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The structure of the diencephalic prepacemaker nucleus revisited: Light microscopic and ultrastructural studies
Author(s) -
Zupanc Günther K. H.,
Heiligenberg Walter
Publication year - 1992
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903230408
Subject(s) - biology , cytoarchitecture , nucleus , diencephalon , axoplasmic transport , anatomy , ultrastructure , nissl body , midbrain , horseradish peroxidase , fourth ventricle , neuroscience , central nervous system , staining , biochemistry , genetics , enzyme
Abstract The prepacemaker nucleus (PPn), a bilateral cluster of neurons at the boundary of diencephalon and mesencephalon, controls frequency modulations of the electric organ discharge in weakly electric knifefish ( Eigenmannia sp. ). Previous light microscopic studies employing retrograde labelling with horseradish peroxidase suggested that the PPn is restricted to a small area, located approximately 400 μm laterally from the third ventricle and fusing at its medial edge with the thalamic central posterior nucleus (CP). In the present investigation we used Phaseolus vulgaris ‐leucoagglutinin and cholera toxin as highly sensitive markers. In contrast to the previous studies, these experiments yielded a large number of labelled cells not only in the region of the traditionally defined PPn but also in an area reaching far into the CP. Since the PPn has been defined by retrograde labelling rather than by topographic criteria, this result questions the traditional separation between PPn and CP. Such a notion is in agreement with observations of Nissl‐stained sections at the light microscopic level and with a quantitative analysis of several morphological characteristics of the cell bodies in the PPn and CP at the ultrastructural level. Both sets of experiments failed to find differences between the two nuclei. Furthermore, autoradiographic studies have shown that, even in adulthood, cells are continuously born within the ventricular zone of the CP, and at least some of these newborn cells differentiate into CP cells and migrate laterally towards the PPn. Therefore, we postulate that CP and PPn form one large complex, with the medial CP providing precursors of neurons in the lateral CP and PPn. © 1992 Wiley‐Liss, Inc.