Male Sprague-Dawley rats (BK-Universal, Stockholm, Sweden) at postnatal ages of 8, 18, and 26 days (eight animals per group) as well as 60 days (four animals per group) were housed at the animal facilities of Karolinska Hospital (Stockholm, Sweden) under an alternating 12L:12D photoperiod. The 8- and 18-day-old rats were placed in the same cages as their mothers, and the other animals were housed two in each cage. Free access to water and food was provided in all cases. itat on
After killing the rats with CO2, the testes from four animals were removed. One testis from each animal was decapsulated, following which 1-mm sequential segments of a single long seminiferous tubule were prepared under a transillumination stereomicroscope in a Petri dish containing
PBS (pH 7.4; 2 mM NaH2PO4, 8 mM Na2HPO4, and 150 mM NaCl). The immature seminiferous tubule exhibited no transillumination pattern comparable to that visualized in the adult testis. The contralateral testis was frozen for protein analysis. From another four animals at postnatal ages of 8, 18, and 26 days, one testis was fixed for subsequent electron microscopy and the contralateral testis for immunohistochemistry (see below).
The present study was approved by the animal ethics committee of the Karolinska Institute (PN. 169/97).