Arginine-vasotocin expression and participation in reproduction and social behavior in males of the cichlid fish Cichlasoma dimerus.

In non-mammalian vertebrates, the nonapeptide arginine-vasotocin (AVT) is involved in the regulation of social behavior related to reproduction and aggression. The cichlid fish Cichlasoma dimerus is a monogamous species with complex social hierarchies. Males are found in one of two basic alternative phenotypes: Non-territorial and territorial males. In this work we characterize the vasotocinergic system in males of C. dimerus in relation to social status with particular emphasis on the various putative sites of action of AVT across the hypothalamic-pituitary-gonad (HPG) axis, and its effects on reproductive and social behavior. The location and distribution of vasotocinergic neurons in the brain was studied, highlighting a morphometric analysis of AVT producing neurons in males of different social status. The effect of AVT on pituitary gonadotropin secretion was analyzed by single pituitary culture while expression of AVT in peripheral organs was studied by RT-PCR using specific primers. Finally, the role of AVT on testicular androgen release was assessed by in vitro incubation of testis. Results showed a positive effect of AVT on gonadotropin secretion, where ß-LH showcased a triphasic response under increasing AVT concentration, while ß-FSH's response was dose-dependent and directly proportional. AVT showed a positive and concentration-dependent effect over testicular androgens synthesis and secretion in vitro. Vasotocin expression was observed in testicular somatic tissue located in the interstitial compartment. Thus, the AVT system in C. dimerus appears to be of high complexity, with multiple sites of action in the hypothalamus-pituitary-gonadal axis.

Involvement of somatolactin in background adaptation of the cichlid fish Cichlasoma dimerus.

Somatolactin (SL) is a pituitary hormone present exclusively in fish that is involved in different physiological processes. The role of SL was evaluated in Cichlasoma dimerus (Teleostei, Perciformes) exposed for 10 days to a black and white background (BB and WB). Changes in alpha-melanophore stimulating hormone (alphaMSH) and melanin concentrating hormone (MCH) cells were also analyzed for comparison with SL. A melanin dispersing effect was observed in fish exposed to a BB, while a concentrating one was observed in those exposed to a WB. By Western blot, three SL-immunoreactive (ir) bands (32, 28 and 23.5 kD) were evidenced. Pituitary SL-ir levels were 2.66- and 2.67-fold greater in the 32 Kd and 28 kD bands, respectively, in BB fish compared with those of WB fish. The SL-ir 23.5 Kd band was not included in the analysis because of its unknown identity. In addition, SL-ir cell number and area were significantly higher in the BB condition (BB 22.73+/-1.46, WB 7.37+/-0.54 and BB 27.39+/-1.00 microm2; WB: 16.61+/-0.65 microm2). No significant differences were observed in the number of the hypothalamic MCH-ir neurons. However, a significant difference was observed in their nuclear area (BB 11.61+/-0.42 microm2, WB 17.80+/-0.84 microm2). alphaMSH-ir cells showed a marked increased in number (BB 35.96+/-1.22, WB 24.36+/-1.04), but no significant differences were observed in the cell area. In conclusion, this study presented clear evidence towards a possible involvement of SL in the adaptation to background colors in teleost together with alphaMSH and MCH.