Morphometric studies on the lateral habenular nucleus of Wistar rats after bilateral excision of the superior cervical ganglia and cold exposure with special reference to the pineal gland
Tomalik, T.; Peschke, D.; Peschke, E.
Gegenbaurs Morphologisches Jahrbuch 134(2): 131-141
1988
ISSN/ISBN: 0016-5840 PMID: 3402714 Document Number: 317672
To analyse the role of peripheral sympathetic fibres in the regulation of thyroxine (T4), serum thyrotropin (TSH), pituitary TSH, and nuclear size of the lateral habenular nuclei rats were studied 30 d after bilateral cervical ganglionectomy (GX). In order to examine the influence of GX at normal temperature (24 degrees C) and exposure to cold (10 degrees C), rats were subjected to a 72 h exposure to cold before killing. 4 times a day (light-dark cycle: 14L: 10D, light on 05h00) the rats were sacrificed: middle light, middle darkness, 1 h after "light on" and 1 h after "light off". Ganglion removal resulted in a highly significant decrease of serum-T4 and increase of serum- and pituitary-TSH (primary hypothyroidism). Under these circumstances, the karyometric findings are showing a statistically significant magnification of the lateral habenular nuclear volume. In contrast to GX, exposure to cold increased T4- and TSH-levels and reduced the lateral habenular nuclear size. GX diminished the effect of exposure to cold of the T4- and TSH-levels and normalized the habenular nuclear volume. These results indicate that there exists a negative correlation between T4 (but not TSH) and lateral habenular nuclear size. Under consideration of previous investigations of the pineal nuclear size in hypo- and hyperthyroid state, our results are in agreement with the hypothesis of other authors that it is probably an inhibitory feed-back loop between the lateral habenula and the pineal gland (see also the high gamma-aminobutyric acid [GABA] content in the habenular complex). On the other hand, it was possible to confirm that the habenular complex is integrated into the thyroid circuit.