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Reproduction in Domestic Ruminants III

Reproduction in Domestic Ruminants III

Regulation of Gonadotrophin Secretion

bp0003rdr16 | Regulation of Gonadotrophin Secretion | REDR1994

Distribution of neurotransmitters in the sheep brain

Tillet Y

Although the general organization of the sheep brain is similar to that of other mammals, there are species differences in the fine architecture and neurotransmitter distribution. In sheep, perikarya are generally scattered, unlike the situation in rodents where they are clustered. The same organization is observed in cows and primates. The density of neurones immunoreactive for tyrosine hydroxylase in the dorsorostral diencephalon of sheep is lower than in rodents; A14 and Al...

bp0003rdr17 | Regulation of Gonadotrophin Secretion | REDR1994

Gamma amino-butyric acid and the control of GnRH secretion in sheep

Robinson JE

The release of GnRH from nerve terminals in the median eminence into the portal vessels is influenced by factors in the internal and external environment of the animal. In the former category are the gonadal steroid hormones oestrogen and progesterone which alter the characteristics of GnRH secretion during the oestrous and seasonal cycles. These cannot exert their actions directly on the GnRH neurones as they do not possess hormone receptors. Therefore, some other steroid-sen...

bp0003rdr18 | Regulation of Gonadotrophin Secretion | REDR1994

Electrophysiological approach to the hypothalamic GnRH pulse generator

Mori Y , Tanaka T

The hypothalamic GnRH pulse generator that regulates intermittent GnRH discharge into the pituitary portal circulation and thereby modulates pulsatile secretion of LH has been recognized as a key determinant of the reproductive function in mammals. Thus, various internal, as well as external, factors first modify the electrical activity of the GnRH pulse generator, which then alters the pulsatile pattern of gonadotrophin secretion and eventually influences reproductive functio...

bp0003rdr19 | Regulation of Gonadotrophin Secretion | REDR1994

The preovulatory gonadotrophin-releasing hormone surge: a neuroendocrine signal for ovulation

Caraty A , Evans NP , Fabre-Nys CJ , Karsch FJ

Recent studies have demonstrated that an important component of the positive feedback response to oestradiol in mammals is an action within the central nervous system to induce a large surge in the secretion of gonadotrophin-releasing hormone (GnRH). This oestradiol-induced neuroendocrine signal for ovulation has been best characterized in ewes. The GnRH surge is high in amplitude; the amount secreted increases on average more than 40 times above the pre-surge baseline value. ...

bp0003rdr20 | Regulation of Gonadotrophin Secretion | REDR1994

Molecular biology of gonadotrophins

Hamernik DL

Regulation of gonadotrophin synthesis involves a complex interaction between hypothalamic and gonadal hormones. Chronic administration of oestrogens and androgens to gonadectomized animals blocked the postcastration rise in amounts of mRNA encoding gonadotrophin subunits. Removal of endogenous GnRH decreased amounts of mRNA encoding gonadotrophin subunits. Pulsatile administration of GnRH to GnRH-deficient animals increased amounts of mRNA encoding gonadotrophin subunits. Stud...

bp0003rdr21 | Regulation of Gonadotrophin Secretion | REDR1994

Neurochemical identity of neurones expressing oestrogen and androgen receptors in sheep hypothalamus

Herbison AE

Gonadal steroids exert important feedback influences on hypothalamic neurones involved in regulating reproductive behaviour and pituitary hormone secretion. The recent development of antibodies specific for individual gonadal steroid receptors has been of great use in determining precisely which cells in the hypothalamus express androgen, oestrogen and progesterone receptors. In the sheep brain, both oestrogen and androgen receptor antibodies have been used successfully and th...

bp0003rdr22 | Regulation of Gonadotrophin Secretion | REDR1994

Dopaminergic control of LH secretion by the Al5 nucleus in anoestrous ewes

Thiery JC , Gayrard V , Le Corre S , Viguié C , Martin GB , Chemineau P , Malpaux B

Annual variations in the secretion of LH are responsible for seasonal changes in ovulatory activity in ewes. This hormonal pattern reflects an increase in the intensity of the negative feedback exerted by oestradiol under long days. Neuro-pharmacological studies have shown that this inhibition of LH secretion involves activation of catecholaminergic systems from preoptic and mediobasal hypothalamus (MBH) by oestradiol during anoestrus, and that 5-hydroxytryptamine inputs may a...

bp0003rdr23 | Regulation of Gonadotrophin Secretion | REDR1994

Negative feedback regulation of the secretion and actions of GnRH in male ruminants

Tilbrook AJ , Clarke IJ

The roles of testicular hormones in the negative feedback regulation of the secretion and actions of GnRH in male domestic ruminants are reviewed, concentrating mainly on research conducted with rams. Testicular steroids have major feedback actions directly at the hypothalamus to inhibit the secretion of GnRH, although it is apparent that, under certain circumstances, the steroids also have actions directly at the pituitary gland. Further research is necessary to delineate the...