Stimulatory role of substance P on gonadotropin release in ovariectomized rats

The Effects of Tachykinin1 Gene Products on Prepubertal Dabry's Sturgeon (Acipenser dabrynus) Pituitary Hormone Secretion and Gene Expression

As an ancient and endangered species unique to the Yangtze River in China, the wild population of the Dabry's sturgeon has become scarce. Due to the long time till the first sexual maturity of Dabry's sturgeon, the population of artificially bred Dabry's sturgeon recovered slowly. As a member of the tachykinin family, TAC1 has been reported to have a variety of functions in mammals such as pain control, smooth muscle contraction and reproductive cycle regulation, but the function of Tac1 in fish has been rarely reported. In this study, we synthesized two tac1 gene products, Substance P (SP) and neurokinin A (NKA), and further verified the effect of two tac1 gene products on the secretion of related hormones in the pituitary of Dabry's Sturgeon by intraperitoneal injection and co-culture of primary cells. Expression studies revealed that the newly cloned tac1 were mainly distributed in the hypothalamus and pituitary tissue of the brain. In prepubertal Dabry's sturgeon, this study showed that the two gonadotropins' mRNA levels in pituitary tissue can be significantly increased by SP and NKA through intraperitoneal injection, and the LH protein level in serum was also increased. Further study showed that both NKA and SP could promote the two gonadotropins' mRNA expression in pituitary cells of Dabry's sturgeon. In addition, we explored the optimal dose and time of SP and NKA on pituitary cells is 24 h and over 10 nM. These results, as a whole, suggested that tac1 gene products play an important role in gonadotropin release and gonadal development in prepubertal Dabry's sturgeon.

Sequences analysis and pituitary actions of tachykinins in Chinese sturgeon (Acipenser sinensis)

Tachykinins belong to a large, evolutionarily conserved family of brain/gut peptides that are involved in a variety of physiological functions in mammals, such as reproductive regulation. However, little information was available about tachykinins in ancient fish lineage. In the present study, we firstly identified three tachykinin genes (named tac1, tac3 and tac4) and three neurokinin receptors (named nk1r, nk2r and nk3r) from Chinese sturgeon brain and pituitary. Sequence analysis showed that tac1 encoded substance P (SP) and neurokinin A (NKA), tac3 encoded neurokinin B (NKB) and NKB-related peptide (NKBRP), and tac4 encoded hemokin 1 (HK-1) and hemokin 2 (HK-2), respectively. The luciferase reporter assay results showed that NK1R preferentially selected asSP, NK2R preferentially selected asNKA, and NK3R preferentially selected asNKB. Tissue expression analysis showed that the three tac genes were highly detected in the telencephalon and hypothalamus, whereas nkr genes were widely expressed in peripheral tissues. Spatio-temporal expression analysis showed that all three tac genes were highly expressed in unknown sex individuals. Intraperitoneal injection experiments showed that both asSP and asNKB could stimulate luteinizing hormone (LH) release in Chinese sturgeon serum. At the transcriptional level, asSP and asNKB could significantly reduce pituitary follicle-stimulating hormone beta (fshβ) mRNA expression, but induce pituitary growth hormone (gh) mRNA expression. In addition, estradiol (E2) could stimulate tac3 mRNA expression in hypothalamus. Taken together, this study provided information on the tachykinin family in Chinese sturgeon and demonstrates that asNKB and asSP could be involved in reproductive and growth regulation in pituitary.

Tachykinins, new players in the control of reproduction and food intake: A comparative review in mammals and teleosts

In vertebrates, the tachykinin system includes tachykinin genes, which encode one or two peptides each, and tachykinin receptors. The complexity of this system is reinforced by the massive conservation of gene duplicates after the whole-genome duplication events that occurred in vertebrates and furthermore in teleosts. Added to this, the expression of the tachykinin system is more widespread than first thought, being found beyond the brain and gut. The discovery of the co-expression of neurokinin B, encoded by the tachykinin 3 gene, and kisspeptin/dynorphin in neurons involved in the generation of GnRH pulse, in mammals, put a spotlight on the tachykinin system in vertebrate reproductive physiology. As food intake and reproduction are linked processes, and considering that hypothalamic hormones classically involved in the control of reproduction are reported to regulate also appetite and energy homeostasis, it is of interest to look at the potential involvement of tachykinins in these two major physiological functions. The purpose of this review is thus to provide first a general overview of the tachykinin system in mammals and teleosts, before giving a state of the art on the different levels of action of tachykinins in the control of reproduction and food intake. This work has been conducted with a comparative point of view, highlighting the major similarities and differences of tachykinin systems and actions between mammals and teleosts.

Elinzanetant (NT-814), a Neurokinin 1,3 Receptor Antagonist, Reduces Estradiol and Progesterone in Healthy Women

CONTEXT

The ideal therapy for endometriosis (EM) and uterine fibroids (UFs) would suppress estrogenic drive to the endometrium and myometrium, while minimizing vasomotor symptoms and bone loss associated with current treatments. An integrated neurokinin-kisspeptin system involving substance P and neurokinin B acting at the neurokinin (NK) receptors 1 and 3, respectively, modulates reproductive hormone secretion and represents a therapeutic target.

OBJECTIVE

This work aimed to assess the effects of the novel NK1,3 antagonist elinzanetant on reproductive hormone levels in healthy women.

METHODS

A randomized, single-blinded, placebo-controlled study was conducted in 33 women who attended for 2 consecutive menstrual cycles. In each cycle blood samples were taken on days 3 or 4, 9 or 10, 15 or 16, and 21 or 22 to measure serum reproductive hormones. In cycle 2, women were randomly assigned to receive once-daily oral elinzanetant 40, 80, 120 mg, or placebo (N = 8 or 9 per group).

RESULTS

Elinzanetant dose-dependently lowered serum luteinizing hormone, estradiol (120 mg median change across cycle: -141.4 pmol/L, P = .038), and luteal-phase progesterone (120 mg change from baseline on day 21 or 22: -19.400 nmol/L, P = .046). Elinzanetant 120 mg prolonged the cycle length by median of 7.0 days (P = .023). Elinzanetant reduced the proportion of women with a luteal-phase serum progesterone concentration greater than 30 nmol/L (a concentration consistent with ovulation) in a dose-related manner in cycle 2 (P = .002). Treatment did not produce vasomotor symptoms.

CONCLUSION

NK1,3 receptor antagonism with elinzanetant dose-dependently suppressed the reproductive axis in healthy women, with the 120-mg dose lowering estradiol to potentially ideal levels for UFs and EM. As such, elinzanetant may represent a novel therapy to manipulate reproductive hormone levels in women with hormone-driven disorders.

Rfamide-related peptide-3 suppresses the substance P-induced promotion of the reproductive performance in female rats modulating hypothalamic Kisspeptin expression

RFamide-related peptide-3 (RFRP-3) has been postulated as the suppressor of the reproductive axis at hypothalamic, pituitary and gonadal levels. Considering the hypothalamic level, RFRP-3 can suppress the activity of gonadotropin-releasing hormone (GnRH) neurons and their upstream neuronal stimulator, namely; the kisspeptin neurons. The effects of the RFRP-3 on the other regulators of GnRH neurons, however, are not completely investigated. Furthermore, substance P (SP) has been known as one of the coordinators of GnRH/ luteinizing hormone (LH) and the kisspeptin/G protein-coupled receptor 54 (GPR54) systems. The present study was aimed at investigating the impacts of RFRP-3 on the effects of SP on the reproductive performance in ovariectomized female rats. After intracerebroventricular (ICV) cannulation, the rats were subjected to the ICV injection of either SP or RFRP-3 and simultaneous injection of them and their selective antagonists. Blood and hypothalamic samplings and also sexual behavioral test were carried out on two main groups of rats. The analyses of the results of LH radioimmunoassay, gene expression assay for hypothalamic Gnrh1, Kisspeptin and Gpr54 accompanied by sexual behavioral examination revealed that the SP administration promotes reproductive behavior and GnRH/LH system and upregulates Kisspeptin expression. The RFRP-3 administration suppressed reproductive behavior, GnRH / LH system and Kisspeptin expression; however, the simultaneous injection of SP and RFRP-3 was devoid of significant alterations in the assessed parameters. The results showed that RFRP-3 can modulates the impacts of SP on the reproductive performance in ovariectomized female rats in part through adjusting Kisspeptin expression.

Characterization of the Role of NKA in the Control of Puberty Onset and Gonadotropin Release in the Female Mouse

The tachykinin neurokinin B (NKB, Tac2) is critical for proper GnRH release in mammals, however, the role of the other tachykinins, such as substance P (SP) and neurokinin A (NKA) in reproduction, is still not well understood. In this study, we demonstrate that NKA controls the timing of puberty onset (similar to NKB and SP) and stimulates LH release in adulthood through NKB-independent (but kisspeptin-dependent) mechanisms in the presence of sex steroids. Furthermore, this is achieved, at least in part, through the autosynaptic activation of Tac1 neurons, which express NK2R (Tacr2), the receptor for NKA. Conversely, in the absence of sex steroids, as observed in ovariectomy, NKA inhibits LH through a mechanism that requires the presence of functional receptors for NKB and dynorphin (NK3R and KOR, respectively). Moreover, the ability of NKA to modulate LH secretion is absent in Kiss1KO mice, suggesting that its action occurs upstream of Kiss1 neurons. Overall, we demonstrate that NKA signaling is a critical component in the central control of reproduction, by contributing to the indirect regulation of kisspeptin release.

Central Substance P Attenuates RF-amid-related Peptide-3 Impacts on the Serum Level of Luteinizing Hormone in Wistar Rats

Introduction: It is well-established that gonadotropin-inhibitory hormone (GnIH) and its mammalian orthologues (RFRP: RF-amid related peptides) can decrease gonadotrophin secretion. Moreover, substance P (SP) is another modulator of the secretion of gonadotropins in a species-dependent manner. This study aimed to find out the impacts of concomitant infusion of RFRP-3 and SP on luteinizing hormone (LH) concentration. Methods: Forty-two rats were arbitrarily assigned to 7 groups (n=6 per group). Animals in the experimental groups were intracerebroventricularly injected with saline +DMSO, SP, RFRP-3, SP + RFRP-3, SP + RF9 (RFRP-3 receptor antagonist), SP + P234 (kisspeptin receptor antagonist) + RFRP-3 and SP + CP-96,345 (SP receptor antagonist) + RFRP-3 in a final volume of 3 µL. Blood samples were collected at 30-minute intervals after injections, and serum was used to measure the LH concentration by radioimmunoassay. Results: According to the results, injections led to the elevation of LH serum concentration at 30-minute post injection (P<0.05) in the SP and SP+RF9 groups. Moreover, administration of either RFRP-3 or SP + RFRP-3 + SP receptor antagonist strikingly decreased the LH mean serum concentration at 30-minute after injections (P<0.05). On the contrary, the infusion of SP+RFRP-3 and SP+RFRP-3+P234 caused no dramatic changes in the LH mean serum concentration. Conclusion: In general, the data showed that SP suppresses the impacts of RFRP-3 on the serum levels of LH.

Disentangling puberty: novel neuroendocrine pathways and mechanisms for the control of mammalian puberty

BACKGROUND

Puberty is a complex developmental event, controlled by sophisticated regulatory networks that integrate peripheral and internal cues and impinge at the brain centers driving the reproductive axis. The tempo of puberty is genetically determined but is also sensitive to numerous modifiers, from metabolic and sex steroid signals to environmental factors. Recent epidemiological evidence suggests that the onset of puberty is advancing in humans, through as yet unknown mechanisms. In fact, while much knowledge has been gleaned recently on the mechanisms responsible for the control of mammalian puberty, fundamental questions regarding the intimate molecular and neuroendocrine pathways responsible for the precise timing of puberty and its deviations remain unsolved.

OBJECTIVE AND RATIONALE

By combining data from suitable model species and humans, we aim to provide a comprehensive summary of our current understanding of the neuroendocrine mechanisms governing puberty, with particular focus on its central regulatory pathways, underlying molecular basis and mechanisms for metabolic control.

SEARCH METHODS

A comprehensive MEDLINE search of articles published mostly from 2003 to 2017 has been carried out. Data from cellular and animal models (including our own results) as well as clinical studies focusing on the pathophysiology of puberty in mammals were considered and cross-referenced with terms related with central neuroendocrine mechanisms, metabolic control and epigenetic/miRNA regulation.

OUTCOMES

Studies conducted during the last decade have revealed the essential role of novel central neuroendocrine pathways in the control of puberty, with a prominent role of kisspeptins in the precise regulation of the pubertal activation of GnRH neurosecretory activity. In addition, different transmitters, including neurokinin-B (NKB) and, possibly, melanocortins, have been shown to interplay with kisspeptins in tuning puberty onset. Alike, recent studies have documented the role of epigenetic mechanisms, involving mainly modulation of repressors that target kisspeptins and NKB pathways, as well as microRNAs and the related binding protein, Lin28B, in the central control of puberty. These novel pathways provide the molecular and neuroendocrine basis for the modulation of puberty by different endogenous and environmental cues, including nutritional and metabolic factors, such as leptin, ghrelin and insulin, which are known to play an important role in pubertal timing.

WIDER IMPLICATIONS

Despite recent advancements, our understanding of the basis of mammalian puberty remains incomplete. Complete elucidation of the novel neuropeptidergic and molecular mechanisms summarized in this review will not only expand our knowledge of the intimate mechanisms responsible for puberty onset in humans, but might also provide new tools and targets for better prevention and management of pubertal deviations in the clinical setting.

The Role of Kiss1 Neurons As Integrators of Endocrine, Metabolic, and Environmental Factors in the Hypothalamic-Pituitary-Gonadal Axis

Kisspeptin-GPR54 signaling in the hypothalamus is required for reproduction and fertility in mammals. Kiss1 neurons are key regulators of gonadotropin-releasing hormone (GnRH) release and modulation of the hypothalamic-pituitary-gonadal (HPG) axis. Arcuate Kiss1 neurons project to GnRH nerve terminals in the median eminence, orchestrating the pulsatile secretion of luteinizing hormone (LH) through the intricate interaction between GnRH pulse frequency and the pituitary gonadotrophs. Arcuate Kiss1 neurons, also known as KNDy neurons in rodents and ruminants because of their co-expression of neurokinin B and dynorphin represent an ideal hub to receive afferent inputs from other brain regions in response to physiological and environmental changes, which can regulate the HPG axis. This review will focus on studies performed primarily in rodent and ruminant species to explore potential afferent inputs to Kiss1 neurons with emphasis on the arcuate region but also considering the rostral periventricular region of the third ventricle (RP3V). Specifically, we will discuss how these inputs can be modulated by hormonal, metabolic, and environmental factors to control gonadotropin secretion and fertility. We also summarize the methods and techniques that can be used to study functional inputs into Kiss1 neurons.

Expanding the Role of Tachykinins in the Neuroendocrine Control of Reproduction

Reproductive function is driven by the hormonal interplay between the gonads and brain-pituitary axis. Gonadotropin-releasing hormone (GnRH) is released in a pulsatile manner, which is critical for the attainment and maintenance of fertility, however, GnRH neurons lack the ability to directly respond to most regulatory factors, and a hierarchical upstream neuronal network governs its secretion. We and others proposed a model in which Kiss1 neurons in the arcuate nucleus (ARC), so called KNDy neurons, release kisspeptin (a potent GnRH secretagogue) in a pulsatile manner to drive GnRH pulses under the coordinated autosynaptic action of its cotransmitters, the tachykinin neurokinin B (NKB, stimulatory) and dynorphin (inhibitory). Numerous genetic and pharmacological studies support this model; however, additional regulatory mechanisms (upstream of KNDy neurons) and alternative pathways of GnRH secretion (kisspeptin-independent) exist, but remain ill defined. In this aspect, attention to other members of the tachykinin family, namely substance P (SP) and neurokinin A (NKA), has recently been rekindled. Even though there are still major gaps in our knowledge about the functional significance of these systems, substantial evidence, as discussed below, is placing tachykinin signaling as an important pathway for the awakening of the reproductive axis and the onset of puberty to physiological GnRH secretion and maintenance of fertility in adulthood.

Altered Gene Expression Profiles of the Hypothalamic Arcuate Nucleus of Male Mice Suggest Profound Developmental Changes in Peptidergic Signaling

Neuropeptides of the hypothalamic arcuate nucleus (ARC) regulate important homeostatic and endocrine functions and also play critical roles in pubertal development. The altered peptidergic and aminoacidergic neurotransmission accompanying pubertal maturation of the ARC is not fully understood. Here we studied the developmental shift in the gene expression profile of the ARC of male mice. RNA samples for quantitative RT-PCR studies were isolated from the ARC of 14-day-old infantile and 60-day-old adult male mice with laser capture microdissection. The expression of 18 neuropeptide, 15 neuropeptide receptor, 4 sex steroid receptor and 6 classic neurotransmitter marker mRNAs was compared between the two time points. The adult animals showed increased mRNA levels encoding cocaine- and amphetamine-regulated transcripts, galanin-like peptide, dynorphin, kisspeptin, proopiomelanocortin, proenkephalin and galanin and a reduced expression of mRNAs for pituitary adenylate cyclase-activating peptide, calcitonin gene-related peptide, neuropeptide Y, substance P, agouti-related protein, neurotensin and growth hormone-releasing hormone. From the neuropeptide receptors tested, melanocortin receptor-4 showed the most striking increase (5-fold). Melanocortin receptor-3 and the Y1 and Y5 neuropeptide Y receptors increased 1.5- to 1.8-fold, whereas δ-opioid receptor and neurotensin receptor-1 transcripts were reduced by 27 and 21%, respectively. Androgen receptor, progesterone receptor and α-estrogen receptor transcripts increased by 54-72%. The mRNAs of glutamic acid decarboxylases-65 and -67, vesicular GABA transporter and choline acetyltransferase remained unchanged. Tyrosine hydroxylase mRNA increased by 44%, whereas type-2 vesicular glutamate transporter mRNA decreased by 43% by adulthood. Many of the developmental changes we revealed in this study suggest a reduced inhibitory and/or enhanced excitatory neuropeptidergic drive on fertility in adult animals.

The Distribution of Substance P and Kisspeptin in the Mediobasal Hypothalamus of the Male Rhesus Monkey and a Comparison of Intravenous Administration of These Peptides to Release GnRH as Reflected by LH Secretion

Substance P (SP) was recently reported to be expressed in human kisspeptin/neurokinin B/dynorphin (KNDy) neurons and to enhance KNDy neuron excitability in the mouse hypothalamus. We therefore examined (1) interactions of SP and kisspeptin in the mediobasal hypothalamus of adult male rhesus monkeys using immunofluorescence, and (2) the ability of SP to induce LH release in GnRH-primed, agonadal juvenile male monkeys. SP cell bodies were observed only occasionally in the arcuate nucleus (Arc), but more frequently dorsal to the Arc in the region of the premammillary nucleus. Castration resulted in an increase in the number of SP cell bodies in the Arc but not in the other regions. SP fibers innervated the Arc, where they were found in close apposition with kisspeptin perikarya in the periphery of this nucleus. Beaded SP axons projected to the median eminence, where they terminated in the external layer and intermingled with beaded kisspeptin axons. Colocalization of the two peptides, however, was not observed. Although close apposition between SP fibers and kisspeptin neurons suggest a role for SP in modulating GnRH pulse generator activity, i.v. injections of SP failed to elicit release of GnRH (as reflected by LH) in the juvenile monkey. Although the finding of structural interactions between SP and kisspeptin neurons is consistent with the notion that this tachykinin may be involved in regulating pulsatile GnRH release, the apparent absence of expression of SP in KNDy neurons suggests that this peptide is unlikely to be a fundamental component of the primate GnRH pulse generator.

Substance p regulates puberty onset and fertility in the female mouse

Puberty is a tightly regulated process that leads to reproductive capacity. Kiss1 neurons are crucial in this process by stimulating GnRH, yet how Kiss1 neurons are regulated remains unknown. Substance P (SP), an important neuropeptide in pain perception, induces gonadotropin release in adult mice in a kisspeptin-dependent manner. Here, we assessed whether SP, through binding to its receptor NK1R (neurokinin 1 receptor), participates in the timing of puberty onset and fertility in the mouse. We observed that 1) selective NK1R agonists induce gonadotropin release in prepubertal females; 2) the expression of Tac1 (encoding SP) and Tacr1 (NK1R) in the arcuate nucleus is maximal before puberty, suggesting increased SP tone; 3) repeated exposure to NK1R agonists prepubertally advances puberty onset; and 4) female Tac1(-/-) mice display delayed puberty; moreover, 5) SP deficiency leads to subfertility in females, showing fewer corpora lutea and antral follicles and leading to decreased litter size. Thus, our findings support a role for SP in the stimulation of gonadotropins before puberty, acting via Kiss1 neurons to stimulate GnRH release, and its involvement in the attainment of full reproductive capabilities in female mice.

The integrated hypothalamic tachykinin-kisspeptin system as a central coordinator for reproduction

Tachykinins are comprised of the family of related peptides, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB). NKB has emerged as regulator of kisspeptin release in the arcuate nucleus (ARC), whereas the roles of SP and NKA in reproduction remain unknown. This work explores the roles of SP and NKA in the central regulation of GnRH release. First, central infusion of specific agonists for the receptors of SP (neurokinin receptor 1, NK1R), NKA (NK2R) and NKB (NK3R) each induced gonadotropin release in adult male and ovariectomized, estradiol-replaced female mice, which was absent in Kiss1r(-/-) mice, indicating a kisspeptin-dependent action. The NK2R agonist, however, decreased LH release in ovariectomized-sham replaced females, as documented for NK3R agonists but in contrast to the NK1R agonist, which further increased LH release. Second, Tac1 (encoding SP and NKA) expression in the ARC and ventromedial nucleus was inhibited by circulating estradiol but did not colocalize with Kiss1 mRNA. Third, about half of isolated ARC Kiss1 neurons expressed Tacr1 (NK1R) and 100% Tacr3 (NK3R); for anteroventral-periventricular Kiss1 neurons and GnRH neurons, approximately one-fourth expressed Tacr1 and one-tenth Tacr3; Tacr2 (NK2R) expression was absent in all cases. Overall, these results identify a potent regulation of gonadotropin release by the SP/NK1R and NKA/NK2R systems in the presence of kisspeptin-Kiss1r signaling, indicating that they may, along with NKB/NK3R, control GnRH release, at least in part through actions on Kiss1 neurons.

The hypothalamic ventral premammillary nucleus: A key site in leptin's regulation of reproduction

Reproduction is an energy-expensive process that relies on indicators of energy availability to adjust its proper functioning. The adipokine leptin provides one such metabolic signal, with leptin receptor-expressing neurons at sites widespread within the CNS, including regions associated with the neuroendocrine reproductive axis. One substantial population lies within the hypothalamic ventral premammillary nucleus (PMv), a region itself linked to reproductive control, which may provide a strategic site for the integration of energy availability, sensory and gonadal cues. Here we review our current understanding of leptin and PMv regulation of reproduction, including emerging details about intracellular mechanisms of leptin action at this site.

Lack of sensorial innervation in the newborn female rats affects the activity of hypothalamic monoaminergic system and steroid hormone secretion during puberty

There is evidence that sensory innervation plays a role regulating ovarian functions, including fertility.Since sensory denervation by means of capsaicin in newborn female rats results in a lower response togonadotropins, the present study analyzed the effects that sensory denervation by means of capsaicin in neonatal rats has on the concentration of monoamines in the anterior(AH) and medium (MH) hypothalamus, and on steroid hormone levels in serum. Groups of newborn female rats were injected subcutaneously with capsaicin and killed at 10, 20, and 30 days of age and on the first vaginal estrous.The concentrations of noradrenaline, dopamine, serotonin(5-HT), and their metabolites in the AH and MH were measured using HPLC, and the levels of estradiol (E),progesterone (P), testosterone (T), FSH, and luteinizing hormone using radioimmunoanalysis. The results show thatat 20 days of age, capsaicin-treated rats have lowernoradrenergic and serotonergic activities in the AH, and that the dopaminergic activity was lower in the MH. These results suggest that the sensorial system connections within the monoaminergic systems of the AH and MH are different.Capsaicin-treated animals had lower T, E, and P levels than in the control group, suggesting that the lower activity in the AH monoaminergic system and lower hormonesecretion could be explained by the blockade of information mediated by the sensory innervation (probably substance P), mainly between the ovary and the AH.

Afferent neuronal control of type-I gonadotropin releasing hormone neurons in the human

Understanding the regulation of the human menstrual cycle represents an important ultimate challenge of reproductive neuroendocrine research. However, direct translation of information from laboratory animal experiments to the human is often complicated by strikingly different and unique reproductive strategies and central regulatory mechanisms that can be present in even closely related animal species. In all mammals studied so far, type-I gonadotropin releasing hormone (GnRH) synthesizing neurons form the final common output way from the hypothalamus in the neuroendocrine control of the adenohypophysis. Under various physiological and pathological conditions, hormonal and metabolic signals either regulate GnRH neurons directly or act on upstream neuronal circuitries to influence the pattern of pulsatile GnRH secretion into the hypophysial portal circulation. Neuronal afferents to GnRH cells convey important metabolic-, stress-, sex steroid-, lactational-, and circadian signals to the reproductive axis, among other effects. This article gives an overview of the available neuroanatomical literature that described the afferent regulation of human GnRH neurons by peptidergic, monoaminergic, and amino acidergic neuronal systems. Recent studies of human genetics provided evidence that central peptidergic signaling by kisspeptins and neurokinin B (NKB) play particularly important roles in puberty onset and later, in the sex steroid-dependent feedback regulation of GnRH neurons. This review article places special emphasis on the topographic distribution, sexual dimorphism, aging-dependent neuroanatomical changes, and plastic connectivity to GnRH neurons of the critically important human hypothalamic kisspeptin and NKB systems.

The effects of neurokinin B upon gonadotrophin release in male rodents

Growing evidence suggests the tachykinin neurokinin B (NKB) may modulate gonadotrophin secretion and play a role in sex-steroid feedback within the reproductive axis. NKB signalling has recently been identified as being necessary for normal human reproductive function, although the precise mechanisms underpinning this role remain to be established. We have used rodents to explore further the role of NKB within the reproductive axis. In particular, we have studied its interactions with kisspeptin, a neuropeptide essential for reproductive function in rodent and human with close anatomical links to NKB within the hypothalamus. Intraperitoneal administration of NKB (50 nmol) to male mice had no effect on circulating luteinsing hormone (LH) levels and, although i.p. kisspeptin (15 nmol) increased LH five-fold, co-administration of NKB and kisspeptin was indistinguishable from kisspeptin alone. Intracerebroventricular administration of NKB (10 nmol) to male mice also had no effect on LH levels, with 1 nmol kisspeptin i.c.v. significantly increasing LH compared to control (0.37 +/- 0.18 versus 5.11 +/- 0.28 ng/ml, respectively). Interestingly, i.c.v. co-administration of NKB and kisspeptin caused a significant increase in LH concentrations compared to kisspeptin alone (8.96 +/- 1.82 versus 5.11 +/- 0.28 ng/ml respectively). We used hypothalamic explants from rats to assess the effect of NKB on gonadotrpohin-releasing hormone (GnRH) secretion ex vivo. Doses of NKB up to 1000 nm failed to stimulate GnRH secretion, whereas 100 nm kisspeptin robustly increased GnRH secretion. Of note, co-administration of NKB with kisspeptin abrogated the effect of kisspeptin, producing no GnRH release above basal state. Finally, we analysed the expression of Tac2/Tacr3 (genes encoding NKB and NK3R, respectively) within the arcuate nucleus in different nutritional states. After a 48-h fast, the expression of both Tac2 and Tacr3 showed a significant increase, in contrast to levels of Kiss1 and Kiss1r mRNA, which remained unchanged. In male rodent models, NKB and kisspeptin have different effects upon gonadotrophin release and appear to interact in a complex manner.

Administration of an antagonist of neurokinin receptors 1, 2, and 3 results in reproductive tract changes in beagle dogs, but not rats

SCH 206272, an antagonist of neurokinin receptors 1, 2, and 3, was administered orally by gavage for 1 month to 8- to 10-month-old dogs at doses of 0, 15, 30, or 60 mg/kg, and to 6-week-old rats at doses of 0, 30, 100, or 300 mg/kg. The most important changes occurred in the reproductive tract of the dogs at all doses. Absolute and relative group mean organ weights for the testes, prostate gland, epididymides, ovaries, and uterus were 33-86% lower than concurrent controls in groups receiving SCH 206272. Organ weight changes were not dose-related. Microscopic changes that correlated with the organ weight changes occurred in all groups receiving SCH 206272. For males, they included minimal to severe atrophy of the testes, epididymides, and prostate gland. In addition, the epididymides exhibited severe oligospermia or aspermia, minimal epithelial apoptosis and mild epithelial vacuolation. In female dogs, the ovaries and uteri appeared immature. Microscopic changes were similar in incidence and severity in dogs receiving 30 or 60 mg/kg, but were slightly less in dogs receiving 15 mg/kg. In contrast, similar findings were not observed in the reproductive tract of male or female rats, despite overlapping systemic, hypothalamic, and pituitary gland concentrations of SCH 206272.

Neuropeptides, neurotransmitters, neurosteroids, and the onset of puberty

Puberty results from withdrawal of the "gonadostat" mechanisms and from increased gonadotropin sensitivity to GnRH. It has been hypothesized that GnRH release may be modulated by a non-steroid-mediated mechanism. Modifications of neuropeptides, neurotransmitters, and neurosteroids may underlie the onset of pubertal processes. Neuropeptides mainly involved in the control of GnRH release are opioids, neuropeptide Y (NPY), galanin, and corticotropin-releasing factor (CRF), whereas neurotransmitters are noradrenaline, dopamine, serotonin, melatonin and gamma-aminobutyric acid (GABA). Norepinephrine, epinephrine, and dopamine stimulate GnRH, whereas the effect of serotonin on hypothalamic-pituitary-ovarian axis seems to be norepinephrine-mediated. Neurosteroids are steroid hormones that bind to the GABA-A receptor, synthesized in the brain de novo or from blood-borne precursors. DHEA, a GABA-A antagonistic neurosteroid, and allopregnanolone, a GABA-A agonistic neurosteroid, may be important in the onset of gonadarche. In conclusion, the onset of puberty derives from the complex interplay among neuropeptides, neurotransmitters, and neurosteroids that occurs in the awakening of hypothalamic-pituitary-ovarian axis.

Interaction between substance P and gastrin-releasing peptide on thyrotropin secretion by rat pituitary in vitro

The effect of substance P (SP) on thyrotropin (TSH) secretion is controversial. In this study we evaluated the effect of SP on TSH secretion by hemipituitaries of 3-month-old Wistar rats in vitro and its interaction with gastrin-releasing peptide (GRP) at equimolar concentrations (1 microM and 10 microM). TSH release was measured under basal conditions and 30 min after incubation in the absence or presence of SP, GRP or both peptides. Pituitary TSH content was also measured in the pituitary homogenate after incubation. SP at both concentrations caused a significant (P<0.05) increase in TSH secretion compared with all other groups, which was approximately 60% (1 microM) and 85% (10 microM) higher than that of the control group (23.3 +/- 3.0 ng/ml). GRP at the lower concentration did not produce a statistically significant change in TSH secretion, whereas at the concentration of 10 microM it produced a 50% reduction in TSH. GRP co-incubated with substance P completely blocked the stimulatory effect of SP at both concentrations. Pituitary TSH content decreased in the SP-treated group compared to controls (0.75 +/- 0.03 microg/hemipituitary) at the same proportion as the increase in TSH secretion, and this effect was also blocked when GRP and SP were co-incubated. In conclusion, in an in vitro system, SP increased TSH secretion acting directly at the pituitary level and this effect was blocked by GRP, suggesting that GRP is more potent than SP on TSH secretion, and that this inhibitory effect could be the predominant effect in vivo.

Modulation of gonadotropin levels by peptides acting at the anterior pituitary gland

There are several lines of evidence that point to peptides participating in the regulation of LH and/or FSH levels by action at the pituitary. This evidence includes altered secretion of gonadotropins from the anterior pituitary cells or tissue in vitro when exposed to the peptide. Additionally, modification of GnRH-stimulated LH/FSH secretion has been observed. Furthermore, there is potential for a separately modulated interaction with the primed response. Another potential of action is by interaction among non-GnRH peptides on gonadotropin-regulating processes, although there are no good data available on this aspect. Other observations, consistent with a pituitary role for the peptides in modulation of LH, include detection of the peptides in portal blood, detection of high-affinity receptors or receptor mRNA in the pituitary, and detection of intrapituitary peptide or peptide mRNA in the pituitary. The modulation by steroids of both concentrations and type of activities provides a further level of physiological refinement. There is, however, some confusion regarding the involvement of these peptides in gonadotropin control. The reasons can be seen by considering aspects of investigations. There are experimental variations such as 1) species studied, e.g., NPY has been reported to have an effect on LH secretion from rat cells (168) but not on sheep anterior pituitary tissue (64), and substance P inhibits GnRH-stimulated release from rat cells (182) but potentiates the response in prepubertal porcine cells (92); 2) the steroidal conditions under which the study is performed, e.g., NPY has opposite effects in certain endocrine environments, augmenting GnRH-stimulated LH release in proestrus-like conditions (168), and inhibiting in metestrus-like environment (66); 3) the type of cell preparation, e.g., responsiveness to substance P might depend on whether cells in overnight culture were in separated or clustered state (91); 4) the time course considered, e.g., oxytocin that might induce marked LH release from pituitary cells after a longer length of incubation than GnRH requires (68); 5) length of exposure to peptide, e.g., endothelin that augmented or inhibited GnRH-stimulated LH release (50); 6) In addition, it is possible that the traditional endpoint selected in such studies, namely, observation of gonadotropin secretion, is not necessarily the most important for these peptides (56, 81, 117). Unfortunately, at this stage a definitive answer to the question "What do the peptides actually do?" cannot be provided and we remain tantalized by the glimpses of potential roles. Perhaps in a few years an updated review will be able to include a more complete answer. It is necessary for the full understanding of LH control that not only the properties of the peptides in isolation be characterized but also their interactions.

The in vitro effect of substance P on the GnRH-induced LH release depends on the steroidal environment and is reverted by a NK1 receptor antagonist (RP 67580) in the cycling female rat

A previously study reported that administration of substance P on the morning of the proestrous day induces an inhibition of afternoon gonadotropin preovulatory surges in the female rat. It has also been shown, with a non-peptide specific antagonist of the neurokinin 1 (NK1) receptor (RP 67580), that this effect is mediated by NK1 receptors. The present study used perifused anterior pituitaries from proestrous morning female rats and showed that the SP modulation of the GnRH-induced LH release is markedly dependent on the steroidal environment. In the absence of steroids or in the presence of 17beta estradiol, or a combination of 17beta estradiol and progesterone, SP inhibited the GnRH-induced LH release. In contrast, SP stimulated the GnRH-induced LH secretion in the presence of progesterone alone. However, the inhibitory or stimulatory effect of SP was antagonized by the specific NK1 receptor antagonist RP 67580.

Effects of halothane and methoxyflurane on regional brain and spinal cord substance P-like and beta-endorphin-like immunoreactivities in the rat

Effects of acute exposure (2 hr) to either 1.5% halothane or 0.5% methoxyflurane were investigated in the Sprague Dawley rat. Pituitary (PIT) and central nervous system (CNS) substance P (SP)-like and beta-endorphin (beta-end)-like immunoreactivities were evaluated immediately after anesthetic exposure (2 h), after righting reflex (4 h) or 24 hr postexposure (24 h). Only halothane significantly reduced SP-like immunoreactivity in olfactory bulbs in both the 2-h and 4-h groups. Halothane elevated SP-like immunoreactivity of hippocampus at all three time periods, and in the hypothalamus at 2 h. Both anesthetics significantly depleted thalamic concentrations of SP-like immunoreactivity. Methoxyflurane anesthesia resulted in a drastic decrease in SP-like immunoreactivity in PIT at all three time periods periods, while halothane elevated PIT concentrations of this peptide at 4 h. Both anesthetics significantly decreased beta-end-like immunoreactivity in the olfactory bulbs and thalami at 2, 4, and 24 h. However, halothane alone significantly elevated beta-end-like immunoreactivity in the spinal cord at 24 h. Halothane significantly elevated PIT beta-end-like immunoreactivity at 2 and 24 h, while methoxyflurane significantly lowered it in the 4-h group, but elevated the levels of the same in the 24-h group. Brain stem beta-end immunoreactivity were significantly reduced at 2 h by both anesthetics, and at 4 h by methoxyflurane. Results indicate that halothane and methoxyflurane may differ significantly in their actions on SP and beta-end secreting neurons in the CNS.

Synaptic connections between substance P-containing axons and estrogen receptor-synthesizing neurons in the medial preoptic area of the rat brain

Dual-label immunocytochemical procedures were employed to provide ultrastructural evidence for the presence of substance P (SP) in afferents to estrogen-receptive neurons in the medial preoptic area (MPO) of the female rat. SP-immunoreactive axon terminals were observed to innervate the periventricular (PvPO) and medial (MPN) preoptic nuclei of the MPO densely, and to form synaptic connections at these sites with neurons which contain estrogen receptors in their nucleus. These results indicate that estrogen-receptive preoptic neurons may be regulated by SP-containing neuronal pathways via synaptic mechanisms.

Variations in levels of substance P-encoding beta-, gamma-preprotachykinin and substance P receptor NK-1 transcripts in the rat hypothalamus throughout the estrous cycle: a correlation between amounts of beta-preprotachykinin and NK-1 mRNA

Using a sensitive RNase protection assay, the simultaneous quantification of hypothalamic beta-, gamma-preprotachykinin (PPT) and SP receptor NK-1 transcripts was performed throughout the estrous cycle. The amounts of these 3 transcripts were up-regulated during diestrus II-proestrus night (2-, 1.5- and 1.3-fold, respectively). These levels returned to low values during the proestrous day in the case of gamma-PPT mRNA and during the estrus-diestrus I night in the cases of beta-PPT and NK-1 mRNAs. These results implicate a differential regulation in amounts of the two alternatively spliced PPT transcripts. The 160 hypothalami of this study had been previously assayed for amounts of substance P (SP) and neurokinin A (NKA) peptides [P. Duval, V. Lenoir, S. Moussaoui, C. Garret and B. Kerdelhué, Substance P and neurokinin A variations throughout the rat estrous cycle; comparison with ovariectomized and male rats: I. Plasma, hypothalamus, anterior and posterior pituitary, J. Neurosci. Res., 45 (1996) 598-609]. Variations in mRNA and peptide levels were compared by statistical analysis. Surprisingly, variations in SP level paralleled those in beta-PPT mRNA level and variations in NKA level paralleled those of gamma-PPT mRNA level, although beta- and gamma-PPT transcripts encode both SP and NKA. Furthermore, the level of NK-1 mRNA was positively correlated with the level of beta-PPT mRNA (r = 0.90, P < 10(-58)) and with the level of SP peptide (r = 0.30, P < 10(-3)) but not with the level of NKA peptide. This analysis suggests that SP receptor NK-1 mRNA could be physiologically regulated by SP peptide in the rat hypothalamus.

Localization of neurons expressing substance P and neurokinin B gene transcripts in the human hypothalamus and basal forebrain

In situ hybridization histochemistry was used to map the distribution of neurons expressing the substance P (SP) or neurokinin B (NKB) genes in the human hypothalamus and basal forebrain. Hypothalami from five adult males were frozen in isopentane at -30 degrees C and serially sectioned at 20 jm thickness. Every 20th section was hybridized with [35S]-labeled, 48-base synthetic cDNA probes that were complementary to either SP or NKB mRNAs. Slides were dipped into nuclear emulsion for visualization of mRNAs at the single-cell level. The location of labeled neurons (greater than x 5 background) was mapped by using an image-combining computer microscope system. A distinct and complementary distribution pattern of SP and NKB neurons was observed in the human hypothalamus and basal forebrain. NKB was the predominant tachykinin in the rostral hypothalamus, whereas SP mRNA predominated in the posterior hypothalamus. Numerous NKB neurons were identified in the magnocellular basal forebrain, the bed nucleus of stria terminalis, and the anterior hypothalamic area. Scattered NKB neurons were present in the infundibular and paraventricular nuclei, paraolfactory gyrus, posterior hypothalamic area, lateral division of the medial mammillary nucleus, and amygdala. Numerous neurons expressing SP mRNAs were identified in the premammillary, supramammillary, and medial mammillary nuclei; the posterior hypothalamic area; and the corpus striatum. Scattered SP neurons were also observed in the preoptic area; the infundibular, intermediate, dorsomedial, and ventromedial nuclei; the infundibular stalk; the amygdala; the bed nucleus of stria terminalis; and the paraolfactory gyrus. These studies provide the first description of the location of neurons that express tachykinin gene transcripts in the human hypothalamus.

Reduction of the amplitude of preovulatory LH and FSH surges and of the amplitude of the in vitro GnRH-induced LH release by substance P. Reversal of the effect by RP 67580

The effects of Substance P (SP) and of a specific nonpeptide antagonist of the NK1 receptor (RP 67580) on preovulatory gonadotropin surges and on the in vitro GnRH induced LH surge were investigated in cycling female rats. A subcutaneous injection of SP (0.5 mg/kg body weight) at 12.00 h on the proestrous day significantly decreased the LH preovulatory surge. RP 67580 (1.5 mg/kg) significantly increased this LH surge. However, when SP and its antagonist were administered together, LH preovulatory surge was normal. The FSH preovulatory surge at 18.00 h and also at 19.00 h was significantly inhibited by SP administration. RP 67580 alone had no effect on the FSH preovulatory surge. When SP and RP 67580 were both administered, there was no diminution of FSH plasma levels at 18.00 h and 19.00 h. In vitro perifusions of anterior pituitaries showed that SP inhibits GnRH-induced LH release via a NK1 receptor. Thus, SP inhibits the LH preovulatory surge via NK1 receptors and SP modulation of gonadotropin surges is at least partly exerted at the pituitary.

Induction of substance P-immunoreactivity by estrogen in neurons containing estrogen receptors in the anterovental periventricular nucleus of female but not male rats

Effects of gonadal steroids on numbers of neurons containing estrogen receptor (ER) and/or substance P (SP) were examined in the anteroventral periventricular nucleus (AVPV) of female and male rats by double-labeling immunohistochemistry employing antibodies specific for ER and SP. Animals were gonadectomized and received subcutaneously either oil alone (Control group), sequential injections of estradiol benzoate and oil (EB + Oil group), or those of EB and progesterone (EB + P group). In the female control rat, a large population of ER-immunoreactive (IR) cells were found clustered throughout the AVPV. They were counted more than 2,000 in total of 4 sections in this nucleus. On the contrary, SP-IR neurons were scarcely observed in the same area of this group. Administration of estrogen to female animals decreased the total number of ER-IR cells to 67% of the control group. In contrast to the supressive effect of estrogen to its own receptor, it induced SP-IR neurons in the AVPV of the female. Approximately 50-80 SP-IR neurons were counted in the 4 sections, and 59% of these neurons expressed ER-IR material in their nuclei. In the female EB + P group, the number of ER-IR neurons also decreased to 79% of the control group. Although the number of SP-IR neurons in this group decreased to 32% of that in the EB + Oil group, a ratio of coexistence of ER-IR material in these neurons increased to 75%. The male control group contained a smaller population of ER-IR cells relative to the female control (1497 vs 2143).(ABSTRACT TRUNCATED AT 250 WORDS)

Unanswered questions in hormonal replacement therapy

This review addresses many of the unanswered questions existing relative to the use of exogenous estrogens and progestins in postmenopausal women (PMW). The literature in the field is reviewed and summarized, with a particular effort to identify key questions of major concern. The effect of selection bias on conclusions reached from retrospective studies involving hormone replacement therapy (HRT) has not been examined. Less is actually known about the effects of progestins than estrogens. Many of the endocrine changes that occur with aging remain poorly defined. Effects of estrogens and progestins on the breast and on breast cancer are unclear. Estrogens have recognized beneficial effects and progestins have detrimental effects on lipoprotein metabolism. Estrogens also have direct effects on the vasculature and may impact on cardiovascular risk in other ways. Although estrogens are the only agents known to eliminate hot flushes, the mechanism by which flushes arise is not known. Estrogens may have ameliorating effects on mood and behavior and may improve dementia, but research in this area has been limited to date. Lastly, the preferred estrogens and progestins, their dosages and routes of administration, remain to be more completely defined.

Gonadal steroids regulate immunoreactive tachykinin in the ventromedial nucleus of the rat hypothalamus

The ventromedial nucleus of the hypothalamus (VMH) is an important site in the mediation of female receptive behavior (lordosis); however, the sequence of events that eventually facilitate this estrogen-dependent behavior is only partially understood. Here, evidence is presented, suggesting that an interaction between gonadal steroids and tachykinin peptides is involved. Tachykinin-immunoreactive (TACir) neurons were distributed throughout the anterior (VMHa), dorsomedial (VMHdm), central (VMHc), and ventrolateral (VMHvl) subdivisions in the adult male and female rat. Numbers of cells in the VMH of intact males and males that had been castrated for three weeks were similar. Among females, numbers of TACir cells in the VMHvl were significantly increased over numbers seen in ovariectomized females by a two day (1.5 x) and by a two week (1.6 x) exposure to estrogen. In the VMHa, numbers of TACir cells were also significantly higher in females that received replacement estrogen compared to ovariectomized females. Since estrogen concentration by TACir neurons is common in the VMHvl and rare in the VMHa, estrogen may have both direct and indirect effects on tachykinin synthesis. In the caudal pole of the VMH, staining intensity of TACir fibers varied with endocrine state. In intact males, castrated males, and ovariectomized females, fibers were lightly stained. In females exposed to estrogen for two days, fibers were moderately intense, and in females exposed to estrogen for two weeks, they formed a darkly stained plexus. These responses to estrogen suggest that production of tachykinin peptides in the VMH is involved in facilitation of female typical sexual behavior.

Effect of chronic DDC treatment on LHRH and substance P amidation processes in the rat

We examined the effects of chronic diethyldithiocarbamate (DDC) treatment on the concentrations of methionine-enkephalin, mature and unamidated forms (-Gly) of luteinizing hormone releasing hormone (LHRH) and substance P (SP) in various regions of the central nervous system (CNS). Chronic DDC treatment resulted in elevations of LHRH-Gly like immunoreactivity in the preoptic area (POA) and the medial basal hypothalamus (MBH), as well as elevations in SP-Gly like immunoreactivity in all areas of the CNS examined. Castration altered the ratios of SP-G-like/SP-like immunoreactivity in the pons, and LHRH-Gly like immunoreactivity in the MBH. Met-enkephalin concentrations were significantly elevated in the pons and medulla of intact DDC-treated animals, and in the POA of both intact- and castrated DDC-treated animals. Results demonstrate that it is possible to detect basal levels of unamidated LHRH and SP in many areas of the CNS, with ratios of unamidated/amidated peptides representing a unique and sensitive method for determining altered posttranslational processing of these transmitters, especially under altered endocrine states such as castration. Pharmacological blockade of terminal enzymatic processing of these peptides may be useful in studying upstream regulatory events in peptidergic neurons.

Bioactive peptides in anterior pituitary cells

The anterior pituitary (AP) has been shown to contain a wide variety of bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various other peptides. The localization of most of these peptides was first established by immunocytochemical methods and some of the peptides were localized in identified cell types. Although intracellular localization of a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these peptides in the AP based on the identification of their messenger-RNA (mRNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are not expected. There is more evidence for paracrine, autocrine, or intracrine roles in growth, differentiation, and regeneration, or in the control of hormone release. To demonstrate such functions, in vitro AP experiments have been designed to avoid the interference of hypothalamic or peripheral hormones. The strategy is first to show a direct effect of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the peptide.

Calcitonin gene-related peptide- and substance P-like-immunoreactive innervation of the anterior pituitary in the rat

In our previous studies substantial amounts of substance P- and calcitonin gene-related peptide-like-immunoreactive nerve fibers have been identified in the anterior pituitary of the monkey and the dog. They were found to be in close proximity to the gland cells, even making synaptic contacts with some types of the gland cells. The present study investigated in detail the calcitonin gene-related peptide- and substance P-like immunoreactivities of the anterior pituitary in the rat. Though the immunoreactive fibers were not as abundant as in the anterior pituitary of the monkey and the dog, they still appeared in notable amounts. The calcitonin gene-related peptide- and substance P-like-immunoreactive nerve fibers occurred mostly as thin, tortuous, and densely varicose fibers, weaving among the gland cells. They are widely distributed, more in the central part of the gland. Double-immunostaining proved nearly complete co-localization of these two peptides in the nerve fibers. It is hypothesized that the anterior pituitary can be regulated by direct neural factors as well as humoral factors.

Androgen concentration by a sexually dimorphic population of tachykinin-immunoreactive neurons in the rat ventral premammillary nucleus

Strong connections with sexually dimorphic nuclei suggest that the ventral premammillary nucleus (PMv) may be involved in the mediation of reproductive behavior. Steroid autoradiography and immunohistochemistry were used to show that: (1) there is a sex difference in the numbers of PMv neurons that contain tachykinin peptides, (ii) dihydrotestosterone concentrating cells are densely distribution in the PMv and about a quarter of these also contain immunoreactive tachykinin and, (iii) size of the immunoreactive tachykinin population does not respond to alterations in levels of gonadal steroids in adulthood. Thus the PMv appears to make a contribution to the regulation of sexual behavior through androgen-concentrating, tachykinin-containing pathways that are anatomically distinct from estrogen receptive circuitry.

Neurokinin A in the anterior pituitary of female rats: effects of ovariectomy and estradiol

The effect of acute and chronic ovariectomy and the substitutive treatment with 17-beta estradiol and/or progesterone on anterior pituitary levels of neurokinin A (NKA) was studied in female rats. Acute ovariectomy did not result in significant changes of NKA in the anterior pituitary gland as compared with the levels in diestrous intact rats, but a single injection of 5 micrograms of estradiol in ovariectomized rats significantly decreased NKA levels in the anterior pituitary gland. Progesterone was without effect and did not modify the decrease of NKA in the anterior pituitary gland induced by estradiol. In rats examined 11 to 17 days after ovariectomy, NKA in the anterior pituitary gland was significantly higher than in diestrous intact rats. In the hypothalamus, ovariectomy resulted in decreased levels of NKA in the median eminence-arcuate nucleus. Estradiol significantly reduced NKA stores in the anterior pituitary gland but increased them in the whole hypothalamus and in the median eminence-arcuate nucleus. Thus, estradiol seems to be a powerful regulator of NKA stores in the adenohypophysis and also in the hypothalamus.

Luteinizing hormone response to an intravenous infusion of substance P in normal men

The effect of synthetic substance P (SP), infused intravenously in doses of 0.5, 1.0, or 1.5 pmol/kg-1/min-1 for 60 minutes, on gonadotropin secretion was evaluated in seven healthy men. SP tests and a control test with normal saline were randomly performed at weekly intervals. During the tests, SP infusion did not produce untoward side effects or changes in blood pressure. Plasma testosterone concentrations were normal in all subjects and remained unmodified during all tests, regardless of the infused dose of SP. Plasma luteinizing hormone (LH) levels were not modified when either normal saline or the lowest dose of SP were infused, whereas they were significantly increased in a dose-dependent fashion when larger amounts of SP were administered. In contrast, plasma follicle-stimulating hormone (FSH) concentrations did not change significantly during any test. These data demonstrate for the first time in normal men that the systemic infusion of SP stimulates LH release, without modifications of FSH secretion.

Hormonal influences on morphology and neuropeptide gene expression in the infundibular nucleus of postmenopausal women

Neuronal hypertrophy occurs in a subpopulation of neurons in the infundibular nucleus of post-menopausal women. The hypertrophied neurons contain NKB, SP and estrogen receptor gene transcripts. Although associated with reproductive aging, post-menopausal neuronal hypertrophy is not a sign of central nervous system degeneration. Quite the opposite, because the hypertrophy is accompanied by marked increases in tachykinin gene expression, reflecting increased neuronal activity. We have proposed that infundibular neurons containing NKB, SP and estrogen receptor mRNAs participate in the hypothalamic circuitry regulating estrogen negative feedback on gonadotropin release in the human. In addition, there is evidence to suggest that the hypertrophied tachykinin neurons may be involved in the initiation of menopausal flushes. Because menopause affects a well characterized system, and has consistent and substantial changes in hormone levels, we have had the rare opportunity to correlate changes in hormone secretion with structural and neurochemical changes in the human hypothalamus. We suspect that future studies of the hypothalami of post-menopausal women will continue to be a fruitful avenue for investigating neuroendocrine regulation in the human.

Effects of various tachykinins on pituitary LH secretion, feeding, and sexual behavior in the rat

Our investigations of the four tachykinines tested have shown that NPK characteristically evoked a spectrum of biological effects in male and female rats. NPK suppressed pituitary LH release by inhibiting the release of hypothalamic LHRH, presumably by activation of NK-2 tachykinin receptor subtypes. However, NPK may also act at the level of gonadotrophs to stimulate LH release in male rats. Central injection of NPK rapidly disrupted copulatory behavior in sexually active male rats. NPK also suppressed feeding, but, in this case, peripheral injections were more effective than central injections. Taken together, these observations strongly imply that NPK may be an inhibitory messenger molecule in the hypothalamic control of reproduction, sexual, and feeding behaviors.

Distribution of substance P, GnRH, Met-enkephalin in the central nervous system of the pig

The distribution of substance P (SP), gonadotropin releasing hormone (GnRH) and Met-enkephalin in the brain and spinal cord of the domestic pig is described for the first time. The levels of SP, GnRH and Met-enkephalin were measured by specific radioimmunoassays in various regions of the brain and spinal cord of the pig. Substance P and Met-enkephalin are widely distributed within the central nervous system of the pig. High levels of SP were found in the preoptic area (POA), suprachiasmatic area (SCA), medial basal hypothalamus (MBH) and brain stem while moderate amounts of SP were found in olfactory bulb (OB). High levels of Met-enkephalin were found in POA, SCA and MBH, and moderate levels of Met-enkephalin in OB and brain stem. Both SP and Met-enkephalin levels were higher in the dorsal spinal cord in comparison with the levels of these peptides in the ventral spinal cord. This finding is in agreement with the predominant role played by these neural systems in primary afferent mediation of nociceptive impulses. The POA and SCA contained only low levels of GnRH while the MBH contained high levels of GnRH. Finally, some differences in the quantitative distribution of these peptides in the pig and rat are discussed.

Substance P and substance K in the rat hypothalamus following monosodium glutamate lesions of the arcuate nucleus

Adult rats treated neonatally with monosodium glutamate (MSG) exhibit lesions in the arcuate nucleus of the hypothalamus. Following MSG lesioning, dopamine content in median eminence/arcuate nucleus (ME/AN) tissue extracts declined by 60-70%. Substance P (SP) content as determined by radioimmunoassay was significantly decreased in the paraventricular nucleus (PVN) (531 +/- 30 pg, mean +/- SEM) compared to controls (871 +/- 110 pg) but was unchanged in ME/AN extracts. Substance K (SK) content decreased to 257 +/- 20 pg in the PVN of lesioned animals compared to controls (367 +/- 31 pg) and the ME/AN content of SK was also significantly decreased (236 +/- 36 pg compared to control levels of 619 +/- 65 pg). The CRF-41 content of the PVN and ME/AN was unchanged by MSG lesioning, indicating that these areas are not affected by MSG. The partial depletion of SP and SK in the PVN following MSG treatment provides evidence that at least some of the neurokinin content of the PVN may originate in cell bodies of the arcuate nucleus. However, the lack of response of ME/AN SP to MSG treatment may suggest that the arcuate nucleus is not the major source of SP in the median eminence.

Ethanol-related changes in substance P in the hypothalamus and anterior pituitary

The effect of the administration of a rabbit anti-substance P serum (ASPS) was studied in rats receiving an acute injection of ethanol. ASPS lowered serum prolactin levels and reduced the hyperprolactinemia induced by ethanol. ASPS also decreased LH serum levels in both saline- and ethanol-treated rats. The effect of ethanol on the concentration of substance P-like immunoreactivity (SP-LI) in the mediobasal hypothalamus and the anterior pituitary gland was also investigated. Ethanol reduced SP-LI in the mediobasal hypothalamus but increased it in the anterior pituitary gland. The presence of ethanol (50 mM) did not affect the K(+)-evoked release of SP-LI from either mediobasal hypothalamus or anterior pituitary gland, though it increased the SP-LI concentration remaining in this gland. These results indicate that ethanol increases the content of SP-LI in the anterior pituitary gland and suggest that substance P may be involved in the prolactin release induced by the acute administration of ethanol.