Stimulation of Brain Pregnenolone Synthesis by Mitochondrial Diazepam Binding Inhibitor Receptor Ligands In Vivo

Abstract

Evidence that neurosteroids are potent modulators of the action of GABA at GABAA receptors has prompted the investigation of the mechanism that controls brain neurosteroid synthesis by glial cell mitochondria in vivo. In vitro studies suggest that the interaction of the diazepam binding inhibitor (DBI)--a polypeptide that is abundant in steroidogenic cells--with glial mitochondrial DBI receptors (MDRs) is a crucial step in the physiological regulation of neurosteroid biosynthesis. MDRs bind 4'-chlorodiazepam (4'-CD), N,N-di-n-hexyl-2-(4-fluorophenyl)-indol-3-acetamide (FGIN-1-27), and the isoquinoline carboxamide PK 11195 with high affinity, and these ligands have been used to investigate whether the stimulation of glial MDRs increases brain pregnenolone production in vivo. Adrenalectomized and castrated (A-C) male rats (to eliminate peripheral sources of pregnenolone) were pretreated with trilostane (to prevent pregnenolone metabolism to progesterone), and the pregnenolone content in brain regions dissected after fixation with a 0.8-s exposure to microwave irradiation focused to the head was determined by HPLC followed by specific radioimmunoassay. The forebrain and cerebellum of A-C rats contained 4-7 ng of pregnenolone/g of tissue, and the olfactory bulb contained 10-14 ng/g. These concentrations of brain pregnenolone are only 30-40% lower than those of sham-operated rats. In contrast, the plasma pregnenolone content of sham-operated rats was 2-3 ng/ml, but it was only 0.15-0.20 ng/ml in the plasma of A-C rats. In A-C rats, treatment with the MDR ligands 4'-CD and FGIN-1-27 increased the pregnenolone content in the brain but failed to change the plasma or peripheral tissue content of this steroid. The effect of 4'-CD on brain pregnenolone content was maximal (70-100% increase) at the dose of 18 mumol/kg, 5-10 min after intravenous injection. The effect of oral administration of FGIN-1-27 on brain pregnenolone content was maximal (80-150% increase) at doses of 400-800 mumol/kg and peaked at approximately 1 h. That this effect of FGIN-1-27 was mediated by the MDR was documented by pretreatment with the MDR partial agonist PK 11195 (100 mumol/kg, i.p.). PK 11195 did not affect basal brain pregnenolone content but prevented the accumulation of brain pregnenolone induced by FGIN-1-27. FGIN-1-27 and 4'-CD failed to increase the brain concentration of dehydroepiandrosterone in A-C rats. These data suggest that glial cell MDRs play a role in neurosteroid biosynthesis in vivo.

2‐Phenyl‐imidazo[1,2‐a]pyridine derivatives as ligands for peripheral benzodiazepine receptors: stimulation of neurosteroid synthesis and anticonflict action in rats

“…PK 11195 also induced signi®cant increases in both the cortical and plasma concentrations of neuroactive steroids, consistent with previous studies showing a similar e cacy of PK 11195 in stimulating steroidogenesis in brain mitochondria and in Y1 cells (McCauley et al, 1995;Zisterer & Williams, 1997). In contrast, Korneyev et al (1993) showed that PK 11195 is a speci®c blocker of PBR-mediated steroidogenesis but itself lacks steroidogenic activity. The later result may be due to the fact that in this study animals were killed 80 min after injection of PK 11195.…”

“…Thus, selective PBR ligands stimulate steroidogenesis in CNS and peripheral cells both in vitro and in vivo Papadopoulos et al, 1992;Romeo et al, 1992;Korneyev et al, 1993;McCauley et al, 1995). The observation that peripheral and central synthesis of neuroactive steroids can be modulated pharmacologically, together with the marked anxiolytic, anticonvulsant, sedative and hypnotic e ects elicited by i.c.v.…”

Production of 5α-Reduced Neurosteroids Is Developmentally Regulated and Shapes GABAAMiniature IPSCs in Lamina II of the Spinal Cord

“…Neurosteroidogenesis has been first described to occur in glial cells of the central and peripheral nervous system (Compagnone and Mellon, 2000), but recently, some key enzymes have also been localized to neurons (Zwain and Yen, 1999;Follesa et al, 2000;Tsutsui et al, 2000;Patte-Mensah et al, 2003). Stimulation of PBR was shown to increase the concentration of pregnenolone, progesterone, and related steroids in brain tissue and in the plasma (Korneyev et al, 1993;Zwain and Yen, 1999;Serra et al, 2001). Here, we clearly show that stimulation of the PBR induces a modulation of synaptic GABA A R function that is independent of the activation of central benzodiazepine sites on GABA A Rs, because it persisted in the presence of flumazenil, an antagonist of the CBR.…”

Structural Effects and Neurofunctional Sequelae of Developmental Exposure to Psychotherapeutic Drugs: Experimental and Clinical Aspects

“…Prenatal exposure to BZDs in the rat has been linked to subsequent altered binding to this site (Schlumpf et al, 1993) and altered mitochondrial function (Miranda et al, 1989). In adults, action at the mitochondrial BZD receptor stimulates steroid synthesis in the brain (Korneyev et al, 1993), and specific neurosteroids are potent agonists at the GABA A receptor (Rupprecht and Holsboer, 1999). Furthermore, drug action at the mitochondrial BZD receptor can affect GABA A receptor function (Costa et al, 1994).…”