DISCUSSIONS 



Charles A. Barraclough: One of the principal difficulties encountered in an investigation 

 of the neural factors concerned with the control of ovulation in the rat is the fact that 

 this species ovulates spontaneously. Thus, the general approach used in investigations 

 of this phenomenon has been to study factors which will inhibit ovulation and to 

 correlate such inhibition with the destruction or depression of specific regions in the 

 central nervous system. Another method of study has been described by Dr. Everett 

 this morning in which the natural stimulus for ovulation is blocked by pentobarbital 

 anesthesia and ovulation is then induced by electrical stimulation of various hypo- 

 thalamic areas. Although this latter procedure permits a more accurate localization 

 of the regions of the hypothalamus concerned with the ovulatory discharge of gonado- 

 tropin from the adenohypophysis, under these conditions the factor of central nervous 

 depression with a drug is still present. 



In our investigations we have used a preparation which does not require prior 

 inhibition of ovulation to study central nervous control of ovulation, the androgen- 

 sterilized rat. In previous studies we observed that administration of a single sub- 

 cutaneous injection of 1 .0 mg of testosterone propionate to the 5-day-old rat resulted in 

 permanent sterility (Barraclough, C. A., Ariat. Rec. 130, 267, 1958). When autopsied at 

 100 days of age, the ovaries of these animals contained numerous large vesicular 

 follicles as well as follicles in various other stages of development, but ovulation had 

 not occurred and corpora lutea were absent (Figs. 1 and 2). Furthermore, these ovaries 

 secrete estrogen as evidenced by the persistence of a comified vaginal mucosa. Seemingly 

 the particular malfunction in adenohypophysial gonadotropin secretion of the sterile 

 rat does not reside in the inability of this gland to secrete FSH or LH (ICSH) but 

 rather in the failure of this gland to release gonadotropin in sufficient quantity to 

 cause ovulation, a function controlled by the hypothalamus. Thus, it may be that 

 androgen administration during infancy alters hypothalamic-hypophysial inter- 

 relationships by rendering the hypothalamic areas responsible for the ovulatory 

 discharge of gonadotropin refractory to intrinsic activation. As such, the proper 

 impetus for the ovulatory release of gonadotropin is not supplied to the adenohypo- 

 physis and sterility ensues. To test this hypothesis, experiments were designed to 

 determine whether the pituitary of the sterile rat would respond to hypothalamic 

 activation by discharging sufficient gonadotropin to cause ovulation. Six adult sterile 

 rats (235-250 gm body wt.) were given an intraperitoneal injection of 25 mg/kg of 

 pentobarbital sodium. This dosage was selected as it does not block ovulation in the 

 normal cyclic rat nor the stress-induced discharge of ACTH, but will keep the animals 

 sufficiently subdued to be placed in a stereotaxis apparatus. In these rats, bipolar 

 concentric electrodes were stereotaxically oriented in the median eminence region of 

 the hypothalamus and stimulation was performed in this and subsequent experi- 

 ments using the following parameters: 100 ^A current delivered at a frequency of 

 100/sec with a duration of 1 msec, for 15-sec on/off periods over a 15-min total 

 period. These parameters were selected as they had been shown previously by Critchlow 

 (Anier. J. Physiol. 195, 171, 1958) to be effective in inducing ovulation in the Nembutal- 

 blocked rat, and they are quite similar to the parameters reported by Dr. Everett in his 

 studies. At autopsy, 24 hr after stimulation, the Fallopian tubes were examined for the 

 presence of ova and the ovaries for corpora lutea. All autopsy results and electrode 

 placements were confirmed histologically. Under these circumstances, electrical 

 stimulation of the median eminence failed to induce ovulation. However, considering 

 the ovarian-pituitary axis of the persistent-estrous rat, in which pituitary gonadotropin 

 is being released in response to the constant blood levels of estrogen, the possibility 



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