The effect of LHRH antagonist analogs and an antibody to LHRH on mating behavior in female rats

Food Restriction-Induced Changes in Gonadotropin-Inhibiting Hormone Cells are Associated with Changes in Sexual Motivation and Food Hoarding, but not Sexual Performance and Food Intake

We hypothesized that putative anorectic and orexigenic peptides control the motivation to engage in either ingestive or sex behaviors, and these peptides function to optimize reproductive success in environments where energy fluctuates. Here, the putative orexigenic peptide, gonadotropin-inhibiting hormone (GnIH, also known as RFamide-related peptide-3), and the putative anorectic hormones leptin, insulin, and estradiol were examined during the course of food restriction. Groups of female Syrian hamsters were restricted to 75% of their ad libitum food intake or fed ad libitum for 4, 8, or 12 days. Two other groups were food-restricted for 12 days and then re-fed ad libitum for 4 or 8 days. After testing for sex and ingestive behavior, blood was sampled and assayed for peripheral hormones. Brains were immunohistochemically double-labeled for GnIH and the protein product of the immediate early gene, c-fos, a marker of cellular activation. Food hoarding, the number of double-labeled cells, and the percent of GnIH-Ir cells labeled with Fos-Ir were significantly increased at 8 and 12 days after the start of food restriction. Vaginal scent marking and GnIH-Ir cell number significantly decreased after the same duration of restriction. Food hoarding, but not food intake, was significantly positively correlated with cellular activation in GnIH-Ir cells. Vaginal scent marking was significantly negatively correlated with cellular activation in GnIH-Ir cells. There were no significant effects of food restriction on plasma insulin, leptin, estradiol, or progesterone concentrations. In the dorsomedial hypothalamus (DMH) of energetically challenged females, strong projections from NPY-Ir cells were found in close apposition to GnIH-Ir cells. Together these results are consistent with the idea that metabolic signals influence sexual and ingestive motivation via NPY fibers that project to GnIH cells in the DMH.

Gonadotropin-releasing hormone II stimulates female sexual behavior in marmoset monkeys

GnRH II (pGlu-His-Trp-Ser-Try-Gly-Leu-Arg-Pro-GlyNH2), an evolutionarily conserved member of the GnRH family, stimulates reproductive behavior in a number of vertebrates. To explore a role for GnRH II in regulating primate sexual behavior, eight adult female common marmosets, each fitted with an indwelling intracerebroventricular (icv) cannula, were ovariectomized, implanted subcutaneously with empty (n = 4) or estradiol-filled (n = 4) SILASTIC brand capsules, and pair housed with an adult male mate. After icv infusion of vehicle or peptides, females were placed in an observation cage for 90 min, out of visual contact with other marmosets, before the 30-min behavioral test with their male partner. Compared with vehicle, GnRH II (1 and 10 microg) increased the total number of proceptive (sexual solicitation) behaviors (tongue flicking, proceptive stares, and frozen postures) exhibited by females toward their pair mates and specifically increased the frequency of freeze postures. Effects were maximal at 1 microg and not dependent upon estradiol supplementation. GnRH II agonists/GnRH I antagonists 135-18 (1 microg) and 132-25 (1 microg), which stimulate inositol phosphate production via the marmoset type II receptor, increased the frequency of total proceptive behavior but did not specifically stimulate freeze-posture behavior. In contrast, GnRH I, at 1 mug, did not alter the frequency of proceptive behaviors. Female receptivity (female compliance with male sexual behavior) was not altered by any of the peptides tested. These findings implicate a role for GnRH II and the cognate GnRH type II receptor in stimulating female marmoset sexual behavior.

Co-regulation of female sexual behavior and pregnancy induction: an exploratory synthesis

This paper will review both new and old data that address the question of whether brain mechanisms involved in reproductive function act in a coordinated way to control female sexual behavior and the induction of pregnancy/pseudopregnancy (P/PSP) by vaginocervical stimulation. Although it is clear that female sexual behavior, including pacing behavior, is important for induction of P/PSP, there has been no concerted effort to examine whether or how common mechanisms may control both functions. Because initiation of P/PSP requires that the female receive vaginocervical stimulation, central mechanisms controlling P/PSP may be modulated by or interactive with those that control female sexual behavior. This paper presents a synthesis of the literature and recent data from our lab for the purpose of examining whether there are interactions between behavioral and neuroendocrine mechanisms which reciprocally influence both reproductive functions.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

Actions of two forms of gonadotropin releasing hormone and a GnRH antagonist on spawning behavior of the goldfish Carassius auratus

The central effects of two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), and a GnRH antagonist, ¿Ac-delta 3-Pro(1), 4FD-Phe(2), D-Trp(3, 6)mGnRH (analog E), on the spawning behavior of sexually recrudescent female goldfish were investigated. The effects of analog E were also observed in mature males. Female spawning behavior was induced by intramuscular injection of females with prostaglandin F(2alpha) and placing them in the presence of mature males. Behavioral responses were quantified by recording the numbers of spawning acts performed by each pair of fish for 2 h following brain intracerebroventricular (icv) injection of different dosages of peptide or saline as control. For males, the time spent courting the female was recorded. Each pair of fish was pretested to determine their level of spawning behavior, for comparison to spawning behavior following icv treatment. Icv injection of analog E caused a significant decrease in the number of spawning acts performed by females, suggesting a role of endogenous GnRH in modulating female spawning behavior. icv injection of 0.5 ng/g of sGnRH or cGnRH-II significantly stimulated female spawning behavior, whereas doses of 1 ng/g and higher resulted in an almost complete inhibition of spawning, reflecting a down-regulation as a result of the excessive dosages. Analog E suppressed the actions of exogenous sGnRH and cGnRH-II on spawning behavior, as both the sGnRH- and cGnRH-II-induced increases in the number of spawning acts were inhibited by concomitant treatment with analog E. Analog E-injected males showed no alteration in courtship behavior. These results indicate that GnRH peptides play a major role in the control of female reproductive behavior in goldfish, but have little or no role in the control of male behavior.

Importance of the gonadotropin-releasing hormone (GnRH) surge for induction of the preovulatory luteinizing hormone surge of the ewe: dose-response relationship and excess of GnRH

The preovulatory LH surge in the ewe is stimulated by a large sustained surge of GnRH. We have previously demonstrated that the duration of this GnRH signal exceeds that necessary to initiate and sustain the LH surge. The objective of the present study was to determine whether a similar excess exists for amplitude of the GnRH surge. Experiments were performed using an animal model in which GnRH secretion was blocked by progesterone, which in itself does not block the pituitary response to GnRH. To assess the amplitude of the GnRH surge needed to induce the LH surge, we introduced artificial GnRH surges of normal contour and duration but varying amplitudes. Twelve ewes were run through 3 successive artificial follicular phases (total of 36). Six of these artificial follicular phases were positive controls, in which progesterone was removed, the estradiol stimulus was provided, and vehicle was infused. In these control cycles, animals generated endogenous LH surges. In the remaining artificial follicular phases, progesterone was not withdrawn, the estradiol stimulus was provided, and either vehicle (negative control) or GnRH solutions of varying concentrations (experimental) were infused. The circulating GnRH concentrations achieved by infusion were monitored. No LH surges were observed in negative controls, whereas LH surges were induced in experimental cycles provided a sufficient dose of GnRH was infused. A highly significant dose-response relationship was observed between the amplitude of the GnRH surge and both the amplitude of the LH surge and the area under the curve describing the LH response, but no such relationship existed between the amplitude of the GnRH surge and the duration of the LH response. In numerous cases, LH surges similar to those in the positive control animals resulted from infusion of amounts of GnRH estimated to be considerably less than those delivered to the pituitary during the endogenously generated GnRH/LH surge. These findings indicate that, in the ewe, increased GnRH secretion drives the preovulatory LH surge in a dose-dependent fashion, and they provide evidence that the amplitude of the GnRH surge may exceed that needed to generate the LH surge.

What nature's knockout teaches us about GnRH activity: hypogonadal mice and neuronal grafts

The hypogonadal mouse is one of "nature's knockouts," bearing a specific deletion in the gene for gonadotropin-releasing hormone (GnRH), with the result that no GnRH peptide is detectable in the brain. The lack of reproductive development after birth provides an animal model that has proved fruitful in clarifying the role of GnRH in reproductive behavior and physiology. Behavioral studies with hypogonadal mice convincingly demonstrate that although GnRH may facilitate the appearance of sexual behavior, this peptide is not essential for either male or female sexual behavior in the mouse. Administration of GnRH to hypogonadal mice with regimens mimicking GnRH pulsatility initiates reproductive development. Surprisingly, continuous exposure to GnRH stimulates remarkable ovarian and uterine growth and increased FSH release, although pituitary content of LH and FSH remains unchanged. In contrast, when brain grafts of normal fetal preoptic area (POA), containing GnRH cells, are implanted in the third ventricle of adult hypogonadal mice, both pituitary and plasma gonadotropin levels increase. Grafted GnRH neurons innervate the median eminence of the host and support pulsatile LH secretion in the majority of animals with graft-associated gonadal development. Studies of hypogonadal mice with POA grafts demonstrate that distinct components of reproductive function are dissociable: hosts may demonstrate reflex but not spontaneous ovulation; others may show positive but not negative feedback. Activation of grafted GnRH cells in response to sensory input to the host, as revealed in Fos expression studies, is an example of the integration of the graft with the host brain that underlies such capabilities. A goal of these studies is to elucidate the specific connectivity underlying discrete aspects of reproductive function.

Hormonal and neurotransmitter regulation of GnRH gene expression and related reproductive behaviors

Gonadotropin-releasing hormone (GnRH), having a highly conserved structure across mammalian species, plays a pivotal role in the control of the neuroendocrine events and the inherent sexual behaviors essential for reproductive function. Recent advances in molecular genetic technology have contributed greatly to the investigation of several aspects of GnRH physiology, particularly steroid hormone and neurotransmitter regulation of GnRH gene expression. Behavioral studies have focused on the actions of GnRH in steroid-sensitive brain regions to understand better its role in the facilitation of mating behavior. To date, however, there are no published reports which directly correlate GnRH gene expression and reproductive behavior. The intent of this article is to review the current understanding of the way in which changes in GnRH gene expression, and modifications of GnRH neuronal activity, may ultimately influence reproductive behavior.

Distribution of chicken-II gonadotropin-releasing hormone in mammalian brain

Brains of nonmammalian vertebrates typically contain multiple forms of gonadotropin-releasing hormone (GnRH). Until recently, only the mammalian form of GnRH (mGnRH) had been isolated in placental mammals. Biochemical and histological data show that both mGnRH and chicken-II GnRH (cGnRH-II) are present in a primitive placental mammal, the musk shrew (Suncus murinus). Similar to the case in nonmammalian species, in the musk shrew, neurons that express cGnRH-II are located in a discrete cluster in the midbrain. We have used a combination of radioimmunoassay and immunocytochemistry, analyzed at the light level and with electron microscopy, to describe the distribution of cGnRH-II cell bodies and fibers in the musk shrew brain. All cGnRH-II-immunoreactive (ir) neurons reside in the midbrain, and this area contains the greatest concentration of cGnRH-II peptide in the brain. At the light and electron micrographic levels, we have identified synaptic terminals containing dense core vesicles that are immunoreactive for cGnRH-II in the medial habenula. Radioimmunoassay reveals that this region contains the second greatest concentration of cGnRH-II in the brain. Widely scattered cGnRH-II-ir fibers are present throughout the forebrain, particularly in the medial septum, hypothalamus, and midbrain central gray. Scant cGnRH-II fibers are present in the median eminence, arcuate nucleus, and infundibular stem, and only low concentrations of the peptide are detected in these areas. Finally, intravenous administration of mGnRH is ten times more effective than cGnRH-II in promoting ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by N-methyl-D-aspartic acid (NMDA) receptor antagonist of lordosis behavior induced by estrogen followed by progesterone or luteinizing hormone-releasing hormone (LHRH) in the rat

The effects of glutamate receptor antagonists on sexual receptivity induced by progesterone and LHRH were examined in ovariectomized, estradiol-primed rats (OVX-EB). Enhancement of lordosis/mounts quotient (L/M) by progesterone (0.5 mg) or LH-RH (150 ng; third ventricle, IVT) in OVX-EB rats was significantly decreased by IVT injection of (+) 2-amino-7-phosphonoheptanoic acid a competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist. On the contrary, there were no changes in L/M quotient after IVT injection of 6,7-dinitroquinoxaline-2,3,dione at two dose levels, a Non-NMDA receptor antagonist. The NMDA antagonist did not modify lordosis behavior in OVX-EB rats. The results indicate that the NMDA type of glutamate receptors appears to mediate progesterone and LHRH facilitatory actions and suggest that glutamatergic synapses may be involved in lordosis-facilitating neural mechanisms.

Electrophysiological identification of a pathway from the septal area to the medial amygdala: sensitivity to estrogen and luteinizing hormone-releasing hormone

Medial amygdala neurons responsive to electrical stimulation of the medial septal area were electrophysiologically identified in ovariectomized, urethane-anesthetized female rats. Peristimulus time histograms were collected and used to define the orthodromic response. The action of iontophoretically applied luteinizing hormone-releasing hormone (LHRH) and an LHRH fragment, Ac-LHRH5-10, on the activity of orthodromically responsive neurons was tested. Of a total of 187 neurons recorded, 119 were identified as orthodromically responsive. Three types of orthodromic responses were observed: excitatory, inhibitory, and complex. Priming the animals with 5 micrograms estradiol benzoate (EB) 48 hr prior to recording had no effect on the overall number of neurons responding to septal area stimulation, but EB priming did significantly reduce the percentage of orthodromically excited neurons. The firing rate of the majority of amygdala neurons responsive to septal area stimulation was not affected by iontophoretically applied LHRH (59 of 76) or LHRH fragment (41 of 65). In some cases, application of LHRH (10 of 76) or Ac-LHRH5-10 (12 of 55) produced a change in neuronal firing that was similar in direction to the orthodromically evoked response. When applied during the collection of peristimulus time histograms, both peptides were also able to modulate the orthodromically evoked response (five of 18 cells tested with LHRH and three of 14 cells tested with Ac-LHRH5-10). The results demonstrate a large projection from the septal area to the amygdala, one component of which is altered by estrogen priming.(ABSTRACT TRUNCATED AT 250 WORDS)

Lordosis facilitation in estrogen primed rats by intrabrain injection of pregnanes

Progesterone (P) and nine of its natural metabolites were bilaterally injected (5 micrograms in 0.5 microliter oil) into either the ventromedial hypothalamus (VMH) or the medial preoptic area (MPOA) of estrogen primed rats to assess their relative potencies for stimulating lordosis. P, 5 alpha-pregnanedione and 5 beta, 3 beta-pregnanolone elicited lordosis when injected at either VMH or MPOA. By contrast, 5 alpha, 3 beta-pregnanolone as well as 20 alpha-OH and 20 beta-OH-pregnenone were much more effective in stimulating lordosis when implanted in the MPOA. Finally, 5 beta-pregnanedione and 5 beta,3 alpha-pregnanolone did not stimulate lordosis at neither VMH nor MPOA. The observation that lordosis was induced in estrogen primed rats both by pregnanes that bind to the P receptor (i.e., P; 5 alpha-pregnanedione; 20 alpha- and 20 beta-OH-pregnenone) and by pregnanes that do not (i.e., 5 alpha, 3 beta-; 5 beta,3 beta- and 5 alpha,3 alpha-pregnanolone) indicates that diverse cellular mechanisms are involved in the facilitation of lordosis by pregnanes.

Electrophysiological test of an amphiphilic beta-structure in LHRH action

Micropipettes were used to record electrical activity from single neurons in hypothalamic tissue slices, in the hypothalamic arcuate nucleus (ARC), and in the periventricular and suprachiasmatic preoptic nuclei (POA). Responses were measured following in vitro application of luteinizing hormone releasing hormone (LHRH), and two analogues: LHRH models 1 and 3. Model 1 (pyroGlu-His-Trp-Ser-Phe-Thr-Ile-Lys-Ile-ThrNH2) had amino acid substitutions in residues 5-10 designed to form an amphiphilic beta-strand structure. Model 3 (pyroGlu-His-Trp-Ser-Phe-Gly-Ile-Lys-Pro-SerNH2) was also designed to possess amphiphilic characteristics, but also more closely to resemble the native peptide. Electrical recording results showed that LHRH was able both to excite or inhibit different hypothalamic neurons, and that it was more effective in the preoptic area than in the arcuate nucleus. Responses to LHRH model 3 were strongly correlated with responses to LHRH, in their occurrence and their direction, for both of the brain regions studied. Moreover, LHRH models 1 and 3 also retained the neuromodulatory effects of LHRH on cellular responses to norepinephrine and serotonin. Thus, LHRH analogues, designed to possess an amphiphilic beta-structure, preserved some of the properties of LHRH when tested electrophysiologically in the central nervous system.

The amygdala and male reproductive functions: I. Anatomical and endocrine bases

The present review is mainly concerned with the role of the amygdala (AMY) in male sexual behaviour and presents the characteristics of neuroanatomical and neuroendocrine organization of the cortico-medial amygdala as compared to the medial preoptic area (MPOA), in relation to sexual behaviour and gonadotropin secretion. It stresses the part played by AMY in processing sensory information which afterwards reaches the hypothalamus (HYP). Some data on the different function of steroids and luteinizing hormone releasing hormone (LHRH) systems within AMY and MPOA are provided. The role of AMY in the positive feedback effect on luteinizing hormone (LH) secretion and the involvement of steroid and opiate interaction as its mechanism are suggested. AMY is proposed to integrate external and internal sensory information granting the optimal conditions for sexual performance and possibly for regulation of LH release according to the behavioural context. The steroid content of AMY may influence these processes.

Central nervous system effects of peptides, 1980-1985: a cross-listing of peptides and their central actions from the first six years of the journal Peptides

A tabular synopsis is presented for articles concerned with the effects of peptides on the central nervous system that appeared in the journal Peptides from 1980-1985. A table arranged alphabetically by peptide and one arranged by effects, both listing routes of injection, species, direction of change, and qualifying notes, provides easy cross-referencing of peptides and their effects. Over 80 peptides and over 135 effects are listed. The list of peptides includes, but is not limited to: ACTH, angiotensin, bombesin, bradykinin, calcitonin, casomorphin, CCK, ceruletide, CGRP, CRF, dermorphin, DSIP, dynorphin, endorphins, enkephalins, GRF, gastrin, LHRH, litorin, metkephamid, MIF-l, motilin, MSH, NPY, NT, oxytocin, ranatensin, sauvagine, substances P and K, somatostatin, TRH, VIP, vasopressin, and vasotocin. The list of effects includes, but is not limited to: aggression, alcohol, analgesia, attention, avoidance, behavior, cardiovascular regulation, catalepsy, conditioned behavior, convulsions, dopamine binding and metabolism, discrimination, drinking, EEG, exploration, feeding, fever, gastric secretion, GI motility, grooming, learning, locomotor behavior, mating, memory, neuronal activity, open field, operant behavior, rearing, respiration, satiety, scratching, seizure, sleep, stereotypy, temperature, thermoregulation and tolerance.

Sexual behavior in the female rat following removal of the vomeronasal organ

We used female Wistar rats from which the vomeronasal organ (VNO) has been removed. The first question addressed was whether such females would show deficits in sexual behavior. The data left no doubt that removal of the VNO severely depressed lordosis as well as such proceptive behaviors as "darting" and "hopping." We then injected estrogen and progesterone and, in still another experiment, estrogen and luteinizing hormone-releasing hormone (LHRH). Estrogen and progesterone significantly enhanced lordosis, but only estrogen and LHRH raised the lordosis quotient of VNO-ablated females to that of the control females. We discuss the results in terms of a theoretical model involving the complementary action of estrogen and LHRH in inducing lordosis in the intact female.

Hyperprolactinemia: its electrophysiologic and pharmacologic effect on neurons of the ventromedial nucleus of the hypothalamus

Extracellular action potentials were recorded from 691 neurons in the ventromedial hypothalamus (VMH) of urethane anesthetized female rats under acute and chronic sham-operated and hyperprolactinemic conditions. Hyperprolactinemia was produced by transplanting pituitaries under the kidney capsules. Neuronal excitability was recorded and analyzed during spontaneous, baseline activity and following the iontophoretic application of prolactin, dopamine (DA) and luteinizing hormone-releasing hormone (LH-RH). No statistically significant changes were observed in the spontaneous electrical activity of VMH neurons under the conditions tested. Of the responsive neurons, approximately 90% of the neurons recorded and tested with prolactin displayed an increase in firing activity while DA produced a decrease, independent of the endogenous plasma prolactin levels (basal or elevated). However, the response to LH-RH was modified in the chronic hyperprolactinemic animal. The predominant response of VMH neurons to LH-RH in acute sham-operated and hyperprolactinemic as well as in chronic sham-operated animals was one of inhibition, while in the chronic hyperprolactinemic animal, the application of LH-RH initiated excitation rather than inhibition. These results provide evidence that chronic (long-term) exposure to elevated prolactin levels is a sufficient stimulus to modify the neuronal response pattern of VMH nerve cells to iontophoretically applied LH-RH but not to prolactin nor to DA.

Intrahypothalamic infusions of a synthetic heroin substitute, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, potentiate mating behaviour in the female rat

Acute microinfusions of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) bilaterally into the arcuate-ventromedial area of the hypothalamus (ARC-VMH) produced a dose-dependent facilitation of lordosis behaviour in oestrogen- and oestrogen-progesterone-treated ovariectomized female rats. This facilitation could be blocked by pretreatment of the ARC-VMH site with pargyline but not by a potent antagonist analogue of gonadotropin releasing hormone (GnRH). MPTP was not effective in potentiating lordosis when microinfused into other brain sites which are intimately involved in the neural circuitry for this oestrogen-dependent behavioural response. This action of MPTP in the ARC-VMH may be dependent upon the high MPTP receptor densities which are known to occur in the arcuate and periventricular hypothalamic nuclei. Chronic infusions of MPTP (once daily for 21 days) into the ARC-VMH did not result in any significant cell loss and did not interfere with the ability of a later acute MPTP infusion to potentiate lordosis nor with the ability of oestrogen and progesterone to promote the full display of lordosis behaviour. These results provide the first demonstration of neurally placed MPTP in the regulation of a specific hormone-dependent neuroendocrine response.

Luteinizing hormone-releasing hormone facilitates the display of sexual behavior in male voles (Microtus canicaudus)

To investigate whether luteinizing hormone-releasing hormone (LHRH) influences the sexual behavior of male gray-tailed voles (Microtus canicaudus), subcutaneous injections of LHRH (500 ng) were given to intact males and to castrated males with different levels of testosterone replacement. Intact voles, as well as castrated voles with Silastic capsules of testosterone propionate, showed significant facilitation of several parameters of masculine sexual behavior 2 hr after LHRH injection, compared to saline controls. Castrated voles without testosterone replacement showed no sexual behavior, even when injected with LHRH. These results support the hypothesis that LHRH regulates sexual behavior in M. canicaudus and that the behavioral response to LHRH is dependent on testosterone. The specific behavioral parameters affected suggest that LHRH changes the arousal component of masculine behavior in voles.

Effect of luteinizing hormone-releasing hormone antiserum on sexual behavior in the female rat

Various components of sexual receptivity were measured in ovariectomized, estrone-primed female rats following direct placement of luteinizing hormone releasing hormone (LH-RH) or a LH-RH antiserum into the medial preoptic area. Two hours after treatment with LH-RH antiserum, rats showed a significant increase in lordosis behavior indicative of increased sexual receptivity. When tested 3 and 7 hours after treatment, both LH-RH antiserum and LH-RH-treated rats displayed increased lordosis behavior. Similar treatment with a specific peripheral LH-RH agonist and antagonist had no effect on sexual behavior. Proceptive behavior was absent or minimal in all groups and therefore was not affected by the different treatments. Similarly, there was no difference in the rejection quotients of the females representing the various treatment groups. These results demonstrate that the same behavioral response can be observed in animals treated centrally with LH-RH and a highly specific LH-RH antiserum. Similar treatments with a specific peripheral LH-RH agonist or antagonist were without effect. These results suggest that the characteristics of LH-RH recognition sites in the brain are different from those in the pituitary.

GnRH in the spinal subarachnoid space potentiates lordosis behavior in the female rat

Gonadotropin releasing hormone (GnRH) (100 ng) infused directly into the spinal subarachnoid space via a chronically implanted catheter, induced a prompt facilitation of lordosis behavior in estrogen-primed ovariectomized female rats. Facilitation occurred within 5 min and lasted for 3 1/2 hr. This effect of GnRH could be blocked by a GnRH antagonist analog, [D-Phe2, Pro3, D-Phe6] GnRH (250 ng) which also completely abolished lordosis within 2 1/2 hr. The antagonist analog (250 ng) but not a high titre specific anti-GnRH antiserum (enough to neutralize 24 micrograms of GnRH) abolished lordosis when infused alone in the subarachnoid space in estrogen-primed rats. The antagonist but not the anti-GnRH antiserum also significantly suppressed lordosis in estrogen-progesterone primed female rats. Supporting experiments showed that the effects of GnRH and its antagonist may not be due to their effects on supraspinal structures by diffusion from the spinal subarachnoid space. These results may indicate a direct effect of GnRH and its antagonist at the level of the spinal cord and may suggest a possible role for GnRH in the processing of somatosensory information necessary for the trigger of lordosis.