Sertoli cell maturation is impaired by neonatal passive immunization with antiserum to luteinizing hormone-releasing hormone

New Horizons: Gonadotropin-Releasing Hormone and Cognition

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for activating and maintaining the function of the hypothalamic-pituitary-gonadal axis, which controls the onset of puberty and fertility. Two recent studies suggest that, in addition to controlling reproduction, the neurons in the brain that produce GnRH are also involved in the control of postnatal brain maturation, odor discrimination, and adult cognition. This review will summarize the development and establishment of the GnRH system, with particular attention to the importance of its first postnatal activation, a phenomenon known as minipuberty, for later reproductive and nonreproductive functions. In addition, we will discuss the beneficial effects of restoring physiological (ie, pulsatile) GnRH levels on olfactory and cognitive alterations in preclinical Down syndrome and Alzheimer disease models, as well as the potential risks associated with long-term continuous (ie, nonphysiological) GnRH administration in certain disorders. Finally, this review addresses the intriguing possibility that pulsatile GnRH therapy may hold therapeutic potential for the management of some neurodevelopmental cognitive disorders and pathological aging in elderly people.

A role for GnRH in olfaction and cognition: Implications for veterinary medicine

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for the activation and maintenance of the function of the hypothalamic-pituitary-gonadal (HPG) axis, which controls the onset of puberty and fertility. Two provocative recent studies suggest that, in addition to control reproduction, the neurons in the brain that produce GnRH are also involved in the control postnatal brain maturation, odour discrimination and adult cognition. Long-acting GnRH antagonists and agonists are commonly used to control fertility and behaviour in veterinary medicine, primarily in males. This review puts into perspective the potential risks of these androgen deprivation therapies and immunization on olfactory and cognitive performances and well-aging in domestic animals, including pets. We will also discuss the results reporting beneficial effects of pharmacological interventions restoring physiological GnRH levels on olfactory and cognitive alterations in preclinical models of Alzheimer's disease, which shares many pathophysiological and behavioural hallmarks with canine cognitive dysfunction. These novel findings raise the intriguing possibility that pulsatile GnRH therapy holds therapeutic potential for the management of this behavioural syndrome affecting older dogs.

Immunization of dogs with recombinant GnRH-1 suppresses the development of reproductive function

This study was designed to evaluate the effect of active immunization using recombinant GnRH-I protein on reproductive function in dogs. Six male and six female dogs were randomly assigned to either a control group or an immunization group (n = 3 males or 3 females/group). Dogs (aged 16 weeks) were immunized against GnRH-I with a maltose-binding protein-gonadotropin-releasing hormone I hexamer generated by recombinant DNA technology. Blood samples were taken at 4-week intervals after immunization. The serum concentrations of testosterone and estradiol and anti-GnRH-I antibodies were determined by RIA and ELISA, respectively. The results showed that active immunization with recombinant GnRH-I increased the serum levels of anti-GnRH antibodies (P < 0.05) and reduced the serum concentrations of testosterone (P < 0.05) and estradiol (P < 0.05) as compared with the controls. At 28 weeks of age, testes and ovaries were taken surgically for morphologic evaluation. Histologic studies performed on testicular and ovarian tissues revealed clear signs of atrophy in the recombinant GnRH-I-immunized dogs and a significant reduction (P < 0.05) in the weights and sizes of paired testes and ovaries in the treated dogs. Microscopically, spermatogonia were visible, but no spermatids and spermatozoa were detected in the seminiferous tubules. Neither early antral nor antral follicles were found in the immunized group. These results demonstrate that recombinant GnRH-I is an effective immunogen in dogs.

Passive transfer of maternal GnRH antibodies does not affect reproductive development in elk (Cervus elaphus nelsoni) calves

Gonadotropin-releasing hormone is intermittently released from the hypothalamus in consistent patterns from before birth to final maturation of the hypothalamic-pituitary-gonadal axis at puberty. Disruption of this signaling via GnRH vaccination during the neonatal period can alter reproduction at maturity. The objective of this study was to investigate the long-term effects of GnRH-antibody exposure on reproductive maturation and function in elk calves passively exposed to high concentrations of GnRH antibodies immediately after birth. Fifteen elk calves (eight males and seven females) born to females treated with GnRH vaccine or sham vaccine during midgestation were divided into two groups based on the concentration of serum GnRH antibodies measured during the neonatal period. Those with robust (>15 pmol (125)I-GnRH bound per mL of serum) titers (N = 10; four females and six males) were designated as the exposed group, whereas those with undetectable titers (N = 5; three females and two males) were the unexposed group. Onset of puberty, reproductive development, and endocrine function in antibody-exposed and unexposed male and female elk calves were compared. Neonatal exposure to high concentrations of GnRH antibodies had no effect on body weight (P = 0.968), endocrine profiles (P > 0.05), or gametogenesis in either sex. Likewise, there were no differences between groups in gross or histologic structure of the hypothalamus, pituitary, testes, or ovaries. Pituitary stimulation with a GnRH analog before the second potential reproductive season induced substantial LH secretion in all experimental elk. All females became pregnant during their second reproductive season and all males exhibited similar mature secondary sexual characteristics. There were no differences between exposure groups in hypothalamic GnRH content (P = 0.979), pituitary gonadotropin content (P > 0.05) or gonadal structure. We concluded that suppressing GnRH signaling through immunoneutralization during the neonatal period likely does not alter long-term reproductive function in this species.

Assessment of the immunological and biological efficacy of two different doses of a recombinant GnRH vaccine in domestic male and female cats (Felis catus)

This study has assessed the immunological and biological efficacy of two different doses of a recombinant GnRH vaccine administered to intact domestic cats. Fifteen kittens, 8-9 weeks of age, were allocated to three unequal treatment groups: group 1, 1 male control cat; group 2, 5 females administered 10 microg of GnRH antigen; and group 3, 4 males and 5 females administered 100 microg of GnRH antigen. Animals in groups 2 and 3 were immunized at study days 0, 28 and 643. One of the four males (AJZ3) in the high dose group showed a more rapid decline in GnRH antibody titers and received an additional immunization at day 461. Blood samples were collected on study days 28, 35, 56, 97, 157, 213, 270, 325, 377, 433, 496, 549, 605, and 685. The injection sites were monitored for tissue reactivity on study days 5, 7, 12, and 28. The animals' general health and demeanor was monitored on a daily basis. Sera obtained from 11 animals on day 549 were submitted for biochemistry analysis. Two males and two females were necropsied at the completion of the study and histopathological examination of the gonads, hypothalamus, pituitary, kidneys and uterus was performed. All 14 immunized animals developed immunoneutralizing titers to GnRH. GnRH titers peaked at day 56 and 13 of 14 cats maintained these titers for >20 months. Except for AJZ3, the immunized males' serum testosterone concentrations were below the assay's level of detection after the second immunization. None of the 10 immunized females showed signs of estrous behavior or became pregnant. Testicular and ovarian histology was consistent with suppression of LH and FSH activity. The majority of tissue reactions resolved by 28 days post-vaccination. Serum biochemistry and tissue histopathology revealed no evidence of tissue or organ damage. This study was unique in that a recombinant GnRH antigen was used to stimulate and maintain biologically relevant titers in very young male and female cats for at least 20 months.

Serum and testicular testosterone and androgen binding protein profiles following subchronic treatment with carbendazim

While the general toxicity of the benzimidazole pesticides for mammals is low, one of these compounds, carbendazim (MBC), causes degeneration of testicular tissue and decreases spermatogenic activity at doses well below the LD50 value. A study conducted by S. D. Carter, R. A. Hess, and J. W. Laskey (1987, Biol. Reprod. 37, 709-717) showed that treatment with 400 mg/kg/day MBC resulted in severe seminiferous tubular atrophy and infertility. Since spermatogenesis is an androgen-dependent process, we characterized the effects of MBC (0-400 mg/kg/day) on the endocrine function of the rat testes. Following subchronic (85 day) exposure, serum hormones (TSH, LH, FSH, and Prl) were measured as were androgen binding protein (ABP) and testosterone in testicular fluids (interstitial fluid and seminiferous tubule fluid). In addition, the functional capacity of the Leydig cell to secrete testosterone was assessed in vitro following an hCG challenge. Subchronic treatment with MBC at doses of 50-100 mg/kg/day had no effect on pituitary or testicular hormone concentrations: 200 mg/kg/day elevated the testosterone concentration in the seminiferous tubule fluid and the ABP concentration in both the interstitial fluid and the seminiferous tubule fluid without affecting serum testosterone or ABP concentrations. The 400 mg/kg/day dose resulted in increased concentration of both testosterone and ABP in the interstitial fluid and seminiferous tubule fluid and elevated serum ABP, with no change in serum testosterone. This endocrine profile is consistent with the testicular atrophy and "Sertoli cell-only" syndrome seen in these animals as reported by Gray et al. (1987, Toxicologist 7, 717). We conclude that seminiferous tubule fluid testosterone may be a result of two factors: (1) increased interstitial fluid testosterone concentrations and (2) decreased testosterone outflow from the testis to the general circulation. Also, increased ABP in the interstitial fluid may reflect a change in the relative secretion of ABP into the interstitial fluid and the seminiferous tubules.

Presence of immunoreactive beta-endorphin and calcitonin in human seminal plasma, and their relation to sperm physiology

Opioid peptides and calcitonin are found in high concentrations in the male reproductive tract. To further elucidate their role in sperm physiology, we studied semen samples from 49 infertile men and 25 men with proven fertility. beta-endorphin and calcitonin were measured in each sample by radioimmunoassay and then were correlated with seminal plasma testosterone (T) and dihydrotestosterone levels as well as sperm count, total motile sperm/milliliter, and percentage of penetrated hamster eggs. The levels of beta-endorphin (308 +/- 22 pg/ml) and calcitonin (331 +/- 32 pg/ml) in seminal plasma were 10 and 20 times higher than levels found in venous plasma (32 +/- 2 and 14.5 +/- 1.2 pg/ml, respectively) (P less than 0.001). There was no difference between the levels of beta-endorphin and calcitonin in seminal plasma of fertile and infertile men. However, seminal plasma T was significantly higher in fertile than infertile men (19.4 +/- 2 versus 11.5 +/- 1 ng/dl; P less than 0.05). No correlation could be demonstrated between either beta-endorphin or calcitonin and any of the parameters studied. In conclusion, beta-endorphin and calcitonin are produced locally in the male reproductive tract; however, their role in male reproduction remains to be elucidated.

Changes in testicular and serum hormone concentrations in the male rat following treatment with m-dinitrobenzene

m-Dinitrobenzene (m-DNB)-induced testicular atrophy has been attributed to a direct effect upon the germinal epithelium. However, such degenerative changes in the germinal epithelium should induce shifts in the testicular hormonal milieu, which would in turn alter the hypothalamic-pituitary gonadal axis in general. This study evaluated the endocrine status of male rats (killed 3 hr, 24 hr, 1 week, and 2 weeks) following a single oral dose of m-DNB (32 mg m-DNB/kg). Serum and pituitary leuteinizing hormone, follicle-stimulating hormone (FSH), and protactin and hypothalamic gonadotropin-releasing hormone (GnRH) concentrations were determined. Testosterone and androgen-binding protein concentrations in serum, interstitial fluid, seminiferous tubule fluid, and caput epididymis were also determined. In vitro basal and hCG-stimulated testosterone release was determined in the decapsulated testis. Results of the present study indicate that pituitary hormone concentrations and hypothalamic GnRH were unaffected after a single oral dose of m-DNB. Serum FSH was elevated at 2 weeks. There was a transient decrease in serum testosterone at 24 hr, which returned to control values at 1 and 2 weeks. Interstitial fluid, seminiferous tubule fluid, and caput epididymal testosterone concentrations were increased at 1 and 2 weeks. Basal testosterone release in vitro was increased at 2 weeks, while hCG-stimulated testosterone release was increased at 1 and 2 weeks. Androgen-binding protein concentrations in serum and interstitial fluid were increased at 1 and 2 weeks. Androgen-binding protein was increased at 24 hr and 1 week in seminiferous tubule fluid, but returned to control concentrations by 2 weeks. However, the total tubular content of androgen-binding protein was dramatically decreased at 2 weeks. Androgen-binding protein in the caput epididymis was unaltered following m-DNB treatment. These data demonstrate that m-DNB exerts a direct effect on the testes and not through alterations in hypothalamic and pituitary control of gonadal function.

Changes in the secretion of ABP into testicular interstitial fluid with age and in situations of impaired spermatogenesis

Androgen-binding protein (ABP) was measured in serum and testicular interstitial fluid (IF) from rats during sexual maturation or in adult rats in which impairment of spermatogenesis had been induced by (i) testosterone withdrawal following Leydig cell destruction, (ii) local heating (43 degrees C) of the testes for 30 min or (iii) induction of unilateral cryptorchidism (UCD). The changes observed were related to the IF levels of testosterone and, in most instances, to the serum levels of FSH. The levels of ABP in serum and IF decreased together with age, being highest at 30 days, falling steeply by 40 days and then slowly but progressively up to 100 days of age. A similar pattern was observed for serum FSH, except that the initial fall occurred beyond 40 days of age. Treatment with EDS or exposure to local heating caused comparable reductions in testicular weight (25-30% by 7 days after treatment, 50% by 21-28 days) and raised the serum levels of FSH. In both groups the levels of ABP in IF were increased by two- to three-fold while the levels of testosterone were either reduced markedly (EDS-treatment) or remained unchanged (local heating). In rats made UCD for 60 days, the weight of the abdominal testis was reduced by 75%, compared with the contralateral scrotal testis, while the IF levels of ABP and testosterone were significantly increased (55%) and decreased (90%), respectively. Short-term (3 days) deprivation of testosterone in adult rats, following immunoneutralization of LH, was without significant effect on IF levels of ABP. It is concluded that ABP secretion into IF is increased in situations of subnormal (or sub-adult) numbers of germ cells and this is usually associated with high levels of FSH. Measurement of ABP levels in IF should prove of value for the monitoring of Sertoli cell function in vivo and may be of diagnostic use for the detection of changes in germ cell numbers.

Passive immunization of fetal rats with antiserum to luteinizing hormone-releasing hormone (LHRH) or transection of the central roots of the nervus terminalis does not affect rat pups' preference for home nest

Luteinizing hormone-releasing hormone (LHRH) is found immunocytochemically in cell bodies and fibers of the nervus terminalis, a cranial nerve which courses from the nasal septum through the cribriform plate of the ethmoid bone (medial to the olfactory and vomeronasal nerves) and enters the forebrain, caudal to the olfactory bulbs. Immunoreactive LHRH is first detected in the nervus terminalis of the fetal rat at 15 days of gestation, preceding its detection by immunocytochemistry in any other area of the brain, including the median eminence, and preceding detection of immunoreactive luteinizing hormone (LH) in the anterior pituitary. During development of the rat fetus, the nervus terminalis is the principal source of LHRH in the nervous system from days 15 through 19 of a 21 day gestation period. We tested the notion that the LHRH system of the nervus terminalis is important for olfactory performance by examining the effects of administration of antisera to LHRH during fetal development (versus saline controls), or medial olfactory peduncle transections, in the neonatal rat, which would sever the central projections of the nervus terminalis (versus lateral peduncle transection, complete transection of the olfactory peduncles and the central nervus terminalis or controls) on preferences of rat pups for home nest. The hypothesis that LHRH is important for this chemosensory response was not confirmed. Neither antisera to LHRH nor medical olfactory peduncle transection disrupted preference for home shavings. Only complete olfactory peduncle transection had a significant effect compared to unoperated and sham-operated controls.

Concentrations of free testosterone, total testosterone, and androgen binding protein in the peripheral serum of male rats during sexual maturation

To investigate the relationship between free testosterone and sexual maturation in the male rat, animals were decapitated every 5 days from 25 through 75 days of life. Serum was assayed for androgen binding protein and total testosterone by radioimmunoassay. Free testosterone concentrations were calculated from the total testosterone concentration and the free testosterone fraction. The free testosterone fraction was determined by ultrafiltration. The pubertal increase in relative prostate and relative seminal vesicle weights began between 45 and 50 days and 40 and 45 days, respectively. Although the over-all trend in the free testosterone fraction was to increase with increasing age (r = 0.46, P less than 0.0001), there was a significant secondary peak at 50 days. The serum concentration of androgen binding protein was highest on day 25, fell rapidly until day 40, and declined slowly thereafter. Despite these variations in both androgen binding protein and the free testosterone fraction during sexual maturation, the calculated serum concentration of free testosterone was remarkably similar in pattern to that of total testosterone (r = 0.99, P less than 0.0001). These data indicate that the serum concentration of total testosterone is an accurate reflection of the serum concentration of free testosterone during the sexual maturation of the male rat.

The effects of the indazole carboxylic acid derivative, tolnidamine, on testicular function: I. Early changes in androgen binding protein secretion in the rat

The indazole carboxylic acid derivative, tolnidamine, has marked antispermatogenic activity in several animal species. In this study, we assessed the effect of tolnidamine on rat Sertoli cell function both in vivo and in vitro, using androgen binding protein (rABP) as a marker. Groups of six male rats were killed 2, 4, 8, 16, 32, 64 hours and 5, 8, and 12 days following tolnidamine administration (250 mg/kg by oral gavage). There was a progressive reduction in both testicular and epididymal weights. Serum FSH levels did not change and LH showed a transient increase between 64 hours and 8 days. Except for an initial increase at 2 hours, there were no changes in serum testosterone. Epididymal rABP concentration and content declined as early as 8 hours, with the lowest values occurring at 5 and 12 days. By 16 hours, there was an increase in testicular rABP, which was also evident at 8 days and 12 days. Within 16 hours after tolnidamine, there was a rise in serum rABP, which persisted until the end of the experiment. When another indazole carboxylic acid derivative, lonidamine, was administered (250 mg/kg), similar changes were evident in epididymal and serum rABP at 32 hours, but the rapid decrease in testicular rABP suggested a different mechanism of action. In another experiment, single oral doses of tolnidamine (50, 100, 250, and 500 mg/kg) were administered to other groups of rats and the animals were killed after 24 hours and 5 days. With increasing doses of tolnidamine, there was a reduction in epididymal rABP concomitant with an increase in testis and serum rABP levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and possible function of pro-opiomelanocortin-derived peptides in the testis

Using antibodies against peptides derived from different portions of the POMC molecule, immunocytochemical evidence suggests that this precursor and/or the peptides present within it are localized in testicular Leydig cells of at least five species. There is no evidence for the localization of these peptides or their precursor in any other cell type in this organ. Examination of testicular extracts by gel filtration, SDS-PAGE, and RP-HPLC indicate that the testis contains low concentrations of POMC-derived peptides relative to brain. Further analysis indicates that POMC is processed to alpha-MSH and beta-endorphin similar to its processing in intermediate pituitary lobe and brain. The relative mobilities of immunoreactive alpha-MSH and beta-endorphin on RP-HPLC columns indicate that they are in the unacetylated state as in brain and in contrast to the acetylated forms in the intermediate pituitary lobe. The potential for Leydig cells to synthesize POMC and its peptides was suggested by the demonstration of POMC-like mRNA in total testis and Leydig cell cultures. The size of the POMC-like mRNA is approximately 150 base pairs shorter than anterior or intermediate pituitary POMC mRNA. POMC-like mRNA activity has also been localized to Leydig cells in sections of testes using in situ hybridization. Immunostainable beta-endorphin and other POMC-derived peptides are present in testicular Leydig cells during fetal life and following puberty at times when testosterone secretion is maximal. The accumulation of immunostainable POMC-derived peptides in Leydig cells is dramatically increased by LH and hCG. A variety of observations suggests that testicular cells can respond to POMC-derived peptides. ACTH and the MSHs stimulate growth and cAMP accumulation in Sertoli cells. By contrast, studies using antagonists suggested that beta-endorphin and/or another testicular opioid inhibit Sertoli cell proliferation and ABP secretion. These observations are consistent with the postulate that different portions of the POMC molecule may have opposite effects on Sertoli cell function and suggest a mechanism by which Leydig cells could modulate Sertoli cell activity. Intratesticular administration of opiate antagonists inhibits testosterone secretion both in vivo and in vitro. These observations suggest that Leydig cell-derived beta-endorphin may facilitate testosterone secretion either directly or indirectly. The finding of POMC and its derivative peptides in testis, ovary, adrenal, and placenta suggests that all steroid hormone-secreting organs in mammals may utilize this peptidergic system.

Pituitary-testicular function in immature rats after treatment with GnRH antagonist, GnRH antiserum and bromocriptine

The effects of a GnRH antagonist analogue (N-acetyl-Ala1,D-p-Cl-Phe2,D-Trp3,6-GnRH, Ant.) and a GnRH antiserum (A/S) on the development of pituitary-testicular function were studied in immature (23/24-31/32-day-old) rats. In another experiment the Ant. treatment was combined with bromocriptine (BR)-induced hypoprolactinaemia. Ant. and A/S decreased serum and pituitary levels of LH and FSH, and BR those of Prl (P less than 0.01-0.05). Testicular testosterone (T) and progesterone (P) contents were significantly decreased only by Ant. (P less than 0.01). Ant. decreased the weights of the testes, ventral prostates and seminal vesicles, as well as testicular LH, FSH and Prl receptors (R) (P less than 0.01-0.05). BR decreased LH-R but had no effect on Prl-R. Both Ant. and A/S decreased available pituitary GnRH-R (P less than 0.01), but free testicular GnRH-R were reduced only by Ant. BR increased GnRH receptors in the pituitaries. It is concluded that Ant.-induced low gonadotropin levels in immature animals inhibit the developmental increase of testicular weight, gonadotropin and Prl-R, steroidogenesis and androgen action on accessory sex glands. Hypoprolactinaemia had an additive inhibitory effect to the antigonadal effects of Ant. The testis tissue of immature (23/24-day-old) animals already contains GnRH-R. In general, developing animals are clearly very sensitive to the antigonadal actions of Ant. and BR, whereas the effect of GnRH-A/S is less pronounced than in adults.