Effects of estradiol on concentrations of gonadotropin-releasing hormone receptor messenger ribonucleic acid following removal of progesterone

To test the hypothesis that low levels of estradiol are sufficient to increase concentrations of GnRH receptor mRNA in the absence of progesterone, ewes were ovariectomized and immediately treated with estradiol implants for 12 h to achieve circulating concentrations of estradiol typical of the early (n=5) or late (n=4) follicular phase. Five additional ewes underwent lutectomy, and control ewes were untreated. Treatment of ewes with 1/2 or 1 estradiol implant increased concentrations of estradiol in serum to 3.0 ± 0.8 pg/ml or 6.3 ± 0.3 pg/ml, respectively, and concentrations of estradiol in lutectomized ewes (2.4 ± 0.5 pg/ml) were intermediate. Ovariectomy did not alter concentrations of GnRH receptor mRNA or numbers of GnRH receptors. Treatment of ewes with 1 estradiol implant increased concentrations of GnRH receptor mRNA and numbers of GnRH receptors. In ewes treated with 1/2 estradiol implant, concentrations of GnRH receptor mRNA were intermediate between controls and ewes treated with 1 estradiol implant, and numbers of GnRH receptors were greater than controls. Lutectomy increased concentrations of GnRH receptor mRNA but did not affect numbers of GnRH receptors. We conclude that estradiol stimulates expression of the GnRH receptor gene and numbers of GnRH receptors in the absence of progesterone. However, effects of estradiol on expression of the GnRH receptor gene were clearly evident only when concentrations of estradiol were elevated to levels typical of the late follicular phase.     

Leech giant glial cell: functional role in a simple nervous system

The giant glial cell in the central nervous system of the leech Hirudo medicinalis has been the subject of a series of studies trying to link its physiological properties with its role in neuron-glia interactions. Isolated ventral cord ganglia of this annelid offer several advantages for these studies. First, single giant glial cells can easily be identified and are quite accessible to electrophysiological and microfluorometric studies. Second, only two giant macroglial cells are located in the neuropil of each ganglion, rendering them well suited for studying neuron-glia interactions. Third, many neurons can be identified and are well known with respect to their physiology and their roles in controlling simple behaviors in the leech. This review briefly outlines the major recent findings gained by studying this preparation and its contributions to our knowledge of the functional role of glia in nervous systems. Emphasis is directed to glial responses during neuronal activity and to the analysis of intracellular Ca(2+) and H(+) transients mediated by neurotransmitter receptors and ion-driven carriers. Among its numerous properties, the leech giant glial cell prominently expresses a large K(+) conductance, voltage-dependent Ca(2+) channels, ionotropic non-NMDA glutamate receptors, and an electrogenic, reversible Na(+)-HCO(3)(-) cotransporter.     

Survival and developmental disability in infants with birth weights of 501 to 800 grams, born between 1979 and 1994

OBJECTIVE: Because the survival rate has increased for extremely low birth weight neonates, many have raised the concern that the rate of developmental disability among survivors will also increase. To address this concern, we analyzed changes over time in survival and major neurosensory impairment in a sample of extremely low birth weight infants born between July 1, 1979, and June 30, 1994. METHODS: The study sample included 513 infants with birth weights of 501 to 800 g who were cared for in either of the two neonatal intensive care units that serve a 17-county region in northwest North Carolina and who were born to mothers residing in that region. At 1 year of age (corrected for gestation), survivors were examined by a pediatrician and were tested using the Bayley Scales of Infant Development. Major neurosensory impairment was defined as cerebral palsy, a Bayley Mental Developmental Index <68, or blindness. A total of 209/216 (97%) of survivors were examined at 1 year of age. Epoch of birth was defined as follows: epoch 1, July 1, 1979 to June 30, 1984; epoch 2, July 1, 1984 to June 30, 1989; and epoch 3, July 1, 1989 to June 30, 1994. RESULTS: Survival rates for epochs 1, 2, and 3 were, respectively, 24/120 (20%), 63/175 (36%), and 129/218 (59%). In contrast, the proportions with a major neurosensory impairment did not increase over time; rates for successive epochs were 6/24 (25%), 17/61 (28%), and 26/124 (21%). Rates of cerebral palsy were 3/24 (13%), 12/61 (20%), and 9/124 (7%); rates of delayed mental development were 4/24 (17%), 12/61 (20%), and 17/124 (14%); and rates of blindness were 2/24 (8%), 0/62, and 5/124 (4%), respectively. CONCLUSIONS: This analysis suggests that the increasing survival of extremely low birth weight neonates since the late 1970s has not resulted in an increased rate of major developmental problems identifiable at 1 year of age.     

Aberrant crypt focus promotion and glucose intolerance: correlation in the rat across diets differing in fat, n-3 fatty acids and energy

McKeown-Eyssen (Cancer Epidemiol. Biomarkers Prevent., 3, 687-695, 1994) and Giovannucci (Cancer Causes Control, 6, 164-179, 1995), noting the striking similarity in lifestyle risk factors for colorectal cancer and insulin resistance, proposed that the hyperinsulinemia, glycemia and hypertriglyceridemia associated with insulin resistance promotes colon cancer. To compare the effect of diet on colon cancer promotion and insulin resistance in the F344 rat, we assessed the effect of fat, n-3 fatty acids and energy in pairwise comparisons on average size of aberrant crypt foci (ACF) and on glucose intolerance in the same animals in a single experiment. Diets high in fat and energy increased and diets with increased n-3 fatty acids and calorie restriction decreased both ACF growth and glucose intolerance compared with control diets. The measures of promotion of colon cancer and insulin resistance were strongly correlated (n = 98, r = 0.67, P < 0.001). In addition, both were highly correlated with daily energy intake (r = 0.62 and 0.66) and were also correlated with basal (post-prandial) insulin, glucose and triglycerides (r = 0.31-0.53, P < 0.01). We concluded that ACF growth and glucose intolerance are correlated for a wide range of diets and that increased circulating energy (glucose and triglycerides) may lead to both colon cancer promotion and insulin resistance.