Immunocytochemical demonstration of salmon GnRH and chicken GnRH‐II in the brain of masu salmon, Oncorhynchus masou

Abstract

We have recently developed sensitive and specific radioimmunoassays (RIAs) for salmon gonadotropin-releasing hormone (sGnRH) and chicken GnRH-II (cGnRH-II) and have measured the contents of both GnRHs in the rainbow trout brain. Our results showed that contents of the two GnRHs are variable among different brain regions. Therefore, in order to confirm the differential distribution of the two GnRHs by a different technique, we examined the distribution of immunoreactive sGnRH and cGnRH-II in the brain of masu salmon by using immunocytochemical techniques. sGnRH immunoreactive (ir) cell bodies were scattered in the transitional areas between the olfactory nerve and the olfactory bulb, the ventral olfactory bulb, between the olfactory bulb and the telencephalon, the ventral telencephalon, and the preoptic area. These sGnRH-ir cell bodies were dispersed in a strip-like region running rostrocaudally in the most ventral part of the ventral telencephalon. sGnRH-ir fibers were distributed in the various brain regions from the olfactory bulb to the spinal cord. They were especially abundant in the olfactory bulb, ventral telencephalon, preoptic area, hypothalamus, deep layers of the optic tectum, and thalamus. sGnRH-ir fibers also innervated the pituitary directly. cGnRH-II-ir cell bodies were found in the nucleus of the medial longitudinal fasciculus (nMLF). The distribution of cGnRH-II-ir fibers was similar to that of sGnRH-ir fibers, except that cGnRH-II-ir fibers were absent in the pituitary. The number of cGnRH-II-ir fibers was much fewer than that of sGnRH-ir fibers. The results of the present immunocytochemical study are in basic agreement with those of our previous RIA study. Thus, we suggest that in masu salmon, sGnRH not only regulates gonadotropin (GTH) release from the pituitary but also functions as a neuromodulator in the brain, whereas cGnRH-II functions only as a neuromodulator.

Antisense for gonadotropin-releasing hormone reduces gonadotropin synthesis and gonadal development in transgenic common carp (Cyprinus carpio)

“…Furthermore, among the transgenic fish with sGnRH antisense, some AS(+) fish without sperm had no or abnormal gonadal development and lower GtH levels suggesting that inhibiting sGnRH produces completely, or partially, sterile transgenic fish. Thus, these data confirm previous studies showing that sGnRH is required for development of male gonads (Amano et al, 1991;Ashihara et al, 1995). No morphological or histological differences in ovarian development were observed among AS(+) females and controls, which suggests that further studies need to be performed to understand the role of sGnRH in female gonadal development.…”

Genomic Structure and Expression Sites of Three Gonadotropin-Releasing Hormone Genes in One Species

“…. oriented rostrocaudally'') are the same as those of the GnRH neurons found in the terminal nerve population (Amano et al, 1991). Conversely, these data are consistent with the idea that expression of 5Trp 7 Leu 8 6GnRH occurs primarily in the telencephalic region in salmonids, as has been previously shown in other teleosts where in situ hybridization has been performed.…”

“…Similarly, in situ hybridization in masu salmon (Suzuki et al, 1992), rainbow trout, and Atlantic salmon (Bailhache et al, 1994), using 5Trp 7 Leu 8 6GnRH-specific probes, found robust GnRH gene expression in the terminal nerve region yet only weak expression in the preoptic area. Comparing the immunocytochemical staining of GnRH neurons by Amano et al (1991) in masu salmon and Bailhache et al (1994) in Atlantic salmon and rainbow trout with in situ labeling in these species shows significantly less labeling in the preoptic area with in situ probes. Indeed, Bailhache et al concluded that this could ''.…”

Brain morphology and immunohistochemical localization of the gonadotropin-releasing hormone in the bluefin tuna, Thunnus thynnus

“…Anti sGnRH-immunoreactive neurons were smaller than the anti cGnRH ones. The presence of GnRH neurons in the preopticus nucleus has been detected as a sGnRH variant in Cypryniformes (Yu et al, 1988;Powel et al, 1996) and Salmoniformes (Okuzawa et al, 1990;Amano et al, 1991), whereas the cGnRH-II form has been reported in midbrain tegmentum of most of the fish species studied (see Lethimonier et al, 2004 for review). In bluefin tuna, we were able to find weakly immunostained nerve fibres in both the preopticus nucleus and the neurohypophysis.…”