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      Lordosis of Rats Is Modified by Neurosteroidogenic Effects of Membrane Benzodiazepine Receptors in the Ventral Tegmental Area

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          Progestins modulate lordosis through actions in the ventral tegmental area (VTA). Whether neurosteroidogenesis of 5α-pregnan-3α-ol-20-one (3α,5α-THP), involving mitochondrial benzodiazepine receptors (MBR), is important for lordosis was investigated. Ovariectomized (Ovx), hormone-primed rats (experiments 1, 3, 5, 6) and rats in behavioral estrus (experiments 2 and 4) were unilaterally infused via chronic guide cannula to the VTA with a MBR agonist, N,N-dihexyl-2-(4-fluorophenyl) indole-30-acetamide (FGIN 1–27) or antagonist 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboximide (PK-11195). Experiment 1: Estradiol benzoate (EB)-primed (25 µg) rats administered 0 or 25 µg progesterone (P<sub>4</sub>) SC showed increased lordosis when infused with 5.0 µg FGIN 1–27 to the VTA; those administered 100 or 200 µg P<sub>4</sub> SC exhibited greater lordosis when infused with 2.5 or 5.0 µg FGIN, relative to saline-infused rats. Experiment 2: Rats, near the termination of behavioral estrus, infused with 2.5 or 5.0 µg of FGIN 1–27 to the VTA, showed increased lordosis compared to that seen following vehicle administration. Experiment 3: EB-primed rats administered 200 or 500 µg P<sub>4</sub> SC showed decreased lordosis when infused with 100, 200, or 400 ng PK-11195, relative to saline-infused rats. Experiment 4: Rats infused at the peak of behavioral estrus with 100, 200, or 400 ng PK-11195 to the VTA exhibited reduced lordosis compared to that seen following vehicle administration. Experiment 5: 3α,5α-THP (100 ng) infusions to the VTA reinstated lordosis of hormone-primed rats infused with PK-11195 (100 ng) to the VTA. Experiment 6: FGIN 1–27 (5.0 µg) and PK-11195 (100 ng) infusions aimed at the VTA respectively increased and decreased midbrain levels of 3α,5α-THP compared to vehicle. Notably, the specific effects observed with infusions to the VTA were not seen with infusions to the control site, the substantia nigra. These data suggest that neurosteroidogenesis involving MBRs in the VTA mediates lordosis of hormone-primed or behavioral estrous rats.

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          Most cited references 21

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                Author and article information

                S. Karger AG
                January 2003
                10 March 2003
                : 77
                : 1
                : 71-82
                aDepartment of Psychology, bBiological Sciences, cCenter for Neuroscience Research, The University at Albany-SUNY, Albany, N.Y., USA
                68338 Neuroendocrinology 2003;77:71–82
                © 2003 S. Karger AG, Basel

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                Page count
                Figures: 6, References: 72, Pages: 12
                Reproductive Neuroendocrinology


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