J. D. Neill

Bio: J. D. Neill is an academic researcher from Emory University. The author has contributed to research in topics: Prolactin & Luteinizing hormone. The author has an hindex of 24, co-authored 29 publications receiving 3770 citations.

The control of progesterone secretion during the estrous cycle and early pseudopregnancy in the rat: prolactin, gonadotropin and steroid levels associated with rescue of the corpus luteum of pseudopregnancy.

Abstract: The hormonal factors associated with converting a corpus luteum of estrous cycle into a corpus luteum of pseudopregnancy were studied by measuring LH and FSH prolactin, estradiol and progesterone levels in decapitated rats during the 4-day estrous cycle and a comparable time of pseudopregnancy (lights on 0600-0800 hr.). During the estrous cycle, prolactin, LH and FSH remained low and unchanging except on the afternoon of proestrus, when typical proestrous surges were observed. In contrast, estradiol levels began to increase on D-1, from baseline values of 7 pg/ml to approximately 15-20 pg/ml. These levels were maintained until the afternoon of D-2 when estradiol further increased to reach peak levels of 40-50 pg/ml by 0900 hr on proestrus. Estradiol then declined in relation to the increase in LH secreation and had returned to baseline by estrus. Progesterone secretion by the corpora lutea of the cycle also increased on the afternoon of D-1 and reached a maximum value of 25-30 ng/ml early on the morning of D-2. At this time, a precipitious fall in progesterone occurred, returning to baseline values of 5-1- ng/ml by 0700 on D-2 signifying the regression of the corpora lutea of the cycle. Progesterone remained low thereafter until the afternoon of proestrus when levels increased in response to the proestrus when levels increased in response to the proestrous surge of LH. Following cervical stimulation at 1900 hr on proestrus, no differences were noted, with respect to the estrous cycle, in LH, FSH or estradiol secreation through the afternoon of D-2. Surprisingly, progesterone levels did not differ in the cycle and pseudopregnancy until the early morning of D-29 instead of progesterone levels falling to baseline as they had during the cycle, the corpora lutea of pseudopregnancy were rescused, progesterone increasing dramatically to reach levels of 45-50 ng/ml by 1700 hr on that same day. The only difference in hormone secretion that was noted which could account for this marked divergence in progesterone secretion was the pattern of prolactin secretion following cervical stimulation. In contrast to the low levels seen during the estrous cycle, biphasio surges of prolactin secretion occured each day, one being nocturnal (0100-0900 hr) and the other diurnal (1500-2100 hr). The rescue of the corpus luteum occured in association with the nocturnal surge on D-2. These results suggest that nocturnal surge on D-2, PROLACTIN IS THE MAJOR Luteotropic stimulus which transforms and estrous cycle into pseudopregnancy by prolonging progesterone secretion from the corpus luteum. Moreover, if LH is important for progesterone secretion, no changes were observed in the pattern of LH secretion which can account for the rescue of the corpus luteum.

Dopamine Levels in Hypophysial Stalk Blood in the Rat are Sufficient to Inhibit Prolactin Secretion In Vivo

Abstract: Much evidence indicates that dopamine can inhibit PRL secretion However, it is still unclear whether dopamine acts on hypothalamic neurons to stimulate PRL-inhibiting factor (PIF) release or whether dopamine is itself PIF, acting directly on the pituitary This study was designed to determine if PRL secretion is inhibited by dopamine infusions producing plasma dopamine levels which mimic those found in hypophysial stalk plasma Stalk plasma dopamine concentration in urethane-anesthetized diestrus-1 rats was 60 ± 11 ng/ml (mean ± SE; n = 10) During a dopamine infusion, stalk plasma dopamine levels were 70% of arterial levels Therefore, dopamine was infused at a rate which achieved arterial levels of 9–10 ng/ml and the effect on PRL secretion in urethane-anesthetized female rats was measured In diestrus rats, dopamine did not inhibit PRL secretion In rats pretreated with α-methyl-p-tyrosine to elevate serum PRL levels, dopamine suppressed PRL secretion 70% In rats with PRL levels elevated by median

Effect of "stress" on serum prolactin and luteinizing hormone levels during the estrous cycle of the rat.

Abstract: The effect of method of blood col-lection on serum prolactin and LH levels was determined throughout the estrous cycle of the rat. Five animals were decapitated and 5 were bled from the abdominal aorta following lap-arotomy under ether anesthesia at each of the following times during the estrous cycle: 3 PM on diestrus days 1, 2 and 3 and 10 AM and 3 PM on the days of proestrus and estrus. Compared to decapitation, laparotomy and bleeding under ether anesthesia induced 3- to 8-fold increases in serum prolactin values at all times studied dur-ing the estrous cycle except on the afternoon of proestrus, when no further increase in already elevated levels was observed. Ether-laparotomy also elevated prolactin titers in ovariectomized females but not in males. Prolactin levels on the morning of proestrus in animals anesthetized with ether and then decapitated were higher than in decapitated animals but less than in ether-laparotomized animals. Serum concentrations of LH were not affected by any of the procedur...

Sexual differences in the hypothalamic regulation of prolactin secretion.

Abstract: Estrogen treatment of female rats ovariectomized when adult or of adult neonatally castrated males resulted, on the afternoon and evening of the 3rd day after initiation of treatment, in surges of prolactin secretion which reached 100 ng/ml. Males castrated when adult or androgen sterilized females ovariectomized when adult did not produce surges in response to estrogen treatment, prolactin levels remaining in the range of 10–20 ng/ml. In contrast to these sexual differences, baseline prolactin levels in untreated gonadectomized males or androgen sterilized females were significantly higher than in untreated gonadectomized females or neonatally castrated males. The surge of prolactin secretion in estrogen-treated female rats ovariectomized when adult was inhibited by a retrochiasmatic cut separating the anterior from the medial part of the hypothalamus. These results demonstrate fundamental sexual differences in the regulation of prolactin secretion. These differences may result from androgens inhibiting,...

Ovarian and hypothalamic control of the daily surges of prolactin secretion during pseudopregnancy in the rat.

Abstract: Cervical stimulation in the rat institutes a pattern of prolactin secretion consisting of two daily surges, one diurnal and one nocturnal, which continue for the greater part of pseudopregnancy. This contrasts with the diestrous day 1–2 interval of the estrous cycle wherein prolactin levels are low and relatively unchanging. A variety of noxious procedures such as aortic cannulation and serial blood sampling, sham ovariectomy and sham surgical cuts in the hypothalamus selectively and temporarily suppresses the diurnal prolactin surges of pseudopregnancy; the nocturnal surges remained unaffected. In the absence of the ovaries (removed on day 0 of pseudopregnancy) the diurnal prolactin surges have disappeared no later than day 5, whereas the nocturnal surges are present at day 6 but have disappeared by day 10. Hypothalamic retrochiasmatic cuts abolish immediately both surges. These results demonstrate the existence of an apparently unique kind of neuroendocrine reflex, copulation-induced, which results in r...

Prolactin: Structure, Function, and Regulation of Secretion

Abstract: Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Sexual differentiation of the central nervous system

Abstract: Sexual differentiation of reproductive and behavior patterns is largely effected by hormones produced by the gonads. In many higher vertebrates, an integral part of this process is the induction of permanent and essentially irreversible sex differences in central nervous function, in response to gonadal hormones secreted early in development.

Determination of the estrous cycle phases of rats: some helpful considerations

Abstract: The short length of the estrous cycle of rats makes them ideal for investigation of changes occurring during the reproductive cycle. The estrous cycle lasts four days and is characterized as: proestrus, estrus, metestrus and diestrus, which may be determined according to the cell types observed in the vaginal smear. Since the collection of vaginal secretion and the use of stained material generally takes some time, the aim of the present work was to provide researchers with some helpful considerations about the determination of the rat estrous cycle phases in a fast and practical way. Vaginal secretion of thirty female rats was collected every morning during a month and unstained native material was observed using the microscope without the aid of the condenser lens. Using the 10 x objective lens, it was easier to analyze the proportion among the three cellular types, which are present in the vaginal smear. Using the 40 x objective lens, it is easier to recognize each one of these cellular types. The collection of vaginal lavage from the animals, the observation of the material, in the microscope, and the determination of the estrous cycle phase of all the thirty female rats took 15-20 minutes.

The neuroendocrine control of the menstrual cycle.

Abstract: Publisher Summary This chapter discusses the construction of a model of the neuroendocrine control system that governs the 28-day ovarian cycle of the rhesus monkey. This model has three basic components: the arcuate nucleus of the hypothalamus, the gonadotrophs of the pituitary gland, and the ovary. The arcuate nucleus is the central component of the control system. The gonadotrophs respond to this unvarying pulsatile gonadotropin releasing hormone (GnRH) stimulation by releasing pulses of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Immature follicles respond to this unvarying gonadotropic stimulus by increasing in size and secreting increasing quantities of estradiol, which achieve maxima near mid-cycle. This process occupies approximately 14 days. The magnitude of the response to each GnRH pulse is modulated by estradiol acting directly on the gonadotrophs. The characteristic duration of the rhesus monkey ovarian cycle is thus determined by the duration of follicular development. This can occur in the presence of an absolutely unvarying pattern of hypophysiotropic stimulation.

Estradiol mediates fluctuation in hippocampal synapse density during the estrous cycle in the adult rat.

Abstract: We have found that the density of synapses in the stratum radiatum of the hippocampal CA1 region in the adult female rat is sensitive to estradiol manipulation and fluctuates naturally as the levels of ovarian steroids vary during the 5 d estrous cycle. In both cases, low levels of estradiol are correlated with lower synapse density, while high estradiol levels are correlated with a higher density of synapses. These synaptic changes occur very rapidly in that within approximately 24 hr between the proestrus and estrus stages of the estrous cycle, we observe a 32% decrease in the density of hippocampal synapses. Synapse density then appears to cycle back to proestrus values over a period of several days. To our knowledge, this is the first demonstration of such short-term steroid-mediated synaptic plasticity occurring naturally in the adult mammalian brain.