The Effect of Hypothalamic Lesions on Ovarian Function in the Ewe1

Clegg, M. T.; Ganong, William F.

doi:10.1210/endo-67-2-179

Cited by 22 publications

(15 citation statements)

References 1 publication

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“…This study confirms and expands findings from our own laboratory (18)(19) and those of others (20,(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31). demonstrating that Specifically.…”

Section: Discussionsupporting

confidence: 91%

Disruption of Reproductive Rhythms and Patterns of Melatonin and Prolactin Secretion Following Bilateral Lesions of the Suprachiasmatic Nuclei in the Ewe

Scott

Jansen

Kao

et al. 1995

J Neuroendocrinology

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To determine whether the photoperiodic responses of reproductive and prolactin (PRL) rhythms in the ewe requires an intact suprachiasmatic nucleus (SCN) driving the pineal rhythm of melatonin secretion, four groups of ovary-intact ewes over a 6-year period were subjected to bilateral (n = 40) or sham lesions (n = 15) of the SCN. Animals were exposed to an alternating 90-120 day photoregimen of 9L:15D and 16L:8D photoperiods. Blood samples taken twice weekly were assayed for prolactin and for progesterone to monitor oestrous cycles. On several occasions blood samples also were taken at hourly intervals for 24 h and analyzed for melatonin. Melatonin concentrations in sham lesioned ewes were basal during the lights-on period and rose robustly during darkness. Those sheep bearing unilateral lesions of the SCN (n = 13) or where the lesion spared the SCN entirely (n = 8) had patterns of melatonin secretion similar to sham ewes. The remaining ewes, having complete (n = 9) or incomplete bilateral (n = 8) destruction of the SCN, with one exception, had disrupted patterns of melatonin secretion. The nature of this disruption varied from complete suppression to continuously elevated levels. In lesioned ewes where melatonin secretion was not affected the onset and cessation of ovarian cycles were similar to sham ewes; stimulation of oestrous cycles under 9L:15D and cessation of oestrous cycles under 16L:8D. In contrast, 13 of 17 ewes with disrupted melatonin secretion also exhibited disrupted patterns of ovarian activity. In these animals oestrous cycles were no longer entrained by photoperiod but still occurred in distinct clusters, that is, groups of cycles began and ended spontaneously. Sheep with normal melatonin patterns showed low levels of PRL secretion during short days and elevated PRL levels during long days. However, 8 of 13 ewes with disrupted melatonin showed patterns of PRL secretion that were no longer entrained by photoperiod. A minority of ewes with disrupted melatonin patterns still showed reproductive (n = 4) and PRL (n = 5) responses similar to those of sham-lesioned ewes. These results show that bilateral destruction of the SCN in the ewe disrupts the circadian pattern of melatonin secretion and that this disruption usually, but not always, is associated with altered photoperiodic responses. These results strongly suggest that the SCN are important neural elements within the photoperiod time-keeping system in this species. A role for the SCN in the generation of endogenous transitions in reproductive activity (refractoriness) and prolactin secretion is not supported.

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Section: Discussionsupporting

confidence: 91%

Disruption of Reproductive Rhythms and Patterns of Melatonin and Prolactin Secretion Following Bilateral Lesions of the Suprachiasmatic Nuclei in the Ewe

Scott

Jansen

Kao

et al. 1995

J Neuroendocrinology

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“…Oestrous behaviour and ovulation are under hypothalamic control in the ewe, although these two phenomena appear to be mediated via different centres; e.g. electrolytic lesions in discrete areas of the hypothalamus may inhibit oestrus but not ovulation (Clegg & Ganong, 1960;Radford, 1967). The behavioural modifications observed in the androgenized ewes are presumably a result of the action of testosterone or its metabolites at the hypothalamic level ; further evidence of this was the failure of ovulation in ewes which had been androgenized before Day 80 of fetal life (Short, 1974;Clarke et al, 1977).…”

Section: Discussionmentioning

confidence: 99%

The sexual behaviour of prenatally androgenized ewes observed in the field

Clarke

1977

Reproduction

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Pregnant ewes were implanted with 1 g testosterone between Days 30-80, 50-100, 70-120 or 90-140 of gestation. Treatments which began on Days 30, 50 or 70 resulted in the birth of androgenized females which failed to show regular oestrous cycles in adult life, but which exhibited patterns of male-like behaviour. This was most marked in the Day 50-100 and 70-120 groups, whereas complete masculinization of the external genitalia was confined to the Day 30-80 group. Animals in the Day 90-140 group had regular oestrous cycles although they showed slight enhancement of masculine behaviour compared to the control ewes. These results demonstrate that androgenization involves both a suppression of female behavioural patterns, and the development of male patterns; these are not mutually exclusive.

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“…Neural mechanisms through which dose of injected oestrogen may influence measurable characteristics of oestrous behaviour It has been demonstrated that oestrous behaviour in the ewe is controlled by the accumulation and action of oestrogen on specific regions in the hypothalamus (Clegg, Santolucito, Smith & Ganong, 1958;Clegg & Ganong, 1960;Radford, 1967). Variation in the expression of oestrous behaviour induced by different doses of injected oestro¬ gen must therefore be due to variation in the amount of oestrogen acting on the hypo¬ thalamus.…”

Section: Discussionmentioning

confidence: 99%

Effect of Oestrogen on Oestrous Behaviour and Its Variation With Season in the Ewe

Fletcher¹,

Lindsay²

1971

Journal of Endocrinology

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The effects of dose of oestrogen and season on the expression of oestrous behaviour was studied in 60 spayed and 16 intact ewes.In progesterone-primed spayed ewes the incidence and duration of oestrous behaviour increased and the interval between injection of oestrogen, and onset of oestrous behaviour decreased as the dose of oestrogen was increased. The linear regression of duration of oestrus on log dose of injected oestrogen provided the most precise measure of the effect of changing dose level of oestrogen on oestrous behaviour.The sensitivity of spayed ewes to constant levels of oestrogen increased to a maximum near the middle of the breeding season and then declined to a minimum during the non-breeding season. In progesterone-synchronized intact ewes the interval between the end of progesterone treatment and onset of oestrus was at a minimum, and duration of oestrus at a maximum, near the middle of the breeding season. By bioassay it was estimated that endogenous oestrogen production was greater near the middle ofthe breeding season than at either the beginning or end.It is concluded that seasonal variation in the expression of oestrous behaviour in intact ewes is controlled by changes in both the production of endogenous oestrogen and the sensitivity of ewes to it.

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The Effect of Hypothalamic Lesions on Ovarian Function in the Ewe1

Cited by 22 publications

References 1 publication

Disruption of Reproductive Rhythms and Patterns of Melatonin and Prolactin Secretion Following Bilateral Lesions of the Suprachiasmatic Nuclei in the Ewe

Disruption of Reproductive Rhythms and Patterns of Melatonin and Prolactin Secretion Following Bilateral Lesions of the Suprachiasmatic Nuclei in the Ewe

The sexual behaviour of prenatally androgenized ewes observed in the field

Effect of Oestrogen on Oestrous Behaviour and Its Variation With Season in the Ewe

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