Effect of maternal separation and chronic stress on hippocampal-dependent memory in young adult rats: evidence for the match-mismatch hypothesis.

Adverse experiences early in life may sensitize the hippocampus to subsequent stressors throughout the individual's life. We analyzed in male rats, whether, the interaction between early maternal separation and chronic stress affects: (1) the volume of the dorsal hippocampus, (2) CA1, CA2/3 and dentate gyrus (DG) and (3) hippocampal-dependent memory in adulthood. Male Wistar rats were subjected to daily maternal separation for 4.5 h between postnatal days 1-21. From postnatal day 50, animals were exposed to a chronic unpredictable stress paradigm during 24 days. The volumes of the dorsal hippocampus, their areas or strata did not reveal significant differences between treatments. Non-maternally separated and stressed animals showed poor hippocampal performance in a contextual fear conditioning test, with a significant reduction in freezing behavior during post-conditioning compared with control and maternally separated and stressed animals. Also, memory retrieval 24 h after conditioning was significantly weaker in this group than in control animals. Memory performance in maternally separated and stressed rats was similar to control animals. Our results show an interaction between early environment experiences and chronic variable stress in young adulthood as evidence that early stressful experiences do not necessarily lead to a negative outcome but can help in maintaining brain plasticity and increase fitness when animals reach adulthood.

Endosulfan induces changes in spontaneous swimming activity and acetylcholinesterase activity of Jenynsia multidentata (Anablepidae, Cyprinodontiformes).

We assessed changes in spontaneous swimming activity and acetylcholinesterase (AchE) activity of Jenynsia multidentata exposed to Endosulfan (EDS). Females of J. multidentata were exposed to 0.072 and 1.4 microg L(-1) EDS. Average speed and movement percentage were recorded during 48 h. We also exposed females to EDS at five concentrations between 0.072 and 1.4 microg L(-1) during 24 h, and measured the AchE activity in brain and muscle. At 0.072 microg L(-1) EDS swimming motility decreased relative to the control group after 45 h, while at 1.4 microg L(-1) EDS swimming motility decreased after 24 h. AchE activity significantly decreased in muscle when J. multidentata were exposed to EDS above 0.072 microg L(-1), while no significant changes were observed in brain. Thus, changes in swimming activity and AchE activity in muscle are good biomarkers of exposure to EDS in J. multidentata.

The stimulatory effect of alpha-melanotropin on progesterone release from rat granulosa cells is inhibited by interleukin-1beta and by tumour necrosis factor-alpha.

AIM: Several studies have shown that a variety of peptides and cytokines are involved in ovarian regulatory mechanisms; however, their exact function is still unclear. In this work we study whether the administration of peptide alpha-melanotropin and the cytokines interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha) on their own modify the release of progesterone in cultured granulosa cells (GC) from pro-oestrous rats. We also investigate an interaction between these cytokines and alpha-melanotropin in the modulation of progesterone secretion. METHODS: Granulosa cells were collected from the ovaries of female Wistar rats and cultured for up to 24 h in the presence of different concentrations of alpha-melanotropin, cytokines or a combination of both. Progesterone concentration was measured by radioimmunoassay. RESULTS: The addition of alpha-melanotropin in a dose of 0.01 and 0.1 mm had no effect on progesterone release, whereas a dose of 1 mm significantly increased progesterone release (P < 0.01) compared with the control culture. Progesterone release was not modified when different concentrations of interleukin-1beta or TNF-alpha were added to the cell cultures. However, when interleukin-1beta or TNF-alpha were added simultaneously with 1 microm alpha-melanotropin, a significant reduction (P < 0.01 for interleukin-1beta and P < 0.05 for TNF-alpha) of the steroid release was found with respect to the alpha-melanotropin-treated group. CONCLUSIONS: These results lead us to suggest that, although alpha-melanotropin stimulates progesterone release in pre-ovulatory GC, this effect is blocked by the presence of interleukin-1beta or TNF-alpha.

Effects of alpha-MSH on progesterone and nitric oxide release by cultured ovarian granulosa cells in experimental rat autoimmune oophoritis.

The peptide alpha-melanocyte-stimulating hormone (alpha-MSH) occurs within the pituitary, brain, skin, ovary and other tissues, and has potent anti-inflammatory activity. For this reason, we examined its effects on an autoimmune disease: the experimental autoimmune-oophoritis (EAO). We analyzed the effect of the peptide on the release of nitric oxide (NO) and progesterone from cultured ovarian granulosa (GL) cells at 0, 7, 14, 21 and 28 days after sensitization of the rats. On day 0 the progesterone levels were higher in estrous rats than those in proestrus and diestrus. The NO amount did not differ among the diverse days of the cycles. The administration of alpha-MSH induced a decrease of NO in estrus and diestrus, but did not affect progesterone release. The EAO rats showed a period of constant diestrus ranging from about 7 to 14 days after immunization. At the onset (day 7) and the end of this period (day 14), the NO significantly increased in estrous rats which was correlated with a reduction in progesterone concentration. This effect was reverted by alpha-MSH. At 21 and 28 days, progesterone release increased only when the rats were in proestrus, while NO production was similar to that on day 0. Administration of alpha-MSH reduced progesterone release when the rats were in proestrus and these results were correlated with an increase in NO only at day 14. The results obtained suggest that alpha-MSH could act as a modulator of EAO, specially when the rats are in estrus.

In vitro effect of alpha-MSH administration on steroidogenesis of prepubertal ovaries.

The effects of alpha-MSH on ovarian progesterone (P) and estradiol (E2) release were investigated. To this purpose, different doses of alpha-MSH were administered to prepubertal ovaries incubated under the following conditions: ten 5 min-pulses of perfusion medium (PM) plus LH at 160 ng/ml each one followed by a 25-min period of PM. The medium of the treated group contained alpha-MSH (0.1, 1, 5, or 10 microg/ml, in saline solution) and the control group saline solution. PM was assayed for P and E2 release. The area under the curve, pulse amplitude and width, and basal hormonal release were calculated for each hormone profile. With respect to P release, an increase in the areas under the curve could be observed in ovaries treated with 1, 5 and 10 microg alpha-MSH/ml. This increment generally coincided with an increase in P pulse amplitude and/or basal P release. The P pulse width was not modified. No significant variations were observed in the parameters under analysis with regard to E2 release. It is concluded that alpha-MSH administered to prepubertal ovaries could exert a physiological role through stimulation of P release.

Possible mechanism by which alpha-melanotropin advances the time of vaginal opening.

The aim of this work was to determine whether the acute administration of alpha-melanotropin (alpha-MSH) advances the time of vaginal opening (VO) by modifying the secretion of luteinizing hormone (LH), prolactin, growth hormone (GH), progesterone (P), estradiol (E2) and/or testosterone (T). Female rats received a subcutaneous injection of estradiol benzoate (EB; 10 micrograms/100 g body weight) on day 26 and 27 postnatal (PN). On day 28 PN, a third dose of EB was given together with either intraperitoneal alpha-MSH (treated group) or 0.1 ml saline (control group). On day 32 PN, the animals were inspected for VO and groups of rats were decapitated at hourly intervals between 12:00 and 18:00 hours. Serum concentrations of the hormones listed above were measured by radioimmunoassay. Acute administration of alpha-MSH significantly advances (P < 0.001) the day of VO compared to the control group, as well as increased serum LH levels (P < 0.001) in the period under study, in comparison to controls, but had no significant effect on any of the others hormones analyzed. LH profiles were determined in more detail beginning on the day after alpha-MSH administration (day 29 PN) to VO (day 33 PN). Blood samples were collected from the cannulated external jugular vein at 20 minutes intervals daily between 14:00 and 18:00 hours. alpha-MSH treatment did not significantly modify plasma LH levels on days 29 and 30 PN, although treated animals showed a sustained increase in LH on day 31 PN. On this day, mean LH levels of treated animals was significantly (P < 0.05) higher than the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible mechanism by which alpha-melanotropin advances the time of vaginal opening.

The aim of this work was to determine whether the acute administration of alpha-melanotropin (alpha-MSH) advances the time of vaginal opening (VO) by modifying the secretion of luteinizing hormone (LH), prolactin, growth hormone (GH), progesterone (P), estradiol (E2) and/or testosterone (T). Female rats received a subcutaneous injection of estradiol benzoate (EB; 10 micrograms/100 g body weight) on day 26 and 27 postnatal (PN). On day 28 PN, a third dose of EB was given together with either intraperitoneal alpha-MSH (treated group) or 0.1 ml saline (control group). On day 32 PN, the animals were inspected for VO and groups of rats were decapitated at hourly intervals between 12:00 and 18:00 hours. Serum concentrations of the hormones listed above were measured by radioimmunoassay. Acute administration of alpha-MSH significantly advances (P < 0.001) the day of VO compared to the control group, as well as increased serum LH levels (P < 0.001) in the period under study, in comparison to controls, but had no significant effect on any of the others hormones analyzed. LH profiles were determined in more detail beginning on the day after alpha-MSH administration (day 29 PN) to VO (day 33 PN). Blood samples were collected from the cannulated external jugular vein at 20 minutes intervals daily between 14:00 and 18:00 hours. alpha-MSH treatment did not significantly modify plasma LH levels on days 29 and 30 PN, although treated animals showed a sustained increase in LH on day 31 PN. On this day, mean LH levels of treated animals was significantly (P < 0.05) higher than the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute administration of alpha-melanotropin exerts a stimulatory control on puberty.

The present experiments were undertaken to throw light on the physiological role played by alpha-MSH in the advent of female puberty. The serum and pituitary alpha-MSH concentrations were determined in prepubertal rats 5, 15, 25, 30, 33 days old and at vaginal opening. The serum levels showed a significant increase on day 30 and the pituitary alpha-MSH levels increased steadily from day 5 to day 33. To determine if a relation exists between the increase in alpha-MSH levels and the peak of LH prior to vaginal opening, prepubertal rats of the same age range as above received an injection of alpha-MSH or saline solution and were sacrificed 30 min later. The peptide increased LH serum levels only at 30 days of age. To examine the hypothesis that alpha-MSH was involved in determining the timing of puberty, prepubertal rats pretreated with estradiol benzoate received an injection of alpha-MSH or saline solution on day 28. This treatment advanced the time of vaginal opening by 2 days in the experimental animals. With the same experimental procedure, an increase in serum levels of LH and progesterone was also observed at 29 days of age. The action of alpha-MSH on GnRH was analysed by incubating median eminence from prepubertal rats 20, 25 and 30 days of age, with the peptide, alpha-MSH increased GnRH release only in 25-day-old rats. The above results show that acute treatment with alpha-MSH induces modifications in the hormones related to puberty and hence allows us to include alpha-MSH in the chain of neuroendocrine events involved in reproductive maturation.