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PubMed1980

Descending projections of the locus coeruleus and subcoeruleus/medial parabrachial nuclei in monkey: axonal transport studies and dopamine-beta-hydroxylase immunocytochemistry.

Spinal projections originating in the dorsolateral pons in the ventral locus coeruleus and in the subcoeruleus and medial parabrachial nuclei were identified in monkeys (Macaca fascicularis) using the retrograde horseradish peroxidase tracing technique. Anterograde autoradiographic tracing studies were then carried out to determine the brain stem and spinal cord terminations of the neurons. Finally, results obtained with the axonal transport tracing methods were compared with the pattern of staining for noradrenergic cells and terminals revealed immunocytochemically with an antibody to dopamine-beta-hydroxylase (DbetaH), the synthesizing enzyme for norepinephrine. The major findings of these studies are that two presumed noradrenergic cell groups of the dorsolateral pons, one corresponding to the nucleus locus coeruleus, the second to the subcoeruleus/medial parabrachial nuclei, give rise to descending projections. They differ significantly in their patterns of termination in the lower brain stem and spinal cord. Among the major terminations of the locus coeruleus pathway are projections to parasympathetic neurons of the dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, and the sacral spinal cord. The terminations of the descending subcoeruleus/medial parabrachial pathway, in contrast, include projections to sympathetic preganglionic neurons of the intermediolateral cell column of the thoracic cord and heavier projections to somatic cranial nerve nuclei. Both pathways have additional widespread and bilateral terminations in various nuclei of the reticular formation, in the spinal dorsal horn (including the marginal zone), in the region around the central canal and in the ventral spinal gray matter. Since the origins and terminations of both these pathways correspond closely to the locations and patterns of terminations of noradrenaline-containing neurons, demonstrated here with DbetaH immunocytochemistry, norepinephrine (or epinephrine) is suggested to be the transmitter in both these descending systems.

Animals↗
PubMed1994

Cyclic AMP modulates fast axonal transport in Aplysia bag cell neurons by increasing the probability of single organelle movement.

Stimulation of Aplysia bag cell neurons triggers elevation of cAMP and prolonged secretion of ELH neuropeptide. Using video-enhanced microscopy to track individual organelle movements in bag cell neurons, we find that organelle translocation consists of periods of movement interrupted by stationary episodes. cAMP elevation leads to a 2- to 3-fold enhancement of the average rate of organelle transport in both anterograde and retrograde directions. This effect does not result from alteration of the instantaneous velocity of organelle transport along microtubules, but rather from an increase in the proportion of time individual organelles spend in motion. Biochemical measurements also provided evidence that cAMP elevation promotes ELH peptide translocation from the somata into axons. Enhanced transport of ELH as a result of these effects may contribute to the replenishment of neuropeptide-containing vesicles at release sites during prolonged periods of secretion.

Animals↗
PubMed1978

Axonal transport of [3H]proteins in a noradrenergic system of the rat brain.

Proteins synthesized from [3H]leucine injected into the rat nucleus locus coeruleus (LC) were transported through the hypothalamus in 5 successive waves at rates of 72-192, 24-48, 13-20, 3-4 and 1.4-2.9 mm/day (waves I through V, respectively). Waves I through IV began axoplasmic transport in the LC within the first few hours after [3H]protein synthesis began in the LC. Wave V was delayed in onset for 1.7-3.7 days and was also probably transported through the contralateral hypothalamus. Wave IV was not transported within the LC-hypothalamic axons ascending through the dorsal noradrenergic bundle since its transport was not blocked by 6-OHDA lesions in this bundle, as was transport of the other 4 waves. Unilateral dorsal bundle lesions caused a well defined caudal backup of dopamine-beta-hydroxylase immunofluorescence and a fall in dopamine-beta-hydroxylase activity in the ipsilateral frontal cortex and hypothalamus of 55% and 9%, respectively. Bilateral lesions caused only a significantly further reduction in hypothalamic levels indicating crossed innervation of the hypothalamus by the LC of 27%. Waves I and II have been classified as rapid transport and contained 33% of the transported [3H]protein. Wave V was slowly transported and contained 51% of the transported [3H]protein, while wave III was intermediate in rate and contained 16% of transported [3H]proteins.

Adrenergic Fibers↗
PubMed1983

The use of wheat germ agglutinin--horseradish peroxidase conjugates for studies of anterograde axonal transport.

Injection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), into the hemisected spinal cord of the rat, cat and monkey consistently resulted in the intense anterograde labeling of ascending spinal projections such as the spinothalamic tract and spinocerebellar tracts and their terminal fields. Injections of WGA-HRP in the dorsal column nuclei resulted in the anterograde labeling of the medial lemniscus and its terminal fields in the thalamus. Injection of similar amounts of horseradish peroxidase alone (HRP) in hemisected animals or the dorsal column nuclei resulted in little anterograde labeling. The rate of the anterograde transport of WGA-HRP in cut axons appears to be greater than 200 mm/day. Small amounts of transneuronal labeling appeared to occur after injection of WGA-HRP in both cut axons and undamaged cell bodies. These results suggest that the amount of anterograde labeling observed after injection of WGA-HRP into both cut axons and undamaged cell bodies is significantly greater than the anterograde labeling observed after injections of HRP alone. Therefore, in the central nervous system WGA-HRP appears to be a far more effective anterograde tracer than HRP alone.

Animals↗
PubMed1985

Ultrastructural localization of slow retrograde axonal transport: an autoradiographic study.

We used [3H]-N-succinimidylpropionate ([3H]-N-SP) to covalently label endogenous intra-axonal proteins within the nerve in order to study their bidirectional transport. At the time of injection virtually all of the labeled proteins are found at the injection site. At later times specific patterns of labeled proteins are found within the nerve both proximal to and distal from the injection site, as a result of retrograde and anterograde axonal transport, respectively. We undertook the current study to determine the ultrastructural distribution of the [3H]-N-SP-labeled transported proteins in the nerve. One microliter of [3H]-N-SP was injected subepineurially in sciatic nerve, and 5 days later the nerves were processed either for light and electron microscopic autoradiography or for gel electrophoresis and fluorography. At the injection site the labeled proteins are predominantly myelin proteins. Distally, a pattern similar to that described for slow anterograde transport is seen. Proximal to the injection site a constellation dominated by the 68-kilodalton protein is seen. Light microscopic autoradiography shows diffuse labeling both in axons and in myelin at the injection site, with predominant axonal labeling distant from the injection site. Electron microscopic autoradiography of segments distal to the injection site show silver grains which are distributed within the axoplasm without apparent relationship to organelles. In contrast, segments proximal to the injection site show silver grains which seem closely related to membrane-bound organelles, predominantly mitochondria. These results suggest that slow retrograde transport has a unique subcellular distribution that is distinct from that of slow anterograde transport.

Animals↗
PubMed1973

Metabolic aspects of the synthesis and intra-axonal transport of noradrenaline storage vesicles.

1. Constricted cat hypogastric nerve/inferior mesenteric ganglion preparations have been maintained for 24 hr in vitro, in either test-tubes or a two compartment box, and used to study the roles of energy metabolism, protein synthesis and calcium ions in the synthesis and transport of noradrenaline storage vesicles in sympathetic neurones.2. When preparations were incubated so that the nerve trunks but not the ganglia were made anoxic, dense-cored vesicles lost their store of noradrenaline and did not accumulate above the ligature. This was accompanied by profound ultrastructural damage to the nerves.3. When in contact with the ligated nerve trunks, sodium fluoride inhibited the intra-axonal movement of dense-cord vesicles but did not deplete them of their stored noradrenaline. When sodium fluoride and pyruvate were present in the medium bathing the nerve trunks the movement of noradrenaline storage vesicles was unaffected.4. Whilst a reduction of the calcium ion concentration in the incubation medium and the inhibition of protein synthesis by cycloheximide prevented the synthesis of dense-cored vesicles in the neuronal perikaryon they had no effect on the movement of preformed dense-cored vesicles along non-myelinated axons.

Animals↗
PubMed1985

Anterograde axonal transport and intercellular transfer of WGA-HRP in trigeminal-innervated sensory receptors of rat incisive papilla.

The ultrastructure and identification of WGA-HRP-labeled sensory receptors in the rat incisive papilla (the most anterior part of hard palate) were studied using semiserial thin sections. Various sensory receptors were organized according to three locations: dome region (ventral), chemosensory corpuscle region (medial to orifice of incisive canal), and lateral labium (apposing the incisive canal). In the dome region, the sensory receptors were localized in three sensory zones that were associated with surface ridges (one medial and two lateral). In each of these zones, intraepithelial receptor axons and Merkel receptors occurred in the epithelium, while simple unencapsulated corpuscles, glomerular-Meissner corpuscles, and incisive (encapsulated) corpuscles occurred in the lamina propria. In the chemosensory corpuscle region, chemosensory corpuscles and intraepithelial receptor axons were located in the epithelium, and incisive corpuscles were present in the lamina propria. In the lateral labium, only intraepithelial receptor axons were prominent. In all these sensory receptors, the preterminal axons and axon terminals were labeled with the tracer protein. In addition, some nonneuronal cells closely associated with the axon terminals were selectively labeled, e.g., terminal Schwann cells, lamellar Schwann cells, Merkel cells, corpuscular basal cells and chemosensory cells. Other adjacent cells were not labeled, e.g., unspecialized epithelial cells, capsular cells, corpuscular sustentacular cells, and fibroblasts. In both labeled axons and cells, WGA-HRP was incorporated into vesicles, tubules, and vacuolar organelles. The specific intercellular transfer of tracer protein may indicate trophic interactions between axon terminals and support cells in sensory receptors. The specific organization of multiple sensory receptors in the rat incisive papilla may provide a useful alternative system for studying somatosensory physiology.

Animals↗
PubMed1988

Deficient axonal transport of substance P in streptozocin-induced diabetic rats. Effects of sorbinil and insulin.

This study measured the accumulation of substance P-like immunoreactivity (SPLI) proximal and distal to 12-h constricting ligatures applied to rat sciatic nerves. There were three separate experiments, and the baseline for each consisted of control and age-matched rats with 3 wk of untreated streptozocin-induced diabetes. We compared the effects of twice-daily insulin treatment, daily sorbinil (25 mg.kg-1.day-1 p.o.), and a combination of both treatments. In untreated diabetic rats the anterograde accumulation of SPLI was reduced by 30-40%. This deficit was unaffected by sorbinil alone but was attenuated by insulin and prevented completely by insulin and sorbinil combined. There were also indications that diabetes caused reductions in retrograde accumulation of SPLI and its content in unconstricted nerve and the L4 dorsal root ganglion. The fraction of SPLI undergoing net anterograde or retrograde movement and the velocities of accumulation were unaffected by diabetes or the treatment regimens. These findings indicate a reduction in the amount of substance P moved by axonal transport in diabetic rats that is related partly to aldose reductase activity and partly to some other insulin-correctable consequence of experimental diabetes.

Animals↗
PubMed1979

Forebrain projections of the ventral tegmentum as studied by axonal transport of [3H]dopamine in the rat.

Twenty-four hours after [3H]dopamine ([3H]DA) injections into different parts of the ventral tegmentum the radioactivity recovered in the forebrain showed a highly regional distribution which corresponded to well-known DA projections. Selective degeneration of DA-neurons with 6-hydroxydopamine (6-OHDA) markedly reduced the axoplasmic transport after [3H]DA injections. The ventral tegmental area (VTA) was found to project primarily to the nucleus accumbens, olfactory tubercle and amygdala. The DA-innervation of the entorhinal cortex and the amygdala derive from cells widely distributed in the VTA and SN.

Animals↗