Anxiolytic activity of progesterone in progesterone receptor knockout mice
Introduction
Progesterone has long been known to have anxiolytic activity in animals (Fernández-Guasti and Picazo, 1992, Freeman et al., 1993, Reddy and Kulkarni, 1996, Reddy and Kulkarni, 1997a, Reddy and Kulkarni, 1997b, Reddy and Kulkarni, 1997c, Friess et al., 1997, Frye et al., 2000, Frye et al., 2004) and man (Little et al., 1974, Kroboth and McAuley, 1997), although the underlying mechanisms have not been fully elucidated. Progesterone regulates diverse neuroendocrine functions by binding to progesterone receptors (PRs), intracellular receptor proteins that are members of the nuclear receptor superfamily of transcription factors (Etgen, 1984, Tsai and O'Malley, 1994, Mulac-Jericevic et al., 2000). Many of the behavioral effects of progesterone are believed to be mediated by PRs that are expressed in hypothalamic and extrahypothalamic cell populations within the brain. In particular, PRs in the hypothalamus and limbic areas are required for the induction of progesterone-dependent reproductive behaviors in females and are also involved in the regulation of maternal and aggressive behaviors (Parsons et al., 1982, Mani et al., 1997, Conneely et al., 2001, Levine et al., 2001). In addition, progesterone can influence behavior through its metabolite allopregnanolone, a neurosteroid that does not interact with PRs but which can rapidly influence brain excitability as a result of its activity as a potent positive allosteric modulator of GABAA receptors (Rupprecht, 2003, Lambert et al., 2003). Studies in various animal models of anxiety have demonstrated that allopregnanolone has anxiolytic activity (Bitran et al., 1991, Wieland et al., 1991, Wieland et al., 1995, Carboni et al., 1996, Brot et al., 1997, Reddy and Kulkarni, 1996, Reddy and Kulkarni, 1997a, Reddy and Kulkarni, 1997b, Reddy and Kulkarni, 1999, Rodgers and Johnson, 1998, Frye et al., 2000, Finn et al., 2003). Moreover, several lines of evidence indicate that the anxiolytic effects of progesterone occur as a result of its conversion to allopregnanolone. Thus, progesterone-induced anxiolytic responses have been found to be correlated with blood and brain allopregnanolone levels and with the degree of facilitation of GABAA receptor-mediated chloride current responses (Bitran et al., 1993, Bitran et al., 1995). In addition, anxiety measures are closely correlated with natural fluctuations in progesterone levels during the ovarian cycle and the corresponding changes in plasma and brain allopregnanolone (Schmidt et al., 1994, Wang et al., 1996, Rapkin et al., 1997, Rubinow et al., 1998, Genazzani et al., 1998, Frye and Bayon, 1998, Concas et al., 1998). Finally, treatment with a 5α-reductase inhibitor that prevents the conversion of progesterone to allopregnanolone eliminates the anxiolytic activity of progesterone (Bitran et al., 1995). However, the anxiolytic activity of progesterone is absent in some but not all anxiety models in mice deficient in type I 5α-reductase (Frye et al., 2004). Notably, there is no reduction in the anxiolytic effects of progesterone in the elevated plus maze, despite the fact that brain allopregnanolone levels are reduced by 60%.
Even if allopregnanolone is primarily responsible for the anxiolytic action of progesterone, PRs are activated when endogenous levels of the hormone rise or when progesterone is administered exogenously. The parent steroid could therefore play a role in the overall anxiolytic response by influencing gene expression relevant to the anxiety behaviors. In addition, although allopregnanolone does not bind directly to PRs (Gee et al., 1988, Rupprecht et al., 1993, Rupprecht et al., 1996), allopregnanolone is capable of indirectly influencing PRs as a result of its in situ conversion to 5α-pregnane steroids that do activate PRs (Rupprecht et al., 1993). Therefore, in the present study, we examined the possible contribution of PRs to the anxiolytic activity of progesterone using progesterone receptor knockout (PRKO) mice. PRs exist in two protein isoforms (PR-A and PR-B) that are transcribed from a single gene. In PRKO mice, both isoforms are functionally ablated by targeting the PR gene in the germ line (Lydon et al., 1995). PRKO mice showed no overt behavioral abnormalities compared with wild-type (WT) animals and the anxiolytic activity of progesterone was not diminished in the knockout animals, providing strong confirmation that PRs are not required for the anxiolytic actions of progesterone.
Section snippets
Animals
Adult female PRKO and WT mice (25–30 g) were used in the study. The development of PRKO mice has been described previously (Lydon et al., 1995). A breeding colony of PRKO mice was established at the North Carolina State University (NCSU) College of Veterinary Medicine. WT and PRKO mice on a C57BL6/129SvEv hybrid background were housed separately, four to a cage with food and water available ad libitum. Because female PRKO mice are infertile, heterozygous and homozygous PRKO pups were derived by
PR expression in brain
PR immunoreactive neurons were observed in the hypothalamus (Fig. 1), hippocampus and various other brain regions of WT mice. The number of immunoreactive neurons was highest in the subregions of the hypothalamus, in accordance with prior studies demonstrating a high density of PR receptors in the mouse hypothalamus (Moffatt et al., 1998). Labeled neurons were present but more sparse in forebrain regions relevant to anxiety, including neocortex, hippocampus and amygdala (Parsons et al., 1982,
Discussion
The observation that the activity of progesterone in the elevated plus maze is undiminished in PRKO mice compared to WT littermates demonstrates that PRs are not required for the anxiolytic action of progesterone. This is the same conclusion as that reached by Bitran et al. (1995) using a pharmacological antagonist of PRs. However, not only was the anxiolytic effect of progesterone preserved in the PRKO mice, but it was actually larger than in WT controls (the difference was significant only at
Acknowledgements
Supported by NIH grants HD 07857/07495 (B.W.O'M.), NC State CVM grant (D.S.R.) and NINDS (M.A.R.).
References (74)
- et al.
Inhibition of rat 5α-reductases by finasteride: evidence for isozyme differences in mechanism of inhibition
Journal of Steroid Biochemistry and Molecular Biology
(1997) - et al.
The influence of subunit composition on the interaction of neurosteroids with GABAA receptors
Neuropharmacology
(2002) - et al.
Anxiolytic effects of 3α-hydroxy-5α[β]-pregnan-20-one: endogenous metabolites of progesterone that are active at the GABAA receptor
Brain Research
(1991) - et al.
Anxiolytic effect of progesterone is associated with increases in cortical allopregnanolone and GABAA receptor function
Pharmacology Biochemistry and Behavior
(1993) - et al.
Anxiolytic effects of the neuroactive steroid pregnanolone (3α-OH-5β-pregnan-20-one) after microinjection in the dorsal hippocampus and lateral septum
Brain Research
(1999) - et al.
The anxiolytic-like effects of the neurosteroid allopregnanolone: interactions with GABAA receptors
European Journal of Pharmacology
(1997) - et al.
Reproductive functions of the progesterone receptor isoforms: lessons from knock-out mice
Molecular and Cellular Endocrinology
(2001) - et al.
Brain neurosteroids during the mouse estrous cycle
Brain Research
(1997) Progestin receptors and the activation of female reproductive behavior: a critical review
Hormones and Behavior
(1984)- et al.
Neurosteroid consumption has anxiolytic effects in mice
Pharmacology Biochemistry and Behavior
(2003)
Changes in burying behavior during the estrous cycle: effect of estrogen and progesterone
Psychoneuroendocrinology
Progesterone enhances motor, anxiolytic, analgesic, and antidepressive behavior of wild-type mice, but not those deficient in type 1 5α-reductase
Brain Research
Rapid anxiolytic activity of progesterone and pregnanolone in male rats
Pharmacology Biochemistry Behavior
Neurosteroid modulation of GABAA receptors
Progress in Neurobiology
Progesterone receptors as neuroendocrine integrators
Frontiers in Neuroendocrinology
Progesterone receptor function from a behavioral perspective
Hormones and Behavior
Biosynthesis and action of neurosteroids
Brain Research Reviews
Progesterone metabolite allopregnanolone in women with premenstrual syndrome
Obstetrics and Gynecology
Differential anxiolytic effects of neurosteroids in the mirrored chamber behavior test in mice
Brain Research
Sex and estrous cycle-dependent changes in neurosteroid and benzodiazepine effects on food consumption and plus-maze learning behavior in rats
Pharmacology Biochemistry and Behavior
Development of neurosteroid-based novel psychotropic drugs
Progress in Medicinal Chemistry
Gonadal, adrenal, and neuroactive steroids' role in ictal activity
Brain Research
Behaviorally selective effects of neuroactive steroids on plus-maze anxiety in mice
Pharmacology, Biochemistry and Behavior
Neuroactive steroids: mechanisms of action and neuropsychopharmacological properties
Psychoneuroendocrinology
Progesterone receptor-mediated effects of neuroactive steroids
Neuron
Steroid receptor-mediated effects of neuroactive steroids: characterization of structure-activity relationship
European Journal of Pharmacology
Anxiolytic activity of the progesterone metabolite 5α-pregnane-3α-ol-20-one
Brain Research
Anxiolytic effect of progesterone is mediated by the neurosteroid allopregnanolone at brain GABAA receptors
Journal of Neuroendocrinology
A paracrine role for the epithelial progesterone receptor in mammary gland development
Proceedings of the National Academy of Sciences USA
Anxiolytic properties of endogenously occurring pregnanediols in two rodent models of anxiety
Psychopharmacology (Berlin)
Endocrine defects in mice carrying a null mutation for the progesterone receptor gene
Endocrinology
Role of brain allopregnanolone in the plasticity of γ-aminobutyric acid type A receptor in rat brain during pregnancy and after delivery
Proceedings of the National Academy of Sciences USA
Effects of a naturally occurring neurosteroid on GABAA IPSCs during development in rat hippocampal or cerebellar slices
Journal of Physiology
Brain 5α-dihydroprogesterone and allopregnanolone synthesis in a mouse model of protracted social isolation
Proceedings of the National Academy of Sciences USA
The mouse brain in stereotaxic coordinates
Anxiolytic metabolites of progesterone: correlation with mood and performance measures following oral progesterone administration to healthy female volunteers
Neuroendocrinology
Progesterone-induced changes in sleep in male subjects
American Journal of Physiology
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