Ontogeny and distribution of gonadotropin-releasing hormone (GnRH) neuronal systems in the brain of the cichlid fish Cichlasoma dimerus

Abstract

Using immunocytochemistry we have described the distribution and ontogeny of three distinct gonadotropin-releasing hormone (GnRH) neural systems, emphasizing the analysis during the period of sex differentiation in the South American cichlid fish Cichlasoma dimerus. In the forebrain a group of neurones immunoreactive to salmon GnRH that formed clusters in the nucleus olfacto retinalis (NOR), was located at the junction of the olfactory bulb and the telencephalon. These neurones differentiated 3 days after fertilization from the olfactory placodes. GnRH immunoreactive neurones along the olfactory nerves through the rostrobasal olfactory bulb were observed on day 4 and at the NOR on day 10. A group of neurones immunoreactive to chicken GnRH II was seen in the dorsal midbrain tegmentum. They originate from the ventricular ependyma between days 5 and 6. These neurones remained close to blood vessels throughout development. Between days 22 and 30 a group of neurones immunoreactive to seabream GnRH was detected in the anterior basal preoptic area. GnRH innervation of the pituitary was detected after the differentiation of preoptic neurones and in coincidence with gonadal differentiation. We hypothesize that the GnRH neural systems have three distinct embryonic origins. Furthermore, we show that the NOR and the midbrain GnRH neurones might have functions other than gonadal development, whereas the preoptic GnRH neurones in C. dimerus might be associated with gonadal sex differentiation.

Identification of immunoreactive FSH and LH cells in the cichlid fish Cichlasoma dimerus during the ontogeny and sexual differentiation

“…When treated with rhFSH, 80% of the gonads were differentiated to presumptive ovaries, based on the morphological description available for this species (Meijide et al 2005). The results of this experiment reinforce our previous hypothesis about a correlation between the innervation of pituitary cells by GnRH1 fibers and the release of FSH that will be acting in any of the important steps of the sexual differentiation process (Pandolfi et al 2002).…”

“…A correlation between the innervation of the pituitary gland by GnRHI fibers and the onset of the sexual differentiation process was already reported for this species suggesting that GTHs may be involved in this process (Pandolfi et al 2002). The second aim of this study was to evaluate the effect of FSH on the gonadal differentiation in vitro.…”

Seabream GnRH immunoreactivity in brain and pituitary of XX and XY Nile tilapia, Oreochromis niloticus during early development

“…However, in this study no such migratory pattern was observed in the sbGnRH neurons with respect to both XX, XY fish. This is unlike in mammals but similar observations were made in some other cichlid fish like Cichlasoma dimerus (Pandolfi et al, 2002). It appears that in these fish a population of POA-H neurons originate in the POA-H itself or else migrate from some other cerebral or extra-cerebral region and start synthesis of GnRH (i.e.…”

Gonadal development and sex differentiation in the cichlid fishCichlasoma dimerus (Teleostei, perciformes): A light- and electron-microscopic study

“…In this context, the possibility that the hypothalamo-pituitary-gonadal axis is involved in triggering gonadal sex differentiation is currently under debate (see Fitzpatrick et al, 1993;Kah et al, 1993;Feist and Schreck, 1996;Baroiller and Guiguen, 2001;Miranda et al, 2001;Devlin and Nagahama, 2002;Pandolfi et al, 2002).…”