Sixth Postnatal Day Research Articles

The development of innervation in the rat atrioventricular node.

The problem of development of the innervation of the rat atrioventricular node has been investigated by electron microscopy. Nerve bundles appear in relation to the node as early as the second postnatal day and vesiculated axons are seen throughout the entire node by the fourth day. Intimate contacts between nodal cells, axons and terminal varicosities are frequently observed. Use of the 5-hydroxydopamine tracer technique has enabled the identification of both cholinergic and adrenergic axons. It is concluded that the node has a dual innervation although cholinergic endings far outnumber those classified as adrenergic on the sixth postnatal day. These results are quite different to earlier findings made at the light microscope level and the discrepancies are discussed with respect to the histochemical techniques used. The suggestion that nodal differentiation is induced by nerves is considered in relation to the differences in cholinesterase activity exhibited by nodal cells during normal development and following neonatal sympathectomy.

Development of the barrels and barrel field in the somatosensory cortex of the mouse.

Barrels of the PMBSF of the mouse somatosensory cortex become apparent in Nissl-stained tangential sections simultaneously, on the fourth postnatal day. At this time they are miniatures of those in the adult and are situated in the deepest sublamina of the trilaminar cortical plate. An early barrel appears as a patch of decreased cell density: the prospective hollow of the barrel. Septa become noticeable during the sixth postnatal day. From that period to adulthood, the relative contribution of the PMBSF to the total cortical surface area increases -- an increase that goes against one's expectation: the barrel related periphery matures very early and so does the central, lateral region of the cortex. Barrel growth parallel to the pial surface is greater along the major axes than along the minor axes. By using the barrels to identify prospective layer IV in immature cortex, we could determine that layers V and VI attain their adult height during the sixth postnatal day -- an age when prospective layers I-IV are only half their adult height. The onset of barrel formation coincides with the moment after which injury to the pertinent somatosensory periphery (the vibrissal papillae) no longer causes profound alterations in barrel morphology.

Morphology of hereditary mouse cataract

Histological changes of hereditary cataractous mice lens were studied by light and electron microscope. Until the sixth postnatal day the lens of the defective mouse appeared to develop normally. However, immediately after this period, the denucleation process of the lens cells appeared impaired. Another abnormality observed at this period is the swelling at the distal portion of the lens fibers in the deep posterior suture area of the perinuclear zones. In the bow area, the lens of 12–13-day-old mice the abnormal persistence of the nuclei becomes most apparent. In addition, the lens cells which had failed to show normal denucleation appear to become hydropic. Electron microscopic study revealed that the cytoplasm of the affected lens fibers contained coarse granular substance and many micro-organelles, which are absent in the normal lens fibers.

Changes in the rate of axoplasmic transport during postnatal development of the rabbit's optic nerve and tract

Change in the rates of the rapid and slow phases of axoplasmic transport have been studied in the optic nerve and tract of a large series of albino rabbits after the intravitreal injection of tritiated leucine ( 3H-leucine) at different ages. The rate of the rapidly transported proteins has been found to increase from about 120 mm/day on the sixth postnatal day to about 150 mm/day at the end of the third week. During the fourth week the rate increases rather rapidly to approximately 200 mm/day but it subsequently remains fairly constant at between 220 and 240 mm/day into adult life. The slow phase of protein transport, on the other hand, declines in rate from approximately 5 mm/day at the end of the first week to about 2 mm/day in animals over 4 weeks of age; again the change in rate of this component is not gradual but occurs rather suddenly during the fourth week. These observations indicate that the fourth postnatal week is a critical period in the development of the rabbit visual system, and evidence from the accumulation of radioactive material in the superior colliculi after the intravitreal injection of 3H-leucine suggests that it may coincide with the establishment of definitive synaptic connections by the retinal ganglion cell axons.

Repair of the external granular layer of the hamster cerebellum after prenatal and postnatal administration of methylazoxymethanol.

AbstractThe purpose of this experiment was to examine the influence of methylazoxymethanol acetate (Mam ac) on cell proliferation and regeneration of the external granular layer in the cerebellum of the hamster. Pregnant hamsters were treated with 10 mg/kg/day Mam ac on days 13–15 of gestation and youngsters on the second, third, and fourth or fourth, fifth and sixth postnatal days. In animals treated during intrauterine life and examined on the day of birth a large number of cells in the external granular layer were destroyed, but some seemingly healthy ones always remained. In those permitted to live, surviving cells formed a new external granular layer and by the 20th postnatal day no morphological differences could be detected between the treated and control animals. In animals treated on the second to fourth postnatal days practically all the cells of the external granular layer were destroyed. By the tenth day the Purkinje cells were located throughout the molecular zone. Many of them showed a cytoplasmic cone extending centrally instead of toward the periphery. The internal granular layer contained only a few cells, apparently owing to failure of the normal inflow of neurons from the external granular layer. In animals treated on the fourth to sixth postnatal days most cells in the external granular layer were destroyed. During the following days surviving cells presumably gave rise to a new external granular layer. The cells of this layer failed to migrate centrally. Instead they remained located in the molecular layer where they formed an extra layer of cells, which had the appearance of granule cells. The animals were ataxic, although retinal abnormalities may have been partially responsible for the symptoms.

Perinatal changes in epidermal innervation in rat and mouse.

AbstractThe development of cutaneous innervation in the rat and the rat and the mouse has been studied by silver techniques. In particular, the innervation patterns of adult and of perinatal skin have been compared. From the second parental day until the sixth postnatal day, the relatively thick epidermis is freely penetrated by nerve fibers; thereafter, the nerve endings appear to be confined to the dermis. The intra‐epidermal axons are directed obliquely, with a rough (and not exact) correspondence to the plane of future emergence of the hair shafts. The appearance of a transitory development of intra‐epidermal nerves elsewhere.

Effects of Injections of Equine Gonadotrophin upon the Gonads and Adrenals ot Fetal Rats.

Using a method recently described. fetuses of the Sprague-Dawley strain of rats were transferred to the abdominal cavity of the mother and subjected to subcutaneous injections of equine gonadotrophin. Thirty-two fetuses received injections twice daily and about 12 hours apart. Near term, the 16 that had survived were secured by severing the umbilical cord. Fourteen and certain littermate controls were immediately autopsied. while 2 were placed in the nest of a foster mother. Although one was promptly destroyed by the mother, the other one received 3 additional injections before it was sacrificed by decapitation (Fetus 20, Table I). Litter 112 (Fetuses 35 and 36) differs from others in that the mother received subcutaneous injections of progesterone for the purpose of delaying parturition. Injections, each containing 1.0 mg, were made twice daily on days 20, 21 and 22 of pregnancy. In all cases, the procedure at autopsy was to open the abdominal cavity before placing the specimen in Bouin's fixing fluid. After fixation, the lumbar and pelvic regions of ihe body were sectioned serially and the sections stained with hematoxylin and eosin. In some instances, certain sections of the series were segregated for special staining (Dominici's. Mallory's triple and Heidenhain's iron hematoxylin). When sections of testes Tere examined with the aid of a micro-comparator, an instrument which brings half the field of each of 2 microscopes int view, it was found that the interstitial cells of Leydig of each injected mdle mere larger and more abundant than ihoze of litter-mate controls (Fig. 1 to 4). They were most abundant in the 2 fetuses which received the most hormone (3 and 5, Table I). Although it is reasonable to suppose that the interstitial cells secreted androgen more rapidly than normally (?), evidence that they actually did could not be detected by inspecting serial sections of such developing organs as the prostate, the seminal vesicles and the bulbo-urethral glands. Price and Ortiz'! report that in rats injected after parturition and autopsied on the sixth postnatal day, the combined weight of the seminal vesicles and the coagulating glands was 25% greater than in controls.