Effects of late intrauterine 5-bromo-2'-deoxyuridine administration on the development of mouse GnRH neurons

We have studied the effect of prenatal (late intrauterine) 5-bromo-2’-deoxyuridine (BrdU) administration on the development of the GnRH pathway. BrdU is widely accepted as a tool to study neurogenesis (pre and postnatal); in addition, this thymidine analogue proved to be effective to influence different developmental events. Dams of C57Bl6 mice were treated with BrdU (15 ug/g body weight ) on the last days of pregnancy (between E16, E17, E18, E19 and the time of birth, E20/21 days, respectively) by subcutaneous daily injections. BrdU treatment during the last 3-4 days of pregnancy resulted in a significant decrease of the number of GnRH immunoreactive (IR) neuronal cell bodies and fibers, measured at postnatal ages (P0/P1, P3/4, P6/8 and P21/23). The higher accumulative doses of BrdU produced a more significant decrease of the GnRH-IR compared to the lower ones. The morphology of GnRH-IR neuronal cell bodies was different from that of the controls: bipolar cells were few in number, and most of the cells were round shaped, smaller in size, and in many cases they did not exhibit neuritic arborization. As far as the distribution of GnRH-IR neurons is concerned, it was similar to that of the control animals (most of the cells were found in the preoptic area), however, a large number of immunopositive cells were also detected in the nasal septum and along their migratory root at later postnatal ages (up to P6/P8 postnatal days) in comparison with the control (up to P3 postnatal day). Significant differences were seen in the amount of GnRH IR fibers in BrdU treated animals at all postnatal ages studied. In conclusion, these results indicate that late intrauterine BrdU administration influences the development of the GnRH system in a dose- and time-dependent manner. Application of the BrdU during the proper time-window of the pregnancy may be a useful tool to further study ‘in vivo’ several aspects of the migratory process of GnRH neurons in normal and, possibly, in pathological conditions. (Grants: Ministero degli Affari Esteri, XVI Executive Program of Scientific and Technological Co-operation between Italy and Hungary; MIUR COFIN).