Adenylate cyclase activity in rat submandibular gland during postnatal development

Adenylate cyclase activity was measured in homogenates of submandibular glands of 1 to 42 day old rats. During this period of time the gland reached its final stage of differentiation. Adenylate cyclase activity was higher in the glands of one day old rats than in those of 7 and 14 day old animals. Between 14 and 28 days of age the enzyme activity more than doubled and approached the level that characterized the glands of adult animals. Fluoride (10mM) stimulated the enzyme activity in all age groups but the stimulation was less in the case of one day old rats as compared to older animals. Isoproterenol (10^?4 M) stimulated adenylate cyclase by 50–60% in the gland of adult rats but had no effect on the enzyme activity in 7 to 28 day old animals. Administration of isoproterenol for 5 days to 9 day old rats increased the weight of the submandibular gland by 70 per cent. Total adenylate cyclase activity increased parallel with the weight of the gland but the specific activity of the enzyme remained unchanged. It is concluded that during the postnatal development of the submandibular gland the rapid increase in adenylate cyclase activity occurs after weaning and it coincides with an accelerated rate of functional differentiation of the acinar cells.     

Formation of "caudate spindles" in the rabbit sensomotor cortex during ontogeny

Electrical activity of the sensomotor and visual areas of the neocortex during stimulation of the caudate nucleus was recorded in young rabbits aged 3–60 days and in adults. Single stimulation of the caudate nucleus was found to cause the appearance of characteristic bursts of spindle-like rhythmic activity ("caudate spindles"), described previously in cats and monkeys, in the adult rabbit cortex. The latent period of the caudate spindle was about 200 msec, its duration 1–3 sec, and the frequency of its oscillations of the order of 12 Hz. Caudate spindles were most marked in the sensomotor cortex of the ipsilateral hemisphere. In rabbits under 10 days old caudate spindles were not found even if the intensity of stimulation was increased many times. Starting from the age of 15 days bursts of rhythmic activity resembling caudate spindles, but with lower frequency (about 8 Hz), longer latent period (up to 350 msec), and also with a higher threshold, appeared in the sensomotor cortex. The definitive type of caudate spindles was established toward the end of the first month of postnatal life, corresponding to the time of formation and complication of conditioned-reflex activity in developing animals.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 11–15, March, 1985.     

Functional Role of Cerebellar Purkinje Cells in Ontogenesis of Postural-Motor Reactions in Mature- and Immature-Born Mammals

In experiments on guinea pigs, cats, and rats of different ages, from newborns to adults, the postural and stato-kinetic reflexes were studied with subsequent recording of electrical activity of identified cerebellar Purkinje cells (PC) in the same animals. Simultaneously in same age group of the animals, a morphometrical study of the shape and size of Purkinje cells and their nuclei was carried out. The first signs of manifestation of reflexes of standing and of the support reaction were observed in mature-born guinea pigs as early as at the first day after birth. At this time the PC fire has an irregular and low-frequency character with long inhibitory pauses and a great dispersion of the frequency-time characteristics. In the course of postnatal ontogenesis the parameter of the ratio of frequencies of simple and complex spikes increased in all the studied animals, guinea pigs, rat puppies, and kittens, but to different degrees. The complete maturation of the PC activity in the mature-born guinea pigs took 3–4 weeks after birth, whereas in the immature-born rat puppies and kittens this process took, on average, 5–6 and 8–9 weeks, respectively. By this time, all the studied postural-motor reactions were formed. The comparison of the course of formation of the frequency-time characteristics of the Purkinje cell activity in mature- (guinea pigs) and immature-born (rats and cats) animals allowed establishing that the highest rate of maturation of the Purkinje cell activity in the mature-born animals is observed during the first half, whereas in immature-born animals, during the second half of postnatal ontogenesis. A similar rate of changes also took place at maturation of postural-motor reflexes. The complete functional maturity of the Purkinje cell occurred, as a rule, at the time period when the shape and size of the Purkinje cell body became close to the definitive ones, and their vertical and horizontal diameters reached the values characteristic of adult animals.     

Temporal and spatial dimensions of postnatal growth of the mouse urinary bladder urothelium

Postnatal growth and renewal of mouse urothelium start on the day of birth. In the present study, temporal and spatial dimensions of urothelial growth were studied during the first two postnatal weeks. Quantitative analysis showed that the rate of urothelial cell proliferation is significantly higher during all 14 postnatal days than in adult mice. Three peaks of proliferative and mitotic activity were revealed: on the day of birth and postnatal day 1, on days 6 and 7, and on day 14. The high proliferation rate around the day of birth and at postnatal days 6 and 7 coincides with cell death in the urothelium. Semiquantitative analysis showed that during all 14 postnatal days, the urothelial proliferative response is mostly confined to the basal cell layer. Urothelial cells divide predominantly in parallel to the plain of the urothelium on all chosen postnatal days. Increased portions of urothelial cells, dividing perpendicularly to the urothelium were observed only on the day of birth and on postnatal day 7. Our results suggest that postnatal growth of mouse urothelium is particularly the result of an increasing number of cells in individual cell layers and not the result of an increasing number of cell layers.     

Age-related changes in nitroxidergic neurons in some nuclei of rat medulla oblongata

The paper presents a comparative study of NO neurons in the solitary tract nucleus, giant-cell, and lateral reticular nuclei in rats at 4, 7, 10, 14, 30, 45, and 60 days old and 3, 6, 12, 18, 24 months old. We determine the active quantitative and qualitative changes that occur in NO-positive neurons in the studied nuclei during the course of postnatal development. A low level of enzyme activity is observed on the first day; it reaches a peak level around the first-third month, then slowly declines. The size and number of nitroxidergic neurons increases, while the relative cell density decreases until the third month of life. We reveal local differences in the ontogenetic development of NO neurons in the studied nuclei. Solitary tract neurons have the highest rate of development, while NO neurons of old animals undergo early and extreme changes as compared to other studied nuclei of rat medulla oblongata.     

The development of histochemically demonstrable cholinesterases in the rat neostriatum in vivo and in vitro

Summary The development of acetylcholinesterase (AChE) and non-specific cholinesterase (NsChE) activity was studied in the rat neostriatum by the light and electron microscope using three thiocholine methods. The AChE activity was first demonstrable only in the lateral parts of the nucleus, and during the early postnatal development the most intense activity was in the cell bodies, whilst the typical intense staining of the neuropil of adult animals was seen in two-week-old rats. Two types of AChE-containing cells were observed in the neostriatum of rats younger than two weeks and in cultures of newborn rat neostriatal cells. The neuropil of the cultures showed weak activity in the membranes of thin preterminal processes. In the neuropil of old rats, NsChE activity was present in the membranes of nerve cell processes. The capillary endothelial cells of newborn rats contained both AChE and NsChE. During subsequent development, the AChE activity disappeared, whilst for NsChE no change was seen in the distribution of activity seen in newborn or young adult rats less than three months old.     

Variable effect of ghrelin administration on pancreatic development in young rats. Role of insulin-like growth factor-1.

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor, has been primarily isolated from the human and rat stomach. Ghrelin has been shown to stimulate appetite and fat deposition in adult rats and humans. The aim of this study was to investigate the effect of ghrelin administration on pancreatic growth in suckling, weaned and peripubertal seven week old rats. Rats were treated with saline or ghrelin (4, 8 or 16 nmol/kg/dose) intraperitoneally twice a day: suckling rats were treated for 7 or 14 days starting from the first postnatal day, three week old weaned rats and seven weeks old rats were treated for 5 days. Treatment with ghrelin did not affect animal weight in suckling or weaned rats, whereas in young seven week old rats, ghrelin caused a significant increase in body weight. Ghrelin decreased food intake in weaned rats; whereas in seven week old rats, food intake was enhanced. In suckling rats, ghrelin decreased the pancreatic weight, pancreatic amylase content, DNA synthesis and DNA content. In contrast, ghrelin increased pancreatic weight, DNA synthesis, DNA content and amylase content in weaned or young seven week old rats. Pancreatic blood flow was not affected by ghrelin in any group of rats tested. Ghrelin increased serum level of growth hormone in all rats. This effect was weak in suckling rats, higher in weaned and the highest in seven week old animals. Ghrelin did not affect serum level of insulin-like growth factor-1 (IGF-1) in suckling rats. In weaned and in seven week old rats, treatment with ghrelin caused increase in serum level of IGF-1. We conclude that ghrelin reduces pancreatic growth in suckling rats; whereas in weaned and young seven week old animals, treatment with ghrelin increases pancreatic growth. This biphasic effect of ghrelin in young animals on pancreatic growth seems to be related to age-dependent changes of the release of anabolic IGF-1.     

The development of histochemically demonstrable cholinesterases in the rat neostriatum in vivo and in vitro

The development of acetylcholinesterase (AChE) and non-specific cholinesterase (NsChE) activity was studied in the rat neostriatum by the light and electron microscope using three thiocholine methods. The AChE activity was first demonstrable only in the lateral parts of the nucleus, and during the early postnatal development the most intense activity was in the cell bodies, whilst the typical intense staining of the neuropil of adult animals was seen in two-week-old rats. Two types of AChE-containing cells were observed in the neostriatum of rats younger than two weeks and in cultures of newborn rat neostriatal cells. The neuropil of the cultures showed weak activity in the membranes of thin preterminal processes. In the neuropil of old rats, NsChE activity was present in the membranes of nerve cell processes. The capillary endothelial cells of newborn rats contained both AChE and NsChE. During subsequent development, the AChE activity disappeared, whilst for NsChE no change was seen in the distribution of activity seen in newborn or young adult rats less than three months old.     

Differing postnatal development of the somatostatin- and luliberin- systems in the male and female rat

By means of light-microscopic immunohistochemistry the perikarya of the luliberin-(LRF-) and somatostatin systems of neonate rats were found to be in differing stages of development. At a time point when the LRF-producing neurons had obviously attained their final shape and size, the somatostatin-immunoreactive perikarya were still in a postnatal phase of maturation. Whereas the number of the latter perikarya increases with advancing age, the number of LRF-immunoreactive perikarya decreases significantly from postnatal day 7 onward. Both peptide-hormone systems do not project concomitantly and to the same extent to their principal neurohemal regions in the organum vasculosum laminae terminalis (OVLT) and the median eminence (ME). In all presently studied stages of development, despite considerable individual variations in one age group, among the components of the LRF-system the OVLT displays a more intense immunoreactivity than the ME. The somatostatin system, however, projects to the OVLT with a conspicuous temporal delay compared to the ME, and, furthermore, in the OVLT the pattern of immunoreactivity characteristic of adult rats is not yet attained at postnatal day 21. Evidence for differences in the immunoreactivity between male and female animals was restricted to the LRF-system. Finally, the results obtained on the stria terminalis speak in favour of the fact that the long-range extrahypothalamic projections of the somatostatin system also undergo postnatal maturation. In the stria terminalis, somatostatin-immunoreactive fibers can be demonstrated initially on postnatal day 7. They attain their full immunoreactivity on postnatal day 21. Furthermore, in the bed nucleus of the stria terminalis an intermittent cytoplasmic immunoreactivity is observed, which is limited to the animals of postnatal day 7 and disappears completely during the further course of development.     

Formation and maturation of axo-glandular synapses and concomitant changes in the target cells of the rat subcommissural organ

Synapse formation and maturation in the subcommissural organ (SCO) of Wistar rats were studied from birth to the end of the first month. Modifications of the secretory ependyma were analyzed over the same period. On the 1st postnatal day, the large varicosities in contact with the SCO ependymocytes appeared immature (absence or low density of vesicular population, no synaptic membrane differentiation). The synaptic contacts were formed from the 3rd postnatal day, near the glandular cell nuclei (0.1 micron distance); progressively, the content of the axonal boutons and the pre- and post-synaptic specializations became similar to those of adults. From the 21st day on, the axo-glandular innervation was considered analogous to that in the adult. Using immunocytochemistry, it was found that the increase in the serotonin-immunoreactive fiber density in the whole organ was time-dependent. Light and electron microscopy demonstrated changes in the morphology of SCO ependymocytes during the first postnatal weeks, notably in the endoplasmic reticulum and content ot apical protrusions. On postnatal day 14, two types of ependymal cells, neonatal-like and adult-like, coexisted. The evolution of SCO ependymocytes coincided with the progressive onset and maturation of axo-glandular innervation taking place after birth.     

The formation of predatory aggressiveness in the ontogeny of rats

In tests on outbred male rats the problem was studied of the existence of "sensitive periods" in the formation of rats predatory aggression. Breeding of small rats together with mice from the first till 60-th postnatal day considerably inhibits their muricidity in the adult age, what is manifest in tests of predatory aggressiveness till the 270-th day of rats life. Breeding of mice together with rats in the age of 1-20, 20-40, 40-60 and 20-60 postnatal days does not influence significantly their muricidity. Antiaggressive effect of breeding of mice with adult rats from the 150-th to the 210-th day is a short-term one, and breeding of mice with old rats in the age of 540-600 postnatal days does not significantly effect the muricidity.     

Establishment of the afferent function of the striatum in the rabbit during early ontogenesis

The study is dedicated to electrophysiological analysis of development of the caudate nucleus afferent function in rabbits in early postnatal ontogenesis. By amplitude-temporal parameters of the evoked potentials (EPs) of the caudate nucleus, recorded in response to stimulation of afferent inputs from the cortical regions (motor and limbic) and substantia nigra, similar dynamics of these afferent pathways functional maturation is revealed from the beginning of functioning (in the age of 3-5 days) to the definitive level (by the 30th day of life). The most significant changes of the amplitude-temporal parameters of the evoked potential, particularly of latencies are observed during the 3d week of postnatal life. On the basis of the obtained data, the conclusion is made on the formation of a common system of striatum sensory integration in the 3d-4th week of rabbits life. This age period is considered as critical.     

Disturbances in Formation of the New and Old Cortex at Changes of Conditions of Embryonic Development

Using a model of acute hypoxia during pregnancy of rats, changes in the development of old (hippocampus) and new (sensorimotor) cortex associated with disturbance of neuronogenesis have been revealed in the studied brain structures at the period of action of a pathological factor. It was found that in rats submitted to hypoxia at the 13–14th days of embryogenesis, the number of degenerating neurons (including the pyramidal ones) at various levels of chromatolysis increased since the 5th day after birth; the increase was present for the entire first month of postnatal development. In the cortex of rat pups submitted to prenatal hypoxia there were observed deformation of neuronal bodies, vacuoles in the cytoplasm, shrinkage of apical dendrites of pyramidal neurons and delayed development of the structure (time of the appearance of spikes, formation of structural elements and the size of the cells) of the nervous tissue of the brain of the rat pups exposed to prenatal hypoxia. The columnar structure of the cortex was disturbed. In hippocampus, the process of degeneration of neurons started by 2–3 days later than in the cortex; by two weeks of postnatal development a massive degeneration and death of a part of neurons were also revealed. The morphometrical analysis showed a decrease in the number of neurons and their total area in the sensorimotor cortex (the layer V) and an increase in the number of glial elements at the 10–17th days after birth. In the hippocampus a decrease in the area occupied by neurons and in their size was detected in adult animals. The adult rats submitted to prenatal hypoxia were found to have disturbances of memory and learning. A correlation was shown between the disturbances of the conditions of embryonic development and the changes in the ability of learning and storage of new skills in the offspring.     

Role of the monoaminergic system in the transmission of the effect of androgens on neurons of separate limbic structures of the rat brain

By means of the histochemical method intensity of monoamines fluorescence has been studied in 3-, 5-, 7-, 10-, 20-, 30- and 60-day-old intact and neonatally androgenized female rats. The neonatal androgenization increases fluorescent intensity of monoamines in the neuropil of the adjoining nucleus of the septum, of the nucleus in the terminal stripe bed and the caudate nucleus. This is especially evident on the 3d, 7th and 30th days. On the 5th day of the postnatal life the difference in fluorescent intensity of monoamines in the brain of control and test animals is statistically insignificant. Possible mechanisms responsible for the fluorescent intensity of monoamines and the role of the latter in transmitting the sex hormones effect to the neurons of the forebrain structures investigated are discussed.     

Postnatal development of conditioned reflex behavior: comparison of the periods related to the onset of the different forms of hippocampal plasticity in rats

Fear conditioning, escape and active avoidance reactions in two-way avoidance paradigm were compared in rats of different ages. Fear conditioning, but not escape and active avoidance reactions could be acquired on the 16-17th postnatal days, and the acquisition was more effective than in adults. Escape behavior matured beginning from the 18th postnatal day reaching the adult level within the 3d-4th postnatal weeks. Maturation of the mechanisms of Pavlovian (fear reaction) and instrumental (escape reaction) conditioning did not facilitate the acquisition of two-way avoidance until the 4th postnatal week, young animals displayed low acquisition in this period. The maturation of these memory processes is proposed to be related to developmental stages of different mechanisms of hippocampal plasticity.     

Neurophysiological analysis of postnatal development of corticostriate connections in rabbits

Evoked potentials were recorded in the caudate nucleus of adult rabbits and young rabbits aged 2–30 days in response to stimulation of the ipsilateral motor cortex. The response of the caudate nucleus in the adult rabbit consisted of a positive-negative complex with latent period of 3–5 msec. Maximal amplitude of the response was observed in the dorsorostral region of the nucleus. As the recording electrode was inserted deeper, the amplitude of the response gradually decreased but without reversal of its polarity. Responses of the caudate nucleus to stimulation of the motor cortex were recorded as early as on the 3rd day after birth. These responses were indistinguishable in configuration from responses of the nucleus of adult rabbits. Their latent period was about 10 msec. Between the 16th and 20th day after birth the latent period of the response decreased considerably — from 9 to 5 msec, and by the 30th day of life it had reached its definitive value. With age the amplitude of the response increased but the threshold of stimulation decreased, The results indicate early functional maturation of connections of the motor cortex with the caudate nucleus and they agree with the results of morphological investigations of the structural development of the afferent systems of this nucleus.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 284–289, May–June, 1982.     

MORPHOLOGICAL AND BIOCHEMICAL CHANGES IN RAT SYNAPTOSOME FRACTIONS DURING NEONATAL DEVELOPMENT

A biochemical and quantitative morphologic study of presynaptic endings during postnatal development was carried out in subcellular fractions from cerebral cortex of 1, 4, 8, 12, and 18 day old and adult rats. Crude mitochondrial fractions were subfractionated in Ficoll gradients and all resulting fractions were examined in the electron microscope. Presynaptic terminals and other intact processes were counted. Protein content and enzyme activities were assayed in the fractions and in total brain homogenate. In the first and fourth day of life, most of the presynaptic terminals were found in two "light" fractions, between supernatant and 7.5% Ficoll, where they accounted, respectively, for 6 and 22% of all the processes. Progressively with age, more presynaptic terminals were found in the traditional "synaptosomal" fractions between 7.5 and 13% Ficoll. In that region of the gradient, 40, 54, 75, and 89% of the processes were presynaptic endings at 8, 12, and 18 postnatal days and in the adult animal, respectively. A similar shift from the lighter to the heavier fractions was observed in the distribution of choline acetyltransferase and acetylcholinesterase between days 8 and 12. The rate of increase of the specific activity of these two enzymes paralleled that of the percentage of the presynaptic endings after day 8. This study indicates that subcellular fractions can be used to study formation and maturation of synapses during postnatal development.     

The expiration reflex during ontogenesis in the rat.

The authors studied the elicitability of the expiration and aspiration reflex and of the respiratory reaction from the tracheobronchial area in 131 anaesthetized rats (aged 1-15 days, adult and biologically old). They found that the expiration reflex could be elicited, in the rat, from the first day of life, at a time when other respiratory reflexes were not yet stable. In young rats, the expiration reflex was often followed by a cough reaction which was absent in adult animals. The findings indicate that the expiration reflex is one of the most important respiratory reflexes of the early postnatal period in the rat, because the aspiration reflex and the respiratory reaction from the bronchi were not stable until the 15th day of life. In biological old rats, the expiration reflex is less frequently elicited and its intensity attains about half the value found in adult animals. The aspiration reflex and the respiratory reaction from the bronchi are likewise less readily elicited than in adult animals, but when the intensity of their maximum expiratory effort is increased, it is far greater.     

Ⅰ型囊泡膜谷氨酸转运体在生后发育大鼠三叉神经运动核中的表达

目的观察Ⅰ型囊泡膜谷氨酸转运体在大鼠三叉神经运动核生后发育过程中的表达变化。方法取生后不同发育阶段大鼠脑干,行冰冻切片和Ⅰ型囊泡膜谷氨酸转运体免疫染色,光镜观察。结果刚出生大鼠三叉神经运动核背外侧部即可以观察到Ⅰ型囊泡膜谷氨酸转运体免疫染色阳性结构,随着发育进展,免疫染色阳性逐渐增加,出生7天后Ⅰ型囊泡膜谷氨酸转运体免疫染色模式接近成年水平。结论大鼠三叉神经运动核内Ⅰ型囊泡膜谷氨酸转运体阳性终末在出生后1周内较快地成熟。