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4.1 INTRODUCTION

Previous studies o f the anatomy and histology o f the reproductive tra c t o f the naked m ole-rat were limited, and were conducted before it was fully appreciated th a t reproduction was restricted to one female and one to three males in any one colony. Hill et al. (1957) provided a comprehensive description o f the anatomy o f the naked m ole-rat, which included the reproductive organs. In females, the genital organs were described thus: "The general arrangement here recalls the embryonic condition", and presumably referred to non-breeding females only (see results). Kayanja & Jarvis (1971) reported histological observations o f six females, three o f which were believed to be in oestrus (due to the presence o f a p erfo rate vagina, distended vulva and enlarged mammary glands), and three believed to be in anoestrus (due to the ovaries and reproductive tra c ts o f these individuals being smaller than the oestrous females). The "oestrous" animals had a highly vascular uterus and their ovaries contained follicles a t all stages of development, together with large accumulations o f interstitial gland (luteal) tissue. In contrast, "anoestrous" animals had reproductive tra c ts that were smaller and much less vascular, and the ovaries contained predominantly primordial and primary follicles.

In male naked m ole-rats, the testis do not descend and are situated in the abdominal cavity on either side o f the bladder (Hill et al., 1957). Fawcett (1973) described the histology o f the testis, although the breeding status o f the four animals studied was not specified. The seminiferous tubules were sparsely distributed, and the testes contained large quantities o f interstitial (Leydig) cells. This was in contrast to common laboratory rodents, such as the mouse and ra t, and other hystricomorphs like the guinea pig and the chinchilla (Faw cett, 1973).

Despite the f a c t that a t any one time there are only 1-3 breeding males per colony (Jarvis, 1981; Lacey and Sherman, 1990), most males appear to produce mature spermatozoa. Autopsies o f 84 wild-caught males having a body weight over 20 g revealed th at 76% had spermatozoa in their vasa deferentia, implying th at fully developed spermatozoa were present in many

males in a colony. In addition, 51% o f males that weighed over 30 g had large accumulations o f spermatozoa in their vasa deferentia (Jarvis, 1990 a). The aim o f the investigation undertaken fo r this chapter was as follows: (i) to determine in detail the qualitative and quantitative differences in the reproductive tra c ts o f both breeding and non-breeding male and female naked m ole-rats, (ii) Relate these findings to the results from the endocrine studies o f breeding and non-breeding animals o f both sexes, to ascertain the degree o f gonadal inhibition in non-breeding animals in more detail (Chapters 5, 6, & 7).

4.2 METHODS

4.2.1 COLLECTION AND FIXATION OF TISSUE

In captive colonies, reproductive tra c ts were either removed a t post­ mortem, no more than 12 h a fte r the death o f the animal, or removed within 30 minutes o f euthanasia. In females, the vagina was cut ju st below the cervix, and the bicornate uterus, oviducts and ovaries dissected from the abdominal cavity. In males, the reproductive tr a c t was cut ju st below the junction o f the left and right vasa deferentia, and the abdominal testes, together with the attached vasa deferentia were removed. Tissue was fixed by immersion in 10% formol saline.

Tissue samples collected from colonies in the wild were fixed by immersion in 4% paraformaldehyde in saline within 15 minutes o f culling the animal. For further details o f the capture method see Chapter 2.

All samples were fixed fo r a period which ranged from seven days to 24 months (in both captive and wild-caught animals) prior to anatomical measurement and histology. Because an accurate balance and binocular microscope were not available in the field, it was not possible to measure and weigh the reproductive tra c ts and gonads o f wild-caught animals before fixatio n. Therefore, all anatomical measurements were made on fixed material, and the results are based on the assumption th at any size changes in the tissues examined, resulting from the process o f fixatio n, were constant across all the samples.

4.2.2 ANATOMICAL MEASUREMENTS 4.2.2.1 FEMALES

In both captive and wild-caught females, non-breeders were readily distinguished from breeders by the presence o f well developed external genitalia, a p erfo rate vagina, and well developed mammary glands in the la tte r females.

Measurements were taken from both captive breeding (n=8 from eight colonies) and non-breeding female naked mole-rats (n=5 from three colonies), together with wild-caught non-breeding females (n=9 from two colonies). Firstly, the tissue was blotted to remove excess fixative, and the entire reproductive tra c t including ovaries weighed. Next, each ovary was removed and weighed individually, and the mean mass per ovary was calculated. The following dimensions were then taken (illustrated in Figure 4.1), using a binocular microscope fitte d with a graduated graticule: the length, breadth and depth o f each ovary; the length o f each uterine horn from the cervix to the s ta rt o f the oviduct; the diameter o f the uterine horns, expressed as the mean o f three measurements taken a t points approximately 1/4, 1/2 and 3 /4 along the length o f each uterine horn.

OD

UL

UD

FIGURE 4.1 - Diagrammatic representation o f the ovaries and reproductive tra c t o f a female naked m ole-rat showing the positions o f measurements described above. UL= Uterine length, UD= uterine diameter, 0L = ovarian length, 0B= ovarian breadth, 0D= ovarian depth.

In addition, the to tal mass o f the reproductive tr a c t, including ovaries, o f a fu rth er 45 non-breeding females from four wild colonies was determined, using the same procedure described above.

Because the breeding female is usually the largest and heaviest animal in the colony, to ta l mass o f the reproductive tra c t and ovaries, and the mean ovary mass was also calculated relative to body mass in both breeding and non-breeding females, to correct fo r body size differences.

4.2 .2 .2 MALES

Testes, including the vasa deferentia, from captive breeding (4 males from 4 colonies), captive non-breeding (6 males from 3 colonies), and wild- caught male naked m ole-rats (n=52 from 1 colony) were individually weighed. Although the reproductive status o f the wild-caught males was not known, they were assumed to be non-breeders because the mass o f their reproductive tra c ts resembled those o f captive non-breeders (see results). Their testes masses were included in this study to increase the sample size in the investigation o f the relationship between body mass and reproductive tra c t mass.