[The role of the ventrolateral part of the medulla oblongata in the control of gonadotropin secretion. II. The effect of ovarian steroid implantation into the ventrolateral part of the medulla oblongata on LH secretion in the female rat].
To investigate whether neurons in the ventrolateral part of the medulla oblongata (VLMO) are sensitive to ovarian steroid, estradiol benzoate (EB) or progesterone (Prog.) was implanted through a stainless steel double cannula into the VLMO of ovariectomized, EB-primed rats and serum LH was measured. Two weeks after ovariectomy, rats were primed with 20 micrograms EB at 1200h and this day was arbitrarily defined as day 0. At 1200h on day 3, powdery steroid, EB or Prog., was unilaterally implanted into the VLMO. Implantation of EB into the VLMO was effective in increasing serum LH at 1600, 1800 and 2000h on days 3 and 4, but the serum LH concentration at 1600, 1800 and 2000h was much more increased on day 4 than on day 3. Implantation of Prog. into the VLMO failed to induce a significant increase in serum LH on days 3 and 4. To further investigate the effects of anterolateral hypothalamic (ALH) transection and complete spinal transection at T4-T7 levels on EB implantation into the VLMO was examined. It has been shown that both ALH transection and spinal transection at high thoracic levels (T4-T7) significantly blocked proestrous gonadotropin surges and ovulation. In rats with ALH transection, EB implantation into the VLMO was not effective in increasing serum LH at 1600, 1800 and 2000h on days 3 and 4, but in rats with complete spinal transection, EB implantation into the VLMO was effective in increasing serum LH at 1800 and 2000h on days 3 and 4. These results suggest that EB exerts its stimulatory feedback action on the VLMO and the anterolateral hypothalamic area is involved in the mechanism of this stimulatory feedback action of EB.
D000818:Animals; D002818:Cordotomy; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage*; D005260:Female; D007031:Hypothalamus / Q000601:surgery; D007986:Luteinizing Hormone / Q000097:blood*; D008526:Medulla Oblongata / Q000502:physiology*; D011374:Progesterone / Q000008:administration & dosage*; D051381:Rats; D011919:Rats, Inbred Strains
D004343:Drug Implants; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone