A selective lesion of striatonigral neurons decreases presynaptic binding of [3H]hemicholinium-3 to striatal interneurons

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.

Targeted toxins in pain

Although only recently applied to the study of nociception, 'molecular neurosurgery', producing highly selective neural lesions using targeted cytotoxins, has proven a valuable tool for analysis of nociceptive systems and promises to yield much more information on the role of specific types of neurons in pain perception and possibly new pain therapies. Neuropeptide-toxin conjugates, particularly, substance P-saporin, have proven useful research tools and may find clinical applications. Targeting non-lethal moieties (enzymes, genes, viruses) also may prove useful for research and therapeutic purposes.

Unilateral 6-hydroxydopamine lesions of meso-striatal dopamine neurons and their physiological sequelae

One of the primary approaches in experimental brain research is to investigate the effects of specific destruction of its parts. Here, several neurotoxins are available which can be used to eliminate neurons of a certain neurochemical type or family. With respect to the study of dopamine neurons in the brain, especially within the basal ganglia, the neurotoxin 6-hydroxydopamine (6-OHDA) provides an important tool. The most common version of lesion induced with this toxin is the unilateral lesion placed in the area of mesencephalic dopamine somata or their ascending fibers, which leads to a lateralized loss of striatal dopamine. This approach has contributed to neuroscientific knowledge at the basic and clinical levels, since it has been used to clarify the neuroanatomy, neurochemistry, and electrophysiology of mesencephalic dopamine neurons and their relationships with the basal ganglia. Furthermore, unilateral 6-OHDA lesions have been used to investigate the role of these dopamine neurons with respect to behavior, and to examine the brain's capacity to recover from or compensate for specific neurochemical depletions. Finally, in clinically-oriented research, the lesion has been used to model aspects of Parkinson's disease, a human neurodegenerative disease which is neuronally characterized by a severe loss of the meso-striatal dopamine neurons. In the present review, which is the first of two, the lesion's effects on physiological parameters are being dealt with, including histological manifestations, effects on dopaminergic measures, other neurotransmitters (e.g. GABA, acetylcholine, glutamate), neuromodulators (e.g. neuropeptides, neurotrophins), electrophysiological activity, and measures of energy consumption. The findings are being discussed especially in relation to time after lesion and in relation to lesion severeness, that is, the differential role of total versus partial depletions of dopamine and the possible mechanisms of compensation. Finally, the advantages and possible drawbacks of such a lateralized lesion model are discussed.

Effects of suicide transport lesions of the striatopallidal or striatonigral pathways on striatal ultrastructure

In the basal ganglia, centrally active suicide transport agents produce selective lesions of the striatopallidal and striatonigral pathways based on receptor binding and neuropeptide mRNA studies. Anatomical analyses indicate a selective, albeit modest, loss of projection neurons. In the present study, we sought to determine the ultrastructural sequelae in the striatum of suicide transport injections of the globus pallidus (GP) or substantia nigra (SN). Neostriata of adult rats were examined 10 days after lesions of the striatopallidal or striatonigral pathways with OX7-saporin or volkensin. Controls consisted of normal unoperated rats and animals injected into either target with ricin, a toxic lectin that is not transported in the central nervous system. Injections with OX7-saporin or volkensin into the GP or SN produced a decrease in striatal synaptic density of approximately 20%, relative to the contralateral side. Dark degenerating profiles, though very rare in the contralateral striata, were present throughout the neuropil in the ipsilateral striata. In animals with striatopallidal lesions, axospinous synapses of both the asymmetric and symmetric type were decreased in density, while the number of synapses formed with dendritic shafts was unaffected. In addition, the number of striatal mitochondrial profiles was decreased ipsilateral to the lesions. In animals with striatonigral lesions, the number of axospinous and axodendritic synapses of the asymmetric type was decreased ipsilateral to the lesions. Synaptic density and ultrastructural integrity remained unaffected in the striata of animals receiving ricin injections and in the contralateral striata of animals receiving OX7-saporin or volkensin injections. Our results, taken together with previous studies showing marked loss of receptors, uptake sites and mRNA, suggest that while most synapses are present and intact, the efficacy of synaptic transmission may be altered.

Differential localization of A2a adenosine receptor mRNA with D1 and D2 dopamine receptor mRNA in striatal output pathways following a selective lesion of striatonigral neurons

We have used the suicide transport agent volkensin to produce selective lesions of striatonigral neurons. By in situ hybridization histochemistry unilateral volkensin injections in the substantia nigra decreased the number of D1 receptor mRNA-expressing neurons in the ipsilateral striatum but did not change the number of D2 receptor and A2a adenosine receptor mRNA-expressing neurons. These findings confirm that striatonigral neurons express D1 receptors and suggest that D2-A2a receptor expressing neurons are predominantly localized to other neuronal populations within the striatum.