Cytotoxic effects of adriamycin on mouse hypoglossal neurons following retrograde axonal transport from the tongue

Synaptic Plasticity on Motoneurons After Axotomy: A Necessary Change in Paradigm

Motoneurons axotomized by peripheral nerve injuries experience profound changes in their synaptic inputs that are associated with a neuroinflammatory response that includes local microglia and astrocytes. This reaction is conserved across different types of motoneurons, injuries, and species, but also displays many unique features in each particular case. These reactions have been amply studied, but there is still a lack of knowledge on their functional significance and mechanisms. In this review article, we compiled data from many different fields to generate a comprehensive conceptual framework to best interpret past data and spawn new hypotheses and research. We propose that synaptic plasticity around axotomized motoneurons should be divided into two distinct processes. First, a rapid cell-autonomous, microglia-independent shedding of synapses from motoneuron cell bodies and proximal dendrites that is reversible after muscle reinnervation. Second, a slower mechanism that is microglia-dependent and permanently alters spinal cord circuitry by fully eliminating from the ventral horn the axon collaterals of peripherally injured and regenerating sensory Ia afferent proprioceptors. This removes this input from cell bodies and throughout the dendritic tree of axotomized motoneurons as well as from many other spinal neurons, thus reconfiguring ventral horn motor circuitries to function after regeneration without direct sensory feedback from muscle. This process is modulated by injury severity, suggesting a correlation with poor regeneration specificity due to sensory and motor axons targeting errors in the periphery that likely render Ia afferent connectivity in the ventral horn nonadaptive. In contrast, reversible synaptic changes on the cell bodies occur only while motoneurons are regenerating. This cell-autonomous process displays unique features according to motoneuron type and modulation by local microglia and astrocytes and generally results in a transient reduction of fast synaptic activity that is probably replaced by embryonic-like slow GABA depolarizations, proposed to relate to regenerative mechanisms.

Graphene oxide and adenosine triphosphate as a source for functionalized carbon dots with applications in pH-triggered drug delivery and cell imaging

A folate-functionalized carbon dot-based nanocarrier system has been successfully synthesized for cancer cell targeted drug delivery.

Intraneural OX7-saporin for neuroma-in-continuity in a rat model

We employed 54 rats to devise a model of neuroma-in-continuity and explore the effect of the immunotoxin OX7-saporin on the neuroma. The left common peroneal, tibial or sciatic nerves were crushed by one 10-s application of a micro-artery forceps. At 3 and 6 weeks, the nerve was cut distal to the site of nerve crush, and retrograde fluorescent labeling was done. Pressure microinjection of 2 μl of natural saline or 2 μl of the immunotoxin conjugate OX7-saporin was done at the nerve stump 2 days later. Sacrifice was done after 3 weeks. In all control and saline-injection nerve specimens, gross observation and histology showed a neuroma-in-continuity. In 19 of the 24 OX7-saporin nerve specimens, gross observation showed a narrowed area at the site of nerve crush. Histology showed inhibition of neuroma-in-continuity formation. Fluorescent microscopy showed ablation of the labeled neurons in the dorsal root ganglia corresponding to the OX7-saporin subgroups.

Current treatment concepts for neuromas-in-continuity

A neuroma-in-continuity is a neuroma that results from failure of the regenerating nerve growth cone to reach peripheral targets. It occurs within an intact nerve in response to internally damaged fascicles, resulting in a distal portion of the nerve that no longer functions properly. Management of neuromas-in-continuity is challenging. Chemical methods, and microsurgical techniques including fascicular ligation, and burying into muscle and bone have been reported to prevent neuroma-in-continuity formation. The purpose of this article is to present novel techniques for neuroma-in-continuity management, and to discuss the related literature.

Neuronal lesioning with axonally transported toxins

Axonally transported toxins can be used to make selective lesions of the nervous system. Collectively, these techniques are termed 'molecular neurosurgery' because they exploit the surface molecular identity of neurons to selectively destroy specific types of neurons. Suicide transport, is anatomically selective but not type-selective. The most widely used suicide transport agents are the toxic lectins (ricin, volkensin) and the immunotoxin, OX7-saporin. The toxic lectins and saporin are ribosome inactivating proteins that irreversibly inhibit protein synthesis. The toxic lectins have binding subunits but saporin requires a targeting vector to gain entrance into cells. Immunolesioning uses monoclonal anti-neuronal antibodies to deliver saporin selectively into neurons that express a particular target surface antigen. Neuropeptide-saporin conjugates selectively destroy neurons expressing the appropriate peptide receptors. Notable experimental uses of these agents include analysis of the function of the cholinergic basal forebrain (192-saporin) and pain research (anti-DBH-saporin, substance P-saporin). It is likely that more immunolesioning and neuropeptide-toxin conjugates will be developed in the near future.

Pharmacology of botulinum toxin

BACKGROUND

Botulinum toxin has a well-defined role among dermatologists for the treatment of facial wrinkling, brow position, and palmar and axillary hyperhidrosis.

OBJECTIVE

The purpose of this study is to educate dermatologists on the pharmacology of botulinum toxin.

METHODS

A retrospective review of the literature on botulinum toxin from 1962 to the present was conducted. We examined the clinical applications of botulinum toxin, cholinergic neuromuscular transmission, the toxin's structure and molecular actions, drug and disease interactions at the neuromuscular junction, toxin assays, determinants of clinical response, and adverse side effects.

RESULTS

Botulinum toxin blocks the release of acetylcholine from the presynaptic terminal of the neuromuscular junction. Several drugs and diseases interfere with the neuromuscular junction and the effects of botulinum toxin. The mouse bioassay, the most sensitive and specific measurement of toxin activity, is the gold standard for botulinum toxin detection and standardization. The major determinants of clinical response to treatment are the toxin preparation, individual patient's anatomy, dose and response relationships, length of toxin storage after reconstitution, and immunogenicity. To minimize potential antibody resistance, one should use the smallest effective dose, utilize treatment intervals of more than 3 months, and avoid booster injections. Uncommon adverse effects include ptosis, ectropion, diplopia, bruising, eyelid drooping, hematoma formation, and temporary headaches.

CONCLUSION

Botulinum toxin is a safe and effective treatment. Knowledge of the pharmacologic basis of therapy will be useful for standardizing techniques and achieving consistent therapeutic results in the future.

Doxorubicin chemomyectomy: effects on evoked vocal fold tension and mucosal wave

Chemomyectomy of the thyroarytenoid muscle is a potential alternative approach to the management of spasmodic dysphonia (laryngeal dystonia) that could provide a prolonged response. To be useful, chemomyectomy should produce weakening of vocal fold closure without disruption of the mucosal wave. Sixteen dogs were studied. In 8 animals, doxorubicin hydrochloride (3 mg) and verapamil hydrochloride (0.5 mg) were injected unilaterally into the thyroarytenoid muscle 2 months before evaluation. The remaining animals served as noninjected controls. Injection of doxorubicin and verapamil decreased the average evoked tension of the vocal fold by 74.7%, compared to an average side-to-side difference of 12.7% in the control group (p = .001). A mucosal wave was recognized bilaterally with videostroboscopy in all dogs. Doxorubicin did not significantly change the vocal fold appearance or mucosal wave amplitude. These results support further laboratory study of chemomyectomy as a potential alternative treatment for laryngeal dystonia.

Cell size and geometry of spinal cord motoneurons in the adult cat following the intramuscular injection of adriamycin: comparison with data from aged cats

Adriamycin (ADM), an antineoplastic antibiotic, when injected intramuscularly, is taken up by motoneuron axonal terminals and retrogradely transported to the motoneuron soma where it exerts its neurotoxic effect. In the present study, ADM was injected into the hindlimb muscles of five adult cats. Measurements of the electrophysiological properties of the lumbar motoneurons innervating these muscles were obtained using intracellular techniques. Based upon these data the equivalent cylinder model of motoneurons was employed to evaluate ADM-induced changes in cell size and cell geometry. The size of cell somas in the ventral horn was also measured using light microscopy and computer imaging software. There were significant increases in the membrane time constant (25%) and input resistance (50%) in motoneurons whose muscles were treated with ADM (ADM-MNs) compared with data from control motoneurons (control-MNs). The increase in membrane time constant is attributed to an increase in membrane resistance; the increase in input resistance appears to depend upon both an increase in membrane resistance and a decrease in total cell surface area. Cell capacitance, which is proportional to the total cell surface area, was significantly reduced (15%) in ADM-MNs. Calculations based on cable theory indicate that while there was no significant change in the length of the equivalent cylinder for ADM-MNs, there was a significant decrease (17%) in the diameter of the equivalent cylinder. These data indicate that there is a decrease in total cell surface area which can be attributed to the shrinkage of branches throughout the dendritic tree. There was also a small (7%) but statistically significant decrease in the electrotonic length of ADM-MNs. Morphological analysis also revealed that the mean cross-sectional area of the somas of those ventral horn neurons which are likely to correspond to the motoneuron population was significantly reduced on the ADM-treated side compared to that of neurons on the control side. We conclude that significant geometrical changes were induced in lumbar motoneurons of adult cats after ADM was injected to their muscles. In old cats, spinal cord motoneurons exhibit similar patterns of changes in their electrophysiological characteristics which have also been suggested to be correlated with changes in cell geometry. The question then arises as to whether the response of motoneurons to ADM and the aging process reflects a stereotypic reaction of motoneurons to a variety of insults or whether the response to ADM mirrors specific aspects of the aging process.

Injection of doxorubicin into rabbit eyelid does not result in loss of facial motor neurons

In both laboratory and clinical studies, injection of doxorubicin directly into the eyelid results in permanent muscle loss of the majority of fibers within treated eyelids. A first clinical trial of this technique in blepharospasm and hemifacial spasm patients has been performed. All patients who completed a full course of doxorubicin treatment showed a permanent decrease in eyelid strength, with over 50% of these patients requiring no further treatment. Doxorubicin is known to be carried by retrograde axonal transport to the brain and is a known neurotoxin. This raises the question of the effect of these treatments on the facial neurons which innervate the orbicularis oculi muscle in the eyelids. The effect on the number of facial neurons present after injection of doxorubicin into the eyelid of rabbits was determined using both HRP and diI retrograde labeling techniques. Despite the extensive and permanent muscle loss caused by the doxorubicin treatments, there was no measurable loss of facial neurons on the doxorubicin treated sides. DiI was shown to be myotoxic at high concentrations and amplified the myotoxic effect of doxorubicin. Lack of neuronal loss may offer assurance of clinical safety to the facial motor neurons of muscle spasm patients who receive doxorubicin injections into their eyelids.

A review of axonal transport of metals

Neurons have efficient mechanisms for the transport of organelles and chemical substances in axons to the nerve terminals and back to the cell bodies. Enzymes involved in transmitter synthesis, peptide transmitters and their precursors are examples of macromolecules that are transported down the axon, anterogradely. For final degradation and possible reuse, many constituents are transported back to the cell body, retrogradely. Retrograde transport is also a pathway by which certain toxins may bypass the blood-brain barrier and accumulate in neurons. In recent years, it has been shown that certain metals may accumulate in neurons following retrograde transport. The metals for which retrograde transport has been demonstrated include lead, cadmium and mercury. In this article recent findings regarding axonal transport of metals are reviewed. The putative mechanisms involved in the uptake of metals into the nerve terminal and the fate of metals in the cell body are outlined. Axonal transport of metals as a possible etiological factor in diseases of the human nervous system is discussed.

Neural lesioning with ribosome-inactivating proteins: suicide transport and immunolesioning

Toxic lectins, plant proteins that inactivate ribosomes, irreversibly inhibit protein synthesis with high efficiency. After intraneural (subepineurial) microinjection, these agents are taken up by axons and are retrogradely transported to the perikarya, where they result in cell death. These 'suicide transport' toxins can produce pathway-specific lesions that are useful in several types of experiment, including cellular localization of neurotransmitter receptors. The toxins can be coupled to monoclonal antibodies to produce immunotoxins: reagents that can make highly selective lesions of specific types of neurons. Central or peripheral neurons that express the low-affinity NGF receptor are selectively destroyed by the immunotoxin 192 IgG-saporin. Development of other anti-neuronal immunotoxins should provide a variety of powerful selective lesioning tools.

Clinical doxorubicin chemomyectomy. An experimental treatment for benign essential blepharospasm and hemifacial spasm

Doxorubicin (DXR) was injected as a treatment for benign essential blepharospasm and hemifacial spasm. The other eyelids were treated concurrently with botulinum toxin (BT). No DXR-treated eyelid has maintained 0 strength (commonly achieved with BT). Two patients with benign essential blepharospasm and four patients with hemifacial spasm have achieved major improvement, sustained for more than 6 months. Eyelids have been swollen and inflamed for up to 3 months. No spontaneously irreversible complication has occurred. A single injection at the maximum safe dose (1 mg in the upper lid and 1.5 mg in the lower lid) has not proven sufficient to produce cure. Treatment of each lower eyelid of a muscular male with severe blepharospasm may require cumulative doses of up to 4.0 mg, delivered in three injection events separated by at least 2 months, with each injection no greater than 1.5 mg DXR per site. At the present time, there is no assurance that a permanent cure will result.

Animal models of amyotrophic lateral sclerosis and the spinal muscular atrophies

The causes of human amyotrophic lateral sclerosis (ALS) and the spinal muscular atrophies (SMA) are, almost without exception, unknown. This ignorance has stimulated the search for animal models to obtain insight into the etiology, pathogenesis and biochemical mechanisms underlying the human disorders. None of the 38 animal models, described in this review, provides an exact animal copy of a specific human motor neuron disease. Most of the models reproduce certain structural or physiological aspects of their human counterparts. The various experimental models can be classified according to the pathogenetic mechanism involved and according to the structural changes observed. Models based on experimentally induced disease, include heavy metals and trace elements (lead intoxication in guinea pigs, rabbits, rats, cats and primates; mercury intoxication in rats; aluminium intoxication in rabbits; swayback in goat kids; calcium and magnesium deficient rabbits and primates and calcium deficient cynomolgus monkeys), toxins (IDPN, vincristine, vinblastine, podophyllotoxin, colchicine, maytansine, maytanprine, L-BMAA, lectins, adriamycin), nutritional factors (ascorbic acid deficient guinea pigs), virus infection (spongiform polioencephalomyelitis, attenuated poliovirus, lactate dehydrogenase-elevating virus), and immunological factors (immunization with motor neurons). Hereditary models comprise hereditary canine spinal muscular atrophy, hereditary neurogenic amyotrophy in the pointer dog, Stockard paralysis, Swedish Lapland dog paralysis, "wobbler" mouse, "shaker" calf, and hereditary spinal muscular atrophy in zebra foals, crossbred rabbits,

Localization of neural epitopes that bind to IgM monoclonal autoantibodies (M-proteins) from two patients with motor neuron disease

We investigated IgM monoclonal antibodies (M-proteins) specific for the carbohydrate epitopes Gal(beta 1-3)GalNAc and Gal(beta 1-3)GlcNAc from two patients with motor neuron disease. The M-proteins from these patients immunostain central nervous system (CNS) and peripheral nervous system (PNS) tissue from human, monkey, dog and cat at greater dilutions than tissue from rabbit, guinea pig, rat and mouse, and immunostain gray matter at greater dilutions than white matter and nerve trunks. They also bind selectively to presynaptic structures at the motor endplate region, as denervation of muscle eliminates binding. Following in vivo injection of serum into the extracellular space of the spinal cord, the M-proteins appear to bind at the surface of cells and cell processes. These studies suggest that the M-proteins might act at any one of several anatomical sites in the nervous system. This information may be helpful in selecting an animal species for further investigation of the role of M-proteins in motor neuron disease.

Formation of microglia-derived brain macrophages is blocked by adriamycin

Injection of ricin, the toxic lectin from Ricinus communis, into the rat facial nerve leads to rapid degeneration of motor neurons and concomitant proliferation and transformation of endogenous microglia into brain macrophages. Using [3H]-thymidine autoradiography, immunocytochemistry for microglial markers and electron microscopy, we could show that when ricin was administered together with the cytostatic drug adriamycin, the retrogradely transported adriamycin inhibits the macrophage response induced by toxic ricin. It is concluded that under conditions of neuronal degeneration, e.g., following ricin intoxication, brain macrophages are predominantly, if not exclusively, derived from endogenous microglia.

Experimental retrograde adriamycin trigeminal sensory ganglionectomy

Direct destruction of the sensory ganglion or its root, by either surgical transection or injection of phenol, has been employed as preferred treatment for a variety of neuralgic pain syndromes. In this report, the suicide axoplasmic transport of adriamycin is described as a novel approach to sensory ganglionectomy. When injected into a branch of the trigeminal nerve in the cat, adriamycin was swiftly transported by way of retrograde axoplasmic flow to the sensory neurons parental to the injected nerve, where adriamycin-specific autofluorescence was observed. Trigeminal sensory evoked potentials became unobtainable 24 to 48 hours after injection of adriamycin in concentrations of 1% to 10%. The sensory neurons underwent subacute degeneration within a week due to the delayed action of adriamycin, and consequently the primary afferents degenerated in a restricted projection field of the brain-stem trigeminal sensory nuclei. These results indicate that retrograde axoplasmic transport of adriamycin is a unique approach to noninvasive sensory ganglionectomy with strict, albeit simple, safe targeting of sensory neurons and little likelihood of regeneration.

Modeccin and volkensin but not abrin are effective suicide transport agents in rat CNS

Suicide transport is a term applied to the technique of producing anatomically selective neural lesions using axonally transported cytotoxins. Because the cytotoxic lectins, abrin, modeccin and volkensin are effective suicide transport agents in the peripheral nervous system, the present study sought to determine if they were effective suicide transport agents in the rat CNS. Toxins were stereotactically pressure microinjected unilaterally into the caudate nucleus of rats. After 2-13 days survival, brain sections were processed for catecholamine histofluorescence or Nissl stained with Cresyl violet. All 3 agents produced extensive necrosis at the caudate injection site. In addition, modeccin and volkensin but not abrin produced destruction of neurons in the ipsilateral substantia nigra and intralaminar thalamus. Histofluorescence confirmed loss of dopaminergic neurons from the ipsilateral substantia nigra after modeccin or volkensin but not abrin injections. These results indicate that modeccin and volkensin are effective suicide transport agents within the rat CNS, presumably due to retrograde axonal transport of the toxins. These agents may prove extremely useful in producing anatomically selective lesions of neurons afferent to a toxin injection site.

Neurotoxicity in primary sensory neurons of adriamycin administered through retrograde axoplasmic transport in rats

Neurotoxic effects of adriamycin (ADM) were examined in rats. The drug was administered through retrograde axoplasmic transport from the transected sciatic nerve in very small amounts (0.05 mg of adriamycin). Using the autofluorescence specific to adriamycin as a histological tracer, alterations in primary sensory neurons in dorsal root ganglia (DRG) and in motor neurons in the spinal cord were observed chronologically by light and electron microscopy. In the DRG at the fifth and sixth lumbar levels, small neurons initially showed alterations in mitochondria, wavy nuclear membranes and enlarged cisternae of rough endoplasmic reticulum, and disappeared early in the experiments. Large neurons, which showed accumulation of neurofilaments, dense bodies and vacuoles in the perikarya in addition to nucleolar and nuclear chromatin alterations, degenerated slowly. In contrast, motor neurons in the anterior horn at the sixth lumbar level survived throughout the administration of adriamycin despite the presence of transient weak adriamycin autofluorescence and vacuoles in the cytoplasm. Thus, the susceptibility and vulnerability of motor neurons in spinal cord to adriamycin differed from that of primary sensory neurons; small neurons in the DRG were more susceptible than large sensory neurons. Administration through retrograde axoplasmic transport proved to be a useful technique for the evaluation of the neurotoxicity of adriamycin without the complications of systemic effects.

Neuronotoxicity of axonally transported toxic lectins, abrin, modeccin and volkensin in rat peripheral nervous system

In an attempt to find new and more useful suicide transport agents, the cytotoxic lectins abrin, modeccin and volkensin were pressure microinjected into peripheral nerves (vagus, hypoglossal and sciatic) of adult rats. After 33 h-5 days survival, the brainstems, spinal cords and corresponding sensory ganglia were examined histologically. All three lectins produced profound chromatolysis, and destruction of sensory and motor neurons projecting axons through the injected nerves. Volkensin and modeccin were significantly more potent than any previously reported suicide transport agent. It is concluded that abrin, modeccin and volkensin are effective, unselective suicide transport agents in the rat peripheral nervous system but none is clearly superior to ricin for making restricted sensory and motor neuron ablations. However, modeccin and volkensin are fundamentally different from any previously reported suicide transport agents with respect to spread within the CNS which destroyed neurons adjacent to those initially taking up and transporting the toxin. Possibly this is due to the different oligosaccharide binding specificity of modeccin and volkensin compared to other suicide transport agents. Modeccin and/or volkensin may prove useful in making lesions of CNS interneurons using the suicide transport strategy.

Wheat germ agglutinin-ricin A-chain conjugate is neuronotoxic after vagal injection

'Suicide transport' is a term coined to describe the use of retrogradely axonally transported toxin to produce anatomically selective neural lesions. As a first step in developing neuron type-selective, systemically non-toxic suicide transport agents, a prototype hybrid toxin consisting of ricin A-chain (RTA) disulfide coupled to wheat germ agglutinin (WGA) was synthesized by first derivatizing WGA by reaction with N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP) in the presence of N-acetylglucosamine and then formation of WGA-SS-RTA by mixing the derivatized WGA with reduced RTA. The ability of this conjugate to inhibit protein synthesis was tested on two cell lines in vitro; the ID50 was 0.2 nM using the K562 hematopoietic stem cell line and 0.02 nM for the 2a neuroblastoma cell line. Suicide transport activity was assessed by microinjection of hybrid into the cervical vagus nerve of rats. Intact WGA-SS-RTA, but not hybrid that was pretreated with dithiothreitol to uncouple RTA from the WGA carrier, reliably killed vagal motor neurons. Both intact and reduced hybrid killed vagal sensory neurons. Indirect peroxidase immunohistochemistry demonstrated transport of RTA to vagal sensory neurons and WGA to both vagal sensory and motor neurons. These results are the first evidence that a hybrid toxin can be active as a suicide transport agent.

Anatomically selective peripheral nerve ablation using intraneural ricin injection

Anatomically selective destruction of sensory and motor neurons based upon which nerve contains the corresponding axons can be accomplished by intraneural pressure microinjection of the toxic lectin, ricin. Ricin is taken up by axons at the injection site and axonally transported to perikarya resulting in destruction of the neurons. In the present report, we describe a reliable procedure for making such lesions using pressure microinjection of ricin into nerve trunks. Consistent, complete lesions restricted to the appropriate sensory and motor neurons are documented after injection of the vagus, hypoglossal, phrenic and sciatic nerves and the superior cervical ganglion. Complete vagal ablations could be achieved with 100 ng or less of ricin; whereas, 1-3 micrograms was required to obtain similar results with hypoglossal and sciatic nerves. Although most neurons are dead within 24 h after the injection, survival times of 10-14 days may be necessary for complete disappearance of poisoned neurons. This technique can be valuable in making highly selective lesions for anatomical, neurochemical and neurophysiological experiments.

Primary degeneration of motor neurons by toxic lectins conveyed from the peripheral nerve

In attempts to degenerate motor neurons experimentally by way of retrograde axoplasmic transport, ricinus communis agglutinin (RCA), a potent protein inhibitor, was intraneurally injected into the rat sciatic nerve. Immunohistochemically, RCA was shown to be intra-axonally carried up to motor neuronal soma and to the dorsal root ganglia of L4-6. Within a few days, these dorsal root ganglion cells and large motor neurons giving rise to sciatic nerve efferents in the lumbar spinal cord degenerated, whereas small internuncial neurons and glia remained unaffected. The degeneration of motor neurons was characterized by a profound diffuse chromatolysis and subsequent dissolution, after which a mild gliosis remained. The retrograde axoplasmic flow of neurotoxic substance and motor neuron degeneration observed here may be a phenomenon implicated in the pathogenesis of human motor neuron diseases.

Suicide transport of ricin demonstrates the presence of substance P receptors on medullary somatic and autonomic motor neurons

Suicide transport of the toxic lectin, ricin, by hypoglossal and vagus neurons resulted in motor neuron loss in the associated nuclei, and reduced the binding of the 125I-Bolton-Hunter labeled substance P in the same nuclei. These data show that substance P receptors are located on the cell bodies of medullary somatic and preganglionic motor neurons of the hypoglossal and vagus nerves, and that suicide transport is a useful technique to determine the cellular localization of binding sites within a nucleus.

Cytofluorescence localization of ethidium bromide in the nervous system of the mouse. I. Ethidium bromide: its distribution in regions within and without the blood-brain barrier after intravenous injection

A direct fluorescence-microscopic technique was effected to determine in the central nervous system (CNS) of the mouse the distribution of ethidium bromide after intravenous (i.v.) injection. The compound was visualized in thin cryostat sections of the brain fixed by vascular perfusion through the heart with a 10% buffered formalin solution. Ethidium bromide emitted a bright red fluorescent light in model experiments. The compound could not be detected in the vessel walls or brain parenchyma of the cerebral gray and white matters after i.v. injection indicating the presence of a blood-brain barrier (BBB) phenomenon to this compound. Signs of extravasation of ethidium bromide were present in the choroid plexus, the postremal area, the Gasserian ganglion, and in the circumventricular organs of the brain (neurohypophysis, organum vasculosum lamina terminalis, and median eminence) 3 min after the i.v. injection. Intense fluorescence was present in the nucleus and the cytoplasm of the cells in these areas, located outside of the BBB. Fluorescence had disappeared 24 h after the injection. Unexpectedly, red fluorescent material was seen in the parenchyma of the olfactory lobes of some animals, indicating, possibly, the presence of ethidium bromide. Ethidium bromide is known to suppress RNA, DNA, and protein synthesis in mammalian cells and has been used previously in neuropathology for studies on myelin lesions after injury to oligodendroglial cells. It can now, by a simple fluorescence-microscopic method, be traced directly in fixed tissue. Correlations can therefore be made between localization of the compound and its cytotoxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

The temporal evolution of hypoglycemic brain damage. I. Light- and electron-microscopic findings in the rat cerebral cortex

In the course of a study on the pathogenesis of neuronal necrosis in severe hypoglycemia, the morphological characteristics reflecting reversible and irreversible neuronal lesions were examined as a function of time following normalization of blood glucose. To that end, closely spaced time intervals were studied in the rat cerebral cortex before, during, and up to 1 year after standardized pure hypoglycemic insults of 30 and 60 min of cerebral isoelectricity. Both the superficial and deep layers of the cerebral cortex showed dark and light neurons during and several hours after the insult. By electron microscopy (EM) the dark neurons were characterized by marked condensation of both karyoplasm and cytoplasm, with discernible, tightly packed cytoplasmic organelles. The light neurons displayed clustering of normal organelles around the nucleus with clearing of the peripheral cytoplasm. Some cells, both dark neurons and neurons of normal electron density, contained swollen mitochondria with fractured cristae. Light neurons disappeared from the cerebral cortex by 4 h of recovery. Some dark neurons in the superficial cortex and almost all in the deep cortex evolved through transitional forms into normal neurons by 6 h recovery. Another portion of the dark neurons in the superficial cortex became acidophilic between 4 and 12 h, and by EM they demonstrated karyorrhexis with stippled electron-dense chromatin. The plasma membrane was disrupted, the cytoplasm was composed of amorphous granular debris, and the mitochondria contained flocculent densities. These definitive indices of irreversible neuronal damage were seen as early as 4-8 h recovery. Subsequently, the acidophilic neurons were removed from the tissue, and gliosis ensued. Thus, even markedly hyperchromatic "dark" neurons are compatible with survival of the cell, as are neurons with conspicuous mitochondrial swelling. Definite nerve cell death is verified as the appearance of acidophilic neurons at which stage extensive damage to mitochondria is already seen in the form of flocculent densities, and cell membranes are ruptured. Our previous results have shown that hypoglycemic neocortical damage affects the superficial laminae, chiefly layer 2. The present results demonstrate that, following the primary insult, this damage evolves relatively rapidly within the first 4-12 h. We have obtained no evidence that additional necrotic neurons are recruited after longer recovery periods.

Cytofluorescence localization of propidium iodide injected intravenously into the nervous system of the mouse

Propidium iodide, like its analogue ethidium bromide, is a compound which can be used as a marker of nucleic acids. This substance emits a red fluorescent light after exposure to UV light and has therefore been used previously as a nuclear stain in immunofluorescence studies and in flow cytometry. The present experiments were carried out to find out if propidium iodide could be traced in sections of the nervous system after i.v. injections. Due to the general toxicity of the compound detectable amounts of propidium iodide could not be obtained by a single i.v. injection. However, multiple injections of small amounts (0.1 mg) over a period from 15 min to 8 h (total dose 0.7-1.0 mg) were tolerated without any signs of adverse effects. In such experiments propidium iodide did not extravasate into the cerebral gray or white matter, i.e., areas of the brain located within the blood-brain barrier (BBB). On the other hand, the compound spread into the choroid plexus, the circumventricular organs, the Gasserian ganglion, and sciatic nerve, i.e., regions located outside the BBB. It had a strong tendency to label the nucleus and the perikaryon of the cells in each of these territories. Perifascicular injection of propidium iodide around the sciatic nerve was followed by a marked cellular uptake not only in the epineurium but also in the endoneurium. The shape and position of the labeled nuclei strongly indicated that they were the nuclei of Schwann cells. Previous studies have shown that propidium iodide can be used as a retrograde tracer in neuroanatomic research.(ABSTRACT TRUNCATED AT 250 WORDS)

Feline dysautonomia (the Key-Gaskell syndrome): an ultra structural study of autonomic ganglia and nerves

Recently a feline dysautonomia of unknown aetiology, the Key-Gaskell syndrome, has caused widespread morbidity in the UK. This report describes the ultrastructural appearances of the autonomic ganglia and axons of the sympathetic chain in this condition. Nuclei of affected neurones were eccentric and abnormally crenated. Nucleolar abnormalities such as increased electron density (due to loss of the intranucleolar vacuoles), nucleolar segregation and ring nucleoli were observed in a proportion of neurones. There was marked loss of ribosomes, both bound and unbound, and cisternae of the rough endoplasmic reticulum were distended with a floccular electron dense material. Numerous smooth-walled cisternae were also present and complex stacks of smooth semi-parallel membranes were observed, probably derived from the smooth endoplasmic reticulum or Golgi apparatus. No normal Golgi formations were seen. Frequent autophagic vacuoles and membranous dense bodies were present in some cells. Many unmyelinated fibres in the sympathetic chain were swollen and contained vesiculo-tubular profiles, disordered neurotubules and filaments and various degenerating membranous organelles. Myelinated fibres within the sympathetic chain were also degenerating. These studies indicate that the organelles involved with protein biosynthesis are severely affected by the disease.

Ultrastructural and histophysiological studies on the blood-nerve barrier and perineurial barrier in leprosy neuropathy

Onset and nature of ultrastructural changes in endoneurial vasa nervorum during the pathogenesis of leprosy neuropathy and possibly associated alterations in the "blood-nerve barrier" were investigated, together with perineurial barrier functioning, in mice infected 20-28 months previously with Mycobacterium leprae and in (ageing) non-infected mice. Barriers were tested by i.v. administration of markers (Trypan blue and ferritin) 1-4 days before killing the mice. Twenty-eight months after infection, histopathology of sciatic nerves was comparable to that seen in sensory nerves in clinically early human (borderline-) lepromatous leprosy. Schwann cells and endoneurial macrophages were bacillated, endothelia of endoneurial vessels not, and the perineurium rarely. Many infected mice and all (ageing) controls possessed ultrastructurally and functionally normal endoneurial vessels. Their continuous endothelium with close junctions had prevented marker passage, even when surrounding endoneurial tissue cells were quite heavily bacillated. The perineurium was also normal. By contrast, in infected mice showing hind limb paralysis serious histopathologic involvement and large globi of bacilli intrafascicularly in sciatic nerves, endoneurial blood vessels were abnormal. Open endothelial junctions, extreme attenuation, fenestrations, and luminal protrusions were all features comparable to neural microangiopathy encountered in leprosy patients (Boddingius 1977a, b). The "blood-nerve barrier" clearly had become defective allowing excessive exudation of Trypan blue and ferritin, via four pathways from the vessel lumen, deep into surrounding endoneurial tissues but halted by a normal perineurial barrier. Markers in such "blue" nerves were not found in bacillated or non-bacillated Schwann cells, thus denying significant phagocytotic and lysosomal activities of Schwann cells at this stage of neuropathy. Possible implications of barrier performances for anti-leprosy drug treatment of patients are discussed.

Toxic effects of adriamycin on the central nervous system. Ultrastructural changes in some circumventricular organs of the mouse after intravenous administration of the drug

Recent experimental studies have shown that the cytotoxic antibiotic adriamycin (doxorubicin) after systemic administration can enter the so-called circumventricular organs (CVO) of the brain of the mouse. The present experiments were performed to find out whether such penetration of the brain is associated with signs of neurotoxic injury. For this purpose, light- and electron-microscopic observations were carried out on three of these organs: the neurohypophysis (NH), median eminence (ME), and postremal area (PA). Pronounced widening of the extracellular space indicating the presence of edema was present in all the regions, particularly in animals examined within 3 days of injection of the drug. Many degenerated axon terminals were observed in the NH and ME. The glial cells within these regions showed rarefaction of the nuclear chromatin, nucleolar segregation, and also cytoplasmic changes. The PA presented marked cellular changes resulting in degeneration of neurons, which was most evident 30 days after the injection. Hence, regions of the CNS outside the blood-brain barrier can be reached by adriamycin after systemic administration, and the drug can induce morphological changes there. The doses of the drug used in the present experiments were comparable to those given to patients for the treatment of malignant tumors.