Is. Balan et al., BIRTH-DATES OF THE TYROSINE-HYDROXYLASE IMMUNOREACTIVE NEURONS IN THEHYPOTHALAMUS OF MALE AND FEMALE RATS, Neuroendocrinology, 64(6), 1996, pp. 405-411
This study determined the birthdates of the tyrosine hydroxylase(TH) i
mmunoreactive (IR) neurons in the zona incerta (ZI), periventricular n
ucleus (PeVN) and arcuate nucleus (AN) of male and female rats. 'Long-
survival' [H-3]thymidine autoradiography combined with TH immunocytoch
emistry, the first enzyme of catecholamine synthesis, was used. In mal
es, TH-IR neurons originate in the ZI between embryonic days (E) 12 an
d 13, while in the PeVN and AN this process is prolonged until E16. Th
e majority of TH-LR neurons became postmitotic at E12 in the ZI, betwe
en E12 and E14 in the PeVN and at E15 in the AN. The birthdate of TH-I
R neurons was sexually dimorphic with (a) generation of the majority o
f TH-IR neurons in the ZI in males preceding that in females, (b) gene
ration of TH-IR neurons in the AN of males delayed as compared to fema
les, and (c) average daily fractions of the newborn TH-IR neurons in e
ach hypothalamic region of females exceeding that seen in males. This
sexual dimorphism was observed prior to E16, i.e. before the onset of
sex difference in androgen levels, implying a hormone-independent mech
anism, determined at the genetic level.