Biomedical subjects

M B Heaton

Publications and source records attributed to M B Heaton.

At least 55 records · Page 3Linked to original sources

PubMed1994

Ethanol neurotoxicity in vitro: effects of GM1 ganglioside and protein synthesis inhibition.

Cultures of septal and hippocampal neurons from fetal rat and dorsal root ganglion neurons from embryonic chick were pretreated with GM1 ganglioside or cycloheximide and then supplemented with toxic concentrations of ethanol. GM1 provided significant protection against ethanol neurotoxicity in each population. The inhibition of protein synthesis by cycloheximide, however, which protects against cell death resulting from withdrawal of neurotrophic factor support, did not ameliorate ethanol-induced neuronal loss.

Animals↗

PubMed1994

Chronic alcohol ingestion: nerve growth factor gene expression and neurotrophic activity in rat hippocampus.

Chronic ethanol treatment induces memory deficits accompanied by anatomical and biochemical changes in basal forebrain and hippocampus. Cholinergic neurons in the septohippocampal pathway are especially vulnerable to alcohol neurotoxicity. Several studies showed that an adequate supply of neurotrophins, such as Nerve Growth Factor and Brain-Derived Neurotrophic Factor, is required for the normal function and survival of cholinergic neurons in basal forebrain and medial septal nuclei. We tested the hypothesis that chronic alcohol ingestion may alter the gene expression level of Nerve Growth Factor in hippocampus, the major source of neurotrophins to the cholinergic neurons in the septohippocampal pathway. We measured Nerve Growth Factor protein and Nerve Growth Factor mRNA contents using sensitive two-site ELISA and Northern analysis. We also tested the endogenous neurotrophic activity, including and excluding Nerve Growth Factor, contained in 5%, 2%, 1%, 0.5% and 0.1% (w/v) hippocampal tissue extracts on sympathetic ganglia neurons. Twenty-eight weeks of chronic ethanol treatment did not reduce Nerve Growth Factor protein, Nerve Growth Factor mRNA, or total neurotrophic activity contained in the rat hippocampus when measured on sympathetic ganglia neurons.

Alcoholism↗

PubMed1993

Modulation of ethanol neurotoxicity by nerve growth factor.

Dorsal root ganglion (DRG) neurons were cultured with varying concentrations of ethanol and NGF. At low concentrations of NGF (0.1 ng/ml) moderate initial ethanol levels (250 mg/dl) significantly suppressed neurite outgrowth. Higher NGF concentrations (5 ng/ml) protected against this neurotoxicity. At this higher NGF concentration, neuronal survival was not significantly affected by exposure to 0.25-4 g/dl ethanol, although survival was significantly diminished at 5 and 6 g/dl. Neurite outgrowth was a more sensitive indicator of ethanol neurotoxicity in this population, with significant decreases in process extension seen with 1 g/dl ethanol. When cultures were supplemented with 10 ng/ml NGF, however, process elaboration was significantly greater at 1 g/dl ethanol than that measured with 5 ng/ml NGF, and in fact did not differ from NGF controls. These studies indicate that NGF can provide neuroprotective effects against ethanol toxicity under these conditions. The results are discussed in relation to other recent reports of trophic factor neuroprotection.

Animals↗

PubMed1993

Disruption of species-specific behavior in neonatal quail following chronic prenatal ethanol exposure.

Bobwhite quail embryos were exposed to ethanol (5 mg every other day) from E5 to E21. Control embryos received comparable saline injections or were untreated. At 24 h posthatch, the neonates were tested in a single call approach test, using a Bobwhite maternal exodus call which had previously been shown to be a potent attractant to these animals. Almost all animals in all three groups approached the call, and latency of approach did not differ among the groups. The ethanol-treated animals, however, spent significantly less time within the approach area and exited the area significantly more often than did either the saline or untreated controls. Overall hyperactivity or loss of auditory acuity did not appear to account for the response deficits. These results suggest that species-specific behaviors might be a useful paradigm for the study of fetal alcohol effects.

Animals↗

PubMed1993

Effect of chronic ethanol on the septohippocampal system: a role for neurotrophic factors?

The mechanisms by which chronic ethanol exposure produces neuronal damage have not been established. Potentially ethanol may reduce normal neurotrophic influences necessary for neuronal survival, growth, and function. We hypothesized that chronic ethanol exposure might produce a decrease in the synthesis, availability, upregulation, delivery, and/or the biological activity of normally occurring neurotrophic factors, or may alter the capacity of target neurons to respond to these factors. The available evidence leading to this hypothesis and supporting data from our laboratory are discussed.

Alcoholism↗

PubMed1993

Neurotrophic activity in embryonic chick brain: early appearance and differential regional distribution.

Homogenate extracts were prepared from various regions of the embryonic chick brain from E6 to E19. The extracts were applied to cultured dorsal root ganglia (DRGs), sympathetic ganglion cells, PC12 cells and E5 spinal cord neurons. Potent neurotrophic activity with respect to DRGs was found in an extract from the forebrain (FBX) from the earliest stage assayed (E6). This activity was comparable to that of nerve growth factor (NGF), and it was not appreciably altered during later stages. By E8, extracts prepared from the optic lobe also induced responsiveness, although to a lesser extent than the FBX and NGF. At E12-19, extracts from the hippocampus (HCX) and cerebellum (CBX) were also tested. Activity found in the HCX resembled that in the FBX, but responsiveness to the CBX was similar to that in control (unsupplemented) cultures. The responsiveness of sympathetic neurons in the FBX was comparable to that with NGF. The FBX induced only moderate differentiation of PC12 cells, and spinal cord neurons were not responsive. Antibodies to NGF and basic fibroblast growth factor did not diminish the influence of the FBX, and the FBX and NGF when combined had synergistic effects. The results demonstrate potent neurotrophin-like activity in the embryonic brain at much earlier stages than had previously been seen, with differential regional and temporal distributions.

Animals↗

PubMed1992

Chronic ethanol consumption reduces the neurotrophic activity in rat hippocampus.

The effect of chronic ethanol treatment (CET) for 21-26 weeks on the neurotrophic activity contained in the rat hippocampus (HPC) was determined with a bioassay in cultures of dissociated dorsal root ganglion cells (DRG) obtained from E7-8 chick embryos. Extracts of the HPC from CET or pair-fed control rats were used as experimental media, and neuronal survival and neurite-outgrowth of DRG cultures were determined. Both neuronal survival (-25%) and neurite-outgrowth (-50%) were reduced in the presence of HPC extracts from CET rats relative to controls. These data suggest that CET reduces the neurotrophic content of the HPC which may result in damage to septohippocampal neurons.

Animals↗

PubMed1990

Comparative responsiveness of early chick neural tube neurons to muscle-conditioned medium, laminin, NGF and fibronectin.

Dissociates from the metencephalic basal plate of early chick embryo neural tubes containing the trigeminal (V) motor nucleus were cultured on substrates conditioned with appropriate target-derived muscle conditioned medium (MCM), laminin (LAM), MCM with nerve growth factor (NGF) in the medium, and fibronectin (FN). Comparisons were made of neuronal survival, the number of neurons with processes, and the length of processes elaborated. It was found that both MCM and LAM significantly enhanced survival and neuritic production from this population when compared to controls grown on a collagen-polyornithine substrate, but MCM surpassed LAM in these measures. When the neurons were grown on an MCM-conditioned substrate with an NGF-supplemented medium, no improvements were produced over the MCM or the NGF conditions alone. Therefore, the two do not appear to act in synergy, as NGF and LAM have been shown to do. FN produced no enhancement of any of the measures taken from this population. An ELISA analysis revealed no detectable LAM in the early target MCM. These results indicate that the specific responsiveness of this early neural tube population to its target MCM is not mediated by LAM, but the growth-enhancing component acts in a similar manner, although its influence is more potent.

Animals↗

PubMed1990

The response of cultured trigeminal and spinal cord motoneurons to nerve growth factor.

Dissociated neurons from the trigeminal (V) region of the metencephalic basal plate or the ventral spinal cord from chick embryos of Day 4 (V basal plate) or Day 5 (spinal cord) were cultured on a laminin substratum either in the presence of nerve growth factor (NGF) or in control medium. Assessment was made of neuronal survival, the amount of neurite elaborated, and the percentage of neurons initiating neurites. The presence of motoneurons was verified by retrograde labeling with the fluorescent dye diI. NGF was found to significantly increase the quantity of neuritic processes produced by the spinal cord dissociates at both 24 and 48 hr in vitro. The percentage of neurons initiating neuritic processes was significantly increased by NGF in the trigeminal population at 48 hr in vitro. Neuronal survival was not enhanced by NGF in either group. Both trigeminal and spinal cord neurons were also found to specifically bind 125I-NGF in culture. These results provide direct evidence for an influence of NGF on process formation of early embryonic motoneurons in culture.

Animals↗

PubMed1990

The ontogeny of specific retrograde transport of nerve growth factor by motoneurons of the brainstem and spinal cord.

Radiolabeled Nerve Growth Factor (NGF) was injected into either the mandibular process of the first visceral arch or the limb bud of chick embryos at Days 3.5-14 or Days 4-13 of incubation, respectively. Control embryos received injections of labeled cytochrome-C or labeled NGF plus an excess of unlabeled NGF. The tissues were then processed for autoradiography. The 125I-NGF was retrogradely transported by motoneurons of the trigeminal (V) motor nucleus on Days 3.5-8 of incubation, but not at later stages. Similar transport was seen in motoneurons of the spinal cord lateral motor column from Days 4-10 of incubation, but not at later stages. Sensory neurons of the V ganglion and of the dorsal root ganglia transported NGF at all injection ages. In no instance was the 125I-cytochrome-C transported by sensory or motor neurons. The injection of an excess of cold NGF along with labeled NGF resulted in no evidence of retrograde transport of the labeled NGF indicating that the transport was saturable. The time of transport by these brainstem and spinal cord motoneurons corresponds closely to the points during development at which they have been found to exhibit specific NGF binding. The present results, then, provide further evidence for a possible biological role for NGF during early developmental stages of these motoneuron populations.

Afferent Pathways↗

PubMed1989

Influence of laminin on the responsiveness of early chick embryo neural tube neurons to nerve growth factor.

Dissociated neurons from the neural tube containing the trigeminal motor nucleus from early chick embryos were cultured on laminin or collagen-polyornithine substrates, with and without nerve growth factor (NGF). Control cultures were grown in similar conditions with cytochrome-C. It was found that neuronal survival was not affected by NGF or cytochrome-C, but it was enhanced by laminin. The expression of neuritic processes, however, was significantly enhanced in the presence of NGF on both laminin and collagen-polyornithine surfaces, with the greatest number of neurons producing processes seen in the laminin-plus-NGF group. The length of processes was similarly enhanced by laminin and by NGF. Cytochrome-C did not influence any of these measures. The results indicate that while laminin potentiates the NGF effect on these early neuronal populations, NGF in conjunction with other substrata can have similar, though less dramatic, effects. These results, together with prior evidence of NGF receptors and specific NGF retrograde transport, suggest that this growth factor may play a significant role in the normal ontogeny of early motoneuron populations.

Animals↗

PubMed1989

Comparative responsiveness of early chick embryo brainstem and spinal cord neurons to target-conditioned medium.

Neurons from the early trigeminal (V) region of the basal plate and from the early ventral spinal cord of chick embryos were dissociated. Their responsiveness to muscle-conditioned medium (MCM) derived from age-matched appropriate and inappropriate target was compared. The V neurons responded to appropriate but not inappropriate MCM by enhanced survival and increased neurite production. Conversely, there were no differences in these measures in spinal cord neurons cultured in control medium and in MCM derived either from appropriate or inappropriate (trigeminal) target. The differences in specificity expressed by these two early populations is discussed.

Animals↗

PubMed1989

Axonal transport and central visual projections of ganglion cells in congenitally blind chickens.

The rd (retinal degenerate) strain of chicken is an example of a recessively inherited mutation characterized by blindness at the time of hatching, as defined by behavioral and electrophysiological tests. Paradoxically, blind mutants have normal retinal morphology, even at the ultrastructural level. Eventually, however, the entire retina degenerates in this strain, perhaps as a result of disuse atrophy. Results of preliminary studies imply that a defect in the visual transduction cascade in photoreceptor cells is responsible for the lack of vision. As well as being an important animal model for studies on photochemistry and transduction, the rd chicken may afford a paradigm for studies on inner retinal physiology and pathology, as electrical input to this inner neuronal system appears to be absent. In the current study we examined axonal transport (both retrograde and anterograde) in rd retinal ganglion cells and connectivity of ganglion cells to visual centers in the brain and compared these to normally sighted chicks. All visuorecipient nuclei were present in rd animals and appeared normal at the light microscopic level. When 3H-proline was injected into one eye of a blind chicken on the day of hatching, labeled polypeptides or proteins were transported via a fast transport mechanism to the same visual centers in roughly the same quantities as in normally sighted chicks. When horseradish peroxidase (HRP) was injected in the optic tectum of blind and normal 1 day old chicks, this label was transported retrogradely to the soma of retinal ganglion cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Species specificity in the responsiveness of chick embryo neural tube explants to target-conditioned medium.

Explants from the metencephalic region of 40-h chick embryo neural tubes containing the trigeminal (V) motor nucleus were cultured in appropriate target muscle-conditioned media (MCM) derived from chick, quail and rat embryos. Enhanced neuritic outgrowth was found only in the presence of chick MCM, indicating that this early, initial responsiveness to target-released materials within this system is species-specific.

Animals↗

PubMed1988

Some characteristics of muscle-conditioned media with excitatory and inhibitory influences on neurite outgrowth from early neural tube explants.

This study examined the growth of basal plate explants from 40-hr chick embryos containing the trigeminal motor nucleus in the presence of target muscle-conditioned medium (MCM) from day-4, day-10, and day-18 embryos. We had previously found that MCM derived from the 4-day target tissue enhanced neurite outgrowth from these explants, while target MCM from 10- and 18-day embryos inhibited it. For the present study, target MCM was treated with trypsin to assess the nature of the active fractions, or pre-incubated in polyornithine-coated dishes to determine the possible presence and relative contributions of substrate-binding vs. soluble components. Both trypsinization and pre-incubation abolished the outgrowth-enhancing potential of the 4-day MCM, indicating a protein or polypeptide substrate-binding active fraction, with no appreciable active soluble component. When the 10-day and 18-day target MCM were trypsinized, the inhibitory influence was reversed, and neurite outgrowth was enhanced. Similarly, when the MCM from these embryos was pre-incubated over polyornithine, the inhibitory influence was lost and was replaced by a stimulatory one. These results suggest that the 10- and 18-day MCM contain an active inhibitory fraction that is a protein or polypeptide, and which binds to a positively charged substrate. When this inhibitory fraction is inactivated or depleted, an excitatory soluble fraction is revealed. Such a dual nature in MCM has not been seen previously and may be expressed only when the media are assayed with very early neural tissue.

Animals↗

PubMed1988

The influence of laminin on the initial differentiation of cultured neural tube neurons.

Portions of the metencephalic neural tube containing the trigeminal (V) motor nucleus from 40-hr chick embryos were excised and held freely floating in culture medium for 36-40 hr, so that neuronal generation within motor V could be completed, but precluding neuronal differentiation. The explants were then dissociated and plated either on 1) glass coverslips that had been coated with the extracellular matrix (ECM) glycoprotein, laminin, and subsequently irradiated to produce a grid pattern; or 2) coverslips, one-half of which had been coated with laminin, and the other one-half with collagen, another component of the ECM. The purpose of these studies was to assess possible laminin influences on neuronal adhesion and nerve fiber expression and extension during these periods of initial neuronal differentiation. The early neural tube neurons selectively adhered to the established laminin grid pattern; neuronal survival, elaboration of neurites, and extent of neurites were significantly enhanced on the laminin side of the laminin/collagen preparations. These latter effects were specifically blocked by the application of anti-laminin. In demonstrating these influences during stages of initial neuronal differentiation, the results support the hypothesis that laminin may play a role in normal neurogenesis, presumably by providing an adhesive surface for outgrowing growth cones.

Animals↗

PubMed1988

Retrograde transport of NGF by early chick embryo spinal cord motoneurons.

Neuronal retrograde transport of nerve growth factor (NGF) was examined in chick embryos at 5, 6, and 7 days of incubation. Radiolabeled NGF was injected in the target limb muscle and the retrograde transport was viewed following processing for autoradiography. Silver grains were localized in the peripheral nerve, in the ventral root, in neuronal cell bodies within the dorsal root ganglion, and in motoneurons of the lateral motor column. Comparable injections of 125I-cytochrome c resulted in the presence of label at the peripheral injection site only. The possible developmental significance of these observations is discussed.

Animals↗

PubMed1987

Influence of nerve growth factor on chick trigeminal motor nucleus explants.

Explants of the metencephalic basal plate from stage 11 (40-hour) chick embryos containing the trigeminal (V) motor nucleus were cultured in standard control medium, in medium supplemented with nerve growth factor (NGF), in medium supplemented with NGF and specific antibodies to NGF (anti-NGF), and in medium supplemented with anti-NGF alone. The explants grown in the presence of NGF displayed an enhanced density and complexity of neuritic outgrowth, with this growth significantly surpassing that seen in the control group (p less than .001). The explants grown in NGF plus anti-NGF and those grown in anti-NGF alone did not differ from controls. The results indicate that this early cholinergic population is specifically responsive to NGF. This finding is consistent with recent studies in which NGF receptor binding has been found in this and other early brainstem and spinal cord motor neuron populations. The possible relevance of these observations to the normal sequence involved in the development of the V motor nucleus is discussed, particularly as they may relate to the relationship between the V ganglion and the developing V motor population.

Animals↗