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

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.

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.

Nitric oxide and ERK/MAPK mediation of estrous behavior induced by GnRH, PGE2 and db-cAMP in rats

We tested the hypothesis that GnRH, PGE2 and db-cAMP act via the nitric oxide (NO)-cGMP and MAPK pathways to facilitate estrous behavior (lordosis and proceptivity) in estradiol-primed female rats. Estradiol-primed rats received intracerebroventricular (icv) infusions of pharmacological antagonists of NO synthase (L-NAME), NO-dependent soluble guanylyl cyclase (ODQ), protein kinase G (KT5823), or the ERK1/2 inhibitor PD98059 15 min before icv administration of 50 ng of GnRH, 1 microg of PGE2 or 1 microg of db-cAMP. Icv infusions of GnRH, PGE2 and db-cAMP enhanced estrous behavior at 1 and 2 h after drug administration. Both L-NAME and ODQ blocked the estrous behavior induced by GnRH, PGE2 and db-cAMP at some of the times tested. The protein kinase G inhibitor KT5823 reduced PGE2 and db-cAMP facilitation of estrous behavior but did not affect the behavioral response to GnRH. In contrast, PD98059 blocked the estrous behavior induced by all three compounds. These data support the hypothesis that the NO-cGMP and ERK/MAPK pathways are involved in the lordosis and proceptive behaviors induced by GnRH, PGE2 and db-cAMP. However, cGMP mediation of GnRH-facilitated estrous behavior is independent of protein kinase G.

Effects of manipulating progesterone and NMDA receptors in the ventral tegmental area for lordosis of hamsters and rats

RATIONALE

Progesterone (P4) has actions in the ventral tegmental area (VTA) to regulate female sexual behavior in rodents. However, there are few intracellular progestin receptors (PRs) that have been identified in the VTA through which P4 may have its actions to facilitate lordosis. There are N-methyl-D: -aspartate receptors (NMDARs) in the VTA that may be a substrate for P4's effects.

OBJECTIVE

We investigated the effects of pharmacologically manipulating NMDARs in the VTA for E2- and P4-facilitated lordosis of hamsters and rats.

MATERIALS AND METHODS

We examined the effect of systemic injections (intraperitoneal; IP) and bilateral infusions to the VTA of the highly specific, competitive NMDAR antagonist, 9-0-6-phosphonomethyl-deca-hydroisoquinoline-3-carboxylic acid (LY235959); 0, 0.3, and 1 mg/kg IP and 0, 1.0, and 10 ng/mul intra-VTA), on lordosis of estradiol-primed (E2; 10 microg) and P4-primed (0, 50, 250, or 500 microg) ovariectomized hamsters and rats.

RESULTS

Intra-VTA administration of the NMDAR antagonist, LY235959, produced similar effects as systemic administration to enhance lordosis, particularly in E2-primed rats or hamsters administered moderate P4 levels (less than 500 microg). Administration of LY235959 to the substantia nigra did not produce similar effects as intra-VTA infusions for lordosis.

CONCLUSIONS

Together, these data suggest that blocking NMDARs in the VTA enhances lordosis of hamsters and rats.

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.

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.

Engaging in paced mating, but neither exploratory, anti-anxiety, nor social behavior, increases 5alpha-reduced progestin concentrations in midbrain, hippocampus, striatum, and cortex

Sequential actions of 17beta-estradiol (E(2)) and progesterone (P(4)) in the hypothalamus and the P(4) metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), in the midbrain ventral tegmental area (VTA) respectively mediate the initiation and intensity of lordosis of female rats and may also modulate anxiety and social behaviors, through actions in these, and/or other brain regions. Biosynthesis of E(2), P(4), and 3alpha,5alpha-THP can also occur in brain, independent of peripheral gland secretion, in response to environmental/behavioral stimuli. The extent to which engaging in tasks related to reproductive behaviors and/or mating increased E(2) or progestin concentrations in brain was investigated. In Experiment 1, proestrous rats were randomly assigned to be tested in individual tasks, including the open field, elevated plus maze, partner preference, social interaction, or no test control, in conjunction with paced mating or no mating. Engaging in paced mating, but not other behaviors, significantly increased dihydroprogesterone (DHP) and 3alpha,5alpha-THP levels in midbrain, hippocampus, striatum, and cortex. In Experiment 2, proestrous rats were tested in the combinations of the above tasks (open field and elevated plus maze, partner preference, and social interaction) with or without paced mating. As in Experiment 1, only engaging in paced mating increased DHP and 3alpha,5alpha-THP concentrations in midbrain, hippocampus, striatum, and cortex. Thus, paced mating enhances concentrations of 5alpha-reduced progestins in brain areas associated with reproduction (midbrain), as well as exploration/anxiety (hippocampus and striatum) and social behavior (cortex).

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.

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.

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.

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.

Differential effect of kinase A and C blockers on lordosis facilitation by progesterone and its metabolites in ovariectomized estrogen-primed rats

Dose response curves for lordosis behavior was obtained for progesterone (P) and its two ring A-reduced metabolites: 5alpha-pregnanedione (alpha-DHP) and 5alpha,3alpha-pregnanolone (5alpha,3alpha-Pgl) by infusing these progestins in the right lateral ventricle (rlv) of ovariectomized (ovx) estradiol-treated rats (2 microg estradiol benzoate; EB), 40 h before intracerebro-ventricular (icv) injection. Effective doses 50 (ED50) revealed that ring A-reduced progestins were more potent than P itself to induce lordosis behavior. Two dose levels, one producing the maximal effect and the other one producing a submaximal response (ED50-ED60), were selected for testing the capacity of RpAMPS, a kinase A blocker, and H7, a kinase C blocker, to modify the response to the three progestins. rlv injection of RpAMPS significantly depressed the lordosis response to the two dose levels of P and alpha-DHP but failed to significantly inhibit that of 5alpha,3alpha-Pgl. The administration of H7 prevented the effect of both 5alpha-reduced progestins without affecting the response to P. The results suggest that P and its ring A-reduced metabolites stimulate lordosis behavior through different cellular mechanisms: P acting mainly through the cAMP-kinase system; alpha-DHP through both kinase A and kinase C signaling pathways and 5alpha,3alpha-Pgl through the kinase C system.

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.

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.