Retrograde axoplasmic transport to inactive dopamine beta-hydroxylase in sciatic nerves

Anterograde axonal transport of Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme in rat sciatic nerves: cleavage occurs between basic residues

Axonal transport of Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme activity was studied in rat sciatic nerves from 12 to 120 h after double ligations. The anterograde axonal transport increased and peaked 72 h after ligation. The optimum pH for Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme activity was 6.5 to 6.9 and did not require Ca(2+) for the activity. Two molecular forms with enzyme activity were identified by size-exclusion chromatography and the molecular masses of the two enzymes were estimated to be 98 and 52 kDa. Two enzyme activities were strongly inhibited by Hg(2+), Cu(2+) and trypsin inhibitors such as TLCK, antipain and leupeptin. It cleaved the substrate, Boc-Arg-Val-Arg-Arg-MCA, between the dibasic sequence Arg-Arg, and needed a support of aminopeptidase B-like enzyme activity for the liberation of 7-amino-4-methylcoumarin. These results suggest that the enzyme is transported in rat sciatic nerves and involved in the post-translational processing of precursor proteins under the anterograde axonal transport. But there is absolutely no evidence for a role in precursor processing and such a putative role is purely speculative.

Noradrenaline storing vesicles in sympathetic neurons and their role in neurotransmitter release: an historical overview of controversial issues

More than 25 years have passed since the original demonstration that proteins such as chromogranin A and dopamine-beta-hydroxylase, which are co-stored together with noradrenaline in large dense cored vesicles in adrenergic nerves, are released by exocytosis. Despite much evidence in favour, it was for a long time thought that large dense cored vesicles were not eminently involved in the release of noradrenaline. The present review attempts to demonstrate, making use of evidence from different approaches, that the release of noradrenaline from sympathetic neurons occurs ultimately from large dense cored vesicles. A model of the secretory cycle is proposed.

The role of tonic preganglionic neuron firing in the turnover of the large dense-cored vesicle store in sympathetic preganglionic nerve terminals

Large dense-cored vesicles are transported centrifugally in the cervical sympathetic trunk and are depleted in a calcium-dependent manner from synaptic boutons of the cat superior cervical ganglion during orthodromic stimulation at 20-40 Hz [P. Weldon et al. (1993) Neuroscience 55, 1045-1054]. In the present study, we tested in awake cats whether the normal tonic firing of the sympathetic preganglionic neuron contributes to the turnover of large dense-cored vesicles in synaptic boutons of the superior cervical ganglion. Tetrodotoxin was applied with a mini-osmotic pump to one cervical sympathetic trunk, while vehicle alone was applied to the contralateral cervical sympathetic trunk, for two, four or seven days. The appearance of Horner syndrome ipsilateral to the tetrodotoxin application demonstrated block of action potential propagation. Both superior cervical ganglia were excised and processed for electron microscopy. The number of large dense-cored vesicles per bouton cross-section was higher in the ganglion with tetrodotoxin-treated input than in the control. The content at four days was higher than at two days; the content at seven days was similar to that at four days. The number of lysosomes per bouton profile also increased in the ganglion with tetrodotoxin-treated input. No changes were observed in size of bouton profiles, number of boutons or of synapses per grid square and length of the presynaptic densities in the ganglion with tetrodotoxin-treated input.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in the distribution of cytochrome b561 and synaptophysin in dog splenic nerve: a biochemical and immunocytochemical study

Compared with neurons of the CNS, the organization of the peripheral adrenergic axon and nerve terminal is more complex because two types of neurotransmitter-containing vesicles, i.e., large (LDVs) and small dense-core vesicles, coexist with the axonal reticulum (AR) and the well-characterized small synaptic vesicles. The AR, which is still poorly examined, is assumed to play some role in neurosecretion. We have studied the subcellular localization of noradrenaline, cytochrome b561, and synaptophysin in control and ligated dog splenic nerve using both biochemical and ultrastructural approaches. Noradrenaline and cytochrome b561 coaccumulated proximal to a ligation, whereas distally only the latter was found. Despite a codistribution with noradrenaline at high densities in sucrose gradients, synaptophysin did not accumulate on either side of the ligation. At the ultrastructural level, cytochrome b561 immunoreactivity was found on LDVs and AR elements, both accumulating proximal to the ligation. Distally, the multivesicular bodies (MVBs), immunolabeled for cytochrome b561, account for the retrograde transport of LDVs and AR membranes retrieved at the nerve terminal. No synaptophysin immunoreactivity could be detected on LDVs, AR, or MVBs. The results obtained from the ligation experiments together with the ultrastructural data clearly illustrate that synaptophysin is absent from LDVs and AR elements in adrenergic axons.

Anterograde axonal transport of peptidylglycine alpha-amidating monooxygenase in rat sciatic nerves

Axonal transport of peptidylglycine alpha-amidating monooxygenase (PAM) activity was studied in rat sciatic nerves from 12 to 120 h after double ligations. The anterograde axonal transport increased and reached a plateau between 48 and 72 h and then decreased. The flow rate was 100 mm/day, and the molecular mass of the active entity was 70 kDa, which was determined by gel filtration. In contrast, there was no evidence for significant retrograde axonal transport. Anterograde axonal transport of immunoreactive cholecystokinin, a carboxy-terminal-amidated putative neuropeptide, was also found. These results suggest that PAM is transported by a rapid axonal flow and may play a role as a processing enzyme during transport or in the terminals of rat sciatic nerves.

Storage and fast transport of noradrenaline, dopamine beta-hydroxylase and neuropeptide Y in dog sciatic nerve axons

The axonal transport and subcellular distribution of noradrenaline (NA), dopamine beta-hydroxylase (DBH) and neuropeptide Y (NPY) were determined in dog sciatic nerve using an accumulation technique. The results were compared with those obtained by application of the same procedures and methods on the splenic nerve in the same animal species. Evidence was found for the coexistence of NA and NPY in large dense-cored vesicles in dog sciatic nerve axons. After differential centrifugation and isopyenic sucrose density gradient centrifugation of 24 h ligated sciatic nerve pieces NA and NPY equilibrated around 1M sucrose. The DBH activity was dispersed broadly on the gradient. Subsequently, the accumulation of NA, DBH and NPY was studied in proximal and sital segments of 8, 12 and 24 h dog ligated sciatic nerve and inferences were made concerning the axonal transport of these compounds. NA, DBH and NPY displayed a divergent accumulation proximal to the ligation. After 12 h of ligation a transport rate was calculated of 4.8 +/- 1.8 mm/h for NA, of 5.9 +/- 1.5 mm/h for DBH and of 4.9 +/- 2.0 mm/h for NPY. With a correction for the stationary fractions, a similar fast transport rate of approximately 10 to 12 mm/h was proposed for NA, DBH and NPY. The occurrence was shown of a limited retrograde transport of DBH and possibly NPY, but not of NA.

Partial isolation of two classes of dopamine beta-hydroxylase-containing particles undergoing rapid axonal transport in rat sciatic nerve

The rapid bidirectional transport of dopamine beta-hydroxylase (DBH) in adrenergic axons provides a means of analyzing the life cycle of adrenergic storage vesicles. We compared the physical characteristics of DBH-containing particles traveling to or returning from the terminal varicosities of ligated rat sciatic nerves. Density gradient centrifugation and Sephacryl S1000 gel-permeation chromatography were used to fractionate extracts from nerve segments proximal or distal to the ligatures. A series of experiments indicated the existence of at least two populations of rapidly transported DBH-containing particles, a "light" 85-nm particle and a larger "dense" 120-nm particle. The 85-nm particles were prevalent in unligated nerve, but accounted for only one-third of the total anterogradely transported DBH activity accumulated after 18 h. The 120-nm particles were barely detectable in the unligated nerve, but they accumulated at twice the rate of the 85-nm particles and accounted for the rest of the anterogradely transported particulate DBH activity. These two populations of particles were readily isolated from proximal nerve extracts by sucrose density gradient centrifugation. Similar-appearing dense and light peaks of particulate DBH activity were obtained from distal nerve extracts. Much of the retrogradely transported DBH of the extracts, however, was associated with large particles (greater than 300 nm) not resolved by Sephacryl S1000. Retrogradely transported exogenous NGF was found only in the dense sucrose gradient peak. We propose that the 85-nm DBH-containing particles correspond to "large dense-cored vesicles," and that the 120-nm particles are derived from the dense tubules visualized in adrenergic nerves by the chromaffin reaction.

Loss of material from the retrograde axonal transport system in frog sciatic nerve

Rapid axonal transport was studied in sciatic nerve preparations of the amphibian Xenopus laevis maintained in vitro at 23.0 +/- 0.2 degrees C. A pulse of [35S]methionine-labeled material was allowed to move in the anterograde direction until encountering a lesion, at which a portion of the pulse reversed directions and moved in the retrograde direction. By constricting the nerve during the course of the experiment, it was possible to prevent continuous return of label from the lesion, thus creating a retrogradely moving pulse that contained a defined quantity of radiolabel. Movement of both the anterograde and the retrograde pulse were monitored continuously for up to 24 h using a position-sensitive detector of ionizing radiation. The front and the back edge of the anterograde pulse were found to move at the rates of (mm/day) 179.9 +/- 3.9 (+/- SEM) and 149.9 +/- 5.9, respectively, and the front and the back edge of the retrograde pulse moved at the rates of 155.8 +/- 11.3 and 84.6 +/- 2.9, respectively. By comparison of the quantity of label lost to the stationary phase to the quantity of label calculated to have been present in the anterograde pulse, it was determined that 0.068 +/- 0.009 of the anterograde pulse is lost to each 3.18-mm region of nerve. Comparison of the quantity of label calculated to have been present in the retrograde pulse to that in the anterograde pulse revealed that 0.057 +/- 0.014 of the retrograde pulse is lost to each 3.18-mm region of nerve. It is concluded that protein originating in the cell body and which reverses its direction of transport at a lesion can be lost from the retrograde axonal transport system.

Quantitative immunofluorescence of tyrosine hydroxylase in the adrenal medulla of spontaneously hypertensive rats

The amount of tyrosine hydroxylase protein in the adrenal medulla, which was estimated by a quantitative immunofluorescence method, was higher in spontaneously hypertensive rats than in normotensive control Wistar-Kyoto rats at 4 and 16 weeks of age before and after the development of hypertension.

Orthograde, retrograde, and turnaround axonal transport of dopamine-beta-hydroxylase: response to axonal injury

Reversal of the direction (turnaround) of orthograde axonal transport of dopamine-beta-hydroxylase (DBH) activity was studied at a ligature placed on rat sciatic nerve. DBH was allowed to accumulate at a ligature in vivo for selected intervals, at which time a second ligature was placed proximal to the first and turnaround transport measured just distal to the second tie after incubation in vivo or in vitro. Orthograde accumulation of DBH activity proximal to a ligature peaked at 2 days, and then rapidly decreased as a result of turnaround transport and injury-induced reduction of orthograde transport. Destruction of postganglionic sympathetic axon terminals in vivo with 6 hydroxydopamine resulted in a decrease in orthograde transport similar to that seen after axotomy and turnaround at or proximal to the site of chemical injury. Turnaround transport of DBH in vitro was blocked by incubation in the cold and in the presence of NaCN and vinblastine. Orthograde transport of DBH appeared to reverse direction within a few millimeters of a ligature.

Exocytosis from large and small dense cored vesicles in noradrenergic nerve terminals

The noradrenergic nerve terminals and their vesicle populations have been subject to much ultrastructural research which has served to support and extend data from biochemical analysis and pharmacological-physiological experiments. Although a great deal of information has been collected, there are still many problems which need further investigation before the various aspects of large and small dense-cored vesicle function and their possible relationship to the various types of clear vesicles and vacuoles in the terminals can be fully explained. In particular, the ontogeny of microvesicles (30-40 nm), intermediate clear vesicles (45-55 nm) and large vacuoles or cisternae (150-200 nm) needs clarification before they can be fruitfully compared to similar structures assigned various roles in other types of terminals. From the data presently available the following conclusions can be drawn (Fig. 32): (1) both large and small dense-cored vesicles participate in exocytosis. (2) The various steps of the exocytotic process from vesicle fusion to vesicle membrane retrieval can be captured by ultrastructural methods but the mode(s) of membrane recapture remains to be resolved. (3) A morphologically heterogeneous population of clear vesicles probably reflects organelles of different ontogeny some being formed via terminal membrane endocytosis and some representing smooth endoplasmic reticulum or small "dense-cored" vesicles devoid of noradrenaline. (4) The small dense-cored vesicles may be formed in the cell body and transported to the terminals as this type of vesicle can be seen in the axons (where they probably are not undergoing retrograde transport as suggested for some of the small clear vesicles). Some small dense-cored vesicles may also be formed from the permanganate and dichromate-positive tubular structures common in rodent terminals. (5) There is no morphological evidence for the presence of large protein molecules such as dopamine beta-hydroxylase in the dense core of small vesicles. Their staining properties appear to reflect mainly noradrenaline and small molecules that can leak out from the vesicles in parallel with the transmitter. (6) Dopamine beta-hydroxylase and opioid peptides secreted from the noradrenergic terminals most probably originate from the large vesicles. (7) The hypothesis that only the large dense-cored vesicles contain and secrete dopamine beta-hydroxylase and opioids can help to explain the species differences in the concentrations of these substances observed in certain tissues.

Mechanism of uptake and retrograde axonal transport of noradrenaline in sympathetic neurons in culture: reserpine-resistant large dense-core vesicles as transport vehicles

The uptake and retrograde transport of noradrenaline (NA) within the axons of sympathetic neurons was investigated in an in vitro system. Dissociated neurons from the sympathetic ganglia of newborn rats were cultured for 3-6 wk in the absence of non-neuronal cells in a culture dish divided into three chambers. These allowed separate access to the axonal networks and to their cell bodies of origin. [3H]NA (0.5 X 10(-6) M), added to the axon chambers, was taken up by the desmethylimipramine- and cocaine-sensitive neuronal amine uptake mechanisms, and a substantial part was rapidly transported retrogradely along the axons to the nerve cell bodies. This transport was blocked by vinblastine or colchicine. In contrast with the storage of [3H]NA in the axonal varicosities, which was totally prevented by reserpine (a drug that selectively inactivates the uptake of NA into adrenergic storage vesicles), the retrograde transport of [3H]NA was only slightly diminished by reserpine pretreatment. Electron microscopic localization of the NA analogue 5-hydroxydopamine (5-OHDA) indicated that mainly large dense-core vesicles (700-1,200-A diam) are the transport compartment involved. Whereas the majority of small and large vesicles lost their amine dense-core and were resistant to this drug. It, therefore, seems that these vesicles maintained the amine uptake and storage mechanisms characteristic for adrenergic vesicles, but have lost the sensitivity of their amine carrier for reserpine. The retrograde transport of NA and 5-OHDA probably reflects the return of used synaptic vesicle membrane to the cell body in a form that is distinct from the membranous cisternae and prelysosomal structures involved in the retrograde axonal transport of extracellular tracers.

Cytofluorimetric scanning: a tool for studying axonal transport in monoaminergic neurons

A new technique is described which makes it possible to measure several substances and parameters related to axonal transport in peripheral nerves. The technique is based on histofluorescent techniques and measures accumulated amounts of fluorescent substances, e.g. proximal to a crush or local cooling of the nerve. Sections from nerves, treated according to the FIF method for visualization of catecholamines or for immunofluorescence, are placed in a cytofluorimeter (Leitz MPV 2). The nerve sections are passed under a measuring slit by a motor-driven cross-table and the fluorescence intensity is continuously registered via a recorder with integrator which gives a graphical "nerve-accumulation profile." Comparisons between accumulation curves obtained with the cytofluorimetric scanning technique and biochemically determined accumulation curves of noradrenaline, dopamine-beta-hydroxylase and tyrosine-hydroxylase in the sciatic nerve following crush operations, demonstrated a striking similarity. With this technique it is possible to semiquantify the accumulated amount of a fluorescent substance, study morphology, perform morphometry and photographical documentation in the same section. This scanning technique may prove useful, since the accumulation and distribution of several substances in consecutive sections, along the length of a nerve, can be demonstrated graphically using superimposed curves.

Morphology of axonal transport abnormalities in primate eyes

The ultrastructure of the retina and optic nerve head was studied in primate eyes after central retinal artery occlusion. Within 2 hours of the vascular occlusion the inner retinal layers undergo watery (isosmotic) swelling. This watery swelling of axons and astroglia extends into the nerve head as far back as the anterior boundary of the scleral lamina cribrosa. The swelling is increased 4 hours after the occlusion, and by 24 hours disintegration has occurred. At the optic nerve head mitochondria and vesicles of smooth endoplasmic reticulum begin to accumulate within 2 hours. The accumulation increases at 4 hours and persists to 24 hours. The watery swelling seems characteristic of ischaemic axons. Membranous organelles accumulate at the boundary of an ischaemic zone when material carried by axonal transport is brought via the healthy axon segment to the boundary, but they cannot proceed further into the ischaemic zone. Such accumulation is typical of locations where rapid orthograde axonal transport or retrograde axonal transport is blocked. In contrast, when slow axonal flow is impaired, the swelling is characterised by an excess of cytoplasmic gel without a marked accumulation of organelles. Rapid orthograde transport and retrograde transport seem to be closely related to one another, while slow axoplasmic flow seems fundamentally different. From morphological findings we suspect that, in experimental glaucoma, intraocular pressure first affects the intracellular physiological process of rapid orthograde and retrograde axonal transport. Watery swelling may not occur unless the ischaemic injury to cell metabolism is more advanced. In contrast, in experimental papilloedema, the swelling results predominantly from impaired slow axoplasmic flow.

Axonal transport and subcellular distribution of dopamine-beta-hydroxylase in the cod, Gadus morhua

The axonal transport of dopamine-beta-hydroxylase (DBH; E.C. 1.14.17.1) was studied in the splanchnic nerve of the cod in vivo, and the subcellular localization of the same enzyme was studied in the chromaffin tissue from the cod head kidney. The mean rate of axonal transport for cod DBH was 18.6 mm/24 h at 10 degrees C. The mobile fraction was estimated to 22%, giving an absolute rate of transport of 85 mm/24 h at 10 degrees C. Evidence for a retrograde transport of DBH was also obtained, with an accumulation distal to a ligature of 12% of the accumulation proximal to the ligature at 3 days. DBH from the chromaffin tissue appeared to be strongly bound to the adrenergic granules, with only a small amount (ca 4%) recovered in the soluble phase.

Phentolamine increases neuronal binding and retrograde transport of dopamine beta-hydroxylase antibodies

When 125I-labelled antibodies against dopamine beta-hydroxylase (DBH) were injected into the anterior eye chamber of guinea-pigs they bound to sympathetic nerve terminals, were internalized into the axons and retrogradely transported to the ipsilateral superior cervical ganglion (SCG). This process was demonstrated to depend on specific binding sites since neutralized antibodies were not taken up and transported. The alpha-receptor antagonist phentolamine caused a 2.5-fold increase in binding in the iris and a 2.1-fold increase in accumulation of [125I]anti-DBH in the SCG. The results demonstrate that retrograde axonal transport of synaptic vesicle components is coupled to their turnover in nerve terminals.

Reversal of axonal transport: similarity of proteins transported in anterograde and retrograde directions

Reversal of axonal transport of endogenous labeled protein was studied in intact and injured nerve axons. Nerve crushes were used to collect labeled protein transported in anterograde and retrograde directions in rat sciatic nerve motoneuron axons after administration of L-[35S]methionine to the vicinity of the cell bodies. The collected proteins were characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis and subsequent fluorography. In injured nerves, where the nerves were ligated distally at the time of precursor injection, the polypeptide composition of proteins moving in anterograde and retrograde directions, 9-11 h after precursor injection, was identical, indicating that reversal at a ligature is a nonselective process. In intact nerves, protein moving in the anterograde direction 22-24 h after injection was different from that found 9-11 h after injection, and was also different from protein moving in the retrograde direction 22-24 h after injection. However, protein moving in the retrograde direction 22-24 h after injection was similar to protein moving in the anterograde direction 9-11 h after injection. Thus it appears that the same group of proteins originally transported into the axon are later returned toward the cell body. In intact axons, also, reversal was nonselective, except that one major labeled polypeptide was reduced in amount in the protein moving in the retrograde direction.

Retrograde axonal transport of endogenous proteins in sciatic nerve demonstrated by covalent labeling in vivo

Extracellularly applied N-succinimidyl [2,3-3H]propionate was used in vivo to covalently label intra-axonal proteins in the rat sciatic nerve. This technique permitted a unique view of axonal transport of proteins independent of biosynthesis. The proteins detected in slow anterograde transport (1 to 2 millimeters per day) correspond to cytoskeletal proteins described in previous papers. The slowly retrogradely transported component (3 to 6 millimeters per day) was composed primarily of a single protein with a molecular weight of 68,000.

Dopamine beta-hydroxylase in health and disease

DBH is a copper-containing oxygenase that catalyzes the hydroxylation of the beta carbon of a wide variety of phenylethylamine derivatives using molecular oxygen ascorbate as cofactors. It is a glycoprotein with a molecular weight of 290,000 and consists of four identical subunits, each with a single copper atom and 5% carbohydrate by weight. The enzyme is a constituent of catecholamine storage vesicles in chromaffin cell and adrenergic neurons in the peripheral and central nervous system where it functions to synthesize noradrenaline from dopamine. Although endogenous inhibitors have been isolated, they have not been demonstrated to have a physiological function, and the kinetics of the enzyme in vitro and in vivo suggest that the enzyme is not a rate limiting step in catecholamine synthesis under normal conditions. DBH exists in both a soluble form within vesicles and as a constituent of their membranes with its active site directed inward. The significance of the partition of the enzyme into soluble and membrane forms is not understood, although the soluble form has a fivefold greater homospecific activity. DBH has been one of the most intensively investigated enzymes in neurochemistry for several reasons. It is a readily assayable constitutent of catecholamine storage vesicles and, as such, provides a convenient biochemical marker for subcellular fractionation work and studies of the cellular regulation of catecholamine synthesis, storage, and release. The adrenal medulla is a rich source of the enzyme for purification, and the purified enzyme is highly antigenic, thereby enabling the use of several immunological techniques to study the cellular dynamics of the enzyme and the organelles in which it is located. These include radioimmunoassay, immunohistochemistry, and cytochemistry. This review firstly summarizes the present state of knowledge concerning the molecular properties of DBH. It then describes the tissue, cellular, and subcellular localization of the enzyme and its physiological regulation. The remainder of the review concentrates on those aspects of research on DBH in which the authors have participated that have led to general advances such as the development of the concept of homospecific activity, the introduction of immunohistochemistry for the localization of enzymes involved in transmitter metabolism, the release of macromolecules from synaptic vesicles during the process of exocytosis, the use of antibodies to DBH administered in vivo to study the fate of synaptic vesicle membranes and to produce specific immunological lesions of noradrenergic nerves in the peripheral and central nervous system, the genetic, environmental, and physiological determinants of serum DBH activity as an index of sympathetic function in animals and man, and the question of its diagnostic value in disease.

Specific uptake and retrograde flow of antibody to dopamine-beta-hydroxylase by central nervous system noradrenergic neurons in vivo

This study sought to determine whether the administration in vivo of antibody to dopamine-beta-hydroxylase (AD beta H) is taken up by central noradrenergic neurons and transported by retrograde flow to the cell bodies of origin. AD beta H serum or preimmune serum (control) in volumes of 1--20 microliter were stereotaxically injected into the lateral ventricle. Rats were sacrificed at times ranging from 1 h to 8 days. Cryostat sections were stained with fluorescein conjugated IgG. After 24 h, a bilateral granular fluorescence was seen only in neuronal cell bodies corresponding to noradrenergic cell groups A1--A7 with the most intense fluorescence localized within perikarya and processes of the locus coeruleus (A6) and subcoeruleus. This technique also permitted the visualization of the ascending dorsal and ventral noradrenergic bundles as well as varicose fibers and terminals in a pattern identical to that reported with histofluorescence, autoradiographic, biochemical and classical immunofluorescence techniques for the identification of noradrenergic fiber distributions. At 3 and 6 h, the first detectable fluorescence was observed in forebrain noradrenergic terminals and in fibers of the dorsal and ventral noradrenergic bundles. At 10 h fluorescent varicosities were first visualized within the caudal dorsal bundle and some cytoplasmic fluorescent particles were seen within locus coeruleus cell bodies. After 18 h locus coeruleus and subcoeruleus cell bodies were heavily stained, whereas medullary noradrenergic cell groups and nerve fibers were not labeled until after 24 h. An intense locus coeruleus fluorescence remained for 3 days and was completely absent after 6 days. Bilateral transection of the dorsal noradrenergic bundle in the rostral mesencephalon, at the time of injection, effectively blocked the retrograde transport of fluorescing material to the locus coeruleus. The overall staining pattern suggests that, in vivo, central noradrenergic fibers are capable of taking up antibody to dopamine-beta-hydroxylase. The ability of a dorsal bundle transection to abolish locus coeruleus staining, as well as the time course of AD beta H staining in noradrenergic neurons, suggests that AD beta H is transported via a rapid retrograde flow process. This technique combines retrograde transport of a marker protein with the sensitivity and specificity of immunocytochemical procedures to provide a new tool for the neuroanatomical study of neurotransmitter systems.

Dopamine beta-hydroxylase distribution in density gradients: physiological and artefactual implications

Knowledge of the vesicular origin of circulating dopamine beta-hydroxylase (DbetaH) is indispensable for any attempts to explain the parallelism or lack of it between circulating enzyme and catecholamines as they may relate to physiological stress, forms of hypertension, neurological disorders, and the response to pharmacological agents. The present study represents an effort to evaluate and to place in proper perspective data based on the DbetaH activity found in the region of the light vesicle peak of noradrenaline (NA), which is used as a quantitative measure of a population of small terminal vesicles. Distributions of vesicles and subvesicular components are compared with DbetaH and NA in sucrose-D2O density gradients used to prepare relatively pure fractions of large dense cored vesicles (LDV) from bovine splenic nerve. Although NA in sedimentable particles of the light vesicle peak is likely to be a valid measure of a small vesicle population, the following is demonstrated: (1) A substantial fraction (25%-37%) of the total sedimentable DbetaH activity can be proven to distribute in the region of the light vesicle peak from a tissue with an insignificant small vesicle population. Based on studies of vesicles from sequential nerve segments, this enzyme activity probably corresponds to a population of "immature" LDV which are undergoing axoplasmic transport and have not synthesized their full complement of transmitter. (2) Physical lysis which depletes the matrix of LDV causes redistribution of DbetaH activity from the heavy vesicle peak into the region of the light vesicle peak. Analogously, DbetaH associated with exocytosed LDV and retrograde transport particles is also likely to contaminate the region of the light vesicle peak. (3) Based on available data, it can be calculated that each small dense cored vesicle could contain only 0.1-0.5 molecules of DbetaH and that a contamination of only 0.016% LDV can account for all of the DbetaH reported to occur in the light vesicle peak of normal rat vas deferens preparations.

Retrograde axonal and transsynaptic transport of macromolecules: physiological and pathophysiological importance

Anterograde and retrograde transport within axons and dendrites of nerve cells represent an integral part of the nerve cell function and biochemistry. A few exogenous macromolecules with most different molecular weights and physico-chemical properties (Nerve Growth Factor, tetanus toxin, cholera toxin, various lectins, antibodies against dopamine-beta-hydroxylase) have been shown to be taken up and transported with the retrograde axonal transport in exceedingly high amounts if compared to most other macromolecules. Specific binding to membrane receptors seems to be the prerequisite for this highly efficient retrograde transport. Upon arrival at the cell body tetanus toxin is able to leave the neuron and to migrate transsynaptically to presynaptic nerve terminals of second-order neurons. For NGF, tetanus toxin and some neurotropic viruses retrograde axonal transport eventually followed by transsynaptic transport may be crucially involved in their mechanism of action. Indirect evidence suggests the existence of a variety of endogenous molecules carrying specific information from the target cell and the nerve terminal to the cell body and eventually transsynaptically into second- or third-order neurons.