ラットの閉口筋運動ニューロン開口筋運動ニューロンのアセチルコリンエステラーゼ活性の差について

Abstract

The acetylcholinesterase (AChE) activity in the rat masseter (jaw-closing) and anterior digastric (jaw-opening) motoneurons was examined quantitatively. After the masseter and anterior digastric motoneurons were retrogradely labeled by fluorescent tracers, the rats were administered with diisopropyl fluorophosphate, an irreversible AChE inhibiter, and then allowed to survive for 3 hr for the subsequent synthesis of AChE, followed by transcardial perfusion with fixatives. Serial frozen 20 μm sections of the brainstems were prepared and processed for AChE histochemistry. The AChE activity of motoneurons which were tracerlabeled was determined by measuring the absorbance at 470 nm in their cytoplasms using a microspectrophotometer. The areas of the somas of motoneurons were also measured using an image analyzer. The results are as follows.1) The AChE activity of 24∼58 cells for each motoneuron group in the trigeminal motor nuclei from four mature (10-week-old) rats (n=8) was measured. In all motor nucleus preparations, the mean values of AChE activity in the anterior digastric motoneurons were 1.4∼1.9 times higher than those in the masseter motoneurons (p<0.001). The AChE activity of the digastric motoneurons was 1.6 fold of that of the masseter motoneurons, when all values obtained from 8 nuclei were pooled and the means of the two groups of motoneurons were compared (p<0.001).2) In 8 samples from four suckling (16-day-old) rats, some showed significant differences in the AChE activity between the jaw-closing and jaw-opening motoneurons and some did not. The AChE activity of the digastric motoneurons was 1.2 times significantly higher than that of the masseter motoneurons (p<0.001) when all values obtained from 4 rats were pooled.3) The AChE activity in the masseter motoneurons of adult animals seemed to be slightly higher than that in the suckling rats, but there was no significant difference between them. On the other hand, the AChE activity in the anterior digastric motoneurons of adult animals was significantly higher than that in the suckling rats (p<0.001).4) The effect of soft diet on increases of AChE activity during growth after weaning was examined. Day 21 after birth, rats were removed from their mother. Then control rats (n=4) were fed a solid diet, and experimental rats (n=4) were fed a powder diet. After 7 weeks, ratios of AChE activity of the anterior digastric motoneuron to the masseter motoneuron were determined. Differences in the activity levels between the two motoneuron groups were larger in a solid diet group than in a powder diet group, suggesting that soft diet influenced normal development of AChE activity.5) There was no relationship between the AChE activity and soma area of motoneuron.