The rat abducens nucleus: a histo- and immunohistochemical study.

The number and proportion of motoneurons and interneurons present in the rat abducens nucleus was determined by the use of ChAT immunostaining and of HRP staining after retrograde transport from the injected right lateral rectus muscle. After HRP injection 67% of abducens neurons took up HRP and were hence motoneurons to the muscle. The cell bodies were mainly located in the middle third of the nucleus and were either spindle-shaped or pyriform. By ChAT-immunohistochemistry, 77% of the rat abducens neurons were ChAT-positive. After considering and discarding the hypotheses that the lateral rectus muscle could be incompletely filled by HRP, and that other muscles may be innervated by abducens motoneurons, it is concluded that some interneurons of the abducens nucleus of the rat are probably cholinergic.