Allopregnanolone (ALLO) and tetrahydrodeoxycorticosterone (THDOC) are potent positive allosteric modulators of GABA action at GABAA receptors. ALLO and THDOC are synthesized in the brain from progesterone or deoxycorticosterone, respectively, by the sequential action of two enzymes: 5α-reductase (5α-R) type I and 3α-hydroxysteroid dehydrogenase (3α-HSD). This study evaluates 5α-R type I and 3α-HSD mRNA expression level in mouse brain by using in situ hybridization combined with glutamic acid decarboxylase 67/65, vesicular glutamate transporter 2, glial fibrillary acidic protein, and S100β immunohistochemistry. We demonstrate that 5α-R type I and 3α-HSD colocalize in cortical, hippocampal, and olfactory bulb glutamatergic principal neurons and in some output neurons of the amygdala and thalamus. Neither 5α-R type I nor 3α-HSD mRNAs are expressed in S100β- or glial fibrillary acidic protein-positive glial cells. Using glutamic acid decarboxylase 67/65 antibodies to mark GABAergic neurons, we failed to detect 5α-R type I and 3α-HSD in cortical and hippocampal GABAergic interneurons. However, 5α-R type I and 3α-HSD are significantly expressed in principal GABAergic output neurons, such as striatal medium spiny, reticular thalamic nucleus, and cerebellar Purkinje neurons. A similar distribution and cellular location of neurosteroidogenic enzymes was observed in rat brain. Taken together, these data suggest that ALLO and THDOC, which can be synthesized in principal output neurons, modulate GABA action at GABAA receptors, either with an autocrine or a paracrine mechanism or by reaching GABAA receptor intracellular sites through lateral membrane diffusion.

https://www.pnas.org/content/pnas/103/39/14602.full.pdf

Characterization of brain neurons that express enzymes mediating neurosteroid biosynthesis.

The discovery of central monoamine neurons gave volume transmission to the wired brain.

Dlx Transcription Factors Promote Migration through Repression of Axon and Dendrite Growth

BACKGROUND The steroid hormone progesterone is indispensable for mammalian procreation by controlling key female reproductive events that range from ovulation to implantation, maintenance of pregnancy and breast development. In addition to activating the progesterone receptors (PRs)-B and -A, members of the superfamily of ligand-dependent transcription factors, progesterone also elicits a variety of rapid signalling events independently of transcriptional or genomic regulation. This review covers our current knowledge on the mechanisms and relevance of non-genomic progesterone signalling in female reproduction.

METHODS PubMed was searched up to August 2008 for papers on progesterone actions in ovary/breast/endometrium/myometrium/brain, focusing primarily on non-genomic signalling mechanisms.

RESULTS Convergence and intertwining of rapid non-genomic events and the slower transcriptional actions critically determine the functional response to progesterone in the female reproductive system in a cell-type- and environment-specific manner. Several putative progesterone-binding moieties have been implicated in rapid signalling events, including the ‘classical’ PR and its variants, progesterone receptor membrane component 1, and the novel family of membrane progestin receptors. Progesterone and its metabolites have also been implicated in the allosteric regulation of several unrelated receptors, such as γ-aminobutyric acid type A, oxytocin and sigma1 receptors.

CONCLUSIONS Identification of the mechanisms and receptors that relay rapid progesterone signalling is an area of research fraught with difficulties and controversy. More in-depth characterization of the putative receptors is required before the non-genomic progesterone pathway in normal and pathological reproductive function can be targeted for pharmacological intervention.

/pdf/non-genomic-progesterone-actions-in-female-reproduction-4ey83poy4q.pdf

Non-genomic progesterone actions in female reproduction

Neurosteroid regulation of central nervous system development.

The neurosteroid pregnenolone (PREG) and its chemically synthesized analog 3β-methoxypregnenolone (MePREG) bind to microtubule-associated protein 2 (MAP2) and stimulate the polymerization of microtubules. PREG, MePREG, and progesterone (PROG; the physiological immediate metabolite of PREG) significantly enhance neurite outgrowth of nerve growth factor-pretreated PC12 cells. However, PROG, although it binds to MAP2, does not increase the immunostaining of MAP2, contrary to PREG and MePREG. Nocodazole, a microtubule-disrupting agent, induces a major retraction of neurites in control cultures, but pretreatment with PREG/MePREG is protective. Decreasing MAP2 expression by RNA interference does not modify PROG action, but it prevents the stimulatory effects of PREG and MePREG on neurite extension, showing that MAP2 is their specific receptor.

/pdf/microtubule-associated-protein-2-map2-is-a-neurosteroid-1ko81uv6cn.pdf

Microtubule-associated protein 2 (MAP2) is a neurosteroid receptor

MAPREG (microtubule-associated protein/neurosteroidal pregnenolone) is a start-up company that was created in October 2000. Its acronym recalls the basic discovery (Murakami et al., 2000) from which drug(s) will hopefully be developed that are useful for neuroprotection and repair in conditions such as post-traumatic and postischemic lesions, as well as defects proper to normal aging and neurodegenerative diseases, that is, principally Alzheimer's disease. Pregnenolone, the main steroid synthesized from cholesterol in the nervous system (therefore, a neurosteroid), binds specifically with high affinity (> or = 40 nM) to microtubule-associated protein 2 (MAP2), a protein family involved in the assembly and stabilization of microtubules made from tubulin alpha and beta polymers, and in the bundling of several microtubules by MAP2 projection arms. Pregnenolone binding increases MAP2-induced microtubule polymerization, when purified tubulin and MAP2 are coincubated in GTP containing buffer at 37 degrees C. Therefore, MAP2 can be considered as a receptor for a novel mechanism of steroid action. The underlying principle and its potential pharmacological consequences are described in an INSERM patent (FR 0003430; March 17, 2000). MAPREG has established its own laboratory in a space rented to Bicetre hospital, near the research building of INSERM, where two of the main founders of the company (Drs. E. Baulieu and P. Robel) work. The company has been quite successful, largely thanks to the support of ISOA (attributed in October 2002). A lead compound (pregnenolone derivative) was tested and patented by MAPREG early in 2003 (FR 0300507; January 17, 2003). Activities and results reported at the ISOA meeting on Oct. 2, 2003, include in vitro basic studies, in vitro and in vivo neuroprotection trials in rodent systems, and studies with human cells and an AD transgenic mouse model.

Yann Duchossoy

Papers

Microtubule-associated protein 2 (MAP2) is a neurosteroid receptor

MAPREG: toward a novel approach of neuroprotection and treatment of Alzheimer's disease.