Effect of nerve stimulation on rat skeletal muscle. A study of plasma membrane

The gastrocnemius muscle of the rat showed no morphological, histometric or plasma membrane changes, after sciatic nerve stimulation with a 5mA current for 30 to 60 min, 10 mA for 30 min and 15 mA for 5 min. However, 10 mA for 60 and 200 min gave rise to mitochondrial and plasma membrane abnormalities. These changes were absent after a rest period. The results indicated that the sciatic nerve stimulation at 10 mA for 60 and 200 min caused reversible changes in the rat skeletal muscle mitochondria and plasma membrane.     

Modifications in the type distribution of muscle fibers induced by repeated local freezings the rat sciatic nerve]

In the Rat, after a localized freezing of the sciatic nerve inducing a complete denervation of the medial head of the gastrocnemius muscle, the reinnervation took place within 16-18 days under our experimental conditions. After only one freezing, a limited and stable "type-grouping" of muscle fibres is observed from 30 to 360 days. After 2 to 5 freezing repeated every three weeks, the muscular changes observed one month after the last freezing are much more pronounced than when only one freezing is performed. These changes consist of a progressive increase in the number of type I and type II C fibres. This transformation is not stable: 3 months after the 3rd freezing, the muscle pattern does not differ from that which is noted after a single freezing.     

The time course of plasma enzyme changes accompanying skeletal muscle stimulation

Summary 30 min electrical stimulation of hind limb skeletal muscle in nembutal anaesthetised dogs was accompanied by increases in arterial haematocrit, plasma GOT and plasma LDH, which were almost completed within the first 10 min of stimulation. This fast response indicated that a rapid change in either the entry and/or clearance of enzyme from the plasma must have occurred.     

Do peripheral nerves contain a factor inducing acetylcholine sensitivity in skeletal muscle?

A crude extract of the sciatic nerve, eluate of dialyzed nerve extract or 2 folin-positive sephadex fractions induced acetylcholine sensitivity of extrajunctional regions in extensor digitorum longus muscle fibres of the rat, when released from silastic plates implanted for 3--4 days onto the muscle surface.     

Variation in the number and size of myelinated nerve fibers regenerated after repeated localized freezing of the sciatic nerve of rats]

The number and size of myelinated fibres have been determined in the nerve to medial head of the gastrocnemius muscle of Rats in which the sciatic nerve had been frozen locally 1 to 5 times at monthly intervals. The contralateral nerve was used as a control. When the measurements were made one month after the last freezing, the number of fibres increased progressively until the 3rd freezing, reaching about 220% of the normal value. No higher values were observed after 4 or 5 freezings. The mean diameter of fibres decreased with the number of operations. When the measurements were made 3, 6, 12 or 18 months after the 3rd freezing, the number of fibres decreased by about 30% between the 1st and the 3rd month and then stabilized. The mean diameter of fibres increased progressively. However, at the 18th month, the size of the myelinated fibres had not reached the normal value.     

Differential effects of disuse preceding denervation on the onset and development of fibrillation in fast and slow muscles

Summary Section of the sciatic nerve, performed after a week of muscular disuse, is followed by fibrillation earlier in the soleus (S) than in the anterior tibialis (AT) muscle of the rat. The subsequent development of fibrillation, which is different in the control denervated S as compared with the control denervated AT, tends to become similar in the disused-denervated muscles.This work was aided, in part, by a grant from U. I. L. D. M. (Unione Italiana Lotta alla Distrofia Muscolare), Sezione di Trieste.     

The effects of time of equilibration with cryoprotectants at 0 degree C prior to freezing on the survival of mouse embryos frozen by the two-step method

Mouse embryos were frozen by the two-step method after equilibration for 0.1-60 min with cryoprotectants at 0 degree C. No survival or a very low survival was obtained after equilibration for only 0.1 min. The morulae showed the highest survival rates when equilibration time was 5-30 min with 2 M DMSO, 20-30 min with 2 M glycerol, 5-10 min with 2 M ethylene glycol and 20-30 min with 2 M propylene glycol, respectively.     

Membrane interiorization by phagocytosing macrophages — an ultrastructural morphometric approach

Summary Stereological methods have been used to quantify selected membrane compartments of normal and activated rat peritoneal macrophages, before and after phagocytosis of latex beads. Despite being rounder, activated cells are more efficient phagocytes: 30 min after latex challenge they suffer a greater nett depletion of plasma membrane and sequester more and larger phagocytic vacuoles. However, phagocytosis of latex is not the major route of membrane interiorization.We wish to thank Professor R. Barer for his advice and criticism. The work was undertaken by L.O. as a research project in partial fulfilment of requirements for a B.Sc. degree in Human Biology and Anatomy, University of Sheffield.     

Changes in the protein kinase C activity or rat sternomastoid muscle during development and after denervation

Summary The relationship between the activity of protein kinase C (PKC) and muscle innervation was explored in the rat sternomastoid muscle (SM) from day 18 of gestation (E18) to adult age. Between E18 and birth, PKC activity rose 5-fold, and during the day after birth, diminished to a level characteristic of the mature muscle. The rise chiefly occurred in the neural part of the muscle, in both the membrane and the cytosol fractions. Between E18 and day 5 after birth, the ratios of membrane to cytosol PKC activity rose from 0.5 to 10 and 3 respectively in the neural and aneural parts of the muscle. Denervation of adult SM reduced PKC activity by half in the membrane fraction of the neural part but did not significantly change it in the membrane or cytosol fractions of the aneural parts. These results suggest that innervation plays an important part in determining the level of PKC activity in muscle.     

Changes in the protein kinase C activity or rat sternomastoid muscle during development and after denervation

The relationship between the activity of protein kinase C (PKC) and muscle innervation was explored in the rat sternomastoid muscle (SM) from day 18 of gestation (E18) to adult age. Between E18 and birth, PKC activity rose 5-fold, and during the day after birth, diminished to a level characteristic of the mature muscle. The rise chiefly occurred in the neural part of the muscle, in both the membrane and the cytosol fractions. Between E18 and day 5 after birth, the ratios of membrane to cytosol PKC activity rose from 0.5 to 10 and 3 respectively in the neural and aneural parts of the muscle. Denervation of adult SM reduced PKC activity by half in the membrane fraction of the neural part but did not significantly change it in the membrane or cytosol fractions of the aneural parts. These results suggest that innervation plays an important part in determining the level of PKC activity in muscle.     

The effects of time of equilibration with cryoprotectants at 0°C prior to freezing on the survival of mouse embryos frozen by the two-step method

Summary Mouse embryos were frozen by the two-step method after equilibration for 0.1–60 min with cryoprotectants at 0°C. No survival or a very low survival was obtained after equilibration for only 0.1 min. The morulae showed the highest survival rates when equilibration time was 5–30 min with 2 M DMSO, 20–30 min with 2 M glycerol, 5–10 min with 2 M ethylene glycol and 20–30 min with 2 M propylene glycol, respectively.     

Periodate oxidation of lymphocyte membrane glycoconjugates]

Mouse spleen cells free of erythrocytes were suspended in PBS at a concentration of 2 X 10(7) cells/ml and mixed with an equal volume of sodium periodate in PBS for 10 min. at 4 degrees C to give a final concentration of periodate ranging from 10(-4) M to 5 X 10(-3) M. The cells were then washed and suspended (60 X 10(6) ml) in PBS containing 3H-labelled sodium borohydrate and incubated for 30 min, at 23 degrees C. Following this, the cells were washed and the pellets treated with H2SO4 0.1 N for 60 min. at 80 degrees C. Compounds liberated by such treatment, were identified by chromatography as derivates of sialic acid. The data provide direct evidence that the mitogenic effect of sodium periodate is associated to the oxidation of the sialic acid residues on the lymphocyte membrane.     

Testosterone derivatives are neuroprotective agents in experimental diabetic neuropathy

In this study we have assessed the effect of testosterone (T), dihydrotestosterone (DHT) and 5αandrostan-3α, 17β-diol (3α-diol) therapies on diabetic neuropathy. Diabetes was induced in adult male rats by the injection of streptozotocin and resulted in decreased T and increased 3α-diol levels in plasma and in decreased levels of pregnenolone and DHT in the sciatic nerve. Moreover, a reduced expression of the enzyme converting Tinto DHT (i.e., the 5α-reductase) also occurs at the level of sciatic nerve, suggesting that the decrease of DHT levels could be due to an impairment of this enzyme. Chronic treatment for 1 month with DHT or 3α-diol increased tail nerve conduction velocity and partially counteracted the increase of thermal threshold induced by diabetes. Treatment with DHT increased tibial Na⁺,K⁺-ATPase activity and the expression of myelin protein P0 in the sciatic nerve.DHT, 3α-diol and T reversed the reduction of intra-epidermal nerve fiber density induced by diabetes. These observations indicate that T metabolites can reverse behavioral, neurophysiological, morphological and biochemical alterations induced by peripheral diabetic neuropathy. I. Roglio, R. Bianchi: These authors contributed equally to this study. Received 4 January 2007; received after revision 13 February 2007; accepted 27 March 2007     

Acceleration of the speed of neuronal growth by a new neurotropic substance: N-isopropyl-amino-2-pyrimidine]

16 hrs. after per os administration of 14C N-isopropyl-amino-2-pyrimidine (IAP) in the Rat, radioactivity of the sciatic nerve is significantly higher than in plasma and other organs. In vitro IAP (base, orthophosphate or dichloracetate) accelerates neurite outgrowth of explained spinal ganglion after 48 hrs. of incubation in nutritive medium. Results suggest that IAP incorporated in nerve cell acts on cellular mechanisms controlling nerve growth.     

Differences in luteinizing hormone release stimulated in rat anterior pituitary cells by leukotriene C4 and by gonadotropin-releasing hormone in vitro

Continuous administration of leukotriene C4 (LTC4, 10(-10) M) to superfused rat anterior pituitary cells increased LH release for 40 min only, whereas in a parallel experiment gonadotropin-releasing hormone (GnRH, 10(-9) M) evoked a continuous increase in hormone secretion. In contrast to GnRH, LTC4 did not desensitize rat anterior pituitary cells. The secretory action resulting from the administration of LTC4 (10(-10) M) was abolished for 40 min after previous stimulation. The results documented the dual action of LTC4 on LH exocytosis.     

Time and theophylline influence on the quantitative variations of the glomerular basement membrane ferritin pathway (author's transl)

A fine quantitative evaluation of ferritin aggregates in rat GBM permits to counts 5.08 +/- 1.51 and 18.30 +/- 3.21 g/cm2, respectively 30 and 60 min after ferritin injection; likewise, 30 min after ferritin administration, 5.08 +/- 1.51 and 17.11 +/- 3.9 g/cm2, respectively in normal and theophylline-treated animals.     

Effects of disuse and nerve stump length on the development of fibrillation in denervated soleus muscle

Summary Both in normal (control) and in cordotomized (disused) rats, the soleus muscle was denervated either by cutting the sciatic nerve near the trochanter (proximal denervation) or by cutting the soleus nerve near the insertion into the muscle (distal denervation). In the control muscles, the development of fibrillation was not dependent on the level of nerve section. In disused muscles, the development of fibrillation was greater following distal denervation than following the proximal one.     

Rapid effects of insulin on cyclic GMP location in an intact protozoan.

We studied rapid changes in location of cyclic GMP in Tetrahymena pyriformis. Insulin caused cGMP localization in cilia and near the plasma membrane (0.5-1 min). Later (1-5 min) cGMP localization was diffuse in cytoplasm with perinuclear accentuation. Inactive insulin analogs did not elicit these changes.     

Electromyographic responses elicited by cutaneous and mixed nerve stimulation in human tibialis anterior muscle

The rectified and averaged myoelectrical responses of the anterior tibial muscle to stimulation of the posterior tibial, peroneal and sural nerves at the ankle were recorded during a weak isometric contraction in man. The stimulation of the posterior tibial nerve elicited two excitatory phases (short and long latency excitations) at 40 ms and 78 ms latencies, respectively, separated by a phase of reduced activity. With peroneal and sural nerve stimulation such triphasic responses were less consistent; only a monophasic inhibitory response occurred in some recordings. These results indicate that well-identifiable responses with distinct latencies can be obtained in human leg muscle with cutaneous and mixed nerve stimulation distal to the muscle.     

Effect of free fatty acids and cholesterol in vitro on liver plasma membrane-bound enzymes

The effect of cholesterol and fatty acid treatment in vitro was tested on rat liver plasma membrane-bound enzymes and lipid fluidity. The observed alterations of membrane fluidity affect both (Na+-K+)-ATPase and Mg2+-ATPase activities but not 5'-nucleotidase; basal adenylate cyclase as well as its hormonal sensitivity were differentially affected by changes of membrane microenvironment.