Presence of β-Follicle-Stimulating Hormone and β-Luteinizing Hormone Transcripts in the Brain of <i>Cichlasoma dimerus</i> (Perciformes: Cichlidae)

Abstract

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) play key roles in vertebrate gametogenesis and steroidogenesis. They are mainly synthesized in the pituitary gland. While investigating the ontogeny of FSH and LH cells in the cichlid fish Cichlasoma dimerus by immunohistochemistry (IHC), we unexpectedly found immunoreactive neurons in the preoptic area, sending their projections through different brain areas and neurohypophysis. Our previous work using Western blot and IHC techniques applied to the adult brain confirmed these findings. To further demonstrate the extrapituitary expression of these hormones, we performed RT-PCR detecting sequences coding for β-FSH and β-LH subunits in the C. dimerus pituitary and brain (preoptic-hypothalamic area). The expression of these transcripts in both organs was consistent with their peptide expression showing a high sequence homology when compared with other phylogenetically related fish. An individual pituitary in vitro culture system was utilized to study the possible modulatory effect of brain-derived gonadotropins on pituitary hormone secretion. Pituitary explants were cultured with different concentrations of LH or FSH, and the culture media were analyzed by Western blot. Exogenous LH produced a dose-dependent increase in pituitary β-LH, β-FSH and somatolactin (SL) releases. No effect was observed on growth hormone (GH). The effect on prolactin (PRL) was not consistent among treatments. Exogenous FSH produced an inhibition in β-LH release, dose-dependent increases in β-FSH and SL releases, and no effect on PRL and GH releases. These findings support the concept of regulation of pituitary trophic hormones by brain-derived gonadotropins.

The interrenal gland in males of the cichlid fish Cichlasoma dimerus: Relationship with stress and the establishment of social hierarchies

“…Similar results were obtained in subordinate male green swordtails (Xiphophorus helleri) (Scott and Currie, 1980). The South American cichlid fish, Cichlasoma dimerus (Heckel, 1840), inhabits the Parana and Paraguay Rivers' basins and has recently been used as a laboratory model to study teleost reproduction, neuroendocrinology and behavior (Alonso et al, 2011(Alonso et al, , 2012Fiszbein et al, 2010;Pandolfi et al, 2009;Ramallo et al, 2012;Tubert et al, 2012). In this species, under laboratory conditions, the largest male usually emerges as the dominant and reproductively active male of the group.…”

Social and reproductive physiology and behavior of the Neotropical cichlid fish Cichlasoma dimerus under laboratory conditions

“…during 6 months of the year under natural conditions and throughout the year in the laboratory under long photoperiod (14 h) and controlled temperature (20-26ºC). Due to these advantageous characteristics, C. dimerus is becoming an interesting model for reproductive and developmental studies (Pandolfi et al, 2009). In addition, C. dimerus displays an elaborate social system and complex, relatively stereotyped breeding activities, which make this species very suitable for studies of intraspecific social interactions on reproduction.…”

Signal transduction mechanisms for autocrine/paracrine regulation of somatolactin-α secretion and synthesis in carp pituitary cells by somatolactin-α and -β

“…These findings suggest that SL gene expression and secretion are controlled by hypothalamic regulation as well as feedback signals from the periphery. Recently, a report on in vitro culture of cichlid fish pituitary has shown that treatment with exogenous LH and FSH could directly elevate SL secretion at the pituitary level (32), indicating that SL release is also under the control of antocrine/paracrine regulation of pituitary hormones.…”