiol, testosterone, dihydrotestosterone) can regulate the expression of glial fibrillary acidic protein in the adult male rat brain. Previously, we showed that castration of adult male rats increased glial fibrillary acidic protein messenger RNA in the hippocampus and that this increase was additive with the increase induced by deafferenting entorhinal cortex lesions [Day et al. (1990) Molec. Endocr. 4, 1995-2002 . We extended these effects of castration and entorhinal cortex lesion to glial fibrillary acidic protein, using immunoassays. Furthermore, we found regional differences in responses to castration and inhibited by sex steroids. In contrast, hypothalamic glial fibrillary acidic protein expression was inhibited by castration. Similar regional differences were also shown for astrocyte glial fibrillary acidic protein distribution by immunocytochemistry. The regional specificity of glial fibrillary acidic protein expression after castration and sex steroid replacement is pertinent to the role of astrocytes in synaptic plasticity in unlesioned adults as well as in responses to lesions where the steroid milieu has been shown to influence sprouting.

Animals↗

PubMed1992

New mRNA probes for hippocampal responses to entorhinal cortex lesions in the adult male rat: a preliminary report.

Three new mRNA responses were found in the hippocampus of the adult male rat after entorhinal cortex lesions (ECL) that induce synaptic reorganization. Hippocampus cDNA libraries were screened by a subtractive hybridization strategy designed to detect ECL-induced mRNAs. Partial sequencing showed clones with similarities to mouse vimentin, ferritin, and polypeptide 7B-2. A sequence similar to mouse SNAP-25 sequence was also detected. Using a mouse SNAP-25 probe, rat SNAP-25 mRNA increased in the hippocampus after ECL.

Animals↗

PubMed1991

Prolactin stimulates dopamine release from the rat corpus striatum in the absence of extra-cellular calcium.

Prolactin (PRL) increased basal dopamine (DA) release and attenuated amphetamine (AMPH)-stimulated DA release in vitro from rat corpus striatum in a concentration-dependent manner with 10(-5) M PRL being the most effective. The effects of PRL on DA release were enhanced in the absence of extracellular calcium. PRL at 10(-5) M did not alter the DA post-superfusion content of the striatal tissue. These results indicate that the stimulatory effect of PRL on basal DA release does not require extra-cellular calcium and the inhibitory effect on AMPH-stimulated DA release is not due to depletion of DA stores.

Animals↗

PubMed1991

Sulfated glycoprotein-2 is increased in rat hippocampus following entorhinal cortex lesioning.

Thios study showed responses of sulfated glycoprotein-2 (SGP-2) in the rat hippocampus after deafferenting lesion. SGP-2 is a plasma protein that also occurs in many peripheral tissues. In some circumstances, elevations of SGP-2 mRNA are associated with cell degeneration and responses to injury. This study used entorhinal cortex lesions (ECL) to partially deafferent the hippocampus by damaging the perforant path and to induce synaptic remodeling. SGP-2 mRNA is increased in hippocampal astrocytes after ECL. Western blot analysis of soluble hippocampal proteins identified 3 major forms of rat SGP-2 protein: a precursor (61 kDa) and 2 reduced subunits at 39.5 and 35 kDa. These forms increased at 4 days post ECL ipsilaterally to the lesion. By immunocytochemistry (ICC), SGP-2 showed an increased immunoreactivity on the lesioned side by 2 days post ECL that continued through 14 days post ECL. Besides immunopositive astrocytes, punctate immunochemical reaction products occurred among the degenerating fibers of the perforant path. We conclude that changes of SGP-2 protein in the hippocampus after ECL occur roughly in parallel with increases of SGP-2 mRNA. The punctate immuno-deposits could represent secreted SGP-2 and may be useful as a marker for degenerating pathways.

Animals↗

PubMed1991

Increases in transforming growth factor-beta mRNA in hippocampus during response to entorhinal cortex lesions in intact and adrenalectomized rats.

Transforming growth factor-beta mRNA was detected with a rat TGF-beta 1 coding sequence probe as a 2.5 kb band by RNA blot hybridization of total RNA from the adult male rat hippocampus. Following electrolytic lesions of the entorhinal cortex that cause hippocampal deafferentation and synaptic remodeling, TGF-beta mRNA increases 5-fold in ipsilateral hippocampus when compared with intact controls. This increase was independent of prior adrenalectomy or corticosterone-replacement. These data demonstrate that TGF-beta gene expression increases in response to hippocampal deafferentation.

Adrenal Cortex↗

PubMed1991

Corticosterone differentially regulates the bilateral response of astrocyte mRNAs in the hippocampus to entorhinal cortex lesions in male rats.

This study examined the effect of adrenalectomy (ADX) and corticosterone (CORT) replacement on the levels of two astrocyte mRNAs during responses to unilateral entorhinal cortex lesions (ECL) to identify molecular mechanisms involved in glucocorticoid modulation of astrocyte activation following deafferentation. Both glial fibrillary acidic protein (GFAP) and sulfated glycoprotein-2 (SGP-2) mRNA were increased in the ipsilateral hippocampus 4 days following unilateral ECL. In unlesioned ADX rats CORT replacement decreased both messages in the hippocampus. CORT replacement suppressed the ECL-induced increase of GFAP mRNA in the contralateral, but not ipsilateral hippocampus of ADX rats. In contrast, CORT decreased SGP-2 mRNA both ipsi- and contralaterally. It is clear that several regulatory mechanisms are responsible for maintaining a physiological balance of astrocyte activity in the adult brain, and that changes in circuit integrity and the endocrine milieu can alter this balance.

Adrenalectomy↗

PubMed1990

Yawning behavior in male rats is associated with decreases in in vivo DOPAC efflux from the caudate nucleus.

Young adult male rats were implanted with a push-pull cannula aimed at the dorsal and rostral areas of the caudate nucleus. Perfusate samples were collected at two-minute intervals for approximately one hour and assayed for DOPAC concentrations. Simultaneously, yawning, penile erections and grooming behavior were recorded. Yawns were induced by systemic prolactin or apomorphine injections. While mean DOPAC efflux was elevated following prolactin (PRL) and apomorphine decreased mean DOPAC efflux as expected, yawns and penile erections induced by both compounds were associated with rapid momentary decreases in DOPAC efflux in these living animals. Although yawning was associated with significant decreases in DOPAC output, not every momentary DOPAC decrease was associated with a yawn, suggesting that the 'yawning generator' most likely requires additional inputs for the expression of a yawn.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1990

Castration enhances expression of glial fibrillary acidic protein and sulfated glycoprotein-2 in the intact and lesion-altered hippocampus of the adult male rat.

This study concerns effects of the testes on two macromolecules in the rat hippocampus that were previously not known to be responsive to this endocrine axis. Castration for 3 weeks elevated the expression of glial fibrillary acidic protein (GFAP) and sulfated glycoprotein-2 (SGP-2) in male rat hippocampus, as shown by Northern blots and immunocytochemistry. SGP-2 mRNA was colocalized with GFAP, implying increased prevalence in astrocytes after castration. During hippocampal responses to deafferentation by entorhinal cortex lesions that damage the perforant path and induce synaptic reorganization, both mRNA and protein for SGP-2 and GFAP increase. Moreover, prior castration had an additive effect with entorhinal cortex lesions in the increase in GFAP and SGP-2 mRNA. These data suggest that testicular hormones regulate hippocampal astrocyte activity in intact adult rats as well as during synaptic reorganization in response to deafferenting lesions.

Animals↗

PubMed1988

The importance of striatal interneurons in age-related effects upon potassium- and amphetamine-stimulated dopamine release.

The ability of superfused corpus striatal tissue fragments to release endogenous dopamine (DA) in response to potassium (K+ 30 mM) stimulation was significantly attenuated in 18- to 24-month- compared to 2- to 4-month-old male rats. These age-related effects on K+ stimulation were completely abolished with the addition of tetrodotoxin (1 microM) to the superfusion medium. Moreover, no difference in stimulated DA release was obtained between these two age groups following amphetamine stimulation (10 microM).

Aging↗

PubMed1988

Prolactin-induced yawning behavior requires an intact nigro-striatal dopamine system.

Herein, we evaluate the importance of the nigro-striatal dopamine system in prolactin-, apomorphine-, and physostigmine-induced yawning behavior. Bilateral 6-OH-dopamine lesions of the substantia nigra were performed on male rats (2-4 months old). The lesioned as well as control rats were injected with either physiological saline, physostigmine (200 micrograms/kg), apomorphine (50 micrograms/kg), or ovine prolactin (0.25 micrograms/kg) 72 hours after the surgical procedure. The results show that bilateral lesions of the substantia nigra did not affect physostigmine-induced yawning whereas both apomorphine- and prolactin-induced yawning were reduced by the lesion. Following the observation period the caudate nuclei were removed and analyzed for dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) content. The lesions reduced DA and DOPAC content in all treatment groups compared to the respective intact groups. Also, both DA and DOPAC concentrations were lower in the intact apomorphine and prolactin treated groups compared to intact saline controls, at times that were temporally related to the display of yawning behavior suggesting a decrease in dopamine activity following apomorphine and prolactin treatment. Interestingly, DA and DOPAC concentrations were higher in the lesioned apomorphine group compared to lesioned saline controls; however, in the lesioned prolactin group only the DA concentrations were higher when compared to lesioned saline controls. These results indicate that prolactin- and apomorphine-induced yawning require an intact nigro-striatal dopamine system and that these substances induce yawning by different mechanisms.

3,4-Dihydroxyphenylacetic Acid↗