Effect of lithium in pyramidal neurons of Cornu Ammonis in an animal model

Bipolar disorder has been associated with a decrease in hippocampal size, and lithium appears to reverse this neuroanatomical abnormality. The objective of this work was to evaluate, at a cellular level, the size of both cell body and nucleus of pyramidal neurons located throughout the Cornu Ammonis (CA1 to CA4 regions). To perform this duty, we used 16 rats that were randomized into two groups: control and dietary lithium-treated. After one month, they were sacrificed and their brains removed for histopathological analysis. Serial photos of the entire Cornu Ammonis were taken and, after dividing them into 4 regions of interest, we measured the cell body and nucleus on each pyramidal neuron belonging to the first 5 photos of each region of interest. As a result of this histological analysis, cell body area and nuclear area were significantly larger in the experimental group in a specific area of the Cornu Ammonis that could correspond to CA2 or the transition between CA1 and CA2. These results suggest that the effect of lithium is not homogeneous throughout the hippocampus and allows directing future studies to a specific area of this structure.

Effect of di(2-ethylhexyl) phthalate on the neuroendocrine regulation of reproduction in adult male rats and its relationship to anxiogenic behavior: Participation of GABAergic system

The endocrine disruptor di-(2-ethylhexyl) phthalate (DEHP) is used in a variety of consumer products made with polyvinyl chloride and also in the manufacture of medical devices. DEHP disrupts reproductive tract development in an antiandrogenic manner and also may induce neurobehavioral changes. The aim of this study was to investigate the effects of chronic postnatal exposure to DEHP (30 mg/kg body weight/day, orally from birth to day 60) on the neuroendocrine regulation of the gonadal axis and its impact on the anxiety-like behavior in adult male rats, as well as the probable participation of the GABAergic system in these effects. DEHP produced a significant increase in plasmatic luteinizing hormone and follicle stimulating hormone, as well as significant testosterone decrease, accompanied with a decrease in hypothalamic gamma-aminobutyric acid (GABA) concentration. On the other hand, DEHP increased the anxiety-like behavior in the elevated plus maze test, evidenced by a significant decrease in the percentages of time spent in the open arms and the frequency in the open arm entries and a significant increase in the percentage of time spent in closed arms. Neuroendocrine and behavioral effects were reversed by GABA agonists, muscimol (2 mg/kg i.p. ) and baclofen (10 mg/kg i.p.). In conclusion, chronic DEHP postnatal exposure induced a disruption in the neuroendocrine regulation of the testicular axis in young adult male rats, and this effect was correlated with an anxiety-like behavior. Since GABA agonists reversed these effects, the results suggest that GABA could participate in the modulation of reproductive and behavioral DEHP effects.

Exposure to a low dose of bisphenol A impairs pituitary-ovarian axis in prepubertal rats: effects on early folliculogenesis

The research work studies the effect of providing a low dose of bisphenol A (BPA), on the reproductive axis of prepubertal female rats. Wistar mated rats were treated with either 0.1% ethanol or BPA in their drinking water until their offspring were weaned on the 21 day of birth. The estimated average dose of exposure to dams was approximately 3μg/kg/day. The pups were sacrificed at the 30th day of life. Body weight at the moment of the sacrifice was significantly higher in the group exposed to BPA; ovarian weight and its relative weight were not modified. LH and estradiol levels increased significantly, meanwhile FSH ones showed no significant changes. The number of primary, secondary and atretic follicles increased and antral ones was decreased. Our results demonstrated that early exposure to a low dose of BPA disrupts the normal function of the reproductive axis in prepubertal female rats.

Antiandrogenic effect of perinatal exposure to the endocrine disruptor di-(2-ethylhexyl) phthalate increases anxiety-like behavior in male rats during sexual maturation

Di-2-ethylhexyl phthalate (DEHP) is the most widely used phthalate to convey flexibility and transparency to plastic products made of polyvinyl chloride. It has been recognized as endocrine disruptor and associated with reproductive toxic effects. We examined the effects of perinatal exposure to DEHP on anxiety-like behavior, using the Elevated Plus Maze (EPM) test, in male and female rats at different stages of sexual development. Anxiety-like behavior was expressed as a) frequency of open arm entries over the total arm entries (% FEO); b) time spent in them compared with total time the animal stayed in the EPM (% TSO) and c) time spent in closed arms (TSC). Because DEHP has anti-androgenic action we also tested control and exposed immature male rats pretreated with testosterone. We found sex differences in behavior induced by DEHP; while male rats of 45 and 60 days of age showed a significant decrease in FEO and TSO percentages, as well as an increase in TSC, no changes were observed in anxiety-like behavior in perinatal DEHP exposed females at these ages of sexual maturation. In 60-day-old male rats, DEHP exposure produced a significant decrease in serum testosterone levels. Testosterone replacement was able to antagonize the adverse effects of DEHP exposure on LH, activating the negative feed-back mechanism of this steroid on reproductive axis, as well as increasing FEO and TSO percentages to similar values observed in the control group. These findings suggest that the anti-androgenic action of this chemical could be one possible mechanism underlie anxiogenic-like behavior produced by perinatal DEHP exposure in 60-day-old male rats.

Impact of the UV-B filter 4-(Methylbenzylidene)-camphor (4-MBC) during prenatal development in the neuroendocrine regulation of gonadal axis in male and female adult rats

4-(Methylbenzylidene)-camphor (4-MBC), a UV-B ray filter, is an endocrine disruptors (ED). Our goal was to study the effect of 4-MBC on the neuroendocrine parameters that regulate reproduction in adult female and male rats that received this disrupter during prenatal development. The 4-MBC was administered (sc) to female rats (FO) since pregnancy onset, in doses of 100mg/kg every other day. The litters (F1) were sacrificed at 70 days to determine gonadotrophin serum levels and also GnRH and the amino acids glutamate, aspartate and GABA release from the hypothalamus. The male litter rats (F1) present at adult age a decrease in serum LH and FSH concentration and so also GnRH, excitatory amino acids and GABA hypothalamic secretion. The female litters (F1) rats present at adult age an increase in serum LH and FSH concentration, whereas hypothalamic GnRH release was not modified. In these animals a significant increase of hypothalamic aspartate release as well as GABA secretion decrease were observed. Glutamate secretion was not modified. All these changes were accompanied by an advance (3 days) on the vaginal opening in 4-MBC rats group. In conclusion, prenatal administration of 4-MBC disrupts the gonadal axis in a sexual dimorphic mode that could be connected with the physiological sexual differences in the development of gonadotrophin secretion hypothalamic control mechanisms.

Nitric oxide synthase inhibition prevents leptin induced Gn-RH release in prepubertal and peripubertal female rats

The aim of the present paper was to study the role of NO as a mediator of leptin action at the hypothalamic level during sexual maturation. First, we analyzed the effect of different leptin concentrations (10 (-13), 10 (-11) and 10 (-9) M) on Gn-RH release from anterior preoptic area and medio basal hypothalamus (APOA-MBH) of prepubertal (15 days old) and peripubertal (30 days old) female rats. Leptin 10 (-13) M was the most effective concentration in releasing Gn-RH in both groups of animals. Since glutamate (GLU) and GABA are involved in the hypothalamic control of Gn-RH neurons and also in the neuroendocrine mechanism of puberty, in a second serie of experiments, we evaluated the effect of a competitive inhibitor of nitric oxide synthase (NOS), N-monomethyl-L-arginine (NMMA) on Gn-RH, GLU and GABA release in response to leptin. Co incubation of APOA-MBH with NMMA 0.5 mM, completely blocked Gn-RH and GLU release induced by leptin 10 (-13) M in prepubertal and peripubertal rats. NMMA also blocked the stimulation of GABA release in prepubertal rats, as well as the inhibition of GABA release induced by leptin in peripubertal rats. It can be proposed that the different effect of NO on GABA release, could be related to ontogenic changes, e.g, maturation of receptors and/or interneuronal connections during sexual development. Present results provide evidence that leptin acts at the hypothalamic level to stimulate NO release, which in turn modifies the release of amino acid neurotransmitters involved in Gn-RH control.

Endogenous hypertriglyceridemia intensifies the course of cerulein-induced pancreatitis in rat: relation with changes in the VLDL composition

AIMS

To study if the course of cerulein-induced pancreatitis in rats changes in a state of triglyceride-rich lipoprotein metabolism alteration.

METHODS

Two groups of rats received control diet during a 90-day period (A) and sucrose-rich diet to induce endogenous hypertriglyceridemia (B). Subgroups A2 and B2 received i.p. 45 microg cerulein/kg body weight (to induce acute pancreatitis). Histological examination of pancreas tissue, serum pancreatic lipase, lipoprotein profile and VLDL chemical composition were assessed. Then, pancreatic lipase hydrolytic activity on VLDL-triglycerides was evaluated in vitro.

RESULTS

Cellular vacuolization was observed in all of the cerulein-injected rats, but only in subgroup B2 fat necrosis was present. Serum triglycerides were higher in subgroup B1 than in subgroup A1 (mean +/- SEM, mg/dl 123,77 +/- 25.7 vs. 65.8 +/- 7, p < 0.01). Triglycerides from rats fed with sucrose-rich diet, decreased after cerulein-induced pancreatitis (80.38 +/- 11.3 vs. 123,77 +/- 25.7, p < 0.02). Moreover, the endogenous hypertriglyceridemic rats showed an increment of VLDL triglyceride content, which decreased when rats were injected with cerulein. A negative correlation was found between VLDL-triglyceride content and serum pancreatic lipase activity (r = 0.58, p < 0.02). The in vitro assay showed a decrease in VLDL-triglyceride content post incubation with pancreatic lipase enriched serum (mean +/- SD: 59.2 +/- 27.7%, p < 0.01).

CONCLUSIONS

The endogenous hypertriglyceridemia intensifies the course of cerulein-induced pancreatitis and it could be related to the decrease in VLDL-triglycerides as a consequence of pancreatic lipase hydrolytic activity.

Leptin Stimulates the Reproductive Male Axis in Rats during Sexual Maturation by Acting on Hypothalamic Excitatory Amino Acids

The purpose of the present study was to determine the effect of treatment with leptin on gonadotrophin secretion and hypothalamic GnRH, excitatory and inhibitory amino acids release, in prepubertal (15 days old) and peripubertal (30 days old) male rats. Rats of both ages received a single (ip) injection of 30 microg/kg leptin 60 minutes previous to sacrifice. Serum LH was determined, and the hypothalamus dissected and incubated in Earle's medium. GnRH and amino acids release were determined in the media. LH and GnRH were measured by RIA. Amino acids were assessed by HPLC-UV detection. In the two prepubertal stages, (prepubertal and peripubertal, 15 and 30 days of age respectively) leptin increased plasmatic LH levels (p < 0.01) and hypothalamic GnRH release (p < 0.01). Glutamate (GLU) release showed an increment in leptin-treated rats (p < 0.01) at both ages, while only the 30 days old rats showed an increment of the aspartate (ASP) release. GABA secretion was not modified by leptin treatment. In conclusion, the results demonstrated that leptin stimulates the LH-GnRH axis during sexual development in male rats, increasing the secretion of both hormones. The hypothalamic excitatory amino acid neurotransmitter system appears to be involved in this change.

Effect of leptin on hypothalamic release of GnRH and neurotransmitter amino acids during sexual maturation in female rats

The purpose of the present study was to analyse the effect of leptin treatment on the hypothalamic release of GnRH, GABA, and the excitatory amino acids (EAA), aspartate (ASP) and glutamate (GLU) involved in NMDA neurotransmission in prepubertal (15 day old) and peripubertal (30 day old) female rats. The animals were treated with a single dose of leptin (30 microg/kg i.p.) and sacrificed 60 min later. Hypothalamic samples were incubated in Earle's medium; GnRH was determined by RIA and GLU, ASP and GABA by HPLC by UV detection. The hypothalamic release of GnRH was increased by leptin at both ages, the release being significantly higher in peripubertal than in prepubertal rats. The levels of hypothalamic GABA release were different in the two groups; whereas in prepubertal rats the hypothalamic release of GABA increased with leptin administration, the neurotransmitter release decreased in the peripubertal group. On the other hand, the release of ASP was modified only in the peripubertal group, where leptin significantly increased its hypothalamic release. No modifications in leptin-induced hypothalamic release of GLU were observed at the two ages studied. In conclusion, the results showed that leptin increased GnRH release by the hypothalamus of prepubertal and peripubertal rats. In peripubertal rats this increase was accompanied by a significant decrease in the hypothalamic release of GABA as well as an enhanced release of ASP. These results and previous reports suggest that at this stage of sexual maturation, leptin exerts an stimulatory effect on GnRH by inducing release of excitatory amino acids (ASP) and reducing release of inhibitory amino acids (GABA) involved in GnRH control. In prepubertal rats the stimulating effect of the adipocyte hormone on GnRH appears to be related to its stimulative action on GABA which at this age increases GnRH release.

Changes in the sensitivity of gonadotrophin axis to leptin during sexual maturation in female rats

OBJECTIVES

The aim of the present paper was to determine the sensitivity of the GnRH-LH axis to leptin administration during sexual maturation in female rats.

METHODS

For this purpose the hypothalamic concentration of GnRH, the pituitary content and the plasmatic levels of LH were determined in prepubertal (15 days of age) and peripubertal female rats (30 days of age), treated with leptin at a dose of 30 microg/kg. i.p. in a single injection, 90 min before sacrifice.

RESULTS

The results indicate that leptin significantly increased the GnRH concentration at 15 days of age (p <0.01). At 30 days of age the hormone did not significantly modify the hypothalamic GnRH content. Leptin increased the pituitary LH levels, both in prepubertal and peripubertal rats. Nevertheless, while the increase at 15 days of age was around 180%, in peripubertal rats it was about 51,2 %. In spite that leptin significantly increased LH plasmatic levels at both ages (p < 0.01 ), in rats of 15 days of age leptin increased LH in about 244%, at 30 days of age this increase was only about 102%.

CONCLUSION

These results clearly demonstrated that leptin has stimulatory effect on gonadotrophin axis been higher in prepubertal than in peripubertal rats. On these basis, and on the results of previous papers, (in which it has been demonstrated that the hypothalamic control of gonadotrophins by neurotransmitters and neuromodulators also showed qualitative and quantitative changes during sexual maturation), it is proposed that these differences are connected with the maturation of the neuroendocrine mechanisms involved in the regulatory action of leptin on the gonadotrophins axis.

Interrelationships of GABAergic, serotoninergic and excitatory amino acid systems in its regulatory effect on prolactin secretion in prepubertal rats

GABAergic, serotoninergic and excitatory amino acid systems (EAAs) regulate the prolactin (PROL) secretion in prepubertal female rats. The aim of the present paper was to determine the interrelationships of these systems on the control of this pituitary hormone. It was carried out through the following scheme: 1. The participation of the EAAs and serotonin in the effect of GABAergic system on PROL release, determined by evaluating the GABA A and GABA B receptor agonists. It was carried out on animals that were previously treated with AAEs receptor antagonist or p-chlorophenylamphetamine (PCA), this one depleting serotonin in the hypothalamus. 2. The participation of GABAergic system in the effect of serotonin and EAAs systems, determined by the evaluation of the effects of EAAs receptor agonists and of 5-HTP, a serotonin precursor. With this purpose the rats were previously treated with GABA A and GABA B receptor antagonists. 3. The interrelationships between the EAAs and the serotoninergic systems in the control of PROL secretion, determined (a) by using EAAs agonists (in rats depleted of serotonin by PCA) and (b) using EAAs antagonists (in rats treated with 5-HTP, a serotonin precursor). The administration of GABAergic agonists significantly increased PROL secretion in prepubertal female rats. Neither EAAs antagonists nor the depletion of serotonin in the brain, modified the stimulatory effects of the GABAergic system on PROL levels. This is a clear indication that the activity of the GABAergic system is independent of the serotoninergic and of the EAAs system effects on the pituitary hormone. The EAAs neurotransmitter system agonists significantly increase PROL levels. This effect was blocked by the GABAergic system antagonists but was not modified by serotonin depletion. Taking into account these facts it may be considered that the GABAergic system is involved in the stimulatory effect of EAAs on PROL secretion, this effect being independent of the serotoninergic system. 5-HTP significantly increased PROL plasma levels, and this effect was modified neither by the GABAergic nor by the EAAs receptor antagonists. These results indicate that the stimulatory effect of serotonin on PROL release is independent of the GABAergic and EAAs systems. In conclusion it may be considered that in prepubertal female rats, the GABAergic and serotoninergic systems stimulate PROL secretion by independent mechanisms that do not include EAAs. On the other hand, the effects of EAAs neurotransmission are exerted via the GABAergic system.

Aproteic diet decreases hypothalamic catecholamine turnover in adult male rats

Previous reports indicate that malnutrition reduces reproductive functions. We have demonstrated that protein deprivation in the diet also causes reproductive dysfunction by reducing hypothalamic GnRH secretion. Noradrenaline and nitric oxide are modulators of GnRH secretion. Noradrenaline stimulates GnRH secretion and nitric oxide inhibits catecholamine release. This work studies the hypothalamic catecholaminergic and nitrergic neuron activity in Wistar adult male rats fed on an aproteic diet (AP) during 21 days; this treatment was started when rats were 70 days old. Our first experiment studied catecholamine turnover rate after inhibition of tyrosine hydroxylase activity by injecting (i.p.) 400 mg/kg alpha-methyl-p-tyrosine. Our second experiment studied in vitro hypothalamic nitric oxide synthase (NOS) activity in animals under the same diet. AP diet significantly decreased both noradrenaline (P<0.05) and dopamine (P<0.05) hypothalamic turnover rate. Noradrenaline turnover in cerebral cortex was not altered by the aproteic diet. However, hypothalamic NOS activity was not affected in animals fed on an AP diet. These results indicate that the lack of protein in the diet reduces catecholaminergic neuron activity in adult male rats by a NO-independent mechanism, thus suggesting that a decrease in noradrenergic activity may be involved in the reduction of GnRH secretion induced by an AP diet.

Effect of an aproteic diet on gonadotropin release response to GnRH and estrogen-progesterone in rats

The fasting-induced gonadotropin function decrease is unspecific, because in this situation there is a lack of all nutrients. We report here the effect of specific protein lack in the diet during 21 days, on pituitary gonadotropin synthesis and response to exogenous GnRH in adult male rats. We also studied the effect of the aproteic diet (AP) on the positive feedback mechanism in adult female castrated rats. The AP diet decreased significantly, both LH and FSH pituitary concentration and also basal gonadotropin plasma levels in male rats. GnRH produced a significantly increment in LH secretion in both treated and control groups, reaching similar levels after stimulation. Nevertheless, the percentile increment from basal levels in the aproteic group was almost four times the controls, suggesting an increased sensitivity in pituitary response to GnRH in rats fed with AP diet. In female castrated rats, the aproteic diet imposed 3 weeks after the surgery was unable to reduce basal gonadotropin secretion, and so also prolactin secretion. Estradiol/progesterone (EP) administration produced the activation of positive feedback mechanism, increasing significantly LH and FSH secretion in both controls and AP groups. Nevertheless, both gonadotropin responses to EP were significantly greater in rats fed with AP diet. Basal prolactin levels and response to EP were not different between both groups. This results suggest that selective protein lack in a diet, reduced pituitary LH and FSH synthesis and secretion. This type of diet also increments pituitary sensitivity to GnRH administration in male rats, and gonadotropin response to positive feedback mechanism in female rats.

[Cerulein-induced acute pancreatitis enhanced by chronic hyperlipidic diet in the rat]

The object of the present work was to study the relationship between acute pancreatitis (PA) and hyperlipidic diets. PA was induced by Caerulein (CE) by a single intraperitoneal doses (50 mcg/kg), after feeding the rats during 6 weeks with an hyperlipidic diet (45%). Rats with a normolipidic diet (lipids 5%) were used as control. The increase of serum lipase was similar in both groups treated with CE (control and with hyperlipidic diet). There were increase of interstitial edema, cariorrexis and a specially marked increase in the level of vacuolization of acinar cells with respect to the control group. It was concluded that chronic hyperlipidic diet increases histopathologic lesions in PA induced by CE in rats.