SEASONAL-CHANGES IN SPERMATOGENESIS AND TESTICULAR STEROIDOGENESIS INTHE MALE BLACK BEAR URSUS-AMERICANUS

American black bears, Ursus americanus, are seasonal breeders with a m ating season in late spring to early summer. The objectives of this st udy were to determine whether there are seasonal changes in spermatoge nesis and immunolocalization of testicular steroidogenic enzymes, and to correlate these changes with peripheral steroid concentrations. Thr ee captive mature bears were maintained in open cages during the summe r season and provided with chambers for denning during the winter. Tes ticular biopsies and blood samples were obtained from anaesthetized be ars on 12 March; 15 lune, 12 October and 15 January. Steroidogenic enz ymes were immunolocalized using polyclonal antisera raised against bov ine adrenal cholesterol side-chain cleavage cytochrome P450 (P450scc), human placental 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), por cine testicular 17 alpha-hydroxylase cytochrome P450 (P450c17) and hum an placental aromatase cytochrome P450 (P450arom). Spermatogenesis cha nged seasonally: spermatogonia and degenerating spermatocytes were obs erved in October; spermatogonia and primary spermatocytes were present in January; spermatogonia, spermatocytes and round spermatids were pr esent in March; and spermatogonia through spermatozoa were present in June. P450scc and P450c17 were immunolocalized in spermatids and Leydi g cells in June, whereas in October these enzymes were present only in Leydig cells. 3 beta HSD was localized in Leydig cells in June and Oc tober with more intense staining in June. Localization of P450arom cha nged seasonally: no immunostaining in October; positive immunostaining in Sertoli cells in January; more extensive immunostaining in Sertoli cells, peritubular-myoid cells and round spermatids in March; and str ong immunostaining in Sertoli cells and round and elongating spermatid s in June. Serum testosterone and oestradiol concentrations changed se asonally: testosterone and oestrogen were low in October and January, slightly higher in March, and high in June. The present study demonstr ates that in the black bear seasonal changes in spermatogenesis are ac companied by changes in the immunolocalization of testicular steroidog enic enzymes that are correlated with changes in serum testosterone an d oestradiol concentrations. The presence of P450arom in Sertoli cells at the beginning of testicular recrudescence suggest that aromatase a nd oestrogen may play a role in re-initiating spermatogenesis.