gms | German Medical Science

The increasing awareness of complex neural networks involved in neurodegenerative disorders already in early stages (Braak and Del Tredici, 2008) requires focusing research on the potentially affected fibre tracts, besides their nuclear origin. Furthermore, for any lesion study of neurodegenerative as well as -regenerative issues, meticulous localization of specific pathways is crucial, for example of the questionable impact of nigrostriatal projections on neurogenesis in the subventricular zone. Here, TaClo that is endogenously formed from trichloroethylene and chloral hydrate, is proposed as a candidate toxin.

Han-Wistar rats were injected with 0.03 µmol of TaClo in 2 µl control solution or the control solution alone, unilaterally above the anterior region of the substantia nigra (SN) and killed after six weeks. Major histocompatibility complex II-immunoreactive (ir) cells markedly spread out in the medial lemniscus (ml), the fields of Forel and into the caudal zona incerta above and in the dorsal surface of the anterior SN pars compacta, on the lesioned side of TaClo-treated animals. Staining of tyrosine hydroxylase (TH)-ir fibres were reduced in the dorsal part of the MFB system and within and around the medial border of the ml, compared to the unlesioned side and to the control group. Staining in the ventral, principal, part of the MFB remained well preserved.

In accordance to previous stereological data, which revealed a greater reduction of TH-ir neurons in dorsolateral and ventrolateral subnuclei than in anterior parts of the SN (Zielke et al., 2007), the results indicate toxic effects of TaClo upon axons that exit from the lateral part (Felten et al., 1983) and the posteroventral region of the SN (Prensa et al., 2001) to enter the nigrostriatal pathway (ns). Furthermore, catecholaminergic pathways from the pontine and medullary cell groups pass through the above described regions into the MFB system. The different projection systems in the central tegmental tract and periventricular system will be superimposed from literature data upon missing delineations in Paxinos and Watson's The Rat Brain in Stereotaxic Coordinates (2009), and their relations in the MFB complex and to the ns discussed.

These results should encourage further studies to clarify which types of axons and origins of nuclear groups are directly and possibly transsynaptically affected by TaClo-lesioning.

Literature available from the author: barbara.zielke@uni-wuerzburg.de