Neonatal Male Mice Research Articles

Levels of 4‐aminobiphenyl‐induced somatic H‐ras mutation in mouse liver DNA correlate with potential for liver tumor development

The utility of liver H-ras codon 61 CAA to AAA mutant fraction as a biomarker of liver tumor development was investigated using neonatal male mice treated with 4-aminobiphenyl (4-ABP). Treatment with 0.1, 0.3, or 1.0 mumol 4-ABP produced dose-dependent increases in liver DNA adducts in B6C3F(1) and C57BL/6N mice. Eight months after treatment with 0.3 mumol 4-ABP or the DMSO vehicle, H-ras codon 61 CAA to AAA mutant fraction was measured in liver DNA samples (n = 12) by allele-specific competitive blocker-polymerase chain reaction (ACB-PCR). A significant increase in average mutant fraction was found in DNA of 4-ABP-treated mice, with an increase from 1.3 x 10(-5) (control) to 44.9 x 10(-5) (treated) in B6C3F(1) mice and from 1.4 x 10(-5) to 7.0 x 10(-5) in C57BL/6N mice. Compared with C57BL/6N mutant fractions, B6C3F(1) mutant fractions were more variable and included some particularly high mutant fractions, consistent with the more rapid development of liver foci expected in B6C3F(1) mouse liver. Twelve months after treatment, liver tumors developed in 79.2% of 4-ABP-treated and 22.2% of control B6C3F(1) mice; thus measurement of H-ras mutant fraction correlated with subsequent tumor development. This study demonstrates that ACB-PCR can directly measure background levels of somatic oncogene mutation and detect a carcinogen-induced increase in such mutation.

Androgen-Regulated Transcripts in the Neonatal Mouse Testis as Determined Through Microarray Analysis1

Androgens are required for normal spermatogenesis in mammalian testes. These hormones directly regulate testicular somatic cells that, in turn, support germ cell differentiation. However, the identity of genes under androgen regulation in the testis are not well known. In the present study, neonatal male mice (8 days postpartum) treated by testosterone propionate (TP) were used to study androgen action in the testis as evidenced by alterations in gene expression. Mice were treated with 0.5 mg of TP or dihydrotestosterone (DHT) or vehicle (oil), and testes were harvested 4, 8, and 16 h after treatment. Global gene expression was monitored by microarray analysis. Real-time reverse transcription-polymerase chain reaction was performed to confirm the microarray results. The methodology was verified by confirming the presence of previously characterized TP-regulated genes, including Pem in Sertoli cells and Cyp17a1 in Leydig cells. No significant differences in gene expression were found between TP- and DHT-treated samples. Microarray analysis identified 141, 119, and 109 up-regulated genes at 4, 8 and 16 h after TP treatment, respectively, and 83, 99, and 111 down-regulated genes at the same corresponding time points. The androgen regulation of the selected gene was verified further using testes from flutamide-treated adult mice and isolated Sertoli cells in culture. The data generated in the present study may serve as a foundation for hypothesis-driven research and provide insights regarding gene networks and pathways under androgen control in the testis.

Neurofunctional deficits and potentiated apoptosis by neonatal NMDA antagonist administration

The early postnatal brain development, when many potentially sensitive processes occur, has been shown to be vulnerable to different pharmacological and environmental compounds. In the present investigation, four groups of neonatal NMRI male mice were administered the glutamate NMDA receptor antagonist ketamine (50 mg/kg, s.c.), or the GABA A receptor agonist diazepam (5 mg/kg, s.c.), or co-administered ketamine (50 mg/kg, s.c.) and diazepam (5 mg/kg, s.c.), or vehicle (0.9% saline, s.c.) on day 10 after birth. On day 11, mice from each treatment group were sacrificed and brains were taken for analysis of neuronal cell degeneration, using Fluoro-Jade staining technique. Ketamine, but not diazepam, induced a severe degeneration of cells in the parietal cortex. The opposite was observed for diazepam in the laterodorsal thalamus. The most pronounced cell degeneration was seen in parietal cortex of mice exposed to both ketamine and diazepam. At 2 months of age each treatment group was tested for motor activity and learning performance. Ketamine and ketamine + diazepam treated mice displayed severe deficits of habituation to the test chamber in the spontaneous motor activity test, marked deficits of acquisition learning and retention memory in the radial arm maze-learning task and less shift learning in the circular swim maze-learning task. This study indicates that the observed functional deficits can be related to cell degeneration induced during a critical stage of neonatal brain development. The potentiated apoptosis induced by ketamine and diazepam may have implications for the selection of drugs used in neonatal paediatric anaesthesia.

Neonatal exposure to polybrominated diphenyl ether (PBDE 153) disrupts spontaneous behaviour, impairs learning and memory, and decreases hippocampal cholinergic receptors in adult mice

Neonatal exposure to polybrominated diphenyl ether (PBDE 153) disrupts spontaneous behaviour, impairs learning and memory, and decreases hippocampal cholinergic receptors in adult mice. Flame retardants are used to suppress or inhibit combustion processes in an effort to reduce the risk of fire. One class of flame retardants, polybrominated diphenyl ethers (PBDEs), are present and increasing in the environment and in human milk. The present study shows that neonatal exposure to 2,2′,4,4′,5,5′-hexaBDE (PBDE 153), a PBDE persistent both in environment and in human milk, can induce developmental neurotoxic effects, such as changes in spontaneous behaviour (hyperactivity), impairments in learning and memory, and reduced amounts of nicotinic receptors, effects that get worse with age. Neonatal NMRI male mice were orally exposed on day 10 to 0.45, 0.9, or 9.0 mg of PBDE 153/kg of body weight. Spontaneous behaviour (locomotion, rearing, and total activity) was observed in 2−, 4−, and 6-month-old mice, Morris water maze at an age of 6 months. The behaviour tests showed that the effects were dose-response and time-response related. Animals showing defects in learning and memory also showed significantly reduced amounts of nicotinic receptors in hippocampus, using α-bungarotoxin binding assay. The observed developmental neurotoxic effects seen for PBDE 153 are similar to those seen for PBDE 99 and for certain PCBs. Furthermore, PBDEs appear to as potent as the PCBs.

A brominated flame retardant, 2,2',4,4',5-pentabromodiphenyl ether: uptake, retention, and induction of neurobehavioral alterations in mice during a critical phase of neonatal brain development.

Polybrominated diphenyl ethers (PBDEs) are used in large quantities as flame retardant additives. In a recent study, we have seen that neonatal exposure to some brominated flame retardants can cause permanent aberrations in spontaneous motor behavior that seem to worsen with age. In view of an increasing amount of PBDEs in mother's milk and in the environment, the present study was undertaken to investigate whether there is a critical and limited phase, during neonatal life, for induction of persistent neurotoxic effects of 2,2',4,4',5-pentaBDE (PBDE 99). Neonatal NMRI male mice were exposed on day 3, 10, or 19 to 8 mg 2,2',4,4',5-pentaBDE/kg body weight. Uptake and retention of 2,2',4,4',5-penta[(14)C]BDE were studied in the mouse brain after exposure to 1.5 M becquerel (Bq) 2,2',4,4',5-penta[(14)C]BDE /kg body weight (bw) on postnatal day 3, 10, or 19. Spontaneous motor behavior was observed in 4-month-old mice. Mice exposed to 2,2',4,4',5-pentaBDE on day 3 or 10 showed significantly impaired spontaneous motor behavior, whereas no effect was seen in mice exposed on day 19. Neonatal mice exposed to 2,2',4,4',5-penta[(14)C]BDE 99 on postnatal day 3, 10, or 19 were sacrificed 24 h or 7 days posttreatment. The amount of radioactivity, given as per mille ( per thousand) of total amount administered, was between 3.7 and 5.1 per thousand in the three different age categories at 24 h after administration. Seven days after the administration, 2,2',4,4',5-penta[(14)C]BDE or its metabolites could still be detected in the brain. The amount of radioactivity in the brain was not higher in mice exposed on day 3 or 10 when compared to exposure on day 19. Thus, the behavioral disturbances observed in adult mice following neonatal exposure to 2,2',4,4',5-pentaBDE are induced during a defined critical period of neonatal brain development.

Developmental effects of early immune stress on aggressive, socially reactive, and inhibited behaviors.

The origins of individual differences in social development are examined in relation to early stress (immune challenge) and social milieu (maternal behavior) in a genetic-developmental analysis using an animal model. Neonatal male mice (5 or 6 days of age) from two lines of mice selectively bred for high versus low levels of inter-male aggressive behavior received a standard immune challenge (i.p. injections of 0.05 mg/kg endotoxin or saline). Animals were reared by their line-specific biological dam or by a foster dam from a line bred without selection. Adult levels of social behaviors were assessed in a dyadic test (age 45-50 days). Mice from the high-aggressive line show more developmental sensitivity to immune challenge than mice from the low-aggressive line, and line differences persist regardless of the early maternal environment. As adults, endotoxin-treated mice from the high-aggressive line have lower levels of aggressive behavior, longer latency to attack, and higher rates of socially reactive and inhibited behaviors compared to saline controls. Developmental effects of endotoxin in the low-aggressive line are minimal: endotoxin increases socially reactive behaviors, compared to saline controls, but only for mice reared by their biological dams. Rearing by foster dams increases social exploration in the low-aggressive line. The findings raise novel questions regarding the openness of behavioral systems to effects of nonobvious but omnipresent features of the environment, such as antigenic load, how these effects are integrated to affect social development and psychopathology, and the nature of intrinsic factors that contribute to individual differences in sensitivity to early stressors.

Social dominance rank and accessory sex glands in wild adult male house mice born to food-deprived mothers

Food deprivation after weaning often has greater effects on the reproduction of females than males. However, if animals are deprived prenatally (i.e., through deprivation of the mother during gestation), the reproduction of males may be more negatively impacted because it may decrease their ability to compete with other males and their attractiveness to females. We tested the predictions that adult sons of females that are food-deprived during gestation would tend to lose agonistic encounters with sons of well-nourished (control) females and would have smaller accessory sex glands as well. Sons of control mothers were more frequently dominant to sons of deprived mothers. They also had heavier vesicular-coagulating gland complexes and tended to have heavier preputial glands. However, among males that had not been tested for social dominance rank, there were no such differences in accessory gland weights. These data indicate that maternal food deprivation affects sons only if they engage in agonistic encounters. These effects may be due to a disruption of the organizational effects of testosterone that occur in neonatal male mice and they are likely to have a strong negative impact on the reproduction of the sons of deprived mothers.

Stereoselective Metabolism of Anthracene, 9-Methylanthracene, 9,10-Dimethylanthracene, 9-Chloroanthracene, and 9-Nitroanthracene by Liver Microsomes of Neonatal Male B6C3F1 Mice

Stereoselective metabolism of anthracene, 9-methylanthracene (9-M-A), 9, 10-dimethylanthracene (9, 10-DMA), 9-chloroanthracene (9-Cl-A), and 9-nitroanthracene (9-nitro-A) by liver microsomes of neonatal (15-day old) male B6C3F1 mice in the presence of a NADPH regenerating system was conducted. After incubation, reversed-phase HPLC separation, and spectral analyses the following were identified: anthracene trans-1,2-dihydrodiol, 9-M-A trans-1,2- and -3,4-dihydrodiol, 9,10-DMA trans-1,2-dihydrodiol, 9-Cl-A trans-1,2- and -3,4-dihydrodiol, and 9-nitro-A trans-1,2- and -3,4-dihydrodiol. Circular dichroism (CD) spectral analysis indicated the major enantiomers of the anthracene, 9-M-A, 9,10-DMA, and 9-Cl-A trans-dihydrodiols all had R,R absolute configurations. These results indicate that these compounds are metabolized in a stereoselective manner by liver microsomes of neonatal male B6C3F1 mice.

Benz[A]Anthracene is a Potent Liver Tumorigen in the Neonatal B6C3F1 Mouse

Benz[a]anthracene (BA) has been reported to be a noncarcinogen or a borderline weak carcinogen in several chronic bioassay systems. For comparison, we determined its tumorigenicity in the neonatal male B6C3F1 mouse. Mice were administered i.p. injections (1600 nmol total dose per mouse) within 24 hrs of birth and at 8 and 15 days of age. BA induced hepatocellular adenomas and carcinomas in 75 and 25% of the mice, respectively, while the solvent control (DMSO) induced 8 and 4%, respectively. Analysis by RT-PCR indicated that 86% (12/14) of BA-induced liver tumors had activated ras protooncogenes, 11 with a pattern of GGC→CGC at K-ras codon 13. Our results clearly demonstrate that BA is a potent tumorigen in the neonatal B6C3F1 mouse and induces a unique type of K-ras-oncogene activation.

Age-dependent response of the electrocardiogram to K(+) channel blockers in mice.

Developmental changes in electrocardiogram (ECG) and response to selective K(+) channel blockers were assessed in conscious, unsedated neonatal (days 1, 7, 14) and adult male mice (>60 days of age). Mean sinus R-R interval decreased from 120 +/- 3 ms in day 1 to 110 +/- 3 ms in day 7, 97 +/- 3 ms in day 14, and 81 +/- 1 ms in adult mice (P < 0.001 by ANOVA; all 3 groups different from day 1). In parallel, the mean P-R interval progressively decreased during development. Similarly, the mean Q-T interval decreased from 62 +/- 2 ms in day 1 to 50 +/- 2 ms in day 7, 47 +/- 8 ms in day 14 neonatal mice, and 46 +/- 2 ms in adult mice (P < 0.001 by ANOVA; all 3 groups are significantly different from day 1). Q-T(c) was calculated as Q- interval. Q-T(c) significantly shortened from 179 +/- 4 ms in day 1 to 149 +/- 5 ms in day 7 mice (P < 0.001). In addition, the J junction-S-T segment elevation observed in day 1 neonatal mice resolved by day 14. Dofetilide (0.5 mg/kg), the selective blocker of the rapid component of the delayed rectifier (I(Kr)) abolished S-T segment elevation and prolonged Q-T and Q-T(c) intervals in day 1 neonates but not in adult mice. In contrast, 4-aminopyridine (4-AP, 2.5 mg/kg) had no effect on day 1 neonates but in adults prolonged Q-T and Q-T(c) intervals and specifically decreased the amplitude of a transiently repolarizing wave, which appears as an r' wave at the end of the apparent QRS in adult mice. In conclusion, ECG intervals and configuration change during normal postnatal development in the mouse. K(+) channel blockers affect the mouse ECG differently depending on age. These data are consistent with the previous findings that the dofetilide-sensitive I(Kr) is dominant in day 1 mice, whereas 4-AP-sensitive currents, the transiently repolarizing K(+) current, and the rapidly activating, slowly inactivating K(+) current are the dominant K(+) currents in adult mice. This study provides background information useful for assessing abnormal development in transgenic mice.

Exposure to nicotine during a defined period in neonatal life induces permanent changes in brain nicotinic receptors and in behaviour of adult mice

Neonatal exposure to low doses of nicotine has been shown to prevent the development of low-affinity nicotine-binding sites, and to elicit a different behaviour response to nicotine in the mice as adults. This study has identified a defined period during the development of neonatal mouse brain for the induction of these permanent changes. Neonatal mice, aged either 3, 10, or 19 days were exposed to nicotine, 66 μg nicotine-base/kg b.wt., s.c. twice daily, on 5 consecutive days. In the cerebral cortex, high- and low-affinity (HA and LA) nicotine-binding sites were assayed ( 3 H -nicotine/nicotine) in neonatal male mice aged 8, 15, and 24 days and in adult mice aged 4 months. Spontaneous behaviour and nicotine-induced behaviour were observed in 4-month-old male mice. The spontaneous behaviour test did not indicate any difference between saline- and nicotine-treated mice, whereas the nicotine-induced behaviour test revealed a hypoactive response to nicotine, though only in mice given nicotine on days 10–14. The response of controls and the other age categories to nicotine was an increased activity. At no time during the neonatal period could LA nicotine-binding sites be found following nicotine treatment, but the persistence of this effect was evident only in adult mice exposed on days 10–14.

Genistein exerts estrogen-like effects in male mouse reproductive tract

The aim of this study was to evaluate the estrogenicity of genistein in the neonatal and adult male mouse reproductive tract. In intact adults, genistein (2.5 mg s.c./kg of body weight/day for 9 days) reduced testicular and serum testosterone concentrations, pituitary LH-content and prostate weight. In castrated adults, genistein (0.025–2.5 mg s.c./kg of body weight) increased expression of c-fos gene in prostatic urethra. In adult, neonatally estrogenized mice showing an increased estrogen sensitivity, a 10-day treatment with genistein (2.5 mg s.c./kg of body weight) induced development of squamous epithelial metaplasia in prostatic collecting ducts. Neonatally, only a very high dose of genistein (1 mg/pup per day; i.e. ≈500 mg/kg of body weight) induced persistent structural changes, similar to those seen in mice treated neonatally with diethylstilbestrol, in the urethroprostatic complex. These results suggest that in adult males, genistein induces the typical estrogenic effects in doses comparable to those present in soy-based diets, while in neonatal animals, considerably higher doses are required to show estrogen-like activity.

Potent tumorigenicity of 7-chlorobenz[a]anthracene and 7-bromobenz[a]anthracene in the neonatal B6C3F (1) male mouse.

The tumorigenicity of 7-chlorobenz[a]anthracene (7-Cl-BA, and environmental contaminant, and 7 bromobenz[a]anthracene (7-Br-BA) was determines in the male B6C3F(1) newborn mouse. Mice receiving 7-Cl-BA and 7-Br-BA by i.p. injections at a dose of 1600 nmol per mouse on 1, 8, and 15 days after birth developed 92 and 96% hepatocellular adenomas, and 100 and 83% hepatocellular carcinoma, respectively. Metabolism by liver microsomes of 15-day-old mice each produced the corresponding trans-3,4-dihydrodiol. Analysis by (32)P-postlabeling/HPLC indicated the presence of DNA adducts derived from 7-Cl-BA trans-3,4-dihydrodiol and 7-Br-BA trans-3,4-dihydrodiol. Our results indicate that both 7-Cl-BA and 7-Br-BA are potent carcinogens and that bay-region diol epoxides are the ultimate metabolites that lead to DNA adduct formation and tumor initiation.

Prenatal in vivo bulbourethral gland development is not affected by prostaglandin E2 inhibition.

Investigation of bulbourethral gland (BUG) development is useful to study genitourinary (GU) tract growth and differentiation. Understanding GU tract growth and differentiation is relevant to testing the hypothesis that the initial lesion of human benign prostatic hyperplasia involves focal re-expression of inductive processes in the periurethral region of the prostatic transitional zone. Prostaglandins play a role in regulating growth and morphogenesis of different organ systems. Previous reports have proposed that prostaglandin E2 (PgE2) mediates the masculinizing effects of testosterone in the developing neonatal male GU tract. We have previously shown that androgens lower rather than raise BUG PgE2 levels. Further studies led us to conclude that PgE2 does not play a major role in postnatal BUG growth and morphogenesis in vitro. In order to investigate the possible role of PgE2 in prenatal BUG development, indomethacin (INDO, 1.0 mg/kg- day, subcutaneously) was administered to pregnant BALB/c mice on gestational days 12-18. Control pregnant mice were either untreated or injected with dimethylsulfoxide vehicle. Anogenital distances were measured within 12 hours after birth in male and female offspring on day 19. In male neonatal mice, BUGs were examined histologically and PgE2 levels were measured by radioimmunoassay in BUGs and whole genital tracts. We observed no significant morphological differences in INDO-exposed BUGs compared to controls. No significant differences in mean anogenital distances of INDO-exposed male offspring or controls were detected. Mean anogenital distances of female offspring were similar in the three respective groups. Mean BUG PgE2 levels in INDO-exposed neonates were significantly lower (P < 0.05) than in untreated neonates.(ABSTRACT TRUNCATED AT 250 WORDS)

5 alpha-reductase activity in developing urogenital tracts of fetal and neonatal male mice

5 alpha-Reductase activity in testes and urogenital tract tissues from male mice at 14.5 days gestation and 0 days of age (birth) was assessed by measurement of metabolites of testosterone released into the medium in a serum-free culture system. In male mice at 14.5 days gestation, the testis and the cranial portion of the urogenital ridge (UGR), which develops into the epididymis, had little 5 alpha-reductase activity. The caudal portion of the UGR, which develops into the seminal vesicle (SV), and the cranial portion of the urogenital sinus (UGS) had 12-fold higher activity than the cranial portion of the UGR. 5 alpha-Reductase activity in the middle portion of UGR was intermediate between that of its cranial and caudal portions. The highest levels of 5 alpha-reductase activity were detected in the caudal portion of UGS, even though this higher value was not significantly different from those in the caudal UGR or the cranial UGS. In 0-day-old male mice, 5 alpha-reductase activity of testis remained low at a level similar to that observed at 14.5 days gestation. The epididymis also exhibited low 5 alpha-reductase activity in 0-day-old mice, even though this activity had increased 2.2-fold relative to that observed in the cranial UGR at 14.5 days gestation. 5 alpha-Reductase activity of the cranial portion of UGS (prostatic rudiment) was relatively high on day 0 and similar to that in the same region at 14.5 days gestation. The SV and bulbourethral gland (BUG) on day 0 had high 5 alpha-reductase activity, which had increased 1.4- and 1.3-fold, respectively, compared to their 14.5 day embryonic anlage, although the increase was not significant. Through examination of 5 alpha-reductase activity regionally in the developing urogenital tract, it is evident that the concept that testosterone is the active androgen during Wolffian development is overly simplified. The present study suggests the importance of spatial/regional factors in Wolffian duct development in regard to the role of dihydrotestosterone. 5 alpha-reductase activity in the caudal Wolffian duct (SV rudiment) equals or exceeds that in the developing prostate, and at birth, dihydrotestosterone production is virtually identical in the SV and prostate. This suggests that 5 alpha-reduced androgens play a prominent role in the development of SV.

5 alpha-reductase activity in developing urogenital tracts of fetal and neonatal male mice.

5 alpha-Reductase activity in testes and urogenital tract tissues from male mice at 14.5 days gestation and 0 days of age (birth) was assessed by measurement of metabolites of testosterone released into the medium in a serum-free culture system. In male mice at 14.5 days gestation, the testis and the cranial portion of the urogenital ridge (UGR), which develops into the epididymis, had little 5 alpha-reductase activity. The caudal portion of the UGR, which develops into the seminal vesicle (SV), and the cranial portion of the urogenital sinus (UGS) had 12-fold higher activity than the cranial portion of the UGR. 5 alpha-Reductase activity in the middle portion of UGR was intermediate between that of its cranial and caudal portions. The highest levels of 5 alpha-reductase activity were detected in the caudal portion of UGS, even though this higher value was not significantly different from those in the caudal UGR or the cranial UGS. In 0-day-old male mice, 5 alpha-reductase activity of testis remained low at a level similar to that observed at 14.5 days gestation. The epididymis also exhibited low 5 alpha-reductase activity in 0-day-old mice, even though this activity had increased 2.2-fold relative to that observed in the cranial UGR at 14.5 days gestation. 5 alpha-Reductase activity of the cranial portion of UGS (prostatic rudiment) was relatively high on day 0 and similar to that in the same region at 14.5 days gestation. The SV and bulbourethral gland (BUG) on day 0 had high 5 alpha-reductase activity, which had increased 1.4- and 1.3-fold, respectively, compared to their 14.5 day embryonic anlage, although the increase was not significant. Through examination of 5 alpha-reductase activity regionally in the developing urogenital tract, it is evident that the concept that testosterone is the active androgen during Wolffian development is overly simplified. The present study suggests the importance of spatial/regional factors in Wolffian duct development in regard to the role of dihydrotestosterone. 5 alpha-reductase activity in the caudal Wolffian duct (SV rudiment) equals or exceeds that in the developing prostate, and at birth, dihydrotestosterone production is virtually identical in the SV and prostate. This suggests that 5 alpha-reduced androgens play a prominent role in the development of SV.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of neonatally administered monosodium glutamate on the sexually dimorphic profiles of circulating growth hormone regulating murine hepatic monooxygenases

Neonatal male and female mice were treated with monosodium glutamate (MSG) at either 2.0 or 4.0 mg/g body weight on alternate days during the first 9 days of life. As adults, mice were catheterized to obtain unstressed, serial blood samples for the determination of ultradian profiles of circulating growth hormone. In addition, monooxygenase levels (i.e. steroi d hydroxylasesand drug-metabolizing enzymes) were measured in hepatic microsomes. Generally, both doses of MSG produced the same developmental defects. Mice neonatally exposed to the amino acid developed a syndrome characterized by retarded growth, obesity and reduced organ weights. While vehicle-treated mice secreted growth hormone in sexually dimorphic patternss defined by pulse frequency (i.e. F>M), hormone concentrations in plasma samples obtained during 8 continuous hr of serial blood collections from both male and female MSG-treated mice were barely detectable at best, and exhibited no pulsatility. Approximately 15% of the measured monooxygenases were male-predominant, 35% were female-predominant and 50% had no sex differences. The enhanced expression of the hepatic monooxygenases in response to MSG-induced depletion of plasma growth hormone indicates that the hormone basically functions as a suppressor of the murine enzyme system.

IGF-I and IGF-I 24–41 but not IGF-I 57–70 affect somatic and neurobehavioral development of newborn male mice

Insulin-like growth factor (IGF-I) is a trophic factor for both neurons and glial cells. Its presence in developing and adult nervous system suggests an important role for this peptide in the development of neural circuitries. Neonatal male mice of the CD-1 outbred strain were injected intracerebroventricularly with either recombinant IGF-I, synthetic IGF-I fragment 24–41 or IGF-I fragment 57–70 on postnatal days (PND) 2, 4, and 7. Physical traits such as body weight gain, body length, and tail length were recorded daily from PND2 to PND13. Sensorimotor development was scored according to a modified Fox's scale. The ultrasonic vocalization pattern on PND8 and homing performance on PND10 were also recorded. Measures for body weight gain and tail length of the pups were significantly increased following treatment with the whole IGF-I peptide. However, neither IGF-I nor the smaller fragments affected mice sensorimotor development. IGF-I and IGF-I 24–41 but not IGF-I 57–70 increased the rate of ultrasonic calls of the pups measured on PND8. These data provide evidence that IGF-I regulates somatic growth and behavioral development when administered in newborn mice and that different portions of the peptide can exert different effects.

Calcitonin Gene-Related Peptide Stimulates Motility of the Gubernaculum Via Cyclic Adenosine Monophosphate

Calcitonin gene-related peptide (CGRP), N-truncated CGRP fragments CGRP 8-37 and [Tyr0]-CGRP 28-37, and dibutyryl cyclic adenosine monophosphate (DBcAMP) were studied for their effects on the neonatal male mouse gubernaculum in organ culture. Rhythmic contractions were shown in 18% of control gubernacula, which were enhanced with CGRP, inhibited by CGRP 8-37 and not affected by [Tyr0]-CGRP 28-37. A total of 60 gubernacula was exposed to increasing concentrations of DBcAMP and the percentage of gubernacula showing rhythmic contractions increased from 18 to 60%. These studies demonstrate that the neonatal mouse gubernaculum exhibits endogenous contractility that can be enhanced with CGRP or DBcAMP. These results suggest that cyclic adenosine monophosphate may act as the intracellular second messenger for receptor bound CGRP in the gubernaculum. This finding is consistent with the hypothesis that CGRP from the genitofemoral nerve provides directional, chemotactic guidance for inguinoscrotal gubernacular migration during testicular descent.

Androgens lower prostaglandin E2 levels in neonatal mouse bulbourethral gland in in vitro cultures

The neonatal mouse bulbourethral gland (BUG) in vitro culture model is useful to study hormone-induced genitourinary (GU) tract growth and differentiation. Like the prostate, the BUG is a derivative of the urogenital sinus and may have relevance to understanding growth processes involved in normal and pathological GU tract development. Previous studies have reported androgen-induced elevation of prostaglandin E2 (PgE2) levels in mouse GU tract in vivo. PgE2 has been proposed to mediate neonatal GU tract masculinization. In our studies, tissues were obtained from neonatal male mice and cultured in serum-free Dulbecco's Modified Eagle's Medium-Ham's F-12 Medium (1:1) supplemented with varying concentrations of androgen. PgE2 levels were measured by RIA in the medium, and tissue specimens were cultured for 7 days or less. During this period, androgens induced proliferation and glandular morphogenesis in the BUGs. In the absence of androgen, tissue and medium PgE2 levels increased over 7 days. Significant (P < 0.05) PgE2 increases over day 1 control values were observed from days 5-7 in tissues and on day 7 in media. During this same time period, androgen supplementation decreased PgE2 levels. Significant (P < 0.05) PgE2 decreases from day 1 cultures were observed from days 3-7 in tissues and on day 7 in media. PgE2 was decreased significantly (P < 0.05) by androgen compared to control values from days 3-7 in tissues and from days 5-7 in media. On day 7 of culture, PgE2 levels were significantly (P < 0.05) inhibited by androgen in a concentration-dependent fashion in tissues and media. Maximal androgen-induced inhibition of PgE2 levels was 96% and 99% in tissues and media, respectively. Although the addition of indomethacin to control cultures markedly inhibited PgE2 production, BUG morphology was unaffected. In addition, the morphology of androgen-stimulated BUGs does not appear to be affected by the addition of exogenous PgE2. We conclude that although androgens induce development and decrease PgE2 levels, PgE2 does not appear to play a major role in in vitro BUG postnatal growth and morphogenesis. The BUG in vitro culture model may mimic growth and morphogenetic processes occurring in the human GU tract. Further understanding of the role of steroid hormones and PG metabolism may yield additional insight into developmental and proliferative GU tract disorders.