Muscimol facilitates sexual receptivity in hamsters when infused into the ventral tegmentum

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.

Novel substrates for, and sources of, progestogens for reproduction

Steroid hormones, such as progesterone, are typically considered to be primarily secreted by the gonads (albeit adrenals can also be a source) and to exert their actions through cognate intracellular progestin receptors (PRs). Through its actions in the midbrain ventral tegmental Area (VTA), progesterone mediates appetitive (exploratory, anxiety, social approach) and consummatory (social, sexual) aspects of rodents' mating behaviour. However, progesterone and its natural metabolites ('progestogens') are produced in the midbrain VTA independent of peripheral sources and midbrain VTA of adult rodents is devoid of intracellular PRs. One approach that we have used to understand the effects of progesterone and mechanisms in the VTA for mating is to manipulate the actions of progesterone in the VTA and to examine effects on lordosis (the posture female rodents assume for mating to occur). This review focuses on the effects and mechanisms of progestogens to influence reproduction and related processes. The actions of progesterone and its 5α-reduced metabolite and neurosteroid, 5α-pregnan-3α-ol-20-one (3α,5α-THP; allopregnanolone) in the midbrain VTA to facilitate mating are described. The findings that 3α,5α-THP biosynthesis in the midbrain occurs with mating are discussed. Evidence for the actions of 3α,5α-THP in the midbrain VTA via nontraditional steroid targets is summarised. The broader relevance of these actions of 3α,5α-THP for aspects of reproduction, beyond lordosis, is summarised. Finally, the potential role of the pregnane xenobiotic receptor in mediating 3α,5α-THP biosynthesis in the midbrain is introduced.

6-hydroxydopamine lesions enhance progesterone-facilitated lordosis of rats and hamsters, independent of effects on motor behavior

The Ventral Tegmental Area (VTA) is an important brain area for progesterone (P(4))'s effects to facilitate female sexual behavior of rodents. We investigated the importance of dopaminergic neurons in the VTA, and two dopaminergic projection sites, the Nucleus Accumbens (NAc), and Caudate Nucleus of the Striatum (CN), in modulating P(4)-facilitated sex and motor behavior. Ovariectomized (ovx) rats and hamsters, administered estradiol benzoate (10 microg) and P(4) (0, 50, 100, 200, or 500 microg), were tested for motor behavior in a chamber that automatically records horizontal beam breaks, and for sexual behavior in response to a sexually-experienced male. Animals were tested once a week until each P(4) dosage was received; animals then had bilateral 6-hydroxydopamine (6-OHDA) or sham lesions to the VTA, NAc, or CN and were re-tested at each P(4) dosage on subsequent weeks. Fixed brains were stained with cresyl violet and processed for dopamine transporter (DAT) immunoreactivity. The number of cresyl violet stained cells was significantly lower in all 6-OHDA infusion sites compared to non-6-OHDA infusion sites of rats and hamsters. Also, in rats, the number of DAT-immunoreactive neurons was lower in all 6-OHDA infusion sites compared to non-6-OHDA infusion sites. In rats, 6-OHDA but not sham, lesions to the VTA, NAc, or CN produced P(4)-dependent increases in lordosis quotients and resulted in modest increases in motor behavior. In hamsters, 6-OHDA, but not sham, lesions to the VTA, NAc, or CN produced P(4)-dependent increases in total lordosis durations and produced modest decreases in motor behavior. This suggests that the dopaminergic output neurons of midbrain VTA may play an important role in modulation of P(4)-facilitated sexual lordosis among rodents.

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.

Rapid and estrogen receptor beta mediated actions in the hippocampus mediate some functional effects of estrogen

The steroid hormone, estradiol (E(2)), has numerous targets in the central nervous system, including the hippocampus, which plays a key role in cognition and affective behavior. This review focuses on our evidence from studies in rodents that E(2) has diverse mechanisms in the hippocampus for its functional effects. E(2) has rapid, membrane-mediated effects in the hippocampus to enhance cognitive performance. Administration of E(2) to the hippocampus of rats for 10 min following training enhances performance in a hippocampus-mediated task. Increased cell firing in the hippocampus occurs within this short-time frame. Furthermore, administration of free E(2) or an E(2) conjugate, E(2):bovine serum albumin (BSA), to the hippocampus produces similar performance-enhancing effects in this task, suggesting that E(2) has membrane actions in the hippocampus for these effects. Further evidence that E(2) has rapid, membrane-mediated effects is that co-administration of E(2) and inhibitors of mitogen-activated protein kinase (MAPK), rather than intracellular E(2) receptors (ERs) or protein synthesis, attenuate the enhancing effects of E(2) in this task. Despite these data that demonstrate E(2) can have rapid and/or membrane-mediated effects in the hippocampus, there is clear evidence to suggest that intracellular ERs, particularly the beta (rather than alpha) isoform of ERs, may be important targets for E(2)'s functional effects for hippocampal processes. Administration of ligands that are specific for ERbeta, but not ERalpha, have enhancing effects on hippocampal processes similar to that of E(2) (which has similar affinity for ERalpha and ERbeta). These effects are attenuated when ERbeta expression is knocked down in transgenic models or with central administration of antisense oligonucleotides. Thus, there may be a convergence of E(2)'s actions through rapid, membrane-mediated effects and intracellular ERs in the hippocampus for these functional effects.

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.

In the ventral tegmental area, the membrane-mediated actions of progestins for lordosis of hormone-primed hamsters involve phospholipase C and protein kinase C

Progestin-facilitated lordosis of rodents is enhanced by activation of dopamine type 1 (D(1)) or GABA(A) receptors, their downstream G-proteins, and/or second messengers in the ventral tegmental area (VTA). We examined whether the ability of progestins to enhance lordosis via actions at D(1) and/or GABA(A) receptors is contingent upon activation of the second messenger phospholipase C (PLC) and its associated kinase, protein kinase C (PKC), in the VTA. If the actions of progestins through D(1) and GABA(A) receptors in the VTA are mediated through PLC and PKC, then inhibiting PLC formation (Experiment 1) or blocking PKC (Experiment 2) should reduce progestin-facilitated lordosis and its enhancement by D(1) (SKF38393) or GABA(A) (muscimol) receptor agonists. In Experiment 1, ovariectomised hamsters, primed with oestradiol (10 microg; h 0) + progesterone (100 microg; h 45), were pretested for lordosis and motor behaviour (h 48) and then infused with the PLC inhibitor, U73122 (400 nM/side), or vehicle. Thirty minutes later, hamsters were retested and then received infusions of SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle to the VTA. Hamsters were post-tested for lordosis and motor behaviour 30 min later. In Experiment 2, a similar protocol was utilised except that instead of the PLC inhibitor hamsters were infused with the PKC inhibitor, bisindolylmaleimide (75 nM/side). Systemic progesterone, SKF38393-, and muscimol-facilitated lordosis was attenuated by infusion of the PLC inhibitor, U73122, or the PKC inhibitor, bisindolylmaleimide, compared to vehicle to the VTA. Thus, the actions of progestins in the VTA to enhance lordosis through D(1) and/or GABA(A) may include downstream activity of PLC and PKC.

Release of orphanin FQ/nociceptin in the medial preoptic nucleus and ventromedial nucleus of the hypothalamus facilitates lordosis

Opioid regulation of reproduction has been widely studied. However, the role of opioid receptor-like 1 receptor (NOP; also referred to as ORL-1 and OP4) and its endogenous ligand orphanin FQ/nociceptin (OFQ/N) have received less attention despite their extensive distribution throughout nuclei of the limbic-hypothalamic system, a circuit that regulates reproductive behavior in the female rat. Significantly, the expression of both receptor and ligand is regulated in a number of these nuclei by estradiol and progesterone. Activation of NOP in the ventromedial nucleus of the hypothalamus (VMH) of estradiol-primed nonreceptive female rats facilitates lordosis. NOPs are also expressed in the medial preoptic nucleus (MPN), however, their roles in reproductive behavior have not been studied. The present experiments examined the role of NOP in the regulation of lordosis in the MPN and tested whether endogenous OFQ/N in the MPN and VMH mediates reproductive behavior. Activation of NOP by microinfusion of OFQ/N in the MPN facilitated lordosis in estradiol-primed sexually nonreceptive female rats. Passive immunoneutralization of OFQ/N in either the MPN or the VMH reduced lordosis in estradiol-primed females, but had no effect on lordosis in estradiol+progesterone-primed sexually receptive rats. These studies suggest that OFQ/N has a central role in estradiol-only induced sexual receptivity, and that progesterone appears to involve additional circuits that mediate estradiol+progesterone sexual receptivity.

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.

MK-801 infusions to the ventral tegmental area and ventromedial hypothalamus produce opposite effects on lordosis of hormone-primed rats

Progesterone initiates female sexual behavior of rodents (lordosis) through actions at intracellular progestin receptors in the ventromedial hypothalamus. Progesterone's metabolite, 5alpha-pregnan-3alpha-ol-20-one, mediates the intensity and duration of lordosis through its actions at GABA(A) receptors in the ventral tegmental area. Whether progestins can influence sexual behavior through actions that involve N-methyl-D-aspartate receptors (NMDARs) in the ventromedial hypothalamus and ventral tegmental area was investigated. The current study examines the effect of bilateral ventral tegmental area or ventromedial hypothalamus infusions of the non-competitive NMDAR antagonist (+)-MK-801 hydrogen maleate (MK-801; 0, 20, or 200 ng) on lordosis, motor activity, and NMDA R1 subtype (NMDAR1) immunoreactivity in estradiol benzoate (10 microg)+progesterone (50 microg)- and estradiol benzoate+vehicle primed rats. Compared to vehicle infusions, infusions of MK-801 to the ventral tegmental area facilitated lordosis of estradiol benzoate (10 microg)+progesterone (50 microg)- and estradiol benzoate+vehicle primed rats. Infusions of MK-801 to the ventromedial hypothalamus inhibited lordosis of estradiol benzoate (10 microg)+progesterone (50 microg)- and estradiol benzoate+vehicle primed rats, compared to vehicle. There was no effect of MK-801 infusions to the ventral tegmental area or the ventromedial hypothalamus on motor behavior. Immunocytochemistry for NMDAR1 revealed MK-801 (200 ng) infusions to the ventral tegmental area or ventromedial hypothalamus of estradiol benzoate (10 microg)+progesterone (50 microg)- or estradiol benzoate+vehicle primed rats significantly reduced the number of darkly stained NMDAR1-immunoreactive cells, compared to vehicle infusions. These data suggest NMDARs may be important in the mediation of hormonal actions in both the ventral tegmental area and the ventromedial hypothalamus for sexual receptivity of rodents, but in different ways.

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.

Progestin facilitation of lordosis in rodents involves adenylyl cyclase activity in the ventral tegmental area

Increasing cAMP, or activating dopamine type 1 (D(1)) or GABA(A)/benzodiazepine receptor complexes (GBRs), in the ventral tegmental area (VTA) enhances lordosis of rodents. Whether D(1)- and/or GBR-mediated increases in progestin-facilitated lordosis involve the cAMP-synthesizing enzyme, adenylyl cyclase, in the VTA, was investigated. In Experiment 1, ovariectomized estradiol (E(2); 10 microg at h 0)+progesterone (P; 250 microg at h 45)-primed hamsters first received bilateral infusions of the adenylyl cyclase inhibitor, 2',5'-dideoxyadenosine (DDA; 12 microM/side), or vehicle, and then were infused with the D(1) agonist, SKF38393 (100 ng/side), the GBR agonist, muscimol (100 ng/side), or vehicle, to the VTA. Lordosis was evaluated before and 30 min after each infusion. In Experiment 2, ovariectomized, E(2)-primed (10 microg at h 0) rats received VTA infusions of DDA (12 microM/side) or vehicle; SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle; and the neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 100 or 200 ng/side), or beta-cyclodextrin vehicle. Lordosis was assessed before the series of infusions, immediately after drug infusions and 10 or 60 min after 3alpha,5alpha-THP infusions. Progestin- or progestin plus SKF38393-or muscimol-mediated increases in lordosis were blocked by DDA pretreatment. Thus, in the VTA, progestins' membrane action may involve adenylyl cyclase.

A rapid neuromodulatory role for steroid hormones in the control of reproductive behavior

The long-term transcriptional actions of steroids that shape neuronal morphology and the probability of behavioral expression are well established. More recently, attention has been focused on the role of rapid (minute-by-minute) steroid actions on neuronal mechanisms of reproductive behavior. In this review, we first consider the rapid actions of steroids on mating and copulatory behaviors in tetrapod vertebrates. Evidence for rapid effects of steroids is presented for chemoinvestigatory behavior (genital sniffing of females by male mice), lordosis (arched-back mating posture in female rats), copulatory mounting (male mice and male Japanese quail), reproductive clasping (pre-copulatory mounting in newts), and paced mating (copulation rate as determined by female rats). We then review recent studies in teleost fish that demonstrate the rapid actions of steroids on vocal patterning at two levels: (1) central pattern generators and (2) social behavior in natural environments. Thus, we propose that steroid-dependent modulation of central pattern generators can govern the overt expression of reproductive behaviors via rapid non-transcriptional mechanisms that are likely to be widespread among vertebrates.

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, 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.

Perinatal maternal exposure to picrotoxin: Effects on sexual behavior in female rat offspring

A previous study in our laboratory showed that perinatal maternal picrotoxin exposure (0.75 mg/kg) in rats improved heterosexual behavior in male offspring. In the present study, we examined the effects of this maternal treatment on sexual behavior in the female offspring. The dams received 0.75 mg/kg picrotoxin treatment (PT) once a day on the 18th and 21st day of pregnancy, 2 h after parturition and once a day during the first 4 days of lactation. The results showed that (1) at birth, the body weight and anogenital distance were not modified by treatment; (2) female sexual behavior was improved in experimental animals. These results demonstrate that perinatal picrotoxin exposure improves adult sexual behavior in female rat offspring as suggested by increase in the lordosis quotient.

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 and place preference conditioning after paced mating

When female rats pace their coital interaction, a reward state evaluated by conditioned place preference is induced. Progesterone (P) is essential for the expression of proceptive behavior and for the induction of CPP. However, the functional significance of ring A reduction of P for the induction of this state during estrous is unsettled. In the present study, we evaluated whether ring A-reduced metabolites of P are involved in the reward state induced when the females are allowed to pace their sexual contacts. Ovariectomized (ovx) female rats treated with estradiol benzoate (EB, 5 microg) and P (13 microg), Megestrol acetate (MA; 13 microg ), 5 alpha-pregnan-20 dione (5 alphaDHP; 3 microg), or 5 beta-pregnan-3 alpha-ol-20-one (5 beta,3 alpha-Pgl; 3 microg) were used. Progestins were dissolved in propylene glycol and intravenously (iv) injected through an indwelling jugular catheter before females were tested for pacing behavior. After 15 intromissions or one ejaculation, females were gently placed in the nonpreferred compartment of a CPP box. Paced mating in all groups treated with progestins induced a clear change of preference. The administration of progestins alone did not induce CPP. These results suggest that P and ring A-reduced metabolites facilitate the reward state following pacing.

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

Hamsters are highly dependent upon the central actions of progesterone (P4) for facilitation of sexual behaviour. In the ventral tegmental area (VTA), P4 has actions through its neurosteroid metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). The effects of enhancing or inhibiting neurosteroidogenesis (and thereby 3alpha,5alpha-THP concentrations), through manipulations of mitochondrial benzodiazepine receptors, in the VTA on socio-sexual behaviour of female hamsters were examined. Intact, naturally receptive hamsters and ovariectomized (OVX), hormone-primed hamsters were unilaterally infused via chronic guide cannula to the VTA with the mitochondrial benzodiazepine receptor antagonist 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboximide (PK-11195) or the mitochondrial benzodiazepine receptor agonist, N,N-dihexyl-2-(4-fluorophenyl)indole-30-acetamide (FGIN 1-27) and tested for sexual responsiveness and lordosis. PK-11195 (5.6, 11.2 or 22.4 nm) to the VTA attenuated sexual responsiveness of naturally receptive or oestradiol benzoate (EB) + P4-primed hamsters compared to vehicle. In addition, FGIN 1-27 (11.4 nm) infusions to the VTA increased sexual responsiveness and lordosis of cycling or OVX, EB + P4-primed hamsters, compared to vehicle infusions. In OVX, EB + P4-primed hamsters, decrements in sexual responsiveness produced by VTA infusions of PK-11195 (5.6 nm) were attenuated by VTA infusions of 3alpha,5alpha-THP. VTA infusions of PK-11195 (5.6 nm) or FGIN 1-27 (11.4 nm), respectively, decreased and increased midbrain levels of 3alpha,5alpha-THP compared to each other. Together, these findings indicate that manipulating actions of mitochondrial benzodiazepine receptors in the VTA can augment and inhibit neurosteroidogenesis and sexual responsiveness of hormone-primed and naturally receptive hamsters.

Lordosis of rats is modified by neurosteroidogenic effects of membrane benzodiazepine receptors in the ventral tegmental area

Progestins modulate lordosis through actions in the ventral tegmental area (VTA). Whether neurosteroidogenesis of 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-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 microg) rats administered 0 or 25 microg progesterone (P4) SC showed increased lordosis when infused with 5.0 microg FGIN 1-27 to the VTA; those administered 100 or 200 microg P4 SC exhibited greater lordosis when infused with 2.5 or 5.0 microg FGIN, relative to saline-infused rats. Experiment 2: Rats, near the termination of behavioral estrus, infused with 2.5 or 5.0 microg 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 microg P4 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: 3alpha,5alpha-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 microg) and PK-11195 (100 ng) infusions aimed at the VTA respectively increased and decreased midbrain levels of 3alpha,5alpha-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.

Olanzapine and progesterone have dose-dependent and additive effects to enhance lordosis and progestin concentrations of rats

There is evidence that actions of both progesterone (P) and its metabolite, 5alpha-pregnane-3alpha-ol-20-one (3alpha,5alpha-THP), are important for sexual behavior of estradiol (E(2))-primed rodents. Olanzapine, an atypical antipsychotic, dose-dependently increases 3alpha,5alpha-THP in the cortex of male rats. These experiments investigated the effects of olanzapine administration on female sexual behavior and progestin concentrations. In Experiment 1, ovariectomized (ovx) rats (N=128) were primed with estradiol benzoate (EB) at Hour 0 and were administered P (0, 50, 100, or 200 microg sc) at Hour 44 and olanzapine (0.0, 2.5, 5.0, or 10.0 mg/kg ip) at Hour 47. At Hour 48, rats were tested for sexual receptivity with a stimulus male. Administration of 10.0 mg/kg of olanzapine, irrespective of P, significantly increased the occurrence (lordosis quotients, LQs) and the intensity (lordosis ratings, LRs) of lordosis compared to all other dosages. Administration of 2.5 or 5.0 mg/kg of olanzapine, irrespective of P, increased LQs and LRs compared to vehicle administration. Olanzapine without P dose-dependently increased LQs and LRs. As expected, administration of P without olanzapine also dose-dependently increased LQs and LRs. In Experiment 2, ovx rats (N=44, n=4 per group) received EB (0 or 10 microg sc), P (0 or 200 microg sc), and/or olanzapine (0.0, 2.5, 5.0, or 10.0 mg/kg ip). The same pattern of effects seen for lordosis was observed on progestin concentrations. Whole brain and plasma P and 3alpha,5alpha-THP concentrations were increased with olanzapine or P dosing and were greatest with coadministration. Together, these data demonstrate that olanzapine and P have independent effects to increase lordosis, P, and 3alpha,5alpha-THP concentrations of adult rats and additive effects in combination, suggesting complimentary mechanisms of action.

The role of neurosteroids and non-genomic effects of progestins and androgens in mediating sexual receptivity of rodents

Progestins and androgens modulate sexual receptivity in rodents, in part through mechanisms independent of traditional intracellular steroid receptors. Progesterone (PROG) in the ventromedial hypothalamus (VMH) and ventral tegmental (VTA) facilitates lordosis but has different actions in these brain areas. Primarily using lordosis in rodents as an in vivo experimental model, we have examined the effects that progestins exert in the midbrain and hypothalamus. Localization and blocker studies indicate that PROG's actions in the VMH require intracellular progestin receptors (PRs) but in the VTA they do not. Progestins that have rapid, membrane effects, and/or are devoid of affinity for PRs, facilitate lordosis when applied to the VTA. Manipulation of GABA and/or GABA(A)/benzodiazepine receptor complexes (GBRs) in the VTA alters lordosis, which suggests that progestins may interact with GBRs to facilitate receptivity by enhancing the function of GABAergic neurons. Interfering with PROG's metabolism to, or the biosynthesis of, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG or allopregnanolone), the most effective endogenous GBR agonist, in the VTA attenuates female sexual behavior in rodents. Stimulation of mitochondrial benzodiazepine receptors (MBRs), which enhances neurosteroid production, by infusions of an MBR agonist to the VTA enhances lordosis. 3alpha,5alpha-TH PROG is increased in the midbrain of mated>proestrous>diestrous rodents. These data suggest that in the VTA, PROG may facilitate lordosis following metabolism to and/or biosynthesis of 3alpha,5alpha-TH PROG, which may have subsequent actions at GBRs and/or MBRs to acutely modulate female sexual behavior in rodents. The 3alpha-hydroxysteroid oxidoreduced metabolite of dihydrotestosterone (DHT), 5alpha-androstane-3alpha,17beta-diol (3alpha-androstanediol), is important for termination of sexual receptivity in rodents and has these effects in the absence of functional intracellular androgens receptors. As well, altering GBR function in the hypothalamus can influence 3alpha-androstanediol's inhibition of sexual receptivity. Through actions in the hypothalamus that are independent of intracellular androgen receptors but involving GBRs, 3alpha-androstanediol inhibits lordosis. These findings suggest that the PROG metabolite and pregnane neurosteroid, 3alpha,5alpha-TH PROG, and the testosterone metabolite and androstane neurosteroid, 3alpha-androstanediol, can have proximate influences on lordosis that is via nonclassical actions at intracellular steroid receptors.

The role of neurosteroids and nongenomic effects of progestins in the ventral tegmental area in mediating sexual receptivity of rodents

Progesterone (P(4)) in the ventromedial hypothalamus (VMH) and ventral tegmental (VTA) is important for facilitation of lordosis; however, P(4)'s actions in these brain areas are different. Using lordosis in rodents as in vivo experimental models, we have examined the effects progestins exert in the midbrain and hypothalamus. Localization and blocker studies indicate that P(4)'s actions in the VMH require intracellular progestin receptors (PRs) but in the VTA they do not. Progestins that have rapid, membrane effects, and/or are devoid of affinity for PRs, facilitate lordosis when applied to the VTA. Manipulation of GABA and/or GABA(A)/benzodiazepine receptor complexes (GBRs) in the VTA alter lordosis, which suggests that progestins may interact with GBRs to facilitate receptivity by enhancing the function of GABAergic neurons. Interfering with P(4)'s metabolism to 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP), the most effective endogenous positive modulator of GBRs, or the biosynthesis of the neurosteroid 3 alpha,5 alpha-THP in the VTA attenuates female sexual behavior in rodents. Stimulation of mitochondrial benzodiazepine receptors (MBRs), which enhance neurosteroid production, by infusions of a MBR agonist to the VTA enhances lordosis. 3 alpha,5 alpha-THP is increased in the midbrain of mated > proestrous > diestrous rodents. These data suggest that 3 alpha,5 alpha-THP has a proximate modulatory role on lordosis. In summary, the actions of P(4) in the VTA are different from those in the VMH that involve PRs. In the VTA, P(4) may facilitate lordosis following metabolism to and/or biosynthesis of 3 alpha,5 alpha-THP, which may have subsequent actions at GBRs and/or MBRs to acutely modulate female sexual behavior in rodents.

Anti-sense oligonucleotides, for progestin receptors in the VMH and glutamic acid decarboxylase in the VTA, attenuate progesterone-induced lordosis in hamsters and rats

Immunocytochemical (ICC) staining for progesterone (P) receptors (PRs) and glutamic acid decarboxylase (GAD), the enzyme responsible for GABA production, reveal that there are many PRs in the ventral medial hypothalamus (VMH) and many GAD containing neurons in the ventral tegmental area (VTA). To investigate P's action on lordosis in the VMH and VTA, anti-sense oligos specific to PRs and GAD(65&67) were intracerebrally infused into the VMH and VTA of 24 ovariectomized hamsters and 40 ovariectomized rats. Estradiol benzoate (2 microg) primed hamsters and rats were infused to the VMH and the VTA with either PR (250 ng/1.0 microl infusion) or GAD (500 ng/1.0 microl infusion) anti-sense oligos, their scramble controls, or saline vehicle at hour 0 and again at hour 24. At hr 44, rodents were subcutaneously injected with P (500 microg) and were tested for sexual receptivity with a male 4 h later. There were significant reductions in lordosis of hamsters and rats following PR anti-sense infusions to the VMH compared to scrambled or vehicle control infusions. Effects of PR anti-sense to the VMH were not different from combined VMH and VTA PR anti-sense infusions; however, VMH infusions reduced lordosis compared to VTA-only anti-sense infusions. GAD anti-sense infusions reduced lordosis when infused into the VTA, compared to scrambled or saline vehicle infusions. Lordosis responsiveness following VTA GAD anti-sense infusions was not different from combined VMH and VTA infusions, but VTA infusions of GAD anti-sense reduced lordosis compared to VMH-only anti-sense infusions. These data suggest that in the VMH, PRs are important for P-facilitated lordosis, whereas in the VTA, GABAergic neurons may be an important substrate for mediating P's actions on lordosis of rodents.

Progestins' rapid facilitation of lordosis when applied to the ventral tegmentum corresponds to efficacy at enhancing GABA(A)receptor activity

Progestins may have actions in the midbrain though gamma-aminobutyric acid (GABA)A/benzodiazepine receptor complexes (GBRs) that are relevant for sexual receptivity. The efficacy and time course of various progestins to enhance lordosis when applied to the ventral tegmental area (VTA), following progesterone to the ventral medial hypothalamus (VMH) was investigated. Ovariectomized, oestrogen-primed rats and hamsters with contralateral VMH/VTA cannulae were tested for lordosis before and after implants of P to the VMH and progestins to the VTA. The progestins were P, 5alpha-pregnan-3,20-dione (DHP), 5alpha-pregnan-3alpha-ol-20-one(3alpha,5alpha-TH P), 5alpha-pregnan-3alpha,21-diol-20-one (THDOC), 5beta-pregnan-3alpha-ol-20-one(3alpha,5beta-THP) , 17alpha-ol-6-methyl-4,6-pregnadiene-3,20-dione-17-acetate (megestrol acetate, MA), and 6-chloro-17-ol-4,6-pregnadiene-3, 20-dione-17-acetate (chlormadinone acetate, CA). Progestins' effects on GABA-mediated chloride influx and SR 95531 binding in cortical and midbrain tissue, respectively, were examined in rats and hamsters. 3alpha,5alpha-THP and THDOC implants to the VTA were the most effective at immediately facilitating lordosis of rats and hamsters. Two hours later all other progestins, except MA and CA, increased lordosis in rats; only P, 3alpha,5alpha-THP, and THDOC were effective in hamsters. The progestins' effectiveness at facilitating lordosis were similar to their effects on GABA-stimulated chloride influx and SR 95531 receptor binding (3alpha,5alpha-THP and THDOC>P>DHP>3alpha, 5beta-THP>MA and CA). These findings suggest that progesterone lordosis enhancing effects in the rodent VTA may be via GBRs.

GABA(A), D1, and D5, but not progestin receptor, antagonist and anti-sense oligonucleotide infusions to the ventral tegmental area of cycling rats and hamsters attenuate lordosis

In hamsters, progesterone (P) in the hypothalamus and ventral tegmental area (VTA) is necessary for receptivity; in rats, hypothalamic P induces receptivity and midbrain P further enhances it. How P exerts its effects in the VTA on lordosis is of interest because few estrogen-induced P receptors (PRs) have been identified there. Sexual receptivity of rats and hamsters is enhanced when P's actions in the VTA are restricted to the membrane and when the gamma-aminobutyric acid (GABA)A agonist, muscimol, is infused into the VTA, but attenuated with infusions of the GABA(A) antagonist, bicuculline. The dopamine (DA) agonist. SKF38393, rapidly enhances receptivity when infused intravenously; this effect can be blocked by both DA receptor (DR) and PR antagonists. This study investigated the importance of PRs, glutamic acid decarboxylase (GAD), the enzyme responsible for GABA production, GABA(A) receptors (GBRs), and DRs in the VTA of cycling rats and hamsters for the expression of lordosis. Proestrous and diestrous animals implanted with bilateral VTA cannulae were pre-tested for receptivity, infused with either an antagonist (RU38486 (20 microg), bicuculline (100 ng), SCH23390 (100 ng)), anti-sense oligonucleotide (against PR (250 ng), GAD (500 ng), D1 (500 ng), D5 (250 ng)), or control infusions to each cannulae and re-tested. Vehicle and scrambled oligonucleotides were infused as controls and elicited similar effects. Antagonists of GBRs and DRs significantly reduced lordosis on post-tests compared to the PR antagonist and control conditions in rats and hamsters. Lordosis was significantly reduced, compared to controls, only by anti-sense oligonucleotides for GAD and D1- and D5-DR subtypes. These data suggest that in the VTA GABAergic and dopaminergic neurons may be more important in the mediation of sexual receptivity than neurons containing intracellular PRs.

Indomethacin inhibits lordosis induced by ring A-reduced progestins: possible role of 3alpha-oxoreduction in progestin-facilitated lordosis

Progestins with a delta-4-3-keto configuration bind to the progestin receptor (PR) and facilitate estrous behavior in estrogen-primed rats. Some ring A-reduced progestins [5alpha-dihydroprogesterone (alphaDHP), allopregnanolone, and epipregnanolone] are more potent estrus-inducing agents than progesterone when iv injected despite their lower affinity for the PR. Yet the estrus-inducing action of such progestins is reduced by the antiprogestin RU486, suggesting that binding to the PR is required for this effect. Because allo- and epi-pregnanolone are oxidized to alpha- and betaDHP, respectively, by 3alpha-hydroxysteroid oxo-reductase (3alphaHSOR), part of their estrus-inducing action may occur through the binding of such DHPs to the PR. Conversely, because 3alphaHSOR reduces alpha- and betaDHP to allo- or epi-pregnanolone, both of which exert membrane effects, the estrus-inducing effect of DHPs may involve actions independent of the PR. To test these possibilities we assessed the effect of indomethacin, a blocker of 3alphaHSOR, on the estrus-inducing action of such progestins. Because indomethacin also inhibits cyclooxygenases, we selected a dose and treatment schedule that does not interfere with prostaglandin-mediated brain processes (e.g., LHRH release). Indomethacin did not significantly modify the effect of progesterone or megestrol acetate on lordosis. Yet, it significantly reduced the action of all ring A-reduced progestins. Results suggest that: (a) oxidation is essential for lordosis facilitation by 3alpha-pregnanolones and (b) reduction of 3-keto progestins generates 3alpha-hydroxy metabolites which synergize with processes triggered by occupation of the PR by 3-keto progestins. The possible participation in this response of other events influenced by indomethacin (e.g., prostaglandin or melatonin synthesis) is discussed.

The neurosteroids, progesterone and 3alpha,5alpha-THP, enhance sexual motivation, receptivity, and proceptivity in female rats

The effects of progesterone (P) and the neurosteroid and P metabolite, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) on ovariectomized (ovx), estradiol-3-benzoate (EB)-primed rats on sexual motivation, receptivity, and proceptivity were examined. Changes in central P and 3alpha,5alpha-THP were measured following administration of EB, EB+P, EB+3alpha,5alpha-THP, or EB+inhibitor of 5alpha-reductase or P metabolism (epostane and finasteride)+P (Expt. 1). Partner preference was measured as the duration of time females in these different hormonal treatments spent in proximity to a male vs. female conspecific (Expt. 2). Receptivity (lordosis quotients and ratings) and proceptivity (darting, hopping, ear wiggling, and pacing), for different hormone treatments were assessed (Expt. 3 and Expt. 4, respectively). Conditioned place preference following hormone treatments and paced mating enabled assessment of sexual motivation (Expt. 5). Central P and 3alpha,5alpha-THP were measured in various combinations of hormone/mating conditions (Expt. 6). Studies revealed that 3alpha,5alpha-THP has a significant role in these reproductive measures. Brain concentrations of 3alpha, 5alpha-THP were significantly higher in animals receiving EB+P or EB+3alpha,5alpha-THP compared to animals receiving EB alone, or EB+P in conjunction with an inhibitor of P metabolism. EB+P and EB+3alpha, 5alpha-THP significantly increased time spent in proximity to the male, receptivity and proceptivity. When administered to ovx, EB-primed rats, the progestin metabolite, 3alpha,5alpha-THP, had effects on these behaviors similar to P. Epostane, an inhibitor of P and 3alpha,5alpha-THP biosynthesis, and finasteride, an inhibitor of P metabolism to 3alpha,5alpha-THP, administered to EB+P animals reduced male partner preference, proceptive, and receptive behaviors to levels seen in EB+vehicle animals. Notably, whole brain 3alpha, 5alpha-THP levels were significantly increased and whole brain P levels were significantly reduced in paced mated rats compared to standard mated, and receptive non-mated animals. These studies suggest that P and 3alpha,5alpha-THP may have some common effects on reproductive behavior, e.g., sexual motivation, receptivity, and proceptivity.

Nucleus accumbens dopamine release modulation by mesolimbic GABAA receptors-an in vivo electrochemical study

The role of GABA receptors in regulating the mesolimbic dopamine (DA) system and drug reinforced behaviors has not been well characterized. Using fast-cyclic voltammetry, the effects of specific GABA receptor modulation on DA release in the nucleus accumbens (NAcc) and heroin self-administration (SA) behavior was investigated. The GABAA agonist muscimol, administered either intravenously or directly into the ventral tegmental area (VTA), significantly increased DA release in the NAcc in 7 of the 10 rats tested. DA release decreased in the remaining three rats; both effects were blocked by pretreatment with the GABAA receptor antagonist bicuculline. In contrast, the GABAB agonist baclofen decreased, while 2-OH-saclofen (a GABAB antagonist) increased DA release in the NAcc. However, when VTA GABAB receptors were previously activated or inactivated by microinjections of baclofen or 2-OH-saclofen, systemic injections of muscimol caused an inhibition of NAcc DA release. These results suggest that GABAA receptors may be co-localized on both DA neurons and non-DA (GABAergic) interneurons in the VTA, with the effects of GABAA determined by the net effect of both direct inhibition and indirect disinhibition of DA neurons. Finally, although a DA releaser, muscimol was neither self-administered in drug naive rats, nor did it substitute for heroin in rats previously trained to self-administer heroin, suggesting that GABAA receptors appear to play a complex role in mediating drug reinforcement, depending upon the dynamic functional state of GABAA receptors on both tegmental DA and non-DA neurons.

Behavioral effects of 3 alpha-androstanediol. II: Hypothalamic and preoptic area actions via a GABAergic mechanism

We investigated whether 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-androstanediol; 3 alpha-Diol), a neurosteroid whose effects are primarily inhibitory to sexual behavior, may act through interactions with gamma-aminobutyric acid (GABA) receptor complexes (GBRs) in the medial basal hypothalamus (MBH) and the preoptic area (POA). In Experiment (Exp.) 1, ovariectomized (ovx) rats were implanted with bilateral guide cannulae aimed above the MBH and were later treated with 17 beta-estradiol (E2, 2 injections of 1 microgram/0.2 ml in 10% ethanol) and either 3 alpha-Diol (3.0 mg/kg, s.c.) or vehicle. Progesterone (0.5 mg, s.c.) was given 24 h after the first E2 injection and a pre-test for lordosis responsiveness was carried out 4 h later. The GABAA agonist, muscimol (50 ng), then was infused into the MBH and rats were tested 10, 30 and 60 min later. Muscimol infusion facilitated lordosis behavior in vehicle-treated controls, but 3 alpha-Diol-treated animals failed to show this facilitation. To ascertain whether 3 alpha-Diol would also prevent muscimol's action in the POA, a site in which muscimol inhibits, rather than facilitates, sexual receptivity, ovx animals in Exp.2 were implanted with bilateral guide cannulae aimed above the POA and were treated with E2, 3 alpha-Diol, and P and infused and tested as in Exp. 1. Muscimol and 3 alpha-Diol each significantly inhibited receptivity; when they were combined, the inhibition was more pronounced. In Exp. 3, POA infusions of the GABAA antagonist, bicuculline, counteracted muscimol's and 3 alpha-Diol's inhibition of sexual behavior. In Exp. 4, in vitro treatment of POA and MBH membrane fractions with 3 alpha-Diol (30 microM) enhanced maximal [3H]muscimol binding without altering the affinity of the binding sites for the agonist. These data suggest that 3 alpha-Diol inhibits E2 and progestin-induced lordosis behavior via actions at the GBR in both the MBH and POA.

Progesterone and the neural mechanisms of hamster sexual behavior

Stimulation of both the ventral medial hypothalamus (VMH) and the ventral tegmental area (VTA) by progesterone is necessary to facilitate sexual behavior in female hamsters. Recently obtained evidence indicates that progesterone exerts its behaviorally relevant actions in the VTA by acting on cell membranes. When progesterone conjugated to bovine serum albumin, which cannot permeate the cell membrane, is applied to the VTA concurrent with free progesterone to the VMH, estrogen-primed hamsters become sexually receptive. Since the reverse treatment is ineffective, this suggests that progesterone's nongenomic effects in the VTA may require concurrent genomic activation by progesterone in the VMH. The nongenomic action of progesterone on sexual receptivity may involve the GABAA receptor complex, as progestins are known to modulate this receptor complex. VTA infusions of GABAA agonists enhance, and antagonists inhibit, progesterone's effectiveness on receptivity. Finally, the behavioral effectiveness of progesterone metabolites in the VTA, concurrent with progesterone in the VMH, is consistent with their relative biochemical efficacy at the GABAA complex. These data suggest that progesterone may exert its behavioral effects in the VTA through GABAA. However, it is not yet clear whether progesterone normally acts directly on GABAA in the VTA. Progesterone may also act at some other membrane binding site and GABAA may represent an indirect mechanism for progesterone.

5 alpha-reduced progesterone metabolites are essential in hamster VTA for sexual receptivity

Progesterone's (P) actions in the ventral medial hypothalamus (VMH) and the ventral tegmental area (VTA) are essential for sexual receptivity in hamsters. This study investigates the notion that P works in the VTA in the absence of intracellular P receptors (PRs) by 5 alpha-reduction to progestins, which would subsequently bind to membrane gamma-Aminobutyric Acid receptor complexes (GBRs). To test the importance of P metabolism, a 5 alpha-reductase inhibitor, 17 beta-N, N-diethylcarbamoyl-4-methyl-4aza-5 alpha-androstan-3-one (4MA) was administered SC (0, 3, 9, 15, 24, or 30 mg/kg) to ovx estradiol benzoate(EB)-primed hamsters, followed by one of six doses of SC P (0, 25, 50, 100, 200, or 500 micrograms) and sexual receptivity testing. 200 micrograms P-treated animals administered higher (24 and 30 mg/kg) doses of 4MA had significantly decreased total lordosis durations (TLDs) compared to 0 mg/kg 4MA controls (exp 1). In exp 2, 4MA was aimed bilaterally at the VTA prior to SC P. After 200 micrograms P, animals had significantly lower TLDs than after 500 micrograms P, 3 hours following bilateral VTA implantation of 4MA, but not cholesterol. In exp 3, cycling female hamsters were infused with 1.0 microgram 4MA or vehicle unilaterally into the VTA on diestrus, proestrus, and estrus. 4MA, but not vehicle, infusions into the VTA interrupted receptivity in estrus and proestrus animals, but had no effect on diestrus animals. 4MA's reduction of receptivity when given systemically and intracranially strongly supports the hypothesis that 5 alpha-reduced P metabolites, possibly interacting with GBRs in the VTA, are essential for sexual receptivity in hamsters.

Bicuculline infused into the hamster ventral tegmentum inhibits, while sodium valproate facilitates, sexual receptivity

Progesterone's (P) actions on both the ventral medial nucleus of the hypothalamus (VMH) and the ventral tegmental area (VTA) are essential for sexual receptivity in female hamsters. Evidence suggests that progesterone's actions in the hamster VMH may be genomic while those in the VTA may be mediated nongenomically, via GABAA. Ovariectomized female hamsters were bilaterally implanted with cannulae aimed toward the VTA. One week after surgery, animals were SC injected with 10 micrograms estradiol benzoate (EB) and 40 h later with 200 or 500 micrograms P. At hour 43.5, 50 ng bicuculline, a GABAA antagonist, was infused into each available cannula. Control animals received 0.5 microliter sterile saline vehicle, or no infusion. At hour 44, animals were tested for sexual receptivity in an observation arena with a sexually experienced male. Histology revealed that only animals with bicuculline infused into the VTA had reduced lordosis durations compared to controls. Other animals, primed with EB and 200 micrograms progesterone, showed a facilitation of sexual receptivity after infusion into the VTA of 50 micrograms sodium valproate, a GABAA transaminase inhibitor. These results suggest that GABAA plays a necessary role in the mechanism of progesterone's actions on sexual receptivity in hamster VTA.

3 alpha-OH-DHP and 5 alpha-THDOC implants to the ventral tegmental area facilitate sexual receptivity in hamsters after progesterone priming to the ventral medial hypothalamus

Progesterone (P) stimulation to both the ventral medial hypothalamus (VMH) and the ventral tegmental area (VTA) is necessary to facilitate sexual receptivity in female hamsters, despite the sparse population of estrogen-induced P receptors found in the VTA. Instead, P may act at neuronal membranes in the VTA. These P effects may be mediated by actions on the gamma-aminobutyric acid A-(GABAA)-benzodiazepine receptor complex (GBR). Many progestin metabolites have a greater effect in vitro on benzodiazepine binding and Cl- flux than P. If P's actions are due to metabolism to a progestin more potent at the GBR, then applying one of those progestin metabolites directly to the VTA should facilitate receptivity, if coupled with P to the VMH. To test this hypothesis three P metabolites, in decreasing order of activity at cortical synaptosome GBR, were tested: 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha-OH-DHP), 5 alpha-pregnan-3 alpha,21-diol-20-one (5 alpha-THDOC) and 5 beta-pregnan-3 alpha,21-diol-20-one (5 beta-THDOC). Ovariectomized hamsters were implanted with chronic cannulae, one aimed above the VMH and the other over the contralateral VTA. Animals were estrogen-primed and tested for sexual receptivity 4 h after a P containing insert was applied to the VMH and a metabolite containing insert was applied to the VTA. The following week the contents of the tubes were reversed; on the third week P was applied to both sites. Facilitation of receptivity occurred only when P was applied to the VMH and either P or a metabolite was applied to the VTA.(ABSTRACT TRUNCATED AT 250 WORDS)

P-3-BSA, but not P-11-BSA, implants in the VTA rapidly facilitate receptivity in hamsters after progesterone priming to the VMH

Recent evidence suggests that progesterone (P) may have behaviorally relevant actions on neuronal membranes in the ventral midbrain. In the present experiments, we exploited the rapid time course predicted for non-genomic actions of steroid hormones. Ovariectomized hamsters were implanted with chronic guide cannulae, one aimed above the ventromedial hypothalamus (VMH) and the other over the contralateral ventral tegmental area (VTA). The following week animals were estrogen-primed (10 micrograms estradiol benzoate) and pre-tested for sexual receptivity 2 h after a P or P conjugated to the macromolecule bovine serum albumin (P-3-BSA) containing tube was applied to the VMH. P-3-BSA binds well to neuronal membranes, but does not penetrate them because of the large size of the BSA molecule. After the pre-test, the opposite hormone-containing insert was applied to the VTA and hamsters were tested again for sexual receptivity 5 min after this implantation. The following week, the contents of the tubes were reversed. Receptivity only occurred when P was applied to the VMH and 2 h later P-3-BSA was applied to the VTA; the reverse treatment was ineffective. These data indicate that P is capable of rapidly facilitating receptivity by actions on cell membranes in the VTA if P has been applied to the hypothalamus 2 h earlier. Progesterone conjugated to BSA at carbon 11 (P-11-BSA) was ineffective compared to P-3-BSA using the same paradigm. This suggests that the mechanism which responds to P in the ventral midbrain may require the 11 region.