Melatonin expression in periodontitis and obesity: An experimental in-vivo investigation

BACKGROUND AND OBJECTIVE

Melatonin deficiency has been associated with obesity and systemic inflammation. This study aims to evaluate whether melatonin could interfere with the mechanisms of co-morbidity linking obesity and periodontitis.

MATERIAL AND METHODS

Twenty-eight male Wistar rats were randomly divided in 4 groups: control group (Con) (fed with standard diet); high-fat diet group (HFD) (fed with a diet containing 35.2% fat); Con group with induced periodontitis (Con-Perio) and HFD group with induced periodontitis (HFD-Perio). To induce periodontitis, the method of oral gavages with Porphyromonas gingivalis ATCC W83K1 and Fusobacterium nucleatum DMSZ 20482 was used. Circulating melatonin levels were analyzed by multiplex immunoassays. Periodontitis was assessed by alveolar bone loss (micro-computed tomography and histology) and by surrogate inflammatory outcomes (periodontal pocket depth, modified gingival index and plaque dental index).

RESULTS

Plasma melatonin levels were significantly decreased (P < .05) in the obese rats with periodontitis when compared with controls or with either obese or periodontitis rats. Alveolar bone loss increased 27.71% (2.28 µm) in HFD-Perio group compared with the Con group. The histological analysis showed marked periodontal tissue destruction with osteoclast activity, particularly in the HFD-Perio group. A significant negative correlation (P < .05) was found between periodontal pocket depth, modified gingival index and circulating melatonin levels.

CONCLUSION

Obese and periodontitis demonstrated significantly lower melatonin concentrations when compared with controls, but in obese rats with periodontitis these concentrations were even significantly lower when compared with either periodontitis or obese rats. These results may indicate that melatonin deficiency could be a key mechanism explaining the co-morbidity effect in the association between obesity and periodontitis.

Citrus essential oils inhalation by mice: Behavioral testing, GCMS plasma analysis, corticosterone, and melatonin levels evaluation

The use of orange essential oils (EOs) as a complementary treatment is very common in Brazilian popular culture. The levels of melatonin (MEL) and corticosterone (CORT) hormones were investigated simultaneously, by the Luminex™ immunoassay system in mice plasma, after Citrus aurantium and Citrus sinensis EOs inhalation for 30 min. The plasma was analyzed by headspace through gas chromatography coupled to mass spectrometry for investigation of the EO components. Mice were submitted to behavioral testing to research anxiolytic-like, sedative, and antidepressant-like effects. The inhalation of atmosphere obtained from vaporization of 10% solution of this Citrus EO separately did not affect MEL or CORT plasma levels; that is, the MEL and CORT levels did not present variation in function of the EO in the schedule used. On the other hand, the imipramine positive control used altered the level of MEL as expected. The EO constituents were detected in plasma at different ratios that is present in inhaled EO. Behavioral tests showed that the inhalation of 10% C. sinensis EO presents an anxiolytic-like and sedative effect. Thus, C. sinensis EO can be a valuable tool for treatment of the anxiety disturbs, apparently without interference with MEL and CORT physiological levels.

Cadmium chronotoxicity at pituitary level: effects on plasma ACTH, GH, and TSH daily pattern

Cadmium is an endocrine disruptor that has been shown to induce chronotoxic effects. The present study was designed to evaluate the possible cadmium effects on the daily secretory pattern of adrenocorticotropin hormone (ACTH), growth hormone (GH), and thyroid-stimulating hormone (TSH) in adult male Sprague-Dawley rats. For this purpose, animals were treated with cadmium at two different doses [25 and 50 mg/l cadmium chloride (CdCl(2))] in the drinking water for 30 days. Control age-matched rats received cadmium-free water. After the treatment, rats were killed at six different time intervals throughout a 24-h cycle. Cadmium exposure modified the 24-h pattern of plasma ACTH and GH levels, as the peak of ACTH content between 12:00 and 16:00 h in controls appeared at 12:00 h in the group treated with the lowest dose used, while it appeared between 16:00 and 20:00 h in rats exposed to 50 mg/l CdCl(2). In addition, the peak of GH content found at 04:00 h in controls moved to 16:00 h in rats exposed to 25 mg/l CdCl(2), and the highest dose used abolished 24-h changes of GH secretion. The metal treatment did not modify ACTH secretory pattern. Exposure to cadmium also increased ACTH and TSH medium levels around the clock with both doses used. These results suggest that cadmium modifies ACTH and TSH medium levels around the clock, as well as disrupted ACTH and GH secretory pattern, thus confirming the metal chronotoxicity at pituitary level.

Toxic effects of methoxychlor in rat striatum: modifications in several neurotransmitters

Neurotoxic effects of methoxychlor (MTX) are poorly understood at present. This study was undertaken to evaluate the possible effects of MTX in norepinephrine, dopamine and amino acid contents and serotonin turnover in rat striatum. For this purpose, adult male Sprague-Dawley rats were administered 25 mg/kg/day of MTX in sesame oil or vehicle only for 30 days. The neurotransmitters of interest were measured in the striatum by HPLC. MTX decreased norepinephrine and 5-hydroxyindole acetic acid (5-HIAA) content and serotonin turnover (measured as 5-HIAA/serotonin ratio), and increased glutamate and GABA concentrations. However, the content of serotonin, aspartate, glutamine and taurine was not modified by MTX exposure. These data suggest that MTX exposure inhibits norepinephrine synthesis and serotonin metabolism. The inhibitory effect on norepinephrine could be explained, at least in part, by the increase of both GABA and glutamate contents. Further studies are needed to understand the effects of MTX on serotonin. Also a disruptive effect of MTX on the metabolisms of glutamate, aspartate, glutamine and GABA emerges.

Melatonin, environmental light, and breast cancer

Although many factors have been suggested as causes for breast cancer, the increased incidence of the disease seen in women working in night shifts led to the hypothesis that the suppression of melatonin by light or melatonin deficiency plays a major role in cancer development. Studies on the 7,12-dimethylbenz[a]anthracene and N-methyl-N-nitrosourea experimental models of human breast cancer indicate that melatonin is effective in reducing cancer development. In vitro studies in MCF-7 human breast cancer cell line have shown that melatonin exerts its anticarcinogenic actions through a variety of mechanisms, and that it is most effective in estrogen receptor (ER) alpha-positive breast cancer cells. Melatonin suppresses ER gene, modulates several estrogen dependent regulatory proteins and pro-oncogenes, inhibits cell proliferation, and impairs the metastatic capacity of MCF-7 human breast cancer cells. The anticarcinogenic action on MCF-7 cells has been demonstrated at the physiological concentrations of melatonin attained at night, suggesting thereby that melatonin acts like an endogenous antiestrogen. Melatonin also decreases the formation of estrogens from androgens via aromatase inhibition. Circulating melatonin levels are abnormally low in ER-positive breast cancer patients thereby supporting the melatonin hypothesis for breast cancer in shift working women. It has been postulated that enhanced endogenous melatonin secretion is responsible for the beneficial effects of meditation as a form of psychosocial intervention that helps breast cancer patients.

Effects of moderate consumption of distilled and fermented alcohol on some aspects of neuroimmunomodulation

Alcoholic beverages are characterized by their fermented versus distilled origin and also by their degree of alcohol. The toxic effects of chronic alcohol consumption have been widely studied. However, there is less evidence about possible beneficial effects of moderate alcohol intake. This work was aimed at evaluating the effects of moderate alcohol consumption (beer or ethanol) on plasma hormone concentrations, blood and thymus lymphocyte phenotypes and brain neurotransmitter levels. For this purpose, 40 adult Wistar male rats were administered ethanol or beer for 4 weeks (experimental groups). Age-matched rats were administered beer without alcohol or water to be used as controls. Rats were killed by decapitation and plasma from the trunk blood was collected to measure plasma prolactin, growth hormone and ACTH concentrations by homologous specific double antibody radioimmunoassays. Thymus and blood lymphocyte subsets were measured by flow cytometry. Neurotransmitter concentrations [dopamine, gamma-aminobutyric acid (GABA) and taurine] were measured by high pressure liquid chromatography in the median eminence and the pituitary. Blood and thymus lymphocyte subsets were not significantly changed by either ethanol or beer consumption, compared to controls. Plasma prolactin levels significantly decreased in ethanol-administered groups (p < 0.05) compared to control animals drinking water, although plasma levels of growth hormone and ACTH were not modified by either alcohol used. Dopamine and GABA concentrations in the median eminence or in the adenohypophysis remained unmodified by moderate beer or ethanol consumption. However, taurine concentration was significantly increased in the pituitary (p < 0.05) in the group drinking ethanol compared to those groups drinking beer with or without alcohol. These data suggest that moderate alcohol consumption may change the regulatory mechanism of prolactin secretion. Whether these modifications have a physiological significance deserves further research.

Oestrus synchronisation of rabbit does at early post-partum by doe–litter separation or ECG injection: Reproductive parameters and endocrine profiles

Inseminating rabbit does at early post-partum, in combination with early weaning, can increase prolificacy (total kits born and still born per parturition) and decrease parturition intervals. Oestrus synchronisation increases fertility and prolificacy, while decreasing the number of inseminations required for gestation. However, little is known about the effectiveness of different oestrus synchronisation methods at early post-partum. In this study, does (n = 138) were artificially inseminated nine times (over a period of 1 year, kits weaned at 25 days), on day 4 post-partum after separation from the litter (for 48 or 24 h) or 48 h after 25 UI eCG injection. Plasma levels of prolactin and estradiol were also evaluated in a subsample of 12 multiparous lactating does per treatment, on days 2, 3 and 4 post-partum. The three treatments increased overall fertility of multiparous females compared to controls (which were not synchronised), but there were no differences among treatments in total kits born or stillborn. Does treated with eCG had a higher culling rate. The interval between parturitions and the number of inseminations required for gestation tended to decrease with increasing number of inseminations. In lactating does, there was an interaction between treatment and insemination order. Fertility decreased with increasing inseminations in eCG does but tended to increase above control values in the separated does until the fourth insemination. Control lactating does had significantly less kits per parturition compared to treatments, but eCG lactating does had more stillborn kits. Oestradiol levels increased on day 4 post-partum in all synchronised lactating does (and immediately before artificial insemination in 48 h doe-litter separation), so ovarian activity could be stimulated at early post-partum using all treatments. However, the increase could not be explained by prolactin levels, since there were no effects of suckling absence on plasma prolactin in separated does. In conclusion, separating does from the litter before insemination can be just as effective as eCG treatment, especially during for the first four inseminations.

Circadian rhythms of prolactin secretion in neonatal female rabbits after acute separation from their mothers

Newborn rabbits (Oryctolagus cuniculus) are only nursed for 3-5 min every 24 h and show a circadian increase in activity in anticipation of nursing. The objective of this study was to determine, in neonatal female rabbits after acute separation from the doe for 48 h, the changes in 24-h rhythms of plasma prolactin and median eminence and anterior pituitary concentration of dopamine (DA) and serotonin (5HT). In addition, median eminence concentration of the excitatory amino acid transmitters glutamate (GLU) and aspartate (ASP) and of the inhibitory amino acid transmitters gamma-aminobutyric acid (GABA) and taurine (TAU) was measured. A significant 21% increase of circulating prolactin occurred in isolated pups. In controls pups, plasma prolactin levels showed two peaks, during the first half of the light phase and at the beginning of the scotophase, respectively. In the isolated pups, a phase advance of about 4 h occurred for the two prolactin peaks. Hemicircadian changes of median eminence DA were found in controls, whereas a single daily peak (at 17:00 h) was found in the separated pups. Plasma prolactin and median eminence DA correlated significantly and inversely in the control group only. Pituitary DA content exhibited a single peak in controls and a hemicircadian pattern in isolated pups. Plasma prolactin and pituitary DA correlated significantly in isolated pups only 00000. Pup isolation decreased median eminence 5HT levels, augmented pituitary 5HT levels and disrupted their 24 h rhythmicity. Circulating prolactin correlated inversely with median eminence 5HT and directly with adenohypophysial 5HT only in controls. Isolation of pups generally modified the 24 h pattern of median eminence excitatory and inhibitory amino acid content by causing a prominent decrease at the beginning of the light phase. The results indicate that circadian rhythmicity of prolactin secretory mechanisms in female rabbit pups is significantly affected by pup's isolation from the doe.

Twenty-four hour rhythm of plasma prolactin in female rabbit pups

Lactation in the rabbit is a nocturnal activity, extremely short and regular, that can be a strong synchronizer for the development of circadian rhythmicity in the pups. In the present study, 24-h rhythmicity of plasma prolactin and median eminence and anterior pituitary content of dopamine (DA), serotonin (5HT), gamma-aminobutyric acid (GABA) and taurine were examined in 11 days old female pups kept under 16 h light:8 h dark photoperiods (lights on at 08:00 h). Groups of six to seven female rabbit pups were killed by decapitation at six different time points throughout a 24-h cycle, starting at 09:00 h. Plasma prolactin levels changed significantly throughout the day, showing two peaks, one at first half of rest span (at 13:00 h) and another one at the beginning of the scotophase (at 01:00 h), just preceding doe visit. Median eminence DA content changed in a bimodal way as a function of time of day, displaying two maxima, at the beginning of the rest span and of the activity phase. Median eminence DA and plasma prolactin correlated significantly in an inverse way. Two maxima in median eminence 5HT levels were found, about 4 h in advance to the prolactin peaks. Circulating prolactin correlated inversely with median eminence 5HT content and directly with adenohypophysial 5HT content. Median eminence GABA content reached its maximum at the beginning of the scotophase and correlated significantly with plasma prolactin concentration. A positive correlation between plasma prolactin and adenohypophysial taurine content was observed. These results show that the circadian rhythmicity in prolactin secretory mechanisms in female rabbit pups develops during the early neonatal life.

Melatonin, immune function and aging

Aging is associated with a decline in immune function (immunosenescence), a situation known to correlate with increased incidence of cancer, infectious and degenerative diseases. Innate, cellular and humoral immunity all exhibit increased deterioration with age. A decrease in functional competence of individual natural killer (NK) cells is found with advancing age. Macrophages and granulocytes show functional decline in aging as evidenced by their diminished phagocytic activity and impairment of superoxide generation. There is also marked shift in cytokine profile as age advances, e.g., CD3+ and CD4+ cells decline in number whereas CD8+ cells increase in elderly individuals. A decline in organ specific antibodies occurs causing reduced humoral responsiveness. Circulating melatonin decreases with age and in recent years much interest has been focused on its immunomodulatory effect. Melatonin stimulates the production of progenitor cells for granulocytes-macrophages. It also stimulates the production of NK cells and CD4+ cells and inhibits CD8+ cells. The production and release of various cytokines from NK cells and T-helper lymphocytes also are enhanced by melatonin. Melatonin presumably regulates immune function by acting on the immune-opioid network, by affecting G protein-cAMP signal pathway and by regulating intracellular glutathione levels. Melatonin has the potential therapeutic value to enhance immune function in aged individuals and in patients in an immunocompromised state.

Toxic effects of cadmium on GABA and taurine content in different brain areas of adult male rats

This work assesses the possible changes in gamma amino butyric acid (GABA) and taurine content in the hypothalamus, the median eminence and striatum after the exposure to various doses of cadmium. Cadmium chloride (CdCl2) was administered in the drinking water at the doses of 5, 10, 25, 50 or 100 ppm to adult male rats for 1 month. In the anterior hypothalamus, taurine and GABA content decreased with the dose of 10 ppm of CdCl2 only. Cadmium exposure decreased both GABA and taurine content in mediobasal hypothalamus except for the 50 ppm dose. In posterior hypothalamus GABA and taurine content was not affected by cadmium treatment. As far as the median eminence, 5 or 10 ppm of CdCl2 increased taurine concentration, and at a dose of 5 ppm enhanced GABA content. A significant decrease of GABA and taurine concentration was seen in the striatum at any dose of cadmium used. The concentration of cadmium increased in the hypothalamus and in the striatum in animals receiving CdCl2 in the drinking water at doses of 25, 50 or 100 ppm. The results indicate that cadmium globally decreased GABA and taurine content in the brain areas studied through effects that were not dose dependent.

Experimental allergic encephalomyelitis in male Lewis rats subjected to calorie restriction

This work analyzes the effect of calorie restriction on the development of experimental allergic encephalomyelitis (EAE) in Lewis rats. Plasma levels of ACTH, corticosterone, prolactin and growth hormone (GH) and mitogenic responses in submaxillary lymph nodes were measured. Male Lewis rats (6 weeks-old) were submitted to a calorie restriction equivalent to 66% of food restriction or to a normal diet. Fifteen days later, rats were injected with complete Freund's adjuvant plus spinal chord homogenate (SCH) or with complete Freund's adjuvant alone. Rats were monitored daily for clinical signs of EAE and were killed on day 15 after immunization. Only rats subjected to normal diet exhibited clinical signs of the disease. The increase in plasma ACTH and corticosterone found after SCH immunization in controls was not detectable in calorie restricted rats. Likewise, the correlation between circulating ACTH and corticosterone was no longer found after calorie restriction. Generally, calorie restriction by itself augmented plasma ACTH or corticosterone and this increase was not further amplified by SCH immunization. Only calorie restricted rats exhibited augmented plasma prolactin levels after SCH immunization, and decreased plasma GH levels regardless of immunization. Calorie restriction depressed the mitogenic response of lymphoid cells to concanavalin A but not to lipopolysaccharide. Calorie restricted rats did not exhibit augmented mitogenic response to concanavalin A following SCH immunization as those found in controls. The results are compatible with the view that the course of EAE can be significantly modified by caloric restriction.

Toxic effects of cadmium on the regulatory mechanism of dopamine and serotonin on prolactin secretion in adult male rats

This work was designed to analyze the effects of cadmium on the regulatory mechanism of prolactin in cadmium-exposed rats. Adult male rats were given cadmium at a dose of 25 ppm of cadmium chloride (CdCl2) in the drinking water for 1 month. At the end of the treatment, the rats were killed at six different time intervals throughout a 24 h cycle to measure circulating prolactin levels and dopamine and serotonin content in the median eminence and in both anterior and posterior pituitary. Control and cadmium-exposed animals exhibited significant time of day-dependent variations in plasma prolactin levels and in dopamine and serotonin concentration in all analyzed tissue. Cadmium exposure did not modify the mean values of the hormone around the clock but it modified the amplitude of the secretory peaks at 08:00 and 12:00 h. Cadmium decreased dopamine content in the median eminence, while increased its content in the posterior pituitary and induced a phase advanced peak at 20:00 h. On the other hand, serotonin content was not modified in the median eminence. Only differences in specific time points were observed, while serotonin concentration in anterior and posterior pituitary were increased in cadmium-treated rats. Differences in time peaks were also observed. The negative correlation between plasma prolactin and dopamine content in pituitary, and between plasma levels of the hormone and serotonin content in posterior pituitary, disappeared in cadmium-treated animals.

Role of melatonin in neurodegenerative diseases

The pineal product melatonin has remarkable antioxidant properties. It scavenges hydroxyl, carbonate and various organic radicals, peroxynitrite and other reactive nitrogen species. Melatonyl radicals formed by scavenging combine with and, thereby, detoxify superoxide anions in processes terminating the radical reaction chains. Melatonin also enhances the antioxidant potential of the cell by stimulating the synthesis of antioxidant enzymes like superoxide dismutase, glutathione peroxidase and glutathione reductase, and by augmenting glutathione levels. The decline in melatonin production in aged individuals has been suggested as one of the primary contributing factors for the development of age-associated neurodegenerative diseases, e.g., Alzheimer's disease. Melatonin has been shown to be effective in arresting neurodegenerative phenomena seen in experimental models of Alzheimer's disease, Parkinsonism and ischemic stroke. Melatonin preserves mitochondrial homeostasis, reduces free radical generation, e.g., by enhancing mitochondrial glutathione levels, and safeguards proton potential and ATP synthesis by stimulating complex I and IV activities. Therapeutic trials with melatonin have been effective in slowing the progression of Alzheimer's disease but not of Parkinson's disease. Melatonin's efficacy in combating free radical damage in the brain suggests that it may be a valuable therapeutic agent in the treatment of cerebral edema after traumatic brain injury.

Superior cervical ganglionectomy differentially modifies median eminence and anterior and mediobasal hypothalamic GABA content in male rats: effects of hyperprolactinemia

This work was undertaken to analyze the changes in GABA concentrations in the anterior and mediobasal hypothalamus and in the median eminence after acute or chronic superior cervical ganglionectomy (SCGx), and whether high prolactin levels interfere with the effects of SCGx on GABA content. Acute but not chronic SCGx increased GABA content in all the areas studied, as compared to controls. The presence of a pituitary graft abolished the effects of acute SCGx in the median eminence and anterior hypothalamus, as compared to controls, but potentiated its effects in the mediobasal hypothalamus. Chronic SCGx increased GABA content in the mediobasal and anterior hypothalami, as compared to pituitary grafted controls. Acute SCGx decreased plasma prolactin and GH levels, but chronic surgery did not modify these hormone plasma levels. Acute SCGx increased plasma ACTH levels, whereas chronic SCGx did not modify them. Pituitary grafting increased circulating values of prolactin, ACTH and GH, as compared to controls. Acute SCGx did not modify plasma prolactin levels in grafted animals, although it increased plasma GH levels and decreased those of ACTH in this experimental group. Chronic SCGx further increased both plasma prolactin and GH levels, without modifying plasma ACTH levels. These results suggest that SCGx differentially modifies GABA content within the hypothalamus and median eminence. Induction of hyperprolactinemia in the neonatal age interferes with SCGx effects on both GABA content within the hypothalamus and median eminence and the secretory patterns of the pituitary hormones studied.

Cadmium exposure differentially modifies the circadian patterns of norepinephrine at the median eminence and plasma LH, FSH and testosterone levels

This work was designed to analyze the cadmium effects on time-of-day variations of norepinephrine (NE) content in median eminence and on plasma levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone in adult male rats. Rats were given cadmium at a dose of 25 ppm of cadmium chloride (CdCl(2)) in the drinking water for 1 month. Significant 24-h changes of NE content in the median eminence, plasma LH and testosterone levels occurred in control animals. Cadmium exposure induced a phase advance of the nocturnal peak of NE content that was described in the control group, to 12h and increased its amplitude. However, the mean NE content was not changed by cadmium. Metal exposure abolished the daily pattern of plasma LH levels, although the mean levels of the hormone were not modified by cadmium. For testosterone, the metal increased the amplitude of its nocturnal peak and induced the appearance of another peak during the light phase at 12h, thus increasing the mean plasma levels of this hormone. An interaction between the metal and time for NE and plasma testosterone levels was observed. These data suggest that cadmium exerts differential effects at the median eminence, the pituitary and the testes, that may explain the changes in the 24-h pattern of plasma testosterone levels.

Changes of prolactin regulatory mechanisms in aging: 24-h rhythms of serum prolactin and median eminence and adenohypophysial concentration of dopamine, serotonin, (γ-aminobutyric acid, taurine and somatostatin in young and aged rats

Twenty-four hour rhythmicity of serum prolactin and median eminence and anterior pituitary content of dopamine (DA), serotonin (5HT), gamma-aminobutyric acid (GABA), taurine and somatostatin were examined in 2 months-old and 18-20 months-old Wistar male rats. The concentration of prolactin was higher in aged rats, with peaks in both groups of rats at the early phase of the activity span. Median eminence DA content of young rats attained its maximum at the middle of rest span and decreased as prolactin levels augmented while the lowest values of adenohypophysial DA were observed at the time of prolactin peak. DA rhythmicity disappeared in aged rats. GABA content of median eminence and adenohypophysis was lower in aged rats, with maximal values of median eminence GABA at light-dark transition in young rats and at the second half of activity span in aged rats. Serum prolactin correlated positively with median eminence GABA in young rats and negatively with pituitary GABA in young and aged rats. Median eminence somatostatin peaked at the beginning of the activity phase (young rats) or at the end of the rest phase (aged rats). Prolactin levels and somatostatin content correlated significantly in young rats only. Median eminence and pituitary 5HT and taurine content did not change with age. The results indicate disruption of prolactin regulatory mechanisms with aging in rats.

Differential effects of light/dark recombinant human prolactin administration on the submaxillary lymph nodes and spleen activity of adult male mice

OBJECTIVES

Day/night variations in cellularity, percentage of CD4+, CD8+ and double-positive (CD4+-CD8+) lymphocytes, lipopolysaccharide (LPS)- and concanavalin A (Con A)-induced lymphocyte proliferation and natural killer (NK) activity, and the effect of timed administration of recombinant human prolactin (h-PRL) on the above-mentioned parameters were investigated in the submaxillary lymph nodes and spleen of adult male mice.

RESULTS

In controls, the percentage of CD4+, double-positive lymphocytes, LPS- or Con A-induced blastogenic proliferation and NK activity in the spleen differ during the dark phase as compared to the light phase. When administered during the dark period, h-PRL induced immunosuppresion in the percentage of CD4+, double-positive (CD4+-CD8+) lymphocytes. Con A- and LPS-induced lymphocyte proliferation and NK activity as compared to untreated controls. When h-PRL was administered during the light period, the cellularity increased, and h-PRL was immunosuppressive in Con A- and LPS-induced lymphcoyte proliferation and NK activity as compared to controls. Moreover, in control submaxillary lymph nodes the cellularity, percentage of CD8+, double-positive lymphocytes, blastogenic proliferation in the presence of Con A and LPS and NK activity differ when comparing the dark with the light phase. When administered during the dark period h-PRL induced immunosuppression in the percentage of double-positive (CD4+-CD8+) lymphocytes, Con A- and LPS-induced lymphocyte proliferation as compared to controls. When h-PRL is administered during the light period, no effects were observed.

CONCLUSIONS

These results indicate the existence of differential day/night variations in the cellular immune response depending upon the lymphoid organ considered. Because of the administration of h-PRL a differential modulation of this circadian variation was also observed.

Effect of cadmium on 24-h variations in hypothalamic dopamine and serotonin metabolism in adult male rats

This study was designed to analyze the possible cadmium effects on time-of-day variations of anterior, mediobasal, and posterior hypothalamic contents of dopamine (DA), serotonin (5-HT), and norepinephrine (NE) content in adult male rats. Also DA and 5-HT metabolism, as expressed by the ratio 3,4-dihydroxyphenyl acetic acid (DOPAC) to DA and 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT, respectively, were studied. Adult male rats were given cadmium at a dose of 25 ppm of cadmium chloride in drinking water for 1 month. Age-matched rats having access to cadmium-free water were used as controls. Weight gain for the whole period was not changed by cadmium exposure. The metal accumulated in the hypothalamus of rats. In the three hypothalamic regions, significant 24-h variations of NE and 5-HT concentration were found in controls, while DA content changed rhythmically in mediobasal hypothalamus only. Mean content of NE, 5-HT, and DA of anterior, mediobasal, and posterior hypothalamus decreased after cadmium exposure. After cadmium the 24-h pattern of NE changed only in mediobasal hypothalamus, whereas the metal changed significantly the pattern of 5-HT in all regions. DOPAC to DA and 5-HIAA to 5-HT ratios decreased and were differentially changed in all hypothalamic regions analyzed in cadmium-treated rats. There was a statistically significant relationship between time of administration of metal and time that the change took place in biogenic amines in the hypothalamus. These results indicate that cadmium may depress hypothalamic biogenic amine release.

Effect of cadmium on lymphocyte subsets distribution in thymus and spleen

This work was designed to analyze the possible dose dependent effects of cadmium on the distribution of lymphocyte subsets within the thymus and spleen. Cadmium accumulation was also evaluated in these tissues. For this purpose, adult male rats were exposed for one month to 0, 5, 10, 25, 50 or 100 ppm of cadmium chloride (CdCl2) in the drinking water. In both spleen and thymus, the B lymphocytes increased with the doses of 5 and 10 ppm of CdCl2, and decreased with the doses of 25-100 ppm. In spleen, the doses of 25 and 50 ppm decreased CD4+ cells and the doses of 5 and 10 ppm increased CD8+ cells, while the percentage of thymus T, CD4+, CD8+ and CD4(+)-CD8+ cells was not modified by cadmium treatment at any dose used in this study. After cadmium exposure, the metal was accumulated in the spleen only from the dose of 50 ppm on, and in the thymus, from the dose of 10 ppm on. In conclusion, although the accumulation of the metal is higher in thymus than in spleen, the metal affected CD4+ and CD8+ lymphocytes at the spleen but not at the thymus.

Superior cervical ganglionectomy effects on median eminence and anterior and mediobasal hypothalamic taurine content in male rats: effects of hyperprolactinemia

The neuroendocrine sequelae of acute or chronic superior cervical ganglionectomy in control or pituitary-grafted rats were studied by analyzing both plasma prolactin, growth hormone (GH) and ACTH levels, and taurine (TAU) content in the hypophysiotropic area of the hypothalamus or the median eminence. As expected, after either acute or chronic ganglionectomy, norepinephrine (NE) content decreased in the brain areas studied, although the values remained higher in hyperprolactinemic rats. TAU content was differentially modified by acute vs. chronic surgeries, thus indicating the possible existence of hypothalamic interactions between TAU and NE to regulate pituitary hormone secretion. Indeed, associated differential changes in plasma prolactin, GH and ACTH levels may be due to the observed TAU changes. As expected, pituitary grafting increased plasma prolactin, GH and ACTH levels, so that the presence of a pituitary graft differentially interferes with the effects of either surgery not only on TAU content but also on the plasma levels of the hormone studied. Globally, ongoing studies confirm the differential effects of acute and chronic superior cervical ganglionectomy on plasma prolactin, GH and ACTH levels, and provide new evidence about its effects on TAU content in the hypophysiotropic area of the hypothalamus and the median eminence that may partially explain the changes observed in the pituitary hormones studied.

Effects of overexpression of growth hormone on T cell activity in transgenic mice

Growth hormone plays a key role in the maturation and maintenance of the immune response, however, the effects of chronic high circulating concentrations of the hormone on the immune system is poorly understood. Transgenic mice overexpressing bovine growth hormone (b-GH) gene, fused to the rat phosphoenolpyruvate carboxykinase promoter (PEPCK), with very high plasma concentration of heterologous b-GH and their littermate normal siblings were used. Spleen cellularity, percentages of total T lymphocytes, CD4+ and CD8+ cells, ratio of T cell subpopulations, mitogen-induced lymphocyte proliferation and natural killer (NK) cell activity were examined in male transgenic mice and normal littermate mice at 2 and 6 months of age. The number of splenic lymphocytes was greater in transgenic mice than in matched normal littermates at both ages. The NK cell activity was lower in transgenic mice than in the matched normal littermates at both ages, with the lowest values found in older mice. The b-GH transgenic mice had lower percentages of T cells at both ages, however, in young transgenic mice, the percentage of CD4+ cells was reduced while percentage of CD8+ cells was increased in comparison to normal controls. Both basal and mitogen-induced proliferation capacity of splenocytes were reduced in PEPCK-b-GH-25 mice as compared to normal littermates of both ages. Proliferative indexes in response to concanavalin A and phytohemagglutinin were markedly decreased in 6 month old PEPCK-b-GH-25 mice as compared to littermate controls or younger mice. These results indicate that overexpression of b-GH in mice is associated with decreased T cell function and that these abnormalities are age-dependent.

Chronobiological features of the immune system. Effect of calorie restriction

The circadian organization of living organisms is fully established being a key component the activity of the neuro-endocrin-immune system that maintains the homeostasis. Secondary lymph organs, such as submaxillary lymph nodes and spleen, have been shown to exhibit a 24 h variation in blastogenic proliferative capacity and distribution of B and T subsets, with specific achrophases depending on the parameter studied or the lymphoid organ considered. However, less is known about the thymus. The immune system has been shown to change by calorie restriction, although no information is available about possible effects in 24 h variations. Similar questions can be posed for the neuro-endocrine system. As an example, some data are shown in this article about the effects of calorie restriction on the neuro-endocrin-immune system in growing male Wistar rats. Calorie restriction blunted the circadian secretory pattern of TSH observed in the control group that was characterized by the existence of two peaks at 17:00 or 01:00 h and that explained the low basal metabolic rate of these animals under this experimental condition. Concerning the immune system, the thymus gland exhibited 24 h variations in T, B and immature cells in both control and calorie-restricted male rats, thus confirming the circadian organization of the immune system. Moreover this circadian organization was changed by calorie restriction.

Effects of oral cadmium exposure through puberty on plasma prolactin and gonadotropin levels and amino acid contents in various brain areas in pubertal male rats

This work was undertaken to analyze if the effects of oral cadmium exposure through puberty, on plasma prolactin and gonadotropin levels are mediated by changes in amino acid contents in various brain areas in male rats. The contents of glutamate, glutamine, aspartate, GABA and taurine in the median eminence, anterior, mediobasal and posterior hypothalamus and prefrontal cortex in pubertal male rats exposed to 50 ppm of cadmium chloride (CdCl2) in the drinking waterfor 1 month (through puberty) were measured by high performance liquid chromatography (HPLC). Plasma prolactin, LH and FSH levels were measured by specific RIA methodology. Plasma prolactin levels decreased after cadmium exposure, whereas plasma levels of LH and FSH were not changed by the metal administration. After cadmium exposure, both glutamine and glutamate contents decreased in the median eminence and in anterior and posterior hypothalamus. Metal exposure also decreased aspartate content in anterior and posterior hypothalamus, but increased it in prefrontal cortex. GABA content decreased in any studied brain region after cadmium administration. Besides, the metal decreased taurine content in the median eminence, anterior and posterior hypothalamus and in prefrontal cortex. The results suggest that cadmium effects on plasma prolactin levels may be partially explained by the changes in aspartate, glutamate or taurine contents, but not by the decrease in GABA content in the brain regions studied.

Possible role of glutamate, aspartate, glutamine, GABA or taurine on cadmium toxicity on the hypothalamic pituitary axis activity in adult male rats

This work was designed to evaluate the possible changes in glutamate, aspartate, glutamine, GABA and taurine within various hypothalamic areas the striatum and prefrontal cortex after oral cadmium exposure in adult male rats, and if these changes are related to pituitary hormone secretion. The contents of glutamine, glutamate, aspartate, GABA and taurine in the median eminence, anterior, mediobasal and posterior hypothalamus, and in prefrontal cortex in adult male rats exposed to 272.7 micromol l(-1) of cadmium chloride (CdCl2) in the drinking water for one month. Cadmium diminished the content of glutamine, glutamate and aspartate in anterior hypothalamus as compared to the values found in the untreated group. Besides, there is a decrease in the content of glutamate, aspartate and taurine in the prefrontal cortex. The amino acids studied did not change in median eminence, mediobasal and posterior hypothalamus or the striatum by cadmium treatment. Plasma prolactin and LH levels decreased in rats exposed to the metal. These results suggest that (1) cadmium differentially affects amino acid content within the brain region studied and (2) the inhibitory effect of cadmium on prolactin and LH secretion may be partially explained by a decrease in the content of both glutamate and aspartate in anterior hypothalamus, but not through changes in GABA and taurine.

Fos immunoreactivity in the suprachiasmatic nuclei of golden hamsters bearing an ectopic pituitary graft

Young male golden hamsters, made hyperprolactinemic by a pituitary graft under the kidney capsule, were exposed to a light pulse (1,000 lx/30 min) at Zeitgeber time (ZT) 18. Controls included hamsters receiving a sham graft (muscle). Fos immunoreactive cells were counted in both suprachiasmatic nuclei (SCN) of each animal, using an image analyzer system. The Fos immunoreactivity (Fos-ir) of the ventrolateral and dorsomedial SCN regions was greater in the pituitary-grafted hamsters. Indeed, light induced the greatest response in grafted animals in both SCN regions. However, the SCN of pituitary-grafted hamsters in the absence of light showed the lowest Fos-ir in both regions. The results support the occurrence of a dual effect of hyperprolactinemia on Fos-ir in the SCN of hamsters at ZT 18, with inhibition of Fos expression in the absence of light and potentiation of early gene expression when animals were exposed to a light pulse.

Alternate cadmium exposure differentially affects amino acid metabolism within the hypothalamus, median eminence, striatum and prefrontal cortex of male rats

This work was designed to analyze the possible changes in glutamate, aspartate and glutamine content induced by cadmium exposure in the hypothalamus, striatum and prefrontal cortex of rats, using an alternate schedule of metal administration. Pubertal-adult differences were also evaluated. In adult control rats, glutamate and aspartate contents in the anterior hypothalamus decreased as compared to pubertal controls. After cadmium administration from day 30 to 60 of life, the content of anterior hypothalamic glutamate and aspartate diminished. In adult control animals, the glutamine content increased in mediobasal hypothalamus as compared to pubertal controls. After cadmium exposure from day 30 to 60 of life, the mediobasal glutamine content increased, and after cadmium treatment from day 60 to 90 of life, the mediobasal aspartate content decreased. In adult control rats the content of glutamine, glutamate and aspartate of the posterior hypothalamus decreased significantly. After cadmium administration in pubertal animals, posterior hypothalamic contents of glutamine, glutamate and aspartate diminished. Cadmium treatment of adult animals caused a decrease in glutamine content, as compared to controls. In adult control rats, only glutamate and aspartate content increased in the prefrontal cortex as compared to the values found in pubertal controls. When cadmium was administered to adult animals, only the aspartate content decreased. In the striatum, cadmium decreased the glutamine and aspartate contents when administered from day 60 to 90 of life. These data suggest that cadmium differentially affects amino acid metabolism in the hypothalamus, striatum and prefrontal cortex. Age-dependent effects of cadmium on these brain areas appeared to have occurred.

Cadmium effects on dopamine turnover and plasma levels of prolactin, GH and ACTH

This paper analyzes possible dopamine (DA) mediated cadmium effects on plasma levels of prolactin, growing hormone (GH) and adrenocorticotropic hormone (ACTH), and if these changes are related to metal accumulation. For that purpose, adult male rats were treated with 50 mg/L of CdCl2 in the drinking water for one month. Plasma levels of prolactin, ACTH and GH were measured by specific double antibody radioimmunoassays. DA was measured by high performance liquid chromatography using electrochemical detection. Cadmium content in the tissues was measured by atomic absorption spectometry with graphite furnace. Analysis was performed by using a T-Student test. Metal exposure increased DA content (34.79+/-3.06 vs. 18.2+/-2.88 pg/mg protein) and decreased its turnover (0.40+/-0.07 vs. 0.75+/-0.06) in posterior hypothalamus. Cadmium also decreased DA turnover in median eminence (0.48+/-0.15 vs. 1.50+/-0.63). Plasma levels of prolactin and GH decreased (2.4+/-0.11 vs. 3.1+/-0.15 ng/mL and 5.37+/-0.05 vs. 9.87+/-1.8 ng/mL respectively), while those of ACTH increased (2.73+/-0.14 vs. 1.7+/-0.16 ng/mL). Cadmium concentration increased in both hypothalamus (4.88+/-0.34 vs. 0.72+/-0.2 microg/g) and pituitary (22.82+/-4.57 vs. 5.02+/-1.25 microg/g) after the metal exposure. These results suggest that cadmium effects on the secretion of these hormones are not mediated by dopamine and might be correlated to the metal accumulation at pituitary level.

Effect of parasympathetic decentralization on interferon-gamma release from rat submandibular lymph nodes in vitro

The aim of this study was to examine the regulation of interferon (IFN)-gamma release by cells from submandibular lymph nodes of rats subjected to a unilateral parasympathetic decentralization by severing the ipsilateral chorda tympani 7 days earlier. Cells obtained from contralateral sham-operated submandibular lymph nodes were employed as control. Parasympathetic decentralization of lymph nodes resulted in significantly less IFN-gamma release as compared to that found in innervated lymph nodes. Mitogens (lipopolysaccharide, concanavalin A) stimulated IFN-gamma release in cells derived from the innervated lymph nodes only. The muscarinic agonist metacholine decreased IFN-gamma release in cells derived from innervated lymph nodes. At the highest concentration employed (10(-4) M), metacholine suppressed the stimulatory effect of mitogens on IFN-gamma release in cells of innervated lymph nodes while the muscarinic antagonist atropine (10(-8) - 10(-4) M) lacked to affect IFN-gamma release. Addition of nicotine (10(-5) - 10(-3) M) failed to modify IFN-gamma release. The results support the occurrence of significant effects of local parasympathetics in modulating IFN-gamma release by submandibular lymph nodes.

Cadmium effects on hypothalamic-pituitary-testicular axis in male rats

This study analyzes cadmium effects at the hypothalamic-pituitary-testicular axis. Male rats were given cadmium during puberty or adulthood. Cadmium exposure through puberty increased norepinephrine content in all hypothalamic areas studied, but not in the median eminence. Metal exposure increased serotonin turnover in median eminence and the anterior hypothalamus, while decreased it in mediobasal hypothalamus. Also, decreased plasma levels of testosterone were found. Cadmium exposure during adulthood increased norepinephrine content in posterior hypothalamus and decreased the neuro-transmitter content in anterior and mediobasal hypothalamus. Decreased circulating levels of luteinizing hormone (LH) and testosterone and increased plasma follicle stimulating hormone (FSH) levels were also observed. Cadmium accumulated in all analyzed tissues. Various parameters showed age-dependent changes. These data suggest that cadmium globally effects hypothalamic-pituitary-testicular axis function by acting at the three levels analyzed and that an interaction between cadmium exposure and age emerge.

Changes in substance P content at the hypothalamic-pituitary axis during the Wallerian degeneration of peripheral sympathetic neurons after superior cervical ganglionectomy in male rats: effect of hyperprolactinemia

The effects of Wallerian degeneration of the peripheral sympathetic neurons projecting to the hypothalamus on the mechanism of interaction between prolactin and substance P (SP) were examined. The effects of superior cervical ganglionectomy (SCGx) on SP content in various hypothalamic regions and in the hypophysis were evaluated in control and hyperprolactinemic rats. Male rats that received pituitary transplants at the age of 5 days and age-matched sham-operated controls were used. Pituitary grafting significantly increased circulating values of prolactin, as did SCGx. In hyperprolactinemic rats, SCGx partially decreased plasma prolactin levels. Neonatal hyperprolactinemia decreased SP content in the anterior (AH) and posterior (PH) hypothalamus and in the median eminence (ME), but increased it in the mediobasal hypothalamus (MBH). Acute SCGx significantly increased SP in the MBH, PH, and ME. SCGx in hyperprolactinemic animals further increased SP content in MBH. In the ME and Ah, SCGx in pituitary grafted rats decreased SP content as compared with the controls. In the pituitary gland (PG), SCGx only decreased SP content in hyperprolactinemic, but not in control rats. An interaction between peripheral nor-adrenergic neurons and prolactin to regulate SP within the hypothalamus was positive in the MBH, AH, ME, and PG, but not in the PH. These data indicate the existence of interactive mechanisms between prolactin and the peripheral sympathetic neurons to regulate SP content at the hypothalamic-pituitary axis. Interrelationships between prolactin and SP were also observed.

Effect of melatonin on 24h changes in plasma protein levels during the preclinical phase of Freund's adjuvant arthritis in rats

The 24h rhythms in plasma protein concentration were examined in rats on the third day after injection of Freund's complete adjuvant or adjuvant's vehicle, performed 3h after light on. In rats treated with adjuvant's vehicle, peak values of albumin and gamma globulin occurred during the nocturnal activity span (P < .02 and P < .0001, respectively), while those of alpha-1, alpha-2, and beta globulins were found late during the rest span (P < .002, P < .0001, and P < .0004, respectively). Freund's adjuvant administration abolished temporal changes in plasma albumin and beta globulin levels. It also decreased the amplitude of daily changes in alpha-1 and alpha-2 globulin (P < .05) and diminished mean values of alpha-2 globulin (P < .01). Pretreatment of rats with melatonin (30 microg daily) for 11 days, 11h after light on, counteracted mycobacterial adjuvant-induced suppression of the 24h rhythms in albumin and alpha-1, alpha-2, and beta globulins. The results further support the existence of preventive properties of a pharmacological dose of melatonin in situations in which a lost of circadian rhythmicity is expected.

Alternate cadmium exposure differentially affects the content of gamma-aminobutyric acid (GABA) and taurine within the hypothalamus, median eminence, striatum and prefrontal cortex of male rats

This work examines changes of gamma aminobutyric acid (GABA) and taurine contents in the hypothalamus, striatum and prefrontal cortex of the rat after an alternate schedule of cadmium administration. Age-associated changes were also evaluated, of those before puberty and after adult age. In control rats GABA content decreased with age in the median eminence and in anterior, mediobasal and posterior hypothalamus, prefrontal cortex and the striatum. Taurine content showed similar results with the exception of mediobasal hypothalamus and striatum, where no changes were detected. In pubertal rats treated with cadmium from 30 to 60 days of life, GABA content significantly decreased in all brain regions except in the striatum. When cadmium was administered from day 60 to 90 of life, GABA content was significantly changed in prefrontal cortex only compared with the age matched controls. Taurine content showed similar results in pubertal rats, with the exception of the median eminence and the mediobasal hypothalamus, neither of which showed a change. However, when cadmium was administered to rats from day 60 to 90 of life, taurine content only changed in prefrontal cortex compared with the age matched controls. These results suggest that cadmium differentially affects GABA and taurine contents within the hypothalamus, median eminence, striatum and prefrontal cortex as a function of age.

Effect of superior cervical ganglionectomy on 24-h variations in hormone secretion from the anterior hypophysis and in hypothalamic monoamine turnover during the preclinical phase of Freund's adjuvant arthritis in rats

The effect of superior cervical ganglionectomy (SCGx) on 24-h rhythms of circulating adrenocorticotropic hormone (ACTH), growth hormone (GH), prolactin and luteinizing hormone (LH) and of hypothalamic noradrenaline content and dopamine and serotonin turnover, was assessed in rats 3 days after administering Freund's complete adjuvant. In sham-operated rats, Freund's adjuvant injection increased serum ACTH without affecting its diurnal rhythmicity. SCGx, performed 10 days earlier, suppressed 24-h rhythmicity and augmented mean values of circulating ACTH. A depressive effect of immunization on GH release was found in both sham-operated and SCGx rats. GH concentrations did not exhibit diurnal rhythmicity and decreased after immunization. Time-of-day-related changes in serum prolactin were significant for all examined groups, except for SCGx-immunized rats. Freund's adjuvant administration augmented prolactin secretion. Daily changes in serum LH concentration and a decrease after immunization were found in both sham-operated and SCGx rats. SCGx: (i) counteracted inhibition of daily variations of noradrenaline content in medial hypothalamus of Freund's adjuvant-injected rats; (ii) decreased anterior hypothalamic dopamine turnover and augmented it in the medial hypothalamus; (iii) lowered amplitude of serotonin turnover rhythm in medial hypothalamus. The data indicate that several early changes in levels and 24-h rhythms of circulating ACTH and prolactin, and in hypothalamic noradrenaline content and dopamine and serotonin turnover, were modified by a previous SCGx in Freund's adjuvant-injected rats.

Aging-induced changes in 24-h rhythms of mitogenic responses, lymphocyte subset populations and neurotransmitter and amino acid content in rat submaxillary lymph nodes during Freund's adjuvant arthritis

In young (two months) and aged (18 months) male rats injected s.c. with Freund's adjuvant or adjuvant's vehicle 18 days earlier, 24-h variations in mitogenic responses, lymphocyte subsets and monoamine and amino acid content were examined in submaxillary lymph nodes. Mitogenic responses to concanavalin A (Con A) and lipopolysaccharide (LPS) were higher during the light phase of daily photoperiod. Old rats exhibited a suppressed or impaired mitogenic response to Con A but not to LPS. Acrophases of 24-h rhythm in lymphocyte subset populations in submaxillary lymph nodes were: 18:37-19:44h (B cells), 09:00-10:08h (T and CD4(+) cells) and 12:19-15:58h (CD8(+) cells). Aging augmented B cells and decreased T, CD4(+) and CD8(+) cells. Significant correlations were found between Con A activity and T cells, between lymph node 5HT content and B, T and CD8(+) lymphocytes, and between lymph node 5HT and taurine and GABA content. Aging increased lymph node 5HT content but did not modify NE content. Lymph node concentration of aspartate, glutamate and taurine was higher at night while that of GABA attained peak values at late afternoon. Old rats injected with Freund's adjuvant showed a higher mean value (glutamate) and smaller amplitude (glutamate, taurine) than their respective young controls. The results further document the effects of aging on the chronobiology of the immune system.

Effect of local sympathectomy on 24-h changes in mitogenic responses and lymphocyte subset populations in rat submaxillary lymph nodes during the preclinical phase of Freund's adjuvant arthritis

Wistar male rats received a bilateral superior cervical ganglionectomy or sham-operation and 10 days later were injected with Freund's complete adjuvant or its vehicle. Two days later, rats were killed at six different time intervals throughout a 24-h cycle. The mitogenic effect of lipopolysaccharide (LPS) and concanavalin A (Con A) and the relative size of lymphocyte subset populations were measured in submaxillary lymph nodes. Cells from sympathectomized lymph nodes showed a lower response to Con A. Freund's adjuvant injection decreased amplitude of daily rhythm in Con A response, an effect prevented by denervation. Generally, ganglionectomy increased Con A response at the early phase of arthritis. Acrophases for Con A and LPS effect occurred at early afternoon and did not change after ganglionectomy. Administration of Freund's adjuvant caused a 10-h advance in acrophase of LPS mitogenic activity, an effect prevented by ganglionectomy. Significant 24-h rhythms were observed in relative size of lymph node B and T cells. Denervation augmented amplitude of rhythm in B cells in adjuvant's vehicle-injected rats. As far as T lymphocyte subsets, acrophases occurred at the afternoon (CD4(+) and CD4(+)-CD8(+) cell types) or at night (CD8(+) cell types). Immunization augmented amplitude of 24-h rhythms in CD4(+)-CD8(+) cells regardless of innervation whereas denervation counteracted the suppression of daily rhythm in CD8(+) cells seen in arthritis. The results indicate that some of the changes seen in 24-h organization of immune responses in lymph nodes at an early phase of arthritis are modified by severing the local sympathetic nerves.

Age-dependent changes in 24-hour rhythms of thymic and circulating growth hormone and adrenocorticotropin in rats injected with Freund's adjuvant

OBJECTIVE

To analyze the 24-hour changes in thymic and serum concentration of growth hormone (GH) and adrenocorticotropin (ACTH) and their correlation with thymic concentrations of glutamate, aspartate, taurine and GABA in young and old rats during the acute phase of adjuvant's arthritis.

METHODS

Young (50-day-old) and old (18-month-old) rats were injected subcutaneously with Freund's adjuvant or its vehicle (paraffin oil containing 15% mannide monooleate). Eighteen days later, they were killed at six different time intervals throughout a 24-hour cycle. Serum and thymic levels of GH and ACTH were measured by radioimmunoassay. Thymic amino acid concentration was measured by HPLC. A quantitative assessment of arthritis was made in an independent group of rats by plethysmography.

RESULTS

Old rats injected with Freund's adjuvant exhibited fewer clinical signs of inflammation than young rats. Significant 24-hour changes in thymic and serum GH occurred, except for serum GH in adjuvant's vehicle-treated old rats. Aging augmented thymic GH and decreased serum GH. Immunization with Freund's adjuvant did not modify GH concentration. Thymic and serum concentration of GH correlated negatively. Thymic ACTH varied significantly over 24 h with maxima during the dark phase, except in Freund's adjuvant-treated young rats. Maximal serum ACTH levels occurred in the late afternoon except in Freund's adjuvant-treated old rats which showed maxima at night. Immunization with Freund's adjuvant augmented thymic and circulating concentrations of ACTH. Thymic and serum concentration of ACTH correlated positively. Thymic concentration of glutamate, aspartate and taurine decreased in aged rats and correlated significantly with thymic ACTH.

CONCLUSION

The results support the existence of a thymic compartment of GH and ACTH that may be independently regulated.

Pubertal and postpubertal cadmium exposure differentially affects the hypothalamic-pituitary-testicular axis function in the rat

The effects of administration of cadmium on levels of hormones along the hypothalamic-pituitary-testicular axis were studied in rats. Male rats were treated subcutaneously from days 30 to 60 (pubertal rats) or from days 60 to 90 of life (postpubertal rats), with cadmium chloride (CdCl2) at a dose of 0.5 or 1 mg/kg, every 4 days in an alternate schedule, starting from the lower dose. Age-matched control rats received 0.3 m of saline subcutaneously every 4 days. The levels of norepinephrine (NE) increased on cadmium exposure in pubertal rats in all hypothalamic areas studied, but decreased in the median eminence. In contrast, in postpubertal rats the levels of NE only did not decrease in the posterior hypothalamus. Serotonin (5-HT) concentration in pubertal and postpubertal rats decreased in all hypothalamic regions, while serotonin turnover (measured by the ratio 5-hydroxyindolacetic acid/serotonin [5-HIAA/5-HT]) increased in the anterior hypothalamus. The serotonin metabolism was also increased in the median eminence in the pubertal and in the posterior hypothalamus in the postpubertal rats. Plasma levels of luteinizing hormone (LH) were not modified by cadmium in both age groups, but follicle stimulating hormone (FSH) levels decreased in postpubertal rats, but was not altered in pubertal rats. Plasma levels of testosterone increased in pubertal rats but decreased in postpubertal rats. Cadmium accumulation increased in the hypothalamus and testes in all the cadmium-treated animals, whereas in the pituitary accumulation of cadmium was found only in postpubertal rats. These data suggest that cadmium exerts age-dependent effects on the hypothalamic-pituitary-testicular axis function, and a disruption of the regulatory mechanisms of the hypothalamic-pituitary-gonadal axis emerges.

Effect of chronic hyperprolactinemia on daily changes of glutamate and aspartate concentrations in the median eminence and different hypothalamic areas of male rats

The 24h changes of glutamate (GLU) and aspartate (ASP) were studied in the median eminence (ME) and hypothalamic areas. It was analyzed whether prolactin may change their daily patterns. The hypothalamic concentration of these amino acids was measured by high-performance liquid chromatography (HPLC) with fluorometric detection. Plasma prolactin levels increased over the 24h light-dark cycle after pituitary grafting compared to controls, and its circadian rhythm was disrupted. In controls, aspartate and glutamate in the hypothalamic areas studied followed a specific daily variation or showed no rhythmicity. In the median eminence, hyperprolactinemia seem to phase advance the aspartate or glutamate peaks from 16:00 to 12:00. In the mediobasal hypothalamus, hyperprolactinemia altered daily changes of aspartate and significantly decreased its concentration. Also, it seems to delay the nocturnal glutamate peak compared to controls. In the posterior hypothalamus, hyperprolactinemia did not change aspartate and glutamate concentrations and their daily changes, although it increased the glutamine concentration. These data show the existence of 24h changes of amino acid concentration in three of the hypothalamic regions studied. Increased plasma prolactin levels differentially affected these patterns depending on the hypothalamic area analyzed.

Psychoimmune neuroendocrine integrative mechanisms revisited

This review analyzes recent publications on the topic of psycho-immune-neuroendocrine integrative mechanisms. Results on the role of cytokines in cognitive processes and in a major neuroendocrine event, i.e. the release of gonadotropin-releasing hormone, are discussed, as are the effects of cytokines on central neurotransmission. The control of immune responses by local sympathetic nerves, a major pathway in neuroimmune communication, is discussed. This review also updates information indicating that melatonin is a circulating signal affecting the periodic organization of the immune response.

Effect of melatonin treatment on 24-h variations in responses to mitogens and lymphocyte subset populations in rat submaxillary lymph nodes

Wistar male rats were injected s.c. with melatonin (30 microg) or vehicle, 1 h before lights off, for 11 days. Ten days after beginning melatonin treatment, rats received Freund's complete adjuvant or its vehicle s.c., and after 2 days, they were sacrificed at six different time intervals throughout a 24-h cycle. The mitogenic effect of lipopolysaccharide (LPS) and concanavalin A (Con A), the activity of ornithine decarboxylase (ODC) and the relative size of lymphocyte subset populations were measured in submaxillary lymph nodes. In control rats, the mitogenic effects of LPS and Con A and ODC activity peaked during the afternoon. Injection of Freund's adjuvant induced a 10-h shift in the diurnal rhythm of the mitogenic effect of LPS to attain maximal values at night. Melatonin pretreatment blunted the daily variations in the mitogenic activity of Con A or LPS and, when given to Freund's adjuvant-injected rats, augmented mesor and amplitude of diurnal rhythm in ODC activity. Maxima in B cell number occurred at night whereas those of T and B-T cell number occurred during the afternoon. During the early phase of immunization tested, the number of B cells augmented and the amplitude of its diurnal rhythmicity increased both after immunization and following melatonin pretreatment. Maxima of 24-h rhythms in CD4+ and CD4+/CD8+ cell populations occurred during the afternoon while those of CD8+ cells occurred at late night. Melatonin significantly augmented CD4+ cell number and decreased CD8+ cell number; it therefore augmented the CD4+:CD8+ ratio. The results suggest that pretreatment with a pharmacological dose of melatonin exerts immunomodulating effects at an early, preclinical, phase of Freund's adjuvant-induced arthritis in rats.

Possible estrogenic and/or antiandrogenic effects of methoxychlor on prolactin release in male rats

Methoxychlor (MTX) is a pesticide currently used as a substitute for dichloro-diphenyl-trichloroethane (DDT). This organochloride insecticide has some estrogenic properties, and may modify the feedback mechanisms of steroids on the hypothalamus and pituitary. This work was undertaken to explore the possible effects of MTX on the episodic prolactin release and to analyze whether these effects are mediated by dopamine (DA), luteinizing hormone (LH), and/or testosterone. Adult male Sprague-Dawley rats were administered 25 mg/kg/day of MTX in sesame oil for 30 days. Control animals received vehicle only. The episodic prolactin release and plasma testosterone levels were measured as well as the dopamine (DA) content in the median eminence (ME) and in the anterior (AH), mediobasal (MBH), and posterior (PH) hypothalamus. The mean serum prolactin levels and absolute pulse amplitude of the hormone increased after the xenobiotic administration, whereas its relative pulse amplitude diminished. The frequency and duration of prolactin peaks and its half-life were not modified by the treatment with the pesticide. On the other hand, methoxychlor decreased the DA content in ME, increased it in AH, and did not change it in MBH or PH. MTX decreased plasma levels of LH and testosterone compared with controls. These data suggest estrogenic and antiandrogenic effects of MTX on the episodic prolactin secretion; the changes observed in prolactin release could be explained, at least in part, by some of the changes of DA at the hypothalamus and of LH at the pituitary, but not by changes of testosterone at the testicular level.

Prolactin and cyclosporine modulate adenosine transporters and adenosine A1 receptors in the rat brain

The existence of adenosine A1 receptors and adenosine transporters in the central nervous system has been well demonstrated, although their possible modulation by hormones and/or exogenous drugs is poorly understood. To further analyze these modulatory mechanisms, the effects of prolactin and cyclosporine (CyA) on adenosine A1 receptors and transporters were analyzed in the central nervous system. For this purpose the number and affinity of adenosine A1 receptors were measured using the specific antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) and the transporters with the high affinity ligand nitrobenzylthioinosine (NBTI). This procedure was carried out in hyperprolactinemic and control male rats treated with CyA or its vehicle for 8 days. As expected, pituitary grafting increased plasma prolactin levels (p<0.01). CyA treatment reduced but did not normalize (p<0.05) this parameter in hyperprolactinemic rats and did not modify circulating prolactin in control animals. Both hyperprolactinemia and CyA treatment reduced the number of adenosine transporters by 70% and by 40% the number of A1 receptors. The Kd for transporters was also reduced in all experimental groups. Hyperprolactinemia increased the affinity of A1 receptors (p<0.01) and CyA treatment did not further modify this parameter. These data demonstrated that prolactin and CyA influence adenosine transporters and A1 receptors at the central nervous system and suggest the existence of an interaction between prolactin and CyA may be operating to modulate these processes.

Differential effect of interferon-gamma injection on mitogenic responses in sympathetically denervated submaxillary lymph nodes of rats

This study aimed to assess the effect of interferon (IFN)-gamma treatment on mitogenic responses in submaxillary lymph nodes in the presence or absence of local sympathetic nerves. Adult male rats were subjected to a unilateral superior cervical ganglionectomy and to a contralateral sham-operation. Seven days later, rats received five i.p. daily injections of human IFN-gamma (10(5) U.I./kg) or saline. On the day after the last injection, rats were killed at six different times throughout a 24-h cycle and the mitogenic effect of lipopolysaccharide (LPS) and concanavalin A (Con A) was assessed in single-cell suspensions of lymph nodes. In vehicle-treated rats, proliferation responses to LPS in innervated lymph nodes did not show time-of-day variations while those in denervated lymph nodes attained a maximum at 17:00 h. Following IFN-gamma administration, a promoting effect of LPS mitotic response was detected at 01:00 h at the innervated side only. As far as the mitogenic responses to Con A, proliferation in innervated lymph nodes of vehicle-treated controls attained a maximum at 09:00 h. Such a daily variation in response to Con A was not detectable at the denervated side. IFN-gamma treatment increased significantly Con A activity by promoting a greater mitogenic response at 01:00 h. Sympathetic denervation of lymph nodes brought about a shift in the maximum in number of cells per mg of lymph node from 21:00 to 13:00 h. After IFN-gamma treatment, maxima in cell number occurred at 05:00 h at both the innervated and denervated side. The results indicate that IFN-gamma effects in rat submaxillary lymph nodes are under substantial modulation by local sympathetic nerves.

Effects of ageing and exogenous melatonin on pituitary responsiveness to GnRH in rats

The effect of age and melatonin on the activity of the neuroendocrine reproductive system was studied in young cyclic (3-5 months-old), and old acyclic (23-25 month-old) female rats. Pituitary responsiveness to a bolus of GnRH (50 ng per 100 g body weight) was assessed at both reproductive stages in control and melatonin-treated (150 micrograms melatonin per 100 g body weight each day for 1 month) groups. After this experiment, female rats were treated for another month to study the influence of ageing and melatonin on the reproductive axis. Plasma LH, FSH, prolactin, oestradiol and progesterone were measured. A positive LH response to GnRH was observed in both control groups (cyclic and acyclic). However, a response of greater magnitude was observed in old acyclic rats. Melatonin treatment reduced this increased response in acyclic rats and produced a pituitary responsiveness similar to that of young cyclic rats. FSH secretion was independent of GnRH administration in all groups, indicating desynchronization between LH and FSH secretion in response to GnRH in young animals and during senescence. No effect on prolactin was observed. Significantly higher LH (3009.11 +/- 1275.08 pg ml(-1); P < 0.05) and FSH concentrations (5879.28 +/- 1631.68 pg ml(-1); P < 0.01) were seen in acyclic control rats. After melatonin treatment, LH (811.11 +/- 89.71 pg ml(-1)) and FSH concentrations (2070 +/- 301.62 pg ml(-1)) decreased to amounts similar to those observed in young cyclic rats. However, plasma concentrations of oestradiol and progesterone were not reduced. In conclusion, the results of the present study indicate that, during ageing, the effect of melatonin is exerted primarily at the hypothalamo-pituitary axis rather than on the ovary. Melatonin restored the basal concentrations of pituitary hormones and pituitary responsiveness to similar values to those observed in young rats.

Effects of ageing and exogenous melatonin on pituitary responsiveness to GnRH in rats

The effect of age and melatonin on the activity of the neuroendocrine reproductive system was studied in young cyclic (3-5 months-old), and old acyclic (23-25 month-old) female rats. Pituitary responsiveness to a bolus of GnRH (50 ng per 100 g body weight) was assessed at both reproductive stages in control and melatonin-treated (150 micrograms melatonin per 100 g body weight each day for 1 month) groups. After this experiment, female rats were treated for another month to study the influence of ageing and melatonin on the reproductive axis. Plasma LH, FSH, prolactin, oestradiol and progesterone were measured. A positive LH response to GnRH was observed in both control groups (cyclic and acyclic). However, a response of greater magnitude was observed in old acyclic rats. Melatonin treatment reduced this increased response in acyclic rats and produced a pituitary responsiveness similar to that of young cyclic rats. FSH secretion was independent of GnRH administration in all groups, indicating desynchronization between LH and FSH secretion in response to GnRH in young animals and during senescence. No effect on prolactin was observed. Significantly higher LH (3009.11 +/- 1275.08 pg ml(-1); P < 0.05) and FSH concentrations (5879.28 +/- 1631.68 pg ml(-1); P < 0.01) were seen in acyclic control rats. After melatonin treatment, LH (811.11 +/- 89.71 pg ml(-1)) and FSH concentrations (2070 +/- 301.62 pg ml(-1)) decreased to amounts similar to those observed in young cyclic rats. However, plasma concentrations of oestradiol and progesterone were not reduced. In conclusion, the results of the present study indicate that, during ageing, the effect of melatonin is exerted primarily at the hypothalamo-pituitary axis rather than on the ovary. Melatonin restored the basal concentrations of pituitary hormones and pituitary responsiveness to similar values to those observed in young rats.