Although it has been known for some time that estrogen exerts a profound inf luence on brain development a definitive demonstration of the role of the classical estrogen receptor (ER␣) in sexual differentiation has remained elusive. In the present study we used a sexually dimorphic population of dopaminergic neurons in the anteroventral periventricular nucleus of the hypothalamus (AVPV) to test the dependence of sexual differentiation on a functional ER␣ by comparing the number of tyrosine hydroxylase (TH)-immunoreactive neurons in the AVPV of wild-type (WT) mice with that of mice in which the ER␣ had been disrupted by homologous recombination (ERKO␣). Only a few ER␣-immunoreactive neurons were detected in the AVPV of ERKO␣ mice, and the number of TH-immunoreactive neurons was three times that of WT mice, suggesting that disruption of the ER␣ gene feminized the number of THimmunoreactive neurons. In contrast, the AVPV contains the same number of TH-immunoreactive neurons in testicular feminized male mice as in WT males, indicating that sexual differentiation of this population of neurons is not dependent on an intact androgen receptor. The number of THimmunoreactive neurons in the AVPV of female ERKO␣ mice remained higher than that of WT males, but TH staining appeared to be lower than that of WT females. Thus, the sexual differentiation of dopamine neurons in the AVPV appears to be receptor specific and dependent on the perinatal steroid environment.From an evolutionary perspective, the most adaptive physiological responses are those that ensure successful reproduction. Coordinated sex-specific behaviors and physiological mechanisms have evolved to facilitate reproduction and it is now clear that most are determined by the central action of steroid hormones during brain development. For example, only female rats display a massive surge in gonadotropin secretion in response to treatment of gonadectomized animals with estrogen and progesterone, and exposure of genetic females to high levels of gonadal hormones such as testosterone near the time of birth results in defeminization of the sexually dimorphic pattern of luteinizing hormone (LH) secretion that triggers ovulation (1-4). Abundant evidence from a variety of animal models indicates that steroid hormones secreted by the gonads during development cause profound sex-specific changes in the structure and neurochemistry of certain forebrain regions, including sexually dimorphic regions in the hypothalamus thought to play key roles in mediating the preovulatory secretion of LH (4-7). A particularly important and sexually dimorphic part of neural circuits that regulate the secretion of LH is the anteroventral periventricular nucleus of the preoptic region (AVPV). The AVPV has been shown to play a critical role in transducing hormonal feedback on LH secretion and is required for spontaneous ovulation (8, 9). Consistent with this functional role, the AVPV contains high densities of neurons that express receptors for estrogen and progesterone (10) and implan...

Field studies were conducted over a 2-year period at Urbana, Illinois, to evaluate soybean (Glycine max (L.) Merr., var. Harosoy 63 and Wayne) and weed yields as influenced by row spacing, variety, weed control methods, and 2,3,5-triiodobenzoic acid (hereinafter referred to as TIBA). Soybean yield increased and weed yield decreased as row spacing was decreased. Compared to the yield from 40-inch rows, soybean yield increase was 10, 18, and 20% for 30, 20, and 10-inch rows, respectively. Both cultivation and applications of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) controlled annual grass weeds at all row spacings. Cultivation controlled broadleaf weeds at all row spacings. Some broadleaf weeds, unaffected by trifluralin, made sufficient growth to impair soybean yields in wide rows but not in narrow rows.

Information from the northern Corn Belt comparing tillage systems and corn (Zea mays L.)/soybean [Glycine max. (L.) Merr.] rotations over years is limited. Field studies were conducted near Arlington, WI for 3 yr (1987–1989) on a Plano silt loam soil (fine‐silty, mixed, mesic Typic Argiudoll). The objectives were to determine the influence of tillage, N fertilizer level, and hybrid/cultivar on growth and grain yield of corn and soybean grown in various rotation sequences. Yields of both corn and soybean declined with consecutive years of monocropping, but only soybean had 15% lower yields with annually alternating corn and soybean than for the 1st yr of production following several years of the other crop. For the least “monocropping‐sensitive” hybrid (Pioneer 3737) or cultivar (BSR 101) evaluated and for either corn hybrid under conventional tillage (CT), the yield benefit of 1st yr compared to continuous cropping was similar for corn and soybean at about 15%. But with corn hybrid DeKalb 524 under no‐till (NT), and the brown stem rot (BSR) (caused by Phialophora gregata) susceptible soybean cultivar in 1987 and 1989, yields were more than 25% higher for 1st yr crop production. Average NT yields were similar to CT for both crops with 1st yr or alternate corn and soybean, but yields were usually lower under NT with monocropping.

Field investigations were conducted at Urbana, III., concerning the relationship of leaf angle and canopy shape to grain yield and apparent photosynthesis of Zea mays L. A backcross‐derived isogenic single cross hybrid (‘C103’ ✕ ‘Hy’) carrying the lg2 gene for erect leaf produced 40% more grain than its counterpart with normal (horizontal) type leaf, when compared in rows 51 cm wide at 59,304 plants/ha. Mechanical manipulation of the leaves of a widely grown commercial hybrid. ‘Pioneer 3306’ into a more upright nature resulted in grain yields above that produced by the same hybrid in its normal leaf orientation and canopy shape. Apparent photosynthesis measurements on individual corn leaves showed the relative efficiency of CO2 fixation/unit of incoming sunlight to steadily increase as the leaf angle decreased. The results strongly support corn breeding programs in the area of plant geometry and crop canopy.