Blockade Of Axoplasmic Transport Research Articles

Axonal Transport in Coats’ Disease and Congenital Oculodentodigital Syndrome

Introduction: Axoplasmic transport blockade has been demonstrated in acute experimental glaucoma in animals but has not been documented in childhood glaucoma. The purpose of this study was to detail findings and axoplasmic transport status in one eye of a two-year old male with Coat’s disease using the two eyes from a 10-month-old female with Oculodentodigital Syndrome (ODDS) as controls for background axoplasmic transport. We document for the first-time axonal transport block in the lamina cribrosa (LC) in a blind and painful right eye associated with Coats’ disease, (Case 1). Enucleation was done for suspected retinoblastoma without imaging. Histopathology demonstrated myriad macrophages migrated from the vitreous infiltrate into the anterior chamber and meshwork explaining the glaucoma. Two eyes from Case 2, diagnosed at autopsy as having congenital Oculodentodigital Syndrome (ODDS), with a history of surgically normalized intraocular pressures were included as controls for the Coats’ case immunohistochemistry (IHC) and to report additional findings in this rare disorder. Methods: We reviewed available history and performed histopathology on one enucleated Coats’ globe and two additional autopsy eyes from an ODDS case with routine staining of paraffin-processed tissues and amyloid precursor protein (APP-A4) IHC, the only available IHC marker for orthograde axonal transport in human surgical or autopsy tissues. The two eyes from the 10-month-old infant with ODDS had normal IOPs following trabeculotomies at five months of age. Results: In addition to typical pathology for Coats’ the lamina cribrosa portion of the optic nerve from Case 1 demonstrated marked orthograde axonal transport block. Both eyes from Case 2 with ODDS had a history of congenital glaucoma treated medically before bilateral trabeculotomies at five months-age with normalization of IOPs. Descemet scrolls found OD were judged residual to goniotomy. Both globes from Case 2 demonstrated multiple anomalies previously reported in ODDS including microphthalmos, optic disc dysplasia OD, and features of persistent hyperplastic primary vitreous (PHPV) OU. The right eye also demonstrated spontaneous retinal detachment prompting an exam under general anaesthesia at 10-months age when, during induction, she expired with malignant tachycardia. Retinal ganglion cells (RCGs) labeled with APP-A4 OU, but optic nerve LC axons demonstrated only background accumulations of the IHC marker. Conclusions: Orthograde axonal transport was interrupted in the LC of the Coats’ nerve due to secondary inflammatory glaucoma. The angle remained open histologically in-spite-of-early neovascularization and pupillary margin ectropion. Block of orthograde axonal transport in the LC has been well established as the site of initial optic nerve damage in glaucoma in experimental studies and this report reinforces its importance to the pathophysiology of glaucoma optic nerve damage. The primary importance of the two ODDS globes for our report was as comparison controls for background APP-A4 staining in the Coats’ case. Our additional findings in the ODDS eyes suggest delayed spontaneous retinal detachment, and lens epithelial abnormalities are additional anomalies to add to the list of known malformations in this rare disorder. Case 2 also serves as a caution in ODDS regarding vulnerability to combinations of medications when general anaesthesia is contemplated.

Reversible blockade of retrograde axonal transport in the rat sciatic nerve by vincristine.

Altered axoplasmic transport has been implicated as a contributing factor in neuropathic pain states. Treatments which produce transient axoplasmic transport blockade have shown initial promise as therapeutic procedures in the management of chronic neuropathic pain. The present study evaluated the capacity of the vinca alkaloid, vincristine to produce reversible blockade of retrograde axoplasmic transport. Results indicated that intraneural administration of 10(-5)M vincristine resulted in blockade of retrograde axoplasmic transport of [3H]leucine 24 h following administration. Importantly, the effect reversed over the next four days and axoplasmic transport was re-instated fully at day five. The implications of these results are discussed in relation to the potential use of axoplasmic transport blocking agents in the management of chronic neuropathic pain.

Iontophoretically applied microtubule inhibitors induce transganglionic degenerative atrophy of primary central nociceptive terminals and abolish chronic autochtonous pain.

Transcutaneous iontophoresis of microtubule inhibitors (Vinblastin, Vincristin, Formyl-Leurosin) in rats induces depletion of fluoride-resistant acid phosphatase (FRAP) and transganglionic degenerative atrophy (trggl. deg. atr.) of the central terminals of primary nociceptive neurons, probably via blockade of axoplasmic transport in the peripheral sensory nerves. Radiochemical experiments prove that about 0.2% of the microtubule inhibitors applied iontophoretically at the skin reach the level of nociceptive axon terminals. 40 out of 48 patients suffering from chronic intractable pain of diverse etiology (postherpetic, paresthetic, ischaemic and trigeminal neuralgia, alcoholic and diabetic polyneuropathy, meralgia, brachialgia, discopathia, arthropathia and terminal pain) were successfully treated with Vinblastin or Vincristin iontophoresis. Iontophoretically applied microtubule inhibitors do not affect the blood cell count, have no side-effects and do not impair the skin at the site of application.

Ganglion cell death in rat retina by persistent intraocular pressure elevation.

Glaucoma is characterized by loss of retinal ganglion cells (RGCs) and their axons. Retrograde axoplasmic transport blockade and excitotoxicity were proposed to be a major cause of RGC apoptosis. We conducted this study to characterize the episcleral vessel cauterization glaucoma model in the rat with respect to decreased retrograde axoplasmic flow and subsequent apoptotic RGC death. After episcleral vessels were cauterized in Sprague-Dawley rats, Fluorogold was injected into their superior colliculi by stereotactic method. Retrograde axoplasmic flow and TUNEL-stained apoptotic dead cells were observed microscopically. Elevated intraocular pressure was maintained for up to 6 weeks during follow-up. Retrograde axoplasmic flow to the rat retina was significantly decreased. Apoptotic RGC was selectively TUNEL-stained in the retina, especially at the ganglion cell layers. We concluded that elevated intraocular pressure caused apoptotic RGC death through retrograde axoplasmic flow blockage. Further studies will elucidate the neuroprotection strategies in glaucoma patients.

Prevention of galanin upregulation following neonatal infraorbital nerve transection or attenuation of axoplasmic transport does not rescue central vibrissae-related patterns in the rat

Neonatal transection of, or blockade of axoplasmic transport in, the infraorbital nerve [ION, the trigeminal (V) branch that supplies the mystacial vibrissae follicles] results in a loss of all central patterns corresponding to the vibrissae follicles in the brainstem, thalamus and cortex except for those of the central terminal arbors of ION primary afferents that survive this lesion. Both of these manipulations also result in a rapid and dramatic upregulation of at least two peptides, galanin and neuropeptide Y, in surviving vibrissae-related primary afferents. Galanin is of particular interest, because this peptide has effects on neuronal activity and growth, both factors which may be involved in the disappearance of central vibrissae-related patterns in rats that have sustained neonatal ION transection or axoplasmic transport blockade. The present study used antisense technology to determine whether the upregulation of galanin in the central terminals of ION primary afferents is necessary for the loss of central vibrissae-related patterns in rats. Newborn rats had their left ION transected or axoplasmic transport in this nerve blocked by application of a vinblastine-impregnated implant, and at the same time received an injection of commercially synthesized phosphorothioate oligodeoxynucleotide sequences (15-20 bases) directly into the V ganglion in order to block galanin upregulation. These injections effectively prevented the upregulation of this peptide which is normally associated with ION transection or axoplasmic transport blockade. Preventing galanin upregulation, however, did not prevent or attenuate the loss of central vibrissae-related patterns in the brainstem or cortex normally observed following ION transection or axoplasmic transport blockade in this nerve. These results are thus consistent with the conclusion that the upregulation of galanin in the central terminals of V primary afferents, observed after damage to or attenuation of axoplasmic transport in the ION, is not necessary for the reorganization that results in a disappearance of central vibrissae-related patterns in the V neuraxis.

Effects of Neonatal Attenuation of Axoplasmic Flow or Transection of the Rat's Infraorbital Nerve on the Morphology of Individual Trigeminal Primary Afferent Terminals in the Brainstem

Attenuation of axoplasmic transport in the infraorbital nerve (ION), or transection of this trigeminal (V) branch at birth, results in degradation of the central cellular aggregates related to the mystacial vibrissae. However, blockade of axoplasmic transport does not result in the nearly 90% loss of ION ganglion cells that follows neonatal transection of this nerve. The present study was undertaken to further characterize the response of individual ION axons to attenuation of axoplasmic transport and to compare these effects to the changes observed following nerve transection. Neurobiotin injections were made into the V ganglion on postnatal day (P-) 6 in normal rats and animals that had vinblastine applied to the ION or received transection of the ION on P-0. Individual labeled fibers in the portions of V nucleus principalis (PrV) and subnucleus interpolaris (SpI) innervated by the ION were drawn from single sections with the aid of a computer. Morphological analysis of fibers drawn in SpI indicated no significant differences between axons from normal and vinblastine-treated animals. The fibers drawn from rats that sustained ION transection had significantly more branch points (P<0.05) than those from either normal or vinblastine-treated animals. In PrV, fibers drawn from vinblastine-treated rats had a slightly, but significantly, larger total process length and cross-sectional area than those from the normal animals (P<0.05). There were no other significant differences among the three groups of axons. These results support the conclusion that application of vinblastine to the developing ION does not dramatically alter the morphologic patterning of the central arbors of its axons.

Protective effect of a low dose of colchicine on the delayed cell death of hippocampal CA1 neurons following transient forebrain ischemia

Transient forebrain ischemia in rats preferentially causes neuron death in the striatum and hippocampal CA1 area. Prior injection of a low dose (1 μl) of colchicine (1 μM) into the unilateral hippocampus prevented ischemic damage of CA1 neurons in both hippocampal hemispheres, whereas no protection against ischemic damage was seen in the striatum. These results suggest that disconnection of hippocampal neurons by blockade of axoplasmic transport with colchicine specifically protects ischemic damage of CA1 neurons.

231 Region-specific increase in capsaicin-evoked release of glutamate from lumbar dorsal horn of rat given three different inflammatory stimuli

The aim of this study was to assess the effect of blocking the axonal transport of sensory neuropeptides, by local injection of colchicine at pelvic ganglia level, on the sensory and efferent functions mediated by capsaicin-sensitive primary afferent neurons innervating the rat urinary bladder. Bilateral injection of colchicine in the prostatic tissue underneath the pelvic ganglia of male rats induced a time-dependent reduction (maximal at 72 h, 100% reduction) of the in vitro contraction of the bladder strips induced by capsaicin (1 μM). The response to electrical field stimulation was also reduced, although to a lesser extent. The direct contractions induced by substance P (100 nM) or KCl (80 mM) were not affected by colchicine pretreatment. In vivo, perigangliar injection of colchicine (72 h before) greatly increased bladder capacity, and reduced the amplitude of micturition contractions and micturition frequency. Capsaicin-induced plasma protein extravasation was abolished in the urinary bladder and reduced in the distal, but not the proximal ureter of colchicine-treated rats. Topical application of capsaicin onto the urinary bladder or onto the stomach induced a cardiovascular pressor reflex in urethane-anaesthetized, spinalized rats. Colchicine pretreatment reduced (by about 50%) the pressor response elicited by chemonociceptive stimulation of the bladder but not that arising from the stomach.Colchicine pretreatment did not produce overt changes of nerve profiles immunoreactive for calcitonin gene-related peptide- or tachykinin-like material in the rat urinary bladder. A more intense staining of nerve fibres positive for calcitonin-gene related peptide-like immunoreactivity and tachykinin-like immunoreactivity was observed in pelvic ganglia of colchicine-pretreated rats. No changes were detected in the dorsal horns of spinal cord segments where pelvic bladder afferents project (L6-S1). Colchicine pretreatment reduced, but did not abolish, bladder levels of substance P-, neurokinin A-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity. However, vasoactive intestinal peptide-like immunoreactivity levels were not changed. The capsaicin-evoked (1 μM) release of calcitonin gene-related peptide was abolished in capsaicin as well as in colchicine-pretreated animals.The present findings demonstrate that local treatment of pelvic ganglia with colchicine totally eliminates the “efferent” functions of capsaicin-sensitive afferent nerves in the urinary bladder. Although reduced, tissue levels of sensory neuropeptides are not completely depleted, thus indicating the existence of a releasable versus non-releasable pool. The chemically induced blockade of axoplasmic transport also induces a limited impairment of the sensory function of capsaicin-sensitive afferents. and of the parasympathetic efferent system.

Region-specific increase in capsaicin-evoked release of glutamate from lumbar dorsal horn of rat given three different inflammatory stimuli

The aim of this study was to assess the effect of blocking the axonal transport of sensory neuropeptides, by local injection of colchicine at pelvic ganglia level, on the sensory and efferent functions mediated by capsaicin-sensitive primary afferent neurons innervating the rat urinary bladder. Bilateral injection of colchicine in the prostatic tissue underneath the pelvic ganglia of male rats induced a time-dependent reduction (maximal at 72 h, 100% reduction) of the in vitro contraction of the bladder strips induced by capsaicin (1 μM). The response to electrical field stimulation was also reduced, although to a lesser extent. The direct contractions induced by substance P (100 nM) or KCl (80 mM) were not affected by colchicine pretreatment. In vivo, perigangliar injection of colchicine (72 h before) greatly increased bladder capacity, and reduced the amplitude of micturition contractions and micturition frequency. Capsaicin-induced plasma protein extravasation was abolished in the urinary bladder and reduced in the distal, but not the proximal ureter of colchicine-treated rats. Topical application of capsaicin onto the urinary bladder or onto the stomach induced a cardiovascular pressor reflex in urethane-anaesthetized, spinalized rats. Colchicine pretreatment reduced (by about 50%) the pressor response elicited by chemonociceptive stimulation of the bladder but not that arising from the stomach.Colchicine pretreatment did not produce overt changes of nerve profiles immunoreactive for calcitonin gene-related peptide- or tachykinin-like material in the rat urinary bladder. A more intense staining of nerve fibres positive for calcitonin-gene related peptide-like immunoreactivity and tachykinin-like immunoreactivity was observed in pelvic ganglia of colchicine-pretreated rats. No changes were detected in the dorsal horns of spinal cord segments where pelvic bladder afferents project (L6-S1). Colchicine pretreatment reduced, but did not abolish, bladder levels of substance P-, neurokinin A-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity. However, vasoactive intestinal peptide-like immunoreactivity levels were not changed. The capsaicin-evoked (1 μM) release of calcitonin gene-related peptide was abolished in capsaicin as well as in colchicine-pretreated animals.The present findings demonstrate that local treatment of pelvic ganglia with colchicine totally eliminates the “efferent” functions of capsaicin-sensitive afferent nerves in the urinary bladder. Although reduced, tissue levels of sensory neuropeptides are not completely depleted, thus indicating the existence of a releasable versus non-releasable pool. The chemically induced blockade of axoplasmic transport also induces a limited impairment of the sensory function of capsaicin-sensitive afferents. and of the parasympathetic efferent system.

Functional, biochemical and anatomical changes in the rat urinary bladder induced by perigangliar injection of colchicine.

The aim of this study was to assess the effect of blocking the axonal transport of sensory neuropeptides, by local injection of colchicine at pelvic ganglia level, on the sensory and efferent functions mediated by capsaicin-sensitive primary afferent neurons innervating the rat urinary bladder. Bilateral injection of colchicine in the prostatic tissue underneath the pelvic ganglia of male rats induced a time-dependent reduction (maximal at 72 h, 100% reduction) of the in vitro contraction of the bladder strips induced by capsaicin (1 microM). The response to electrical field stimulation was also reduced, although to a lesser extent. The direct contractions induced by substance P (100 nM) or KCl (80 mM) were not affected by colchicine pretreatment. In vivo, perigangliar injection of colchicine (72 h before) greatly increased bladder capacity, and reduced the amplitude of micturition contractions and micturition frequency. Capsaicin-induced plasma protein extravasation was abolished in the urinary bladder and reduced in the distal, but not the proximal ureter of colchicine-treated rats. Topical application of capsaicin onto the urinary bladder or onto the stomach induced a cardiovascular pressor reflex in urethane-anaesthetized, spinalized rats. Colchicine pretreatment reduced (by about 50%) the pressor response elicited by chemonociceptive stimulation of the bladder but not that arising from the stomach. Colchicine pretreatment did not produce overt changes of nerve profiles immunoreactive for calcitonin gene-related peptide- or tachykinin-like material in the rat urinary bladder. A more intense staining of nerve fibres positive for calcitonin-gene related peptide-like immunoreactivity and tachykinin-like immunoreactivity was observed in pelvic ganglia of colchicine-pretreated rats. No changes were detected in the dorsal horns of spinal cord segments where pelvic bladder afferents project (L6-S1). Colchicine pretreatment reduced, but did not abolish, bladder levels of substance P-, neurokinin A-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity. However, vasoactive intestinal peptide-like immunoreactivity levels were not changed. The capsaicin-evoked (1 microM) release of calcitonin gene-related peptide was abolished in capsaicin as well as in colchicine-pretreated animals. The present findings demonstrate that local treatment of pelvic ganglia with colchicine totally eliminates the "efferent" functions of capsaicin-sensitive afferent nerves in the urinary bladder. Although reduced, tissue levels of sensory neuropeptides are not completely depleted, thus indicating the existence of a releasable versus non-releasable pool. The chemically induced blockade of axoplasmic transport also induces a limited impairment of the sensory function of capsaicin-sensitive afferents, and of the parasympathetic efferent system.

Neonatal infraorbital nerve transection and blockade of axoplasmic transport reduce expression of acetylcholinesterase by thalamocortical axons

Acetylcholinesterase (AChE) is transiently expressed by ventrobasal thalamic neurons and their axons in the primary somatosensory cortex and this enzyme has been used as a marker for these axons in studies concerned with cortical development and plasticity. The present experiment evaluated the effects of both peripheral nerve transection and blockade of axoplasmic transport upon the expression of AChE in thalamic axon terminals in the primary somatosensory cortex. Both manipulations resulted in marked reductions in the density of AChE in thalamocortical axons and less dramatic decreases in the density of this enzyme in thalamic neurons. These results indicate that AChE may not invariably provide unequivocal information about the distribution of somatosensory thalamocortical axon terminals in developing rodents.

Studies related to the use of colchicine as a neurotoxin in the septohippocampal cholinergic system

Colchicine has been shown to be neurotoxic to cholinergic neurons in the medial septum 1 week following intracerebroventricular injections. The experiments described here were designed to examine the selectivity of this effect over a longer time course, and to examine the role of axoplasmic transport in the neurotoxic effect. As previously reported, 1 week after intracerebroventricular injections of colchicine, the numbers of choline acetyltransferase (ChAT)-immunoreactive neurons in the medial septum-diagonal band complex (MSDB) were reduced to 38% of control; this reduction was stable 2 and 3 weeks post injection. Injections of colchicine placed into the body of the fornix produced similar results. GAD-immunoreactive somata, the other major population of neurons in the MSDB, were unaffected 3 weeks following colchicine, as previously reported 1 week following similar injections. The normal AChE staining pattern in the hippocampus, particularly the dentate gyrus, was depleted following either ICV or intrafornical injections of colchicine. This depletion was more severe with longer survival times. Injections of lumicolchicine, an isomer of colchicine which does not bind tubulin, had no effect on ChAT-immunoreactive neurons in the MSDB or on AChE staining in the hippocampus. Injections of colchicine, but not of lumicochicine, partially blocked the retrograde transport of the fluorescent dye Fluoro-Gold from the hippocampus to the MSDB. In addition, the content of NGF in the hippocampus rose 84% above control values 2 weeks following colchicine and remained elevated at three weeks. Together these results indicate that colchicine is selectively toxic for cholinergic neurons in the septohippocampal system, and suggest that the alkaloid's neurotoxic effects work via the blockade of axoplasmic transport.

Neurotrophic control of myosin synthesis by guinea pig slow muscle

After experimental cease of neurotrophic control of skeletal muscle by denervation no changes in myosin ATP-ase histochemistry and immunohistochemical profile in slow (m. soleus) muscle of guinea pig were found. All muscle fibers in intact muscle fibers). However after colchicine blockade of axoplasmic transport in this slow muscle some muscle fibers reacting with monoclonal antibodies against fast myosin heavy chain were found. At the same time no changes in histochemical ATP-ase profile were observed. Validity of myosin ATP-ase histochemistry for muscle fibers typing as well as possible influence of nerve activity and neurotrophic control itself were discussed.

Immunocytochemical evidence for stimulatory control by the ventral noradrenergic bundle of parvocellular neurons of the paraventricular nucleus secreting corticotropin releasing hormone and vasopressin in rats

The regulation, by catecholaminergic innervation, of parvocellular neurons of the paraventricular nuclei (PVN) secreting corticotropin releasing hormone (CRH) and vasopressin (Vp) was studied by immunocytochemical visualization of both neurohormones in control rats and in rats given discrete injections of 6-hydroxydopamine in the ventral noradrenergic ascending bundle (VNAB). In both groups, the changes in immunostaining intensities observed in axon terminals of the external median eminence and in PVN perikarya 48 h after a blockade of axoplasmic transport by intraventricular injections of colchicine, served as an index for hormonal release and synthesis. In controls, this treatment induced a strong decrease in CRH and Vp immunoreactivity within the terminals, together with intense labeling of PVN perikarya containing CRH. By contrast, bilateral VNAB lesions strikingly inhibited both the colchicine-induced reduction of the CRH and Vp immunoreactivity in axons and the accumulation of CRH in the perikarya. Unilateral VNAB lesions induced similar alterations but these were restricted to the ipsilateral PVN and median eminence. Comparison of these immunocytochemical data with earlier physiological observations on the effects of VNAB lesions on ACTH secretion indicates that the catecholaminergic afferents to the PVN conveyed by the VNAB stimulate the release and the synthesis of CRH and Vp by parvocellular neurons projecting into the external median eminence.

Axoplasmic transport of substances in motoneuronal axons of the spinal cord in old age

Seven to eight microliters of aqueous solution of spl-[ 14C]Leucine (spec. act. 339 mCi/mmol) were introduced in the zone of ventral horn (L 5—L 6) of the spinal cord of adult (8–12 months) and old (26–28 months) rats. The radioactivity of various parts of the corresponding ventral roots was measured 1–2.5 h thereafter. Labelled substances (including protein) were found to migrate with fast flow in adult rats at the rate of 408 ± 10.9 and 380 ± 22 mm/24 h. respectively, as compared with 217 ± 11.3 and 200 ± 40 mm/24 h in old rats. The axoplasmic flow slows down in old rats with the increase of distance from the neuronal body. Uncoupling of oxidation and phosphorylation by the administration of 2,4-dinitrophenol, inhibition of glycolysis with NaF, hypoxemia produce more marked deceleration of axoplasmic flow in old rats, while small doses of NaF accelerate the flow, which correlates with the rise of cAMP in ventral roots. Sex steroids accelerate significantly the rate of axoplasmic flow. There is a marked increase in the rate due to the adminsitration of estradiol dipropionate in old rats and due to testosterone propionate in adult animals. Changes in resting membrane potential and direct excitability thresholds of some muscles following colchicine blockade of axoplasmic transport are less marked in old rats that evidences for the weakening of neurotrophic control in old age.

Effect of axoplasmic transport blockade on end-plate currents in frog muscle fibers

Evoked and spontaneous end-plate currents (EPC) were studied in normal voltage-clamped frog sartorius muscle fibers and 2 weeks after application of colchicine to the nerve innervating the muscle to block axoplasmic transport in its fibers. Application of colchicine was found to reduce the rate of rise and to prolong decay of EPC without affecting the amplitude of the EPC and miniature EPC, the quantum composition of EPC, and the frequency of miniature EPC. The histogram of distribution of the time constant (τ) of EPC decay under normal conditions follows the normal law, but after application of colchicine to the nerve it is shifted to the right, with separation of two modes (τ1 and τ2). Three types of synapses can be distinguished from the character of EPC decay: monoexponential decay with τ1 (44%), biexponential decay with τ1 and τ2 (39%), and monoexponential decay with τ2 (19%). An increase in τ of EPC decay is accompanied by strengthening of the dependence of this process on the clamping voltage. The current-voltage characteristic and reversal potential of EPC are unchanged. It is suggested that the change in character of EPC decay after application of colchicine to the motor nerve is due to the appearance of acetylcholine-activated ionic channels in the muscle membrane with a longer duration of the open state and with potential-dependence of the open state similar to that taking place after muscle denervation.

Effect of inhibitors of protein synthesis on denervation-like changes in frog muscle fiber membranes induced by axoplasmic transport blockade by colchicine

Blocking neurotrophic influences on muscle by denervation alters the electrophysiological properties of the muscle fiber membrane: The resting membrane potential (RMP) is reduced, input resistance (Ro) and the time constant (T) of the muscle membrane are increased, and extrasynaptic sensitivity to acetylcholine (ACh) develops [2, 6, 8, 13]. Administration of inhibitors of protein synthesis (actinomycin D or cycloheximide) to experimental animals at the same time as the nerve is divided inhibits the development of postdenervation changes in mammals. It has accordingly been postulated that neurotrophic control is exerted through the muscle fiber gene [9].

Electrophysiological study of transmitter release in frog neuromuscular synapses under colchicine blockade of axoplasmic transport

Electrophysiological study of transmitter release in frog neuromuscular synapses under colchicine blockade of axoplasmic transport

Electrical and acetylcholine-receptive properties of the muscle fiber membrane after axoplasmic transport blockade by colchicine

Electrical properties of the membrane and sensitivity of the fibers to acetylcholine were investigated in the frog sartorius muscle after denervation and a single application of colchicine to the nerve. After both types of procedure the electrical properties showed similar changes and extrasynaptic sensitivity to acetylcholine appeared. No such changes took place in the fibers of the contralateral muscle. Injection of colchicine into the lymphatic sac did not affect the electrical properties of the membrane, but widened the zone of sensitivity to acetylcholine. The results are regarded as further evidence in support of the view that denervation-like changes after application of colchicine to the motor nerve, when the transmission of excitation of nerve to muscle is preserved, are the result of a disturbance of the supply of neurotrophic substances along the axon by means of axoplasmic transport.

Neurotrophic regulation of muscle autolytic activity

Axoplasmic transport is involved in the neurotrophic regulation of muscle metabolism. Nevertheless, the mechanism of this transsynaptic regulation is still unknown. In the present work, the effect of axoplasmic transport on muscle autolytic activity was studied. Colchicine, a drug known to interfere with axoplasmic transport, was injected under the epineurium of the hypoglossal nerve and the autolytic activity of the corresponding geniohyoid muscle was measured at different times after drug treatment. A blockade of axoplasmic transport by colchicine produced a significant and reversible increase in muscle autolytic activity. This result suggests that neurogenic molecules play an important role in the regulation of muscle catabolism.