No abstract

Male rats castrated at 1, 5, 10, 20, 30, and 90 days of age and females ovariectomized at 90 days of age were compared as adults for female mating behavior when given estradiol and progesterone. The Day-1 and Day-5 castrates displayed more feminine behavior than those castrated after Day 5. When males castrated at similar ages received testosterone as adults, Day 1 and Day-5 castrates displayed fewer intromissions and ejaculations than Ss castrated later. The data support the hypothesis that the action of gonadal hormones on differentiating genital tracts and neural tissues is analogous. Feminization occurs in genotypic females or in either sex when gonads are absent. Masculinization occurs when androgen is present, regardless of genotypic sex.

No abstract

Congenital absence of one or both internal carotid arteries (ICAs) has a high association with circle of Willis aneurysm formation. Since the carotid canals in the skull base form secondary to the presence of the embryonic ICA, absence or hypoplasia of a carotid canal on a computed tomographic (CT) scan through the skull base should suggest a congenital ICA abnormality and prompt a search for associated intracranial vascular abnormalities. Of four patients with carotid canal underdevelopment evident at CT, two had associated circle of Willis aneurysms and a third had an extensive skull base rete mirabile supplying an abnormal tangle of vessels in the basal cisterns. Only two patients (one with an aneurysm, one with the skull base rete mirabile) presented with subarachnoid hemorrhage. One patient presented with monocular decreasing vision due to an enlarging aneurysm, and one patient was essentially asymptomatic. If asymmetry or absence of the carotid canals is evident on CT scans of the head, further evaluation to rule out a potentially life-threatening intracranial vascular abnormality such as those found in these patients should be seriously considered, even in a young or asymptomatic patient.