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M B Laskowski

Publications and source records attributed to M B Laskowski.

36 records · Page 2Linked to original sources
PubMed1988

Topographically selective reinnervation of adult mammalian skeletal muscles.

In 2 rat muscles, serratus anterior and the diaphragm, the rostrocaudal axis of the motor pool is mapped onto the rostrocaudal axis of the muscle's surface (Laskowski and Sanes, 1987a). One possible basis for this orderly topography is that motor axons and intramuscular structures bear labels that favor connectivity among positionally matched partners. To test for the existence of such labels, we asked whether axons would selectively reinnervate appropriate portions of the muscles following nerve transection. We found that, on average, rostral and caudal halves of each muscle were preferentially reinnervated by axons from the rostral and caudal halves of its motor pool, respectively. In the serratus anterior, reinnervation was more selective following denervation in neonates than following denervation in adults, although in neither case was the normal pattern of innervation reestablished completely. These results show that motor axons can selectively reinnervate adult rat muscles, and support the idea that positional cues play a role in organizing neuromuscular topography.

Animals↗
PubMed1987

Topographic mapping of motor pools onto skeletal muscles.

We have studied the segmental innervation of 2 rat skeletal muscles, the diaphragm and the serratus anterior. Both muscles are thin, flat, and composed of several sectors that form a clear rostrocaudal progression. Each is innervated through a single nerve, which is in turn supplied by motor neurons from several cervical spinal segments. Using intracellular recording, we found that in both cases, the rostrocaudal axis of the motor pool is systematically mapped onto the rostrocaudal axis of the muscle's surface. For the diaphragm, electrophysiological results were confirmed by immunohistochemical identification of denervated fibers following section of single ventral roots and by retrograde labeling of motoneurons following localized application of fluorescent dyes. In addition, an immunohistochemical method was used to study the arrangement of motor axons in the phrenic nerve, which supplies the diaphragm, and to show that contributions from individual ventral roots are compartmentalized within this nerve. We suggest that segmental ordering of axons in the nerve, axonal guidance at branch points in the nerve, and positional labels within the muscle may all contribute to the rostrocaudal mapping of motor pools onto muscle.

Animals↗
PubMed1986

Detection and characterization of beta-adrenergic receptors and adenylate cyclase in coated vesicles isolated from bovine brain.

To assess whether internalization of beta-adrenergic receptor occurs in the CNS, we have isolated clathrin-coated vesicles from bovine forebrain and examined them for the presence of beta-adrenergic receptor binding and adenylate cyclase activities. A coated vesicle enriched preparation isolated by successive D2O-Ficoll density gradient centrifugations was applied to a glass bead permeation column to achieve further purification. Two major peaks of protein were eluted from the column and monitored by electron microscopy and SDS-PAGE. Peak II contained almost exclusively coated vesicles (98%), whereas peak I, which appeared in the void volume, contained larger smooth vesicles and few coated vesicles. beta-Adrenergic receptor binding to peaks I and II was measured with 125I-cyanopindolol (CYP) as ligand in Sepharose 4B column assays. 125I-CYP was found to bind specifically and saturably to both peaks I and II with a Bmax of 28 +/- 4 and 32 +/- 3 fmol/mg protein, respectively. 3H-CGP 12177, a hydrophilic beta-adrenergic receptor ligand, did not label receptors present in peak II, but it specifically bound to synaptic plasma membranes (SPM) prepared from bovine hippocampus and, to a lesser extent, to peak I. These results suggest that receptors present in coated vesicles are cryptic in nature. In the displacement of 125I-CYP binding by (-)-isoproterenol, addition of 50 microM GppNHp caused a significant "right shift" with SPM and peak I but not the peak II preparation. Adenylate cyclase activities could also be detected in both peaks I and II (specific activities, 21 +/- 0.6 and 24 +/- 0.5 pmol cAMP/mg protein/min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1985

Stereospecific opiate-binding sites occur in coated vesicles.

We prepared clathrin-coated vesicles from bovine forebrain utilizing sucrose or deuterium oxide-Ficoll density gradient centrifugation followed by permeation chromatography. Homogeneity was monitored by electron microscopy (EM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). EM revealed that the predominant (up to 98% of the total) organelles were coated vesicles and empty hexagonal baskets. Diameters of the coated vesicles ranged from 37 to 120 nm with a mean of 65.2 +/- 2.2. Upon SDS-PAGE of the coated vesicle fraction, the most prominent band appeared at 180,000 daltons. There were also three additional bands at 100,000, 50,000 and 35,000 daltons, giving the overall pattern characteristic of coated vesicles. Both 0.5 nM tritiated naltrexone and etorphine displayed specific binding to coated vesicles. Naltrexone binding in coated vesicles from gradient fractions was increased 2.5-fold over the original 100,000 X g pellet. An additional 4-fold enrichment in specific binding was observed after permeation chromatography which was concomitant with an increase in the volume density of coated vesicles in electron micrographs. Naltrexone binding was stereospecific and etorphine binding was inhibited by 100 mM NaCl (40%). Both naltrexone and etorphine binding were inhibited by 50 microM guanyl-5'-yl imidodiphosphate (40 to 50%). In summary, purified bovine brain-coated vesicles contained high affinity stereospecific opiate alkaloid-binding sites with characteristic opioid binding properties.

Animals↗
PubMed1983

The ultrastructure of the sinu-atrial node of the bat.

The sinu-atrial node (SAN) of the bat, Pipistrellus subflavus, is capable of generating a wide range of spontaneous activity varying from 20 bpm when hibernating to bursts of 800 bpm during active flight. Electrophysiological studies have shown an absence of arrhythmias even below 4 degrees C body temperature. In order to determine whether these physiological capabilities are based upon unique ultrastructural features of the bat SAN, the present study was conducted. We found that the structure of the SAN of the bat is typically mammalian. Diameters of all three cell types in the SAN (nodal, transitional, and atrial) are smaller than those observed in any other mammalian species. A morphometric analysis of cell junctions reveals that nodal-nodal and transitional-transitional cell contacts are primarily undifferentiated with few nexuses. Atrial-atrial cell contacts have a dominance of fasciae adherentes-type junctions with a small area left undifferentiated. Nexuses are much more prevalent in atrial-atrial cell contacts.

Action Potentials↗
PubMed1982

Microsomal opiate receptors differ from synaptic membrane receptors in proteolytic sensitivity.

We have found that opiate receptors in smooth microsomal fractions differ from synaptic membrane-associated receptors in proteolytic sensitivity. With 3 proteases of different substrate specificities (trypsin, chymotrypsin and S. griseus protease) smooth microsomal opiate receptors from rat brain were consistently less sensitive to limited proteolysis than were synaptic membrane receptors. Thiamine pyrophosphatase, a luminal Golgi membrane marker enzyme, exhibited a similar resistance to S. griseus protease in microsomal preparations, while microsomal Na+/K+-ATPase (ouabain-sensitive) was readily destroyed by trypsin. We also discovered that smooth microsomal opiate receptors co-migrate with both Golgi membrane and endoplasmic reticulum marker proteins on equilibrium density gradients under isopycnic conditions. Electron microscopic examination of the Golgi-enriched fraction showed the typical cisternae frequently associated with isolated Golgi membranes. Synaptic junctions, presynaptic membranes, myelin and mitochondria were conspicuously absent from this fraction. Since the microsomes isolated in vitro showed similar topography to those in vivo, the binding sites for opiates could be localized on the luminal surface membranes of the microsomal fractions. The exquisite sensitivity of synaptic membrane opiate receptors to proteolysis suggests that these receptors are found on the extracellular surface of the synaptic junction.

Animals↗
PubMed1981

Biochemical and ultrastructural changes in skeletal muscle induced by a creatine antagonist.

To evaluate the essentiality of creatine and phosphocreatine for the maintenance of the ultrastructure of skeletal muscle, chicks were fed a creatine antagonist, beta-guanidinobutyric acid (beta-GBA), as 2% of a Chow diet. Chicks fed beta-GBA exhibited growth retardation and weakness, and they accumulated large amounts of a monosubstituted guanidino compound, presumably beta-GBA, in their skeletal muscles. After 2 wk, there was a 74% decrease in the uptake of [14C]-1-creatine into pectoralis muscles of chicks fed beta-GBA. After 2 wk there as a significant decrease in phosphocreatine concentrations in pectoralis muscles from 20.1 +/- 2.8 mumoles per g wet weight (mean +/- S.D.) for 8 control chicks to 16.5 +/- 2.5 for 7 chicks fed beta-GBA. Selected fibers of the pectoralis and gastrocnemius muscles of chicks fed beta-GBA exhibited ultrastructural abnormalities including loss of thick and thin filaments, disruption of the Z band, dilated mitochondria, and dilated and displaced sarcoplasmic reticulum. The pectoralis muscles of chicks given 6% creatine in addition to 2% beta-GBA in the diet accumulated little beta-GBA, maintained normal phosphocreatine concentrations, and exhibited no significant ultrastructural abnormalities. These findings are the first experimental evidence that high concentrations of phosphocreatine are essential for the maintenance of the ultrastructural integrity of skeletal muscle.

Animals↗
PubMed1980

Presynaptic and postsynaptic neuromuscular effects of a specific inhibitor of acetylcholinesterase.

Previous studies have shown indirectly that the neuromuscular effects of nonselective cholinesterase inhibitors are mediated through the inhibition of acetylcholinesterase (AChE). To test this hypothesis more directly we studied the effects of the specific inhibitor of AChE, BW 284c51, at the neuromuscular junction of rat diaphragms. BW 284c51 inhibits AChE in a dose-dependent partially reversible manner at all concentrations tested (10(-9) to 10(-4) M). Maximum inhibition was never greater than 92%. The drug increased miniature end-plate potential (MEPP) amplitude and prolonged half-decay time at 10(-7) and 10(-6) M. However, BE 284c51 had no effect on the resting membrane potential at any concentration. BW 284c51 at 10(-7) M reversibly increased MEPP frequency by almost 4-fold. There was a 2-fold increase in the occurrence of giant MEPPs in the presence of BW 284c51. The quantum content (m) of the end-plate potential was increased in 10(-7) M BW 284c51 as were end-plate potential amplitude and quantum size (q). Animals injected subcutaneously with 10 mg/kg of BW 284c51 displayed typical signs of AChE inhibition including salivation, whole body tremor and prostration. Spontaneous muscle fasciculation was more noticeable after in vivo injection of BW 284c51 than after in vitro administration. Furthermore, MEPP frequencies were considerably faster when the drug was injected in vivo than when applied in vitro. The data are discussed with respect to the hypothesis that inhibition of AChE causes presynaptic as well as postsynaptic effects.

Aniline Compounds↗
PubMed1977

Imidazole myopathy. Production of the myopathy and its dependence on acetylcholine.

An acetylcholine-mediated myopathy has been produced in the soleus muscle of the rat by the daily injection of imidazole, a compound that accelerates the metabolism of adenosine 3':5' cyclic phosphate by activating the enzyme phosphodiesterase. The imidazole-treated muscles were found to have a lowered resting membrane potential. This study suggests that a decrease in resting membrane potential may make skeletal muscle more vulnerable to necrosis by acetylcholine released during normal activity.

Acetylcholine↗
PubMed1975

Presynaptic effects of neuromuscular cholinesterase inhibition.

Paraoxon, an irreversible organophosphorus inhibitor of cholinesterase, produces a myopathy beginning at the neuromuscular junction in rat diaphragm muscles. Thirty minutes after paraoxon was injected i.p. (0.5 mg/kg), neuromuscular cholinesterase activity was reduced to 36% of control. The frequency of miniature end-plate potentials (MEPPs) in diaphragms from paraoxon-treated rats was 109/sec compared with 2.9/sec in saline-injected controls. The faster frequency was seen after paraoxon gradually declined to control rates within 6 hours after injection. The quantum content of end-plate potentials was reduced to 66% of that seen in saline controls. Spontaneous and impulse-related antidromic activity was observed along the phrenic nerve after paraoxon which also gradually diminished with time. When the phosphorylated acetylcholinesterase was reactivated with 10(-3) pyridine-2-aldoxime methiodide, MEPP frequency was reduced significantly and antidromic activity was abolished. Block of axonal excitability with 10(-6) M tetrodotoxin reduces the effects of paraoxon on MEPP frequency and antidromic activity, while acetylcholinesterase remains inhibited. In vitro perfusion with 6 times 10(-8) M paraoxon increases MEPP frequency and initiates antidromic activity. It is concluded that inhibition of neuromuscular cholinesterase by paraoxon leads to an alteration of transmitter release, and this may be associated with ultrastructural abnormalities observed at the motor endplate.

Action Potentials↗