Biomedical subjects

M W Miller

Publications and source records attributed to M W Miller.

At least 253 records · Page 14Linked to original sources

PubMed1988

Structure and action of buccalin: a modulatory neuropeptide localized to an identified small cardioactive peptide-containing cholinergic motor neuron of Aplysia californica.

A model system that consists of a muscle utilized in biting, the accessory radula closer (ARC), and the two cholinergic motor neurons innervating this muscle, neurons B15 and B16, has been used to study the expression of food-induced arousal in the marine mollusk Aplysia. The ARC muscle receives modulatory input from an extrinsic source, the serotonergic metacerebral cells, which partially accounts for the progressive increase in the strength of biting seen in aroused animals. Another source of modulation may arise from the ARC motor neurons themselves, which synthesize neuropeptides that can potentiate ARC contractions. Neuron B15 synthesizes the two homologous peptides, small cardioactive peptides A and B, whereas neuron B16 synthesizes the structurally unrelated peptide myomodulin. Here we report the purification and sequencing of a neuropeptide termed buccalin and show that it is colocalized with the small cardioactive peptides to neuron B15. Buccalin is also bioactive at the ARC neuromuscular junction but, in contrast to the small cardioactive peptides, when exogenously applied, it decreases rather than increases the size of muscle contractions elicited by firing of the motor neurons. Also unlike the small cardioactive peptides, which exert postsynaptic actions, buccalin seems to act only presynaptically. It has no effect on muscle relaxation rate and decreases motor neuron-elicited excitatory junction potentials in the ARC without affecting contractions produced by direct application of acetylcholine to the muscle. Neuron B15, therefore, appears to contain three modulatory neurotransmitters, two of which may act postsynaptically on the muscle to potentiate the action of the primary neurotransmitter acetylcholine and one of which may act presynaptically on nerve terminals to inhibit acetylcholine release.

Amino Acid Sequence↗

PubMed1988

Normal in-vivo development of marmoset monkey embryos after trophectoderm biopsy.

A procedure was developed to remove trophectoderm cells from day-8 blastocysts of the marmoset monkey. Using micromanipulative techniques, a tear was made in the zona pellucida opposite the inner cell mass which facilitated the controlled herniation of trophectoderm cells as the blastocysts developed in vitro. After 24 h (day-9 blastocysts) and 48 h (day-10 blastocysts) of culture approximately 20% and approximately 50% respectively of the blastocyst had herniated. The herniated trophectoderm was cut off by freehand and the biopsied blastocysts transferred to recipients. Normal offspring were born but pregnancies could be established from day-10 blastocysts only if the recipients were treated with human chorionic gonadotrophin during early pregnancy. One pregnancy was established after the transfer of three frozen biopsied day-10 blastocysts. Biopsies of 30-50 cells from day-10 blastocysts could be readily grown in vitro as trophoblast vesicles to in excess of 1000 cells but biopsies of less than 20 cells from day-9 blastocysts formed a monolayer of binucleated and multinucleated cells with limited cell replication. Assuming human trophectoderm cells have a similar capacity to the marmoset to grow in vitro, the application of this technique to human blastocysts would provide sufficient cells on which the preimplantation diagnosis of a genetic disorder could be made.

Animals↗

PubMed1988

Effect of prenatal exposure to ethanol on the development of cerebral cortex: I. Neuronal generation.

Prenatal exposure to ethanol causes profound disruptions in the development of the cerebral cortex. Therefore, the effect of in utero ethanol exposure on the generation of neurons was determined. Pregnant rats were fed a liquid diet in which ethanol constituted 37.5% of the total caloric content (Et) or pair-fed an isocaloric control diet (Ct) from gestational day (GD) 6 to the day of birth. The time of origin of cortical neurons was determined in the mature pups of females injected with [3H]thymidine on one day during the period from GD 10 to the day of birth. The brains were processed by standard autoradiographic techniques. Ethanol exposure produced multiple defects in neuronal ontogeny. The period of generation was 1-2 days later for Et-treated rats than for rats exposed prenatally to either control diet. Moreover, the generation period was 1-2 days longer in Et-treated rats. The numbers of neurons generated on a specific day was altered; from GD 12-19 significantly fewer neurons were generated in Et-treated rats than in Ct-treated rats, whereas after GD 19 more neurons were born. The distribution of neurons generated on a specific day was disrupted; most notable was the distribution of late-generated neurons in deep cortex of Et-treated rats rather than in superficial cortex as they are in controls. Cortical neurons in Et-treated rats tended to be smaller than in Ct-treated rats, particularly early generated neurons in deep cortex. The late-generated neurons in Et-treated rats were of similar size to those in Ct-treated rats despite their abnormal position in deep cortex. Neurons in Ct-treated rats tended to be rounder than those in Et-treated rats which were more polarized in the radial orientation. A proliferation index, which was based on the amount of autoradiographic signal over each labeled neuron, indicated that an additional, late surge in proliferative activity occurred in Et-treated rats on GD 20-21. The amount of [3H]thymidine incorporated each day was determined by biochemical analyses. In Ct-treated rats, incorporation increased to a maximum on GD 17 and decreased thereafter. In Et-treated rats, there were two maxima, the first on GD 18 and the second on GD 20. These data fully support the findings of the autoradiographic analyses. The present data show that neuronal generation is profoundly affected by ethanol. Such disturbances result from ethanol-induced abnormalities in neuronal proliferation and migration.

Animals↗

PubMed1988

Effect of neonatal infraorbital nerve transection on substance P- and leucine enkephalin-like immunoreactivities in trigeminal subnucleus caudalis of the rat.

The distributions of substance P-like immunoreactivity (SPLI) and leucine-enkephalin-like immunoreactivity (LENKLI) in subnucleus caudalis of normal adult rats were compared with those observed in the adult rats that sustained transection of the infraorbital (IO) nerve either on the day of birth or in adulthood. All immunocytochemical experiments in the neonatally nerve damaged rats were carried out at least 60 d after the nerve transection. In the animals that sustained nerve transections as adults, brains were processed for immunohistochemistry between 7 and 60 d after the lesions. In the rats that sustained IO nerve transections as adults, there was a transient reduction in the density of the SPLI in layers I and II of ipsilateral subnucleus caudalis. It was most apparent about 2 weeks after the nerve transection and returned to near normal values by 60 d after the lesion. In the rats that sustained IO nerve transections on the day of birth, there was no reduction in the density of SPLI in caudalis, and the band of staining on the deafferented side of the brain stem was actually 40% wider than that on the intact side. Neither neonatal nor adult IO nerve transection had appreciable effects upon the distribution of LENKLI in the rat's trigeminal brain-stem complex. In another series of experiments, rats that sustained neonatal transection of the IO nerve had this same nerve recut in adulthood. Twelve days after the second lesion, the brains of these animals were processed for SPLI. There was a marked reduction in the density of the staining for this peptide on the deafferented side. This last result is consistent with the interpretation that the increased distribution of SPLI in the neonatally nerve damaged rats is due, at least partially, to reorganization of primary afferents.

Aging↗

PubMed1988

Weak low frequency electromagnetic fields and chick embryogenesis: failure to reproduce positive findings.

Fertilised chicken eggs were incubated for 48 hours while exposed to pulsed trains of magnetic fields having a duration of 0-5 ms, a rise time of 42 microsecond, and a pulse repetition rate of 100 at a magnetic field flux density of 1 microT. Some eggs were exposed to 1,552 rad X-rays as a positive control. After exposure the embryos were scored blind for a variety of morphological features. X-irradiated eggs displayed highly significant and repeatable anatomical alterations. There were no differences between magnetic field-exposed, sham-exposed and control eggs.

Animals↗

PubMed1987

Effect of prenatal exposure to alcohol on the distribution and time of origin of corticospinal neurons in the rat.

The distribution and the time of origin of corticospinal neurons were examined in rats prenatally exposed to ethanol and in control rats. The distribution of corticospinal neurons was determined by tracing the retrograde transport of horseradish peroxidase (HRP) from an injection site in the cervical spinal cord. In control rats, HRP-positive neurons were distributed in layer Vb throughout motor area 4, rostral motor area 6/8, dorsal somatosensory area 3, caudal somatosensory area 2, and various "association" regions including parietal areas 14, 39, and 40, occipital areas 18a and 18b, cingulate areas 24a and 24b, and prefrontal area 32. In ethanol-exposed rats, the distribution of retrogradely labeled neurons was similar to control animals with three notable exceptions: (1) HRP-positive neurons were evident throughout the rostrocaudal extent of area 6/8; (2) occasionally ectopic labeled neurons were identified in the supragranular layers, layers Va and Vc, and superficial layer VI; and (3) the density of HRP-labeled neurons and the ratio of labeled neurons to the total number of neurons in areas 4, 6/8, 3 and 2 were significantly greater (20-48%) in ethanol-exposed rats than in controls. There was, however, no intergroup difference in the area of the cell bodies of HRP-positive neurons. Taken together, these findings indicate that ethanol exposure resulted in an increased number of corticospinal neurons. The time of origin of corticospinal neurons was determined by using a technique that combined tritiated thymidine autoradiography and retrograde transport of HRP. In control animals, HRP-positive neurons were double labeled by an injection of tritiated thymidine on gestational day (GD) 15, 16, or 17. In ethanol-exposed rats, corticospinal neurons were generated on GD 16, 17, and 18, the late-generated ones being distributed in caudal area 6/8. These intergroup differences represent a persisting ethanol-induced alteration of cortical structure that may underlie motor dysfunction and mental retardation in fetal alcohol-affected offspring. Moreover, the increase in the number and the delay in the time of origin of corticospinal neurons suggest that the normal process of paring down exuberant corticospinal projections may be affected by prenatal exposure to ethanol.

Animals↗

PubMed1987

Effects of 60-Hz electric fields on cellular elongation and radial expansion growth in cucurbit roots.

Serial longitudinal and transverse sections were prepared from roots of Cucumis sativus and Cucurbita maxima that had been exposed/sham-exposed to 60-Hz electric fields for 0-2 days. Field exposures were selected to produce a 10-20% or a 70-80% growth inhibition in whole roots of both species. Cortical cell length and diameter were measured using a microscope and eyepiece micrometer; measurements were conducted "blind." In both species, inhibition of cellular elongation was associated with exposure to electric fields (EF). Cellular radial expansion was apparently unaffected by exposure to electric fields. The diameters of radially unexpanded or fully expanded C. sativus cortical cells were about 25-30% smaller than those of comparable cells in C. maxima roots. Previous studies of the relationship between rates of root growth and applied EF strength showed that the response thresholds of C. sativus and C. maxima differed by a similar relative amount. These results are consistent with the postulate that EF-induced effects in roots are elicited by induced transmembrane potentials.

Analysis of Variance↗

PubMed1987

The origin of corticospinal projection neurons in rat.

The distribution of corticospinal projection neurons in adult rats was determined using a retrograde tracing technique. Horseradish peroxidase (HRP) and an emulsifier (Nonidet) were injected into the 5th and 6th segments of the cervical spinal cord. The greatest concentrations of HRP-positive neurons were distributed in area 4 and rostral area 6/8 (motor cortices) and medial area 3 and caudal area 2 (somatosensory cortices). The largest labeled neurons were in areas 4 and 3. HRP-positive neurons were absent or few in regions of motor and somatosensory fields which contained the face representation. Less dense concentrations of retrogradely labeled neurons were also in posterior parietal and association areas 14, 39 and 40, rostral occipital visual areas 18a and 18b, and anterior cingulate and prefrontal areas 24a, 24b, and 32. The topography of the corticospinal pathway was determined by injecting HRP without Nonidet into the cervical, upper thoracic, lower thoracic, or lumbar spinal cord. Although the distribution of labeled neurons decreased with distance down the spinal cord, the size of the corticospinal neurons in each cytoarchitectonic area was not significantly different regardless of where the injection was placed. For example, upper thoracic cord injections retrogradely labeled neurons in each of the regions containing neurons filled by cervical cord injections, however, lumbar injections retrogradely labeled neurons only in caudal areas 4 and 3 and in area 18b. The distribution of corticospinal neurons in rats in similar to the organization of the corticospinal system in higher animals. The origin of corticospinal neurons in occipital and cingulate cortices may be related to visuomotor and visceromotor control.

Animals↗

PubMed1987

Structure and localization of synaptic complexes in the cardiac ganglion of a portunid crab.

The cardiac ganglion of Portunus sanguinolentus exhibits spontaneous rhythmic activity when isolated. The ganglion contains five large and four small intrinsic neurons and is innervated by three pairs of fibres originating in the thoracic ganglia. We have identified the processes of the large neurons in electron micrographs by injecting these cells with two electron-dense markers, horseradish peroxidase (HRP) and Procion Rubine (PR). In addition we have studied the processes of the four smaller neurons by light microscopy serial reconstructions and by electron microscopy of selected regions. Both markers were found only in neuronal processes and not in glial cells nor in the extracellular space, except close to the soma of the injected cell. We found contacts between the small secondary (collateral) processes of the large cells but not between their somata or their primary processes (axons and dendrites). Two specialized structures present at the contacts between the collateral processes were small membrane close appositions, possibly the site of electrotonic junctions, and chemical synapses. Contacts between processes marked by HRP and those marked by PR were common, as were contacts between processes marked by either HRP or PR and those of the other intrinsic neurons. Adjacent processes stained by PR could contain PR deposits of different densities, but it is unclear whether this finding was due to intercellular diffusion of the dye or to its diffusing at different rates into branches of the same process. Identified processes of all the intrinsic neurons contained the same type of vesicles, which were different from those found in processes of the extrinsic fibres. Chemical synapses were present at contacts between processes of the extrinsic and intrinsic neurons, as well as at contacts between processes of the intrinsic neurons. The axons of three small cells made a series of contacts at which extensive arrays of membrane close appositions, but not chemical synapses, were found. These three axons also formed contacts, either directly or through their collateral branches, with processes of the large cells, at which both membrane close appositions and chemical synapses were present. The axon of the fourth small cell could not be followed in our series.

Animals↗

PubMed1987

Radiation hormesis in plants.

Many reports discuss plant growth stimulation by exposure of seeds or plants to low doses of ionizing radiation. The reported effects include increased height, weight, growth rate, flowering and yield. The magnitude of the effect(s) is usually small, being about 10% of control values; and the effects often are not reproducible. None has been independently confirmed. The exposure level reported to induce such effects is about an order of magnitude greater than that reported for similar hormetic responses in animals. There is no understanding of the mechanism(s) of such responses or of the cellular and physical factor(s) pertinent to the induction of such effect(s). However, observations that certain low-level exposures result in increased yield (e.g. more branches, flowers and fruits) are consistent with known mechanisms of cellular damage and known responses of plants to a compromise in apical dominance.

Dose-Response Relationship, Radiation↗

PubMed1987

Cooperativity-dependent long-lasting potentiation in the crayfish lateral giant escape reaction circuit.

The ability of sensory neuron firing to cause the lateral giant escape reaction increases following repeated sensory volleys at 4 Hz for 10 sec. The increase occurs only when relatively large numbers of afferents are repetitively stimulated, decays with a mean time constant of 21 hr, is confined to the ganglia at which the repeated sensory volleys enter the nerve cord, and is at least partially specific to those roots of a ganglion that were tetanized. Transmission at the chemical synapses between afferents and the largest of the first-order sensory neurons that link afferents to the lateral giants displays a similar potentiation. This phenomenon shares many properties with hippocampal long-term potentiation.

Animals↗

PubMed1986

Effects of alcohol on the generation and migration of cerebral cortical neurons.

Prenatal exposure to alcohol produces many developmental defects of the central nervous system, such as microcephaly, mental retardation, motor dysfunction, and cognitive deficiencies. Therefore, the generation of neurons in the cerebral cortex was examined in the offspring of female rats fed a diet containing ethanol. Prenatal exposure to ethanol delayed and extended the period during which cortical neurons were generated, reduced the number of neurons in the nature cortex with the same time of origin, and altered the distribution of neurons generated on a particular day. Thus, the proliferation and migration of cortical neurons are profoundly affected by in utero exposure to ethanol.

Animals↗

PubMed1986

Induction of ELF transmembrane potentials in relation to power-frequency electric field bioeffects in a plant root model system. I. Relationship between applied field strength and cucurbitaceous root growth rates.

Seminal roots of Cucumis sativus and Cucurbita maxima were exposed to 60 Hz electric fields of 100-500 V X m-1 in a conducting aqueous inorganic growth medium. Root growth rates were measured to produce a dose-response relationship for each species. The species were selected for study because of their familial relationship, reported sensitivity to 60 Hz, 360 V X m-1 electric fields, and differing average root cell sizes. The latter characteristic influences the magnitude of ELF membrane potentials induced by constant-strength applied electric fields, but does not affect the magnitude of the electric field strength tangent to the cell surface. The difference in average root cell size between C. sativus (smaller cells) and C. maxima (larger cells) was used to evaluate two alternate hypotheses that the observed effect on root growth is stimulated by the electric field tangent to the cell surface, or a field-induced perturbation in the normal transmembrane potential of the cells. The results of the dose-response relationship studies are qualitatively consistent with the hypothesis that the effect is elicited by induced transmembrane potentials. The smaller-celled roots showed a substantially higher response threshold [C. sativus; E0TH approximately 330 V X m-1] than did the larger-celled species [C. maxima; E0TH approximately 200 V X m-1]. At field strengths above the response thresholds in both species, the growth rate of C. sativus roots was less affected than that of C. maxima roots exposed to the same field strength.

Cell Division↗

PubMed1986

Induction of ELF transmembrane potentials in relation to power-frequency electric field bioeffects in a plant root model system. II. The effect of 60 Hz electric fields on the growth of different regions of the cucurbit root elongation zone.

The region of elongation in Cucumis sativus and Cucurbita maxima roots was marked at increasing distances from the apex to provide an analog of increasing cell size. These roots were exposed/sham-exposed to 60 Hz electric fields and the growth rates of the root segments measured. The growth rate effect magnitude varied with increasing distance from the root tip at constant field strength, and with increasing applied field strength. These results provide strong, qualitative support for the postulate that ELF transmembrane potential induction is involved in the stimulation of ELF electric field effects in the plant root model system.

Cell Division↗

PubMed1986

Sister-chromatid exchanges in human lymphocytes exposed in vitro to therapeutic ultrasound.

Human lymphocytes were exposed in vitro to therapeutic levels of ultrasound (1 W/cm2, CW, 0.87 MHz, durations of 80 and 160 sec). There were no significant differences in sister-chromatid exchange frequencies between controls and ultrasound-exposed cells. Exposure of lymphocytes to the positive control (mitomycin C) resulted in a significant increase in sister-chromatid exchanges. The data do not verify a report by Stella et al. (Mutation Res., 138 (1984) 75-85) that such exposures result in increased frequencies of SCEs.

Humans↗

PubMed1986

The migration and neurochemical differentiation of gamma-aminobutyric acid (GABA)-immunoreactive neurons in rat visual cortex as demonstrated by a combined immunocytochemical-autoradiographic technique.

The development of some cortical local circuit neurons was traced using a technique which combined immunocytochemistry to label gamma-aminobutyric acid-immunoreactive (GABA+) neurons and [3H]thymidine autoradiography to identify cells with similar times of origin. Double-labeled neurons (GABA+ neurons with autoradiographic silver grains over their nuclei) are evident only after migration is complete. GABA+ neurons born on gestational day 16 are first identified in layer VIa on postnatal day 0 and those born on day 19 are in layer III on postnatal day 6. The frequency of double-labeled neurons increases during the week following their appearance. Therefore, the migration and the neurochemical differentiation of GABA+ neurons follow inside-to-outside sequences.

Animals↗

PubMed1986

Maturation of rat visual cortex. III. Postnatal morphogenesis and synaptogenesis of local circuit neurons.

The postnatal development of 3 types of local circuit neurons in rat visual cortex was examined in Golgi and electron microscopic preparations. During the first postnatal week, smooth and sparsely spinous stellate, bitufted and bipolar neurons were identified in Golgi material by their characteristic dendritic arborizations. Morphological differentiation begins during this week, as each neuron sprouts dendrites which extend, branch and produce spines, and ends by day 21. This differentiation was traced by quantifying the somatic area and number of primary dendrites on stellate, bitufted and bipolar neurons in layer II/III or layer V. Neurons in deep cortex differentiate earlier than those in superficial laminae. On day 3, axons are evident as short, straight processes, however, by day 6, many axons have branches and varicosities. The increase in the complexity of the axonal trees continues during the second and third postnatal weeks. Since the axons of stellate and bitufted neurons form synapses with the somata of pyramidal neurons, an index of the synaptogenesis of these neurons was traced by counting the numbers of synapses on the somata of pyramidal neurons. The mean number of axosomatic synapses increases steadily from day 3 to day 30. Layer V pyramidal neurons form axosomatic synapses before pyramidal neurons in layer II/III. In conclusion, the morphology of local circuit neurons develops during the period after they migrate into cortex. The principle that cortical local circuit neurons develop after projection neurons only applies for the synaptogenesis of the axon, but not for the maturation of the cell body and dendrites.

Aging↗

PubMed1986

Establishment of calf trabecular meshwork cell cultures.

Trabecular meshwork cell cultures have been grown from excised calf aqueous outflow pathway tissue using two different methods. In one method, tissue explants were placed directly in culture dishes and primary cultures were established by those cells migrating from the tissue. In the second method, a cell suspension was generated by incubating trabecular tissue strips with 0.1% pronase, and the washed cells were used to seed primary cultures. The cell cultures generated by each method appeared to progress through morphological and biochemical changes characteristic of the cell type, although at different respective rates. Comparisons of the cell morphologies, biosynthetic activities, and growth characteristics of the respective subcultures suggested that similar cell populations were obtained by each method. These studies further suggested that sufficient quantities of calf trabecular cells could be grown in culture to permit biochemical and pharmacological studies of trabecular-cell metabolism.

Animals↗