Embryos were immobilized with neuromuscular blocking agents for one to four days between days 10 and 15 of incubation. This treatment reduces spontaneous motility, as well as movement-initiated proprioceptive and cutaneous stimulation. Although the major aim of these experiments was to determine the effects of such treatment on subsequent behavioral development, several indices of neuromuscular and general morphological development were also examined.A single injection of curare on day 10 continues to depress spontaneous motility for virtually the entire remaining incubation period. This effect is due to the persistence of unmetabolized curare in the closed system of the egg. When a comparable dose of a rapidly metabolized neuromuscular blocking agent (succinylcholine) is given, this long term behavioral depression is not found. Embryos treated with SC can remain totally immobilized for up to 60 hours with no apparent repercussions on subsequent behavior; spontaneous embryonic motility, reflex sensitivity, hatching, and several general posthatching behaviors, all appeared normal following such treatment.Embryos immobilized for as little as 48 hours developed joint malformations and were retarded in general growth by about one day whereas 24 hours of paralysis was not sufficient to induce these effects.Twenty-four hours of total paralysis from days 10 to 11, plus a 4030% reduction in motility until days 15 or 16, does not appear to cause any abnormalities in muscle or spinal cord development. Muscle histology, motor endplates, cell number in the spinal cord and choline acetyltransferase and acetylcholinesterase activity in spinal cord and muscle were all comparable to controls. An 80-90'% reduction in motility on days 11 through 15, however, induces a n apparent alteration of the intensity and distribution of histochemically demonstrable AChE in the anterior and posterior latissimus dorsi muscles.The present findings suggest that the suppression of overt motility for a period comprising ca. 5 1 2 % of the total incubation time (21 days) does not modify subsequent behavioral development or the underlying neurogenetic mechanisms. Though these findings provide some support for the notion that the embryonic nervous system develops in forward reference to and without benefit from function or sensory input, only a more complete reduction of neural function, especially CNS activity, can provide a critical test of this concept.
Abstract— Partially purified myelin from brains of 17‐day‐old rats was separated into 4 subfractions on a discontinuous sucrose gradient by virtue of heterogeneity in density and particle size. The protein composition of each subfraction was determined by densitometry following separation of proteins on polyacrylamide gels in buffers containing sodium dodecyl sulphate. The major proteins studied included two basic proteins, proteolipid protein, the major high molecular weight protein (W) and a group of high molecular weight proteins. The percentage of high molecular weight proteins decreased sequentially from fraction D to A, that of the W protein remained constant, while relative amounts of the two basic proteins increased. Proteolipid protein concentration also increased as a percentage of the total protein from fraction D to B, but the uppermost fraction. A, had a markedly lower amount than fraction B. At 1 h after intracranial injection of [3H]leucine, the specific radioactivity of the basic and proteolipid proteins decreased from fraction D to B, with proteolipid protein in fraction A again anomalous (specific radioactivity higher than expected). These results are consistent with (but do not prove) a precursor‐product relationship for individual proteins from denser to lighter subfractions, with the exception of myelin subfraction A. Experiments involving time staggered injections of a [14C] and later a [3H] labelled amino acid gave data which demonstrated that the W and basic proteins were added simultaneously (or with delays of much less than 20 min) to all of the subfractions, while proteolipid protein was added sequentially, from lower to upper fractions on the gradient. This double isotope technique also confirmed our previous observations that proteolipid protein shows a lag in entry into myelin compared to basic protein.
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