Neurons in the mouse anterior commissure. A light microscopic, electron microscopic and autoradiographic study.

Both limbs of the anterior commissure of the mouse brain were examined to find the number, distribution, times of origin and structure of the neurons present, and also the number of synapses within the commissure. Neurons form between 0-1 and 0-4% of the total cell population and are produced between the twelfth and fourteenth days of gestation. It seems likely that the neurons within the anterior commissure are derived from adjacent septal nuclei, with the bed nuclei of the anterior commissure mainly contributing to the posterior limb and the nucleus triangularis septi mainly contributing to the anterior limb. The neurons are almost certainly functional, and distribute to the nuclei from which they are derived. There are probably also other connexions between these nuclei and both limbs of the anterior commissure through dendrites from the septal nuclei which ramify throughout the commissure. The large number of synapses scattered throughout the anterior commissure suggests that the neurons within the commissure, and dendrites entering it, may contribute substantially to the pathways between the anterior and posterior limbs and the septal nuclei without diminishing the number of axons in the commissure.