First Month Of Postnatal Life Research Articles

Aspects of biochemical differentiation in the central nervous system.

A demonstration of cell-specific patterns of development in the immature CNS is provided by examples of characteristic, cell-specific time-courses of enzyme development in different classes of brain cells isolated in highly purified form by bulk-separation from the cerebral and cerebellar cortex of the growing rat. The enzymatic analysis was carried out at the level of the nerve and glial cell lysosomes and mitochondria, two subcellular organelles crucial to the economy of all cells. The findings reveal rather similar developmental patterns for the lysosomal hydrolase N-acetyl-beta-D-glucosaminidase in neurons and glial cells of the cerebral cortex as well as in two different cerebellar nerve cell types, the Purkinje and the granule cell. However, significant differences in the post-natal chronology of development of the mitochondrial enzyme alpha-glycerophosphate dehydrogenase were noted between cortical nerve and glial cells, the glial enzyme exhibiting 6-fold higher levels of activity than the neuronal one throughout the first month of postnatal life. The findings emphasize the feasibility as well as the necessity of studies aimed at the elucidation of the cell-specific aspects of the biochemistry of developing nerve and glial cells.

Thymus rudiment of the athymic nude mouse.

IT is accepted that the polycystic organ, composed of branching ducts and differentiating during the first month of postnatal life into a system of interconnected cysts and acinar arrangements of serous and mucoid cells and containing almost no lymphoid cells, represents the dysgenetic thymus of the nude homozygote mouse1,2. No epithelial cystic cells and no cells with specific inclusions which may be the cellular source of the thymic factors affecting pathways for differentiation of T lymphocytes, were found in the polycystic organ3,4. The nude mouse has, however, not only the prethymic cells capable of differentiating into T cells in a thymic graft from an euthymic donor5, but also surprising numbers of θ-positive cells in the spleen6. It is suggested that these T cells may leak across the placenta from the euthymic mother into the nude foetus, may differentiate under the influence of the maternal thymic hormone, or may acquire their T-cell properties by some kind of non-thymic induction7.

Effect of visual deprivation on evoked potentials in the visual cortex and superior colliculus in rabbits

Evoked potentials arising in the visual cortex and superior colliculus to stimulation of the collateral eye by single, paired, and repetitive flashes were recorded in rabbits reared in darkness or in normal illumination. The absence of significant change in the latent period and amplitudes of the first two components of the collicular responses and of the recovery cycle and response to repetitive stimulation in the light-deprived animals suggest that photic stimulation does not affect the normal functional development of the rabbit retinotectal system. However, functional deafferentation in the early postnatal period gives rise to serious disturbances of visual cortical function, as reflected in a marked decrease in amplitude of the primary response, lengthening of the recovery cycle, and narrowing of the range of rhythm-binding frequencies of flashes. These disturbances were reversible. The period of maximal sensitivity of the rabbit retinocortical system to visual deprivation begins at the end of the first month of postnatal life. The possible mechanisms lying at the basis of these functional disturbances in light-deprived animals are discussed.

Developmental, tissue-specific, and sex differences in activity among three enzymes from human erythrocytes and cultured fibroblasts.

G6PD specific activity (S.A.) was significantly greater in human females than in males, both in fresh erythrocytes from newborns and in prenatal cultural lung. The sex difference in erythrocytes was nullified by 6 years of age via a reduction of G6PD S.A. in the female relative to the male. The sex difference in prenatal lung was nullified during the first month of postnatal life by an abrupt rise of G6PD S.A. in the male rather than by any postnatal change in the female. No sex difference was found for G6PD in cultured skin or for LDH and HGPRT in any of the tissues studied. Qualitative and quantitative tissue-specific and developmental differences were found among G6PD, LDH, and HGPRT in cultured skin and lung. Our data suggest (1) that cultured fibroblasts still can reflect the tissue-specific, developmental, and sex differences of their origin and (2) that sex differences for X-linked loci such as G6PD do not necessarily imply escape of the locus from X-inactivation in the female but rather may result from other unknown regulatory mechanisms in either sex.

Ontogenesis of the states of sleep in rat, cat, and guinea pig during the first postnatal month.

AbstractThe behavioral and polygraphic characteristics of wakefulness and sleep were studied in 20 infant rats, 26 kittens, and 25 infant guinea pigs during their first month of postnatal life. In the infant guinea pig, the electrocorticographic (ECoG) patterns of sleep were similar to those of the adult, except for the absence of spindles during the first 3 weeks. In the rat and the cat, states of vigilance were not clearly differentiated in ECoG patterns during the first week; near the 8th day a fast, high amplitude ECoG appeared during paradoxical sleep (PS). The first signs of slow‐wave sleep (SWS) appeared at 11 to 13 days of age in the rat and at 15 to 21 days in the cat. The greater the immaturity of the animal at birth, the greater was the amount of time spent in PS in the perinatal period. In the rat, which was born the most immature, the decrease in the percent time of PS was very rapid: 70 % at birth, it decreased to 12% on the 30th day. In the cat the decrease was slower. In the guinea pig, despite its relative maturity, the percent time of PS at birth was 7%, approximately double that in the adult. The length of extrauterine life as well as the degree of immaturity at birth, played a role in the development of the sleep‐wakefulness cycle.

The hormone control of ovulation in the calf

1. Unlike many other mammals, the calf is capable of responding to pituitary injections almost from birth. Age has little effect on the ability of the follicles to develop during a series of a.p.h. injections, the follicular response generally being as good 3 weeks after birth as in calves 6–8 months old.2. Ovulation can occur spontaneously in the a.p.h. treated calf before the end of the first month of post-natal life.3. Ova obtained from such ovulations are capable of fertilization, although the percentage becoming fertilized is very low. This is thought to be due to the infantile state of the Fallopian tube and the difficulty in inseminating into the uterus, rather than faulty maturation of ova.4. Although many follicles (10–60) can develop during a series of a.p.h. injections, superovulation was not consistently obtained either by intravenous injections ofa.p.h., l.h.orp.u., or combinations of any of these three.5. Superovulation can generally be obtained, with the formation of many corpora lutea, if the a.p.h. treatment is repeated a second time after a period of luteal activity.6. The inhibitory effect of a corpus luteum on ovulation in cattle can be overridden in tho a.p.h. treated animal if suitable quantities ofa.p.h., l.h.orp.u.are intravenously injected when the newly formed follicles are approaching maturity.7. Ovulation in the calf at all ages up to 8 or 9 months of age, either in the presence or absence of luteal tissue, is unaccompanied by oestrus. Oestrus, when occurring during a series of a.p.h. injections, commenced after 90–100 hr. of treatment. In such cases slaughter has always revealed the presence of luteal tissue, indicating that ovulation during a ‘silent heat’ had occurred before the commencement of pituitary treatment.8. Great individual variation exists in the ability of the ovary to respond to pituitary injections. This insensitivity to gonadotropins is not confined to young calves and has been observed in calves 4–6 months of age.

The senses and intelligence of the Chinese dancing mouse

For a few days during the first month of post-natal life the dancing mice which I have studied respond definitely to sounds, but neither direct nor indirect methods of testing auditory sensitiveness furnish any evidence of it in the adult. Brightness vision is fairly acute; color vision is poorly developed. I have some evidence of the discrimination of red and blue, and of red and green, but no evidence that blue and green can be distinguished. In visual discrimination the mice apparently depend upon brightness differences. The behavior of the dancing mouse is readily modifiable. Choice, by exclusion, of one of two objects which differ in brightness, with electrical stimulation in the case of a wrong choice, indicates that from 40 to 100 repetitions of an experience is necessary for the formation of a perfect habit. Such a modification of behavior lasts for from two to five weeks. Modifications of behavior occur more rapidly in the male than in the female. Individual differences in plasticity and in the permanency of modification are marked.