Effects of estrogen and neurotransmitters on the primary cultures of tilapia brain from different ages

Activation of brain steroidogenesis and neurogenesis during the gonadal differentiation in protandrous black porgy, Acanthopagrus schlegelii

The early brain development, at the time of gonadal differentiation was investigated using a protandrous teleost, black porgy. This natural model of monosex juvenile fish avoids the potential complexity of sexual dimorphism. Brain neurogenesis was evaluated by histological analyses of the diencephalon, at the time of testicular differentiation (in fish between 90 and 150 days after hatching). Increases in the number of both Nissl-stained total brain cells, and Pcna-immunostained proliferative brain cells were observed in specific area of the diencephalon, such as ventromedialis thalami and posterior preoptic area, revealing brain cell proliferation. qPCR analyses showed significantly higher expression of the radial glial cell marker blbp and neuron marker bdnf. Strong immunohistochemical staining of Blbp and extended cellular projections were observed. A peak expression of aromatase (cyp19a1b), as well as an increase in estradiol (E2 ) content were also detected in the early brain. These data demonstrate that during gonadal differentiation, the early brain exhibits increased E2 synthesis, cell proliferation, and neurogenesis. To investigate the role of E2 in early brain, undifferentiated fish were treated with E2 or aromatase inhibitor (AI). E2 treatment upregulated brain cyp19a1b and blbp expression, and enhanced brain cell proliferation. Conversely, AI reduced brain cell proliferation. Castration experiment did not influence the brain gene expression patterns and the brain cell number. Our data clearly support E2 biosynthesis in the early brain, and that brain E2 induces neurogenesis. These peak activity patterns in the early brain occur at the time of gonad differentiation but are independent of the gonads.

Photoperiod affects the development of central neurotransmitter systems of tilapia, Oreochromis mossambicus

The effects of photoperiod on the development of central neurotransmitters were investigated with tilapia, Oreochromis mossambicus. Zero-day-old (the hatching day) tilapia were raised in three different photoperiods (light/dark cycle): 12/1, 24/0, and 0/24 h, respectively. On the 5th day, brain serotonin (5-HT), norepinephrine (NE), gamma-aminobutyric acid (GABA), and glutamate (Glu) contents were quantified by a high-performance liquid chromatograph with electrochemical detection. Similar experiments were performed on the 5-, 10-, 15-, 20-, and 25-day-olds. These results showed that the photoperiod influenced both brain NE and GABA contents during its respective restricted period, before days 10 posthatching. Brain 5-HT content was influenced, either facilitated or suppressed according to the developing stage, whereas, brain Glu content was not altered by the different photoperiod exposure throughout the present studies.

Temperature influences the ontogenetic expression of aromatase and oestrogen receptor mRNA in the developing tilapia (Oreochromis mossambicus) brain

Water temperature has a differential influence on the development of central neurotransmitter systems according to the developmental period in tilapia (Oreochromis mossambicus). Aromatase and oestrogen receptors (ERs) represent important components of the mechanism of brain differentiation. Gene expression of aromatase and ERs is modulated by neurotransmitters in the developing brain. In the present study, the quantitative reverse transcription-polymerase chain reaction method was used to investigate the effects of temperature on the ontogenetic expression of aromatase and ERs in the developing tilapia brain. Before day 10 posthatching, exposure to a higher temperature (32 degrees C) resulted in a significant increase in the expression of brain aromatase; conversely, a lower temperature (20 degrees C) resulted in a decrease. ERalpha expression was depressed in accordance with the decrease of temperature, but ERbeta was unaffected by temperature. Between days 10 and 20, neither brain aromatase nor ERalpha expression was altered by temperature, whereas ERbeta expression was significantly enhanced by exposure to 32 degrees C. Between days 20 and 30, brain aromatase significantly increased at the higher temperature and decreased at 20 degrees C, but neither ERalpha nor ERbeta was affected by temperature. The expression of both brain aromatase and ERs, differentially regulated according to the temperature and to the developmental period, could be related to brain-sex differentiation.