A Golgi Study on the Neuronal Organization of the Habenular Ganglion in the Red Stingray, Dasyatis akajei

Abstract

Summary: 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.The habenular ganglion (HG) is a conspicuous structure in the dorsomedial region of the diencephalon and is known to exist in all vertebrates. One of the most remarkable features of the HG is the structural left-right asymmetry observed in certainspecies (Ariens Kappers, Huber and Crosby 1960;Kuhlenbeck 1977). The selachian HG has been known to exhibit a striking left-right asymmetry and has been the subject of numerous investigations (Edinger

A Golgi Study on the Afferent Fibers to the Habenular Ganglion in the Red Stingray, Dasyatis akajei

“…In these studies, however, the afferent fibers were analyzed mainly in myelin stained sections and minute terminal patterns of the afferents have not been fully elucidated. As was shown in our previous study (Iwahori, Nakamura and Kameda 1991), the neuronal organization of the HG in the red stingray exhibited the striking left-right asymmetry. In order to understand the characteristic features of the structural asymmetry, information on the minute organization of the afferent fibers is needed.…”

“…These fibers branched out many collaterals which were distributed in the intermediate (fibers [13][14][15][16][17][18][19] in Fig. 5) and ventral subnucleus of the MH (fibers 20-30 in Fig.…”

Directional asymmetry of the zebrafish epithalamus guides dorsoventral innervation of the midbrain target

“…Evidence for habenular subnuclear specialization has also come from studies on cartilaginous and teleost fish. Silver staining of the adult red stingray brain enabled the identification of discrete asymmetric subdomains with differences in neuronal size, shape and density of packing (Iwahori et al, 1991a;Iwahori et al, 1991b). The left medial habenula of salmon exhibits a serotoninergic subregion that is not observed on the right (Ekstrom and Ebbesson, 1988).…”

“…DV regionalization of the left habenula has been noted in other lower vertebrates. A lateral subnucleus occupies most of the dorsal left habenula in the stingray brain, but is restricted to a smaller medial posterior region on the right (Iwahori et al, 1991a;Iwahori et al, 1991b). There is also a dorsoventral difference in the distribution of the calcium-binding protein calretinin A in the left habenula of Rana esculenta (Guglielmotti et al, 2004).…”