Variations in serum androgens, estrogens, progestins, gonadotropins and prolactin levels in male rats from prepubertal to advanced age

Age-related changes in endogenous glucocorticoids, gonadal steroids, endocannabinoids and their ratios in plasma and hair from the male C57BL/6 mice

Age-related level changes of hormones, endocannabinoids and their ratios are of pathophysiological significance for understanding functions, activities and interactions of the endocrine systems, including the hypothalamic-pituitaryadrenal (HPA), hypothalamic-pituitary-gonadal (HPG) axes and endogenous cannabinoid system (ECS). The present study aimed to investigate the age-dependent fluctuations of glucocorticoids, gonadal steroids, endocannabinoids and their ratios from 21 days to 10 months in both plasma and hair from the male C57BL/6 mice. A novel framework based on the liquid chromatography-tandem mass spectrometry was developed to simultaneously determine ten hormones and two endocannabinoids in plasma and hair. Results showed that glucocorticoids, corticosterone (CORT), aldosterone (ALD), 11-dehydrocorticosterone (11-DHC), gonadal steroids, progesterone (P), dehydroepiandrosterone (DHEA), testosterone (T) and dihydrotestosterone (DHT) in plasma were unimodally fluctuated (ps < 0.001) along age with the maximum value at 2.7-month-old. In contrast, the other two gonadal steroids, estrone (E1) and estradiol (E2) were declined with age (ps < 0.001). Differently, endocannabinoids, N-arachidonoyl-ethanolamine (AEA) and 1-arachydonoyl glycerol (1-AG) showed nadir and zenith values at 2.7-month-old and 3.4-month-old, respectively (ps < 0.001). Additionally, the ratios of CORT to 11-DHC and ALD in plasma were dropped similarly with age (ps < 0.001). The ratios of 1-AG to AEA, and of T to A4 and DHT, and of DHEA to A4 were unimodally changed (ps < 0.001) along age with maximum value at 2.7- or 3.4-month-old. In contrast, the ratios of E2 to T and E1 to A4 were decreased with age (ps < 0.05). The rest six ratios that reflected the interactions among the three endocrine systems, were similar age-dependent and showed nadir and zenith values at 2.7-month-old and 3.4-month-old, respectively (ps < 0.05). Most importantly, these findings in light of age-related changing patterns in plasma were repeated in hair, suggesting that the fi41-ndings in the two matrices were mutually validated. However, it was worth noting that their magnitude of levels in the two bio-matrices were markedly different. The current findings could provide reliable hormone and endocannabinoid signatures with age on neuroendocrine profiles as well as their ratios for the male C57BL/6 mice.

Androgens modulate chronic intermittent hypoxia effects on brain and behavior

Sleep apnea is associated with testosterone dysregulation as well as increased risk of developing neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). A rodent model of the hypoxemic events of sleep apnea, chronic intermittent hypoxia (CIH), has been previously documented to impair cognitive function and elevate oxidative stress in male rats, while simultaneously decreasing testosterone. Therefore, androgens may modulate neuronal function under CIH. To investigate the role of androgens during CIH, male rats were assigned to one of four hormone groups: 1) gonadally intact, 2) gonadectomized (GDX), 3) GDX + testosterone (T) supplemented, or 4) GDX + dihydrotestosterone (DHT) supplemented. Each group was exposed to either normal room air or CIH exposure for one week, followed by memory and motor task assessments. Brain regions associated with AD and PD (entorhinal cortex, dorsal hippocampus, and substantia nigra) were examined for oxidative stress and inflammatory markers, key characteristics of AD and PD. Gonadally intact rats exhibited elevated oxidative stress due to CIH, but no significant memory and motor impairments. GDX increased memory impairments, regardless of CIH exposure. T preserved memory function and prevented detrimental CIH-induced changes. In contrast, DHT was not protective, as evidenced by exacerbated oxidative stress under CIH. Further, CIH induced significant spatial memory impairment in rats administered DHT. These results indicate androgens can have both neuroprotective and detrimental effects under CIH, which may have clinical relevance for men with untreated sleep apnea.

Relationships between POPs, biometrics and circulating steroids in male polar bears (Ursus maritimus) from Svalbard

The aim of this study was to determine the effects of persistent organic pollutants (POPs) and biometric variables on circulating levels of steroid hormones (androgens, estrogens and progestagens) in male polar bears (Ursus maritimus) from Svalbard, Norway (n = 23). Levels of pregnenolone (PRE), progesterone (PRO), androstenedione (AN), dehydroepiandrosterone (DHEA), testosterone (TS), dihydrotestosterone (DHT), estrone (E1), 17α-estradiol (αE2) and 17β-estradiol (βE2) were quantified in polar bear serum by gas chromatography tandem mass spectrometry (GC-MS/MS), while POPs were measured in plasma. Subsequently, associations between hormone concentrations (9 steroids), POPs (21 polychlorinated biphenyls (PCBs), 8 OH-PCBs, 8 organochlorine pesticides (OCPs) and OCP metabolites, and 2 polybrominated diphenyl ethers (PBDEs)) and biological variables (age, head length, body mass, girth, body condition index), capture date, location (latitude and longitude), lipid content and cholesterol levels were examined using principal component analysis (PCA) and orthogonal projections to latent structures (OPLS) modelling. Average concentrations of androgens, estrogens and progestagens were in the range of 0.57-83.7 (0.57-12.4 for subadults, 1.02-83.7 for adults), 0.09-2.69 and 0.57-2.44 nmol/L, respectively. The steroid profiles suggest that sex steroids were mainly synthesized through the Δ-4 pathway in male polar bears. The ratio between androgens and estrogens significantly depended on sexual maturity with androgen/estrogen ratios being approximately 60 times higher in adult males than in subadult males. PCA plots and OPLS models indicated that TS was positively related to biometrics, such as body condition index in male polar bears. A negative relationship was also observed between POPs and DHT. Consequently, POPs and body condition may potentially affect the endocrinological function of steroids, including development of reproductive tissues and sex organs and the general condition of male polar bears.

Two-hit exposure to polychlorinated biphenyls at gestational and juvenile life stages: 1. Sexually dimorphic effects on social and anxiety-like behaviors

Endocrine disrupting chemicals (EDCs) are widespread environmental contaminants that affect many neuroendocrine functions. The brain is particularly vulnerable to EDCs during critical periods of gestational development when gonadal hormones exert organizational effects on sexually dimorphic behaviors later in life. Peripubertal development is also a time of continued neural sensitivity to organizing effects of hormones, yet little is known about EDC actions at these times. We sought to determine effects of prenatal or juvenile exposures to a class of EDCs, polychlorinated biphenyls (PCBs) at human-relevant dosages on development, physiology, and social and anxiety-related behaviors later in life, and the consequences of a second juvenile "hit" following prenatal treatment. We exposed male and female Sprague-Dawley rats to PCBs (Aroclor 1221, 1mg/kg/day, ip injection) and/or vehicle during prenatal development (embryonic days 16, 18, 20), juvenile development (postnatal days 24, 26, 28), or both. These exposures had differential effects on behaviors in sex and age-dependent ways; while prenatal exposure had more effects than juvenile, juvenile exposure often modified or unmasked the effects of the first hit. Additionally, females exhibited altered social and anxiety behavior in adolescence, while males displayed small but significant changes in sociosexual preferences in adulthood. Thus, the brain continues to be sensitive to organizing effects of EDCs through juvenile development. As humans are exposed to EDCs throughout multiple periods in their life, these findings have implications for our understanding of EDC effects on physiology and behavior.

Two-hit exposure to polychlorinated biphenyls at gestational and juvenile life stages: 2. Sex-specific neuromolecular effects in the brain

Exposures to polychlorinated biphenyls (PCBs) during early development have long-lasting, sexually dimorphic consequences on adult brain and behavior. However, few studies have investigated their effects during juvenile development, a time when increases in pubertal hormones influence brain maturation. Here, male and female Sprague Dawley rats were exposed to PCBs (Aroclor 1221, 1 mg/kg/day) or vehicle prenatally, during juvenile development, or both, and their effects on serum hormone concentrations, gene expression, and DNA methylation were assessed in adulthood. Gene expression in male but not female brains was affected by 2-hits of PCBs, a result that paralleled behavioral effects of PCBs. Furthermore, the second hit often changed the effects of a first hit in complex ways. Thus, PCB exposures during critical fetal and juvenile developmental periods result in unique neuromolecular phenotypes, with males most vulnerable to the treatments.

Adolescent testosterone influences BDNF and TrkB mRNA and neurotrophin-interneuron marker relationships in mammalian frontal cortex

Late adolescence in males is a period of increased susceptibility for the onset of schizophrenia, coinciding with increased circulating testosterone. The cognitive deficits prevalent in schizophrenia may be related to unhealthy cortical interneurons, which are trophically dependent on brain derived neurotrophic factor. We investigated, under conditions of depleted (monkey and rat) and replaced (rat) testosterone over adolescence, changes in gene expression of cortical BDNF and TrkB transcripts and interneuron markers and the relationships between these mRNAs and circulating testosterone. Testosterone removal by gonadectomy reduced gene expression of some BDNF transcripts in monkey and rat frontal cortices and the BDNF mRNA reduction was prevented by testosterone replacement. In rat, testosterone replacement increased the potential for classical TrkB signalling by increasing the full length to truncated TrkB mRNA ratio, whereas in the monkey cortex, circulating testosterone was negatively correlated with the TrkB full length/truncated mRNA ratio. We did not identify changes in interneuron gene expression in monkey frontal cortex in response to gonadectomy, and in rat, we showed that only somatostatin mRNA was decreased by gonadectomy but not restored by testosterone replacement. We identified complex and possibly species-specific, relationships between BDNF/TrkB gene expression and interneuron marker gene expression that appear to be dependent on the presence of testosterone at adolescence in rat and monkey frontal cortices. Taken together, our findings suggest there are dynamic relationships between BDNF/TrkB and interneuron markers that are dependent on the presence of testosterone but that this may not be a straightforward increase in testosterone leading to changes in BDNF/TrkB that contributes to interneuron health.

Testosterone attenuates and the selective estrogen receptor modulator, raloxifene, potentiates amphetamine-induced locomotion in male rats

Although sex steroids are known to modulate brain dopamine, it is still unclear how testosterone modifies locomotor behaviour controlled, at least in part, by striatal dopamine in adolescent males. Our previous work suggests that increasing testosterone during adolescence may bias midbrain neurons to synthesise more dopamine. We hypothesised that baseline and amphetamine-induced locomotion would differ in adult males depending on testosterone exposure during adolescence. We hypothesised that concomitant stimulation of estrogen receptor signaling, through a selective estrogen receptor modulator (SERM), raloxifene, can counter testosterone effects on locomotion. Male Sprague-Dawley rats at postnatal day 45 were gonadectomised (G) or sham-operated (S) prior to the typical adolescent testosterone increase. Gonadectomised rats were either given testosterone replacement (T) or blank implants (B) for six weeks and sham-operated (i.e. intact or endogenous testosterone group) were given blank implants. Subgroups of sham-operated, gonadectomised and gonadectomised/testosterone-replaced rats were treated with raloxifene (R, 5mg/kg) or vehicle (V), daily for the final four weeks. There were six groups (SBV, GBV, GTV, SBR, GBR, GTR). Saline and amphetamine-induced (1.25mg/kg) locomotion in the open field was measured at PND85. Gonadectomy increased amphetamine-induced locomotion compared to rats with endogenous or with exogenous testosterone. Raloxifene increased amphetamine-induced locomotion in rats with either endogenous or exogenous testosterone. Amphetamine-induced locomotion was negatively correlated with testosterone and this relationship was abolished by raloxifene. Lack of testosterone during adolescence potentiates and testosterone exposure during adolescence attenuates amphetamine-induced locomotion. Treatment with raloxifene appears to potentiate amphetamine-induced locomotion and to have an opposite effect to that of testosterone in male rats.

The effect of adolescent testosterone on hippocampal BDNF and TrkB mRNA expression: relationship with cell proliferation

BACKGROUND

Testosterone attenuates postnatal hippocampal neurogenesis in adolescent male rhesus macaques through altering neuronal survival. While brain-derived neurotropic factor (BDNF)/ tyrosine kinase receptor B (TrkB) are critical in regulating neuronal survival, it is not known if the molecular mechanism underlying testosterone's action on postnatal neurogenesis involves changes in BDNF/TrkB levels. First, (1) we sought to localize the site of synthesis of the full length and truncated TrkB receptor in the neurogenic regions of the adolescent rhesus macaque hippocampus. Next, (2) we asked if gonadectomy or sex hormone replacement altered hippocampal BDNF and TrkB expression level in mammalian hippocampus (rhesus macaque and Sprague Dawley rat), and (3) if the relationship between BDNF/TrkB expression was altered depending on the sex steroid environment.

RESULTS

We find that truncated TrkB mRNA+ cells are highly abundant in the proliferative subgranular zone (SGZ) of the primate hippocampus; in addition, there are scant and scattered full length TrkB mRNA+ cells in this region. Gonadectomy or sex steroid replacement did not alter BDNF or TrkB mRNA levels in young adult male rat or rhesus macaque hippocampus. In the monkey and rat, we find a positive correlation with cell proliferation and TrkB-TK+ mRNA expression, and this positive relationship was found only when sex steroids were present.

CONCLUSIONS

We suggest that testosterone does not down-regulate neurogenesis at adolescence via overall changes in BDNF or TrkB expression. However, BDNF/TrkB mRNA appears to have a greater link to cell proliferation in the presence of circulating testosterone.

Testosterone induces molecular changes in dopamine signaling pathway molecules in the adolescent male rat nigrostriatal pathway

Adolescent males have an increased risk of developing schizophrenia, implicating testosterone in the precipitation of dopamine-related psychopathology. Evidence from adult rodent brain indicates that testosterone can modulate nigrostriatal dopamine. However, studies are required to understand the role testosterone plays in maturation of dopamine pathways during adolescence and to elucidate the molecular mechanism(s) by which testosterone exerts its effects. We hypothesized that molecular indices of dopamine neurotransmission [synthesis (tyrosine hydroxylase), breakdown (catechol-O-methyl transferase; monoamine oxygenase), transport [vesicular monoamine transporter (VMAT), dopamine transporter (DAT)] and receptors (DRD1-D5)] would be changed by testosterone or its metabolites, dihydrotestosterone and 17β-estradiol, in the nigrostriatal pathway of adolescent male rats. We found that testosterone and dihydrotestosterone increased DAT and VMAT mRNAs in the substantia nigra and that testosterone increased DAT protein at the region of the cell bodies, but not in target regions in the striatum. Dopamine receptor D2 mRNA was increased and D3 mRNA was decreased in substantia nigra and/or striatum by androgens. These data suggest that increased testosterone at adolescence may change dopamine responsivity of the nigrostriatal pathway by modulating, at a molecular level, the capacity of neurons to transport and respond to dopamine. Further, dopamine turnover was increased in the dorsal striatum following gonadectomy and this was prevented by testosterone replacement. Gene expression changes in the dopaminergic cell body region may serve to modulate both dendritic dopamine feedback inhibition and reuptake in the dopaminergic somatodendritic field as well as dopamine release and re-uptake dynamics at the presynaptic terminals in the striatum. These testosterone-induced changes of molecular indices of dopamine neurotransmission in males are primarily androgen receptor-driven events as estradiol had minimal effect. We conclude that nigrostriatal responsivity to dopamine may be modulated by testosterone acting via androgen receptors to alter gene expression of molecules involved in dopamine signaling during adolescence.

Impacts of stress and sex hormones on dopamine neurotransmission in the adolescent brain

RATIONALE

Adolescence is a developmental period of complex neurobiological change and heightened vulnerability to psychiatric illness. As a result, understanding factors such as sex and stress hormones which drive brain changes in adolescence, and how these factors may influence key neurotransmitter systems implicated in psychiatric illness, is paramount.

OBJECTIVES

In this review, we outline the impact of sex and stress hormones at adolescence on dopamine neurotransmission, a signaling pathway which is critical to healthy brain function and has been implicated in psychiatric illness. We review normative developmental changes in dopamine, sex hormone, and stress hormone signaling during adolescence and throughout postnatal life, then highlight the interaction of sex and stress hormones and review their impacts on dopamine neurotransmission in the adolescent brain.

RESULTS AND CONCLUSIONS

Adolescence is a time of increased responsiveness to sex and stress hormones, during which the maturing dopaminergic neural circuitry is profoundly influenced by these factors. Testosterone, estrogen, and glucocorticoids interact with each other and have distinct, brain region-specific impacts on dopamine neurotransmission in the adolescent brain, shaping brain maturation and cognitive function in adolescence and adulthood. Some effects of stress/sex hormones on cortical and subcortical dopamine parameters bear similarities with dopaminergic abnormalities seen in schizophrenia, suggesting a possible role for sex/stress hormones at adolescence in influencing risk for psychiatric illness via modulation of dopamine neurotransmission. Stress and sex hormones may prove useful targets in future strategies for modifying risk for psychiatric illness.

Molecular profiling of postnatal development of the hypothalamus in female and male rats

Reproductive function is highly dynamic during postnatal developmental. Here, we performed molecular profiling of gene expression patterns in the hypothalamus of developing male and female rats to identify which genes are sexually dimorphic, to gain insight into a more complex network of hypothalamic genes, and to ascertain dynamic changes in their relationships with one another and with sex steroid hormones during development. Using a low-density PCR platform, we quantified mRNA levels in the preoptic area (POA) and medial basal hypothalamus (MBH), and assayed circulating estradiol, testosterone, and progesterone at six ages from birth through adulthood. Numerous genes underwent developmental change, particularly postnatal increases, decreases, or peaks/plateaus at puberty. Surprisingly, there were few sex differences; only Esr1, Kiss1, and Tac2 were dimorphic (higher in females). Cluster analysis of gene expression revealed sexually dimorphic correlations in the POA but not the MBH from P30 (Postnatal Day 30) to P60. Hormone measurements showed few sex differences in developmental profiles of estradiol; higher levels of progesterone in females only after P30; and a developmental pattern of testosterone with a nadir at P30 followed by a dramatic increase through P60 (males). Furthermore, bionetwork analysis revealed that hypothalamic gene expression profiles and their relationships to hormones undergo dynamic developmental changes that differ considerably from adults. These data underscore the importance of developmental stage in considering the effects of hormones on the regulation of neuroendocrine genes in the hypothalamus. Moreover, the finding that few neuroendocrine genes are sexually dimorphic highlights the need to consider postnatal development from a network approach that allows assessment of interactions and patterns of expression.

Developmental profiles of neuroendocrine gene expression in the preoptic area of male rats

Reproductive function is controlled by GnRH cells and their steroid-sensitive regulatory inputs. The proper maturation of this system is critical to sexual development and maintenance of adult function. However, the molecular mechanisms underlying these developmental changes, and the potential roles of gonadal hormones in sculpting these processes, have not been fully explored. We performed a developmental profile from postnatal day (P) 1 through P60 of a network of five genes in the preoptic area (POA) that are critical to reproduction in male Sprague Dawley rats. GnRH, estrogen receptors-alpha, and -beta, androgen receptor (AR), and progesterone receptor (PR) mRNAs in the POA were assayed, and serum hormones were measured, in developing male rats. We also used a Taqman low-density array to identify candidate genes that may be important in development. Of the five targeted genes, only AR and PR changed robustly (7- and 3- to 4-fold increases, respectively) during development. All of the gonadal serum hormones changed markedly and with very different patterns from their receptor mRNAs: testosterone decreased from P1 to P30 and then increased to P60; progesterone peaked on P30; and estradiol decreased from P1 to P30. Using the Taqman low-density array, we identified several genes that changed dramatically in the POA with development, particularly G protein-coupled receptor 30, IGF-I, vitamin D receptor, estrogen-related receptor-alpha, and thyroid receptor-alpha. Our data demonstrate developmental stage-specific changes in neuroendocrine genes, particularly AR and PR. Moreover, the relationships between hormones and their corresponding receptors undergo dynamic changes across development in male rats.

Estrogen-regulated development and differentiation of the prostate

Both androgens and estrogens play a significant role in the prostate and are critical for normal prostate growth and development, as well as the maintenance of adult prostatic homeostasis throughout life. It is the balance of these two hormones, rather than each individually, that is important for prostatic development and differentiation. Estrogen action is mediated by the estrogen receptors, ERalpha and ERbeta. ERalpha is expressed throughout the prostatic tissue during fetal and early neonatal life, and if activated inappropriately, produces late-life disease, including inflammation and emergence of pre-malignant pathologies. In contrast, ERbeta expression is initiated after ERalpha, is localized primarily to the epithelium, and appears to be important during later periods of development such as puberty and adulthood, acting to regulate cellular proliferation and differentiation in the adult tissue. Therefore, there is also a spatial and temporal balance between ERalpha and ERbeta that is critical for development. Together with the shifting balance between androgens and estrogens themselves, the subtle, yet critical, balance between the activity of ERalpha and ERbeta is what ultimately determines the response of the prostate to estrogen, and is crucial for prostate health.

Antihypertensive effects of flutamide in rats that are exposed to a low-protein diet in utero

OBJECTIVE

We investigated whether gestational age of in utero low-protein diet played a role in the subsequent development of adult hypertension and whether it is gender dependent and examined whether flutamide (a specific, nonsteroidal competitive antagonist of the androgen receptor) reduces blood pressure in rat offspring that are exposed to in utero low-protein diet (6%).

STUDY DESIGN

Pregnant rats were fed either with 20% protein (control) or 6% protein (low-protein diet) from day 1 or day 12 of gestation. Fetoplacental weights and mortality rates of pups were assessed. Systolic blood pressure, mean arterial blood pressure, and circulatory hormone levels in offspring were determined. In addition, male and female hypertensive offspring were treated with flutamide, and their blood pressure was monitored.

RESULTS

After delivery, pup weights were reduced, and pup mortality rates increased in the low-protein diet-day 1 group. Systolic blood pressure and mean arterial blood pressure were elevated in low-protein diet-day 1 males and females and low-protein diet-day 2 males. Significant (P < .05) reduction in blood pressure was achieved with flutamide in low-protein diet-day 1 females. Serum estradiol levels were decreased (P < .05) in low-protein diet-day 1 females; flutamide attenuated this effect.

CONCLUSION

The day of in utero insult by low-protein diet is critical in the induction of adult hypertension; the severity is gender dependent. Flutamide was found to protect against hypertension only in females.

Genomic and non-genomic actions of sex steroids in the growth plate

Sex steroids, and particularly estrogens, are important regulators of bone growth and bone mass accrual. For a long time, it was thought that these effects were mainly caused by their modulatory effects on the somatotrophic axis. Data gathered in the past years have challenged this view and it is now widely accepted that many of the effects of sex steroids on growth and bone mass accrual are caused by direct effects on target cells in the growth plate and bone. This review summarizes and discusses some of our latest findings on the expression of sex steroid receptors in the growth plate, the source of the ligands activating these receptors, and their putatitive mechanism of action predominantly focusing on observations in the rat.

Male rats require testosterone to develop contralateral digastric muscle activity in response to noxious stimulation of the temporomandibular joint

The influence of testosterone on the postnatal development of reflex electromyographic (EMG) jaw muscle activity evoked by injection of mustard oil (MO) into the temporomandibular joint region and the later recurrence of this EMG activity after intravenous injection of naloxone, was studied in male rats. MO-evoked EMG activity in the contralateral digastric muscle and naloxone-induced recurrence of this EMG activity were fully developed in intact, 8-week-old rats. Castration at 4 weeks of age inhibited the development of the contralateral MO-evoked EMG activity, but did not influence the naloxone-induced recurrence. Contralateral MO-evoked responses were observed in 8-week-old castrated rats if they received testosterone replacement therapy beginning at 4 weeks of age. These data suggest that testosterone is required for the development of a contralateral nociceptive reflex in the digastric muscle of male rats.

Age-dependent changes in olfactory-mediated behavioral investigations in the male rat

In the present experiment male Sprague-Dawley rats at three different ages (young, middle-aged, and old) were tested in a series of olfactory-mediated behavioral tests. The amount of ano-genital investigation directed to receptive females by old rats was significantly reduced compared to that of young and middle-aged animals. In contrast, general body investigation of receptive females was similar among the three age groups. The amount of anogenital investigation directed to nonreceptive females or immature male rats indicated significant differences only between young and old rats, with values from middle-aged rats being intermediate and not significantly different from either of the two extreme groups. General body investigation of nonreceptive females and immature males did not differ among the three age groups. Old rats showed the best performance in a location of buried food test with latencies to locate food approximately one-half that obtained from young and middle-aged rats. Measures of general locomotor activity indicated significantly greater values from young compared to middle-aged and old rats, with the latter two showing very similar levels. These results demonstrate clear discriminatory differences in olfactory-mediated behavioral performance of the male rat as a function of the specific test and age of the animal. Overall, the results suggest that olfactory-mediated behaviors related to reproduction appear more sensitive to age-related declines, while behavior related to food procurement is more minimally affected.

Trial to induce prostatic cancer in ACI/Seg rats treated with a combination of 3,2'-dimethyl-4-aminobiphenyl and ethinyl estradiol

In an attempt to induce prostatic adenocarcinoma at higher incidence in a shorter period, we administered diet containing 0.75 ppm of ethinyl estradiol (EE) for three weeks to ACI/Seg rats, which are predisposed to develop a high incidence of microscopic adenocarcinoma of the prostate at higher age. Then, feeding was changed to basal diet and a single subcutaneous injection of 50 mg/kg body weight of 3,2'-dimethyl-4-aminobiphenyl (DMAB) was given two days after the change. We repeated this schedule 10 times. The rats were killed in week 60 of the experiment and subjected to routine autopsy. The average body weight of rats in group 1 given EE and DMAB was lower than that of control rats in group 2. The incidence of adenocarcinoma was not significantly different in the two groups, i.e., 6/74 (8.1%) in group 1 and 2/54 (3.7%) in group 2. The lesions were all microscopic. The incidence of atypical hyperplasia was significantly higher in group 1 at 17 of 74 rats (23.0%) whereas in group 2, it was only 2 of 54 rats (3.7%). Simple hyperplasia was also observed in 25 of 74 rats (33.8%) in group 1, which was significantly higher than that in group 2, where six of 54 rats (11.1%) had this lesion. The reduced growth of animals due to treatments with EE and DMAB probably suppressed the development of prostate cancer in this experiment. Further studies are needed to develop an appropriate model to induce prostate carcinoma at higher incidence in a shorter period.

The effect of age of exposure on lead-induced testicular toxicity

The present study was designed to assess the significance of age of exposure on the expression of lead toxicity on the male gonad. Male Wistar rats, age 42 days, 52 days and 70 days were treated with lead acetate in their water for 30 days prior to sacrifice. The lead treated groups in all cases had blood lead values significantly greater than control animals. Blood lead levels in control animal groups were less than 7 micrograms/dl. Serum testosterone and sperm concentration and production rate were significantly suppressed in those animals that were exposed to lead acetate starting at age 52 days and 70 days, but not 42 days. These data indicate that prepubertal rats may be less sensitive to the toxic effects of lead than are rats whose exposure begins after puberty has been initiated.

Gonadal function in aging rats and its relation to pituitary and mammary pathology

In the female rat, aging is characterized by a high incidence of prolactin (Prl)-secreting pituitary adenomas and mammary tumors. In contrast to this, old males show only a moderate to low incidence of pituitary and mammary pathology. Since gonadal steroids and Prl are thought to be key factors in the genesis of the above neoplastic pathologies, it was of interest to compare the serum levels of progesterone (P), estradiol (E2), testosterone (T) and Prl with the incidence of pituitary and mammary tumors in aging male and female rats. Young (3-4-month; YF), old (25-month; OF) and senescent (33-35-month; SF) female and young (3-4-month; YM) and old (24-26-month; OM) male Sprague-Dawley rats were killed by decapitation and their pituitaries weighed. Serum sex steroids and Prl were measured by RIA. The average life span of females but not males was markedly extended by systematic removal of mammary tumors. Females showed a rising incidence of mammary tumors after 14 months of age. In males, this pathology which began to appear at 16 months, had a much lower incidence than in females at all ages. Serum levels of E2 were (means +/- S.E.M.) 22.0 +/- 1.6; 18.9 +/- 0.8; 32.9 +/- 2.5; 37.3 +/- 2.0 and 32.2 +/- 3.0 pg/ml for YM, OM, YF, OF and SF, respectively. Serum P was 1.4 +/- 0.3; 1.6 +/- 0.2; 10.4 +/- 2.2; 9.7 +/- 3.3 and 6.8 +/- 0.8 ng/ml for YM, OM, YF, OF and SF, respectively. Serum T was 1578.9 +/- 188.7; 807.6 +/- 103.0; 197.5 +/- 11.8; 223.7 +/- 25.5 and 176.9 +/- 20.7 pg/ml for YM, OM, YF, OF and SF, respectively. Finally, serum Prl was 14.9 +/- 1.7; 21.9 +/- 4.0; 15.9 +/- 1.4; 52.4 +/- 9.4 and 170.8 +/- 31.1 ng/ml for YM, OM, YF, OF and SF, respectively. A strong correlation was found between serum Prl and anterior pituitary weight in OM, OF and SF, but not between serum Prl and sex steroid levels or sex steroid ratios. We conclude that, although the sex-related differences in mammary and pituitary tumor incidence during aging in rats can be partially accounted for by the different serum profiles of Prl and gonadal steroids in each sex, sex-associated differences in target tissue susceptibility should also be considered as an important determinant of the level of tumor incidence.

Effects of aging and testosterone administration on liver alcohol dehydrogenase activity in male Fischer 344 rats

The activity of alcohol dehydrogenase was measured in liver cytosolic fractions of male Fischer 344 rats at ages representing young adulthood, middle age, and old age. The activities were 1.7 +/- 0.1, 2.3 +/- 0.1, and 2.6 +/- 0.2 mumol/min/g liver in rats aged 4-5, 14-15, and 24-25 months, respectively. Hepatic alcohol dehydrogenase activity in female rats (3.4 +/- 0.2 mumol/min/g liver) was the same in young as in old rats. Castration increased alcohol dehydrogenase activity in young males to levels found in females, and testosterone administration reversed the effect. However, neither physiological nor pharmacological doses of the hormone restored the elevated enzyme activities of old male rats to levels found in young male rats.

Aging changes in synaptology of luteinizing hormone-releasing hormone neurons in male rat preoptic area

This study was undertaken to examine some aspects of the anatomical substrate for reproductive senescence. Immunocytochemically identified luteinizing hormone-releasing hormone neurons and their processes in the male rat brain preoptic area were compared in young adult (2-4 months), middle-aged (12-14 months) and old (20-23 months) animals. At the light microscopic level there were no age-dependent differences in total numbers or sizes of LHRH neurons nor in their distribution in the brain. Examination of these neurons at the electron microscopic level did reveal significant differences in certain organelles and in the degree and kind of synaptic input. Random sections of middle-aged luteinizing hormone-releasing hormone neurons more frequently passed through the nucleolus and the incidence of nematosomes was higher than in luteinizing hormone-releasing hormone neurons from the young and old animals. Quantitative measures of synaptic input to luteinizing hormone-releasing hormone soma and dendrites as well as to unidentified neurons in the same thin section were made. These are reported as percent of membrane that showed synaptic structure. Dendrites of both luteinizing hormone-releasing hormone and nonidentified neurons were more densely innervated than perikarya. The density of synaptic input to luteinizing hormone-releasing hormone neurons was significantly greater than that to nonidentified neurons in young and middle-aged animals, but was equal to that of nonidentified neurons by old age. Age-related changes were noted in synaptic organization with the most significant change being an increased input to luteinizing hormone-releasing hormone perikarya. Indeed, synaptic input to luteinizing hormone-releasing hormone perikaryal membrane was increased three-fold by middle age and ten-fold by old age. Density of synaptic input to luteinizing hormone-releasing hormone dendritic membrane did not change with age. There were no aging changes in percentage of membrane with synaptic structure in nonidentified elements. Synapses were also classified on the basis of their synaptic vesicle content. There were proportionately more synaptic boutons containing round clear than pleomorphic vesicles in the young sample. The proportion of synapses with pleomorphic vesicles increased with age onto both luteinizing hormone-releasing hormone perikarya and their dendrites. The proportion of boutons containing some electron dense-core vesicles along with clear vesicles decreased with age onto both luteinizing hormone-releasing hormone and nonidentified neurons and their processes.

Galactose ingestion increases vascular permeability and collagen solubility in normal male rats

In view of the similarity of cataracts and neuropathy in galactose-fed and diabetic rats, the present experiments were undertaken to determine whether consumption of galactose-enriched diets (10, 25, or 50% by weight) also increases collagen crosslinking and permeation of vessels by 125I-albumin analogous to that observed in diabetic rats. The observations in these experiments: demonstrate that consumption of galactose-enriched diets for 3 wk selectively increases 125I-albumin permeation of the same vascular beds affected in diabetic rats and by diabetic vascular disease in humans (i.e., the aorta and vessels in the eye, kidney, sciatic nerve, and new tissue formed in the diabetic milieu); demonstrate that the susceptibility of the vasculature to aldose reductase-linked injury (increased permeability) varies greatly in different tissues; indicate that collagen solubility (crosslinking) changes in galactose-fed rats differ sharply from those in diabetic rats; and provide new evidence that consumption of galactose-enriched diets induces a hypogonadal state in male rats.

Stimulation of hypothalamic LHRH levels and release by gonadal steroids

The inhibitory feedback effects of steroids on pituitary LH release are believed to be mediated via steroidal effects on the hypothalamic LHRH activity. We have examined the direct effects of individual steroids (T, DHT and E2) on hypothalamic LHRH levels and on LHRH release in vitro. In castrated male rats, replacement of either steroid in physiological doses, resulted in augmentation of the MBH LHRH levels by steroidal action within the MBH. LHRH analyses of microdissected diencephalic nuclei revealed that this accumulation occurred exclusively in LHRH terminals in the ME. Careful examination of the time course of steroid action showed that whereas LH release was suppressed within hours of steroid treatment, the LHRH response occurred after 3-4 days of steroid exposure in 2-week castrated rats and 7-14 days in 8-week castrated rats. This temporal dichotomy in the LH and LHRH responses to steroid action was further substantiated by the differential effects of low, sub-physiological levels of steroids on these two responses. Very low levels of T or E2 evoked maximal accumulation of the MBH LHRH, but LH release in vivo and the rate of LHRH release in vitro were not affected. Surprisingly, physiological levels of T which suppressed LH release concomitant with elevations in LHRH levels, augmented the in vitro rate of LHRH release. In fact, the LHRH release rate was found to be correlated with LHRH concentrations in hypothalami of intact, castrated and castrated rats treated with T. Thus it appears that in the hypothalamo-pituitary axis there are different thresholds of responsiveness to steroids. Apparently, the LHRH neurons, particularly the processes involved in LHRH accumulation are most sensitive to low levels of steroids; however, higher physiological levels of steroids are required to suppress pituitary LH release as well as to promote LHRH release. On the basis of our cumulative data, it is reasonable to speculate that steroid-induced accumulation of LHRH in the ME may not be a consequence of decrease in LHRH release, but may involve synthesis of the neurohormone.

Decreased in vitro secretion of LH, FSH, and free alpha-subunits by pituitary cells from old male rats

Various in vivo and in vitro pituitary-Leydig cell functions were examined in mature (5-8 mo) vs. old (22-25 mo) male Wistar rats. Old rats exhibited decreased serum concentrations of testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) (P less than 0.0025) but similar levels of prolactin (P less than 0.01) both before and 4 wk after castration. The in vitro release of LH, FSH, and free alpha-subunits was measured in primary cultures of dispersed anterior pituitary cells from both intact and castrated rats. During 48 h of incubation, basal secretion rates of the glycoproteins were decreased (P less than 0.001) from cells of both intact and castrated old rats. After stimulation with LH-releasing hormone (LRH) in single (10(-8) M) or multiple (10(-10) - 10(-7) M) doses, the total amounts of the glycoproteins secreted were also less from cells of both intact and castrated old rats. However, repeated measures analysis of variance revealed age-related hyporesponsivity to LRH stimulation only for LH secretion by cells from intact rats. The basal molar ratios of alpha/(LH + FSH) secreted by cells from intact but not castrated old rats were lower than those from cells of the corresponding mature rats. Moreover, after LRH stimulation (10(-10) - 10(-7) M), molar secretory ratios of alpha/(LH + FSH) decreased from cells of intact mature rats but increased from cells of intact old rats. These in vitro data suggest that the reduced serum LH and FSH levels in intact and castrated old male rats result in part from decreased secretion of these glycoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of advancing age on hypothalamic neurotransmitter content and on basal and norepinephrine-stimulated LHRH release

In order to elucidate possible mechanism(s) responsible for the age-related decline in LH secretion, basal and norepinephrine (NE)-stimulated LHRH release was measured from median eminence (ME) fragments of 4-, 11-, 18- and 27-month-old male F344 rats. Serum LH levels declined significantly between 11 and 18 months and were still lower at 27 months of age, while testosterone levels declined continuously between 4 and 27 months. Hypothalamic NE and dopamine (DA) content also declined significantly with age, while serotonin and 5-hydroxy-indoleacetic acid content increased with age. Despite the decline in serum LH levels with age, in vitro basal LHRH release increased gradually with age as did NE-stimulated LHRH release. These data suggest that the age-related reduction in LH secretion by the male rat is due to a reduction in hypothalamic NE metabolism and not to an inability of the LHRH neuron to respond to NE stimulation.

Differences in nonhistone protein changes in rat ventral and dorsolateral prostate during sexual maturation

Age-related changes of chromosomal proteins in the dorsolateral and ventral prostates of rats from 6 to 31 weeks of age were studied by SDS-polyacrylamide gel electrophoresis. A nonhistone protein having a molecular weight of about 20,000 (20K-NHP), abundantly localized in the dorsolateral prostate, increased rapidly in content during the early stage of sexual maturation (6-11 weeks of age) in association with increases of serum testosterone concentration and prostatic tissue weight. Serum testosterone concentration decreased after week 11 and then remained constant until week 31. In contrast, the 20K-NHP content continued to increase after 11 weeks of age in the dorsolateral prostate, but not in the ventral prostate. The rapid increase of 20K-NHP in the dorsolateral prostate during the early stage of sexual maturation could not be attained in immature rats (5 weeks of age) by injection of excess amounts of androgens and/or prolactin for a week. But the 20K-NHP content in the ventral prostate of rats treated with testosterone propionate was almost the same as that of mature rats.

Immunoreactive-beta-endorphin and LHRH levels in the brains of aged male rats with impaired sex behavior

Levels of immunoreactive beta-endorphin and luteinizing hormone releasing hormone (LHRH) were measured in brain tissue of aged male Long-Evans rats. The animals were tested for sex behavior twice in one week at bimonthly intervals between the 7th and 27th month of life and were sacrificed along with a group of young (5-month old) sexually active rats. Thirty-one of the 89 rats which began the study remained healthy and tumor-free. By month 27, 21 of these had completely ceased to mate and 10 continued to show adequate sexual behavior. Diminished levels of beta-endorphin-like immunoreactivity were measured in the hypothalami and hindbrain of the old animals grouped together as compared to young animals and this reduction was shown to be significantly greater in hypothalamic tissue from the behaviorally inactive subgroup. Hypothalamic LHRH levels were not significantly altered by age in these animals. However, a marked reduction of LHRH content in the septal and midbrain regions of the aged-behaviorally inactive subgroup was evident when compared with the behaviorally active group. The data suggest that altered function of beta-endorphin and LHRH neurons of the aged brain may be involved in the behavioral deterioration observed in aged animals.

Gonadal dysfunction in the spontaneously diabetic BB rat

Diabetes which occurs spontaneously in the BB Wistar rat is associated with reduced fertility, predominantly in breeding males. In the first month of diabetes, there is a significant (p less than 0.05) reduction in serum testosterone associated with a transient decrease of serum LH and the accumulation of lipid in Leydig cells. Between one and three months of diabetes, there is an increase in both serum testosterone and LH and a further deposition of lipid droplets in Leydig cells. From three to six months of diabetes, there is a reduction of serum testosterone similar to age-matched controls, but high serum LH levels persist. Similar levels of LH and testosterone are noted after six months of diabetes, and all BB rats show marked changes in seminiferous tubules. These morphological changes in tubules consist of increased tubular wall thickness, severe germ-cell depletion, and Sertoli-cell vacuolization. Similar morphological changes of testes associated with generalized atrophy are noted in all control rats after 16 months of age. Decreased fertility in the BB rat appears to be associated with a primary disorder of Leydig cells, which precedes changes in seminiferous tubules consistent with accelerated aging. Preliminary data in impotent diabetic men suggest that the BB rat may be a valuable model for investigating human diabetic impotence and infertility.

Age-related reproductive decline in the male Japanese quail

A series of experiments was conducted to study the decline in reproduction associated with age in the male Japanese quail. In Experiment 1, eggs were collected from pairs that were 28, 56, 107, and 149 weeks of age. Pairs that were 56 weeks of age or older showed a sharp drop in fertility and hatchability. Subsequent experiments were designed to study the endocrine and behavioral basis for this decline in the male. In Experiment 2, males that were between 23 and 70 weeks of age were tested for mating behavior, plasma testosterone was measured, and testes wet weight was determined. There were no significant differences between the age groups. However, samples taken from an additional group of males 168 weeks of age showed significantly (P less than 0.05) lower serum testosterone and testes weight. Therefore, the third experiment was designed to include age groups of males between 4 and 126 weeks of age in order to further examine this decline in males older than 70 weeks of age. There was a significant (P less than 0.05) drop in this number of males showing sexual behavior and of those males showing sexual behavior; the quantity of mating activity also declined. Plasma testosterone was reduced in the older groups; however, the change was not significant. In addition, the size of the cloacal gland, an androgen-dependent organ, declined with age (P less than 0.05). These results argue that the age-related reproductive decline may have behavioral as well as endocrine basis. Possibly, the behavioral changes may result from altered receptor sensitivity at the level of areas of the brain, which control reproductive behavior, and at the level of the testes, which affect hormone production and spermatogenesis.

Circadian rhythmicity and sleep: effects of aging in laboratory animals

This literature review of research on age-related differences in sleep and rhythmic phenomena in laboratory animals covers three general areas: (1) age-related differences in biorhythms in general; (2) age-related differences in sleep patterns as assessed by psychophysiological measures; and (3) neurobiological correlates of biorhythms and sleep, including consideration of possible morphological, chemical, and endocrine bases of age-related defects in animal models. It is concluded that systematic research bridging these areas is lacking although several promising areas have been explored.

Alterations in daily rhythms of testosterone and progesterone in old male rats

Studies were undertaken to characterize the daily patterns of secretion of testosterone (T), progesterone (P) and dihydrotestosterone (DHT) in young (3-4 months old) and old (19-20 months old) male Sprague-Dawley rats. In young rats, plasma T concentrations show dramatic daily variations with peak and nadir levels at 1130 and 2330 h, respectively. In old male rats, no such rhythmic pattern in plasma T was observed. Plasma P concentrations varied significantly in both young and old male rats, with peak levels occurring 8 h (1930 h) after the plasma T peak in young rats. Additionally, in old male rats, the daily increase in plasma P was significantly larger and was sustained for a longer period than in young rats. Plasma DHT concentrations were similar and changed little during the day in both young and old animals. In view of the known P influence on gonadal secretion, the possible significance of these age-related changes in daily patterns in plasma P and T are discussed.

Changes in the control of enzyme clusters in the liver of adult and senescent rats

The activities of a number of enzymes in rat liver have been measured at different times during adulthood and senescence and expressed as a percentage of maximal activity that can be attained after hormonal stimulation. Three different profiles can be detected. Type I profile shows decreasing activities during adolescence (1--3 months of age), increasing activities during adulthood (4--12 months of age) and relatively high activities thereafter. Enzymes of this group are carbamoyl-phosphate synthase and arginase; DNA content shows the same pattern. Type II profile shows decreasing activities during adolescence and relatively low activities thereafter. Enzymes of this group are tyrosine aminotransferase, glucose-6-phosphatase, and glucokinase. Type III profile shows relatively high activities during adolescence, adulthood and senescence. Enzymes of this group are ornithine transcarbamoylase, glutamate dehydrogenase and hexokinase. Some enzymes are constant with age in females, but slowly decrease in activity with age in males; decreasing levels of androgens and possibly also thyroid hormones can explain this decrease in males. Decreasing activities of carbamoyl-phosphate synthase and arginase during adolescence can be attributed to a depressant effect of gonadal hormones. The difference between relatively high and relatively low basal activities of enzymes in adult and senescent rats corresponds with their relatively long and short half-lives, respectively. This relation implicates a similar rate of synthesis of glucocorticosteroid hormone-dependent enzymes.