Interleukin (IL)-1 and IL-6 regulation of neural progenitor cell proliferation with hippocampal injury: differential regulatory pathways in the subgranular zone (SGZ) of the adolescent and mature mouse brain.

Current data suggests an association between elevations in interleukin 1 (IL-1)α, IL-1ß, and IL-6 and the proliferation of neural progenitor cells (NPCs) following brain injury. A limited amount of work implicates changes in these pro-inflammatory responses with diminished NPC proliferation observed as a function of aging. In the current study, adolescent (21day-old) and 1year-old CD-1 male mice were injected with trimethyltin (TMT, 2.3mg/kg, i.p.) to produce acute apoptosis of hippocampal dentate granule cells. In this model, fewer 5-bromo-2'-deoxyuridine (BrdU)+ NPC were observed in both naive and injured adult hippocampus as compared to the corresponding number seen in adolescent mice. At 48h post-TMT, a similar level of neuronal death was observed across ages, yet activated ameboid microglia were observed in the adolescent and hypertrophic process-bearing microglia in the adult. IL-1α mRNA levels were elevated in the adolescent hippocampus; IL-6 mRNA levels were elevated in the adult. In subgranular zone (SGZ) isolated by laser-capture microdissection, IL-1ß was detected but not elevated by TMT, IL-1a was elevated at both ages, while IL-6 was elevated only in the adult. Naïve NPCs isolated from the hippocampus expressed transcripts for IL-1R1, IL-6Rα, and gp130 with significantly higher levels of IL-6Rα mRNA in the adult. In vitro, IL-1α (150pg/ml) stimulated proliferation of adolescent NPCs; IL-6 (10ng/ml) inhibited proliferation of adolescent and adult NPCs. Microarray analysis of SGZ post-TMT indicated a prominence of IL-1a/IL-1R1 signaling in the adolescent and IL-6/gp130 signaling in the adult.

Increased excitotoxicity and neuroinflammatory markers in postmortem frontal cortex from bipolar disorder patients.

Reports of cognitive decline, symptom worsening and brain atrophy in bipolar disorder (BD) suggest that the disease progresses over time. The worsening neuropathology may involve excitotoxicity and neuroinflammation. We determined protein and mRNA levels of excitotoxicity and neuroinflammatory markers in postmortem frontal cortex from 10 BD patients and 10 age-matched controls. The brain tissue was matched for age, postmortem interval and pH. The results indicated statistically significant lower protein and mRNA levels of the N-methyl-D-aspartate receptors, NR-1 and NR-3A, but significantly higher protein and mRNA levels of interleukin (IL)-1beta, the IL-1 receptor (IL-1R), myeloid differentiation factor 88, nuclear factor-kappa B subunits, and astroglial and microglial markers (glial fibrillary acidic protein, inducible nitric oxide synthase, c-fos and CD11b) in postmortem frontal cortex from BD compared with control subjects. There was no significant difference in mRNA levels of tumor necrosis factor alpha or neuronal nitric oxide synthase in the same region. These data show the presence of excitotoxicity and neuroinflammation in BD frontal cortex, with particular activation of the IL-R cascade. The changes may account for reported evidence of disease progression in BD and be a target for future therapy.

Inter-α-inhibitor deficiency in the mouse is associated with alterations in anxiety-like behavior, exploration and social approach.

In recent years, several genome-wide association studies have identified candidate regions for genetic susceptibility in major mood disorders. Most notable are regions in a locus in chromosome 3p21, encompassing the genes NEK4-ITIH1-ITIH3-ITIH4. Three of these genes represent heavy chains of the composite protein inter-α-inhibitor (IαI). In order to further establish associations of these genes with mood disorders, we evaluated behavioral phenotypes in mice deficient in either Ambp/bikunin, which is necessary for functional ITIH1 and ITIH3 complexes, or in Itih4, the gene encoding the heavy chain Itih4. We found that loss of Itih4 had no effect on the behaviors tested, but loss of Ambp/bikunin led to increased anxiety-like behavior in the light/dark and open field tests and reduced exploratory activity in the elevated plus maze, light/dark preference and open field tests. Ambp/bikunin knockout mice also exhibited a sex-dependent exaggeration of acoustic startle responses, alterations in social approach during a three-chamber choice test, and an elevated fear conditioning response. These results provide experimental support for the role of ITIH1/ITIH3 in the development of mood disorders.

Acrylamide-induced alterations in axonal transport. Biochemical and autoradiographic studies.

Alterations in the axonal transport of proteins, glycoproteins, and gangliosides in sensory neurons of the sciatic nerve were examined in adult male rats exposed to acrylamide (40 mg ip/kg body wt/d for nine consecutive days). Twenty-four hours after the last dose, the L5 dorsal root ganglion (DRG) was injected with either [35S]methionine to label proteins or [3H]glucosamine to label glycoproteins and gangliosides. The downflow patterns of radioactivity for [35S]methionine-labeled proteins and [3H]glucosamine-labeled gangliosides were unaltered by acrylamide treatment. In contrast, the outflow pattern of labeled glycoproteins displayed a severely attenuated crest with no alteration in velocity, suggesting a preferential transfer with the unlabeled stationary components in the axolemma. Retrograde accumulation of transported glycoproteins and gangliosides was unaltered for at least 6 h; however, by 24 h, there was a 75% decrease in the amount of accumulated material. The accumulation of [35S]methionine-labeled proteins was not altered. Autoradiographic analysis revealed an acrylamide-induced paucity of transported radiolabeled glycoproteins selectively in myelinated axons with no effect on "nonmyelinated" axons. The pattern of transported proteins was similar in both control and acrylamide-exposed animals. These results suggest a preferential inhibition of glycosylation or axonal transport of glycoproteins in neurons bearing myelinated axons. More importantly, it suggests that interpretations of axonal transport data must be made with the consideration of alterations in selective nerve fibers and not with the tacit assumption that all fibers in the nerve population are equally affected.

Increase in brain stem cytokine mRNA levels as an early response to chemical-induced myelin edema.

This study examined the early response of pro-inflammatory and regulatory cytokines in the mouse brain following triethyltin (TET)-induced myelin injury characterized by edematous vacuolation. Following an acute intraperitoneal injection of triethyltin (TET) sulfate (3 mg/kg) to 17-day old CD1 mice, significant increases in brain stem TNF-alpha and IL-1alpha mRNA levels occurred at 6 and 24 h, respectively with elevations in TGF-beta1 and MIP-1alpha at 1 h. In the cortex, responses were limited to elevations at 6 h in TNF-alpha, TGF-beta1 and MIP-1alpha. These data suggest that a chemokine/cytokine response can occur with minimal alterations to the integrity of the myelin sheath and may contribute to the initial signaling mechanisms associated with demyelinating disorders.

Trimethyltin increases interleukin (IL)-1 alpha, IL-6 and tumor necrosis factor alpha mRNA levels in rat hippocampus.

Within the central nervous system (CNS), cytokines are though to have active roles in pathophysiological changes seen in various neurological diseases and trauma. The present study was undertaken to examine the early response of pro-inflammatory cytokines following exposure to a specific neurotoxicant (trimethyltin; TMT). mRNA levels for interleukin (IL)-1 alpha, IL-1 beta, IL-6 and tumor necrosis factor (TNF) alpha were measured in the hippocampus of adult male Long-Evans hooded rats following an acute injection of trimethyltin hydroxide (8 mg TMT/kg body weight). At various times following exposure (6 h to 8 days), hippocampal tissues were excised and relative changes in cytokine mRNA levels were assessed by reverse transcription and polymerase chain reaction. IL-1 alpha, IL-6 and TNF alpha mRNA levels in the hippocampus increased within 6 h and remained elevated for 8 days. Quantitative analysis of mRNA transcripts revealed a two-fold increase in both IL-6 and TNF alpha within 6 h and a continued elevation of TNF alpha to 9-fold by 12 h. Within 96 h, glial fibrillary acidic protein (GFAP) mRNA levels were elevated in the hippocampus. Histological examination showed sparse individual neuronal necrosis at this time in both the pyramidal and granule cell regions with no increase in astrocyte GFAP immunoreactivity. However, an early, 24 h, response of microglial cells was indicated by increased lectin binding. This morphological profile progressed over time to a profound neuronal loss in the CA3-4 granule cell layer and marked astrocyte hypertrophy. The onset of pro-inflammatory cytokine mRNA expression appears to be temporally associated with histological evidence of elevated microglia in the hippocampus. It is proposed that microglia and pro-inflammatory cytokines play a modulatory role in the early stages of TMT-induced neurotoxicity.

Differential patterns of nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 mRNA and protein levels in developing regions of rat brain.

The present studies were undertaken to characterize the regional and temporal patterns of neurotrophin messenger RNA and protein levels for beta-nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 in the developing CNS. We have examined the levels of these neurotrophin messenger RNAs with ribonuclease protection assays and corresponding protein levels with enzyme-linked immunosorbent assays in the developing Long-Evans rat hippocampus, neocortex and cerebellum on postnatal days 1, 7, 14, 21, and 92. In addition, immunohistochemistry was used to localize the neurotrophins in these developing brain regions. Results indicated that in neocortex and hippocampus, messenger RNA for both nerve growth factor and brain-derived neurotrophic factor increased in an age-dependent manner, reaching a plateau by postnatal day 14. In the neocortex, nerve growth factor and brain-derived neurotrophic factor protein levels both peaked at postnatal day 14. In hippocampus, nerve growth factor protein peaked at postnatal day 7 while brain-derived neurotrophic factor peaked at postnatal day 14. In cerebellum, nerve growth factor messenger RNA levels were flat, while nerve growth factor protein peaked at postnatal day 7. Brain-derived neurotrophic factor messenger RNA increased in an age-dependent manner while the pattern for its protein levels was mixed. Neurotrophin-3 messeger RNA levels increased in an age-dependent manner in hippocampus, peaked at postnatal day14 in cerebellum, and no changes occurred in neocortex. Neurotrophin-3 protein was at its peak at postnatal day 1 and thereafter decreased at other postnatal days in all three brain regions. Results of neurotrophin immunohistochemistry often paralleled and complemented enzyme-linked immunosorbent assay data, demonstrating specific cell groups containing neurotrophin proteins in these regions. Within each region, patterns with regard to messenger RNA and respective protein levels for each neurotrophin were unique. No consistent relationship between patterns of neurotrophin messenger RNAs and their cognate proteins was observed between regions. The different regional patterns for neurotrophin messengerRNA and protein levels in each brain region indicate that messenger RNA studies of neurotrophin messenger RNA must be augmented by protein determination to fully characterize spatial and temporal neurotrophin distribution.

Persisting learning deficits in rats after exposure to Pfiesteria piscicida.

Pfiesteria piscicida and other toxic Pfiesteria-like dinoflagellates have been implicated as a cause of fish kills in North Carolina estuaries and elsewhere. Accidental laboratory exposure of humans to P. piscicida has been reported to cause a complex syndrome including cognitive impairment. The current project was conducted to experimentally assess the possibility of cognitive effects of P. piscicida exposure in rats. Samples of water from aquaria in which P. piscicida zoospores were killing fish were frozen, a procedure that has been found to induce encystment. Thawed samples were injected into albino Sprague-Dawley rats. A significant learning impairment was documented in rats administered samples of P. piscicida that were recently frozen. Prolonged storage of Pfiesteria samples diminished the effect. No effect was seen in the recall of a previously learned task, but when the rats were called upon to learn a new task, the Pfiesteria-treated animals showed a significant learning deficit. This effect persisted up to at least 10 weeks after a single injection of Pfiesteria. The Pfiesteria-induced learning deficit did not seem to be associated with any obvious debilitation or health impairment of the exposed rats. Deficits in habituation of arousal and rearing behavior were detected using a functional observational battery. No Pfiesteria-induced effects on blood count and white cell differential or in a standard pathological screening of brain, liver, lung, kidney, and spleen tissue were seen at 2 months after exposure. These studies document a persistent learning impairment in rats after exposure to the dinoflagellate P.piscicida in otherwise physically well-appearing rats. This effect may partially model the symptoms of cognitive impairments that humans have shown after Pfiesteria exposure.

In vitro techniques for the assessment of neurotoxicity.

Risk assessment is a process often divided into the following steps: a) hazard identification, b) dose-response assessment, c) exposure assessment, and d) risk characterization. Regulatory toxicity studies usually are aimed at providing data for the first two steps. Human case reports, environmental research, and in vitro studies may also be used to identify or to further characterize a toxic hazard. In this report the strengths and limitations of in vitro techniques are discussed in light of their usefulness to identify neurotoxic hazards, as well as for the subsequent dose-response assessment. Because of the complexity of the nervous system, multiple functions of individual cells, and our limited knowledge of biochemical processes involved in neurotoxicity, it is not known how well any in vitro system would recapitulate the in vivo system. Thus, it would be difficult to design an in vitro test battery to replace in vivo test systems. In vitro systems are well suited to the study of biological processes in a more isolated context and have been most successfully used to elucidate mechanisms of toxicity, identify target cells of neurotoxicity, and delineate the development and intricate cellular changes induced by neurotoxicants. Both biochemical and morphological end points can be used, but many of the end points used can be altered by pharmacological actions as well as toxicity. Therefore, for many of these end points it is difficult or impossible to set a criterion that allows one to differentiate between a pharmacological and a neurotoxic effect. For the process of risk assessment such a discrimination is central. Therefore, end points used to determine potential neurotoxicity of a compound have to be carefully selected and evaluated with respect to their potential to discriminate between an adverse neurotoxic effect and a pharmacologic effect. It is obvious that for in vitro neurotoxicity studies the primary end points that can be used are those affected through specific mechanisms of neurotoxicity. For example, in vitro systems may be useful for certain structurally defined compounds and mechanisms of toxicity, such as organophosphorus compounds and delayed neuropathy, for which target cells and the biochemical processes involved in the neurotoxicity are well known. For other compounds and the different types of neurotoxicity, a mechanism of toxicity needs to be identified first. Once identified, by either in vivo or in vitro methods, a system can be developed to detect and to evaluate predictive ability for the type of in vivo neurotoxicity produced. Therefore, in vitro tests have their greatest potential in providing information on basic mechanistic processes in order to refine specific experimental questions to be addressed in the whole animal.

Methods to identify and characterize developmental neurotoxicity for human health risk assessment. III: pharmacokinetic and pharmacodynamic considerations.

We review pharmacokinetic and pharmacodynamic factors that should be considered in the design and interpretation of developmental neurotoxicity studies. Toxicologic effects on the developing nervous system depend on the delivered dose, exposure duration, and developmental stage at which exposure occurred. Several pharmacokinetic processes (absorption, distribution, metabolism, and excretion) govern chemical disposition within the dam and the nervous system of the offspring. In addition, unique physical features such as the presence or absence of a placental barrier and the gradual development of the blood--brain barrier influence chemical disposition and thus modulate developmental neurotoxicity. Neonatal exposure may depend on maternal pharmacokinetic processes and transfer of the xenobiotic through the milk, although direct exposure may occur through other routes (e.g., inhalation). Measurement of the xenobiotic in milk and evaluation of biomarkers of exposure or effect following exposure can confirm or characterize neonatal exposure. Physiologically based pharmacokinetic and pharmacodynamic models that incorporate these and other determinants can estimate tissue dose and biologic response following in utero or neonatal exposure. These models can characterize dose--response relationships and improve extrapolation of results from animal studies to humans. In addition, pharmacologic data allow an experimenter to determine whether exposure to the test chemical is adequate, whether exposure occurs during critical periods of nervous system development, whether route and duration of exposure are appropriate, and whether developmental neurotoxicity can be differentiated from direct actions of the xenobiotic.

Role of dentate gyrus cells in retention of a radial arm maze task and sensitivity of rats to cholinergic drugs.

Male adult Fischer-344 rats that received bilateral injections of colchicine into two rostrocaudal sites showed relatively long-lasting alterations in the performance of a previously acquired radial arm maze task and specific destruction of dentate granule cells. Results of subsequent experiments with cholinergic drugs indicated that physostigmine or nicotine had no effect on the number of errors made in the maze, although other signs of cholinergic or pharmacological activity were present. RS-86, an analog of the muscarinic agonist arecoline, decreased errors in colchicine-treated rats, but these effects were associated with signs of parasympathetic overstimulation and behavioral sedation. Pretreatment with scopolamine, a muscarinic cholinergic receptor antagonist, increased errors in control rats but had no effect in colchicine-treated rats. Results of subsequent experiments found that colchicine-treated rats were less sensitive to the motor stimulant effect of scopolamine. These effects appeared to be associated with increased levels of choline acetyltransferase in the hippocampus and a down regulation of muscarinic postsynaptic receptors. One interpretation of these data is that intradentate colchicine may destroy granule cells, which leads to a compensatory reinnervation of cholinergic nerve terminals having cell bodies in the septum.

Pharmacological modification of DDT-induced tremor and hyperthermia in rats: distributional factors.

Pretreatment of rats with hydantoin (75 mg/kg, PO, an anticonvulsant), trihexyphenidyl (10 mg/kg, SC, a muscarinic cholinergic antagonist), or piperonyl butoxide (500 mg/kg, PO, a metabolic inhibitor) had no effect on the whole blood or brain tissue levels of orally administered DDT (75 mg/kg) or its metabolites DDD and DDE. Hydantoin and piperonyl butoxide decreased DDT-induced tremor and hyperthermia due to DDT when measured 12 h after DDT exposure, while trihexyphenidyl augmented some components of DDT-induced tremor. Additional experiments found that pretreatment with piperonyl butoxide increased tremor due to permethrin exposure (120 mg/kg, PO), while having no effect on tremor due to chlordecone administration (60 mg/kg, IP). Pretreatment with ellipticine (30 mg/kg, IP, a metabolic inhibitor) also decreased tremor 12 h after DDT exposure. The effects of piperonyl butoxide and ellipticine on DDT-induced tremor are postulated to occur through direct actions of these compounds on nerve or muscle tissue. Hydantoin-induced attenuation of DDT-induced neurotoxicity may be due to the ability of hydantoin to block repetitive firing of nerves by binding to the inactivation gates of sodium.

Developmental profiles of growth-associated protein (Gap43), Ngfb, Bndf and Ntf4 mRNA levels in the rat forebrain after exposure to 60 Hz magnetic fields.

Fischer 344 rats were exposed to 60 Hz magnetic fields (EMFs) during gestation and lactation. Rats received continuous exposure to 2-, 200- or 1000-microT magnetic fields for 18.5 h per day, 7 days a week, or sham exposure (sham controls). During postnatal development, on postnatal days 1, 3, 6, 9, 15 and 20, forebrain tissue from male pups was examined for alterations in mRNA level for developmentally regulated central nervous system-specific proteins. Alterations in these factors during critical periods of development could result in alterations in the final neural network. Gap43 (growth-associated protein 43) mRNA was measured by Northern hybridization as a developmental indicator of axonal growth during the development of the neuron. Between postnatal days 1 and 9, detectable levels of Gap43 mRNA displayed a similar pattern across all sham control and exposure groups. In addition to Gap43, mRNA levels for the nervous system-specific growth factors ciliary neurotrophic factor (Cntf), brain-derived neurotrophic factor (Bdnf), beta nerve growth factor (Ngfb), neurotrophin-3 (Ntf3), and neurotrophin-4 (Ntf4) were examined by RNase protection assay. While there is public concern for developmental neurotoxicity associated with exposure to EMFs, these data, generated from animals exposed to 2-, 200- or 1000-microT magnetic fields during both gestational and lactational periods of development, suggest that under these conditions no significant alterations in these critical factors for brain development occur.

Induction of tumor necrosis factor alpha in cultured glial cells by trimethyltin.

Within the central nervous system, cytokines are thought to play an active role in pathophysiological changes seen in various neurodegenerative diseases and trauma. Previous studies in our laboratory demonstrated that systemic administration of the neurotoxicant trimethyltin (TMT) produced a rapid and sustained elevation of CNS TNF alpha mRNA levels. In order to examine the effects of TMT on glial cultures in the absence of a neuronal component, primary glial cultures were exposed to TMT. Cultured glial cells undergo distinct morphological changes within 6 h of exposure to 10 microM TMT. This is characterized by an initial retraction of astrocytic processes revealing long, thin GFAP-dense processes and enlarged cell bodies, progressing to distinct retraction of plasmalemmna processes by 24 h. Prior to morphological changes, mRNA levels for the astrocyte-specific protein, glial fibrillary acidic protein (GFAP), increased within 3 h, as determined by Northern blot hybridization. Approximately a four-fold increase in TNF alpha mRNA levels was observed after 6 h as determined by competitive RT-PCR. This stimulation resulted in a 10-fold increase in the biologically active form of TNF alpha protein. These results suggest that a direct stimulation of glial cells may produce an early and critical response of the nervous system in chemical-induced neurotoxicity.

Colchicine-induced alterations in receptor-stimulated phosphoinositide hydrolysis in the rat hippocampus.

Intradentate administration of colchicine has been reported to affect the cholinergic muscarinic system in the hippocampus, causing a reduction in quinclidinylbenzilate binding sites and an increase in choline acetyltransferase activity. Since the cholinergic muscarinic system is coupled to the formation of inositolphosphates in the brain, the effect of intradentate administration of colchicine on the agonist-induced turnover of inositollipid was studied in rats. The animals were sacrificed 12 weeks after injection, and the hippocampi removed and sliced. [3H]Inositol was incorporated into slices in the presence of lithium, and carbachol, a cholinergic muscarinic receptor agonist, was used to study the stimulated turnover of inositollipids. Hippocampal slices taken from colchicine-treated rats showed an increased carbachol-stimulated accumulation of inositolmonophosphate. Thus, intradentate colchicine appears to alter the signal transduction process for the muscarinic cholinergic receptor in the hippocampus, a change that may be associated with compensatory processes following damage to the hippocampus.

The use of Synapsin I as a biochemical marker for neuronal damage by trimethyltin.

The content of Synapsin I (Protein I) was examined in brain regions of adult rats exposed to trimethyltin (TMT), and in control animals. Long Evans hooded rats were intragastrically dosed with 4 mg TMT hydroxide/kg body weight for 4 days. No perturbations in Synapsin I levels were evident by 24 h following the fourth dose; however, by 36 h, a significant decrease of 28% in Synapsin I level was present in the hippocampus of TMT treated animals. This decrease was selective, no other brain region examined was affected. As determined by regional analysis of inorganic tin, this specificity was not due to a profound preferential accumulation of tin in the hippocampus. Despite the absence of an alteration in Synapsin I levels at 24 h, morphological examination revealed perturbation in the normal uniform arrangement of granule cell neurons, with dead neurons diffusely distributed throughout the facia dentata. At 36 h, these changes were only slightly more extensive. In contrast, examination of the terminal projection area of these cells, the mossy boutons, showed to be unaffected at 24 h after the 4th dose of TMT. However, by 36 h, many of the mossy boutons contained dense bodies and showed signs of degeneration. This result suggested that the loss of Synapsin I coincides with degeneration of the nerve terminal region. In order to better establish the temporal correlation, a less severe dosing regimen (only 3 days of exposure to 4 mg TMT/kg body wt) was utilized to attenuate the time course of necrosis. Again, necrotic changes were visible in the perikaryon by 1 day after termination of toxicant dosing.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of polychlorinated biphenyl congeners on phosphoinositide hydrolysis and protein kinase C translocation in rat cerebellar granule cells.

Previous reports from our laboratory have suggested that the neuroactivity of some polychlorinated biphenyl (PCB) congeners is associated with perturbations in cellular Ca(2+)-homeostasis. We have characterized further the neurochemical effects of PCBs on signal transduction in primary cultures of cerebellar granule cells. The present experiments found that neither 2,2'-dichlorobiphenyl (DCBP), an ortho-substituted congener, nor 3,3',4,4',5-pentachlorobiphenyl (PCBP), a non-ortho-substituted congener, affected basal phosphoinositide (PI) hydrolysis in cerebellar granule cells. However, at concentrations up to 50 microM, DCBP potentiated carbachol-stimulated PI hydrolysis, while decreasing it at 100 microM. PCBP, on the other hand, had no effect on carbachol-stimulated PI hydrolysis in concentrations up to 100 microM. [3H]Phorbol ester ([3H]PDBu) binding was used to determine protein kinase C (PKC) translocation. DCBP increased [3H]PDBu binding in a concentration-dependent manner and a twofold increase was observed at 100 microM in cerebellar granule cells. PCBP had no effect on [3H]PDBu binding at concentrations up to 100 microM. The effect of DCBP on [3H]PDBu binding was time-dependent and was also dependent on the presence of external Ca2+ in the medium. To test the hypothesis that DCBP increases [3H]PDBu binding by acting on receptor-activated calcium channels, the effects of DCBP were compared to those of L-glutamate. The effects of DCBP (50 microM) and glutamate (20 microM) were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Time-dependent neurobiological effects of colchicine administered directly into the hippocampus of rats.

Rats were given bilateral injections of colchicine into the dorsal and ventral hippocampus. Behavioral, neurochemical and histopathological measurements were taken, up to 12 weeks after surgery. Colchicine produced a consistent increase in spontaneous motor activity, enhanced acoustic startle reactivity, and accelerated acquisition of two-way shuttle box avoidance, but did not affect reactivity to a noxious thermal stimulus. Measurement of dynorphin in the hippocampus indicated that colchicine rapidly depleted this neuropeptide, which is thought to be contained preferentially in the mossy fibers of granule cells of the hippocampus. Colchicine also decreased Met-enkephalin in the hippocampus, but the magnitude of the change (22%) was less than that (89% depletion) observed for hippocampal dynorphin. Examination of hippocampal morphology using light microscopic techniques indicated that colchicine caused approximately 60% degeneration of granule cells in the hippocampus. Although the length of the pyramidal cells was decreased (12-16%), the width of the CA1 and CA3 region of the hippocampus was not affected. These data underscore the importance of the granule cells in the mediation of behavioral processes such as motor activity, startle reactivity and performance of shuttle box avoidance.

Exposure to lead-acetate modulates the developmental expression of myelin genes in the rat frontal lobe.

Postnatal exposure to high levels (4%) of lead (Pb) have been shown to disrupt myelin formation and result in abnormal conduction of nerve impulses, components necessary for information processing in the CNS. To investigate whether the pathological changes in myelin, due to Pb exposure, might be partially mediated by modulations of the expression of genes involved in CNS myelin, we have examined the developmental profiles of the proteolipid protein (PLP) and myelin basic protein (MBP), two major structural constituents of CNS myelin and 2',3'-cyclic nucleotide 3' phosphodiesterase (CNP), a non-structural enzyme associated with myelin formation. Rat pups were postnatally exposed, from birth to weaning, to moderate amounts of Pb (0.2%), in the drinking water of the dam, and their frontal cortices were assayed for changes in the expression profile of the above genes by Northern Analysis. On PND 20, Pb resulted in a dramatic stimulation of the mRNA levels of PLP and a small increase in MBP mRNA levels, but had no effect on the CNP message. These data suggest that moderate levels of Pb selectively interfere with the gene expression of structural proteins of CNS myelin and may thus influence the composition of myelin in this way.

The postnatal development of glial fibrillary acidic protein and neurofilament triplet proteins in rat brain stem.

Cytoskeletal preparations containing both the glial fibrillary acidic protein and the neurofilament triplet proteins were prepared from brain stems of rats at different ages and the individual peptides separated in polyacrylamide gels. Stained peptide bands were quantitated as the area under peaks generated by densitometric scanning. Peak areas were converted to grams of protein based on total gel dye binding and total protein applied to the gels. Between 5 and 30 days, the concentration of the peptide (g of peptide/mg of tissue protein) of apparent molecular weight 51,000 (corresponding to the glial fibrillary acidic protein), increased 3 fold. The corresponding increase in total concentration of the three peptides corresponding to the neurofilament proteins was 4.5 fold. However, the increase in concentration of the individual neurofilament peptides was each different. Very little of the apparent molecular weight 210,000 neurofilament peptide was present at 5 days and its concentration increased 11 fold by 30 days compared to about 3.5 fold for the other two neurofilament peptides. These results are in general agreement with studies using immunological techniques and the methods have the advantages of using readily available techniques and allowing the simultaneous comparison of both neuronal and glial specific filaments during development.