Magnus Löfgren

Neuroactive steroid effects on cognitive functions with a focus on the serotonin and GABA systems.

This article will review neuroactive steroid effects on serotonin and GABA systems, along with the subsequent effects on cognitive functions. Neurosteroids (such as estrogen, progesterone, and allopregnanolone) are synthesized in the central and peripheral nervous system, in addition to other tissues. They are involved in the regulation of mood and memory, in premenstrual syndrome, and mood changes related to hormone replacement therapy, as well as postnatal and major depression, anxiety disorders, and Alzheimers disease. Estrogen and progesterone have their respective hormone receptors, whereas allopregnanolone acts via the GABA(A) receptor. The action of estrogen and progesterone can be direct genomic, indirect genomic, or non-genomic, also influencing several neurotransmitter systems, such as the serotonin and GABA systems. Estrogen alone, or in combination with antidepressant drugs affecting the serotonin system, has been related to improved mood and well being. In contrast, progesterone can have negative effects on mood and memory. Estrogen alone, or in combination with progesterone, affects the brain serotonin system differently in different parts of the brain, which can at least partly explain the opposite effects on mood of those hormones. Many of the progesterone effects in the brain are mediated by its metabolite allopregnanolone. Allopregnanolone, by changing GABA(A) receptor expression or sensitivity, is involved in premenstrual mood changes; and it also induces cognitive deficits, such as spatial-learning impairment. We have shown that the 3beta-hydroxypregnane steroid UC1011 can inhibit allopregnanolone-induced learning impairment and chloride uptake potentiation in vitro and in vivo. It would be important to find a substance that antagonizes allopregnanolone-induced adverse effects.

Tolerance development to Morris water maze test impairments induced by acute allopregnanolone

The progesterone metabolite allopregnanolone, like benzodiazepines, reduces learning and impairs memory in rats. Both substances act as GABA agonists at the GABA-A receptor and impair the performance in the Morris water maze test. Women are during the menstrual cycle, pregnancy, and during hormone replacement therapy exposed to allopregnanolone or allopregnanolone-like substances for extended periods. Long-term benzodiazepine treatment can cause tolerance against benzodiazepine-induced learning impairments. In this study we evaluated whether a corresponding allopregnanolone tolerance develops in rats. Adult male Wistar rats were pretreated for 3 days with i.v. allopregnanolone injections (2 mg/kg) one or two times a day, or for 7 days with allopregnanolone injections 20 mg/kg intraperitoneally, twice a day. Thereafter the rats were tested in the Morris water maze for 5 days and compared with relevant controls. Rats pretreated with allopregnanolone twice a day had decreased escape latency, path length and thigmotaxis compared with the acute allopregnanolone group that was pretreated with vehicle. Pretreatment for 7 days resulted in learning of the platform position. However, the memory of the platform position was in these tolerant rats not as strong as in controls only given vehicle. Allopregnanolone treatment was therefore seen to induce a partial tolerance against acute allopregnanolone effects in the Morris water maze.

Progesterone withdrawal effects in the open field test can be predicted by elevated plus maze performance.

Allopregnanolone (3alpha-hydroxy-5alpha-pregnane-20-one) is a ring-A-reduced metabolite of progesterone, which is naturally produced during the luteal phase of the menstrual cycle, during pregnancy and by stressful events. The steroid hormone inhibits neural functions through increased chloride ion flux through the GABA(A) receptor. The effects and subsequent withdrawal symptoms are similar to those caused by alcohol, benzodiazepines and barbiturates. This study examined the withdrawal effects of progesterone with regards to the influence of individual baseline exploration and risk taking. Rats were tested on the elevated plus maze (EPM) before hormonal treatment, in order to evaluate differences in risk taking and exploration of open and elevated areas. Treatment consisted of ten consecutive once a day progesterone or vehicle s.c. injections. On the last day of treatment, estradiol was injected in addition to progesterone, followed by a 24-h withdrawal before testing in the open field test (OF). Progesterone-treated rats showed a withdrawal effect of open area avoidance in the OF. The vehicle-treated control rats showed strong correlations between the EPM and OF parameters. This relationship was not found for the progesterone group at withdrawal. Rats with greater numbers of open arm entrance in the EPM pretest showed an increased sensitivity to progesterone withdrawal (PWD) compared to rats with low exploration and risk taking. The results indicate that the effects of PWD relate to individual exploration and risk taking. Furthermore, the possible analogy of PWD and PMS/PMDD in relation to individual traits is discussed.

Withdrawal effects from progesterone and estradiol relate to individual risk-taking and explorative behavior in female rats.

Withdrawal from progesterone and estradiol has been used as an animal model of premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD). In the clinical population individual sensitivity to sex steroid hormones, personality and heredity influence PMS/PMDD. Understanding the phenotypic risk factors of PMS/PMDD and drug development requires an animal model which incorporates individual steroid sensitivity. The main objective of this study was to investigate whether the individual trait of risk-taking and exploration influence the severity of PEWD in female rats. Thirty-two female Wistar rats in their diestrus phase were tested in the open field (OF) and divided into high responders (HR) and low responders (LR). Injections were given i.p. twice daily for 6 days, either 5 mg/kg progesterone combined with 10 microg/kg 17beta-estradiol, or vehicle (sesame oil). After a 24-hour withdrawal the animals were tested in the elevated plus maze (EPM). Blood samples for CORT analysis were collected after both behavioral tests. The HR rats withdrawn from progesterone and estradiol, spent less time on the EPM open arms and had lower CORT levels than the HR controls. The LR group showed no differences in EPM behavior and CORT levels during PEWD. The controls showed a stable trait of risk-taking and exploration, indicated by behavioral and CORT level correlations between the OF and EPM tests. These findings show that female rats with the trait of risk-taking and explorative behavior (HR) are more affected by PEWD.

Allopregnanolone induces a diurnally dependent hyperphagic effect and alters feeding latency and duration in male Wistar rats

Gamma‐aminobutyric acid (GABA)‐ergic transmission from the hypothalamus is essential for normal feeding regulation, and hyperphagia can be induced by local application of GABAA‐receptor agonists to different feeding‐associated brain areas. The food intake in rats varies diurnally and that may influence the effect of GABAA‐receptor active compounds. The progesterone metabolite allopregnanolone is a highly potent endogenous positive modulator of the GABAA receptor. Therefore, it is easy to envisage that allopregnanolone would have a hyperphagic effect, but earlier reports in rat have given ambiguous results. However, a contributing factor for the discrepancy may be the time point of the diurnal cycle in which the experiments were performed. The aim of this study was to investigate the effect of allopregnanolone on intake of standard chow in male Wistar rats at different time points of the day.

Repeated allopregnanolone exposure induces weight gain in schedule fed rats on high fat diet.

Ingestion of energy rich high fat diets is one of the determining factors associated with the obesity epidemic. Therefore, much can be learned from studies of obesity-related substances given to animals fed a high fat diet. The progesterone metabolite allopregnanolone is a potent positive modulator of the gamma-aminobutyric acid (GABA)A-receptor, and both allopregnanolone and GABA have been implicated in evoking hyperphagia. In this study, food intake and body weight gain were investigated during repeated allopregnanolone exposure. Male Wistar rats were studied when fed chow ad libitum, with chow access for 4h per day or with 45% high fat pellets for 4h per day. Rats on the high fat diet were separated into obesity prone and obesity resistant individuals. Subcutaneous injections of allopregnanolone were given once daily over five consecutive days. Repeated exposure to allopregnanolone lead to increased weight gain, significantly so in schedule fed rats on a high fat diet. The increased weight gain was correlated to an increased energy intake. Both obesity resistant and obesity prone rats responded to allopregnanolone with increased weight gain. Obesity resistant rats treated with allopregnanolone increased their energy intake and ate as much as vehicle treated obesity prone rats. Their weight gain was also increased to the level of obesity prone rats injected with just the vehicle carrier oil. Thus, it appears that allopregnanolone may be one of the endogenous factors involved in weight gain, especially when the diet is rich in fat.

Allopregnanolone Promotes Success in Food Competition in Subordinate Male Rats

Background/Aims: Allopregnanolone or 3α-hydroxy-5α-pregnan-20-one (AlloP) is normally sedative and anxiolytic, but can under provoking circumstances paradoxically induce aggressive behavior. Therefore, it is of particular interest to determine if there is a relationship between an anxiolytic effect and aggressive behavior following AlloP administration. Method: Male Wistar rats were housed in triads comprising of 1 young rat (35 days) and 2 older rats (55 days), with the intent of producing a social hierarchy. The triads were sampled for total serum testosterone and submitted to a social challenge in the form of a food competition test (FCT), where the rats competed for access to drinking sweetened milk. At baseline, the younger rats were identified as subordinates. To test for the behavioral effect of AlloP, the subordinate rats were given intravenous AlloP injections of 0.5 and 1 mg/kg. To assess the optimal AlloP effect, 6 intervals (5, 10, 15, 20, 30 and 40 min) between injection and the FCT were used. In separate studies, AlloP was also given by subcutaneous and intraperitoneal administration at 10 and 17 mg/kg. Results: AlloP (1 mg/kg, i.v.) increased drinking time and aggressive behavior in subordinate rats, with a positive correlation between these behaviors. The subcutaneous injection (17 mg/kg) also increased drinking time in subordinate animals. Serum testosterone concentration was higher in dominant compared to subordinate rats, and correlated with drinking time and weight. Conclusions: AlloP increased drinking time and aggressive behavior, and the correlation indicates a relationship between an anxiolytic effect and aggressive behavior.

The influence of social subordinate housing on the withdrawal effects from progesterone and estradiol in male rats.

Chronic stress and its concomitant neurobiological consequences are, in all probability, provocateurs of mental disease in humans. To gain some insight into the provocative effects of stress on hormonally dependent conditions, we developed a rat model that combines social subordinate housing (SSH) with withdrawal from combined progesterone (P) and estradiol (E) treatment (PEWD). At the start of the experiment, male Wistar rats were housed in triads consisting of one younger rat (35 days old) and two older rats (55 days old), with the intent of producing subordination stress in the younger animals. Triads containing three 35-day-old rats were used as age controls. Subordination stress was assessed with the elevated plus maze (EPM) and by corticosterone (CORT) analysis. Social rank within the triads was determined using a food competition test (FCT) and a tube test (TT). The younger rats (subordinate) and the dominant rats were assigned to 10 days of treatment with 5mg/kg P combined with 10 μg/kg E, or placebo (vehicle). Twenty-four hours after the last injection, the subordinate and dominant animals were tested in an open-field test (OFT) and a social challenge test (SCT). The SCT consisted of a 10-min exposure to three unfamiliar rats. SSH increased baseline CORT levels and reduced EPM open-arm time and post-EPM CORT levels compared to age-control rats. Only in the subordinate animals did PEWD increase locomotor activity and digging behavior, and reduce wrestling and pinning behavior. The behavioral results indicate an interaction between the effects of the lasting social subordinate stress and PEWD.

The role of progesterone and GABA in PMS/PMDD

The relationship between the luteal phase of the menstrual cycle and symptom development in premenstrual dysphoric disorder/premenstrual syndrome (PMDD/ PMS) is self-evident. Symptoms starts after ovulation and then increase in parallel with the rise in serum progesterone during the luteal phase. The symptom severity reaches a peak during the last five premenstrual days or the first day of menstruation. Thereafter, the symptoms decline and disappear 3–4 days after the onset of menstrual bleeding. During the postmenstrual phase there is a period of well-being, closely following estrogen production, to the estradiol peak. This suggests that there is a symptom-provoking factor produced by the corpus luteum of the ovary.1 This is further supported by the fact that in anovulatory cycles, spontaneous or induced, when a corpus luteum is not formed, no symptom cyclicity occurs.2–4

Neuroactive Steroids in Brain and Relevance to Mood

Depression and anxiety often affect women in relation to reproductive events like menarche, premenstrual periods, post-partum and perimenopause. A prominent example of the interaction between mood, neuroactive-steroids and the GABA system is premenstrual dysphoric disorder (PMDD). Severe premenstrual negative mood symptoms occur in 3–8% of women. Sex and stress hormones are metabolized to neuroactive steroids with effects on brain function as positive modulators of the GABA A receptor (called GABA-steroids) similar to benzodiazepines, barbiturates and alcohol. One example of a neuroactive sex steroid is allopregnanolone, and other GABA-steroids, are produced within the brain, by the adrenals at stress and from the ovary during the menstrual cycle. Animal and human studies show that benzodiazepines, barbiturates, alcohol and allopregnanolone have a bimodal effect on behavior. In high dosages or concentrations the positive GABA A receptor modulators are CNS depressants, anesthetic, and anxiolytic, whereas in certain sensitive individuals low concentrations instead of being anxiolytic cause severe anxiety, irritability, aggressiveness and depressive mood in 3–6% of individuals, and moderate symptoms in up to 30%. Low concentrations of GABA-steroids are found endogenously during the luteal phase and induce adverse emotional reactions. In women with PMDD/ PMS this paradoxical effect of neuroactive steroids seems to provoke negative mood symptoms as tension, irritability and depression. The mechanism behind the effect is called disinhibition that acts together with tolerance development by GABA A receptor active substances. Effective treatments are inhibition of ovarian steroid production or changing the CNS response to neuroactive steroids.