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Biomedical subjects

L W Haynes

Publications and source records attributed to L W Haynes.

At least 55 records · Page 3Linked to original sources
PubMed1989

The trophic responses of avian sensory ganglia in vitro to N-acetylated and des-acetyl forms of alpha-melanocyte stimulating hormone (alpha-MSH) are qualitatively distinct.

alpha-Melanocyte-stimulating hormone (alpha-MSH) accelerates the regrowth of peripheral nerve axons in the rat following their transection (Verhaagen et al., Expl Neurol. 92, 451-454, 1986). The cellular mechanisms of this trophic response were investigated for several naturally occurring derivatives of alpha-MSH using Nerve Growth Factor (NGF)-stimulated quail sensory ganglion explants in vitro in which both neurite outgrowth and non-neuronal cell behaviour could be more reliably observed and quantified. Neurite outgrowth was determined with a semi-quantitative scoring assay. Glial migration into the outgrowth was quantified using a monoclonal antibody, GTE-52, which labels the nuclei of Schwann cells. Des-acetyl alpha-MSH caused a marginal increase in the neurite outgrowth density which was significant at concentrations of 0.04 and 0.1 microgram/ml. The response to acetylated (N-acetyl, N,O-diacetyl) forms of alpha-MSH was characterized by fascicle formation by neurites which resulted in an apparent decrease in the neurite score, and by the outgrowth of non-neuronal cells. Using monoclonal antibody GTE-52, which recognizes a glial nuclear antigen, these cells were identified as Schwann cells. N-Acetyl, but not des-acetyl alpha-MSH increased the number of GTE-52-labelled cells in the NGF-stimulated neurite outgrowth and stimulated their migration in the absence of neurites when NGF was omitted from the culture medium. Exposure of growing explants to two polyclonal antibodies against alpha-MSH resulted in an increased neurite outgrowth density. The results support the hypothesis that alpha-MSH peptides stimulate peripheral nerve growth by modulating the neurite sprouting response, and demonstrate that the nature of the neurotrophic response to naturally occurring melanotropins depends on the existence of acyl substitution at the N-terminal amino acid residue. A possible role of endogenous melanotropin peptides in the regulation of sensory nerve growth is discussed.

Acetylation↗
PubMed1988

Fibroblast (heparin-binding) growing factors in neuronal development and repair.

Nearly thirty growth and trophic factors that have been purified from mammalian tissues in the last 15 yr have been found to share chemical identity. The results of their chemical purification and molecular cloning show that they are two distinct polypeptides (Mr 17,400 and 18,400), each of which gives rise to families of smaller size peptides. These peptides share a common affinity for heparin. In view of this property, a common nomenclature for the two principle peptide growth factors (heparin-binding growth factor classes 1 and 2; HBGF-1 and -2) has been proposed. However, the names acidic and basic Fibroblast Growth Factors (aFGF,bFGF), which were applied to them originally to describe their mitogenic activity, are more commonly in use and will therefore be adopted in this review. Brain tissue is one of the richest sources of FGFs. It has been used as a starting point for their chemical purification and to prepare genomic libraries for molecular cloning of the aFGF and bFGF genes. There is increasing evidence that these growth factors, expressed in neurons and glia throughout the mammalian nervous system, are implicated in neuronal cell proliferation, differentiation, and histogenesis. FGFs have a strong affinity not only for heparin, but also for the related heparan sulphate proteoglycans that are abundant in neural tissues. This fact provides a clue to the importance of tissue-associated proteoglycans in mediating the release, sequestration, and activation of FGFs and the modulation of their receptor binding and bioactivity. The relevance of FGFs to neural development and their mechanisms of action in neurons will be considered in light of the existing literature describing their biological properties and activity in mesodermal cell types. Evidence is reviewed showing that FGFs have in vivo biological activity, ameliorating the degeneration of central and peripheral neurons after axotomy. The presence and implications of high levels of FGFs in adult mammalian brain provides a direction for future research into neural regeneration. The bioactivity of FGFs in neural tissue may not depend on the regulation of their expression per se, but on the subregional modification of their interaction with proteoglycans.

Amino Acid Sequence↗
PubMed1987

Temperature dependency of light adaptation in bullfrog cone photoreceptors.

Isolated, superfused bullfrog retinas were stimulated in such a manner as to allow examination of the dynamics of the shift in the stimulus-response curve that accompanies light adaptation of cone photoreceptors. Observed phenomena were highly temperature dependent with complex Arrhenius relationships, suggesting that the mechanisms responsible for the shift involve multiple enzyme systems.

Adaptation, Ocular↗
PubMed1987

The effects of barium on the suppression-recovery phenomenon in the aspartate isolated mass receptor response.

The relationship between the suppression-recovery phenomenon and sensitivity changes during light adaptation was investigated in the cone photoreceptors of the isolated, superfused bullfrog retina using barium as a tool. Barium reduced the shift of the stimulus-response function that occurs during light adaptation. Barium also reduced the maximum response amplitude seen after recovery from suppression induced by a flickering light stimulus. The effect of barium on the recovered response amplitude could not be explained by barium's known ability to attenuate the dark adapted cone response, since the magnitude of the depression of the recovered response amplitude was significantly greater at all concentrations than was the magnitude of the depression of the response of the dark adapted cones. Moreover, the thresholds for barium's effect, as well as the shapes of the dose-response curves, were quite different for the two types of responses. The results are consistent with the idea that the recovery from suppression induced by flicker is due to the same change in receptor sensitivity that manifests itself as a shift of the stimulus-response curve during light adaptation.

Adaptation, Ocular↗
PubMed1987

Stress-induced release of pituitary beta-endorphin may be mediated by activation of the brain stem defence areas.

In anaesthetized cats, electrical stimulation within the fore-brain defence areas evoked a marked increase in the plasma level of immunoreactive beta-endorphin which reached a peak after 5 minutes. Multiple immunoreactive peptides including "biologically-active" beta-endorphin-(1-31) were detected. It is suggested that the release of pituitary beta-endorphin during emotional stress results from the natural activation of the defence areas.

Animals↗
PubMed1986

Sensitivity and response kinetics alter during suppression-recovery in cone photoreceptors.

Threshold and response amplitude of cone photoreceptors were measured during progression from flicker-induced suppression to recovery. Increases in sensitivity closely paralleled increases in amplitude. Recovered responses exhibited faster kinetics than suppressed responses. The idea that recovery from suppression is a manifestation of the shift in the stimulus-response relationship which occurs with light adaptation is supported.

Animals↗
PubMed1986

The effect of lead on photoreceptor response amplitude--influence of removing external calcium and bleaching rhodopsin.

The relationship between the effect of lead on the amplitude of the photoreceptor response to light and the ability of the photoreceptor response to be enhanced by a light stimulus was studied in the excised, superfused, bullfrog retina. Photoreceptor responses were isolated by treatment of the retina with sodium aspartate and were recorded with extracellular electrodes. Rod and cone responses were monitored separately by employing a stimulus regimen which took advantage of differing rates of rapid dark adaptation. When the ability of the rod response to undergo enhancement by light was severely reduced by bleaching 80% of the rhodopsin in the retina, the usual depressive effect of 12.5 microM lead was not observed. When light enhancement of the rod response was completely eliminated by removing calcium from the superfusing solution, the effect of 12.5 microM lead was actually to increase rather than decrease rod response amplitude. We conclude from this and previous studies that the effect of lead on the rod photoreceptor is complex, that it can involve both inhibitory and excitatory components, and that the inhibitory effect is exerted on the same mechanism which is responsible for the ability of the rod response to be enhanced by exposure of the retina to light. The cone response never exhibited enhancement by light and was never depressed by exposure of the retina to lead, but the ability of lead to increase cone response amplitude appeared to be greater in the absence of calcium.

Animals↗
PubMed1985

Presence of immunoreactive alpha-melanotropin and beta-endorphin in spinal motoneurones of the dystrophic mouse.

Two derivatives of the stem hormone opiomelanocortin, alpha-melanotropin (alpha-MSH) and beta-endorphin, were detected immunocytochemically in the cell bodies and in the peripheral axon terminals of spinal motoneurones in immature but not in adult healthy mice. Immunoreactivity was demonstrated in motoneurones in both immature and adult mice with inherited muscular dystrophy. These results provide evidence for a motoneurone abnormality in murine dystrophy. The observations are discussed in the light of trophic influences over neuromuscular transmission which have been attributed to this family of neuropeptides.

Animals↗
PubMed1984

The effect of lead on photoreceptor response amplitude--influence of the light stimulus.

The mass receptor potential of the excised, superfused retina of the bullfrog was studied. Photoreceptor responses were isolated by addition of sodium aspartate to the Ringer solutions. Responses of the cones were monitored independently from responses of the rods by employing a two-flash method of stimulation which took advantage of the very different rates of rapid dark adaptation of rods and of cones. Stimulation with paired flashes of white light at regular intervals caused enhancement of rod response amplitude in that the response grew larger with subsequent flashes until reaching a stable plateau. The degree of enhancement was directly proportional to the amount of light exposure and increased with either increasing stimulus intensity or decreasing stimulus interval. Only the rod response was affected; the cone response was not enhanced by continued stimulation. The effects of 12.5 microM PbCl2 on rod response amplitude were complex. There was a small (less than 10%) but consistent depression of rod response amplitude even when the rods were in the unenhanced state. However, the most striking effect of lead was on the enhanced response, where treatment with 12.5 microM PbCl2 led to a depression of about 33%. When added prior to light stimulation, lead significantly decreased the degree to which the rod response could be enhanced, but never prevented enhancement entirely. Removal of lead resulted in a very large increase in the degree to which the rod response was enhanced by light, even when compared to the first, lead-free control. The cone response was unaffected by 12.5 microM PbCl2.

Animals↗
PubMed1984

Evidence for the neurotrophic regulation of collagen-tailed acetylcholinesterase in immature skeletal muscle by beta-endorphin.

Acetylcholinesterase (AChE) was extracted in a high-saline medium from gastrocnemius muscles of rat embryos and young rats aged 14 days' gestation to 40 days post partum. The molecular forms of the enzyme were separated by low-salt precipitation, followed by velocity sedimentation. During gestation, all molecular forms increased in activity, particularly the 16 S (A12) form. During the first 2 weeks of life, there was a large increase in the activity of soluble AChE (G forms), whilst the activity of insoluble AChE (A forms) was reduced. Denervation of the muscle reversed the change in the relative proportions of the molecular forms. The embryonic pattern of activities of AChE forms persisted in cultures of myotubes obtained at 20 days' gestation and maintained in the absence of spinal cord. When myotubes were maintained in medium previously conditioned by developing spinal cord explants, 16 S AChE declined while the soluble (4 and 6 S) forms increased in activity in a manner resembling that seen in early postnatal muscles in vivo. beta-Endorphin (beta-EP) immunoreactivity was detected in the spinal cord-conditioned medium and was identified by HPLC and ion-exchange chromatography as beta-EP-(1-31) plus its shortened and N-acetylated forms. Cultivation of myotubes in the presence of synthetic camel beta-EP resulted in a reversible change in the pattern of AChE forms which was similar to that seen with spinal cord-conditioned medium. These studies provide evidence for the neuroregulation of AChE A and G forms in immature skeletal muscle. A major candidate for this role is beta-EP, produced and released by developing spinal cord.

Acetylcholinesterase↗
PubMed1984

Structural requirements and species specificity of the inhibition by beta-endorphin of heavy acetylcholinesterase from vertebrate skeletal muscle.

The molecular forms of acetylcholinesterase in extracts of gastrocnemius muscle from four vertebrate species and in electric eel (Electrophorus) electric organ were separated and identified by low-salt precipitation and velocity sedimentation. The activity of the heavy insoluble (A12) form of human muscle acetylcholinesterase was inhibited by synthetic human beta-endorphin (500 mM). The homologous form in rat muscle extracts was poorly inhibited by human beta-endorphin at the same concentration, but was more effectively inhibited by camel beta-endorphin. The activities of heavy forms of pseudocholinesterase, present in small amounts in both species, were not reduced by beta-endorphin. Selective inhibition of homologous heavy forms of acetylcholinesterase activity by camel and human beta-endorphin was also seen in skeletal muscle extracts from frog and pigeon, but with decreased effectiveness. No inhibition was detectable in the heavy acetylcholinesterase form from extracts of electric organ tissue of the electric eel. The inhibition of heavy acetylcholinesterase activity in human muscle by human beta-endorphin was dependent on the presence of its NH2-terminal pentapeptide sequence. Maximal inhibitory potency depended on the presence of the entire amino acid sequence, since potency was considerably reduced in synthetic peptide analogues lacking either middle or COOH-terminal segments of beta-endorphin. The relative potency of beta-endorphin from various species as inhibitors of rat heavy acetylcholinesterase activity was also investigated. beta-Endorphin sequences most closely resembling that of the rat peptide (camel, equine) were most potent, whereas those with sequence differences of more than one amino-acid were less potent (turkey, human) or had no inhibitory activity (ostrich). The selective inhibition of heavy acetylcholinesterase by beta-endorphin thus exhibits species specificity, even among mammals, in which homologues of this molecular form of the enzyme are otherwise indistinguishable.

Acetylcholinesterase↗
PubMed1984

Dichotomous effects of cadmium on the cone photoreceptor response to light.

The effects of cadmium (1.0 to 400.0 microM CdCl2) on the cone photoreceptor's response to light were studied in the superfused bullfrog retina. The effects of cadmium were complex, characterized by a purely excitatory component at the lower levels and an inhibitory component that became evident with 75.0 microM CdCl2. The maximum increase in cone response amplitude due to the excitatory component was about 60% at 100.0 microM CdCl2. At 400.0 microM CdCl2, the highest concentration examined in this study, cone response amplitude was suppressed by about 35%. Both components were dose-dependent. The excitatory component was reversible only at CdCl2 concentrations below 50.0 microM, and irreversible at levels at and above 50.0 microM. The inhibitory component was always reversible. The slope of the dose-response curve describing the excitatory component (0.60) was about twice that describing the inhibitory component (0.31). The effects of cadmium on cone response amplitude are discussed in terms of the most probable sensitive sites.

Animals↗
PubMed1983

Neuronal and glial localization of acetylcholinesterase and GABA transaminase in organized cultures of developing rat spinal cord.

Acetylcholinesterase (AChE) and gamma-aminobutyrate transaminase (GABA-T) were localized in organized cultures of rat embryo spinal cord. AChE was seen in neurones of the ventral horn and intermediate nucleus and in the dorsal horn neuropil. AChE was also present on the soma membrane of neuroglia, even in areas devoid of AChE-stained neuronal processes. GABA-T activity was present chiefly in dorsal horn neurones, and was absent from neuroglia.

4-Aminobutyrate Transaminase↗
PubMed1982

Immunocytochemical localization of beta-endorphin (lipotropin C-fragment) in the developing rat spinal cord and hypothalamus.

Immunocytochemical studies have been performed on rat spinal cord and hypothalamus during development, using an antibody to beta-endorphin. Specific immunoreactivity was demonstrated in histological sections of spinal cord, in ventral and dorsal horn cells and nerve fibres, in the meningeal layer, the ependymal lining of the central canal, and in the endothelium of the ventral spinal artery and other blood vessels. beta-Endorphin immunoreactivity was also distributed widely in neurones, central and peripheral nerve fibres, and in non-neuronal cells in cultures of spinal cord tissue explanted from rat embryos 7--10 days before birth. Immunofluorescence disappeared abruptly after the 28th postnatal day in vivo, and in the fourth week of incubation of embryonic spinal cultures. In contrast, cultures of the ventral diencephalic (hypothalamic) region of embryonic brain at the same gestational age showed a characteristically different pattern of beta-endorphin immunoreactivity which persisted for more than 7 weeks. The results provide evidence for the biosynthesis of a beta-endorphin-like peptide in rat spinal cord during development. The biosynthesis terminates at an early stage both in vivo and in vitro, suggesting that control of the biosynthesis is intrinsic to spinal cord tissue and possibly to the peptide-producing cells themselves.

Acetylcholinesterase↗
PubMed1982

Selective inhibition of 'motor endplate-specific' acetylcholinesterase by beta-endorphin and related peptides.

The effects of beta-endorphin (lipotropin 61-91) and related naturally-occurring peptides upon acetylcholinesterase activity in rat hind-limb muscles was investigated. beta-endorphin weakly inhibited the activity in a plasma membrane-enriched fraction. The inhibition by beta-endorphin of the membrane-associated acetylcholinesterase was less marked when the fractions were prepared from muscles which had been denervated 4-6 days previously. The membrane-associated acetylcholinesterase was solubilised from normal muscle preparations and separated by sucrose density gradient centrifugation into three major peaks (16S, 10S and 4S). beta-Endorphin inhibited the activity in the 16S peak but not that in the 10S and 4S peaks, whilst tensilon, a competitive inhibitor of acetylcholinesterase, inhibited the activity of all three peaks. beta-Endorphin inhibited the activity in the 16S peak but not that in the 10S and 4S peaks, whilst tensilon, a competitive inhibitor of acetylcholinesterase, inhibited the activity of all three peaks. beta-Endorphin inhibited the 16S activity in a concentration-dependent manner and its action was partly prevented if naloxone was added simultaneously. Purified natural porcine and bovine beta-endorphin were equipotent in terms of effective concentration range but the maximum inhibition was greater with the bovine peptide. beta-Lipotropin was approximately 4 times less potent than beta-endorphin, whilst C-fragment (lipotropin 61-87) was 100 times less potent. Prolonged treatment with collagenase did not reduce the catalytic activity of 16S acetylcholinesterase, but it was no longer susceptible to the inhibitory action of beta-endorphin. Kinetic studies indicated a complex type of inhibition by beta-endorphin (hyperbolic Lineweaver-Burke plot). Methionine enkephalin inhibited acetylcholinesterase in a weakly non-competitive manner and its action was not abolished if the enzyme was predigested with collagenase. beta-Endorphin produces a novel form of inhibition of acetylcholinesterase, acting only on the 16S (A12 or 'motor endplate-specific') form of the enzyme. The findings are discussed in the light of evidence that beta-endorphin-related immunoreactivity is expressed in motor nerve axons in the immature rat.

Animals↗