Allopregnanolone alters the luteinizing hormone, prolactin, and progesterone serum levels interfering with the regression and apoptosis in rat corpus luteum.

Steroids synthesized in the central nervous system are termed "neurosteroids". They are synthesized and metabolized in several brain areas. The objective of this work was to determine if 1 intracerebroventricular allopregnanolone injection in rats can interfere in luteal regression in a close relationship with modifications in LH, progesterone, and prolactin serum concentrations. Allopregnanolone was injected during proestrus morning and the animals were sacrificed on oestrous morning. Ovulation test and histological analysis were performed in the oestrus morning with light and electron microscopy. Serum prolactin, LH, and progesterone levels were measured by radioimmunoassay. The allopregnanolone injection significantly decreased luteinizing hormone serum level and the number of oocytes on oestrus. Progesterone and prolactin serum levels were increased after this injection. The inhibition of apoptotic figures due to allopregnanolone administration was detected in the already formed corpora lutea belonging to the previous ovary cycle and it was significantly lower than in vehicle group (control). When the GABA(A) antagonist (bicuculline) was administered alone or previously to allopregnanolone, no effect on the ovulation rate was observed. No changes in the apoptotic cell numbers were observed with respect to those of vehicle group. These results show that the effect of centrally injected allopreganolone over reproductive function could be due to a centrally originated LH mediated effect over ovarian function that affects luteal regression, through the inhibition of apoptosis and stimulation of progesterone and prolactin release.

Prazosin blocks the glutamatergic effects of N-methyl-D-aspartic acid on lordosis behavior and luteinizing hormone secretion in the estrogen-primed female rat

We have observed that intracerebroventricular (icv) injection of selective N-methyl-D-aspartic acid (NMDA)-type glutamatergic receptor antagonists inhibits lordosis in ovariectomized (OVX), estrogen-primed rats receiving progesterone or luteinizing hormone-releasing hormone (LHRH). When NMDA was injected into OVX estrogen-primed rats, it induced a significant increase in lordosis. The interaction between LHRH and glutamate was previously explored by us and another groups. The noradrenergic systems have a functional role in the regulation of LHRH release. The purpose of the present study was to explore the interaction between glutamatergic and noradrenergic transmission. The action of prazosin, an alpha1- and alpha2b-noradrenergic antagonist, was studied here by injecting it icv (1.75 and 3.5 µg/6 µL) prior to NMDA administration (1 µg/2 µL) in OVX estrogen-primed Sprague-Dawley rats (240-270 g). Rats manually restrained were injected over a period of 2 min, and tested 1.5 h later. The enhancing effect induced by NMDA on the lordosis/mount ratio at high doses (67.06 ± 3.28, N = 28) when compared to saline controls (6 and 2 µL, 16.59 ± 3.20, N = 27) was abolished by prazosin administration (17.04 ± 5.52, N = 17, and 9.33 ± 3.21, N = 20, P < 0.001 for both doses). Plasma LH levels decreased significantly only with the higher dose of prazosin (1.99 ± 0.24 ng/mL, N = 18, compared to saline-NMDA effect, 5.96 ± 2.01 ng/mL, N = 13, P < 0.05). Behavioral effects seem to be more sensitive to the alpha-blockade than hormonal effects. These findings strongly suggest that the facilitatory effects of NMDA on both lordosis and LH secretion in this model are mediated by alpha-noradrenergic transmission.

Prazosin blocks the glutamatergic effects of N-methyl-D-aspartic acid on lordosis behavior and luteinizing hormone secretion in the estrogen-primed female rat.

We have observed that intracerebroventricular (icv) injection of selective N-methyl-D-aspartic acid (NMDA)-type glutamatergic receptor antagonists inhibits lordosis in ovariectomized (OVX), estrogen-primed rats receiving progesterone or luteinizing hormone-releasing hormone (LHRH). When NMDA was injected into OVX estrogen-primed rats, it induced a significant increase in lordosis. The interaction between LHRH and glutamate was previously explored by us and another groups. The noradrenergic systems have a functional role in the regulation of LHRH release. The purpose of the present study was to explore the interaction between glutamatergic and noradrenergic transmission. The action of prazosin, an alpha1- and alpha2b-noradrenergic antagonist, was studied here by injecting it icv (1.75 and 3.5 microg/6 microL) prior to NMDA administration (1 microg/2 microL) in OVX estrogen-primed Sprague-Dawley rats (240-270 g). Rats manually restrained were injected over a period of 2 min, and tested 1.5 h later. The enhancing effect induced by NMDA on the lordosis/mount ratio at high doses (67.06 +/- 3.28, N = 28) when compared to saline controls (6 and 2 microL, 16.59 +/- 3.20, N = 27) was abolished by prazosin administration (17.04 +/- 5.52, N = 17, and 9.33 +/- 3.21, N = 20, P < 0.001 for both doses). Plasma LH levels decreased significantly only with the higher dose of prazosin (1.99 +/- 0.24 ng/mL, N = 18, compared to saline-NMDA effect, 5.96 +/- 2.01 ng/mL, N = 13, P < 0.05). Behavioral effects seem to be more sensitive to the alpha-blockade than hormonal effects. These findings strongly suggest that the facilitatory effects of NMDA on both lordosis and LH secretion in this model are mediated by alpha-noradrenergic transmission.

The anxiolytic effect of allopregnanolone is associated with gonadal hormonal status in female rats.

The behavioural display in the plus-maze, an established experimental model of anxiety, was studied in rats injected into the lateral brain ventricle (i.c.v.) with the neurosteroid 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone). Female rats under different gonadal hormonal status were chosen. Allopregnanolone enhanced exploration of the open arms in both estrous rats and ovariectomized estrogen and progesterone primed rats. No effect was observed in diestrous 1 and ovariectomized not-primed rats. In all cases, the plus-maze locomotor-exploratory behaviour was not affected by allopregnanolone. The GABA(A) receptor antagonist, bicuculline (9.8 microM i.c.v.) reversed the allopregnanolone action in the ovariectomized primed rats. When bicuculline was injected i.c.v. in conjunction with allopregnanolone, the anxiogenic effect of bicuculline was reversed by the highest dose (25 microM) of allopregnanolone only. These results suggest that allopregnanolone exerts an anxiolytic action interacting with the GABA(A) receptor in an estrogen-dependent manner.

Effects of prenatal exposure to a mild chronic variable stress on body weight, preweaning mortality and rat behavior

Early stimulation has been shown to produce long-lasting effects in many species. Prenatal exposure to some strong stressors may affect development of the nervous system leading to behavioral impairment in adult life. The purpose of the present work was to study the postnatal harmful effects of exposure to variable mild stresses in rats during pregnancy. Female Holtzman rats were submitted daily to one session of a chronic variable stress (CVS) during pregnancy (prenatal stress; PS group). Control pregnant rats (C group) were undisturbed. The pups of PS and C dams were weighed and separated into two groups 48 h after delivery. One group was maintained with their own dams (PS group, N = 70; C group, N = 36) while the other PS pups were cross-fostered with C dams (PSF group, N = 47) and the other C pups were cross-fostered with PS dams (CF group, N = 58). Pups were undisturbed until weaning (postnatal day 28). The male offspring underwent motor activity tests (day 28), enriched environment tests (day 37) and social interaction tests (day 42) in an animal activity monitor. Body weight was recorded on days 2, 28 and 60. The PS pups showed lower birth weight than C pups (Duncan's test, 0.05). The PS pups suckling with their stressed mothers displayed greater preweaning mortality (C: 23 percent, PS: 60 percent; 2 test, 0.05) and lower body weight than controls at days 28 and 60 (Duncan's test, 0.05 and 0.01, respectively). The PS, PSF and CF groups showed lower motor activity scores than controls when tested at day 28 (Duncan's test, 0.01 for PS group and ;0.05 for CF and PSF groups). In the enriched environment test performed on day 37, between-group differences in total motor activity were not detected; however, the PS, CF and PSF groups displayed less exploration time than controls (Duncan's test, 0.05). Only the PS group showed impaired motor activity and impaired social behavior at day 42 (Duncan's test, 0.05). In fact, CVS treatment during gestation plus suckling with a previously stressed mother caused long-lasting physical and behavioral changes in rats. Cross-fostering PS-exposed pups to a dam which was not submitted to stress counteracted most of the harmful effects of the treatment. It is probable that prenatal stress plus suckling from a previously stressed mother can

Turnover rate and stimulus-evoked release of dopamine by progesterone and N-methyl-D-aspartic acid in rat striatum during pregnancy.

The proposed modulatory role of progesterone on dopaminergic nerve terminal activity in the striatum was examined in pregnant rats. Endogenous dopamine concentration and the in vitro effect of exogenous progesterone in association with N-methyl-D-aspartic acid (NMDA) upon [3H]dopamine release from striatal slices were determined. Striatal dopamine and 3,4-dihidroxyphenylacetic acid (Dopac) contents on day 5 of pregnancy were significantly higher than those found at the other stages of pregnancy and proestrus. On days 5 and 15 of pregnancy, progesterone (400 nM) was able to enhance [3H]dopamine release stimulated by NMDA (50 microM). A similar effect was found in striatal slices from proestrus rats. In contrast, progesterone was without an effect on days 1, 10 and 20 of pregnancy and postpartum. The results suggest that an increased synthesis and/or release of dopamine takes place on certain days of pregnancy and, simultaneously, that there is a significant increase in the responsiveness of striatal dopaminergic nerve terminals to excitatory inputs. They provide further support for a modulatory role of progesterone in relation with a glutamatergic action on dopaminergic activity in the corpus striatum.

Progesterone in vitro increases NMDA-evoked [3H] dopamine release from striatal slices in proestrus rats.

The dopaminergic nerve terminals in rat striatum appear to be an important target for progesterone (Pg) and the excitatory amino acid glutamate. In the present study the possible interaction between glutamate and Pg upon [3H]DA release in striatal slices from rats in proestrus was examined. [3H]DA release was augmented by NMDA in a concentration-dependent manner. The presence of Pg (400 nM) in the perfusion medium produced an amplification of the responses to NMDA (50 microM) as shown by significant increase in the tritium outflow. The NMDA selective antagonists AP-7 (100 microM) and MK-801 (0.1 microM) prevented the effects of both NMDA and NMDA plus Pg on [3H]DA release. In contrast, the AMPA/kainate receptor antagonist CNQX (10 and 20 microM) was ineffective. Furthermore, AP-7 (100 microM) attenuated the enhancing effect of 400 nM Pg on [3H]DA release evoked by 28 mM K+. The antagonist was unable to alter the effect produced by K+ alone. These results indicate a specific action of Pg on dopaminergic terminals mediated by NMDA receptors and suggest a close interaction between glutamate and dopamine systems in the striatum, apparently modulated by progesterone.

Regulation of luteinizing hormone-releasing hormone and luteinizing hormone secretion by hypothalamic amino acids.

1. The present review discusses the proposed roles of the amino acids glutamate and GABA in the central regulation of luteinizing hormone-releasing hormone (LHRH) and in luteinizing hormone (LH) secretion. 2. Descriptions of the mechanisms of action of these neurotransmitters have focused on two diencephalic areas, namely, the preoptic-anterior hypothalamic area where the cell bodies of LHRH neurons are located, and the medial basal hypothalamus which contains the nerve endings of the LHRH system. Increasing endogenous GABA concentration by drugs, GABA agonists, or blockade of glutamatergic neurotransmission by selective antagonists in rats and non-human primates prevents ovulation and pulsatile LH release, and blunts the LH surges induced by estrogen or an estrogen-progesterone combination. In contrast, glutamate and different glutamate agonists such as NMDA, AMPA and kainate, can increase LHRH/LH secretion. 3. The simultaneous enhancement of glutamatergic activity and a decrease of GABAergic tone may positively influence the maturation of the pituitary-gonadal system in rats and non-human primates. Administration of glutamate receptor agonists has been shown to significantly advance the onset of puberty. Conversely, glutamate antagonists or increased endogenous GABA levels may delay the onset of puberty. The physiological regulation of LHRH/LH secretion may thus involve a GABA-glutamate interaction and a cooperative action of the various types of ionotropic glutamate receptors. 4. The inhibitory actions of GABA on LH release and ovulation may be exerted at the level of afferent nerve terminals that regulate LHRH secretion. A likely candidate is noradrenaline, as suggested by the synaptic connections between noradrenergic nerve terminals and GABAergic interneurons in the preoptic area. Recent experiments have provided complementary evidence for the physiological balance between inhibitory and excitatory transmission resulting in modulation of the action of noradrenaline to evoke LHRH release.

Regulation of luteinizing hormone-releasing hormone and luteinizing hormone secretion by hypothalamic amino acids

1. The present review discusses the proposed roles of the amino acids glutamate and GABA in the central regulation of luteinizing hormone-releasing hormone (LHRH) and in luteinizing hormone (LH) secretion. 2. Descriptions of the mechanisms of action of these neurotransmitters have focused on two diencephalic areas, namely, the preoptic-anterior hypothalamic area where the cell bodies of LHRH neurons are located, and the medial basal hypothalamus which contains the nerve endings of the LHRH system. Increasing endogenous GABA concentration by drugs, GABA agonists, or blockade of glutamatergic neurotransmission by selective antagonists in rats and non-human primates prevents ovulation and pulsatile LH release, and blunts the LH surges induced by estrogen or an estrogen-progesterone combination. In contrast, glutamate and different glutamate agonists such as NMDA, AMPA and kainate, can increase LHRH/LH secretion. 3. The simultaneous enhancement of glutamatergic activity and a decrease of GABAergic tone may positively influence the maturation of the pituitary-gonadal system in rats and non-human primates. Administration of glutamate receptor agonists has been shown to significantly advance the onset of puberty. Conversely, glutamate antagonists or increased endogenous GABA levels may delay the onset of puberty. The physiological regulation of LHRH/LH secretion may thus involve a GABA-glutamate interaction and a cooperative action of the various types of ionotropic glutamate receptors. 4. The inhibitory actions of GABA on LH release and ovulation may be exerted at the level of afferent nerve terminals that regulate LHRH secretion. A likely candidate is noradrenaline, as suggested by the synaptic connections between noradrenergic nerve terminals and GABAergic interneurons in the preoptic area. Recent experiments have provided complementary evidence for the physiological balance between inhibitory and excitatory transmission resulting in modulation of the action of noradrenaline to evoke LHRH release.