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Biomedical subjects

S C Wilson

Publications and source records attributed to S C Wilson.

At least 73 records · Page 4Linked to original sources
PubMed1983

An investigation of diurnal and cyclic changes in the secretion of luteinizing hormone in the domestic hen.

The characteristics of the diurnal rhythm in the concentration of LH in plasma of the domestic hen varied according to age and duration of photoperiod. A pronounced increase in LH was observed at the onset of darkness in immature hens whether maintained on schedules of 16 h light: 8 h darkness (16L:8D) or 8L:16D. During weeks 4.5-15 or -17.5 raised concentrations of LH were maintained until 6 and 12 h after the onset of darkness in hens held on 16L:8D and 8L:16D respectively. By 19 weeks of age the diurnal rhythm of LH secretion had changed to resemble more closely that observed in the laying hen. An increase in the concentration of LH in plasma at the onset of darkness was of comparatively short duration and gave way, within 2-3 h, to a steep decline before a further slight increase in LH, which tended to occur at 11-14 h after the onset of darkness. Superimposed on this diurnal rhythm of LH secretion in the laying hen were a one- to threefold increase in the concentration of LH during 8-4 h before ovulation and a much less pronounced increase in LH during 0-8 h after ovulation. The pattern of changes in the concentration of LH in plasma during the ovulatory cycle was not modified by the repeated withdrawal of blood at intervals of 2 h.

Animals↗
PubMed1983

Evidence for the involvement of central conversion of testosterone to oestradiol-17 beta in the regulation of luteinizing hormone secretion in the cockerel.

Treatment of intact cockerels with the synthetic antioestrogen tamoxifen caused a significant increase in the plasma concentration of LH. In contrast, passive immunization with an antiserum raised against oestradiol-17 beta did not lead to an increase in plasma LH. A pronounced depressive effect of injections of 0.1 mg testosterone propionate (TP) or 0.1 mg oestradiol benzoate (OB) on plasma concentrations of LH was prevented by tamoxifen. Furthermore, a pronounced rise in the concentration of LH releasing hormone in the posterior hypothalamus after the injection of cockerels with OB was completely inhibited by tamoxifen. Neither 0.1 nor 0.5 mg androstenedione modified the concentration of LH in plasma. A dose of 0.05 mg TP, which failed to depress the concentration of LH in plasma of intact cockerels, caused a marked fall in plasma LH in castrated cockerels. Tamoxifen itself exhibited weak oestrogen agonist activity in castrated cockerels by causing a reduction in the concentration of LH in plasma. However, tamoxifen prevented any further depressive effect on LH resulting from the injection of TP. These findings suggest that testosterone exerts an inhibitory influence on LH secretion at the central neural level, partially at least, by means of the product of its aromatization, oestradiol-17 beta.

Animals↗
PubMed1982

Contact-promoting behavior, social development, and relationship with parents in sibling juvenile degus (Octodon degus).

This study describes infant socialization in captive parent-young units of the caviomorph rodent Octodon degus. Types of parent-young contact (huddling or squatting) and social interaction (body nosing and accompanying behaviors) are described and their ontogenetic trends examined between postnatal Days 1 and 46. Fathers spent less time than mothers in contact with the young. Mother-young contact decreased postnatally, whereas the amounts of mother-young and father-young social interaction, measured in terms of body-nosing exchanges, showed a continuous increase postnatally; sibling interactions also showed a continuous increase. Father-young interactions tended to be dominated by the father. Young reared with the father cohabiting huddled less with their mother, and engaged in less body-nosing, than young reared in the father's absence. Observations suggested that paternal control of the young may curb juvenile interactions. Young observed without their parents in an unfamiliar enclosure did not groom or "play" as in their home cage with parents present, but engaged in relatively more vocalizing, neck-nosing and forepaw-clasping.

Animals↗
PubMed1982

Concentrations of luteinizing hormone and progesterone in plasma during sexual development of the Khaki Campbell duck.

Concentrations of LH and progesterone were measured in the plasma of ducks which were, from 3 weeks of age, raised on either a constant photoperiod of 16 h light: 8 h darkness or a lighting schedule which stimulated natural changes in daylength. In ducks raised on a constant photoperiod of 16 h light: 8 h darkness the plasma concentration of LH increased steeply between 7 and 3.5 weeks before the onset of lay. Concentrations of LH then declined, gradually at first, but them rapidly during the 7 days before the first oviposition in association with a pronounced increase in the plasma concentration of progesterone. During the 18 days before the first egg was laid there was a significant (P less than 0.01) negative correlation between the plasma concentrations of LH and progesterone. The patterns of LH release during sexual development of ducks raised on a schedule which stimulated natural changes in daylength were variable but could be categorized according to the daylength at which each duck came into lay. In ducks coming into lay soon after the winter solstice when daylength was short (8.0-8.5 h light/day) there was a pronounced 15-fold prepubertal increase in the plasma concentration of LH although in some ducks high LH levels were not maintained until 3-4 weeks before the first oviposition and were not always followed by a rise in the plasma concentration of progesterone. In contrast, in ducks coming into lay when daylength had increased to 11.0-11.5 h light/day there were only minor fluctuations in the plasma concentration of LH until a small two- to threefold increase in LH was observed during the 2 weeks before the first oviposition.

Animals↗
PubMed1982

Evidence for the involvement of central catecholaminergic mechanisms in mediating the preovulatory surge of luteinizing hormone in the domestic hen.

The effects of various pharmacological treatments, designed to perturb central catecholaminergic neurotransmission, on the pattern of LH release during the preovulatory period in the domestic hen were studied. Treatment of hens with either L-dihydroxyphenylalanine or diethyldithiocarbamate which raised the concentration of dopamine in the hypothalamus by 42 and 110% respectively, or with apomorphine, attenuated the preovulatory surge of LH. In contrast, treatment with either alpha-methyl-p-tyrosine which produced a 65% decline in the concentration of dopamine in the hypothalamus without affecting the concentrations of noradrenaline or adrenaline or treatment with pimozide did not affect the LH surge. While treatment with propranolol was similarly ineffective, phenoxybenzamine attenuated the LH surge to a marked extent. These observations suggest that the preovulatory surge of LH in the hen is influenced by facilitatory alpha-adrenergic and inhibitory dopaminergic mechanisms. Evidence to corroborate these findings was sought by determining the steady-state concentrations of dopamine, noradrenaline and adrenaline in five discrete diencephalic regions of the hen throughout the ovulatory cycle.

Adrenergic alpha-Agonists↗
PubMed1981

Effects of an anti-oestrogen, tamoxifen (ICI 45,474), on luteinizing hormone release and ovulation in the hen.

The role of oestradiol in the regulation of LH release in the hen was studied by use of the anti-oestrogen, tamoxifen (ICI 46,474). Intramuscular injection of laying hens with 2 or 4 mg tamoxifen on 2 successive days delayed or prevented the occurrence of the preovulatory release of LH and ovulation expected on day 3. Ovulation could be restored by i.v. injection of 20 micrograms LH releasing hormone (LH-RH). Tamoxifen at a dose of 1 mg affected neither the timing of the preovulatory release of LH nor ovulation. Treatment with 2 or 4 mg tamoxifen on 2 successive days reduced the effectiveness of an i.m. injection of progesterone to stimulate a release of LH. Injection of 1, 2 or 4 mg tamoxifen on 2 successive days significantly raised basal levels of LH in the blood at 24 h after the last injection. This was associated with an increase in the capacity of the pituitary gland to respond to an injection of synthetic LH-RH by a release of LH. These studies suggest that oestradiol has at least two roles in the regulation of LH release in the hen. First, it maintains a low basal level of LH-RH. Secondly, oestradiol has a facilitative role in the mechanism by which progesterone stimulates the preovulatory release of LH.

Animals↗
PubMed1981

Effect of photoperiod on the concentrations of corticosterone and luteinizing hormone in the plasma of the domestic hen.

Ovipositions in hens maintained under schedules of 16h light : 8h darkness (16L : 8D) or 8L: 16D were restricted to a 12h period of the day while in hens maintained on continuous light, ovipositions occurred at times throughout the whole of the 24h day. In hens maintained in continuous light a significant rise in the plasma concentration of corticosterone was observed 11-9h before ovulation/oviposition. In hens in 16L : 8D there was an increase in the concentration of corticosterone in the plasma during the first 1.5h of darkness which, under that schedule, coincides with the onset of the "open period" for the occurrence of the preovulatory release of LH. In hens ovulating the first egg of a sequence the rise in the secretion of corticosterone was only transient and levels fell as preovulatory concentrations of LH rose to a peak. However, in hens undergoing an ovulation late in a sequence or in those not expected to ovulate, the concentration of corticosterone in the plasma continued to rise to attain a maximal concentration 8h later. In hens maintained in 8L : 16D there was a tendency for the concentration of corticosterone in the plasma to increase at the beginning of the open period, 4 h after the onset of darkness, though this rise was much smaller than that observed at the beginning of the open period of hens on 16L : 8D. A further, more pronounced, increase in concentration of corticosterone was observed between 11 and 15h after the onset of darkness. It is suggested that the rise in the concentration of corticosterone at 11-9 h before ovulation in hens in continuous light reflects the beginning of an open period with a free-running circadian periodicity of 26-27 h.

Animals↗
PubMed1980

Modification by metyrapone of the "open period" for pre-ovulatory lh release in the hen.

1. A single injection into laying hens of 60 mg metyrapone 28 h after the final ovulation of a sequence induced increases in the plasma concentrations of LH and progesterone, followed by premature ovulation. Injection of metyrapone 8 h after ovulation, however, did not affect plasma concentrations of either LH or progesterone. 2. Injection of laying hens with 60 mg metyrapone on 5 successive days reduced the effectiveness of exogenous ACTH in increasing the plasma concentration of corticosterone and abolished the system of "open" and "closed periods" for pre-ovulatory LH release. Thus, pre-ovulatory LH surges and ovipositions occurred throughout the 24-h day instead of being restricted to an 8 to 10-h period of the day. 3. These observations suggest that changes in environmental stimuli such as light act via the adrenal gland in regulating the timing of the "open period" for the pre-ovulatory release of LH in the hen.

Animals↗
PubMed1980

Concentrations of corticosterone and luteinizing hormone in plasma during the ovulatory cycle of the domestic hen and after the administration of gonadal steroids.

Plasma concentrations of corticosterone and LH were measured in hens in relation to the ovulation of an egg either early or late in a sequence and also in hens injected with gonadal steroids. In hens about to ovulate an egg early in the sequence, the plasma concentration of LH rose at the onset of darkness while levels of corticosterone remained low. As levels of LH fell during the 4 h preceding ovulation, those of corticosterone increased steeply to reach a maximum at about the time of ovulation, which is shortly after dawn. In contrast, in hens about to ovulate an egg late in a sequence, the concentration of LH in plasma fell and that of corticosterone tended to increase during the hours of darkness. During the 7 h preceding ovulation the temporal relationship of LH to corticosterone was similar to that observed before an early ovulation such that levels of corticosterone increased rapidly on the descending slope of the preovulatory LH surge and reached maximum values at the time of oviposition and ovulation. Infections of oestradiol benzoate and testosterone propionate did not alter plasma concentrations of either corticosterone or LH. On the other hand, the injection of progesterone was associated with a rapid fall in levels of corticosterone. It is suggested that progesterone may suppress the pituitary-adrenal system and thus modulate the pattern of corticosterone secretion during the ovulatory cycle.

Animals↗
PubMed1979

Concentrations of luteinizing hormone in the plasma or hemicastrated cockerels.

The concentrations of LH in plasma were measured, using a radioimmunoassay, during sexual development of intact cockerels and cockerels hemicastrated at 2 weeks of age. The pattern of LH secretion during maturation was characterized by a series of at least four consistently observed periods of rising and falling blood levels of the hormone. Levels of luteinizing hormone were higher in hemicastrated than in intact cockerels between 2 and 4 weeks after the operation (4--6 weeks of age) and then fell to values below those seen in intact cockerels between 8 and 11 weeks of age. Thereafter, until 28 weeks of age, levels of LH in plasma in both hemicastrated and intact birds were similar. The transient changes in LH concentration after hemicastration were thought to be a direct consequence of an alteration in the concentration of testicular steroids in the blood after the removal of one gonad.

Animals↗