Alterations in the GnRH-LH system in relation to gonadal stage and Aroclor1254 exposure in Atlantic croaker

Exposure of Atlantic croaker (Micropogonias undulatus) to the polychlorinat ed biphenyl mixture (Aroclor 1254, PCB; 1 mg/kg body wt/day for 30 days) du ring the early-recrudescence phase of the gonadal cycle results in the impa irment of LH secretion and gonadal growth. In order to determine whether im pairment was due to disruption of the stimulatory GnRH neuroendocrine pathw ay, we compared various parameters of the GnRH-LH system in early recrudesc ing vs. spermiating (mature) fish. Seabream GnRH (GnRH) content in the preo ptic anterior hypothalamic area (POAH) and pituitary, pituitary GnRH recept or concentrations, and basal and GnRH analog (GnRHa)-induced LH secretion w ere significantly higher in gonadally mature croaker compared to early-recr udescing fish. In a subsequent experiment, the effects of PCB on the same n euroendocrine indices were investigated during the gonadal recrudescence ph ase of croaker. PCB exposure during the period of testicular maturation pre vented the natural increase in GnRH content in the POAH but not in the pitu itary. This finding suggests that PCB may impair GnRH synthesis in the POAH . The number of pituitary GnRH receptors also remained significantly lower in the PCB-exposed group, which was likely due to an impairment of GnRH rel ease. The GnRH content in the POAH, number of pituitary GnRH receptors, and LH secretion in the PCB-exposed group were comparable to those in early-re crudescing fish, suggesting an impairment of normal maturation of the GnRH- LH system during the gonadal recrudescence phase. This impairment may be du e to a direct action of PCB on GnRH neurons and/or indirectly via interfere nce with other neurotransmitter pathways that modulate GnRH function. (C) 2 001 Elsevier Science Inc. All rights reserved.