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Biomedical subjects

M B Heaton

Publications and source records attributed to M B Heaton.

At least 19 recordsLinked to original sources
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

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↗
PubMed1978

Species-specific auditory discrimination in bobtail quail neonates.

Incubator-hatched bobwhite quail neonates were tested individually in a variety of single call and simultaneous auditory choice tests involving 6 adult quail vocalizations and a chicken exodus call. The quail showed a high degree of responsiveness (100%) to 3 adult quail vocalizations and significantly less responsiveness (40-50%) to 3 other quail calls and to the chicken exodus call in single call tests. In simultaneous choice tests, the quail were selectively responsive to a call of their own species over the chicken call, and they also showed certain intraspecific preferences. Because of their high degree of responsiveness, coupled with selectivity of their approach responses, bobwhite quail neonates are ideal for the laboratory investigation of the development of auditory perception.

Animals↗
PubMed1977

Tectal projection of displaced ganglion cells in avian retina.

Labeled displaced ganglion cells (DGC's) were observed in chick embryos (day 12 to 18) and hatchings following discrete tectal injections of horseradish peroxidase (HRP). Average DGC diameter was 10 to 15 mu, approximately twice the size of orthotopic ganglion cells. Six to 12 DGC's were found per 15 mu section. These findings conclusively demonstrate a tectal projection for the DGC.

Animals↗
PubMed1977

A technique for introducing localized long-lasting implants in the chick embryo.

A technique is described for making chronic, localized implants of drug-impregnated Silastic in early chick embryos. This silicone material has been shown to gradually and uniformly release its impregnated contents under such conditions. Following implantation of pieces of Silastic treated with the metaphase-blocking drugs colchicine and vinblastine into the wing-buds of 41/2-5 day chick embryos, 53-75% survived 4-5 days, at which time they were sacrificed. Non-impregnated (control) Silastic was also implanted in a group of embryos. In this group, 90% survived 4-5 days. The antimitotic effects of the drugs were very well localized to implanted wings, which were reduced in size by approximately 55% at the time of sacrifice (day 8-9 of incubation). In control embryos, the implanted wings were normal in size and general morphology. It is suggested that the technique could have numerous applications for the study of neuroembryology or other aspects of embryogenesis.

Animals↗
PubMed1976

Developing visual function in the red jungle fowl embryo.

The onset of visual system function in the wild red jungle fowl embryo was measured by the pupillary reflex technique and compared with its domesticated descendant, the domestic chick. The first neurally mediated pupillary reflex in the jungle fowl embryos was found at Day 15 of incubation after 77% of incubation was completed. This point did not differ significantly from the onset of this reflex in the domestic chick embryo (after approximately 83% of incubation). Thus, it was concluded that the relatively late onset of overt visual system function in the chick, as compared with several other precocial avian species, was not a result of its history of intense domestication but rather was most likely a normal characteristic of this and other closely related species.

Age Factors↗
PubMed1975

The retrograde transport of horseradish peroxidase from the developing limb of the chick embryo.

Chick embryos ranging in age from 4.0 to 18 days of incubation and 1-2-day-old hatchlings received injections of HRP solutions directly into the leg musculature. After survival periods of from 5 to 25 h motoneurons and cells in the spinal sensory ganglia were found to be stained with the HRP reaction product. It was found that the first appearance of a positive HRP reaction coincided with the time when nerve processes are first detected in the limb-bud by silver techniques (i.e. at 4.5 days of incubation). Only neurons with processes in the region of injection showed a positive reaction. The demonstration of a retrograde transport mechanism in neurons and axons which are still undergoing growth and differentiation provides a possible mechanism for the peripheral regulation of certain features of CNS neurogenesis. The application of this technique during development may also allow one to map neuroanatomical pathways during their formation.

Animals↗