Sustained effects of a single injection of ethanol on the hypothalamic-pituitary-gonadal axis in the male rat

The effects of repeated forced ethanol consumption during adolescence on reproductive behaviors in male rats

Adolescence is a sensitive period of brain development when changes in hormone levels may have long-lasting effects on synaptic connections and behavior. In humans, alcohol consumption frequently begins during this critical period, although the impact of early exposure has not been fully examined. The current study was designed to investigate short- and long-term effects of repeated forced ethanol consumption during adolescence on emerging reproductive behaviors. Twenty-six young male Long-Evans rats were assigned to ethanol (Young EtOH, n = 12) or water (Young Control, n = 14) groups at postnatal day (P) 32, receiving a modified binge protocol of 3 g/kg of solution via gavage twice per week from P32 to P80. For comparison, another cohort of rats received a similar treatment paradigm in adulthood from P75-P133 (Adult EtOH, n = 8; Adult Control, n = 10). Reproductive behavior was assessed with tests for copulation, partner preference, and 50-kHz vocalizations during forced consumption (intoxication) and again after a 4-5 week period of abstinence. During forced consumption, the Young EtOH group showed significantly longer latencies on copulation tests than Young Controls, but these differences did not persist after abstinence. Different patterns were observed in Adult animals, who only showed significant, delayed impairments in the post-ejaculatory interval. Preference for sexually receptive females increased with sexual experience in both adolescent and adult rats, regardless of treatment during the forced consumption phase. However, after abstinence, the Young EtOH group showed a significantly reduced partner preference compared to the Young Control group, which may indicate long-term effects on sexual motivation. Additionally, during forced consumption the Young EtOH group tended to emit fewer ultrasonic vocalizations, perhaps reflecting impairments in sexual communication. Adult groups showed no differences in partner preference or vocalization tests at any time. Taken together, these findings indicate that repeated, intermittent ethanol exposure may have moderate effects on reproductive behavior that vary as a function of age. After abstinence, differences were only observed in the younger group, suggesting that the adolescent brain and behavior are more sensitive to ethanol exposure than the adult brain for sexual motivation and performance.

Systemic Administration of Alcohol to Adult Rats Inhibits Leydig Cell Activity: Time Course of Effect and Role of Nitric Oxide

BACKGROUND

Alcohol has been shown to interfere with testosterone (T) release from Leydig cells. However, the mechanisms responsible for this phenomenon, which may include decreased activity of the luteinizing hormone-releasing hormone (LHRH)-LH axis, as well as a direct influence of the drug on the testes, are not fully understood. In this work, we investigated the influence of alcohol, administered intragastrically (i.g.) or delivered via vapors, on Leydig cell activity and T release. Leydig cell function was studied by measuring changes in the levels of the steroidogenic proteins steroidogenic acute regulatory (StAR), the peripheral-type benzodiazepine receptor (PBR), and the cytochrome P450 side-chain cleavage enzyme (P450scc). Testosterone release was studied under basal conditions or in response to human chorionic gonadotropin (hCG). Finally, to identify potential factors mediating the influence of alcohol, we measured the testicular variant of the neuronal nitric oxide (NO) synthase (NOS), TnNOS, in semipurified Leydig cells.

METHODS

Adult male Sprague-Dawley rats were either injected with alcohol i.g. once or exposed to alcohol vapors (4 h/d) for 1 or 5 days. Controls received the vehicle (i.g. model) or were kept in boxes through which no vapors were circulated. Following these treatments, one series of experiments was devoted to investigate Leydig cell responsiveness by measuring plasma T levels before or after the intravenous injection of hCG (1 U/kg). In another series of experiments, we used semipurified Leydig cell preparations to measure StAR, PBR, P450scc, and TnNOS by Western blot analysis.

RESULTS

In the i.g. model, the T response to hCG was blunted for 12 hours following alcohol injection, but showed a rebound at 48 hours. Levels of StAR protein and of PBR, but not of P450scc, were significantly decreased within 10 minutes of drug administration. While StAR then remained depressed for 24 hours, PBR values were variable over this time course. By 48 hours, StAR, PBR, and P450scc levels had increased above control values. Both StAR and PBR levels showed correlations with plasma T levels. In the alcohol vapor models, both regimens of the drug also significantly depressed StAR and PBR protein concentrations, blunted the T response to hCG, and did not alter P450scc. Finally, we observed that alcohol delivered i.g. or via vapors up-regulated TnNOS levels in Leydig cells, but that blockade of NO formation failed to restore a normal T response to hCG.

CONCLUSIONS

Collectively, these results suggest that (a) the ability of Leydig cells to release T does not show a simple correlation with changes in StAR, PBR, and P450scc levels; (b) the time course of the alcohol-induced changes were protein-specific; and (c) despite the ability of alcohol to stimulate TnNOS expression, NO does not appear to mediate the inhibitory influence of this drug on testicular steroidogenesis in the models that we studied.

Using an animal model to assess the long-term behavioral and biological consequences of adolescent abuse and exposure to alcohol

During adolescence or adulthood, male hamster siblings were divided into control and experimental groups and exposed to periods of either mild or traumatic stress outside their individual nests. Mild stress is the simple exposure to a novel environment while the traumatic stressor is repeated daily subjugation by a dominant hamster. Over adolescence and adulthood, animals had free access to alcohol. The behavior and neuroendocrinology were assessed over these developmental periods in response to these environmental conditions. As adults, animals with a history of traumatic stress in adolescence showed inappropriate and excessive aggressive behavior. Their aggression was context dependent. In the presence of equal size hamsters, they showed little aggression; however, they were excessively aggressive toward smaller, younger animals. Testosterone levels and reproductive behavior were normal after adolescent subjugation; however, release of cortisol during agonistic encounters was suppressed. In comparison, hamsters exposed to chronic social subjugation as adults had low plasma testosterone, reduced reproductive behavior, and exaggerated cortisol release during agonistic encounters. Self-ingestion of alcohol during adolescence enhanced testosterone release around the peripubertal period but reduced plasma testosterone levels in adulthood. Exposure to alcohol as adolescents enhanced aggression in adulthood. These data demonstrate a pronounced difference in behavior and neuroendocrinology between adolescent and adult hamsters in their response to traumatic stress.

The response of the hypothalamic-pituitary-gonadal axis to fasting is modulated by leptin

Reproductive function is intimately related to caloric consumption. During fasting states, the hormones regulating reproduction, those of the hypothalamic-pituitary-gonadal axis, in particular, are severely altered. With the exciting observations that the obese (ob) gene product leptin, may also modulate neuroendocrine functions, we examined leptin's ability to prevent the consequences of fasting on reproductive hormones. Two groups of male rats, aged 65 days old, were either fasted and saline-injected or fasted and leptin-treated for approximately three days. Another group was given free access to rat chow. Leptin was able to prevent the fasting-induced fall of serum testosterone. Similar to testosterones dependence on leptin, leptin concentrations were somewhat dependent on testosterone. Castration accelerated the normal, age-related increase in serum leptin. Leptin also prevented the fasting-induced fall in luteinizing hormone (LH). The increase of beta-LH mRNA seen in the fasting state was prevented by leptin. There were no differences noted in luteinizing hormone releasing hormone (LHRH) mRNA among any of the groups. While neither fasting nor fasting plus leptin caused changes in serum prolactin, the increase in prolactin mRNA seen in fasted animals was prevented by leptin treatment. These data support the hypothesis that leptin plays a specific role in mediating the response of reproductive hormones to the nutritional status of the organism.

The effects of acute melatonin and ethanol treatment on antioxidant enzyme activities in rat testes

The pineal hormone melatonin (N -acetyl, 5-methoxytryptamine) was recently accepted to act as an antioxidant under both in vivo and in vitro conditions. In this study, we examined the possible preventive effect of melatonin on ethanol-induced lipid peroxidation in rat testes. Thirty-seven male Wistar albino rats, 5.5--6 months old, were randomly divided into four groups (9--10 animals in each). The first group (control animals) received 4% ethanol at similar intervals to the experimental groups to equalize the stress effect. The second group received only melatonin i.p. 7 mg kg(-1)bw three times over 1.5 h intervals. The third group received only 30% alcohol 3 g kg(-1)bw twice daily. The fourth group were treated with melatonin and ethanol according to the above protocol, melatonin injections preceding ethanol treatments. The product of lipid peroxidation, malondialdehyde (MDA) and antioxidant enzymes, superoxide dismutase (Cu--Zn SOD), glutathione peroxidase (GPx) and catalase (CAT) were measured in the post-mitochondrial fraction of the testes. MDA levels were significantly increased due to acute ethanol intoxication. GPx activity was higher in the three experimental groups than the control levels. The activity of CAT was increased significantly in the melatonin plus ethanol-treated group but the other groups appeared not to be influenced by acute ethanol treatment. Cu--Zn SOD activity remained unaltered. These results suggest that antioxidants may be a protective agent for the testicular injury caused by ethanol consumption.

Ethanol exposure enhances apoptosis within the testes

BACKGROUND

Chronic ethanol abuse causes testicular atrophy and male infertility in alcoholic men. It is well known that ethanol exposure disrupts the hypothalamic-pituitary-gonadal axis, adversely affects the secretory function of Sertoli cells, and produces oxidative stress within the testes. It is still not clear what cellular mechanisms are responsible for the morphologic alteration of the testes that results in a reduction of testicular mass as a consequence of ethanol exposure. The hypothesis tested was that ethanol enhances apoptosis of testicular germ cells.

METHODS

In the experiments of chronic ethanol exposure, male Sprague Dawley rats (Harlan Sprague Dawley, Inc., Indianapolis, IN) were fed Liber-Decarlie liquid diet for 9 weeks. In the experiments of acute ethanol exposure, a small volume of 20% ethanol solution was administered by intratesticular injection. Both 3'-end labeling of isolated testicular deoxyribonucleic acid (DNA) and labeling of apoptotic cells in situ by the terminal deoxynucleotidyl transferase-mediated deoxyuridine 5'-triphosphate nick end-labeling method were used to determine apoptosis rates within the testes. The expression of proteins involved in apoptosis was assessed by reverse transcription-polymerase chain reaction and by Western blotting.

RESULTS

The testes of rats that were fed an ethanol-containing liquid diet had more testicular DNA fragmentation than did those of animals that were fed an isocaloric control diet. Ethanol increased the number of apoptotic spermatogonia as well as spermatocytes. Direct intratesticular injections of ethanol solution enhanced testicular DNA fragmentation, suggesting an increase in apoptosis. Moreover, Fas ligand levels were increased within the testes of rats that were chronically fed ethanol. In vitro, ethanol treatment of cultured Sertoli cells enhanced the production of Fas ligand. In addition, testicular levels of p53 messenger ribonucleic acid were increased in rats that were chronically fed ethanol.

CONCLUSIONS

All of these observations suggest that ethanol enhances testicular germ cell apoptosis.

Voluntary ethanol consumption in male adolescent hamsters increases testosterone and aggression

The immediate and long-term biologic and behavioral consequences of voluntary ethanol (EtOH) exposure during male adolescence are unknown. In the present study, male golden hamsters voluntarily drank from a 15% EtOH solution in addition to consuming dry laboratory chow and water ad lib from Postnatal Day 25 to Postnatal Day 43. Over this adolescent period, they drank an average of 13 g/kg/day of EtOH, resulting in a mean blood EtOH concentration of ca. 53 mg %. On Postnatal Day 35, a period of enhanced sensitization and activation of the gonadal axis, testosterone levels were twice as high in EtOH animals than in sucrose-yoked controls. However, this difference disappeared by Postnatal Day 53, as EtOH and control animals showed comparable adult levels of plasma testosterone. When tested for aggression several days after the cessation of EtOH exposure, hamsters showed enhanced attack behavior toward smaller intruders placed into their home cage. These results suggest that voluntary EtOH exposure during male adolescence has specific neuroendocrine effects with lasting behavioral consequences.