Inhibition of axonal transport in vitro in frog sciatic nerves by chlorpromazine and lidocain. A biochemical and ultrastructural study

A calmodulin inhibitor with high specificity, compound 48/80, inhibits axonal transport in frog nerves without disruption of axonal microtubules

The calmodulin inhibitor compound 48/80 has previously been shown to arrest axonal transport in vitro in the regenerating frog sciatic nerve. The inhibition was limited to the outgrowth region of nerves, which had been allowed to regenerate in vivo for 6 days after a crush lesion, before they were incubated with or without drugs in vitro overnight. The effects of compound 48/80 on the regenerating nerve were further investigated. A concentration of compound 48/80 (50 micrograms ml-1), which effectively inhibits axonal transport, did not cause observable changes of the microtubules of regenerating axons in the outgrowth region as judged by electron microscopy. Furthermore, it was shown that also a lower concentration (25 micrograms ml-1) inhibited axonal transport. As a measure of possible metabolic effects, the level of ATP was assessed in the regenerating nerve after exposure to compound 48/80. Compound 48/80 at 25 micrograms ml-1 did not change the level of ATP in the nerve. The assembly of bovine brain microtubule proteins in a cell-free system was unaffected by 25 micrograms ml-1 of compound 48/80 and slightly inhibited by 50 micrograms ml-1. At higher concentrations (greater than 100 micrograms ml-1) assembly of microtubules appeared stimulated, and microtubule spirals as well as closely aligned microtubules could be seen. These effects appeared to be unrelated to the transport effects. The present results indicate that compound 48/80 arrests axonal transport via mechanisms other than destruction of axonal microtubules or interference with the energy metabolism. It is possible that these mechanisms involve inhibition of calmodulin-regulated events essential to the transport.

Mechanisms of the inhibition of fast axonal transport by local anesthetics

The present study attempted to clarify the mechanism(s) by which local anesthetics inhibit fast axonal transport. Spinal nerves of the bullfrog were incubated with local anesthetics under conditions known to inhibit transport and the effects of these exposures to local anesthetics on the content of adenosine triphosphate and creatine phosphate in nerves and on the density of microtubules in unmyelinated axons were examined. Lidocaine, at concentrations of 14 or 20 mM, did not reduce significantly the content of adenosine triphosphate (although significant reductions in creatine phosphate were observed); the density of microtubules was also not affected by 14 mM lidocaine. Some mechanism other than inhibition of oxidative metabolism or disruption of microtubules must therefore be responsible for the inhibition of fast axonal transport by 14 mM lidocaine. Significant reductions in the content of adenosine triphosphate were observed with 1 or 2 mM tetracaine and with 0.5 or 1 mM dibucaine (this latter concentration of dibucaine also reduced the content of creatine phosphate); however, comparison with the effects of 2,4-dinitrophenol indicated that these inhibitions of oxidative metabolism were insufficient to inhibit transport in the case of 0.5 mM dibucaine or could at best only partly explain the inhibition of transport in the other cases. Since the density of microtubules was not affected by 1 mM tetracaine and was not sufficiently reduced by 0.5 mM dibucaine to inhibit transport, some other effect must again largely contribute to or be solely responsible for the inhibition of fast axonal transport by these concentrations of dibucaine and tetracaine.

Dissociation of the inhibition of fast axonal transport by chlorimipramine from an effect on axonal microtubules

The effect of in vitro exposure of bullfrog spinal nerves to 0.2 mM chlorimipramine on the density of axonal microtubules was studied in an attempt to clarify the mechanism by which chlorimipramine inhibits fast axonal transport. A 17-h exposure to chlorimipramine reduced the density of microtubules in unmyelinated axons by only 18%; this microtubular loss does not reach the upper limit of the range of microtubule reduction associated with inhibition of fast axonal transport. A 23-h exposure to chlorimipramine, which had decreased microtubular density in unmyelinated axons by 40% in a previous study, did not decrease microtubular density in myelinated axons in the present study. These results rule out microtubular destruction as the mechanism responsible for inhibition of fast orthograde axonal transport by chlorimipramine, and greatly reduce the likelihood that microtubular destruction plays a significant role in the inhibition of fast retrograde transport by chlorimipramine.

Calmodulin-binding proteins within the slow phase of axonal transport in the rabbit vagus nerve

Calmodulin-binding proteins (CBPs) in the rabbit vagus nerve were studied by means of calmodulin-Sepharose affinity chromatography and polyacrylamide gel electrophoresis. The soluble fraction (10(5) g supernatant) of a nerve homogenate contained four CBPs with molecular weights of 44, 55, 91, and 93 kD, respectively. Slowly transported proteins were recovered in the vagus 3 days after injection of [35S]methionine into the nodose ganglion. Four labelled CBPs with molecular weights of 44, 55, 69, and 83 kD, respectively were found. The nodose ganglion contained two labelled CBPs, 44 and 55 kD. The 55-kD CBP was identified as tubulin after immunoblotting. In separate experiments it was also shown that bovine brain tubulin bound to the calmodulin column.

The effects of trifluoperazine on fast and slow axonal transport in the rabbit vagus nerve

The effects of trifluoperazine (TFP) on fast and slow axonal transport (AXT) of labeled proteins were examined in the rabbit vagus nerve. Cuffs soaked in a 10 mM, but not 0.1 mM or 1 mM, concentration of TFP applied locally around the vagus nerve in vivo blocked both fast and slow AXT, as measured by the accumulation of 3H-labeled proteins. In vitro, fast AXT was affected by 0.1 mM TFP. The TFP cuff treatment caused a reduction in the number of axonal microtubules (MT) whereas cuffs soaked in saline had no effect. The levels of ATP, ADP, and AMP were not significantly lowered by the TFP treatment. The results suggest that both fast and slow AXT are sensitive to TFP treatment, and that the axonal MT-system may be the main target of the drug.

Inhibition of fast axonal transport in bullfrog nerves by dibenzazepine and dibenzocycloheptadiene calmodulin inhibitors

The effects of the calmodulin inhibitors amitriptyline, desipramine, imipramine, and clomipramine on fast axonal transport, oxidative metabolism, and density of axonal microtubules were measured in bullfrog spinal nerves in vitro. The four drugs tested inhibited the fast orthograde transport of [3H]leucine-labelled proteins and the fast retrograde transport of acetylcholinesterase at a concentration of 0.2 mM. Amitriptyline, desipramine, and imipramine were equipotent inhibitors of transport, and clomipramine was a more potent inhibitor than imipramine. The adenosine triphosphate content of the nerves was reduced by at most 19% by the compounds under study; such a reduction cannot account for the inhibition of fast axonal transport. Desipramine and imipramine had no significant effect on the density of microtubules in unmyelinated axons, whereas amitriptyline only reduced it by 18%; the inhibition of axonal transport by these three drugs can therefore not be explained by microtubule disruption. Clomipramine reduced microtubular density by 40%, and this effect may have contributed to the inhibition of fast axonal transport. The inhibition of fast axonal transport by desipramine, imipramine, and amitriptyline may be related to the inhibition of calmodulin function by these drugs. The similar potency of these three drugs as inhibitors of fast axonal transport goes in parallel with their known similar potency as calmodulin antagonists.

Pineal neural connections with the brain in two teleosts, the crucian carp and the European eel

The neural connections between the pineal organ and the brain were investigated in two teleost species: the crucian carp and the European eel. Horseradish peroxidase (HRP) was administered into the pineal parenchyma in vivo or in vitro. After 12-96 hours, the brains were fixed, and HRP was reacted in frozen sections with either diaminobenzidine (DAB) or Hanker-Yate's reagent. The HRP had entered the pineal neurons, and had labeled their axonal processes (the pineal tract) in a Golgi-like manner. In both species, HRP-labeled axons were observed in the habenular nuclei, the pretectal area, the dorsal and ventral thalamus, the dorsal periventricular tegmentum, and in the posterior periventricular hypothalamus. In the eel, single axons were also observed in the anterior hypothalamus and in the brain stem. Thin, varicose (preterminal) axons were observed in great numbers in the pretectal area and dorsal thalamus in both species, and in small numbers in the habenular nuclei and posterior periventricular hypothalamus. For comparison, the retinofugal projections were visualized after intraocular HRP-injection. A close association of retinal and pineal terminal fields were noted in the pretectal area and the dorsal thalamus, whereas other diencephalic retinal and pineal recipient areas seem more segregated.

Effects of phenothiazines and dibenzazepines on axonal transport and microtubule assembly in vitro

Various phenothiazines (thioridazine, trifluoperazine and chlorpromazine) and dibenzazepines (lofepramine, amitriptyline and desipramine) were studied for effects on fast axonal transport (AXT) in vitro in frog sciatic nerves. AXT, measured as the accumulation of (3H) leucine-labelled proteins in front of a ligature, was inhibited by more then 50% by all the drugs tested at 0.2 mM concentrations. Thioridazine and lofepramine were the most potent inhibitors. These effects were not due to decreased ganglionic incorporation. Some of the drugs also reduced the levels of high energy phosphates, adenosinetriphosphate (ATP) and creatinephosphate (CrP), but not to an extent which is likely to explain the arrested AXT. The polymerization of purified brain tubulin was inhibited by the phenothiazines but unaffected by the dibenzazepines at concentrations which inhibited AXT. Phenothiazines and dibenzazepines are chemically related and known to have a high affinity for calmodulin. The possibility that these drugs interefere with calmodulin regulated processes of importance for AXT will be discussed.

Relation of somal lipid synthesis to the fast axonal transport of protein and lipid

The role of somal lipid synthesis in the fast axonal transport of protein and lipid was examined in vitro utilizing spinal/sciatic nerve preparations of bullfrog. Inhibition of phospholipid synthesis in dorsal root ganglia by the amphiphilic cation, fenfluramine (0.1-2.0 mM) was monitored as decreased incorporation of [3H]choline into phosphatidyl choline. This inhibition was directly proportional to a decrease in the amount of [3H]protein undergoing fast axonal transport, the two variables being related by a slope close to unity. [3H]Choline-labeled lipid undergoing fast transport in the axon was unaffected by inhibition of somal phospholipid synthesis. Levels of fenfluramine up to 1.0 mM had no effect on uptake or incorporation of [3H]leucine. Selective exposure of desheathed nerve trunks to 1.0 mM fenfluramine had no effect on [3H]protein translocation, indicating that local phospholipid synthesis is not required to maintain ongoing transport in the axon. Inhibition of cholesterol synthesis in the ganglia with the analog 20,25-diazacholesterol also resulted in depression of [3H]protein transport. Since synthesis of both phospholipid and cholesterol are required at the level of the ganglion, it is suggested that the initiation of fast axonal transport of protein is dependent on the assembly of lipoprotein structures in the soma.

Observations on fast axoplasmic transport in peripheral nerve following repetitive electrical stimulation

In a series of 13 cats the effect of electrical stimulation of peripheral nerve on the mechanism of fast axoplasmic transport was studied. Electrical stimulation was used for varying time periods at parameters reported in the range of those used to produce electroanalgesia in man. Our results indicate that at these parameters, electrical stimulation produced no effect on this important aspect of nerve function, and, therefore, our work lends support to the safety of these devices in pain states.

In vitro effects of chlorpromazine on microtubules and the Golgi complex in embryonic chick spinal ganglion cells: an electron microscopic study

Spinal ganglia from 11-day-old chick embryos were incubated in media containing chlorpromazine (CPZ), lidocaine or D-amphetamine and subsequently examined by transmission electron microscopy. CPZ and lidocaine both caused a structural modification of the neuroblasts similar to that induced by the microtubular-disrupting drugs colchicine and vinblastine. That is, there was a partial disappearance of cytoplasmic microtubules with a concomitant increase in the number of microfilaments and the dictyosomes of the Golgi complex changed, with the number of narrow cisternae decreasing and the number of associated vacuoles increasing. Moreover, the dictyosomes were more distinctly separated from each other than in control ganglia. D-Amphetamine did not give rise to any clear changes in either the microtubular system or the Golgi complex and, furthermore, opposed the colchicine-like effects of CPZ. On the basis of these results it is suggested that the subcellular mechanism of action of CPZ involves the cytoplasmic microtubular system and thus secondarily leads to structural and functional alterations in the Golgi complex, viz., in the case of nerve cells, a disturbance in the production and packaging of material destined for the axon terminals.

Fast axonal transport: effect of antimitotic drugs and inhibitors of energy metabolism on the rate and amount of transported protein in frog sciatic nerves

Mitosis inhibitors, drugs affecting the energy metabolism, heavy water, and ouabain were used to partially inhibit fast axonal transport in frog sciatic nerves. Effects on the rate and on the amount of pulse labeled protein could be separated. The pulse of labeled protein, released after a cold-block, rapidly reached a maximum height which indicated that the transport system was saturated in the nerve segment occupied by the pulse. Both the rate and the amount were reduced by the mitosis inhibitors colchicine, vinblastine, and griseofulvin. Colchicine had a differential effect and reduced the rate of material migrating in the advancing front of the pulse less than the rate of that moving in the peak. Preincubation at low temperature potentiated the effects of colchicine. Two inhibitors of energy metabolism, NaCN and IAA, reduced the amount of labeled material in the pulse. The slope of the pulse was markedly reduced and multiple peaks appeared. The distance covered by the migrating pulse was largely unaffected, but some retardation of late components might have occurred. In contrast, 2.4-DNP reduced the rate without any effects on the amount of migrating material. Heavy water uniformly reduced the rate of the migrating pulse, whereas the main effect of ouabain was a diminished amount and multiple peaks as with NaCN and IAA. All drugs were tested for their effects on the electrical activity of sciatic nerves. The compound action potential was not affected by the mitosis inhibitors and heavy water, but was depressed by the inhibitors of energy metabolism and abolished by ouabain. The results indicate that the effects of various transport inhibitory drugs can be differentiated if both the rate and the amount are considered.

Time- and dose-dependent influence of ouabain on the ultrastructure of optic neurones

The cardiac glycoside ouabain was injected into the eye-bulb of the teleost fish, Carassius carassius. Three doses of ouabain were used: 10(-4) M, 10(-5) M, 10(-6) M. The final concentrations in the vitreous body of the eye were approximately 3-10(-5) M, 3-10-6 M and 3-10-7 M, respectively. After 8 hrs, 1, 2, 4, 6 and 8 days the ultrastructural alterations of retinal ganglion cells, the optic axons near the bulb and the terminal segments in the optic tectum were studied. The high doses of ouabain induced an early necrobiosis of the cell bodies in the retina followed by degeneration in the nerve. This is characterized as a protracted form of Wallerian degeneration. The significance of the inhibition of Na+ -K+-activated ATPase at the perikaryal level for both the integrity of axonal morphology and the axonal flow is discussed.

Reversal of morphological differentiation of mouse neuroblastoma cells by mitosis-inhibitors and anesthetics

Differentiated mouse neuroblastoma cells (C 1300) were exposed to various mitosis-inhibitors (vinblastine, colchicine and griseofulvin) and substances with anesthetic action (lidocaine, tetracaine, chlorpromazine and sodium dodecyl sulphate). All the drugs caused rapid retraction of the neurites, which was reversible in all cases but for sodium dodecyl sulphate, and showed a sigmoid dose-response relationship. The two groups of substances caused morphologically similar effects in that the microtubules disappeared and the intracellular orientation was lost. The order of potency of the anesthetics corresponded to their efficiency to cause nerve-block and antihemolysis as reported by others. Colchicine, griseofulvin, lidocaine and chlorpromazine were tested for effects of agglutination of undiffentiated cells. They inhibited agglutination at doses that were only slightly higher than those causing neurite retraction. The possibility of a close relationship between the cell membrane and microtubule system will be considered.

Slow axonal transport or proteins; blockade by interruption of contact between cell body and axon

The influence of ligation and colchicine treatment on the axonal transport of slowly migrating [3H]leucine-labelled proteins was studied in the vagus nerve of the rabbit. Two days after [3H]leucine labelling of the dorsal motor nucleus of the vagus nerve, ligation or local application of 60 mM colchicine immediately blocked the further progression of slowly migrating proteins distal to the site of treatment. Application of 50-100 mug colchicine to the nerve cell bodies 2 days after labelling blocked the transport of slowly migrating proteins within the next 24 h. It is suggested that contact between nerve cell body and the axon is necessary for the maintenance of the slow transport of proteins in these nerves.