Eur J Anat, 9 (1): 35-48 (2005)

Axonal and terminal degeneration in the mediobasal forebrain after lesions of brainstem pathways

Liesenfeld H., Laue M., Mestres-Ventura R.

Department of Anatomy and Cell Biology, Saarland University, 66421 Homburg, Germany; Anatomie und Zellbiologie, Universität des Saarlandes, D-66421 Homburg, Germany

ABSTRACT Lesion studies in animals are widely used for evaluating physiological parameters. However, changes in anatomical structures of the neuropil have often been neglected in the interpretation of the physiological results. Our study shows that anatomical data should also be considered. Here, the Fink-Heimer-method was used to demonstrate degeneration patterns after lesions in the rat brain. In detail, the ascending noradrenergic fibres were incised at the level of the dorsal tegmental area of the mesencephalon. The resulting degeneration pattern corresponds largely with the noradrenergic projection. The extent of degeneration is less than the physiological results in the literature predict. The interruption of the medial forebrain bundle at the posterolateral hypothalamic level led to a degeneration of the supraoptic decussation, where, according to physiological data, locus coeruleus fibres had been assumed to cross to the contralateral hemisphere. Beside axotomy, the lesions caused edema, hemorrhage and necrosis. They were not restricted to the width of the blade and did not only affect the catecholaminergic system but led to degeneration in mediobasal forebrain sites where gonadotropin-releasing hormone-neurons are present, in fibre systems which carry afferents and efferents of these neurons and in hypothalamic and extrahypothalamic structures that influence the release of the gonadotropin-releasing hormone. Thus, both anatomical and physiological aspects are important for a correct evaluation of lesion studies in brain/behavior research.

Keywords: gonadorelin, animal experiment, animal model, animal tissue, article, brain edema, brain hemorrhage, brain necrosis, brain nerve cell, brain region, brain stem injury, catecholaminergic system, controlled study, efferent nerve, female, Fink Heimer method, forebrain, gonadorelin release, histopathology, hypothalamus, locus ceruleus, mesencephalon, nerve ending, nerve fiber degeneration, nerve fiber transection, nerve projection, neuropil, nonhuman, noradrenergic nerve, parameter, rat, sensory nerve, supraoptic nucleus, technique, tegmentum, tissue structure