A comparison of the neural regulation of tyrosine hydroxylase activity in sympathetic ganglia of adult mice and rats

Stages of neurotransmitter development in autonomic neurons

The ontogeny of neurotransmitters in autonomic neurons proceeds through the successive stages of early expression, definitive expression, modulation, and regulation, extending from embryonic life to maturity. Although different extracellular signals influence development at different stages, a number of signals that influence development continue to govern transmitter function during maturity. The sequential ontogenetic stages parallel the progressive restriction of mutability of phenotypic expression; however, some degree of neuronal mutability appears to persist through maturity.

Developmental influences on vascular structure and function

Blood vessels with apparently similar structures show remarkable functional heterogeneity. Differences exist in the nature and extent of their innervation, synaptic architecture, receptor characteristics, excitation coupling systems, capacity for intrinsic tone, contractility, elasticity and calcium-pool dependence, to mention only a few variables. The underlying basis of these differences is unknown. Similarity between the distribution of particular features in the vascular bed and the early patterns of embryological development suggest that some specific functional characteristics are determined during the process of gastrulation, if not before. Examples are given of receptor characteristics and tissue sensitivity that seem to reflect the different mesenchymal origins of particular vessels. Studies on vessels from immature fetal lambs confirm that individuality of specific vessels is established early. Interruption of sympathetic nerve traffic influences the function of vascular smooth muscle cells in a complex manner which is expressed differently at different ages. If the findings of experiments on the ear artery of the rabbit reveal a general principle seen in the circulation, then the level of sympathetic nerve traffic during growth would be expected to influence both qualitatively and quantitatively the structure and reactivity of the adult circulation. By this effect the sympathetic nervous system exerts a long-term influence on blood pressure. The characteristics of a particular blood vessel in the adult depend on many factors such as the level of blood pressure and the amplitude of the pulse wave which are not discussed in this chapter. These studies show that the character of the mature vessels also reflects influences that occur during early development and growth.

Comparison of nerve terminal events in vivo effecting retrograde transport of vesicles containing neurotrophins or synaptic vesicle components

Although vesicular retrograde transport of neurotrophins in vivo is well established, relatively little is known about the mechanisms that underlie vesicle endocytosis and formation before transport. We demonstrate that in vivo not all retrograde transport vesicles are alike, nor are they all formed using identical mechanisms. As characterized by density, there are at least two populations of vesicles present in the synaptic terminal that are retrogradely transported along the axon: those containing neurotrophins (NTs) and those resulting from synaptic vesicle recycling. Vesicles containing nerve growth factor (NGF), NT-3, or NT-4 had similar densities with peak values at about 1.05 g/ml. Synaptic-derived vesicles, labeled with anti-dopamine beta-hydroxylase (DBH), had densities with peak values at about 1.16 g/ml. We assayed the effects of pharmacologic agents in vivo on retrograde transport from the anterior eye chamber to the superior cervical ganglion. Inhibitors of phosphatidylinositol-3-OH (PI-3) kinase and actin function blocked transport of both anti-DBH and NGF, demonstrating an essential role for these molecules in retrograde transport of both vesicle types. Dynamin, a key element in synaptic vesicle recycling, was axonally transported in retrograde and anterograde directions, and compounds able to interfere with dynamin function had a differential effect on retrograde transport of NTs and anti-DBH. Okadaic acid significantly decreased retrograde axonal transport of anti-DBH and increased NGF retrograde transport. We conclude that there are both different and common proteins involved in endocytosis and targeting of retrograde transport of these two populations of vesicles.

Ectopic endplates induce localized changes in skeletal muscle ultrastructure

To investigate the processes by which motoneurons control protein synthesis, and thus the ultrastructure of the muscle fibers they innervate, ectopic endplates were induced to form on adult mouse skeletal muscle fibers by transplantation of a foreign nerve onto the muscle. In the dually innervated muscle fibers thus created, we examined two ultrastructural parameters that correlate with the expression of distinct isoforms of the myofibrillar proteins alpha-actinin and titin, specifically, Z-line width and sarcomere length. It was found that Z-lines were significantly thinner (98 vs. 128 nm) and sarcomeres were significantly shorter (1.69 vs. 2.06 microm) near the ectopic than near the original endplates. Thus, ectopic endplate formation on adult skeletal muscle fibers induces a localized alteration in myofibrillar morphology. These results may help to elucidate the role played by motoneurons in the determination and maintenance of muscle fiber properties and the processes that occur following muscle reinnervation after nerve injury.

A comparison of the changes in the non-neuronal cell populations of the superior cervical ganglia following decentralization and axotomy

Transecting the axons of neurons in the adult superior cervical ganglion (SCG; axotomy) results in the survival of most postganglionic neurons, the influx of circulating monocytes, proliferation of satellite cells, and changes in neuronal gene expression. In contrast, transecting the afferent input to the SCG (decentralization) results in nerve terminal degeneration and elicits a different pattern of gene expression. We examined the effects of decentralization on macrophages in the SCG and compared the results to those previously obtained after axotomy. Monoclonal antibodies were used to identify infiltrating (ED1+) and resident (ED2+) macrophages, as well as macrophages expressing MHC class II molecules (OX6+). Normal ganglia contained ED2+ cells and OX6+ cells, but few infiltrating macrophages. After decentralization, the number of infiltrating ED1+ cells increased in the SCG to a density about twofold greater than that previously seen after axotomy. Both the densities of ED2+ and OX6+ cells were essentially unchanged after decentralization, though a large increase in OX6+ cells occurred after axotomy. Proliferation among the ganglion's total non-neuronal cell population was examined and found to increase about twofold after decentralization and about fourfold after axotomy. Double-labeling experiments indicated that some of these proliferating cells were macrophages. After both surgical procedures, the percentage of proliferating ED2+ macrophages increased, while neither procedure altered the proliferation of ED1+ macrophages. Axotomy, though not decentralization, increased the proliferation of OX6+ cells. Future studies must address what role(s) infiltrating and/or resident macrophages play in regions of decentralized and axotomized neurons and, if both are involved, whether they play distinct roles.

Growth associated protein 43 (GAP-43) mRNA is upregulated in the rat superior cervical ganglia after preganglionic transection

Growth-associated protein 43 (GAP-43) is a growth-associated protein which is synthesised in high amounts in neurons during neuronal outgrowth. In a previous study we have shown that GAP-43 immunoreactivity is increased in neurons in superior cervical ganglia (SCG) and in nerve terminals in the irides after preganglionic denervation. We have now examined changes in GAP-43 mRNA using in situ hybridisation. GAP-43 mRNA was seen to be constitutively expressed by principal neurons of the rat superior cervical ganglion. Expression was increased further by section of the cervical sympathetic trunk, reaching a maximum (increased by about 30%) 3 days after decentralisation. The increased GAP-43 protein seen after decentralisation thus appears to be due to an upregulation of GAP-43 mRNA in the adrenergic neurons. The results imply that GAP-43 expression in the SCG is under presynaptic control, acting at least partly by control of mRNA levels.

Localization, regulation and functions of neurotransmitters and neuromodulators in cervical sympathetic ganglia

Cervical sympathetic ganglia represent a suitable model for studying the establishment and plasticity of neurochemical organization in the nervous system since sympathetic postganglionic neurons: (1) express several neuromediators, i.e., short acting transmitters, neuropeptide modulators and radicals, in different combinations; (2) receive synaptic input from a limited number of morphologically and neurochemically well-defined neuron populations in the central and peripheral nervous systems (anterograde influence on phenotype); (3) can be classified morphologically and neurochemically by the target they innervate (retrograde influence on phenotype); (4) regenerate readily, making it possible to study changes in neuromediator content after axonal lesion and their possible influence on peripheral nerve regeneration; (5) can be maintained in vitro in order to investigate effects of soluble factors as well as of membrane bound molecules on neuromediator expression; and (6) are easily accessible. Acetylcholine and noradrenaline, as well as neuropeptides and the recently discovered radical, nitric oxide, are discussed with respect to their localization and possible functions in the mammalian superior cervical and cervicothoracic (stellate) paravertebral ganglia. Furthermore, mechanisms regulating transmitter synthesis in sympathetic neurons in vivo and in vitro, such as soluble factors, cell contact or electrical activity, are summarized, since modulation of transmitter synthesis, release and metabolism plays a key role in the neuronal response to environmental influences.

Histochemical detection of age- and injury-related changes in signal transduction in the superior cervical ganglion

The superior cervical ganglion (SCG) is thought to be a good model for correlation studies of morphology, function and metabolism of neurons. The SCG has a relatively simple organization, it can be easily manipulated in situ, and it maintains synaptic transmission and a high metabolic rate during in vitro incubations. The histology and structure of SCG neurons have been characterized in detail, and physiologic stimuli, injury and aging have all been found to induce changes in the SCG morphology. During the last decade, research in the field of signal transduction has greatly expanded. Several signal transduction pathways have been identified that participate in the regulation of neurotransmitter synthesis, gene expression, neuronal excitability and growth factor responses of sympathetic neurons. We have been interested in using the SCG to study some of the second and third messengers involved in converting external stimuli received by sympathetic neurons into cellular short- and long-term events. Using immunohistochemistry, we have investigated protein kinase C-subtypes and the immediate early gene product Fos in the SCG, and characterized some of the changes induced by injury and aging in these messenger molecules. We will review the results and discuss the advantages and disadvantages of using histological methods in the study of signal transduction in sympathetic neurons.

Differential regulation of tyrosine hydroxylase protein and activity in rabbit sympathetic neurones after long-term cold exposure: altered responses in ageing

The aim of this study was to investigate the response of sympathetic neurones to prolonged neural stimulation, using cold exposure as a non-invasive experimental paradigm. We examined the effects of prolonged (8 days and 4 wk) cold exposure on tyrosine hydroxylase (TH) protein and activity and neuropeptide Y (NPY) levels in sympathetic neurones of the superior cervical ganglion (SCG), together with NPY levels in the ear artery from young and aged rabbits. The main findings were as follows. In young rabbits, TH levels and TH activity were differentially regulated in response to prolonged cold exposure. TH levels rose whilst TH activity tended to decline. Decentralization of SCG from young animals before cold exposure abolished the rise in TH levels. TH activity in SCG from young rabbits was reduced by decentralization whilst cold exposure resulted in an increase in TH activity. Thus, TH activity was induced in the SCG in the absence of pre-ganglionic input, demonstrating a non-synaptic regulatory mechanism. In old rabbits, cold-induced changes were either delayed or failed to occur, indicating that the responses of sympathetic neurones to cold stress are impaired in old age.

Quantitation of tyrosine hydroxylase and neuropeptide Y immunoreactivity in single rat sympathetic neurons: effects of preganglionic nerve activity

Using computerised densitometry to measure immunocytochemical reaction product in a model system, we established conditions that produced a linear relationship between the logarithm of antigen concentration and the measured intensity of staining. We then applied the densitometric technique to assess the changes in tyrosine hydroxylase (TH) and neuropeptide tyrosine (NPY) within sympathetic neurons of rat superior cervical ganglion following chronic decentralization and following reserpine treatment. One week after surgical or pharmacological decentralization, there was appreciable reduction of neuronal levels of both TH and NPY. However, there remained considerable variation in the immunoreactivities of individual cells. Three days of treatment with reserpine elevated TH levels but substantially reduced NPY. Both these effects were prevented by prior decentralization of the ganglia. No differences were seen between normotensive and the Otago strain of genetically hypertensive rats, either in basal TH or NPY immunoreactivities or in responses to the maneuvers performed. Comparison of our findings with previous biochemical data indicate that densitometric immunocytochemistry provides an accurate index of neuronally localised antigen concentrations but also allows analysis of interneuronal differences that are not otherwise apparent.

Regulation of molecular components of the synapse in the developing and adult rat superior cervical ganglion

Rat superior cervical sympathetic ganglion was used to begin studying the regulation of molecular components of the synapse. Ganglionic postsynaptic densities (PSDs)exhibited a thin, disc-shaped profile electron microscopically, comparable to that described for brain. Moreover, the presumptive ganglionic PSD protein (PSDp) was phosphorylated in the presence of Ca2+ and calmodulin, bound 125I-labeled calmodulin, and exhibited a Mr of 51,000, all characteristic of the major PSD protein of brain. These initial studies indicated that ganglionic PSDp and the major PSD protein of brain are comparable, allowing us to study synaptic regulation in the well-defined superior cervical sympathetic ganglion. To obtain enough quantities of ganglionic PSDp, we used synaptic membrane fractions. During postnatal development, calmodulin binding to the ganglionic PSDp increased 411-fold per ganglion from birth to 60 days, whereas synaptic membrane protein increased only 4.5-fold. Consequently, different synaptic components apparently develop differently. Moreover, denervation of the superior cervical sympathetic ganglion in adult rats caused an 85% decrease in ganglionic PSDp-calmodulin binding, but denervation caused no change in synaptic membrane protein 2 weeks postoperatively. Our observations suggest that presynaptic innervation selectively regulates specific molecular components of the postsynaptic membrane structure.

Catecholamines in kidneys of normotensive and genetically hypertensive rats. Effects of salt load

The tissue content of norepinephrine, dopamine, and epinephrine was determined in different zones of the kidney in normotensive Sprague-Dawley and Otago Wistar rats and in genetically hypertensive Otago Wistar rats. One kidney in each animal was chronically denervated to allow estimation of the neuronal contribution to renal catecholamine content. In all strains, the renal cortex contained negligible amounts of nonneuronal norepinephrine and dopamine, while outer and inner medullary layers contained progressively larger amounts. Nonneuronal epinephrine was distributed fairly evenly through cortex and medulla. Neuronal norepinephrine content was similar in inner and outer cortex, substantially less in outer medulla, and not discernible in inner medulla. The amounts of neuronal dopamine were consistent with its localization predominantly in noradrenergic nerves. The renal cortices of normotensive Wistar rats contained more neuronal norepinephrine and less neuronal dopamine than those of Sprague-Dawley rats, and the cortices of hypertensive Wistar rats contained slightly more norepinephrine than those of normotensive Wistar rats. In both normotensive strains, long-term salt loading decreased selectively the neuronal norepinephrine in renal cortex. By contrast, in hypertensive animals, cortical norepinephrine was not reduced by salt loading. These results indicate that the genetically hypertensive rat may have an abnormal sympathetic reflex response to increased blood volume.

The role of axonal transport in the regulation of enzyme activity in sympathetic ganglia of adult rats

The relationship of perikaryal and presynaptic enzyme activity to axonal transport was studied in adult sympathetic neurons in the rat superior cervical ganglion (SCG). Surgical axotomy or local colchicine application to the postganglionic nerves resulted in a significant decrease in ganglionic tyrosine hydroxylase (T-OH) activity without a significant alteration in choline acetyltransferase activity. Colchicine did not appear to block axonal impulse conduction since pupillary and eyelid function remained normal. Consequently, the reduced T-OH activity resulted from alteration of other axonal functions. Axotomy or colchicine application decreased T-OH activity in decentralized ganglia, suggesting that the depression of perikaryal T-OH was not secondary to altered orthograde transsynaptic interactions. Colchicine did not prevent transsynaptic induction of T-OH by reserpine, suggesting that axonal transport is not necessary for enzyme induction. Nerve growth factor (NGF) treatment partially prevented the effects of colchicine application. It is concluded that in adult sympathetic neurons both orthograde transsynaptic mechanisms and the retrograde transport of NGF normally govern perikaryal T-OH activity.

Storage and release of acetylcholine in the isolated superior cervical ganglion of the rat

The storage and release of acetylcholine and choline were studied in the isolated superior cervical ganglion of the rat by a radioenzymic method. The acetylcholine and choline contents were 202.2 +/- 5.1 and 624.7 +/- 20.2 pmole/ganglion, respectively. The transmitter tissue store was unaffected during 1 h of superfusion in choline--Krebs solution, while a 20% decrease was exhibited after 2 h and then remained approximately stable. Conversely, choline content declined to 50% within 1 h and further to 37% of the original level by 4 h. About 24% of the choline assayed in the intact preparation is located in the connective sheath. Preganglionic nerve stimulation at 10--20/sec or potassium stimulation (40 mM KCl) invariably decreased the transmitter tissue stores by 25--45%; such a depletion is independent of the presence or absence of external choline. By contrast, the presence of choline proved to be a prerequisite for the efficient release of acetylcholine from eserinized ganglia during continuous 10/sex stimulation. A drastic depression in the acetylcholine release is described which is related to the time of preincubation of the ganglia with eserine prior to stimulation. Indeed, a 30 min exposure to eserine, compared with a 5 min period, resulted in a 4-fold decrease in the steady output rate. Under optimal conditions, the initial volley output at 10/sec was 1.3 X 10(-4) of the releasable transmitter pool and 1.9 X 10(-4) during the steady-state output. These results are discussed in the light of the electrophysiological knowledge of the quantal release process at the ganglionic synapse.

Ultrastructure and biochemistry of sympathetic ganglia in idiopathic orthostatic hypotension

The role of transsynaptic dysfunction in the pathogenesis of idiopathic orthostatic hypotension (IOH, or idiopathic autonomic insufficiency) was examined microscopically and biochemically in autopsy specimens. Light microscopy of the sympathetic ganglia showed abnormalities in all 4 IOH patients, including focal phagocytosis of neurons, increased numbers of satellite cells, and perivascular lymphocytic infiltrates. Electron microscopy revealed proliferation and hypertrophy of satellite cells and abnormalities in the unmyelinated axons. In contrast, the spinal cord intermediolateral columns, containing the presynaptic neurons, were unremarkable in 1 patient, exhibited only mild gliosis in another, and showed neuron loss and fibrillary gliosis in 2 patients. Postsynaptic dopamine-beta-hydroxylase (DBH) activity was decreased at least fourfold (p less than 0.02) in sympathetic ganglia of patients with IOH, while tyrosine hydroxylase (T-OH) was normal. Ganglion choline acetyltransferase (ChAc) activity, an index of presynaptic function and integrity, was normal in the IOH group. A number of our observations suggest that presynaptic disease is not an absolute requirement for adrenergic abnormalities in IOH. The intermediolateral columns of the spinal cord were histologically normal in 2 of the patients with IOH, and ultrastructural abnormalities in sympathetic ganglia were consistent with primary adrenergic degeneration. In addition, presynaptic ChAc activity was normal in IOH ganglia, whereas postsynaptic DBH activity was depressed. Finally, postsynaptic T-OH activity, which is regulated by transsynaptic mechanisms, was normal in IOH ganglia.

The effect of guanethidine and hydrochlorothiazide on blood pressure and vascular tyrosine hydroxylase activity in the spontaneously hypertensive rat

The present study examined the effects of antihypertensive drugs (hydrochlorothiazide and guanethidine) on blood pressure and tyrosine hydroxylase (TH) activity in the spontaneously hypertensive rat (SHR). Hydrochlorothiazide (50 mg/kg X 4 days) lowered blood pressure in the SHR to a degree equivalent to that produced by reserpine (0.3 mg/kg X 3 days). However, while reserpine increased vascular and adrenal TH activity, hydrochlorothiazide had no effect. Guanethidine (30 mg/kg X 2 days) reduced blood pressure in the SHR and also depleted cardiac, vascular and adrenal gland catecholamines; However, guanethidine administration did not increase TH activity in the mesenteric vasculature or adrenal glands. These studies indicate that at equieffective blood pressure lowering doses, different antihypertensive drugs have different effects on TH activity in the SHR. Neither blood pressure reduction nor catecholamine depletion in peripheral tissues are sufficient prerequisties for increasing TH activity. The data support the suggestion, however, that amine depletion in the central nervous system or ganglia may be an important factor in the regulation of TH.

Effect of decentralization and glucose withdrawal on the potassium-induced cAMP increase in the rabbit superior cervical ganglion

The concentration of cAMP in the isolated rabbit superior cervical ganglion (SCG) increases when the tissue is exposed to high potassium media for short periods. The increase was found not to be affected by agents that are known to potentiate or to antagonize the postsynaptic effects of acetylcholine. Pretreatment of the rabbits with various sympaticolytic substances did not appear to affect the cAMP increase in the isolated SCG. It was found that the K+-induced cAMP synthesis occurred neither in ganglia which had been decentralized 3 days before isolation nor in intact ganglia preincubated in a glucose-free medium. Under both these conditions the effect of potassium declines with a time course which is characteristic for the degeneration of the presynaptic terminals. These terminals therefore, appear to be the most likely site for the cAMP increase.

A quantitative comparison of the formation of synapses in the rat superior cervical sympathetic ganglion by its own and by foreign nerve fibres

The rat superior cervical sympathetic ganglion (SCG) has about 36,000 neurones in a volume of about 1 cu.mm. There are about 8.8 X 10(6) synapses, and 6000-9000 preganglionic axons. Section of the preganglionic chain causes a loss of 93% of the synapses. In the denervated SCG there are 0.6 X 10(6) remaining ('intrinsic') synapses, and a proportion of the synaptic sites are identifiable as vacated synaptic thickenings (3 X 10(6) per SCG, as compared with 0.5 X 10(6) in the normal intact SCG). After deducting the intrinsic synapses, this indicates that each preganglionic axon forms about 1100 (900-1400) synapses. After freezing the preganglionic chain, subsequent axonal regeneration restores synapse numbers to 85% of normal (7.5 X 10(6) synapses per SCG). After anastomotic repair by suture of the cut ends of the preganglionic chain (a necessary control for the foreign nerve anastomoses), the SCG contains only 60% of the normal complement of synapses (5.2 X 10(6) synapses per SCG). The results of this anastomosis are very variable. However, in individual ganglia the numbers of synapses are directly correlated with the numbers of axons which reach the SCG. After deducting the intrinsic synapses it can be calculated that each axon forms about 700 synapses. This is probably an underestimation of the numbers which would be achieved at longer survival times. After anastomosis of the vagal nerve into the denervated SCG there are about 4.4 X 10(6) synapses per SCG. Morphologically the majority have axon terminals with large dense cored vesicles, and it is likely that these belong to the axons of the parasympathetic preganglionic neurones in the dorsal motor nucleus of the vagus. A smaller population of axon terminals are devoid of large dense cored vesicles; their origin is unknown. The dorsal motor nucleus of the vagus has between 1000 and 2000 neurones. After deducting the intrinsic synapses, this indicates that each axon may form up to 1900-3800 synapses. To the extent that other, unidentified vagal fibres also contribute to the synapses found after this anastomosis, this figure is an overestimate. After anastomosis of the hypoglossal nerve into the denervated SCG, there are 1.5 X 10(6) synapses per SCG. A morphologically distinctive type of axon terminal is found, and it is argued that this may belong to a special category of skeletomotor neurones located in the caudoventral part of the hypoglossal nucleus and distinguished by pseudocholinesterase staining. There are about 600 of these neurones, which would indicate that they form about 1500 synapses per axon (after deducting the numbers of intrinsic synapses). The majority of the hypoglossal neurones do not form intraganglionic synapses; this suggests that although the possession of a cholinergic mechanism may be necessary for axons to be able to form ganglionic synapses, it is not in itself sufficient. For each of the types of anastomosis, the numbers of vacated thickenings are inversely proportional to the numbers of synapses...

Some properties of the transmitter release mechanism at the rat ganglionic synapse during potassium stimulation

In the present investigation a study has been made using intracellular recordings in the rat superior cervical ganglion of the mode of transmitter release induced by raised external potassium ion concentration (40 mM), after acetylcholine synthesis has been blocked by hemicholinium-3. It is shown that the progressive decline in the rate of acetylcholine output from the ganglion is related to a decrease in the number of quanta being released. Furthermore, under these conditions there is no evidence for a reduction in the size of the transmitter quantum. The statistical foundations of the quantal release process at the rat ganglionic synapse have been investigated by comparing the distribution of the number of miniature EPSPs during successive constant time intervals in the tracings with the corresponding Poisson and binomial predictions. Analyses have shown that the probability for a quantum to be released is so small as to produce a binomial distribution of responses indistinquishable fro- the corresponding Poisson distribution, both at the beginning of the potassium-induced quantum discharge and when transmitter release level is low after exhaustion of acetylcholine tissue content.

Effects of axotomy on the trans-synaptic regulation of enzyme activity in adult rat superior cervical ganglia

The effects of surgical transection of the postganglionic nerve trunk of the superior cervical ganglion on the total protein content and levels of the enzymes tyrosine hydroxylase, DOPA decarboxylase and choline acetyltransferase have been studied in the adult rat. There is a minor decrease in the total activities of these 3 enzymes accompanied by a large increase in the total protein content of the ganglion. The trans-synaptic induction of the enzyme tyrosine hydroxylase by reserpine is not affected by postganglionic axotomy. Increased activity mediated by reserpine caused no change in the total activities of either DOPA decarboxylase or choline acetyltransferase. Previously observed effects of postganglionic axotomy on preventing transmission through the ganglion are compared with these results and the possible mechanisms by which trans-synaptic induction may occur are discussed.

Effect of recurrent stress on postnatal increase of tyrosine hydroxylase

Tyrosine hydroxylase is present at birth and reaches adult levels in the hypothalamus usually during the second month. Recurrent stimulation of intrahypothalamic noradrenergic structures shortened this period of maturation in a statistically significant manner.

Reversible changes in the accumulation and activities of tyrosine hydroxylase and dopamine-beta-hydroxylase in neurons of nucleus locus coeruleus during the retrograde reaction

To examine the biochemical events associated with the retrograde reaction in central noradrenergic neurons, changes in the activities of several enzymes subserving the metabolism of catecholamines, including tyrosine hydroxylase (TH),dopamine-beta-hydroxylase (DBH), DOPA decarboxylase (DDC), and monoamine oxidase (MAO), were measured in the nucleus locus coeruleus of rat brain following transection of the ascending axons from neurons in this nucleus by electrolytic lesions of the posterolateral hypothalamus. Such lesions produced a triphasic response in the activities of TH and DBH consisting of: (a) an increase to approximately 150 percent of control during the first 48 h followed by (b) a reduction reaching 60 percent of control by day 14, and (c) a full recovery of activity by day 21-28. In contrast, the activities of DDC and MAO, enzymes non-specific for catecholamine neurons, were unchanged. Immunochemical titration with specific antibodies to TH and DBH demonstrated that the fall in enzyme activity was entirely attributable to reduced accumulation of specific enzyme protein and not inhibition of pre-existing enzyme molecules. There was no reduction in the number of neurons in the nucleus locus coeruleus as a consequence of the lesion. We conclude that a reduction in the accumulation of specific enzymes subserving transmitter biosynthesis characterizes a reversible retrograde reaction of central noradrenergic neurons. The coincidence of the time course of reduced enzyme accumulation with regenerative sprouting from damaged noradrenergic axons and also the absence of classical signs of chromatolysis in locus coeruleus neurons following comparable lesions suggest that, first, during the retrograde reaction there may be a reordering of priorities governing accumulation of specific proteins favoring accumulation of those required for reconstitution of cellular processes by sprouting at the expense of proteins utilized in the synthesis of neurotransmitters, and second, some intrinsic neurons of the CNS may undergo reversible biochemical changes of a retrograde reaction in the absence of the classical morphological appearance of chromatolysis.

Neuronal control of neurotransmitters biosynthesis during development

Studies on neuronal control mechanisms of neurotransmitters biosynthesis during the development of peripheral and central autonomic synapses are reviewed. Particular emphasis is placed on investigations of developing peripheral sympathetic ganglia and brain in chick embryo and chick. Studies on the development of autonomic neurons and synapses under different pharmacological conditions are reported. Principally the effect of a) the administration of drugs and precursors such as L-dopa, 3H-dopa, 6-OH dopa; b) the prenatal administration of reserpine; c) the blockade of cholinergic receptors; d) the nerve growth factor (NGF) is analyzed. Results of developmental studies on chick ciliary ganglia are summarized. The review particulary underlines the importance of combining the use of sensitive microchemical methods to pharmacological tools in exploring the development of regulatory mechanisms at the cellular level.