Development of interscapular brown adipose tissue in the hamster. II - Differentiation of transplants in the anterior chamber of the eye: role of the sympathetic innervation

The relationship between brown adipose tissue (BAT) and its sympathetic innervation during development was investigated by transplantation of undifferentiated (white fat-like) hamster BAT into the anterior eye chamber of adult hamsters. Such transplants are known to be revascularized and reinnervated by the vessels and the nerves of the host iris. The morphology of the BAT transplants was analysed during the post-operative weeks by light and electron microscopy, and the ingrowth of sympathetic nerve fibres from the iris was followed by radioautography. BAT appeared to differentiate in oculo, i.e. presented increasing amounts of adipocytes with multilocular fat deposits and abundant, well-developed mitochondria, but only after a delay of approx. 10 days, and remained much fatter than in situ. The establishment of the sympathetic innervation was not synchronous with the revascularization process. It occurred simultaneously with the morphological differentiation of the BAT transplants, and the nerve fibre density remained low. In the absence of sympathetic innervation, i.e. when the host irides were sympathectomized prior to transplantation, BAT still differentiated, but the process was further delayed and the proportion of differentiated brown adipocytes after 20 days in oculo was clearly lower than in control transplants. It is concluded that the sympathetic innervation in BAT is involved in the regulation of differentiating activity in the tissue, but is not obligatory for differentiation to occur.

Autonomic nervous control of heart rate: sympathetic-parasympathetic interactions and age related differences

A factorial experimental design was used to quantify the changes in heart rate produced by stimulation of the cardiac sympathetic and vagal nerves in eleven adult dogs and four puppies, and to quantify the extent of the peripheral sympathetic-vagal interactions. The chronotropic responses to autonomic stimulation were significantly less in the puppies than in the adult dogs, which suggests that autonomic regulation is functionally incomplete in the puppies. In both adult dogs and puppies, the chronotropic responses to autonomic nerve stimulation were bilaterally asymmetrical. The heart rate responses to a given level of right-sided stimulation of either the sympathetic or vagal nerves were greater than those to comparable left-sided stimulation. In both adult dogs and puppies, there were significant sympathetic-vagal interactions, such that the sympathetic enhancement of heart rate was less effective the higher the background level of vagal activity. The sympathetic-vagal interactions were prominent in the puppies as well as in the adult animals, regardless of whether the stimulated sympathetic and vagal nerves were located ipsilaterally or contralaterally to one another. Thus, the mechanisms responsible for the sympathetic-vagal interactions appear to be fully developed in puppies. Also, the cardiac sympathetic nerve endings that originate from one side of the body must lie in close apposition to the cardiac vagal nerve endings that originate from either the same side or from the opposite side of the body.

[Axons of sympathetic neurocytes and their relation to lemmocytes during postnatal ontogeny in the rat]

The external carotid nerves have been studied electronmicroscopically in rats at the age of 1, 6, 13, 30 days and 5 months. The growth dynamic of diameter of the axons composing the nerve has been followed, as well as formation of glial membranes around them and quantitative changes of microtubules in the axons. During the first month of life, the average axonal diameter increases more than twice, the content of organells rises in them. Concentration of the microtubules is higher in thin axons (0.1--0.2 mcm), with increasing of their diameter it becomes lower. No correlation between concentration of the microtubules and age of the animal is noted. In newborn rats the glial membranes around the axons are nearly completely absent, by the end of the second week of life, most of the axons already have them. Sometimes, in one groove of the lemmocyte there can be seen several of them. By the first month of life, the axons are situated in individual grooves, this is specific for mature animals. In a 2-week-old rat one lemmocyte surrounds several dozens of axons, in a mature one--about 5--13.

Development of sympathetic innervation to proximal and distal arteries of the rat mesentery

The changes which occur during the post-natal development of sympathetic innervation to proximal and distal arteries of the rat mesentery have been examined using intracellular recording and histochemical techniques. In the youngest animals examined, single perivascular stimuli initiated slow depolarizing potentials which were not calcium-dependent. After day 4, single stimuli failed to initiate membrane potential changes in a proportion of preparations. This stage coincided with the period of extensive ramification of sympathetic nerve fibres over the surface of the arterioles. From day 9 onwards, membrane potential changes were again initiated by single stimuli in the distal arteries. These responses were distinct from those recorded from the younger animals and in many ways resembled excitatory junction potentials recorded from the arteries of mature animals. There was a gradient in the development of the innervation to the arteries of the rat mesentery, with that to the distal vessels maturing earlier than that to the more proximal vessels.

Development of cholinergic sympathetic neurons: evidence for transmitter plasticity in vivo

Most principal neurons in sympathetic ganglia are noradrenergic. A small population, especially those that innervate sweat glands in rat footpads, are cholinergic. We have characterized the innervation of the glands in adult and developing rats to determine whether sympathetic neurons undergo a transition from noradrenergic to cholinergic during normal development as has been observed in culture. In adult rats, the fibers innervating sweat glands exhibited strong acetylcholinesterase (AChE) staining and vasoactive intestinal peptide (VIP)-like immunoreactivity. None of the axons contained endogenous catecholamines detectable with formaldehyde-induced fluorescence or permanganate fixation. However, like cholinergic sympathetic neurons in culture, all axons could take up and store exogenous catecholamine. The sweat glands and their innervation develop postnatally. At 7 days, the axons innervating sweat glands possessed endogenous catecholamine histofluorescence and small granular vesicles but not AChE or VIP. By 14 days, AChE and VIP staining was pronounced. In contrast, catecholamine fluorescence and the number of small granular vesicles were reduced, and by 21 days they were absent. Further, neonatal treatment with 6-hydroxydopamine, a toxic norepinephrine congener, resulted in the loss of cholinergic as well as noradrenergic sympathetic innervation. These observations are consistent with a transition from noradrenergic to cholinergic function in vivo.

Maturation of sympathetic neurotransmission in the rat heart. IX. Development of transsynaptic regulation of cardiac adrenergic sensitivity

The number of beta adrenoceptors and the cardiac sensitivity to adrenergic stimulation increase substantially in the immediate postnatal period of the rat. To determine whether transsynaptic input influences this developmental process, the effects of a sympathomimetic and of agents which destroy noradrenergic nerve terminals on regulation of adrenergic postsynaptic sensitivity were compared in hearts from adult and developing rats. In mature animals, chronic exposure to the beta agonist isoproterenol (2.5 mg/kg s.c.) led to rapid onset (3-5 days) of chronotropic adrenergic subsensitivity accompanied by a loss of beta adrenoceptor binding sites; chemical sympathectomy by daily administration of guanethidine (50 mg/kg s.c.) or by 6-hydroxydopamine (100 mg/kg s.c. given once daily for 3 days) resulted in chronotropic adrenergic supersensitivity and increases in binding sites. These data in the adult agree with classical transsynaptic modulation of adrenergic postsynaptic reactivity. In contrast, identical drug treatments of immature rats beginning 1 day after birth failed to evoke changes in either chronotropic adrenergic sensitivity or in numbers of beta adrenoceptor binding sites until the 3rd to 4th week. Consequently, the initial development of beta adrenoceptors and responsiveness to catecholamines in the neonatal myocardium are not transsynaptically regulated; rather, other (e.g. hormonal) factors appear to control early maturation of cardiac adrenergic sensitivity.

Small intensely fluorescent (SIF) cells and sympathetic nerves in the adult rabbit portal vein and during perinatal development

The ontogenesis of small intensely fluorescent (SIF) cells and the adrenergic nerve plexus is described in stretch preparations of the rabbit portal vein. On the 25 to 26th days of gestation there was a predominance of SIF cells (8 to 30 microns in diameter), but a few nerve fibres in bundles were also present. Each portal vein preparation contained 6 to 9 groups of cells. The distribution and number of SIF cells and nerve bundles remained constant until the 31st day of gestation at which stage the number of SIF cells had decreased, while the density of the nerve plexus had increased approximately 4-fold. The adult portal vein exhibited a dense adrenergic plexus, but SIF cells were absent from nine out of ten preparations.

Abnormal functional development of sympathetic nerve terminal-smooth muscle complex in neonatal spontaneously hypertensive rats

In neonatal and young adult SH and WK rats, maturation of a functional unit consisting of sympathetic nerve terminals and smooth muscle (levator palpebrae) was assessed in vivo by measuring the contractile response to tyramine, an agent which releases endogenous norepinephrine from sympathetic nerve terminals. Responses in SH are comparable to WK at 5-6 days postnatally, smaller from the 8th through 19th day and larger in young adults (41-46 days old). Results indicate that functional maturation of the nerve terminal-smooth muscle complex is retarded in SH relative to WK during the 2nd and 3rd postnatal weeks. It is suggested that retardation in the neonatal SH rat is an expression of a genetic defect in the growth of the complex and that the enhanced response in young adult SH is a consequence of the neonatal abnormality.

Postnatal development of sympathetic innervation of rat brown adipose tissue reevaluated with a method allowing for monitoring flavoprotein redox state

1. A reflection spectrometric method was developed which allowed the simultaneous measurement of flavoprotein absorption and fluorescence on an in vitro preparation of brown adipose tissue. 2. From their spectral characteristics and from the effects of substrates and a metabolic inhibitor (amytal) it was shown that the absorption and fluorescence signals are associated with different flavoproteins. 3. The fluorescence signal is mainly due to changes in the redox state of NADH dehydrogenase, and the absorption signal to changes in redox state of he flavoproteins in the acyl-CoA dehydrogenase pathway. 4. The results suggest that changes in the flavoprotein redox state in response to electrical nerve stimulation, exogenous norepinephrine and substrate addition reflect changes in the metabolic activity of the tissue. These responses were studied in the postnatal period. 5. The amplitude of the tissue response to either nerve stimulation or norepinephrine administration is already maximal at birth and decreases in animals 50 days old. The frequency of nerve stimulation of the concentration of norepinephrine required to produce a half maximum response is significantly higher for the new-born as compared to 13 day and 50 day old animals. 6. For small stimulation intensities a steady state oxidation of the NADH dehydrogenase concomitant with a steady state reduction of the flavoproteins in the acyl-CoA dehydrogenase pathway was recorded. 7. It is concluded that in rats less than 12 hours old, brown adipose tissue is functionally innervated although previous histochemical studies had failed to detect nerve terminals containing catecholamines at this early age.

Binding, internalization, and retrograde transport of 125I-nerve growth factor in cultured rat sympathetic neurons

Sympathetic neurons internalize nerve growth factor (NGF) and transport it retrogradely to their cell bodies where it appears to serve a trophic function in maintaining neuronal survival. We have characterized the binding, internalization, and retrograde transport of 125I-NGF by cultured rat sympathetic neurons. After 3 to 4 weeks in culture, sympathetic neurons possessed approximately 2 X 10(7) specific, cell surface NGF binding sites per neuron with an apparent affinity constant of 2 to 5 X 10(9) M. The density of binding sites on the plasma membrane of the neurites approximately twice that on the plasma membrane of the cell bodies. Because of the extensive network of neuronal processes, the neurites probably account for more than 99.5% of the total binding in mature cultures. Using electron microscope autoradiography, we localized the distribution of 125I-NGF in the cell body following a 1-hr exposure to 125I-NGF. The majority of silver grains were associated with lysosomal organelles, including secondary lysosomes, residual bodies, and multivesicular bodies (MVB). The MVB were the most heavily labeled, with a labeling density (L.D.) of 21, while the lysosomes had a L.D. of 3.1. To study the retrograde transport of 125I-NGF, neurons were grown in compartmentalized culture dishes and their distal processes were exposed to 125I-NGF. Radioactive material was transported to the cell bodies at the rate of approximately 3 mm/hr. The transport mechanism was sensitive to colchicine and was saturable with respect to NGF. After 8 hr of transport, when the radioactivity in the cell bodies had reached a steady state, the label again was localized primarily to the MVB (L.D. = 16.8) and the lysosomes (L.D. = 3.8). The nuclei were not labeled significantly and had an overall L.D. of 0.47. We saw no evidence for the accumulation of NGF by the nuclear membrane, the nucleolus, or chromatin.

[Formation of the ultrastructure and adrenergic innervation of magistral vessel walls in chicken ontogenesis]

Histochemical and electron microscopic investigation on dynamics of ultrastructure and adrenergic innervation formation in the wall of the femoral artery and vein, in the mesenteric artery and vein and in the aorta has been performed in 10-20-day-old chick embryos and in chickens during first days of life. In the course of embryogenesis, myoblasts of the media tunica have been demonstrated to transform into highly differentiated and strictly specialized smooth muscle cells. Simultaneously, neural fibres from the periphery of the vascular wall gradually penetrate up to the border of the external tunica and tunica media and varicosities with axoplasmic vesicles appear along their course. Owing to these two processes, by the time of hatching, the vascular wall has possessed a certain morphological substrate for the neural-muscular relations.

Growth of sympathetic postganglionic axons after partial chemical destruction with guanethidine

Partial sympathectomy of neonatal rats was produced by treatment with guanethidine. The number of neurons of the superior cervical ganglion decreased to 15% of control values and remained constant throughout the subsequent observation period of 4 months. The volume of the remaining neuronal perikarya increased faster than that of control animals during the observation period, and the density of adrenergic innervation of the iris and the noradrenaline content of the heart were found to partially recover after the initial decrease produced by the guanethidine treatment, reaching 33% and 30% of control values, respectively, after 4 months. The noradrenaline content of the duct of the vas deferens was greatly reduced by guanethidine treatment, but almost recovered after 4 months. The frequency of sympathetic preganglionic impulses was elevated throughout the 4 months observation period, and it is suggested that this increase is responsible for the compensatory changes in cell volume, terminal density and terminal noradrenaline content of the remaining neurons.

[Development of extracardiac influences in the ontogeny of the dog]

Using pharmacological drugs, studies have been made on the development of sympathetic and parasympathetic innervation of the heart in ontogenesis of dogs. It is concluded that sympathetic and parasympathetic innervation operates already at the delivery of animals. Originally their effect is observed only as regulation of cardiac pacemakers, influences on the contractile properties of the heart being exerted in later ontogenesis.

Maturation of sympathetic neurotransmission in the rat heart. IV. Effects guanethidine-induced sympathectomy on neonatal development of synaptic vesicles, synaptic terminal function and heart growth

Sympathetic nerve input has been proposed to regulate cardiac growth and differentiation. In the present study, this hypothesis was tested by giving the neurotoxic adrenergic neuron blocking agent, guanethidine (50 mg/kg, s.c.), daily to rats for 21 consecutive days to produce long-term peripheral sympathectomy in neonatal rats. Ontogeny of the sympathetic nerve terminal was measured by the ablity of synaptic vesicle preparations to take up radiolabeled norepinephrine, and heart growth in the sympathectomized animals was monitored by organ weight as well as by RNA and protein synthesis. Guanethidine treatment produced a massive sympathectomy, as synaptic vesicle development was totally arrested; the functional consequence of this treatment was confirmed by the attenuation of chronotropic responses to tyramine, a drug which acts by displacement of norepinephrine from the noradrenergic terminal. Despite the clear-cut effectiveness of guanethidine to prevent formation of functional sympathetic innervation of the heart, no significant alterations in heart growth or RNA and protein synthetic capabilities were observed in the developing rats. These results suggest that the presence of sympathetic innervaton is not obligatory for normal growth of the heart to occur.

Ontogeny of mammalian cardiac alpha 1-adrenergic receptors

We find a similar number of alpha 1-adrenergic receptors in fetal mouse hearts of 15--20 day gestational age as compared to adult mouse hearts, and a significantly greater number of alpha 1-adrenoceptors in the early neonate (7--21 days) hearts. Cardiac norepinephrine (NE) concentrations were extremely low in the fetus and increased continuously after birth to reach adult levels at about 21 days of age. The cardiac alpha 1-adrenergic receptors mature prior to the development of a presynaptic component (NE) and show a dramatic increase in density without a change in affinity in the early neonate which then decreases with innervation.

Hormonal control of neurotransmitter choice in sympathetic neurone cultures

Manipulation of the cellular and hormonal environment of cultures of dissociated primary neurones can be used to explore a neurone's developmental potential and to investigate the factors required for normal development. For example, developing adrenergic sympathetic neurones can be influenced to become cholinergic by both diffusible and membrane-bound factors from certain types of non-neuronal cells; when medium conditioned by incubation on heart cell cultures (CM) is placed on the neurones, they develop the ability to produce acetylcholine (ACh) and they form functional cholinergic synapses with each other. Hormones could also contribute to the control of this transmitter choice, and McLennan et al. recently reported that corticosterone treatment of whole superior cervical ganglia (SCG) greatly inhibited the cholinergic development of these ganglia in culture. It was not clear, however, whether the hormone acted directly on the neurones or indirectly via the non-neuronal cells. To study the role of hormones on this transmitter choice, I have now developed a serum-free medium (based on that of Sato and co-workers) for the preparation of conditioned medium. The results obtained with this system show that glucocorticoids and epidermal growth factor (EGF) exert dramatic and antagonistic effects on the adrenergic-cholinergic transmitter choice and do so indirectly, by controlling the ability of heart cells to produce cholinergic CM.

Development of adrenergic innervation in rat peripheral vessels: a fluorescence microscopic study

The postnatal development of adrenergic innervation was followed in peripheral blood vessels of Wistar rats. The femoral vessels and their branches, the superficial epigastric and saphenous vessels, and the tail artery, were investigated from birth to maturity. The proximal ends of the vessels were studied with fluorescence microscopy after the catecholamine was converted to a fluorophore by hot formaldehyde vapour, and ultrastructural morphology confirmed that the nerve varicosities mainly contained small vesicles with dense cores, typical of adrenergic innervation. Further confirmation was obtained with reserpine pre-pretreatment, the sodium borohydride specificity test, and experiments to alter the non-specific fluorescence of elastin. The nerves in the arteries were immediately adjacent to the external elastic lamina, and they retained this position throughout postnatal development. Of the three muscular arteries, the development of innervation was earlier and more intense in the saphenous and superficial epigastric arteries than in the tail artery. However, the tail artery surpassed the other two both in the total number of nerves and in the density of innervation per unit area beyond 12 days of age, and maintained this lead to maturity. The superficial epigastric artery had the smallest total number of nerves but had a greater density of innervation than the saphenous. The femoral artery did not develop any appreciable innervation. The femoral vein demonstrated the greatest amount of fluorescence of any of the veins, the others having considerably less innervation than their companion arteries.

Sexual dimorphism in extent of axonal sprouting in rat hippocampus

Sympathetic axons, normally innervating the extracerebral vasculature, sprout into denervated regions of the hippocampal formation after lesions of the medial septal nucleus or fimbria in adult female rats. Similar lesions in adult males also elicit the sympathetic ingrowth; however, the number of anomalous axons is greatly reduced and their distribution is altered. In adult males the sympathetic axons do not send out collaterals within the stratum oriens of region CA3 or the molecular layer or deep hilar regions of the area dentata, as they do in adult females. Lesions in juveniles of both sexes result in more vigorous sprouting than in their adult counterparts. In the young males the anomalous axons are distributed more extensively into the dentate molecular layer; in the young females the axons merely send out more collaterals within the same regions as in the adults. This sexually dimorphic response to central nervous system damage suggests either that the sprouting is affected by the hormonal environment of the mature hippocampal system or that this brain region, like the hypothalamus, may express permanent morphological or physiological differences as a result of exposure to sex steroids during development.

Development of autonomic heart rate control in the kitten during sleep

Development of cardiac rate control was studied in 34 kittens aged 4 days to 6 wk during quiet and active sleep, using atropine and propranolol to quantitatively assess the degree of tonic parasympathetic and sympathetic control, with the analysis based on the Rosenblueth and Simeone model. The order of blocking agent administration did not significantly affect the results if a correction was made for the baroreceptor-mediated heart rate change after the blockade of a single autonomic branch. During the first 4 wk, the heart rate in quiet sleep was lower than in active sleep due to a significantly higher parasympathetic tone. The heart rate decreased with age in both sleep states: the decrease in quiet sleep was accompanied by a transition from sympathetic to parasympathetic dominance. The intrinsic rate of the pharmacologically denervated heart was maximum at about 2 wk and decreased steadily thereafter. The observed changes may help explain some features of the development in heart rate previously reported for sleeping human infants.

Intracisternal dose-response analysis of 6-hydroxydopamine-induced noradrenergic sprouting in the neonatal rat cerebellum

The dose-response relationship between neonatal 6-hydroxydopamine and noradrenergic regenerative sprouting in the cerebellum was characterized by using intracisternal doses of 10 to 80 micrograms of the drug. Noradrenergic regeneration was assessed in seven subregions of the cerebellum by measurement of norepinephrine (NE) levels once the rats were one-month-old. Regenerative sprouting occurred to a significant extent at drug doses between 10 to 40 micrograms, with peak NE elevations occurring after a 20-microgram dose. Recovery of NE was not uniform throughout the cerebellum but was maximal in the anterior vermis and minimal in the posterior vermis. An 80-microgram dose produced near total loss of cerebellar NE. This is contrasted to the cerebral cortical noradrenergic innervation which responded with significant long-term degeneration to a dose as low as 10 micrograms. In both areas, the initial effect of the drug treatment was to reduce NE levels by 95% or more. A couple of conclusions can be made. The magnitude of the difference between the cerebellar and cerebral cortical dose-response relationships is consistent with a regenerative mechanism subserving the recovery of NE in the cerebellum. Secondly, the increase of NE in the cerebellum is reciprocally related to destruction of the forebrain noradrenergic projection.

Adrenergic innervation and cyclic adenosine 3':5'-monophosphate levels in response to norepinephrine in stomach of postnatal rats

Changes in receptor function, innervation and cyclic adenosine 3':5'-monophosphate (cAMP) levels in response to norepinephrine were investigated in the stomach of postnatal developing rats. We found that although the beta adrenergic receptor function and responsiveness of cAMP-generating system to norepinephrine are present in the early postnatal stage (3-day-old), these systems are not fully developed at birth and that increase in sensitivity comes with age. Adrenergic innervation is present at birth in Auerbach's plexus but not in smooth muscle, during the 1st postnatal week. Direct adrenergic innervation to smooth muscle appears 1 week after birth and matures during the first 4 weeks. This maturation of direct adrenergic innervation runs in parallel with the increased sensitivity of beta receptors and is accompanied by an elevated responsiveness of the cAMP-generating system to norepinephrine.

Age-related cardiovascular effects of catecholamines in anesthetized piglets

We studied cardiac and peripheral circulatory effects of graded doses of catecholamines (0.05-1.0 microgram/kg) in piglets aged less than or equal to 1 day, 2--4 days, 1 wweek, 2 weeks, and 2.5-3 months, under anesthesia with pentobarbital. We evaluated cardiovascular function from simultaneous recordings of aortic pressure, ventricular pressure and its first derivative, heart rate, and phasic carotid and femoral blood flows. We calculated vascular resistance as the ratio of mean aortic pressure to mean flow. The age of onset of a given cardiovascular response was determined, and magnitudes of each type of response were compared among the age groups. Norepinephrine elevated the blood pressure at all doses in piglets of all ages, elicited reflex bradycardia only in older piglets, and increased carotid resistance. Epinephrine elevated the blood pressure at all doses in piglets less than 1 week old, but low doses lowered the blood pressure in piglets older than 1 week of age; resistance changes in the femoral and carotid circulations were variable except in the 2.5-3 month age group. Isoproterenol increased cardiac contractility at all doses in piglets of all ages and increased heart rate at low doses in piglets older than 2 days of age; however, blood pressure and femoral resistance decreases were age and dose dependent. There were age-related differences in the catecholamine dose required to elicit a given cardiac or peripheral circulatory effect and age-related differences in the direction and magnitude of such effects. These results provide evidence for differing rates of postnatal maturation of cardiovascular alpha- and beta- adrenergic mechanisms in swine.

Evolution of QRS-T relationship from birth to adolescence in Frank-lead orthogonal electrocardiograms of 1492 normal children

Patterns of evolution of QRS-T relationship were investigated by determining statistical distributions of QRS and STT integral vectors and the ventricular gradient vector in 1492 normal children divided into 12 age groups from birth to the age of 16 years. From birth to the age of 4 days, the ventricular gradient vector shifts posteriorly and to the left due to posterior shift of the STT integral vector and an increase in the spatial angle between QRS and STT integral vectors to a mean value of 103 degrees. These early neonatal changes in QRS-T relationship probably reflect the sudden reduction of hemodynamic load and the subsequent postnatal atrophy of the right ventricle while the left ventricular load slowly increases. The magnitude of the ventricular gradient vector increases from age 3 weeks until about 7 years. The increase appears to be related to a gradual increase in the magnitude of the QRS and STT integral vectors and a drastic decrease in the spatial angle between them. The spatial angle between QRS and STT integral vectors reaches it minimum (22 degrees) in the age group 1.5--4.5 years, suggesting that at that age the average direction of ventricular excitation and repolarization wavefronts are nearly opposite to each other. In addition to the shifting balance between the left and right ventricular hemodynamic load, other factors, such as the maturation of the sympathetic nervous system, may be important in determining spatial gradients in the duration of action potentials, thus influencing the relationship between ventricular excitation and repolarization.

[Mediator stage in the functioning of the autonomic nervous system in pre- and postnatal ontogeny and the importance of its study for clinical application]

In 1972 a new definition "mediatory stage" in the development of the vegetative nervous system during ontogenesis was introduced and it was stated that at the prenatal stage in the heart, along the course of magistral vessels, and into other organs begin to sprout up at first nervous truncs lacking in mediators, and then, beginning from 8--9 weeks (in man), the mediators appear at first in cholinergic and then in adrenergic plexus (V. N. Shvalev et al., 1972). In clinical embryonal mortality is especially great during the stage of premediatory development, that corresponds to the period of placentation. The beginning of the mediatory stage (the 3d month of prenatal life) is characterized by an intensive differentiation of the neural apparatus in the heart and its innervated structures. At first cholinergic and then adrenergic nerve plexus are formed, nevertheless, by the time of birth these plexus, especially adrenergic ones are not yet fully differentiated. During the first year of life there is noted a rather high rate of so called "sudden death". During the following 3--4 years there is a new intensive rise in differentiation of the cardiac cholinergic and adrenergic nerve plexus and by the 6--8th year of age the density of these plexus reaches its maximum (about 10%). This index is constant up to 40 years of age, and then a noticeable decrease in the density of adrenergic plexus takes place, while that of cholinergic plexus remains rather constant. After 60 years of age an involution takes place at first in adrenergic and then in cholinergic plexus, and the "postmediatory" stage occurs. The problem of "sudden death" is closely connected with the changes described for the mediators in the cardiac and vascular plexuses (V. N. Shvalev, R. A. Stropus and E. K. Morozov, 1978).

Presynaptic and postsynaptic contributions to ontogeny of sympathetic control of heart rate in the pre-weanling rat

1. The dependence of heart rate on sympathetic nerve development and on ontogeny of cardiac responses to sympathetic neurotransmitters was evaluated in neonatal rats by use of the ganglionic blocking agent, chlorisondamine, and the beta-adrenoceptor agonist, isoprenaline. 2. Basal heart rates of anaesthetized 4, 7 and 11 day old rats were the same as in adult rats, but the heart rate in 16 day old rats (an age at which sympathetic tone appears to be elevated) was significantly higher. 3. Chlorisondamine failed to lower heart rate significantly in 4 or 7 day old rats, but lowered the rate by 50 to 80 beats per min in the older animals and eliminated the difference in rate between 16 day old and the other ages; atropine had little or no effect on heart rate. 4. Heart rate responses to isoprenaline were lower in 4, 7 and 11 day old rats than they were in adults but were indistinguishable from them by 16 days of age, indicating that the heart is less sensitive to beta-adrenoceptor stimulation early in neonatal life. 5. The ontogeny of sympathetic control of heart rate in the rat depends upon maturational changes in both presynaptic and postsynaptic elements.

Appearance of catecholamine-synthesizing enzymes during development of rat sympathetic nervous system: possible role of tissue environment

We sought to determine, in rat embryo, when and at what site in their migration cells derived from the neural crest differentiate into sympathetic neuroblasts. This has been accomplished by immunocytochemical detection, within the cells, of the enzymes catalyzing catecholamine biosynthesis-tyrosine hydroxylase [TH; tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] dopamine-beta-hydroxylase [DBH; 3,4-dihydroxyphenylethylamine,ascorbate:oxygen oxidoreductase (beta-hydroxylating), EC 1.14.17.1)]-and, as a marker of prospective adrenal medullary cells, the enzyme phenylethanolamine N-methyltransferase (PNMT; S-adenosyl-L-methionine:phenylethanolamine N-methyltransferase, EC 2.1.1.28). TH and DBH, not detected in the neural crest, appear almost simultaneously in cells of the thoracic sympathetic ganglia in 11-day-old embryos, and in abdominal and lumbar ganglia 1-2 days later, thereby exhibiting a characteristic rostral-caudal gradient of differentiation. Cells stained for TH and DBH are seen in the gut wall from day 11 to day 14, but not thereafter. Cells stained for TH and DBH appear in the adrenal anlage at day 15. However, PNMT is not detected in the adrenal until day 17 of development, and is present only in the sympathoblasts in contact with the adrenal cortex. Treatment of pregnant rats with dexamethasone failed to accelerate the appearance of PNMT in the embryo or to initiate its expression in cells of other sympathetic organs. We conclude that neural crest cells express a noradrenergic phenotype only after leaving the neural crest and that these cells are labile with respect to their neurotransmitter and are capable of transformation in response to environmental stimuli.

Some observations on the development of adrenergic innervation in rabbit intestine

1 Stimulation of periarterial nerves to the ileum of 1 to 12 day old rabbits with supramaximal voltages and frequencies of 1, 2, 5, 10 and 20 Hz with square wave pulses of 2--5 ms duration for 30--40 s produced responses that were initially contractor. In the course of the first week, the responses changed from motor to inhibitory, the change occurring first at the highest rates of stimulation. By the 7th day of life, almost all responses were inhibitory. 2 The motor responses were potentiated by physostigmine and blocked by hyoscine suggesting that they were mediated by acetylcholine. 3 In preparations from rabbits older than 3 days, motor responses could be converted to inhibitory ones by prior exposure to noradrenaline (NA, 1 microgram/ml) for 20 min. This procedure also significantly increased the responses which were already inhibitory. 4 The ability of the ileum to take up NA increased with age. This uptake was blocked by cocaine. 5 The following explanations are possible: (a) changeover from cholinergic to adrenergic transmission in sympathetic fibres; (b) existence of 'parasympathetic' splanchnic nerves or a permanent cholinergic 'sympathetic' component of splanchnic nerves and (c) temporal delay in the development of adrenergic nerves (compared with cholinergic nerves) in the intestine.

Development of sympathetic nerve--muscle transmission in chick

The development of sympathetic nerve--muscle transmission was investigated pharmacologically by using the nerve-expansor secundariorum muscle preparation of 2- to 35-day-old chicks. The nerve-induced muscle contraction was not affected by atropine and neostigmine after hatch but was slightly depressed by phentolamine and completely depressed by guanethidine. Since the responsiveness of the muscle to some adrenomimetic drugs remained constant after hatch, adrenergic receptor function does not change during development. The nerve-induced muscle response was scarcely influenced by cocaine or reserpine in neonatal chick while it was potentiated by cocaine and changed by reserpine in mature chicks. These results suggest that cocaine- and reserpine-sensitive mechanisms gradually develop in sympathetic nerve function after hatch. The presence of a potentiating effect of cocaine on the nerve-induced muscle response in dimethylphenylpiperazinium-treated neonatal chick suggests that the development of sympathetic nerve function is regulated by nerve activity itself.

Early development of noradrenaline-containing sympathetic nerves in the choroid plexus system of the rabbit

The development of the adrenergic sympathetic innervation of the rabbit choroid plexus system was studied prenatally and up to two months after birth by a combination of fluorescence histochemistry (formaldehyde and glyoxylic acid methods) and quantitative enzymatic determinations of noradrenaline. The first signs of adrenergic nerves are found in the plexus of the third ventricle within the first day after birth. Fluorescent fibres subsequently appear in the choroid plexuses of the lateral ventricles (five days post partum) and the fourth ventricle (two weeks post partum). During the following development nerve fibres grow along blood vessels to form a plexus located between small vessels and the overlying epithelium. The nerve plexus, with varicose axon terminals, is fully developed at three weeks post partum, and maturation is then established by an increase in the number of terminals within the network of axons. There is a good agreement between (a) the development of the fluorescent nerves and histochemically visible adrenergic innervation, and (b) the tissue level of noradrenaline in the various choroid plexuses. Against the background of available information on the development of the secretory functions in choroid plexus, it is concluded that possibilities for a sympathetic neurogenic influence on the formation of cerebrospinal fluid exist already a few weeks after birth.

Functional development of cardiac sympathetic nerves in newborn dogs: evidence for asymmetrical development

The functional development of cardiac sympathetic nerves was investigated in 52 puppies, 1 to 6 weeks of age. The effect of nerve stimulation on refractory period shortening at eight epicardial sites was used as criterion. Zero or minimal effect was observed at the first week of life for all the nerves tested, then a sharp increase of effect was observed at the second week, while at the third week, an unexpected decrease was observed for all nerves. At the fourth week, the effect increased again and remained high for the subsequent weeks. Thus functional sympathetic innervation of the heart is not complete at birth, but continues to develop throughout the first 6 weeks of life, following an irregular pattern of progression. The nonuniform maturation of cardiac nerves coupled with the localised distribution of the nerves may provide a basis for regional sympathetic imbalance and subsequent arrhythmiogenesis in early life.

Postnatal development of inotropic responses to nerve stimulation and tyramine in rat atria

Inotropic responses were measured in isolated rat left atria using an isometric force transducer. In atria from adult rats tyramine administration or field stimulation of intramural cardiac nerves (in the presence of atropine) caused a positive inotropic response which was as great as that obtainable with exogenous noradrenaline. In contrast, atria from newborn animals showed very poor inotropic responses to nerve stimulation or tyramine although they already responded well to noradrenaline. The responses developed progressively with age, reaching adult levels at 3 to 4 weeks of age. It is concluded that the postnatal development of myocardial sympathetic nerves is correlated with a development of the positive inotropic response to sympathetic nerve stimulation or to tyramine.