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Biomedical subjects

M Chen

Publications and source records attributed to M Chen.

At least 829 records · Page 46Linked to original sources
PubMed1989

Innervation of vascular and cardiac muscle of Aplysia by multimodal motoneuron L7.

1. The cardiovascular system of Aplysia has proven to be a useful preparation for study of the neural control of circulation. To better understand the neural integration of function in this system, we have attempted to gain a more complete picture of its morphology and innervation patterns, with particular emphasis on the abdominal aorta and heart. 2. The vasoconstrictor muscle fibers of the abdominal aorta were found by dye injection to be extensively branched, with many processes that are less than 1 micron in diameter. Because of the wide spacing between individual muscle fibers, these fine processes, which have relatively few contractile filaments, may be required to mediate the electrical coupling that is observed between muscle cells. 3. L7, an identified cell in the abdominal ganglion, had been shown by others to be an excitatory motoneuron for the gill, the siphon, and the sheath-contracting muscles of the pleuroabdominal connectives, and also to excite the gill motoneurons in the branchial ganglion (5, 43, 56). We have found that this multimodal motoneuron also directly excites the auricle of the heart and the vasoconstrictor muscle of the abdominal aorta. 4. The excitatory effect of L7 on the abdominal aorta interacts synergistically with that produced by the other known excitatory inputs to that structure, the LBVc vasoconstrictor motoneurons. 5. The abdominal aorta is also richly innervated by axons immunoreactive for serotonin and for the neuropeptide FMRFamide. Serotonin inhibits the contractions of the aorta elicited by firing either L7 or the LBVC cells. In contrast, FMRFamide selectively inhibits the contractions elicited by the LBVC cells. 6. Our results suggest that a significant amount of the functional integration of the cardiovascular and respiratory systems is achieved by the use of a motoneuron common to both systems, and that there is likely to be extensive peripheral inhibitory modulation of the vasoconstrictor inputs to the abdominal aorta.

Animals↗
PubMed1989

Central administration of aldosterone increases blood pressure in rats.

Experiments were designed to determine whether hypertension in rats caused by a central infusion of aldosterone requires supplemental sodium and uninephrectomy. Group 1 was uninephrectomized and received an intracerebroventricular (i.c.v.) infusion of aldosterone (9 ng/h) plus 1M NaCl, dissolved in 0.01% ethyl alcohol-artificial cerebrospinal fluid (vehicle). Group 2 received the same infusion but was not uninephrectomized. Group 3 received an i.c.v. infusion of aldosterone alone in vehicle. Group 4 received an i.c.v. infusion of vehicle with intravenous (i.v.) infusion of aldosterone plus NaCl. All rats received a diet of standard Purina rat chow and tap water ad libitum. Systolic blood pressure of groups 1 and 2 was significantly increased. Rats treated with i.c.v. aldosterone alone also showed a significant increase in blood pressure on day 21. However, i.v. infusion of the same dose of aldosterone did not change blood pressure. The results show that hypertension induced with chronic central infusion of aldosterone does not require uninephrectomy. We conclude that aldosterone may act directly within the central nervous system to increase blood pressure.

Aldosterone↗
PubMed1989

Clonidine and morphine increase atrial natriuretic peptide secretion in anesthetized rats.

In order to determine whether the activity of central alpha 2-adrenergic and opioid receptors influence plasma atrial natriuretic peptide (ANP) levels, clonidine and morphine were infused into the lateral cerebral ventricle for 45 min in anesthetized Sprague-Dawley rats. The central administration of a low dose of clonidine (10 ng/min) caused a significant increase in plasma ANP without changing arterial blood pressure or central venous pressure. Pretreatment with yohimbine (5 micrograms/min) completely blocked the effect of clonidine. Central infusion of morphine (100 ng/min) also elevated plasma ANP levels and naloxone (5 micrograms/min) blunted this effect. Intravenous infusion of the same dose of clonidine or morphine did not affect plasma ANP levels. Moreover, the effect of clonidine on plasma ANP was partially blocked by pretreatment with naloxone (5 micrograms/min). These results suggest that central alpha 2-adrenergic and opioid receptors may be involved in ANP secretion.

Anesthesia↗
PubMed1989

[Studies on antifertility constituents of Siegesbeckia glabrescens Mak].

Three diterpenes including a new compound were isolated from the whole plant of Siegesbeckia glabrescens Mak. The new one was named as neodarutoside and its structure was elucidated as ent-3 alpha, 15,16-trihydroxy pimarane 3,15-bis-(beta-glucopyranoside) based on the spectral evidence and chemical transformation. The other two were darutigenol and darutoside. Darutoside possesses the activity of termination of early pregnancy in experimental rats at a dosage of 20-40 mg/kg.

Abortifacient Agents, Nonsteroidal↗
PubMed1989

[Effects of nicardipine on left ventricular function in patients with hypertrophic cardiomyopathy].

Calcium channel blockers have emerged as important adjuncts to pharmacotherapy of hypertrophic cardiomyopathy. Nicardipine, a new hydropyridine calcium channel blocker, was evaluated for its short-term effects (14 days, 20 mg tid) on left ventricular function in 16 patients with hypertrophic cardiomyopathy (HCM) with UCG. Results indicated that heart rate, blood pressure and systolic function changed very little after nicardipine (P greater than 0.05). However, the following changes were noted after administration: IVRT decreased (132.4 +/- 21.2----120.7 +/- 27.0, P less than 0.02); left ventricular posterior wall rapid filling amplitude and mean velocity increased (8.86 +/- 2.23----9.68 +/- 2.41, P less than 0.01; 54.96 +/- 13.6----59.66 +/- 18.36, P less than 0.05); EF slope increased (3.52 +/- 1.33----3.88 +/- 1.37, P less than 0.01); left ventricular end diastolic pressure and pulmonary capillary wedge pressure decreased (11.79 +/- 3.32----9.72 +/- 2.46, P less than 0.01; 11.11 +/- 2.97----9.19 +/- 2.42, P less than 0.01). The conclusion is that nicardipine may improve left ventricular diastolic function of patients with HCM without serious side effects. It is valuable to conduct further study.

Cardiomyopathy, Hypertrophic↗
PubMed1989

Time course of structural changes at identified sensory neuron synapses during long-term sensitization in Aplysia.

We have used the gill- and siphon-withdrawal reflex of Aplysia californica to explore the morphological basis of the synaptic plasticity that underlies long-term sensitization. In earlier studies (Bailey and Chen, 1983, 1988a), we described 2 classes of structural changes at identified sensory neuron synapses that occur following long-term sensitization: (1) increases in the number, size, and vesicle complement of active zones and (2) an overall increase in the total number of synaptic varicosities per sensory neuron. In the present study, we have begun to examine which of these anatomical changes might be necessary for the maintenance of long-term sensitization by exploring the time course over which they occur and, in particular, their duration relative to the persistence of the memory assessed behaviorally. Toward this end we have quantitated changes in both the total number of varicosities and their active zone morphology in single HRP-labeled sensory neurons taken from long-term sensitized and control animals at different intervals (1-2 d, 1 week, and 3 weeks) following training. We have found that long-term sensitized animals examined within 48 hr after the completion of training demonstrate an increase in the total number of varicosities per sensory neuron as well as an increase in the incidence, size, and vesicle complement of their synaptic active zones compared with control animals. The increase in the number of varicosities and active zones persists unchanged for at least 1 week, and the increase in active zone number is only partially reversed at the end of 3 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

[Microbiological dehydrogenation of intermediate of fluocinanide acetate].

Both compound I and II are intermediates in fluocinanide acetate synthesis. I could be dehydrogenated to II in 62% approximately 63% yields by Arthrobactor simplex No. A-1, which was selected in our laboratory. When concentration of I was 0.1%, it was transformed so fast that II could not be accumulated. When concentration was increased to 0.2%, four intermediates IV, V, VI and VII were formed in addition to a little amount of product II. When concentration of substrate I was increased to 0.5% and B-CS buffer solution and 4% alcohol (95%, V/V) were added, compound II in cuboidal microcrystalline form was obtained. Under this condition, the yield was steady and melting point was above 250 degrees C.

Arthrobacter↗
PubMed1988

Alpha-actinin and calmodulin interact with distinct sites on the arms of the clathrin trimer.

In the present study, the interaction of alpha-actinin and calmodulin with clathrin heavy chain are demonstrated using Western blot analysis and rotary shadowing electron microscopy. The results show that alpha-actinin and calmodulin bind the clathrin heavy chain. The interaction is specific and affected by calcium. However, the interaction of both proteins with the clathrin heavy chain is distinct; the proteins do not block each other's ability to bind, and they interact with different protein fragments of the clathrin heavy chain. Furthermore, using rotary shadowing the results show that alpha-actinin differentially affected the terminal region of the clathrin trimer. Whereas, the effects of calmodulin were most noticeably detected along the length of trimer arms. The possible existence of distinct binding sites on the arms of the clathrin trimer for these cytosolic proteins supports the contention that these cytosolic proteins play an important role in cellular trafficking.

Actinin↗
PubMed1988

Corpus callosum transection reduces binocularity of cells in the visual cortex of adult cats.

The possible involvement of the corpus callosum in binocular functions of the visual cortex was studied in adult cats. Unit recording was made in areas 17, 18 boundary following posterior or complete transection of the corpus callosum, acutely as well as chronically, after short (3-4 months) and long (5.5-39 months) survival periods. A considerable reduction of binocularly driven cells was found in the posteriorly callosally transected cats (acute: 41% cells; short-chronic: 65%; long-chronic: 32%). Similar results, albeit smaller in the long-survival group, were found following complete callosal transection. In comparison, the proportion of binocular cells in the normal cats was 85%. It was concluded that the corpus callosum is involved in interhemispheric integration and enhancement of binocularity in visual cortex cells. No recovery occurs as function of time following cancellation of the interhemispheric interaction by callosal transection.

Animals↗
PubMed1988

Association of neuroactive peptides with the protein secretory pathway in identified neurons of Aplysia californica: immunolocalization of SCPA and SCPB to the contents of dense-core vesicles and the trans face of the Golgi apparatus.

The subcellular distribution of two molluscan neuropeptides, the small cardioactive peptides A and B (SCPA and SCPB), has been determined in two identified Aplysia buccal ganglion neurons, B1 and B2. These neurons were previously shown to synthesize and release these neuropeptides. B1 and B2, identified by their size and location within the ganglion, were labeled by intrasomatic injection of an electron-dense particulate marker (ferritin or Imposil) permitting the unequivocal identification of their somata and proximal processes in thin sections. The somatic cytoplasm of both neurons had a conspicuous population of large dense-core vesicles along with a smaller number of compound vesicles and small lucent vesicles. All three vesicle types are found in the neurites within the neuropil and proximal axon in the esophageal nerve. Immunoreactivity was localized on the surface of thin sections by the indirect immunogold method. The primary antiserum was shown to recognize both SCPA and SCPB after the neuropeptides had been immobilized on protein-coated nitrocellulose membranes by means of glutaraldehyde, the primary fixative used to immobilize SCPA and SCPB in situ. SCP immunoreactivity was present in the lumens of the dense-core vesicles distributed throughout the cytoplasm of B1 and B2 and in dense-core regions of the Golgi apparatus in the somatic cytoplasm. Taken together with biochemical evidence that B1 and B2 synthesize and release SCPs, these data suggest that the neuropeptides are sequestered into the protein secretory pathway of B1 and B2, a distribution that supports the notion that the SCPs function physiologically as neurotransmitters or neuromodulators.

Animals↗
PubMed1988

Increased plasma membrane permeability to Ca2+ in anti-Ig-stimulated B lymphocytes is dependent on activation of phosphoinositide hydrolysis.

The biochemical basis of Ca2+ mobilization after anti-Ig binding to B cell Ag-R has been further characterized by flow cytometric analysis of indo-1-loaded B cells. The ability to distinguish intracellular Ca2+ release from extracellular Ca2+ influx by using an extracellular calcium depletion-repletion approach has allowed us to study the relationship between the mobilization of Ca2+ from these sources. Studies involving manipulation of the Ca2+ gradient across the plasma membrane indicate that a significant portion of the Ca2+ mobilization response is preserved even when the normal inwardly directed Ca2+ gradient is reversed. In the presence of an extracellular calcium concentration ([Ca2+]o) of 10 microM, the response to anti-Ig is not blocked by the organic Ca2+ channel blockers. This response is not reduced by further depletion of [Ca2+]o by EGTA Ca2+-binding buffers. Thus, the Ca2+ response that occurs when [Ca2+]o less than or equal to 10 microM represents intracellular calcium release. Analysis of B cells stimulated with anti-Ig in low Ca2+ medium ([Ca2+]o = less than 10 microM) followed by repletion of [Ca2+]o to 1 to 5 mM reveals that a significant increase in permeability of the plasma membrane to Ca2+ develops in the stimulated cells. The resultant Ca2+ influx is nimodipine (20 microM) sensitive. Both intracellular Ca2+ release and Ca2+ influx are reduced in parallel as the concentration of anti-Ig stimulus is decreased, suggesting that Ca2+ influx may be coupled to the release of intracellular stores. Neomycin blocks anti-Ig-stimulated formation of inositol trisphosphate, which mediates release of Ca2+ from the endoplasmic reticulum. It also blocks the anti-Ig-induced release of intracellular Ca2+ stores as well as Ca2+ influx, indicating that both responses may be dependent upon phosphatidylinositol 4,5-bisphosphate hydrolysis.

Animals↗
PubMed1988

Split chiasm developmentally induced in kittens: plasticity of interhemispheric transfer in visual cortex cells.

Visual callosal transfer during development was studied in order to reveal plasticity-related compensation for the absence of direct contralateral inputs. The optic chiasm was midsagittally sectioned in 6-8 weeks old kittens (OCK) and for comparison, in adult cats (OCA). Unit recording was made during adulthood in the border area between visual cortex areas 17 and 18, namely the callosal projection zone. The proportion of cells showing interhemispheric transfer in the OCK group, as indicated by the presence of visual input from the contralateral eye was 10.5%; in the OCA cats their proportion was 4.0%. Moreover, 2.3% of the cells showed a pure transfer of input from the contralateral eye in the OCK, although none was seen in the OCA cats. Thus, during the developmental period, a plasticity induced process, albeit limited, takes place in the enhancement of interhemispheric transfer of visual information.

Animals↗
PubMed1988

The distribution and movement of organelles in maturing growth cones: correlated video-enhanced and electron microscopic studies.

The morphology of growth cones from identified neurons of Aplysia californica was analysed both with video-enhanced contrast differential-interference contrast (VEC-DIC) microscopy, and through serial electron microscopic reconstructions of the same growth cones. The largest structures seen in the living growth cones, the large irregular refractile bodies (LIRBs), were shown in electron micrographs to be unique structures, composed predominantly of dense-core vesicles but including mitochondria and smooth membrane profiles. The LIRBs were stratified in the growth cones, occurring predominantly in sections distant from the substrate and relatively devoid of microtubules. VEC-DIC observations showed that LIRBs formed in the peripheral regions of the organelle-rich central growth cone, and grew in size through fusion with other LIRBs, accumulating into a large central mass in more proximal regions. The distribution of microtubules and LIRBs and the movements of LIRB suggest that there is an overall circulatory pattern in the growth cones, with the delivery of new vesicles occurring at distal areas close to the substrate, and the accumulation and retrograde processing of organelles occurring in more proximal areas away from adhesive contacts.

Animals↗
PubMed1988

Midsagittal transection of the optic chiasm and the corpus callosum induces visual split brain in cats: the effect on ocular dominance and responsiveness to cells in the visual cortex.

The geniculocortical pathways from the contralateral eye and the callosal pathway were interrupted in cats in order to study how cortical cells are influenced by changes induced in the interhemispheric transfer of visual information. Unit recording was carried out from areas 17 and 18 boundary, the callosal projection zone. The ocular dominance distribution of cortical cells showed absence of interhemispheric interaction. The visual areas in the two sides of the brain thus functioned independently, presenting a condition of visual split brain. This also has been reflected by the absence of compensatory visual inputs via an alternative commissural pathway. Furthermore, remarkable diminution in the excitability level was found as indicated by the reduction in the proportion of visually responsive cells. Finally, the results of the split brain cat reflect the condition of the individual operations from which it is composed.

Animals↗
PubMed1988

Adverse effects of (15S)-15-methyl-prostaglandin E1 in normal and paraquat-exposed rats.

Single, daily injections of approximately 1 mg/kg of (15S)-15-methyl-PGE1 (mPGE1), a PGE1 analog, have been reported to inhibit inflammation and to prolong survival in several animal models of local and systemic inflammation. We examined the effect of this dose of mPGE1 on paraquat toxicity in rats. A significant increase in early mortality was identified in mPGE1-treated rats as early as 3 hr following injection of paraquat and appeared associated with increased respiratory effort. Rats given mPGE1 without paraquat also appeared to increase respiratory effort but did not die. Rats killed at 3 hr following injections demonstrated increased lung weights in both paraquat-injected and control animals receiving mPGE1. Although a neutrophilia was identified in these animals, no significant increase in lung lavage neutrophils or albumin was identified. These data suggest that large intermittent doses of a PGE1 analog may adversely affect the respiratory system of normal and injured animals, and will accelerate mortality following exposure to potentially lethal doses of paraquat.

Alprostadil↗