The Effect of Unilateral Orbital Enucleation on Acetylcholine and Muscarinic Receptors in Visual Pathway, and Physical Activity of Rats

ABSTRACT

Acetylcholine is one of the major neurotransmitters in visual system of rats. Cholinergic, serotonergic and gamma-aminobutyric acid(GABA) ergic projections are known as modulators of visual processing. The purpose of this study was to examine the effects of unilateral orbital enucleation on the amount of acetylcholine and its receptor bindings in dorsolateral geniculate body, superior colliculus and visual cortex of rats, and on motor activites. The amount of acetylcholine was measured by gas chromatography; whereas [3H]quinuclidinyl benzilate(QNB) bindings to muscarinic receptors were examined by autoradiography. Motor activity was measured by activity meter for 24 hours. The results of this study were as follows: 1. The amount of acetylcholine in superior colliculus significantly increased at 1 week after enucleation, but it decreased at 2 and 4 weeks after enucleation. In visual cortex, the amount of acetylcholine did not change at 1 week after enucleation, but it significantly decreased at 2 and 4 weeks after enucleation. 2. After enucleation, [3H]-QNB binding to muscarinic receptors gradually decreased over the 4 weeks in dorsolateral geniculate body, superior colliculus and visual cortex. 3. Locomotor activity of rats did not show any change at 1 week after enucleat ion, but it decreased at 2 and 4 weeks after enucleation. In conclusion, unilateral orbital enucleation resulted in a reduction in the amount of acetylcholine and muscarinic receptors in rat visual system, which was speculated to be a major cause of a decrease in physical activity.