Effect on Testicular Development in Rats
by Differences in Timing of γ-ray Irradiation
Dai YAMAMOTO 1, Junko SATO 1, Takuya DOI 1, Jun SASAKI 1, Takeshi KANNO 1, and Toshiaki KOKUBO 2
1. Mediford Corporation, 2. National Institutes for Quantum Science and Technology
We have no COI regarding this presentation.

Radiation is likely to affect male reproductive organs, and fetuses and children are more susceptible. Azoospermia and Delayed puberty
in humans are currently a problem, there are many causes, and fetal and childhood influences may be one of them. This study investigated
how irradiation at fetal, neonatal, weaning, and early sexual maturation periods affect the testicular development until adulthood.

ObjectiveAll experimental protocols involving rats in this study were reviewed and approved by the Institutional Animal Care and Use
Committee of the National Institute of Radiological Sciences (NIRS) and were performed in strict accordance with the NIRS
Guide for Care and Use of Laboratory Animals.

Materials and Methods

Radiation exposure: Pregnant F344 rats, at GD15 and GD19, and F1 rats, on
postnatal day 5 (PND5), PND20, and PND49, were whole-body irradiatedwith 0.5 or 2 Gy of 137Cs gamma irradiation at the dose rate of 0.7 Gy/min.
Exposure was conducted using a Gammacell 40 (Atomic Energy of Canada).
The F1 rats not irradiated with γ-rays, were set up as control animals.

Animals: F1 hybrids of male Eker rats and female Fischer-344 (F344) rats (CLEA Japan)
Mating: Pro-estrous or estrous females were placed with an individually housed male overnight.
Pregnancies were dated from gestational day 0 (GD0), being the day after mating.
Experimental protocol is as follows.
Fetal

Early sexual

Neonatal Weaning‧‧‧ Adultmaturation

27 weeks age

Group No.
1(Control)
2

GD15
GD193PND54

PND205PND49

6: Irradiation (2 or 0.5 Gy),

Number ofanimals
0.5 Gy 2 Gy

‧‧‧

1612

‧‧‧

2214

‧‧‧

15

16

‧‧‧

1713

‧‧‧

1815

‧‧‧

16

17

Histopathological examination: The testis was removed and prepared thehistopathological specimens in accordance with the prescribed method. The
total number of tubules in a central transverse section was counted. Moreover,②
the number of tubules in the three types was counted and compared for eachdose and timing of γ-ray Irradiation. Tubular lesions were divided into below.
① Normal tubules③ Partial Sertori cell tubules(PSTs; partial absence of all germ cells)

Fertilization
GD0< Total number of tubules / one cross section>

15

19

Sertoli cells: Proliferative activity↑
Aab③: Necropsy, GD: Gestational day, PND: Postnatal day

Results and Discussion
a①② Sertori cell-only tubules(S-onlyTs; absence of all germ cells)

aA

aAb
BB

***BirthPND5peak↑↑Gonocytes: Proliferation activity↑ undividedWeaning
2049

Puberty

GST (Proliferation activity↑)

GST: Gonocytes-to-spermatogonia transition● Normal formation (Control)B******● GD15***: p < 0.001 (vs 0.5 Gy)
b: p < 0.001 (vs Control at 0.5 Gy [a]), B: p < 0.001 (vs Control at 2 Gy [A])It is reported that the Sertoli cell population increases from
GD 13.5 until PND 15 to 20. The number of Sertori cell tubules
was lower at 2 Gy than at 0.5 Gy. => Elongation of testis cord=> formation of convoluted seminiferous tubules● GD19It was found that when Sertoli cells were irradiated with
γ-ray at the time they were dividing, the elongation of
the seminiferous tubules was inhibited.
< Each number of normal tubule, S-onlyTs, and PSTs at 2 Gy >*: p < 0.05, ***: p < 0.001

Gonocyte
Spermatogonia
Tubule (Sertoli cell)
Normal tubule
Sertoli-only tubule
Partial Sertori cell tubule(vs each tubule of control at 2 Gy)

***

***

● PND5*** *** ****** ****** **● PND20 or 49*GonocyteGD15: The gonocyte is in the process of dividing; however, the division
resumes after the irradiation.

Nascentspermatogonia

Differentiating
spermatogonia
Undifferentiatedspermatogonia=> Not only PSTs and S-onlyTs, but also normal tubules are also noted. The first division of spermatogonia gives rise to undifferentiatedspermatogonia and differentiating spermatogonia.The former
remain as stem cells, while the latter progress to spermatogenesis.
γ-ray Irradiation is thought to damage the cells that progress tospermatogenesis including differentiating spermatogonia, but the=> S-onlyTs comprises the majority.
undifferentiated spermatogonia (stem cells) then divide andPND 5: The gonocyte differentiates into spermatogonia after PND 4;
become differentiating spermatogonia, and spermatogenesis
however, not all gonocytes finish differentiating immediately.
resumes. => Normal tubules are occupied in the testis.
GD19: During the stopping of the gonocyte dividing, a sensitive toirradiation is high, and the gonocyte are lost by apoptosis.
Methylation did not occur propery.

27 weeks oldundivided→