volkensin and Nerve-Degeneration

Retrogradely transported toxins are widely used to set up protocols for selective lesioning of the nervous system. These methods could be collectively named "molecular neurosurgery" because they are able to destroy specific types of neurons by using targeted neurotoxins. Lectins such as ricin, volkensin, or modeccin and neuropeptide- or antibody-conjugated saporin represent the most effective toxins used for neuronal lesioning. Some of these specific neurotoxins could be used to induce selective depletion of spinal motoneurons. In this review, we extensively describe two rodent models of motoneuron degeneration induced by volkensin or cholera toxin-B saporin. In particular, we focus on the possible experimental use of these models to mimic neurodegenerative diseases, to dissect the molecular mechanisms of neuroplastic changes underlying the spontaneous functional recovery after motoneuron death, and finally to test different strategies of neural repair. The potential clinical applications of these approaches are also discussed.

Topics: Animals; Cholera Toxin; Disease Models, Animal; Nerve Degeneration; Nerve Regeneration; Neuronal Plasticity; Rats; Ribosome Inactivating Proteins, Type 1; Ribosome Inactivating Proteins, Type 2; Saporins

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.

Topics: Animals; Antibodies, Monoclonal; Axonal Transport; Axotomy; Central Nervous System; Glycoproteins; Immunoconjugates; Immunotoxins; N-Glycosyl Hydrolases; Nerve Degeneration; Neural Pathways; Neurons; Neuropeptides; Neurotoxins; Plant Lectins; Plant Proteins; Ribosome Inactivating Proteins, Type 1; Ribosome Inactivating Proteins, Type 2; Ricin; Saporins

Studies have shown that the nucleus accumbens shell plays an integral role in the expression of psychostimulant-induced behavioural sensitization. Dopaminergic regulation of excitatory amino acid inputs in this region of the brain could be a key factor in the neural influence of this phenomenon. Alterations in the dopaminergic innervation patterns in the shell have been demonstrated in rats that received repeated cocaine injections. Furthermore, lesions of brain regions that send projections to the shell alter psychostimulant-induced locomotion, both acutely and in sensitization paradigms. A previous study from our laboratory demonstrated that lesions of the shell before repeated cocaine treatment decrease the locomotor response to cocaine during the induction phase of behavioural sensitization. To better understand the role of this brain region during the expression phase of behavioural sensitization, the present study examined the effects of two forms of cytotoxic lesions of the shell. Rats received a sensitization-inducing regimen of cocaine (bi-daily injections of 15 mg/kg i.p. for 5 consecutive days). Two days after the last injection, rats demonstrating behavioural sensitization received one of three bilateral microinjections into the shell: (i) 0.5 micro L 0.9% saline; (ii) 2.5 micro g/0.5 micro L ibotenic acid (which lesions the cell bodies at the injection site); or (iii), 0.5 ng/0.2 micro L of volkensin (a retrograde suicide transport lectin). Upon challenge with cocaine (15 mg/kg) 12 days after surgery, neither ibotenic acid- nor volkensin-lesioned rats showed any difference in their locomotor response compared with sham controls. These data indicate that bilateral shell lesions do not affect the long-term expression of behavioural sensitization in cocaine-sensitized rats.

Topics: Animals; Cocaine; Cocaine-Related Disorders; Dopamine; Drug Administration Schedule; Excitatory Amino Acids; Glycoproteins; Ibotenic Acid; Male; Motor Activity; N-Glycosyl Hydrolases; Nerve Degeneration; Neural Pathways; Neurons; Neurotoxins; Nucleus Accumbens; Plant Lectins; Rats; Rats, Sprague-Dawley; Ribosome Inactivating Proteins, Type 2; Synapses; Synaptic Transmission; Ventral Tegmental Area

The aim of this study was to examine the time course and cellular localization of clusterin mRNA after neurodegeneration. Selective neuronal death was achieved in the rat inferior olivary complex after volkensin injection in the contralateral cerebellar cortex. Quantitative analysis of the in situ hybridization signal demonstrated over-expression of clusterin mRNA in living neurons at 6 days and outside the neuronal cell bodies at 10 days post-injection. We conclude that, in our experimental model, clusterin over-expression occurs as an early and transient neuronal and as a delayed glial response to selective neuronal death, supporting the view that clusterin may be involved in cytoprotection and tissue remodeling.

Topics: Animals; Brain; Cell Death; Clusterin; Glycoproteins; In Situ Hybridization; Male; Molecular Chaperones; N-Glycosyl Hydrolases; Nerve Degeneration; Nerve Tissue Proteins; Neuroglia; Neurons; Plant Lectins; Plant Proteins; Rats; Rats, Sprague-Dawley; Ribosome Inactivating Proteins, Type 2; RNA, Messenger; Up-Regulation

We have examined the time course of neurodegeneration in subcortical nuclei and other cortical areas known to project to the rat parietal cortex, following unilateral injection of the suicide transport agent, volkensin, into the cortex of one side. Degenerating neurons, visualized by Gallyas silver staining were most prominent 21 days after injection. At this time darkly staining neurons were present in nuclei and areas known to project to the injected cortical area but not in other sites. Affected subcortical nuclei included the ipsilateral ventral thalamus and intralaminar nuclei, the basal nucleus of Meynert and claustrum of the same side, and the dorsal median raphé nucleus of both sides. Within the cortex degenerating pyramidal neurons were visible in the contralateral parietal cortex and in the frontal cortex of the same side. The distribution of degenerating cells is in agreement with the conclusion that only neurons projecting to the injection site were affected. The time course of the appearance of the degeneration and its distribution are in keeping with axonal transport rather than spread by diffusion of the toxin. Neuronal counts in Nissl-stained sections of the contralateral SMI confirmed significant neuronal loss 28 days after injection. In situ hybridization studies using an oligonucleotide probe directed against GAD mRNA and counts of GAD mRNA-positive neurons in the contralateral cortex confirmed that this population of cortical interneurons, which do not project to the injection site, were unaffected.

Topics: Animals; Biological Transport, Active; Cell Count; Cerebral Cortex; Coloring Agents; Glycoproteins; Horseradish Peroxidase; In Situ Hybridization; Injections; Male; N-Glycosyl Hydrolases; Nerve Degeneration; Neurons; Plant Lectins; Plant Proteins; Rats; Rats, Wistar; Ribosome Inactivating Proteins, Type 2

Volkensin and ricin, either free or conjugated with colloidal gold, were injected into the cerebellar cortex of rats. The inferior olive and pontine nuclei were examined to verify the retrograde axonal transport of these two toxins, and the consequent neuronal damage. No evidence was obtained of a retrograde axonal transport of ricin in these pathways. Injection of gold-conjugated volkensin in the cerebellar cortex resulted in retrogradely labelled neurones in the inferior olive after 3 h, and in the pontine nuclei after 6 h. Degenerative changes were very severe in the retrogradely labelled neurones 48 h after the gold-conjugated volkensin injection. In the Nissl-stained material, neuronal degeneration started to be evident in the inferior olive 12 h, and in pontine nuclei 6 h, after volkensin injection. The neuronal degeneration in both the inferior olive and pons increased up to 4 days after the injection. These findings provide direct evidence of the retrograde axonal transport of volkensin in the central nervous system, and the time course of the consequent degenerative changes in the afferents to the cerebellar cortex.

Topics: Animals; Axonal Transport; Benzoxazines; Biological Transport; Cerebellum; Glycoproteins; Histocytochemistry; Lectins; Male; N-Glycosyl Hydrolases; Nerve Degeneration; Neurons; Neurons, Afferent; Olivary Nucleus; Oxazines; Plant Lectins; Plant Proteins; Pons; Rats; Rats, Sprague-Dawley; Ribosome Inactivating Proteins, Type 2; Ricin