Unilateral lack of the terminal nerve affects number and distribution of
LHRH-immunoreactive neurons but not that of "dark-spot cells" in the CNS of the African mole-rat.

Holger Jastrow1 and Helmut A. Oelschläger2

1) Department of Anatomy, Johann Wolfgang Goethe-University, Theodor Stern-Kai 7, D-60590 Frankfurt a.M.;
2) Department of Anatomy, J. Gutenberg-University, Becherweg 13, D-55128 Mainz.

The terminal nerve (tn; nervus terminalis) plays an important role in the establishment of the hypothalamo-hypophyseal-gonadal axis as it is the source of Luteinizing Hormone-Releasing Hormone (LHRH)- immunoreactive (-ir) neurons that immigrate into the CNS. The brains and meningeal portions of the tn were analysed in 3 early postnatal (2 m, 1f) and 3 non-reproductive adult female specimens of the African mole-rat (Cryptomys spec.), a subterranean rodent with only one reproductive female in a family, looking for differences in LHRH-ir cell distribution. LHRH-ir neuron counts in the CNS of 5 animals with a bilateral tn revealed that the spreading of ir neurons was more or less equal on both sides. In one of the adult females, however, the right tn was lacking, and within the CNS only very few ir neurons were found on the right side, whereas an exceptionally large number was present on the left side. Thus the total number of LHRH-ir neurons in this female did not differ significantly from that in the other adult animals. In the 3 adult non-reproductive females (including the animal with the unilateral tn) an additional population of LHRH-ir cells was detected in the area of the parafascicular and dorsomedial thalamic nuclei. These cells were present on both sides of the brain in about the same quantity. Their perikarya had large or small vacuoles heavily labelled for LHRH, thus they were named "dark-spot cells" (DSCs). This investigation shows that unilateral absence of the tn is correlated with an almost total lack of ipsilateral LHRH-ir neurons but does not affect the DSC population. The results obtained provide strong evidence for ipsilateral migration of LHRH neurons. The larger number of LHRH neurons in the specimen with the unilateral tn raises the question as to the regulation of LHRH cell numbers (decreased apoptosis?). The distribution of the newly described DSCs suggests that they are independent of the tn.

This oral presentation was at the 93th Meeting of the Anatomical Society at Greifswald, Germany, 27-31. March 1998, published in Ann Anat 180 (Suppl), p. 51. 

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