Different Stages Of Postnatal Development Research Articles

Neuromuscular contacts in the developing rat soleus depend on muscle activity

Neuromuscular transmission of the rat soleus muscle was interrupted by blocking the response of the postsynaptic membrane with α-bungarotoxin (α-BTX) at two different stages of postnatal development, i.e. at birth and at 10 days. The effect of this treatment on the maintenance of synaptic contacts was studied using histological and electrophysiological criteria. Following treatment at birth fewer muscle fibres were polyneuronally innervated 5–7 days later. After this initial loss of synaptic contacts, the subsequent rate of synapse elimination was slower than in control animals, so that even at 3 weeks muscles treated with α-BTX at birth had higher levels of polyneuronal innervation than their unoperated controls. Thus, interference with the response of the postsynaptic membrane at birth has prolonged effects on synaptic development. In muscles treated with α-BTX at 10 days the elimination of polyneuronal innervation was arrested and more neuromuscular contacts preserved.

An immunocytochemical study of the proliferating cell nuclear matrix antigen p125/6.5 during rat spermatogenesis

In previous studies of proliferating mammalian cells a p125/6.5 nuclear matrix antigen displaying a marked increase in mitotic cells has been identified. This antigen was investigated by immunocytochemistry of cryosections of testes at different stages of postnatal development: newborn, 20 days after birth and sexually mature rats. In Sertoli cells, the distribution of the p125/6.5 antigen parallels [3H]thymidine incorporation: present in newborn and absent in sexually mature testes. The p125/6.5 antigen is present also in some prespermatogonia of the newborn rat testis, which do not incorporate [3H]thymidine. At later stages of development, the p125/6.5 antigen is present also in first meiotic prophase spermatocytes displaying an extrachromosomal nucleoplasmic distribution, while absent in spermatids and spermatozoa. These results show that the p125/6.5 antigen increases not only during mitosis, but also during meiosis. They suggest further that this antigen is characteristic of both proliferating cells and cells (prespermatogonia) committed to proliferation.

Ontogeny of the novel tachykinins neurokinin A, neurokinin B and neuropeptide K in the rat central nervous system

Neurokinin A, neurokinin B and neuropeptide K content has been measured in several regions of the rat central nervous system at different stages of postnatal development. For this, we have employed a combination of HPLC separation and radio-immunoassay detection using a neurokinin A antiserum which also recognizes neurokinin B and neuropeptide K. All 3 tachykinins were detectable during postnatal development in the various regions studied (hypothalamus, striatum, substantia nigra, cerebral cortex and spinal cord). Interestingly, a general increase in the tachykinin concentrations was observed during the second week of life. Some of these concentrations reached values on postnatal day 15 which far exceeded those observed in the adult. After day 15 most areas showed a slow decline in their tachykinin content until adult values were finally achieved. The developmental profiles obtained for these tachykinins are in good agreement with previous studies on the ontogeny of substance P and its receptors and support the view that tachykinins may play an important role in the organization and maturation of the developing central nervous system.

Somatostatin expression in the cerebellar cortex during postnatal development

The distribution of somatostatin-immunoreactive (SOM-IR) elements in the cerebellar cortex of the rat has been studied at different stages of postnatal development (from birth to day 30) and in adult animals using immunohistochemistry. The results showed that in vermis of new born animals there are three main groups of SOM-IR structures within the cortex which subsequently spread along the Purkinje cell layer. In addition, both in the vermis and in the lateral lobes, numerous more evenly distributed SOM-positive cells and fibers could be seen. SOM-IR Golgi cells, Purkinje cells and climbing fibers could then be recognized during the subsequent developmental stages. In the vermal zone, SOM-IR Purkinje cells formed patches, which seemed to be part of a sagittal columnar or band-like organization. This was most obvious between days 5 and 21 of postnatal development. Subsequently there was a reduction in the number of immunoreactive Purkinje cells but a patchy disposition remained. In addition high numbers of SOM-IR Purkinje and Golgi cells and also climbing fibers were identified in the flocculus and paraflocculus at all stages of development studied, and they were also seen in the adult rats in these regions. In the lateral lobes expression of SOM-like immunoreactivity (LI) decreased and almost completely disappeared in adult animals. The present results demonstrate that a SOM or a SOM-LI peptide can be transiently detected in many Purkinje and Golgi cells in the cerebellar cortex, suggesting a role in events related to developmental processes. However, in some regions and structures SOM-LI can be seen also in adult animals.

Developmental changes in the expression of rabbit left ventricular troponin T.

We examined cardiac troponin T (TnT) isoform expression in rabbit left ventricular myocardium at three different stages of postnatal development. Using sodium dodecyl sulfate gel electrophoresis (PAGE), we resolved five isoforms: TnT1, TnT2, TnT3, TnT4, and TnT5. TnT1 had the slowest electrophoretic mobility and TnT5 the fastest. The predominant isoforms were TnT2, TnT3, and TnT4. The relative amounts of TnT2, TnT3, TnT4, and TnT5 were examined in myocardium from three age-groups: 3 days (Group 1), 21-22 days (Group 2), and 99-109 days (Group 3). The amount of TnT2 relative to the total amount of TnT (determined by the ratio of the areas under the densitometric curves) decreased significantly (p less than 0.01) with age from 42 +/- 4% in Group 1 to 25 +/- 3% in Group 3. In contrast, the relative amount of TnT4 increased with age from 23 +/- 2% in Group 1 to 33 +/- 4% in Group 3 (p less than 0.01). The relative amounts of the other two isoforms change biphasically with development: TnT3 decreased from Group 1 to Group 2 and increased from Group 2 to Group 3. TnT5, a minor isoform, increased from Group 1 to Group 2 and decreased from Group 2 to Group 3. These developmental changes in troponin T expression may account for some of the maturational changes observed in the physiological and biochemical properties of the myocardium.

In vitro neurotoxicity of excitatory acid analogues during cerebellar development

The neurotoxic effects of the selective excitatory amino acid receptor agonists, quisqualate, kainate and N-methyl- d-aspartate, were studied in slice preparations of cerebellum from rats at different stages of postnatal development. With increasing age, (i) Purkinje cells became more vulnerable to kainate and quisqualate but remained insensitive to N-methyl- d-aspartate (up to 300 μM); (ii) Golgi cells became more sensitive to kainate, quisqualate and N-methyl- d-aspartate; (iii) granule cells became more sensitive to kainate, less sensitive to N-methyl- d-aspartate and remained unaffected by quisqualate (up to 100 μM), and (iv) basket and stellate cells and, up to 14 days of age, neurones of the deep cerebellar nuclei, became more vulnerable to kainate and quisqualate, but their sensitivity to N-methyl- d-aspartate stayed the same. The neurotoxicity of N-methyl- d-aspartate, but not that of kainate in 8-day-old cerebellar slices was prevented by 2-amino-5-phosphonovaleric acid; tetrodotoxin did not affect the toxicity of the agonists in 8-day-old or adult slices. The results with kainate are consistent with other studies indicating an insensitivity of the immature brain to its neurotoxic effects, but suggest that this property is not a peculiarity of kainate. Alterations in excitatory potency can explain some of the observed developmental changes. However, other observations cannot readily be accounted for on the basis of either changes in excitatory potency, the functional maturation of cerebellar circuits, changes in synaptic density, or the developmental appearance of Ca 2+ channels in susceptible cells, suggesting that additional factors play an important role in the neurotoxic effects of the excitants.

An HRP study of the cat's spinal respiratory motoneurones during postnatal development

The localization and morphology of spinal respiratory motoneurones (phrenic and intercostal) were studied in the cat by retrograde labelling using Horseradish Peroxidase (HRP), at different stages of postnatal development. At birth, the distribution of the phrenic and intercostal motoneurones in the cervical and thoracic ventral horn, respectively, is similar to that observed in adult animals. At birth, the phrenic and intercartilaginous motoneurone somata have respectively 60% and 40% of their adult volume, appearing much more developed than the motoneurones involved in the motor control of limbs. During postnatal development, the phrenic and intercartilaginous motoneurones undergo a characteristic sagittal elongation without evident modification along their transverse axes. From birth, the ratio of the somatic volume to that of its corresponding motor column markedly decreases inside of the phrenic column compared to the data obtained in the limb's muscle motor columns by other authors. Similar determinations in intercostal motor columns give intermediate values between those obtained from the phrenic column and from the motor system. These results indicate that the motoneurones innervating the respiratory muscles have some specific features of development.

The relation of neuromuscular synapse elimination to spinal position of rabbit and rat soleus motoneurones.

We have examined recent claims that neuromuscular synapse elimination occurs preferentially among motoneurones from the more rostral of the two spinal roots contributing to the soleus muscle of the rat. The number of synapses made by individual motoneurones contributing to the soleus muscles of the rabbit and rat were estimated at different stages of post-natal development. The assay was based on measurements of twitch tensions in response to stimulation of individual motor axons in ventral root filaments. Contrary to the previous claims, we found that synapses were lost by motoneurones passing through all contributing spinal roots in both the rabbit and rat. Furthermore, in both species there was little or no difference in the extent of synapse elimination associated with the various spinal roots.

Patterns of vascularization in the developing cerebral cortex.

The vascular system of the cerebral cortex can be adapted to changing metabolic requirements which occur during development. Apart from a purely nutritive function the intracerebral vessels influence embryonal gliogenesis and migration of neuroblasts. The internal vascularization of the cerebral cortex starts during embryonic development and continues until the postnatal period. The formation of new penetrating vascular trunks and intracortical capillary branching is terminated before global brain growth reaches a plateau. The information necessary to develop a vascular system designed for functional needs later in development may already be expressed in the basic fetal pattern. The formation of such a system is probably not under direct metabolic control. The cellular composition of the capillary tube changes with the developmental stage and the actual growth rate of the endothelial cells. In the cerebral cortex the maximal growth rate of capillaries proceeds in a regional- and lamina-specific manner according to a defined ontogenetic time-scale. The importance of a local factor in the regulation of vascular growth is strengthened by this observation. The vascular system of the cerebral cortex is evaluated using morphometry and reconstructions of serial sections at different stages of postnatal development. This study aims to provide a morphological basis which may help to define cellular mechanisms associated with vascular patterning during brain development.

Postnatal changes in dolichol-pathway enzyme activities in cerebral cortex neurons.

Neuronal perikarya were isolated from rat cerebral cortex at different stages of postnatal development. Membranes sedimenting at 100000 g were obtained from these neurons to study several glycosyltransferases of the dolichol pathway. Enzyme activities from stages before and during synapse formation were compared (days 5 and 15 respectively). Dolichyl diphosphate (Dol-P-P) N-acetylglucosamine, dolichyl phosphate mannose and dolichyl phosphate glucose synthases and the enzymes catalysing Dol-P-P-GlcNAc2Man9Glc3 formation were higher at day 15 of postnatal development. The glycosyl transfer of the latter compound to endogenous protein(s) as well as to a dinitrophenyl-heptapeptide was also measured. The activity was higher at day 15. Furthermore, the activity of dolichyl phosphate mannose synthase was also measured during the time when the number of synapses ceased to increase (day 36) and in the adult stage. The activity of dolichyl phosphate mannose synthase was higher at day 36 than at day 15, and declined in the adult stage. From these results it may be concluded that there is an increase in the glycosylation of asparagine-type glycoproteins during synapse formation in the neurons of the cerebral cortex.

Investigation of transcription in rat sympathetic neurons at different stages of postnatal development

Investigation of transcription in rat sympathetic neurons at different stages of postnatal development

Choline and ethanolamine phosphorylation in rodents as a function of age

The activities of choline kinase and ethanolamine kinase in rat and mouse liver and mouse kidney were evaluated at different stages of postnatal development. The activities were calculated as units per g tissue, units per mg protein and as units in the organ mass corresponding to 100 g body weight. Developmental variations were observed in the enzyme activities and in the ratio of ethanolamine kinase to choline kinase activity with age of animal. The weaning of animals was not accompanied by any marked and consistent changes in the kinase activities by all parameters in the liver of rat and mouse or kidney of mouse. The results obtained also support the possible distinction between the proteins catalyzing the phosphorylation of choline and ethanolamine.

Cytosolic thyroxine-binding protein and brain development

The properties of cytosolic thyroxine binding protein were studied in the cortex and cerebellum of the rat at different stages of postnatal development: 1. (1) Polyacrylamide-gel electrophoretic analysis showed that rat-brain cortex and cerebellum contain the same cytosolic thyroxine-binding protein which is very similar to the liver-corresponding entity. No changes in the electrophoretic mobility were seen during development in the 2 brain regions. In contrast, no defined triiodothyronine-binding component could be observed by the same technique. 2. (2) Kinetic analysis studies revealed that the equilibrium of binding is reached in ∼10 min whatever the brain region, the concentration of cytosolic protein and the stage of development. In all these cases saturation was obtained with the same thyroxine concentration (∼5 × 10 −7 M). Scatchard analysis also showed that whatever the experimental conditions, brain cytosolic protein contains a single class of thyroxine-binding sites with a K A of ∼8 × 10 7 M −1. 3. (3) Comparison of the K A during development showed that this constant remains unchanged from day 3 after birth until day 35 in both the cortex and the cerebellum. In contrast the number of binding sites significantly decreases in the cortex (∼2-fold; p < 0.001) from day 3 to 35 with an already significant decline from day 3 to 6 ( p < 0.001). In the cerebellum this decline was even more marked since almost no binding activity was left at adulthood. Comparison of cortex and cerebellum binding activities also showed that this latter region contains ∼ half the binding sites ( p < 0.001) at every stage of development studied.

The development of descending and dorsal root connections in the lumbosacral spinal cord of the postnatal rat

AbstractLight and electron microscopy were used to study degenerating axons and synaptic endings in the lumbosacral spinal cord at different stages of postnatal development in the rat. After dorsal root section (L5‐S1) or mid‐thoracic hemisection of the spinal cord (T6‐T8), the distribution and type of degeneration argyrophilia were studied with the light microscope over varied post‐operative survival periods using a modified Fink‐Heimer method (Leonard, '74). The light microscopic results were correlated with the appearance of electron dense degeneration seen using the electron microscope.The distribution of degeneration found in the lumbosacral spinal cord after dorsal root section was similar at the neonatal (4d), weanling (21d) and adult stages. At the neonatal stage, the type of degeneration argyrophilia appeared at an earlier postoperative survival period (12 hours), and was maximal at an earlier time (12‐18 hours) than in older animals. The appearance of electron dense degeneration using the electron microscope matched the light microscopic findings. Electron dense degenerating synaptic knobs were found at the neonatal stage making asymmetrical contact with small dendrites in areas of the dorsal horn showing degeneration argyrophilia.No degeneration was found in the dorsal funiculus, dorsal horn or intermediate nucleus of Cajal (INC) after mid‐thoracic hemisection at the neonatal stage although degeneration was present elsewhere in the intermediate gray, in the ventral gray, and in the ventral and lateral funiculi. At this stage, the type of degeneration argyrophilia and time course of degeneration in the gray and white matter was identical to that found after dorsal root section in neonatal animals. The distribution of degeneration was not mature in the lumbosacral enlargement until 15d of age and the degeneration was still immature in the dorsal horn and INC at 21d of age.Although degeneration argyrophilia and electron dense degeneration was found in the ventromedial gray (lamina VIII) and lateral gray (laminae VI‐VII) at the neonatal stage, electron dense degenerating synaptic knobs were not observed in these areas until 12d of age for the ventromedial and 18d of age for the lateral gray matter even using a large number of different survival periods.Degenerating synaptic endings were first observed after mid‐thoracic hemisection during the period when behavioral maturation is nearing completion in the hindlimbs, and when response depression (spinal shock) increases and response recovery decreases after mid‐thoracic spinal transection (Weber and Stelzner, '77). Our data suggest that either the number of connections from descending sources increases markedly in the gray matter of the lumbosacral spinal cord during this period or connections, already present, reach a state of maturity where they can first be observed using the degeneration method of analysis.

Functional development of the dorsolateral prefrontal cortex: An analysis utilizing reversible cryogenic depression

The dorsolateral prefrontal cortex of rhesus monkeys was functionally inactivated by local hypothermia as the monkeys performed spatial delayed-response and spatial delayed-alternation tasks at different stages of postnatal development. Cryogenic depression of prefrontal cortex at a temperature sufficient to induce 21–25% decrements in delayed-response performance in 34–36-month-old monkeys, produced deficits of only 7–8% in 19–31-month-olds and no detectable loss in younger monkeys, 9–16 months of age. Delayed-alternation performance was impaired by local hypothermia as early as 8.5 months of age, but maximal cooling-induced deficits on this task were not observed before 33 months of age. Thermal gradients mapped in representative monkeys at different stages of development were remarkably similar, indicating that the age-dependent differences in behavior were not attributable to technical factors. The results obtained in the present study on normal developing monkeys confirm the interpretation of previous research on brain-damaged infants that functional maturation of the dorsolateral prefrontal cortex is protracted over several years of postnatal life, and extends the earlier studies by indicating that the lower limit for maturity of dorsolateral function is close to puberty in this species. Further, the present study revealed that delayed-response and delayed-alternation performance are dissociable dorsolateral functions which achieve maturity at different rates. The convergence of evidence from reversible neural depression and permanent lesion methods provides strong validation for neurobehavioral analysis as a general approach to the study of regional maturation of the brain.

Formation of the accessory apparatus of chemical sensation in the rat tongue during development: A scanning electron microscopic investigation

The formation of the accessory apparatus for chemical sensation in the rat tongue during ontogeny was studied by scanning electron microscopy. Different chemically sensitive structures in the tongue were found to mature at different times, possibly in connection with changes in the dietary pattern at different stages of postnatal development.

Localization of actin and myosin in the rat oocyte and follicular wall by immunofluorescence

The distribution of actin and myosin in the rat ovary at different stages of postnatal development was studied by examination of cryostat sections treated with antibodies to chicken smooth muscle (gizzard) myosin or to chicken (pectoral muscle) actin and subsequently with fluoresceinated goat anti-rabbit gamma-globulins. Staining with either antiserum revealed several layers of intensely fluorescent elongated cells within the theca externa, forming a coherent band around the larger Graafian follicles. In smaller follicles, this band of fluorescent cells was incomplete, and ovaries of immature (6-day-old) rats were devoid of strongly fluorescent cells. Corpora lutea contained only scattered fluorescent cells at their circumference. Sections of mature ovaries incubated with antibodies raised against striated (pigeon pectoral) muscle myosin generated no significant fluorescence. Large oocytes stained with either anti-actin or anti-smooth muscle myosin showed a thin fluorescent band just beneath the zona pellucida, suggesting that actin and myosin are associated with the oolemma. The distribution of the two antigens in serial sections of follicles coincided, suggesting that the same cells contained both actin and myosin. It is suggested that follicular growth and maturation is attended by the development of a smooth muscle layer in the theca and that contraction of this layer in response to catecholamines and/or prostaglandins may play a role in the extrusion of the oocyte. The role of contractile elements in the oocyte remains to be elucidated.

Postnatal study on the histochemistry of epididymis in buffalo (Bubalus bubalis).

The histochemical localisation and development of carbohydrates, acid mucopolysaccharides, lipids and desoxyribonucleic acid has been determined in the head, body and tail segments of buffalo epididymis at different stages of postnatal development from 3-76 weeks of age. The cytoplasm contains numerous Schiff-positive, diastase-resistant granules which are abundant in the apical region of the epithelial cells at 3-52 weeks. They decrease in number at 72-76 weeks and instead, a diffuse Schiff-positive material is observed in the cytoplasm of the cells, particularly in regions III-VI of the epididymis. In all the stages of development, the basement membrane and the luminal border of the epithelial cells have strong PAS-positive reaction. The intertubular connective tissue is mildly PAS-reactive, with moderate activity on the endothelial lining and smooth muscles of blood vessels. The capsule shows an intense Schiff-positive material in the fibers while the stereocilia are mildly reactive. PAS activity is less in region I and greater in regions V-VI as compared with the other regions of the epididymis. A moderate quantity of lipids is present in the epithelial cells and smooth muscles of the tubules. Sudanophilia is more pronounced in the tail region as compared with the head and body regions of the epididymis. Acid mucopolysaccharides are present, minutely, in the epithelial cell cytoplasm, with moderate activity on the stereocilia of the tubules. The Feulgen reaction is deep in region I and light to moderate in the other regions of the epididymis.

Histochemical study of ubiquinones in the central nuclei of the cerebellum of the mouse during its development.

For a histochemical study of ubiquinones in newborn and adult mice, the hydroquinone-tetrazolium-reductase reaction was performed in cryostat serial sections of the central cerebellar nuclei. This enzyme was studied in various structures at different stages of postnatal development. The present study shows that in the central nuclei the ubiquinones display less activity during development than in the adult mouse. The histochemical maturation is slow as compared with Purkinje cells, the rest of the molecular layer, the motor nuclei of the brain stem and the anterior horns of the medulla. The relationship of these histochemical findings and the metabolic significance of changes in the patterns of ubiquinones is discussed.

Dye permeability and alkaline phosphatase activity of testicular capillaries in the postnatal rat.

Staining of testicular and epididymal tissues after intravenous, intraperitoneal or subcutaneous administration of a number of dyes was investigated in rats at different stages of postnatal development. After light green injections heavy staining of both testis and epididymis was visible to the naked eye in neonatal animals up to the age of 10 days, while in rats over 15 days old no appreciable staining of the testis could be seen, although the caput epididymis was strongly coloured. From 3–8 hours after subcutaneous acriflavine administration, the nuclei in the blood vessel walls of the testis, as well as the nuclei in the rete testis, tubuli efferentes and caput epididymis, fluoresced in all age groups. The nuclei of the interstitial and tubular cells were stained intensely until the age of 5 days. Thereafter the intensity gradually diminished until the age of 20 days, when no nuclear fluorescence was visible in the seminiferous tubules and even the interstitial nuclei fluoresced weakly or not at all. The histochemical alkaline phosphatase activity of the testicular capillaries was studied by Gomori's method, using fresh and postfixed cryostat sections from postnatal rat testes. The testicular capillaries exhibited appreciable activity at the age of 10 days. On the basis of the present and previous observations on the permeability of the testicular capillaries, the existence of a blood-testis barrier in the puberal and adult rat testis is suggested. Development of the blood-testis barrier and the alkaline phosphatase activity of the testicular capillaries are suggested to reflect general vascular maturation at the beginning of puberty in the rat.