Localization of the motor neuron somata of geniohyoid muscle in rat: A horseradish peroxidase study.

Abstract

The aim of the study was to investigate the location of motor neuron somata of geniohyoid muscle in rat. Nine Sprague-Dawley rats were used in this study. Operations were performed under general anaesthesia. Nembutal sodium, 40mg per kg intraperitoneally was used for anaesthesia. 0.02 to 0.05ml of 30% horseradish peroxidase (Sigma Type VI) solution in normal saline was injected into the exposed right geniohyoid muscle. After 48hr, the animals were fixed by perfusion through left ventricle of heart, first by 100ml normal saline and then with 500ml of 1.25% glutaraldehyde and 1% paraformaldehyde in 0.1M phosphate buffer, pH 7.4, at room temperature, and finally with 500ml of 10% sucrose in the same buffer at 4°C. The medulla oblongata and first cervical segment of spinal cord were removed, kept in 10% sucrose in above phosphate buffer at 4°C for 24hr. Thereafter, their serial transverse sections were cut in a cryostat at a thickness of 60μm. The sections were treated according to tetramethyl benzidine (TMB)-horseradish peroxidase (HRP) method. HRP-labelled neuron somata were observed at the following sites: (a) In ventral part of right main hypoglossal nucleus in upper two-thirds of the closed part of medulla oblongata. (b) In ventrolateral subnucleus of hypoglossal nucleus in lower third of closed part of medulla oblongata. (c) At spinomedullary junction, they were located in dorsomedial part of right ventral grey column; a few were also seen here scattered on right side of central canal and among corticospinal fibres.