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Thyroid hormone and long days interact to programme American tree sparrows (Spizella arborea) for seasonality (i.e. thyroid hormone-dependent photoperiodic gonadal growth, photorefractoriness, and postnuptial moult). This study explored in radiothyroidectomized (THX) males given thyroid hormone replacement therapy whether thyroid hormone acts within the(More)
This study tested the hypothesis that T3 (triiodothyronine) is the tissue-active "seasonality" hormone by determining whether T3 could mimic T4 (thyroxine) and program photostimulated thyroidectomized (THX) male American tree sparrows (Spizella arborea) for three components of seasonality (i.e., full-blown testicular growth, photorefractoriness, and(More)
Fifty infants who weighed 1250 g or less at birth were studied with serial real time cerebral ultrasound to evaluate the temporal relation of various perinatal factors to the onset and progression of periventricular haemorrhage (PVH). The significant antecedents of PVH were severe bruising at birth, low birthweight, short gestation, ratio of arterial oxygen(More)
Chest physiotherapy, including posturing the patient head downwards while the chest is percussed and vibrated, was used in the treatment of patients with an exacerbation of chronic bronchitis. In seven patients the mean FEV declined from 1.38 litres plus or minus 0.39 to 1.25 litres plus or minus 0.37 after postural drainage and percussion (P less than(More)
To assess the role of the hypothalamic neurosecretory system in the mechanism of photoperiodic control of testicular growth in Spizella arborea, we have examined the effect of (1) photostimulation on the density of paraldehyde-fuchsin-stainable (PAF+) material in the neurovascular zone of the median eminence, and (2) interruption of the(More)
Songbirds exhibit seasonal changes in the volumes of song control nuclei. Birds on long, spring-like days have larger nuclei than do birds on short, winter-like days. The mechanisms mediating volumetric changes have not been determined unequivocally, but testosterone (T) is probably involved. This study examined whether testicular factors are uniquely(More)
Photoperiodic control of gonadotrophin secretion in male tree sparrows was studied by examining changes in plasma LH in castrated birds retained on short daylengths and in castrated birds transferred to long daylengths. Plasma LH concentrations were markedly higher in photostimulated birds than in non-photostimulated birds throughout the 25-day experiment,(More)
Photorefractoriness, a reversible state of unresponsiveness to daylengths of gonadostimulatory duration, terminates seasonal breeding in many photoperiodic species of birds. Whether the eyes are components of the mechanism that triggers photorefractoriness is an important, but heretofore unresolved, question. Although a role for extraocular photoreception(More)
  • F E Wilson
  • 1992
The time course of regaining photosensitivity was monitored in intact and in castrated Harris' sparrows (Zonotrichia querula) held on short days. Measured endpoints, assumed to be equivalent indicators of the photosensitive state, were photoinduced testicular growth in intact males and a photoinduced elevation in plasma LH (luteinizing hormone)(More)