Mitochondrial benzodiazepine receptors in the ventral tegmental area modulate sexual behaviour of cycling or hormone-primed hamsters

Effects and Mechanisms of 3α,5α,-THP on Emotion, Motivation, and Reward Functions Involving Pregnane Xenobiotic Receptor

Progestogens [progesterone (P(4)) and its products] play fundamental roles in the development and/or function of the central nervous system during pregnancy. We, and others, have investigated the role of pregnane neurosteroids for a plethora of functional effects beyond their pro-gestational processes. Emerging findings regarding the effects, mechanisms, and sources of neurosteroids have challenged traditional dogma about steroid action. How the P(4) metabolite and neurosteroid, 3α-hydroxy-5α-pregnan-20-one (3α,5α-THP), influences cellular functions and behavioral processes involved in emotion/affect, motivation, and reward, is the focus of the present review. To further understand these processes, we have utilized an animal model assessing the effects, mechanisms, and sources of 3α,5α-THP. In the ventral tegmental area (VTA), 3α,5α-THP has actions to facilitate affective, and motivated, social behaviors through non-traditional targets, such as GABA, glutamate, and dopamine receptors. 3α,5α-THP levels in the midbrain VTA both facilitate, and/or are enhanced by, affective and social behavior. The pregnane xenobiotic receptor (PXR) mediates the production of, and/or metabolism to, various neurobiological factors. PXR is localized to the midbrain VTA of rats. The role of PXR to influence 3α,5α-THP production from central biosynthesis, and/or metabolism of peripheral P(4), in the VTA, as well as its role to facilitate, or be increased by, affective/social behaviors is under investigation. Investigating novel behavioral functions of 3α,5α-THP extends our knowledge of the neurobiology of progestogens, relevant for affective/social behaviors, and their connections to systems that regulate affect and motivated processes, such as those important for stress regulation and neuropsychiatric disorders (anxiety, depression, schizophrenia, drug dependence). Thus, further understanding of 3α,5α-THP's role and mechanisms to enhance affective and motivated processes is essential.

Effects of neurosteroid actions at N-methyl-D-aspartate and GABA A receptors in the midbrain ventral tegmental area for anxiety-like and mating behavior of female rats

RATIONALE

In the midbrain ventral tegmental area (VTA), actions of neurosteroids, such as the progesterone metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP), can facilitate mating and influence stress-related processes. Some actions of 3α,5α-THP may occur via positive modulation of GABA(A) receptors (GBRs), or negative modulation of N-methyl-D: -aspartate receptors (NMDARs), to influence anxiety-like behavior; but this is not known.

OBJECTIVES

We aimed to assess the role that neurosteroids and stress factors play on intra-VTA NMDAR- and/or GBR-mediated anxiety-like and mating behavior.

METHODS

Estradiol-primed, ovariectomized rats, which were partially or completely adrenalectomized (ADX), received infusions of vehicle, an NMDAR blocker (MK-801; 200 ng), or a GBR antagonist (bicuculline, 100 ng) to the VTA. Rats then received intra-VTA vehicle or a neurosteroidogenesis enhancer (N,N-Dihexyl-2-(4-fluorophenyl)indole-3-acetamide, FGIN 1-27, 5 μg) and anxiety-like and sexual behavior was assessed.

RESULTS

Complete, compared to partial, ADX significantly reduced open arm exploration on an elevated plus maze, the proportion of females that engaged in mating, lordosis quotients, pacing of sexual contacts, and defensive aggression towards a sexually vigorous male. Intra-VTA MK-801 enhanced open arm investigation and the proportion of females that engaged in mating. Infusions of either, MK-801 or FGIN 1-27, enhanced lordosis and, when co-administered, FGIN 1-27 attenuated MK-801's lordosis-enhancing effects. Intra-VTA infusions of bicuculline, prior to FGIN 1-27, blocked FGIN 1-27's effects to enhance lordosis.

CONCLUSIONS

Together, these data suggest that reduced NMDAR activity in the VTA may influence motivation to explore and engage in sexual behavior. These data suggest that neurosteroid actions at NMDARs and GBRs in the VTA are important for exploration and/or sexual behavior.

Fluoxetine-induced decrements in sexual responses of female rats and hamsters are reversed by 3α,5α-THP

INTRODUCTION

Sexual dysfunction, as a result of selective-serotonin reuptake inhibitor (SSRI) treatment among women, is relatively common and is a factor in medication compliance. The mechanisms that underlie these side-effects of SSRIs are not well-understood. SSRIs can alter activity of catabolic enzymes that are involved in progesterone's conversion to 5 α-pregnan-3 α-ol-20-one (3 α,5 α-THP). 3 α,5 α-THP plays a key role in female reproductive physiology and behavior.

AIMS

This study aimed to determine whether 3 α,5 α-THP, in the midbrain ventral tegmental area (VTA) may be a potential mechanism for fluoxetine's reduction in sexual responding of female rodents. We hypothesized that if fluoxetine induces decrements in sexual responding in part through actions of 3 α,5 α-THP, then fluoxetine will inhibit sexual receptivity concomitant with reducing 3 α,5 α-THP levels, effects which can be reversed by 3 α,5 α-THP administration.

METHODS

  Experiment 1 investigated effects of acute systemic fluoxetine [20 mg/kg intraperitoneal (IP)] and/or 3 α,5 α-THP [500 µg, subcutaneous (SC)] administration on sexual responding of ovariectomized, hormone-primed rats. Experiment 2 examined effects of 3 α,5 α-THP administration to the midbrain VTA (100 ng) on fluoxetine-induced decrements in lordosis of ovariectomized, hormone-primed rats and hamsters.

MAIN OUTCOME MEASURES

Sexual responding was determined in rats and hamsters. For rats, the percentage of times that the lordosis response occurred following mounting by a sexually-vigorous male (lordosis quotients) was utilized. For hamsters, lateral displacement, the pelvic movement that females will make to facilitate intromissions by a male hamster, was utilized.

RESULTS

Fluoxetine significantly reduced lordosis, and this was reversed SC 3 α,5 α-THP. Intra-VTA 3 α,5 α-THP attenuated fluoxetine's detrimental effects on lordosis quotients and lateral displacement of rats and hamsters, respectively.

CONCLUSIONS

Thus, fluoxetine's effects to disrupt female sexual responses may involve its effects on progestogens in the midbrain VTA.

Infusions of anti-sense oligonucleotides for DARPP-32 to the ventral tegmental area reduce effects of progesterone- and a dopamine type 1-like receptor agonist to facilitate lordosis

Manipulating dopamine and/or adenosine 3',5' monophosphate regulated phosphoprotein of 32 kDa (DARPP-32) can influence sexual behavior of rodents. The ventral tegmental area (VTA) is an important brain site for progestogens to facilitate sexual behavior of rodents. We hypothesized that, in the VTA, dopamine type 1-like receptor (D1)-mediated increases in progesterone (P4)-facilitated lordosis involve DARPP-32. To investigate this, ovariectomized hamsters and rats, primed with estradiol (E2; 10 microg), received infusions to the VTA of saline vehicle or sense or anti-sense oligonucleotides targeted against DARPP-32 (4 nM). Subjects were then administered P4 via subcutaneous injection (hamsters: 200 microg; rats: 0 or 100 microg). Hamsters and rats were pre-tested for lordosis 3.5 h post-P4 injections, and then infused with the D1 agonist SKF38393 (100 ng) or vehicle to the VTA, and re-tested for sexual behavior 30 min later. Anti-sense oligonucleotides targeted against DARPP-32, but not infusions of sense oligonucleotides, to the VTA blocked the ability of systemic P4 to enhance receptive behavior of hamsters and rats. Similarly, SKF38393-mediated increases in P4-facilitated sexual behaviors were blocked by DARPP-32 anti-sense oligonucleotides to the VTA. The same pattern of effects was not observed in rats that were primed with E2-alone. Together, these findings suggest that, in the midbrain VTA, P4's actions to facilitate sexual behavior of female rodents, involving D1 receptors, may require DARPP-32.

Membrane actions of progestins at dopamine type 1-like and GABAA receptors involve downstream signal transduction pathways

In the ventral tegmental area (VTA), progestins facilitate lordosis via rapid actions at membrane dopamine Type 1-like (D(1)) and/or GABA(A) receptors (GBRs), rather than via cognate, intracellular progestin receptors (PRs). Downstream signal transduction pathways involved in these effects were investigated using lordosis as a bioassay. If progestins' actions at D(1) and/or GBRs in the VTA require activation of G-proteins, adenylyl cyclase, cyclic AMP-dependent protein kinase A (PKA), phospholipase C (PLC), and/or PKC, then pharmacologically blocking these pathways would be expected to attenuate progestin-facilitated lordosis and its enhancement by D(1) and GBR activity. Ovariectomized, estradiol-primed rats were infused first with vehicle or signal transduction inhibitor, and second with vehicle, a D(1) or GBR agonist, and then with vehicle or progestins to the VTA. Rats were tested for lordosis following infusions. Results indicated that initiation of G-proteins, adenylyl cyclase, PKA, PLC, or PKC in the VTA is required for rapid effects of progestins through D(1) and/or GBRs to facilitate lordosis. As well, progestins' actions at n-methyl-d-aspartate receptors (NMDARs) may modulate activity at D(1) and/or GBRs and mitogen activated protein kinase (MAPK) may be a common signaling pathway. Findings from a microarray study demonstrated that there was upregulation of genes associated with steroid metabolism, GBRs, D(1), NMDARs and signal transduction factors in the midbrain VTA of naturally receptive mated compared to non-mated rats. Thus, in the VTA, progestins have rapid membrane-mediated actions via D(1), GBRs, NMDARs and their downstream signal transduction pathways.

Increasing 3alpha,5alpha-THP following inhibition of neurosteroid biosynthesis in the ventral tegmental area reinstates anti-anxiety, social, and sexual behavior of naturally receptive rats

The progesterone metabolite and neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), has actions in the midbrain ventral tegmental area (VTA) to modulate lordosis, but its effects on other reproductively relevant behaviors are not well understood. Effects on exploration, anxiety, and social behavior resulting from inhibition of 3alpha,5alpha-THP formation, as well as 3alpha,5alpha-THP enhancement, were investigated in the midbrain VTA. Naturally sexually receptive, female rats (n=8-10/group) received infusions aimed at the midbrain VTA of vehicle, PK11195 (an inhibitor of neurosteroidogenesis), and/or indomethacin (an inhibitor of 3alpha,5alpha-THP formation from prohormones), and were subsequently infused with vehicle or FGIN 1-27 (a neurosteroidogenesis enhancer). The rats were then assessed in a behavioral battery that examined exploration (open field), anxiety (elevated plus maze), social (social interaction), and sexual (paced mating) behavior. Inhibition of 3alpha,5alpha-THP formation decreased exploratory, anti-anxiety, social, and sexual behavior, as well as midbrain 3alpha,5alpha-THP levels. Infusions of FGIN 1-27 following 3alpha,5alpha-THP inhibition restored these behaviors and midbrain 3alpha,5alpha-THP levels to those commensurate with control rats that had not been administered inhibitors. These findings suggest that 3alpha,5alpha-THP formation in the midbrain VTA may influence appetitive, as well as consummatory, aspects of mating behavior.

Activity of protein kinase C is important for 3alpha,5alpha-THP's actions at dopamine type 1-like and/or GABAA receptors in the ventral tegmental area for lordosis of rats

In the ventral tegmental area, progestogens facilitate sexual receptivity of rodents via actions at dopamine type 1-like and/or gamma-aminobutyric acid type A receptors and activation of downstream signal transduction molecules. In the present study, we investigated whether effects of progesterone's metabolite, 3alpha,5alpha-THP, to enhance lordosis via actions at these receptors in the ventral tegmental area requires phospholipase C-dependent protein kinase C. The objective of this study was to test the hypothesis that: if progestogens' actions through dopamine type 1-like and/or gamma-aminobutyric acid type A receptors in the ventral tegmental area for lordosis require protein kinase C, then inhibiting protein kinase C in the ventral tegmental area should reduce 3alpha,5alpha-THP-facilitated lordosis and its enhancement by dopamine type 1-like or gamma-aminobutyric acid type A receptor agonists. Ovariectomized, estradiol (E(2); 10 microg s.c. at h 0)-primed rats were tested for their baseline lordosis responses and then received a series of three infusions to the ventral tegmental area: first, bisindolylmaleimide (75 nM/side) or vehicle; second, SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle; third, 3alpha,5alpha-THP (100, 200 ng/side) or vehicle. Rats were pre-tested for lordosis and motor behavior and then tested for lordosis after each infusion and 10 and 60 min after the last infusion. Rats were tested for motor behavior following their last lordosis test. As has been previously demonstrated, 3alpha,5alpha-THP infusions to the ventral tegmental area increased lordosis and effects were further enhanced by infusions of SKF38393 and muscimol. Infusions of bisindolylmaleimide to the ventral tegmental area attenuated 3alpha,5alpha-THP-, SKF38393-, and/or muscimol-facilitated lordosis. Effects on lordosis were not solely due to changes in general motor behavior. Thus, 3alpha,5alpha-THP's actions in the ventral tegmental area through membrane receptors may require activity of protein kinase C.

Exploratory, anti-anxiety, social, and sexual behaviors of rats in behavioral estrus is attenuated with inhibition of 3alpha,5alpha-THP formation in the midbrain ventral tegmental area

The progesterone (P(4)) metabolite and neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) acts in the midbrain ventral tegmental area (VTA) to modulate lordosis of female rats. 3alpha,5alpha-THP also mediates exploratory, affective, and social behaviors; whether actions of 3alpha,5alpha-THP in the VTA mediate these behaviors is of interest. To elucidate the role of the VTA in mediating exploratory, affective, and social behaviors, the present study examined effects of inhibiting 3alpha,5alpha-THP formation in the VTA. Rats received intra-VTA infusions of either PK11195 (400ng/mul, which inhibits de novo 3alpha,5alpha-THP production), indomethacin (10mug/mul, which blocks metabolism of P(4) to 3alpha,5alpha-THP), PK11195 and indomethacin together, or beta-cyclodextrin vehicle and tested on a battery of anxiety (open field and elevated plus maze), social (partner preference and social interaction), and sexual (paced mating) tasks. Compared to rats infused with vehicle to the VTA, rats infused with inhibitor(s) demonstrated significant reductions in central entries in the open field, time on open arms of an elevated plus maze, time spent interacting with a conspecific, initiation and intensity of lordosis, sexual solicitations, and midbrain 3alpha,5alpha-THP levels. These findings suggest that actions of 3alpha,5alpha-THP in the VTA are important for mediating aspects of exploration, anxiety, and social behavior related to mating.

Infusions of 3alpha,5alpha-THP to the VTA enhance exploratory, anti-anxiety, social, and sexual behavior and increase levels of 3alpha,5alpha-THP in midbrain, hippocampus, diencephalon, and cortex of female rats

17beta-Estradiol (E2) and progesterone (P4) influence the onset and duration of sexual behavior and are also associated with changes in behaviors that may contribute to mating, such as exploration, anxiety, and social behaviors (socio-sexual behaviors). In the midbrain ventral tegmental area (VTA), the P4 metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), modulates lordosis of E2-primed rodents; 3alpha,5alpha-THP can also influence anxiety and social behaviors. To examine if 3alpha,5alpha-THP in the VTA mediates socio-sexual behaviors, we infused 3alpha,5alpha-THP to the VTA of diestrous and proestrous rats. As expected, proestrous, compared to diestrous, rats showed more exploratory (open field), anxiolytic (elevated plus maze), pro-social (partner preference, social interaction), and sexual (paced mating) behavior and had increased E2, P4, dihydroprogesterone (DHP), and 3alpha,5alpha-THP in serum, midbrain, hippocampus, diencephalon, and cortex. Infusions of 3alpha,5alpha-THP to the VTA, but not control sites, such as the substantia nigra (SN) or central grey (CG), of diestrous rats produced behavioral and endocrine effects akin to that of proestrous rats and increased DHP and 3alpha,5alpha-THP levels in midbrain, hippocampus, and diencephalon. Levels of DHP and 3alpha,5alpha-THP, but neither E2 nor P4 concentrations, in midbrain, hippocampus, diencephalon, and/or cortex were positively correlated with socio-sexual behaviors. Thus, 3alpha,5alpha-THP infusions to the VTA, but not SN or CG, can enhance socio-sexual behaviors and increase levels in midbrain, hippocampus, and diencephalon.

Progestins influence motivation, reward, conditioning, stress, and/or response to drugs of abuse

Progesterone (pregn-4-ene-3,20-dione; P) and its metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) are secreted by ovaries, adrenals, and glial cells. 3alpha,5alpha-THP in the midbrain ventral tegmental area mediates sexual receptivity of rodents through its actions at GABA(A), NMDA, and/or D(1) receptors. The extent to which 3alpha,5alpha-THP may influence anti-anxiety/anti-stress effects, conditioning and/or reward through these substrates and/or by altering hypothalamic pituitary adrenal axis function is discussed. Biosynthesis of 3alpha,5alpha-THP occurs in responses to mating and may underlie some of the rewarding aspects of sexual behavior. Recent findings from our laboratory which demonstrate that progestins can enhance approach to novel stimuli, conditioning, and reinforcement are reviewed. How progestins' effects on these processes may underlie response to drugs of abuse is considered and new findings which demonstrate interactions between progestins and cocaine are presented.

Infusions of 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) to the ventral tegmental area, but not the substantia nigra, enhance exploratory, anti-anxiety, social and sexual behaviours and concomitantly increase 3alpha,5alpha-THP concentrations in the hippocampus, diencephalon and cortex of ovariectomised oestrogen-primed rats

Sequential actions of 17beta-oestradiol (E2) and progesterone (P4) in the ventromedial hypothalamus (VMH) and ventral tegmental area (VTA) mediate sexual behaviour of female rodents. In the presence of appropriate environmental stimuli, E2 and P4 can facilitate initiation of sex behaviour (i.e. lordosis), in part through classic actions at intracellular progestin receptors in the VMH. However, the effects of P4 in the VTA to modulate lordosis involve its metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), which can have paracrine effects in the brain to reduce anxiety and stress. We investigated the effects of 3alpha,5alpha-THP infusions to the VTA, and a control site, the substantia nigra (SN), on exploratory, anti-anxiety, social and sexual behaviours (socio-sexual behaviours) and hormone levels in the midbrain and other regions (hippocampus, diencephalon and cortex) that may mediate these functions. Ovariectomised, rats were E2-primed (10 microg, s.c.) at 0 h and were infused with beta-cyclodextrin vehicle or 3alpha,5alpha-THP to the VTA or SN 44-48 h later. Ten minutes after infusions, rats were tested in the open field, plus maze, partner preference, social interaction and paced mating tasks, or served as nontested controls. Infusions of 3alpha,5alpha-THP to the VTA, but not the SN, increased central entries in the open field, open arm time in the plus maze, time spent in proximity to a male, duration of social interaction, incidence and intensity of lordosis, pacing, proceptivity, and anti-conflict behaviour. 3Alpha,5alpha-THP, but not vehicle, infusions to the VTA (but not the SN) also increased 3alpha,5alpha-THP levels in the midbrain, as well as the hippocampus, diencephalon and cortex. Behavioural testing increased levels of the precursor of 3alpha,5alpha-THP precursor, dihydroprogesterone (DHP). Thus, infusions of 3alpha,5alpha-THP to the VTA enhance socio-sexual behaviours and increase 3alpha,5alpha-THP levels in the hippocampus, diencephalon and cortex, and behavioural testing increases DHP levels in brain areas involved in modulating socio-sexual behaviours.

In the ventral tegmental area, cyclic AMP mediates the actions of progesterone at dopamine type 1 receptors for lordosis of rats and hamsters

Progesterone-facilitated lordosis is enhanced by activation of, and inhibited by antagonism of, dopamine type 1 receptors (D1) in the ventral tegmental area (VTA). Given that D1 activation leads to increases in cyclic AMP (cAMP), we hypothesised that, in the VTA, progesterone's actions on lordosis that involve D1 are mediated, in part, by cAMP. In Experiment 1, naturally receptive rats and hamsters were pretested for lordosis, infused with the cAMP analogue 8-bromo-cAMP (200 ng) or vehicle to the VTA, and tested again 30 min later. In Experiments 2 and 3, ovariectomised, oestradiol (10 microg) + progesterone (0 or 100 microg)-primed rats and oestradiol (10 microg) + progesterone (0 or 200 microg)-primed hamsters were pretested for lordosis and infused with 8-bromo-cAMP (200 ng), the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine (12 microM) or vehicle to the VTA. Subjects were tested again 30 min later. In Experiment 4, oestradiol + progesterone-primed rats and hamsters were pretested and infused with the D1 agonist SKF38393 (0 or 100 ng) to the VTA. Thirty minutes later, subjects were tested again and infused with 2',5'-dideoxyadenosine (12 microM) or vehicle. Subjects were tested again 30 min later. VTA infusions of 8-bromo-cAMP enhanced lordosis of naturally receptive or hormone-primed rats and hamsters and 2',5'-dideoxyadenosine decreased lordosis of oestradiol + progesterone-primed rats and hamsters. D1-mediated increases in progesterone-facilitated lordosis were reduced by 2',5'-dideoxyadenosine. These data suggest that progesterone-facilitated lordosis of rats and hamsters may be modulated by D1 and cAMP activity in the VTA.

In the ventral tegmental area, progestins have actions at D1 receptors for lordosis of hamsters and rats that involve GABA A receptors

In the ventral tegmental area (VTA), progestins facilitate lordosis via actions at gamma-aminobutyric acid (GABA)(A)/benzodiazepine receptor complexes (GBRs) and dopamine type 1 receptors (D1). The relationship between progestins' actions at GBRs and D1 in the VTA for facilitating sexual behavior of hamsters and rats was examined. Ovariectomized (ovx), estradiol (E(2); 10 microg)+progesterone (P; 250 microg; SC)-primed hamsters, with bilateral guide cannulae to the VTA, were pre-tested for sexual and motor behavior and infused with the GBR antagonist bicuculline (100 ng/side) or vehicle. Thirty minutes later, hamsters were re-tested and then infused with the D1 agonist SKF38393 (100 ng/side) or vehicle. Hamsters were post-tested 30 min later. Ovx, E(2) (10 microg)-primed rats were pre-tested, infused first with bicuculline or vehicle, second with SKF38393 or vehicle, third with 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 0, 100, or 200 ng) and were post-tested 10 and 60 min after 3alpha,5alpha-THP infusions. VTA infusions of SKF38393 increased lordosis of hamsters or rats. Bicuculline pretreatment reduced SKF38393- and/or progesterone-mediated increases in lordosis of E2-primed hamsters. In E2-primed rats, bicuculline blocked SKF38393- and/or 3alpha,5alpha-THP-mediated increases in lordosis. There were no effects on motor behavior. Thus, in the VTA, GBR activity modulates D1-mediated actions for lordosis of hamsters and rats.

Progestins' effects on sexual behaviour of female rats and hamsters involving D1 and GABA(A) receptors in the ventral tegmental area may be G-protein-dependent

In the ventral tegmental area (VTA), progestins have actions involving dopamine type 1-like receptors (D(1)) and gamma-aminobutyric acid (GABA)(A)/benzodiazepine receptor complexes (GBRs) for lordosis. Evidence suggests that D(1) and GBRs can have G-protein-mediated effects. We investigated if, in the VTA, inhibiting G-proteins prevents D(1)- and/or GBR-mediated increases in progestin-facilitated lordosis. Hamsters, with bilateral guide cannulae to the VTA, received systemic E(2) (10 microg) at hour 0 and progesterone (P, 250 microg) at hour 45. At hour 48, hamsters were pre-tested for lordosis and infused with the G-protein inhibitor, guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S, 50 microM/side), or 10% DMSO saline vehicle. Thirty minutes after initial infusions, hamsters were re-tested and then immediately infused with the D(1) agonist, SKF38393 (100 ng/side), the GBR agonist, muscimol (100 ng/side), or saline vehicle. Hamsters were post-tested for lordosis 30 min later. For rats, E(2) (10 microg) priming at hour 0 was followed by lordosis pre-testing at hour 44. After pre-testing, rats received infusions of GDP-beta-S or vehicle, followed by infusions of SKF38393, muscimol, or vehicle and then infusions of the neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP, 100 or 200 ng/side), or beta-cyclodextrin vehicle. Rats were tested immediately after each infusion of SKF38393, muscimol or vehicle, as well as 10 and 60 min after 3alpha,5alpha-THP or vehicle infusions. Inhibiting G-proteins, in the VTA, reduced the ability of systemic P or intra-VTA SKF38393 or muscimol to facilitate lordosis of E(2)-primed hamsters. Blocking G-proteins, in the VTA, prevented SKF38393-, muscimol- and/or 3alpha,5alpha-THP-mediated increases in lordosis of E(2)-primed rats. Thus, progestins' actions in the VTA for lordosis that involve D(1) and/or GBRs may also include recruitment of G-proteins.

In the ventral tegmental area, G-proteins mediate progesterone's actions at dopamine type 1 receptors for lordosis of rats and hamsters

RATIONALE

Previous reports indicate that the ventral tegmental area (VTA) and/or progesterone (P) can modulate the reinforcing effects of drugs of abuse, food, and sexual behavior.

OBJECTIVES

We investigated if, in the VTA, P's membrane-mediated actions for lordosis involve dopamine type 1 receptors (D(1)). Also, whether P's actions at D(1) for lordosis are mediated by typical G-protein coupled mechanisms was examined.

METHODS

In Exps 1 and 2, rats received estradiol (E(2) 10 microg) at h 0 and infusions of the D(1) antagonist SCH23390 (100 ng), the D(1) agonist SKF38393 (100 ng), or vehicle, to the VTA, at h 44. Thirty minutes later, rats received systemic P (0, 50, 100, or 200 microg). Subjects were tested for lordosis and motor behavior 2.5 h later. In Exps 3 and 4, E(2)+P (rats 0 or 100 microg; hamsters 200 microg)-primed animals were pretested for lordosis and motor behavior at h 47.5 and infused with SKF38393 (100 ng) or vehicle to the VTA. Thirty minutes later, subjects were retested and infused with the G-protein inhibitor guanosine 5'-O-(2-Thiodiphosphate) (GDP-beta-S; 50 microM) or vehicle. Post-testing occurred 30 min later.

RESULTS

Pretreatment with SCH23390-reduced and SKF38393-enhanced P's actions, in the VTA, for lordosis of E(2)-primed rats and hamsters. As well, D(1)-mediated increases in P-facilitated lordosis of rats and hamsters were inhibited by GDP-beta-S. Changes in lordosis were independent of large alterations in motor behavior.

CONCLUSIONS

In the VTA, P has actions for modulating reinforcing behaviors, such as lordosis, at D(1) that are G-protein-mediated.

Rapid effects of aromatase inhibition on male reproductive behaviors in Japanese quail

Non-genomic effects of steroid hormones on cell physiology have been reported in the brain. However, relatively little is known about the behavioral significance of these actions. Male sexual behavior is activated by testosterone partly through its conversion to estradiol via the enzyme aromatase in the preoptic area (POA). Brain aromatase activity (AA) changes rapidly which might in turn be important for the rapid regulation of behavior. Here, acute effects of Vorozole, an aromatase inhibitor, injected IP at different doses and times before testing (between 15 and 60 min), were assessed on male sexual behavior in quail. To limit the risk of committing both types of statistical errors (I and II), data of all experiments were entered into a meta-analysis. Vorozole significantly inhibited mount attempts (P < 0.05, size effect [g] = 0.527) and increased the latency to first copulation (P < 0.05, g = 0.251). The treatment had no effect on the other measures of copulatory behavior. Vorozole also inhibited appetitive sexual behavior measured by the social proximity response (P < 0.05, g = 0.534) or rhythmic cloacal sphincter movements (P < 0.001, g = 0.408). Behavioral inhibitions always reached a maximum at 30 min. Another aromatase inhibitor, androstatrienedione, induced a similar rapid inhibition of sphincter movements. Radioenzyme assays demonstrated that within 30 min Vorozole had reached the POA and completely blocked AA measured in homogenates. When added to the extracellular milieu, Vorozole also blocked within 5 min the AA in POA explants maintained in vitro. Together, these data demonstrate that aromatase inhibition rapidly decreases both consummatory and appetitive aspects of male sexual behavior.

In the ventral tegmental area, progestins' membrane-mediated actions for lordosis of hamsters and rats involve protein kinase A

Progestin-facilitated lordosis of hamsters and rats is enhanced by activation of dopamine type 1 (D1) or GABAA/benzodiazepine receptor complexes (GBRs) in the ventral tegmental area (VTA) and these effects involve G-proteins and second messengers, such as adenosine 3',5'-monophosphate (cAMP). We examined whether D1- and/or GBR-mediated increases in progestin-facilitated lordosis of female hamsters and rats involve the cAMP-dependent protein kinase, protein kinase A (PKA), in the VTA. In experiment 1, ovariectomized hamsters, primed with estradiol (E2; 10 microg at h 0) + progesterone (P; 100 microg at h 45), were first pre-tested for lordosis and motor behavior (h 48) and then infused with the PKA inhibitor, Rp-cAMP (100 ng/side), or vehicle. Thirty minutes later, hamsters were retested and then received infusions of the D1 agonist, SKF38393 (100 ng/side), the GBR agonist, muscimol (100 ng/side), or vehicle to the VTA. Hamsters were post-tested for lordosis and motor behavior 30 min later. In Experiment 2, ovariectomized rats, primed with E2 (10 microg at h 0), were first pre-tested for lordosis and then infused with Rp-cAMP (100 ng/side) or vehicle to the VTA at h 44. Immediately after testing, rats received infusions of SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle and were retested for lordosis. Rats were then infused with the neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 100 or 200 ng/side), or beta-cyclodextrin vehicle and were post-tested for lordosis and motor behavior 10 and 60 min later. The enhancing effects of progestins or progestins plus D1 or GBR activation on lordosis of E2-primed hamsters and rats were blocked by the PKA inhibitor, Rp-cAMP. Thus, in the VTA, progestins' membrane actions involving D1 or GBRs are mediated, in part, by PKA.

Rats bred for high versus low anxiety responses neonatally demonstrate increases in lordosis, pacing behavior, and midbrain 3α,5α-THP levels as adults

Duration and intensity of lordosis is mediated by actions of the progesterone (P) metabolite, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-THP) at GABA-sub(A) receptors in the midbrain ventral tegmental area. Because rats selectively bred for infantile vocalizations may differ in endogenous 3 alpha,5 alpha-THP secretion, their sexual behavior, midbrain, and plasma 3 alpha,5 alpha-THP levels as adult rats in behavioral estrus was examined. Rats bred for high rates of infantile vocalizations had shorter latencies and intervals between intromissions and ejaculation, higher lordosis quotients and ratings, more pacing of their sexual contacts, and had higher P and 3 alpha,5 alpha-THP levels in plasma and midbrain than did rats bred for low rats of infantile vocalizations. Thus, levels of 3 alpha,5 alpha-THP in the midbrain are associated with differences in sexual behavior of these rats.

3alpha-hydroxy-5alpha-pregnan-20-one in the midbrain ventral tegmental area mediates social, sexual, and affective behaviors

Progestins mediate the onset and duration of lordosis, the mating posture of female rodents, through actions in the hypothalamus and ventral tegmental area. In the hypothalamus, progesterone has traditional, "genomic" actions via intracellular progestin receptors. In the ventral tegmental area, 3alpha-hydroxy-5alpha-pregnan-20-one has "non-genomic" actions independent of progestin receptors to facilitate lordosis that involve GABA(A)/benzodiazepine receptors, NMDA type glutamate receptors, and/or dopamine receptors. 3alpha-Hydroxy-5alpha-pregnan-20-one levels also change with behavioral and/or environmental stimuli and may have a role in other reproductively-relevant behaviors, such as affiliation, exploration, and anxiety (socio-sexual behaviors). Data are reviewed that support the notion that: 1) effects of 3alpha-hydroxy-5alpha-pregnan-20-one in the midbrain ventral tegmental area facilitate lordosis and other reproductively-relevant behaviors. 2) 3alpha-Hydroxy-5alpha-pregnan-20-one, formed in the ventral tegmental area from metabolism of progestins, produced peripherally by endocrine glands, or centrally from biosynthesis in glial cells mediates socio-sexual behaviors. 3) 3alpha-Hydroxy-5alpha-pregnan-20-one's actions at GABA(A)/benzodiazepine receptors, NMDA type glutamate receptors, and dopamine receptors in the ventral tegmental area are important for lordosis; however, effects at these substrates on socio-sexual behaviors have not been elucidated. Given 3alpha-hydroxy-5alpha-pregnan-20-one's involvement in stress responses, its putative role as a homeostatic regulator and in the pathophysiology and treatment of neuropsychiatric disorders is discussed.

Inhibiting biosynthesis and/or metabolism of progestins in the ventral tegmental area attenuates lordosis of rats in behavioural oestrus

In the ventral tegmental area (VTA), lordosis of rats is facilitated by 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). Central 3alpha,5alpha-THP results from metabolism of peripheral progesterone, from the ovaries and/or adrenals, by sequential enzymatic activity of 5alpha-reductase and 3alpha-hydroxysteroid oxidoreductase (3alpha-HSOR). In addition, in glial cells, cholesterol is converted into pregnenolone by the P450 side-chain cleavage enzyme (P450scc), which is then metabolized to progesterone by 3beta-hydroxysteroid dehydrogenase, and subsequently reduced to 3alpha,5alpha-THP. We hypothesize that, in the VTA, formation of 3alpha,5alpha-THP by both metabolism and biosynthesis is necessary for facilitation of lordosis of female rats. In Experiment 1, naturally-receptive rats received bilateral VTA infusions of a P450scc inhibitor, digitoxin (1 microg/side); a 5alpha-reductase inhibitor, finasteride (10 microg/side); digitoxin (1 microg/side)+finasteride (10 microg/side); or vehicle and were tested 3 h later for lordosis. In Experiment 2, the effects of VTA infusions of digitoxin, finasteride, digitoxin+finasteride, or vehicle on lordosis and midbrain and plasma 3alpha,5alpha-THP levels were examined. In Experiment 3, we investigated whether infusions of 3alpha,5alpha-THP to the VTA reinstated lordosis and midbrain 3alpha,5alpha-THP levels following administration of inhibitors. VTA infusions of digitoxin, finasteride, or digitoxin+finasteride, significantly and similarly reduced lordosis and midbrain, but not plasma 3alpha,5alpha-THP levels, compared to vehicle. Following receipt of inhibitor infusions, 3alpha,5alpha-THP to the VTA restored lordosis and midbrain 3alpha,5alpha-THP levels. These data suggest that, in the VTA, both central biosynthesis of progesterone and metabolism of progesterone (from central and/or peripheral sources) to 3alpha,5alpha-THP are important for mediating lordosis of rats.

Progestin-facilitated lordosis of hamsters may involve dopamine-like type 1 receptors in the ventral tegmental area

Hamsters are highly-dependent upon the central actions of progesterone (P) to facilitate sexual behavior. P has membrane mechanisms of action in the ventral tegmental area (VTA) to facilitate sexual receptivity of rodents. The present experiments examined whether P's membrane actions in the VTA include dopamine (DA) type 1 (D(1)) or dopamine type 2 (D(2)) receptors. Ovariectomized (ovx), estradiol (E(2))- and P-primed hamsters were infused with D(1) (Experiment 1) or D(2) (Experiment 2) antagonists or agonists (0 or 100 ng) to the VTA and tested 30 min later. The D(1) agonist, SKF38393, enhanced P-facilitated lordosis. The D(1) antagonist, SCH23390, attenuated P-facilitated lordosis. The D(2) agonist, quinpirole and the D(2) antagonist, sulpiride, had no significant effects on P-facilitated lordosis. These data suggest that, in hamsters, P's actions for lordosis may involve D(1) receptors in the VTA.

Progesterone's 5α-reduced metabolite, 3α,5α-THP, mediates lateral displacement of hamsters

5 alpha-Pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP), progesterone (P4)'s 5 alpha-reduced, 3 alpha-hydroxysteroid oxidoreduced product, facilitates lordosis of rodents in part via agonist-like actions at GABA(A)/benzodiazepine receptor complexes in the ventral tegmental area (VTA). Whether 3 alpha,5 alpha-THP influences another reproductively-relevant behavior, lateral displacement, of hamsters was investigated. Lateral displacement is the movement that female hamsters make with their perineum towards male-like tactile stimulation. This behavior facilitates, and is essential for, successful mating. Hamsters in behavioral estrus had greater lateral displacement responses when endogenous progestin levels were elevated compared to when progestin levels were lower. Administration of P4, a prohormone for 3 alpha,5 alpha-THP, dose-dependently (500 > 200 > 100, 50, or 0 microg) enhanced lateral displacement of ovariectomized hamsters that had been primed with SC estradiol benzoate (5 or 10 microg). Inhibiting P4's metabolism to 3 alpha,5 alpha-THP by co-administering finasteride, a 5 alpha-reductase inhibitor, or indomethacin, a 3 alpha-hydroxysteroid oxidoreductase inhibitor, either systemically or to the VTA, significantly decreased lateral displacement and midbrain progestin levels of naturally receptive or hormone-primed hamsters compared to controls. These data suggest that lateral displacement is progestin-sensitive and requires the formation of 3 alpha,5 alpha-THP in the midbrain VTA.

In the ventral tegmental area picrotoxin blocks FGIN 1-27-induced increases in sexual behavior of rats and hamsters

RATIONALE AND OBJECTIVES

There are two types of benzodiazepine receptors, mitochondrial benzodiazepine receptors (MBRs), and gamma-aminobutyric acid (GABA(A))/benzodiazepine receptor complexes (GBRs). MBR activation increases neurosteroidogenesis. Ventral tegmental area (VTA) infusions of the MBR agonist, FGIN 1-27, increase midbrain levels of the progesterone metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) and lordosis of rats and hamsters. Activation of GBRs leads to membrane hyperpolarization. In the VTA, infusions of GBR agonists enhance 3alpha,5alpha-THP-facilitated lordosis. Thus, if, in the VTA, MBR-mediated increases in 3alpha,5alpha-THP enhance sexual responses via actions at GBRs, then blocking GBRs with picrotoxin will reduce FGIN 1-27-induced increases in sexual behavior of female rodents.

METHODS

Ovariectomized rats and hamsters, with unilateral guide cannula to the VTA, received estradiol benzoate (10 mug; EB) at hour 0. Hamsters also received progesterone (100 mug) at hour 44. At hour 47.5, all animals were infused first with 10 ng or 20 ng picrotoxin or saline, vehicle to the VTA and, 30 min later, with 5 mug/11.4 nM FGIN 1-27 or saline, vehicle. Ten minutes later, animals were tested for sex and motor behavior.

RESULTS

Picrotoxin, but not vehicle, infusions blocked FGIN 1-27-mediated increases in lordosis of rats and hamsters, proceptivity of rats, and sexual responsiveness of hamsters. In addition, midbrain 3alpha,5alpha-THP levels were higher in animals that received VTA infusions of FGIN 1-27, compared to those infused with saline, vehicle.

CONCLUSION

In the VTA, GBRs are required for MBR-enhanced sexual behavior of EB-primed rats and EB- and progesterone-primed hamsters.

Progestins' actions in the VTA to facilitate lordosis involve dopamine-like type 1 and 2 receptors

In the ventral tegmental area (VTA), 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) facilitates lordosis. Whether this involves dopamine type 1 (D1) or dopamine type 2 (D2) receptors is of interest. Ovariectomized (ovx) rats with guide cannulae to the VTA were estradiol (E2) primed and pretested for lordosis. Rats were then infused with the D1 (Experiment 1) or D2 (Experiment 2) antagonists or agonists (0, 100, or 200 ng) to the VTA and were retested. After a second infusion of 3alpha,5alpha-THP (0, 100, or 200 ng) or vehicle, rats were tested 10, 60, and 120 min later. In Experiment 3, rats were administered a progestin receptor antagonist, RU38486, systemically or to the VTA 1 h prior to vehicle, SKF38393 and/or 3alpha,5alpha-THP infusions. 3alpha,5alpha-THP infusions increased lordosis over that seen with E2 priming. The D1 antagonist, SCH23390, attenuated 3alpha,5alpha-THP, but not E2-facilitated lordosis. The D1 agonist, SKF38393, augmented 3alpha,5alpha-THP, but not E2-facilitated lordosis. The D2 antagonist, sulpiride, had no significant effects on lordosis. The D2 agonist, quinpirole, prevented 3alpha,5alpha-THP-facilitated lordosis. RU38486 (subcutaneous) inhibited lordosis, whereas infusions to the VTA decreased lordosis produced by SKF38393 and 3alpha,5alpha-THP, but not 3alpha,5alpha-THP alone. Thus, 3alpha,5alpha-THP's actions in the VTA for lordosis may involve D1 and/or D2 receptors.

In the ventral tegmental area, G-proteins and cAMP mediate the neurosteroid 3alpha,5alpha-THP's actions at dopamine type 1 receptors for lordosis of rats

Progestins have multiple mechanisms of action in the central nervous system that are important for modulating lordosis of female rats. In the ventral tegmental area (VTA), progestins, such as the progesterone metabolite and neurosteroid 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), regulate lordosis via actions independent of intracellular progestin receptors. We hypothesized that if, in the VTA, dopamine type 1 receptors (D1), G-proteins, and adenosine 3',5'-monophosphate (cAMP) are downstream effectors of 3alpha,5alpha-THP's actions for lordosis, then pharmacological manipulations of these signaling molecules will produce changes in 3alpha,5alpha-THP-facilitated lordosis of estradiol (E2)-primed rats. VTA infusions of 3alpha,5alpha-THP (50 ng) or 3alpha,5alpha-THP and the D1 agonist SKF38393 (100 ng) increased lordosis of ovariectomized, E2 (10 microg)-primed rats, compared to vehicle. Both 3alpha,5alpha-THP- and 3alpha,5alpha-THP plus SKF38393-facilitated lordosis was reduced by VTA infusions of the G-protein inhibitor guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S; 50 microM), but not vehicle. Also, in the VTA, blocking D1 with SCH23390 (100 ng) decreased, or increasing cAMP with 8-bromo-cAMP (200 ng) enhanced, 3alpha,5alpha-THP-facilitated lordosis of E2-primed rats. Notably, SCH23390's inhibitory effects on 3alpha,5alpha-THP-facilitated lordosis were reversed by 8-bromo-cAMP. Thus, in the VTA, 3alpha,5alpha-THP's actions for lordosis may involve activation of D1 and initiation of the G-protein-mediated second messenger cAMP.