Ovulation in the Domestic Fowl 151 



remained at injection sites, as some always followed the needle track and 

 appeared on the surface as the needle was withdrawn. All injections were 

 timed for effect on ovulation of the Q follicle, and results were established 

 by usual palpation procedures. 



Ovulation was induced following injections, 1 mm bilaterally, in the 

 anterior and ventral hypothalamus, and in the caudal neostriatum (Fig. 4). 

 The more anterior and dorsal effective sites in the hypothalamus are found 

 within the preoptic paraventricular nucleus. Those along the dorso-caudal 

 surface of the optic chiasma lie in the anterior hypophysial tract, and the 

 four most posterior sites are within the tubero-mammillary region. 



The stimulatory action of progesterone in the paraventricular nucleus and 

 in the anterior hypophysial tract might have been expected in view of the 

 earlier finding that lesions in these regions, placed within 2 hr following the 

 systemic administration of progesterone, regularly prevent the expected 

 ovulation. Such lesions, however, destroy only a part of the progesterone- 

 sensitive structures, and raise the question as to the effectiveness of lesions 

 in these structures. Exploratory probings indicated no interruption of 

 progesterone-induced ovulation following the placement of lesions of about 

 2 mm diameter in the neostriatum. The effect of lesions in the tubero- 

 mammillary region has not been investigated. 



Two other investigations in this series may be mentioned briefly. Small 

 lesions in the median diencephalon of regularly ovulating hens interrupted 

 ovulation in most hens (53). Lesions in the preoptic hypothalamus, anterior 

 hypophysial tract or dorso-caudal thalamus resulted in lengthier 

 interruptions than did lesions in the central diencephalon, but there was 

 much variability. All lesions were placed 12 hr or more before next-expected 

 ovulation, and comparisons of relative immediacy of interruption of OIH 

 release are not possible. A selective effect on OIH release could not have 

 been detected in hens which resumed ovulation before termination of the 

 observation period (42 days), but the regressed condition of ovaries and 

 oviducts in some hens sacrificed at the close of this period points to a more 

 general interference with gonadotropin secretion. 



Destruction of the supraoptic region of the hypothalamus of the hen was 

 shown by Ralph (50) to result, as a rule, in polydipsia. Most of the birds 

 were out of lay when selected for test, but a number resumed ovulation and 

 lay while under observation. Follicular maturation, ovulation and ovi- 

 position thus proceeded, apparently normally, in some birds bearing 

 extensive lesions and exhibiting polydipsia. The supraoptic nucleus would 

 therefore appear not to be essential for reproduction in the hen, at least not 

 under the conditions of these experiments. It is of some interest that the 

 lesions causing polydipsia were located, in all instances, lateral to the 

 paraventricular region shown to be essential for maintenance of gonadotropin 

 secretion and for OIH release (48, 52). 



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