A Golgi study on the neuronal organization of the habenular ganglion in the red stingray, Dasyatis akajei.

The neuronal organization of the habenular ganglion (HG) was studied in the red stingray using the rapid Golgi method. The HG was made up of the medial (MH) and lateral habenular nucleus (LH), and the former nucleus was further divided into a dorsal, intermediate and ventral subnucleus. Only one type of neurons were observed in the MH, while the LH was composed of two types of neurons. In the left HG cut at the rostrocaudal middle of the ganglion, the LH was located in the dorsolateral region, while the dorsal, intermediate and ventral subnuclei of the MH occupied the dorsomedial, intermediate and ventral portions of the ganglion, respectively. In contrast, the right ganglion seen at this level was composed exclusively of the MH, with the dorsal, intermediate and ventral subnuclei located in the dorsomedial, intermediate and ventral portions, respectively. In the caudal level of the left ganglion, each nucleus was seen almost in the same region as in the level of the rostrocaudal middle, however, three subnuclei of the MH fused with the same subnuclei of the opposite side. In the right ganglion at the caudal level, the LH appeared in the intermediate area. The right LH was far smaller and was located more ventrocaudally than the left LH. On account of the LH, the intermediate subnucleus of the MH was divided into a dorsal and ventral part. The dorsal and ventral subnuclei of the MH remained in the same region as in the rostral level. Thus, the HG of the red stingray exhibited a striking left-right asymmetry, the most remarkable aspect of which was considered to be differences of the size, form and location of the LH between the left and right HG.