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Biomedical subjects

G Le Douarin

Publications and source records attributed to G Le Douarin.

At least 19 recordsLinked to original sources
PubMed1988

Nicotinic and muscarinic responses of embryonic chick ventricular myocardium to acetylcholine: chronotropic and electrophysiological effects.

Sensitivity of 7-day-old chick embryo ventricular heart fragments to acetylcholine was investigated. Low doses mainly produced a positive chronotropic effect, whereas high doses of acetylcholine provoked a decrease in the heart beat rhythm. The positive chronotropic effect of acetylcholine was related to the presence of nicotinic receptors that were evidenced within ventricular myocardium by autoradiography. Membrane potential recording showed that acetylcholine hyperpolarizes the diastolic membrane potential when the drug had a negative chronotropic effect. This effect of acetylcholine on the membrane potential was not observed when the drug had a positive chronotropic effect. In many cases, the diastolic membrane potential exhibited spontaneous small depolarizing potentials. Their amplitude was low and their frequency was irregular. These potentials were suppressed by treatment with alpha-bungarotoxin, suggesting that they are triggered by nicotinic receptor activation.

Acetylcholine↗
PubMed1988

Developmental changes in myosin isoforms from slow and fast latissimus dorsi muscles in the chicken.

In the course of muscle differentiation, changes in fibre-type population and in myosin composition occur. In this work, the expression of native myosin isoforms in developing fast-twitch (posterior latissimus dorsi; PLD) and slow-tonic (anterior latissimus dorsi; ALD) muscles of the chick was examined using electrophoresis under nondissociating conditions. The major isomyosin of 11-day-old embryonic PLD comigrated with the adult fast myosin FM3. Two additional components indistinguishable from adult fast FM2 and FM1 isomyosins appeared successively during the embryonic development. The relative proportion of these latter isoforms increased with age, and the adult pattern was established by the end of the 1st month after hatching. Between day 11 and day 16 of embryonic development, PLD muscle fibres also contained small amounts of slow isomyosins SM1 and SM2. This synthesis of slow isoforms may be related to the presence of slow fibres within the muscle. At all embryonic and posthatch stages, ALD was composed essentially of slow isomyosins that comigrated with the two slow components SM1 and SM2 identified in adult. Several studies have reported that the SM1:SM2 ratio decreases progressively throughout embryonic and posthatching development, SM2 being predominant in the adult. In contrast, we observed a transient increase in SM1:SM2 ratio at the end of embryonic life. This could reflect a transitional neonatal stage in myosin expression. In addition, the presence in trace amounts of fast isomyosins in developing ALD muscle could be related to the presence of a population of fast fibres within this muscle.

Animals↗
PubMed1988

[Innervation, activity rhythm and accumulation of myosin light chains in a fast muscle of chickens].

The fast posterior latissimus dorsi muscle (PLD) of the chick ceases to accumulate slow myosin light chains (MLC) during neonatal development. On day 18 of embryonic life slow MLC represented only 2% of total MLC, and LC3F was first detected. In chick embryo, spinal cord stimulation at a slow rhythm modifies PLD differentiation toward the slow type: LC3F did not accumulate and slow MLC increased. In contrast, stimulation at a fast rhythm accelerated LC3F accumulation. PLD denervation on day 2 after hatching inhibited the synthesis of LC3F. Direct stimulation at a fast rhythm led to post-hatching development into normal fast type while a slow rhythm influenced the development of denervated PLD towards the slow type. In innervated PLD, the effect of stimulation at a slow rhythm was less important than in denervated PLD. These results suggest that the rhythm of the neural and/or contractile activity plays an important role in the MLC expression during embryonic and post-natal development of the chicken fast muscle.

Animals↗
PubMed1987

Effects of electrical stimulation upon post-hatching development of fibre types in normally innervated fast and slow latissimus dorsii muscles of the chicken.

In chicken, the main characteristic properties of muscle fibre types in slow anterior (ALD) and fast posterior (PLD) latissimus dorsii are acquired during post-hatching development. At day 4 it becomes possible to distinguish between alpha' and beta' fibre types in ALD muscle. At the same time, mATPase staining and NADH-TR activity permit recognition of alpha w and alpha R fibres within PLD muscle. During further development, muscle fibre typology progressively changes towards the adult slow and fast type. Chronic stimulation at a slow rhythm (5 Hz) of PLD prevents the change in relative proportions of alpha R and alpha W fibres within the muscle that occurs in normal post-hatching development and increases the number of beta R fibres. Moreover, oxidative activity is increased in all muscle fibre types following stimulation. In ALD muscle, chronic stimulation at a fast rhythm (40 Hz) results in a decrease in oxidative activity and inhibits the differentiation of alpha' and beta' muscle fibre types. This study demonstrates that in young chicken, the pattern of activity influences the differenciation of fibre types in slow and fast muscles.

Adenosine Triphosphatases↗
PubMed1985

Influence of spinal cord stimulation upon myosin light chain and tropomyosin subunit expression in a fast muscle (posterior latissimus dorsi) of the chick embryo.

Latissimus dorsi muscles of the chick consist of a slow (ALD) and a fast (PLD) muscle. The influence of chronic spinal cord stimulation in the chick embryo upon the expression of myosin light chains and tropomyosin subunits was investigated. Early in development the two muscles exhibited the same ratio of alpha- and beta-tropomyosin subunits. Later, in the slow muscle the ratio beta:alpha decreased and in chicken the amounts of the two components were about the same. In the fast muscle, the alpha-subunit increased and reached 66% in young chicken. In the fast muscle, the alpha-subunit increased and reached 66% in young chicken. In the In the early stages of embryonic development, both muscles accumulated slow and fast light chains. However, in ALD the amount of slow light chains was greater than that of fast light chains and the reverse was observed in PLD muscle. Later during development, the slow components decreased in PLD while the fast components increased; the reverse was observed in ALD muscle. The fast myosin LC3f has been detected in 18-day-old embryonic PLD. Chronic spinal cord stimulation at a low rhythm was performed from day 10 of embryonic development to day 15 or 16. In both muscles from spinal cord-stimulated embryos, the beta-tropomyosin subunit was lower than in control embryos. In ALD, the pattern of light chains was unaffected by chronic stimulation while in PLD muscle the slow and fast components were modified. In particular the ratio LCs:LCf was increased in spinal cord-stimulated embryos with regard to controls.

Animals↗
PubMed1985

Sensitivity of cultured chick embryo heart cells to acetylcholine. Evidence for nicotinic and muscarinic receptors.

Sensitivity of cultured chick embryo heart cells to acetylcholine changes with time in culture. In 24 h cultures, about 25% of the cells exhibit a positive chronotropic response to acetylcholine. This effect is no longer observed after 48 h in culture. Positive and negative chronotropic effects of acetylcholine can be related to the presence of nicotinic and muscarinic receptors evidenced by autoradiography. Some data suggest a possible relationship between the type of sensitivity to acetylcholine and the changes in cell membrane properties occurring in culture.

Acetylcholine↗
PubMed1983

Developmental change in choline acetyltransferase activity in nerve endings of latissimus dorsii muscles in the chick embryo: influence of chronic spinal cord stimulation.

Choline acetyltransferase (CAT) activity of chick latissimus dorsii muscles was studied during embryonic development and at post-hatching states. CAT activity was always higher in anterior (ALD) than in posterior (PLD) muscles. At embryonic stages, chronic spinal cord stimulation at a low rhythm did not modify CAT activity in ALD nerve endings but caused a transient increase in PLD terminals. This increase in CAT activity seems to be related to an acceleration of neuronal maturation rather than to the occurrence of the multiple innervation that results from the central stimulation.

Acetylcholine↗
PubMed1981

[Effect of a return of motor neurons to spontaneous activity on the multi-innervation of muscular fibers induced in chick embryo by chronic slow-rhythm spinal cord stimulation].

The multi-innervation of posterior latissimus dorsi muscle caused in Chick embryo by chronic spinal cord stimulation at low rhythm (0.5 HZ) from the 10th until 14th day of incubation remains but does not increase if the stimulating period is prolonged. If the stimulating period is stopped and the embryo allowed to develop for several more days the number of acetylcholinerase sites on the muscle fibres decreases. This result suggests that the multi-innervation regresses after the cessation of the experimentally-imposed nervous signal.

Animals↗
PubMed1981

[Effects of chronic medullary stimulation on the total number of sites of acetylcholinesterase activity of the posterior latissimus dorsi muscle of chick embryo].

From incubation day 10 to 15, the spinal cord of Chick embryos are electrically stimulated in ovo at 0.5 Hz at the level of the motor roots innervating the latissimus dorsi muscles. As a consequence, the total number of spots of acetylcholinesterase determined on serial sections of posterior latissimus dorsi muscle increased 2.3 fold. This increase parallels that of acetylcholine receptor clusters, supporting the interpretation that these clusters are of synaptic origin.

Acetylcholinesterase↗
PubMed1977

[Ultrastructure of the embryonic mouse sinus node at the early stages of development (author's transl)].

At early stages of development in the mouse embryo (12-13 days post-coitum) the cells of the sino-atrial node are homogeneous but are different to the atrial myocardic cells at this stage of development or a younger stage (9-10 days post-coitum). Sino-atrial node cells are small; they have many ribosomes, the myofibrillar material and the Golgi apparatus are poorly developed. Membrane contacts are represented by simple appositions and some fascia adherentes. These cells show many pinocytic invaginations and subsarcolemmic vesicles. From the 14th day post-coitum the sino-atrial node becomes heterogeneous. 'Clear cells' are present in the middle part of the node; they are characterized by their irregular shape and the poor development of their myofibrillar material 'Dark cells' are observed at the periphery of the node and seem related to myocardial type cells described in the sino-atrial node of the late mouse foetuses. Our observations do not support the existence of a 3rd cellular population, called by some authors: 'transitional cells'. The problem of the segregation between sino-atrial cells and myocardial cells is discussed.

Animals↗