Research Article
Rocio Ortiz-ButrÃÂ
Abstract
The study examined serotonergic- (5-HT) and muscarinic-receptor binding in the hypothyroid versus the euthyroid rat brain. Wistar rats were randomly divided into two groups; 1) hypothyroid, treated with methimazole (60 mg/kg per day) in their drinking water for four weeks, and 2) euthyroid, which were given only tap water. The animals were sacrificed and their brains were used for autoradiographic experiments. When compared to the euthyroid group, the hypothyroid rats had significantly enhanced 3H-5-hydroxytriptamine-receptor binding in the cingulate (53%), parietal (19%), and temporal (32%) cortices, the caudate putamen (29%), anterior amygdala nucleus (39%), fields CA1-3 (54%), periaqueductal gray (45%), substantia nigra pars reticulata (71%), and compacta (19%). Autoradiograhic experiments revealed that in the hypothyroid group the 3H-quinuclinidyl benzilate receptor binding (a muscarinic agonist) was reduced in the frontal (42%), parietal (46%), temporal (42%), and entorhinal (41%) cortices, the caudate putamen (45%), the anterior (40%), medial (33%), and basolateral (46%) amygdaloid nuclei, dentate gyrus (53%), fields CA1-3 (43%), periaqueductal gray (45%), substantia nigra pars reticulata (35%), and compacta (35%). The present data suggest that alterations in both 5-HT- and muscarinic-receptor binding could be associated with the changes in behavioral alterations and in the enhanced excitability seen in hypothyroid rats.