66 Jeffrey Pudney, Jacob A. Canick, Gloria V. Callard 



tous arrangement thus allows a direct comparison to be made of the 

 ability of these isolated tissue compartments to formulate estrogens and 

 so provide information on the exact site of aromatization in Necturus 

 testes. A recent study using these isolated tissues from N. maculosus 

 testes demonstrated that the glandular tissue contained two key enzymes 

 in estrogen biosynthesis, 17 a-hydroxylase and aromatase (Callard et al. 

 1980). Also, spectral measurements showed that cytochrome P-450 spe- 

 cies that bind progesterone and androstenedione, respectively, the ster- 

 oidal substrates for 17 a-hydroxylase and aromatase, were concentrated 

 in the glandular tissue. Levels of both the steroidogenic enzymes and 

 cytochrome P-450 were negligible in the isolated seminiferous lobule 

 fractions, indicating that the glandular tissue and its Leydig cells (identi- 

 fied by electon microscope observations) were the site of aromatization 

 in the testes of Necturus. This study on N. maculosus was carried out in 

 the fall when the glandular tissue was fully developed along the entire 

 length of the testes. 



The longitudinal wave of spermatogenesis that Necturus undergoes 

 results in the spatial segregation of both germ cells and Leydig cells at 

 different stages of development in the testes during the breeding season. 

 This is an important consideration, since the relationship between sper- 

 matogenesis and Leydig cells during specific stages of germ cell devel- 

 opment is very difficult to study in most common laboratory animals. 

 In these species all spermatogenic stages occur simultaneously in the 

 testes from the onset of puberty. Moreover, the seminiferous tubules 

 and interstitial tissues are uniformly distributed and intermingled through- 

 out the entire organ. Therefore, using these species it is technically diffi- 

 cult to obtain precise information on the functional interdependence of 

 the two tissue compartments without disrupting their normal anatomi- 

 cal relationships. These difficulties, however, can be circumvented by 

 studying the testes of Necturus with its discrete temporal and spatial 

 segregation of germ cell stages and accompanying interlobular tissue 

 (Pudney at al. 1983). 



Figure 2 demonstrates salient morphological features that have 

 been diagrammatically represented for the testis of N. maculosus as it 

 appears towards the close of the breeding season (Pudney et al. 1983). 

 At this time of the year essentially the same anatomical arrangment of 

 tissues also occurs in the testes of N. lewisi, which were separated trans- 

 versely into a cephalic region and a caudal region. Both regions con- 

 tained the immature portions of the seminiferous lobules and associated 

 undifferentiated interlobular tissue. The cephalic region, however, also 

 possessed the maturing lobular portions filled with cysts containing 

 spermatozoa, while the caudal region was composed of the spermiated 

 degenerating lobules plus the hypertrophied Leydig cells forming the 

 glandular tissue. The isolated regions were analyzed for 17 a-hydrox- 



